Cartilage Restoration

Cartilage restoration is a group of surgical procedures designed to repair, replace or stimulate new tissue within a localized area of damaged articular cartilage. The main objective is to create a more functional joint surface, reduce symptoms and preserve the natural knee when the surrounding joint remains suitable for joint-preserving treatment.

Articular cartilage is the smooth tissue covering the ends of the bones inside the knee. It allows the femur, tibia and patella to move with very little friction while distributing substantial forces during walking, running, jumping, stairs and sport.

When this surface is damaged, the joint can become painful and swollen. An unstable cartilage fragment can also catch within the joint. Deeper injuries can expose the underlying subchondral bone and alter the way forces are transmitted through the knee.

Articular cartilage has limited natural healing capacity because it contains very little direct blood supply. Unlike skin, muscle or bone, a cartilage defect does not necessarily heal by forming new tissue identical to what was originally present.

Cartilage restoration attempts to overcome this limitation using different biological and mechanical strategies.

Is Cartilage Restoration the Same as Cartilage Regeneration?

Not exactly.

Cartilage regeneration usually refers to the biological formation of new cartilage or cartilage-like tissue. The phrase is commonly used when discussing cell therapies, scaffolds, tissue engineering and biological stimulation.

Cartilage restoration is the broader orthopedic concept. It includes procedures that regenerate tissue, but it also includes procedures that physically transplant healthy cartilage into a damaged area.

Microfracture, for example, stimulates a repair response from the bone marrow. The resulting tissue is mainly fibrocartilage rather than completely normal native hyaline cartilage.

Osteochondral autograft transplantation works differently. It transfers an actual plug containing mature articular cartilage and underlying bone from another region of the patient's own knee.

Osteochondral allograft transplantation also transfers mature cartilage and bone, but the tissue comes from a screened human donor.

MACI uses the patient's own cartilage cells, expands them outside the body and returns them to the defect on a collagen membrane.

All of these can be described as cartilage restoration, but they do not restore cartilage through the same biological mechanism.

For SEO purposes, this page should therefore target both cartilage restoration and cartilage regeneration while explaining the medical distinction clearly.

What Is Articular Cartilage?

Articular cartilage is a specialized form of connective tissue that covers the bone surfaces inside synovial joints.

The healthy surface is smooth and highly organized. It contains chondrocytes surrounded by a matrix rich in collagen, water and proteoglycans.

This structure allows cartilage to withstand repeated compressive forces while creating a very low-friction gliding surface.

Articular cartilage also protects the bone immediately beneath it.

Once a significant cartilage defect develops, the supporting bone can become exposed to forces it was not designed to experience directly.

Why Cartilage Damage Can Be Difficult to Treat

Cartilage has limited access to the body's normal blood-based healing response.

A shallow injury that remains within the cartilage layer may have little biological capacity to repair itself.

A full-thickness defect that reaches the subchondral bone can produce a stronger healing response because marrow elements enter the area. However, the tissue formed through this process is generally different from original articular cartilage.

This is why orthopedic surgeons distinguish between repair tissue and true transplantation of mature cartilage.

The choice of treatment depends partly on how durable the new surface needs to be.

What Is a Focal Cartilage Defect?

A focal defect is a localized region of damaged cartilage surrounded by relatively better-preserved joint surfaces.

This is the typical problem targeted by cartilage restoration.

For example, a patient may have a full-thickness cartilage injury measuring a few square centimeters on the medial femoral condyle while the remainder of the knee remains relatively healthy.

That patient is very different from someone with advanced osteoarthritis affecting the medial compartment, lateral compartment and patellofemoral joint simultaneously.

Cartilage restoration is generally better suited to the first situation.

Cartilage Restoration Versus Knee Replacement

Cartilage restoration attempts to preserve the patient's natural knee.

Knee replacement removes and resurfaces larger portions of the joint using metal and polyethylene components.

A young active adult with one symptomatic cartilage defect usually does not need an artificial knee simply because one region of cartilage is damaged.

Conversely, cartilage restoration is usually not an appropriate substitute for total knee replacement when widespread end-stage arthritis has destroyed several joint surfaces.

The decision therefore depends on whether the problem is localized and reconstructable or diffuse and degenerative.

Chondral Versus Osteochondral Defects

A chondral defect primarily involves the cartilage layer.

An osteochondral defect involves both cartilage and the underlying bone.

This distinction is clinically important because cartilage treatment needs a healthy foundation.

If substantial subchondral bone is missing, diseased or cystic, the surgeon may need to reconstruct both the bone and the cartilage.

OATS and osteochondral allograft transplantation are particularly useful in this situation because the graft includes both components.

Cell-based cartilage procedures can sometimes be used when bone involvement exists, but significant bony defects may require bone grafting as part of the reconstruction.

What Causes Focal Cartilage Damage?

Cartilage damage can occur after a traumatic knee injury. Twisting injuries, patellar dislocation, direct impact or a knee dislocation can shear or crush part of the articular surface.

Osteochondritis dissecans can produce an osteochondral lesion, particularly in younger patients.

Cartilage can also deteriorate when knee mechanics remain abnormal for a prolonged period. Chronic ACL instability, malalignment and meniscal deficiency can repeatedly overload particular areas.

Previous fractures can leave an irregular joint surface.

Less commonly, previous infection or surgery may contribute to cartilage loss.

The cause matters because successful restoration often requires treatment of the mechanical reason the cartilage was overloaded.

Where Can Cartilage Damage Occur?

The medial femoral condyle is one of the most frequently treated areas.

Lesions can also involve the lateral femoral condyle, trochlea, patella or tibial plateau.

The location changes the mechanical environment.

A femoral condyle defect experiences repetitive weight-bearing forces.

Patellar and trochlear defects experience substantial patellofemoral compression as the knee bends.

Tibial plateau lesions can be particularly challenging because of their location and shape.

A cartilage operation that performs well on a femoral condyle cannot automatically be assumed to perform identically on the patella.

Why Lesion Size Matters

Small, moderate and large defects have different surgical options.

A small defect can sometimes be treated effectively with marrow stimulation or a limited osteochondral autograft.

As defect size increases, microfracture becomes less attractive because fibrocartilage may not provide sufficient long-term durability.

OATS is also limited by the amount of healthy donor tissue that can safely be harvested from the same knee.

Larger lesions can therefore be stronger candidates for MACI or osteochondral allograft transplantation.

There is no universal surface-area cutoff that applies to every patient because location, activity, previous surgery and bone involvement also matter.

Why Defect Depth Matters

A cartilage-only lesion differs from one with deep bone loss.

If the underlying bone is healthy, the surgeon may focus primarily on restoring the articular surface.

If the defect includes several millimeters of unhealthy bone, a cartilage-only technique may not provide enough structural support.

Osteochondral grafts can replace the diseased bone and cartilage together.

Other cases may require staged or simultaneous bone grafting before the cartilage layer is reconstructed.

Why Knee Alignment Matters

Cartilage restoration should not be viewed as patching a hole while ignoring the forces that created it.

A varus knee places greater load through the medial compartment.

If the patient has a medial femoral condyle defect and significant varus alignment, restoring the cartilage without correcting the overload can expose the repair to continued excessive pressure.

An osteotomy can be used to shift the mechanical axis away from the damaged region.

A high tibial osteotomy is commonly considered for selected medial-compartment overload patterns.

Distal femoral osteotomy can be used in selected valgus knees.

Not every patient requires realignment surgery, but alignment should be evaluated before major restoration.

Why the Meniscus Matters

The meniscus is one of the principal load-distributing structures of the knee.

When a substantial portion of the meniscus has been removed, contact pressure across the adjacent cartilage increases.

A cartilage defect located in a meniscus-deficient compartment therefore faces a different mechanical environment.

Repairable meniscus tears should generally be preserved whenever appropriate.

In selected younger patients who have already lost most of a meniscus, meniscal allograft transplantation can sometimes form part of a broader joint-preservation strategy.

Ignoring major meniscal deficiency can compromise cartilage restoration.

Why Ligament Stability Matters

Ligaments control knee translation and rotation.

An ACL-deficient knee can expose the menisci and cartilage to abnormal shear.

If significant instability remains untreated, a cartilage graft or repair can continue experiencing abnormal forces.

ACL reconstruction can therefore be performed at the same time as cartilage restoration when both conditions are clinically important.

The same principle applies to other ligament injuries.

The objective is to create a mechanically stable environment around the new cartilage surface.

Cartilage Restoration Is an Umbrella Procedure

Patients frequently assume that cartilage restoration refers to one standardized surgery.

It does not.

The term includes several distinct procedures:

• marrow stimulation such as microfracture;

• drilling techniques;

• scaffold-enhanced marrow stimulation;

• osteochondral autograft transfer or OATS;

• mosaicplasty;

• osteochondral allograft transplantation;

• autologous chondrocyte implantation;

• MACI;

• selected minced-cartilage techniques.

Each has a different mechanism, indication and rehabilitation programme.

The best operation is therefore the one that fits the defect and the patient, not necessarily the newest or most expensive technology.

Defining the Cartilage Lesion

Successful cartilage restoration begins with precise characterization of the defect.

The surgeon needs to understand its length, width, depth and location.

The surrounding cartilage is assessed for quality and stability.

The condition of the subchondral bone is equally important.

The surgeon also determines whether the lesion is contained by healthy cartilage on all sides or whether one edge extends toward an uncontained region.

These details influence the choice between microfracture, osteochondral transplantation and cell-based restoration.

Medical History

The evaluation begins with how the symptoms developed.

A traumatic event can suggest an acute osteochondral injury.

Gradual symptoms may indicate chronic overload or a previously unrecognized focal defect.

Patients often describe activity-related pain and recurrent swelling.

Some experience catching or discomfort during particular ranges of movement.

The surgeon asks about previous ligament injuries, meniscus surgery, fractures and earlier cartilage procedures.

Previous surgery can significantly influence the current treatment strategy.

Physical Examination

The knee is assessed for swelling, motion, tenderness and mechanical symptoms.

The surgeon evaluates the patient's gait and observes lower-limb alignment.

Ligament stability is tested.

Meniscal examination is also performed.

Patellar tracking becomes particularly important when the lesion involves the patellofemoral joint.

The hip and lower limb may also be assessed because abnormal movement patterns can contribute to loading of the knee.

Weight-Bearing X-Rays

X-rays are essential even though cartilage itself cannot be seen directly.

Weight-bearing images reveal how much joint space remains.

They can show osteophytes, subchondral changes and previous fractures.

Long-leg alignment films may be obtained to measure varus or valgus deformity.

Patellofemoral views can provide additional information about the patella and trochlear groove.

These images help distinguish focal cartilage damage from established generalized osteoarthritis.

MRI

MRI is one of the principal imaging tests for cartilage restoration planning.

Modern sequences can show cartilage thickness, defect extent and subchondral bone changes.

MRI also identifies bone-marrow edema, meniscal injury and ligament damage.

Osteochondritis dissecans and osteochondral lesions can be characterized in detail.

MRI measurements are extremely useful, but they are not perfect.

The defect can prove larger during surgery after unstable cartilage is removed.

The surgeon therefore prepares for some variation between imaging and the final intraoperative measurement.

CT

CT provides detailed information about bone.

It is useful when a cartilage defect has a significant bony component or when previous surgery has altered the subchondral region.

CT can also help assess osteochondral grafts, previous tunnels and some revision situations.

Long-standing alignment or rotational problems can sometimes require CT-based planning.

Not every primary cartilage lesion needs a CT scan.

Assessing the Subchondral Bone

Cartilage and bone function as one osteochondral unit.

Abnormal bone beneath the defect can influence both symptoms and treatment.

Subchondral cysts, sclerosis, edema and previous microfracture channels are important findings.

A surface-only procedure may be inappropriate when the supporting bone is severely damaged.

In that situation, an osteochondral graft can be more attractive because it replaces both the damaged cartilage and abnormal bone.

Assessing Alignment

The surgeon determines whether forces are being distributed appropriately across the joint.

Varus alignment overloads the medial side.

Valgus alignment can overload the lateral compartment.

A cartilage defect in an overloaded compartment has a higher risk of continued mechanical stress.

The degree of deformity and lesion location determine whether an osteotomy should accompany the restoration.

The goal of osteotomy is not to repair cartilage directly but to protect the new surface by redistributing load.

Assessing the Meniscus

The amount of functioning meniscus is documented.

MRI can show tears, extrusion and previous loss of tissue.

Old operative reports can be particularly useful when the patient has undergone previous partial meniscectomy.

A repairable tear can often be treated during the same operation.

Severe meniscal deficiency may require additional reconstruction in carefully selected patients.

Assessing Ligaments

The ACL, PCL and collateral ligaments are assessed for functional stability.

A stable knee provides a better mechanical environment for cartilage restoration.

When an ACL tear causes clinically important instability, ligament reconstruction can be incorporated into the surgical plan.

The rehabilitation programme will then need to protect both the cartilage restoration and the ligament graft.

Diagnostic Arthroscopy

Some patients undergo arthroscopy before the definitive restoration.

This can allow direct inspection and measurement of the defect.

Cartilage quality elsewhere in the knee can also be evaluated.

For MACI, the first arthroscopy is commonly used to harvest a small sample of healthy cartilage for cell expansion.

The final reconstruction occurs during a later operation.

Measuring the Defect

The surgeon records the defect dimensions after unstable cartilage has been removed.

The depth and shape are also important.

A well-contained defect can retain an implanted membrane or graft differently from an uncontained defect.

The area is usually calculated in square centimeters.

This measurement helps guide technique selection.

The treatment algorithm is not based on size alone, but size is one of the central variables.

Nonsurgical Treatment Before Surgery

Not every cartilage defect requires immediate restoration.

Physiotherapy can improve muscle strength and movement control.

Activity modification can reduce repetitive loading.

Weight management may reduce symptoms in patients carrying excess body weight.

Pain and inflammation can sometimes be managed with appropriate medication.

The objective is to determine whether the structural defect continues to produce clinically important symptoms despite reasonable conservative management.

Injections

Injections may be used for symptom management in selected patients.

Corticosteroid injection can reduce inflammation temporarily but does not regenerate articular cartilage.

Hyaluronic acid is used in some healthcare systems for symptomatic knee treatment.

PRP has also been investigated for knee symptoms.

These treatments should not be presented as equivalent to surgically restoring a full-thickness structural defect.

The evidence and regulatory status of injection-based regenerative claims vary considerably.

Prehabilitation

Preoperative rehabilitation helps control swelling and restore knee motion.

Quadriceps strength should be optimized where possible.

The patient can also learn how to use crutches before surgery.

This is particularly useful because several restoration procedures require restricted weight-bearing for weeks.

Preparing the hip and core musculature can also make postoperative mobility easier.

Choosing the Procedure

The patient should know exactly which cartilage restoration procedure is planned.

Saying only “cartilage surgery” is not enough.

The surgeon should explain whether treatment will involve marrow stimulation, OATS, osteochondral allograft or MACI.

The patient should understand why that technique fits the defect and what alternatives exist.

The expected rehabilitation should also be discussed before surgery.

Preparing for OATS

Patients undergoing OATS should understand that healthy osteochondral tissue is harvested from a lower-demand region of the same knee.

The surgeon attempts to minimize donor-site consequences.

Only a limited amount of tissue can safely be harvested.

This is one reason OATS is usually more suitable for small and moderate defects than very large lesions.

Preparing for Osteochondral Allograft

Osteochondral allograft requires appropriate donor tissue.

Graft availability can therefore affect surgical scheduling.

The graft is selected according to the size and contour of the patient's joint surface.

Donor tissue is screened and processed according to tissue-bank standards.

The graft contains actual human cartilage and supporting bone rather than a metal or synthetic prosthesis.

Preparing for MACI

MACI generally involves two stages.

The first operation obtains a cartilage biopsy.

The cartilage cells are then expanded under controlled laboratory conditions on a collagen membrane.

The definitive implantation is performed later.

Patients therefore need to plan for two procedures rather than assuming the first arthroscopy completes the restoration.

Medical Optimization

Diabetes, cardiovascular disease and other relevant medical conditions are assessed before surgery.

Anaemia can be important in more extensive open procedures or combined osteotomy.

Smoking and nicotine use deserve particular attention because they can impair biological healing.

Patients should provide a complete medication and supplement list.

Anticoagulants and antiplatelet medication require individual instructions.

Planning Home Recovery

Crutches can be required for six weeks or longer after some procedures.

Patients should prepare their home before surgery.

Stairs, bathroom access and transport need to be considered.

International patients should organize postoperative physiotherapy before travelling whenever possible.

The rehabilitation protocol should be provided in writing so that the home physiotherapist understands the lesion, restoration technique and weight-bearing restrictions.

Cartilage restoration surgery begins by preparing a focal cartilage defect and then treating it using a technique selected for the lesion's size, depth and biological requirements. The surgeon may stimulate bone marrow, transfer the patient's own cartilage and bone, transplant donor osteochondral tissue or implant cultured cartilage cells.

Some procedures are entirely arthroscopic.

Others require a small or moderate open incision.

Complex cases can combine cartilage restoration with osteotomy, meniscus surgery or ligament reconstruction.

Arthroscopic Assessment

The surgeon introduces an arthroscope through small portals.

The joint is inspected systematically.

The cartilage lesion is probed and unstable edges are identified.

The size can be measured directly.

Menisci, ligaments and the opposing cartilage surface are assessed at the same time.

This inspection can occasionally change the operative plan if the defect differs substantially from MRI predictions.

Preparing the Defect

Damaged unstable cartilage is removed until a stable border remains.

The objective is not to enlarge the lesion unnecessarily.

The surgeon creates a defined region capable of supporting the chosen restoration.

The underlying bone is treated differently according to procedure.

Microfracture deliberately penetrates the bone.

MACI generally aims to avoid unnecessary violation of healthy subchondral bone.

Osteochondral transplantation deliberately replaces part of the bone with the graft.

Microfracture

How Microfracture Works

Microfracture is a marrow-stimulation procedure.

After unstable cartilage is removed, the surgeon creates multiple small openings in the exposed subchondral bone.

Blood and marrow components emerge through these openings.

A clot forms within the defect.

Cells contained in the marrow environment contribute to development of repair tissue.

The resulting tissue is predominantly fibrocartilage rather than normal native hyaline cartilage.

When Microfracture Is Most Appropriate

Microfracture is generally most attractive for smaller focal defects.

Lower-demand patients can be stronger candidates than elite athletes with large lesions.

The health of the subchondral bone matters.

A small lesion with intact surrounding cartilage is different from a medium or large defect with extensive underlying bone abnormalities.

Advantages of Microfracture

Microfracture can usually be performed arthroscopically.

It is a single-stage procedure.

No donor tissue or cell-culture laboratory is required.

Implant costs are relatively limited.

For selected small defects, the procedure can provide meaningful symptom improvement.

Limitations of Microfracture

Fibrocartilage is mechanically different from native hyaline cartilage.

Its durability can decline over time, especially in larger lesions and highly active patients.

Long-term evidence has raised particular concern about using microfracture for medium and large defects.

Previous marrow stimulation can also alter the subchondral bone and may complicate later restorative surgery.

This is why microfracture should not automatically be performed simply because it is technically straightforward.

Drilling

How Drilling Works

Drilling follows the same broad biological principle as microfracture.

The surgeon creates channels into subchondral bone so blood and marrow cells can reach the defect.

The procedure can be performed using small drills or wires.

The repair tissue is mainly fibrocartilage.

Advantages and Limitations

Drilling is a single-stage marrow-stimulation technique.

Modern low-speed drilling can reduce heat generation compared with older techniques.

However, the fundamental biological limitation remains: marrow stimulation does not transplant mature hyaline cartilage.

The technique is therefore used selectively rather than as the default option for every focal defect.

Scaffold-Enhanced Marrow Stimulation

What Is AMIC?

Autologous matrix-induced chondrogenesis combines marrow stimulation with a membrane or scaffold placed over the defect.

The marrow openings provide cells and biological material.

The scaffold is intended to stabilize the repair clot and provide an environment in which tissue can organize.

AMIC is generally a single-stage procedure.

Is AMIC Better Than Microfracture?

The concept is attractive, and some comparative studies report advantages in selected outcomes.

However, available randomized evidence has not demonstrated overwhelming superiority across every patient group and every endpoint.

Scaffold enhancement should therefore be considered one option rather than a universally superior replacement for every microfracture procedure.

Osteochondral Autograft Transfer

What Is OATS?

OATS transfers a cylinder of healthy articular cartilage and supporting bone from a lower-demand area of the patient's own knee into the cartilage defect.

The procedure is also known as osteochondral autograft transfer.

Because the graft already contains mature cartilage, the surgeon is not waiting for fibrocartilage to form.

The transplanted bone incorporates into the recipient site while the cartilage surface becomes part of the joint.

Harvesting the Graft

The surgeon identifies an area with healthy cartilage that experiences relatively low mechanical demand.

A cylindrical coring instrument removes an osteochondral plug.

The diameter and length are chosen according to the recipient defect.

The donor site remains within the same knee.

The surgeon therefore needs to balance the amount of tissue required against the desire to minimize donor-site morbidity.

Preparing the Recipient Socket

The damaged cartilage and underlying bone are removed using a matching cylindrical instrument.

The depth is measured carefully.

The recipient bed needs to accommodate the graft precisely.

A plug that sits too high can create excessive contact pressure.

A plug that sits too low can leave an irregular surface.

Surface congruity is therefore one of the technical priorities.

Implanting the Osteochondral Plug

The plug is gently inserted into the recipient socket.

Many grafts are held through a precise press fit without permanent hardware.

The surgeon checks the surrounding surface from several angles.

When more than one plug is needed, the grafts are arranged to cover the defect.

Mosaicplasty

Multiple small osteochondral plugs can be used to reconstruct a larger area.

This creates a mosaic-like appearance.

The small spaces between plugs can fill with repair tissue.

The technique increases the amount of area that can be covered, but donor tissue remains limited.

Large lesions can therefore exceed the practical range of autograft transplantation.

Advantages of OATS

OATS transfers mature articular cartilage immediately.

The graft also includes healthy supporting bone.

It is usually a single-stage operation.

There is no donor-tissue availability issue because the graft comes from the same patient.

Limitations of OATS

The amount of donor tissue is limited.

Harvesting creates a second osteochondral site within the knee.

Large defects can require too much donor tissue.

Lesion location can also make accurate perpendicular graft insertion technically difficult.

Osteochondral Allograft Transplantation

What Is Osteochondral Allograft?

Osteochondral allograft transplantation uses a graft obtained from a screened human donor.

Like OATS, the graft contains mature cartilage and underlying bone.

The major difference is that the patient's own knee does not need to provide the donor plug.

This allows much larger defects to be treated.

When OCA Is Considered

OCA is especially useful for larger osteochondral lesions.

It can also be used when substantial subchondral bone needs replacement.

Osteochondritis dissecans and traumatic osteochondral loss are common indications.

OCA is also an important revision option after failed previous cartilage surgery.

Matching the Donor Tissue

The donor joint surface is selected according to the recipient's anatomy.

The surgeon uses imaging and measurements to estimate the required size and contour.

Fresh osteochondral tissue is preferred for many knee applications because viable chondrocytes are an important component of the graft.

Availability can affect the timing of surgery.

Preparing the Recipient Site

The damaged region is removed until healthy supporting tissue remains.

For a cylindrical graft, a coring system creates a precisely shaped socket.

For very large or irregular defects, a shell-type graft may be required.

The surgeon measures depth at several points because articular surfaces are curved rather than flat.

Preparing the Donor Graft

A matching region is cut from the donor tissue.

The surgeon reproduces the dimensions of the recipient site as closely as possible.

The bony portion may be adjusted to an appropriate depth.

The graft is thoroughly irrigated according to the surgical protocol.

The cartilage surface is handled gently to protect chondrocytes.

Implantation

Many cylindrical grafts are press-fit.

The surgeon seats the graft until its cartilage surface aligns with the surrounding native cartilage.

Large shell grafts can require screws or other fixation.

The transplanted bone then needs to incorporate with the recipient bone over time.

Advantages of OCA

Large defects can be reconstructed.

Both cartilage and bone are restored.

No osteochondral tissue needs to be harvested from another region of the patient's own knee.

It can also be effective as a salvage procedure following failed previous cartilage restoration.

Limitations of OCA

Fresh donor tissue has limited availability.

The procedure is technically demanding.

The graft can fail to incorporate or can deteriorate over time.

Reoperations are not uncommon in complex cartilage patients even when the graft remains functional.

Tissue-bank screening makes disease transmission extremely uncommon, but biological donor tissue can never be described as carrying absolutely zero risk.

Autologous Chondrocyte Implantation

What Is ACI?

Autologous chondrocyte implantation uses the patient's own cartilage cells.

A small cartilage biopsy is harvested from a lower-demand area.

Chondrocytes are isolated and expanded in a specialized laboratory.

The cells are later implanted into the defect during a second procedure.

Older generations used injected cells covered by a membrane.

Modern matrix-based approaches have become more common.

MACI

What Is MACI?

Matrix-induced autologous chondrocyte implantation, or MACI, uses the patient's cultured cartilage cells placed on a collagen membrane that is implanted into the cartilage defect.

MACI is used for selected symptomatic full-thickness cartilage defects of the knee.

It is particularly useful when the lesion is too large for practical osteochondral autograft treatment and when the underlying bone does not require extensive osteochondral replacement.

Stage One: Cartilage Biopsy

The first stage is usually arthroscopic.

The surgeon confirms the defect and assesses the entire joint.

Small cartilage biopsies are harvested from a lower-load region.

The tissue is sent to a specialized laboratory.

Chondrocytes are isolated, expanded and placed onto a collagen membrane.

Stage Two: Implantation

At a later operation, the defect is exposed.

Damaged cartilage is carefully removed until stable borders remain.

A template can be created that matches the lesion.

The cell-containing membrane is cut to the correct shape.

It is then placed into the defect and commonly secured using fibrin sealant.

The implant should lie flush with the surrounding cartilage without folds or excessive overlap.

Biological Maturation

The implanted cells need time to produce and organize extracellular matrix.

The new surface therefore matures gradually over months.

The patient can feel substantially better before the biological process is complete.

This is why rehabilitation remains cautious even after symptoms have improved.

Advantages of MACI

Large focal cartilage defects can be treated without harvesting multiple osteochondral plugs.

The cells originate from the patient.

Long-term studies show durable improvements in appropriately selected patients.

Multiple defects can potentially be treated when clinically suitable.

Limitations of MACI

MACI generally requires two procedures.

Laboratory cell processing adds complexity and cost.

Implantation can require an open incision.

The rehabilitation is lengthy.

MACI does not correct malalignment, ligament instability or major meniscal deficiency by itself, so those mechanical issues still need separate treatment.

Minced Cartilage

What Is Minced Cartilage Repair?

Minced cartilage is a single-stage technique in which small pieces of viable cartilage are distributed through the prepared defect.

The concept is that chondrocytes within these fragments can migrate and contribute to formation of new tissue.

The cartilage can be combined with a scaffold or fibrin adhesive to keep the fragments within the defect.

Current Role

Clinical interest in minced cartilage has increased.

Short- and mid-term results are promising in selected patients.

However, the evidence base is less mature than for established techniques such as OATS, OCA and MACI.

Direct high-quality comparisons remain limited.

The technique should therefore be presented as an evolving option rather than as proven superiority over established cartilage restoration.

Bone Grafting

Why Bone Sometimes Needs Reconstruction

Cartilage depends on healthy subchondral bone.

A deep lesion, cyst or failed previous procedure can leave a substantial bony defect.

The surgeon may remove abnormal bone and reconstruct it with bone graft.

Cartilage treatment is then performed over the restored foundation.

Depending on the severity of the defect, bone and cartilage reconstruction can occur during the same operation or in stages.

Patellar and Trochlear Cartilage Restoration

Patellofemoral cartilage surgery requires special planning.

The patella experiences high compressive forces during knee flexion.

Abnormal tracking or alignment can repeatedly overload one portion of the joint.

The surgeon therefore evaluates patellar height, tilt, trochlear anatomy and tibial tubercle position.

In selected patients, a tibial tubercle osteotomy can redistribute pressure away from the restored surface.

The cartilage procedure and mechanical correction can be performed during the same surgical episode.

Cartilage Restoration With Osteotomy

When alignment places excessive load through the defect, cartilage restoration can be combined with osteotomy.

The surgeon cuts and repositions the tibia or femur to shift the mechanical axis.

A plate and screws stabilize the osteotomy while the bone heals.

The cartilage procedure then addresses the structural joint-surface defect.

This combined approach has a longer rehabilitation because both cartilage maturation and bone healing need protection.

Cartilage Restoration With ACL Reconstruction

ACL reconstruction can be performed simultaneously when clinically significant instability exists.

The ligament graft restores stability.

The cartilage procedure restores or repairs the focal surface defect.

The surgeon coordinates tunnel placement and the order of operations.

Postoperative rehabilitation usually follows the most restrictive aspects of the cartilage procedure.

Cartilage Restoration With Meniscus Surgery

A repairable meniscus tear can be repaired at the same operation.

Preserving meniscal function can reduce contact pressure on the cartilage.

When the patient has severe meniscal deficiency, cartilage restoration alone may not be enough.

Selected joint-preservation cases can involve meniscal transplantation in addition to cartilage treatment.

Final Assessment

At the end of surgery, the reconstructed surface is inspected.

The surgeon checks graft height, membrane stability or fixation depending on the procedure.

The knee may be moved through a controlled range to ensure the restoration remains stable.

Incisions are closed and sterile dressings are applied.

A brace is fitted when required.

The patient is then transferred to postoperative recovery.

Is Cartilage Restoration Day Surgery?

Many isolated procedures are performed as day surgery.

Microfracture, OATS and some other arthroscopic procedures commonly allow discharge on the same day.

Larger osteochondral allografts or open MACI implantation may justify overnight observation.

Combined osteotomy or ligament reconstruction can require a longer stay.

The hospital stay should therefore be linked to the actual operation rather than the broad term cartilage restoration.

Immediately After Surgery

The recovery team monitors circulation, sensation, pain and wound condition.

Swelling is expected.

A multimodal pain strategy is generally used.

Paracetamol or acetaminophen, anti-inflammatory medication when medically appropriate, local anaesthetic and regional blocks can reduce the need for stronger medication.

Weight-Bearing

Weight-bearing restrictions are central to cartilage rehabilitation.

A femoral condyle graft or cell implant can require several weeks of reduced loading.

The patient commonly uses crutches.

Some procedures allow partial weight-bearing early, while others begin with very limited load.

The restriction depends on graft biology, lesion size and location.

Patients should never substitute a generic cartilage protocol for the written instructions from the operating surgeon.

Patellofemoral Procedures

Patellar and trochlear lesions can have different restrictions.

Walking with the knee relatively straight produces different patellofemoral forces from deep flexion.

A patient may therefore be permitted more weight-bearing while still having limits on knee bending.

The rehabilitation plan should specify both weight-bearing and range of motion rather than simply saying “protect the knee.”

Brace Use

A brace can help control knee motion.

It may be locked during walking and progressively opened during rehabilitation.

Not every cartilage procedure needs a brace.

The decision depends on lesion location, associated procedures and surgeon preference.

Patients should understand how to adjust and wear it correctly.

Early Motion

Controlled movement often begins early.

Joint motion can support cartilage nutrition and reduce the risk of stiffness.

Some programmes use continuous passive motion machines.

Others use therapist-guided or home range-of-motion exercises.

The target is not aggressive stretching.

Movement should stay within the mechanical limits of the restoration.

Physiotherapy Before Discharge

The physiotherapist teaches crutch technique and permitted exercises.

Quadriceps activation begins early.

Ankle pumps help maintain lower-leg circulation.

Hip and core exercises can also begin without stressing the cartilage surface.

Patients should demonstrate safe transfers and mobility before discharge.

Discharge Information

The written discharge plan should state:

• the exact cartilage restoration procedure;

• defect location and approximate size;

• whether bone was reconstructed;

• weight-bearing status;

• permitted knee flexion;

• brace instructions;

• wound care;

• medication;

• physiotherapy milestones;

• follow-up dates.

This information becomes especially important when the patient receives postoperative rehabilitation outside the treating hospital.

Cartilage Restoration Recovery Time

Cartilage restoration recovery commonly takes approximately six to twelve months before unrestricted high-impact sport, while biological maturation can continue beyond one year.

Patients generally regain basic daily function much earlier.

The length of full recovery depends on the procedure.

Microfracture, OATS, OCA and MACI should not be placed on one identical timetable.

The tissue created through marrow stimulation matures differently from a transplanted osteochondral plug or cultured-cell implant.

Why Cartilage Recovery Takes Months

Articular cartilage is exposed to enormous repetitive forces.

A newly restored surface cannot immediately tolerate the same loads as a mature joint.

Early rehabilitation protects the repair while maintaining movement and muscle function.

Load is gradually increased as biological healing progresses.

Symptoms alone cannot determine whether tissue is mature.

A patient may feel little pain long before the restoration is ready for running or pivoting sport.

Recovery After Microfracture

Weight-bearing is frequently limited during the early period for defects on weight-bearing surfaces.

Motion generally begins early.

The fibrocartilage repair tissue then matures gradually.

The patient transitions from protected loading to strengthening and later impact activity.

Smaller defects generally have a more favorable rehabilitation pathway than medium and large defects.

High-impact sport should not be resumed simply because the procedure was arthroscopic.

Recovery After OATS

The transplanted bone plug needs to integrate with the surrounding recipient bone.

Loading is initially protected.

Knee motion usually progresses early.

Once bone incorporation and symptoms permit, weight-bearing increases.

Because the graft already carries mature articular cartilage, the biological process differs from marrow stimulation.

However, the bone interface still requires adequate healing before repeated high-impact loading.

Recovery After Osteochondral Allograft

Larger grafts frequently require longer protection.

The donor bone needs to incorporate with the recipient.

Crutches are commonly used for several weeks.

Strength is rebuilt gradually.

Running is introduced only after adequate graft integration and functional recovery.

Return to sport is often around eight to twelve months but can take longer after very large lesions or combined procedures.

Recovery After MACI

MACI requires a particularly gradual rehabilitation.

The implanted cells and matrix develop repair tissue over time.

Controlled motion begins relatively early because complete immobilization is undesirable.

Weight-bearing increases gradually.

High-impact loading is delayed.

Patients may continue improving for one to two years after implantation.

Recovery After Combined Osteotomy

When cartilage restoration is combined with osteotomy, bone healing becomes another limiting factor.

Weight-bearing can remain restricted while the osteotomy consolidates.

X-rays are used to monitor healing.

Strength training progresses more slowly than after isolated cartilage surgery.

Return to running and sport is therefore usually later.

Return to Work

Desk-based work may be possible within approximately two to six weeks.

Working from home can allow an earlier return because the patient can elevate the leg and avoid commuting with crutches.

Jobs involving prolonged standing take longer.

Heavy physical occupations involving climbing, squatting, lifting or repeated impact can require several months.

The correct timeline depends on both the cartilage procedure and the actual demands of the job.

Driving

Driving should resume only when the patient can control the vehicle safely.

The patient must be able to perform an emergency stop.

A brace or major weight-bearing restriction can prevent safe driving.

Strong pain medication is another reason to delay.

Right-knee surgery generally affects pedal control more directly.

Flying

Long-distance flying soon after lower-limb surgery requires specific medical advice.

Surgery and temporary reduced mobility can increase thrombosis risk.

Long flights add prolonged sitting.

International patients should therefore obtain individualized clearance before planning their return journey.

The hospital discharge date should not automatically be treated as the safe flight date.

Return to Sport

Return to sport after cartilage restoration is possible for many athletes.

Contemporary studies report that a substantial majority return to some form of sport, but returning to exactly the same competitive level is less predictable.

Procedure selection matters.

OATS and MACI have demonstrated strong contemporary return-to-sport profiles in appropriately selected populations.

Microfracture can permit return but may be associated with lower-level return in some higher-demand populations.

The patient's own lesion and sport remain more important than any pooled percentage.

Cartilage restoration can provide meaningful improvement in pain and function when a focal lesion is treated with an appropriate procedure.

Results depend heavily on patient selection.

A small contained defect in a stable, well-aligned knee cannot be expected to behave like a large revision lesion in a meniscus-deficient compartment.

The procedure therefore cannot be discussed using one universal success percentage.

The broad evidence for modern restorative procedures is encouraging, particularly for OATS, OCA and cell-based treatments in appropriately selected patients.

What Does Success Mean?

Different studies define success differently.

One may measure improvement in knee scores.

Another may define success as avoiding another operation.

Another may evaluate graft survival on MRI.

Athletes may define success primarily by returning to sport.

These are not interchangeable endpoints.

A patient can have major pain improvement but never return to elite competition.

Another can return to sport while still demonstrating an imperfect MRI appearance.

Overall Functional Outcomes

Contemporary comparative evidence shows that major restorative techniques such as ACI, MACI, osteochondral autograft and osteochondral allograft generally improve knee pain and function.

No technique has demonstrated universal superiority for every lesion type.

Patient and defect characteristics remain essential.

The best outcomes are generally achieved when the biological procedure and mechanical environment are addressed together.

Return to Sport

Contemporary systematic evidence across cartilage-restoration procedures suggests that roughly four out of five athletes can return to some level of sport after surgery.

This pooled number should not be presented as an individual prediction.

MACI and OATS have shown particularly favorable probabilities of returning at the same or a higher level in contemporary athlete studies.

Microfracture can allow return to sport but has shown less favorable high-level return patterns in some comparisons.

Lesion size, sport, competition level and previous surgery all influence the result.

Microfracture Outcomes

Microfracture can produce good short-term improvement in selected small lesions.

The main concern is durability.

Long-term evidence becomes less favorable as lesion size increases.

For medium and large defects, studies have reported deterioration in outcomes, osteoarthritis progression and substantial reoperation variability over long follow-up.

This does not make microfracture a poor procedure in every patient.

It means it should be reserved for the lesion types where its biological limitations are acceptable.

OATS Outcomes

OATS can provide durable improvement in well-selected patients.

The technique is particularly attractive for smaller osteochondral lesions in younger active individuals.

The graft introduces mature cartilage immediately, while the bony portion integrates with the recipient.

Long-term success is affected by lesion size, previous surgery and patient age.

Larger defects are less suitable because only a limited amount of donor cartilage can be harvested from the same knee.

Osteochondral Allograft Outcomes

OCA can provide long-term joint preservation for large focal defects.

Historical and contemporary cohorts report useful graft survivorship extending beyond ten years in many patients.

Recent data continue to show roughly four out of five grafts functioning at around ten years in broad cohorts, although results vary substantially according to lesion type.

Revision cases and very large defects tend to have less favorable outcomes than straightforward primary procedures.

Reoperation is also more common than graft failure itself.

A patient can undergo another arthroscopy or hardware procedure while the osteochondral graft continues functioning.

OCA After Failed Previous Cartilage Surgery

Osteochondral allograft is an important salvage option.

Patients who have undergone previous microfracture or another cartilage procedure can still experience meaningful improvement.

However, revision cartilage surgery generally has less predictable outcomes than a well-selected primary procedure.

Large defects and multiple previous surgeries increase complexity.

The surgeon should assess the subchondral bone and mechanical causes of the original failure carefully.

MACI Outcomes

Long-term data for MACI are encouraging.

Studies with more than ten years of follow-up report durable improvements in patient-reported outcomes in appropriately selected patients.

Graft failure and progression to arthroplasty occur in a minority rather than being expected outcomes.

Patellofemoral MACI has also demonstrated durable results in long-term cohorts when appropriate mechanical correction accompanies the restoration where necessary.

The key limitation is that these results apply to carefully selected cartilage patients rather than to every person with knee arthritis.

OATS Versus MACI Versus OCA

The procedures should not be ranked without considering the defect.

OATS provides mature cartilage but is limited by donor-site availability.

OCA allows large osteochondral reconstruction without harvesting from the patient's knee but requires donor tissue.

MACI can treat large cartilage-surface defects using the patient's own cells but requires two stages and lengthy maturation.

The best procedure therefore changes with lesion size, bone involvement, location and previous treatment.

Does Cartilage Restoration Regrow Normal Cartilage?

The answer depends on the technique.

Microfracture creates primarily fibrocartilage.

This is repair tissue rather than a perfect recreation of native hyaline cartilage.

OATS and OCA physically transfer mature articular cartilage into the defect.

MACI aims to create durable cartilage-like repair tissue through cultured chondrocytes.

Even sophisticated regenerative procedures should not be advertised as guaranteeing a completely normal joint surface.

MRI Outcomes

MRI can be used to evaluate defect fill, integration and the structure of repair tissue.

Special scoring systems can describe the appearance of cartilage restoration.

An excellent MRI does not necessarily correspond perfectly with symptoms.

Likewise, a patient can function very well despite an imperfect imaging appearance.

Imaging should therefore support rather than replace clinical evaluation.

Reoperation

Reoperation after cartilage restoration does not always mean the restoration failed.

A patient may undergo arthroscopy for scar tissue, hardware removal, graft assessment or another knee condition.

Different studies use different definitions of failure, making comparisons difficult.

Revision surgery and conversion to arthroplasty are more clinically significant endpoints than a minor secondary procedure.

Factors Associated With Better Outcomes

Results are generally more favorable when the defect is localized, alignment is acceptable and ligaments are stable.

Functional meniscal tissue also matters.

Lower body weight and good rehabilitation participation can help reduce unnecessary load during healing.

Appropriate procedure selection is particularly important.

Using a technique outside the biological range where it performs best can reduce durability.

Factors Associated With Less Favorable Outcomes

Very large lesions are more challenging.

Previous failed cartilage surgery can reduce predictability.

Advanced age can correlate with poorer cartilage biology, although age alone should not determine candidacy.

Diffuse osteoarthritis is a major negative factor.

Severe meniscal deficiency, untreated malalignment and ligament instability can also overload the restoration.

Long-Term Osteoarthritis

Cartilage restoration aims to preserve the knee, but it cannot guarantee prevention of osteoarthritis.

The original injury may have already altered the joint.

Meniscus loss, ligament damage and genetic or metabolic factors also influence long-term degeneration.

A successful restoration may improve mechanics and delay progression, but patients should not be promised that arthritis can never develop.

When Cartilage Restoration Fails

Failure can present as persistent pain, recurrent swelling or deterioration in function.

Imaging can show incomplete defect fill, graft delamination, osteochondral nonunion or progressive degeneration depending on the procedure.

The surgeon then reassesses alignment, meniscus status, ligament stability and subchondral bone.

Revision treatment can involve another cartilage procedure, osteochondral allograft, osteotomy or eventually arthroplasty depending on the condition of the joint.

Arthroscopy Systems

Modern cartilage restoration frequently begins with high-definition arthroscopy.

The surgeon uses a small camera to inspect the joint and measure defects.

HD and 4K systems can provide detailed visualization of cartilage margins, menisci and associated pathology.

Fluid-management systems maintain visibility by controlling sterile fluid flow through the joint.

Technology improves visualization, but the critical decisions remain clinical: defect selection, mechanical correction and restoration technique.

Cartilage Measurement Instruments

Arthroscopic probes and calibrated rulers help measure lesion dimensions.

The surgeon needs an accurate surface-area estimate because procedure choice often depends partly on defect size.

Special templates can also be used during open restoration.

Three-dimensional measurements become particularly important when preparing matching osteochondral grafts.

Microfracture Awls

Traditional microfracture uses small awls to create holes through the subchondral plate.

The instrument produces controlled perforations rather than removing a large volume of bone.

Modern marrow-stimulation systems can use alternative drilling or needling devices.

The technology remains relatively simple compared with osteochondral transplantation or cell-based procedures.

Low-Speed Drilling Systems

Drilling devices create small channels through subchondral bone.

Low-speed systems are designed to minimize thermal injury.

The channels allow marrow contents to enter the defect.

Like microfracture, drilling is a marrow-stimulation technology rather than a true cartilage implant.

Scaffolds and Membranes

Scaffolds provide a three-dimensional environment in which cells and repair tissue can organize.

Collagen membranes are among the materials used.

A scaffold can be combined with marrow stimulation, cultured chondrocytes or minced cartilage depending on the technique.

The biological composition and regulatory approval of these products differ across countries.

Patients should therefore be told exactly what product is being proposed rather than receiving the generic description “cartilage scaffold.”

OATS Coring Systems

OATS requires specialized cylindrical instruments.

One coring device harvests the osteochondral plug.

A matching instrument prepares the recipient socket.

The close dimensional match allows the graft to be seated using a press fit.

Different diameters are available so the surgeon can adapt to lesion size.

Accurate instrumentation is important because graft height and joint-surface congruity influence local contact pressure.

Osteochondral Graft Workstations

OCA transplantation can use specialized cutting and measurement systems.

The recipient site is measured at several points.

The donor graft is then shaped to reproduce the same geometry.

Large shell grafts require additional instrumentation.

Some systems allow highly controlled preparation of both recipient and donor surfaces.

Fresh Osteochondral Allograft

The graft itself is the principal biological implant.

It contains viable donor cartilage and supporting bone.

Modern tissue banks use screening, processing and controlled storage protocols.

Preserving chondrocyte viability is important because living cartilage cells contribute to graft function.

Processing and storage methods remain areas of ongoing research.

Press-Fit Fixation

Many cylindrical OATS and OCA grafts do not require screws.

A precise fit between graft and recipient bone can provide mechanical stability.

This avoids permanent hardware across the cartilage surface.

Large or irregular grafts can require additional fixation.

Bioabsorbable Pins and Screws

Certain osteochondral fragments or large grafts can be stabilized using bioabsorbable fixation.

These implants gradually change within the body rather than remaining as permanent metal hardware.

They must be positioned beneath the cartilage surface to avoid joint abrasion.

The use of fixation depends on graft size and stability.

Metal Screws

Large shell grafts occasionally require metal screws.

The screw heads are countersunk below the cartilage surface.

Hardware can sometimes be removed after graft healing if it becomes symptomatic or if the surgeon prefers planned removal.

Hardware selection depends on the reconstruction.

MACI Membrane

MACI is a specialized cellular implant.

The patient's own cultured chondrocytes are placed on a porcine-derived collagen membrane.

The membrane is cut to match the lesion.

The cells and scaffold are then implanted into the prepared defect.

Because the cells belong to the patient, the treatment differs fundamentally from donor osteochondral transplantation.

Fibrin Sealant

A biological adhesive can secure a MACI membrane within the defect.

The surgeon applies a thin layer before positioning the implant.

The membrane is held in place while the sealant sets.

The knee can then be moved gently to confirm that the membrane remains stable.

This avoids the need for extensive suturing in many contained lesions.

Cartilage Cell Expansion

MACI requires specialized laboratory technology.

Chondrocytes obtained during biopsy are isolated and expanded under controlled manufacturing conditions.

The cells are then incorporated into the implant.

This laboratory component explains why MACI is not an immediate single-stage operation.

Minced Cartilage Systems

Minced cartilage techniques use small pieces of viable cartilage.

Some surgeons manually mince the tissue.

Commercial systems can standardize cutting and delivery.

The fragments are combined with fibrin or another scaffold to keep them within the defect.

These approaches remain less standardized than established OATS, OCA and MACI procedures.

MRI Cartilage Mapping

Modern MRI sequences allow increasingly detailed evaluation of cartilage morphology.

Standard MRI remains the principal imaging tool in most clinical settings.

Advanced quantitative imaging can assess tissue composition in research and specialist centers.

These techniques can help study graft maturation but are not required for every patient.

MOCART Assessment

The Magnetic Resonance Observation of Cartilage Repair Tissue system is one method used in research and specialist follow-up.

It evaluates characteristics such as defect fill, integration and surface appearance.

MOCART scores are useful for describing repair tissue but should not be interpreted independently of symptoms and function.

3D Planning

Three-dimensional imaging and planning can be useful for large osteochondral grafts or complex alignment correction.

A surgeon can evaluate the geometry of a donor graft and recipient joint.

3D planning is particularly useful when cartilage restoration forms part of a broader joint-preservation reconstruction.

It is less important for a small straightforward arthroscopic lesion.

Osteotomy Plates

When cartilage restoration is combined with realignment, a plate and screws stabilize the osteotomy.

These implants hold the corrected bone position while healing occurs.

Modern locking plates provide strong fixation.

The hardware can usually remain permanently unless it becomes symptomatic.

Robotic Technology

Robotic systems are not a routine requirement for cartilage restoration.

Most established orthopedic robots are designed primarily for arthroplasty.

Cartilage transplantation remains dependent on direct arthroscopic or open visualization, graft preparation and surgeon-controlled implantation.

Experimental technologies may improve planning in the future, but robotic branding should not be presented as evidence of superior cartilage restoration.

Stem Cells

Stem-cell therapies are frequently discussed under the term cartilage regeneration.

Research into mesenchymal stromal cells and tissue engineering continues.

However, commercially marketed stem-cell injections should not be treated as proven equivalents to established cartilage restoration operations.

The regulatory status and quality of evidence vary significantly between products and countries.

Patients should distinguish experimental regenerative medicine from established reconstructive procedures.

PRP

Platelet-rich plasma contains platelets and associated signaling molecules.

PRP has been investigated for knee symptoms and as an adjunct to cartilage procedures.

Evidence remains heterogeneous.

PRP cannot currently be described as a replacement for an osteochondral graft, MACI or another established procedure when a large structural cartilage defect requires restoration.

Future Cartilage Regeneration Technology

Research continues into cell therapies, gene-based treatments, hydrogels, three-dimensional scaffolds and tissue-engineered cartilage.

The long-term objective is to create tissue that reproduces native articular cartilage more closely and can integrate reliably with surrounding cartilage and bone.

Some approaches are promising experimentally.

They should not be marketed as established standard care until appropriate human clinical evidence and regulatory approval are available.