Courtesy – Dr Dinshaw Pardiwala, Dr Ashok Shyam, Ortho TV

Modern Approach to Articular Cartilage Restoration

Importance of Articular Cartilage

• Articular cartilage plays a critical role in knee joint function.

• It provides a smooth, low-friction surface for joint movement.

• It helps in even distribution of load across the joint surface.

• This load distribution reduces peak stresses on the subchondral bone.

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Limited Healing Capacity of Cartilage

• Articular cartilage has very limited ability to heal spontaneously.

• Full-thickness cartilage defects usually progress over time.

Natural History of Untreated Defects

• Cartilage defects tend to enlarge progressively.

• Subchondral bone edema may develop.

• Over time, degenerative changes appear.

Long-term observations show:

• Approximately half of patients develop osteoarthritis within fourteen years if defects remain untreated.

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Progression of Untreated Cartilage Lesions

Consider a patient with a full-thickness medial femoral condyle cartilage defect.

Initial features:

• Active middle-aged distance runner

• Mild varus alignment

• Continued high load on the joint

Disease Progression

• Three weeks: localized cartilage defect

• Three months: enlargement of the lesion

• Six months: subchondral bone edema appears

• Five years: early arthritic changes with osteophyte formation

• Seven years: established medial compartment osteoarthritis

This illustrates the poor prognosis of untreated cartilage lesions.

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Surgical Options for Cartilage Restoration

Over the years, several surgical strategies have been developed.

Common options include:

• Osteochondral fracture fixation

• Bone marrow stimulation procedures

• Osteochondral autograft transfer

• Synthetic plugs

• Osteochondral allografts

• Autologous chondrocyte implantation

• Limited surface replacement implants

Treatment selection depends on lesion characteristics and patient factors.

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Management Algorithm for Cartilage Lesions

Treatment decisions are based on:

• Nature of the lesion

• Size of the defect

• Location of the defect

• Patient age and activity level

• Associated mechanical factors

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Traumatic Osteochondral Fractures

Acute traumatic osteochondral fractures are best treated with fixation.

Surgical Principles

• Arthroscopic evaluation of the fragment

• Assessment of subchondral bone viability

• Anatomical reduction and fixation

Fixation is often performed through a mini-open approach because it allows:

• Accurate reduction

• Better control of rotational alignment

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Fixation Techniques

Fragments can be fixed using:

• Countersunk metal screws

• Bioabsorbable screws

Healing typically occurs through subchondral bone integration.

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Management of Delayed Osteochondral Fractures

Delayed presentation does not always preclude fixation.

Research observations have shown:

• Chondrocytes in osteochondral fragments may remain viable for up to three months.

• If the cartilage surface appears healthy, fixation may still be successful.

Therefore, even chronic fragments can sometimes be reduced and fixed successfully.

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Osteochondritis Dissecans Lesions

For unstable lesions with displaced fragments:

• Fixation may not always be appropriate.

• Alternative cartilage restoration procedures may be required.

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Partial Thickness Cartilage Defects

Partial thickness defects are commonly treated with chondroplasty.

Indications

• Symptomatic cartilage flaps

• Mechanical symptoms such as catching or locking

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Surgical Technique

• Remove unstable cartilage flaps.

• Smooth and stabilize the surrounding cartilage edges.

Key principle:

• Avoid aggressive debridement.

• Preserve as much healthy cartilage as possible.

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Full Thickness Cartilage Defects

Full thickness cartilage defects require restorative procedures.

Several surgical options exist.

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Bone Marrow Stimulation Techniques

Bone marrow stimulation procedures aim to stimulate cartilage repair.

Technique

• Remove unstable cartilage edges.

• Create small perforations in the subchondral bone.

This allows:

• Bone marrow elements

• Mesenchymal stem cells

• Growth factors

to enter the defect and form a fibrocartilage repair tissue.

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Technical Considerations

• Previously, holes were created approximately three millimetres apart.

• Current understanding suggests that fewer holes may be adequate.

• Excessive perforation can weaken the subchondral plate.

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Limitations

Bone marrow stimulation produces fibrocartilage rather than hyaline cartilage.

Outcomes are variable:

• Some patients experience excellent results.

• Others show incomplete or poor cartilage regeneration.

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Osteochondral Autograft Transfer

For restoration of hyaline cartilage, osteochondral autograft transfer is often preferred.

This technique is commonly known as mosaicplasty.

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Mosaicplasty Technique

• Osteochondral plugs are harvested from non-weight-bearing areas of the femoral condyle.

• These plugs are transplanted into the cartilage defect.

The grafts contain:

• Hyaline cartilage

• Subchondral bone

This provides a biological restoration of the joint surface.

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Indications for Mosaicplasty

Best suited for:

• Small focal defects

• Lesions smaller than approximately two square centimetres

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Donor Site Considerations

Harvesting multiple grafts increases the risk of:

• Donor site morbidity

• Patellofemoral symptoms

Therefore, graft harvesting should be limited.

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Technical Challenges

Successful mosaicplasty requires:

• Accurate perpendicular socket preparation

• Proper graft sizing

• Correct depth placement

Important principle:

• Grafts should not protrude above the articular surface.

Slightly recessed placement is preferable to avoid joint surface irregularity.

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Autologous Chondrocyte Implantation

For larger defects, autologous chondrocyte implantation is an important option.

Technique

• Cartilage biopsy is obtained arthroscopically.

• Chondrocytes are cultured in a laboratory.

• Cultured cells are implanted into the defect.

Gel-based implantation systems are widely used in several countries.

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Advantages of Autologous Chondrocyte Implantation

This method allows:

• Restoration of large cartilage defects

• Reconstruction of complex joint contours

It is particularly useful in areas where shape restoration is critical.

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Osteochondral Allograft Transplantation

Osteochondral allografts are used for large structural defects.

Indications

• Massive osteochondral lesions

• Failed previous cartilage procedures

• Segmental condylar defects

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Advantages

• Restoration of both cartilage and subchondral bone

• Ability to reconstruct large joint surface segments

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Limitations

• High cost

• Limited availability

• Need for graft matching

For these reasons, allografts are often reserved for complex cases.

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Treatment Based on Lesion Size

A practical treatment strategy can be summarized as follows:

Very Small Lesions

• Bone marrow stimulation procedures

Small to Medium Lesions

• Osteochondral autograft transfer

Larger Lesions

• Autologous chondrocyte implantation

Massive Defects

• Osteochondral allograft transplantation

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Importance of Correcting Predisposing Factors

Cartilage repair will fail if underlying mechanical problems are not addressed.

These include:

• Limb malalignment

• Patellofemoral maltracking

• Ligament instability

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Example

In a patient with a cartilage defect and varus alignment:

• Cartilage repair alone is insufficient.

• High tibial osteotomy may be required to unload the medial compartment.

Correcting alignment can significantly improve long-term outcomes.

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Focal Degenerative Cartilage Defects

A newer option for focal degenerative defects is patient-specific focal resurfacing implants.

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Indications for Focal Surface Implants

These implants may be considered in patients with:

• Localized degenerative cartilage damage

• Preserved joint alignment

• Minimal generalized arthritis

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Surgical Technique

The procedure involves:

• Patient-specific implant design based on imaging

• Creation of a matching socket using custom instrumentation

• Implant placement slightly recessed below the cartilage surface

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Implant Positioning

Implants are usually positioned:

• Approximately half to one millimetre below the surrounding cartilage.

This prevents the implant from becoming prominent during weight-bearing.

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Summary of Treatment Strategy

Management depends on:

• Lesion size

• Lesion location

• Patient characteristics

• Associated mechanical abnormalities

General principles include:

• Fix traumatic osteochondral fractures whenever possible.

• Treat partial thickness lesions with chondroplasty.

• Select restorative procedures for full thickness defects based on defect size.

• Correct malalignment or instability when present.

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Evolving Perspective on Cartilage Repair

Historically, articular cartilage was believed to have little capacity for repair.

Modern surgical techniques now allow:

• Restoration of joint surface structure

• Improved functional outcomes

• Delay of degenerative arthritis

Advances such as osteochondral transplantation, cell-based therapies, and biological implants have significantly expanded treatment possibilities.