Cartilage Injuries in the Knee

Cartilage injuries in the knee are becoming increasingly common among athletes, fitness enthusiasts, and even individuals with sedentary lifestyles. Unlike muscle or bone, cartilage does not heal on its own due to its limited blood supply. When left untreated, a damaged cartilage surface can progress to chronic pain, joint instability, and early-onset osteoarthritis. Modern orthopaedic advancements, however, have introduced a powerful solution: cartilage transplantation.

Cartilage transplant procedures aim to restore the joint surface with healthy cartilage cells or grafts, enabling smoother movement, reduced pain, and a significantly higher chance of long-term knee preservation. This blog explores the types of cartilage transplant techniques, how they work, who qualifies for them, and what patients can expect from the procedure.

Understanding Knee Cartilage Damage

The knee joint is covered with articular cartilage, a smooth, rubbery tissue that allows friction-free movement. When this cartilage is damaged due to sports injuries, trauma, degenerative changes, or repeated stress, the underlying bone becomes exposed. This results in:

• Sharp knee pain during movement
• Swelling and stiffness
• Clicking, locking, or catching sensations
• Difficulty bearing weight
• Decreased athletic performance

Cartilage defects rarely heal naturally. Hence, advanced regenerative and transplant-based procedures have become crucial in modern knee preservation strategies.

What Is Cartilage Transplantation?

Cartilage transplantation (also called cartilage restoration surgery) refers to procedures where a surgeon replaces damaged cartilage with new, healthy cartilage cells or tissues. The purpose is to:

• Regenerate natural joint surfaces
• Delay or prevent arthritis
• Reduce pain and mechanical symptoms
• Restore functional mobility
• Allow athletes to return to sport safely

Unlike partial or total knee replacement, cartilage transplantation aims to preserve the native knee joint, making it ideal for younger or active patients.

Types of Cartilage Transplant for Knee Injuries

There are several advanced cartilage restoration techniques used globally. Each type is selected based on the size, depth, location, and severity of the defect, as well as the patient’s age and activity levels.

Below are the major types of cartilage transplant procedures used in orthopaedic practice.

1. Microfracture Surgery (Bone Marrow Stimulation)

Overview Microfracture is a minimally invasive arthroscopic procedure where tiny holes are created in the bone beneath the damaged cartilage. This triggers the body’s natural healing process by releasing bone marrow cells that form repair tissue.

Suitable For

• Small cartilage defects
• Younger patients experiencing early symptoms
• Individuals with low-impact activity levels

Benefits

• Least invasive
• Cost-effective
• Faster recovery compared to other techniques

Limitations The new cartilage formed is fibrocartilage, which is not as durable as natural hyaline cartilage and may break down under high-intensity sports.

2. Osteochondral Autograft Transfer (OATS)

Overview In OATS, cylindrical plugs of healthy cartilage and underlying bone are taken from a non-weight-bearing area of the patient’s knee and transplanted into the damaged region.

Suitable For

• Small to medium-sized defects
• Isolated cartilage lesions
• Young athletes or physically active individuals

Benefits

• Uses the patient’s own tissue
• Immediate structural stability
• Restores natural hyaline cartilage

Limitations Limited donor sites in the patient’s knee; not suitable for widespread cartilage loss.

3. Mosaicplasty

Overview Mosaicplasty involves transferring multiple small cartilage plugs that form a mosaic-like pattern to fill the defect.

Best For

• Medium-sized defects
• Trauma-related cartilage injuries
• Patients with stable knee alignment and ligaments

Advantages

• Biological cartilage restoration
• Long-lasting results in properly selected patients

Drawbacks Surface may not be perfectly smooth; possible donor site discomfort.

4. Osteochondral Allograft Transplantation

Overview This procedure uses fresh cartilage tissue from a donor and implants it into the patient’s knee.

Ideal For

• Large cartilage defects
• Patients with previous failed cartilage surgeries
• Individuals wanting to avoid joint replacement at a young age

Benefits

• No donor site morbidity
• Can cover wide or deep cartilage losses
• Restores native cartilage properties

Limitations Availability of donor tissue; higher cost; requires compatibility assessment.

5. Autologous Chondrocyte Implantation (ACI)

Overview ACI is a two-stage procedure where cartilage cells are harvested, grown in a lab, and then re-implanted.

Best For

• Medium to large cartilage defects
• Younger and active individuals
• Patients with stable knees and intact ligaments

Benefits

• Uses patient’s own cartilage cells
• Produces long-lasting hyaline-like cartilage
• Ideal for athletes aiming to return to sports

Challenges Two surgeries required; longer recovery; higher cost.

6. Matrix-Induced Autologous Chondrocyte Implantation (MACI)

Overview MACI places cultivated chondrocytes on a collagen membrane fixed over the defect.

Suitable For

• Large defects requiring precise repair
• Patients wanting predictable outcomes
• Those with failed previous cartilage treatments

Advantages

• Better integration
• Stronger cartilage quality
• Lower complication rate

Limitations Costly and requires skilled expertise.

7. Particulated Juvenile Cartilage

Overview Uses fresh juvenile cartilage fragments placed into the defect.

Best For

• Small-to-medium defects
• Patients who want faster recovery
• Individuals not suitable for autografts

Benefits

• High cell density
• Excellent healing potential
• Single-stage procedure

Limitations Not suitable for very large lesions.

How Surgeons Choose the Right Type

Specialists evaluate:

1. Size of Cartilage Defect
   • Small: Microfracture, OATS
   • Medium: OATS, Mosaicplasty
   • Large: ACI, MACI, Allograft
2. Location of Lesion Femoral defects respond to OATS or ACI; patellar defects to MACI.
3. Age and Activity Level
4. Knee Alignment
5. Ligament Stability

Eligibility Criteria

1. Focal Cartilage Defects
2. Age 16–50 Years
3. Healthy Body Weight
4. Stable Knee
5. Correct Alignment
6. Non-Smokers
7. Realistic Expectations

Recovery After Cartilage Transplant

1. Initial Weeks
   • Protected weight-bearing
   • Physiotherapy
   • Swelling control
2. 3–6 Months
3. 6–12 Months

Full Recovery Timeline

• Microfracture: 4–6 months
• OATS/Mosaicplasty: 6–9 months
• ACI/MACI/Allograft: 9–18 months

Benefits of Cartilage Transplant

• Pain reduction
• Improved function
• Lower arthritis risk
• Enhanced sports performance
• Joint preservation
• Delays knee replacement

Risks and Considerations

• Infection or bleeding
• Graft failure
• Incomplete healing
• Prolonged rehabilitation
• Possible revision surgery

Conclusion

Cartilage transplantation has transformed the treatment of knee cartilage injuries, offering tailored solutions based on defect size, alignment, activity level, and long-term goals. Timely consultation with a knee specialist helps determine candidacy and the most suitable procedure.