What is the recommended management for a knee trochlear cartilage defect?

Management of Knee Trochlear Cartilage Defects

For small, contained trochlear cartilage defects (<4 cm²) with intact subchondral bone, arthroscopic microfracture is the recommended first-line surgical treatment, while larger defects (>2.5 cm²) or those with subchondral bone involvement require osteochondral autograft or allograft transplantation. 1

Initial Conservative Management

• Young, active patients with stable lesions ≤1 cm² and minimal symptoms should undergo a 3-6 month trial of activity modification and quadriceps strengthening before considering surgery. 1

• Monitor specifically for mechanical symptoms (locking, catching), persistent joint effusion, or focal tenderness—these indicate lesion instability and warrant earlier surgical intervention. 1

• Conservative management is appropriate only when the lesion is stable; any signs of instability or fragment displacement necessitate surgical referral. 1

Surgical Treatment Algorithm Based on Defect Size and Characteristics

Small Lesions (<2 cm²): Microfracture or Autograft

Microfracture is indicated for focal, contained lesions <4 cm² with minimal osteoarthritis, stable surrounding cartilage, and an intact subchondral plate. 1

Microfracture Technique:

• Debride friable cartilage to create perpendicular healthy edges using a shaver and ringed curets. 2
• Create 3-4 mm deep perpendicular holes spaced 3-4 mm apart using a microfracture awl until bleeding is visualized. 1
• Maintain subchondral bone bridges between holes to preserve structural integrity. 2
• The goal is to recruit pluripotent marrow cells and growth factors to form fibrocartilage fill. 2

Expected Outcomes:

• Second-look arthroscopy at 17 months demonstrates 93% ± 17% defect fill with good-quality cartilage macroscopically. 1
• Significant improvements in pain and functional scores occur, with patients showing substantial clinical improvement. 2
• This is a single-stage procedure with no donor-site morbidity and minimally invasive approach. 1

Osteochondral autograft (mosaicplasty) should be considered for patients <45 years old with focal full-thickness lesions <3 cm² when microfracture has failed or when subchondral bone is involved. 1, 3

• Autograft provides hyaline cartilage with superior mechanical properties compared to the fibrocartilage produced by microfracture. 1, 3
• Allows immediate or near-immediate weight-bearing postoperatively. 1
• Harvest grafts from the lateral trochlea (non-weightbearing surface) to minimize donor-site morbidity. 1
• Main limitation is donor-site morbidity, which can be minimized with careful harvest technique and limiting the number of plugs. 3

Medium to Large Lesions (2-6 cm²): Osteochondral Allograft

Osteochondral allograft transplantation is the first-line treatment for lesions >2.5 cm² in patients ≤50 years old without radiographic osteoarthritis. 1, 4

• Allograft eliminates donor-site morbidity while providing immediate mechanically functional hyaline cartilage. 3, 4
• Reserved specifically for revision cases with substantial subchondral bone loss or when autograft harvest sites are insufficient. 1
• Fresh allografts should be used within 28 days to maintain chondrocyte viability. 3
• Limitations include risk of disease transmission and relative paucity of donor tissue. 3

Very Large Lesions (>6 cm²): Osteochondral Allograft Only

For lesions >6 cm², osteochondral allograft is preferred due to donor site limitations with autograft. 3

Advanced Cartilage Restoration: Autologous Chondrocyte Implantation

Matrix-assisted autologous chondrocyte implantation (MACI) can be performed arthroscopically for trochlear defects and demonstrates superior outcomes compared to simple debridement. 2, 5

• MACI is a two-stage procedure: initial arthroscopic cartilage biopsy followed by 4-6 weeks of in vitro chondrocyte expansion, then arthroscopic re-implantation. 5
• For trochlear lesions specifically, autologous chondrocyte implantation improves function and reduces symptoms in young to middle-aged patients with symptomatic full-thickness defects. 6
• Patients report significant improvement in overall condition scores (from 3.1 to 6.4 points), pain (2.6 to 6.2 points), and swelling (3.9 to 6.3 points) at mean 59-month follow-up. 6
• MACI can be performed entirely arthroscopically using dry scoping technique with fibrin glue fixation. 5

Critical Prerequisites for Allograft Procedures

Patients must complete and document at least 6 weeks of supervised, in-person physical therapy with objective documentation of compliance and failure before allograft approval. 4

• Definitive imaging assessment of the opposing tibial plateau is mandatory to confirm the surface is free of significant disease or bipolar involvement. 4
• Bipolar lesions (both femoral and tibial involvement) are absolute contraindications for isolated osteochondral allograft. 4
• Meniscal deficiency must be addressed—either document adequate remaining meniscal tissue or plan concurrent meniscal allograft transplantation. 4
• The knee must be stable with negative Lachman, anterior/posterior drawer, and pivot shift tests. 4

Special Consideration: Trochlear Dysplasia

In patients with trochlear dysplasia and a supratrochlear spur ≥6 mm, the risk of developing trochlear cartilage damage increases substantially (adjusted odds ratio 3.4). 7

• Supratrochlear spur height ≥6 mm is significantly associated with both patellar and trochlear cartilage defects. 7
• High-grade trochlear dysplasia types B and D with supratrochlear spur >5 mm may require sulcus deepening trochleoplasty in addition to cartilage restoration procedures. 8
• Address underlying patellofemoral maltracking before or concurrent with cartilage restoration to prevent recurrent damage. 8

Critical Pitfalls to Avoid

Never apply micronized cartilage allograft in a "proud" configuration (extending beyond surrounding cartilage)—this results in 70% delamination in trochlear defects compared to 38% with recessed application. 9

• Recessed application (fibrin level even with or below surrounding cartilage) significantly reduces delamination risk. 9
• 82% of graft displacement occurs within the first 15 minutes of range of motion, supporting strict postoperative motion restrictions. 9
• Increasing defect size dramatically increases delamination risk, particularly in the trochlea. 9