Clinical Significance of Near Full-Thickness Patellar Cartilage Defects
A near full-thickness focal cartilage defect of the patellar articular surface is clinically significant and warrants active intervention, as it represents a precursor to progressive patellofemoral osteoarthritis, causes persistent pain and functional limitation, and has poor natural history without treatment.
Understanding the Severity
Near full-thickness defects correspond to Outerbridge grade 3-4 lesions (fragmentation/fissuring >1.5 cm or exposed subchondral bone) 1. These are not benign findings—they represent advanced cartilage pathology that:
- Accelerates joint degeneration through focal overload of the articular surface 2
- Causes persistent anterior knee pain that limits activities like squatting, stair climbing, and running 3
- Predicts poor long-term outcomes, with >50% of patellofemoral pain patients reporting persistent symptoms beyond 5 years 3
- Increases risk of patellofemoral osteoarthritis development 3
Key Clinical Implications
Symptom Profile
Patients typically present with:
- Diffuse retropatellar or peripatellar pain
- Pain during loaded knee flexion activities (stairs, squatting, running)
- Mechanical symptoms (catching, locking) 1
- Reduced physical activity levels and quality of life 3
Associated Risk Factors to Assess
The presence of anatomic abnormalities significantly increases clinical significance 4:
- Trochlear dysplasia (36% of patellar cartilage lesions)
- Patella alta (27.6% of cases)—though interestingly associated with less severe full-thickness defects 5
- Abnormal patellar tilt (24.7% of cases)
- Elevated TT-TG distance indicating malalignment
Critical point: Patellar lesions occur more frequently in younger women and are more closely associated with anatomic risk factors than trochlear lesions 4.
Treatment Decision Algorithm
For Focal, Contained Lesions <3-4 cm²
Primary intervention: Arthroscopic microfracture when:
- Intact subchondral plate present
- Healthy surrounding cartilage
- No diffuse osteoarthritis 1
Evidence shows 93% defect fill at second-look arthroscopy with significant functional improvement 1.
For Larger Lesions (>2 cm²) or Failed Microfracture
Consider advanced cartilage restoration 6, 7, 8, 9:
Matrix-induced autologous chondrocyte implantation (MACI): Two-stage procedure showing superior outcomes to simple debridement (HHS 87.4 vs 56.3) 1
Particulated juvenile allograft cartilage: Single-stage option with 82-85% good-to-excellent fill rates at 6-24 months 7
Osteochondral autograft transplantation: For isolated defects, using grafts from lesser weightbearing surfaces 10
Address Underlying Biomechanics
Do not treat the cartilage defect in isolation if anatomic abnormalities exist 6, 8:
- Tibial tubercle osteotomy (anteromedialization/distalization) when TT-TG >15-20 mm or patella alta present
- MPFL reconstruction if patellar instability documented
- Combined procedures protect cartilage restoration and prevent recurrence 6, 8
Common Pitfalls
Treating cartilage alone without addressing malalignment—leads to graft failure and persistent symptoms 6
Assuming all full-thickness defects need immediate surgery—but given poor natural history and progression risk, early intervention is justified in symptomatic patients 3
Overlooking the psychological impact—patients with patellofemoral pain are 6 times more likely to have anxiety/depression 3
Ignoring patient age and activity level—younger, active patients (<45 years) are ideal candidates for joint-preserving procedures 1
Prognosis Without Treatment
The natural history is unfavorable:
- Articular cartilage has minimal healing capacity 1
- Focal overload accelerates disease progression 2
- Aberrant loading creates a degenerative cycle 2
- Risk of progression to patellofemoral osteoarthritis 3
Bottom line: Near full-thickness patellar cartilage defects require thorough assessment of anatomic risk factors, consideration of joint-preserving surgical intervention (particularly in younger patients), and cannot be dismissed as incidental findings given their association with progressive joint degeneration and persistent disability.