What is a Full-Thickness Cartilage Defect of the Knee?
A full-thickness cartilage defect of the knee is complete loss of articular cartilage extending down to the exposed subchondral bone, representing the most severe grade of cartilage injury. This is distinct from partial-thickness defects where some cartilage remains intact 1.
Classification and Definition
Full-thickness defects are consistently defined across multiple grading systems as:
- Outerbridge Grade 4: Complete loss of cartilage with exposed subchondral bone 1
- Beck Grade 5: Full-thickness defect 1
- ALAD Grade 4: Complete loss of cartilage and exposed subchondral bone 1
The key distinguishing feature is that the defect penetrates through all layers of hyaline cartilage, leaving bare bone exposed at the joint surface.
Clinical Significance
Full-thickness defects have extremely poor healing capacity and represent a major risk factor for progression to osteoarthritis and eventual total knee arthroplasty 2, 3, 4. These defects are particularly concerning because:
- They increase the risk of knee replacement 5-fold for larger defects (≥2 cm²) and 2.6-fold for smaller defects (<2 cm²), even after controlling for baseline arthritis severity 3
- The incidence of knee arthroplasty jumps from 0.57% per person-year in patients without defects to 2.15% in those with full-thickness defects 3
- Unlike partial-thickness injuries, full-thickness defects cannot heal spontaneously due to the avascular nature of cartilage and exposure of subchondral bone 2, 4
Presentation and Diagnosis
Patients typically present with:
- Persistent joint line pain
- Swelling and effusion
- Mechanical symptoms (catching, locking) 5, 6
- Pain that may radiate from the primary location 1
Plain radiographs can detect joint space narrowing but cannot visualize focal full-thickness defects—MRI or arthroscopy is required for definitive diagnosis 1, 6.
Treatment Implications
The presence of a full-thickness defect fundamentally changes treatment strategy:
For defects <2 cm²: Microfracture, chondroplasty, or osteochondral autograft transfer are first-line options 1, 6
For defects 2-6 cm²: Osteochondral allograft transplantation or autologous chondrocyte implantation (ACI/MACI) are preferred 1, 7
For defects >6-8 cm²: Total knee arthroplasty should be considered 1
Important Caveats
- Full-thickness defects are independent predictors of arthroplasty risk regardless of radiographic arthritis grade 3
- Treatment should be pursued early in younger patients (typically <45-50 years) to prevent progression to diffuse osteoarthritis 1, 4
- Concomitant pathology (malalignment, meniscus tears, ligament instability) must be addressed simultaneously for successful outcomes 4, 6
The critical distinction is that full-thickness defects represent complete cartilage loss down to bone, not just surface damage or partial thinning—this fundamentally affects both prognosis and treatment approach 1.