Treatment of Subchondral Knee Injury
For subchondral knee injuries, treatment should be stratified by lesion size and depth: lesions <2 cm² with subchondral involvement require osteochondral autograft transplantation, while larger lesions >2.5 cm² necessitate osteochondral allograft transplantation, with microfracture reserved only for small cartilage-only defects <2 cm² without significant subchondral bone loss. 1, 2
Initial Assessment and Conservative Management
Before considering surgical intervention, attempt conservative management for 3-6 months, particularly in patients without mechanical symptoms or osteochondral collapse 3:
- NSAIDs (topical preferred in patients ≥75 years) for inflammation control 4, 5
- Quadriceps strengthening exercises initiated immediately, as these improve knee stability and reduce mechanical stress on the subchondral bone 6, 4
- Weight reduction to BMI <25 kg/m² in overweight patients to decrease mechanical load 4, 5
- Activity modification to avoid high-impact loading 7
Critical caveat: If MRI demonstrates osteochondral collapse or large lesion size with extensive bone marrow edema, conservative management will likely fail and surgical intervention should not be delayed 3.
Surgical Treatment Algorithm
Small Lesions (<2 cm²)
For cartilage-only defects without subchondral bone involvement:
- Chondroplasty alone is preferred over microfracture, as microfracture has not demonstrated superiority and carries risks of cyst formation and intralesional osteophyte development 1
- Microfracture may be considered with biologic augmentation (bone marrow aspirate concentrate or platelet-rich plasma) for lesions <2 cm² 2
For osteochondral defects with subchondral bone involvement:
- Osteochondral autograft transplantation (mosaicplasty) is the treatment of choice 8, 1
- Harvest grafts from the lateral trochlea (non-weightbearing surface) 8
- Provides immediate hyaline cartilage replacement with superior mechanical properties compared to fibrocartilage 8
- Allows immediate or near-immediate weight bearing 8
Large Lesions (>2.5 cm²)
For large osteochondral defects with substantial subchondral bone loss:
- Osteochondral allograft transplantation is the definitive treatment 8, 1
- Indicated in patients aged ≤50 years without evidence of osteoarthritis 8
- Use fresh, size-matched cadaveric allografts in press-fit technique 8
- Single plug placement produces better outcomes than multiple "snowman" pattern plugs 2
For large cartilage-only lesions without significant bone involvement:
- Matrix-induced autologous chondrocyte implantation (MACI) is preferred, particularly for patellofemoral lesions where matching native topology is difficult 1, 2
- Provides good long-term durability 2
Special Consideration: Subchondral Insufficiency Fracture
If imaging shows bone marrow lesion with intact, healthy-appearing cartilage cap:
- Core decompression with bone marrow aspirate concentrate and bony scaffold (bioplasty) should be performed 2
- This addresses the subchondral pathology while preserving native cartilage 2
Addressing Concomitant Pathology
Critical requirement: All mechanical factors must be corrected to ensure cartilage restoration success 2:
- Malalignment: Correct with distal femoral, proximal tibial, or tibial tubercle osteotomy 2
- Meniscal deficiency: Address with meniscal transplant 2
- Ligamentous instability: Reconstruct cruciate or collateral ligaments 2
Procedures to Avoid
Arthroscopic surgery for degenerative subchondral lesions provides no benefit over conservative management and should not be performed 5.
Long-Term Prognosis
Natural history studies demonstrate that young patients with isolated severe subchondral damage can achieve excellent outcomes (79% good-to-excellent function at 14 years) with minimal intervention, though 43% develop radiographic joint space narrowing limited to the affected compartment 9. However, large lesion size and osteochondral collapse significantly increase osteoarthritis risk 3, making early surgical intervention critical in these cases.