import { ComparisonTable, ContentSection, EvidenceCard, ExamCheatSheet, ExamPearl, ExamWarning, InfoCard, InfoCardGrid, MedicalImage, MnemonicCard, OnePagerSummary, SafetyAlert, Tab, Tabs, Timeline, TimelineItem, VivaScenario, VivaScenarioSection } from '@/components/mdx' {/* REMOVED: 2-average-outcome-scores-at-each-time-point-for-all-.png */} **Fresh graft is essential**. Frozen allografts have less than 1% chondrocyte viability. Fresh grafts stored at 4°C maintain 70%+ viability for up to 28 days. This is a key exam distinction. OCA is **first-line for lesions over 4cm²** where OATS donor site availability is limiting. No donor site morbidity. Can address extensive bone and cartilage defects. Unlike OATS or ACI, OCA can **restore subchondral bone**. Ideal for defects with bone loss, osteonecrosis, or post-traumatic bone defects. **Limited availability** in Australia. Requires tissue bank coordination. Size matching delays surgery. Storage window is narrow (28 days). {/* At a Glance Table */} OCA is the only cartilage restoration option that transfers large amounts of mature hyaline cartilage with subchondral bone in a single stage. It fills a critical niche for large defects, failed prior surgery, and lesions with bone loss. Understanding fresh vs frozen and the storage window is essential. - **Large lesions over 4cm²** - **Failed OATS or microfracture** - **Osteonecrosis with cartilage damage** - **Post-traumatic defects with bone loss** - **Bipolar (kissing) lesions** - **Young patients not suitable for arthroplasty** - **Diffuse OA** - **Inflammatory arthropathy** - **Active infection** - **Uncorrected malalignment** - **Non-compliant patient** - **Unrealistic expectations** **Fresh OCA** stored at 4°C maintains 70%+ chondrocyte viability for up to 28 days. **Frozen OCA** has less than 1% chondrocyte viability because freezing destroys cells. The matrix remains intact in frozen grafts but the cartilage is essentially dead. Fresh grafts are essential for cartilage restoration. - **Avascular** - no blood vessel access for immune cells - **Chondrocytes encased** in matrix - **Low immunogenicity** of cartilage matrix - Bone is immunogenic - deeper grafts may generate response - **Bone-to-bone healing**: 8-12 weeks - **Cartilage**: Minimal integration (fibrocartilaginous junction) - **Subchondral bone** remodels over 1-2 years - Deep grafts integrate more slowly ### Graft Geometry Classification The choice of graft geometry depends on lesion size, location, and associated bone loss. Dowel grafts are most common for focal defects, while shell grafts preserve more bone stock. ### Common OCA Locations - **Prior cartilage surgery** (failed OATS, microfracture, ACI) - **Large traumatic defect history** - **Osteonecrosis symptoms** (night pain, rest pain) - **Mechanical symptoms** (catching, locking, swelling) - **Activity level** and expectations - **Joint effusion** - often present - **Crepitus** - may indicate cartilage damage - **Tenderness** - localized to affected compartment - **Alignment** - assess for malalignment - **Stability** - rule out ligamentous insufficiency Before OCA, assess and address: malalignment (osteotomy), ligament insufficiency (reconstruction), meniscal deficiency (allograft or preserve). OCA alone will fail if mechanical factors are not corrected. Weight-bearing AP, lateral, Rosenberg, skyline. Assess joint space, alignment, OA changes, subchondral bone status. Sizing X-rays for tissue bank matching. Lesion size and location. Subchondral bone status (edema, cysts, AVN). Associated meniscal/ligament pathology. Bone marrow lesion extent. Precise sizing for tissue bank matching. 3D reconstruction may help with complex defects. Assessment of bone stock. Tissue banks use CT or XR measurements to match donor-recipient size. The graft should be matched to within 2-3mm of recipient dimensions. Oversized grafts can be trimmed; undersized grafts cannot fill the defect adequately. ### Treatment Selection **Choose OCA when:** - Lesion over 4cm² (exceeds OATS capacity) - Failed prior cartilage surgery - Bone loss or AVN present - Bipolar lesions - Young patient unsuitable for arthroplasty **Choose OATS instead when:** - Lesion 1-4cm² and single - No bone loss - Availability/timing is critical **Choose ACI instead when:** - Large lesion but no bone loss - OCA unavailable - Patient preference for autologous This decision framework helps guide treatment selection based on lesion characteristics and patient factors. ### Associated Procedures Malalignment MUST be addressed or OCA will fail. The entire biomechanical environment needs optimization. Contact tissue bank. Provide sizing imaging (CT/XR). Request size-matched graft. Confirm availability and timing. Confirm graft arrival and harvest date. Verify within storage window (under 28 days from harvest). Review donor screening documentation. Prepare graft bench. Have backup plan if graft unsuitable intra-operatively. Standard arthroscopy and open equipment. Fresh OCA should be implanted within 28 days of harvest for optimal chondrocyte viability. Beyond this, viability drops significantly. This creates logistical challenges - patient and OR must be available when graft arrives. The window between harvest and surgery cannot be flexible. ### Dowel/Plug Technique Mini-open approach typical. Medial or lateral parapatellar as needed. Adequate exposure for instrumentation. Mark lesion boundaries. Use recipient sizing corer to create cylindrical hole. Match depth to available graft depth. Create perpendicular hole with stable rim. Harvest dowel from allograft using matching corer. Match curvature and orientation. Trim bone depth to match recipient. Insert graft into recipient site. Press-fit stability. Graft should be flush or 1mm proud. Never recessed. Press-fit often sufficient. Bioabsorbable pins if unstable. Avoid metal hardware if possible. Handle cartilage surface gently. Keep moist with saline throughout. Minimize tourniquet time. Do not compress or traumatize the cartilage surface during insertion. ### Shell Graft Technique For larger lesions or when preserving bone stock is important: **Steps:** 1. Outline lesion on recipient condyle 2. Create shallow recipient bed (5-10mm depth) 3. Prepare shell graft from allograft matching shape 4. Trial fit and adjust as needed 5. Fix with bioabsorbable pins or headless screws **Advantages of shell technique:** - Preserves more recipient bone stock - Allows custom shaping for irregular defects - Can cover larger surface area Shell grafts are an excellent option when preserving recipient bone stock is important or when lesion geometry is irregular. ### Hemicondylar/Large Segment Grafts For massive defects, entire hemicondylar segments can be transplanted: **Indications:** - Extensive AVN involving entire condyle - Massive post-traumatic defects - Failed arthroplasty salvage (selected cases) **Technical Considerations:** - Precise osteotomy matching required - Rigid fixation essential (plates/screws) - Longer rehabilitation - Higher failure rate than focal grafts This is a salvage procedure for complex cases where alternatives are limited. While rare, disease transmission is possible with allografts. All donors undergo rigorous screening (serology, NAT, culture, medical history review). HIV and Hepatitis C transmission have been reported historically but are extremely rare with modern protocols. ### Weight-Bearing Protocol Strict NWB or toe-touch only. Longer protection than OATS due to deeper bone integration required. Progressive weight-bearing 25% to 75%. Crutches continued. Wean from crutches. Full WB by 16 weeks. Continue avoiding impact. OCA rehabilitation is longer than OATS because deeper bone grafts require more time for integration. Hemicondylar grafts may need 3-4 months of protection before full weight-bearing. ### Return to Sport Swimming, cycling, elliptical. No running or jumping. Jogging progression. Sport-specific drills begin. Return to sport if criteria met. Longer than OATS or microfracture. Consider permanent activity modification for large grafts. {/* REMOVED: 2-average-outcome-scores-at-each-time-point-for-all-.png */} In young patients unsuitable for arthroplasty, OCA can delay TKA by 10-15 years on average. Even if OCA eventually fails, it preserves bone stock and allows eventual arthroplasty. This "bridge" strategy is valuable in patients too young for definitive replacement. **Q: At what temperature should fresh osteochondral allograft be stored?** A: **4°C (refrigerated)** - Fresh OCA is stored at 4°C in nutrient medium. Frozen storage (-80°C) kills chondrocytes and is not used for cartilage restoration. **Q: What is the approximate chondrocyte viability of fresh OCA at 28 days?** A: **Greater than 70%** - Fresh OCA maintains over 70% chondrocyte viability when stored at 4°C for up to 28 days. Beyond this, viability drops significantly. **Q: What is the chondrocyte viability of frozen osteochondral allograft?** A: **Less than 1%** - Freezing destroys chondrocytes. Frozen allografts have essentially no living cartilage cells, making them unsuitable for cartilage restoration (used only for structural bone). **Q: What is the typical lesion size indication for OCA?** A: **Greater than 4cm²** - OCA is typically indicated for lesions over 4cm² where OATS donor capacity is exceeded. It fills the gap for large lesions that cannot be treated with autograft. **Q: What is the approximate 10-year survivorship of unipolar OCA?** A: **75-85%** - OCA provides durable medium-term results with 75-85% survivorship at 10 years. This may serve as a bridge to eventual arthroplasty in young patients. **Q: How do bipolar OCA outcomes compare to unipolar?** A: **Worse - approximately 65% survivorship at 10 years vs 80%+** - Bipolar (kissing) lesions involving both articulating surfaces have lower success rates than single-surface OCA. - OCA availability limited in Australia - Requires tissue bank coordination - Some centers import from US tissue banks - Cost and logistics are barriers - Alternative: OATS or ACI when OCA unavailable - Document graft harvest date and storage duration - Record donor screening documentation - Document surgical technique and fixation - Consent must include disease transmission risk - Record size matching process **Key documentation requirements:** - Consent must include: disease transmission risk (very low but real), potential for failure and conversion to TKA, realistic sport expectations - Document graft arrival and harvest date (confirm within window) - Record donor screening documentation reviewed - If graft fails early, documentation of proper storage and surgical technique is protective

Osteochondral Allograft (OCA)

Osteochondral Allograft (OCA)