import { ComparisonTable, ContentSection, EvidenceCard, ExamCheatSheet, ExamPearl, ExamWarning, InfoCard, InfoCardGrid, MedicalImage, MnemonicCard, OnePagerSummary, SafetyAlert, Tab, Tabs, Timeline, TimelineItem, VivaScenario, VivaScenarioSection } from '@/components/mdx' {/* SECTION 1: ONE-PAGER SUMMARY */} {/* SECTION 2: EXAM WARNING */} **Key advantage over microfracture**: OATS transfers mature hyaline cartilage with Type II collagen. This has superior biomechanical properties and durability compared to fibrocartilage. **The limiting factor**: Donor sites have 10-15% morbidity. Limited harvest area restricts to 3-4 plugs maximum. Larger lesions should have ACI or allograft. **Flush or 1mm proud** - never recessed. Perpendicular to articular surface. Press-fit stability without gaps. The fibrin clot fills gaps between plugs. **1-4cm² optimal** - fills the gap between microfracture (under 2cm²) and ACI (over 2-4cm²). Beyond 4cm², donor site availability becomes limiting. {/* SECTION 2.5: QUICK DECISION GUIDE */} {/* SECTION 3: MNEMONICS */} {/* SECTION 4: OVERVIEW AND EPIDEMIOLOGY */} OATS fills a critical niche in the cartilage treatment algorithm. Unlike microfracture (fibrocartilage) or ACI (two-stage), OATS provides true hyaline cartilage in a single surgery. Understanding its advantages and limitations compared to alternatives is essential for exam success. - **Full-thickness cartilage defect 1-4cm²** - **Femoral condyle or trochlea lesions** - **Failed microfracture** - **Young active patients** - **Single contained lesion** - **Lesion over 4cm²** (donor limitation) - **Diffuse OA** - **Bipolar (kissing) lesions** - **Inflammatory arthropathy** - **Uncorrected malalignment** - **Patellofemoral defects (relative)** {/* SECTION 5: ANATOMY AND BIOMECHANICS */} OATS transfers mature hyaline cartilage containing Type II collagen, proteoglycans, and organized chondrocytes. This is biomechanically superior to the fibrocartilage (Type I collagen) produced by microfracture. Integration studies show 90-95% Type II collagen at 1 year with OATS. - **Superolateral trochlear margin**: Accessible, low-load - **Superomedial trochlear margin**: Alternative site - **Intercondylar notch walls**: Large plugs possible - **All are non-weight-bearing areas** - **Bone-to-bone healing**: 6-8 weeks - **Cartilage integration**: Fibrocartilage fills gaps - **Chondrocyte survival**: 90%+ viability - **Subchondral bone remodels**: By 1 year {/* SECTION 6: CLASSIFICATION SYSTEMS */} ### Classification by Lesion Size The maximum lesion size for OATS is approximately 4cm² due to donor site limitations. Harvesting more than 3-4 plugs causes unacceptable donor site morbidity. For larger lesions, use ACI or osteochondral allograft. ### Lesion Location Considerations The femoral condyles are ideal for OATS due to accessibility, curvature matching, and favorable biomechanics. Patellar lesions are technically challenging and often better treated with ACI. {/* SECTION 7: CLINICAL ASSESSMENT */} - **Mechanism**: Trauma vs insidious onset - **Symptoms**: Mechanical (catching, locking), pain - **Previous treatment**: Prior cartilage procedures - **Activity demands**: Sport level and goals - **Duration**: Acute vs chronic lesion - **Effusion**: Often present with cartilage damage - **Tenderness**: Over affected compartment - **Crepitus**: May indicate cartilage pathology - **Alignment**: Assess for malalignment - **Ligamentous stability**: Rule out associated instability Malalignment is a major risk factor for OATS failure. Always assess alignment clinically and with long-leg standing films if concerned. Consider concomitant or staged osteotomy if significant varus or valgus is present. {/* SECTION 8: INVESTIGATIONS */} **Weight-bearing AP, lateral, Rosenberg (45° PA), skyline**. Assess joint space, alignment, OA changes. May show subchondral changes or cysts in chronic lesions. Assess lesion size, location, depth, and containment. Evaluate subchondral bone integrity. Identify associated pathology (meniscal, ligamentous). Donor site assessment. May be helpful for precise lesion sizing and bone stock assessment, particularly in revision cases or complex geometries. On MRI, evaluate: lesion dimensions (measure in 2 planes), depth (partial vs full-thickness), subchondral bone (cysts, edema), containment (stable shoulders), and donor site availability. MRI can underestimate lesion size - confirm at arthroscopy. {/* SECTION 9: MANAGEMENT ALGORITHM */} The 10-20% gap between mosaicplasty plugs fills with fibrocartilage, which is acceptable for integration. Complete coverage is not necessary, but aim for at least 80% hyaline cartilage coverage. {/* SECTION 12: COMPLICATIONS */} The most common complaint is donor site symptoms - anterior knee pain, crepitus, or pain with stair descent. This is why limiting harvest to 3-4 plugs maximum is essential. Counsel patients preoperatively about this expected morbidity. {/* SECTION 13: POSTOPERATIVE CARE */} ### Weight-Bearing Protocol Toe-touch weight-bearing only. Crutches mandatory. Protect healing bone-to-bone junction. Progress to 50% weight-bearing. Wean crutches by week 8. Continue protected activities. Full weight-bearing. Discontinue assistive devices. No impact activities. OATS rehabilitation is generally faster than ACI because the mature bone-to-bone junction heals more predictably than ACI cell integration. Full weight-bearing is typically achieved by 8-12 weeks. ### ROM and Strengthening Protocol CPM or early ROM exercises immediately. Full ROM goal by 4-6 weeks. Quad sets, SLR when quadriceps control achieved. Progressive closed-chain strengthening. Stationary bike when ROM allows. Pool therapy. Avoid open-chain loading. Jogging progression. Agility drills. Sport-specific training. No cutting or pivoting until month 6+. ### Return to Sport Timeline Swimming, cycling, elliptical. No running or cutting. Jogging progression if asymptomatic. Light sport-specific drills. Full sport return if functional criteria met. May be faster than ACI return. Full return to high-level sport is typically expected at 9-12 months, though individual variation exists based on lesion size and patient factors. {/* SECTION 14: OUTCOMES AND PROGNOSIS */} Unlike microfracture (which deteriorates at 2-5 years), OATS outcomes are durable to 10+ years. This is attributed to the transfer of true hyaline cartilage with mature Type II collagen matrix. {/* SECTION 15: EVIDENCE BASE */} {/* SECTION 16: VIVA SCENARIOS */} {/* SECTION 17: MCQ PRACTICE POINTS */} **Q: What type of collagen is transferred in an OATS procedure?** A: **Type II collagen** - OATS transfers mature hyaline cartilage containing Type II collagen, unlike microfracture which produces Type I collagen fibrocartilage. This is the key biomechanical advantage. **Q: What is the maximum recommended lesion size for OATS?** A: **4cm²** - Due to donor site limitations (3-4 plugs maximum before significant morbidity), OATS is limited to lesions approximately 4cm² or less. Larger lesions should have ACI or allograft. **Q: What are the common donor sites for OATS?** A: **Superolateral trochlear margin and intercondylar notch** - These non-weight-bearing areas are used to minimize functional donor site morbidity while providing accessible plug harvest. **Q: How should an OATS plug be seated relative to surrounding cartilage?** A: **Flush or up to 1mm proud** - Plugs should never be recessed as this causes load shielding and poor integration. Slightly proud plugs are worn level over time by normal joint loading. **Q: What is the approximate donor site morbidity rate for OATS?** A: **10-15%** - Approximately 10-15% of patients have symptomatic donor sites, typically anterior knee pain or crepitus. This is the main limitation of the technique. **Q: How many surgical stages are required for OATS?** A: **Single stage** - Unlike ACI which requires two stages (biopsy then implantation), OATS is completed in a single surgery. This is a significant practical advantage. {/* SECTION 18: AUSTRALIAN CONTEXT */} - OATS widely available and commonly performed - Insurance typically covers the procedure - Instrumentation systems available (Arthrex, Zimmer) - Osteochondral allograft limited availability - Record lesion size precisely at arthroscopy - Document donor site(s) used - Record plug sizes and number - Note plug seating (flush/proud) - Consent for donor site morbidity **Key documentation requirements:** - Pre-operative consent must include donor site morbidity discussion (10-15%) - Document lesion size confirms OATS suitability (1-4cm²) - Record technical details: plug sizes, number, seating - Document alignment assessment - If outcome is poor, documentation of proper technique and indications is protective {/* SECTION 19: EXAM CHEATSHEET */}

Osteochondral Autograft Transfer (OATS)

Osteochondral Autograft Transfer (OATS)