High-yield overview

Fresh Cadaveric Transplant | Large Lesions | Hyaline Cartilage

Clinical Imaging

Critical OCA Exam Points

Fresh vs Frozen

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.

Large Lesion Solution

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.

Bone Stock Restoration

Unlike OATS or ACI, OCA can restore subchondral bone. Ideal for defects with bone loss, osteonecrosis, or post-traumatic bone defects.

Availability Limitation

Limited availability worldwide. Requires accredited tissue-bank coordination (AATB in the US; equivalent national tissue authorities elsewhere). Size matching delays surgery. Fresh storage window is narrow (commonly quoted as 28 days, though superficial-zone chondrocyte viability already declines beyond about 2 weeks at 4°C).

OCA vs Other Cartilage Procedures

Mnemonic

FRESHFRESH - Why Fresh Matters

Hook:Keep it FRESH - fresh allografts have living cells, frozen ones are dead!

Mnemonic

LARGELARGE - When to Use OCA

Hook:OCA is for LARGE problems that need big solutions!

Mnemonic

SCREENGraft Processing

Hook:SCREEN every graft thoroughly - safety first!

Overview and Epidemiology

Why This Topic Matters

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.

Indications

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

Contraindications

Diffuse OA
Inflammatory arthropathy
Active infection
Uncorrected malalignment
Non-compliant patient
Unrealistic expectations

Pathophysiology and Mechanisms

Fresh vs Frozen - The Critical Distinction

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.

Fresh vs Frozen Allograft

Why Cartilage is Immune-Privileged

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

Graft Integration

Bone-to-bone healing: 8-12 weeks
Cartilage: Minimal integration (fibrocartilaginous junction)
Subchondral bone remodels over 1-2 years
Deep grafts integrate more slowly

Classification Systems

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.

Clinical Assessment

History

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

Examination

Joint effusion - often present
Crepitus - may indicate cartilage damage
Tenderness - localized to affected compartment
Alignment - assess for malalignment
Stability - rule out ligamentous insufficiency

Assess Contributing Factors

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.

Investigations

Investigation Protocol

First LineX-rays

Weight-bearing AP, lateral, Rosenberg, skyline. Assess joint space, alignment, OA changes, subchondral bone status. Sizing X-rays for tissue bank matching.

EssentialMRI

Lesion size and location. Subchondral bone status (edema, cysts, AVN). Associated meniscal/ligament pathology. Bone marrow lesion extent.

For SizingCT

Precise sizing for tissue bank matching. 3D reconstruction may help with complex defects. Assessment of bone stock.

Size Matching

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.

Management Algorithm

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.

Pre-operative Planning

Pre-operative Steps

Weeks PriorTissue Bank Coordination

Contact tissue bank. Provide sizing imaging (CT/XR). Request size-matched graft. Confirm availability and timing.

Days PriorGraft Arrival

Confirm graft arrival and harvest date. Verify within storage window (under 28 days from harvest). Review donor screening documentation.

Day OfOperating Room

Prepare graft bench. Have backup plan if graft unsuitable intra-operatively. Standard arthroscopy and open equipment.

The 28-Day Window

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.

Surgical Technique

Dowel/Plug Technique

Surgical Steps

Step 1Exposure

Mini-open approach typical. Medial or lateral parapatellar as needed. Adequate exposure for instrumentation.

Step 2Recipient Preparation

Mark lesion boundaries. Use recipient sizing corer to create cylindrical hole. Match depth to available graft depth. Create perpendicular hole with stable rim.

Step 3Graft Preparation

Harvest dowel from allograft using matching corer. Match curvature and orientation. Trim bone depth to match recipient.

Step 4Implantation

Insert graft into recipient site. Press-fit stability. Graft should be flush or 1mm proud. Never recessed.

Step 5Fixation

Press-fit often sufficient. Bioabsorbable pins if unstable. Avoid metal hardware if possible.

Maintain Cartilage Viability

Handle cartilage surface gently. Keep moist with saline throughout. Minimize tourniquet time. Do not compress or traumatize the cartilage surface during insertion.

Complications

Disease Transmission Risk

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.

Postoperative Care and Rehabilitation

Weight-Bearing Protocol

Progression

Non-weight-bearingWeeks 0-6

Strict NWB or toe-touch only. Longer protection than OATS due to deeper bone integration required.

Partial Weight-BearingWeeks 6-12

Progressive weight-bearing 25% to 75%. Crutches continued.

Full Weight-BearingWeeks 12-16

Wean from crutches. Full WB by 16 weeks. Continue avoiding impact.

Longer Protection for Deep Grafts

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.

Outcomes and Prognosis

Long-term Outcomes

OCA as Bridge to Arthroplasty

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.

Evidence Base and Key Trials

OCA Long-term Survivorship of the Femoral Condyle

Levy YD, Gortz S, Pulido PA, McCauley JC, Bugbee WD • Clin Orthop Relat Res (2013)

Clinical Implication: OCA gives durable femoral-condyle results into the second decade; younger patients with fewer prior operations do best. Reoperation is common even when the graft survives - counsel accordingly.

Limitation: Retrospective single-center series from a high-volume centre; results may not generalise.

Verify on PubMed (PMID 22961315)

Storage Temperature and Chondrocyte Viability

Pallante AL, Bae WC, Chen AC, Gortz S, Bugbee WD, Sah RL • Am J Sports Med (2009)

Clinical Implication: The classic 28-day '4°C window' is generous: superficial-zone viability is already compromised beyond about 2 weeks, which is why earlier implantation is preferred and why physiologic (37°C) storage is being investigated.

Limitation: Controlled laboratory study in caprine osteochondral samples; not a clinical outcome study.

Verify on PubMed (PMID 19861697)

OCA for Steroid-associated Femoral Condyle Osteonecrosis

Gortz S, De Young AJ, Bugbee WD • Clin Orthop Relat Res (2010)

Clinical Implication: OCA is a reasonable joint-preserving salvage for high-grade osteonecrosis in young patients, restoring both bone stock and cartilage and deferring arthroplasty.

Limitation: Small retrospective case series from a high-volume centre; steroid-associated osteonecrosis specifically.

Verify on PubMed (PMID 20143191)

Return to Sport After OCA

Krych AJ, Robertson CM, Williams RJ III • Am J Sports Med (2012)

Clinical Implication: High rate of return to sport is achievable, but counsel that early surgery (shorter symptom duration) and younger age favour full return; high-level return is not guaranteed.

Limitation: Single-centre case series; heterogeneous sports and follow-up only 2.5 years.

Verify on PubMed (PMID 22316548)

Fresh OCA for Post-traumatic Knee Defects

Gross AE, Shasha N, Aubin P • Clin Orthop Relat Res (2005)

Clinical Implication: Fresh OCA gives durable reconstruction of post-traumatic femoral and tibial defects; tibial-plateau survivorship declines faster in the second decade. The same group's data indicate bipolar grafts, older age and uncorrected malalignment predict poorer outcomes.

Limitation: Prospective single-centre cohort; results from a highly experienced unit.

Verify on PubMed (PMID 15930924)

Exam Viva Scenarios

Use these scenarios to practise clinical reasoning and management decisions

CLINICAL SCENARIOStandard

Scenario 1: Large Femoral Condyle Lesion (~2-3 min)

CLINICAL PROMPT

"A 28-year-old male has a 5cm² full-thickness cartilage defect on the medial femoral condyle after failed microfracture 2 years ago. What are your treatment options?"

PRACTICAL APPROACH

This young patient with a large (5cm²) lesion after failed microfracture is an excellent candidate for osteochondral allograft. My rationale: At 5cm², this exceeds the safe donor capacity for OATS (maximum ~4cm²). ACI is an option but requires two stages. OCA provides mature hyaline cartilage in a single surgery without donor site morbidity. My approach would be: 1. Confirm alignment is normal - if malaligned, plan osteotomy 2. Assess associated pathology (meniscus, ligaments) - address concurrently 3. Coordinate with tissue bank for size-matched fresh femoral condyle allograft 4. Ensure surgery within 28 days of graft harvest for optimal chondrocyte viability 5. Dowel technique if lesion is circular/oval; shell graft if irregular For this MFC lesion, I would likely use a dowel technique with a large (15-20mm) allograft plug or potentially 2 plugs if irregular shape. Post-operatively: NWB 6 weeks, progressive to full WB by 12-16 weeks. Return to sport 12-18 months. I would counsel about 75-85% survivorship at 10 years, and that this may serve as a bridge to eventual TKA if needed.

CLINICAL SCENARIOChallenging

Scenario 2: Fresh vs Frozen (~2-3 min)

CLINICAL PROMPT

"An examiner asks: Why do we use fresh osteochondral allograft instead of frozen? What are the storage considerations?"

PRACTICAL APPROACH

This is a fundamental principle of osteochondral allograft transplantation. **Fresh vs Frozen - The Key Difference:** Fresh allograft stored at 4°C maintains over 70% chondrocyte viability for up to 28 days. The living chondrocytes continue to maintain the cartilage matrix, providing durable cartilage function. Frozen allograft stored at -80°C has less than 1% chondrocyte viability because freezing destroys the cells. While the matrix structure remains intact, the cartilage is essentially dead tissue. Frozen allografts are used for structural bone grafting where living cartilage is not needed. **Storage Considerations:** 1. **Temperature**: 4°C (refrigerated, not frozen) 2. **Medium**: Nutrient culture medium to support chondrocytes 3. **Time window**: Optimal use within 14-28 days of harvest 4. **Testing**: Donor screening during this window (serology, cultures, NAT) 5. **Logistics**: Surgery must be scheduled when graft is ready, not vice versa **The 28-day window creates challenges:** - Patient must be available when graft arrives - Operating room scheduling flexibility needed - Cannot store graft indefinitely waiting for optimal timing - Size matching delays add pressure to the timeline This is why OCA requires more coordination than autograft procedures like OATS.

CLINICAL SCENARIOCritical

Scenario 3: Bipolar Lesions (~2-3 min)

CLINICAL PROMPT

"A 35-year-old has bipolar (kissing) lesions on the medial femoral condyle and tibial plateau after failed HTO. What are your options?"

PRACTICAL APPROACH

Bipolar or kissing lesions are among the most challenging cartilage problems. This patient with both femoral and tibial involvement after failed HTO requires careful evaluation. **Assessment:** 1. Current alignment - did HTO fail mechanically or is alignment now acceptable? 2. Size of each lesion - femoral and tibial separately 3. Bone stock - any bone loss from prior surgery? 4. Associated pathology - meniscal status critical **Treatment Options:** **1. Bipolar OCA (femoral + tibial):** - Can address both surfaces - Clearly lower success than unipolar OCA (bipolar grafting is a recognised predictor of failure) - Complex surgery with higher risk - May still delay arthroplasty 5-10 years **2. Unipolar OCA + other treatment:** - OCA for larger lesion - Microfracture or debridement for smaller opposing lesion - Reduces complexity but may not address both fully **3. Meniscal allograft + cartilage treatment:** - If meniscal deficiency contributes, add meniscal allograft - Addresses load distribution **4. TKA:** - Definitive option at age 35 but young - Should be considered if biology fails - Patient may still need revision in lifetime Given her age (35), I would counsel toward attempting biological solution first. Bipolar OCA with meniscal allograft if meniscal deficient would be my preferred approach, with clear counseling about reduced success rates compared to unipolar disease.

MCQ Practice Points

Storage Temperature Question

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.

Viability Question

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.

Frozen Viability Question

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).

Lesion Size Question

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.

Survivorship Question

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.

Bipolar Outcomes Question

Q: How do bipolar OCA outcomes compare to unipolar? A: Substantially worse - Bipolar (kissing) lesions involving both articulating surfaces have markedly lower survivorship than single-surface (unipolar) OCA. Bipolar grafting is a recognised independent predictor of graft failure, alongside older age and uncorrected malalignment.

Guidelines, Registries and Global Practice

Access and Regulation

Fresh OCA availability is limited everywhere because of the narrow storage window
Tissue must come from an accredited bank: AATB (US), and national tissue authorities/EU Tissue Directive standards elsewhere
Some regions import grafts from US tissue banks where domestic supply is scarce
Cost and logistics are universal barriers
Alternative when fresh OCA is unavailable: OATS (smaller lesions) or ACI/MACI (no bone loss)

Documentation Standards

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

Medicolegal Considerations

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