Meniscal Allograft Transplantation (MAT)

Indication. Symptomatic meniscal deficiency — persistent ipsilateral compartment pain — in a patient who has had a subtotal or total meniscectomy, with a stable, well-aligned knee and minimal chondral wear (Outerbridge grade 2 or better), that has failed non-operative management. Done well, MAT reliably relieves post-meniscectomy pain and may slow the progression of osteoarthritis; in the wrong knee it fails early. The ideal candidate is young (typically less than 50 years, relative upper limit 55), symptomatic, with intact or reconstructed cruciates, neutral or correctable alignment, and chondral surfaces that are still preserved. Confirm each of these before listing the patient. Absolute contraindications — any one rules MAT out:

• Advanced osteoarthritis — Outerbridge grade 3-4 diffuse change, or greater than 50 percent joint-space loss
• Uncorrected malalignment — varus or valgus thrust greater than 5 degrees, or weight-bearing line deviation outside the central 40 to 60 percent of the plateau (a varus or valgus thrust greater than 5 degrees or weight-bearing line deviation greater than 50 percent requires a concurrent or staged osteotomy before or with MAT)
• Active infection or inflammatory arthropathy
• Obesity (BMI greater than 35) in most centres Relative contraindications — age greater than 55 years, smoking (raises failure risk), and the low-demand patient with realistic non-operative alternatives.

Concurrent procedures are the rule, not the exception. ACL reconstruction, high tibial osteotomy and cartilage repair are frequently performed at the same sitting and do not worsen MAT outcomes — provided the knee is rendered stable and aligned. Plan them together: an unstable or malaligned knee will extrude and destroy the graft. Setup. Supine with a leg holder or lateral post allowing full flexion and extension. A thigh tourniquet is applied but left uninflated unless a concurrent osteotomy is planned. General or spinal anaesthesia with a regional block for post-operative analgesia. Fluoroscopy must be available throughout — slot and tunnel position are confirmed on fluoro before the graft is seated.

The goal: arthroscopically deliver a size-matched meniscal allograft into the deficient compartment, anchor its horns anatomically to within 2 mm of the native tibial footprints, and secure the periphery to the capsule so the graft cannot extrude. The medial meniscus is usually fixed with a single bone-bridge (slot); the lateral meniscus with separate anterior and posterior bone plugs. Soft-tissue-only fixation carries the highest extrusion rates and is largely abandoned.

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Rehabilitation | Phase | Timing | Weight-bearing and bracing | Therapy | |-------|--------|----------------------------|---------| | 1 | 0 to 6 weeks | Non- or toe-touch weight-bearing; brace locked in extension for 2 weeks then unlocked | Passive and active-assisted ROM from day 1, aiming for 90 degrees by week 4; quadriceps sets and straight-leg raises | | 2 | 6 to 12 weeks | Progressive to full weight-bearing by week 8 to 10 | Closed-chain strengthening and stationary cycling; full ROM by week 8 to 10 | | 3 | 3 to 6 months | Full weight-bearing | Proprioceptive training; sport-specific drills after 6 months if the graft is incorporated | Return to sport. Low-impact activities from 6 to 9 months; high-impact or pivoting sports are generally discouraged or delayed to 12 months and undertaken with caution. An MRI at 3 to 6 months assesses graft incorporation and extrusion. Outcomes. In appropriately selected patients, 70 to 85 percent gain meaningful pain relief and improved function at 5 to 10 years, with graft survival of roughly 70 to 80 percent at 10 years. The chondroprotective effect is real but not absolute — disease still progresses once grade 3-4 changes are established. Complications

Danger zones and exam traps

The problem MAT addresses. After a subtotal or total meniscectomy the knee loses the meniscus's hoop-stress distribution, shock absorption and joint conformity; compartment contact pressures rise and osteoarthritis accelerates — the post-meniscectomy syndrome. MAT is a salvage operation for the young, symptomatic, meniscus-deficient knee: it aims to relieve pain and slow, though not reverse, that degenerative trajectory. Chondroprotective effect. Level III-IV studies show slower radiographic progression of osteoarthritis after MAT than after meniscectomy alone, with the effect most pronounced when the graft is implanted before significant chondral wear develops. Once Outerbridge grade 3-4 change is established the benefit is largely lost, which is why patient selection is the dominant determinant of outcome.

Concurrent procedures. Simultaneous ACL reconstruction, high tibial osteotomy or cartilage repair does not increase MAT failure rates when the knee is rendered stable and aligned; staged procedures are reserved for complex deformity correction. Anatomic horn placement within 2 mm of the native footprint — shown to reduce extrusion on MRI — is the technical factor most consistently linked to graft survival.