Size-matched non-irradiated meniscal allograft transplantation for symptomatic meniscal deficiency | advanced
Surgical Imaging
The trap: Accepting a graft that is more than 10 percent larger or smaller than the measured tibial plateau leads to either extrusion (oversized) or inadequate coverage (undersized).
The fix: Use calibrated radiographs or MRI with the Pollard method (coronal width equals plateau width minus 8 percent for medial, minus 7 percent for lateral). Confirm size match with the tissue bank before accepting the graft.
Location: The posterior horn insertion of the medial meniscus lies immediately anterior to the PCL tibial footprint; the anterior horn lies 7-9 mm anterior to the medial tibial eminence.
Risk: Placing the bone block more than 2 mm posterior or anterior changes meniscal excursion and hoop stresses. Use fluoroscopic confirmation of the slot position relative to the PCL and eminence before seating the graft.
Location: The meniscal periphery must be sutured to the capsule with vertical mattress sutures at 5 mm intervals from posterior to anterior horn.
Risk: Fewer than 8-10 sutures or reliance on all-inside devices alone allows extrusion greater than 3 mm. Combine all-inside devices for the posterior third with inside-out or outside-in sutures for the middle and anterior thirds.
Deformity threshold: Greater than 5 degrees varus or valgus or weight-bearing line deviation outside the central 40-60 percent of the plateau.
Consequence: Increased compartment pressure on the allograft leads to early extrusion, tearing, and failure. Always correct alignment with high tibial or distal femoral osteotomy before or concurrent with MAT.
Grading limit: Outerbridge grade 3 or 4 focal defects or diffuse grade 2 changes are relative contraindications.
Implication: MAT in the presence of advanced arthritis yields poor pain relief and rapid graft failure. Perform diagnostic arthroscopy or review recent MRI cartilage sequences before listing the patient.
Definition: Greater than 3 mm extrusion of the meniscal body beyond the tibial margin on coronal MRI at 3-6 months post-operatively.
Prevention and management: Ensure anatomic horn fixation, adequate peripheral suturing, and secure bone-plug or bridge fixation. Minor extrusion (less than 3 mm) may be observed; symptomatic extrusion greater than 3 mm may require revision with additional sutures or conversion to arthroplasty.
M.A.T.C.H.MAT — Indications and Contraindications
S.I.Z.E.P.A.S.S.MAT — Operative Sequence
Surgical Indications
Absolute Indications
- Symptomatic meniscal deficiency after prior subtotal or total meniscectomy
- Age typically less than 50 years (relative upper limit 55 years in selected patients)
- Persistent ipsilateral compartment pain despite non-operative management
- Stable knee (native or reconstructed ACL/PCL)
- Neutral or correctable alignment (less than 5 degrees varus/valgus)
- Chondral surfaces Outerbridge grade 2 or better
Relative Indications
- Concurrent ACL reconstruction or cartilage restoration procedures
- Prior meniscal repair that failed with resultant deficiency
- Young athletic patient with high functional demand
Contraindications
Absolute:
- Advanced osteoarthritis (Outerbridge grade 3-4 diffuse or greater than 50 percent joint space loss)
- Uncorrected malalignment greater than 5 degrees or weight-bearing line deviation outside central 40-60 percent
- Active infection or inflammatory arthropathy
- Obesity (BMI greater than 35) in most centres
Relative:
- Age greater than 55 years
- Smoking (increases failure risk)
- Worker compensation or low-demand patient with realistic non-operative alternatives
Evidence Base
Chondroprotective Effect
Level III and IV studies demonstrate slower radiographic progression of osteoarthritis after MAT compared with meniscectomy alone. The effect is most pronounced when the graft is implanted before significant chondral wear develops.
Outcomes by Fixation Technique
Bone-plug and bone-bridge techniques show lower extrusion rates than soft-tissue-only fixation. Anatomic horn placement within 2 mm of the native footprint is critical for load transmission and graft survival.
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.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 38-year-old man presents with persistent medial knee pain 18 months after subtotal medial meniscectomy. He has a stable ACL, neutral alignment, and Outerbridge grade 2 chondral changes on the medial femoral condyle. MRI shows no meniscal tissue remaining. How do you evaluate him for meniscal allograft transplantation?”
“During medial meniscal allograft transplantation you have seated the bone bridge but notice that the posterior horn sits 4 mm too far posterior relative to the PCL footprint. What do you do?”
“A 42-year-old woman 9 months after lateral MAT complains of lateral knee pain and mechanical catching. MRI shows a radial tear in the mid-body of the allograft with 3.5 mm extrusion. What are your options?”