3. GRAFT PREPARATION AND PLACEMENT
At the time of surgery, the meniscus allograft is thawed in sterile saline and prepared on the back table. This can be done before or after the diagnostic arthroscopy and bone-slot preparation. Excess soft tissue surrounding the meniscal rim and/or anterior and posterior horns should be removed. Several techniques for MAT have been described, but we generally prefer a bridge-in-slot technique for both medial and lateral MAT.21 To prepare the meniscus allograft for a bridge-in-slot technique, the graft is cut with an oscillating saw to a width of 7 mm, with care taken to ensure that the bony insertions of both meniscal horns are preserved. Next, a transverse cut is made 10 mm below the meniscal horns to set the depth of the bone bridge. To assist with the sizing of the bone bridge, a rectangular sizing block and cutting jig is used (Figures 2A-2C). After marking the middle and posterior thirds of the meniscus, a No. 2 non-absorbable suture is placed at the junction of the posterior and middle thirds of the meniscus. This completes preparation of the allograft prior to implantation.
Attention is then turned to back the arthroscopy. A standard posteromedial (medial meniscus) or posterolateral (lateral meniscus) accessory incision is made, and a Henning retractor is carefully placed in order to receive the sutures that will be placed through the meniscus allograft via a standard inside-out repair technique. First, a zone-specific cannula is used to place a nitinol wire out the accessory incision. The looped end of the wire is pulled out of the anterior arthrotomy incision that will be used to shuttle the meniscus allograft into the joint. In order to pass the meniscal allograft into the joint, the passing suture previously placed through the meniscus is shuttled through the nitinol wire, and the wire is then pulled out the accessory incision, advancing the meniscus through the anteiror arthrotomy. As the meniscus is introduced, the traction suture is then gently tensioned to get the allograft completely into the joint. Next, the bone bridge is seated into the previously created bone slot, as the soft tissue component is manually pushed beneath the ipsilateral femoral condyle. Under direct visualization, the soft tissue component is reduced with a probe using firm, constant traction. To aid in reduction, it may be useful to apply compartment-specific varus or valgus stress and to cycle the knee once the meniscal complex is reduced.
4. GRAFT FIXATION
Once the graft has been passed completely into the joint, with the bone bridge seated into the bone slot, the long end of an Army-Navy retractor is placed firmly through the arthrotomy on the meniscal bone bridge, maintaining a downward force to allow the bridge to remain slotted. To lever down on the posterior aspect of the graft, a freer elevator is used from anterosuperior to posteroinferior. The bone bridge is then secured using a bioabsorbable interference screw, placed central to the bone bridge opposing the block to the ipsilateral compartment. The remainder of the meniscus is secured with an inside-out repair technique, working from posterior to anterior through a standard medial or lateral meniscal repair approach. In total, approximately 6 to 10 vertical mattress sutures are placed, and these can be placed both superiorly and inferiorly on the meniscus. Posteriorly, an all-inside suture repair device may be helpful. Finally, the anterior aspect of the meniscus is repaired to the capsule in an open fashion prior to closing the arthrotomy. Sutures are tied with the leg in extension. The meniscal repair incision is closed in a standard fashion using layers.
5. CONCOMITANT PATHOLOGY AND MAT
The presence of concomitant knee pathology in the context of meniscus deficiency is a challenging problem that requires careful attention to all aspects of the underlying condition of the knee. In cases where MAT is indicated, issues of malalignment, cartilage defects, and/or ligamentous instability may also need to be addressed either concomitantly or in staged fashion. For example, medial meniscal deficiency in the setting of varus alignment can be addressed with a concomitant HTO, whereas lateral meniscal deficiency in the setting of valgus malalignment can be addressed with a concomitant DFO. In both cases, the osteotomy corrects an abnormal mechanical axis, offloading the diseased compartment. This accomplishes 2 goals, namely to preserve the new MAT graft and to protect underlying articular cartilage.22-24 The osteotomy is an important contributor to additional pain relief by offloading the compartment, and clinical studies have demonstrated that failure to address malalignment in the setting of surgical intervention for cartilage and meniscal insufficiency leads to inferior clinical outcomes and poor survival of transplanted tissue.25-28
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