Master Techniques in Orthopedic Surgery Knee CH27

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27 Mobile-Bearing Medial Unicompartmental Knee Arthroplasty

FIGURE 27-17. The final meniscal bearing is snapped into place.

FIGURE 27-16. The femoral component is cemented in place.

The arthrotomy and skin are closed. The author uses a running PDS Quill suture for the arthrotomy and the skin incision is closed with interrupted 2-0 monocryl, running 3-0 monocryl, and Prineo.

POSTOPERATIVE MANAGEMENT Today, this procedure is performed in an outpatient setting. We recommend weight bearing as tolerated from the first postoperative day. Patients generally are able to begin ambulating within 1 to 2 hours of surgery. Our protocol is to place intraoperative Davol drains to bulb suction and send patients to outpatient recovery. These drains are pulled after several hours. During their postoperative recovery period, patients are evaluated by our physical therapy colleagues and given instructions on passive range of motion.

PITFALLS TO FEMUR-FIRST TECHNIQUE Improper Placement of Femoral Guide

As with any knee arthroplasty, it is essential to perform the cuts on the femur with the appropriate coronal and sagittal balance. Accurate placement of the intramedullary femoral guide is essential to avoid varus–valgus malrotation of the components. The flexion–extension alignment is determined by ensuring the guide is placed in the center of the condyle perpendicular to the axis of intercondylar notch. Several studies reported early failure because of femoral component loosening, which may be attributed to malposition of the femoral component. 9-11 Mariani et al hypothesized that extension of the femoral components, in combination with increased knee flexion, may result in edge loading and eventual loosening of the femoral component. 12 This has been thought to be more prevalent in fixed-bearing designs because of increased constraint. It has been shown that in the OUKA design, malrotation of up to 10° in the femoral component can be tolerated without adverse effect or increased risk of component loosening. 13 In addition, if the medial to lateral placement of the femoral drill guide is incorrect, the femoral component will be rotationally unbalanced causing asymmetric wear of the polyethylene, which is another common cause of early failure. Inadequate Posterior Bone Removal If the femoral trial is not sitting on the distal bone, then the posterior cut was made with slope and there may have been inadequate removal of posterior femur. Replacement of the guide and assessment of the posterior condylar cut should remedy this problem.