Balancing the Flexion Gap: Relationship Between Tibial Slope and Posterior Cruciate Ligament Release and Correlation with Range of Motion

Abstract

The success of total knee arthroplasty has been shown to depend on the attainment of appropriate limb alignment with balanced flexion and extension gaps (Figs. 1-A and 1-B)1-3. While several techniques can be used to accomplish these goals, the technique of measured resection is widely accepted4. Simply stated, this technique involves resection of the amount of bone that will be replaced by metal and polyethylene (Figs. 2-A and 2-B). The technique fosters the reestablishment of the joint line, not only distally but also posteriorly, and thus reestablishes appropriate posterior femoral offset. With respect to the tibia, it is not only the coronal alignment that affects the results of the arthroplasty; the sagittal alignment (the degree of posterior slope) also has a substantial effect on the flexion and extension gaps5-11. The initial exposure is carried out with standard techniques. Release of the deep medial collateral ligament and the meniscal capsular ligament assists with exposure both in knees with varus deformity and in those with valgus deformity (Fig. 3). Additional releases are performed after osseous resections are accomplished. A measured distal femoral resection is performed with the assistance of an intramedullary alignment guide and with removal of the requisite amount of bone to be replaced with metal (Fig. 4). Proximal tibial resection follows with use of either an extramedullary or an intramedullary alignment guide, which is set perpendicular to the tibial shaft axis in the coronal plane; the degree of posterior slope in the sagittal plane is adjusted according to implant specifications (Fig. 5). Implants that do not incorporate posterior slope in the polyethylene usually require mimicking of the posterior slope of the native tibia, whereas implants that have posterior slope incorporated into the design usually require minimization of the amount …