RADIOLOGICAL JOINT SPACE WIDENING OF THE UNAFFECTED COMPARTMENT IN VARUS OR VALGUS KNEES IS ASSOCIATED WITH ABNORMAL INTRAOPERATIVE LIGAMENTOUS LAXITY

Introduction Krackow Type II valgus deformity is defined by attenuation of the medial collateral ligament (MCL). However, little quantitative information exists about associated intra-operative MCL laxity. Furthermore, a corollary may exist in varus deformity with associated lateral ligament laxity but is poorly described. Robotic-assisted total knee arthroplasty (raTKA) includes quantitative assessment of intraoperative ligament function. This study evaluated whether increased preoperative medial or lateral radiographic joint space width (JSW) in valgus or varus knees, was associated with increased intraoperative soft tissue laxity of the respective compartment. Methodology Intraoperative data from 348 consecutive raTKAs with 270 varus knees (hip-knee-ankle angle [HKA]<-2°), and 78 valgus knees, (HKA>2°) were retrospectively reviewed. For varus knees, lateral JSW was measured on preoperative, standing anteroposterior radiographs to determine lateral widening (threshold 8.0mm). For valgus knees, medial JSW was evaluated to determine medial widening (threshold 7.0mm). Intraoperative medial and lateral gaps at 0° and 90° had been recorded during manual stress testing. Linear regression was performed to determine associations between intra-operative gaps, radiographic JSW, and HKA. Results 51 varus knees demonstrated lateral widening and 15 valgus knees had medial widening. In varus knees, lateral JSW was positively associated with the lateral extension (β=0.76, P <0.001) and flexion (β=0.74, P <0.001) gaps. Similarly, for valgus knees, medial JSW was positively associated with the medial extension (β=0.75, P <0.001) and flexion (β=0.77, P <0.001) gaps. Conclusion Increased preoperative radiographic JSW of the medial and lateral compartment in valgus and varus knees, predicted increased intraoperative gaps of that compartment, consistent with ligament attenuation.