Radiographic Joint Space Widening of the Unaffected Compartment in Varus or Valgus Knees Is Associated With Abnormal Intraoperative Ligamentous Laxity.

BACKGROUND

Krackow described type II valgus deformity as valgus alignment with obvious attenuation of the medial collateral ligament complex. However, little quantitative information exists documenting the associated medial collateral ligament laxity encountered intraoperatively. Furthermore, a corollary may exist in advanced varus deformity with associated lateral ligament laxity, but this has not been well described. This study evaluated whether increased preoperative medial or lateral radiographic joint space width (JSW) in valgus or varus knees, respectively, was associated with increased intraoperative soft-tissue laxity of the associated compartment in patients undergoing robotic-assisted total knee arthroplasty (raTKA).

METHODS

A retrospective review of 348 consecutive raTKAs with varus or valgus deformity was performed. There were 270 varus knees (hip-knee-ankle angle [HKA] less than -2°) and 78 valgus knees (HKA greater than 2°). For varus knees, the lateral JSW was measured on the preoperative standing antero-posterior knee radiograph to determine if there was lateral widening (threshold 8.0 mm). For valgus knees, the medial JSW was measured to determine if there was medial widening (threshold 7.0 mm). Data from the intraoperative manual stress examination were reviewed to obtain medial and lateral gaps at 0 and 90°. The relationship between the gaps, JSW, and HKA was assessed using linear regression analysis.

RESULTS

There were 51 varus knees with lateral widening and 15 valgus knees with medial widening. Linear regression analysis showed that for 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.

CONCLUSIONS

Increased preoperative radiographic JSW of the medial and lateral compartments in valgus and varus knees, respectively, was significantly associated with increased intraoperative gaps of that compartment, consistent with ligament attenuation.