Soft tissue laxity should be considered to achieve a constant polyethylene thickness during total knee arthroplasty

In total knee arthroplasty (TKA), the gap expansion effect by soft tissue laxity and bone resection amount influence directly on the proper gap size and ideal polyethylene insert thickness. In this study, we hypothesized if bone resection level could be controlled lesser as gap expansion effect resulted in the effects on gap expansion of the collateral release and lax lateral structure, appropriate gap size would be attained without extensive medial soft tissue release even in severe varus deformed knee. The purpose of this study was to show the usefulness of preoperative calculation of soft tissue laxity for determining the appropriate gap size for the targeted PE thickness in TKA.

The preoperative varus stress view was used to estimate the effect of soft tissue release on extension gap expansion after primary bone resection. The amount of bone resection was determined with a parallel bone resection device used in our institution. Lateral laxity amount was applied into the device. This study was a retrospective review of 850 TKAs [451 with <10º varus deformity of the mechanical femoro-tibial angle (group 1); 399 with ≥10º varus deformity (group 2)] with a minimum follow-up of 1 year. We compared the range of motion (ROM), the knee society score (KSS), and the incidence of surgical complications at postoperative 1 year between the two groups.

The mean PE thickness was 10.8 ± 1.1 in group 1 and 10.9 ± 1.1 in group 2. The proportion of patients with appropriate PE thickness (i.e., 10-12 mm) was 97.6 % in group 1 and 97.2 % in group 2. The ROM and KSS did not differ significantly between groups.

This study showed the usefulness of preoperative calculation of soft tissue laxity for appropriate gap size for targeted polyethylene thickness and possibility to attain constant extension gap regardless of preoperative varus deformity.