Varus/Valgus or Hinge Constraint in Primary Total Knee Arthroplasty: Indications and Outcomes of Planned and Unplanned Use.

Abstract

Varus/valgus constrained and rotating hinge prosthetic designs are occasionally required in primary total knee arthroplasty (TKA) to manage major instability. This study evaluated the clinical indications and postoperative outcomes of both planned and unplanned use of constraint in primary TKA. We retrospectively reviewed 121 primary TKA cases that used varus/valgus constraint or hinge prosthetic designs performed between 2000 and 2023 at a high-volume joint arthroplasty center. The mean patient age was 65 years (range, 36 to 90), 78% were women, and the body mass index (BMI) was 33.2 (range, 16.7 to 55.4). All implants were cemented, and most employed stems. Cases were stratified by planned versus unplanned use of constraint. Indications included severe preoperative deformity, iatrogenic medial collateral ligament (MCL) injury, intraoperative instability, preexisting laxity, poor bone quality, and surgeon discretion. The primary outcomes were revision rates, reasons for revision, ranges of motion (ROM), and available patient-reported outcome measures (PROMs), with a mean follow-up of 6.8 years (range, two to 17). Planned use (n = 72) was driven by severe deformity (mean 9° valgus), prior trauma, and comorbidities. Unplanned use (n = 46) arose from intraoperative instability and had less severe preoperative alignment (mean of one degree of varus). Revision rates were 10% in the planned group and 6% in the unplanned group (P = 0.543), most commonly due to infection or instability. There were no significant differences observed in ROM, complication rates, or PROMs between the two groups. Varus/valgus constrained and hinge prosthetic designs provide effective stability in select primary TKA cases without compromising arthroplasty longevity. Whether planned preoperatively or utilized intraoperatively in response to instability, constrained components demonstrated comparable survivorship and functional results. Preoperative risk assessment can support planning, but intraoperative adaptability remains essential.