Lateral tibial baseplate translation and targeted medial decompression for pseudo-oversizing in varus total knee arthroplasty

To describe pseudo-oversizing in varus total knee arthroplasty (TKA) and to compare postoperative mediolateral tibial baseplate fit between two centres using different routine tibial keel preparation practices. This retrospective, two-centre, routine-practice comparative study included 52 primary TKAs performed for varus knee osteoarthritis with the same implant system. One centre routinely used standard tibial keel punching alone ( n = 28), whereas the other centre routinely used modified punching with targeted medial decompression ( n = 24). The primary radiographic outcome was lateral overhang, interpreted as the principal edge-based measure of postoperative lateral tibial baseplate translation. Medial undercoverage was analysed as a mechanically related corroborative measure, not as an independent endpoint. Postoperative Knee injury and Osteoarthritis Outcome Score (KOOS), Oxford Knee Score (OKS), and maximal knee flexion were evaluated as exploratory secondary outcomes. The modified routine-practice group showed lower postoperative lateral overhang than the standard group (0.53 ± 0.28 vs. 1.99 ± 1.02 mm; p < 0.001). Medial undercoverage showed a parallel reduction (0.65 ± 0.32 vs. 1.83 ± 0.89 mm), consistent with the same lateral translation pattern rather than an independent endpoint. Lateral overhang ≥ 2 mm occurred in 13 of 28 knees in the standard group and in none of the 24 knees in the modified group. Medial undercoverage ≥ 2 mm showed the same numerical distribution and, on case-level review, involved the same 13 knees. Exploratory postoperative clinical outcomes also favoured the modified group, but these comparisons were not adjusted for preoperative clinical status or centre-related factors. In this retrospective two-centre routine-practice comparison, targeted medial decompression during tibial keel punching was associated with less postoperative lateral tibial baseplate translation in varus TKA. Because technique was fully confounded with centre and postoperative clinical outcomes lacked preoperative baselines, the clinical findings should be interpreted as exploratory. The pseudo-oversizing concept and the proposed mechanism require confirmation in prospective studies with standardized imaging and intraoperative assessment.