Does proximal tibial osteotomy with a novel osteotomy system obtain coronal plane correction without affecting tibial slope and patellar height?

Purpose: To determine changes in tibial slope, patellar height, and coronal plane alignment after medial opening wedge proximal tibial osteotomy (PTO) using a modern osteotomy system. Methods: Patients undergoing medial opening wedge PTO for any indication with follow-up until radiographic union were identified. Pre- and post-operative tibial slope (referenced off the anterior tibial cortex, proximal tibial anatomic axis, and posterior tibial cortex), patellar height (Caton–Deschamps, Blackburne–Peel, and Insall–Salvati indices), and coronal plane [mechanical axis and weight-bearing line (WBL) ratio] measurements were taken by two observers and compared. Results: Review of 27 patients demonstrated unchanged tibial slope and slightly decreased patellar height post-operatively (Caton–Deschamps: −0.10 ± 0.09; Blackburne–Peel: −0.11 ± 0.10). Coronal plane measurements showed 6.4° ± 1.8° mean change in mechanical axis. Mean post-operative WBL ratio was significantly lower (51.6 ± 11.5 %) than mean goal WBL ratio (62.2 ± 2.5 %). Preoperative mechanical axis >6° varus and osteoarthritis alone as the surgical indication were risk factors for undercorrection >10 %. Conclusions: Medial opening wedge PTO using a recently developed instrumentation system was found to have no effect on tibial slope. Patellar height was decreased after osteotomy using this system, although clinical significance of these findings is unknown. Coronal plane undercorrection of 10.6 % of the target WBL ratio was seen in the group as a whole, although secondary analysis of these results indicated that patients with medial compartment osteoarthritis and/or preoperative mechanical axis of >6° varus accounted for the majority of the cases of undercorrection. Level of evidence: Retrospective case series, Level IV.