Patellar height relevance in opening-wedge high tibial osteotomy

Abstract

Introduction: The decrease of patellar height following opening-wedge proximal tibial osteotomy can affect function, and subsequent total knee arthroplasty may be more difficult and give poorer results.

Hypothesis: Pre-operative patellar height is an objective predictor of functional result in opening-wedge osteotomy.

Patients and methods: The effect of opening-wedge high tibial osteotomy (HTO) and internal fixation on patellar height and its functional outcome were assessed. Forty supra-tuberosity medial opening wedge osteotomies were performed in 36 patients presenting with medial femorotibial osteoarthritis and varus deformity. Mean age was 55 years. Mean varus was 9 degrees and mean opening 11 degrees. Minimum follow-up was 22 months, with a mean of 4.2 years. Clinical results were assessed on the International Knee Society (IKS) scale. X-ray measurements (HKA angle, tibial slope, and patellar height as per Caton-Deschamps [CD], Insall-Salvati [IS] and Blackburne-Peel [BP]) were taken pre-operatively, postoperatively and on follow-up.

Results: Patellar height decreased by 10 to 15% (p < 0.0001), depending on the selected ratio. Mean CD index was 0.85 preoperatively (S.D. = 0.12), 0.76 postoperatively (S.D. = 0.14) and 0.75 at follow-up (S.D. = 0.14). Mean IS index was 0.95 preoperatively (S.D. = 0.11), 0.86 postoperatively (S.D. = 0.12) and 0.87 at follow-up (S.D. = 0.12). Mean BP index was 0.68 preoperatively(S.D. = 0.10) and 0.58 postoperatively and at follow-up (S.D. = 0.12). Tibial slope was altered by a mean of 1.5 degrees (range: -4 to + 9 degrees). There was no correlation between opening angle and patellar lowering. Patellar height decrease did not affect functional results whether height remained normal or became low (total IKS score, 179 and 170, respectively); the poorest functional results, however, were associated with patella infera (total score, 147).

Discussion: Medial opening-wedge HTO is an established treatment for unicompartmental varus knee osteoarthritis. We do not, however, recommend it in case of preoperative patellar height of less than 0.6 on the CD ratio.

Level of evidence: Retrospective, level IV.