Original ArticleOpen wedge high tibial osteotomy does not decrease patellar height relative to femur: A three-dimensional computer model analysis
Introduction
Open wedge high tibial osteotomy (OWHTO) is a successful treatment option for medial unicompartmental arthritis of the knee. However, concerns about the negative effects of OWHTO on the patellofemoral joint have been growing over the past decade. Many clinical studies have revealed a significant decrease in the patellar height measured by radiographic evaluation, including the Caton-Deschamps index (CDI) and the Blackburne-Peel index (BPI), after OWHTO [[1], [2], [3], [4], [5]]. Several clinical studies have reported worsening of cartilage damage in the PF joint after OWHTO [[6], [7], [8], [9]]. Therefore, some researchers recommend performing other procedures that do not induce patellar infera, including closed wedge high tibial osteotomy (CWHTO) or distal tuberosity osteotomy in OWHTO, in patients with patella infera or cartilage degeneration in the patellofemoral joint [10,11].
The problem with assessment methods of patellar height is that post- OWHTO, it is dependent on the index used. There are two types of radiographic methods to measure patellar height: those that relate the patellar position to the tibia (tibia-referenced measurements), including the CDI and the BPI, and those that relate it to the femur (femur-referenced measurement) [12]. Theoretically, changes in the anatomical location of the proximal tibia after high tibial osteotomy (HTO) affect methods based on tibial references and result in inconsistent pre- and postoperative patellar height values. Gaasbeek et al. stated that the BPI and the CDI do not accurately measure the alteration of patellar height after HTO because they are dependent on the tibial inclination and the anteroposterior translation of the proximal tibia [13]. Recently, Ihle et al. proposed a simple method for patellar height measurement based on femur as reference, using anteroposterior radiographs and this new method revealed no change in patellar height following OWHTO [14]. However, it would be unreasonable to compare the results based on tibia-referenced measurements with those based on femur-referenced measurement, since the two methods differ in the reference point used, knee flexion angle (30° flexion or full extension), and patient position (supine or standing position). In addition, the measurement baseline, including TEA and femoral joint surface, used for femur-referenced methods, also change as the lower limb alignment changes after OWHTO. The evaluation of patellar height after OWHTO is controversial.
Recent technological advances in three-dimensional (3D) visualization have enabled the recognition and quantitative evaluation of human knees with high accuracy and reproducibility [[15], [16], [17], [18], [19]]. Yamada et al. reported a new measuring system for the evaluation of patellar height based on femoral references using in vivo 3D computer models [16]. This method would allow for the assessment of subtle changes in patellar position relative to the femur after OWHTO. The purpose of the present study was to evaluate the changes in patellar height based on femur-referenced measurements after OWHTO using in vivo 3D computer models, and compare the results with those of the conventional methods based on tibia-referenced measurements. We hypothesized that the relative patellar height position to the femur does not change after OWHTO when using femur-referenced measurements.
Section snippets
Materials and methods
This study was approved by the ethics review board of the hospital. In total, 38 patients underwent OWHTO between May 2013 and December 2014. OWHTO was indicated by the presence of symptomatic medial compartment osteoarthritis or osteonecrosis of the medial femoral condyle with varus malalignment. There were no age restrictions. The contraindications were the presence of patellofemoral joint-related symptoms, radiographic evidence of joint space narrowing in the lateral compartment or
Results
The process of patient inclusion and exclusion is shown in Fig. 3. Consequently, 14 patients were included in this study (Table 1). Fig. 4 shows the mean KOOS before OWHTO, 1 year postoperatively, and at the latest follow-up visit (mean: 48 months). Scores for all subscales of the KOOS, except QOL, significantly improved 1 year postoperatively. The symptoms, pain, and QOL scores at the latest follow-up visit were significantly higher than those preoperatively.
Discussion
Patellar height position relative to the femur was analyzed after OWHTO using 3D computer models without being affected by changes in the proximal tibia following OWHTO. The most important finding was that the patellar center angle based on femur-referenced measurements did not significantly change after OWHTO, whereas conventional radiographic measurements based on tibia-referenced measurements showed a decrease in all cases. Three-dimensional computer models facilitated comparisons of pre-
Conclusion
Patellar height position relative to the femur in the 3D computer model did not decrease after OWHTO, whereas tibia-referenced conventional radiographic measurements significantly decreased. When evaluating patellar height, characteristics of each parameter should be considered.
Funding
We do not have any specific grants.
Ethics approval
This study was approved by the ethics review board of the hospital. All participants provided informed consent.
Declaration of competing interest
The authors declare that they have no conflict of interest.
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