Introduction
Medial open-wedge high tibial osteotomy(OWHTO) has been reported to deteriorate the patellofemoral(PF) joint due to a decrease in patellar height. Our previous study demonstrated that OWHTO significantly increased the stress distribution pattern of the lateral trochlea of the femur and the medial portion of the lateral facet of the patella using Computed tomography (CT)–osteoabsorptiometry (OAM). Inverted V-shaped(iV) HTO, which was classified as a neutral-wedge(NW) (hemi-closing wedge and hemi-opening wedge) osteotomy, does not distalized the position of the tibial tuberosity. Therefore, NWHTO might not have a harmful effect on the PF joint compared to OWHTO. However, the alteration of the stress distribution patterns of the PF joint after NWHTO remains unclear. The hypotheses were that (1) the stress distribution pattern on the PF joint decreased after NWHTO, (2) NWHTO may be significantly improved in PF joint congruity after surgery. The purpose of this study was to assess these hypotheses.
Methods
A retrospective study was conducted with 12 patients (16 knees) who underwent NWHTO between 2016 and 2019. There were 6 men and 6 women with a mean age of 59 (range: 46-72) years at the time of surgery. Radiographic and CT evaluations were performed before and at 1 year after HTO. In CT-OAM, the distribution patterns of subchondral bone density through the articular surface of the femoral trochlea and patella were evaluated. Articular surface of femoral trochlea and patella were divided to four sub-regions from lateral to medial, latero-lateral region (LL), latero-medial region (LM), medio-lateral region (ML), and medio-medial region (MM). The quantitative analysis of the obtained mapping data focused on location of the high-density area (HDA) through the articular surface. HDA was defined as 30% highest density area. The percentage of each subregion represented by the HDA was calculated (%HDA). This study design had been accepted by the institutional review board clearance in our hospital. Statistical analysis was performed using the paired t test. The significance level was set at p=0.05.
Results
The correction angle averaged 13.5±3.6°. The CD index was not significantly different between before (0.80) and after HTO (0.82). The tilting angle significantly changed from 10.7° to 8.5°, and lateral shift ratio significantly changed from 15.4% to 10.7% (p=0.004 for each). The TT-TG distance significantly changed from 14.5 mm to 12.3 mm (p =0.017). %HDA in the patellar LL and LM region significantly decreased after NWHTO (p=0.022 and p=0.026, respectively). There was no significant change in %HDA of each region of femoral trochlea and MM and ML regions of patella.
Discussion
This study clearly demonstrated that there were no significant changes in the CD index between pre- and post-operative periods. The tilting angle, lateral shift ratio, and TT-TG distance significantly decreased after NWHTO. Subchondral bone density on the lateral facet of patellar articular surface significantly decreased after NWHTO. These results showed that NWHTO did not change the patellar height, and improved PF joint congruity. NWHTO significantly decreased the stress distribution pattern on the lateral facet of patella.