Summary

Anteromedialization tibial tubercle osteotomy decreases patellar height and the osteotomy cut angles does not correlates with patellar distalization.

Abstract

Background

The effect of anteromedialization (AMZ) tibial tubercle osteotomy (Fulkerson procedure) on patellar height remains elusive. No previous study comprehensively determined the change in patellar height after AMZ comparing pre- and postoperative radiographic imaging.
 

Purpose

The purpose of this study was to assess the effect of an AMZ on patellar height utilizing pre- and postoperative radiographic images, and to determine the relationship between osteotomy cut angle and change in patellar height.
 

Methods

Medical records of all patients submitted to AMTTO between April 2007 and July 2017 by a single surgeon were retrospectively assessed. Patients with adequate lateral radiographic imaging and without other osteotomies around the knee (distal femoral or high tibial osteotomy) were included in the current study. Two radiographic patellar height indices - Caton-Deschamps index (CDI) and Blackburne-Peel index (BPI) – were measured by two blinded independent observers on both pre- and postoperative radiographic images. Interobserver reliability was assessed with the intraclass correlation coefficient (ICC) and the paired t-test was performed to compare pre- and postoperative measurements. The osteotomy cut angle was measured using magnetic resonance imaging (MRI) and a bivariate regression analysis was used to evaluate its relationship with changes in patellar height.
 

Results

A total of 184 knees (176 patients) submitted to AMZ were initially screened. 120 knees (116 patients) met the inclusion criteria and were enrolled for the imaging analysis. The mean follow-up time for postoperative radiographic acquisition was 40.7 days (SD, 23.8; range, 9 to 93). Of the included knees, 107 (89.2%) underwent concomitant cartilage repair in at least one compartment including autologous chondrocyte implantation, matrix-induced autologous chondrocyte implantation, osteochondral allograft transplantation, osteochondral autograft transfer or particulated allograft cartilage transplantation. The ICC for CDI and BPI was considered excellent, ranged between 0.75 and 0.86. Postoperative radiography demonstrated a statistically significant decrease in patellar height with a mean decrease of 0.05 (p < 0.001) and 0.12 (p < 0.001) for CDI and BPI, respectively. Postoperative MR imaging was obtained in 81 knees (67.5%), which allowed for osteotomy cut evaluation. AMZ cut angle averaged 55 degrees (SD, 12.0; range, 24 to 83) and showed no correlation with patellar height mean changes for both CDI (p = 0.912) and BPI (p = 0.598).
 

Conclusion

This is the first study that identified a small, yet significant decrease of patellar height after AMTTO. This may not be clinically significant for patients with normal patellar height, but caution is advised when performed in patients with low patellar height parameters. Contrarily, this study suggests that an isolated AMZ, as describbed by Fulkerson, may be insufficient for correcting patella alta, in which a concomitant procedure to address distalization of the tibial tubercle should be performed.