# Increased Posterior Condylar Offset Decreases the Extension Gap in Cases With Flexion Contracture in Modified Gap Technique Total Knee Arthroplasty

## TL;DR

This study investigates how changes in posterior condylar offset affect knee extension gaps during total knee arthroplasty, particularly in patients with flexion contracture.

## Contribution

The study reveals an inverse correlation between increased posterior condylar offset and extension gaps in knees with significant flexion contracture.

## Key findings

- No overall correlation was found between posterior condylar offset changes and extension gaps.
- Increased posterior condylar offset was inversely correlated with extension gaps in knees with ≥15° flexion contracture.
- Gap differences were significantly larger in knees with greater flexion contracture in specific groups.

## Abstract

Purpose

There have been no reports comparing the change in medial and lateral posterior condylar offset (PCO) and the extension gaps. The purpose of this study was to elucidate the relationship between the change in medial and lateral PCO and the extension gap in total knee arthroplasty (TKA). The hypothesis is that an increase in both medial and lateral PCO can be a factor for a decrease in the extension gap, especially in cases of flexion contracture.

Methods

This retrospective study included 63 patients with medial osteoarthritis who underwent mobile-bearing PS-TKA using the modified gap techniques. Patients consisted of seven men (seven knees) and 53 women (56 knees), with the mean age of 76 (range, 58-88) years. The patients with valgus knee and cruciate retaining TKA were excluded. The medial ΔPCO (ΔPCO defined as the amount of change of the PCO before the resection of the posterior condyle and after the implant setting), lateral ΔPCO, the rotation angle of the posterior condyle osteotomy, and the gap differences were evaluated. The data were compared among three groups（Group A: ΔPCO increase on both sides, Group B: ΔPCO increase on only one side, Group C: ΔPCO decrease on both sides. The gap differences were compared between the cases with flexion contracture of ≥ 15° and the cases with flexion contracture of < 15°. The correlations between the gap differences and flexion contracture were evaluated in each group.

Results

There was no gap difference evident in any group (P≥0.05). The gap difference in Groups A (P=0.0067) and group C (P=0.0484) was significantly larger in cases with flexion contracture of ≥ 15° compared to those with flexion contracture of < 15°.

Conclusions

There was no correlation between the change in PCO and the extension gap. However, there was an inverse correlation between the flexion contracture and extension gap in cases with increased medial and lateral PCO.