# Long-term outcomes of the modified Dunn procedure in moderate and severe slipped capital femoral epiphysis: a prospective case series with 7-year follow-up

## TL;DR

This study shows that the modified Dunn procedure improves hip function and anatomy in adolescents with moderate to severe SCFE, but carries risks like avascular necrosis and arthritis.

## Contribution

The study provides long-term follow-up data (7 years) on the modified Dunn procedure for moderate-to-severe SCFE, a gap in existing literature.

## Key findings

- The modified Dunn procedure significantly reduced slip angles and improved hip function scores in patients with moderate-to-severe SCFE.
- Avascular necrosis occurred in 16.7% of cases, and arthritis developed in 8.3%, with 25% of patients experiencing significant complications.
- Functional improvements were sustained over 7 years, with no postoperative instability or wound infections reported.

## Abstract

Slipped capital femoral epiphysis (SCFE) is the most common hip disorder in adolescents and may lead to femoroacetabular impingement, early osteoarthritis, and long-term functional disability if inadequately treated. While in situ pinning remains the standard treatment for mild slips, it fails to correct the deformity in moderate and severe cases, potentially predisposing to degenerative changes. The modified Dunn procedure (MDP) was developed to restore proximal femoral anatomy through surgical hip dislocation while preserving vascular supply.

The aim of the study is to evaluate the long-term radiological and functional outcomes of the MDP in patients with moderate (14 cases) and severe (10 cases) SCFE, and to assess the incidence of avascular necrosis (AVN), osteoarthritis, and other complications.

A prospective case series was conducted between August 2015 and January 2019 at a single tertiary institution. A total of 24 hips with moderate-to-severe SCFE and open physis were treated using the MDP via surgical hip dislocation. Mild and acute-only slips were excluded. MDP was used as a primary procedure, performed early in severe slips and in selected moderate slips after clinical assessment. Patients were followed clinically and radiologically for a mean duration of 84 ± 2.6 months (range 80–88 months). Functional outcomes were assessed using the Harris Hip Score (HHS) and Merle d’Aubigné and Postel score. Radiographic outcomes and complications, including AVN and secondary arthritis, were documented. Fixation was performed using Schanz screws, cannulated screws, or K-wires according to intraoperative findings.

The mean preoperative slip angle (48.3° ± 7.2°) significantly improved postoperatively (11.4° ± 3.1°, p < 0.001). HHS improved from a preoperative mean of 70.4 ± 5.8 to 92.9 ± 4.2 at final follow-up (p < 0.001). The Merle d’Aubigné and Postel score improved from 13.8 ± 1.6 preoperatively to 17.5 ± 0.9 at final follow-up (p < 0.001). AVN developed in 4 out of 24 hips (16.7%). Arthritis developed in 2 out of 24 hips (8.3%, degenerative OA; no septic arthritis or chondrolysis), representing a total of 6 out of 24 hips (25%) with significant complications when combined with AVN. No cases of postoperative instability or wound infection occurred. Functional scores showed sustained improvement in the majority of patients.

MDP offers favorable long-term anatomical correction and functional recovery in moderate-to-severe SCFE. However, the risk of AVN and arthritis, particularly in unstable or severe cases, warrants careful patient selection and technical precision. Extended follow-up is essential to detect late complications and evaluate procedural durability.