Iatrogenic Hip Instability Is a Devastating Complication After the Modified Dunn Procedure for Severe Slipped Capital Femoral Epiphysis

Abstract

Background: The modified Dunn procedure facilitates femoral capital realignment for slipped capital femoral epiphysis (SCFE) through a surgical hip dislocation approach. Iatrogenic postoperative hip instability after this procedure has not been studied previously; however, we were concerned when we observed several instances of this serious complication, and we wished to study it further.

Questions/purposes: The purpose of this study was to evaluate the frequency, timing, and clinical presentation (including complications) associated with iatrogenic instability after the modified Dunn procedure for SCFE.

Methods: Between 2007 and 2014, eight international institutions performed the modified Dunn procedure through a surgical dislocation approach in 406 patients. During the period in question, indications varied at those sites, but the procedure was used only in a minority of their patients treated surgically for SCFE (31% [406 of 1331]) with the majority treated with in situ fixation. It generally was performed for patients with severe deformity with a slip angle greater than 40°. Institutional databases were searched for all patients with SCFE who developed postoperative hip instability defined as hip subluxation or dislocation of the involved hip during the postoperative period. We reviewed in detail the clinical notes and operative records of those who presented with instability. We obtained demographic information, time from slip to surgery, type of fixation, operative details, and clinical course including the incidence of complications. Followup on those patients with instability was at a mean of 2 years (range, 1-5 years) after the index procedure. Complications were graded according to the modified Dindo-Clavien classification. Radiographic images were reviewed to measure the preoperative slip angle and the presence of osteonecrosis.

Results: A total of 4% of patients treated with the modified Dunn procedure developed postoperative hip instability (17 of 406). Mean age of the patients was 13 years (range, 9-16 years). Instability presented as persistent hip pain in the postoperative period or was incidentally identified radiographically during the postoperative visit and occurred at a median of 3 weeks (range, 1 day to 2 months) after the modified Dunn procedure. Eight patients underwent revision surgery to address the postoperative instability. Fourteen of 17 patients developed femoral head avascular necrosis and three of 17 patients underwent THA during this short-term followup.

Conclusions: Anterolateral hip instability after the modified Dunn procedure for severe, chronic SCFE is an uncommon yet potentially devastating complication. Future studies might evaluate the effectiveness of maintaining anterior hip precautions for several weeks postoperatively in an abduction brace or broomstick cast to prevent this complication.

Level of evidence: Level IV, therapeutic study.

Fig. 1A–G

(A) AP and (B) frog lateral radiographs show a 13-year-old boy who presented with 6 months of posterolateral hip pain aggravated by activity. He was able to ambulate without assistive devices with a mild antalgic limp. He was diagnosed with a severe, chronic, stable left SCFE and mild right slip deformity. He underwent in situ pin fixation of the right hip and a modified Dunn procedure for the left. (C) AP radiograph at 6 weeks postoperatively demonstrates severe subluxation of the left hip with no clear evidence of avascular necrosis. (D) AP radiograph after application of an articulated hip external fixator. (E) AP radiograph after sequential 1-mm distraction daily until the femoral head was at the level of the acetabulum. Nearly 4 weeks after application of the distractor, he returned to the operating room to remove the external fixator. An arthrogram was performed to check reduction and stability followed by a limited anterior surgical approach to directly visualize the reduction. A static external fixator was then used to keep the hip concentrically reduced and the patient was maintained nonweightbearing. (F) AP and (G) frog lateral radiographs 2 years after surgery demonstrate femoral head collapse resulting from avascular necrosis with joint space narrowing. He had a severe left-sided Trendelenburg gait and ambulated with a cane.

Fig. 2A–H

(A) AP and (B) lateral radiographs show a 12-year-old boy who presented to the emergency department with worsening right hip pain and limp. He had been experiencing right knee and hip pain for more than 1 year. He was diagnosed with a moderate, chronic, stable SCFE. (C) AP and (D) frog lateral radiographs after in situ pin fixation. (E) AP radiograph after the modified Dunn procedure was performed 4 months after the index procedure. (F) AP radiograph at the 2-week postoperative visit demonstrates high dislocation. This was treated with open reduction and 6 weeks of abduction bracing. (G) AP and (H) lateral radiographs 2 years after the modified Dunn procedure. There is radiographic evidence of mild lateral femoral head avascular necrosis; however, the patient has no hip pain. He has a reciprocal heel-toe gait with approximately 10° externally rotated foot progression angle. Hip flexion is comfortable to 100°. He has 20° of internal rotation and 40° of external rotation symmetrically.