Modified Dunn Procedure is Superior to In Situ Pinning for Short-term Clinical and Radiographic Improvement in Severe Stable SCFE

Abstract

Background: In situ pinning is the conventional treatment for a stable slipped capital femoral epiphysis (SCFE). However, with a severe stable SCFE the residual deformity may lead to femoroacetabular impingement and articular cartilage damage. A modified Dunn subcapital realignment procedure has been developed to allow for correction at the level of the deformity while preserving the blood supply to the femoral head.

Questions/purposes: We compared children with severe stable SCFE treated with the modified Dunn procedure or in situ pinning in terms of (1) proximal femoral radiographic deformity; (2) Heyman and Herndon clinical outcome; (3) complication rate; and (4) number of reoperations performed after the initial procedure.

Methods: In this nonmatched retrospective study, 15 patients treated with the modified Dunn procedure (between 2007 and 2012) and 15 treated with in situ pinning (between 2001 and 2009) for severe but stable SCFE were followed for a mean of 2.5 years (range, 1-6 years). During the period in question, the decision regarding which procedure to use was based on the on-call surgeon's discretion; six surgeons performed in situ pinning and three surgeons performed the modified Dunn procedure. A total of 15 other patients were treated for the same diagnosis during the study period but were lost to followup before 1 year; of those, 12 were in the in situ pinning group. Radiographs were reviewed to measure the AP and lateral alpha angles, femoral head-neck offset, and Southwick angle preoperatively and at the latest clinical visit. The Heyman and Herndon clinical outcome, complications, and subsequent hip surgeries were recorded.

Results: At latest followup, the median AP alpha angle (52°, range 41°-59° versus 76°, interquartile range [IQR]: 68°-88°; p = 0.0017), median lateral alpha angle (44°, IQR: 40°-51° versus 87°, IQR: 74°-96°; p < 0.001), median head-neck offset (7 mm, IQR: 5-9 mm versus -5, IQR: -11 to -4 mm; p < 0.001), and median Southwick angle (16°, IQR: 6°-23° versus 58°, IQR: 47°-66°; p < 0.001) revealed better deformity correction with the modified Dunn procedure compared with in situ pinning. Nine patients had good or excellent results in the modified Dunn group compared with four of 15 in the in situ pinning group (p = 0.0343; odds ratio, 5.86; 95% CI, 1.13-40.43). With the numbers available, there were no differences in the numbers of complications in each group (five versus three complications in the in situ and modified Dunn groups, respectively; p = 0.66), but there were more reoperations in the in situ pinning group (three versus seven; p = 0.0230).

Conclusions: The modified Dunn procedure results in better morphologic features of the femur, a higher rate of good and excellent Heyman and Herndon clinical outcome, a lower reoperation rate, and a similar occurrence of complications when compared with in situ pinning for treatment of severe stable SCFE.

Level of evidence: Level III, therapeutic study.

Fig. 1A–F

Radiographs from an 11-year-old girl with severe chronic stable SCFE treated by a modified Dunn procedure are shown. (A) The preoperative frog lateral radiograph shows abnormal femoral head-neck morphologic features with an increased alpha angle and reduced offset. (B) An AP radiograph taken preoperatively shows the severe deformity of the proximal femur. (C) An intraoperative photograph of the proximal aspect of the femur after surgical dislocation of the hip before development of the retinacular flap is shown. The anterior periosteum (black arrow) is torn and the metaphysis (asterisk) is prominent and severely displaced from the epiphysis. (D) An intraoperative photograph of the acetabulum shows articular cartilage damage extending from the superior to the anterior portion of the acetabular rim with chondral labral delamination (black arrow) and pitting malacia (white arrow). (E) The frog lateral radiograph taken at 2 years after surgery shows improved femoral head-neck offset and alpha angle. (F) An AP radiograph taken 2 years after surgery shows restored proximal femoral anatomy with normal alignment of the epiphysis in relation to the femoral neck.

Fig. 2A–D

Radiographs from a 13-year-old boy with severe stable SCFE treated by in situ fixation with an additional complication of progressive slip and osteonecrosis of the femoral head are shown. (A) The preoperative frog lateral radiograph shows a severe SCFE of the left hip. (B) The radiograph taken 2 months after in situ pinning shows progression of the slip and inadequate position of the screw in relation to the center of the femoral head. (C) The patient underwent revision of the fixation with an additional screw. The lateral radiograph shows lucency in the femoral head with sclerosis on the acetabular rim. (D) The frog lateral radiograph taken 4 years after a proximal femoral valgus flexion derotational osteotomy shows the femoral head has lost its sphericity secondary to osteonecrosis and there is a residual deformity of the femoral head and neck junction with a large prominence. The patient has a mild limp, mild pain exacerbated by activities, and limited flexion, internal rotation, and abduction of the left hip compared with the contralateral normal hip.