The modified Dunn procedure has the potential to restore the anatomy in hips with slipped capital femoral epiphyses (SCFE) while protecting the blood supply to the femoral head. However, there is controversy about the risks associated with the procedure especially in the most severe capital slips.

Therefore, we report on (1) clinical outcome, (2) the cumulative survivorship with endpoints AVN and/or OA progression and (3) radiographic anatomy of the proximal femur at followup in patients treated with a modified Dunn procedure for severe SCFE.

We performed a retrospective analysis involving 46 hips of 46 patients treated with a modified Dunn procedure for severe SCFE (slip angle >60°) between 1999 and 2016.

Followup averaged 8 years, (range 1–17) with 2 patients lost to followup after one year.

The mean age was 13 years (range 9–19 years). Mean preoperative slip angle was 64° (range 60–90) and 14 out of 46 hips (30%) presented with unstable slips.

Clinical scores and PROMs were evaluated and the hips were followed standard x-rays. Cumulative survivorship (Kaplan-Meier) with three defined endpoints: (1) AVN; (2) progression by at least one OA grade according to Tönnis; (3) non-preserved hip joint.

(1)Mean Harris Hip score (HHS) was 93 points (66–100) and mean Hip Disability and Osteoarthritis Outcome Score (HOOS) was 90 points (67–100) at last followup.

(2)Cumulative survivorship was 93% at 10-year followup. Three hips reached an endpoint. Two hips (4%) had AVN, one of them underwent hip arthrodesis. One hip had OA progression.

(3)Postoperative slip angle was 7° (1–16). Alpha angle on axial radiograph was 39° (26–71) at followup. 41/44 hips (93%) had no OA (Tönnis 0).

The modified Dunn procedure largely corrected slip deformities with low apparent risk of progression to avascular necrosis or osteoarthritis at mean 8-years followup. The AVN rate in severe and unstable (30%) capital slip was 4% (2 hips) with this procedure.

Posterior extraarticular ischiofemoral hip impingement can be caused by high femoral torsion and is typically located between the ischium and the lesser trochanter. We asked if patients undergoing derotational femoral osteotomies for posterior FAI have (1) decreased hip pain and improved function and evaluated (2) subsequent surgeries and complications?

Thirty-three hips undergoing derotational femoral osteotomies between 2005 and 2016 were evaluated retrospectively. Of them 15 hips underwent derotational femoral osteotomies and 18 hips underwent derotational femoral osteotomies combined with varisation (neck-shaft angle >139°). Indication for derotational osteotomies was a positive posterior impingement test in extension and external rotation, high femoral torsion (48° ± 9) on CT scans and limited external rotation. Offset improvement was performed to avoid intraarticular impingement in hips with a cam-type FAI. All patients were female and mean followup was 3 ± 2 (1 – 11) years.

At latest followup the positive posterior and anterior impingement test decreased from preoperatively 100% to 5% (p< 0.001) and from preoperatively 85% to 30% (p< 0.001). The mean Merle d'Aubigné Postel score increased from 14 ± 1 (11 – 16) to 16 ± 1 (13 – 17) at latest followup (p< 0.001). At followup 32/33 hips had been preserved and one hip had been converted to a total hip arthroplasty (THA). In two hips (6%) revision osteosynthesis was performed for delayed healing of the femoral osteotomy.

Derotational femoral osteotomies for the treatment of posterior extraarticular ischiofemoral impingement caused by high femoral torsion result in decreased hip pain and improved function at midterm followup but had 6% delayed healing rate requiring revision surgery.