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AimsThe modified Dunn procedure has the potential to restore the anatomy in hips with severe slipped capital femoral epiphyses (SCFE). However, there is a risk of developing avascular necrosis of the femoral head (AVN). In this paper, we report on clinical outcome, radiological outcome, AVN rate and complications, and the cumulative survivorship at long-term follow-up in patients undergoing the modified Dunn procedure for severe SCFE.Patients and MethodsWe performed a retrospective analysis involving 46 hips in 46 patients treated with a modified Dunn procedure for severe SCFE (slip angle > 60°) between 1999 and 2016. At nine-year-follow-up, 40 hips were available for clinical and radiological examination. Mean preoperative age was 13 years, and 14 hips (30%) presented with unstable slips. Mean preoperative slip angle was 64°. Kaplan–Meier survivorship was calculated.ResultsAt the latest follow-up, the mean Merle d’Aubigné and Postel score was 17 points (14 to 18), mean modified Harris Hip Score was 94 points (66 to 100), and mean Hip Disability and Osteoarthritis Outcome Score was 91 points (67 to 100). Postoperative slip angle was 7° (1° to 16°). One hip (2%) had progression of osteoarthritis (OA). Two hips (5%) developed AVN of the femoral head and required further surgery. Three other hips (7%) underwent implant revision due to screw breakage or change of wires. Cumulative survivorship was 86% at ten-year follow-up.ConclusionThe modified Dunn procedure for severe SCFE resulted in a low rate of AVN, low risk of progression to OA, and high functional scores at long-term follow-up. The slip deformities were mainly corrected but secondary impingement deformities can develop in some hips and may require further surgical treatment.Cite this article: Bone Joint J2019;101-B:403–414.

Die Berner periazetabuläre Osteotomie (PAO) nach Ganz ist eine Operationstechnik zur Behandlung der (1) Hüftdysplasie und des (2) femoroazetabulären Impingements bei einer ausgeprägten azetabulären Retroversion mit dem Ziel, eine sekundäre Coxarthrose zu verhindern oder zumindest herauszuzögern. Im Unterschied zu anderen Beckenosteotomien bleibt der hintere Pfeiler intakt, was die primäre Stabilität der Reorientierung erhöht und den Geburtskanal nicht verändert. Über eine geschwungene verkürzte ilioinguinale Inzision werden vier Osteotomien und eine kontrollierte Fraktur durchgeführt, was eine Reorientierung des Azetabulums mit großem Freiheitsgrad erlaubt. Während die Sequenz der Osteotomien für beide Indikationen identisch ist, unterscheidet sich aber die Reorientierung des Azetabulums. Der Zugang gestattet zudem eine anteriore Kapsulotomie mit femoraler Offset-Korrektur. Obwohl die Operation technisch anspruchsvoll ist, ist die Komplikationsrate verhältnismäßig klein. Der Schlüssel für ein erfolgreiches Langzeitergebnis liegt in der optimalen Reorientierung des Azetabulums bei beiden Indikationen. Klinisch kann mit einer guten azetabulären Einstellung in 80–90 % der Fälle ein gutes bis sehr gutes Resultat nach 10 Jahren erzielt werden. Die kumulative Überlebensrate der weltweit ersten Hüften 20 Jahre nach PAO liegt bei 60 %. Die vorläufige Evaluation derselben Serie nach 30 Jahren zeigt eine Überlebensrate von etwa 30 %. Die PAO hat sich zu einer standardisierten Therapie der Hüftdysplasie bei Adoleszenten und Erwachsenen etabliert. The Bernese periacetabular osteotomy (PAO) is a surgical technique for the treatment of (1) hip dysplasia and (2) femoroacetabular impingement due to acetabular retroversion. The aim of the surgery is to prevent secondary osteoarthritis by improvement of the hip biomechanics. In contrast to other pelvic osteotomies, the posterior column remains intact with this technique. This improves the inherent stability of the acetabular fragment and thereby facilitates postoperative rehabilitation. The birth canal remains unchanged. Through a shortened ilioinguinal incision, four osteotomies and one controlled fracture around the acetabulum are performed. The direction of acetabular reorientation differs for both indications while the sequence of the osteotomies remains the same. This surgical approach allows for a concomitant osteochondroplasty in the case of an aspherical femoral head-neck junction. The complication rate is relatively low despite the complexity of the procedure. The key point for a successful long term outcome is an optimal reorientation of the acetabulum for both indications. With an optimal reorientation and a spherical femoral head, the cumulative survivorship of the hip after 10 years is 80–90 %. For the very first 75 patients, the cumulative 20-year survivorship was 60 %. The preliminary evaluation of the same series at a 30-year follow-up still showed a survivorship of approximately 30 %. The PAO has become the standard procedure for the surgical therapy of hip dysplasia in adolescents and adults.

A new and computationally efficient method is developed for characterizing a spherically focused, ultrasonic transducer (and its accompanying test system). Procedures for determining the probe's effective radius, effective focal length, and system efficiency factor are described. Predicted responses that make use of these effective parameters are shown to correspond very well to measured responses for a number of different transducers.