Introduction

Hip dysplasia in the adult can lead to pain and limping. Unfavorable leverages are responsible for the fatiguing of the abductors, whereas an insufficient coverage of the femoral head causes overload at the acetabular rim with shearing forces that result in lesions of the labrum and acetabular cartilage that eventually lead to osteoarthrosis (OA) of the hip.

The natural history of the dysplastic hip without subluxation is not well known, but it is estimated that 40% to 50% of patients with dysplasia develop OA before the age of 50 years and that approximately 50% have their first reconstructive surgeries before the age of 60 years. It appears that hips with a lateral center-edge angle (LCE angle) of less than 16 degrees or an acetabular index of more than 15 degrees will ultimately develop end-stage OA. Alternatively, it is well known that all dysplastic hips with subluxation evolve into OA during the second to third decade of life. Surgical interventions aim to alter the natural course of this degeneration.

Reorientation procedures include single, double, and triple osteotomies as well as spheric and periacetabular osteotomies. The inherent drawbacks of these osteotomies are a limited range of displacement; the potential narrowing of the pelvic cavity; and the need for a substantial internal fixation, because some techniques create a discontinuity of the pelvic ring. The medialization of the joint is difficult to achieve, and some osteotomies have an intra-articular course, because the radiologically visible teardrop remains in situ. To avoid these disadvantages, the Bernese periacetabular osteotomy (PAO) was developed in 1984. The polygonally shaped juxta-articular osteotomy respects the vascular blood supply to the acetabular fragment. It also facilitates extensive acetabular reorientation, including the correction of the version and mediolateral displacement. The posterior column remains intact, which protects the sciatic nerve and enables minimal internal fixation. The dimensions of the true pelvis remain unchanged, thus permitting unimpaired vaginal delivery. All steps of the acetabular osteotomy are performed with the use of the modified Smith-Petersen approach. During the early stages of this technique, some centers preferred the ilioinguinal approach; however, this was abandoned after several cases of thrombosis of the femoral artery, with serious consequences in some patients. In addition, the Smith-Petersen approach allows for an anterior capsulotomy for the inspection and correction of labral pathology and of potential femoroacetabular impingement. Initially, PAO was designed for the treatment of the dysplastic hip. With the recognition of orientation problems of the acetabulum—particularly retroversion—as a cause of impingement, the technique was also applied for the correction of acetabular pathologies other than dysplasia. It is currently used for the treatment of acetabular retroversion and for selected cases of protrusio.

Basic science

The insufficient coverage of the femoral head by a too-small acetabulum leads to high loads at the acetabular roof. Most often, coverage is not only insufficient, but it is also maloriented with a steep acetabular roof. This results in a small inclined plane and leads to instability and the migration of the femoral head, thus further increasing load and shear stresses at the acetabular rim. The acetabular labrum initially hypertrophies to maintain the femoral head within the joint. If the chronic shear stresses persist, the labral soft-tissue compensation fails, and the labrum is torn off of the acetabular rim, sometimes with an osseous fragment. Acetabular rim fractures usually occur only in the presence of bone cysts, which have weakened the bony rim.

Histomorphologically, the labrum shows myxoid degeneration of its fibrocartilage structure and adjacent ganglion formation within the bone or soft tissues. In addition to increased femoral head instability, the joint-sealing function, which is required for cartilage lubrication and the distribution of joint pressures, is also lost. In this mechanically adverse situation, an increase of joint contact pressures at the acetabular rim is directly related to the onset of cartilage degeneration. As an adaptation to the increased load transmission, an increase in the subchondral bone density at the anterolateral acetabular rim can be observed.

Indications

In the presence of severe dysplasia or aspheric congruency, simultaneous femoral osteotomy for optimal positioning of the femoral head has to be evaluated.

Contraindications

A definite upper age limit does not exist. However, patients who are more than 50 years old are rarely treated with an acetabular osteotomy. In contrast with distant pelvic osteotomies, the Bernese PAO crosses the posterior line of the triradiate cartilage. Therefore, this osteotomy is not indicated if substantial growth potential remains within this physis.

Brief history and physical examination

Imaging and diagnostic studies

Surgical technique

The patient is in a supine position with the lower limb draped free. The iliac crest and the proximal half of the thigh should be accessible. Surgery is performed through a modified Smith-Petersen approach with osteotomy of the anterosuperior iliac spine (ASIS). The first part of the dissection is performed with the hip in extension. The incision starts at the gluteal tubercle of the iliac crest, curves just lateral to the ASIS, and continues in a curved way to the lateral aspect of the proximal thigh. The subcutaneous tissue is incised in line, and a lateral skin flap is developed until the fat layer between the fascia of the sartorius and the tensor fasciae latae becomes visible. The main branch of the lateral femoral cutaneous nerve lies in this fatty tissue. The muscle belly of the tensor fasciae latae is identified, and its fascia is split lengthwise. The dissection follows the fascia medially into the interval between the tensor fasciae latae and the sartorius muscle. The tensor is pulled laterally with a narrow Langenbeck retractor. Slight abduction of the lower limb helps to relax this muscle. The floor of the muscle compartment is incised longitudinally, and the lateral border of the muscle belly and the tendon of the rectus femoris, including its reflected part, are visualized. The fascia between the rectus and the tensor can be of quite variable thickness, and, in the distal part of the incision, the ascending branch of the lateral femoral circumflex artery runs within this fascial layer between the rectus and the tensor fasciae latae. These blood vessels represent an important source of vascularization of the tensor fasciae latae and therefore have to be protected. The blood vessels are mobilized from the fasciae to allow for the spread of the deep layers of the approach.

The origin of the external oblique muscle that overhangs the iliac crest is lifted and detached subperiosteally from the iliac crest to about 1.5 cm from the ASIS. The ASIS is osteotomized about 1.5 cm to 2 cm proximal to the palpable tip of the ASIS. The osteotomized ASIS is mobilized medially together with the origin of the sartorius and the inguinal ligament. The dissection of the inner table of the iliac wing is continued strictly subperiosteally down to the pelvic brim. In approximately half of patients, the nutrient artery of the iliolumbar artery enters the iliac wing lateral to the pelvic brim. This blood vessel has to be visualized carefully and coagulated. There may be considerable backflow from the bone; if this happens, hemostasis can be performed with the use of bone wax to obstruct the blood vessel. In the other half of patients, the nutrient artery enters the bone medial to the pelvic brim and cannot be controlled. In these cases, blood loss through the supra-acetabular osteotomy can be substantial and can only be controlled by bone wax after the mobilization of the acetabular fragment. The periosteal and muscle connection with the osteotomized ASIS should be preserved, thus preventing a stretching of the femoral cutaneous nerve, even if the wound is considerably spread. The intact periosteum that covers the iliac muscle protects this muscle during the entire operation. The exposure of the inside of the pelvis is continued by detaching the origin of the iliac muscle along the interspinous crest until the origins of the direct and reflected heads of the rectus become visible. At this time, it is advantageous to hold the hip in 40 degrees of flexion with the leg holder to relax the medial soft tissues.

The direct head of the rectus is detached from the anteroinferior iliac spine (AIIS), and the indirect head is divided. The rectus femoris then is retracted medially with a Langenbeck retractor, and the lateral limit of iliocapsularis muscle becomes visible. Particularly among patients with dysplastic hips, the iliocapsular muscle (i.e., the capsular part of the iliac muscle) can be hypertrophic and well visible lying on the joint capsule. The main site of origin lies at the distal border of the AIIS.

The iliocapsular muscle is detached from the capsule by sharp dissection going from lateral to medial until the iliopectineal bursa is opened and the psoas tendon becomes visible. The psoas tendon is undermined and retracted medially with the use of a pointed Hohmann retractor driven into the pubic ramus 1 cm to 1.5 cm medial to the iliopectineal eminence. The psoas tendon protects not only the femoral nerve but also the femoral vessels from overstretching; therefore, it should never be divided. The iliocapsularis muscle is now completely detached from the capsule, thus exposing the anteroinferior part of the capsule around the calcar. Any accidental opening of the capsule should be closed, because a closed capsule being put under tension facilitates the dissection of the ischial ramus. During this stage, a large, curved pair of scissors with rounded ends is advanced along the anteroinferior capsule, and the space between the capsule and the obturator externus is enlarged by spreading the scissors (Figure 26-1). The transversely running muscle belly of the obturator externus can often be seen. Because the medial femoral circumflex artery that supplies the femoral head runs distal to the muscle belly, scissors and other instruments must stay strictly proximal to the muscle belly. If visualization is impossible, it is safe to keep the instruments in close contact with the capsule.

Figure 26–1 The completed approach. The osteotomy of the anterosuperior iliac spine allows for the preparation of the inner pelvis. A Hohmann retractor sits on the pubis. The iliocapsularis is detached from the capsule, and the scissors are placed around it. With the tip of the scissors, the ischium is palpated.