The Bernese Periacetabular Osteotomy for Hip Dysplasia and Acetabular Retroversion

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CHAPTER 26 The Bernese Periacetabular Osteotomy for Hip Dysplasia and Acetabular Retroversion

Martin Beck, Reinhold Ganz

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.

Principles of Pelvic Osteotomy

In the dysplastic hip, the goal of pelvic osteotomy is to change acetabular orientation to optimize the joint mechanics by increasing the weight-bearing area and by transforming shearing forces into compressive forces. The coverage of the femoral head can be increased by either an augmentation of the acetabular roof or by changing the spatial orientation of the acetabulum. Augmentation procedures such as the Chiari osteotomy and the shelf procedure reduce joint-loading forces by augmenting the weight-bearing area of the joint. With both methods, lateral osseous coverage can be reproducibly improved; however, the posterior aspect of the femoral head often remains uncovered. The interposed capsule undergoes metaplastic transformation to fibrocartilage, and the labrum remains within the main weight-bearing area. A high failure rate is reported after Chiari osteotomies when the labrum was torn. As compared with hyaline cartilage, fibrocartilage has inferior mechanical properties for withstanding axial loading. Although augmentation procedures can provide reliable pain relief for some years, they should be regarded as salvage procedures.

Reorienting procedures change the orientation of the acetabular articular surface, thereby correcting the area of deficiency. These procedures provide a greater surface area for load transmission while reestablishing or maintaining the stability of the joint. During reorientation procedures, coverage is achieved with hyaline cartilage supported by subchondral bone, which has optimal mechanical qualities for weight bearing. Reorientation procedures include single, double, and triple osteotomies as well as spheric and periacetabular osteotomies. The dysplastic acetabulum can be reoriented with the use of a single innominate osteotomy, such as that described by Salter. Although this may be beneficial for children, the degree of correction that is possible in adolescents and adults is limited by the age-related increase in the stiffness of the symphysis pubis. Moreover, this osteotomy retroverts and lateralizes the joint because of a hinged angulation of the acetabulum around a fixed axis. The dysplastic hip joint is usually relatively lateralized. Additional lateralization and distalization are undesirable, because they further increase adverse joint reactive forces. As a result, a variety of double and triple osteotomies and PAOs have been developed in an attempt to improve the degree and accuracy of correction. The double and triple osteotomies—as a result of their considerable distance from the acetabulum, the size of the fragment, and the tension of the sacropelvic ligaments—have a limited range of displacement. Triple osteotomies closer to the joint, as described by Le Coeur, Tönnis and colleagues and Carlioz and colleagues, permit a considerable correction, but they potentially narrow the pelvic cavity. In addition, they require a substantial internal fixation, because these techniques create a discontinuity of the pelvic ring. The spheric osteotomies allow for a good lateral and anterior correction, but the medialization of the joint can only be obtained with great difficulty. These osteotomies also run intra-articular, because the radiologically visible teardrop remains in situ. Finally, given the proximity of these procedures to the joint, the vascular supply depends on the vessels of the capsule and the acetabular branch of the obturator artery. After spheric osteotomies, the acetabular fragment relies on the blood supply provided through the acetabular artery and the capsule, so a simultaneous capsulotomy should not be performed. On the basis of both mechanical and biologic considerations and in the light of the limitations of previous techniques, the Bernese PAO was developed. The polygonally shaped juxta-articular osteotomy respects the vascular blood supply to the acetabular fragment. It facilitates extensive acetabular reorientation, including the correction of 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, even in cases with bilateral osteotomy. An anterior joint capsulotomy provides information about and treatment options for lesions of the acetabular rim, and it allows for the treatment of labral pathology and potential postcorrection femoroacetabular impingement. There are some concerns regarding the vascularity of the acetabular fragment with juxta-articular (spheric) osteotomies. The blood supply of the acetabular fragment is secured by the acetabular and supra-acetabular branches of the gluteal arteries.

Indications

• Acetabular dysplasia around or after the closure of the physes
• Acetabular retroversion
• An anteroposterior pelvic radiograph that shows improved coverage of the femoral head and good congruence in 20 degrees to 30 degrees of abduction (abduction film)

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

Contraindications

• Marked cephalad dislocation
• Secondary acetabulum with fibrocartilage
• Deterioration of congruence on abduction films
• Osteoarthrosis with a Tönnis grade of more than 1

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

History

The majority of patients treated with PAO are young adults with symptoms of labral pathology and pain related to the overload and fatigue of the abductor musculature. Labral pathology often presents as a sharp, knife-like groin pain that subsides as acutely as it presents. Occasionally, the hip appears to be mechanically blocked, but this can be relieved by shaking or twisting the leg. The groin pain may also have an aching, more chronic character, and prolonged sitting or walking can exacerbate the pain. The pain can be reproduced by activities that involve forced hip flexion, adduction, and internal rotation (e.g., breaststroke swimming, entering or exiting a motor vehicle, sport activities with cutting or twisting movements). As the symptoms increase in frequency, residual pain may result in a slight limp. Symptoms of muscular overload range from early fatigue to clear weakness of the abductors, with irritation at the tendinous insertion on the greater trochanter.

Physical Examination

A complete physical examination includes the assessment of gait, limb length, muscle power, and range of motion as well as special tests. Abductor strength is assessed with the Trendelenburg test and with a leg raise against resistance in the lateral position. Range of motion, particularly for internal rotation, is often increased in a patient with hip dysplasia. With the onset of secondary osteoarthrosis, however, the range of motion may decrease again. A snapping psoas tendon is often present. A lesion of the acetabular rim (i.e., labral pathology) is suspected if the impingement test is positive. With the patient supine, the hip is flexed to 90 degrees. With additional internal rotation and adduction, the labrum will be squeezed between the femoral neck and the acetabular rim. In the presence of a damaged labrum, this will elicit the typical groin pain about which the patient is complaining. Occasionally a positive apprehension test may be possible, which is indicative of symptomatic anterior instability as a result of deficient anterior acetabular coverage. During this test, the patient lies supine, and the hip is extended, adducted, and externally rotated. Discomfort and a sense of instability are felt as the femoral head is subluxing anteriorly. In a very thin patient, this external rotation in extension can produce a mass in the inguinal region when the femoral head subluxes anteriorly; this is referred to as the lump sign.

Signs of trochanteric irritation indicate abductor muscle insufficiency. The bicycle test is performed by placing the patient in the lateral position with the affected hip up; a bicycle pedaling maneuver is then performed, and the lateral and posterior margins of the trochanter are palpated. Tenderness is most commonly palpated along the posterior border of the gluteus medius muscle.

Imaging and diagnostic studies

Conventional Radiography

An anteroposterior pelvic radiograph, a lateral cross-table view, and a false-profile view of the pelvis are required. The anteroposterior pelvic view allows for the visualization of the acetabular cover and version. The false-profile view permits the evaluation of the anterior acetabular coverage and the anterior migration or subluxation of the femoral head. The lateral cross-table view provides information about femoral torsion and the head–neck offset. Finally, anteroposterior abduction radiographs are used to assess the joint congruency that can be achieved with the reorientation of the acetabulum and the potential need for a concomitant femoral osteotomy.

Magnetic Resonance Arthrography

Magnetic resonance arthrography (MRA) is currently the method of choice for the imaging of the hip joint. The application of intra-articular gadolinium-diethylenetriamine pentaacetic acid as a contrast agent allows for the improved visualization of intra-articular joint structures, particularly the acetabular labrum and the cartilage surface of the hip. The technique includes high-field-strength magnetic resonance imaging and the use of surface coils. In addition to standard T1- and T2-weighted sagittal oblique and coronal oblique images, MRA includes proton-weighted radial sequencing in the axis of the femoral neck. This has the advantage that the acetabular and femoral articular cartilage as well as the labrum are visualized orthogonally at any point around the circumference of the acetabular rim and the femoral head. MRA including radial sequences has been shown to be extremely helpful for detecting labral lesions, and it enables a better assessment of the cartilage damage, which is always more extensive than it appears on conventional radiographs.

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.

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