Pelvic Osteotomy for Acetabular Dysplasia

Updated: Sep 22, 2017
  • Author: Dinesh Thawrani, MBBS, D'Ortho, DNB(Orth), MNAMS; Chief Editor: Jeffrey D Thomson, MD  more...
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Overview

Background

The purpose of this chapter is to discuss pelvic osteotomy as a means of stabilizing the hip and preventing early osteoarthritis. The different general categories of pelvic osteotomies commonly performed in current pediatric orthopedic practice are summarized, their principles are discussed, their indications are reviewed, and some of their key technical points are briefly explained.

The development of the hip socket (acetabulum) during the growth period depends largely on the interstitial growth within the triradiate cartilage. However, the concavity of the acetabulum develops in response to the presence of the spherical femoral head within it. Thus, any abnormality in the position of the femoral head with respect to the acetabulum during the growth period can produce an abnormal acetabulum. [1, 2, 3]

This altered congruency of the acetabulum resulting from its maldevelopment is referred to as acetabular dysplasia. More often than not, the concentric reduction of the subluxated or dislocated hip achieved at an early age takes advantage of the inherent growth of the acetabulum to ultimately obtain a well-developed acetabulum and a congruent hip joint. [1]

Some dysplasias of the acetabulum may persist until adolescence. Although the true incidence of persistent or residual acetabular dysplasia is unknown, it is well established that persistent acetabular dysplasia can lead to early degenerative joint disease. [4, 5]  Emphasis is therefore placed on early recognition and timely treatment of persistent acetabular dysplasia by means of an appropriately selected pelvic osteotomy before any irreversible cartilage damage occurs. [6]

Pelvic osteotomy is a powerful surgical tool for realigning the dysplastic acetabulum and providing a biomechanically sound hip joint with essentially normal bearing surfaces. The goal is to preserve the natural bone and obviate the need for hip joint arthroplasty at a young age. Each type of pelvic osteotomy has its place, and each has its own advantages, disadvantages, and potential complications.

Selection of the proper pelvic osteotomy is the critical step in treatment. It depends on various factors, such as maturity of the triradiate cartilage, underlying disease and precise pathoanatomy of the hip joint in a particular case. The results of pelvic osteotomy are generally good, with remarkably durable restoration of the hip joint—provided that sufficient attention is paid to the indications for and the technical details of each particular osteotomy.

Pelvic osteotomies, though still in an evolutionary phase, have had a tremendous impact. By introducing the periacetabular osteotomy (PAO) and the concept of femoroacetabular impingement, Ganz et al [7, 8, 9]  greatly changed the thinking of many surgeons involved in treating adolescents and adults with hip joint pathology requiring surgical treatment. Technical advancements in imaging are also helping practitioners detect and treat the degenerative process at a much earlier stage.

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Anatomy

For the surgeon planning a pelvic osteotomy, the anatomy of the posterior pelvic ligaments (ie, the sacrotuberous and sacrospinous ligaments) and the blood supply of the acetabulum are the two most relevant anatomic considerations. [10]

Posterior pelvic ligaments

The sacrotuberous ligament is long, flat, and triangular. It is superiorly attached to the posterior superior and posterior inferior iliac spines, the back and the side of the lower part of the sacrum and the coccyx. The fibers converge below to end on the ischial tuberosity. The ligament is in line with the long head of the biceps femoris and may be considered as being derived from there. The posterior surface of the ligament gives origin to the gluteus maximus.

The sacrospinous ligament, also triangular in form, is attached by its apex to the ischial spine. Its broader base arises from the side of the lower sacral and coccygeal segments. This ligament converts the greater sciatic notch into the greater sciatic foramen. With the sacrotuberous ligament, which crosses it dorsally, it likewise converts the lesser sciatic notch into the lesser sciatic foramen.

The attachment of these two ligaments in close proximity to the acetabulum has induced orthopedic surgeons to design a number of different ischial cuts (see the image below). The relevance of these ligaments during the performance of a pelvic osteotomy is addressed more fully elsewhere (see Redirectional Osteotomies).

Posterior view of pelvis demonstrating lines of va Posterior view of pelvis demonstrating lines of various pelvis osteotomies

Blood supply

The acetabulum is supplied primarily by the periosteal arteries, with contributions from numerous local arteries. Each contributing bone carries its own vascular supply. The superior gluteal artery (SGA), the obturator artery (OA), and the superficial circumflex iliac artery (SCIA) contribute to the periosteal supply of the ilium. The pubis is supplied by a periosteal anastomosis of branches from the OA, the inferior epigastric artery (IEA), and the medial circumflex femoral artery (MCFA). The superficial and deep external pudendal arteries may also contribute.

Multiple vascular foramina are present, mainly at the lateral (acetabular) end of the bone, but there is no consistently placed nutrient foramen. The ischium carries multiple vascular foramina at its acetabular margin, along with a few on the pelvic surface. This bone is supplied by branches of the OA, the MCFA, and the inferior gluteal artery (IGA).

The risk of osteonecrosis of the acetabular fragment after PAO is one of the main arguments used by opponents of this procedure. [11] However, a cadaveric study done by Beck et al using colored latex proved that even after PAO, the blood supply to the acetabulum is maintained through the OA and through the supra-acetabular and acetabular branches of the SGA. [12]

Similarly, a shelf acetabuloplasty or a Chiari osteotomy compromises the blood supply through the SGA, and the blood supply to the acetabular fragment will rely on the OA and on the branches of the MCFA to the anterior wall. [12]

Musculoskeletal structures

In addition, surgeons should be acquainted with other normal musculoskeletal structures around the hip and some of the probable bony pathologic findings of the hip joint and pelvis in acetabular dysplasia. They should be comfortable with various surgical approaches to the hip and pelvis. Any combination of movement planes is possible within the limits of the restraining ligaments and muscular attachments.

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Pathophysiology

In acetabular dysplasia, the stress across the hip joint is increased as a consequence of the following [13, 14] :

  • A decreased acetabular weightbearing zone
  • Increased joint reaction forces across the hip joint secondary to the laterally displaced center of rotation of the hip

Accordingly, pelvic osteotomy is indicated to reduce the joint loading and increase the contact surface area; this undoubtedly affects cartilage and bone adaptation, resulting in beneficial joint remodeling. [13] Thus, pelvic osteotomy primarily redistributes the load (ie, changes the stress gradient) rather than changing overall hip joint pressure. Medialization of the hip joint center decreases the abductor muscles forces necessary to counteract the adductor forces and decreases the force across the hip joint.

The final goal of any pelvic osteotomy is to provide a stable hip joint, either by changing the shallow acetabulum into a deeper one or by redirecting the existing maldirected acetabulum and thus expanding the coverage of the femoral head by the native acetabulum. Besides normalizing the weightbearing forces, pelvic osteotomies relax the capsule and muscles around the hip joint, improve the moment arm of the hip joint, and reduce the secondary stress on the lumbar spine by normalizing the anatomy and biomechanics of the whole pelvis. [13]

Because the pathomechanics of the hip joint vary greatly, depending on the age of the patient and the underlying pathology of acetabular dysplasia, and because there numerous different types of pelvic osteotomy (see Surgical Options), it is often difficult for a surgeon to predict which type of pelvic osteotomy will most improve the biomechanical environment in a given situation.

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Etiology

An abnormally shallow acetabulum can result from several developmental diseases of the hip joint. Invariably, acetabular dysplasia is a part of developmental dysplasia of the hip (DDH), which is the most common developmental hip disease. In addition, other childhood bony diseases, such as slipped capital femoral epiphysis and Legg-Calves-Perthes disease, can also produce residual acetabular dysplasia. [15, 16]

Acetabular dysplasia can also arise secondary to certain neuromuscular conditions, such as cerebral palsy (CP), [17, 18, 19] Charcot-Marie-Tooth disease, myelomeningocele, and arthrogryposis. [20] It may be seen as an associated finding in syndromes such as Ehlers-Danlos syndrome and Larson syndrome. Essentially, any condition that interferes with the interdependent relation between the femoral head and the acetabulum during the growth period can lead to acetabular dysplasia.

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