Open Treatment for Hip Cartilage Injuries

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CHAPTER 33 Open Treatment for Hip Cartilage Injuries

Michael K. Shindle, Dean G. Lorich, Robert L. Buly, Bryan T. Kelly

Introduction

Articular cartilage injuries of the hip are one of the most challenging orthopedic injuries to treat, and they have received considerably less attention as compared with other joints. Before the advent of cartilage-sensitive magnetic resonance imaging, hip pain in a young patient was typically diagnosed as early arthritis, and it resulted in progressive generalized joint deterioration (e.g., osteoarthritis, rheumatoid arthritis).

Nonarthritic cartilage injuries in the hip refer to focal chondral defects on either the acetabular or femoral side of the joint. Focal chondral defects on the femoral head are relatively uncommon and may result from shear injury or the axial loading of the head within the socket. Traumatic instability from either a hip dislocation or subluxation, as occurs during high-energy contact sports or motor vehicle accidents, may result in these types of focal chondral injuries. Another mechanism of injury includes a lateral impact injury in which there is loading at the greater trochanter in association with a high-energy activity. The subcutaneous location of the greater trochanter limits its ability to absorb large forces. Thus, an impact on this area can transfer a significant amount of energy and load to the hip joint surfaces, thereby resulting in chondral lesions of the femoral head or acetabulum without associated osseous injury. In addition to trauma, other mechanisms that can cause focal chondral lesions of the femoral head include osteonecrosis, underlying bony deformity, and dysplastic conditions.

In a patient with osteonecrosis, the articular cartilage injury of the femoral head is a result of the loss of structural integrity of the subchondral bone. The degree of chondral pathology depends on the extent of the collapse of the underlying subchondral bone. The spectrum of cartilaginous lesions associated with osteonecrosis is wide and may range from mild chondromalacia to severe chondral fractures with complete collapse.

Anatomic abnormalities such as congenital hip disease (e.g., Legg-Calvé-Perthes disease, dysplasia) or slipped capital femoral epiphysis can lead to cartilage lesions of the femoral head. Acute chondrolysis may occur after slipped capital femoral epiphysis, and narrowing of the joint space may occur as early as 1 year after the acute slip injury.

The grade and character of the cartilage lesions depend on the mechanism of injury and the stage at which the lesion is detected. Lesions can be classified as shear injuries, delamination, fissuring, chondral flaps, fractures, and punch or impaction injuries. As these lesions progress to an advanced-stage degenerative condition, they often lose their specific characteristics.

Cartilage injuries on the acetabulum are more common and typically present as localized cartilage delamination defects in the anterosuperior weight-bearing zone of the acetabular rim. The cause of these defects is most commonly femoroacetabular impingement, which will be discussed in chapter 28.

Basic science

The normal thickness of articular cartilage ranges from 2 mm to 5 mm, and it is determined by the contact pressures that occur across a joint. The articular cartilage of the femoral head is thickest on the central and medial surfaces, which corresponds with the loading pattern of the hip joint. The majority of the femoral head chondral surface is involved in load transfer across the joint, which makes the area particularly vulnerable to injury.

Even with minor trauma, cartilage injury may occur, and chondrocyte death has been reported to occur at 20% to 30% of strain of the articular cartilage specimens. Injured cartilage that loses it congruity by fragmentation, indentation, or a crush injury results in a loss of joint function and progressive joint deterioration. Animal models suggest that large, full-thickness osteochondral defects will undergo degenerative changes around the rim of the defect, which can progress to global joint degradation in as little as 1 year. Finite-element models of osteochondral damage have also predicted a similar progression, because compressive strains reach maximum values around the rim of a defect, and the compressive strain values increase concomitantly as the defects become larger.

Indications

Patients with continued pain despite conservative treatment (e.g., activity modification, weight reduction, physical therapy, bracing, medications), who have imaging that is consistent with cartilage defects, and who demonstrate a positive response to an intra-articular injection are candidates for surgical intervention. Larger cartilage defects may be amenable to cartilage resurfacing procedures such as autogenous osteochondral transfer or fresh or fresh-frozen allograft femoral head transplants.

Conventional joint replacements have a long history of restoring function and relieving pain among patients with arthritis. However, primary total hip arthroplasty procedures have high rates of failure in young (i.e., less than 40 years old) and early–middle-aged (i.e., 40 to 60 years old) patients. To preserve bone stock, partial resurfacing procedures that require a minimum amount of bone removal have been developed. Devices have been developed that only require the removal of the affected area of cartilage in an attempt to maintain the natural radius of the curvature of the femoral head.

Brief history and physical examination

In the young patient, hip pain is often characterized by nonspecific symptoms, vague clinical findings, and normal radiographs. Common causes of groin and hip pain among young patients include hip flexor tendonitis, adductor muscle pathology, osteitis pubis, and trochanteric bursitis. However, the goal of the history and physical examination is to narrow down the differential diagnosis to intra-articular pain, extra-articular pain, or central pubic pain associated with athletic pubalgia. The intra-articular nonarthritic pathology of the hip joint includes disorders of the labrum, the iliofemoral ligament, the ligamentum teres, and the chondral surfaces of the femoral head and the acetabulum.

Patients with an intra-articular cause of hip pain may present with pain in the anterior groin, the anterior thigh, the greater trochanter, the buttock, or the medial knee. Other symptoms may include catching, clicking, locking, giving way, or restricted range of motion. Symptoms may be insidious in onset, or they may be preceded by a traumatic event.

Physical examination should include an assessment of the patient’s gait and posture as well as of his or her pelvic obliquity, limb-length inequality, muscle contractures, and scoliosis. The examination of the hip begins with the palpation of specific regions, but, if the pain is truly intra-articular, palpation does not typically cause pain. The active and passive range of motion of both hips should be performed with the patient in both the seated and supine positions. Mechanical symptoms that result from intra-articular pathology can be elicited by applying an axial load while performing an internal rotation of the hip or by having the patient perform a resisted leg raise while in the supine position.

Imaging and diagnostic studies

The initial workup of a patient with a suspected hip injury should include a standing anteroposterior view of the pelvis, a cross-table lateral view, and false-profile views of both hips. The main purpose of radiographs is to evaluate for the presence of femoroacetabular impingement, joint space narrowing, or acetabular dysplasia. A variety of normal radiographic indices have been described to differentiate normal from abnormal bony anatomy and include the center-edge angle, the Tönnis angle, the neck-shaft angle, the anterior offset, and the crossover sign.

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