Hip Arthroscopy for Structural Hip Problems

Introduction

Arthroscopy has been used successfully to address intraarticular hip pathology due to functional or morphologic alterations of the hip. Historically, trauma was believed to be the cause of most labral tears in the hip; however, improved understanding of pathophysiology has revealed that up to 80% of such lesions are related to subtle structural problems. For many years, this led surgeons to classify most hip osteoarthritis cases as primary or idiopathic. However, both the femur and acetabulum can present with abnormal shapes that predispose to impingement, instability, or both, which ultimately induce degenerative changes of osteoarthritis (OA). Hip arthroscopy aims to treat intraarticular damage and its causes, preferably in the early stages of the disease. It has been shown to improve symptoms and is expected to improve joint biomechanics to prevent or delay the natural progression of joint degeneration.

A common structural problem is developmental dysplasia of the hip (DDH), in which the acetabulum is shallow, is inclined laterally, and insufficiently covers the femoral head. In this situation, the labrum is known to function as a key factor in joint stability and is usually hypertrophic. Higher stress loads on the lateral margin of the acetabulum and labrum were found to occur in an inverse relation to acetabular coverage, as shown by the center edge (CE) angle. The lesser the coverage, the greater the stresses that are found, and the earlier joint degeneration is observed. When the labrum fails to manage those stresses, the patient may present with a tear or detachment. Subluxation, joint incongruence, and rapid progression to joint degeneration have been documented.

On the other hand, the acetabulum can present with excessive coverage leading to joint impingement at the extremes of range of motion. An example of such morphologic alteration is protrusio acetabuli, in which the center of rotation of the femoral head lies too medially in an abnormally deep socket. Another condition is general acetabular retroversion, in which the whole acetabulum is oriented posteriorly, producing anterior overcoverage, predisposing to impingement against the femoral neck during hip flexion, and posterior hip instability due to relative undercoverage posteriorly. Focal cranial acetabular retroversion is seen more commonly, and the superior hemisphere of the acetabulum is posteriorly oriented, provoking localized impingement on the anterior superior aspect of the acetabular rim, proximal to the psoas valley or U, in between the origins of the heads of the rectus femoris muscle.

Extraarticular impingement can also occur on the acetabular side owing to an overly prominent anterior-inferior iliac spine (AIIS). A low-hanging AIIS can be responsible for a radiographic crossover sign, which may be confused for acetabular retroversion.

In many instances, the femur is the site of the deformity. A posterior tilt of the femoral head relative to the axis of the femoral neck is often observed after slipped femoral capitis (clinical or subclinical). The decreased femoral head-neck offset is responsible for a cam effect, in which that region is forced into the acetabulum, especially on hip flexion, adduction, and internal rotation. This effect can also be elicited in maximum abduction, when the bump is more laterally based. In many cases, the center of rotation of the femoral head is in line with the femoral neck axis, but insufficient offset is present. Cam deformities seem to be deleterious to the hip joint because they can predispose to impingement at earlier degrees of range of motion, inducing cartilage and labral damage. Other variations on proximal femur morphology, such as excessive anteversion and coxa valga, can be components of DDH and can worsen joint function.

To restore normal interaction between femur and acetabulum, hip arthroscopy can be used to modify the shape of the femoral head-neck junction and the acetabular rim. When correctly indicated, the arthroscopic approach provides the great advantages of effective treatment, low morbidity, reproducibility, and excellent results.

However, deterioration in hip function can occur when hip arthroscopy is applied for an incorrect diagnosis, and/or a suboptimal surgical treatment is performed. Strict attention to appropriate surgical indications, patient selection, and technical execution of the procedure are paramount to achieving successful outcomes and avoiding complications and treatment failures.

Box 53.1 shows pearls and pitfalls related to this topic.