7.7 The young arthritic hip

The cause of osteoarthritis of the hip can be viewed as a mechanical dysfunction resulting from either instability (hip dysplasia) or impingement, or a combination of both. Treatment is directed at the underlying disease process. Where there is no or minimal degenerative changes radiographically in a young patient who is normally fit and healthy, a reconstruction procedure is the preferred option (see Chapter 7.9). If there is evidence of severe osteoarthritis, an arthroplasty or salvage procedure should be considered.

Obtain the pertinent information: patient’s age; occupation; and onset, nature, and duration of pain. Are there any limitations of work or sporting activities? Past medical history of childhood illness or pain affecting the hip along with any previous operation should be documented, along with any positive family history. History of trauma or any other associated illness should be gathered.

It should be ascertained whether the pain is present on weight bearing or at rest, such as sitting. History of locking is very suggestive of intra-articular pathology, such as labral tears, loose bodies, or chondral flap.

Patients with hip dysplasia typically have good hip flexion and, due to femoral anteversion, good internal rotation. In femoroacetabular impingement (FAI), passive flexion of the hip to 90 degrees with adduction and internal rotation will be restricted and will elicit pain in the groin similar to the pain they are complaining of. This is the basis of the impingement test. In Perthes disease, abduction in extension will be severely restricted in the presence of hinge abduction.

The anteroposterior (AP) pelvic radiograph illustrates the femoral head and its sphericity. The position of the joint centre and any subluxation can also be noted by integrity of Shenton’s line. The acetabular coverage of the femoral head is depicted as is the acetabular inclination, also known as the sourcil (the weight-bearing superior dome of the acetabulum), which should measure 0–10 degrees and is between a line parallel to the weight-bearing dome (sourcil) and a line parallel to the inter-teardrop line. Loss of joint space and version of the acetabulum can also be seen. The vertical centre edge angle of Wiberg should be greater than 25 degrees. The anterior or lateral centre edge angle quantifies the anterior cover of the femoral head, and angles of less than 20 degrees are considered abnormal. An AP projection may also show cyst formation at the superior lateral aspect of the acetabulum representing damage at the labrochondral junction.

A retroverted acetabulum can be identified through the ‘cross-over’ sign (Figure 7.7.4). The cross-over sign is seen when the anterior rim of the acetabulum ‘crosses over’ its posterior rim, as their outlines are traced from proximal to distal on the radiograph. Retroverted acetabulae have been correlated with radiological evidence of osteoarthritis of the hip. A comparison of six radiographic projections to assess femoral head/neck asphericity demonstrated that the Dunn view in 45-degree or 90-degree flexion or a cross-table projection in internal rotation best show femoral head/neck asphericity, whereas AP or externally rotated cross-table views are likely to miss asphericity.

Computed tomography (CT) is useful in assessing the congruency and coverage of the femoral head and as an aid to preoperative planning for osteotomy.

CT can provide detailed information on bony architecture and any subtle pathology such as cam lesions (Figures 7.7.5 and 7.7.6). It also can assess version and is extremely helpful in imaging grossly abnormal anatomy.

This is used valuation of painful hip and exclusion of other sources of hip pathology. It allows for assessment of concavity of head neck junction. The angle of Notzli (Figure 7.7.7) is used to confirm cam lesion. A normal alpha angle is approximately 40 degrees while patients with FAI have average alpha angles of 74 degrees. The gadolinium enhanced magnetic resonance imaging of cartilage has the potential of predicting outcome of Bernese pelvic acetabular osteotomy by assessing the integrity of the cartilage.

The concept of FAI started to become widely accepted at about the same time that enthusiasts of hip arthroscopy started to publish their experiences and results. One of the main indications and supposed benefits of hip arthroscopy was the diagnosis and debridement of labral tears. Unfortunately, results were disappointing due to the fact that the labral tear was not the underlying pathology but usually a result of FAI which itself went untreated. The study by Beck and colleagues has shown that cam impingement in particular leads to extensive damage to the acetabular cartilage and that separation between the labrum and the cartilage arises because the cartilage is ripped off the labrum. The tear of the labrum is only part of the pathology and is secondary to impingement.

The aim of surgical treatment for FAI is to improve the femoral head–neck offset thereby improving joint clearance and preventing abutment of the femoral neck against the acetabulum. The open surgical approach pioneered by Ganz and colleagues involves dislocation of the femoral head through a trochanteric flip osteotomy and allows full visualization of the femoral and acetabular articular surface. Excision osteoplasty is performed to regain a spherical femoral head and appropriate head–neck offset; acetabular rim excision is performed where there is a prominent anterolateral rim and any damage to the labrum can be addressed. Open dislocation of the femoral head involves technically challenging surgery with a long learning curve. Complications following open dislocation of the hip include heterotrophic ossification (37%), failure of trochanteric fixation, incomplete trochanteric union (27%), and sciatic nerve injury. The approach is extensile and requires sacrificing the ligamentum teres and 6–8 weeks of non-weight bearing with crutches until the trochanteric osteotomy unites.

Hip arthroscopy has recently become popular, but even in experienced hands cam lesions, and in particular acetabular rim trimming and labral refixation, can be technically very difficult. Complications following arthroscopic treatment include sciatic and femoral nerve palsy, perineal injury, and intra-articular breakage of instruments. Arthroscopic treatment of FAI is said to have results comparable to the open procedure although outcome measures were unclear and the methodology unclear.

Treating impingement of the hip through a direct open approach is not a novel idea. Even the authors behind the Bernese surgical dislocation of the hip routinely open the hip joint through a modified Smith–Petersen approach to assess for any impingement following periacetabular osteotomy, and, when necessary, undertake a resection osteoplasty of the femoral head–neck junction. A direct anterior approach allows for easy access to the site of impingement and correction of cam, pincer, and labral lesions. This can be performed after intra-articular assessment and treatment by hip arthroscopy or on its own. At the Royal National Orthopaedic hospital it is the senior surgeon’s preference to use a mini-arthrotomy based on the Heuter approach.

Resection of the cam lesion by whatever technique should not exceed 30% of the femoral neck as the risk of femoral neck fracture becomes unacceptably high.