Hip pain in active adults with apparently normal radiographs: the role of hip arthroscopy

Modern active lifestyles and sport have lead to patients seeking attention for hip problems from health care professionals at a much earlier stage than in the past.

Careful clinical evaluation can usually identify the hip joint itself as the source ofthe problem rather than the surrounding muscles. Patients describe an activity related groin ache with a sharp catching in the front of the hip, particularly indeep flexion. The pain may have started acutely following a pivoting injury or started more insidiously. They may also describe clicking, instability or a grating sensation.

A frequent complaint is that the inconsistent hip function interferes with recreational exercise and visits to the gym.

Examination can reproduce the catching in the groin with adduction and internal rotation of the fully flexed hip, although hip movements are often unrestricted. Inflammatory arthropathy must be excluded with the appropriate blood tests. Radiographs are often normal, and whilst this excludes end-stage disease of the hip, it cannot exclude injury to the soft tissues in the same way as a normal knee xray cannot identify injuries to the menisci, cruciate ligaments or articular cartilage.

Fortunately, precision of diagnosis is now possible in these patients with normal xrays due to advances in MRI of the hip and the development of hip arthroscopy into a reliable day-case procedure. The small size and deep location of the joint has posed technical challenges. Longer cannulated arthroscopic equipment is needed for hip arthroscopy as well as special distraction apparatus to separate the joint surfaces sufficiently to allow the arthroscope to be inserted. Two or three
portals are usually used and are located just above the greater trochanter. Hip arthroscopy not only allows diagnoses to be made when all other imaging modalities are negative but also permits arthroscopic treatment such as resection of labral tears, joint debridement and removal of loose bodies.

A common sporting injury is damage to the acetabular labrum. The labrum is a skirt of fibrous material attached to the margins of the acetabulum giving more depth to the bony acetabulum. The tears usually occur anteriorly as the femoral neck abuts on the acetabular margin during flexion and rotation of the hip thereby trapping the labrum in between the bony surfaces. Tears can occur acutely
following an injury or more gradually with repeated flexion and pivoting maneouvres. They are associated with early degenerative change of the articular cartilage and acetabular dysplasia. Tears may be missed on conventional MRI scanning but can usually be identified on MR arthrography, in which the labrum can be outlined with an intra-articular injection of contrast material. Tears can be
resected arthroscopically with a success rate of 80-90% if there is no adjacent articular cartilage damage and some larger tears can even be re-attached with arthroscopic techniques.

Hip arthroscopy is the only reliable way of detecting lesions of the articular cartilage well before any changes are visible on radiographs. This has lead to a greater understanding of the early changes of osteoarthritis of the hip and the association with labral pathology. Whilst debridement of a degenerate tear and irrigation of the hip joint can produce worthwhile symptom relief in the short to medium term, the ultimate prognosis depends on the severity of the degeneration. Despite this, patients are often relieved to have a firm diagnosis and a prognosis so they may plan for the future. In the presence of severe symptoms metal-on-metal hip resurfacing or conventional hip replacement may be indicated.
Acetabular dysplasia is another important cause of hip symptoms that is easily overlooked on radiographs. It is much more common in females and is characterized by a shallow, upwardly sloping acetabulum. This may be the residual effect of congenital dislocation of the hip or represent failure of the acetabulum to complete normal growth during late childhood. The shallow socket puts abnormal stresses through the articular cartilage, causing it to degenerate, and the labrum hypertrophies and tears as it attempts to contain the hip. Early osteoarthritis is inevitable without treatment. Surgical re-orientation of the acetabulum (peri-acetabular osteotomy or PAO) is highly effective at relieving pain and postponing arthritis for many years providing the surgery is carried out before arthritis has developed. It is therefore important for young women with groin pain to be carefully assessed for this condition. Hip arthroscopy can be used as a prelude to PAO to assess the degree of degeneration before embarking on major pelvic surgery.

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