We read with interest the case report by Haroon et al (1) in a recent issue of Arthritis Care & Research. The authors describe a 26-year-old male construction worker who had groin pain for 2 years and was referred to the Spondylitis Clinic for further evaluation. They report that the radiographic findings were normal and that magnetic resonance imaging (MRI) showed mild synovitis. The patient's detailed history revealed a mechanical type of pain, and clinical examination showed restriction of internal rotation of the hip. MR arthrography showed a tear of the anterosuperior labrum and small marginal osteophytes arising from the femoral head (1).
We believe that an important diagnosis was missed in this patient and disagree that the radiograph shown in Figure 1 of the case report is normal. The femoral head is deformed (with a nonspherical extension of the femoral head), there is a decreased anterior head–neck offset, and, as later confirmed by MR arthrography, there is an osteophyte at the femoral head visible in the plain radiograph. Therefore, we believe that the patient described above is experiencing a cam-type femeroacetabular impingement (2).
Cam impingement usually occurs in young men who are physically active, and these patients are often seen by orthopedic surgeons because of groin pain of unknown origin (2). Internal rotation is typically found to be diminished (3). The radiographic appearance of the deformity has different names, such as pistol grip deformity, tilt deformity, or cam-type deformity. It has been associated with an increased risk of hip osteoarthritis (OA) in the elderly (4) and was proposed to cause early OA in the nondysplastic hip (5). Cartilage and labral damage are explained by the increased radius of the femoral head entering the acetabulum, resulting in shearing forces against the acetabular cartilage, especially during flexion and internal rotation. High-velocity movements, frequently occurring during athletic exercises or heavy labor, may play a detrimental role. These lead to an outside-in abrasion of the anterosuperior acetabular cartilage, and to an avulsion of the cartilage at the labrum and the subchondral bone at the anterior superior rim (6).
Cam impingement is not uncommon and should be recognized not only by orthopedic surgeons but also by rheumatologists. If conservative treatment fails and a surgical treatment is chosen, the prognosis depends not only on the presence of early OA, but also on the correction of the underlying deformity; if this is missed, resection of the labral tear will probably not yield the expected results (7–11).