Workup of pelvic joint impingement saves hip

Early diagnosis and treatment of femoroacetabular impingement (FAI) syndrome could prevent delayed diagnosis of early osteoarthritis of the hip and keep patients from invasive and possibly suboptimal treatment. But the best way to diagnose, characterize, and treat patients with FAI remains open to debate.

"If you Google 'femoroacetabular impingement,' you will find many orthopedic centers talking about this condition, or accounts from the surgeons who are operating on it. But we don't really know specifically who requires what kind of intervention," said Dr. Bruce Forster, an associate professor of radiology at the University of British Columbia in Vancouver.

Musculoskeletal radiologists have lagged behind orthopedic surgeons in identifying and treating FAI, but their interest is starting to rise. In several abstracts presented at the 2006 European Congress of Radiology, researchers noted the importance of early diagnosis and treatment of this entity. They also made clear that not all FAIs are created equal. In one presentation, Dr. Christian W. A. Pfirrmann, a radiologist at the Orthopaedic University Clinic of Zurich, distinguished between "cam" and "pincer" impingement. A jamming of an abnormal femoral head-neck junction into the acetabulum creates the former. Linear contact between the acetabular rim and the femoral head-neck junction accounts for the latter.

In another study, a team of British and Australian investigators discussed the use of MRI for identifying labral and articulage cartilage lesions in patients suspected of FAI. They found noncontrast MRI useful for noninvasive diagnosis.

Researchers have identified FAI as a leading cause of osteoarthritis. According to Dr. David W. Stoller, director of musculoskeletal MRI at the California Pacific Medical Center in San Francisco, the pathology reflects repetitive microtrauma caused by the abnormal abutment of the femoral head against the acetabulum in the position of flexion and internal rotation. FAI findings may exist in developmental dysplasia of the hip (DDH), also known as lateral acetabular rim syndrome, and nondysplastic hips.

Key MR findings include recognition of acetabular chondral lesion, labral tears, fibrocystic changes, and a dysplastic bump on the anterolateral femoral head-neck junction, as well as acetabular retroversion and overcontainment, Stoller said.

Orthopedists estimate that about 3% of the U.S. population suffers from degenerative arthritis of the hip. This disabling condition may require costly and invasive interventions such as total hip replacement. Increasing numbers of physicians, however, recommend that patients under 50 avoid hip replacement surgery in favor of less invasive strategies. Radiologists worry about the lack of clinical data that could indicate the best imaging modalities and courses of treatment. The early excitement about FAI may lead to overtreatment, Forster said.

Introduction of high-resolution MRI of the hip using pelvic phased-array coils has contributed greatly to the proper identification and characterization of FAI. Identifying FAI early can assure patients less invasive diagnosis and treatment. Current treatments include minimally-invasive arthroscopic surgery, surgical debridement with hip dislocation, and peri-acetabular osteotomy.

Researchers at the 2005 RSNA meeting addressed concerns about misdiagnosis of the condition. Dr. Kenjirou Ohashi and colleagues at the University of Iowa compared the diagnostic performance of orthopedic trauma surgeons and MSK radiologists who reviewed more than 100 x-rays of acetabular fractures over a period of about three years. They found that experienced orthopedists were only moderately reliable and no better than radiologists when classifying these lesions on radiography.

"Early recognition of FAI is an important diagnosis at this time and radiologists need to be aware of the entire spectrum of MR findings," Stoller said.