Atypical hip anatomy, lesions, pain among signs of femoral acetabular impingement

Author notes the importance of a systemic patient interview in diagnosis.

Orthopedists interested in the etiology of osteoarthritis of the hip have recently put a lot of energy into identifying methods of diagnosing and treating femoroacetabular hip impingement. They theorize this mechanical hip abnormality, which has either a cam or pincer type presentation, may be a major cause of damaged hip joints in adults.

“With time we have more and more evidence that chronic impingement leads to unstable cartilage destruction and osteoarthritis,” Reinhold Ganz, MD, of Bern, Switzerland, said during a symposium on femoroacetabular impingement (FAI).

According to the symposium’s moderator, William H. Harris, MD, of Boston, “This is one of the most exciting developments in the entire field of hip pathology, hip disease and the surgical management of hip disease in the last decade.”

The symposium was held during the Hip Society section of the American Association of Hip and Knee Surgeons Specialty Day Meeting at the American Academy of Orthopaedic Surgeons 76th Annual Meeting.

Abnormal motion, anatomy

FAI arises from bony or mechanical abnormalities in the femoral head, the head/neck junction of the femur or the acetabulum, but can also result from combined problems, according to Ganz.

Harris called Ganz the “godfather” of FAI for his extensive research in this area.

“The key to recognition of FAI is that even minor abnormalities of the proximal end of the femur, but also abnormal orientation and offset can lead to difficult motion and may lead to impingement within the well-constrained hip joint,” he said in his presentation.

Understand causes

Femoral or acetabular problems can lead to FAI. Some of these are visible on imaging studies. Often these problems occur in the native hip and are similar to difficulties seen in prosthetic hips, including situations that limit or affect hip flexion and internal rotation, Ganz noted.

“Femoral causes are mainly problems with the offset between the head and neck,” or cam impingement, according to Ganz. The waist of the head-neck junction may be insufficient and, due to poor hip biomechanics, it is forced extra hard into the acetabular cartilage producing cartilage lesions or abrasion.

Treating cam impingement should involve modifying the femoral head/neck position relative to the acetabulum. Furthermore, in this type of FAI, the labrum remains intact until late-stage impingement, Ganz said.

Degenerated labrum

Acetabular causes of FAI mainly consist of over- or under-coverage of the femoral head by the acetabulum, including retroversion, coxa profunda and related conditions. Most hips Ganz sees with FAI are due to a combination of retroversion and a cam-type femoral lesion.

Ganz uses the status of the labrum to identify pincer-type FAI. “The area which is damaged first is the acetabular labrum. Cartilage damage is another finding,” he said. This type of FAI is common in women 30 to 40 years old and younger active men.

Occasionally, lines produced by the impaction forces within the hip joint can be seen on MRI. Other signs that may signal FAI: bone apposition in the area in question, high anteversion of the femoral neck and patients who avoid FAI-related painful hip positions.

Ganz discussed the importance of conducting a systematic interview with individuals suspected of having FAI, particularly those with adductor muscle pain and men who present with post-activity groin pain and similar complaints. In women, multidirectional hip pain is usually indicative of pincer-type impingement, he wrote in his abstract.

Painful rotation

During the physical examination, Ganz recommended checking the hip’s internal rotation in flexion using the anterior impingement test. If it is limited or is especially painful when the range of motion is executed forcefully, this may indicate cam or pincer impingement from hip retroversion.

The classic sign of posteroinferior impingement is limited or extremely painful external rotation in hyperextension or a positive posterior impingement test, he noted.

Ganz recommended getting high-quality radiographs that show the anterior and posterior acetabular rims and has also found cross table lateral projects to be reliable, however he said MRI arthrography is the FAI imaging gold standard.

Various FAI treatments, such as osteotomies to correct femoral neck or socket problems, are being studied. “The more we know, the more we should go towards prophylactic operative treatment, because we know if there is damage we will not return to point 0. We never do,” Ganz said.

For more information:

• Reinhold Ganz, MD, can be reached in the Department of Orthopaedic Surgery, Bern, Switzerland CH-3010; 41-31-632-2111; e-mail: reinhold.ganz@insel.ch. He receives miscellaneous non-income support from Smith & Nephew.
• William H. Harris, MD, can be reached at 15 Parkman St., WACC Suite 533, Boston, MA 02114; 617-726-3556; e-mail: wharrishm@hotmail.com. He receives royalties and research/institutional support from Zimmer and research/institutional support from Biomet.

Reference:

• Ganz R. Femoral acetabular impingement: What forms does it take? How do you recognize it? Presented at the 15th Combined Open Meeting of the Hip Society and American Association of Hip and Knee Surgeons. Feb. 28, 2008. Las Vegas.