Hip and Thigh Pain: Femoroacetabular Impingement

Femoroacetabular impingement syndrome: a narrative review for the chiropractor | J Can Chiropr Assoc. 2010 Sep

This syndrome is better treated with surgery than chiropractic.

Femoroacetabular impingement (FAI) is now widely recognized as a major cause of pain and early osteoarthritis (OA) of the hip in young adults. 

The pathomechanics of this disorder involve abutment of the proximal femur (i.e. head-neck junction) against the acetabular rim during end-range hip motion.

Inside the joint, repetitive impingement can damage the acetabular labrum, the adjacent cartilage, or both. 

Plain film radiographs may appear normal at first; however, careful inspection will often uncover subtle osseous abnormalities.

There are two distinct types—cam and pincer—although, many patients have a combination of both.

FAI syndrome presents most often in athletes of sports requiring forceful and repetitive hip flexion, internal rotation, and adduction

The cam-type is most common in young men between the ages of 20–30; whereas, the pincer-type is more common in middle-aged women.

Initially, FAI symptoms are insidious and include intermittent groin pain, lateral trochanteric pain, or bothAs the acetabular labrum and articular cartilage degenerate, pain frequency increases.

The chief complaint is a dull ache in the anterior groin, especially after prolonged sitting.

Occasionally, a sharp or catching pain is felt during activity, indicating a tear of the acetabular labrum

Passive hip joint range of motion (ROM) is limited, and often painful, in flexion and internal rotation. The hip impingement test elicits anterior groin pain in most patients.

Radiographic Features

Cam Impingement

Cam FAI is characterized on radiographs by an aspheric femoral head with morphologic rounding (i.e. lack of concavity) of the anterolateral head-neck junction, creating a decreased femoral head-neck offset.

Because of this abnormal morphology, hip flexion and internal rotation force the aspheric femoral head/convex head-neck junction into the anterosuperior acetabulum, inducing compression to the cartilage and shear stress between it and the labrum.

As a result, the majority of chondral and labral lesions in cam impingement are located anterosuperiorly.

Pincer Impingement

Pincer FAI is distinguished from the cam-type by the presence of either focal or generalized acetabular over-coverage of the femoral head (e.g. acetabular retroversion, coxa profunda). The crossover sign has been validated as a reliable indicator of retroversion on conventional AP pelvic radiographs. 

With hip flexion and internal rotation in pincer FAI, the femoral neck abuts against the anterosuperior acetabular labrum (which in this case acts as a buffer), compressing it into the articular cartilage and subchondral bone.

As a result, chondral damage is restricted in pincer FAI to a narrow band along the acetabular rim. Repeated microtrauma induces bone growth with subsequent ossification at the labral base.

Radiographic Pitfalls

Chiropractors taking their own x-ray films must use good radiographic technique when examining patients.

For example, without 15° of internal rotation on the AP pelvic view, normal hips can be incorrectly diagnosed with lateral cam impingement.

When measuring for acetabular retroversion, improper patient positioning (e.g. pelvic rotation, improper pelvic tilt) on the AP pelvic radiograph can also lead to an apparent crossover sign,

Magnetic Resonance Imaging

Subsequent to plain film, FAI is often further medically imaged with magnetic resonance imaging (MRI) arthrography (with gadolinium joint injection), and is used to confirm injury to the acetabular labrum or adjacent articular cartilage.

MRI is also useful in determining the α-angle and the femoral head-neck ratio. In a retrospective study, Pfirrman et al.found that patients with cam FAI had larger α-angles and chondral lesions at the anterosuperior femoral head-neck junction, as well as osseous bump formation at the femoral neck—when compared to those with pincer FAI.

The latter were found to have more pronounced chondral and labral lesions posteroinferiorly, along with greater acetabular depth.

Conservative Treatment

Initial treatment must include temporarily limiting or stopping the aggravating activities (e.g. ice hockey, running). Treatment can also address hip flexor tightness, which is often associated with hip impingement. 

Conservative approaches may be effective in the short-term for relieving acute pain, but they do not address the underlying osseous abnormalities of FAI. If the patient returns to sports activity, the symptoms will likely return.

Warning about chiropractic treatment:

Chiropractic treatment focusing on stretching and manipulation/mobilization of the FAI hip to improve passive ROM may actually exacerbate the condition.

More importantly, Leunig et al. believe that delay in the surgical correction of symptomatic patients with clinical and radiographic evidence of FAI (including MRI findings of labral or chondral damage) may lead to disease progression—to the point where joint preserving surgery is no longer indicated.

Surgical Treatment

Less invasive surgical approaches utilizing arthroscopy are also evolving. This is an attractive alternative to patients, particularly professional athletes, because arthroscopy involves smaller incisions, a shorter recovery time, and a lower morbidity rate

Discussion

In the current literature, surgical treatment of FAI has been shown to be most successful in the absence of advanced degenerative OA.3 It is still unclear, however, whether ‘preventative’ surgery should be performed in asymptomatic patients, despite radiographic evidence of FAI

Conclusion

FAI syndrome typically presents in young adults with insidious onset groin pain, often in association with sports activity. The hip impingement test is positive in most of these patients. Hip joint radiographs may appear normal at first—particularly if the clinician is unfamiliar with FAI.

For more on FAI, see Thigh Pain: Femoroacetabular impingement syndrome

 

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