Impact between femur and acetabulum (femoroacetabular impingement) is a frequent cause of hip pain. This disease is the leading cause of hip harness and cartilage damage in young adults. It is also the main indication for hip arthroscopy surgery.
The hip bone structure is composed of the acetabulum and femoral head. In normal hips, the femoral head does not impact (“do not hit”) the acetabulum edge during routine movements or exercises.
What types of femoroacetabular impact?
There are two types of deformities that impact the femoral head against the acetabulum: cam type (cam) and pincer type (“clamping”). Cam-like deformity is characterized by the abnormal contour of the transition between the neck and femoral head. The pincer deformity represents excessive coverage of the femoral head by the acetabulum.
The pincer impact is more frequent in women and the cam type in men. Although IFA deformities are classified into two types, 50 to 75% of patients have a combination of both types (cam and pincer).
What causes cam and pincer deformities?
Most deformities in the femur and acetabulum are believed to be secondary to hip disease in childhood and adolescence. Diseases such as slippage of the proximal femoral epiphysis and Legg-Calvé-Perthes may lead to cam and pincer deformities. In some children these diseases cause no symptoms and will only be recognized in adulthood with the process of arthrosis.
Some research has shown that children and adolescents with high levels of physical activity are at higher risk of developing cam-like deformities. In addition, studies in football players report that about 80% have one or more signs of AFI on radiographs. Evolution in the hip shape of monkeys to man also helps explain cam and pincer deformities. Consolidated (healed) femoral and acetabulum fractures with deformity can result in AFI. There are other causes of impact between the femur and acetabulum, such as benign tumors, hip osteotomies, and hip arthroplasty.
Why does femoroacetabular impingement cause pain?
The acetabular labrum and cartilage are damaged in the IFA. The labrum is richly innervated by pain fibers that are stimulated by impact injury. In addition, cartilage damage can cause pain. In the impact position (usually with the hip flexed), the cam-like deformity compresses the acetabular cartilage and stretches the shoulder.
The pincer deformity also injures the cartilage and the labral bone, but the greatest allusion is in the labial bone, which is compressed between the femur and the acetabular bone at the impact position. This process can cause calabra calcification and increase impact.
Does femoroacetabular impingement cause arthrosis?
New research is published each year showing the relationship between femoroacetabular impact and hip arthrosis. However, there is still no consensus on this topic. Some patients with cam or pincer deformities develop arthrosis and some do not. Thus, there appear to be other factors that also influence the development of arthrosis, for example genetic predisposition.
What are the symptoms caused by femoroacetabular impact?
Pain is the main complaint, usually greater during physical activities. Some patients have pain in the knee, pubis and sacroiliac joint as a consequence of hip disease. Other complaints include: reduced hip mobility, locking and clicking.
Are complementary exams needed in the diagnosis?
X-ray examinations (radiography) are used to evaluate bone structure and cam and pincer deformities. Computed tomography and magnetic resonance imaging may also be helpful, especially in cases with surgical indication. Other tests may be necessary to rule out differential diagnoses.
However, the most important diagnostic features are history and physical examination. Imaging exams often show cam and pincer deformities in patients with no hip symptoms. Additionally, soft tissue disorders of the hip may be responsible for symptoms such as muscle, tendon, capsular and neurovascular injuries. Therefore, the definition of the cause of pain depends primarily on physical examination and history, followed by joint analysis with imaging exams.
Conservative methods of treating IFA may be tried in the first months. They include medications for pain, physical therapy, and changes in physical activity. However, femoroacetabular impingement is a mechanical disease and most patients do not progress well with treatment without surgery and eventually abandon sports or practice with pain.
The femoroacetabular impact surgeries are divided into two groups:
- Joint replacement surgeries or hip arthroplasty , indicated in cases of advanced articular cartilage injury;
- Joint preservation surgeries, osteoplasty and osteotomies, indicated in cases of preserved cartilage or with initial injury;
The shape of the bone structures (morphology) will define the type of surgery to be employed. The vast majority of pincer or cam deformities can be treated by video arthroscopy , using special materials that allow resection of excessive bone. In cases where the removal of part of the acetabular bone is required, anchors are usually used for reworking the harab. Patients with femoroacetabular impingement often have diseases in other layers of the hip that also need treatment and can make surgery more complex, especially in cases of hip instability. Some complex cases require the use of open techniques such as hip surgical dislocation or acetabular osteotomy surgeries.