So, you have hip pain, but the X-rays and MRI are normal. Now what? Now your doctor may want to consider that you might have hip impingement, formally known as Femoroacetabular Impingement. Considering the anatomy of the hip joint as a ball and socket joint, this diagnosis is really not surprising because some bones just do not fit together perfectly to form a perfectly symmetrical, precise joint. The hip joint is a ball and socket joint. Sometimes the ball is not perfectly round and sometimes the socket is too deep. A shallow socket is considered hip dysplasia which is different than hip impingement. Hip impingement literally means that there is abnormal friction producing abnormal wear within the hip joint. If the ball has an abnormal bump, then this is termed CAM Impingement which wears out the dome of the ball as is rubs against the socket. If the socket is too deep, then this is termed Pincer Impingement which wears out the neck of the femoral head as it rubs against the rim of the socket. Most people who experience the symptoms of hip impingement have a combination of both CAM and Pincer because both the ball and socket are imprecisely formed. An anatomical predisposition to impingement can lead to hip pain early in life and lead one down the road towards end-stage hip arthritis. But this road does not always have to lead to hip replacement surgery if the hip impingement is identified early.
Identifying hip impingement can be a bit tricky because oftentimes the imaging studies are interpreted as normal or someone who has an abnormal image does not necessarily have symptoms. The lack of correlation between imaging findings and actual symptoms leaves the diagnosis of hip impingement a bit vague and controversial. The diagnosis of hip impingement really hinges on the history and examination. The history of hip pain usually corresponds to an aggravating activity that requires deep hip flexion with a loading force. For example, cyclists, dancers, hockey players and horseback riders, all participate in an activity highly associated with hip impingement symptoms. On examination, a person with symptomatic hip impingement may have reduced hip range of motion especially in a flexed, adducted and internally rotated position. Even a history and examination can be misinterpreted and hip impingement can be mistaken for everything from endometriosis to lumbar disc herniation. A clinician really needs a high index of suspicion to correctly identify hip impingement.
Once hip impingement is identified, then appropriate treatment has a chance to slow down the arthritic process that can ultimately lead to end-stage hip arthritis and a hip replacement surgery. Treatment of hip impingement is called joint preservation. Avoiding surgery and preserving original body parts is a wonderful goal. Physical therapy can help to rebalance the hip joint by rehabilitating the stabilizing muscle system. Weak muscles like the hip extensors and external rotators are strengthened and strong muscles like the hip flexors and adductors are lengthened. Additionally, physical therapy can address any secondary pain that occurs in the pelvis and/or low back. Physical therapists are important members of the joint preservation team. Sometimes surgery cannot be avoided because the anatomical imperfections are too great to overcome. In these cases, either open or arthroscopic surgery is needed to correct these minor hip joint imperfections that can lead to major joint destruction over time.
Timing is critical because catching hip impingement early can save the hip joint from destroying itself. An anatomical predisposition does not mean that someone is doomed to need a new joint if early recognition leads to early prevention. So, if you have hip pain, but the imaging is normal and your doctor is unsure, add hip impingement onto the list of possibilities. A second look at the mechanics of the hip joint might just save you from going down the road towards end-stage hip arthritis.