The hip joint functions as a ball-and-socket mechanism, where the rounded top of the thigh bone (femoral head) rotates smoothly within the cup-shaped depression of the pelvis (acetabulum). Seamless movement relies on the spherical shape of the femoral head and the cartilage lining both surfaces. Cam deformity is a specific anatomical irregularity that disrupts this harmony. It is one of the primary forms of Femoroacetabular Impingement (FAI), a condition where the bones of the hip joint abnormally contact and rub against each other during movement. This mechanical conflict, driven by the irregular bone shape, eventually leads to pain and progressive joint damage.
The Structural Abnormality Defining Cam Deformity
Cam deformity is characterized by an abnormal bony prominence or “bump” that develops at the junction where the femoral head meets the femoral neck. This structural change causes the femoral head to lose its natural, round shape, making it “aspherical.” Due to this extra bone, the head-neck junction lacks the normal offset required for unrestricted movement within the hip socket.
The mechanism of injury occurs when the hip moves into positions involving deep flexion, such as squatting, combined with internal rotation. During these movements, the abnormal bony prominence on the femur jams against the rim of the acetabulum. This repeated contact generates friction that damages the labrum, a ring of fibrocartilage surrounding the acetabulum, and the smooth articular cartilage lining the joint surfaces. This microtrauma can lead to labral tears, cartilage breakdown, and the eventual onset of hip osteoarthritis. Cam deformities are often observed in young, active males, and the bony change is believed to develop during the adolescent growing years, potentially in response to high-impact athletic activities.
Recognizing the Pain and Movement Limitations
The primary symptom associated with cam impingement is a deep, aching pain felt primarily in the groin area (anterior hip pain). This discomfort is often described as a dull ache that can intensify into a sharp, stabbing sensation. While the groin is the usual site, some patients may also feel pain radiating toward the outside of the hip or into the buttocks.
Symptoms are aggravated by activities that force the hip into positions of extreme flexion and internal rotation, directly provoking the bone-on-bone contact. Common pain-inducing movements include sitting for extended periods, driving, or performing pivoting motions. Patients also report hip stiffness and a noticeable limitation in their range of motion. Mechanical symptoms, such as a clicking or catching sensation deep within the hip joint, may also be present, often indicating damage to the labrum or articular cartilage.
Confirming the Diagnosis Through Imaging
The diagnostic process begins with a focused physical examination, including specific movements designed to reproduce the patient’s pain. The anterior impingement test, which involves flexing the hip to 90 degrees, internally rotating it, and bringing it across the body, is highly sensitive for FAI and often elicits sharp groin pain. Imaging studies are then used to confirm the presence and nature of the bony abnormality.
Standard X-rays are the initial imaging tool, providing clear visualization of the hip’s bony structure. Specialized views, such as the Dunn view, are often necessary to visualize the anterosuperior portion of the femoral head-neck junction where the deformity occurs. The severity of the deformity is quantified by measuring the alpha angle. This angle measures the deviation from the normal sphere of the femoral head; a measurement of 60 degrees or more often defines a pathological cam morphology.
Magnetic Resonance Imaging (MRI) or an MR arthrogram provides supplemental information by allowing physicians to assess vulnerable soft tissues. These scans detect secondary damage, such as labral tears or early breakdown of the articular cartilage. A comprehensive diagnosis requires the triad of symptoms, a positive physical exam, and characteristic findings on the imaging studies.
Options for Managing and Correcting the Deformity
Initial management of cam deformity is non-surgical, focusing on modifying activities to avoid deep hip flexion and internal rotation positions that trigger pain. Physical therapy is a primary component of treatment, concentrating on strengthening the muscles surrounding the hip and core to improve stability and control.
Over-the-counter anti-inflammatory medications may be used to manage pain and reduce joint inflammation. If symptoms persist despite non-operative treatment, or if significant mechanical damage is evident on imaging, surgical correction may be recommended. The surgical procedure used to correct a cam deformity is called a femoral osteoplasty, sometimes referred to as a femoroplasty.
This procedure is most commonly performed using minimally invasive hip arthroscopy, where a camera and specialized instruments are inserted through small incisions. The primary goal of the osteoplasty is to remove the excess bone from the femoral head-neck junction, reshaping the femur back into a smooth, spherical contour. By restoring the correct anatomy, the abnormal contact between the ball and socket is eliminated, relieving the impingement. During the same arthroscopic procedure, the surgeon addresses associated injuries, such as repairing a torn labrum or treating damaged cartilage. Following surgery, a structured physical therapy regimen is immediately initiated to restore range of motion and strength, with a gradual return to full activity over several months.