Total hip replacement (THR) is a highly successful orthopedic procedure that alleviates pain and restores mobility for countless individuals. However, a small percentage of patients experience persistent anterior hip pain, often localized to the groin, which can be confusing and frustrating. This lingering discomfort may be caused by a specific complication known as iliopsoas impingement (IPI). Iliopsoas impingement occurs when the powerful hip flexor tendon is mechanically irritated by the prosthetic components, particularly the acetabular cup, following the surgery. This condition is frequently overlooked.
Understanding Iliopsoas Impingement
The iliopsoas is a compound muscle group formed by the psoas major and the iliacus, with its tendon crossing the front of the hip joint before attaching to the inner thigh bone. This muscle is the primary engine for hip flexion, enabling movements like lifting the leg or bending at the waist. In a healthy hip, the iliopsoas tendon glides smoothly over the underlying structures.
Impingement occurs when the tendon rubs repeatedly against the anterior edge of the implanted acetabular cup, causing mechanical irritation and inflammation. This constant friction leads to a specific type of discomfort that is typically described as a sharp or burning pain deep within the groin. The pain often intensifies with activities that require active hip flexion, such as climbing stairs, getting into a car, or attempting to stand up from a low chair. Patients may also notice pain when the hip is passively extended, as this movement stretches the iliopsoas tendon over the prosthetic rim.
Implant-Related Causes and Risk Factors
The primary reason a total hip replacement can lead to iliopsoas impingement lies in the placement and design of the acetabular component, the prosthetic socket. The cup must be positioned within specific angles of inclination (upward tilt) and anteversion (forward tilt) to function correctly and avoid soft tissue conflict. If the cup is placed in a position with reduced anteversion or excessive inclination, its anterior rim can protrude beyond the native bone, creating an abrasive surface for the iliopsoas tendon.
Excessive overhang of the acetabular cup is a common mechanical cause of the problem. Studies suggest that an overhang exceeding 12 millimeters significantly increases the risk of impingement because the tendon is forced to track over the prominent edge. Furthermore, the use of oversized cups can also push the tendon anteriorly into the path of the cup rim.
Specific design features of the implant, such as prominent anterior screw holes or retained cement from the fixation process, can also contribute to the irritation. Pre-existing conditions like iliopsoas tendinitis or bursitis prior to the THR can make the tendon more susceptible to mechanical irritation from the new hardware. Excessive leg lengthening during the procedure, which increases tension on the tendon, is another contributing risk factor.
Diagnosing the Condition
Diagnosing iliopsoas impingement is challenging because groin pain after a total hip replacement can stem from many causes, including infection, loosening of components, or spine issues. The diagnostic process begins with a thorough physical examination, looking for specific signs of iliopsoas irritation. A positive iliopsoas stretch test, which reproduces the patient’s groin pain upon passive hip hyperextension, is a strong clinical indicator.
The clinician may also check for pain with resisted seated hip flexion. Imaging studies are then used to visualize the hardware and confirm mechanical conflict. Standard X-rays can provide a basic assessment of cup positioning, but a Computed Tomography (CT) scan offers a more precise, three-dimensional measurement of the acetabular component’s version and overhang.
The definitive diagnostic tool is a targeted injection of a local anesthetic and corticosteroid medication. This procedure is performed under image guidance, typically ultrasound or fluoroscopy, to ensure the medicine is delivered directly into the iliopsoas tendon sheath or bursa. If the patient experiences marked temporary relief of the groin pain immediately following the injection, the diagnosis of iliopsoas-related impingement is confirmed.
Treatment Pathways
The management of iliopsoas impingement generally follows a stepped approach, moving from conservative methods to more invasive procedures. Initial treatment typically involves conservative measures aimed at reducing inflammation and modifying activity. This includes a period of rest, avoiding movements that provoke pain, and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) to decrease tendon irritation.
Physical therapy focuses on gentle stretching and strengthening exercises designed to improve muscle balance without aggravating the tendon. If conservative treatment fails to provide sufficient relief, the next step is the therapeutic use of image-guided corticosteroid injections. These injections can provide prolonged pain relief by significantly reducing local inflammation around the tendon.
For cases where pain relief is only temporary or conservative measures are unsuccessful, surgical intervention may be necessary. The two main surgical options are iliopsoas tenotomy or revision arthroplasty. A tenotomy involves releasing or lengthening the iliopsoas tendon, which alleviates the tension and friction against the prosthetic cup. This procedure is often performed arthroscopically and is generally preferred when the acetabular cup position is considered acceptable. If imaging shows excessive anterior overhang, revision surgery may be necessary to reposition or replace the component, eliminating the mechanical source of the impingement.