The evaluation of a patient with persistent pain (>3 months) after total hip arthroplasty (THA) can be a diagnostic challenge. Pain after THA may present in the lateral hip, groin, buttock, flank, or thigh. The two most common intra-articular causes for persistent groin pain include aseptic loosening and periprosthetic joint infection (PJI) . There are several extra-articular sources of periarticular pain including heterotopic ossification, vascular lesions, referred pain from the spine or abdomen, lateral femoral cutaneous nerve injury, and soft-tissue inflammation. Soft-tissue inflammation originates from either trochanteric bursitis or iliopsoas tendonitis [1]. Anterior iliopsoas tendonitis, or impingement, has been reported in up to 4% of patients after total hip arthroplasty [1–5]. Symptoms can occur within months of THA or present several years later.

Anatomically, the iliopsoas tendon is the distal confluence of the psoas and iliacus muscles which passes anterior to the acetabular rim to insert onto the lesser trochanter. The iliopsoas is a powerful hip flexor and weak external rotator [6]. The tendon is bordered posteriorly by a bursa which may become intracapsular after anterior capsulectomy during THA. Iliopsoas impingement or tendinitis most often occurs at the level of the acetabular psoas recess but can occur anywhere along its musculotendinous course. A proud acetabular screw may irritate the iliacus muscle along the inner table of the ilium, a protruding anterior acetabular component can injure the iliopsoas tendon at the level of the acetabulum, and a prominent femoral collar can rub the mostly tendinous insertion at the level of the lesser trochanter. The anterior border of the acetabulum, the convex surface of the femoral head, and the overlying anterior capsule act like a pulley around which the iliopsoas tendon runs and anything that increases the likelihood of direct contact of the iliopsoas tendon with the acetabular or femoral components can potentially cause iliopsoas inflammation and subsequent tendonitis and groin pain .

Anything that results in the mechanical irritation of the iliopsoas muscle or tendon is a risk factor for iliopsoas impingement. This most commonly originates from an acetabular component that projects past the anterior wall resulting in abrasion of the iliopsoas tendon at the level of the psoas recess. Insufficient acetabular anteversion produces a prominent and sharp acetabular component projecting past the anterior rim [7]. Cyteval et al. [8] reported on eight cases of iliopsoas impingement and found that acetabular overhang >12 mm was a significant risk factor for groin pain. Oversized acetabular components (>6 mm compared to the native femoral head size) have also been associated with an increased risk of postoperative groin pain [9]. Excessive lateralization of the acetabular component will also increase the amount of bony uncoverage and anterior component prominence. Patients with anterior wall deficiency may also be at increased risk due to insufficient anterior bony coverage of the acetabular component. An oversized, lateralized, acetabular component with decreased anteversion or frank retroversion has the highest risk for anterior acetabular component prominence and iliopsoas impingement. Less common causes for iliopsoas tendonitis that have been reported in the literature include retained cement, excessively long screws projecting into the iliacus muscle [10], and a prominent acetabular cage [11].

On the femoral side, tendon impingement can also occur as the tendon wraps around the femoral neck to insert in the lesser trochanter, which is a posteromedial structure. For this reason osteophytes along the anterior aspect of the femoral neck may lead to tendon impingement [7]. In one report a prominent femoral collar produced iliopsoas tendonitis and was treated with revision to a collarless prosthesis with resolution of symtpoms [13]. The authors advised the use of a collarless cemented component when a low neck cut is planned as a collared prosthesis may rub against the tendon insertion on the lesser trochanter. Large femoral head metal on metal and hip resurfacing had a 15% reported rate of groin pain [14]. And while adverse reaction to meta debris must first be excluded, authors have hypothesized that the increased in groin pain was secondary to abrasion of the iliopsoas tendon as it articulated with the large femoral head and the sharp transition point at the inferior margin. This led to the development of an anatomically contoured large-diameter femoral head with the peripheral region contoured to stay within the articular margin [15]. There are also circumstances in which iliopsoas tendonitis may occur without identfication of an underlying risk factor [16].

The risk of iliopsoas tendonitis can be minimized with careful attention to cup position and its relationship to the anterior wall of the acetabulum. The posterior, anterolateral, and direct anterior surgical approaches all allow for palpation of the anterior acetabular wall and the acetabular component should be flush, or slightly recessed with the native anterior acetabular rim. The acetabulum should not be reamed more than 6 mm of the native femoral head diameter in order to reduce the risk of peripheral rim prominence which has been correlated with increased rates of groin pain after THA [17]. In patients with a deficient anterior wall, increased anteversion and greater cup medializaiton may be necessary to avoid anterior overhang. Prevention of iliopsoas impingement on the femoral side includes removal of all osteophytes from the anterior aspect of the femoral neck, avoiding complete resection of the anterior capsule, and avoiding the use of a large-collared femoral component, especially when combined with a low femoral neck resection .

Iliopsoas impingement presents with anterior groin pain that is exacerbated with hip flexion activities. The workup for a patient who presents with pain after a total hip arthroplasty should include a clinical history, physical exam, laboratory tests to rule out PJI, and radiographic imaging. A systemic approach to the evaluation of a painful total hip arthroplasty reliably excludes other causes of pain after THA since iliopsoas tendonitis , or iliopsoas impingement, is a diagnosis of exclusion.

A comprehensive history and physical are essential to determine the underlying cause of pain. Symptom onset from time of surgery, location, duration, intensity, inciting activities, rest pain, and pain quality are all important features in the history. A history of postoperative wound drainage raises concerns for underlying PJI and must be ruled out. Periarticular pain within the first 6 weeks after surgery should be treated conservatively with activity modification, use of an assistive walking device, focused physical therapy, and nonsteroidal anti-inflammatories. Pain that persists after 6 weeks should be investigated further with imaging and possibly laboratory values depending on the clinical presentation. The characteristic clinical history for iliopsoas tendonitis is groin pain with activity and that resolves with rest. Activity-related groin pain is worse with hip flexion maneuvers such as climbing stairs or getting into or out of a car. Getting in and out of a car is particularly painful, and the majority of patients if not all complain of this, and commonly have to lift the affected leg when entering a low vehicle. Driving is particularly painful for patients with a right THA as alternating between the brake and gas pedal requires repeated hip flexion. Rising from a deep-seated position with hips flexed past 90° can also exacerbate groin pain symptoms.

On physical examination, gait should be assessed for evidence of start-up pain that could indicate component loosening. An antalgic or Trendelenburg gait may suggest other sources of THA dysfunction as walking on level ground is usually not painful in patients with iliopsoas impingement. On supine examination, hip range of motion should be assessed for hip positions that trigger pain. A positive Stinchfield’s test due to psoas activation and irritation with straight leg raise against gravity is common, but is less painful than when the hip is externally rotated. The most provocative test is positive groin pain with resisted hip flexion and pain with passive hip extension. As with any complete physical exam, the hip area should be assessed for other areas of tenderness, presence of any swelling or masses, appearance of the incision, nerve root tension signs, and a distal neurovascular exam.

Every patient with a persistently painful THA should be assessed for PJI with laboratory studies including erythrocyte sedimentation rate and C-reactive protein. If elevated, a fluoroscopic- or ultrasound-guided hip aspiration is recommended. Any patient with persistent groin pain and a metal-on-metal articulation should be evaluated with serum cobalt and chromium serum metal ion levels and cross-sectional imaging, whether that be an ultrasound or magnetic resonance imaging. Recently, adverse reaction to metal debris, pseudotumor formation, and soft-tissue necrosis has been reported in articulations with cobalt–chrome femoral heads on highly cross-linked polyethylenes [18]. Mechanically assisted crevice corrosion at the head–neck junction between the cobalt–chrome head and titanium stem, known as trunnionosis, produces metallic debris that can trigger this adverse tissue response. For this reason, serum metal ion testing should be included in the complete laboratory profile for patients with groin pain and a cobalt–chrome femoral head and titanium alloy stem. Iliopsoas impingement could be the first symptom associated with adverse soft-tissue reactions and should prompt further investigation.

Every patient with persistent pain after THA should have anteroposterior (AP) and lateral imaging of the pelvis and femur. The AP pelvis radiograph should be evaluated closely for any signs of prosthetic loosening of the acetabular or femoral component. The AP pelvis radiograph can also be evaluated for leg length and offset restoration. Serial radiographs should be reviewed if available for the presence of progressive radiolucencies or component migration. The cross-table lateral radiograph provides important information on the position of the acetabular component in relation to the anterior wall and allows for objective measurement of component overhang. The amount of overhang is measured from the anterior bony rim of the acetabulum to the anterior rim of the acetabular component on the cross-table radiograph. Computer tomography (CT) also provides information on component version and anterior overhang of the acetabular component. A CT scan can also provide a more detailed assessment when body habitus obscures component visualization on plain radiographs. Moreover, a CT scan can visualize prominent screws within the inner pelvic table, and their position in regard to the psoas muscle.