A 50-year-old man underwent left total hip replacement to treat osteoarthritis. Because of his age and activity level, a large resurfacing socket was used to maximize stability and minimize wear ( Fig. 41.1 , A ). The patient presented 3 years later with continued discomfort localized in his hip. Radiographs demonstrated socket migration with evidence of a complete radiolucent line around the socket. The stem showed the hallmarks of bone ingrowth with reactive bone streaming into the implant and calcar round-off (see Fig. 41.1 , B ). A socket revision was performed with a porous metal socket and metal–polyethylene articulation. The patient underwent an uneventful recovery with resolution of his pain. At 1 year, there was good evidence of osseointegration of the new socket with absence of radiolucent lines and migration. Consolidation of the impaction allograft of the medial defect was still in progress (see Fig. 41.1 , C ).
This chapter discusses the radiographic changes that lead to a diagnosis of failed total hip arthroplasty (THA) and/or identify normal remodeling occurring with a well-functioning THA.
Identify the normal radiographic changes surrounding a well-fixed THA.
Alternatively, identify radiographic findings consistent with implant failure.
Correlate radiographic findings with clinical symptoms to identify the mechanism of failure.
Identification of the mechanism of failure allows for the appropriate decision making and planning in terms of surgical approach and revision principles.
Radiographic identification of the implant mode of fixation and track record are important determinants in preoperative surgical templating.
Total hip arthroplasty (THA) is a clinically successful surgical procedure for the treatment of end-stage arthritic hip conditions. Improvements in surgical technique, implant designs, and perioperative management have improved outcomes and decreased complications. With the number of primary THAs projected to reach 500,000 in the United States by the year 2030, there will be a corresponding increase in revision THA procedures. Furthermore, introduction of new techniques to improve outcomes and durability have encountered less than optimal results, leading to higher than expected failure rates. This chapter reviews the radiographic findings necessary to identify the mode of failure of the painful THA.
Radiographic evaluation of THA should routinely include an anteroposterior (A/P) radiograph of the pelvis centered over the symphysis pubis and a true lateral view of the acetabulum—either a cross-table lateral radiograph or a Lowenstein radiograph. The Lowenstein lateral view is obtained with the affected hip flexed to 45 degrees with external rotation so that the thigh touches the radiographic cassette to assess the femoral shaft and acetabulum in an orthogonal view. Orthogonal views are necessary because obvious malpositioning can be easily missed on an A/P view ( Fig. 41.2 , A and B ). The tip of the implant should also be visualized. Radiographs of the femur or knee or both may be necessary, because plates or stemmed knee implants can limit the options in the revision hip setting. Finally, serial radiographs are optimal to identify implant migration or progression of radiolucent lines. This remains the hallmark to definitively diagnose a failed total hip implant.
On a neutral rotation A/P view of the pelvis, a checklist of radiographic findings must be assessed. An obvious clinical or radiographic finding should not preclude the clinician from making a complete radiographic evaluation in a stepwise fashion. A complete assessment includes (1) implant position on the acetabular and femoral side, (2) implant osseointegration, (3) osseous reactive changes, and (4) soft tissue reactive changes. Osseous changes are often primarily identified; however, factors such as implant competence and soft tissue changes are frequently missed. Implant incompetence, such as trunion notching, may require revision procedures. If this is not identified preoperatively, appropriate implant availability and surgical exposure may not be chosen ( Fig. 41.3 ). Soft tissues changes such as heterotopic ossification or pseudotumors may manifest as soft tissue shadows; such a finding can aid the discussion for a more focused diagnostic testing regimen. Magnetic resonance imaging (MRI) with metal subtraction has been increasingly studied to identify soft tissue pseudotumors that have developed as a result of adverse reactions to metal–metal hip articulations ( Fig. 41.4 ).
Component position is an important factor in the differential diagnosis of the painful THA. A neutral rotation A/P pelvis view with 15 degrees internal rotation of the femur provides alignment measurements on the socket and femur. With the popularity of alternative bearings and resurfacing implants, socket position in terms of abduction angle and anteversion has increased in importance. Socket positioning at the extremes can lead to increased wear or bearing fracture. Socket inclination angle can be assessed with neutral rotation radiographs. Socket anteversion can also be approximated on a standard A/P pelvis radiograph with the use of a mathematical formula ( Fig. 41.5 ). One should be aware that the appearance of a socket anteversion may actually represent socket retroversion. A standardized cross-table lateral radiograph can determine socket anteversion with the assumption that the horizontal axis is collinear with the long axis of the body. Other conditions, such as iliopsoas impingement due to anterior socket impingement from lack of coverage, can also be diagnosed.
The important parameters of femoral implant positioning include placement in the coronal plane and rotational alignment. From a clinical standpoint, implant position affects leg length and offset. Implant placement in the coronal plane is described as varus or valgus in relation to the long axis of the femoral intramedullary canal. Initially, with cemented fixation, malposition leads to increased stresses on the cement mantle, which affect implant durability. With the introduction of cementless femoral implants, the concerns with coronal alignment are not as great, although excessive malalignment may affect the ability to obtain osseointegration, overall femoral offset, and presence of endosteal irritation. Femoral anteversion is difficult to assess with conventional radiography. A cross-table lateral radiograph with the femur in neutral rotation may demonstrate that the trunion is pointed anterior. Computed tomography (CT) imaging with metal suppression provides the most accurate information to determine both socket and femoral version.
Radiographic evaluation of the acetabulum can be supplemented by Judet or oblique views of the pelvis. These 45-degree oblique views improve visualization of bony defects or columnar incompetence behind the socket. CT with metal suppression has become the gold standard to identify osteolytic defects behind the socket.
Radiographic Osseous Changes
Sir John Charnley ushered in the modern era of THA with low-friction arthroplasty performed through a lateral approach using a cemented, all-polyethylene liner and a cemented femoral component. Meticulous surgical technique with optimal implant placement allows for durable outcomes. Familiarity with the radiographic changes that occur with cemented fixation is necessary, because many patients with implants may present in the second or third decade for routine follow-up or with complaints of pain. With reliable results, cementless fixation has increased in popularity. It is important to identify radiographic findings consistent with implant failure, as opposed to normal remodeling changes.