Radiological Imaging Evaluation of the Failing Total Hip Replacement

Abstract

Total hip replacements (THR) have been performed in the UK from the 1960s and since then we have seen surgical techniques, the design of implants, and imaging modalities rapidly develop. This paper will aim to review the different complications and imaging appearance which help to evaluate each problem. As for all investigations for bone and joints, a radiograph is the first imaging to be performed for any patient with a THR and can detect a majority of complications. CT is relatively low-cost, simple to perform and easily available making it an excellent tool to supplement radiographs when trying to evaluate a hip prosthesis. Single photon emission computed tomography with CT (SPECT-CT) is an emerging modality which has shown to combine the sensitivity that bone scintigraphy offers with the high specificity of CT. SPECT imaging also has the advantage of showing the bone's metabolic activity and is less prone to metal artifact than Magnetic resonance imaging (MRI). MRI has evolved to become an important diagnostic tool for the evaluation of THR in the post-operative period. Optimized pulse sequences and metal artifact reduction techniques have made MRI a useful tool in diagnosis of soft tissue abnormalities and is particularly useful in identifying adverse local tissue reactions in metal on metal implants. CT and MRI are accurate in identifying the diagnosis of most causes of THR complications except infection. Research confirms that leukocyte-marrow scintigraphy is the modality of choice for accurately diagnosing prosthetic joint infection and reassures us of its superiority over other nuclear medicine imaging. However, due to the limited availability and increased costs when performing leukocyte-marrow scintigraphy, CT and SPECT-CT would be a more preferred option when suspecting prosthesis infection. Ultrasound (US) has a limited role in the assessment of most THR complications but can be useful to identify peri-prosthetic fluid collections and the presence of soft tissue sinus tracts. Being aware of the imaging modalities that are available to orthopedic surgeons, and discussing these challenging cases with specialist radiologists will enable optimal management of THR complications.

Keywords: magnetic resonance imaging; complications; computed tomography; hip replacement; imaging; nuclear medicine.

Figures

Figure 1

CT pelvis- minimally displaced left proximal femur peri-prosthetic fracture. Small round stimulant beads visible around the left side tracking down toward the left hip wound.

Figure 2

(A,B) NM technetium and white cell scan—SPECT CT. On SPECT-CT, there is image degradation seen at the level of the hip joint, despite this, there is some fluid visible lateral to the hip joint which co-localizes to the intense focus of white cell uptake. This fluid appears to track from the hip joint into the deep subcutaneous tissue, representing bursitis, or soft-tissue abscess formation. A focus of uptake can also be seen at the skin surface at the level of the umbilicus, most likely related to recent surgery.

Figure 3

(A) Metal Artifact Reduction MRI image. Reduction sequence is utilized here in assessment of prosthesis failure in the left side following THR. Some metal artifact remains. There is no significant joint effusion, soft tissue oedema or collection seen. Common findings following THR can be seen here, this includes fatty atrophy in the short external rotators and adductor brevis. (B) Metal artifact reduction MRI image. Here, reduction sequence is utilized in order to minimize aberrations from acting as noise in the assessment of the contralateral joint. There is moderate degenerative change in the superior aspect of the right hip with near complete loss of articular cartilage and bone marrow oedema consistent with osteoarthritis. There is no hip effusion or synovitis.

Figure 4

NM dual phase bone scan pelvis. Increased blood pooling lateral to proximal left femur. Increased uptake approximates to acetabular cup and greater trochanter. Suggests loosening of left sided acetabular component with infection involving the left greater trochanter.

Figure 5

(A,B) Ultrasound of left hip—Superficial collection at site of wound tracking down to deep hip joint surface. Extension to borders of skin markers.