CT, MRI and Ultrasound
Previously, CT and MRI were rarely used for patients with arthroplasties due to metallic artifact.
Multislice CT has markedly decreased this artifact, and can visualize bone immediately adjacent to hardware. It can be used to evaluate alignment abnormalities, bone graft, heterotopic ossification, osteolysis, and adjacent soft-tissue structures. Reformatted images in various planes can be generated with minimal artifact as well.
CT arthrography can be used to evaluate intraarticular pathology. Multislice CT is now able to delineate bone, polyethylene cement, intraarticular iodinated contrast, and metallic hardware with minimal artifact.
Axial and sagittal CT images demonstrate cement herniation posteriorly about the peg of the polyethylene glenoid component into the suprascapular and spinoglenoid notches. This is in the course of the suprascapular nerve.
28-year-old woman with painful hemiarthroplasty secondary to low-grade infection. This has resulted in severe labral cartilage narrowing and wear. The humeral head component is resting on subchondral bone with underlying erosions (red arrows) and subchondral cyst formation (white arrow). Note intact and well visualized supraspinatus muscle (blue arrows).
Sudden onset of shoulder pain and decreased range of motion. CT arthrogram demonstrates linear filling defect in the neocapsule between the humeral head and polyethylene glenoid component (red arrow). Entrapped synovium was found at surgery. Not exquisite CT resolution of polyethylene, intraarticular contrast, metal, and bone, with minimal streaking artifact.
MRI can also be used in patients with hardware by applying sequences that minimize metallic artifact. These sequences include T1 and STIR, employing long-echo train lengths. Gradient echo and fat saturation techniques are avoided when hardware is present. Periprosthetic soft tissues, including fluid collections, rotator cuff and other surrounding musculature, and masses can be evaluated.
Axial and sagittal T1 weighted images in patient with shoulder arthroplasty demonstrates marked fatty atrophy of right rotator cuff musculature. The humeral prosthesis is subsequently superiorly subluxed with obliteration of the acromio-humeral space.
Both CT and MRI can be used to evaluate masses adjacent to prostheses. This is particularly important for patients with bone sarcomas that have required resection and placement of modular endoprostheses. If the recurrent disease is not discernable on conventional radiographs, CT and MR can be employed.
18-year-old male with osteosarcoma of proximal humerus. The humerus was resected and a humeral endoprosthesis was placed. Follow up radiograph demonstrates soft-tissue recurrence with multiple ossific soft tissue foci. There are also multiple lung metastases. Baseline radiograph after sarcoma resection and below follow-up radiograph 1 year later.
Mass in patient with modular endoprosthesis placed after resection of femur for osteosarcoma. Axial CT demonstrates mass immediately adjacent to the right femoral endoprosthesis (arrows).
Correlative axial T1 image demonstrate similar findings.
Axial STIR image demonstrates similar findings, also.
Correlative coronal reformatted CT image and then coronal T1 weighted image clearly demonstrate mass adjacent to module endoprosthesis (arrows).
14-gauge needle biopsy performed under CT guidance with patient in prone position demonstrated recurrent osteosarcoma.
Ultrasound can also be used to evaluate periprosthetic soft tissues. It is particularly useful for localizing periarticular fluid collections and guiding aspiration and drainage.
Transverse ultrasound of shoulder demonstrating mixed echoic fluid collection in subdeltoid bursa, just deep to the deltoid muscle (D). Fluid was aspirated under ultrasound guidance and was sterile.