Figure 1. Anteroposterior radiograph of the left knee obtained 1 year prior to consultation.
Figure 2. Photograph of the left knee during revision total knee arthroplasty.
A 73-year-old woman presents with pain in her left knee that has been present for several years. The patient underwent a total knee replacement on the affected knee 24 years ago. Anteroposterior radiograph obtained last year (Figure 1) suggests that she may have polyethylene wear on the medial side. She was recently referred for a bone scan that revealed some increased uptake of debris around the tibia, femur, and patella. She has significant pain and mechanical symptoms in the knee that is not relieved with bracing. On physical examination, the knee has moderate effusion without erythema, warmth, or signs of infection. It is recommended that the patient have revision total knee replacement; while surgery is performed, a black, hypertrophic synovium is identified (Figure 2).
Submit your diagnosis to see full explanation.
Imaging of the left knee shows a collapse of the medial space between the femoral and tibial components of the knee replacement, which indicates a likely polyethylene failure. Polyethylene wear is the most prevalent mechanism of total knee replacement failure. When the polyethylene spacer fails and breaks apart, the metal components of the tibial and/or femoral implants can come in contact with each other.1,2
When the patient’s bone scan indicated that the prosthetic components were loose, and an infection was ruled out, the patient was taken to the operating room for a revision arthroplasty. Intraoperatively, when the arthrotomy was performed, severe metallosis was noted. The polyethelene spacer on the medial side was thin and cracked, and the femoral prosthesis had caused a crescent-shaped depression on the tibial prosthesis.
Metallosis is a metal-induced synovitis that is caused by the release of metal debris when the prosthetic components rub together.1 The metal debris triggers a foreign body inflammatory reaction that results in a thickened, black-stained synovium and osteolysis of adjacent bone.1,2
In this patient, an extensive synovectomy was performed to remove most of the black synovium, and the femoral and tibial components were revised.
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Salem KH, Lindner N, Tingart M, Elmoghazy AD. Severe metallosis-related osteolysis as a cause of failure after total knee replacement. J Clin Orthop Trauma. 2020;11(1):165-170.
2. Romesburg JW, Wasserman PL, Schoppe CH. Metallosis and metal-induced synovitis following total knee arthroplasty: review of radiographic and CT findings. J Radiol Case Rep. 2010;4(9):7-17.