Conversion of Cemented Revision Total Knee Prostheses to Arthrodesis Using Custom-made Arthrodesis Modules That Preserve the Cemented Stem Anchorage in Patients with Long-established Extensor Mechanism Insufficiency: A Case Series

Introduction: Long-established extensor mechanism insufficiency that defies reconstruction is a rare, but devastating, complication after revision total knee arthroplasty (RTKA) that may require arthrodesis. For cemented stem guided knee prostheses with firmly attached stems, prosthesis explantation can lead to significant bone stock loss that may, at worst, make knee arthrodesis significantly more difficult or impossible to achieve. Under these circumstances, conversion of the cemented knee prosthesis with custom-made arthrodesis modules that preserve the existing stem anchorage may be a low-risk alternative. This case series presents this type of conversion to arthrodesis, which was performed for patients with a non-reconstructable, long-established extensor mechanism insufficiency.

Methods: After intraoperatively ascertaining that reconstruction of the extensor mechanism insufficiency was impossible, the inlying revision prosthesis was converted into arthrodesis with custom-made arthrodesis modules, without explanting the cemented stems.

Results: Conversion to arthrodesis was performed in four patients. There was no histopathological or microbiological evidence of a periprosthetic joint infection. Clinical follow-up showed a low level of pain, with a stable knee joint and proper implant position. The Oxford Knee Score increased from 20.5 (95% CI 17-26) to 35.5 (95% CI 30-36) points. The visual analog scale decreased from 5.5 (95% CI 4-7) pre-operatively to 1.5 (95% CI 1-2) points at last follow-up. No implant-specific complications occurred.

Conclusions: Conversion of cemented RTKA with firmly attached cemented stems, without evidence of loosening, to arthrodesis might be a surgical treatment strategy for patients with a long-established extensor mechanism insufficiency that cannot be reconstructed.