Primary total knee arthroplasty after extensor mechanism reconstruction with structural allograft (case report)

Abstract

Introduction. Total knee arthroplasty (TKA) in patients with the extensor mechanism insufficiency is traditionally considered as a complex case. Purpose. To demonstrate the specific features of primary TKA in a patient with a history of the extensor mechanism reconstruction using a structural allograft. Case description. A 32-years-old male was admitted to the hospital due to severe pain and decreased range of motion of the left knee 6 month ago. In 2014, due to a road traffic accident, he experienced an open comminuted fracture of the left patella, complicated by infection. During debridement, the partial patellectomy was performed followed by elimination of surgical site infection. One year after the injury, due to significant extension lag and knee instability during walking, an extensor mechanism reconstruction was performed using a structural allograft including the quadriceps tendon-patella-patellar ligament-tibial tubercle. The screws that were fixing the allograft in the tibial crest were removed one year after the reconstruction. The patient resumed an active lifestyle and practiced martial arts. In 2023, he began experiencing increasing pain, limited range of motion (0°–20°–110°), varus deformity (8°), and extensor lag of 20°. Oxford Knee Score (OKS) was 29 points. Due to the low efficacy of conservative treatment TKA was performed in February 2024. Results. After performing standard medial parapatellar approach, the fusion both of the tendon and bone parts of the structural allograft to the surrounding tissues was confirmed. Surprisingly, disintegration of the distal third of the anterior surface of the patella from the retinaculum was identified. To preserve the integrity of the extensor mechanism, the refixation of the patella to the retinaculum was performed with two anchors and non-absorbable sutures. At the 6-month follow-up, the patient reported no pain, full range of motion and walked without additional support or distance limitations. The OKS was 42 points but extensor lag of 5° persisted. Conclusion. After transplantation of structural allograft of the extensor mechanism, the fusion with the native tissues occurs only in the zones of proximal and distal fixation. Despite the reliable long-term mechanical properties, the whole graft did not go through complete revascularization by host tissue and full remodeling. Therefore, during subsequent surgical interventions, including TKA, it is necessary to be technically prepared for augmentation of the extensor mechanism or its secondary reconstruction.