Patellar component failure with patellar dislocation due to direct trauma

Abstract

Isolated patellofemoral osteoarthritis is a degenerative disease of the knee and represents 10-24% of all patients with knee pain. Replacement treatments for isolated patellofemoral osteoarthritis include patellofemoral arthroplasty (PFA) and total knee arthroplasty (TKA). Patellofemoral arthroplasty has many advantages over TKA in the treatment of patellofemoral arthritis. PFA is less invasive, requires shorter tourniquet times, has a faster recovery, and preserves the tibiofemoral compartment, leaving more native bone for possible conversion to TKA. Risk factors for patellar complications include valgus, obesity, and a thin patella before and / or after surgery.

Material and methods: We present a case of a 35-year-old man with a body mass index (BMI) of 20, normal anatomical and mechanical femorotibial axis. With a history of bilateral patellofemoral osteoarthritis managed with cemented PFA, in August 2019.

The patient reported a fall (February 2020) with external rotation, forced flexion and significant valgus mechanism of the left knee. In April 2020, he consulted for pain, but without limitation in his range of motion (ROM). He had quadriceps atrophy, thickening of the anterior region of the knee, with ligament stability and no meniscal symptomatology. Cabinet studies shown lateralization of the patella with evident dislocation of the patellar component (polyethylene).

Procedure: A preoperative radiological analysis was carried out where the described findings were established. A surgical resolution was proposed with a revision of the knee prosthesis and a replacement of the cemented patellar component with a release of the lateral retinaculum.

Results: In the immediate postoperative period, a stable prosthetic construct and adequate patellar tracking were obtained. In the radiographic control we observed an adequate centralization of the patella compared to the femoral component.

Discussion: The percentage of PFA failures has decreased significantly from 17% with first-generation prostheses Inlay-type to 4% with the second-generation Onlay system. Emphasizing the best patello femoral displacement with the Onlay system. The causes of revision mainly due to misalignment of the extensor apparatus that are the cause of patellar instability, progression of FT arthrosis, poor prosthetic positioning, symptoms related to poor prosthetic function and poor choice of the type of prosthesis according to trochlear anatomy. In the final evaluation of the patient, we confirmed absolute stability of the patella, complete ROM, progressive recovery of the quadriceps, and reintegration to non-sports activities.