Proximal tibial morphology and risk of posterior tibial cortex impingement in patients with AA-sized Oxford unicompartmental knee arthroplasty tibial implants

Abstract

Background: In cases of Oxford unicompartmental knee arthroplasty (UKA), an increase in anteroposterior and medial-lateral length is usually disproportional when comparing AA and A-sized tibial components. Asynchronous increments may cause tibial keel impingement leading to complications. Methods: Radiographic measurements were performed in five patients with AA-sized tibial implants. The posterior cortex of proximal tibia had two angles recorded as ∠ M1 and ∠ M2. The minimum distance between the tibial component keel and outer margin of the posterior tibial cortex (mDKC) was measured, and the correlation between the preoperative posterior slope angle (PSA), ∠ M1, and mDKC was analyzed. Results: All patients showed an acceptable component positioning. Only one patient had an mDKC of < 4 mm that fulfilled the criteria for the posterior tibial cortex at risk. The patient had an increased PSA and ∠ M1 compared to other patients. A negative correlation was found between preoperative PSA and mDKC (r = − 0.935, p = 0.0193); and ∠ M1 and mDKC (r = − 0.969, p = 0.0032). However, no stem tip pain, periprosthetic fracture, or component loosening were observed. Conclusions: The distance between the tibial keel and posterior tibial cortex was reduced in AA-sized patients with a large PSA and ∠M1; therefore, the risk of the tibial cortex injury should be considered.

Using MRI Measurement to Improve Accuracy of Femoral Component Sizing in Oxford Unicompartmental Knee Arthroplasty

“…The importance of correct femoral implant size is still debated [ 24 ]. As we know, Phase I and Phase II of the Oxford medial UKA still had a 20-year survival rate of 92%, which is similar to the best reported TKR survival [ 6 ].…”