Short distance from the keel to the posterior tibial cortex
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Tibial plateau fractures are serious complications of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study examined where the fracture lines arises and evaluated the keel–cortex distances (KCDs) using three-dimensional computed tomography (3D-CT) and the effects of technical error (assessed by tibial component positions) and proximal tibial morphology on the KCDs.

This retrospective study included 217 OUKAs with cementless tibial components. 15 patients had tibial fractures after surgery. Anterior and posterior KCDs and fracture line origins were assessed using 3D-CT postoperatively. Proximal tibial morphology was assessed using the medial eminence line (MEL), which runs parallel to the tibial axis and passes through the tip of the medial intercondylar eminence of the tibia on long-leg anteroposterior radiograph.

Knees had overhanging medial tibial condyle if the MEL passed medially to the medial tibial cortex. KCDs were compared between patients with/without fractures. Tibial component positions were evaluated, considering effects of tibial morphologies and component positions on fracture prevalence and KCDs.

Results:
--Fracture lines were found between the keel and posterior cortex in 12/15 patients.

--Posterior KCDs were significantly shorter in patients with fractures than in patients without (2.7±1.6 mm vs 5.2±1.7 mm).

--Patients with medial overhanging condyles were more likely to have fracture (10/51 vs 5/166) and had significantly shorter posterior KCD than those without (3.6±1.5 mm vs 5.5±1.8 mm).

--Patients with tibial component that was set too medial, low, and valgus had higher rates of fracture than those without (7/39 vs 8/178).

--Medial (r=0.30), low (r=-0.33), and valgus implantations (r=0.35) of tibial components were related to shorter posterior KCDs.

In conclusion, a short posterior KCD after OUKA is a risk factor for tibial fracture after surgery. Patients with a medial overhanging condyle and/or a malpositioned tibial portion (too medial, thin, and valgus) have a shorter posterior KCD distance and a higher fracture risk.

Source: https://link.springer.com/article/10.1007/s00167-021-06553-4
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