The role of the femoral anterior offset index on the degree of flexion in total knee arthroplasty

João Maia Rosa, Marcio Oliveira, João Vide, Maria Miguel Carvalho, António Rodrigo Duarte, Henrique Cruz, Ana Paula Fontes, João Paulo Sousa


Background: Anterior projection of the femoral condyles is often disregarded as an issue in knee arthroplasty. Overstuffing the patellofemoral joint may limit knee flexion and be a source of patellofemoral complications, thus having an impact in satisfaction rates after total knee arthroplasty (TKA). Our hypothesis is that excessive anterior projection of the femoral condyles as a negative effect in flexion range after TKA, introducing a new concept, the anterior offset index (AOI).

Methods: From a group of 99 consecutive patients who underwent TKA using patient specific instrumentation (PSI), we selected the patients with good pre-operative flexion range (above 90º) and a 6-minute walk test (6 MWT) ≥ 0 meters, evaluating the correlation between the AOI and the flexion range. A total of 23 patients were included in the study.

Results: A moderate and positive correlation (r=0.488; p=0.018) between AOI and flexion range was found.

Conclusions: Our results seem to indicate that the AOI influences postoperative flexion in TKA, in patients with a good pre-operative flexion and good functional outcome. AOI is an important concept to retain when optimizing knee flexion and minimizing patellofemoral complications. However, more studies need to be done in order to clarify the role of all the factors influencing post op flexion after TKA.


Total knee arthroplasty, Anterior offset index, Knee flexion, Patellofemoral joint, Patellofemoral kinematics, Anterior knee pain

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