Abstract
Patellofemoral offset is influenced by patellar thickness in total knee arthroplasty
(TKA), with effects on extensor mechanism efficiency (EME), patellar contact moment
arm (PCMA), and patellar contact force (PCF). This study utilized a computational
model to better quantify these measures during knee range of motion (ROM). A computational
model of a cruciate-sacrificing, posterior-stabilized TKA design was used to quantify
moments at knee flexion angles from 0° to 135° when patella thickness was increased
(“overstuffed”) or decreased (“understuffed”) by 2 mm and 5 mm from normal. Outcomes
included changes in EME, PCMA, PCF, tibial tubercle moment arm (TTMA), and the quadriceps
moment arm (QMA). Overstuffing of the patellofemoral articulation by 2 mm and 5 mm
decreased EME up to 12 and 28%, respectively, with an 8% and 16% increase in EME with
understuffing that peaked at 25° knee flexion. The QMA increased up to 5 and 12% with
overstuffing by 2 mm and 5 mm and decreased up to 5% and 14% with understuffing, respectively.
There was an increase in the PCMA/PCF, which opposed the QMA, up to 8%/17% and 16%/39%
with overstuffing by 2 mm and 5 mm, respectively. The PCMA/PCF decreased up to 3%/12%
and 8%/33% with understuffing by 2 mm and 5 mm, respectively. In this computational
model, increased patellofemoral offset resulting in overstuffing of the patella resulted
in decreased EME and increased PCMA and PCF during knee ROM. This may contribute to
abnormal patellofemoral mechanics and a potential etiology for anterior knee pain
and quadriceps weakness after TKA.
Keywords
patellar overstuffing - patellofemoral mechanics - patellar contact forces - extensor
mechanism efficiency - quadriceps moment arm
