LIVRE JDG 2012

M. Odumenya, S.J. Krikler, A.A. Amis

294

A previous study [14] assessed the pre- and

post-operative tracking kinematics in vitro of

four patellofemoral arthroplasties: Avon,

Blazina, Leicester (Corin Group, Cirencester,

England) and Lubinus (see fig. 5A-D). The

Avon and Leicester implants had tracking paths

that most resembled the native knee.

Unsurprisingly,theBlazina,hadacomparatively

linear pattern following engagement into the

V-shaped trochlear groove. The Lubinus

demonstrated an inconsistent pattern in some

of the specimens. Assessment of these

specimens identified abrupt changes in patellar

tilt indicating the transition point as the patellar

component moved from articulating with the

trochlear component to the native articular

surface.

Patellofemoral joint reaction forces occur as a

result of the tension in the extensor mechanism.

The force vectors in the sagittal plane are

composed of the quadriceps and patellar tendon

tensions (see fig. 6). The result is a force applied

by the patella posteriorly onto the anterodistal

femur. In the coronal plane this force has a

lateral component caused by the Q angle. Due

to the compressive nature of the force, loosening

is unlikely to occur during point loading

however, as the force moves position with

increasing knee flexion, large forces will be

applied closer to the proximal edge of the

patella. Numerous fixations pegs cemented into

the patellar bone will resist potential

displacement of the component.

Fig. 5A-D : Patellofemoral joint prostheses: [A] Avon prosthesis, [B] Blazina prosthesis, [C] Leicester

prosthesis and [D] Lubinus prosthesis.

Permission to use image granted by copyright owners Lippincott Williams & Wilkins. Amis AA, Senavongse W,

Darcy P. Biomechanics of patellofemoral joint prostheses. Clin Orthop 2005; 436: 20-9.