Isolated patellofemoral arthroplasty reproduces natural patellofemoral joint kinematics when the patella is resurfaced.
OBJECTIVE
The objectives of this in vitro project were to compare the dynamic three-dimensional patellofemoral kinematics, contact forces, contact areas and contact pressures of a contemporary patellofemoral prosthetic implant with those of the native knee and to measure the influence of patellar resurfacing and patellar thickness. The hypothesis was that these designs are capable to reproduce the natural kinematics but result in higher contact pressures.


METHODS
Six fresh-frozen specimens were tested on a custom-made mechanical knee rig before and after prosthetic trochlear resurfacing, without and with patellar resurfacing in three different patellar thicknesses. Full three-dimensional kinematics were analysed during three different motor tasks, using infrared motion capture cameras and retroflective markers. Patellar contact characteristics were registered using a pressure measuring device.


RESULTS
The patellofemoral kinematic behaviour of the patellofemoral arthroplasty was similar to that of the normal knee when the patella was resurfaced, showing only significant (p < 0.0001) changes in patellar flexion. Without patellar resurfacing, significant more patellar flexion, lateral tilt and lateral rotation was noticed. Compared to the normal knee, contact pressures were significantly elevated after isolated trochlear resurfacing. However, the values were more than doubled after patellar resurfacing. Changes in patellar thickness only influenced the antero-posterior patellar position. There was no other influence on the kinematics, and only a limited influence on the contact pressures in the low flexion angles.


CONCLUSIONS
The investigated design reproduced the normal patellofemoral kinematics acceptable well when the patella was resurfaced. From a kinematic point of view, patellar resurfacing may be advisable. However, the substantially elevated patellar contact pressures remain a point of concern in the decision whether or not to resurface the patella. This study therefore not only adds a new point in the discussion whether or not to resurface the patella, but also supports the claimed advantage that a patellofemoral arthroplasty is capable to reproduce the natural knee kinematics.
Department of Development and Regeneration - Orthopaedic Surgery, University Hospitals Leuven, Weligerveld 1, 3212, Pellenberg-Lubbeek, Belgium. hilde.vandenneucker@uzleuven.be.
Hilde
H
Vandenneucker
European Centre for Knee Research, Smith&Nephew, Technologielaan 11 bis, 3000, Leuven, Belgium.
Luc
L
Labey
Biomechanics Section, University of Leuven, Celestijnenlaan 300c, 3000, Leuven, Belgium.
Jos
J
Vander Sloten
Department of Rehabilitation Sciences, University Hospital Leuven, Weligerveld 1, 3212, Pellenberg-Lubbeek, Belgium.
Kaat
K
Desloovere
Department of Development and Regeneration - Orthopaedic Surgery, University Hospitals Leuven, Weligerveld 1, 3212, Pellenberg-Lubbeek, Belgium.
Johan
J
Bellemans
D000368:Aged; D000369:Aged, 80 and over; D001178:Arthroplasty; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D010329:Patella / Q000601:surgery*; D057071:Patellofemoral Joint / Q000503:physiopathology / Q000601:surgery*; D011312:Pressure; D016059:Range of Motion, Articular; D012399:Rotation
Contact pressure; Kinematics; Patellar resurfacing; Patellofemoral arthroplasty