Femoral articular geometry and patellofemoral stability.
BACKGROUND
Patellofemoral instability is a major cause of anterior knee pain. The aim of this study was to examine how the medial and lateral stability of the patellofemoral joint in the normal knee changes with knee flexion and measure its relationship to differences in femoral trochlear geometry.


METHODS
Twelve fresh-frozen cadaveric knees were used. Five components of the quadriceps and the iliotibial band were loaded physiologically with 175N and 30N, respectively. The force required to displace the patella 10mm laterally and medially at 0°, 20°, 30°, 60° and 90° knee flexion was measured. Patellofemoral contact points at these knee flexion angles were marked. The trochlea cartilage geometry at these flexion angles was visualized by Computed Tomography imaging of the femora in air with no overlying tissue. The sulcus, medial and lateral facet angles were measured. The facet angles were measured relative to the posterior condylar datum.


RESULTS
The lateral facet slope decreased progressively with flexion from 23°±3° (mean±S.D.) at 0° to 17±5° at 90°. While the medial facet angle increased progressively from 8°±8° to 36°±9° between 0° and 90°. Patellar lateral stability varied from 96±22N at 0°, to 77±23N at 20°, then to 101±27N at 90° knee flexion. Medial stability varied from 74±20N at 0° to 170±21N at 90°. There were significant correlations between the sulcus angle and the medial facet angle with medial stability (r=0.78, p<0.0001).


CONCLUSIONS
These results provide objective evidence relating the changes of femoral profile geometry with knee flexion to patellofemoral stability.
Musculoskeletal Laboratory, Imperial College London, Charing Cross Hospital, London, United Kingdom.
Farhad
F
Iranpour
Musculoskeletal Laboratory, Imperial College London, Charing Cross Hospital, London, United Kingdom; National Orthopaedic Centre of Excellence for Research and Learning (NOCERAL), Department of Orthopaedic Surgery, University of Malaya, Malaysia.
Azhar M
AM
Merican
National Orthopaedic Centre of Excellence for Research and Learning (NOCERAL), Department of Orthopaedic Surgery, University of Malaya, Malaysia. Electronic address: tseowhui@yahoo.com.
Seow Hui
SH
Teo
Musculoskeletal Laboratory, Imperial College London, Charing Cross Hospital, London, United Kingdom.
Justin P
JP
Cobb
Musculoskeletal Laboratory, Imperial College London, Charing Cross Hospital, London, United Kingdom; Biomechanics Section, Mechanical Engineering Department, Imperial College London, United Kingdom.
Andrew A
AA
Amis
D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000502:physiology; D005269:Femur / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D057071:Patellofemoral Joint / Q000502:physiology*; D014057:Tomography, X-Ray Computed
Biomechanics test; Femoral articular geometry; Patellofemoral joint; Patellofemoral stability