by John P. Fulkerson, MD
Dysplasia of the femoral trochlea is complex and variable. Why it occurs is poorly understood. Some believe that trochlea dysplasia is genetically determined and some believe that it is a result of aberrant forces through the joint (form follows function) during growth. Recent evidence suggests that aberrant forces lead to dysplasia.
We analyzed seven 3D trochlea dysplasia reproductions (special thanks to David Diduch, MD, and the University of Virginia’s Department of Orthopedic Surgery for providing these), created from patients, in an attempt to better understand forces and behavior around the patellofemoral joint in patients with trochlea dysplasia.
It appears likely that functional lateralized tracking of the patella in the femoral trochlea may be a precursor of lateral facet-dominant loading in early flexion, lateral entry into the trochlea of the knee and dysplastic formation of the trochlea.
This dysplastic formation then predisposes patients to a J sign and lateral patella instability. The supratrochlear spur that forms may be filling space created by a functionally lateralized patella that is captured into the deepening femoral trochlea more distally upon progressive knee flexion. It is unknown how patella alta affects this formation.
This analysis suggests the patella and trochlea are generally congruous in trochlea dysplasia, albeit malformed.
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John P. Fulkerson, MD, is a clinical professor of orthopedic surgery at the University of Connecticut School of Medicine and practices at Orthopedic Associates of Hartford in Farmington, Connecticut. He is also president of The Patellofemoral Foundation.
Disclosure: Fulkerson reports he receives royalties from DJO Global and is a patent holder for DJO Global.