The concept of getting a patella into an optimal relationship with its opposing trochlea in patients with recurrent patella instability is well accepted. The idea here is a patella that “tracks” centrally in the trochlea, and has good structural supports around it to keep it there, will be stable. What makes a patella unstable, however, is complicated and is somewhat different in different patients.
Deficient core stability and a flat, dysplastic trochlea will render a patella more vulnerable to displacement. Add to this a malrotated hip (excessive anteversion or excessive internal rotation of the distal femur functionally away from the patella) and sometimes patella alta, and you have a formula for patella instability and dislocation. Intensive work on core stability training through physical therapy to improve the functional relationship of the patella to the trochlea is the hallmark of good nonoperative rehabilitation.
John P. Fulkerson
When these factors cannot be adequately controlled with nonoperative measures, a surgical effort to restore patella stability would logically include correction of those factors causing the instability. In practice, however, aligning the patella by tibial tubercle transfer has been a powerful way to compensate for malalignment occurring at the level of the femur. Tibial tubercle transfer medially, or anteromedially when a patella articular lesion needs unloading, brings the patella into a better and typically central relationship with the internally rotated trochlear groove. A well done, accurate medial or anteromedial tibial tubercle transfer is likely less morbid than femoral derotation (bringing the femoral trochlea back laterally to the patella), in which the femur is transected, rotated and then stabilized with a plate and screws.
Another option is to deepen the trochlea (trochleoplasty) and maybe move the trochlea laterally to a lateral tracking patella, but this has risks related to alteration of subchondral bone and cartilage.
These procedures are effective for patella stabilization. Tubercle transfer and femoral rotation place the patella into an optimal, balanced relationship with the trochlea. All provide stability when properly done, but may require a supplemental medial patellofemoral complex restoration procedure. In general, tibial tubercle transfer medially, anteromedially and sometimes a little distally (in the presence of patella alta), will be the safest option for many patients by most surgeons, when the patella and trochlea are malaligned.
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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, Conn. 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.