Effect of Patella Alta on the Native Anatomometricity of the Medial Patellofemoral Complex: A Cadaveric Study.

BACKGROUND

Patella alta has been identified as an important risk factor for lateral patellar instability and medial patellofemoral complex (MPFC) reconstruction failure.

PURPOSE

To evaluate the length changes of the MPFC at multiple possible reconstruction locations along the extensor mechanism in varying degrees of patella alta throughout knee motion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eight fresh-frozen cadaveric knees were used in this study. The MPFC was identified and dissected with the patellar tendon and quadriceps tendon. A custom-made jig was utilized to evaluate lengths from 0° to 90° of flexion with physiological quadriceps loading. Length was measured with a 3-dimensional robotic arm at 4 possible reconstruction locations along the extensor mechanism: the midpoint patella (MP), the MPFC osseous center (FC), the superior medial pole of the patella (SM) at the level of the quadriceps insertion, and 1 cm proximal to the SM point along the quadriceps tendon (QT). These measurements were repeated at 0°, 20°, 40°, 60° and 90° of flexion. Degrees of increasing severity of patella alta at Caton-Deschamps index (CDI) ratios of 1.0, 1.2, 1.4, and 1.6 were then investigated.

RESULTS

Patella alta and MPFC attachment site location significantly affected changes in MPFC length from 0° to 90° of flexion (

CONCLUSION

Anisometry of the MPFC varies not only with attachment location on the extensor mechanism but also with patellar height. Increased patellar height leads to more significant changes in anisometry in the proximal MPFC attachment point as compared with the distal component. In the setting of patella alta, including a CD ratio of 1.6, the osseous attachments of the MPFC remain nearly isometric wheras the proximal half length changes increase significantly.

CLINICAL SIGNIFICANCE

The results of this study support the idea that the MPFC should be considered as 2 separate entities (proximal medial quadriceps tendon femoral ligament and distal medial patellofemoral ligament) owing to their unique length change properties.