Background: Continued patellar instability can occur following medial patellofemoral ligament (MPFL) reconstruction. Computational simulation of function was used to investigate the influence of the lateral position of the tibial tuberosity, trochlear dysplasia and patella alta on lateral patellar tracking following MPFL reconstruction. Methods: Multibody dynamic simulation models were developed to represent nine knees being treated for recurrent patellar instability. Knee extension against gravity and dual limb squatting were simulated with and without simulated MPFL reconstruction. Graft resting lengths were set to allow 10 mm and five millimeters of patellar lateral translation at 30° of knee flexion. The bisect offset index, lateral tibial tuberosity to posterior cruciate ligament tibial attachment (TT–PCL) distance, lateral trochlear inclination, and Caton–Deschamps index were quantified at every five degrees of knee flexion to characterize lateral tracking, lateral position of the tibial tuberosity, trochlear dysplasia, and patella alta, respectively. For the pre-operative and post-operative conditions and each type of motion, bisect offset index was correlated with the anatomical parameters using stepwise multivariate linear regression. Results: For both motions, the pre-operative and post-operative bisect offset indices were significantly correlated with lateral trochlear inclination and lateral TT–PCL distance. For both motions, the adjusted r2 decreased with MPFL reconstruction, but was still approximately 0.5 for MPFL reconstruction allowing five millimeters of lateral translation. Conclusion: MPFL reconstruction decreases but does not eliminate lateral maltracking related to trochlear dysplasia and a lateralized tibial tuberosity. Patients with these pathologies are likely at the highest risk for instability related to maltracking following MPFL reconstruction.
Bibliographical noteFunding Information:
John Elias has received research grants from MedShape and NorthShore University HealthSystem and is the PI of the grant from the NIH. Andrew Cosgarea has been a committee member for the American Orthopaedic Society for Sports Medicine and the Patellofemoral Foundation, has received grant funding from the Arthroscopy Association of North America, and textbook royalties from Elsevier. Kerwyn Jones is the PI of the grant from the Pediatric Orthopaedic Society of North America. Joseph Gabra, Melanie Morscher and Cyrus Rezvanifar report no conflicts of interest.
Research reported in this publication was supported by the National Institute of Arthritis And Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Number R21AR069150 and a Basic Science Research Grant from the Pediatric Orthopaedic Society of North America .
© 2018 Elsevier B.V.
- Medial patellofemoral ligament reconstruction
- Patellar instability
- Tibial tuberosity
- Trochlear dysplasia