Computational Simulation of Patellar Instability

The two most common stabilization procedures for patients with recurrent patellar instability
are reconstruction of the medial patellofemoral ligament (MPFL) and medialization of the
tibial tuberosity. MPFL reconstruction has been growing in popularity, due in large part to
the technical demands of tibial tuberosity realignment and concerns related to bone healing
across the osteotomy. In cases of severe trochlear dysplasia and/or a dramatically
lateralized tibial tuberosity, an MPFL graft tensioned according to current standards may not
provide sufficient resistance to limit lateral patellar tracking that causes continued
instability. Increasing graft tension could overload medial patellofemoral cartilage. The
proposed study is based on the hypothesis that the ability of MPFL reconstruction to
effectively limit lateral patellar maltracking decreases as trochlear dysplasia and the
lateral position of the tibial tuberosity increase. Computational dynamic simulation of knee
function will be performed to establish anatomical standards for which tibial tuberosity
medicalization is more likely than MPFL reconstruction to limit patellar maltracking without
overloading patellofemoral cartilage. The first specific aim is to computationally replicate
lateral patellar maltracking and pressure applied to cartilage during function for patients
being treated for patellar instability. Multibody dynamics knee models representing patients
being treated for recurrent patellar instability will be based on 3D reconstructions from MRI
scans. The modeling technique treats the bones and cartilage surfaces as rigid bodies with
Hertzian contact determining contact forces and guiding joint motion. Discrete element
analysis techniques will be used to characterize contact pressure patterns based on overlap
of cartilage surfaces. Models will be individually validated by comparing output to in vivo
data. The source of the in vivo data will be computational reconstruction of in vivo function
based on motions performed by the patients who provide the imaging data for model
development. The second specific aim will be to computationally characterize the influence of
surgical stabilization on knee function for individual patients. MPFL reconstruction and
tibial tuberosity medialization, each with variations in surgical parameters, will be
simulated. The actual surgical procedures performed on the patients will be simulated, with
the influence on lateral tracking compared to in vivo results to validate the representation
of the surgical procedures. The third specific aim will be to compare surgical options as a
function of patellofemoral anatomy. Variations in patellar tracking and pressure applied to
cartilage will be compared between MPFL reconstruction and tuberosity medialization. In
addition, techniques to parametrically alter trochlear dysplasia and tuberosity
lateralization within the models will be developed. Simulations will be performed while
varying anatomy to set ranges over which each surgical option can limit patellar maltracking
without elevating contact pressures. The modeling system will be available for future studies
addressing additional surgical options and anatomical parameters related to patellar
instability.

Inclusion Criteria:

- Diagnosis of recurrent patellar dislocation

- Plan to be surgically treated at Akron Children's Hospital

Exclusion Criteria:

- Additional Injuries unrelated to patellar instability for the knee of interest

- Implantation of metallic hardware that could cause artifacts within MRI scans

- Inability to remain still during MRI scans