Thanks very much to the Arthroscopy Association for the opportunity to present this study and for my co-authors for making this study possible. Our disclosures can be found in the final program, and the study was also supported by a grant from Anna. As you know, MPFL reconstruction is performed in patients with patellar instability to restore the soft tissue restraint to lateral patellar translation. Observations at the time of MPFL reconstruction include the assessment of malalignment, patella alta, and trochlear dysplasia to address other pathology for the function of the MPFL graft. Cataveric studies have shown that increased TTTG distance and patellar alta combined can lead to graft anisometry, and it's also been shown that MPFL reconstruction does not restore contact pressures and patellar kinematics in the setting of a TTTG distance greater than 15 millimeters. However, the influence of knee pathology on MPFL graft function has not been fully characterized in terms of patellar tracking and graft tensioning protocols. Therefore, the aim of this study was to evaluate the specific anatomical factors that contribute to MPFL graft loading using dynamic simulation of knee function from models of symptomatic patients with patellar instability. Functional models of 14 patients with patellar instability were included in this study for the mean age of 19 years. Dynamic simulation models were based on each subject's knee function at the time of diagnostic dynamic imaging. Anatomic measurements were quantified during simulated squatting maneuver. These included measurements of patellar height, which included patellotrochlear index, as shown here, as well as the Ketan-Deschan index. Patellar lateralization was quantified using the TTPCL distance. And trochlear dysplasia was quantified using lateral trochlear inclination. Measurements of patellar tracking included lateralization as measured by bisect offset, which is quantifying the percentage of the patella that is lateral to the deepest portion of the trochlear groove, as well as lateral patellar tilt relative to the posterior condylar axis. Each model was analyzed during a simulated squatting motion, comparing the preoperative state without an MPFL graft, as well as the postoperative state with MPFL graft with fixation options of either half a quadrant or a full quadrant of lateral patellar translation at the time of fixation at 30 degrees knee flexion. Patellar kinematics in terms of offset and lateral tilt were compared at five-degree intervals of knee flexion. The graft forces were compared between the two tensioning protocols with Wilcoxon sign rank tests. And regression analyses were performed to relate the maximum graft force to anatomical parameters, including TTPCL distance, trochlear inclination, Katon-Dachon index, and patellar trochlear index. In terms of patellar tracking and patellar lateralization, bisect offset was decreased in both MPFL reconstructed states when compared to the preoperative condition, as shown here, with significant findings from zero to 50 degrees. Of knee flexion, there were fewer significant differences in the setting of graft tensioning, allowing one quadrant of lateral translation. Findings of patellar tilt were similar. Patellar tilt was decreased in both MPFL reconstructed states versus the preoperative condition from zero to 30 degrees of knee flexion, with, again, fewer significant differences when allowing one quadrant of translation as opposed to half a quadrant during setting the graft length. Graft forces were greatest at the lowest flexion angles, and there was no tension in the graft found after 30 degrees of knee flexion in both settings. And in terms of anatomic parameters, the maximum TTPCL distance correlated with graft force. There's a strong correlation in the half quadrant and a moderate correlation in the one that allowed one quadrant, as shown here. In terms of trochlear dysplasia or patella alta, there were no significant correlations found. In summary, the primary preoperative anatomical parameter that determines maximum MPFL graft tension is the most lateral position of the tibial tuberosity during knee function. This was increased when the graft length was set to be more restrictive of patellar translation. Furthermore, MPFL reconstruction was found to decrease patellar maltracking in terms of lateralization and tilt, and MPFL grafts were found to carry minimal load beyond 30 degrees of knee flexion during functional activities. In conclusion, these findings suggest that tibial tuberosity medialization should potentially be considered in patients with an elevated TTPCL distance to decrease the risk of excessive MPFL graft tension. Thank you.

MPFL reconstruction

patellar instability

dynamic simulation

graft fixation options

patellar tracking