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. 2018 Oct;26(10):2883-2890.
doi: 10.1007/s00167-017-4799-9. Epub 2017 Nov 11.

Allowing one quadrant of patellar lateral translation during medial patellofemoral ligament reconstruction successfully limits maltracking without overconstraining the patella

John J Elias  1 , Kerwyn C Jones  2 , Molly K Lalonde  3 , Joseph N Gabra  3 , S Cyrus Rezvanifar  4 , Andrew J Cosgarea  5
Affiliations

Allowing one quadrant of patellar lateral translation during medial patellofemoral ligament reconstruction successfully limits maltracking without overconstraining the patella

John J Elias et al. Knee Surg Sports Traumatol Arthrosc. 2018 Oct.

Abstract

Purpose: Graft tensioning during medial patellofemoral ligament (MPFL) reconstruction typically allows for lateral patellar translation within the trochlear groove. Computational simulation was performed to relate the allowed patellar translation to patellofemoral kinematics and contact pressures.

Methods: Multibody dynamic simulation models were developed to represent nine knees with patellar instability. Dual limb squatting was simulated representing the pre-operative condition and simulated MPFL reconstruction. The graft was tensioned to allow 10, 5, and 0 mm of patellar lateral translation at 30° of knee flexion. The patellofemoral contact pressure distribution was quantified using discrete element analysis.

Results: For the 5 and 10 mm conditions, patellar lateral shift decreased significantly at 0° and 20°. The 0 mm condition significantly decreased lateral shift for nearly all flexion angles. All graft conditions significantly decreased lateral tilt at 0°, with additional significant decreases for the 5 and 0 mm conditions. The 0 mm condition significantly increased the maximum medial pressure at multiple flexion angles, increasing by 57% at 30°, but did not alter the maximum lateral pressure.

Conclusions: Allowing 5 to 10 mm of patellar lateral translation limits lateral maltracking, thereby decreasing the risk of post-operative recurrent instability. Allowing no patellar translation during graft tensioning reduces maltracking further, but can overconstrain the patella, increasing the pressure applied to medial patellar cartilage already fibrillated or eroded from an instability episode.

Keywords: Contact pressure; Medial patellofemoral ligament reconstruction; Patellar instability; Patellar kinematics.

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Conflict of interest statement

Conflicts of Interest

John Elias has received a research grant from MedShape 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, Molly Lalonde and Cyrus Rezvanifar report no conflicts of interest.

Figures

Fig. 1
Fig. 1
Computational model for multibody dynamic simulation for one knee. The model is shown for the pre-operative condition at 0° (A) and 50° (B) of flexion and for the 10 mm MPFL graft condition at 0° (C) and 50° (D). The pressure distribution at 30° for the pre-operative condition is also shown (E).
Fig. 2
Fig. 2
Average (± standard deviation) graft force for the MPFL graft conditions allowing 10 mm, 5 mm, and 0 mm of lateral patellar translation during graft fixation. Open symbols represent data points that are significantly (p < 0.01) different from the 10 mm MPFL graft condition.
Fig. 3
Fig. 3
Average (± standard deviation) patellar lateral shift for the pre-operative condition and MPFL graft conditions allowing 10 mm, 5 mm, and 0 mm of lateral patellar translation during graft fixation. Open symbols represent data points that are significantly (p < 0.01) different from the pre-operative condition.
Fig. 4
Fig. 4
Average (± standard deviation) patellar lateral tilt for the pre-operative condition and MPFL graft conditions allowing 10 mm, 5 mm, and 0 mm of lateral patellar translation during graft fixation. Open symbols represent data points that are significantly (p < 0.01) different from the pre-operative condition.
Fig. 5
Fig. 5
Average (± standard deviation) maximum lateral pressure for the pre-operative condition and MPFL graft conditions allowing 10 mm, 5 mm, and 0 mm of lateral patellar translation during graft fixation.
Fig. 6
Fig. 6
Average (± standard deviation) maximum medial pressure for the pre-operative condition and MPFL graft conditions allowing 10 mm, 5 mm, and 0 mm of lateral patellar translation during graft fixation. Open symbols represent data points that are significantly (p < 0.01) different from the pre-operative condition.
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