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Impact of different medial patellofemoral ligament reconstruction strategies on the patellofemoral contact pressure
Author(s):
Seitz A. (Germany)
,
Seitz A. (Germany)
Affiliations:
Dornacher D.
,
Dornacher D.
Affiliations:
Lippacher Sabine
,
Lippacher Sabine
Affiliations:
Nelitz M.
,
Nelitz M.
Affiliations:
Ignatius Anita
,
Ignatius Anita
Affiliations:
Dürselen L.
Dürselen L.
Affiliations:
ESSKA Academy. Seitz A. May 9, 2018; 209578; P09-488 Topic: Biomechanics
Dr. Andreas Martin Seitz
Dr. Andreas Martin Seitz
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Abstract
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Objectives: The medial patellofemoral ligament (MPFL) is the main stabilizer of the patella and therefore mostly reconstructed in the surgical treatment of patellofemoral dislocation. The aims of this study were to get a better understanding of the influence of altered MPFL graft fixation locations and different graft pre-tensions on mean patellofemoral contact pressure (mPFCP). Thus, the following hypotheses were elaborated: 1.) Increasing graft pre-tension leads to an increased mean mPFCP; 2.) Anatomical double-bundle MPFL reconstruction restores the mPFCP pattern of the native knee; 3.) Non-anatomical patellar and femoral graft fixations lead to excessive mPFCP compared to the native and anatomical reconstructed state.

Methods: Six human cadaveric knee joints were placed in a 6-degree of freedom knee simulator [1]. Mean PFCP (mPFCP) was evaluated in knee flexion of 0°, 30° and 90° using a calibrated pressure measurement system. After data assessment of the native knee joint (Pnat), five MPFL reconstruction conditions were conducted: Anatomical double bundle (Pa, [2]); non-anatomical proximal patellar (Pp); non-anatomical distal patellar (Pd); non-anatomical proximal femoral (Fp); non-anatomical ventral femoral (Fv). The gracilis graft was fixed at a knee flexion of 30° and pre-tensioned to 2N, 10N and 20N. Nonparametric statistical analyses were performed after post-hoc power analysis to check the following hypotheses: 1.) Graft pre-tensioning on the mPFCP using a Wilcoxon test; 2.) mPFCP of Pnat was compared to Pa using a Kruskal-Wallis test followed by a post-hoc Bonferroni-Dunn test; 3.) Pnat and Pa were compared to the the non-anatomical reconstructions (Pp, Pd, Fp, Fv) using a Kruskal-Wallis test followed by a post-hoc Bonferroni-Dunn test.

Results: The study design was appropriate to respond to the previously defined hypotheses: 1.) Discarded, we investigated a decrease in mean PFCP with higher graft tension rather than a decrease. This could be explained with altered patellar kinematics after non-anatomical MPFL reconstruction.
2.) Corroborated, the anatomical double-bundle reconstruction was able to restore the PFCP of the native knee joint, which is also in accordance with literature [3].
3.) Partially corroborated - at a knee flexion of 90° a non-anatomical ventral or proximal femoral positioning of the graft led to an excessive mPFCP: Comparing Pnat and Pa with the non-anatomical reconstructions resulted in no difference in mPFCP both, in knee extension (0°) (p>0.366) and in 30° knee flexion (p>0.349). At 90° knee flexion, the following differences were identified: mPFCP of Pnat, was increased by 257% (p=0.04) for Fp and by 292% (p=0.016) for Fv. Compared to Pa, mPFCP was increased by 199% (p=0.042) for Fp.

Conclusions: With respect to all study findings and in accordance with literature [3] [4] the authors recommend in to use the anatomical footprints [2] in order to restore a physiological mPFCP during MPFL reconstruction and a moderate graft pre-tensioning of 2-10N.

Keywords:
knee, human, MPFL, reconstruction, contact mechanics, contact pressure, mean contact pressure, graft, graft tensioning
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