Summary

We investigated the effect of ACL graft type on walking mechanics in 50 subjects ~6 months after ACL Reconstruction, and found medial tibiofemoral under-loading (which is associated with early osteoarthritis development) in those with bone-patellar tendon-bone versus hamstring autografts.

Abstract

Introduction

Controversy persists regarding graft type selection for anterior cruciate ligament reconstruction (ACLR). A recent systematic review found increased incidence of radiographic osteoarthritis in bone-patellar tendon-bone (BPTB) compared to hamstring autografts[1], but conflicting evidence[2] exists. One factor which could mediate the relationship between graft type and osteoarthritis risk is gait mechanics[3]. Few studies have evaluated the effect of graft type on gait mechanics, and none has investigated muscle or joint contact forces. Reduced tibiofemoral joint loading six months after ACLR is associated with future osteoarthritis[4], thus evaluating the effect of graft type on knee loading at this time is critical to the graft type dilemma. The purpose of this study is to compare gait mechanics and knee loading after BPTB autograft, hamstring autograft, and allograft ACLR.

Methods

Fifty athletes approximately six months after primary ACLR participated following impairment resolution including >80% quadriceps strength index. Subjects were classified by graft type: BPTB autograft, hamstring autograft, and allograft. Subjects underwent motion analysis during over-ground walking. A previously-validated, EMG-informed, patient-specific musculoskeletal model[5] was used to estimate muscle and joint contact forces. Variables of interest were peak knee flexion angle (pKFA) and moment (pKFM), peak knee adduction moment (pKAM), peak medial tibiofemoral contact force (pMCF), and extensor (EXT@pKFM) and flexor (FLEX@pKFM) muscle forces at pKFM. Statistical comparisons were made using a 3x2 ANOVA with group and limb comparisons(a=0.05). Group and inter-limb differences were also compared to previously established minimal detectable change (MDC) values[6].

Results

SECTION: There were 13 BPTB, 29 hamstring, and 8 allograft subjects in this preliminary analysis. BPTB (pMCF: ACLR/uninvolved limb mean±SD[body weight]: 2.5±0.6/2.7±0.5) loaded less than hamstring autografts (2.9±0.5/3.0±0.5; group p=0.017; post-hoc p=0.008). There was a main effect of limb for pKFA (p=0.011), pKFM (p=0.010), and EXT@pKFM (p=0.029), with smaller values in the ACLR versus uninvolved limb for the entire sample. However, BPTB subjects tended to walk with smaller pFKA (p=0.097) and pKFM (p=0.070) compared to hamstrings and allografts. BPTB subjects also walked with meaningful inter-limb pKFA asymmetry (-4.4°), while the other groups’ inter-limb differences did not meet the MDC (2.9°)[6]. Both BPTB (-0.12Nm/Kg*m) and hamstring (-0.10 Nm/Kg*m) subjects walked with inter-limb asymmetries in pKFM exceeding the MDC (0.09 Nm/Kg*m)[6]. Allograft subjects (26.3±7.1years) were older (p=0.001) than both BPTB (19.4±3.5) and hamstring (18.6±3.5) subjects, who did not differ in age (p=0.569). BPTB subjects were tested later (6.7±2.0months post-operatively) than both hamstring (5.2±1.6) and allograft (4.6±1.3) subjects (p=0.013). There were no differences in pKAM, FLEX@pFKM, sex, height, weight, or gait speed.

Discussion

Gait mechanics differed following ACLR with BPTB autograft versus hamstring autograft and allograft procedures. Notably, BPTB subjects loaded the medial compartment less and walked with greater inter-limb asymmetry than hamstring subjects. Underloading is associated with early osteoarthritis development after ACLR[4], thus BPTB subjects could be at higher risk of osteoarthritis due to altered gait mechanics. These findings suggest patients with BPTB autograft may benefit from additional, tailored rehabilitation, and these findings may provide an additional factor in the surgeon’s graft selection decision-making. Further investigation with (ongoing) longitudinal follow-up is warranted.

REFERENCES:
[1]Xie. EJOST(2014). [2]Barenius. AJSM(2014). [3]Andriacchi. JBJS(2009). [4]Wellsandt. AJSM(2016). [5]Manal. JBiomedEng(2013).[6]Gardinier. GaitPosture(2013).