Limb symmetry index on a functional test battery improves between one and five years after anterior cruciate ligament reconstruction, primarily due to worsening contralateral limb function

Highlights

• The contralateral limb had a significantly greater decrease in function for the three hop tests compared to the ACLR limb.

• The LSI improved significantly for the single hop, side hop and one-leg rise between 1- and 5-years post-ACLR.

• The LSI overestimate improvement in functional ability following ACLR, due to worsening contralateral limb function.

• The LSI on all four tests at 1-year post-ACLR was significantly lower than healthy controls.

Abstract

Objective

Evaluate change in functional performance from 1- to 5-years after anterior cruciate ligament reconstruction (ACLR).

Methods

59 participants (38 men) aged 29 ± 16 years completed three hops and one-leg rise 1- and 5-years following ACLR. Linear mixed-effects models evaluated differences in change between the ACLR and contralateral limbs. Participants were classified with stable, improving or worsening function relative to previously published minimal detectable change thresholds. Healthy controls completed the three hops (n = 41) and one-leg rise (n = 31) as reference data.

Results

The contralateral limb had a significantly greater decrease in functional performance between 1- and 5-years for the three hops, compared to the ACLR limb. Worsening was more common in the contralateral limb than the ACLR limb; resulting in significant improvements in the LSI for the single hop (mean 87% at 1-year to 95% at 5-years), side hop (77%to 86%) and one-leg rise (76% to85%). Performance of both ACLR and contralateral limbs and the LSI remained below the healthy controls.

Conclusion

Functional performance changes differ between limbs between 1- and 5-years post-ACLR. The LSI should not be used in isolation to evaluate functional performance changes after ACLR, as it may overestimate functional improvement, due to worsening contralateral limb function.

Introduction

Following anterior cruciate ligament injury and reconstruction (ACLR), functional performance testing is advocated to determine readiness for return-to-sport and mitigate risk of reinjury (Grindem, Arundale, & Ardern, 2018; Kyritsis, Bahr, Landreau, Miladi, & Witvrouw, 2016; van Melick et al., 2016). A limb symmetry index (LSI) is frequently used to describe function of the ACLR limb compared to the contralateral limb, expressed as a percentage (score of ACLR knee divided by contralateral knee, multiplied by 100). An LSI >90% on a functional test battery (e.g. hop tests, muscle strength) frequently defines functional recovery and return-to-sport clearance (Abrams et al., 2014).

Symmetry (>90%) on hop-testing is associated with reduced re-injury risk (Grindem, Snyder-Mackler, Moksnes, Engebretsen, & Risberg, 2016; Kyritsis et al., 2016), better patient-reported symptoms and quality of life (Ericsson, Roos, & Frobell, 2013) and reduced risk of osteoarthritis (OA) (Culvenor et al., 2017; Patterson et al., 2020; Pinczewski et al., 2007). However, the LSI assumes the contralateral limb is the acceptable standard, equivalent to pre-injury status and immune to decline (Benjaminse, Holden, & Myer, 2018; Wellsandt et al., 2017). In reality, bilateral neuromuscular deficits (e.g. muscle strength, activation or size, biomechanics, balance and functional performance) exist following unilateral ACLR (Culvenor et al., 2016a; Gokeler et al., 2017; Ingersoll, Grindstaff, Pietrosimone, & Hart, 2008); hence the LSI may overestimate postoperative knee function (Wellsandt et al., 2017), which is an important consideration given the high risk of second ACL injury (Wiggins et al., 2016). To determine whether the LSI overestimates knee function, it is important to compare raw scores from the ACLR and contralateral limb to healthy uninjured controls, providing the benchmark for functional performance.

While functional improvements in hop-testing LSI are well documented within the first year following ACLR (Abrams et al., 2014; Nagelli & Hewett, 2017; Thomee et al., 2012), functional changes beyond the period of active rehabilitation (i.e. >1–2 years postoperatively) are less often reported (Oiestad et al., 2010). Specifically, it is not known whether functional LSI changes beyond the initial 1–2 postoperative years are driven by changes in the ACLR or contralateral limb. Evaluating the magnitude of functional performance (e.g. hop distance) in the ACLR and contralateral limb, and as expressed with the LSI over time compared to uninjured controls, is important to understand the longer-term functional burden of ACLR.

The primary aim of the current study was to evaluate the change in functional performance in the ACLR and contralateral limbs from 1- to 5-years post-ACLR to determine the influence on LSI. We hypothesised change in functional performance would differ between the ACLR and contralateral limbs, primarily due to worsening contralateral limb function. Our secondary aim was to compare functional performance at 1- and 5-years post-ACLR with uninjured healthy controls. We hypothesised functional performance in those following ACLR at both time points would be significantly lower than uninjured healthy controls.