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Limb Symmetry Indexes Can Overestimate Knee Function After ACL Injury

Wellsandt, E., Failla, M.J. and Snyder-Mackler, L., 2017. Limb symmetry indexes can overestimate knee function after anterior cruciate ligament injury. Journal of Orthopaedic & Sports Physical Therapy, 47(5), pp.334-338.

In today’s letter

• Overview of limb symmetry index & it’s effectiveness

• Rapid Results = 85% to 90% limb symmetry index is not enough to clear athletes to sports

• 3 Reads to check out to further you knowledge about ACL testing

• Meme of the week: Have you forgotten your notes? 😬 

Aim of study

The purpose of this study was to evaluate the uninvolved limb as a reference standard for symmetry indexes used in return-to-sport testing and its relationship with second ACL injury rates

Did you know?

• ACL injury frequently results in muscle weakness, poor knee function, and increased risk for second injury despite surgical reconstruction

• Second ACL injury rates reach up to 49% suggesting that the current criteria used to determine an athlete’s readiness to return-to-sport is ineffective.

• There is a need for evidence-based guidelines to define optimal levels of knee function that minimise the risk of a 2nd ACL injury.

• Return-to-sport criteria commonly rely on assessments of quadriceps strength and single-legged hop tests, comparing limb-to-limb differences using limb symmetry indexes (LSIs).

• LSIs typically reference measures from the unaffected limb as a benchmark for comparison.

• However, studies have shown both side muscle strength deficits following ACL injury, giving doubt on the validity of symmetry measures in assessing readiness for return to sports.

Results

• The study involved 70 patients, with an average age of 26.6 years and a BMI of 24.9 kg

• 32.9% were women.

• Initial assessments included quadriceps strength testing and single-legged hop tests conducted approximately 1.5 and 1.9 months post-ACL injury.

• ACL reconstruction surgery took place around 4.4 months after injury, with 28 patients receiving hamstring gracilis autografts and 42 receiving soft tissue allografts.

• Among the patients, 57.1% achieved 90% limb symmetry indexes (LSIs) for quadriceps strength and all single-legged hop tests.

• Only 28.6% of patients met 90% estimated pre-injury capacity (EPIC) levels for quadriceps strength and hop tests.

• Of those who achieved 90% LSIs for all measures post-ACLR, 34.4% did not reach 90% EPIC levels.

• When LSIs and EPIC levels were not reached, mean quadriceps strength and hop scores were below the 90% cut-off values by 5.1%-14.6%.

• 11 patients experienced a 2nd ACL injury, with the time from ACLR to the second injury ranging from 27 to 276 weeks; eight of these patients passed the 90% LSI return-to-sport criteria, but six did not achieve 90% EPIC levels in these measures

Discussion

• This study aimed to assess the role of the uninvolved limb as a reference standard for symmetry indexes in return-to-sport testing and its correlation with second ACL injury rates.

• Findings show that achieving limb symmetry in quadriceps strength and single-legged hop tests post-ACLR does not necessarily indicate restoration of pre-injury functional levels.

• Initial data suggests that using 90% estimated pre-injury capacity (EPIC) levels may be more effective than 90% limb symmetry indexes (LSIs) in predicting second ACL injuries.

• The lower number of patients meeting 90% EPIC levels compared to LSIs may be due to current rehabilitation practices focusing on one sided strengthening and neuromuscular training.

• Decreased physical activity levels post-injury may lead to compensatory adaptations, which including reduced muscle strength in the uninvolved limb.

  Deterioration of function in the uninvolved limb over time can inflate limb symmetry indexes and misrepresent the functional ability of the ACL-injured limb.

• Among patients with second ACL injuries, 8 passed 90% LSI return-to-sport criteria, but 6 of these did not meet 90% EPIC levels in all measures.

• The small sample size of patients with second ACL injuries in this study requires further investigation with a larger cohort to validate these findings.

• Limited research has explored alternative measurements to LSIs for assessing post-ACLR limb function.

• Pre-season functional testing of athletes could offer valuable insights for setting patient-specific rehabilitation goals after ACL injury.

• However, widespread implementation of pre-injury testing in various settings may be impractical due to resource constraints.

• Incorporating pre-operative rehabilitation presents an opportunity for baseline assessment of uninvolved limb function, helping in later comparison during return-to-sport testing.

• Despite evidence supporting stringent return-to-sport criteria, current practice often permits lower symmetry levels or lacks objective criteria altogether.

Top 3 reads

1. Overcoming jumping deficits

   https://www.sportsmith.co/articles/overcoming-common-vertical-jump-deficits-in-post-aclr-rehab/

2. Risk factors for graft re rupture

   https://sportsmedu.com/2024/02/07/graft-rupture-risk-factors-after-acl-reconstruction/

3. NOT meeting 6 clinical discharge criteria

   https://bjsm.bmj.com/content/bjsports/50/15/946.full.pdf

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