Infographic. Questioning the rules of engagement: a critical analysis of the use of limb symmetry index for safe return to sport after anterior cruciate ligament reconstruction

Introduction

For clinicians to return athletes safely to sport, that is, with minimal risk for second anterior cruciate ligament (ACL) injury, a series of muscle function tests are typically administered prior to clearance for return to sport (RTS). Muscle function tests can include muscle strength for knee extension and flexion and hop performance, all important in sports participation.1 Results from muscle function tests are commonly presented as limb symmetry index (LSI), that is, the ratio of results between injured and uninjured limbs expressed as a percentage of symmetry. The recommended cut-off is LSI ≥90% across a battery of tests before an athlete is determined ‘ready’ for RTS.2 To date, it is unclear if LSI cut-offs can differentiate between athletes who have a safe RTS and athletes who do not. The LSI cut-offs have been accepted through consensus statements3 4 and expert opinions