Clinical Scenario: Anterior cruciate ligament (ACL) injuries are associated with a lengthy recovery time, decreased performance, and an increased rate of reinjury. To improve performance of the injured knee, affected athletes often undergo surgical reconstruction and rehabilitation. Determining when an athlete is ready to safely return to play (RTP), however, can be challenging for clinicians. Although various outcome measures have been recommended, their ability to predict a safe RTP is questionable. Focused Clinical Question: Which outcome measures should be used to determine readiness to return to play after ACL reconstruction?Keywords: anterior cruciate ligament, knee surgery, rehabilitation CritiCally appraised topiCs Clinical ScenarioAnterior cruciate ligament (ACL) injuries are associated with a lengthy recovery time, decreased performance, and an increased rate of reinjury. To improve performance of the injured knee, affected athletes often undergo surgical reconstruction and rehabilitation. Determining when an athlete is ready to safely return to play (RTP), however, can be challenging for clinicians. Although various outcome measures have been recommended, their ability to predict a safe RTP is questionable. Focused Clinical QuestionWhich outcome measures should be used to determine readiness to return to play after ACL reconstruction?Summary of Search, "Best Evidence" Appraised, and Key Findings• The literature was searched for studies pertaining to the rate of reinjury after ACL reconstruction (ACLR) that included criteria used to determine RTP. • The search yielded 5 randomized controlled trials (RCTs) with data regarding reinjury rate and RTP criteria; however, none of these trials directly compared different RTP criteria.• The 5 reviewed studies suggest that multiple factors merit consideration in determining readiness to RTP, including postoperative healing time, the extent of effusion or pain, joint range of motion (ROM), and the magnitude of limb symmetry with single-leg-hop and/or isokinetic muscle testing.• An objective test and specific RTP criteria after ACLR that adequately predict a low risk of reinjury are yet to be determined. Clinical Bottom LineCurrently it is unknown if any tests or measures can accurately identify individuals at low risk of reinjury after ACLR. Authors of the reviewed studies used the following criteria to help determine readiness to RTP after ACLR: at least 6 months of rehabilitation, absence of knee effusion and pain, full knee active and passive ROM, ≥90% bilateral symmetry with single-leg hop, and quadriceps strength of 85% to 90% of the contralateral limb with isokinetic muscle testing. Until more definitive data are available regarding optimal tests for determining readiness to RTP after ACLR, the use of a battery of tests and measures to screen for residual deficits seems reasonable. Strength of Recommendation:The RTP criteria here were gleaned from RCTs that indirectly addressed the clinical question. Although these studies were high quality (level 1), the s...