Athletes who have sustained an anterior cruciate ligament (ACL) injury often opt for an ACL reconstruction (ACLR) with the goal and expectation to resume sports. Unfortunately, the proportion of athletes successfully returning to sport is relatively low, while the rate of second ACL injury has been reported to exceed 20% after clearance to return to sport, especially within younger athletic populations. Despite the development of return-to-sport guidelines over recent years, there are still more questions than answers on the most optimal return-to-sport criteria after ACLR. The primary purpose of this review was to provide a critical appraisal of the current return-to-sport criteria and decision-making processes after ACLR. Traditional return-to-sport criteria mainly focus on time after injury and impairments of the injured knee joint. The return-to-sport decision making is only made at the hypothetical 'end' of the rehabilitation. We propose an optimized criterion-based multifactorial return-to-sport approach based on shared decision making within a broad biopsychosocial framework. A wide spectrum of sensorimotor and biomechanical outcomes should be assessed comprehensively, while the interactions of an individual athlete with the tasks being performed and the environment in which the tasks are executed are taken into account. A layered approach within a smooth continuum with repeated athletic evaluations throughout rehabilitation followed by a gradual periodized reintegration into sport with adequate follow-up may help to guide an individual athlete toward a successful return to sport.

Background Running is a popular form of physical activity with many health benefits. However, the incidence and prevalence of running-related injuries (RRIs) is high. Biomechanical factors may be related to the development of RRIs. Objective This systematic review synthesizes biomechanical risk factors related to the development of RRIs in non-injured runners. Methods PubMed, Web of Science, CINAHL, Embase, and SPORTDiscus were searched in July 2018 for original peerreviewed prospective studies evaluating potential biomechanical factors associated with the development of RRIs. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Two reviewers independently assessed articles for inclusion and methodological quality. Due to methodological heterogeneity across studies, a narrative synthesis of findings was conducted, rather than a meta-analysis. Results Sixteen studies, including 13 of high quality and three of moderate quality, were included. A large number of biomechanical variables were evaluated, producing inconsistent evidence overall. Limited evidence indicated greater peak hip adduction in female runners developing patellofemoral pain and iliotibial band syndrome, but not for a mixed-sex population of crosscountry runners sustaining an RRI. The relationship between vertical loading rate and RRIs was inconsistent. Other kinematic, kinetic and spatiotemporal factors were only studied to a limited extent. Conclusions Current prospective evidence relating biomechanical variables to RRI risk is sparse and inconsistent, with findings largely dependent on the population and injuries being studied. Future research is needed to confirm these biomechanical risk factors and determine whether modification of these variables may assist in running injury prevention and management. Key Points Despite the common belief that biomechanical factors greatly influence running-related injury (RRI) risk, only a limited body of high-quality research, with significant heterogeneity in study populations, methodologies and outcome variables, was identified. Current prospective evidence relating biomechanical variables with the risk to sustain an RRI is inconsistent and largely dependent on the population and injuries being studied. A number of single-study findings related to kinematics, kinetics and spatiotemporal variables require confirmation via further high-quality prospective studies before clinical recommendations can be made.

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