Subjective Causes for Failure to Return to Sport After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis.

CONTEXT: While current literature has explored the outcomes of athletes who return to sport (RTS) after anterior cruciate ligament (ACL) injuries, less is known about the outcomes of those who are unsuccessful in returning to sport. OBJECTIVE: To determine the rate of athletes who did not RTS after primary ACL reconstruction (ACLR) and to identify the specific subjective reasons for failure to RTS. DATA SOURCES: A comprehensive search of the PubMed/MEDLINE, Scopus, and Web of Science databases was conducted through April 2021. STUDY SELECTION: Eligible studies included those explicitly reporting the rate of failure for RTS after ACLR as well as providing details on reasons for athletes' inability to return; 31 studies met the inclusion criteria. STUDY DESIGN: Systematic review and meta-analysis. LEVEL OF EVIDENCE: Level 2 to 4. DATA EXTRACTION: The reasons for failure to RTS referred to in our study are derived from those established previously in the studies included. Data were collected on the number of athletes, mean age, mean follow-up time, type of sport played, failure to RTS rate, and specific reasons for failure to return. RESULTS: The weighted rate of failure to RTS after ACLR was 25.5% (95% CI, 19.88-31.66). The estimated proportion of psychosocial-related reasons cited for failure to RTS was significantly greater than knee-related reasons for failure RTS (55.4% vs 44.6%, P < 0.01). The most cited reason for failure to RTS was fear of reinjury (33.0%). CONCLUSION: This study estimates the rate of failure to RTS after ACLR to be 25.5%, with the majority of athletes citing fear of reinjury as the major deterrent for returning to sports. We highlight how factors independent of surgical outcomes may impact an athlete's ability to return to play given that the predominant reason for no RTS after ACLR was unrelated to the knee.

An analysis of time-varying dynamics in electrically sensitive arthropod hairs to understand real-world electrical sensing.

With increasing evidence of electroreception in terrestrial arthropods, an understanding of receptor level processes is vital to appreciating the capabilities and limits of this sense. Here, we examine the spatio-temporal sensitivity of mechanoreceptive filiform hairs in detecting electrical fields. We first present empirical data, highlighting the time-varying characteristics of biological electrical signals. After which, we explore how electrically sensitive hairs may respond to such stimuli. The main findings are: (i) oscillatory signals (elicited by wingbeats) influence the spatial sensitivity of hairs, unveiling an inextricable spatio-temporal link; (ii) wingbeat direction modulates spatial sensitivity; (iii) electrical wingbeats can be approximated by sinusoidally modulated DC signals; and (iv) for a moving point charge, maximum sensitivity occurs at a faster timescale than a hair's frequency-based tuning. Our results show that electro-mechanical sensory hairs may capture different spatio-temporal information, depending on an object's movement and wingbeat and in comparison with aero-acoustic stimuli. Crucially, we suggest that electrostatic and aero-acoustic signals may provide distinguishable channels of information for arthropods. Given the pervasiveness of electric fields in nature, our results suggest further study to understand electrostatics in the ecology of arthropods and to reveal unknown ecological relationships and novel interactions between species.

Passive electrolocation in terrestrial arthropods: Theoretical modelling of location detection.

The recent discovery that some terrestrial arthropods can detect, use, and learn from weak electrical fields adds a new dimension to our understanding of how organisms explore and interact with their environments. For bees and spiders, the filiform mechanosensory systems enable this novel sensory modality by carrying electric charge and deflecting in response to electrical fields. This mode of information acquisition opens avenues for previously unrealised sensory dynamics and capabilities. In this paper, we study one such potential: the possibility for an arthropod to locate electrically charged objects. We begin by illustrating how electrostatic interactions between hairs and surrounding electrical fields enable the process of location detection. After which we examine three scenarios: (1) the determination of the location and magnitude of multiple point charges through a single observation, (2) the learning of electrical and mechanical sensor properties and the characteristics of an electrical field through several observations, (3) the possibility that an observer can infer their location and orientation in a fixed and known electrical field (akin to "stellar navigation"). To conclude, we discuss the potential of electroreception to endow an animal with thus far unappreciated sensory capabilities, such as the mapping of electrical environments. Electroreception by terrestrial arthropods offers a renewed understanding of the sensory processes carried out by filiform hairs, adding to aero-acoustic sensing and opening up the possibility of new emergent collective dynamics and information acquisition by distributed hair sensors.

The mechanics and interactions of electrically sensitive mechanoreceptive hair arrays of arthropods.

Recent investigations highlight the possibility of electroreception within arthropods through charged mechanosensory hairs. This discovery raises questions about the influence of electrostatic interaction between hairs and surrounding electrical fields within this sensory modality. Here, we investigate these questions by studying electrostatic coupling in arrays of hairs. We establish the notion of sensitivity contours that indicate regions within which point charges deflect hairs beyond a given threshold. We then examine how the contour's shape and size and the overall hair behaviour change in response to variations in the coupling between hairs. This investigation unveils synergistic behaviours whereby the sensitivity of hairs is enhanced or inhibited by neighbouring hairs. The hair spacing and ratio of a system's electrical parameters to its mechanical parameters influence this behaviour. Our results indicate that electrostatic interaction between hairs leads to emergent sensory properties for biologically relevant parameter values. The analysis raises new questions around the impact of electrostatic interaction on the current understanding of sensory hair processes, such as acoustic sensing, unveiling new sensory capabilities within electroreception such as amplification of hair sensitivity and location detection of charges in the environment.

Analysis of aerodynamic and electrostatic sensing in mechanoreceptor arthropod hairs.

We study the mechanics of mechanoreceptor hairs in response to electro- and acousto-stimuli to expand the theory of tuning within filiform mechano-sensory systems and show the physical, biological and parametric feasibility of electroreception in comparison to aerodynamic sensing. We begin by analysing two well-known mechanosensory systems, the MeD1 spider trichobothria and the cricket cercal hair, offering a systematic appraisal of the physics of mechanosensory hair motion. Then we explore the biologically relevant parameter space of mechanoreceptor hairs by varying each oscillator parameter, thereby extending the theory to general arthropods. In doing so, we readily identify combinations of parameters for which a hair shows an enhanced or distinct response to either electric or aerodynamic stimuli. Overall, we find distinct behaviours in the two systems with novel insight provided through the parameter-space analysis. We show how the parameter space and balance of parameters therein of the resonant spider system are organised to produce a highly tuneable hair system through variation of hair length, whilst the broader parameter space of the non-resonant cricket system responds equally to a wider range of driving frequencies with increased capacity for high temporal resolution. From our analysis, we hypothesise the existence of two distinct types of mechanoreceptive system: the general system where hairs of all lengths are poised to detect both electro- and acousto- stimuli, and a stimuli-specific system where the sensitivity and specificity of the hairs to the different stimuli changes with length.