Aisthesis Volume 16, 202577 Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Require Increased Duration of Rehabilitation in Collegiate Athletes by Mallory L. Heinzerling & Estephania D. Nunez Introduction One in four athletes who have experienced an anterior cruciate ligament (ACL) injury will experience a second ACL rupture within the !rst year of returning to their sport.1 Furthermore, one in three athletes experience a general re-injury to the knee within the !rst two years following anterior cruciate ligament reconstruction.2 "is illustrates the importance of comprehensive and e#ective rehabilitation and return to sport progression following ACL reconstruction not only for injury prevention, but also for long term health of the athletes. Anterior cruciate ligament (ACL) injuries are prevalent among collegiate athletes and o$en require surgery and extensive rehabilitation. To our knowledge, no systematic review exists analyzing the relationship between the length of recovery time and reinjury rates attributed to neuromuscular de!cits in collegiate athletes who have undergone anterior cruciate ligament reconstruction (ACLR). Despite advancements in surgical techniques and rehabilitation, reinjury rates remain a large concern with a considerable number of these instances attributed to neuromuscular de!cits. "is paper aims to address the need for comprehensive rehabilitation a$er ACLR that speci!cally addresses neuromuscular speci!c rehabilitation. De!nitions In relation to this paper, the following terms will be used, and their de!nitions will be as follows. Neuromuscular de!cits are impairments to coordination, control, and communication between the nervous system and muscles. Neuromuscular rehabilitation consists of targeted exercises and interventions which assess neuromuscular de!cits that resulted from the initial anterior cruciate ligament injury. Neuromuscular reeducation is the retraining of the neuromuscular system to perform movement patterns correctly, as well as enhancing neuromuscular control and proprioception. "is term will be used synonymously with neuromuscular reconditioning and neuromuscular retraining. Neuromuscular control is the ability of the nervous system to coordinate muscle activity to produce coordinated movements of the body. Methods Studies were included that related to neuromuscular recovery and rehabilitation a$er anterior cruciate ligament repair. Only studies with a publication date between 2019 and 2024 were considered. Some studies were found through the “cited in” tool in older articles, to maintain the publication time criteria. Eight articles were found that matched criteria for the search. "e search terms used were “neuromuscular,” “anterior cruciate ligament,” “reconstruction,” “neuromuscular de!cit,” “anterior cruciate ligament reconstruction,” “athletes,” and “collegiate athletes.” Results In total, sixteen studies were analyzed for synthesis in this systematic review. Two of these studies were systematic reviews of the literature on neuromuscular control and the risk of ACL reinjury in return to sport. Eight of these studies addressed recommendations for comprehensive rehabilitation and return to sport criteria. Six of these studies were experimental and analyzed with the STROBE scale criteria. All studies passed the STROBE scale criteria (see Table 1 in Appendix). Comprehensive Rehabilitation "e need for comprehensive rehabilitation that addresses all impairments following anterior cruciate ligament reconstruction is a main focus of the current literature. Rehabilitation should begin as soon as possible a$er ACLR surgery, particularly on the non-injured leg to reduce loss of muscle Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Aisthesis Volume 16, 202578 strength. "irty percent or more athletes sustain an injury within the !rst two years of returning to sport; comprehensive rehabilitation is necessary to address this issue.3 A variety of exercises must be components of the rehabilitation protocol, including strength training, plyometrics, neuromuscular training, and cardiovascular conditioning. Furthermore, quadriceps muscle strength de!cits are a larger problem within ACLR patients that needs to be addressed in all stages of rehabilitation to adequately restore the strength.4-7 Even with the current rehabilitation protocol, strength de!cits throughout the leg can be seen up to !ve years following injury.8 When quadriceps strength is not adequately restored during rehabilitation, athletes are at a much greater risk of reinjury. "is is a major issue that needs to be addressed and investigated to prevent long-term chances of reinjury in athletes. An example of the current protocol from Sanford Health can be seen in Table 29 (See Appendix). Return to Sport Following the early, mid, and late stage of rehabilitation, athletes will progress towards clearance to return to sport, which is the !nal stage of comprehensive anterior cruciate ligament rehabilitation. However, 35-40 percent of athletes that elect to have anterior cruciate ligament reconstruction do not return to sport a$er their injury, with 20-25 percent of athletes being completely unable to due to residual pains and injuries.3 "e return to sport progression is recommended to begin with on-!eld rehabilitation, then progress into return-to-team training, and !nally return to competition.3 "ere are milestones within each of these progressions that should be met before advancing onto the next stage in order to lower risk of reinjury. Only one study was found proposing a !ve stage return to sport rehabilitation program that focuses on addressing “impairments associated with neuromuscular performance, movement quality, and sport speci!c performance” to fully prepare athletes for return to sport and subsequent competition. It is essential for athletes to meet all return to sport criteria before they return to competition, as they are 25 percent more likely to sustain a reinjury to the ACL if they fail to achieve this criteria.3 "is criteria should include assessments of single leg drop biomechanics, rate of force development, single limb stability, isolated strength techniques, torque through full range of motion in the knee, interlimb symmetry, and other various assessments that assist in the decision of return to sport.1,3,6-7,10-11 Additionally, this criteria should include restoring change of direction ability, bilateral de!cits in proprioception that lead to longer time to stabilization, the addition of cognitive demands into tasks, lower limb performance in multiple directions, capacity to cope with demands of the sport both physically and mentally, and further neuromuscular control.2-4,11-12 Meeting the milestones previously described is essential for an athlete's recovery and improving the chances of returning to sport without reinjury. Another study suggests a di#erent !ve stage return to sport progression including “resumption of noncontact practice, followed by small sided contact practices, full unrestricted practice, return to competition at a restricted workload, and last, return to competition unrestricted.”5 However, this protocol can be hard to implement without adequate support from healthcare professionals, such as physicians and athletic trainers. "e return to sport progression in this study is a longer progression than the previous study, but it progresses the athlete in smaller, more speci!c steps to help reduce the risk of reinjury upon full return to competition. While there are multiple suggestions for return to sport progression, it remains the most important part of rehabilitation, regardless of the di#erent progressions. "ere needs to be athlete supervision from a healthcare worker to decide on the progressions through return to sport, which is not addressed in the current protocol. Neuromuscular Reeducation A two-year recovery period is optimal for neuromuscular re-education to provide adequate time to address the de!cits lost following injury and surgical intervention. As of now, the recommended rehabilitation and return to sport timeline is 9-12 months to allow for gra$ healing.5 However, this timeline does not allow for su%cient neuromuscular retraining to address the persistent neuromuscular control de!cits a$er ACLR. Athletes are at the greatest risk of reinjury within the !rst two years, mainly due to the persistence of these de!cits.5 "e addition of a neuromuscular training program into rehabilitation Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Aisthesis Volume 16, 202579 shows a reduction in de!cits in knee biomechanics which is associated with a lower risk of reinjury to the ACL.10 "is neuromuscular training can restore adequate muscle function and performance. "ere are multiple areas of neuromuscular de!cits that need to be reeducated throughout rehabilitation. Explosive neuromuscular power (strength and power training) and lower limb performance should be tested and addressed in late stage rehabilitation, a$er the athlete has met the criteria of 80-90 percent limb symmetry.2-3 Gait alterations stemming from neuromuscular dysfunction are considered to be a part of the neuromuscular issues resulting from ACLR, and need to be addressed in neuromuscular retraining.2,4 In order for rehabilitation to be comprehensive, it needs to include tasks for restoration of neuromuscular control and performance.2 To adequately reeducate the neuromuscular processes of the body, neuromuscular control de!cits need to be addressed throughout the stages of rehabilitation, and following return to sport. A suggestion for an adequate rehabilitation timeline is presented and compared to the current protocol in Table 39 (See Appendix). Neuromuscular Rehabilitation Neuromuscular rehabilitation needs to be implemented throughout the stages of rehabilitation to accurately prepare an athlete for return to sport. Internal stimuli demands and kinesiophobia need to be considered on an individual basis throughout rehabilitation, so they cannot be generalized into protocol. However, ACL injuries occur most frequently when external stimuli are present in the situation that causes the athlete to fail to maintain neuromuscular control.3 When these cognitive demands and external stimuli are added, athletes have a much greater risk of reinjuring their ACL. "is risk increases substantially due to insu%cient recovery of neuromuscular control during rehabilitation.4,11 Additionally, rehabilitation of sensorimotor control (nerve actions involving both sensory and motor pathways) is essential for movement control during on-!eld practices and play.3 Return to sport clearance should not occur until sensorimotor control is reestablished in the body. Furthermore, the current criteria for neuromuscular rehabilitation does not extend past return to sport. Neuromuscular testing needs to be continually addressed, even a$er the athlete has completed comprehensive rehabilitation and subsequent return to sport to ensure the athlete has retained the bene!cial e#ects of neuromuscular rehabilitation.5-6,10 "e length of time that neuromuscular testing needs to be continually addressed is unknown and is a necessary area for future research. Without this continuation of neuromuscular control testing, athletes become more susceptible to reinjury of the knee joint within the !rst few years of returning to sport and in the long term. Proprioception and Biomechanics Proprioception allows the body to sense its movement and location in the environment, illustrating its importance in neuromuscular training. When athletes fail to restore the changes in their proprioception, knee de!cits persist a$er returning to sport, and the athlete becomes 30- 40% more likely to sustain a subsequent ACL injury.10 "ese subsequent injuries are largely due to the disruptions within the a#erent impulses and mechanoreceptor in the ACLR leg that reorganize the central nervous system processes involved in controlling and stabilizing the knee joint, and the proprioceptive impairments in the sagittal and transverse planes.1,4,6,11-13 Cutting and change of direction athletes work in these planes, illustrating the need for its consideration in neuromuscular rehabilitation. Neuromuscular rehabilitation needs to include restoration of these impairments and control before the athlete returns to sport. Altered biomechanics a$er anterior cruciate ligament injury and subsequent reconstruction are a large focus of rehabilitation. "e retraining of bodily movements is an essential milestone in neuromuscular rehabilitation to address impairments throughout the kinetic chain. It is important to include practice for relearning various movement coordinations during function tasks in rehabilitation to address the “biomechanical and neuromuscular control de!cits” that persist.1-3,6,13 "ese biomechanical di#erences can be seen in both the injured and uninjured limb following ACLR.13 With this information, it becomes necessary to address altered biomechanics in early stages of rehabilitation to prevent persistent de!cits along the entirety of the kinetic chain that may lead to reinjury. Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Aisthesis Volume 16, 202580 Limitations "is study is the !rst, to our knowledge, that analyzes the relationship between the length of recovery time and reinjury rates attributed to neuromuscular de!cits in collegiate athletes who have undergone anterior cruciate ligament reconstruction. Additionally, many of the studies cited in this review are the !rst study of their topic in the sports medicine literature. "is review and many of the included studies do not take gender, gra$ type, or fatigue into consideration with neuromuscular de!cits and their persistence a$er returning to sport. Future research is needed to address disparities in the reinjury rates related to these factors, including the length of time that neuromuscular testing should continue a$er athletes return to sport. Furthermore, limitations exist in the research on kinesiophobia in athletes a$er returning to sport. Athletes not being mentally ready for returning to the demands of their sport can increase their risk of reinjury. Conclusion Understanding the implications of recovery duration on neuromuscular rehabilitation and reinjury rates is crucial for sports medicine professionals, coaches, and athletes. It is important for developing appropriate rehabilitation strategies and injury prevention protocols for collegiate athletes that have undergone ACLR that address neuromuscular de!cits comprehensively, not only for return to sport, but for lifelong function. "e alarming statistics in terms of reinjury rates among athletes highlights the need for e#ective strategies in restoring neuromuscular de!cits before returning athletes to sport. Continual assessment of neuromuscular function beyond return to sport is also essential to address persistent de!cits and their chances of increasing reinjury risk. Future research is needed to address why the current return to sport testing is failing to restore the variables of the criteria, underlying alterations in biomechanics, and further issues that persist a$er ACLR that place athletes at an increased risk of reinjury.3-4,11 References 1. Lanier AS, Knarr BA, Stergiou N, Snyder-Mackler L, Buchanan TS. ACL injury and reconstruction a#ect control of ground reaction forces produced during a novel task that simulates cutting movements. Journal of Orthopaedic Research. 2020;38(8):1746-1752. doi:10.1002/jor.24604 2. Buckthorpe M, Della Villa F. Recommendations for Plyometric Training a$er ACL Reconstruction - A Clinical Commentary. Int J Sports Phys "er. 2021;16(3):879-895. Published 2021 Jun 1. doi:10.26603/001c.23549 3. Buckthorpe M. Optimising the late-stage rehabilitation and return-to-sport training and testing process a$er ACL reconstruction. Sports Medicine. 2019;49(7):1043-1058. doi:10.1007/ s40279-019-01102-z 4. Chou T-Y, Huang Y-L, Leung W, Brown CN, Kaminski TW, Norcross MF. Does prior concussion lead to biomechanical alterations associated with lateral ankle sprain and anterior cruciate ligament injury? A systematic review and meta-analysis. British Journal of Sports Medicine. 2023;57(23):1509-1515. doi:10.1136/ bjsports-2023-106980 5. Brinlee AW, Dickenson SB, Hunter-Giordano A, Snyder-Mackler L. ACL reconstruction rehabilitation: Clinical Data, biologic healing, and criterion-based milestones to inform a return-to-sport guideline. Sports Health: A Multidisciplinary Approach. 2021;14(5):770-779. doi:10.1177/19417381211056873 6. Buckthorpe M, La Rosa G, Villa FD. Restoring knee extensor strength a$er anterior cruciate ligament reconstruction: A clinical commentary. Int J Sports Phys "er. 2019;14(1):159-172. 7. Hart LM, Izri E, King E, Daniels KA. Angle-speci!c analysis of knee strength de!cits a$er ACL reconstruction with patellar and hamstring tendon autogra$s. Scandinavian Journal of Medicine & Science in Sports. 2022;32(12):1781- 1790. doi:10.1111/sms.14229 Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Aisthesis Volume 16, 202581 8. Bagley MC, Harper SA, McDaniel J, Custer L. Single leg aerobic capacity and strength in individuals with surgically repaired anterior cruciate ligaments. Phys "er Sport. 2020;46:131-136. doi:10.1016/j.ptsp.2020.08.013 9. ACL reconstruction. Accessed March 21, 2024. https://www.sanfordhealth.org/-/media/ org/ files/medical-professionals/resources-and- education/acl-reconstruction-guideline.pdf. 10. Nagelli CV, Di Stasi S, Wordeman SC, et al. Knee Biomechanical De!cits During a Single- Leg Landing Task Are Addressed With Neuromuscular Training in Anterior Cruciate Ligament-Reconstructed Athletes. Clin J Sport Med. 2021;31(6):e347-e353. doi:10.1097/ JSM.0000000000000792 11. Blasimann A, Koenig I, Baert I, Baur H, Vissers D. Which assessments are used to analyze neuromuscular control by electromyography a$er an anterior cruciate ligament injury to determine readiness to return to sports? A systematic review. BMC Sports Science, Medicine and Rehabilitation. 2021;13(1). doi:10.1186/ s13102-021-00370-5 12. Calisti M, Mohr M, Federolf P. Bilateral De!cits in Dynamic Postural Stability in Females Persist Years a$er Unilateral ACL Injury and Are Modulated by the Match between Injury Side and Leg Dominance. Brain Sci. 2023;13(12):1721. Published 2023 Dec 16. doi:10.3390/ brainsci13121721 13. Alanazi AD, Mitchell K, Roddey T, et al. "e e#ects of a high-intensity exercise bout on landing biomechanics post anterior cruciate ligament reconstruction: a quasi-experimental study. BMC Sports Sci Med Rehabil. 2021;13(1):36. Published 2021 Apr 7. doi:10.1186/s13102-021- 00263-7 Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Aisthesis Volume 16, 202582 Appendix Neuromuscular De!cits Following Anterior Cruciate Ligament Reconstruction Aisthesis Volume 16, 202583