Recovery of Hip Muscle Strength After ACL Injury 12 and Reconstruction: Implications for Reducing the Risk of Reinjury Sanjeev Bhatia, Jorge Chahla, Mark E. Cinque, and Michael B. Ellman Abstract 12.1 Introduction Recovery of lower extremity muscular strength and neuromuscular control are two An anterior cruciate ligament (ACL) injury can of the most vital aspects of anterior cruciate be a debilitating entity, not only due to the lack of ligament (ACL) rehabilitation, as well as reestablishment of normal knee biomechanics in efforts to prevent noncontact ACL injury. some cases, but also because of the muscular There is strong evidence regarding the asso- imbalance produced after ligament reconstruc- ciation between decreased hip range of tion. A staged and customized muscle rehabilita- motion, particularly internal and external tion program can be tailored to allow the patient rotation, and noncontact ACL injury. Given to return to their activities in a timely fashion and that females are at greater risk for ACL injury diminish the risks of an ACL reinjury. compared with males, increased emphasis Identification of muscular deficits after an has been placed on identifying risk factors in ACL injury is vital to prevent further injuries. In the hip as well as throughout the kinetic this regard, Petersen et al. [1] reported in a recent chain for this injury. In this chapter, we dis- systematic review of 45 articles that all studies cuss the relationship between hip and knee identified strength deficits after ACL reconstruc- injury patterns and its implications for ACL tion compared with control subjects. Of note, reconstruction and rehabilitation and non- some of these deficits persisted up to 5 years after contact ACL injury prevention efforts. surgery depending on the rehabilitation protocol instituted. Knee flexion strength was more impaired with hamstring grafts and quadriceps S. Bhatia (*) Hip Arthroscopy and Joint Preservation Center, strength was more impaired after bone–patellar Cincinnati Sports Medicine and Orthopaedic Center, tendon–bone ACL reconstruction. These authors Mercy Health, Cincinnati, OH, USA suggested that muscular strength testing is impor- J. Chahla tant to determine if an athlete can return to com- Steadman-Philippon Research Institute, petitive sports after an ACL reconstruction. Vail, CO, USA Female athletes are a specific population at e-mail: [email protected] increased risk for both primary and secondary ACL M. E. Cinque injuries. Prodromos et al. conducted a meta-analy- Stanford School of Medicine, Stanford University, Stanford, CA, USA sis of 33 articles and reported that the mean ACL injury rate for females was significantly greater M. B. Ellman Hip Arthroscopy and Joint Preservation, Panorama than males in basketball, (0.28 and 0.08 per 1000 Orthopedics & Spine Center, Denver, CO, USA exposures, respectively, P < 0.0001), soccer (0.32 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 225 F. R. Noyes, S. Barber-Westin (eds.), ACL Injuries in the Female Athlete, https://doi.org/10.1007/978-3-662-56558-2_12 226 S. Bhatia et al. and 0.12 per 1000 exposures, respectively, chological and inherent anatomical factors [3], lim- P < 0.0001), and handball (0.56 and 0.11 per 1000 ited evidence exists regarding the relationship exposures, respectively, P < 0.0001) [2]. Such between the range of motion of the hip (which acts injury rates have resulted in a growing body of lit- as a “buffer” in forced rotation of the knee) in erature focused on the treatment of these injuries in patients with an ACL injury. In this regard, available addition to identifying risk factors and prevention literature suggests an association between decreased programs [3]. Several studies have reported a hip motion in patients with ACL injuries, predomi- reduction in the number of ACL tears after implant- nantly with decreased internal rotation of the hip. ing a preseason neuromuscular training program This suggests that an ACL injury may not only have [3–5]. Furthermore, studies have reported altered an intrinsic knee etiology but can also be related to landing biomechanics in female athletes before and an adjacent joint-based problem [14–17]. after ACL injury. The observed abnormal knee Tainaka et al. [18] reported the possibility of an kinematics are associated with abnormal hip association between noncontact ACL injuries in strength and movements [6]. Because of this, high school athletes and hip range of motion. These increased attention has been directed toward identi- investigators found that the incidence of ACL injury fying the optimal balance of hip and knee motion in increased as hip internal rotation (IR) or external the female athlete, with the aim of preventing or rotation (ER) decreased. However, the odds ratios reducing the rate of female ACL injuries. were small and no other potential risk factors were For the abovementioned reasons, the purpose of included in the analysis. As previously reported, a this chapter is to describe important facts regarding restricted IR of the hip is in most cases associated the recovery of muscle strength after ACL recon- with abnormal proximal femoral or acetabular anat- structions in female athletes and to outline the cur- omy [19] and has been correlated with ACL rup- rent interventions to diminish the risk of ACL tures and reruptures in soccer players [20, 21] and in reinjury. Combined lower limb biomechanics, patho- professional American football athletes [22]. genesis, and prevention strategies will be presented. Both femoral (decreased femoral head–neck offset or increased alpha angle) and acetabular (decreased center-edge angle [CEA]) bone defor- 12.2 Interaction Between Altered mities can place the ACL at risk [15, 23]. Hip Mechanics and Knee Yamazaki et al. [23] reported that the CEA of the Injury Patterns ACL-injured patients group was significantly smaller than that of a control group, suggesting In the United States, approximately 200,000 ACL that ACL-injured patients may have a higher injuries per year are reported, resulting in an prevalence of acetabular dysplasia. Philippon expense of billions of dollars for the health system et al. [15] reported that patients with a decreased [7]. Importantly, one of the most common causes femoral head–neck offset (alpha angle >60°) of osteoarthritis (OA), but often overlooked, is the were at increased risk of having an ACL injury development of post-traumatic osteoarthritis after because of altered lower limb biomechanics. This ACL tears in the young and active population [8, increased risk was evident in both males and 9]. For these reasons, prevention and identification females, with a slight predominance in males. of risk factors for ACL tears are key to prevent the The ACL injury cohort had a mean alpha angle of cascade of joint degenerative process. Importantly, 86° and 79° in males and females, respectively, female athletes are at an increased risk of injury. the values of which are markedly higher than pre- Potential explanations for this include increased viously reported limits of normal alpha angles. knee valgus or abduction moments, generalized Beaulieu et al. [24] performed a simulated joint laxity [10], genu recurvatum [11], a compara- single-leg pivot landing study to assess the peak tively smaller ACL [12], and the hormonal effects relative strain of the anteromedial bundle of the of estrogen on the ACL [13]. ACL in relation to the available range of internal Although many risk factors have been identified femoral rotation. In their statistical model, peak such as age, sex, anthropometric measures, and psy- ACL relative strain increased by 1.3% with every 12 Recovery of Hip Muscle Strength After ACL Injury and Reconstruction 227 10° decrease in femoral rotation. From this con- begin these strength training protocols around cept, these authors suggested that an athlete pre- age 13, when their body mass grows dispropor- senting with femoral acetabular impingement tionally to their hip abduction strength. (FAI) with a 10° deficiency in internal femoral rotation would experience 20% more peak ACL Critical Points strain during landing than a healthy athlete. Importantly, patients with abnormally elevated • Potential association between decreased hip alpha angles may have diminished capacity at the range of motion (especially decreased internal hip to accommodate overall lower extremity rotation) and ACL injury. internal rotation moments, potentially predispos- • Femoral and acetabular bone deformities may ing the knee (and other intra-articular structures) increase risk of ACL injury. to a greater rotational stress. In this regard, Girard – Decreased femoral head–neck offset et al. [25] suggested that improving the femoral – Increased alpha angle head–neck offset could result in an improved – Decreased center-edge angle range of motion in the hip, specifically in flexion, – Femoral acetabular impingement thereby allowing knee forces to be normalized. • Athletes with greater hip abduction strength may Given that females are at greater risk for ACL be less likely to sustain lower extremity injury. injury, increased emphasis has been placed on – Young female athletes should perform hip identifying risk factors throughout the kinetic abduction strengthening exercises begin- chain for ACL injuries in female patients. In this ning around age 13. regard, Imwalle et al. [26] studied lower extrem- ity kinematics during 45° and 90° cutting move- ments and examined the amount of hip and knee 12.3 Femoral Acetabular internal rotation during each movement. Mean Impingement (FAI) and ACL hip and knee internal rotation, in addition to hip Injury flexion, were greater during the 90° cutting motion in female athletes. These authors con- As previously discussed, altered hip kinematics cluded that increased knee abduction in female secondary to pathologic conditions such as FAI athletes was secondary to abnormal coronal plane may increase a patient’s susceptibility to ACL motion of the hip. They proposed that neuromus- injury. FAI is a well-known hip condition caused cular training of the trunk and hips may be able to by alterations in the bony anatomy of the hip.