Physical Therapy Report

Spring 2014

Neuromuscular Training a Key Component Before and After ACL Injury

Anterior cruciate ligament (ACL) rupture is one of the most physically, financially and emotionally devastating sport-related knee injuries. While surgical intervention is a common treatment, a successful return to the previous level of activity following ACL reconstruction is not a certainty. Furthermore, the occurrence of a second ACL injury may be as high as 30%.


Deficits in the neuromuscular control of both lower extremities following ACL reconstruction have been directly implicated in the risk for a second ACL injury and may not only be a result of the initial knee injury and subsequent surgery, but also characterize the athlete’s preinjury movement patterns. Di Stasi et al from The Ohio State University authored a clinical review on the role neuromuscular training plays in this patient population.


Female athletes are several times more likely to sustain an ACL tear than are male athletes. The authors listed neuromuscular deficits that are preinjury risk factors in female athletes, including

  • quadriceps strength deficits
  • altered peak knee and hip flexion angles
  • larger ground reaction forces
  • increased knee and hip frontal plane motion

Postinjury neuromuscular deficits following ACL injury include

  • knee effusion
  • limited joint range of motionreduced quadriceps strength

The majority of patients with these conditions will undergo ligament reconstruction surgery to avoid recurrent instability and significant limitations in function.


The authors recommended postsurgical rehabilitation to address muscle weakness, abnormal neuromuscular control and impaired joint motion. They also stressed the need for comprehensive return-to-sport criteria because motion and force asymmetries can be apparent up to 4 years after surgery. The risk of a second ACL injury is high, with continued deficits in neuromotor control—especially if the athlete wishes to return to higher levels of activity that involve cutting, pivoting and jumping.


To document progress toward function and to evaluate return-to-sport readiness, the authors stressed the importance of using a battery of clinical tests and measures, including objective measures of strength, dynamic knee function and self-reported measures of knee function, at many points throughout the later phase of rehabilitation. They suggested the drop-vertical jump test and tuck jump because the tests assess joint motion and predict external knee abduction loads. Their proposed intervention to prevent second ACL injury was based on 3 criteria:


  • activation potential of the muscles hypothesized to be deficient at the time of return to sport
  • utilization of surfaces and movements that elicit muscle coactivation capable of modifying mechanics theorized to be related to injury risk
  • movements that may replicate conditions experienced during sport


While a second ACL injury in highly active individuals may be predicated on a number of modifiable and nonmodifiable factors, targeted neuromuscular interventions have great potential to address the modifiable postsurgical risk factors. The authors recommended that future research validate their evidence-based, late-phase rehabilitation program to reach the goal of maximizing return-to-activity success and reduction of second-injury risk in highly active individuals.


Di Stasi S, Myer GD, Hewett TE. Neuromuscular training to target deficits associated with second anterior cruciate ligament injury. J Orthop Sports Phys Ther 2013;43:777-792.



Risk Factors in Posterior Shoulder Instability


Although not as common as anterior instability, posterior shoulder (glenohumeral) instability is becoming more frequent among young athletes. A common mechanism of this injury is a fall onto an outstretched hand, but the risk factors are not well understood. To develop primary prevention strategies for shoulder instability in athletes, Owens et al from the United States Military Academy, New York, sought to identify the modifiable and nonmodifiable risk factors for posterior shoulder instability in a high-risk group of individuals.


The researchers prospectively studied 714 young athletes over a 4-year period (2006 to 2010). Initial data collected included a subjective history of instability, clinical instability testing by an orthopedic surgeon, range-of-motion assessment and strength measurement using a handheld dynamometer. Magnetic resonance imaging (MRI) of the shoulder was also performed, the results of which were used by a musculoskeletal radiologist to obtain anatomical measurements, including glenoid version, height and depth, along with rotator interval height, width, area and index. Each participant’s acute posterior instability events were documented during the 4-year period. The time to a posterior shoulder instability event during the follow-up period was the primary outcome of interest.


Of the 714 participants, 46 shoulders sustained documented glenohumeral instability events, 7 of which were posterior in direction. The baseline factors associated with subsequent posterior instability during follow-up were increased glenoid retroversion, increased external rotation strength in adduction and at 45 degrees of abduction, and increased internal rotation strength in adduction.


The researchers found that the increased glenoid retroversion was the most significant risk factor. Increased internal and external strength were also associated with subsequent instability. However, it was not clear if these strength differences were the cause or the result of the increased retroversion in the glenoid anatomy. Even though this study was not the first to report these results, the authors were able to support the contention that an increased retroversion prior to injury is a prospective risk factor for future posterior instability.


Owens BD, Campbell SE, Cameron KL. Risk factors for posterior shoulder instability in young athletes. Am J Sports Med 2013;41:2645-2649.



Risk Factors for Hamstring Strains Remain Elusive


Hamstring muscle strain, a common sports injury, can often be debilitating and may lead to chronic reinjury. Understanding the injury rate, mechanisms and risk factors is essential for prevention and treatment efficacy. Liu et al from the Beijing Sport University, China, conducted a literature review to determine current prevention and treatment strategies for hamstring strains.


Hamstring strains commonly occur in athletes playing sports that involve frequent sprinting and kicking, including Australian rules football, rugby, soccer and American football. Hamstring strains also occur frequently in such individual sports as track and field, cross-country and downhill skiing, waterskiing, and judo; dancers also have a high risk for hamstring muscle strain.


Hamstring strain injury is likely to occur during the late swing phase and late stance phase of sprint running. A common mechanism of hamstring muscle strain is excessive strain in eccentric contraction. Elongation speed and duration of activation before eccentric contraction affect the injury’s severity. The level of evidence for modifiable and nonmodifiable risk factors for hamstring muscle strain is summarized in Table 1. Most of these risk factors are theoretical, based on clinical observation; only a few are evidence-based.


While muscle flexibility may play a role in the risk for this injury, future research with more rigorous methodology is needed to clearly define this factor. No cause–and–effect relationship has been established between hamstring muscle strength imbalance and injury, although some research appears to support a connection. Warm-up activities and their effect on hamstring injury also have limited support in the literature. Injuries subsequent to muscle fatigue indicate that a fatigued athlete may have to increase the elongation to absorb a given amount of energy and thus increase muscle strains in the movement and the risk for muscle strain injury. Hamstring strain injury may be associated with lumbar posture and low back pain.


Many retrospective and prospective studies have suggested age as a risk factor for hamstring strain injury, but other studies refute this relationship. Previous hamstring strain injury may result in shortened optimum lengths of hamstring muscles and thus pose an increased risk for injury, but this relationship has also not been firmly established.


Although the authors found support from basic science studies for some of these variables, clinical studies for the most part have not been definitive. The authors concluded that evidence-based prevention and rehabilitation programs for hamstring injury can only be developed once risk factors have been scientifically established.


Liu H, Garrett WE, Moorman CT, Yu B. Injury rate, mechanism, and risk factors of hamstring strain injuries in sports: a review of the literature. J Sport Health Sci 2012;1:92-101.



Table 1

Proposed risk factors for hamstring muscle strain injury in the literature



Category Proposed risk factor Basic science Clinical
Modifiable Shortened optimum muscle length   Yes    Lacking
Lack of muscle flexibility    Yes Contradictory
Hamstring strength imbalance Lacking Contradictory
Insufficient warm-up Yes Lacking
Fatigue Yes Lacking
Low back pain Lacking Contradictory
NonmodifiableMuscle fiber composition Yes Lacking
Age Lacking Contradictory
Race Yes Yes
Previous hamstring injury Yes Yes



Managing Chronic Nonspecific Neck Pain with Therapeutic Exercise


Neck pain is a frequent musculoskeletal complaint, with more than 30% of neck pain patients developing chronic symptoms lasting longer than 6 months. Therefore, finding interventions with demonstrated efficacy for specific outcomes in patients with chronic nonspecific neck pain is essential. To analyze data from studies that evaluated the ability of therapeutic exercise to relieve pain and improve function and disability in people with chronic nonspecific neck pain, Bertozzi et al from the University of Bologna, Italy, conducted a meta-analysis of randomized controlled trials (RCTs) assessing the effect of therapeutic exercise on pain and disability among people with chronic nonspecific neck pain.


Two reviewers independently searched trials from multiple literature databases. Only RCTs with a control or comparison group were considered for inclusion in the study. To be selected, a study also had to assess pain based on a visual analog scale, a numerical pain rating scale or patient self-report. Disability was included as a primary outcome assessment if the study instrument measured the impact of chronic neck pain on everyday life, beyond just work or leisure-time activities.


The database search identified 2574 articles; the researchers eliminated duplicates and screened the remaining articles’ abstracts. They then assessed 55 full-text articles to verify their eligibility for inclusion in the present study. After 46 were excluded for not meeting the rigorous inclusion criteria, 9 studies remained for the qualitative synthesis, 7 of which were eligible for quantitative meta-analysis through data pooling across studies.


The meta-analysis performed on these 7 pooled studies found a medium and significant overall effect size for therapeutic exercise in reducing chronic nonspecific neck pain over the short term (less than 1 month) and intermediate term (1 to 6 months), but no significant overall effect in reducing disability over the short term and intermediate term. Not enough data were available from these studies to allow evaluation of the efficacy of therapeutic exercise at long-term follow-up (6 to 12 months).


The researchers concluded that therapeutic exercise for the management of pain associated with chronic nonspecific neck pain is advantageous in the short (less than 1 month) and intermediate term (1 to 6 months). As did previous studies, this study supports the use of therapeutic exercise to manage chronic nonspecific neck pain.


The authors encouraged further study using well-designed RCTs with more detailed outcome measures to describe the population more precisely. The time required for tissue adaptation as a result of therapeutic exercise needs to be identified. Then therapists can better understand the effectiveness of therapeutic exercise for chronic nonspecific neck pain in routine clinical practice.


Bertozzi L, Gardenghi I, Turoni F, et al. Effect of therapeutic exercise on pain and disability in the management of chronic nonspecific neck pain: systematic review and meta-analysis of randomized trials. Phys Ther 2013;93:1026-1036.



In the Next Issue
Leg extensor muscle strength and knee joint loading
Jogging after total hip arthroplasty
Effectiveness of pain rehabilitation programs for patients with chronic low back pain