Archive for the ‘Knee Injury’ Category

Arthritis Foundation Recommendations for ACL Injury Prevention

The Arthritis Foundation has developed a series of working groups called the Osteoarthritis Action Alliance. These groups included experts from various areas related to arthritis, including sports medicine. One of the groups was tasked to develop a set of recommendations for ACL injury prevention as individuals with ACL injury are an increased risk of developing osteoarthritis.
The following link goes to one of the informational flyers that was developed by this working group. It outlines an evidence driven set of guidelines for developing an effective ACL injury prevention program. Also, there are links to current programs that can be accessed online without any associated cost. One of the programs was developed by the UNC Sports Medicine Research Laboratory. We are very excited to have been able to be a part of this process and provide this information for the public.

Arthritis Foundation Flyer on ACL Injury Prevention

A direct link to the PEAKc program is also provided

PEAKc Program


Use of Visual and Verbal Feedback to Improve Lower Extremity Biomechanics, Pain and Function


Willy RW, Scholz JP, Davis IS.  Mirror gait retraining for the treatment of patellofemoral pain in female runnersClin Biomech (Bristol, Avon). 2012 Dec;27(10):1045-51. doi: 10.1016/j.clinbiomech.2012.07.011.

What issue was addressed in the study, and why?

Increased contralateral pelvic drop, hip adduction and hip internal rotation are commonly described movement dysfunctions in those with patellofemoral pain (PFP) during functional tasks.  Weakness of the gluteal muscles, which help to stabilize the aforementioned motions, is also observed in those with PFP. However, previous research indicates that isolated hip muscle strengthening is not an effective method for altering lower extremity movement patterns.  Thus, alternative interventions appear to be necessary to ultimately improve these dysfunctional movement patterns.

Real-time feedback using motion analysis has been shown to be an effective means to alter lower extremity movement patterns during running.  In this previous research individual’s lower extremity biomechanics were monitored using an optical motion analysis system while subject’s received real-time feedback on their movement patterns.  A limitation of this research is that it is not clinically feasible to incorporate optical motion analysis equipment for real-time feedback in clinical settings.  Visual feedback using a mirror is a clinically feasible mechanism to provide real-time feedback on lower extremity movement patterns.  However, research has not investigated the effects of visual feedback provided by a mirror on lower extremity biomechanics during running.  Therefore, the purpose of this study was to examine the effects of a 2-week mirror gait retraining intervention on lower extremity biomechanics during running.  In addition, this study investigated whether the effects of mirror gait retraining were transferred to other functional tasks (single leg squatting and stair descent) and retained (1-month and 3 month retention periods).

Who were the participants in the study?

Ten females completed the study and met the following criteria: self-rated patellar pain of at least a 3 out of 10 scale during running, symptoms must be present during running and at least one other activity (squatting, jumping, kneeling, prolonged sitting, stair descent).  Individuals with patellofemoral instability or other knee related pathologies or history of lower extremity surgery were excluded from the study.

What did the researchers do for this study?

Lower extremity biomechanics were quantified using a motion analysis system during 3 tasks: running, single leg squat, and stair descent.  Lower extremity function was quantified using the Lower Extremity Functional Scale.  Pain was quantified using a visual analog scale.  These measures were take at 4 time periods: pre-training, immediately post-training, 1-month post-training, and 3-months post-training.

Participants who demonstrated abnormal hip motion (greater than 20-deg of peak hip adduction) during running were asked to participate in the mirror gait retraining intervention.  Those who met the criteria participated in a 2-week mirror gait retraining intervention where individuals trained 4 days each week (8 total training session).  The mirror gait retraining intervention was conducted as follows:

  • Subjects ran on a treadmill while observing themselves in a full length mirror in front of them (visual feedback).
  • During running the subjects received the following verbal cues: “Run with your knees apart with your kneecaps pointing straight ahead” and “Squeeze your buttocks”
  • No other concurrent interventions (e.g. stretching, strengthening, etc) were performed
  • During the first week of training the amount of visual and verbal feedback was increased each session.
  • During the second week of training the amount of visual and verbal feedback were steadily decreased across each session.  This was performed to shift the individual’s dependence from external cues (verbal and mirror feedback) to internal cues and reinforce motor learning of the new movement patterns.  During the sessions when subjects received less feedback they would receive intermittent feedback during the training session.
  • The duration of each training session was gradually increased from 15 to 30 minutes over the 2-weeks.
  • The participants were instructed to not run outside of their training sessions during the 2-week intervention period.

What new information was learned from this study?

Running Biomechanics:

The following variables were significantly improved immediately following the intervention: peak hip adduction angle, peak thigh adduction angle, peak hip abduction moment, and contralateral pelvic drop.  However, there was no change in hip internal rotation.  After 1-month the following variables remained unchanged from post-test (suggesting successful retention of movement patterns): contralateral pelvic drop, peak thigh adduction moment, and peak hip abduction moment.  Thus, changes in peak hip adduction angle were not retained after 1-month of not performing the intervention.  After 3-months the following variables remained unchanged from post-test (suggesting successful retention of movement patterns): contralateral pelvic drop and peak thigh adduction angle.  Thus, changes in peak thigh adduction angle were not retained after 3-months of not performing the intervention.

Single Leg Squat Biomechanics:

The following variables were significantly improved immediately following the intervention (suggesting successful transfer of the new motor patterns during running to other functional tasks): peak hip adduction angle, peak thigh adduction angle, and peak hip abduction moment.  After 1-month the following variables remained unchanged from post-test: peak hip adduction angle, peak thigh adduction angle, and peak hip abduction moment.  After 3-months the following variables remained unchanged from post-test: peak hip adduction angle and peak thigh adduction angle.  Thus, changes in peak hip and thigh adduction were retained after 1 and 3-months of no training.  However, changes in peak hip abduction were retained after 1-month of no training, but not after 3-months of no training.

Stair Descent Biomechanics

Only peak hip adduction angle was significantly improved immediately following the intervention.  Thus, changes in peak hip adduction angle were transferred from running to stair descent; however, none of the other variables that were changed during running were transferred to stair descent.

Pain and Lower Extremity Function

Both pain and lower extremity function were significantly improved immediately after the intervention.  These improvements were retained at both the 1-month and 3-month follow periods.

What are the clinical applications of this study?

The findings indicate that the 2-week mirror gait re-training program was able to successfully improve hip biomechanics during running.  Also, many of these changes were successfully transferred to other functional tasks (single leg squat and stair descent).  Several of these changes were retained in all tasks.  In general, these findings suggest that the 2-week mirror gait re-training program used in this study was able to facilitate learning a new movement pattern (successful transfer and retention of new movement patterns).

In addition to improved movement patterns, pain and lower extremity function were also improved.  These findings suggest that improvements in pain and function may be associated with lower extremity movement pattern modifications.

Use of verbal feedback in combination with mirror gait retraining may be an important adjunct to a comprehensive and integrated intervention strategy to improve lower extremity biomechanics in those with PFP and altered hip biomechanics.

What are the limitations of the study, and what areas should be considered for future research?

There was no control group utilized in this study.  Thus, it is not clear if changes in lower extremity biomechanics, pain, and lower extremity function were due to the intervention.  However, these findings provide initial evidence to suggest that the intervention utilized in this study may have clinical merit and warrants further investigation.

Neuromuscular characteristics associated with knee valgus collapse during an overhead squat

Padua DA, Bell DR, Clark MA.  Neuromuscular characteristics of individuals displaying excessive medial knee displacement.  Journal of Athletic Training 47(5):525-536, 2012.

What issue was addressed in the study, and why?

Knee valgus motion is frequently hypothesized as a risk factor for multiple lower extremity injuries.  An aim of many exercise programs is to correct for excessive knee valgus motion through a variety of mobility, stability, and strengthening techniques.  The successful correction of knee valgus motion requires an understanding of the underlying neuromuscular characteristics associated with it.  Multiple theories have been proposed to explain the muscle imbalances associated with knee valgus motion; however, there is little scientific evidence to support these theories.  Identifying differences in muscle activation patterns between those who do and do not display knee valgus collapse is an initial step to validating the muscle imbalances associated with this movement dysfunction.  Therefore, the purpose of this study was to compare hip and ankle muscle activation amplitude in those with and without visual presence of knee valgus motion (medial knee displacement) during an double leg (overhead) squat task.

Who were the participants in the study?

A total of 37 participants volunteered for this study and were separated into two groups based on the presence of medial knee displacement during an double leg squat task.  The control group (CON, n=19) did not demonstrate medial knee displacement.  The medial knee displacement group (MKD, n=18) were observed to have their patella move medial to their great toe during the double leg squat, but not once a 2-inch lift was positioned under their heels.  Individuals who displayed MKD during both no-heel lift and heel-lift conditions were excluded from the study.

This was done as there are different muscle imbalances believed to be associated with knee valgus motion during no-heel-lift and heel-lift conditions.  MKD that is displayed during the no-heel-lift condition, but not during the heel-lift condition is believed to be associated with ankle muscle imbalances.  MKD that is displayed during both no-heel-lift and heel-lift conditions is thought to represent a hip muscle imbalance.  Thus, this study focused on identifying the presence of ankle muscle imbalances given the inclusion criteria.

What did the researchers do for this study?

Surface EMG electrodes were used to record the activation amplitude from the medial gastrocnemius, lateral gastrocnemius, tibialis anterior, adductor magnus, gluteus medius, and gluteus maximus muscles.  An electromagnetic motion analysis system was used to quantify medial knee displacement motion.  All variables were measured during two different double leg squat tasks performed at a controlled movement velocity and squat depth.  Subjects performed the double leg squat task during both no-heel-lift and heel-lift (2-inch) conditions.  During all double leg squat trials the individuals were instructed to keep their heels on the floor and maintain their toes pointing straight ahead.

What new information was learned from this study?

There was no difference between the CON and MKD groups for gluteus medius and gluteus maximus activation amplitude during both the no-heel-lift and heel-lift double leg squat tasks.  However, the MKD group demonstrated 34% greater activation of the adductor magnus muscle compared to the CON group.

The MKD group demonstrated greater gastrocnemius (40% greater) and tibialis anterior (25% greater) muscle activation amplitude compared to the CON group during both double leg squat tasks.

What are the clinical applications of this study?

Presence of MKD that is corrected with heel-lifts is associated with increased gastrocnemius, tibialis anterior, and adductor magnus muscle activation amplitude.  However, there was no difference in gluteal muscle activation amplitude between MKD and CON participants.  Thus, there appears to be 2 neuromuscular strategies associated with knee valgus motion.  Increased gastrocnemius and tibialis anterior activation likely increases ankle joint stiffness, thus limits the available dorsiflexion range of motion during functional tasks, which is theorized to lead to compensatory knee valgus motion.  Increased adductor magnus activation can lead to an imbalance between the gluteals and adductor muscles, resulting in a net hip adduction moment during the squat task.  In fact, the MKD participants in the current study demonstrated 4 times greater adductor magnus activation compared to their gluteal muscles, which indicates a significant muscle imbalance between these muscle groups.  This would ultimately result in the visual presence of knee valgus motion as the femur moved medially during the squat task.

Interventions aimed at inhibiting and lengthening the gastrocnemius, tibialis anterior, and adductor magnus muscles may be necessary components of exercise interventions aimed at correcting knee valgus motion.

What are the limitations of the study, and what areas should be considered for future research?

All of the participants were healthy at the time of testing.  Thus, these findings are limited to healthy individuals and it is possible that different muscle activation patterns may exist in those who display knee valgus motion and are symptomatic.  Future research is needed to confirm the presence of ankle muscle imbalances (increased gastrocnemius and tibialis anterior activation) and synergistic dominance of the adductor magnus (increased adductor magnus activation) in those with MKD who are also symptomatic.

The findings from this study are part of a larger study whose findings were previously published in the following article:

ACL Injury Rates Reduced by 50-85% Following Implementation of a Preventive Training Program

Sadoghi P, Keudell von A, Vavken P.  Effect of Anterior Cruciate Ligament Injury Prevention Training Programs. The Journal of Bone and Joint Surgery 94: 1-8, 2012.

PMID: 22456856

RATIONALE & PURPOSE: Anterior cruciate ligament (ACL) rupture has been identified to be a significant encumbrance on today’s healthcare system, and represents a significant financial, emotional, and physical burden for the individual suffering the injury. The most common treatment for the injury is surgical repair, using a tissue graft to replace the damaged structure. Current literature suggests that even with surgical repair there are enduring consequences of injury, with a predisposition for osteoarthritis most commonly being identified as a long-term repercussion. Perhaps the most glaring aftereffect of ACL rupture is that of increased risk of ACL injury compared to those who have never sustained an ACL injury. Recent publications suggest that an individual who has previously sustained an ACL injury is up to 6 times at risk for suffering an ACL injury compared to an individual with no history of ACL rupture. It is thus prudent that effective injury prevention strategies be implemented to help reduce one’s risk of primary injury as well as re-injury.

Up to 80% of ACL injuries have been identified to be a result of a noncontact mechanism, indicating the injury was a result of an individual’s self-imposed motion. Understanding that human movement is modifiable, a substantial volume of research efforts have been aimed at identifying methods to promote safe and efficient movement strategies in individuals who may be exposed to events in which ACL rupture have been known to occur. High-risk circumstances have been identified as athletic activities demanding high-magnitude accelerations/decelerations and changes in direction. As a result, various ACL injury prevention programs have been deployed in the athletic population, and after scientific study have been determined to be individually effective in reducing ACL injury incidence. As such, studies investigating the effects of ACL injury prevention programs on ACL injury incidence are growing numerous. However, different studies present a broad range of prevention programming, thus making it difficult to determine the specific elements of programming that are most efficacious in reducing ACL injury rates. Furthermore, due to deployment of prevention efforts in different populations the general effect of programming has not been described. Thus the purpose of this systematic review study was to evaluate and describe the general effect of ACL injury prevention programming on decreasing injury incidence, and to identify if there is a programming protocol that is “best” in terms of reducing ACL injury incidence.

OVERVIEW OF RESEARCH METHODS: An initial search of online databases of peer-reviewed journals with the search terms “anterior cruciate ligament, knee, injury, prevention, and control” returned 909 results. The authors report including only studies that were described to be “prospective, controlled studies that directly compared ACL injury prevention programs to no treatment in human subjects,” resulting in a final evaluation of 8 studies. Data from the 8 studies was pooled to compare the risk of experiencing an ACL injury between those completing a prevention program and those not executing a prevention program. In addition to evaluating the overall effect of prevention programming on reducing ACL injury risk across the populations of the studies, the effect of programming for males and females was differentiated. An attempt to compare the effectiveness of different programs was unsuccessful due to the differing populations each study represented. However a qualitative analysis of elements common to programs proving to be effective in reducing injury rates was carried out.


  • ACL injury prevention programs effectively decrease ACL injury risk by 62% in male and female soccer, basketball, volleyball, and team handball athletes.
  • ACL injury prevention programs decrease ACL injury risk by 85% in male athletes.
  • ACL injury prevention programs decrease ACL injury risk by 52% in female athletes.
  • There was no specific program that was identified to be the “best” program in reducing ACL injury risk.
  • EffectiveACL injury prevention programs:
    • Include at least 10 minutes of exercises
    • Are executed at least 3 times per week
    • Focus on neuromuscular training

CLINICAL IMPLICATIONS: The results of this systematic literature review provides cogent evidence supporting the implementation of ACL injury prevention programming into clinical practice by sports medicine professionals. ACL injury prevention programming efforts that at a minimum include at least 10 minutes of exercises, conducted at least 3 times per week, focusing on neuromuscular decrease an individual’s risk of ACL injury. Individuals who are exposed to athletic activities representing high-risk exposures such as soccer, basketball, team handball, and volleyball, or any physical activity that incorporates high-magnitude accelerations/decelerations and changes in direction should execute ACL injury prevention programming.

Furthermore, it is understood that the sports medicine professional may not have the ability to individually reach each athlete who may experience exposure to high-risk events, thus it is imperative physicians, athletic trainers, and physical therapists be capable of educating athletes, coaches, parents, and administrators regarding the benefits and of ACL injury prevention programming. Additionally it is imperative sports medicine professionals be able to direct the above individuals to efficacious programming efforts. Currently many effective programming resources are available and are listed below.

Written by Barnett Frank, MA, ATC
Approved by Darin Padua, PhD, ATC

Changes in Movement Control are Influenced by Duration of Training – Implications for Rehabilitation and Injury Prevention


Padua DA, DiSefano LJ, Marshall SW, Beutler AI, de la Motte SJ, DiStefano MJ.  Retention of Movement Pattern Changes After a Lower Extremity Injury Prevention Program Is Affected by Program Duration.  American Journal of Sports Medicine 40(2):300-306, 2012

What issue was addressed in the study, and why?

Prevention of ACL and other knee injuries is an important issue for sports medicine professionals given the high cost and long term disability associated with these injuries.  Recent randomized controlled trial studies have shown that 15-minute injury prevention exercise program scan reduce the rate of ACL and knee injuries during sport.  However, injury rates return to their original levels once individuals cease performing the injury prevention exercise program.

The primary goals of injury prevention exercise programs are to improve neuromuscular control and overall movement quality.  Findings of elevated injury rates once stopping an injury prevention program suggest that changes in neuromuscular control and movement quality are not permanent; however, research has not investigated this topic.  Therefore, the purpose of this study was to determine if changes in movement quality/control are maintained once individuals had stopped performing an injury prevention program for 3 months.  This study also investigated the influence of program duration (3-month training program vs. 9-month training program) on people’s ability to maintain improvements in movement quality/control.

Who were the participants in the study?

A total of 140 youth soccer athletes participated in this study.  Individuals who improved their movement quality/control over the course of the injury prevention program were included in the final analysis (84 total subjects).  Individuals were further subdivided into 2 groups based on the duration of their injury prevention program (3-month training period (short duration) = 33 subjects; 9-month training period (extended duration) = 51 subjects).

What did the researchers do for this study?

All participants performed an integrated exercise program that incorporated flexibility, balance, strength, and plyometric/agility exercises.  The exercise program was performed as a dynamic warm up in replace of the normal warm up routine.  The exercise program took 10-15 minutes to perform and was completed 3-4 times per week during the intervention period.  The Short-Duration group performed the exercises for 3-months.  The Extended-Duration group performed the exercises for 9-months.  Trained research assistants taught the athletes the exercise program and visited the athletes once a week to monitor compliance and correct exercise technique.  Participants were instructed to think about their movement and rely on specific cues when performing the exercises (keep toes pointing forward, keep knees over toes, land as soft as possible).

Prior to beginning the exercise program (Pre Test) the participants performed a jump-landing task (3-trials) that was recorded with a video camera.  The Landing Error Scoring System (LESS) was then used to grade the individual’s overall movement quality.  Participants repeated the jump-landing task after immediately completing the exercise program (Post Test) and again after 3-months of performing the exercise program (Retention Test).  The researchers then compared the Short-Duration and Extended-Duration groups LESS scores across the three time periods (Pre Test, Post Test, Retention Test).

What new information was learned from this study?

Both the Short Duration and Extended Duration groups improved their LESS scores from Pre Test to Post Test.  There was no difference in the amount of improvement in LESS scores between groups.  However, at the Retention Test the Short Duration group’s LESS scores returned to Pre Test levels and were worse than at Post Test.  This was not the case for the Extended Duration group as their Retention Test LESS scores remained the same as at Post Test and were still improved compared to Pre Test.  Thus, the Extended Duration group retained their improvements in movement quality / control while the Short Duration group did not.

This study demonstrates that the duration of training has a significant impact on the ability to maintain improvements (retention) in movement quality/control following an injury prevention program.  Extended Duration exercise programs appear to be an important component of successfully achieving retention of improvements in movement quality/control once ceasing to perform the program.

What are the clinical applications of this study?

Several important clinical applications come from this study.  First, we should not assume that improvements in movement quality/control are permanent once an individual has made initial changes in their movement patterns.  Individuals in the Short Duration group were able to improve their movement quality/control after 3 months of training, but after stopping the program they returned to their baseline levels.  This especially important when considering rehabilitation and corrective exercise programs as it is common to achieve changes in movement quality / control in less then 3 months and then the patient / client stops performing the program.  These findings suggest that individuals will only return to their original movement patterns if continued assessment and maintenance of the exercise program is maintained.

Second, longer duration exercise programs that are continued once individuals have initially improved their movement patterns may be required to elicit more permanent changes in one’s movement patterns.  Individuals in the Extended Duration group likely achieved improvements in movement quality/control after 3-months as did the Short Duration group.  However, the Extended Duration group continued to perform these exercises for an additional 6-months after achieving this improvement.  The additional performance of the exercises after making initial improvements may have allowed for these individuals to master the exercises and elicit more permanent improvements in their movement patterns.  These findings have direct implications to rehabilitation and corrective exercise programs.

These findings suggest that injury prevention training should be a continual process where athletes are repeatedly monitored and perform their exercise program even after making initial improvements.  By replacing the traditional warm up with these types of injury prevention programs we can achieve the same effects as traditional warm ups, but have the added benefit of improving movement quality.

What are the limitations of the study, and what areas should be considered for future research?

Several limitations should be considered.  First, the LESS is a clinical assessment of movement quality/control and is not the same as 3-D motion analysis; however, the LESS has been shown to have good validity and reliability relative to 3-D motion analysis.  Future research may consider using 3-D motion analysis to study retention following an injury prevention program.  Another possible limitation was the age group of study participants (11-17 years).  It is not clear if the duration of training has similar effects in younger or older populations.  Future research may consider investigating different age groups and also different retention time periods.

Research Update on Hamstring Strain Injuries

Mendiguchia J, Alentorn-Geli E, Brughelli M. Hamstring strain injuries: are we heading in the right direction?  British Journal of Sports Medicine 46(2):81-85, 2012.

NOTES:  Hamstring strain injuries are one of the most common injuries to occur during sport, accounting for 6 to 29% of all injuries across a variety of sports.   This article highlights key findings of recent research studies investigating risk factors and rehabilitation considerations for hamstring strain injuries.

History of prior hamstring injury is the greatest risk factor for a future hamstring injury.  12-31% of individuals who suffer an initial hamstring injury go onto suffer re-injury.  Individuals with a prior hamstring injury are 2 to 6 times greater risk for re-injury compared to those without prior hamstring injury.   Given this information, individuals with a prior history of hamstring injury should undergo a thorough screening to identify the presence of additional risk factors for future injury (see below).  In addition, individuals with a previous history of hamstring injury may benefit from a maintenance exercise program focused on those risk factors described below, even after returning to full participation.

Decreased hamstring and hip flexor muscle group flexibility  have both been shown to be associated with increased risk of hamstring injury.  However, it should be noted that research in this area is not consistent regarding the effects of a lack of hamstring and hip flexor flexibility on risk of future hamstring injury.  Most research assesses hamstring flexibility during a passive straight leg test; however, more recent research indicates that a more dynamic active straight leg raise test may be more sensitive for determining risk for future injury and return to play.

Decreased hamstring muscle strength is not consistently shown to be a risk factor for future injury.  Most research assesses hamstring strength using an isokinetic dynamometer as the individual performs knee flexion while in a sitting position (hip flexed to 90-deg).  This may be a limitation of current research.  Research suggests that assessing eccentric hamstring strength (as the knee is extended) and hip extension strength may also be an important considerations.  Intervention studies examining eccentric strengthening (e.g. nordic hamstring exercise) of the hamstrings have shown mixed results.  It is suggested that this may be due to the fact that these exercises do not emphasize the role of the hamstrings as hip extensors.  Incorporation of exercises emphasizing the eccentric control of hip flexion (e.g. single leg deadlift, etc..) may also be important components of successful injury prevention and rehabilitation programs.

Few studies have examined the role of core stability in hamstring injuries.  Preliminary research indicates that individuals incorporating core stabilization training along with conventional hamstring strengthening suffer fewer re-injuries than those who undergo isolated hamstring strengthening.   Thus, exercises promoting lumbo-pelvic control (local and global core stabilization exercises) should be considered in conjunction with isolated hamstring strengthening.

Fatigue is also suggested as a potential risk factor for hamstring injury as more injuries are reported to occur at end of halves during matches.  Thus, training to promote fatigue resistance and muscle endurance should also be considered during the injury prevention and rehabilitation program.

It is clear that hamstring injuries are multi-factorial in nature and require a comprehensive strategy for prevention and rehabilitation.  Based on this article the following strategies may be considered:

  • Increase both hamstring and hip flexor flexibility.
  • Increase concentric and eccentric hamstring strength.  Consider the bi-articular nature of the hamstrings and address both the knee flexion and hip extension functions of the hamstrings.
  • Promote improved lumbo-pelvic motion control (control anterior pelvic rotation) by addressing both the local and global core stabilizing muscles.
  • Promote improved cardiovascular endurance and improved resistance to hamstring muscle fatigue during the later stages of the program.

Risk Factors for Recurrent Hamstring Injuries

de Visser HM, Reijman M, Heijboer MP, Bos PK.  Risk factors of recurrent hamstring injuries: a systematic review.  British Journal of Sports Medicine.  2011 Oct 19 (Epub ahead of print).

PMID: 22011915

NOTES:  The article is a systematic review of published research investigating recurrent hamstring injuries.  The goal of this systematic review was to identify risk factors for re-injury of acute hamstring muscle strains.  A total of 131 articles were reviewed and from this group 5 prospective follow-up studies met the inclusion criteria and were included in the study.  Re-injury rates following initial hamstrings injuries ranged from 14-63% across the studies reviewed.  To be included in the study the following criteria were met: 1) Participants were diagnosed with an acute initial hamstring injury by physical examination using a standardized grading criteria for severity; 2) Prospective studies with a minimal follow-up period of 2 weeks after return to sport; 3) Full text of article was available; 4) Article was written in english, german or dutch.

The following variables were considered as potential risk factors for recurrent hamstrings injury: 1) Injury severity of initial hamstring injury; 2) History of ACL reconstruction; 3) Type of rehabilitation program performed post-initial hamstrings injury (stretching and strengthening vs. stabilization and agility exercises); 4) Age; 5) Height; 6) Weight; 7) Length of injury; (8) Time to return to sports; 9) Specific hamstrings muscle involved; 10) Location of initial hamstrings injury (proximal, mid, distal); 11) Pain severity score of initial hamstrings injury (visual analog scale); 12) Size/volume of hamstrings.

The findings of this systematic literature review indicate that there was limited evidence for 3 risk factors for recurrent hamstrings injury.  These risk factors include: 1) larger initial injury size/volume; 2) previous history of ACL reconstruction (not related to graft type); 3) grade 1 initial hamstrings injury severity.  There was also limited evidence that individuals who performed stabilization and agility exercises rather than simply strengthening and stretching were are reduced risk for recurrent hamstrings injury.

CLINICAL IMPLICATIONS:  Individuals with larger initial hamstrings injury size OR grade 1 initial hamstrings injury severity OR previous history of ACL reconstruction should be considered to be at greater risk for a recurrent hamstrings injury.  Thus, these individuals may benefit from more focused assessment and rehabilitation program to reduce their risk for re-injury.  Specifically, noting for the presence of underlying movement impairments and muscle imbalances that place greater load on the hamstrings may be warranted.  These underlying movement impairments and muscle imbalances may also need to be addressed during the rehabilitation of these high risk individuals to avoid repeat hamstrings injury in the future.

These findings also suggest that incorporation of stabilization and agility training are important components of the rehabilitation process.  Thus, an integrated approach to hamstrings injury rehabilitation (e.g. flexibility, strength, stability, power/agility) is likely required to achieve optimal results. 


Background:  Although recurrent hamstring injury is a frequent problem with a significant impact on athletes, data on factors determining the risk for a recurrent hamstring injury are scarce.  Objective:  To systematically review the literature and provide an overview of risk factors for re-injury of acute hamstring muscle injuries.  Study design:  Prospective studies on risk factors for re-injury following acute hamstring injuries were systematically reviewed. Medical databases and reference lists of the included articles were searched. Two reviewers independently selected potential studies and assessed methodological quality; one reviewer extracted the data. A best-evidence synthesis of all studied risk factors was performed.  Results:  Of the 131 articles identified, five prospective follow-up studies fulfilled our inclusion criteria. These studies reported a recurrence incidence of 13.9-63.3% in the same playing season up to 2 years after initial injury. Limited evidence for three risk factors and one protective factor for recurrent hamstring injury was found; patients with a recurrent hamstring injury had an initial injury with a larger volume size as measured on MRI (47.03 vs 12.42 cm(3)), more often had a Grade 1 initial trauma (Grade 0: 0-30.4%; Grade 1: 60.9-100%; Grade 2: 8.7%) and more often had a previous ipsilateral anterior cruciate ligament (ACL) reconstruction (66.6% vs 17.1%) independent of graft selection. Athletes in a rehabilitation programme with agility/stabilisation exercises rather than strength/stretching exercises had a lower risk for re-injury (7.7% vs 70%). No significant relationship with re-injury was found for 11 related determinants. There was conflicting evidence that a larger cross-sectional area is a risk factor for recurrent hamstring injury.  Conclusions:  There is limited evidence that athletes with a larger volume size of initial trauma, a Grade 1 hamstring injury and a previous ipsilateral ACL reconstruction are at increased risk for recurrent hamstring injury. Athletes seem to be at lower risk for re-injury when following agility/stabilisation exercises.

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