Disease/Disorder
Definition
Hamstring injuries are common injuries in the athletic population and prone to recurrence. Acute mid-hamstring strains and tears of the myotendinous junction are often seen in explosive sporting events. Overuse injury causing proximal hamstring tendinopathy is especially seen in endurance athletes, including runners.
Etiology
Mid-hamstring strains and proximal hamstring tears are most commonly seen in athletes who require explosive force, such as with sprinting. These hamstring injuries tend to occur at terminal swing phase, during which the hamstrings are lengthening while actively contracting.1 Biceps femoris long head is the most commonly affected hamstring muscle with this mechanism of injury.2 In the general population, hamstring injuries are more commonly avulsions of the ischial tuberosity as opposed to tears of the muscle belly; these injuries occur primarily in older females and the skeletally immature and tend to occur with excessive lengthening involving combined hip flexion and knee extension.3 Chronic proximal hamstring tendinopathy is typically seen in the setting of incomplete healing or altered biomechanics such as inflexibility or weakness.
Epidemiology including risk factors and primary prevention
- Accounts for 12-29% of all injuries in athletes depending on the sport4,5
- Hamstring injury incidence rate is estimated at roughly 1.3 per 100 athletes annually6
- Predominately affects the middle-aged population (risk begins increasing in the mid-20s)7
- No gender predominance – generally, injured males are younger than their older female counterparts who endure injuries during everyday activities7,8
- Acute injuries are usually during competition time, while chronic presentations are likely to arise during training season9,10
- Non-Modifiable Risk factors:
- Prior hamstring injury is the strongest predictor of hamstring injury – 22-34% reinjury rate4,5
- Age
- Leg length inequality
- Modifiable Risk Factors:
- Neuromuscular fatigue11-13
- Reduced flexibility
- Muscle strength imbalance
- Poor core stability
- Poor lumbar posture14
- Dehydration
- Decreased hamstring to quadriceps ratio
- Anterior pelvic tilt
- Slight increases in tension and length of the hamstring tendons from ischial tuberosity to distal attachment15
- Overuse
- Primary prevention:
- Education for students and coaches
- Pre-participation flexibility screening
- Incorporate proper flexibility training and adequate warm up into an athletic program16,17
- Eccentric hamstring strength training, particularly Nordic Curl hamstrings exercise18-20
- Eccentric training has been shown to reduce the incidence of hamstring injury by 57% – 70%21
- Training lumbopelvic hip stability22
- Plyometrics
- Primary prevention strategies focused on providing guidance for gradual activity progression, since symptoms often result from a sudden increase in either intensity or duration of training
- Secondary prevention:
- Allow for adequate healing/rest from the initial injury to prevent an immediate recurrence.
- Gradually progress activities, including strengthening, range of motion, and flexibility
- Fifty-nine percent of repeat hamstring injuries will occur within the first month of return to play (RTP). Isometric strength tends to return to level of the uninjured leg by about 20 days post-injury, while flexibility returns within about 50 days post-injury. Notably, dynamic strength deficits persist even after RTP23
- Eccentric strengthening exercise program may be initiated for tendinopathy and for secondary prevention of hamstring injuries[H1]24,25
Patho-anatomy/physiology
- The hamstrings are comprised of three muscles in the posterior thigh
- Semitendinosus – originates on the ischial tuberosity and inserts at the anteromedial proximal tibia on the pes anserinus
- Semimembranosus – originates on the ischial tuberosity and inserts at the posterior medial tibia
- Biceps femoris – long head originates on the ischial tuberosity and inserts on the head of the fibula; short head originates at the posterolateral femur from the linea aspera, inserts on the head of the fibula, and is the only hamstring that does not cross both the hip and knee joints
- The most common tendons injured are the long head of the biceps femoris and semimembranosus. This is likely because their elongation exceeds that of the other hamstring muscles when the knee is in extension.
- The least common tendon injured is the semitendinosus30
- Innervation:
- Semimembranosus, semitendinosus, and long head of the biceps femoris – tibial branch of the sciatic nerve (L5-S2)
- Short head of the biceps femoris – peroneal branch of the sciatic nerve (L5-S2)25
- The hamstrings have a higher proportion of type II muscle fibers compared with other muscles of the lower extremities. This suggests the muscle can generate high intrinsic tension forces27
- Hamstring function during running25
- At end of forward swing phase: Decelerates knee extension
- At foot strike: Eccentric hip extension
- At take-off: Hip extension and knee flexion
- Mechanism of injury: Stretch-type and Sprint-type28
- Stretch-type: Occurs during substantial hip flexion and knee extension maneuvers (i.e., dancing)
- Commonly affecting the proximal free tendon portion of the semimembranosus29
- Stretching injuries have been shown to require a longer recovery time to achieve full return to premorbid levels of activity compared to acute sprinting-type injuries30
- Sprint-type: Usually during eccentric loading during hip flexion and knee extension typically seen in maximal running31
- Commonly affecting the long head of the biceps femoris2,32
- Key points of hamstring injury typically occur in the late swing and early stance28
- Muscle fatigue may promote “Groucho” running pattern,28 that along with anterior pelvic tilt, can place the biceps femoris muscle in a vulnerable state for injury33-35
- These injuries are often characterized by a significant improvement in pain, strength, and flexibility within the first week of injury, so it is important to inform individuals of this and encourage compliance with early activity restrictions to prevent delayed healing and/or recurrent injury.36
- Stretch-type: Occurs during substantial hip flexion and knee extension maneuvers (i.e., dancing)
- Acute hamstring tears or high-grade strains may involve the sciatic nerve due to compression or inflammation. Chronic injuries may be associated with fibrosis and scarring.
- Chronic tendinopathy is characterized by fibrosis with proximal attachment hyaline degeneration in some cases.37
Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)
- Acuity
- Acute: <6 weeks of symptoms
- Chronic: >6 weeks of symptoms
- Muscle Tear Classification
- Grade I (mild)
- No appreciable tissue disruption (elongated fibers with minimal tearing). Minimal or no loss of function or strength (<5%).
- Grade II (moderate)
- Tissue damage (partial tear) that reduces strength and function of musculotendinous unit.
- Grade III (severe)
- Complete loss of musculotendinous unit, with rupture of muscle with retraction and complete loss of function.
- Grade I (mild)
Specific secondary or associated conditions and complications
- Proximal avulsions are typically seen in the pediatric population such as a “hurdler’s fracture” or in water skiers4,38
- Progression of a chronic tendinopathy to a tendon rupture is rare but can occur.
- Associated conditions can include a gait abnormality, leading to dysfunction along the kinetic chain affecting the low back, sacroiliac joint, hip, knee, and ankle joints.
- Sciatic nerve can become entrapped due to fibrosis and scarring (~5% co-incidence), particularly in acute tears. This can cause radiating symptoms down the leg with associated pain, weakness, and numbness.7
Essentials of Assessment
History
- Acute: Sudden onset of pain or pulling sensation in the posterior gluteal region or thigh (with or without a popping sound or sensation) during strenuous activity. High-grade strain or tear may be associated with ecchymosis. There is typically discomfort with activity such as running and kicking as well as with bending at the hips. Pain is often worse with sitting.
- Subacute/Chronic: Gradual onset of deep buttock pain, which may be vaguely localized. Can be associated with posterior thigh pain. Often worse with sitting.
Physical examination
- Assess lumbar spine, hips, and bilateral lower extremities.
- Assess gait for stiff-leg gait pattern
- Inspection: Ecchymosis at site of injury. Assess pelvic tilt/obliquity.
- Palpation: Tenderness to palpation, palpable defect. Examine muscle belly with knee flexed to 90 degrees.
- Range of motion: Reduced flexibility of hamstrings, may be pain-limited. Can assess hamstring flexibility with popliteal angle measurement. Guarding may be seen with hip flexion.
- Neurovascular assessment: Test knee flexion and hip extension strength in both supine and prone position. Seated slump test and straight leg raise may be positive. Testing internal and external rotation of tibia may also be helpful in lateralizing the injury.
- Special tests for chronic proximal hamstring tendinopathy:
- Puranen-Orava test (Sensitivity 76%, Specificity 82%)- This test consists of the patient actively stretching the hamstring in standing position with the heel of the affected side resting on a support so that the hip is flexed to 90 degrees. Pain at the proximal hamstring indicates a positive test39.
- Bent-knee stretch test (Sensitivity 82%, Specificity 87%)39– This test is performed in supine. The examiner passively flexes and hip and knee fully and then slowly extends the knee. Pain with passive knee extension in this position is positive for proximal hamstring tightness.25
- Modified Bent-knee stretch test (Sensitivity 89%, Specificity 91%)- This test is performed similarly to the bent-knee stretch test except that the examiner extends the knee more rapidly.39
- One-legged supine plank test- This test is performed with the patient in supine position, propped on bilateral forearms and heels. The patient then raises the heel of their unaffected leg off the table. Inability to hold proper positioning due to pain or weakness is indicative of a proximal hamstring injury.25
Functional assessment
A sports-specific assessment may be helpful, including run gait analysis, cycling position, etc. Running assessments such as a treadmill analysis, with video evaluation of proper running technique assessing the entire kinetic chain to include the upper body, spine, pelvis, thigh, leg, and foot, can be helpful. These evaluations can assess for and be helpful in correcting functional deficits. Full, pain-free, range of motion (ROM) should be achieved before beginning a strengthening program.
Imaging
- AP pelvis X-ray: Assess for bony avulsion or bony changes of ischial tuberosity such as enthesophytes or cortical irregularity.
- Magnetic resonance imaging (MRI): Consider for suspicion of partial or complete tear as well as surgical planning in refractory cases. May see bony edema, muscular tears/avulsions, and peritendinous edema, as well as concomitant lesions in the area.
- Commonly recognized as the gold standard test if hamstring injury is suspected
- Musculoskeletal ultrasound: Longitudinal and transverse images with high-resolution imaging allow for the dynamic assessment of a tendon tear, muscular edema, or peritendinous edema.
- Cost effective and dynamic imaging modality
- In comparison with MRI, ultrasound has been found to have similar sensitivity for identifying acute hamstring injuries40
Supplemental assessment tools
- Differential diagnosis25
- Lumbar spine discogenic pain or radiculopathy
- Sacroiliac joint-mediated pain
- Sacroiliitis associated with spondyloarthropathy
- Facet-mediated pain
- Ischial bursitis
- Apophysitis/bony avulsion – particularly in pediatric population
- Pelvic stress fracture
- Pelvic floor pain
- Piriformis syndrome
- Obturator internus or gemelli tear
- Gluteal muscle pain
- Chronic posterior thigh compartment syndrome
- Visceral causes, including gastrointestinal and rectal pain
- Sciatic or posterior femoral cutaneous nerve entrapment
Early predictions of outcomes
Hamstring mapping, a means of outlining the size and extent of hamstring injury, can be utilized to some degree to predict RTP. MRI can be used to grade the injury. In a study of professional athletes, RTP occurred at just over two weeks with grade 1 injuries, just over three weeks with grade 2 injuries, and over ten weeks with grade 3 injuries.30 There is moderate evidence that MRI can predict return to play; lesions closer to the ischial insertion tend to require a longer time to RTP, and patients without hyperintensity on fluid-sensitive sequences tend to have shorter time to RTP.41
Environmental
Equipment used in sports may play a role. For example, cyclists may benefit from adjustments to the bicycle to off-load the hamstring. Runners may benefit from running gait analysis and appropriate shoe and orthotic insert fitting. Alpine skiers might consider making adjustments to the stiffness or canting of their ski boots and ensuring their skis and poles are correctly sized.
Social role and social support system
Hamstring injuries can be extremely frustrating. The length of recovery and rehabilitation varies widely and can take up to 9 months for return to play in the case of operative hamstring repair.31 There is often pressure on athletes from coaches, fans and teammates to return to sport prematurely, which can lead to reinjury or a worsening of the original injury.
Professional issues
Hamstring injuries can be frustrating to treat from the medical provider’s standpoint as well. A recent study involving professional football players revealed that the rate of hamstring injuries has doubled over the past 20 years.42 Pressure can mount on the injured athlete as well as the coaching staff to return the athlete to play quickly. Unfortunately, there is often a risk of reinjury or worsening of the original injury without adequate rehabilitation.
Rehabilitation Management and Treatments
Available or current treatment guidelines
Non-operative Management
Hamstring strain rehabilitation can be broken into three phases: acute management, strengthening, and return to competition5,31
- Phase I: Focus on protecting the area and start a rehabilitation program
- Start ROM activities, isometric contractions, and isotonic contractions
- Phase II: Strengthening the area and prepare the area for sport activity and training
- Progressing isometric/isotonic exercises and adding linear running, plyometrics, change of direction movements, and sport-specific drills
- Phase III: Return to competition
- Prior to progressing to this phase, the athlete must be pain-free with near-to-normal strength
- Build on phase II exercises and a graded return to play
- Medications
- Non-steroidal anti-inflammatory drugs (NSAIDs) – indicated in the acute setting but not for chronic tendinopathy43
- Physical therapy25,44
- Soft tissue mobilizations to break up adhesions/scar tissue
- Manual therapy should be applied away from the area of injury during phase I and progressed to the site of injury during phase II and III31
- Progressive stretching and muscle energy techniques to improve flexibility
- Address pelvic tilt, core strength, and neuromuscular control
- Neural glides, if indicated
- Neuromuscular inhibition may impair rehabilitation and lead to subsequent maladaptation of hamstring45
- Progressive (mainly eccentric, particularly swing-phase specific)46 hamstring strengthening exercise program
- Single/double leg bridge
- Single/double leg ball curls
- Single/double leg squats
- Eccentric single leg squats
- Eccentric single leg windmill squats – incorporating transverse plane movements
- Core strengthening exercises
- Nordic hamstring strengthening – shown to decrease incidence and severity of hamstring injuries in rugby players.47 This exercise preferentially recruits semitendinosis.48
- Hip extension exercise tends to activate lateral hamstrings more while knee-flexion exercise tends to recruit more medial hamstrings.48
- One study found that athletes whose rehabilitation program including more agility and trunk stabilization had faster RTP and lower reinjury rates (7.7% compared to 70%) when compared to a program focused more on strengthening and flexibility.49
- Soft tissue mobilizations to break up adhesions/scar tissue
- Injections
- Controversial and generally unproven
- Other
- May consider orthotics
Surgical Management
- Compose of either open primary repair, endoscopic primary repair, or augmentation/reconstruction4
- Usually indicated for complete, proximal avulsion fractures or partial avulsions in at least 2 tendons with greater than 2 cm retraction.May consider for recalcitrant pain after failure of conservative treatments50
- Open surgical repair has a complication rate of 23.17% with acute repairs having better functional outcomes
At different disease stages
New onset/acute
- Control of inflammation/pain and protection of the area (Stage I)
- POLICE (Protection, optimal loading, ice, compression, elevation)31
- NSAIDs
- Physical therapy
- Focusing on soft tissue treatments, flexibility, neural glides
Subacute
- Progression of physical therapy regimen to include strengthening, beginning with open chain exercises and progressing to more advanced closed chain exercises, followed by a progressive eccentric strengthening program.
- Specific focus on eccentric component.
- Secondary prevention with flexibility and adequate warm-up and gradual return to sport.
Chronic
- No benefit of NSAIDs at this stage
- Progression of physical therapy similar to subacute regimen. warm-up, continued eccentric exercise, and gradual return to sport.
- Surgical management for recalcitrant pain can be considered.
Coordination of care
A multi-disciplinary team approach of treatment professionals is helpful to optimize outcomes. In addition to the physiatrist, physical therapists provide a key role for the recovery of these injuries. Other providers involved may include an athletic trainer, orthotist, sports psychologist, and orthopedic surgeon.
Patient & family education
It is important to have communication between the patient/athlete as well as the coach and parents in order to maximize rehabilitation and activity modification to enhance return to sport.
Emerging/unique interventions
- Early incorporation of rehabilitation may provide earlier recovery for an athlete’s return to play.51
- A gradual return to activity depends on multiple factors, including the severity of the injury along with the chronicity of the injury.
- Maintain aerobic fitness early in treatment with swimming and/or upper body ergometer.
- Incorporate lower body aerobic activities such as pool running, cycling or elliptical machine when normal pain-free range of motion has been restored.
- Progress gradually with return to sport/running program.
- Most athletes make a full recovery, although caution remains due to the risk of recurrence.
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
- Acute hamstring injuries are usually self-limiting and generally respond to proper rest and a progressive rehabilitation protocol with good success and return to sport.
- Chronic hamstring injuries / tendinopathies require a careful examination to assess for other differential diagnoses and usually a more prolonged rehabilitation protocol.
- As with most tendon injuries, surgery should be reserved for only those who have truly failed a comprehensive and complete conservative management program, including a progressive eccentric exercise program. The exceptions to this may include an avulsion fracture or complete rupture of tendon with greater than 2 cm of retraction, as described above.
Cutting Edge/Emerging and Unique Concepts and Practice
Surface electromyography (EMG) has been used to assess maladaptive hamstring activation.52
Previous studies have incorporated functional MRI (fMRI) to assess metabolic activity during an athletic task through the transient increase of relaxation time of tissue water in T2 imaging.32,48,53-57
Sciatic nerve hydrodissection may be an alternative method of decompressing the sciatic nerve in cases of scarring.
Gaps in the Evidence-Based Knowledge
Possible other treatments which are controversial or unproven include the following:
- Injections
- Corticosteroid injection (CSI) for an acute tendinitis – avoid injecting into the tendon by using ultrasound for needle guidance in a peritendinous approach.
- In a study evaluating the efficacy of CSI, it was shown to provide pain relief at 1 month in up to 50% of patients58
- Percutaneous needle tenotomy in chronic recalcitrant cases59,60
- Platelet-rich plasma (PRP), dextrose, autologous blood – function as irritants or proinflammatory agents to induce a healing response in chronic injuries
- Sclerosing polidocanol of the neo-vessels61
- Aprotinin62
- Controversies are typically those surrounding injection therapy: Safety profile of corticosteroid injections in weight-bearing tendons is cause for concern, although data suggests that it is beneficial. Few studies have evaluated PRP therapies specifically for hamstring tendon injuries; studies that do exist have shown mixed results.63
- A recent systematic review provided only non-statistically significant evidence for PRP injections with or without physical therapy reducing time to return to play or re-injury rate when compared to physical therapy alone or no treatment.64,65
- Corticosteroid injection (CSI) for an acute tendinitis – avoid injecting into the tendon by using ultrasound for needle guidance in a peritendinous approach.
- Other
- Dry needling66
- Topical nitroglycerin67
- Iontophoresis
- Phonophoresis
- Therapeutic ultrasound
- Low-level laser therapy
- Extracorporeal shock wave therapy68
- Kinesio tape
- Numerous studies are investigating newer tendinopathy treatments, but most are not looking at the treatment of tendinopathy specifically regarding the hamstring.
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Original Version of the Topic
John E. Tobey, MD. Proximal and mid-hamstring strain/tendon tear. 1/9/2013.
Previous Revision(s) of the Topic
Daniel C. Herman, MD, Justin Weppner DO, Sara Raiser MD. Proximal and mid-hamstring strain/tendon tear. 4/28/2017
Sara Raiser MD, Daniel C. Herman, MD, PhD, Justin Weppner DO, Giorgio Negron, MD. Proximal and Mid-Hamstring Strain/Tendon Tear. 4/29/2021
Author Disclosures
Sara Raiser, MD
Nothing to Disclose
Jacqueline Maier, MD
Nothing to Disclose
Justin Weppner, DO
Nothing to Disclose
Giorgio Negron, MD
Nothing to Disclose
Daniel C. Herman, MD, PhD
Nothing to Disclose