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Orthopaedic Surgery - Hamstring Strain

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Basics

The hamstrings are a group of long muscles located in the posterior thigh. They extend from the pelvis toward the knee and play an important role in hip extension, knee flexion, gait, sprinting, and deceleration.

A hamstring strain is a stretch-induced or forceful contraction injury of the muscle-tendon unit.

The injury commonly occurs when the hamstrings are required to change rapidly from controlling limb motion eccentrically to generating force concentrically, particularly during sudden acceleration or deceleration.

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Mechanism

Hamstring strains frequently occur during quick starts, sudden stops, sprinting, jumping, or other explosive movements that produce a powerful contraction while the muscle is lengthened.

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Classification

Hamstring strains are traditionally divided into three grades according to severity.

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Mild Strain

A mild strain produces pain and muscle spasm without a substantial structural tear.

There is minimal loss of strength and usually only mild functional limitation.

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Moderate Strain

A moderate injury involves partial tearing of muscle fibers.

Pain is more pronounced, and measurable weakness and functional limitation are present.

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Severe Strain

A severe injury represents a complete or near-complete tear of the muscle or tendon, sometimes including avulsion from its bony attachment.

Marked weakness and immediate loss of function are typical.

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Limitations of Grading

Traditional strain grading provides a useful description of injury severity, but clinical classification systems do not consistently predict the exact time required for return to sport.

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Prevention

Prevention programs focus on improving hamstring strength, flexibility, fatigue resistance, and neuromuscular control.

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Stretching

Regular hamstring stretching may be beneficial, particularly as part of a structured conditioning program.

Stretching should be performed carefully when the muscles are fatigued.

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Conditioning

Anaerobic interval training and sport-specific drills can improve the ability of the hamstrings to tolerate repeated high-speed loading.

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Strengthening

Eccentric hamstring strengthening is particularly important because the hamstrings undergo substantial eccentric loading during sprinting and deceleration.

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Epidemiology

Hamstring strains are among the most common injuries encountered in athletes.

They are particularly associated with sports requiring sprinting, jumping, kicking, sudden acceleration, and ballistic lower-extremity movements.

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Frequency

Hamstring injuries have been reported to account for a substantial proportion of sports-related injuries, reaching approximately 29% in some athletic populations.

They account for approximately 12% of injuries among professional football players in some series.

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Associated Sports

Activities commonly associated with hamstring injury include running, football, skiing, dancing, skating, jumping, and weight lifting.

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Recurrence

Recurrence is a major clinical problem.

Approximately one-third of hamstring injuries may recur, particularly when return to sport occurs before full recovery of strength and flexibility.

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Risk Factors

Important risk factors include:

Increasing age, previous hamstring injury, muscle weakness, imbalance between quadriceps and hamstring strength, reduced lower-extremity flexibility, impaired trunk or core stability, fatigue, and dehydration.

The strongest predictor of future hamstring injury is often a previous hamstring strain.

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Anatomy and Pathophysiology

The principal hamstring muscles are the biceps femoris, semitendinosus, and semimembranosus.

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Proximal Origin

The semitendinosus, semimembranosus, and long head of the biceps femoris originate from the ischial tuberosity.

The short head of the biceps femoris originates from the posterior femur rather than the pelvis.

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Distal Insertions

The biceps femoris inserts primarily on the fibular head.

The semitendinosus inserts medially on the proximal tibia as part of the pes anserinus, while the semimembranosus inserts on the posteromedial proximal tibia.

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Function

The hamstrings flex the knee and contribute to hip extension.

During running and gait, they contract eccentrically to decelerate knee extension and absorb kinetic energy.

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Common Site of Injury

Muscle strain most often occurs near a musculotendinous junction, frequently involving the biceps femoris, especially during high-speed running.

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Pediatric and Adolescent Considerations

In children and adolescents, the tendon may be stronger than the immature apophysis.

A forceful hamstring contraction can therefore produce an ischial tuberosity avulsion fracture rather than a purely tendinous injury.

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Adult Considerations

In adults, the same mechanism may produce a partial or complete proximal hamstring tendon avulsion.

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Etiology

Hamstring strains usually occur when the muscle is rapidly lengthened while simultaneously generating substantial force.

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Predisposing Factors

Predisposing factors include:

Poor flexibility, inadequate warm-up, fatigue, dehydration, muscle weakness, impaired coordination between opposing muscle groups, and quadriceps-to-hamstring strength imbalance.

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Common Injury Mechanisms

Typical mechanisms include:

Sprinting from starting blocks, clearing a hurdle, forceful jumping or take-off, sudden acceleration, rapid deceleration, and water-skiing falls.

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Water-Skiing Injury

A classic water-skiing mechanism occurs when the hips are suddenly flexed while the knees remain extended, sometimes producing substantial proximal hamstring injury.

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Associated Conditions

Hamstring injuries may coexist with other musculoskeletal problems, including lumbar strain and groin strain.

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Diagnosis

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History

The usual presentation is sudden posterior thigh pain during running, jumping, or another explosive activity.

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Sudden Onset

Most patients describe an abrupt onset of pain and tenderness.

A smaller proportion may develop symptoms more gradually.

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Pop

More severe injuries may be accompanied by a sudden pop or tearing sensation, followed by immediate weakness or inability to continue activity.

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Signs and Symptoms

Common symptoms include:

Posterior thigh pain, tenderness, weakness, swelling, bruising, and difficulty walking or running.

Pain is generally aggravated by stretching the hamstrings or activating them against resistance.

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Physical Examination

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Gait

Patients may demonstrate a stiff-legged gait because they attempt to avoid simultaneous hip flexion and knee extension, which places the hamstrings on stretch.

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Inspection

The posterior thigh should be examined for:

Swelling, bruising, ecchymosis, hematoma, contour abnormality, or a palpable defect.

Marked bruising may indicate a more substantial tear.

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Palpation

The entire hamstring muscle-tendon complex should be palpated from the ischial tuberosity to the distal insertions.

The location of maximal tenderness helps identify the injured structure.

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Resisted Knee Flexion

Pain or weakness with resisted knee flexion supports the diagnosis of hamstring injury.

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Resisted Hip Extension

Pain with resisted hip extension may also occur, especially with proximal injury.

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Stretch Testing

Passive hip flexion combined with knee extension stretches the hamstrings and may reproduce symptoms.

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Pathological Findings

The injury spectrum ranges from microscopic muscle-fiber disruption to a partial or complete tear of the biceps femoris, semitendinosus, semimembranosus, or associated tendons.

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Imaging

Imaging is not routinely required when the history and examination clearly indicate an uncomplicated muscle strain.

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Plain Radiographs

Radiographs should be obtained when fracture or avulsion is suspected.

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Pelvic Radiographs

In adolescents, pelvic radiographs may demonstrate an ischial tuberosity avulsion fracture.

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Knee Radiographs

If symptoms are concentrated near the distal biceps femoris insertion, knee radiographs may demonstrate an associated fibular head avulsion fracture.

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Femoral Radiographs

Plain films of the femur may be helpful when a fracture is suspected after significant trauma.

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MRI

MRI can define the location, extent, and severity of muscle or tendon injury.

It is particularly useful when a complete tendon avulsion, substantial tear, or alternative diagnosis is suspected.

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Stress Fracture

MRI can also differentiate a hamstring strain from an occult stress fracture.

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Bone Scintigraphy

Bone scintigraphy can help distinguish stress fracture from soft-tissue injury, although MRI is generally preferred when available.

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Differential Diagnosis

Important differential diagnoses include:

Acute fracture, stress fracture, muscle contusion, proximal hamstring tendon avulsion, ischial apophyseal avulsion, and other posterior thigh muscle injuries.

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Referred Pain

In more chronic or atypical presentations, referred symptoms from the lumbar spine or hip should also be considered.

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Treatment

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General Principles

Most musculotendinous hamstring strains are treated nonoperatively.

Treatment progresses through phases according to pain, strength, flexibility, and functional recovery rather than following a rigid timeline.

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Acute Phase

During approximately the first week, treatment focuses on controlling pain and swelling.

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Initial Measures

Relative rest, ice, compression, and elevation may be used during the early symptomatic period.

Gentle pain-free motion should begin as tolerated.

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Subacute Phase

As acute inflammation and pain improve, progressive rehabilitation begins.

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Concentric Strengthening

Concentric strengthening can be introduced gradually, together with low-impact cross-training.

Exercises should remain below the threshold that produces significant pain.

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Remodeling Phase

During subsequent weeks, rehabilitation emphasizes restoration of muscle length, strength, and neuromuscular control.

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Stretching

More progressive hamstring stretching can be introduced once acute pain has settled.

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Eccentric Strengthening

Eccentric strengthening is a central component of rehabilitation because the hamstrings must tolerate high eccentric loads during running.

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Agility and Trunk Stabilization

Progressive agility drills and core or trunk stabilization exercises are useful for restoring dynamic lower-extremity control.

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Functional Phase

Running and sport-specific training can resume gradually when the patient is pain free and has recovered adequate strength and motion.

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Return to Sport

Return should be based on functional criteria rather than time alone.

The patient should demonstrate full or near-full range of motion, minimal or no tenderness, symmetric strength, and the ability to sprint and perform sport-specific tasks without pain.

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Competitive Phase

Once full activity resumes, continued strengthening, flexibility training, and neuromuscular conditioning are important to reduce recurrence.

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Activity

Initial rest should be followed by a gradual progression of activity according to symptoms and functional recovery.

Premature return to sprinting increases the risk of reinjury.

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Physical Therapy

Physical therapy is useful for restoring motion, strength, flexibility, and sport-specific function.

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Ice Massage

Ice massage may be used for short-term symptomatic relief during the early phase.

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Therapeutic Modalities

Modalities such as ultrasound have historically been used, although rehabilitation should focus primarily on progressive exercise and functional restoration.

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Aquatic Exercise

Water-based exercise may permit range-of-motion and conditioning work while reducing loading on the injured muscle.

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Exercise Progression

Once soreness has improved, active range of motion can progress to resisted knee flexion, hip-extension exercises, eccentric loading, running drills, and sport-specific movements.

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Medication

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NSAIDs

NSAIDs such as ibuprofen or naproxen may provide short-term relief of pain and swelling.

They have not been shown to accelerate muscle healing and should be used primarily for symptomatic control.

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Acetaminophen

Acetaminophen may be used as an alternative analgesic.

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Biologic Treatments

Platelet-rich plasma and other biologic therapies have been investigated for hamstring injuries.

Evidence supporting routine use remains limited, and these treatments should not replace structured rehabilitation.

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Surgery

Surgery is generally not indicated for uncomplicated musculotendinous junction strains.

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Ischial Tuberosity Avulsion Fracture

Adolescent avulsion fractures require assessment of displacement and functional impairment.

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Displacement

Historically, displacement greater than approximately 2 cm has been considered a possible indication for operative fixation, particularly in active patients.

Significantly displaced fractures have a greater risk of painful nonunion and persistent functional limitation.

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Tendon Avulsion

Complete proximal hamstring tendon avulsions, particularly those involving multiple tendons with substantial retraction, may be considered for surgical repair.

Treatment depends on age, activity level, chronicity, degree of retraction, and functional deficit.

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Referral

Evidence of complete tendon rupture, proximal tendon avulsion, substantial weakness, or a significantly displaced ischial avulsion fracture should prompt referral to an orthopaedic sports-medicine specialist.

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Follow-Up

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Prognosis

Most hamstring strains heal successfully with appropriate rehabilitation.

Recovery time depends on injury severity, location, previous injury, and functional demands.

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Mild Strains

Mild strains may improve within several days to approximately 1 week.

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Moderate Strains

Moderate injuries may require approximately 1–3 weeks or longer, depending on the size and location of the tear.

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Severe Injuries

Severe injuries, tendon avulsions, or displaced ischial tuberosity avulsion fractures may require many weeks to several months before full return to high-level sport.

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Complications

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Recurrent Strain

Previous hamstring injury significantly increases the risk of another strain.

Recurrence is especially common when flexibility, eccentric strength, and sprinting capacity have not been fully restored.

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Chronic Weakness

A significant untreated tendon injury may lead to persistent weakness, reduced endurance, and difficulty with high-speed activity.

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Scar Formation

Healing may produce scar tissue that alters normal muscle-tendon mechanics and contributes to recurrent symptoms.

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Symptomatic Nonunion

Substantially displaced ischial tuberosity avulsion fractures may fail to unite and produce chronic pain, weakness, or sitting discomfort.

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Patient Monitoring

Patients should be followed according to symptom severity and athletic demands.

Monitoring should include pain, tenderness, range of motion, hamstring strength, gait, flexibility, running tolerance, and ability to perform sport-specific movements.

A long-term program of eccentric strengthening, flexibility work, trunk stabilization, and graded athletic conditioning should be continued after return to sport to reduce the risk of recurrence.