Hamstring Injuries

Hamstring injuries are among the most common muscle injuries in sport. They affect sprinters, footballers of every code (AFL, soccer, rugby) and track athletes, and they run from a mild strain to a complete proximal avulsion that needs surgical repair.

Who. Hamstring injuries make up 12-16% of all sports injuries in running-based sports, and approximately 15-20% of all injuries in elite running-and-kicking sport (AFL, soccer, rugby), where the average time loss for a Grade II injury is 3-4 weeks of missed playing time. The peak age is 20-40 years, the years of peak athletic participation, and men outnumber women about 2:1, reflecting higher male participation in sprinting sports.

Which muscle. The long head of biceps femoris takes 80% of injuries, semimembranosus 15% and semitendinosus 5%. Why the long head is the one that tears is set out in the anatomy section.

Mechanism. Four patterns account for the spectrum:

• Eccentric overload in the late swing phase of sprinting, the muscle lengthening under load
• Sudden acceleration or deceleration: change of direction, explosive sprinting
• Extreme hip flexion with the knee extended (the splits, water-skiing): the mechanism of proximal avulsion
• Chronic overuse: accumulated microtears in high-volume training

Sprint-type or stretch-type. The single most useful thing to establish from the history is which of two injuries this is, because they differ in the muscle involved, the site within it, and above all in how long the athlete will be out. Askling's work, which underpins the rehabilitation protocols in this topic, rests on this split.

• Sprint-type. Terminal swing phase at high speed, sudden onset, usually the biceps femoris long head at its proximal myotendinous junction. The athlete typically knows the exact stride. These are the commoner injuries and, grade for grade, the quicker to return.
• Stretch-type. A slow, high-amplitude stretch rather than speed: the sliding tackle, the high kick, dancing, a hurdle, doing the splits. These characteristically involve the proximal semimembranosus close to its free tendon, often with less dramatic initial symptoms, and they are substantially slower to recover, sometimes several times longer than a sprint-type injury that looked worse on day one.

A stretch-type injury with modest pain and a nearly full range of movement can be badly underestimated at first assessment, and an optimistic early prognosis will be wrong. Ask specifically what the leg was doing at the moment of pain, and let the answer, not the initial severity, anchor the timeline you give. The same history decides where to look on MRI: a stretch-type mechanism should send you to the proximal free tendon and its aponeurosis rather than the mid-substance myotendinous junction, which is exactly the free-tendon and intratendinous involvement the BAMIC "c" suffix is designed to capture, and which carries the longer return and higher reinjury risk.

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The three muscles. Semimembranosus, semitendinosus and biceps femoris make up the posterior thigh. Semitendinosus and the long head of biceps femoris arise from the ischial tuberosity as a shared conjoint tendon; semimembranosus arises just lateral to it. All three flex the knee and extend the hip, and semitendinosus also internally rotates the tibia.

The innervation, stated correctly. Biceps femoris as a whole has two nerve supplies because it has two heads: the long head from the tibial division of the sciatic nerve (L5, S1, S2) and the short head from the common peroneal division (L4, L5, S1). There is no medial-to-lateral split within the long head, and "the long head has dual innervation" is routinely written in exam answers and is an anatomical error. The proposed consequence, asynchronous activation between the two heads during high-speed running, remains a hypothesis rather than a demonstrated cause. The short head is the odd one out twice over: a different nerve, and the only hamstring that does not arise from the ischial tuberosity, taking origin from the linea aspera instead.

Why the long head tears. The better-established reasons are mechanical. It is the most eccentrically loaded hamstring in terminal swing, it has the longest fascicles and greatest musculotendinous excursion, and it has a long, thin proximal aponeurosis over which strain concentrates, which is where the tear usually starts.

The sciatic nerve. It lies immediately lateral to the hamstring origin and descends through the posterior thigh. That proximity is why a proximal avulsion can produce sciatic symptoms, and why protecting the nerve is the central step of surgical repair.

Blood supply. Perforating branches of the profunda femoris artery supply the muscles, with the inferior gluteal artery supplying the proximal portion. The myotendinous junction, the most common site of Grade I-II tears, is a watershed zone with relatively poor vascularity and the highest stress concentration during eccentric loading, and that poor blood supply is why it is slow to heal.

The running cycle. The hamstrings fail in late swing (70-80% of the gait cycle), when the muscle lengthens while contracting to decelerate the leg. Peak force occurs just before foot strike, and this eccentric load, up to 2.5 times body weight, exceeds the muscle's capacity in fatigue.

Proximal avulsion is a different injury from the strain: extreme hip flexion with the knee extended (the splits, water-skiing, martial arts kicks) separates one or more tendons completely from the ischial tuberosity, and it is the Grade III injury that may need surgical repair.

Risk factors. Previous hamstring injury is the greatest risk factor.

• Modifiable: inadequate warm-up, hamstring weakness (H:Q ratio less than 0.6), fatigue, limited flexibility
• Non-modifiable: age over 30, previous injury, the anatomy of the long head (long fascicles)

History. The mechanism names the injury. Sprinting or acceleration produces a mid-substance or proximal myotendinous-junction tear; sudden deceleration or a change of direction is eccentric overload; extreme hip flexion with the knee extended (the splits, water-skiing) is the mechanism of proximal avulsion. An acute pop or tearing sensation suggests a Grade II-III injury. Then establish:

• Where the pain is: the posterior thigh points to the mid-substance, the ischium or buttock to the proximal tendon
• How severe it was: mild enough to continue playing, or severe enough to stop immediately
• What the athlete can no longer do: sprint, kick or accelerate
• Any previous hamstring injury, the most significant risk factor for re-injury

Examination. The findings scale with grade, and the discriminators are gait, a palpable defect and strength.

Special tests. Three tests, each with a different job: one clears the athlete for sport, one separates a proximal from a mid-substance injury, and one is specific for a proximal avulsion.

Differential diagnosis. Posterior thigh and buttock pain has a wider differential than the hamstring, and one entry on it must not be missed.

Who needs imaging. The diagnosis is clinical first: severity is determined from the history and examination, and imaging is not required for a Grade 0-I injury when the diagnosis is clear. MRI is indicated for a Grade II or suspected Grade III injury, when surgical planning is needed, and in the elite athlete.

MRI is the gold standard and is mandatory for accurate grading and surgical planning, obtained at 24-72 hours. T2-weighted sequences show muscle oedema as bright signal and T1-weighted sequences show the anatomy, in coronal and axial views. Three measurements predict the return-to-sport timeline: the percentage of cross-sectional area involved, the longitudinal length of the injury and, for a Grade III injury, the retraction distance.

For a proximal avulsion, MRI must document four things, because they decide the surgical approach and the prognosis:

1. The number of tendons avulsed (semitendinosus, semimembranosus, long head of biceps femoris), each reported separately
2. The retraction distance, measured from the ischial tuberosity to the proximal tendon edge on the coronal view, in the position used for surgical planning
3. Muscle quality: fatty infiltration suggests a chronic injury
4. Haematoma size

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Localising the lesion by tendon and zone says more than a generic "hamstring tear", and it separates an avulsion suitable for repair from a muscle-belly or distal injury.

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Ultrasound is the alternative: real-time and dynamic, but operator-dependent. It can show tendon retraction and haematoma, it is less sensitive than MRI for muscle oedema, and it is useful for serial monitoring of healing. Correct identification of the compartments prevents mislabelling the injured muscle and guides safe intervention, and a systematic scan sequence is more reproducible than scanning the painful point alone.

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Repeat imaging. If the athlete is not progressing at 4-6 weeks, reassess with MRI: persistent oedema or an enlarging gap suggests the need for intervention. Serial ultrasound tracks rehabilitation progress.

Other investigations. A plain radiograph only if there is concern for an ischial tuberosity avulsion fracture (rare, adolescents). CT is not routinely indicated.

Algorithm

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The decision. Grade decides treatment. Grade I and II strains are treated conservatively with progressive loading, and return is gated on functional criteria rather than time alone. A proximal avulsion is decided by MRI: a complete three-tendon avulsion, more than two avulsed tendons, or retraction over 2cm goes to urgent surgical referral, with acute repair within 4 weeks preferred. A lesser avulsion has a conservative trial with close monitoring, and a persistent functional deficit after 3 months of conservative care may need delayed reconstruction.

Grade I-II (Conservative)Grade III Proximal AvulsionChronic/Delayed Reconstruction

The goal is progressive loading that restores strength and prevents re-injury. The phases below are gated by criteria, not the calendar, and the evidence-based exercise is the eccentric one.

Rehabilitation Timeline

ProtectionPhase 1: Acute (Day 0-3)

Protect the muscle: rest from aggravating activities, ice for 15-20 minutes every 2-3 hours, a compression bandage and elevation. NSAIDs (ibuprofen 400mg three times daily) for 3-5 days. Pain-free knee flexion and extension, avoiding stretching. Crutches for a Grade II injury with a significant limp.

ProgressivePhase 2: Early Loading (Day 3-14)

Pain-free isometric hamstring contractions (seated knee flexion against resistance), gentle stretching within the pain-free range (aggressive stretching delays healing), walking that increases in distance and speed as tolerated, and aqua jogging in the pool for unloaded work.

CriticalPhase 3: Eccentric Strengthening (Week 2-6)

Nordic hamstring curls, 3 sets of 5-8 repetitions three times a week, are the evidence-based core of rehabilitation. Add single-leg deadlifts for controlled eccentric loading and increase the resistance as strength improves. No sprinting or kicking yet.

FunctionalPhase 4: Sport-Specific (Week 4-8)

Running progresses from light jogging to straight-line sprinting to change of direction. Hopping and bounding plyometrics begin once the Askling test is negative, followed by kicking and acceleration drills specific to the sport. Strength testing: the H:Q ratio must be greater than 0.8.

ClearancePhase 5: Return to Sport (Week 6-12)

Clearance requires all four criteria: (1) Askling H-test negative, (2) H:Q ratio greater than 0.8, (3) pain-free full sprinting, (4) sport-specific drills completed without symptoms. Minimum time is 2-3 weeks for Grade I and 4-8 weeks for Grade II. Nordic hamstring curls continue twice a week indefinitely.

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Do Not Rush Return

Premature return, within 3 weeks of a Grade II injury, carries a 34% re-injury rate. Athletes who complete the full rehabilitation, including eccentric strengthening, re-injure at 12%, the same figure seen in Grade II athletes who return after 6 weeks, and every additional week of rehabilitation reduces re-injury risk by approximately 5%. Take a minimum of 6 weeks for a Grade II injury, and 12 weeks after surgery for Grade III, and rest clearance on functional criteria (strength, the Askling test, pain-free sprinting), not time alone.

Indications for surgery. Any one of the following:

• Retraction greater than 2cm measured on MRI
• More than 2 tendons completely avulsed, which is a complete 3-tendon avulsion, regardless of retraction
• Failed conservative trial (3 months) with persistent functional deficit
• Elite athlete with high functional demands: sprinters and footballers who require full strength

Timing. Acute repair, within 4 weeks, gives the best outcomes and the easiest dissection. Subacute repair at 4-12 weeks is acceptable but more challenging. Beyond 12 weeks the injury is chronic and needs delayed reconstruction, which may require graft augmentation.

The operation is suture-anchor repair of the tendons to the ischial tuberosity with the patient prone and the sciatic nerve protected throughout. The technique is set out step by step in the next section.

Indications. A chronic injury (greater than 12 weeks) with a persistent functional deficit, failed conservative management, sitting pain affecting quality of life, or inability to perform work or sport.

Why it is harder. Tendon retraction and scarring make mobilisation difficult, muscle atrophy and fatty infiltration reduce the strength that can be recovered, and an allograft or autograft may be needed to bridge the gap. Heterotopic ossification at the origin is a recognised consequence of a chronically retracted, untreated avulsion, and it adds excision of the ectopic bone and debridement of scar to the operation, sometimes with a graft and sciatic neurolysis.

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What changes in the operation. An extended dissection to mobilise the retracted tendons, a semitendinosus autograft or Achilles allograft to bridge the gap, more extensive preparation of the ischial tuberosity, internal brace augmentation for the high-demand athlete, and prolonged rehabilitation (6 months minimum).

Outcomes are inferior to acute repair but the improvement is still meaningful for the patient with a persistent deficit: good-to-excellent results in 70-80% against 90-95% for acute repair, persistent weakness in 20-30%, and resolution of sitting pain in 80-90%. Return-to-sport and strength figures by timing are in the outcomes section.

Consent. The figures the patient hears:

• Sciatic nerve injury 1-3% (numbness, weakness, a permanent risk)
• Infection 2-5%, superficial wound infection most common
• Re-rupture 5-10%, if non-compliant with the post-operative protocol
• Persistent weakness 10-20%, especially after chronic repairs
• Sitting discomfort, which may persist for 6-12 months
• Failure to return to sport 10-20%

Equipment. Suture anchors, 5.5mm, 3-5 of them; No.2 non-absorbable suture (Fiberwire or Ethibond); deep retractors for gluteus maximus and the sciatic nerve; a C-arm for anchor placement, the lateral view confirming depth; and a post-operative hip brace limiting flexion to 60 degrees.

Positioning and ApproachTendon IdentificationAnchor PlacementTensioning and Closure

Position. Prone on a radiolucent table so the C-arm can reach, with chest padding to reduce pressure on the chest and abdomen, pelvic bolsters that support the pelvis and allow hip mobility, the knees padded to protect the patellae, and the arms on arm boards or alongside the body. Slight hip and knee flexion reduces tension on the retracted stump and the sciatic nerve. The set-up must still allow fluoroscopy, and distal access if a second incision is needed; confirm on the C-arm lateral view that the ischial tuberosity can be seen.

Preparation. Wide, from the lumbar spine to mid-thigh bilaterally, including the perineum in the field for ischial access, under a transparent adhesive drape.

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Incision. Palpate the ischial tuberosity, the bony prominence inferior to the gluteal fold. A transverse incision in the gluteal crease is preferred, or a longitudinal one, centred over the tuberosity and 8-12cm long, with a longitudinal extension available for chronic retraction. Deepen through the subcutaneous fat, identifying and protecting the posterior femoral cutaneous nerve.

Deep dissection. Split gluteus maximus longitudinally along its fibres, by blunt dissection to avoid bleeding. Identify the sciatic nerve at the lateral border of the incision, deep to gluteus maximus, and place a deep retractor to hold it laterally and protect it throughout. The nerve lies lateral and deep to the ischial tuberosity and is vulnerable during lateral retraction and anchor placement; where scar tethers it and obscures the plane, it must be identified and released.

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Finding the stumps. Evacuate the haematoma with copious irrigation, removing clot and scar, then palpate distally for the retracted stumps, usually 3-8cm distal to the tuberosity, the usual range running to 10cm. Each tendon has a signature:

• Semitendinosus: most medial, a long thin cord, and the easiest to identify
• Biceps femoris long head: lateral and thick
• Semimembranosus: deep to the other two, broad and flat

In chronic cases the tendons may be scarred together and must be separated carefully before repair.

Mobilisation. Gentle traction brings the tendons to the ischial tuberosity. Release adhesions but preserve the muscle belly, and do not over-tension, which causes postoperative stiffness.

Whipstitch. Each tendon is whipstitched with No.2 non-absorbable suture (Fiberwire) over 3-4cm, leaving long tails for passage through the anchors.

Preparing the tuberosity. A rongeur or curette removes soft tissue and fibrous tissue down to bleeding bone, decorticating lightly to create the footprint. Identify the medial, central and lateral zones.

The construct. Three to five 5.5mm anchors, which have good pull-out strength in the ischium, placed in a horseshoe across the medial, central and lateral positions; one described construct uses three, two for the conjoint tendon and one for semimembranosus. Drill perpendicular to the bone surface and angle slightly medially, away from the sciatic nerve, and confirm the depth on the C-arm lateral view. Fluoroscopic orientation and controlled drill depth reduce the risk of pelvic penetration while preserving adequate bone bridges.

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Suture passage. Pass the anchor sutures through the whipstitched tendons in a mattress configuration for each tendon, which compresses tendon to bone, loading multiple sutures per anchor (typically 2-3 tendons).

Anchor Placement Danger

The sciatic nerve lies lateral and deep, so lateral or posterior drilling risks it. Drill perpendicular to the bone surface, aim medially, and confirm depth with the C-arm: anchors belong in cortical bone, not through-and-through.

Tension. Hip neutral (0 degrees of flexion or extension) and the knee at 45 degrees of flexion. Tie the sutures sequentially, medial to lateral, tensioning to restore normal anatomy without over-tightening: the aim is tendon length restored without excessive hip or knee flexion.

Test. Passively flex the hip to 90 degrees with the knee extended: the repair should hold without gapping. Extend the knee: there should be no excessive tension on the repair. Confirm the repair is not strangulated and that the sciatic nerve is freely mobile before closing.

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Closure. A suction drain deep to gluteus maximus, removed at 24-48 hours; the split in gluteus maximus repaired with absorbable sutures; deep fascia with 0 Vicryl; subcutaneous layer with 2-0 Vicryl; skin with staples, removed at 14 days, or a subcuticular 3-0 Monocryl.

Brace. A hip brace limiting flexion to 60 degrees, worn for 6 weeks and removed only for exercises, protects the repair through the critical healing period.

Intraoperative troubleshooting. Four problems recur, and each has a standard answer:

Re-injury is the complication that defines this injury, and the AFL data put numbers on it. Risk remains elevated for approximately 15 weeks after return to play (Orchard 2020), and a recent prior hamstring injury is by far the strongest risk factor (adjusted OR 13.1). Prevention rests on three things: Nordic hamstring exercises (approximately 70% reduction in overall injury and approximately 85% reduction in recurrence, Petersen 2011), functional testing before clearance (the Askling test and the H:Q ratio), and continued eccentric loading and load monitoring well beyond clearance (4-8 weeks for Grade II, 12 or more weeks after surgery).

Platelet-rich plasma. PRP appears in this topic as an "option", in the complications table and the recurrent-injury scenario, so the evidence deserves to be stated plainly. For acute hamstring muscle injury, placebo-controlled randomised trials and subsequent meta-analyses have not shown that PRP shortens return-to-play time or reduces re-injury compared with a structured rehabilitation programme, with or without a blinded placebo injection; the early enthusiasm was not borne out once PRP was tested against blinded saline controls. PRP is therefore not recommended as routine treatment for acute hamstring strain. The intervention with robust (Level 1) evidence remains progressive eccentric loading, the Nordic programme, supported by criterion-based return to play. PRP and other biologics may still be discussed with elite athletes under shared decision-making, but without an evidence-based expectation of faster or safer return.

The principles are strict brace compliance for 6 weeks to prevent re-rupture, Nordic hamstring curls from week 6 onwards, loading that increases gradually with symptoms monitored, and objective functional testing before return. Pain during rehabilitation means the load is excessive. No aggressive stretching for the first 12 weeks, because it delays healing; no running before 12 weeks; and no return to sport before 4 months for athletes.

Conservative management (Grade I-II). Almost every Grade I injury and most Grade II injuries return, and the number that matters is the re-injury column:

Surgical repair (proximal avulsion). Every measure falls as the delay to repair lengthens:

Prognostic factors. The good and the poor are mirror images of each other.

• Good: acute repair within 4 weeks; 2 or fewer tendons involved; no muscle atrophy or fatty infiltration on MRI; a young patient (under 40); compliance with the post-operative protocol (brace, restricted range); a maintained Nordic hamstring programme
• Poor: delayed repair beyond 12 weeks; complete 3-tendon avulsion with extensive retraction; chronic muscle changes (atrophy, fatty infiltration); an older patient (over 50); non-compliance with rehabilitation; premature return to high-demand activities

Long term. Sitting discomfort resolves in 80% by 12 months, and 20% have persistent mild discomfort. Strength recovers to 90-95% in acute repairs and 70-80% in chronic ones, and after an acute repair 85-90% return to their pre-injury level.

Global epidemiology (PubMed-backed):

Hamstring strain injury is consistently the single most common time-loss injury across football codes worldwide (soccer, rugby, AFL, American football, Gaelic football), so the principles below are examinable on any board.

Major guidance and consensus, side by side:

Registry / surveillance evidence:

Hamstring injury has no implant registry; the equivalent high-volume datasets are prospective sports-injury surveillance systems - the AFL injury surveillance database (Orchard, 20+ seasons), UEFA Elite Club Injury Study (European soccer), and various national rugby and athletics audits. These consistently identify hamstring strain as the dominant time-loss injury and a high-recurrence problem, which is what drives the global emphasis on eccentric prevention and criterion-based return.

Global practice variation:

• Imaging access: MRI grading (BAMIC) is routine in elite/high-resource settings; in limited-resource settings, clinical grading and ultrasound guide management, with similar core rehabilitation principles.
• Return-to-play culture: Professional codes increasingly mandate objective functional clearance (strength symmetry, Askling H-test) rather than fixed time, whereas amateur practice still leans on symptom resolution alone.
• Surgery for proximal avulsion: Performed selectively worldwide for complete/displaced avulsions; thresholds and timing differ by surgeon and access, but acute referral is universally favoured because outcomes deteriorate with delay.

Medicolegal and consent considerations (universal):