Hamstring Strain

Partial or complete tear of one or more hamstring muscles (biceps femoris, semitendinosus, semimembranosus), usually at the myotendinous junction, during sprinting, kicking, or sudden stretching. The biceps femoris is injured in about 80% of cases.

• It is among the commonest muscle injuries in sport, accounting for about 12 to 16% of all injuries in running and field sports (football, rugby, athletics, Australian football). The muscles cross two joints and work eccentrically in the late swing phase of sprinting, so they are vulnerable.
• Risk factors: previous hamstring injury (the strongest, recurrence 12 to 30%), age above 25 years, poor eccentric hamstring strength, strength imbalance with quadriceps, inadequate warm up, fatigue, reduced hip flexor and lumbar flexibility, lumbar spine problems, and high sprint load.
• Types: acute sprint type (biceps femoris, at maximal speed), stretch type (semimembranosus, at the proximal tendon during extreme hip flexion and knee extension, as in dancers and splits), and proximal avulsion of the ischial origin.
• Grades: grade 1 (minor fibre damage, no loss of strength), grade 2 (partial tear with loss of strength), grade 3 (complete rupture or avulsion).

• A sudden sharp pain in the posterior thigh during activity, with a pop or a feeling of tearing, and the athlete usually stops at once.
• Grade 1: mild pain and tightness, walks normally. Grade 2: moderate pain, limping, swelling, and bruising within 24 to 48 hours, painful resisted knee flexion, and reduced hamstring strength. Grade 3: severe pain, unable to walk, a palpable gap or a retracted lump, extensive bruising tracking toward the knee, and marked weakness.
• Examination: palpate along the muscle and ischial tuberosity, assess the passive straight leg raise (pain and restricted range), resisted knee flexion at 15 and 90 degrees, and gait. Bruising distal to the injury and a palpable defect suggest a major tear.
• Differential diagnosis: referred pain from the lumbar spine or sacroiliac joint, sciatic nerve irritation, gluteal or piriformis syndrome, adductor magnus strain, hip pathology, proximal hamstring tendinopathy, ischial bursitis, avulsion fracture of the ischial apophysis (adolescents), deep vein thrombosis, compartment syndrome, and tumour.
• Complications: recurrence, chronic pain, scar tissue and reduced flexibility, myositis ossificans, sciatic nerve entrapment by scar tissue, and in avulsion, weakness and loss of function.

• Clinical for most injuries.
• Imaging is considered for severe injuries, suspected avulsion, unclear diagnosis, elite athletes needing return-to-play prognosis, or failure to improve at 2 to 3 weeks. Ultrasound shows the tear and haematoma. MRI is the best test, and defines the extent of the injury, the tendon involvement, and retraction (a retraction of more than 2 cm of a proximal tendon is surgical).
• X-ray in adolescents with ischial pain to show an apophyseal avulsion, and to exclude myositis ossificans later.
• Check for deep vein thrombosis (ultrasound) if swelling and calf pain are out of proportion.

• First 48 to 72 hours: protect from further injury, relative rest, ice for 10 to 15 minutes every 2 to 3 hours, compression, and elevation. Crutches for grade 2 and 3 injuries when walking is painful. Avoid heat, alcohol, massage and stretching in this period.
• Analgesia: paracetamol 1 g orally 6 hourly. Short course NSAIDs (ibuprofen 400 mg orally 8 hourly with food for 3 to 5 days) may be used, though high dose long term use may slow healing. Topical diclofenac 1% gel is an alternative. Avoid opioids except for severe pain.
• Rehabilitation, which is progressive and criteria based, not time based:
  • Phase 1 (days 1 to 5 to 7): pain free gentle movement, isometric hamstring contractions at multiple angles, walking, and stationary cycling at low resistance.
  • Phase 2 (about week 1 to 3): progressive resistance exercises (bridging, hamstring curls, eccentric loading, Nordic hamstring exercises, and single leg bridges), core and lumbopelvic stability, and gradual stretching.
  • Phase 3 (about week 3 to 6): running progression (jogging, striding, then sprint speed running), eccentric strengthening at long muscle length, and agility.
  • Phase 4: sport specific training and return to play when there is no pain, full range, strength at least 90% of the uninjured side (preferably 100%), and tolerance of maximal speed running and sport drills.
  • Typical return: grade 1, 1 to 3 weeks. Grade 2, 4 to 8 weeks. Grade 3, 3 to 6 months or longer.
• Platelet rich plasma injection has not been shown to speed return in acute injuries. Corticosteroid injection is not recommended because it weakens tendon and muscle.
• Surgery (urgent, ideally within 2 to 4 weeks) for proximal complete avulsions of 2 or more tendons with retraction of more than 2 cm, a bony avulsion with displacement over 2 cm, and for chronic tears with persistent weakness, using suture anchor repair. Results are best when done early, with 6 to 12 months of rehabilitation. Sciatic nerve decompression for entrapment.
• Chronic proximal hamstring tendinopathy: loading programme (isometrics, then progressive eccentric and heavy slow resistance, 3 times weekly for 12 weeks), extracorporeal shock wave therapy (3 to 5 weekly sessions), and rarely corticosteroid or platelet rich plasma injection around, not into, the tendon.
• Prevention: Nordic hamstring exercise (reduces injury by about 50%, performed 2 to 3 times weekly, starting with 2 sets of 5 repetitions and building to 3 sets of 8 to 12), eccentric strengthening, adequate warm up, hip and lumbar mobility, and load management.
• Special groups:
  • Adolescents: avulsion of the ischial apophysis needs X-ray, and most heal with rest and gradual loading, with surgery for displaced fragments.
  • Elderly: consider a neurological or vascular cause, and assess for tendon degeneration.
  • Anticoagulation: a haematoma can expand, so ice, compress and seek review if swelling grows.
  • Pregnancy: rest and physiotherapy, with paracetamol only.
• Follow up: review at 1 week and then at 2 to 3 weeks. Refer to sports medicine or orthopaedics for grade 3 injury, suspected avulsion, no progress by 3 weeks, and recurrent injury.