Hamstring Injury: Hamstring Strain Symptoms, Causes, and Management

Hamstring strains are caused by a rapid extensive contraction or a violent stretch of the hamstring muscle group which causes high mechanical stress. This results in varying degrees of rupture within the fibres of the musculotendinous unit.

Hamstring strains are common in sports with a dynamic character like sprinting, jumping, contact sports such as Australian Rules football (AFL), American football and soccer where quick eccentric contractions are regular. In soccer, it is the most frequent injury.

Hamstring injuries can also occur in recreational sports such as water-skiing and bull riding, where the knee is forcefully fully extended during injury.

The hamstrings consist of three muscles :
  • Biceps femoris
  • Semitendinosus and
  • Semimembranosus

Hamstring strains

Epidemiology/Etiology

The cause of a hamstring muscle strain is often obscure. In the second half of the swing phase, the hamstrings are at their greatest length and at this moment, they generate maximum tension.

In this phase, hamstrings contract eccentrically to decelerate flexion of the hip and extension of the lower leg. At this point, a peak is reached in the activity of the muscle spindles in the hamstrings.

A strong contraction of the hamstring and relaxation of the quadriceps is needed. According to “Klafs and Arnheim”, a breakdown in the coordination between these opposite muscles can be a cause for the hamstring to tear.

The greatest musculo-tendon stretch is incurred by the biceps femoris, which may contribute to its tendency to be more often injured than the other 2 hamstring muscles (semimembranosus and semitendinosus) during high-speed running.

Predisposing Factors/Risk Factors

There are various proposed risk factors which may play a role in hamstring injuries:
  • Older age
  • Previous hamstring injury
  • Limited hamstring flexibility
  • Increased fatigue
  • Poor core stability
  • Strength imbalance
  • Ethnicity
  • Previous calf injury
  • Previous substantial knee injury
  • Osteitis pubis
Increased quadriceps flexibility was inversely associated with hamstring strain incidence in a group of amateur Australian Rules footballers

Players presenting certain polymorphisms, IGF2 and CCL2 (specifically its allelic form GG), might be more vulnerable to severe injuries and should be involved in specific prevention programmes

Hamstring strains

Tight hip flexors

previously associated lumbar spine abnormalities. Kicking and executing abdominal strengthening exercises with straight legs have been identified as possible contributory causes of lordosis.

The anatomical reason seems to be that the iliopsoas muscle group is primarily involved in kicking and straight leg raising or straight leg sit-up exercises and contributes to strengthening this muscle'.

Therefore, it is possible that certain athletic activities and training methods that exacerbate postural defects may also predispose the player to injury.

During activities like running and kicking, hamstring will lengthen with concurrent hip flexion and knee extension, this lengthening may reach the mechanical limits of the muscle or lead to the accumulation of microscopic muscle damage.

There is a possibility that hamstring injuries may arise secondary to the potential uncoordinated contraction of biceps femoris muscle resulting from dual nerve supply.

Another debate is on hamstring variation in muscle architecture. The short head of biceps femoris(BFS) possesses longer fascicles (which allow for greater muscle extensibility and reduce the risk of over lengthening during eccentric contraction) and a much smaller cross-section area compared to the long head of biceps femoris(BFL).

Whereas BFL presents with shorter fascicles compared to BFS which undergo repetitive over lengthening and accumulated muscle damage.

Excessive anterior pelvic tilt will place the hamstring muscle group at longer lengths and some studies proposed that this may increase the risk of strain injury.

Characteristics/Clinical Presentation

Hamstring strain results in a sudden, minimal to severe pain in the posterior thigh. Also, a "popping" or tearing impression can be described. Sometimes swelling and ecchymosis are possible but they may be delayed for several days after the injury occurs.

Rarely symptoms are numbness, tingling, and distal extremity weakness. These symptoms require further investigation into sciatic nerve irritation. Large hematoma or scar tissue can be caused by complete tears and avulsion injuries.

Hamstring strains are categorised in 3 groups, according to the amount of pain, weakness, and loss of motion.

Grade 1 (mild): just a few fibres of the muscle are damaged or have ruptured. This rarely influences the muscle's power and endurance. Pain and sensitivity usually happen the day after the injury (depends from person to person).

Normal patient complaints are stiffness on the posterior side of the leg. Patients can walk fine. There can be a small swelling, but the knee can still bend normally.

Grade 2 (medium): approximately half of the fibres are torn. Symptoms are acute pain, swelling and a mild case of function loss. The walk of the patient will be influenced. Pain can be reproduced by applying precision on the hamstring muscle or bending the knee against resistance.

Both the muscle belly and the tendon can suffer from this injury. It causes massive swelling and pain. The function of the hamstring muscle can't be performed anymore and the muscle shows great weakness.

Diagnostic Procedures

Radiographs: a good thing about radiographs is that with that kind of imaging, it's possible to differentiate the etiology of the pain. It can differentiate in muscular disease (e.g muscle strain) or a disease of the bone (e.g. Stress fracture).

Ultrasound (US): this kind of imaging is used a lot because it is a cheap method. It is also a good method because it has the ability to image muscles dynamically. A negative point about Ultrasound is that it needs a skilled and experienced clinician.

Magnetic Resonance Imaging (MRI): MRI gives a detailed view of muscle injury. But sometimes it may not be clear according to the images.

MRI study was done to distinguish between two main groups of muscle injuries: Injury by Direct or Indirect trauma.

Hamstring strains

Examination

Running gait: The physical examination begins with an examination of the running gait. Patients with a hamstring strain usually show a shortened walking gait. Swelling and ecchymosis aren’t always detectable at the initial stage of the injury because they often appear several days after the initial injury.

Observation: The physical examination also exists of visible examination. The posterior thigh is inspected for asymmetry, swelling, ecchymosis and deformity.

Palpation: Palpation of the posterior thigh is useful for identifying the specific region injured through pain provocation, as well as determining the presence/absence of a palpable defect in the musculotendon unit.

With the patient positioned prone, repeated knee flexion-extension movements without resistance through a small range of motion may assist in identifying the location of the individual hamstring muscles and tendons.

With the knee maintained in full extension, the point of maximum pain with palpation can be determined and located relative to the ischial tuberosity, in addition to measuring the total length of the painful region.

The total length, width and the distance between the ischial tuberosity and the area with maximal pain are measured in centemeters. While both of these measures are used, only the location of the point of maximum pain (relative to the ischial tuberosity) is associated with the convalescent period.

That is, the more proximal the site of maximum pain, the greater the time needed to return to pre-injury level. The proximity to the ischial tuberosity is believed to reflect the extent of involvement of the proximal tendon of the injured muscle, and therefore a greater recovery period.

Range of motion: Range of motion tests should consider both the hip and knee joints. Passive straight leg raise (hip) and active knee extension test (knee) are commonly used in succession to estimate hamstring flexibility and maximum length.ypical hamstring length should allow the hip to flex 80° during the passive straight leg raise and the knee to extend to 20° on the active knee extension test.

When assessing post-injury muscle length, the extent of joint motion available should be based on the onset of discomfort or stiffness reported by the patient. In the acutely injured athlete, these tests are often limited by pain and thus may not provide an accurate assessment of musculotendon extensibility. Once again, a bilateral comparison is recommended.

Hip flexibility The hip flexion test combined a passive unilateral straight leg raise test (SLR) with pain estimation according to the Borg CR-10 scale. The sprinters were placed supine with the pelvis and contralateral leg fixed with straps. A standard flexometer was placed 10 cm cranial to the base of the patella.

The foot was plantar flexed and the investigator slowly(approximately 30 degree) raised the leg with the knee straight until the subject estimated a 3 (“moderate pain”) on the Borg CR-10 scale (0 = no pain and 10 = maximal pain). The hip flexion angle at this point was recorded, and the greatest angle of three repetitions was taken as the test result for Range of Motion (ROM).

Values of the injured leg were expressed as a percentage of the uninjured leg for comparisons within and between groups. No warm-up preceded the flexibility measurements.

Knee flexion strength: Isometric knee flexion strength was measured with the sprinter in a prone position and the pelvis and the contralateral leg fixed.A dynamometer was placed at the ankle, perpendicular to the lower leg. The foot was in plantar flexion and the knee in an extended position.

Three maximal voluntary isometric knee flexion contractions were performed, each with gradually increasing effort. Each contraction lasted 3 s with 30 s of rest in-between. The highest force value was taken as the test result for strength.

Attempts to bias the medial or lateral hamstrings by internal or external rotation of the lower leg, respectively, during strength testing, may assist in the determination of the involved muscles.

Medical Management

Surgical intervention is an extremely rare procedure after a hamstring strain. Only in case of a complete rupture of the hamstrings, surgery is recommended. Almost all patients believed that they had improved with surgery.

A study shows that 91% was satisfied after surgery and rated their happiness with 75% or better. Hamstring endurance tests and hamstring strength tests were better and highly scored after a surgical procedure. The muscle strength testing after surgery ranged from 45% to 88%.

The hamstrings endurance testing ranged from 26% to 100%. The physical examination and follow-up reveal that all repairs stayed intact.

Physiotherapy Management

The primary objective of physical therapy and the rehabilitation program is to restore the patient’s functions to the highest possible degree and/or to return the athlete to sport at the former level of performance and this with minimal risk of re-injury.

Hamstring strain injuries remain a challenge for both athletes and clinicians, given their high incidence rate, slow healing, and persistent symptoms. Moreover, nearly one-third of these injuries recur within the first year following a return to sport, with subsequent injuries often being more severe than the original.

The use of a specific and adequate training programme to rehabilitate hamstring strains can be determinant for the healing and prevention of a recurrent hamstrings strain injury.

The use of eccentric strengthening, at long muscle length exercises, as a rehabilitation tool was used to examine the effects to prevent a recurrence hamstring injury following the revalidation. The results shown that the use of eccentric strengthening exercises at long muscle had a positive effect.

On the other hand, a study tried to compare eccentric strengthening exercises (STST) with progressive agility and trunk stabilization exercises (PATS). The rehabilitation of the STST group consisted of static stretching, isolated progressive hamstring resistance exercise, and icing.

The PATS group consisted of progressive agility and trunk stabilization exercises and icing as treatment.
Dr Rohit Bhaskar, Physio
Dr Rohit Bhaskar, Physio Dr. Rohit Bhaskar, Physio is Founder of Bhaskar Health and Physiotherapy and is also a consulting physiotherapist. He completed his Graduation in Physiotherapy from Uttar Pradesh University of Medical Sciences. His clinical interests are in Chest Physiotherapy, stroke rehab, parkinson’s and head injury rehab. Bhaskar Health is dedicated to readers, doctors, physiotherapists, nurses, paramedics, pharmacists and other healthcare professionals. Bhaskar Health audience is the reason I feel so passionate about this project, so thanks for reading and sharing Bhaskar Health.

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