Hamstring Strain

The Hamstring Strain is the most commonly strained condition of the hip joint, with the biceps femoris being the most commonly injured hamstring.

Hamstring tears are typically partial rather than complete, and usually occur during the eccentric phase of muscle usage, when the muscle develops tension as it lengthens. These running related hamstring injuries typically occur along and intramuscular tendon, or aponeurosis, and the adjacent muscle fibers.

Another type of hamstring injury, which involves the semimembranosus and its proximal free tendon, can occur during activities such as kicks that involve simultaneous hip flexion and knee extension. This type of injury tends to require a prolonged recovery before an individual is able to return to his or her preinjury level of performance.

See Also: Hip Muscles Anatomy

Hamstring Strain Risk Factors

A hamstring strain has a varied list of contributing factors including:

Previous hamstring injury:

There is a strong correlation between a history of prior hamstring injury and recurrence. This is likely because of the fact that the initial injury results in a loss of extensibility and a loss of eccentric strength.

Degenerative joint disease of the lumbar spine:

LB pain and injury result in restricted ROM and decreased hamstring extensibility. In addition, research has demonstrated that LB pain decreases proprioception and neuromuscular control of the lower extremities.

See Also: Hip Range of Motion

Advancing age:

It is not clear why injuries to soft tissues served by the L5 and S1 nerves, which supply the hamstring and calf muscles, have such a strong correlation with advancing age, whereas there is little or no correlation between age and the soft tissue injuries with an L2–4 nerve supply. One could summize that the lumbar nerve roots of L5 and S1 are more likely to be affected by age-related spinal degeneration than the nerve supply of the quadriceps muscles (L2, L3, and L4).

Anterior pelvic tilt:

A common finding is anterior tilt of the innominate bones on the injured side that increases tension in the hamstrings and causes a relative lengthened position of their origin and insertion. This altered pelvic position can also contribute to decreased hamstring strength.

Cibulka et al. researched manipulative treatment to correct an anterior innominate position in patients who had hamstring injuries. After only one treatment, isokinetic hamstring peak torque increased by 21.5% when compared with controls.

However, functional improvement from this torque increase was not addressed. One of the reasons cited for the significantly increased incidence in hamstring injuries in athletes of black origin is because they tend to have an increased anteriorly tilted pelvis.

Leg length inequality:

The shorter leg can develop overly tight hamstrings.

Anatomical arrangement:

Being a biarticular muscle group means that the hamstrings are more susceptible to adaptive shortening and can also be subjected to large length changes. Everyday movements, such as walking, squatting, and sitting, flexion of the hip and knee occur together, with opposing effects on hamstring length. In contrast, the knee is extended and the hip is flexed in running and kicking, which places the hamstrings at longer lengths thereby increasing the risk of muscle tears.

Antagonists to prime movers, muscles that are used to control or resist motion, are also at a greater risk of injury than the prime movers themselves. While decelerating the body, these muscles contract while
rapidly lengthening. Therefore, they are performing “eccentric contractions”. ,

Poor posture:

For example, Janda’s lower crossed syndrome, which is associated with adaptive shortening of the hip flexors and the erector spinae, weak/inhibited gluteal and abdominal muscles, an increased anterior pelvic tilt and a hyperlordosis of the spine.

Muscle imbalance:

Muscle balance is a term used to describe the relationship between either:

• Agonist to antagonist muscle groups: The hamstrings are directly antagonistic to the quadriceps during the first 160–165 degrees of leg extension but assume a paradoxical extensor action concurrent with initial contact.
• The relationship of agonist muscle groups between limbs (inhibited gluteus maximus).
• Eccentric to concentric muscle ratios.
• The strength ratios between the hamstrings and trunk stabilizers.

See Also: Hamstring Flexibility

Decreased flexibility:

Although there is little to no evidence to support this theory, decreased flexibility of the hamstrings has long been cited as the primary cause of hamstring injuries. In fact, the evidence has demonstrated that there is no correlation between passive hip flexion measurements and hamstring injuries provided that the minimum range is between 85 and 90 degrees.

However, a differentiation must be made between active flexibility (the absolute range of movement in a joint or series of joints that is attainable in a momentary effort) and passive flexibility (the ability to assume and maintain extended positions) as research has shown that active flexibility is more closely related to sports achievement than is passive flexibility.

Hamstring strength:

The relationship between strength and the potential for a hamstring injury is not made clear in the studies available. Many authors have commented on the limitations of isokinetic testing and the specificity of the types of training. Few studies have reported on the relationship between concentric and eccentric strengths and the frequency of hamstring injury, but those that have suggested that poor eccentric strength in the hamstring muscle group might be a causative factor in hamstring strains.

Kibler stated that sports- or activity-specific testing is more appropriate for evaluating an athlete. Zachazewski commented that for a test to have a predictive value it must incorporate some of the dynamic characteristics specific to that sport. Lephart et al. states that low peak torque values are not necessarily related to functional capacity.

Precipitating activity:

Most hamstring injuries occur during running at the end of the swing phase or at foot strike when the hamstrings are working to decelerate the limb, while also controlling extension of the knee. At this point the greatest muscle–tendon stretch is incurred by the biceps femoris, which may contribute to its tendency to be more often injured than the other two hamstring muscles during high-speed running.

With the forceful flexion of the hip and extension of the knee during the swing phase of sprinting, the hamstring muscle groups are put under extremely high loads in a lengthened position where they must change from functioning eccentrically, to decelerate knee extension in the late swing, to concentrically, becoming an active extensor of the hip joint. It has been proposed that this rapid changeover from eccentric to concentric function of the hamstring is when the muscle is most vulnerable to injury.

Kujala et al. also suggested that, during this swing phase, the hamstrings are placed under extremely high loads in an elongated position.

Inadequate warm-up:

Although most clinicians prescribe warm-up and stretching to help reduce the incidence of muscle strains, the evidence supporting this idea is weak and largely based on retrospective studies.

Fatigue:

In a study of professional soccer players, nearly half (47%) of the hamstring injuries sustained during matches occurred during the last third of the first and second halves of the match.

Kyrolainen et al. looked at the recruitment pattern of leg muscles during different running speeds. The greatest changes in muscle activity pattern were observed in the biceps femoris muscles as the speed increased from a slow jog to maximum speed.

Pinniger et al found that, when footballers became fatigued during sprinting, there was earlier activation of the biceps femoris and semitendinosus muscles. Asynchrony may be because of local muscle fatigue and/or neural fatigue as a result of “irritation or damage along the path of the nerve supplying the muscle.”

General fatigue secondary to poor sleep patterns, stress, or suboptimal nutrition could result in
central nervous system fatigue.

Poor coordination:

Many hamstring strains occur during the last part of the swing phase or at heel strike, during which time the hamstrings work maximally eccentrically to decelerate the leg.

Other factors:

Other unsubstantiated predisposing factors include:

1. playing surface,
2. level of hydration,
3. adverse neural tension,
4. experience of the coach,
5. hormonal levels (abnormally low resting levels of testosterone and unfavorable testosterone/cortisol ratio during recuperation after exercise).

Some of these factors are modifiable, others are not. The modifiable factors include muscle imbalances between flexibility and strength, overall conditioning, and playing surface.

Clinical Findings

Clinical findings associated with hamstring injury include:

1. patient reports of a distinctive mechanism of injury with immediate pain during sprinting or while decelerating quickly. In acute cases, the patient may report a “pop” or tearing sensation.
2. tenderness elicited with passive stretching of the hamstrings.
3. posterior thigh pain, often near the buttock, which is worsened with resisted knee flexion.
4. tenderness to palpation, which is generally located at the muscle origin at the ischial tuberosity but may also be present in the muscle belly and distal insertions.

The differential diagnosis for posterior thigh pain includes:

1. neoplasms,
2. overt lumbar disk protrusions with definite signs of nerve root impingement,
3. ischial tuberosity apophysitis, or an avulsion fracture.

Examination of the lumbar spine is important, because muscle injury may be related to referred pain with subsequent muscle inhibition and weakness.

Hamstring Strain Grading

Hamstring strain can be graded according to findings:

1. Grade I: gait appears normal but there is pain with extreme range of a straight-leg raise.
2. Grade II: antalgic gait or gait with a flexed knee. Resisted knee flexion and hip extension are both painful and weak.
3. Grade III: usually requires the use of crutches for ambulation. In severe cases, ecchymosis, hemorrhage, and a muscle defect may be visible several days postinjury.

Hamstring Strain Treatment

The initial treatment of the acute Hamstring Strain include:

1. The injured extremity is protected with modified ambulation,
2. Nonsteroidal anti-inflammatory medications NSAIDs,
3. Ice or cryotherapy for decreasing pain and inflammation: it should be applied for 10 to 20 minutes to the injured area several times a day.
4. Compression and elevation.
5. Intramuscular Corticosteroid Injection: highly controversial,
6. Therapeutic Exercise: isolated muscle stretching and strengthening.

Hamstring Strain surgery is necessary only in case of a complete rupture of the hamstring.

The Hamstring injury rehab protocol is based on the stage of healing:

1. Patients with a grade I strain can usually continue activities as much as possible.
2. A grade II strain typically requires 5–21 days for rehabilitation,
3. patient with a grade III strain may require 3–12 weeks of rehabilitation.

References

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