Hamstring muscle injury is common in many kinds of sports and often accounts for an extended absence from training and competition. Injury is commonly sustained during eccentric contraction. It is most frequently located proximally and can be divided into the high-speed running type and the stretching type injury.
Physical examination should take place within 2 days post-injury and may reveal bruising, focal swelling, pain, and a decrease in both muscle strength and range of motion. MRI and ultrasound can provide detailed information on the nature and extent of the injury. MRI is the best choice to confirm the diagnosis, provide an accurate prognosis, and monitor healing strains. Mild or moderate hamstring strains are preferably treated conservatively, whereas surgical treatment is reserved for severe hamstring injuries including avulsions and recurrent hamstring injuries that are resistant to a conservative approach. Adequate warming up and eccentric stretching exercises lead to a decrease in the risk of injury, while muscle fatigue increases that risk.
What Is The Function of Hamstrings Muscle?
The hamstring muscles are extensors of the hip and flexors of the knee, absorbing kinetic energy and protecting the hip and knee joints during the gait cycle by limiting knee extension just before and during heel strike. During the gait cycle, there is an interplay between the hamstrings and the quadriceps in an antagonizing way.
Hamstring muscle Injury Mechanism
Hamstring muscle injury occurs during eccentric contraction rather than a concentric contraction. Eccentric contractions take place in a state of muscle stretching, in which the contracting muscle fibres put even more tension on the stretched muscle.
Because the prime function of the hamstring muscle complex is to absorb kinetic energy by eccentric contraction, it is vulnerable to a strain injury, especially in the region adjacent to the MTJ (musculotendinous junction).
Recent studies pointed out that different sports lead to lesions in different regions of the hamstring muscle complex through different injury mechanisms. Two distinct types of injuries are known: the high-speed running type and the stretching type. The high-speed running type, incurred during sports such as football or athletics, is strongly associated with injuries in the long head of the biceps femoris muscle. Injuries of the stretching type occur during stretching exercises carried out to an extreme joint position (hip flexion and knee extension), as is the case with dancing or kicking during rugby. They are often complex, but mainly involve the semimembranosus muscle and its proximal free tendon close to the ischial tuberosity.
These types of injury have different prognoses, which is illustrated by the time that is needed to recover to the pre-injury level, which is longer for the stretching type.
Apart from the injury mechanism, the precise location of the injury within each muscle also corresponds with different prognoses. Hamstring muscle strains, generally occurring at the proximal sections of a muscle, prove to be more problematic as they are located closer to their origin at the ischial tuberosity. Involvement of the free proximal tendon is also associated with a longer time to return to the pre-injury level.
Hamstring Injuries - Symptoms and Signs
While people with a mild hamstring lesion seldom seek medical attention, athletes incurring a moderate or severe injury will typically do so. The patient’s history will relate to a sudden onset of pain in the posterior thigh region, most likely during sprinting or extreme stretch. Hamstring muscle injuries of the high-speed running type occur during sprinting when speed is (close to) maximal, causing the athlete
to stop running at once. Injuries of the stretching type are often experienced as acute pain close to the ischial tuberosity, accompanied by an audible “pop”.
Predisposing factors include inadequate warm-up, muscle fatigue, poor muscle strength, poor lumbopelvic strength and stability, older age, muscle imbalance between quadriceps and hamstrings, muscle imbalance between left and right hamstrings, previous hamstring muscle injury, and L5 nerve root entrapment.
Physical Examination of Hamstring Muscle Injury
Although the value of a physical examination in (suspected) hamstring muscle strains remains controversial, expert opinion and a review of the available literature seem to agree on several issues. The initial assessment should take place within 2 days post-injury to ensure a reliable medical history and the possibility of a quick intervention when necessary, yet allow possible signs of swelling and hematoma to develop.
- Inspection should mainly focus on posture and gait examination, focal swelling, and hematoma. Both inspection and palpation of the injury site can help identify the muscle involved as well as determine the proximity of the injury. For instance, in the case of a true hamstring avulsion, extensive bruises can be seen on the posterior thigh and a defect in the tendon may be felt if there has been sufficient retraction.
- During palpation, athletes with hamstring injuries of the high-speed running type report their highest pain in the lateral part of the posterior thigh, about 11–12 cm distal to the ischial tuberosity. With this type of injury, there is a significant correlation between the location of the point of highest pain and the length of the convalescent period. The more proximal the point of highest pain, the longer the convalescent period. Length of the painful area however does not correlate with the duration of the convalescent period.
- Athletes with the stretching type hamstring injury report their highest pain in the proximal posterior thigh, 2 cm distal to the ischial tuberosity. The convalescent period of the stretching-type injury does not correlate significantly with the location of the highest pain.
- Despite possible inaccuracies due to pain, range of motion (ROM) testing should reveal decreased flexibility in the affected leg. The best way to establish a deficit in the posterior thigh region is by using passive or active straight leg raise and passive or active knee extension tests. The “sit-and-reach” test should be omitted from standard ROM testing due to confounding factors such as spinal mobility (i.e., lumbar flexion), leg length, scapular abduction, and stretch on the peripheral nerves by dorsiflexion of the ankle joint.
- With the patient lying supine, the strength of the hamstring muscles can be examined by comparing knee flexion and hip extension between both legs. In this way, a possible decrease in the strength of the affected leg can be determined, although it is good to realize that this could also be caused by pain instead of fiber disruption. The use
of the “hamstring drag” test remains controversial and needs further validation.
Hamstring Injury: Treatment
The best way to treat a hamstring muscle injury depends on the extent, precise location, and function the muscle is required to regain.
Mild or moderate hamstring strains are to be treated conservatively. The treatment consists of a phased rehabilitation program.
The first phase focuses on hamstring protection and consists of rest to avoid stretching of the hamstrings and application of ice to minimize pain and inflammation, followed by low-intensity pain-free exercises within a limited ROM. These low-intensity exercises involve the entire lower extremity and lumbopelvic region to develop neuromuscular control and minimize atrophy. Avoiding stretching of the hamstring prevents the development of dense scar tissue that can prohibit muscle regeneration.
