Injuries to the hamstring muscles in the back of the thighs are extremely common on all levels of athletic competition.
They account for up to 29% of all lower extremity injuries across all sports and represent an important cause of back of the thigh and buttock pain.1-8 For example, the incidence of hamstring injuries in the National Football League (NFL) was second only to knee sprains over a 10-year period.9 Not surprisingly, the occurrence of hamstring injury in sports such as soccer, rugby, basketball, track and field, and gymnastics has been reported at a similar rate.4,10-13
An acute hamstring injury can commonly occur during exercise, but can also be the result of a fall or other accident. People with suspected hamstring injuries typically experience sudden pain at the back of the thigh with associated weakness, and are advised to seek medical attention.
Injury to the hamstrings can be detrimental with an average number of days lost to injury ranging from 8 to 25, depending on injury location and severity.9,13 Unfortunately, there is a relatively high rate of re-injury, especially in the first two weeks following return to activity.2 Therefore, care must be taken to properly diagnose and treat an acute hamstring injury to avoid long-term complications, such as strength deficits and prolonged pain.
Why Are Early Diagnosis, Treatment, and Rehabilitation Important?
Getting an early diagnosis and receiving proper treatment for a hamstring injury is important because:
- Early recognition and appropriate management of hamstring injuries, followed by a proper return to activity, have been shown to result in improved functional outcome and prevention of future injuries.14-18
- A re-injured hamstring typically takes longer to heal.2,9,19,20, For example, it has been reported that NFL players with recurrent injuries needed 2.5 times longer for recovery and return to play than players with first-time injuries.9
- Hamstring injuries have been shown to result in permanent anatomical findings on MRI scans and in physical exams.
- High (proximal) hamstring injuries, if improperly managed, may eventually lead to a condition called chronic hamstring tendinopathy. This condition results in degeneration of the hamstring tendon, which connects the muscle to the ischial tuberosity (sit bone), and it can potentially cause significant pain and long-term disability. 21-23
This article will discuss the anatomy, mechanism of injury, risk factors, signs and symptoms, diagnosis, treatment, rehabilitation, and prevention of acute hamstring injuries.
Hamstring Muscle Anatomy
What is commonly called the “hamstring” is actually a group of three muscles. These muscles originate near the hip, travel down the back of the thigh, and end just below the knee joint.
The three hamstring muscles include:
- The biceps femoris, which is the outermost muscle
- The semimembranosus
- The semitendinosus24
The hamstrings have tendons at both ends for attachment to the hip and shin bones. Tendons are fibrous tissues that connect muscles to bones. Where the hamstring originates near the hip is called the proximal hamstring, and tendons connect the proximal hamstring to the bottom of the pelvis at the ischial tuberosity (or “sit bone”). Where the hamstring attaches past the knee joint is called the insertion.
All three hamstring muscles have insertions below the knee. Tendons of the semimembranosus and semitendinosus insert at the top of the tibia (shinbone). The biceps femoris tendon inserts at the top of the fibula, the long bone located outside of (lateral to) the tibia.
The hamstrings have a higher proportion of type 2 muscle fibers when compared with other lower leg muscles. These type 2 muscle fibers, or fast twitch muscle fibers, enable hamstrings muscles to provide short, powerful contractions. The hamstring muscles contract while shortening (concentric contraction) during explosive take-offs and contract while lengthening (eccentric contraction) to help slow down the body during quick cutting moves and changes of direction.
Like all muscles in the body, activation of the hamstrings requires a nerve supply. The sciatic nerve (L5-S2 nerve roots), which runs down the back of the leg from the spine, provides nerves (innervation) to the hamstring muscles. Therefore, patients with sciatica may have pre-existing hamstring pain and weakness even prior to hamstring injury. Patients experiencing this type of pain should also be evaluated by a qualified medical professional.