What is the Hamstring?
The hamstring is a group of 3 muscles that are found on the posterior side of the legs, the biceps femoris, the semitendinosus, and the semimembranosus. They originate on the lower part of the pelvis called the ischial tuberosity and attach to the bones of the shin called the tibia and fibula. The main job of these muscles is to flex the knee and extend the hip. When running or sprinting, the main job of the hamstring is to slow down or decelerate the tibia through an eccentric load before it makes contact with the ground.
What causes Hamstring Strains?
If someone overworks their hamstring muscle or stretches it past its normal range of motion, it can result in an injury called a strain. The greatest risk posed to hamstrings is running because they are active for the majority of the leg cycle putting them commonly at their maximum length. Injuries usually happen when the mechanical demand put on the hamstring during running will exceed the mechanical limit of the muscle. There are two different theories as to what is the major cause of hamstring strains. The first is through microscopic muscle tears accumulating over a long period of time, while the second is a tear happening through a single event. In either case, both result in a torn or strained hamstring muscle.
Hamstring strains are graded based on their severity. Grade 1 tears are small disruptions in muscle integrity with mild swelling and pain with minimal to no loss in strength. Grade 2 tears are partial muscle tears with some intact musculotendinous fibers presenting with pain with significant noticeable loss of strength. Grade 3 tears are complete separations of the muscle unit from its attachment site resulting in complete loss of muscle function usually accompanied with a large hematoma.
Who is at risk for Hamstring Strains?
Athletes at highest risk are in sports that require a lot of high acceleration running such as runners, track and field sprinters/hurdlers, soccer players, football players, rugby players. Other sports with high risk are ones that require stretching the hamstrings past their physiological limit including various forms of dance including ballet.
Other risk factors include increased age, increased weight, and decreased muscled mass. The highest risk of developing a hamstring strain is having had a previous injury to the muscle. This is due to the body incorrectly healing itself leading to suboptimal muscle structure and accumulation of scar tissue making it more likely to injure again. Early muscle fatigue is also a risk factor due to it not being able to replenish itself while it is being overworked making it easier to injure.
What are the symptoms?
When a hamstring strain occurs, the most common symptoms someone will feel is sudden pain on the posterior side of the thigh. The patient may also hear an audible pop during the stretch or while running right before the pain starts. The patient may also walk with a noticeable limp. The patient will also feel pain and decreased range of motion with hip flexion and extension on physical exam.
How are Hamstring Strains diagnosed?
The most common way to diagnose hamstring tears are based on the history of the injury and physical exam. Musculoskeletal Ultrasonography “Ultrasound” (US) can be used when available to identify the injury and grade its severity. Other imaging techniques available include Magnetic Resonance Imaging (MRI) and X-rays. MRI’s can also be used to determine the severity of injury, but usually unnecessary unless other diagnoses need to be ruled out. MRI is also quite expensive and rarely can be done at the bedside like an ultrasound evaluation.
How are Hamstring Strains treated?
Treatment options depend on the severity of the strain. For more minor grade 1 injuries options include mostly conservative measures such as protection from further injury with removal from sport, rest, applying ice, using compression with either taping or an ACE wrap. To help with inflammation, ibuprofen can be used as well as keeping the injury elevated.
Movement restriction of the hamstring for the first few days days has shown evidence of reducing the amount of scar tissue formation. Using anti-inflammatory medications such as Ibuprofen (Advil) or Acetaminophen (Tylenol) can also decrease pain and inflammation felt. If pain is not relieved with conservative measures, glucocorticoid or steroid injections can help to relieve pain, but is not usually recommended due to evidence of causing tendon degeneration increasing risk of future rupture. Physical therapy is ultimately the best option for optimal recovery. This usually can begin by the first week with focus on increasing range of motion, core stability, and ultimately muscle strength as healing occurs. If a complete tear happens, a referral to orthopedic surgery may be warranted for surgical repair.
How can Hamstring Strains be prevented?
The best way to prevent hamstring injuries is through a targeted regimen to improve strength, stability, and flexibility. Techniques such as core stability exercises and strength training with certified trainers can go a long way. Stretching the hamstrings both before and after exercise will train them to be more flexible and be able to work for longer periods of time. Some dynamic stretches and exercises include an eccentric load to the hamstring, which has been shown to significantly reduce hamstring tears. See our SPARCC handouts on our website for examples of some of these exercises. Finally, recognition of fatigue and cessation of exercising once you start to get tired can be crucial to preventing injury.
When can I return to my sport?
When it comes to sports injuries, the recovery depends individually patient-to-patient as well as the severity of the injury. With aggressive physical therapy and the patient following all the recommendations from the physician, the recovery time usually lasts about 2-4 weeks for mild injuries, but may last several months if the injury is more severe. For less demanding sport or for getting back to work, recovery usually lasts a few days to a week. However, before the athlete can return to any high intensity sport, they must have near to normal knee and hip range of motion, resolved pain, and near full symmetric strength. Return to play decisions for athletes going back to high intensity sports should be determined by their sports medicine doctors to avoid re-injury.
By Jon Ferlmann and Mo Mortazavi, MD
References:
Hamstring Strain (Pulled Hamstring) (Sportsinjuryclinic.net)
Opar, David A, et al. “Hamstring Strain Injuries: Factors That Lead to Injury and Re-Injury.” Sports Med., 1 Mar. 2012, pp. 210-226. Pubmed.gov, http://www.ncbi.nlm.nih.gov/pubmed/22239734.
Fieldds, Kari B, et al. Hamstring Muscle and Tendon Injuries. UpToDate.com, 20 Apr. 2017.
