eMedicine Specialties > Sports Medicine > Lower Limb

Hamstring Injury

Author: Herman Brad Ruiz, MD, Staff Physician, Department of Physical Medicine and Rehabilitation, Division of Orthopedics and Rehabilitation, Loyola University Medical School at Illinois
Coauthor(s): Syed M Zaffer, MD, Assistant Professor, Department of Physical Medicine and Rehabilitation, Rehabilitation Institute of Chicago, Northwestern University
Contributor Information and Disclosures

Updated: Jun 16, 2008

Introduction

Background

This article focuses on injuries to the hamstring muscles. The word "hamstrings" was derived from the fact that it is these muscles by which a butcher would hang a slaughtered pig.

The hamstrings are a group of muscles (ie, semimembranosus, semitendinosus, biceps femoris) located on the back of the upper leg.^1,2 The hamstrings are a common source of injury and chronic pain in athletes. Injuries to the hamstring muscles primarily occur proximally and laterally, and they usually involve the biceps femoris. The severity of injury to the hamstring muscles is classified according to the following grades:

• Grade 1 is a mild strain, with few muscle fibers being torn.
• Grade 2 is a moderate strain, with a definite loss in strength.
• Grade 3 is a complete tear of the hamstrings.

Hamstring injuries almost always occur at the proximal myotendinous junction. In the biceps femoris, this junction extends over most of its entire length. Injury usually does not occur within the tendon itself unless there is preexisting pathology.

Bony avulsion at the ischial origin may occur as well, but this is usually associated with sudden, large-force, hip-flexion injuries.³ Avulsions are commonly seen in individuals who have been involved in waterskiing accidents in which the knee is extended and the hip is suddenly flexed as the skier falls forward.⁴

One study involving 47 football players with hamstring injuries reported an average of 14 days of convalescence before return to play.

For excellent patient education resources, visit eMedicine's Sports Injury Center, Sprains and Strains Center, and Foot, Ankle, Knee, and Hip Center. Also, see eMedicine's patient education articles Muscle Strain and Ruptured Tendon.

Frequency

United States

As a percentage of lower-extremity injuries, hamstring injuries peak at 33% in persons aged 16-25 years, and they most often occur in sports in which the hamstrings can be stretched eccentrically at high speed.^5,6,7,8,9,10 Prime examples of such sporting activities include sprinting, track and field, and other running contact sports, such as football and soccer. Recreational sports such as waterskiing, in which the knee is fully extended during injury, are also common causes of hamstring injuries.⁴

International

An Australian study involving 1614 individuals with hamstring injuries revealed that such injuries compose 54% of the injuries in rugby, 10% of the injuries in soccer, 14% of the injuries in track, and less than 2% of the injuries in tennis, squash, ballet, and gymnastics.

Functional Anatomy

The hamstrings are composed of 3 muscles, as follows:

• Biceps femoris muscle (long head and short head)
• Semimembranosus muscle
• Semitendinosus muscle

Origins and insertions

All of the muscles of the hamstrings originate on the ischial tuberosity. The second head of the biceps femoris (ie, short head) originates medial to the linea aspera on the distal posterior femur.

The short head of the biceps femoris crosses only one joint to insert with the long head of the biceps femoris onto the fibular head and lateral tibial condyle.

The other hamstring muscles cross 2 joints to reach their insertions. The semitendinosus muscle forms the pes anserinus with the sartorius and gracilis tendons to insert on the medial tibial metaphysis. The semimembranosus muscle interweaves with the fibers of the semitendinosus to eventually insert onto the posteromedial tibial condyle.

Innervations

The short head of the biceps femoris muscle is also unique in that it is innervated by the peroneal portion of the sciatic nerve, whereas the long head of the biceps femoris, semimembranosus, and semitendinosus are innervated by the tibial portion of the sciatic nerve.

Sport-Specific Biomechanics

In track and field events in which the hamstring is eccentrically contracted, the risk of a hamstring injury can be high. Contact sports such as football can result in contusions of the hamstring muscle. The contusion is superficial when the muscle is contracted on impact, and it is deep when the muscle is relaxed on impact. Waterskiing accidents have an association with proximal, bony avulsions because the individual's knee is extended when the hip undergoes a violent, forceful flexion as he/she falls forward.

Related Medscape topics:
Resource Center Exercise and Sports Medicine
Resource Center Trauma
Specialty Site Orthopaedics

Clinical

History

• The onset of pain and/or weakness is usually sudden and may occur during an explosive movement, such as sprinting.
• Patients may report hearing an audible pop at the time of injury.
• Onset of posterior thigh pain is often near the beginning or near the end of the sport activity. This is consistent with the belief that fatigue and lack of warm-up are factors that may lead to muscle injury.
• Patients may only have a sense of apprehension due to a feeling of inadequate leg control as a result of the injury.
• Patients may report pain with sitting or while walking uphill or ascending stairs.
• Swelling and ecchymosis may accompany more severe injuries.

Physical

• Physical findings are absent in many hamstring injuries.
• The patient often has pain with active knee flexion against resistance. The procedure is performed with the hip in a neutral position and the knee in an extended starting position.
  • With the patient in a prone position and the affected extremity's knee flexed at 90 º, palpate from the ischial muscle origins to their insertions. This minimizes patient pain, which can limit detecting muscle defects.
  • Next, with the patient in the supine position and the hips flexed to 90 º, the maximum tolerable active and passive knee extension angle should be noted and compared to the contralateral leg. This allows the physician to assess the severity of the injury and to monitor future rehabilitation progress.
• In severe cases, swelling and ecchymosis may be present.
• With a complete hamstring rupture, the muscle may contract into a ball, with an accompanying strength deficit.

Causes

• The major predisposing factors are lack of warm-up, poor flexibility, fatigue, and a hamstring-to-quadriceps ratio less than 50%.
• A previous hamstring injury is the most recognized risk factor for injury.
• Poor running style, especially overstriding, predisposes some runners to hamstring injuries. Overstriding stretches the hamstring and places it in a position of active insufficiency.
• Dyssynergia secondary to dual innervation of the hamstring muscles may also be a factor that contributes to hamstring injuries.
• Rapid growth seen during adolescence sometimes leads to tight hip flexors with a resultant anterior hip tilt. This can cause a natural predisposition to hamstring injuries for this age group.

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