Anatomy
Lower Limb
You form part of the trauma team caring for a motorcyclist who was involved in a collision with a van. You receive a phone call from the on-call radiologist informing you that the patient has an injury to the nerve supplying the hamstring muscles. The hamstring muscles are innervated by which of the following nerves:
Answer:
The hamstring muscles are all innervated by the sciatic nerve.Hamstring Muscles
Anatomy / Lower Limb / Posterior Thigh
Last Updated: 10th April 2019
The hamstrings are composed of three individual muscles; the biceps femoris, the semitendinosus and the semimembranosus.
Table: Function and Innervation of the Hamstring Muscles
| Muscle | Function | Innervation |
|---|---|---|
| Biceps femoris | Flexion at knee, extension and lateral rotation at hip | Sciatic nerve |
| Semitendinosus | Flexion at knee, extension and medial rotation at hip | Sciatic nerve |
| Semimembranosus | Flexion at knee, extension and medial rotation at hip | Sciatic nerve |
Function
The hamstrings act together to flex the leg at the knee joint and extend the thigh at the hip joint. The biceps femoris also acts to laterally rotate the thigh at the hip joint and the leg at the knee joint. The semimembranosus and semitendinosus also act together to medially rotate the thigh at the hip joint and the leg at the knee joint.
Innervation
The hamstring muscles are all innervated by the tibial division of the sciatic nerve (L5 - S2), except for the short head of the biceps femoris innervated by the common fibular division.
Assessment
To test the hamstrings the patient flexes their leg against resistance. Normally these muscles, especially their tendons on each side of the popliteal fossa, are prominent as they bend the knee.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2017/01/Hamstrings.jpg)
Hamstrings: Biceps Femoris (red), Semitendinosus (blue), Semimembranosus (green). (Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
