Anatomy
Lower Limb
A 32 year old woman is brought to the ED after falling from a horse. Imaging shows multiple injuries to the pelvic region including transection of the nerve that supplies the piriformis muscle. The piriformis muscle acts primarily to produce which of the following movements:
Answer:
The piriformis acts to abduct and laterally rotate the thigh at the hip joint.Gluteal Muscles
Anatomy / Lower Limb / Hip Joint and Gluteal Region
Last Updated: 10th April 2019
Table: Function and Innervation of the Gluteal Muscles
| Muscle | Function | Innervation |
|---|---|---|
| Gluteus maximus | Extension, lateral rotation and abduction at hip | Inferior gluteal nerve |
| Gluteus medius | Abduction and medial rotation at hip | Superior gluteal nerve |
| Gluteus minimus | Abduction and medial rotation at hip | Superior gluteal nerve |
| Piriformis | Lateral rotation and abduction at hip | Branches from S1 and S2 |
Gluteus Maximus
The gluteus maximus is the main extensor of the thigh at the hip joint and also acts to laterally rotate and abduct the thigh. Through its insertion into the iliotibial tract, it also stabilises the knee and hip joints. The gluteus maximus is innervated by the inferior gluteal nerve.
Gluteus Medius and Gluteus Minimus
The gluteus medius and gluteus minimus act to abduct and medially rotate the thigh at the hip joint, and also act to secure the pelvis, reducing pelvic drop on the opposite swing side during walking. They are both innervated by the superior gluteal nerve.
Piriformis
The piriformis acts to abduct and laterally rotate the thigh at the hip joint. It is innervated by the nerve to the piriformis, originating from the sacral plexus (S1, S2).
The obturator internus, gemelli and quadratus femoris muscles act as synergistic femoral lateral rotators and hip stabilisers.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2017/01/Gluteus-Muscles.jpg)
Gluteal Muscles: Gluteus Maximus (red), Gluteus Medius (green), Gluteus Minimus (blue), Piriformis (yellow). (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 |
