Anatomy
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Lower Limb
A 63 year old woman with advanced ovarian malignancy presents to ED complaining of weakness of her left leg while walking. Examination reveals weakness of adduction of the thigh at the hip joint. Which of the following nerves is most likely being compressed to result in this pattern:
Answer:
Adduction at the hip is primarily produced by the adductor longus, brevis and magnus, all innervated by the obturator nerve. The pectineus and gracilis muscles, innervated by the femoral nerve and obturator nerve respectively, assist in this action.Obturator Nerve
Anatomy / Lower Limb / Innervation of Lower Limb / Medial Thigh
Last Updated: 10th April 2019
The obturator nerve arises from the lumbar plexus, formed from the anterior rami of L2 - L4.
Table: Anatomical Overview of the Obturator Nerve
| Nerve | Obturator |
|---|---|
| Nerve roots | L2 – L4 |
| Motor supply | Medial thigh muscles (adductor longus, brevis and magnus, gracilis, obturator externus) |
| Sensory supply | Upper medial thigh |
| Injury | Motor Loss: Loss of hip adduction and difficulty walking with lateral swinging of limb (due to unopposed abduction)
Sensory Loss: Loss of sensation over upper medial thigh |
Anatomical Course
The obturator nerve descends along the posterior abdominal wall, passes through the pelvic cavity and enters the medial thigh by passing through the obturator canal.
Function
The obturator nerve innervates all of the muscles of the medial compartment of the thigh (except for the hamstring part of the adductor magnus innervated by the tibial portion of the sciatic nerve).
It also gives off a cutaneous branch that supplies skin on the medial side of the upper thigh.
Table: Motor Supply of the Obturator Nerve
| Muscle | Function |
|---|---|
| Adductor longus | Adduction and medial rotation at hip |
| Adductor brevis | Adduction at hip |
| Adductor magnus | Adduction and medial rotation at hip |
| Obturator externus | Lateral rotation at hip |
| Gracilis | Adduction at hip and flexion at knee |
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://mrcemsuccess.com/wp-content/uploads/2017/01/Cutaneous-Innervation-Leg.png)
Cutaneous Innervation of Lower Limb. (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 |
