Anatomy
Upper Limb
A 48 year old presents to ED having sustained a deep laceration to his right upper limb. On examination he is unable to extend the interphalangeal joints of the fourth and fifth digits and extension of the interphalangeal joints of the second and third digits is very weak. Extension at the metacarpophalangeal joints is preserved in all digits. Which of the following nerves has most likely been injured:
Answer:
The deep branch of the ulnar nerve innervates the medial two lumbricals and all of the interossei. There is loss of extension at the IPJs of the fourth and fifth digits due to paralysis of the medial two lumbricals and the interossei. Extension at the IPJs of the second and third digits are only weakened as the lateral two lumbricals are spared (innervated by the median nerve). Extension at the MCPJs of all five digits is a function of the radial nerve. The superficial branch of the ulnar nerve has only cutaneous function.Ulnar Nerve
Anatomy / Upper Limb / Anterior Arm / Anterior Forearm / Innervation of Upper Limb
Last Updated: 10th April 2019
The ulnar nerve is a continuation of the medial cord of the brachial plexus, containing fibres from the C8 - T1 nerve roots.
Table: Anatomical Overview of the Ulnar Nerve
| Nerve | Ulnar |
|---|---|
| Nerve roots | C8 – T1 |
| Plexus cords | Medial cord |
| Motor Supply | All the intrinsic muscles of the hand (except for the thenar muscles and the lateral two lumbricals), the flexor carpi ulnaris and the medial half of the flexor digitorum profundus |
| Sensory supply | Medial half of palm, palmar and dorsal surface of medial one and a half fingers and medial dorsum of hand |
Anatomical course
The ulnar nerve descends down the medial side of the upper arm and passes posterior to the medial epicondyle (where it is susceptible to damage) before entering the anterior compartment of the forearm by passing between the two heads of the flexor carpi ulnaris. It continues down the medial aspect of the forearm.
The ulnar nerve emerges from beneath the flexor carpi ulnaris and becomes superficial just proximal to the wrist where it passes superficial to the flexor retinaculum, together with the ulnar artery, to enter the hand through a groove between the pisiform and the hook of the hamate where it bifurcates into its terminal branches.
![By Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Median-Nerve-1.gif)
Ulnar Nerve. (Image by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Branches
Table: Branches of the Ulnar Nerve
| Branches of Ulnar Nerve | Origin | Supply |
| Muscular branch | Forearm | Flexor carpi ulnaris, medial half of flexor digitorum profundus |
| Palmar cutaneous branch | Forearm | Skin of medial half of palm |
| Dorsal cutaneous branch | Forearm | Skin of dorsum of medial one and a half fingers and associated dorsal hand area |
| Deep branch | Hand | Hypothenar muscles (abductor digiti minimi, flexor digiti minimi, opponens digiti minimi), medial two lumbricals, adductor pollicis and interossei |
| Superficial branch | Hand | Skin of palmar surface of medial one and a half fingers |
The ulnar nerve gives off no major branches in the arm.
Three branches arise in the forearm:
- The muscular branch innervating the flexor carpi ulnaris and the medial half of the flexor digitorum profundus
- The palmar cutaneous branch supplying the skin of the medial half of the palm
- The dorsal cutaneous branch supplying the skin of the medial dorsum of the hand and the dorsal surface of the medial one and a half fingers
The ulnar nerve terminates by bifurcating into:
- A deep branch innervating the hypothenar muscles, the medial two lumbricals, the adductor pollicis and the interossei
- A superficial branch supplying the skin of the palmar surface of the medial one and a half fingers
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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 |
