Anatomy
Upper Limb
A 26 year old woman presents to ED having sustained a deep laceration to the dorsum of her ring finger whilst cooking. Her proximal interphalangeal joint is fixed in flexion and the distal interphalangeal joint is hyperextended. Which of the following structures in the digit has most likely been injured:
Answer:
Damage to the central slip of the extensor digitorum tendon would result in loss of extension at the proximal interphalangeal joint resulting in a fixed flexion deformity of this joint, and hyperextension of the distal interphalangeal joint due to a loss of balancing forces. This is called the Boutonniere deformity.Extensor Tendon Injury
Anatomy / Upper Limb / Digital Attachment of Long Tendons
Last Updated: 10th April 2019
Table: Clinical Features of Extensor Tendon Injury
| Structure | Terminal Extensor Tendon | Central Slip of Extensor Tendon |
|---|---|---|
| Attachment | Distal phalanx | Middle phalanx |
| Movements affected in injury | Loss of extension at distal interphalangeal joint | Loss of extension at proximal interphalangeal joint and flexion at distal interphalangeal joint |
| Deformity in injury | Mallet deformity: Distal phalanx held in fixed flexion | Boutonniere deformity: Middle phalanx held in fixed flexion with hyperextension of distal phalanx |
The tendons of the extensor digitorum (and extensor pollicis longus) pass onto the dorsal aspect of the digits and expand over the proximal phalanges to form complex extensor hoods. The central slip inserts into the base of the middle phalanx, and distally the tendon inserts into the distal phalanx of each digit.
![Modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2016/12/Extensor-Hoods-2.gif)
Extensor Tendons. (Image modified by FRCEM Success. Original by Henry Vandyke Carter [Public domain], via Wikimedia Commons)
Central Slip
Division of the central slip of the extensor tendon will result in the Boutonniere deformity, with loss of extension of the proximal interphalangeal joint and loss of flexion of the distal interphalangeal joint. The middle phalanx is held in forced flexion, with hyperextension of the distal phalanx.
Terminal Tendon
Division of the terminal extensor tendon will result in the Mallet deformity, with loss of extension at the distal interphalangeal joint as in this case; the distal phalanx is held in forced flexion due to unopposed action of the flexor digitorum profundus muscle.
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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 |
