Anatomy
Upper Limb
A 34 year old patient presents to ED having sustained an injury to her right hand whilst playing cricket. She is unable to fully straighten her right middle finger as the distal phalanx remains flexed. A picture of her hand is shown below. Which of the following structures within the digit was most likely injured:
![By Howcheng (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2017/01/Mallet_finger-300x225.jpg)
By Howcheng (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0), via Wikimedia Commons
Answer:
Damage to the insertion of the terminal extensor digitorum tendon would result in loss of extension at the distal interphalangeal joint causing a fixed flexion deformity, called the Mallet 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 |
