A 54 year old carpenter has sustained a laceration to his left hand with a stanley knife. He is unable to flex the proximal interphalangeal joint of his middle finger which is held in extension. Which of the following structures has most likely been injured:
Hand movements are complex. The table below shows an overview of hand and thumb movements and the main muscles bringing about these movements.
| Finger Movements | Primary Muscle (Assisting Muscles) | Primary Nerve (s) |
|---|---|---|
| Flexion of MCPJ of digits 2 – 5 | Lumbricals (flexor digitorum superficialis, flexor digitorum profundus, flexor digiti minimi, interossei) | Median and ulnar |
| Flexion of PIPJ of digits 2 – 5 | Flexor digitorum superficialis (flexor digitorum profundus) | Median |
| Flexion of DIPJ of digits 2 – 5 | Flexor digitorum profundus | Median and ulnar |
| Extension of MCPJ of digits 2 – 5 | Extensor digitorum, extensor indicis, extensor digiti minimi | Radial |
| Extension of PIPJ and DIPJ of digits 2 – 5 | Lumbricals and interossei (extensor digitorum) | Ulnar and median |
| Adduction of digits 2 – 5 | Palmar interossei | Ulnar |
| Abduction of digits 2 – 4 | Dorsal interossei | Ulnar |
| Abduction of little finger | Abductor digiti minimi | Ulnar |
| Opposition of little finger | Opponens digiti minimi | Ulnar |
| Thumb Movements | Primary Muscle(s) | Nerve Supply |
|---|---|---|
| Flexion of thumb at MCPJ | Flexor pollicis longus and brevis | Median and ulnar |
| Flexion of thumb at IPJ | Flexor pollicis longus | Median |
| Extension of thumb at CMCJ and MCPJ | Extensor pollicis longus and brevis | Radial |
| Extension of thumb at IPJ | Extensor pollicis longus | Radial |
| Abduction of thumb | Abductor pollicis longus and brevis | Radial and median |
| Adduction of thumb | Adductor pollicis | Ulnar |
| Opposition of thumb | Opponens pollicis | Median |

Muscles of the Hand. (Image by OpenStax [CC BY 4.0 , via Wikimedia Commons)
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| 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 |
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