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Time Completed: 02:04:22

Final Score 72%

129
51

Questions

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Trauma

Question 98 of 180

A 19 year old student fell asleep after a night of drinking with his arm hanging over the back of a chair. He presents to the Emergency Department complaining of an inability to extend his wrist or fingers. Which of the following structures has most likely been injured?

Answer:

The radial nerve (arising from the posterior cord of the brachial plexus) may be damaged in the axilla by proximal humeral fractures, shoulder dislocation, incorrect use of axillary crutches or by sleeping in positions are described above (Saturday night palsy). Radial nerve injury results in weakness of extension of the forearm, wrist and fingers.

Upper Limb Nerve Injuries

Brachial plexus injury

Brachial plexus injury Erb's palsy Klumpke's palsy
Mechanism of injury Excessive increase in angle between neck and shoulder e.g. during breech delivery or from fall from motorbike or horse Sudden excessive abduction e.g. person catching something overhead as they fall or during a difficult delivery
Nerve roots affected C5, C6 C8, T1
Nerves affected Musculocutaneous, axillary, suprascapular and nerve to subclavius Ulnar and median nerves
Muscles affected Supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid and teres minor All small muscles of hand (flexor muscles in forearm innervated by different nerve roots)
Motor loss Abduction, flexion and lateral rotation of arm, flexion and supination of forearm Intrinsic hand movements
Sensory loss Lateral arm Medial arm
Deformities Waiter's tip Claw hand

Long thoracic nerve injury

The long thoracic nerve is prone to injury due to its excessive length and superficial location on the lateral thoracic wall on the external surface of the serratus anterior muscle, just deep to skin and subcutaneous fascia.

Injury to this nerve may occur due to:

  • Trauma or surgery
  • A direct blow to the rib area
  • Overstretching or strenuous repetitive movements of the arms
  • Sustained bearing of excessive weight over the shoulder

Damage to the long thoracic nerve results in weakness/paralysis of the serratus anterior muscle. Loss of function of this muscle causes the medial border, and particularly the inferior angle, of the scapula to elevate away from the thoracic wall, resulting in the characteristic 'winging' of the scapula. This deformity becomes more pronounced if the patient presses the upper limb against a wall. Furthermore, normal elevation of the arm is no longer possible.

Musculocutaneous nerve injury

Nerve Musculocutaneous
Mechanism of injury Stab wound in axilla
Motor loss Weakness of flexion and supination of the forearm, weakness of arm flexion
Sensory loss Lateral aspect of forearm

Axillary nerve injury

Nerve Axillary
Mechanism of injury Dislocation of the glenohumeral joint, fracture of the surgical neck of the humerus, trauma or surgery to the shoulder, incorrect use of axillary crutches
Motor loss Loss of abduction of the arm at the glenohumeral joint and weakness of lateral rotation
Sensory loss Lateral arm (regimental badge area)
Signs Atrophy of deltoid - flattened shoulder appearance

Radial nerve injury

Lesion In axilla In spiral groove In forearm (superficial branch) In forearm (deep branch)
Mechanism Glenohumeral joint dislocation, fracture of proximal humerus, 'Saturday night syndrome' Fracture of midshaft of humerus Stabbing/laceration of forearm Fracture of radial head or posterior dislocation of radius
Motor Loss Loss of extension at elbow, wrist and fingers Loss of extension at wrist and fingers (triceps brachii spared) None Weakness of extension at wrist and fingers (extensor carpi radialis spared)
Sensory Loss Lower lateral arm, posterior arm, posterior forearm, dorsum of lateral hand and three and a half fingers Dorsum of lateral hand and three and a half fingers (cutaneous branches of arm and forearm spared) Dorsum of lateral hand and three and a half fingers None
Signs Wrist drop (unopposed wrist flexion), weakness of hand grip (finger flexion is weak as the long flexor tendons are not under tension) Wrist drop, weak hand grip None Wrist drop not typically seen (extensor carpi radialis spared)

Median nerve injury

Lesion Proximal (arm, elbow, proximal forearm) Distal (wrist)
Mechanisms Supracondylar fracture, stab wound to arm or forearm Lacerations just proximal to flexor retinaculum
Motor Loss Forearm pronation, wrist flexion and abduction, index and middle finger flexion, thumb flexion, abduction and opposition Thumb flexion at MCPJ, abduction and opposition, flexion of index and middle finger MCPJ
Sensory Loss Lateral aspect of palm and palmar surface and fingertips of lateral three and a half digits Palmar surface and fingertips of lateral three and a half digits
Signs Forearm rests in supination with wrist in ulnar deviation and thumb extended, thenar eminence wasting, hand of Benediction (when asked to make a fist, the patient will be able to flex the little and ring fingers but not the index and middle fingers) Thenar eminence wasting

Ulnar nerve injury

Lesion Proximal (at elbow) Distal (at wrist)
Mechanism Fracture of medial epicondyle Laceration at wrist
Motor Loss Wrist flexion and adduction, finger abduction and adduction, flexion of ring and little finger, abduction and opposition of little finger, thumb adduction, extension of IPJs of all digits (less so at index and middle finger due to sparing of lateral two lumbricals) Finger abduction and adduction, flexion of ring and little finger, abduction and opposition of little finger, thumb adduction, extension at IPJs
Sensory Loss Medial half of palm, palmar and dorsal surface of medial one and a half fingers and medial dorsum of hand Palmar surface of medial one and a half fingers
Signs Hand held in abduction (due to unopposed action of flexor carpi radialis), Froment's sign (patient is asked to hold a piece of paper between thumb and flat palm as paper is pulled away, patient will flex thumb at IPJ to maintain hold - tests adductor pollicis muscle), hypothenar eminence wasting, N.B. claw hand not typically seen due to paralysis of the flexor digitorum profundus Claw hand (unopposed extension at MCPJ and unopposed flexion at IPJs of ring and little finger), hypothenar eminence wasting, Froment's sign

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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

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