Peripheral nerve injuries. Injuries of the hand tendons
Peripheral nerve injuries
Injury to the Ulnar nerve can occur at the point the ulnar enters the wrist (Guyon’s canal) or alternatively posterior to the medial epicondyle of the elbow. If compression is at the level of the wrist then sensory information to the lateral 1 and ½ fingers is disrupted, as well as the palmar part of the same zone, however the dorsal part of the hands ulnar innervation is spared. If the injury is at the elbow, then this will not only affect the palmar innervation of the hand but also the dorsal. Motor function of this part of the hand can also be affected, leading to a ‘claw like’ appearance and hypothenar atrophy.
Injury to the Median nerve is more common than the ulnar due to its more superficial path. The median nerve controls the abduction of the thumb, flexion of the hand at the wrist, flexion of the distal phalanx of the fingers and is sensory for the first three fingers of the hand and the first ⅗ of the palmar part. Damage to the median nerve leads to loss of abduction and opposition of the thumb, and loss of the movement of the first three fingers leading to the so called ‘ape’ sign, there is further weakness in the forearm pronation and wrist flexors. Causes of median nerve injury are due to carpal tunnel syndrome, constriction under struthers ligament, constriction when passing the bicipital aponeurosis and as it passes through the heads of pronator teres
Injury to the radial nerve leads to wrist drop, and limitation of extension of the wrist and fingers as well as reduction of supination. The most common cause is fracture of the neck of the humerus, at this point the radial nerve runs closely around the neck, other sites of damage include damage of the nerve in the radial groove, may be caused by sleeping in a funny position such as with the arm draped over a park bench! (Saturday night palsy). The radial nerve also supplies the cutaneous innervation for the dorsal part of the hand around the thumb and first two fingers.
Injuries of the hand tendons
Mallet finger
- Partial or complete disruption of the extensor tendons attachment at the dorsal base of the distal phalanx with the resultant flex deformity of the DIP - it is the most common closed tendon injury