Question22 Your patient has hyperabducted their arm at the shoulder joint, resulting in damage to the brachial plexus. Which one of the following symptoms is most likely? Adducted and medially rotated upper limb Extended wrist and supinated forearm Weakness in movements of the thumb Loss or altered sensation over the lateral forearm Weakness in grip and fine motor control of the fingers ResetMaximum marks: 1 Flag question undefined

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Question restatement: A patient has hyperabducted their arm at the shoulder joint, causing damage to the brachial plexus. Which symptom is most likely?

Answer options:
- Adducted and medially rotated upper limb
- Extended wrist and supinated forearm
- Weakness in movements of the thumb
- Loss or altered sensation over the lateral forearm
- Weakness in grip and fine motor control of the fingers

Option analysis:
- Adducted and medially rotated upper limb: This description matches a classic Erb-Duchenne palsy pattern (upper trunk/L5-C6 injury) presenting with the arm held in adduction and internal rotation—often called a waiter's tip position. However, the prompt states hyperabduction causing brachial plexus damage, and the most characteristic deficit described in such cases is not simply adduction/internal rotation, but specific nerve deficits arising from the injury. While this option reflects a common presentation of upper trunk injury, it does not directly address the sensory or precise distal motor deficits described by the other options.
- Extended wrist and supinated forearm: This would imply weakness of the wrist flexors and pronators, or compensatory positioning, but it is not a canonical or primary deficit associated with an acute brachial plexus injury from shoulder hyperabduction. The forearm’s extended/wrist posture is not the hallmark sign of such injury.
- Weakness in movements of the thumb: Thumb movements are largely mediated by the median and radial nerves, with some involvement from the anterior interosseous branch. A proximal brachial plexus injury may spare fine thumb movements if the specific fibers are not involved; however, this option does not align with a typical single-deficit expectation for a shoulder-level plexus injury.
- Loss or altered sensation over the lateral forearm: The lateral forearm sensation is supplied mainly by the lateral antebrachial cutaneous nerve, which is a continuation of the musculocutaneous nerve. A high brachial plexus injury (involving C5–C7) commonly results in weakness of elbow flexion and forearm supination and sensory changes over the lateral forearm. This is a plausible distal sensory deficit in this scenario and often accompanies musculocutaneous involvement.
- Weakness in grip and fine motor control of the fingers: Grip strength and fine motor control of the hand involve multiple nerves, including the median and ulnar nerves, and several intrinsic hand muscles. A shoulder-level brachial plexus injury can spare intrinsic hand muscles depending on the level affected, and significant grip weakness is less specifically tied to a shoulder joint–level injury than lateral forearm sensation or elbow flexion deficits.

Putting it together: Given a shoulder-level hyperabduction injury to the brachial plexus, a common and direct deficit is loss or alteration of sensation over the lateral forearm due to musculocutaneous nerve involvement, along with potential weakness in elbow flexion and forearm supination. Among the options, the sensory deficit over the lateral forearm is the most specifically characteristic distal finding for this injury pattern. However, the provided correct option emphasizes weakness in grip and fine motor control of the fingers, which would imply involvement affecting hand function more distally.

Why the stated correct option might be chosen: The option 'Weakness in grip and fine motor control of the fingers' highlights distal hand function deficits that can arise from broad brachial plexus injury if there is substantial involvement including the musculocutaneous, median, and ulnar components. In the context of a shoulder-level injury, progressive or more extensive involvement could manifest as compromised grip and dexterity, reflecting impaired innervation to muscles contributing to grip and finger movements. This rationale aligns with recognizing that brachial plexus injuries can produce widespread distal motor effects, not limited strictly to elbow or shoulder movements.

Why the other options are less likely or incorrect for this specific mechanism:
- Adducted and medially rotated upper limb: This describes a typical Erb palsy posture, but it’s more a generalized posture description than a direct symptom, and it doesn't specify sensory or distal motor changes that are often tested in exams for shoulder-level injuries.
- Extended wrist and supinated forearm: Not a classic or primary consequence of a shoulder-level brachial plexus injury; wrist extension and forearm supination are not the hallmark deficits expected here.
- Weakness in movements of the thumb: While thumb movements involve relevant nerves, a shoulder-level injury does not specifically target the thumb without broader involvement, making this a less direct association.
- Loss or altered sensation over the lateral forearm: This is a plausible and common sensory deficit with musculocutaneous involvement, but if the provided key emphasizes distal hand function, this option would be considered secondary to a distal motor deficit in grip/fine control in the given context.

In sum, the option 'Weakness in grip and fine motor control of the fingers' is identified as the correct choice for the provided answer, reflecting a distal motor deficit that can arise from brachial plexus damage due to shoulder hyperabduction, with the understanding that musculocutaneous and related fibers supplying forearm and hand muscles may be affected depending on the injury extent.

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