NORCET 3 - 2022 (Shif…: What injury results in winging of the scapula after mastectomy?

NORCET 3 - 2022 (Shift-1)

Applied Anatomy

Hard

Appeared in: NORCET 3 - 2022 (Shift-1)

Explanation

The clinical sign of a winged scapula is caused by the paralysis of the serratus anterior muscle.
The serratus anterior muscle is innervated by the long thoracic nerve, a nerve that runs along the chest wall.
This nerve is at high risk for injury during axillary lymph node dissection, a common component of mastectomy procedures.
Therefore, an injury to this thoracic nerve is the root cause of the muscle paralysis and subsequent scapular winging.

Option A: This is anatomically imprecise. The primary muscle responsible for holding the scapula to the ribcage is the serratus anterior. The medial scapular muscles (rhomboids) retract the scapula, and their paralysis causes a different, less pronounced winging.
Option C: The triceps brachii muscle is located on the posterior aspect of the arm and its primary function is extension of the elbow joint. It has no role in stabilizing the scapula.
Option D: This describes the effect, not the primary cause. The serratus anterior muscle becomes weak or paralyzed because its nerve supply (the long thoracic nerve) is damaged during the surgery. The initial insult is to the nerve.

Clinical Relevance

Nursing practice connection: Safe nursing care depends on performing Anatomical basis of post-mastectomy complications, specifically scapular winging in the correct sequence, documenting the action clearly, and monitoring for the expected response.
Nurses caring for post-mastectomy patients must perform regular assessments of shoulder and arm function, including checking for scapular winging by having the patient push against a wall.
Early identification of nerve injury is crucial for initiating physiotherapy to preserve range of motion and prevent frozen shoulder.
Patient education should include instructions to avoid heavy lifting or strenuous activity with the affected arm until cleared by a doctor or physical therapist.

How to Approach the Question

First, identify the key clinical sign presented in the question and image: 'winging of the scapula'.
Second, recall the primary muscle responsible for preventing this sign. The serratus anterior muscle holds the scapula against the rib cage.
Third, recall the nerve that innervates this muscle. The long thoracic nerve supplies the serratus anterior.
Fourth, consider the clinical context: 'after mastectomy'. This procedure involves surgery in the axilla, where the long thoracic nerve is located.
Finally, evaluate the options. 'Thoracic nerve injury' is the option that correctly identifies the initial injury to the nerve that leads to the muscle paralysis and the visible sign.

Concept Tested & Keywords

Concept Tested: Anatomical basis of post-mastectomy complications, specifically scapular winging.
Stem keywords: injury, winging of the scapula, mastectomy
Lead-in keywords: What
Clinical cues: The image clearly shows a winged scapula, which is the key clinical sign.
Clinical cues: The context of a mastectomy points towards a complication involving structures in the axilla or chest wall.

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E6 Anatomy Workbook HumanAnatomy Vol 1 p. 75-77

E6 Anatomy BDChaurasia V1 10e pp. 54-56, 53-55