Which of the following bones is not a sesamoid bone?

AIIMS Delhi NO - 2018

Applied Anatomy

Easy

Appeared in: AIIMS Delhi NO - 2018

Explanation

The fibula is classified as a long bone, a primary structural component of the lower leg.
Long bones are characterized by a shaft (diaphysis) and two ends (epiphyses), a structure fundamentally different from sesamoid bones.
Sesamoid bones are defined as bones embedded within a tendon or muscle.
The fibula is not embedded in a tendon; rather, it serves as an attachment point for muscles.
Therefore, the fibula does not meet the definition of a sesamoid bone.

Option A: The pisiform bone, located in the wrist, is classified as a sesamoid bone because it is situated within the tendon of the flexor carpi ulnaris muscle.
Option B: The patella (kneecap) is the largest and most well-known sesamoid bone in the human body, embedded in the quadriceps femoris tendon.
Option D: The fabella is a small sesamoid bone located in the tendon of the lateral head of the gastrocnemius muscle behind the knee. Although not present in everyone, it is by definition a sesamoid bone.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of bones, specifically identifying sesamoid bones as background academic context rather than a clinical decision trigger.
Understanding bone classification is fundamental for nurses in assessing fractures, understanding biomechanics of movement, and anticipating complications. For example, a fracture of the fibula (a long bone) has different implications for weight-bearing than an injury to a sesamoid bone.
Sesamoid bones, like the patella, can fracture or become inflamed (sesamoiditis), causing pain and mobility issues. Nurses need to recognize these conditions and provide appropriate care, such as pain management and activity modification.
What if? - If a patient has persistent pain at the base of the thumb, a nurse knowledgeable about sesamoid bones might suspect sesamoiditis or a fracture of the small sesamoids of the first metacarpal, leading to a more focused assessment and appropriate referral.

How to Approach the Question

First, understand the question's core concept, which is the definition of a 'sesamoid bone'.
Recall or look up the definition: a bone embedded within a tendon or muscle.
Analyze each option against this definition.
Option A, Pisiform: Recall that it's in the wrist, within the flexor carpi ulnaris tendon. It fits the definition.
Option B, Patella: Recall this is the classic, largest example of a sesamoid bone in the knee. It fits the definition.
Option C, Fibula: Recall this is the long, thin bone in the lower leg. It is a structural bone, not embedded in a tendon. It does NOT fit the definition.

Concept Tested & Keywords

Concept Tested: Classification of bones, specifically identifying sesamoid bones.
Stem keywords: bones, sesamoid bone
Lead-in keywords: not
Negative lead-in flag: The question asks which bone is NOT a sesamoid bone.

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