A strong weight bearing synovial joints with irregular elevations and depressions that produce interlocking o… - AIIMS Raipur - 2017 (shift-2)

AIIMS Raipur - 2017 (shift-2)

Applied Physiology

Easy

Appeared in: AIIMS Raipur - 2017 (shift-2)

Explanation

The sacroiliac (SI) joints are strong, weight-bearing joints located between the sacrum and the iliac bones of the pelvis.
They are classified as synovial joints, which is a key requirement mentioned in the question.
A defining feature of the SI joints is their irregular, interlocking articular surfaces, which consist of elevations and depressions that fit together.
This interlocking mechanism provides exceptional stability, which is essential for their function of transmitting the entire weight of the upper body to the lower limbs.
The joint is further stabilized by a network of very strong ligaments, making it one of the most stable joints in the body.

Option A: The vestigial tail refers to the coccyx, which is a remnant of tail bones. It is a bone structure, not a joint itself.
Option B: The symphysis pubis is a secondary cartilaginous joint (a symphysis), not a synovial joint. It is united by a fibrocartilage disc and allows only slight movement.
Option D: The sacrococcygeal joint is also a secondary cartilaginous joint (symphysis) that connects the apex of the sacrum to the coccyx. It is not a synovial joint and not a primary weight-bearing joint in the same manner as the SI joint.

Visual 1: Diagram of the Pelvic Girdle. An annotated diagram showing the sacrum, iliac bones, and the location of the sacroiliac joints, symphysis pubis, and sacrococcygeal joint to help visualize their relationships.
Visual 2: Close-up of the Sacroiliac Joint Surface. An illustration highlighting the irregular, interlocking nature of the auricular surfaces of the sacrum and ilium.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy and classification of pelvic joints as background academic context rather than a clinical decision trigger.
Sacroiliac (SI) joint dysfunction is a common cause of lower back and pelvic pain. Nurses should be aware of this as a potential source of pain when assessing patients.
During pregnancy, the hormone relaxin increases the laxity of ligaments, including those of the SI joints and symphysis pubis, to allow for expansion of the pelvis during childbirth. This can lead to instability and pain.
What if? If a patient presents with lower back pain that radiates to the buttock and posterior thigh, and the pain is worsened by activities like climbing stairs or standing on one leg, the nurse should consider SI joint dysfunction as a possible cause and perform specific assessment tests (e.g., FABER test) or refer for further evaluation.

How to Approach the Question

First, carefully read the question and identify the key descriptive terms for the joint: 'strong', 'weight bearing', 'synovial', and 'interlocking'.
Next, evaluate each option against these criteria.
Eliminate options that do not meet the primary criteria. For example, the term 'synovial joint' immediately rules out cartilaginous joints like the symphysis pubis and sacrococcygeal joint.
Consider the term 'vestigial tail'. Recognize that this refers to a bone structure (coccyx), not a joint as described.
The remaining option, 'Sacroiliac joints', perfectly matches all the descriptors: it is a synovial joint, it is strong and weight-bearing, and it is known for its unique interlocking surfaces.
Confirm this choice based on your anatomical knowledge of the pelvis.

Concept Tested & Keywords

Concept Tested: Anatomy and classification of pelvic joints
Stem keywords: synovial joints, weight bearing, interlocking bones, irregular elevations
Lead-in keywords: is called

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