Applied Anatomy – Pelvis
1. Definition Table
| Category | Explanation |
|---|---|
| What is it? | – Basin-shaped bony structure at the base of the spine – Connects the axial skeleton to the lower limbs |
| Most unique feature | – Transmits body weight from the spine to the lower limbs – Protects pelvic and lower abdominal organs |
| Structurally characterized by | – Composed of paired hip bones, sacrum, and coccyx – Hip bone made of ilium, ischium, and pubis fused together – Pelvic brim separates true pelvis (below) from false pelvis (above) |
| Functionally characterized by | – Supports the body’s weight in standing and locomotion – Protects pelvic organs (e.g., bladder, rectum, reproductive organs) – Provides attachment for muscles of posture, locomotion, and pelvic floor |
| Composed of | – Hip bones (2): Each formed by ilium, ischium, pubis – Sacrum: Posterior part connecting with lumbar spine – Coccyx: Tailbone, inferior tip of the pelvis – Joints: Sacroiliac joints, pubic symphysis |
| Common diseases | – Pelvic fractures – Acetabular fractures – Osteitis pubis – Sacroiliitis – Pelvic tumors (e.g., metastatic disease) |
| Diagnosis – Clinical | – Pelvic pain or instability – Difficulty standing or walking – Tenderness over pubic symphysis or SI joints |
| Diagnosis – Imaging | – X-ray: Good for gross fractures, pelvic ring assessment – CT: Best for complex fracture evaluation – MRI: Best for soft tissue, marrow, sacroiliac inflammation |
| Diagnosis – Labs | – CBC if bleeding suspected – ESR/CRP for inflammatory causes – Bone biopsy if tumor suspected |
| Treatment (Rx) | – Conservative management (e.g., rest, pain control) for minor fractures – Surgical fixation for unstable fractures – Anti-inflammatory therapy for sacroiliitis – Radiation/chemotherapy for pelvic tumors |
2. Parts Table
| Part | Description |
|---|---|
| Ilium | – Uppermost, largest part of hip bone – Forms the iliac crest – Contributes to acetabulum |
| Ischium | – Posteroinferior part of hip bone – Bears body weight when sitting – Forms lower posterior acetabulum |
| Pubis | – Anterior part of hip bone – Left and right pubic bones join at pubic symphysis |
| Sacrum | – Large triangular bone at posterior pelvis – Formed by fusion of 5 sacral vertebrae – Articulates with ilium at sacroiliac joints |
| Coccyx | – Small, triangular bone at base of spine – Formed by fusion of 3–5 coccygeal vertebrae |
| Acetabulum | – Deep socket formed by ilium, ischium, and pubis – Receives the head of the femur to form the hip joint |
| Pubic symphysis | – Cartilaginous joint uniting the left and right pubic bones – Slightly movable to allow pelvic flexibility |
3. Historical Note
| Era | Highlights |
|---|---|
| Ancient Times | – Early understanding of pelvic importance in childbirth – Depicted in Egyptian and Greek medical writings |
| Classical Era | – Galen described pelvic anatomy and emphasized the role of the sacrum – Anatomical studies refined knowledge of pelvic bones and joints |
| Modern Era | – Radiologic imaging enabled early detection of pelvic injuries – Pelvic fixation techniques advanced orthopedic trauma care – Pelvimetry used historically in obstetrics, now largely replaced by clinical assessment |
4. MCQs
🧠 Basic Science
Q1: Which bones fuse to form each hip bone?
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A. Ilium, ischium, sacrum
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B. Ilium, ischium, pubis
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C. Sacrum, coccyx, pubis
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D. Ilium, coccyx, femur
Answer: B. Ilium, ischium, pubis
Explanation:
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Ilium, ischium, pubis (Correct): Fuse during adolescence to form a single hip bone.
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Sacrum (Incorrect): Separate bone, not part of the hip bone itself.
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Coccyx (Incorrect): Forms the tailbone, unrelated to hip formation.
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Femur (Incorrect): Articulates with the hip, but is a limb bone.
Q2: Which pelvic structure directly transmits body weight from the spine to the lower limbs?
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A. Ilium
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B. Sacrum
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C. Acetabulum
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D. Coccyx
Answer: B. Sacrum
Explanation:
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Sacrum (Correct): Forms the posterior part of the pelvis and transmits weight through the sacroiliac joints.
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Ilium (Incorrect): Part of the hip bone, assists but doesn’t directly transmit axial weight.
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Acetabulum (Incorrect): Articulates with the femur but does not transmit weight from the spine.
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Coccyx (Incorrect): Vestigial structure; minor weight-bearing function.
🩺 Clinical
Q3: A fracture disrupting both the anterior and posterior pelvic rings is classified as:
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A. Stable pelvic fracture
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B. Acetabular fracture
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C. Unstable pelvic fracture
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D. Sacral stress fracture
Answer: C. Unstable pelvic fracture
Explanation:
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Unstable pelvic fracture (Correct): Involves disruption of the pelvic ring, leading to instability.
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Stable pelvic fracture (Incorrect): Involves only one area, no mechanical instability.
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Acetabular fracture (Incorrect): Involves the socket of the hip, not necessarily the pelvic ring.
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Sacral stress fracture (Incorrect): Limited to sacrum without affecting the pelvic ring.
Q4: Pain localized over the pubic symphysis in athletes is most commonly caused by:
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A. Osteitis pubis
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B. Pelvic metastasis
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C. Sacroiliitis
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D. Pubic diastasis
Answer: A. Osteitis pubis
Explanation:
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Osteitis pubis (Correct): Inflammatory condition of the pubic symphysis often seen in athletes.
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Pelvic metastasis (Incorrect): Would present with more diffuse, systemic symptoms.
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Sacroiliitis (Incorrect): Involves sacroiliac joints posteriorly.
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Pubic diastasis (Incorrect): Widening of pubic symphysis usually postpartum or traumatic.
🖼️ Imaging
Q5: Which imaging modality provides the most detailed evaluation of complex pelvic fractures?
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A. Ultrasound
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B. X-ray
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C. CT scan
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D. MRI
Answer: C. CT scan
Explanation:
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CT scan (Correct): Gold standard for complex pelvic fracture assessment.
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Ultrasound (Incorrect): Not appropriate for bone evaluation.
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X-ray (Incorrect): Good for gross fractures but limited detail.
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MRI (Incorrect): Best for soft tissue, marrow, and inflammation.
Q6: Sacroiliitis is best evaluated on:
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A. X-ray
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B. CT scan
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C. MRI
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D. Bone scan
Answer: C. MRI
Explanation:
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MRI (Correct): Most sensitive for early inflammatory changes in sacroiliitis.
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X-ray (Incorrect): Late changes only; low sensitivity early.
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CT scan (Incorrect): Detects bony erosion but not active inflammation.
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Bone scan (Incorrect): Sensitive but non-specific for inflammation.
5. Memory Image Idea 💡
| Concept | Components |
|---|---|
| The Basin of Balance | – Visualize the pelvis as a stone basin or cauldron, balancing on two strong columns (legs) – The sacrum sits like a keystone anchoring the back – The hip bones form the sides of the basin – The acetabulum resembles deep carved sockets ready to cradle the femur heads – Flowing inside the basin are the organs: bladder, intestines, uterus (if female) – Title: “The Basin of Balance – TheCommonVein.com“ |