Comprehensive Study Guide to the Anatomy, Radiography, and Patho-Biometrics of the Femur and Pelvis

Osteology of the Femur and Proximal Femoral Anatomy

General Characteristics of the Femur:
- The femur is classified as the longest and strongest bone in the human body.
- Its structural integrity is essential because the entire weight of the upper body transfers through it during standing and locomotion.
- The distal extremity articulates at the knee joint, whereas the proximal extremity articulates with the pelvic girdle at the hip joint.
Processes and Comparative Anatomy:
- The proximal femur features prominent bony processes for muscle attachment that are termed trochanters.
- A critical anatomical distinction must be maintained between the upper and lower extremities: tubercles are located on the humerus in the shoulder, whereas trochanters are located exclusively on the femur.
- Greater Trochanter: A large, prominent process situated on the lateral aspect of the proximal femur. It is visibly prominent from an anterior view, but visualized significantly better from a posterior aspect.
- Lesser Trochanter: A smaller, conical process projecting medially and posteromedially from the junction of the femoral neck and shaft.
- Intertrochanteric Crest: A thick, prominent bony ridge spanning between the greater and lesser trochanters located entirely on the posterior surface of the proximal femur. This ridge is not visible on an anterior projection.
Femoral Head, Neck, and Fovea Capitis:
- Femoral Head: A large, rounded, hemispherical proximal articulation resembling a rounded ball or ice cream scoop that seats directly into the pelvic acetabulum.
- Fovea Capitis (fave capitis / favae capitis): A distinct depression or pit located near the center of the femoral head. It serves as the anatomical attachment site for the ligamentum teres (ligament of the head of the femur), which carries small nutrient vessels to the femoral head.
- Femoral Neck: A constricted, pyramid-shaped column of bone connecting the femoral head to the body or shaft.
- Shaft / Body: The long, cylindrical main segment of the femur.

Proximal Femoral Angulation and Positioning Principles

Anatomical Angles of the Femur:
- Neck-to-Shaft Angle: In the average adult, an imaginary longitudinal line running through the femoral neck intersects with a line running through the long axis of the femoral shaft at an angle of approximately $125^\circ$ .
- Longitudinal Tilt: There is a secondary downward inclination from the neck through the shaft measuring approximately $5^\circ$ to $15^\circ$ .
- Anterior Angle of the Head and Neck: The femoral head and neck project forward (anteriorly) relative to the shaft and the coronal plane of the body at an angle of $15^\circ$ to $20^\circ$ .
Body Habitus Influences on Femoral Angles:
- Patients with shorter limbs and a wider pelvis exhibit a larger neck-to-shaft degree of angle.
- Patients with longer limbs and a narrower pelvis demonstrate a smaller (lesser) degree of angle.
- Average-sized patients exhibit a standard angle between the two extremes (around $125^\circ$ ).
True Anteroposterior (AP) Positioning Rule:
- Because the head and neck sit at an anterior angle of $15^\circ$ to $20^\circ$ , a true AP projection of the femur, hip, or pelvis cannot be achieved with the feet in an upright, neutral anatomical position.
- To place the femoral neck parallel to the image receptor and project the proximal femur in a true AP profile, the patient's entire lower limb must be rotated internally (medially) by $15^\circ$ to $20^\circ$ .
- Clinically, this is executed with the patient supine by rotating the legs inward until the great toes touch or nearly touch.

Pelvic Girdle Architecture and the Innominate Bone

Composition of the Bony Pelvis:
- The complete bony pelvis consists of four separate bones:
  - Two hip bones (also referred to as innominate bones or os coxae), forming the lateral and anterior aspects.
  - One sacrum, located posteriorly as part of the vertebral column.
  - One coccyx (the tailbone), attached to the inferior apex of the sacrum.
- The bony pelvis serves as the basin-shaped architectural base of the human trunk, uniting the axial skeleton with the lower appendicular skeleton.
- Superiorly, the sacrum articulates directly with the fifth lumbar vertebra ( $L_5$ ). Inferiorly, the sacrum articulates with the coccyx.
Trilateral Composition of the Innominate Bone:
- Each adult hip bone appears as a single unified structure but develops from three distinct bones that fuse during late adolescence:
  1. Ilium: The large, superior, flared division resembling a Mickey Mouse ear.
  2. Pubis: The anteroinferior division located anteriorly toward the pubic arch.
  3. Ischium: The posteroinferior division located below and behind the acetabulum.
- In pediatric patients, these three divisions are separate entities connected by cartilage and are not fused into a solid unit.
The Acetabulum:
- The acetabulum is the deep, cup-shaped lateral socket that accepts the head of the femur to form the hip joint.
- All three divisions of the innominate bone fuse together within this socket, contributing specific fractional proportions:
  - Ilium: Contributes two-fifths ( $\frac{2}{5}$ ) of the acetabulum.
  - Ischium: Contributes two-fifths ( $\frac{2}{5}$ ) of the acetabulum.
  - Pubis: Contributes one-fifth ( $\frac{1}{5}$ ) of the acetabulum.
  - Mnemonic Device: The "two I's" (Ilium and Ischium) each form two-fifths ( $\frac{2}{5}$ ), while the pubis provides the remaining one-fifth ( $\frac{1}{5}$ ).

Bony Landmarks of the Ilium, Ischium, and Pubis

Landmarks of the Ilium:
- Ala (Wing): The broad, flared superior expansion of the ilium ("ala" translates to wings). This creates the lateral flaring felt when placing hands on the hips.
- Iliac Crest: The thickened, superior curved ridge of the ala extending from the ASIS to the PSIS. Its most superior level corresponds anatomically to the level of the $L_4$ - $L_5$ interspace.
- Anterior Superior Iliac Spine (ASIS): The prominent bony projection at the anterior termination of the iliac crest. Frequently used as a primary positioning landmark for radiographic central ray localization.
- Anterior Inferior Iliac Spine (AIIS): A less prominent bony projection located immediately inferior to the ASIS on the anterior margin of the ilium.
- Posterior Superior Iliac Spine (PSIS): The posterior termination of the iliac crest.
- Posterior Inferior Iliac Spine (PIIS): A bony prominence located directly inferior to the PSIS on the posterior margin.
- Body of the Ilium: The thicker inferior portion that enters into the formation of the upper two-fifths ( $\frac{2}{5}$ ) of the acetabulum.
Landmarks of the Ischium:
- Ischial Body: Divided into an upper body and a lower body, contributing two-fifths ( $\frac{2}{5}$ ) to the posteroinferior acetabulum.
- Ischial Tuberosity: A prominent, thick, roughened, rounded protuberance on the posteroinferior aspect of the ischium. This landmark supports the body weight in a seated posture. While technically palpable through the soft tissue of the buttock, it is not palpated on patients in clinical practice due to patient comfort and ethical boundaries.
- Ischial Spine: A sharp, pointed triangular projection extending posteromedially from the posterior border of the ischial body.
- Greater Sciatic Notch: A large, deep indentation located superior to the ischial spine between the PIIS and the ischial spine, through which passes the sciatic nerve.
- Lesser Sciatic Notch: A smaller indentation located immediately inferior to the ischial spine, between the spine and the ischial tuberosity.
Landmarks of the Pubis:
- Body of the Pubis: The lateral portion that articulates within the acetabulum, contributing the anterior one-fifth ( $\frac{1}{5}$ ).
- Superior Ramus: A branch projecting medially and anteriorly from the body toward the midline.
- Inferior Ramus: A branch projecting posteroinferiorly from the symphysis to unite with the ramus of the ischium.
- Pubic Symphysis (Symphysis Pubis): The median anterior junction where the right and left superior and inferior pubic rami meet and articulate via a fibrocartilaginous disc. This structure is not directly palpated on patients.
The Obturator Foramen:
- A large aperture bounded by the rami of the pubis and the ischium.
- It is the largest foramen in the entire human skeleton.
- Radiographic Significance: Used systematically to evaluate patient rotation on AP pelvis and abdomen radiographs. When a patient is positioned flat and supine without rotation, the bilateral obturator foramina appear symmetric, wide, and fully open. If the patient is rotated toward either side, the obturator foramen on the side rotated toward will appear narrowed or closed, while the opposite side appears elongated or wide open.

True vs. False Pelvis and Anatomical Gender Variations

Pelvic Divisions (Greater vs. Lesser Pelvis):
- False Pelvis (Greater Pelvis): The expanded, wide area located superior to the pelvic brim, flanked by the broad alae of the ilia. It houses portions of the abdominal viscera.
- True Pelvis (Lesser Pelvis): The smaller, deep cavity situated inferior to the pelvic brim and completely enclosed by bony structures. In females, this cavity accommodates the urinary bladder, uterus, and ovaries.
- Obstetric Dynamics: When a female conceives, the fetus develops initially within the true (lesser) pelvis. As the pregnancy advances and the uterus enlarges, it rises out of the lesser pelvis to occupy the greater (false) pelvis.
Pelvic Apertures:
- Pelvic Inlet (Superior Aperture): The circular-to-oval upper circumference of the true pelvis defined by the pelvic brim.
- Pelvic Outlet (Inferior Aperture): The triangular or diamond-shaped lower boundary bounded anteriorly by the inferior border of the pubic symphysis, laterally by the ischial tuberosities, and posteriorly by the tip of the coccyx. This aperture represents the birth canal exit through which the fetal head delivers.
Structural Comparisons of Male vs. Female Pelves:
- Female Pelvis:
  - Overall structure: Lighter, wider, and more shallow to facilitate childbearing.
  - Iliac wings: More flared laterally and shallow.
  - Pelvic inlet: Wider, rounder, or broadly oval-shaped.
  - Pubic arch / subpubic angle at the outlet: Broad, forming an angle greater than $90^\circ$ ( $> 90^\circ$ ).
- Male Pelvis:
  - Overall structure: Heavier, narrower, and deeper.
  - Iliac wings: Less flared, more vertical.
  - Pelvic inlet: Narrower and characteristically heart-shaped.
  - Pubic arch / subpubic angle at the outlet: Acute and narrow, forming an angle less than $90^\circ$ ( $< 90^\circ$ ).

Pelvic and Hip Articulations

Sacroiliac (SI) Joints:
- Articulations between the articular surfaces of the sacrum and the posterior aspect of each iliac wing (right and left).
- Structural Classification: Synovial.
- Functional Classification: Amphiarthrodial (slightly movable), categorized specifically as a plane (gliding) type joint.
Pubic Symphysis (Symphysis Pubis):
- Median anterior joint between the two pubic bones.
- Structural Classification: Cartilaginous (fibrocartilage).
- Functional Classification: Amphiarthrodial (slightly movable).
- Physiological Purpose of Limited Movement:
  1. Childbirth: Allows the joint to yield and slightly widen to facilitate passage of the fetal skull during labor.
  2. Mechanical Shock Absorption: Provides elasticity during severe impact trauma (such as high-impact falls or motor vehicle accidents), dissipating kinetic energy to minimize the likelihood of pelvic ring fractures.
Union of the Acetabulum:
- The internal junction where the cartilaginous bodies of the ilium, ischium, and pubis meet within the socket.
- Structural Classification: Cartilaginous.
- Functional Classification: Synarthrodial (completely immovable once fully fused).
- Developmental Timeline: Fusion typically solidifies during adolescence, approximately between the ages of $14$ and $17$ .
Hip Joint (Acetabulofemoral Joint):
- The articulation between the cup-shaped acetabulum and the rounded head of the femur.
- Structural Classification: Synovial.
- Functional Classification: Diarthrodial (freely movable), categorized as a spheroidal (ball-and-socket) joint.

Radiographic Localization of the Femoral Head and Neck

Method 1 (Midpoint ASIS-to-Symphysis Perpendicular):
- Palpate the ASIS and locate the midline level corresponding to the superior border of the pubic symphysis (without palpating the pubis directly).
- Establish an imaginary line connecting the ASIS to the superior margin of the pubic symphysis.
- Locate the exact midpoint of this reference line.
- From this midpoint, construct a line dropping inferolaterally at a perpendicular ( $90^\circ$ ) right angle:
  - A distance of $1.5\,\text{inches}$ ( $1\frac{1}{2}\,\text{inches}$ ) along this perpendicular line marks the center of the femoral head.
  - A distance of $2.5\,\text{inches}$ ( $2\frac{1}{2}\,\text{inches}$ ) along this perpendicular line marks the midpoint of the femoral neck.
Method 2 (Medial and Inferior Offset from ASIS - Preferred Method):
- This is the superior clinical method because it eliminates any reference to the pubic symphysis.
- Palpate the prominent anterior bony point of the ASIS.
- From the ASIS, measure medially $1\,\text{to }2\,\text{inches}$ .
- From that medial offset point, direct the path inferiorly $3\,\text{to }4\,\text{inches}$ .
- Mnemonic Device: " $1, 2, 3, 4\,\text{touchdown}$ : in $1\,\text{to }2$ , down $3\,\text{to }4$ ."
- This terminus directly overlays the central long axis of the femoral neck.

Radiographic Positioning Criteria: True AP vs. Rotational Variations

True AP Projection Criteria:
- Patient Maneuver: Supine position with the entire lower extremities medially (internally) rotated $15^\circ$ to $20^\circ$ .
- Radiographic Manifestations:
  - The femoral neck is fully profiled and elongated in its true anatomical position without foreshortening.
  - The greater trochanter is visualized in profile on the lateral aspect of the proximal femur.
  - The lesser trochanter is projected posteriorly behind the femoral shaft and is entirely invisible or visible only as a tiny, barely discernible tip (an acceptable minor variation resulting from slight under-rotation).
Neutral Position Manifestations:
- Patient Maneuver: Patient supine with limbs resting straight without rotation, toes pointing directly upward toward the ceiling.
- Radiographic Manifestations: Because the femoral neck maintains an innate $15^\circ$ to $20^\circ$ anterior tilt, this position is actually externally rotated relative to the neck axis.
- The femoral neck appears foreshortened, and the lesser trochanter is visible projecting medially from behind the femoral shaft.
External Rotation Manifestations:
- Patient Maneuver: Lower limbs rotated laterally or resting relaxed with feet falling outward (frog-leg or natural resting flop).
- Radiographic Manifestations:
  - The femoral neck is severely foreshortened and distorted.
  - The lesser trochanter is seen projecting prominently in full profile along the medial border of the proximal femur.
Trauma Warning for Suspected Fracture:
- If a trauma patient (such as an elderly individual post-fall or a motor vehicle accident victim) presents with one leg in natural control and the injured leg flopped completely out laterally in external rotation ("like a dead fish"), the leg is presumed fractured.
- Absolute Rule: Do not attempt internal rotation or leg manipulation. Medial rotation of an unstable proximal femur or femoral neck fracture can shear surrounding vessels, sever nerves, or displace bony fragments.
- Acquire the initial AP projection strictly "as is" without rotational correction, and notify the reading physician.

Trauma Radiography: Axiolateral (Cross-Table) Hip Projection

Clinical Significance and Competency:
- The axiolateral (cross-table lateral) projection of the hip is a mandatory clinical competency requirement for radiologic technology certification.
- It is specifically indicated for trauma evaluations when an acute femoral neck or pelvic fracture is suspected and the limb cannot be rotated or abducted.
Setup and Procedural Mechanics:
- The patient remains recumbent and supine on the trauma stretcher or radiographic table.
- The affected lower extremity is kept entirely stationary in its presentation posture (no rotation, no movement).
- The unaffected ("good") leg is flexed at the hip and knee, elevating the thigh and leg entirely out of the path of the horizontal x-ray beam.
- The image receptor (IR) is placed vertically against the lateral aspect of the affected hip, with its superior border nestled firmly into the soft-tissue crease superior to the iliac crest and adjusted parallel to the long axis of the femoral neck.
- The x-ray tube is aligned horizontally, angled perpendicularly to the plane of the image receptor, directing the horizontal central ray medially straight through the patient's groin of the affected side.
Bilateral Fracture Consideration:
- If both hips are suspected of being fractured, the cross-table projection with an elevated leg is contraindicated. Alternative trauma views (such as the Clements-Nakayama modification) must be utilized.
Anatomical Structures Visualized on Cross-Table Axiolateral Hip:
- Acetabulum and joint space.
- Femoral head seated within the socket.
- Femoral neck profiled horizontally (the primary site of acute fracture detection).
- Femoral body/shaft.
- Lesser trochanter projected posteriorly/inferiorly.
- Greater trochanter superimposed or projected inferiorly.
- Ischial tuberosity positioned posteriorly.

Questions, Radiograph Analysis & Class Discussion

Medial vs. Lateral Aspect Identification of Innominate Bones:
- Question: When viewing an isolated lateral diagram of a hip bone, how can one definitively identify whether it depicts the lateral or medial surface?
- Response: If the acetabulum (the deep femoral socket) is fully visible, the projection is from the lateral aspect. If looking at a flat surface showing the inner pelvic bowl and the pubic symphysis without the socket, it is the medial aspect.
Radiographic Line Review (Textbook Page 273 Anatomical Labeling):
- Discussion: Group review of radiographic anatomy on a textbook pelvic radiograph:
  - Letter A represents the iliac crest.
  - Letter B represents the anterior inferior iliac spine (AIIS); the ASIS sits immediately higher along the anterior border.
  - The midline joint between the two pubic bones is the pubic symphysis.
  - Letter G correlates to the superior ramus of the pubis.
  - Letter F corresponds to the inferior ramus of the pubis.
  - Letter H denotes the ischial spine, which presents on an AP radiograph as a faint, sharp bony point projecting medially into the pelvis between the greater and lesser sciatic notches.
  - Letter L signifies the head of the right femur seating within the acetabulum.
  - Letter C and associated lines demarcate the femoral neck (divided into superior and inferior margins).
  - Letters K and J distinguish the greater trochanter laterally and the lesser trochanter medially.
Distinguishing Male vs. Female Pelvic Radiographs:
- Question: How can one verify gender on an AP pelvic radiograph?
- Response: Beyond evaluating the broad, oval inlet and wide subpubic arch ( $> 90^\circ$ ) of the female versus the heart-shaped, narrow inlet of the male, radiographers look for the shape of gonadal shielding, though anatomical contour (wide, shallow female vs. narrow, deep male) provides definitive verification.

Administrative and Course Announcements

Exam and Class Schedule:
- There will be no radiographic procedures lecture on Monday.
- The introductory exam with Ms. Hoskins is scheduled for Monday.
- The Monday laboratory group will convene earlier, immediately following the conclusion of the exam.
- Radiographic procedures lecture will resume the following Wednesday to complete pelvic and hip positioning.