"

Lower Extremities

Femur

Anatomy & Pathology

Key Anatomical Structures

  • Femur (longest and strongest bone in the body):
    • Femoral head: Rounded proximal portion that articulates with the acetabulum of the pelvis to form the hip joint.
    • Fovea capitis: Small depression on the femoral head where the ligamentum teres attaches, providing blood supply to the femoral head.
    • Femoral neck: Cylindrical constriction connecting the head to the shaft; forms an angle of approximately 125° with the shaft and 15–20° anterior inclination (anteversion).
    • Greater trochanter: Large, palpable prominence on the lateral aspect; serves as a major muscle attachment site (gluteus medius, minimus).
    • Lesser trochanter: Medial and posterior prominence for attachment of the iliopsoas tendon.
    • Intertrochanteric crest: Posterior ridge connecting the greater and lesser trochanters.
    • Intertrochanteric line: Anterior ridge where the capsule of the hip joint attaches.
    • Femoral body (shaft): Slightly bowed anteriorly; bears weight transmission from hip to knee.
    • Linea aspera: Prominent longitudinal ridge along the posterior shaft where adductor muscles attach.
    • Adductor tubercle: Located on the medial condyle; assists in identifying rotation on distal femur images.
  • Distal Femur:
    • Medial and lateral condyles: Smooth, rounded articular surfaces forming the superior part of the knee joint; the medial condyle extends farther distally.
    • Intercondylar fossa (notch): Deep posterior depression between condyles; attachment for cruciate ligaments (ACL and PCL).
    • Epicondyles: Non-articular prominences superior to each condyle; serve as attachment sites for collateral ligaments.
  • Associated Structures:
    • Patella: Sesamoid bone embedded within the quadriceps tendon; articulates with the patellar surface (trochlear groove) of the femur.
      • Base: Broad superior border.
      • Apex: Inferior point directed toward the tibial tuberosity.
      • Improves leverage of the quadriceps mechanism.
    • Menisci (medial & lateral): Crescent-shaped fibrocartilage pads on tibial plateaus that act as shock absorbers.
    • Acetabulum: Cup-shaped pelvic socket formed by the ilium, ischium, and pubis, articulating with the femoral head.
  • Joints:
    • Hip (acetabulofemoral) joint: Diarthrodial, ball-and-socket type allowing multidirectional movement.
    • Knee (femorotibial) joint: Diarthrodial, hinge type between femoral condyles and tibial plateaus.
    • Patellofemoral joint: Diarthrodial, gliding type between patella and femur.

Common Pathologies

  • Fractures:
    • Femoral neck fracture: Common in elderly patients after falls; may require cross-table lateral imaging.
    • Intertrochanteric fracture: Between the greater and lesser trochanters; often requires traction or surgical fixation.
    • Midshaft fracture: Often spiral or comminuted; may cause angulation or foreshortening; both hip and knee joints must be included.
    • Supracondylar or condylar fracture: Involves distal femur near knee joint; may disrupt condylar alignment.
  • Osteoarthritis (degenerative joint disease): Cartilage loss and osteophyte formation at the hip or knee joints leading to joint-space narrowing and sclerosis.
  • Metastatic lesions: Femur is a common site for secondary malignancy (especially from prostate, breast, or lung). May appear as lytic (“moth-eaten”) or sclerotic areas along the shaft.
  • Osteomyelitis: Infection of bone and marrow, often post-traumatic or post-surgical.
  • Avascular necrosis (AVN): Compromised blood flow to femoral head leads to bone collapse and deformity (commonly post-trauma or steroid use).
  • Osgood-Schlatter disease (in adolescents): Though primarily involving tibial tuberosity, may appear with distal femoral changes from repetitive traction forces.
  • Bone tumors: Include benign lesions (osteoid osteoma) and malignant forms (osteosarcoma, Ewing sarcoma).

Routine Projections (ARRT Required)

AP Femur (with knee or hip included)

CR Location & Positioning

  • SID: 40″
  • Patient position: Supine, pelvis not rotated
  • Adjustments:
    • For distal femur: internally rotate limb to place epicondyles parallel to IR; IR 2″ below knee joint.
    • For proximal femur: rotate limb internally 10–15°; IR top at level of ASIS.
  • CR: Perpendicular to mid-femur and IR center
  • Pt. Instructions: Hold still
  • Exposure: 70–75 kVp, grid, phototime or ~12 mAs

Evaluation Criteria

  • Coverage: Entire femur, including joint closest to area of interest; second image recommended to include opposite joint
  • Rotation checks: Distal femur—no knee rotation, femoral condyles symmetric; Proximal femur—neck not foreshortened, lesser trochanter minimally visible
  • Motion checks: Sharp bony trabeculae, cortices distinct
  • Technique checks: Good contrast, soft tissue and bone detail, entire orthopedic appliance included if present
  • Clinical aim: Evaluate shaft, trochanters, femoral neck, hip and knee joint

Lateral Femur (mediolateral, with knee or hip included)

CR Location & Positioning

  • SID: 40″
  • Patient position: Lateral recumbent on affected side
  • Adjustments:
    • With knee included: flex knee 45°, epicondyles perpendicular, IR extends 2″ beyond knee.
    • With hip included: place IR top at ASIS, roll pelvis posteriorly 10–15° to avoid superimposition, opposite leg drawn posteriorly.
  • Cross-table lateral used if fracture suspected.
  • CR: Perpendicular to mid-femur and IR center
  • Pt. Instructions: Hold still
  • Exposure: 70–75 kVp, grid, phototime or ~12 mAs

Evaluation Criteria

  • Coverage: Entire femur, joint nearest pathology included; both joints imaged in 2 views if necessary
  • Rotation checks:
    • With knee—superimposed femoral condyles, patella in profile, open patellofemoral space.
    • With hip—greater trochanter over distal femoral neck, lesser trochanter visible medially.
  • Motion checks: Clear cortices and trabecular markings
  • Technique checks: Appropriate density, soft tissue detail, orthopedic hardware in full length
  • Clinical aim: Assess fractures, hip and knee prostheses, tumors, alignment

Supplemental Projections

Cross-Table (Horizontal Beam) Lateral

CR Location & Positioning

  • SID: 40″
  • Patient position: Supine, affected leg extended
  • Adjustments:
    • Place IR vertically against medial or lateral aspect of thigh and knee
    • Elevate unaffected leg if necessary to clear the field
    • Support IR with sponges or an assistant
  • CR: Horizontal, directed perpendicular to mid-femur and centered to IR
  • Pt. Instructions: Hold still
  • Exposure: 70–75 kVp, grid, increased mAs to compensate for cross-table technique

Evaluation Criteria

  • Coverage: Femur and joint nearest pathology (hip or knee), full length demonstrated with overlap when using two images
  • Rotation checks: Condyles in profile without excessive overlap; hip visualized without superimposition of opposite leg
  • Motion checks: Sharp trabecular markings and cortical margins
  • Technique checks: Adequate penetration through dense hip region, orthopedic hardware included in entirety
  • Clinical aim: Used for suspected femoral fractures or destructive lesions where patient cannot be rotated

Lateral Proximal Femur (Hip Focused)

(a modification of the standard lateral when hip joint is primary interest)

CR Location & Positioning

  • SID: 40″
  • Patient position: Lateral recumbent on affected side
  • Adjustments: Roll pelvis posteriorly 10–15° to avoid superimposition by opposite thigh, extend unaffected leg posteriorly
  • CR: Perpendicular to mid-proximal femur, IR top at ASIS
  • Pt. Instructions: Hold still
  • Exposure: 70–75 kVp, grid

Evaluation Criteria

  • Coverage: Proximal femur and hip joint, including acetabulum
  • Rotation checks: Greater trochanter superimposed over distal neck, lesser trochanter visible medially
  • Motion checks: Sharp bone detail in head/neck region
  • Technique checks: Adequate density to penetrate hip region
  • Clinical aim: Hip trauma, evaluation of fracture/dislocation, pre/post-op prosthetic assessment

Femur – Common Errors & Fixes

Projection Common Error Image Appearance Cause Fix
AP Femur (distal) Rotation Femoral/tibial condyles not symmetric, patella off midline Limb not internally rotated to true AP Ensure epicondyles are parallel to IR, check patella centered
AP Femur (proximal) Femoral neck foreshortened Neck appears short and not in profile Toes not inverted (limb not internally rotated 10–15°) Internally rotate entire leg and foot 10–15°
AP Femur (any) Lesser trochanter too prominent Lesser trochanter clearly projected medially External rotation of leg Reposition with toes pointed inward
Lateral Femur (distal) Condyles not superimposed Anterior/posterior margins separated Patient rolled forward or backward Adjust pelvis so condyles are perpendicular to IR
Lateral Femur (proximal) Opposite thigh obscures hip Proximal femur and acetabulum overlapped Unaffected leg not displaced posteriorly enough Roll pelvis posteriorly 10–15°, extend unaffected leg backward
Cross-table lateral Hip/knee not visualized fully Anatomy cut off IR not placed high/low enough, CR not centered Adjust IR height and CR centering, overlap images if needed
Any femur projection Motion blur Loss of trabecular detail Patient movement, long exposure time Immobilize, use shorter exposure time
Post-op femur Hardware not fully included Prosthesis cut off IR placement too tight to area of interest Include entire orthopedic appliance, even if 2 films are required

Hows & Whys of Femur Radiography

Anatomy

  • What is the adductor tubercle and why is it important?
    It is a small projection on the medial femoral condyle used as a landmark for detecting rotation on femur and knee images.
  • What structures help confirm a true lateral femur?
    Superimposed condyles and greater trochanter over the shaft indicate proper positioning.

Positioning

  • Why should the limb be internally rotated for AP femur imaging?
    To place the femoral neck in profile and avoid foreshortening.
  • Why is a 10–15° internal rotation used for the proximal femur?
    To correct the natural external rotation of the leg and show the femoral head and neck in full profile.
  • Why is the pelvis rolled slightly posterior (10–15°) for lateral hip/femur views?
    To avoid superimposition of the proximal femur by the opposite thigh.
  • Why should the knee be flexed 45° for the distal lateral femur?
    This relaxes surrounding muscles and opens the joint spaces, making the condyles easier to align.
  • Why is the pelvis rolled posteriorly for the lateral proximal femur?
    To clear the opposite leg from overlapping the hip region.

Technique & Image Evaluation

  • How can you tell the AP femur is not rotated?
    The femoral and tibial condyles are symmetric, and the greater trochanter and femoral head/neck are in proper profile.
  • How do you know the proximal femur was correctly positioned?
    The femoral neck is not foreshortened and only a small portion of the lesser trochanter is visible.
  • What error is indicated if the lesser trochanter is clearly visible on the AP femur?
    The limb was not internally rotated enough.
  • How do you confirm a true lateral femur?
    The femoral condyles are superimposed anterior to posterior, and the greater trochanter is aligned with the femoral shaft.
  • How do you know a cross-table lateral femur was properly positioned?
    Condyles are in profile, hip or knee joint is included, and opposite leg does not superimpose the proximal femur.
  • What error is indicated if the proximal femur is obscured by the opposite thigh on a lateral?
    The pelvis was not rotated posteriorly enough, or the unaffected leg was not displaced.

Clinical Applications

  • Why are two projections (hip and knee) needed for femur imaging?
    To ensure both joints are evaluated for fractures or dislocations along the shaft.
  • Why is a cross-table lateral used if a fracture is suspected?
    It avoids moving the affected limb, preventing displacement of fracture fragments.
  • Why is it important to include orthopedic appliances in their entirety?
    For surgical planning and to assess fixation, alignment, or loosening.
  • Why is a cross-table lateral used in trauma?
    To avoid moving the leg and prevent displacement of fracture fragments.

 

License

Icon for the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License

Radiographic Procedures Review Guide Copyright © 2025 by Carla M. Allen and Taylor M. Otto is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

Share This Book