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HIP BONE & FEMUR — MBBS LEVEL ANATOMY NOTES

Sources: Gray's Anatomy for Students | THIEME Atlas of Anatomy | Netter's Atlas | BD Chaurasia | KLM

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PART 1: THE HIP BONE (Os Coxae / Innominate Bone)

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1.1 Overview

Key Point (BD Chaurasia / KLM): All three parts meet at the acetabulum via the triradiate cartilage (Y-shaped growth plate). This fuses between 14-16 years of life (THIEME Atlas).

• With each other anteriorly at the pubic symphysis (fibrocartilaginous)
• With the sacrum posteriorly at the sacroiliac joints (synovial + fibrous)

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1.2 THE ILIUM

Parts:

• Body of ilium - forms the upper 2/5 of the acetabulum
• Ala (wing) of ilium - the large fan-shaped plate above the body

Surfaces:

• Large concave smooth area on the inner surface
• Gives origin to the iliacus muscle
• Separated from the true pelvis by the arcuate line

• Auricular surface - ear-shaped articular surface for articulation with the sacrum (sacroiliac joint)
• Iliac tuberosity - roughened area above auricular surface; attachment for the interosseous sacroiliac ligament

Iliac Crest:

• The thick curved superior border of the ala
• Extends from ASIS (Anterior Superior Iliac Spine) to PSIS (Posterior Superior Iliac Spine)
• Has an outer lip, inner lip, and intermediate zone
• Tubercle of the iliac crest - palpable bony projection approximately 5 cm posterior to the ASIS (on the outer lip)
• Important as a surface landmark - the highest point of the iliac crest is at the level of L4 vertebra (used for lumbar puncture)

Iliac Spines (4 in total):

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1.3 THE ISCHIUM

Parts:

1. Body of ischium - forms the posteroinferior 2/5 of the acetabulum
2. Ramus of ischium (inferior ramus) - projects anteriorly to join the inferior pubic ramus, forming the ischiopubic ramus

Key Features:

• Sharp bony projection from the posterior border of the body
• Separates the greater sciatic notch (above) from the lesser sciatic notch (below)
• Attachment: sacrospinous ligament; pudendal nerve passes around it
• Can be palpated per rectum / per vaginum - landmark for pudendal nerve block

• Large, rough, oval prominence on the posteroinferior aspect
• Bears the body's weight in sitting
• Attachments: hamstring muscles (semitendinosus, semimembranosus, long head of biceps femoris), adductor magnus (hamstring part), sacrotuberous ligament
• Palpable through buttock when hip is flexed

• Between PIIS and ischial spine
• Converted to greater sciatic foramen by the sacrospinous ligament
• Transmits: piriformis muscle, sciatic nerve, superior and inferior gluteal vessels/nerves, pudendal vessels/nerve (enter and re-enter)

• Between ischial spine and ischial tuberosity
• Converted to lesser sciatic foramen by sacrospinous + sacrotuberous ligaments
• Transmits: obturator internus tendon, pudendal nerve and vessels (re-enter pelvis)

• Large oval opening in the lower part of the hip bone, bounded by ischium and pubis
• Mostly closed by the obturator membrane, except superiorly where the obturator canal transmits the obturator nerve and vessels

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1.4 THE PUBIS

Parts:

1. Body of pubis - forms the anteromedial part; medial surface = symphyseal surface; contributes 1/5 of acetabulum
2. Superior pubic ramus - projects laterally from the body toward the acetabulum
3. Inferior pubic ramus - projects downward and backward to join the ischial ramus

Key Features:

• Small rounded projection on the superior aspect of the body
• Attachment for medial end of the inguinal ligament
• Key landmark for identifying the inguinal ligament and femoral canal

• Sharp ridge on the superior pubic ramus
• Part of the linea terminalis (pelvic brim)
• Attachment: pectineus muscle, pectineal ligament (Cooper's ligament)

• Medial thickening of the superior body surface, between the two pubic tubercles (across the midline)

• Oval, rough, vertical medial face of pubic body
• Articulates with the opposite side at the pubic symphysis (secondary cartilaginous joint / amphiarthrosis)

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1.5 THE ACETABULUM

Parts:

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1.6 SEX DIFFERENCES IN THE HIP BONE (Important for MBBS/Forensics)

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PART 2: THE FEMUR

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2.1 Overview

• Proximally with the acetabulum of the hip bone (hip joint)
• Distally with the tibia and patella (knee joint)

1. Proximal end - head, neck, greater and lesser trochanters
2. Shaft (diaphysis)
3. Distal end - medial and lateral condyles, epicondyles, patellar surface

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2.2 PROXIMAL FEMUR

Head of the Femur:

• Spherical, covered with articular cartilage (except at the fovea)
• Articulates with the acetabulum
• Fovea capitis (fovea of the head): Non-articular pit on the medial surface of the head; attachment for the ligamentum teres (ligament of the head) - contains the artery of the ligamentum teres (branch of obturator artery; small and variable in adults)

Neck of the Femur:

• Cylindrical strut connecting head to shaft
• Projects superomedially from the shaft
• Angle of inclination (CCD angle / Femoral Neck Angle):
  • Newborn: ~150°
  • Adult: ~126° (THIEME Atlas) / ~125° (Gray's)
  • If >126° = Coxa valga (neck more vertical, relative leg lengthening)
  • If <126° = Coxa vara (neck more horizontal, relative leg shortening)
• Angle of anteversion (torsion angle):
  • The neck is twisted forward relative to the condylar axis
  • Newborn: 30-40°; Adult: ~12°
  • If increased = coxa anteverta → toeing-in gait
  • If decreased/reversed = coxa retroverta → toeing-out gait

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2.3 TROCHANTERS

Greater Trochanter:

• Large quadrilateral bony projection extending superiorly from the junction of the neck and shaft, laterally
• Trochanteric fossa: Deep depression on the medial surface of the greater trochanter; where obturator externus inserts
• Muscle attachments (lateral surface):
  • Anterior ridge: Gluteus minimus
  • Posterior ridge: Gluteus medius
• Superior margin (medial to fossa): Obturator internus + gemelli
• Superior-posterior margin: Piriformis
• The greater trochanter is palpable in the lateral thigh (important surface landmark)

Lesser Trochanter:

• Smaller, cone-shaped projection from the posteromedial aspect at the junction of neck and shaft
• Attachment: combined tendon of psoas major + iliacus (iliopsoas)

Connecting Ridges:

• Intertrochanteric line (anterior surface): Runs between the two trochanters on the anterior aspect; marks the anterior limit of the femoral neck and capsular attachment line; attachment for the iliofemoral ligament (superior band)
• Intertrochanteric crest (posterior surface): Thick rounded ridge on the posterior aspect; bears the quadrate tubercle at its midpoint (attachment for quadratus femoris)

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2.4 SHAFT OF THE FEMUR

Cross-Section (middle third):

• Anterior surface
• Medial (posteromedial) surface
• Lateral (posterolateral) surface
• Medial border (rounded)
• Lateral border (rounded)
• Posterior border = Linea aspera (rough crest)

Linea Aspera:

• Major muscular ridge on the posterior surface of the middle third
• Has a medial lip and lateral lip
• Muscle attachments on linea aspera (a favorite MBBS exam question):

Proximal continuations of linea aspera:

• Pectineal line (spiral line): Medial lip curves anteriorly, passing under the lesser trochanter, joining the intertrochanteric line
• Gluteal tuberosity: Lateral lip curves to the base of the greater trochanter; gluteus maximus attaches here (sometimes a 3rd trochanter is present)

Distal continuations of linea aspera:

• Linea aspera splits into medial supracondylar line and lateral supracondylar line, enclosing the popliteal surface (floor of popliteal fossa)
• Medial supracondylar line terminates at the adductor tubercle on the medial condyle
• Adductor tubercle = attachment for adductor magnus (adductor part)

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2.5 DISTAL FEMUR

Medial and Lateral Condyles:

• Large, rounded condyles, broader posteriorly and becoming flatter inferiorly
• Articulate with the tibial plateau inferiorly
• Articulate with the patella anteriorly via the patellar surface (femoral trochlea) - a V-shaped groove; lateral wall is larger and steeper

Intercondylar Fossa (Notch):

• Deep notch separating the condyles posteriorly
• Contains the cruciate ligaments:
  • Anterior cruciate ligament (ACL): Attaches to the medial surface of the lateral condyle (posterosuperior oval facet)
  • Posterior cruciate ligament (PCL): Attaches to the lateral surface of the medial condyle (large oval facet, inferior half)

Epicondyles:

• Non-articular bony elevations on the outer surfaces of condyles
• Medial epicondyle: Attachment for medial collateral ligament of knee; the adductor tubercle lies just above it
• Lateral epicondyle: Attachment for lateral collateral ligament of knee; has two facets posterior to it for the popliteus and lateral head of gastrocnemius

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2.6 IMPORTANT ANGLES (MUST KNOW FOR EXAMS)

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2.7 BLOOD SUPPLY TO THE HEAD OF FEMUR (Extremely Important Clinically)

1. Retinacular vessels (primary supply in adults): Branches of the medial and lateral circumflex femoral arteries form an arterial ring at the base of the neck; from here, vessels run along the neck deep to the capsular periosteum (retinacula) and supply the head
   • Medial circumflex femoral artery supplies most of the head
2. Artery of the ligamentum teres (branch of obturator artery): Small and variable; significant in children, attenuated in adults
3. Medullary artery via nutrient artery: Contributes in youth; in older age, medullary cavity undergoes fatty replacement (reduced supply)

Clinical Pearl: In subcapital fractures of the neck of femur, the retinacular vessels are disrupted, leading to avascular necrosis (AVN) of the femoral head. This is why hemiarthroplasty (not internal fixation) is preferred for displaced subcapital fractures in the elderly.

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PART 3: CLINICAL APPLIED ANATOMY (MBBS Must-Know)

3.1 Fracture of the Neck of Femur

• Elderly woman, fall at home
• Right leg shorter and externally rotated
• Displaced fracture on X-ray

• Psoas major attaches to the lesser trochanter; normally its fulcrum is the femoral head in the acetabulum
• When the neck fractures, psoas overriding action pulls the femur proximally and into external rotation
• Spasm of adductors exacerbates external rotation

• Subcapital: Across head-neck junction - highest AVN risk
• Transcervical: Through midportion of neck
• Basicervical: Across base of neck - lowest AVN risk

• Elderly with displaced subcapital fracture → Hemiarthroplasty (femoral head removed, prosthesis inserted)
• Young patients or undisplaced fractures → Internal fixation (cannulated screws / dynamic hip screw)
• Intertrochanteric fractures → DHS (dynamic hip screw), retinacular vessels not at risk

3.2 Coxa Valga vs. Coxa Vara

3.3 Pelvic Brim (Linea Terminalis)

• Sacral promontory → sacral ala → sacroiliac joint → arcuate line of ilium → pectineal line → pubic crest → pubic symphysis

3.4 Osseofascial Compartments & Nerve Injuries

• ASIS avulsion fracture: Young athletes - sartorius pulls off the ASIS
• AIIS avulsion fracture: Rectus femoris pulls off AIIS in kicking sports
• Ischial tuberosity avulsion: Hamstrings pull off in sprinters (gymnasts doing splits)
• Meralgia paresthetica: Lateral femoral cutaneous nerve compressed at ASIS/inguinal ligament - burning pain/numbness on anterolateral thigh

3.5 Trabecular Pattern of Femoral Head (THIEME Atlas)

• Compression trabeculae: Run from the head downward to the medial cortex - bear compressive loads
• Tension trabeculae: Run from the head to the lateral cortex - bear tensile loads
• The Ward's triangle = area of relative weakness between the two trabecular systems in the neck; first site of fracture in osteoporosis

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PART 4: PELVIC GIRDLE - ARTICULATIONS SUMMARY

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QUICK REVISION TABLE: KEY Attachments at a Glance

Hip Bone - Key Muscle Origins

Femur - Key Muscle Insertions/Origins

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PART 5: OSSIFICATION (Important for MBBS Exams - BD Chaurasia/KLM)

Hip Bone Ossification:

• Ilium: Primary center appears at 8th week of fetal life
• Ischium: Primary center appears at 4th month of fetal life
• Pubis: Primary center appears at 4-5th month of fetal life
• The three centers fuse at the acetabulum (triradiate cartilage) between 14-16 years
• Secondary centers appear at iliac crest, ASIS, ischial tuberosity, pubic tubercle, etc. - fuse by 25 years

Femur Ossification:

Medicolegal Note (BD Chaurasia): The distal femoral epiphysis is visible on X-ray at birth (36 weeks+ gestation). Its presence confirms that the fetus was viable (full-term). This is used in medicolegal examination of newborns.

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SUMMARY MNEMONICS

"P-OI-Gem-Min-Med" = Piriformis, Obturator Internus + Gemelli, Gluteus Minimus, Gluteus Medius

Pectineus → Adductor brevis → Adductor longus → Adductor magnus (medial lip); Vastus lateralis → Biceps short head → Vastus medialis (lateral then medial lips)

"P-Sup G-Sciatic-Inf G-P-PN-I" = Piriformis, Superior gluteal, Sciatic nerve, Inferior gluteal, Posterior cutaneous of thigh, Pudendal nerve (enters), Internal pudendal vessels

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