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Muscles of the Thigh and Leg

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THIGH MUSCLES

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1. Anterior Compartment - Extensor Group

Sartorius

Quadriceps Femoris (4 heads + articularis genus)

Innervation of all heads: Femoral nerve (L1-L4) Key clinical point: Paralysis of quadriceps destabilizes the knee in stance phase. Walking is possible only if the patient hyperextends the knee to lock it, using the line of gravity in front of the knee axis.

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2. Medial Compartment - Adductor Group

Key facts: Adductor magnus is the largest adductor (27% of thigh muscle mass). It has a dual nerve supply. The adductor hiatus in its tendon transmits the femoral artery into the popliteal fossa. Most common injured adductor in athletes: adductor longus.

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3. Posterior Compartment - Hamstrings (Flexor Group)

Pes anserinus ("goose's foot"): The combined tendon insertion of sartorius + gracilis + semitendinosus at the medial tibial surface. A frequent site of bursitis.

Hamstring insufficiency: With the knee extended, the hamstrings are too short to allow full hip flexion (passive insufficiency). With the hip extended, they cannot shorten enough to allow full knee flexion (active insufficiency).

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LEG MUSCLES

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1. Anterior Compartment (Extensors / Dorsiflexors)

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2. Lateral Compartment (Evertors)

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3. Posterior Compartment - Superficial (Plantarflexors)

Triceps Surae (= Gastrocnemius + Soleus)

Plantaris: Origin at lateral femoral epicondyle (just proximal to lateral gastrocnemius head); inserts via Achilles tendon; small cross-section - functionally negligible; may prevent compression of posterior musculature during knee flexion. Nerve: Tibial (S1, S2).

Achilles tendon: Average length 20-25 cm; breaking strength ~60-100 N/mm² (can bear nearly 1 ton). Weakest blood supply (and most common rupture site) = 2-6 cm proximal to calcaneal insertion.

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4. Posterior Compartment - Deep (Plantarflexors + Invertors)

"Tom, Dick, ANd Harry" mnemonic for the order of structures passing posterior to the medial malleolus: Tibialis posterior → Digitorum flexor longus → (posterior tibial) Artery & nerve → Hallucis flexor longus.

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Summary Table: Compartments and Innervation

• THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System, pp. 488-515
• Imaging Anatomy Vol. 3, pp. 268-276
• Miller's Review of Orthopaedics 9th Ed., p. 18

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The Hip Bone (Os Coxae) - Landmarks and Attachments

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PART I: THE ILIUM

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1. Iliac Crest

Clinical note: Avulsion of the iliac crest can occur from forceful contraction of the abdominal muscles in young athletes.

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2. Anterior Superior Iliac Spine (ASIS)

• Sartorius (origin)
• Tensor fasciae latae (origin)
• Inguinal ligament (lateral attachment - runs from ASIS to pubic tubercle)

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3. Anterior Inferior Iliac Spine (AIIS)

• Rectus femoris - straight head (origin)
• Iliofemoral ligament (upper limb - the strongest ligament of the hip joint; extends to the anterior hip joint/intertrochanteric line)

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4. Posterior Superior Iliac Spine (PSIS)

• Sacrotuberous ligament (partial attachment)
• Multifidus (origin)
• Iliolumbar ligament (posterior iliac wing to L5 transverse process)
• Surface landmark: corresponds to the dimple of Venus; lies at level of S2 vertebra

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5. Posterior Inferior Iliac Spine (PIIS)

• Forms the superior boundary of the greater sciatic notch
• Attachment for the posterior capsule of the sacroiliac joint

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6. Iliac Fossa (Inner/Medial Surface)

• Iliacus muscle - large, broad attachment covering most of the iliac fossa
• Iliac fascia (inner lip of crest)

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7. Gluteal Surface (Outer/Lateral Surface) - Three Gluteal Lines

• Piriformis - small attachment at inferior/posterior aspect of gluteal surface (near greater sciatic notch)

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8. Auricular Surface

• Articulates with the sacrum forming the sacroiliac joint (hyaline inferiorly, fibrous superiorly)

9. Iliac Tuberosity (posterior to auricular surface)

• Posterior sacroiliac ligaments and interosseous ligaments

10. Arcuate Line (Iliopectineal Line)

• Separates the greater pelvis (above) from the lesser pelvis (below)
• Forms part of the pelvic brim (inlet)
• Continuous with the pectineal line of pubis

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PART II: THE ISCHIUM

11. Ischial Tuberosity

Avulsion fracture: Forceful contraction of the hamstrings can avulse the ischial tuberosity apophysis - classic in sprinters and football players.

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12. Ischial Spine

Clinical: The sacrospinous ligament, with the ischial spine, separates the greater from lesser sciatic foramina.

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13. Greater Sciatic Notch (above ischial spine)

• Piriformis muscle (exits the pelvis through it)
• Sciatic nerve
• Superior and inferior gluteal vessels/nerves
• Pudendal nerve and internal pudendal vessels (exit here, re-enter via lesser foramen)
• Nerve to obturator internus, nerve to quadratus femoris

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14. Lesser Sciatic Notch (below ischial spine)

• Obturator internus tendon (exits to reach greater trochanter)
• Internal pudendal vessels
• Pudendal nerve

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15. Ischiopubic Ramus (Body/Ramus of Ischium meeting inferior pubic ramus)

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PART III: THE PUBIS

16. Pubic Tubercle

• Inguinal ligament (medial attachment)
• Rectus abdominis (lateral slip)
• Pyramidalis (origin)
• Adductor longus - some fibers attach near the body/crest of pubis

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17. Pubic Crest (superior border of pubic body)

• Rectus abdominis (insertion onto crest)
• Pyramidalis (origin from crest)
• Inguinal ligament medial end

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18. Pectineal Line (Pecten Pubis) - superior ramus

• Part of the pelvic brim
• Pectineus muscle (origin)
• Pectineal ligament (Cooper's ligament)

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19. Symphyseal Surface

• Articulates with the opposite pubis at the pubic symphysis (secondary cartilaginous joint / fibrocartilage)

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20. Iliopubic Eminence (Iliopectineal Eminence)

• Iliopsoas passes over this ridge (potential site of iliopsoas bursitis from friction)

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PART IV: THE ACETABULUM

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PART V: OBTURATOR FORAMEN

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Summary Attachment Map

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Quick Reference: Landmark → Key Attachment

• Imaging Anatomy Vol. 3 - Bones, Joints, Vessels and Nerves, pp. 227-234
• THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System, pp. 433-434
• Gray's Anatomy for Students, p. 638

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The Tibia - Landmarks and Attachments

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PROXIMAL TIBIA

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1. Medial Condyle (Tibial Plateau)

• Larger than lateral condyle; oval articular surface
• Articulates with the medial condyle of the femur and the medial meniscus
• Posterior surface bears a distinct horizontal groove for attachment of semimembranosus (direct head insertion)

2. Lateral Condyle (Tibial Plateau)

• Circular articular surface; articulates with the lateral condyle of the femur and lateral meniscus
• Undersurface bears a circular facet for articulation with the proximal head of the fibula (superior tibiofibular joint)
• Proximal anterior margin: Iliotibial band (ITB) inserts here (Gerdy's tubercle - anterolateral aspect of the lateral condyle)

3. Intercondylar Eminence (Area)

Memory aid for the intercondylar area (front to back): M-A-L / L-M-P (medial meniscus anterior, ACL, lateral meniscus anterior / lateral meniscus posterior, medial meniscus posterior, PCL)

4. Tibial Tuberosity

Osgood-Schlatter disease: Apophysitis/traction injury of the tibial tuberosity in adolescent athletes due to repetitive stress from the patellar ligament.

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SHAFT OF TIBIA

5. Anterior Border ("Shin")

• No direct muscle attachments (subcutaneous throughout)
• Most vulnerable site for direct blows ("shin splints" occur in the surrounding periosteum and musculature)

6. Medial Surface

• Medial and slightly inferior to the tibial tuberosity: the pes anserinus insertion

Pes anserinus bursitis occurs here between the pes anserinus tendons and the medial collateral ligament.

7. Lateral Surface

• Between the anterior and interosseous borders
• Origin of tibialis anterior (upper 2/3 of lateral tibial surface)

8. Posterior Surface

• Upper part crossed by the soleal line (roughened oblique line running inferomedially from the fibular facet region)

9. Interosseous Border

• Also gives origin to tibialis anterior (its posterior aspect)
• Tibialis posterior and FHL also originate from the interosseous membrane

10. Medial Border

11. Nutrient Foramen

• Opens away from the knee ("flees the knee") - a useful anatomical rule for determining the nutrient foramen direction

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DISTAL TIBIA

12. Medial Malleolus

• Anterior colliculus - larger, more prominent
• Posterior colliculus - smaller, separated by the intercollicular groove

The deltoid ligament is the strongest ligament of the ankle.

13. Inferior Articular Surface (Tibial Plafond)

• The horizontal weight-bearing surface that articulates with the superior dome of the talus
• Together with the medial malleolus and lateral malleolus (fibula), forms the ankle mortise

14. Fibular Notch (Distal Lateral Tibia)

• Articulates with the distal fibula
• Distal tibiofibular syndesmosis formed by:
  • Anterior tibiofibular ligament (from Tubercle of Chaput on anterolateral distal tibia)
  • Posterior tibiofibular ligament (from Posterior tibial tubercle)
  • Interosseous tibiofibular ligament
  • Inferior transverse ligament

15. Posterior Malleolus

• A dorsal/posterior projection of the distal tibia
• Deepens the ankle mortise posteriorly
• Attachment of posterior tibiofibular ligament

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Complete Landmark-to-Attachment Reference Table

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Quick Clinically Important Points

• The medial surface is entirely subcutaneous - commonly fractured by direct blows (most tibial shaft fractures are open due to lack of overlying muscle)
• Compartment syndrome most commonly involves the anterior compartment of the leg where tibialis anterior and extensors arise from the lateral tibial surface and interosseous membrane
• Osgood-Schlatter = tibial tuberosity apophysitis (adolescents, patellar ligament traction)
• Tibial stress fractures most commonly occur in the anterior cortex of the midshaft (the "tension side") in runners
• Pes anserinus bursitis - pain over the medial tibial surface 3-4 cm below the joint line, between pes tendons and the MCL of the knee

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The Femur - Landmarks and Attachments

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PART I: PROXIMAL FEMUR

1. Femoral Head

• Almost perfectly spherical (2/3 of a sphere)
• Covered entirely with hyaline cartilage except at the fovea centralis (a small pit on the medial surface)
• Articulates with the acetabulum to form the hip joint

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2. Femoral Neck

• ~5 cm long; connects the head to the shaft
• Projects superomedially at a neck-shaft angle of ~122-135° (decreases with age; coxa valga = increased angle; coxa vara = decreased)
• Also has anteversion of 10-15° (the neck is twisted anteriorly relative to the shaft)
• The anterior surface of the neck is entirely intracapsular (hip joint capsule attaches to the intertrochanteric line anteriorly)
• Posterior neck: only the medial part is intracapsular (capsule attaches halfway along the posterior neck)

Clinical importance: Femoral neck fractures disrupt the retinacular vessels (branches of the medial circumflex femoral artery) running along the posterior neck, causing avascular necrosis of the femoral head. Intracapsular neck fractures are especially at risk.

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3. Greater Trochanter

• Tensor fasciae latae - inserts via the iliotibial band (to lateral condyle of tibia, not GT directly)
• Gluteus medius - main abductor of the hip (posterior fibers to posterior-superior GT)
• Trochanteric bursa overlies the greater trochanter deep to the iliotibial band

Trochanteric fossa: A depression on the medial surface of the greater trochanter, posterior aspect.

• Obturator externus tendon inserts here (trochanteric fossa, not the main GT surface)
• Obturator internus also inserts in this region

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4. Lesser Trochanter

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5. Intertrochanteric Line (Anterior)

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6. Intertrochanteric Crest (Posterior)

Calcar femorale: A dense vertical plate of bone within the medial femoral neck, continuous with the posteromedial cortex - important in distributing compressive forces.

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PART II: FEMORAL SHAFT (DIAPHYSIS)

7. Gluteal Tuberosity (Posterolateral Shaft)

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8. Pectineal Line (Spiral Line)

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9. Linea Aspera (Posterior Shaft)

"BADGE" mnemonic for linea aspera attachments (medial to lateral): Biceps femoris (short head), Adductor magnus/longus/brevis, Vastus medialis/lateralis, Gluteus maximus, and the two intermuscular septa.

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10. Anterior Surface of Shaft

• Vastus intermedius originates from the anterior surface of the femoral shaft (upper 2/3)
• Articularis genus (deepest fibers of vastus intermedius) - origin from anterior distal shaft at level of suprapatellar recess; inserts into the suprapatellar recess of the knee capsule to prevent it from being pinched during extension

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PART III: DISTAL FEMUR

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11. Medial Supracondylar Line

• Vastus medialis continues to arise from this line distally
• Medial head of gastrocnemius - origin from the posterior aspect of the medial supracondylar region / medial epicondyle

12. Lateral Supracondylar Line

• Vastus lateralis continues to arise from this line distally
• Lateral head of gastrocnemius - origin from posterior lateral supracondylar region / lateral epicondyle
• Plantaris - origin from the lower part of the lateral supracondylar line (just proximal to the lateral gastrocnemius head)

13. Popliteal Surface

• No direct muscle origins (smooth surface)
• Popliteal artery lies on it

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14. Medial Epicondyle

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15. Adductor Tubercle

Adductor hiatus: The gap in the distal tendon of adductor magnus between its linea aspera insertion and adductor tubercle insertion - transmits the femoral artery and vein into the popliteal fossa.

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16. Lateral Epicondyle

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17. Medial Femoral Condyle

• Larger and more prominent than the lateral condyle
• Extends further distally
• Articular surface covered with hyaline cartilage for articulation with the medial tibial condyle
• Posterior cruciate ligament (PCL): attachment on the medial wall of the intercondylar fossa (lateral surface of medial condyle)

18. Lateral Femoral Condyle

• Smaller, more anterior
• Articular surface for lateral tibial condyle
• Anterior cruciate ligament (ACL): attachment on the lateral wall of the intercondylar fossa (medial surface of lateral condyle - the "resident's ridge")
• Popliteus tendon: has a groove on the articular margin of the lateral condyle (popliteal sulcus)
• Iliotibial band (ITB): passes over the lateral condyle (does not attach here directly; attaches to Gerdy's tubercle on the tibia)

19. Intercondylar Fossa (Notch)

20. Patellar Surface (Trochlea)

• Articulates with the patella (forming the patellofemoral joint)
• Lateral trochlear ridge is higher (more prominent) than the medial - prevents lateral patellar subluxation
• Articularis genus inserts into the suprapatellar recess above this surface

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Summary Attachment Table

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Key Clinical Correlations

• Femoral neck fractures: Disrupt the retinacular vessels → avascular necrosis of femoral head. Garden classification (I-IV). Intracapsular = higher risk of AVN.
• Intertrochanteric fractures: Extracapsular, preserve blood supply - treated with dynamic hip screw (DHS). Evans-Jensen classification.
• Adductor hiatus is the entry point of the femoral artery into the popliteal fossa - a potential compression site.
• Coxa valga (neck-shaft angle >135°) and coxa vara (<115°) affect hip biomechanics and gait.
• Greater trochanteric pain syndrome: Bursitis and/or gluteus medius/minimus tendinopathy at the GT facets.