HIP JOINT - 15 Marks (MBBS Level)

1. TYPE AND ARTICULAR BONES

• Head of femur (spherical) - covered by hyaline cartilage except at the fovea capitis
• Acetabulum of the hip bone (os coxae) - formed by ilium (2/5), ischium (2/5), pubis (1/5); only the lunate surface is articular (covered by hyaline cartilage); broader superiorly where the greatest weight is transmitted

• Acetabular labrum: a fibrocartilaginous collar around the rim of the acetabulum that deepens the socket and grips the femoral head
• Transverse acetabular ligament: bridges the acetabular notch inferiorly, converting it into a foramen through which vessels and nerves pass

        ANTERIOR VIEW
     _______________
    |   ACETABULUM  |
    |  (Lunate surf)|
  __|_______________| ←── Acetabular labrum
 /    ○ Fovea        \
|   HEAD OF FEMUR    |
 \_______|__________/
         |
       NECK
         |
  -------+-------  ← Intertrochanteric line
  GT              LT
  (Greater      (Lesser
  trochanter)   trochanter)

2. LIGAMENTS

a) Iliofemoral Ligament (Ligament of Bigelow)

• Strongest ligament in the body (inverted Y-shape)
• Apex: Anterior inferior iliac spine (AIIS) and acetabular rim
• Base: Along the intertrochanteric line (upper and lower bands are thicker than the central part - hence "Y" shape)
• Prevents hyperextension and lateral rotation

b) Pubofemoral Ligament

• Antero-inferior to the joint
• Base: Iliopubic eminence, superior rami of pubis, and obturator membrane
• Blends with the deep surface of the iliofemoral ligament
• Prevents excessive abduction and lateral rotation

c) Ischiofemoral Ligament

• Reinforces the posterior aspect of the capsule
• Medial attachment: Ischium, posteroinferior to acetabulum
• Lateral: Greater trochanter (deep to iliofemoral ligament)
• Prevents hyperextension and medial rotation

d) Ligament of Head of Femur (Ligamentum Teres)

• Flat triangular band inside the joint
• From: Fovea capitis (head of femur)
• To: Acetabular fossa, transverse acetabular ligament, and margins of acetabular notch
• Not mechanically important for stability; carries a branch of the obturator artery (supplies head of femur in children)

3. RELATIONS

ANTERIOR:

• Iliopsoas muscle (separated from capsule by iliopectineal bursa)
• Pectineus, Rectus femoris
• Femoral nerve, artery, and vein (in the femoral triangle, lateral to medial: Nerve, Artery, Vein = NAV)

POSTERIOR:

• Sciatic nerve (most important posterior relation - can be injured in posterior dislocation)
• Piriformis, Obturator internus + gemelli
• Gluteus maximus (superficially)

SUPERIOR:

• Reflected head of rectus femoris
• Gluteus minimus

INFERIOR:

• Obturator externus tendon
• Transverse acetabular ligament

              SUPERIOR
         Gluteus minimus
              ↑
ANTERIOR                    POSTERIOR
Iliopsoas →  [HIP]  ← Sciatic nerve
Femoral NVB  [JOINT]   Piriformis
             ↓
           Obturator externus
              INFERIOR

4. ACTIONS AND MUSCLES PRODUCING THEM

Key point (MBBS exam favourite): The Iliopsoas is the most powerful flexor of the hip. Gluteus maximus is the most powerful extensor (acts most powerfully when climbing stairs or rising from a chair). Gluteus medius abducts and prevents pelvic drop during walking - tested by Trendelenburg's test.

• Flexors: Femoral nerve (L2, L3, L4)
• Extensors: Inferior gluteal nerve (L5, S1, S2) for gluteus maximus; sciatic nerve for hamstrings
• Abductors: Superior gluteal nerve (L4, L5, S1)
• Adductors: Obturator nerve (L2, L3, L4)
• Lateral rotators: Nerve to piriformis, obturator nerve

5. APPLIED ASPECTS

a) Dislocation of Hip Joint

• Posterior dislocation - most common (80-85%)
  • Mechanism: Forced flexion + adduction + internal rotation (dashboard injury)
  • Limb position: Flexed, adducted, internally rotated, shortened
  • Danger: Injury to sciatic nerve → foot drop
• Anterior dislocation - rare
  • Limb: Extended, abducted, externally rotated
  • Danger: Injury to femoral vessels and nerve

b) Fracture-Dislocation

• Avascular Necrosis (AVN) of femoral head: The femoral head gets its blood supply mainly from the medial circumflex femoral artery (branch of profunda femoris). Dislocation or neck-of-femur fracture disrupts this supply → AVN. The branch via ligamentum teres (obturator artery) is significant only in childhood.

c) Congenital Dislocation of Hip (CDH / DDH)

• More common in females (6:1)
• Acetabulum is shallow, femoral neck anteversion increased
• Ortolani test (click on abduction) and Barlow test (provocation test)
• Trendelenburg gait if bilateral

d) Trendelenburg's Sign

• Tests the abductor mechanism (gluteus medius/minimus + superior gluteal nerve + hip joint)
• Positive: When standing on the affected leg, the pelvis dips on the opposite side
• Causes: CDH, coxa vara, polio, fracture neck of femur, gluteus medius weakness, superior gluteal nerve injury

e) Osteoarthritis of Hip

• Most common joint disease affecting the hip in elderly
• Pain felt in groin, radiates to the knee (referred via obturator and femoral nerves)
• Thomas's test: To unmask fixed flexion deformity
• Managed by: NSAIDs, physiotherapy, and Total Hip Replacement (THR) in severe cases

f) Femoral Neck Fractures (subcapital)

• Blood supply disrupted → AVN and non-union
• Garden's classification (I-IV)
• Managed by: Internal fixation (Garden I-II) or hemiarthroplasty/THR (Garden III-IV) in elderly

g) Septic Arthritis

• In children, the hip is at risk from spread of proximal femoral osteomyelitis
• Emergency - must drain the joint early to prevent AVN

h) Haemarthrosis

• Blood can accumulate in the joint space - distension of capsule is most felt anteriorly (where capsule is thinnest)

         HIP JOINT
    Ball & Socket (Synovial)
    ┌─────────────────────────┐
    │  HEAD femur + ACETABULUM│
    │  (lunate surface)       │
    │  Labrum deepens socket  │
    └─────────────────────────┘
         ↙           ↘
    LIGAMENTS       RELATIONS
  Ilio (strongest) Ant: Femoral NVB
  Pubo (abduction) Post: Sciatic N.
  Ischio (post)    Sup: Glu.minimus
  Lig.teres(intra) Inf: Obt.externus
         ↓
    MOVEMENTS
  Flex: Iliopsoas
  Ext:  Glu.max
  Abd:  Glu.med
  Add:  Adductors
  Lat.rot: Piriformis
         ↓
     APPLIED
  Post.disloc→Sciatic N.injury
  AVN→Blood supply disrupted
  CDH→Ortolani/Barlow test
  Trendelenburg→Glu.med weakness

KNEE JOINT - 15 Marks (MBBS Level)

1. TYPE AND ARTICULAR SURFACES

1. Tibiofemoral joint - between femoral condyles and tibial condyles (weight-bearing)
2. Patellofemoral joint - between posterior patella and patellar surface of femur (redirects pull of quadriceps)

• Medial meniscus: C-shaped, firmly attached to capsule and tibial collateral ligament (less mobile, more commonly torn)
• Lateral meniscus: More circular (O-shaped), NOT attached to fibular collateral ligament (more mobile, less commonly torn)
• Function: Deepen tibial surface, absorb shock, improve lubrication, fill gaps during complex knee movements

         ANTERIOR
    ________________
   |    Patellar    |
   |    lig. area   |
   |                |
   |  C-shaped   O-shaped|
   | [MEDIAL  ] [LATERAL]|
   | MENISCUS   MENISCUS |
   |     ACL  PCL       |
   |________________|
         POSTERIOR

M = more firmly fixed (more tears)
L = more mobile (fewer tears)

2. LIGAMENTS

EXTRACAPSULAR LIGAMENTS:

• Continuation of quadriceps tendon below the patella
• Apex of patella → Tibial tuberosity
• Strongest anterior structure

• Flat, broad band on medial side
• Medial epicondyle of femur → Medial condyle + medial surface of tibia (below condyle)
• Firmly attached to the medial meniscus and joint capsule
• Prevents valgus (lateral) stress and lateral rotation
• Most commonly injured collateral ligament

• Cord-like (not attached to capsule or lateral meniscus)
• Lateral epicondyle of femur → Head of fibula
• Prevents varus (medial) stress

• Posterior aspect - expansion from semimembranosus tendon
• Prevents hyperextension

• Y-shaped, posterior capsule
• Arches over popliteus muscle

INTRACAPSULAR (CRUCIATE) LIGAMENTS:

• Tibial attachment: Anterior intercondylar area of tibia
• Femoral attachment: Posterior part of medial surface of lateral condyle of femur
• Direction: Passes upward, backward, and laterally
• Function: Prevents anterior displacement of tibia on femur (prevents forward sliding of tibia)
• Test: Anterior Drawer Test, Lachman Test

• Tibial attachment: Posterior intercondylar area of tibia
• Femoral attachment: Lateral surface of medial condyle of femur
• Direction: Passes upward, forward, and medially
• Stronger and tighter than ACL
• Function: Prevents posterior displacement of tibia on femur
• Test: Posterior Drawer Test (tibial sag sign)

Memory tip: ACL and PCL cross like an "X" in the intercondylar notch - ACL goes Anterior on tibia → Lateral femoral condyle; PCL goes Posterior on tibia → medial femoral condyle.

      FEMUR
    Med  |  Lat
     |   |   |
  PCL\  |  /ACL
      \ | /
       \|/
     Intercondylar notch
        |
    [TIBIA]
  Post.area  Ant.area
  (PCL)     (ACL)

3. MOVEMENTS AND MUSCLES PRODUCING THEM

Rotation is only possible when the knee is flexed - in full extension the knee is "locked" and rotation is not possible.

Locking and Unlocking of Knee:

• The medial femoral condyle is longer than the lateral condyle
• As full extension approaches, the lateral condyle finishes its rolling first
• The femur then medially rotates on the tibia (or tibia laterally rotates on femur in open kinetic chain)
• All ligaments become taut → joint is "screwed home" and locked
• Requires NO muscle energy to maintain standing

• Popliteus muscle contracts → laterally rotates the femur (or medially rotates the tibia) → loosens the ligaments → unlocking occurs → flexion can begin

LOCKING:              UNLOCKING:
Knee extension          Popliteus contracts
↓                       ↓
Medial rotation         Lateral rotation of femur
of femur               (or medial rotation of tibia)
↓                       ↓
Ligaments taut          Ligaments loosened
↓                       ↓
Joint LOCKED            Flexion possible

4. APPLIED ANATOMY

a) Unhappy Triad (O'Donoghue's Triad)

• Caused by: Valgus force + lateral rotation on a fixed, weight-bearing foot (common in football/rugby)
• Injuries: MCL + Medial meniscus + ACL torn simultaneously
• Patient unable to bear weight, rapid haemarthrosis
• MRI confirms; surgical repair required

b) Meniscal Tears

• Medial meniscus more commonly torn (attached to MCL and capsule - less mobile)
• Types: Vertical tear, Horizontal tear, Bucket handle tear (longitudinal - fragment displaces into intercondylar notch = joint locking)
• Symptoms: Pain on joint line, clicking, locking, giving way sensation
• Investigation: MRI (gold standard), Arthroscopy for repair

c) ACL Rupture

• Commonest serious knee ligament injury in sports
• Mechanism: Sudden change of direction/cutting, pivoting, landing
• Features: Sudden "pop" sound, rapid haemarthrosis, instability
• Tests: Anterior drawer test, Lachman test (more sensitive)
• Treatment: Physiotherapy in low-demand patients; ACL reconstruction (hamstring/patellar tendon graft) in athletes

d) PCL Injury

• Mechanism: Dashboard injury (knee forced backward when hitting dashboard), hyperextension
• Tibial sag sign / posterior drawer test positive
• Usually needs surgical repair

e) Housemaid's Knee (Prepatellar Bursitis)

• Inflammation of the prepatellar bursa (between patella and skin)
• Caused by: Prolonged kneeling (housemaids, carpet layers, plumbers)
• Features: Fluctuant swelling anterior to patella, knee movements painless
• Treatment: Aspiration, NSAIDs, avoid kneeling; excision for chronic cases

f) Osteoarthritis of Knee

• Commonest joint disease in elderly
• Medial compartment most affected → genu varum (bow legs)
• X-ray: Joint space narrowing, osteophytes, subchondral sclerosis
• Treatment: Weight loss, physiotherapy, NSAIDs; Total Knee Replacement (TKR) in severe cases

g) Locking of Knee

• True locking: Bucket-handle meniscal tear fragment blocks extension
• Springy block at ~30° of extension (cannot fully extend)
• Pseudo-locking: Painful hamstring spasm - gradual onset
• Treatment: Arthroscopic meniscectomy/repair

h) Bursae Around Knee (Enumeration)

1. Suprapatellar bursa - between femur and quadriceps (communicates with joint = largest extension of synovial cavity)
2. Prepatellar bursa - between patella and skin (Housemaid's knee if inflamed)
3. Infrapatellar bursa - superficial (between patellar ligament and skin) and deep (between patellar ligament and tibia) = "Clergyman's knee" if inflamed

i) Intracapsular Structures (Enumeration)

1. Anterior cruciate ligament (ACL)
2. Posterior cruciate ligament (PCL)
3. Medial meniscus
4. Lateral meniscus
5. Infrapatellar fat pad
6. Synovial membrane folds (alar folds, infrapatellar fold)
7. Transverse ligament of knee (connecting anterior horns of menisci)

         KNEE JOINT
     (Modified Hinge - Synovial)
    ┌────────────────────────────┐
    │  2 Tibiofemoral +          │
    │  1 Patellofemoral          │
    │  Menisci: Med(C) + Lat(O)  │
    └────────────────────────────┘
    Ligaments:
    Extracapsular:           Intracapsular:
    - Patellar (ant)         - ACL (ant draw)
    - MCL (valgus stress)    - PCL (post draw)
    - LCL (varus stress)
    - Obl./Arcuate (post)
    
    Movements:
    Flex: Hamstrings         Ext: Quadriceps
    Unlock: Popliteus (key muscle!)
    
    Applied:
    Unhappy triad→MCL+Med.men+ACL
    Housemaid's→Prepatellar bursitis
    Baker's cyst→Semimembranosus bursa
    Locked knee→Bucket handle tear