CH 7 - BONE PT 3 -Appendicular Skeleton: Arm, Hand, Leg, and Pelvis

Arm and Hand: Phalanges, Metacarpals, Carpal Bones, and Joints

• Phalanges (hand bones): total of 14 phalanges per hand; long bones in fingers (long bones longer than they are wide).
  • Each finger (index, middle, ring, little) has three phalanges: proximal, middle, distal.
  • The thumb is unique: it has only two phalanges: proximal and distal.
  • Singular vs plural: phalanx (singular) vs phalanges (plural).
  • Proximal-phalanx joints: proximal ends of finger phalanges form joints with the corresponding metacarpals.
  • Proximal end of the proximal phalanx forms a joint with a metacarpal; the rest are arranged as described.
  • Example: proximal phalanx of the ring finger (finger #4) is the bone labeled as the proximal phalanx in that finger.
• Phalanges per finger and total: each finger has 3 phalanges except the thumb which has 2; total = 14 phalanges per hand.
• Metacarpals: five metacarpal bones, numbered 1-5 from the thumb side. Proximal ends of the metacarpals form joints with the distal ends of the carpals.
• Carpal bones (wrist): eight bones arranged in two rows of four.
  • Proximal row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform.
  • Distal row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate.
  • A mnemonics device is often used to memorize carpal bone names; the video mentions mnemonics and suggests using one that works for you.
  • The carpal bones form a joint with the radius at the wrist (radiocarpal joint); the ulna does not directly articulate with the carpal bones in the standard radiocarpal joint.
• Radius and ulna (forearm bones):
  • Radius is the larger bone at the distal end (wrist side) and forms the major part of the wrist joint with the carpal bones.
  • The ulna forms the major part of the elbow joint with the humerus.
  • At the wrist, the radiocarpal joint is formed primarily with the scaphoid; the ulna has a different relationship via the interosseous connections and the articular disc.
• Humerus and shoulder girdle:
  • The humerus forms a joint with the scapula at the shoulder (glenohumeral joint, a ball-and-socket joint).
  • The scapula sits over the rib cage and is not directly connected to the ribs; it is free to move.
  • The scapula is connected to the clavicle; the clavicle is connected to the sternum, forming the shoulder girdle chain: scapula ↔ clavicle ↔ sternum.
  • The glenohumeral (shoulder) joint is a ball-and-socket joint with a shallow glenoid fossa, which allows extensive movement.
  • The advantage of a shallow socket is huge range of motion; the downside is a higher risk of dislocation due to the head of the humerus not being deeply held in the socket.
• Practical implications in the arm:
  • When you brace a fall with your hands, the radius bears most of the initial impact because of its larger articulation surface at the wrist.
  • Distal radius fractures are common, often called Colles fractures, typically occurring in falls (e.g., skateboarding, biking, tripping).
  • If the distal radius does not fracture, force may be transmitted to the humerus and possibly the clavicle; a fractured clavicle is also common due to its role as the connection between the limb and the axial skeleton.
  • In steering-wheel impacts or other blunt trauma, the clavicle is a frequent fracture site because it connects the appendicular and axial skeletons.
• Arm joint anatomy summary (memory aid):
  • Proximal end of the radius forms joints with the humerus and ulna.
  • Proximal end of the humerus forms a joint with the scapula.
  • Scapula forms a joint with the clavicle.
  • Clavicle forms a joint with the sternum.
  • At the shoulder, the head of the humerus sits in a shallow socket and is stabilized by ligaments and surrounding muscles.

Leg and Foot: Phalanges, Metatarsals, and Tarsal Bones

• Phalanges (toes): total of 14 phalanges per foot; similar pattern to the hand:
  • Big toe (great toe) has two phalanges: proximal and distal.
  • Other toes have three phalanges each: proximal, middle, distal.
• Metatarsals: five metatarsal bones, numbered 1-5 from the big toe side.
• Tarsal bones: seven bones in the ankle/foot region.
  • Key tarsals: Talus (ankle bone), Calcaneus (heel bone), Navicular, Cuboid, and three cuneiforms (Medial, Intermediate, Lateral).
  • The talus forms the ankle joint with the tibia and fibula; the calcaneus is the large heel bone; the navicular, cuboid, and the three cuneiforms form the arch and connect to the metatarsals.
  • Total tarsals: 7.
• Ankle joint: formed by three bones meeting at the ankle—tibia, fibula, and talus.
  • Two important joint spaces: the talotibial joint (between talus and tibia) and the talofibular joint (between talus and fibula).
  • Ligaments in this region are frequently injured in ankle sprains due to the complex arrangement.
• Knee joint: the major hinge between the tibia and the femur.
  • The fibula does not form a knee joint with the femur; it articulates with the tibia and, distally, with the talus and tibia.
  • The patella (kneecap) is a sesamoid bone formed within a tendon and forms a patellofemoral joint with the femur; there is no direct patella-tibia joint.
• Hip joint and pelvis (os coxae):
  • The os coxa (hip bone) consists of three fused bones: ilium, ischium, and pubis.
  • The acetabulum is formed by all three bones and is the socket for the femoral head, creating a deep ball-and-socket hip joint.
  • The femur forms a joint with the acetabulum; this socket is deep and provides stability, reducing dislocation risk but limiting some range of motion compared to the shoulder.
  • The sacroiliac joint is between the ilium (part of the os coxa) and the sacrum (part of the axial skeleton).
  • The pelvis in total consists of two os coxae plus the sacrum (and the coccyx at the bottom).
  • The pelvis flares and shape helps identify sex:
  • Pubic angle (angle formed by the pubic bones at the anterior side) is a practical discriminant.
  • If the pubic angle is less than 90^\u00b0, this is typically a male pelvis.
  • If the pubic angle is greater than 90^\u00b0, this is typically a female pelvis.
• Pelvic outlet and birth relevance:
  • The pelvic inlet/outlet is formed by the sacrum and the two os coxae, which is important for birth passage.
• Practical anatomy connections (general study tips reflected in the lecture):
  • Be able to identify which bones form joints with which other bones for the appendicular skeleton (excluding some carpals and tarsals where the specific joint pairings are not routinely tested).
  • For other long bones, memorize proximal and distal articulations (e.g., proximal radius with humerus and ulna; proximal humerus with scapula).
  • Visualize the connections in a simple sketch to recognize bone names and joint relationships quickly; the instructor emphasized that a simple, non-proportional sketch helps recognition more than rote memorization.
  • Understand the functional trade-offs of joint shapes: e.g., the shoulder’s shallow socket allows great ROM but higher dislocation risk; the hip’s deep socket provides stability but more restricted motion.
• Summary of key joints to know (from memory):
  • Proximal radius shows joints with the humerus and ulna; proximal humerus with scapula; scapula with clavicle; clavicle with sternum.
  • Radiocarpal joint forms the wrist (radius-carpal); elbow hinge is between ulna and humerus; radioulnar articulations provide forearm rotation.
  • Knee: tibia–femur; patella–femur (patellofemoral joint).
  • Hip: femur–acetabulum (hip socket) formed by ilium, ischium, and pubis; sacroiliac joint links os coxa to the sacrum.
• Quick terminology recap:
  • Phalanx (singular) vs Phalanges (plural) – fingers and toes.
  • Os coxa = hip bone; composed of ilium, ischium, and pubis.
  • Acetabulum = hip socket formed by os coxae.
  • Colles fracture = distal radius fracture commonly occurring in falls.
  • Sesamoid bone = bone formed within a tendon (e.g., the patella).
• Final note on exam expectations (as stated in the transcript):
  • You may be asked to identify which bones form joints with which other bones, especially for the long bones of the arm (radius, ulna, humerus) and leg (temporarily including knee and pelvis via hip articulation).
  • You should be able to recall proximal end articulations from memory rather than relying on simple diagram labeling.
  • The focus is on understanding how the skeleton is put together and the functional implications of joint structure, rather than memorizing every single carpals or tarsal articulation.

Quick Reference: Key bone counts and pairings

• Hand:
  • Phalanges: 14 (per hand); each finger has 3 phalanges, thumb has 2.
  • Metacarpals: 5 (1-5, thumb side to little finger).
  • Carpals: 8; two rows of four: proximal row (Scaphoid, Lunate, Triquetrum, Pisiform), distal row (Trapezium, Trapezoid, Capitate, Hamate).
• Forearm and arm:
  • Radius and Ulna; radius forms wrist joint with carpals; ulna forms elbow joint with humerus.
  • Humerus forms shoulder joint with scapula; scapula connected to clavicle; clavicle connected to sternum.
• Leg and foot:
  • Phalanges: 14 (per foot);
  • Big toe: 2; other toes: 3 each.
  • Metatarsals: 5.
  • Tarsals: 7 (Talus, Calcaneus, Navicular, Cuboid, Medial Cuneiform, Intermediate Cuneiform, Lateral Cuneiform).
  • Ankle joint involves: Tibia, Fibula, Talus; two key joints: Talotibial (tibia-talus) and Talofibular (fibula-talus).
• Pelvis:
  • Os coxa = ilium + ischium + pubis (three bones per os coxa).
  • Acetabulum is the hip socket; Sacroiliac joint links pelvis to sacrum.
  • Pelvis includes Sacrum and Coccyx; complete pelvis = two os coxae + sacrum (+ coccyx).
  • Pubic angle as a sex indicator: ext{pubic angle} < 90^\u00b0 ightarrow ext{male}; ext{pubic angle} > 90^\u00b0
    ightarrow ext{female}.
• Practical implications and injuries:
  • Distal radius fractures (Colles) are common in falls due to the radius bearing much of the impact.
  • Clavicle fractures are common in trauma when the arm absorbs impact.
  • Shoulder dislocation risk is higher due to the shallow glenoid fossa in the shoulder joint.
  • Ankle injuries are influenced by the tibia, fibula, and talus alignment and supporting ligaments.
• Visual note: sketching the arm and pelvis can help you recognize bone relationships and joints more quickly than rote naming alone.