Comprehensive Notes – Shoulder, Elbow, Hip & Knee Joints
Shoulder Joint (Glenohumeral)
Bones & Bony Landmarks
Scapula: The shoulder blade; acts as the base for the glenohumeral joint.
Acromion: Lateral extension of the scapular spine, forming the highest point of the shoulder. Articulates with the clavicle.
Coracoid process: A small, hook-like projection from the scapula, serving as an attachment point for various muscles (e.g., short head of biceps, coracobrachialis, pectoralis minor).
Glenoid cavity: A shallow, pear-shaped fossa on the lateral aspect of the scapula, articulating with the humeral head. Its shallow nature contributes to the joint's high mobility but low inherent stability.
Humerus: The bone of the upper arm.
Humeral head: The rounded, proximal end of the humerus that articulates with the glenoid cavity.
Greater tubercle: A large, lateral prominence on the proximal humerus, serving as the insertion point for supraspinatus, infraspinatus, and teres minor muscles of the rotator cuff.
Lesser tubercle: A smaller, medial prominence on the proximal humerus, serving as the insertion point for the subscapularis muscle of the rotator cuff.
Intertubercular sulcus (bicipital groove): A deep groove between the greater and lesser tubercles, housing the long head of the biceps brachii tendon.
Clavicle: The collarbone; articulates medially with the sternum and laterally with the acromion of the scapula. It acts as an anterior strut, keeping the upper limb away from the trunk.
Joint Type & Structural Features
Ball-and-socket (multiaxial): This structural classification indicates a wide range of motion. The humeral head acts as the "ball" fitting into the glenoid cavity "socket."
Large range of motion (ROM): Allows for movements in all three planes – flexion, extension, abduction, adduction, circumduction, medial & lateral rotation. This is facilitated by the shallow glenoid cavity and loose fibrous capsule.
Poor bony congruity and predominantly loose ligaments: The glenoid cavity covers only about one-third of the humeral head, meaning there's limited bone-on-bone stability. This design inherently sacrifices stability for exceptional mobility, making it the most mobile but also the most frequently dislocated large joint in the body.
Stabilising Structures
Rotator cuff: A group of four muscles (supraspinatus, infraspinatus, teres minor, subscapularis) whose tendons merge to form a musculotendinous cuff around the glenohumeral joint. They dynamically hold the humeral head firmly against the glenoid cavity during movement, providing primary dynamic stability.
Long head of biceps brachii: Its tendon originates from the supraglenoid tubercle (above the glenoid cavity) and passes through the intertubercular sulcus. It contributes to anterior stability and helps depress the humeral head during elevation.
Glenoid labrum: A fibrocartilaginous rim attached to the margin of the glenoid cavity. It deepens the socket by approximately 50%, increasing its congruity with the humeral head and providing a larger area for articulation, thus enhancing joint stability.
Principal Muscles & Actions
Pectoralis major (anterior chest wall)
O: Clavicular head (medial half of clavicle); Sternal head (sternum, costal cartilages 1-7).
I: Lateral lip of the intertubercular sulcus of the humerus.
A: Powerful ext{adduction} and ext{flexion} of the GH joint; medial rotation of the arm.
Deltoid (lateral shoulder)
O: Anterior fibres (lateral third of clavicle); Middle fibres (acromion); Posterior fibres (spine of scapula).
I: Deltoid tuberosity on the mid-shaft of the humerus.
A: Overall, primary muscle for shoulder ext{abduction} (especially middle fibres after supraspinatus initiation); anterior fibres assist flexion and medial rotation; posterior fibres assist extension and lateral rotation.
Latissimus dorsi (posterior lower back)
O: Spinous processes of T7-L5 (thoracolumbar fascia), iliac crest, inferior three or four ribs.
I: Floor of the intertubercular sulcus.
A: Powerful arm ext{extension}, ext{adduction}, and medial rotation of the GH joint. Known as the "swimmer's muscle."
Rotator cuff (SITS muscles: Subscapularis, Supraspinatus, Infraspinatus, Teres Minor)
O: Scapular fossae (subscapular fossa, supraspinous fossa, infraspinous fossa).
I: Greater & lesser tubercles of the humerus.
A: Provide dynamic stability to the GH joint by compressing the humeral head into the glenoid cavity. Specific actions include: initiation of abduction (supraspinatus, first 15^{\circ}), medial rotation (subscapularis), lateral rotation (infraspinatus, teres minor).
Movements (with prime movers)
Flexion: Bringing the arm forward and upward. Prime movers: pectoralis major (clavicular head), anterior deltoid, biceps brachii (long head), coracobrachialis.
Extension: Bringing the arm backward and downward. Prime movers: latissimus dorsi, posterior deltoid, teres major, triceps (long head).
Abduction: Raising the arm away from the body laterally. Prime movers: deltoid (middle fibres), supraspinatus (initiates first ext{15}^{ ext{o}} of abduction and aids the deltoid throughout).
Adduction: Bringing the arm towards or across the body, medially. Prime movers: pectoralis major, latissimus dorsi, teres major, triceps (long head).
Medial rotation: Rotating the arm inward (thumb points medially). Prime movers: subscapularis, pectoralis major, latissimus dorsi, anterior deltoid, teres major.
Lateral rotation: Rotating the arm outward (thumb points laterally). Prime movers: infraspinatus, teres minor, posterior deltoid.
Circumduction: A sequential combination of flexion, abduction, extension, and adduction, creating a circular movement of the arm.
LO-1 Question Prompts (with concise answers)
Landmarks that articulate: The humeral head articulates with the shallow glenoid cavity of the scapula.
Actions: The shoulder joint allows for flexion, extension, abduction, adduction, circumduction, medial & lateral rotation, offering the greatest range of motion of any joint in the body.
Main stabilisers: The primary dynamic stabilisers are the rotator-cuff tendons (SITS muscles) and the long head of biceps brachii tendon. Static stabilisers include the glenoid labrum, joint capsule, and glenohumeral ligaments.
Pectoralis major – see origins/insertions/actions above: It originates from the clavicle and sternum and inserts into the intertubercular sulcus. Its primary actions are adduction and flexion of the GH joint, along with medial rotation.
Latissimus dorsi – see origins/insertions/actions above: Originates from the vertebrae, pelvis, and ribs, inserting into the intertubercular sulcus. Its main actions are extension, adduction, and medial rotation of the GH joint.
Abduction muscle: The deltoid (especially the middle fibres) is the primary muscle for abduction. The supraspinatus muscle initiates the first ext{15}^{ ext{o}} of abduction before the deltoid takes over.
Elbow Joint (Humeroulnar + Humeroradial)
Bones & Landmarks
Humerus: The distal end features two condylar structures:
Capitulum (lateral): A rounded eminence that articulates with the radial head.
Trochlea (medial): A spool-shaped surface that articulates with the trochlear notch of the ulna.
Ulna: The medial bone of the forearm.
Olecranon process: The large, proximal projection of the ulna that forms the point of the elbow. It fits into the olecranon fossa of the humerus during extension.
Trochlear notch: A C-shaped depression on the proximal ulna that articulates with the trochlea of the humerus, forming the primary part of the elbow hinge joint.
Coronoid process: A triangular projection on the anterior-proximal ulna that fits into the coronoid fossa of the humerus during flexion.
Radius: The lateral bone of the forearm.
Radial head: A cylindrical structure that articulates with the capitulum of the humerus and the radial notch of the ulna (forming part of the superior radioulnar joint).
Radial tuberosity: An anterior prominence on the radius, serving as the insertion point for the biceps brachii tendon.
Joint Type & Mechanics
Hinge joint (uniaxial): The elbow predominantly allows movement in one plane: flexion and extension. The humeroulnar joint is the primary hinge, while the humeroradial joint provides a gliding articulation.
High stability: The deep trochlear notch of the ulna strongly interlocks with the trochlea of the humerus, providing excellent bony congruity. This is further reinforced by strong collateral ligaments (ulnar/medial collateral ligament and radial/lateral collateral ligament), which prevent side-to-side movement. The radius, while important for pronation/supination (at radioulnar joints), participates functionally in elbow flexion/extension on the lateral aspect of the joint.
Movements
Flexion: Bending the elbow, decreasing the angle between the upper arm and forearm (up to approximately ext{145}^{ ext{o}}). Movement is limited by the biceps muscle mass in full flexion.
Extension: Straightening the elbow, increasing the angle (to ext{0}^{ ext{o}} or slight hyper-extension, typically up to ext{5}^{ ext{o}}- ext{10}^{ ext{o}}, depending on individual).
Key Muscles
Biceps brachii (anterior arm)
Two heads: Long head (originates from supraglenoid tubercle of scapula); Short head (originates from coracoid process of scapula).
I: Radial tuberosity, via the biceps tendon and bicipital aponeurosis.
A: Powerful elbow flexion (especially with forearm supination); secondary forearm supination (its most effective action); weak shoulder flexion.
Triceps brachii (posterior arm)
Three heads: Long head (originates from infraglenoid tubercle of scapula); Medial head (originates from posterior humerus, inferior to radial groove); Lateral head (originates from posterior humerus, superior to radial groove).
I: Olecranon process of the ulna.
A: Primary and powerful elbow extension. The long head also assists in shoulder adduction and extension.
Brachialis: A deep muscle in the anterior arm, considered the "workhorse" elbow flexor as it's the strongest pure flexor of the elbow, inserting directly onto the ulna.
Brachioradialis: A superficial muscle of the forearm, originating from the humerus and inserting on the radius. It acts as an elbow flexor, particularly effective in semi-pronation.
LO-2 Question Prompts
"Biceps" = "two heads"; "brachii" = "of the arm." The biceps brachii crosses both the shoulder and elbow joints.
Main elbow extensor: The triceps brachii is the sole and powerful extensor of the elbow joint.
Origins/insertions of biceps – see above: The biceps brachii originates from two heads on the scapula (long head from supraglenoid tubercle, short head from coracoid process) and inserts primarily onto the radial tuberosity.
Hip Joint
Bones & Landmarks
Os coxae (pelvic bone): Formed by the fusion of three bones: ilium (largest, superior part), ischium (posterior-inferior part), and pubis (anterior-inferior part).
Acetabulum: A deep, concave, cup-shaped socket on the lateral aspect of the os coxae, formed by the fusion of the ilium, ischium, and pubis. It articulates with the femoral head.
Iliac crest: The superior border of the ilium, easily palpable, serving as an attachment for many trunk and thigh muscles.
Ischial tuberosity: A large, rough prominence on the ischium, commonly known as the "sitting bone," providing attachment for hamstring muscles.
Pubic rami: Superior and inferior extensions of the pubis, forming part of the obturator foramen.
Femur: The thigh bone, the longest and strongest bone in the body.
Femoral head: The spherical, proximal end of the femur, covered in articular cartilage, that fits into the acetabulum.
Neck of femur: Connects the femoral head to the shaft, a common site for fractures in older adults.
Greater trochanter: A large, irregular prominence located lateral to the neck of the femur, serving as a major attachment site for various hip abductors and rotators (e.g., gluteus medius, gluteus minimus).
Lesser trochanter: A smaller, conical prominence located medially and inferiorly to the neck of the femur, serving as the insertion point for the iliopsoas muscle.
Joint Type & Stability
Ball-and-socket (multiaxial): Similar to the shoulder, this joint allows for movement in multiple planes: flexion, extension, abduction, adduction, medial (internal) rotation, lateral (external) rotation, and circumduction. However, its ROM is significantly less than the shoulder due to its structure.
High stability prioritised over mobility: The hip joint is designed for weight-bearing and stability.
Deep acetabular socket: The acetabulum is significantly deeper and more encompassing than the glenoid cavity, creating strong bony congruity with the femoral head.
Acetabular labrum: A fibrocartilaginous rim that further deepens the socket and increases the contact area.
Strong capsular & extracapsular ligaments: These dense ligaments reinforce the joint capsule and resist excessive movements:
Iliofemoral ligament: Strongest ligament in the body, located anteriorly, prevents hyperextension.
Pubofemoral ligament: Located anteroinferiorly, prevents excessive abduction and hyperextension.
Ischiofemoral ligament: Located posteriorly, prevents excessive medial rotation and extension.
Robust musculature: Large, strong muscles surrounding the hip provide dynamic stability.
Femoral dislocation rare: Due to the deep socket, strong ligaments, and powerful surrounding muscles, dislocations of the hip joint are far less common than shoulder dislocations and typically require significant trauma.
Movements
Flexion: Moving the thigh anteriorly towards the trunk.
Extension: Moving the thigh posteriorly away from the trunk.
Abduction: Moving the thigh laterally away from the midline.
Adduction: Moving the thigh medially towards or past the midline.
Medial (internal) rotation: Rotating the thigh inward along its longitudinal axis.
Lateral (external) rotation: Rotating the thigh outward along its longitudinal axis.
Circumduction: A combination of flexion, abduction, extension, and adduction in sequence, producing a circular movement of the thigh.
Primary Muscles
Iliopsoas (anterior, deep hip flexor)
O: Iliacus (iliac fossa) and Psoas major (lumbar vertebrae - transverse processes, vertebral bodies, discs).
I: Lesser trochanter of the femur.
A: The most powerful hip flexor; essential for walking, running, and sitting.
Gluteus maximus (posterior, superficial buttock muscle)
O: Posterior ilium, sacrum, and coccyx.
I: Proximal-lateral femur (gluteal tuberosity) and iliotibial tract (IT band).
A: Primary hip extension (especially from a flexed position, such as climbing stairs) and powerful lateral rotation. Important for maintaining erect posture.
Gluteus medius (posterior-lateral, deep to gluteus maximus)
O: External surface of the ilium.
I: Greater trochanter of the femur.
A: Primary hip abduction (along with gluteus minimus) and medial rotation. Crucial for pelvic stability during gait (preventing the opposite side of the pelvis from dropping when walking – Trendelenburg sign if weak).
Adductor group (medial compartment of thigh: Adductor magnus, longus, brevis, gracilis, pectineus)
O: Inferior pubic ramus, ischial ramus, and ischial tuberosity (varied among muscles).
I: Linea aspera of the femur (a rough line on the posterior femur), and proximal tibia (gracilis).
A: Primarily hip adduction; also contribute to hip flexion (except adductor magnus' hamstring part) and some rotation.
LO-3 Question Prompts
Femoral head articulates with: The acetabulum of the os coxae.
Hip dislocation rare because: It has a deep acetabular socket, is reinforced by strong capsular and extracapsular ligaments (iliofemoral, pubofemoral, ischiofemoral), and is surrounded by robust musculature that provides dynamic stability.
Greater trochanter insertion: Key muscles inserting here are gluteus medius and gluteus minimus (hip abductors/medial rotators); lesser trochanter insertion: The iliopsoas (powerful hip flexor).
Action of iliopsoas: Its main action is powerful hip flexion.
Muscle actions relative to joint crossing: Muscles crossing the joint medially primarily perform adduction; anteriorly perform flexion; posteriorly perform extension; laterally perform abduction and/or rotation depending on their specific orientation.
Main action of gluteus medius: Primary actions are hip abduction and medial rotation. It is critically important for maintaining pelvis level while walking (to prevent the contralateral hip drop).
Knee Joint (Tibiofemoral)
Bones & Landmarks
Femur: The distal end has large, rounded structures.
Medial & lateral condyles: Articulate with the tibial plateau. The medial condyle is larger and more oval.
Intercondylar fossa: A deep notch between the femoral condyles posteriorly, where the cruciate ligaments attach.
Tibia: The larger, medial bone of the lower leg.
Tibial plateau (medial & lateral condyles): The flattened superior surface of the tibia that articulates with the femoral condyles.
Tibial tuberosity: A large roughened area on the anterior aspect of the tibia, serving as the distal attachment point for the quadriceps femoris via the patellar ligament.
Patella: The kneecap. It is a sesamoid bone (a bone embedded within a tendon), specifically within the quadriceps femoris tendon. It acts as a fulcrum, increasing the leverage of the quadriceps muscle and protecting the anterior aspect of the knee.
Fibula: The smaller, lateral bone of the lower leg. It does NOT form part of the knee joint articulation with the femur or tibia, but its head provides an attachment point for the fibular collateral ligament and biceps femoris muscle.
Joint Classification
Modified hinge joint (predominantly uniaxial): The knee is primarily a hinge joint, allowing for flexion and extension. However, it's considered "modified" because it also permits a slight degree of axial rotation (medial and lateral rotation of the tibia on the femur) when the knee is in a flexed, non-weight-bearing position. This rotation is crucial for the "screw-home mechanism."
Poor bony congruity: The flattened tibial plateau and rounded femoral condyles present a relatively incongruent articulation, making the joint inherently unstable based on bony structure alone. Therefore, it heavily relies on surrounding soft-tissue stabilisers.
Soft-Tissue Components & Stability
Menisci (medial & lateral): Two C-shaped (medial) and O-shaped (lateral) fibrocartilage wedges located on the tibial plateau.
Functions: They deepen the articular surfaces of the tibial plateau, increasing congruity between the femur and tibia; act as shock absorbers by distributing compressive forces across the joint; facilitate lubrication; and assist in guiding movements.
Ligaments: Provide critical static stability.
Collateral ligaments: Limit varus/valgus (side-to-side) motion.
Medial collateral ligament (MCL or Tibial collateral ligament): Strong, flat ligament on the medial side, connected to the medial meniscus. It prevents excessive valgus (knock-knee) stress.
Lateral collateral ligament (LCL or Fibular collateral ligament): Strong, cord-like ligament on the lateral side, separate from the lateral meniscus. It prevents excessive varus (bow-legged) stress.
Cruciate ligaments: Named for their cross-shaped arrangement within the intercondylar notch (located intra-capsular but extra-synovial).
Anterior cruciate ligament (ACL): Originates from the anterior intercondylar area of the tibia and inserts on the posterior-medial aspect of the lateral femoral condyle. It is crucial for preventing anterior displacement of the tibia relative to the femur and limits hyperextension and rotational movements.
Posterior cruciate ligament (PCL): Originates from the posterior intercondylar area of the tibia and inserts on the anterior-lateral aspect of the medial femoral condyle. It is stronger than the ACL and primarily prevents posterior displacement of the tibia relative to the femur and limits hyperflexion.
These ligaments also guide the "screw-home mechanism" of the knee.
Quadriceps femoris tendon & patellar ligament: The quadriceps tendon extends from the quadriceps muscle to the patella. Distal to the patella, it continues as the patellar ligament (sometimes called patellar tendon) which connects the patella to the tibial tuberosity. Both provide significant anterior reinforcement and are vital for knee extension.
Movements
Extension (straighten): Increasing the angle of the knee, bringing the leg straight. Primary muscle: quadriceps femoris. The knee undergoes a terminal screw-home mechanism (locking) during the last ext{10}^{ ext{o}}- ext{15}^{ ext{o}} of extension, involving a slight lateral rotation of the tibia on the femur to achieve maximal congruity and stability in full extension. Unlocking requires medial rotation of the tibia.
Flexion (bend): Decreasing the angle of the knee, bringing the heel towards the buttocks. Primary muscles: hamstrings.
Limited medial & lateral rotation: Occurs only when the knee is partially flexed and not weight-bearing. This rotation is essential for the screw-home mechanism (unlocking and locking the knee).
Major Muscles
Quadriceps femoris (anterior thigh compartment)
Four heads: Rectus femoris (originates from ilium, crosses hip and knee); Vastus lateralis, Vastus medialis, Vastus intermedius (all originate from proximal femur).
I: All four heads converge into the quadriceps tendon, which encases the patella and continues as the patellar ligament to insert onto the tibial tuberosity.
A: Primary and powerful knee extension. The rectus femoris, being a bi-articular muscle, also assists in hip flexion.
Hamstrings (posterior thigh compartment)
Comprised of three muscles: Biceps femoris (long & short heads); Semitendinosus; Semimembranosus.
O: All long heads (biceps femoris long head, semitendinosus, semimembranosus) originate from the ischial tuberosity. The short head of biceps femoris originates from the femur.
I: Proximal tibia (semitendinosus & semimembranosus, often forming part of the 'pes anserinus' on the medial side) and fibula (biceps femoris).
A: Primary knee flexion. All hamstring muscles (except the short head of biceps femoris) also powerfully extend the hip.
Popliteus: A small muscle located posteriorly to the knee joint. It's crucial for "unlocking" the fully extended knee by medially rotating the tibia (or laterally rotating the femur) to initiate flexion from extension.
LO-4 Question Prompts
"Modified" hinge because it allows limited axial rotation (medial/lateral) in addition to flexion/extension, particularly when the knee is flexed. This allows for movements like the screw-home mechanism.
Main stabilisers: Key static stabilisers include the ligaments (collateral ligaments like MCL/LCL, and cruciate ligaments like ACL/PCL) and the menisci. The quadriceps femoris tendon (and patellar ligament) provides significant anterior dynamic and static reinforcement.
Menisci functions: They improve congruity between the femur and tibia, serve as shock absorbers by distributing forces, aid in lubrication, and contribute to joint stability.
Cruciate ligaments: The ACL restricts anterior displacement of the tibia relative to the femur and hyperextension. The PCL restricts posterior displacement of the tibia relative to the femur and hyperflexion. They also provide rotational stability.
Main action of hamstrings: Their primary action is knee flexion. They also act as powerful hip extensors (except the short head of biceps femoris).
Ligament labelling: MCL (medial collateral ligament), LCL (lateral collateral ligament), ACL (anterior cruciate ligament – located anteriorly within the joint, connecting the anterior tibia to the lateral femoral condyle), PCL (posterior cruciate ligament – located posteriorly within the joint, connecting the posterior tibia to the medial femoral condyle), and the patellar ligament (connecting patella to tibial tuberosity).