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The Shoulder Joint (Glenohumeral Joint)

1. Introduction

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2. Articulating Surfaces

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3. Capsule and Ligaments

• Superior glenohumeral ligament (SGHL): Runs from the upper glenoid margin to the intertubercular groove and lesser tubercle. Forms the "roof" of the biceps pulley (rotator interval).
• Middle glenohumeral ligament (MGHL): Passes at almost a right angle to the subscapularis tendon from the upper glenoid margin to the anatomic neck of the humerus.
• Inferior glenohumeral ligament (IGHL): The most important stabiliser. Has three parts: anterior band, posterior band, and axillary recess (which hangs as a "hammock" during abduction). Extends from the inferior glenoid margin to the surgical neck of the humerus. This is the primary restraint to anterior-inferior dislocation.

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4. Rotator Cuff (Dynamic Stabilisers)

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5. Bursae

1. Subacromial bursa - lies between the coracoacromial arch and the rotator cuff tendons; allows frictionless gliding during arm elevation.
2. Subdeltoid bursa - between the deltoid and greater tubercle; communicates consistently with the subacromial bursa.
3. Subtendinous bursa of subscapularis - between the subscapularis tendon and the scapular neck; may communicate with the joint cavity.
4. Subtendinous bursa of infraspinatus - posterior aspect.

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6. Intracapsular Structures

• Tendon of the long head of biceps brachii: Arises from the supraglenoid tubercle inside the capsule, passes over the humeral head, and exits through the intertubercular groove where it is held by the transverse humeral ligament. It is a weak stabiliser that assists the rotator cuff.
• Synovial membrane: Lines the capsule and extends as a sleeve around the biceps long head tendon, forming the intertubercular tendon sheath.

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7. Movements and Muscles Responsible

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8. Nerve Supply

• Axillary nerve (C5, C6) - primary supply
• Suprascapular nerve (C5, C6) - posterosuperior capsule
• Musculocutaneous nerve (C5, C6, C7) - anterior capsule (small branch)
• Lateral pectoral nerve - anterosuperior capsule

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9. Blood Supply

• Anterior and posterior circumflex humeral arteries (branches of the axillary artery) - form an anastomotic ring around the surgical neck
• Suprascapular artery (from thyrocervical trunk)
• Subscapular artery (from axillary artery)

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10. Clinical Correlations

• Anterior dislocation (95% of cases) - the humeral head is forced anteroinferiorly, typically rupturing the anterior capsule/IGHL. The Hill-Sachs lesion (posterosuperior humeral head impaction defect) and Bankart lesion (avulsion of the anteroinferior glenoid labrum) are characteristic MRI findings.
• Axillary nerve injury is the most common neurological complication.

• Supraspinatus tendon is involved in 95% of complete tears.
• Subacromial impingement is caused by mechanical contact between the calcified or degenerate supraspinatus tendon and the coracoacromial arch during abduction.

• Progressive contracture and fibrosis of the joint capsule, especially the IGHL and rotator interval, leading to loss of external rotation and abduction.

• Detachment of the glenoid labrum and IGHL from the anteroinferior glenoid rim, causing recurrent anterior instability. Treated by arthroscopic Bankart repair with anchor sutures.

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The Knee Joint

1. Introduction

1. Tibiofemoral joint - between the femoral condyles and tibial condyles; weight-bearing.
2. Patellofemoral joint - between the patella and the patellar (trochlear) surface of the femur; redirects the pull of the quadriceps anteriorly over the knee.

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2. Articulating Surfaces

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3. Menisci

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4. Articular Capsule

• Anteriorly: Deficient in midline, replaced by the patella and patellar ligament. Reinforced by the quadriceps expansion and patellar retinacula.
• Posteriorly: Reinforced by the oblique popliteal ligament (expansion of semimembranosus) and arcuate popliteal ligament.
• The cruciate ligaments lie within the fibrous capsule but outside the synovial cavity (they are intracapsular but extrasynovial).

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5. Ligaments

A. Cruciate Ligaments (Intrinsic - inside the capsule)

B. Collateral Ligaments (Extrinsic)

C. Patellar Ligament

D. Other Ligaments

• Transverse ligament of knee: Connects the anterior horns of both menisci.
• Oblique popliteal ligament: Posterior capsule reinforcement.
• Arcuate popliteal ligament: Y-shaped, reinforces posterolateral capsule.

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6. Synovial Membrane and Bursae

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7. Movements and Muscles Responsible

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8. Locking Mechanism

1. The broad, flat inferior femoral condyle surfaces come into contact with the tibial plateau - maximising joint congruence.
2. Because the medial femoral condyle has a longer articular surface, the femur undergoes medial rotation on the tibia during the last few degrees of extension.
3. This tightens all ligaments (especially the collateral and cruciate ligaments), locking the joint in a "close-packed" position.
4. This passive stability reduces quadriceps energy expenditure during prolonged standing.

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9. Blood Supply

• Femoral artery - descending genicular artery
• Popliteal artery - 5 genicular branches (superior medial, superior lateral, middle, inferior medial, inferior lateral genicular arteries)
• Anterior tibial artery - anterior tibial recurrent artery
• Lateral circumflex femoral artery - descending branch
• Circumflex fibular artery

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10. Nerve Supply

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11. Clinical Correlations

• Most common serious knee ligament injury, especially in sports involving pivoting/cutting.
• Positive anterior drawer test and Lachman test. MRI is the investigation of choice.
• Managed arthroscopically with patellar tendon or hamstring graft reconstruction.

• Simultaneous injury to the ACL + MCL + medial meniscus following a valgus force with external rotation (e.g., tackled from the side in football).

• Medial meniscus is more commonly injured due to its firm capsular attachment limiting mobility.
• Patterns: vertical, horizontal, or bucket-handle tear (longitudinal tear where the inner fragment displaces into the intercondylar notch, causing locking).
• MRI is the modality of choice; arthroscopic repair/meniscectomy for treatment.

• "Dashboard injury" - posterior force on the proximal tibia with the knee flexed (e.g., car accident). Positive posterior drawer test.

• A synovial-fluid-filled cyst in the medial popliteal fossa, often secondary to rheumatoid arthritis or osteoarthritis. Formed by fusion of the semimembranosus and gastrocnemius bursae, which communicates with the joint under elevated intra-articular pressure.

• Inflammation of the subcutaneous prepatellar bursa from repeated kneeling (e.g., carpet layers, domestic workers).

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The Brachial Plexus

1. Introduction and Definition

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2. Components: The Five Parts

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A. Roots (5)

• Each root receives gray rami communicantes from the cervical sympathetic trunk (postganglionic sympathetic fibers for peripheral distribution).
• A small contribution from C4 is common (prefixed plexus); T2 contribution can occur (postfixed plexus).

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B. Trunks (3)

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C. Divisions (6)

• Anterior divisions supply anterior (flexor) compartments.
• Posterior divisions supply posterior (extensor) compartments.

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D. Cords (3)

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E. Terminal Branches (Nerves of the Upper Limb)

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3. Branches from Each Cord

Lateral Cord (C5-C7) branches:

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Medial Cord (C8-T1) branches:

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Posterior Cord (C5-T1) branches:

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4. Summary Table: All Branches

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5. Relations

• Supraclavicular part (roots + trunks): lies in the posterior triangle of the neck, between the anterior and middle scalene muscles. The plexus is related to the subclavian artery (inferiorly) and the subclavian vein (anterior to the artery but not in the plexus sheath).
• Infraclavicular part (cords + branches): lies in the axilla, surrounding the axillary artery. The three cords are named relative to the second part of the axillary artery.
• The plexus lies within a fascial sheath continuous with the prevertebral fascia - the basis for interscalene and axillary nerve blocks in regional anaesthesia.

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6. Clinical Correlations

A. Erb's Palsy (Upper Plexus Injury - C5, C6)

• Cause: Forcible separation of head from shoulder (difficult delivery, motorcycle accident).
• Lesion: Superior trunk or C5-C6 roots.
• Muscles paralysed: Deltoid, supraspinatus, infraspinatus, biceps, brachialis, brachioradialis.
• Deformity: "Waiter's tip" (porter's tip) position - arm hangs adducted, internally rotated, elbow extended, forearm pronated, wrist flexed.
• Most common brachial plexus injury; best prognosis.

B. Klumpke's Palsy (Lower Plexus Injury - C8, T1)

• Cause: Upward traction on the arm (grabbing a branch during a fall), thoracic outlet syndrome, Pancoast tumour.
• Lesion: Inferior trunk or C8-T1 roots.
• Muscles paralysed: Intrinsic hand muscles (interossei, lumbricals, thenar, hypothenar), long flexors of fingers.
• Deformity: "Claw hand" - hyperextension at MCPs, flexion at IPJs, wasted hand.
• Associated finding: Horner's syndrome (ptosis, miosis, anhidrosis) if T1 is damaged proximal to the sympathetic trunk - poor prognosis sign.

C. Total Plexus Palsy (C5-T1)

• Complete flail, insensate upper extremity. Worst prognosis.
• Seen in high-velocity road traffic accidents (motorcyclists).

D. Thoracic Outlet Syndrome

• Compression of the lower trunk (C8-T1) between the clavicle and first rib, or by a cervical rib.
• Symptoms worsen with arm elevation and external rotation.

E. Parsonage-Turner Syndrome (Brachial Neuritis)

• Idiopathic inflammatory brachial plexopathy. Sudden onset severe shoulder pain followed by weakness and wasting of upper limb muscles. Most recover in 6-12 weeks.

F. Pancoast Tumour

• Apical lung carcinoma invading the lower brachial plexus (C8-T1), causing lower plexus signs + Horner's syndrome ± hoarseness (recurrent laryngeal nerve).

G. Long Thoracic Nerve Palsy

• Injury to C5-C7 roots (surgical procedures, trauma, radical mastectomy).
• Serratus anterior paralysis → "winging of the scapula" (medial border of scapula lifts away from thoracic wall, especially during forward arm elevation).

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