Upper & Lower Extremity Dysfunctions & Entrapment Neuropathies

• Scapulohumeral Rhythm (2:1 Ratio): Full 180° of shoulder abduction requires 120° of glenohumeral motion combined with 60° of scapulothoracic upward rotation (a 2:1 ratio). The initial 0° to 15°–30° of abduction is initiated by the supraspinatus; from 15° to 90° by the deltoid (axillary nerve); and overhead elevation > 90° requires upward rotation of the glenoid fossa by the serratus anterior (long thoracic nerve) and upper/lower trapezius (CN XI).
• Sternoclavicular (SC) Reciprocal Glide: Because the costoclavicular ligament acts as a fulcrum just lateral to the SC joint, the medial head of the clavicle at the sternum glides OPPOSITE to the movement of the distal acromial end during vertical and horizontal motions:
  • Shoulder Elevation / Abduction: Distal clavicle moves superiorly → Medial SC head glides INFERIORLY.
  • Shoulder Protraction / Flexion (Horizontal Adduction): Distal clavicle moves anteriorly → Medial SC head glides POSTERIORLY.
  • Shoulder Retraction / Extension (Horizontal Abduction): Distal clavicle moves posteriorly → Medial SC head glides ANTERIORLY.
  • Shoulder Internal Rotation: Clavicle rotates ANTERIORLY along its long axis.

• Terminal Knee Extension (Locking): Because the medial femoral condyle has a longer articular surface than the lateral condyle, during the final 15° to 20° of knee extension, the knee automatically 'screws home' into a locked, stable position:
  • Closed-Chain (Foot Planted / Weightbearing): The femur internally (medially) rotates on the fixed tibia.
  • Open-Chain (Foot Off Ground / Non-Weightbearing): The tibia externally (laterally) rotates on the femur.
• Unlocking the Knee (The Popliteus Muscle): To initiate knee flexion from a fully extended locked position, the popliteus muscle (innervated by the tibial nerve, L4–S1) contracts to 'unlock' the joint by externally (laterally) rotating the femur on the planted tibia (or internally rotating the tibia in an open chain). Hypertonicity of the popliteus restricts full knee extension and produces posterior knee pain.

Because the ulna acts as a rigid osseous lever pivoting against the trochlea of the humerus, changes in carrying angle produce reciprocal, inverse motions at the wrist:

When testing passive coronal glide at the elbow with the forearm extended, pushing the proximal ulna medially tests ulnar abduction (which increases the carrying angle, moving the distal wrist laterally into cubitus valgus), whereas pushing the proximal ulna laterally tests ulnar adduction (which decreases the carrying angle, moving the distal wrist medially into cubitus varus). An ulnar abduction somatic dysfunction (increased carrying angle, medial glide of olecranon, restriction in adduction) is coupled with wrist adduction (ulnar deviation), whereas an ulnar adduction dysfunction (decreased carrying angle, lateral glide of olecranon, restriction in abduction) is coupled with wrist abduction (radial deviation).

• Pronation: As the distal radius crosses anteriorly over the ulna, the proximal radial head glides POSTERIOR.
  • Injury Mechanism: Fall On Outstretched Hand (FOOSH) with the forearm in pronation forces the radial head backwards: Posterior Radial Head Somatic Dysfunction.
  • Restriction: The radial head is restricted in moving anteriorly and is restricted in supination (prefers pronation).
• Supination: As the radius and ulna return to parallel alignment, the proximal radial head glides ANTERIOR.
  • Injury Mechanism: Falling backward on an outstretched hand with the forearm in supination drives the radial head forward: Anterior Radial Head Somatic Dysfunction.
  • Restriction: Restricted in moving posteriorly and restricted in pronation (prefers supination).
• Nursemaid's Elbow (Radial Head Subluxation): In pediatric patients (< 5 years), sudden axial traction on an extended, pronated forearm pulls the radial head beneath the annular ligament. Child holds arm flexed and pronated; treated by gentle supination followed by flexion.

To treat the far more common posterior radial head dysfunction (pronation dysfunction; restricted supination) using Muscle Energy, the physician contacts the posterior aspect of the radial head with the thumb (applying an anterior-medial stabilizing force) while supinating and extending the patient's forearm into the restrictive barrier; the patient pronates against isometric resistance for 3 to 5 seconds. For HVLA of a posterior radial head, the physician fully supinates and extends the elbow while delivering a simultaneous anterior-directed thumb thrust over the posterior radial head. Conversely, an anterior radial head dysfunction (supination dysfunction; restricted pronation) is treated by flexing and pronating the forearm while applying a posterior-lateral thumb vector against the anterior radial head.

The classic lateral inversion ankle sprain (inversion and plantarflexion tearing the Anterior Talofibular Ligament / ATFL) creates a devastating mechanical chain reaction:

1. Ankle inversion pulls the distal lateral malleolus anteriorly.
2. Reciprocal leverage forces the proximal fibular head to glide POSTERIORLY: Posterior Fibular Head Somatic Dysfunction.
3. Common Peroneal (Fibular) Nerve Entrapment: The common peroneal nerve winds intimately around the neck of the fibula immediately distal to the fibular head. A posterior fibular head compresses this nerve against bone, producing foot drop (inability to dorsiflex or evert the foot) and numbness over the anterolateral lower leg and dorsum of the foot.
4. Eversion Mechanics: Ankle eversion and dorsiflexion pull the lateral malleolus posteriorly, forcing the proximal fibular head into an anterior glide.

In the classic posterior fibular head dysfunction (resulting from an inversion ankle sprain with plantarflexion, which pulls the distal fibula anteriorly and leverages the proximal fibular head posteriorly), the common fibular nerve is stretched or compressed as it winds around the fibular neck, risking foot drop (weak dorsiflexion/eversion) and dorsal foot paresthesias. To treat a posterior fibular head with MET, the patient lies supine with the knee flexed to 90 degrees; the physician grasps the posterior fibular head to pull it anteriorly while dorsiflexing and everting the ankle (and externally rotating the tibia) into the restrictive barrier, and the patient plantarflexes and inverts against resistance. For an anterior fibular head dysfunction, the physician pushes the anterior fibular head posteriorly while plantarflexing and inverting the ankle into the barrier.

In the upper extremity, compression of the long thoracic nerve (C5–C7) during axillary lymphadenectomy triggers serratus anterior paralysis and medial scapular winging. Compression of the suprascapular nerve (C5–C6) at the suprascapular notch weakens both supraspinatus and infraspinatus, whereas compression at the spinoglenoid notch (common in volleyball players or paralabral cysts) isolates infraspinatus external rotation weakness. Along the humerus, fractures of the surgical neck injure the axillary nerve (C5–C6) (deltoid paralysis), midshaft spiral fractures injure the radial nerve (C5–T1) in the radial groove (wrist drop, sparing triceps), supracondylar fractures injure the median nerve / anterior interosseous nerve ('OK' sign loss), and medial epicondyle fractures or cubital tunnel compression injure the ulnar nerve (C8–T1) (ulnar claw hand, worse with distal Guyon canal lesions due to ulnar paradox).

In the lower extremity, compression of the pure sensory lateral femoral cutaneous nerve (L2–L3) beneath the inguinal ligament (from tight belts, obesity, or pregnancy) causes meralgia paresthetica—burning pain and numbness over the anterolateral thigh with complete motor preservation. Pelvic surgery or anterior hip dislocation injures the femoral nerve (L2–L4) (loss of knee extension and patellar reflex), whereas pelvic masses or obturator hernia injure the obturator nerve (L2–L4) (loss of hip adduction and medial thigh sensation). At the knee and ankle, compression of the common fibular nerve (L4–S2) at the fibular neck causes foot drop and steppage gait, whereas compression of the tibial nerve (L4–S3) beneath the flexor retinaculum behind the medial malleolus causes tarsal tunnel syndrome (burning plantar sole paresthesias and intrinsic foot weakness).

The talocrural mortise (tibia, fibula, talar dome) permits primary sagittal hinge motion. Because the anterior trochlea of the talus is wider than the posterior trochlea:

• Plantarflexion: The narrower posterior talus enters the mortise, rendering the ankle loose and mechanically least stable. The talus glides ANTERIORLY. Plantarflexion with inversion is the prime vector for lateral ligamentous rupture (ATFL).
• Dorsiflexion: The wider anterior talus wedges tightly into the mortise, maximizing osseous stability. The talus glides POSTERIORLY.
• Anterior Talus Somatic Dysfunction: Typically occurs following inversion ankle sprains; the talus resists posterior glide, severely limiting dorsiflexion.

The transverse tarsal joint (talonavicular and calcaneocuboid) governs midfoot shock absorption:

• Cuboid Somatic Dysfunction: The medial border of the cuboid glides inferomedially (drops toward the floor), rotating along an anteroposterior axis. Frequently seen in runners and ballet dancers; manifests as lateral midfoot pain and localized tenderness over the plantar cuboid groove.
• Navicular Somatic Dysfunction: The lateral border of the navicular glides inferolaterally (drops toward the floor), flattening the medial longitudinal arch. Common in pes planus and overpronation syndromes.
• Spring Ligament (Plantar Calcaneonavicular): Supports the talar head; laxity results in flatfoot deformity and valgus heel collapse.

Plantar fasciitis results from repetitive microtrauma at the medial calcaneal tuberosity insertion. Classic presentation is severe sharp heel pain with the first steps in the morning that temporarily improves after walking, then worsens by end of day. If paroxysmal burning heel pain radiates to the lateral plantar foot, suspect Baxter nerve entrapment (compression of the first branch of the lateral plantar nerve beneath the abductor hallucis muscle).

The carpal tunnel is bounded deeply by the carpal bones (sulcus carpi) and superficially by the unyielding transverse carpal ligament (flexor retinaculum). Ten structures traverse this tunnel: 1 nerve (Median Nerve) and 9 tendons (4 FDS, 4 FDP, 1 FPL). Entrapment produces numbness, paresthesias, and pain in the thumb, index, middle, and radial half of the ring finger, sparing the thenar eminence (supplied by the superficial palmar cutaneous branch which passes superficial to the retinaculum):

• Phalen Test: Maximal active wrist flexion held for 60 seconds reproduces paresthesias in the median distribution.
• Tinel Sign: Percussion over the volar flexor retinaculum elicits electric shooting sensations.
• Durkan Carpal Compression Test: Direct thumb pressure over the carpal tunnel for 30 seconds; clinically the most sensitive physical exam test for CTS.
• Thenar Atrophy: Indicates advanced motor denervation (Abductor pollicis brevis, Flexor pollicis brevis, Opponens pollicis) requiring urgent surgical decompression.

The ulnar nerve and artery pass into the hand through Guyon canal (pisohamate tunnel), bounded by the pisiform medially and hook of the hamate laterally. Chronic pressure (e.g., long-distance bicycle handlebar pressure: 'cyclist palsy') compresses the deep motor and superficial sensory branches, producing tingling in the small finger and ulnar half of the ring finger, with intrinsic hand weakness (interossei, hypothenar muscles).

Stenosing tenosynovitis of the first dorsal extensor compartment of the wrist, containing the Abductor Pollicis Longus (APL) and Extensor Pollicis Brevis (EPB) tendons. Common in postpartum mothers repeatedly lifting infants ('baby wrist') and racquet sports players. Diagnosed via the Finkelstein test: the patient folds the thumb inside a closed fist, and the physician gently induces passive ulnar deviation of the wrist, eliciting sharp, excruciating pain over the radial styloid.

During shoulder abduction above 90 degrees, the clavicle must elevate at the acromioclavicular joint (driving the medial sternoclavicular end inferiorly) and rotate posteriorly around its longitudinal axis. For an abduction (superior) sternoclavicular dysfunction (medial clavicle stuck superiorly; fails to drop inferiorly during arm abduction), the physician contacts the superior surface of the medial clavicle and applies an inferior vector while elevating/abducting the patient's arm. For a horizontal extension (posterior) sternoclavicular dysfunction (medial clavicle stuck anteriorly; fails to glide posteriorly during horizontal extension), the physician applies a posterior-directed force on the medial clavicle while bringing the patient's arm into horizontal extension.

At the wrist, wrist flexion is coupled with dorsal glide of the proximal carpal row, whereas wrist extension is coupled with volar (palmar) glide. Carpal tunnel decompression uses the opponens roll myofascial release: the physician grasps the thenar and hypothenar eminences with both thumbs placed dorsally over the carpal arch, applying lateral traction and hyperextension to stretch the transverse carpal ligament. At the ankle, an inversion ankle sprain (anterior talofibular ligament tear) leaves the talus stuck in plantarflexion (anterior talus dysfunction; restricted dorsiflexion) and the subtalar calcaneus inverted (varus). Talocrural HVLA ('ankle tug') engages the dorsiflexion barrier with caudal traction and a rapid anterior-to-posterior vector over the talar neck.