Hand and Wrist Anatomy

Wrist Complex

• Three joints make up the wrist complex: distal radio-ulnar, radio-carpal, and midcarpal joints.
• Radio-carpal articulation includes that between the TFCC disc and the carpals, also known as the ulnomeniscotriquetral joint, which is counted as one functional unit.

Flexion & Extension Mechanics

• Primary axis for flexion-extension in the wrist is through the capitate.
• Flexion primarily occurs at the midcarpal joint, and extension primarily occurs at the radiocarpal joint.

Closed Pack Position of Wrist

• There is slight supination in the wrist with extension.
• "Screw home" movement is needed for the wrist to achieve full close pack position for intrinsic stability.
• Closed pack (max stability) helps with performing functional activities involving force transmission from the hand to the forearm, such as walking on all fours or pushing a heavy object.
• Clinically, if extension or lacking, wrist joint play (scaphoid) may be indicated.
• Carpal bones glide anteriorly/palmarly/ulnarly for extension.
• In flexion, the distal and proximal rows are in a loose-packed position.
• When moving from flexion to extension, the carpals glide anteriorly.
• As the wrist reaches neutral, the distal row stops moving.
• Scaphoid does a small supinatory twist, locking the scaphoid and distal row into CPP
• Once the distal row and scaphoid are close-packed, movement continues at the proximal row.
• Movement between the lunate and the scaphoid must occur to allow the final stage of wrist extension.
• The scaphoid creates an asymmetry, resulting in a supinatory twist - this causes a twist in the capsules and ligaments creating the close pack position on full extension.
• If somebody is struggling with full wrist extension, scaphoid joint play is probably indicated.
• For athletes that spend time on their hands, scaphoid joint play may be beneficial.
• As with most joints, the close-pack position, which is extension, is most susceptible to injury.
• The scaphoid is the most commonly fractured carpal, and the lunate is most commonly subluxed or dislocated (palmarly).

Radial & Ulnar Deviation Mechanics

• Axis of movement for radial and ulnar deviation is through the capitate.
• Ulnar deviation has a greater range because the triquetrum clears the ulnar styloid process more easily than the scaphoid tubercle clears the radial styloid process during radial deviation.
• Both radial and ulnar deviations involve movement at the radiocarpal and midcarpal joints.
• There is also a slight rotary motion during radial and ulnar deviations.
• During radial deviation, the proximal row (in reference to the radiocarpal joint) moves into pronation, and ulnar glide and the distal row (in reference to the metacarpal joint) moves into supination, and radial glide.
• Ulnar deviation yields the opposite movements.

Functional Arches

• All arches work for a common purpose to improve the hand's functional ability.
• The arches are structurally composed of one longitudinal arch per finger, one transverse carpal arch, and one transverse metacarpal arch.
• All of the arches are concave palmarly and relevant to understanding descriptive language for pathologies.
• The longitudinal arch consists of each finger and its corresponding carpal bone, and these arches are centered around their MCP joints.
• The long finger and the capitate form the focal point.
• The transverse carpal, or proximal transverse arch, is formed by the distal row.
• Each of the carpal bones move independently of each other.
• The proximal row is more mobile than the distal row.
• The distal row centers around the capitate and provides less movement (due to its articulations with the metacarpals).
• The transverse metacarpal, or distal transverse arch, is formed by the heads of the metacarpals with the third metacarpal, the capitate, and the lunate being approximately the center.
• It is relatively flat at rest but the curvature considerably increases with strong clenching of the fist or thumb to pinky opposition

Cascade Sign

• Only the index ray flexes in the sagittal plane while the other fingers flex toward the scaphoid

Cupping & Flattening

• Cupping of the hand involves finger flexion, which improves hand mobility for functional use.
• Flattening of the hand involves finger extension; flattening is used to release objects

Length-Tension Relationships

• The wrist provides a stable base for the hand, and its position controls the length of the extrinsic muscles to the digits.
• Muscles of the wrist movement serve two important functions: provide fine adjustment of the hand into its functioning position and, once this position has been achieved, stabilize the wrist to provide a stable base for the hand
• Movements of the wrist are usually in reverse of the movements of the fingers and reinforce the action of the extrinsic muscles of the fingers.
• To prevent the wrist from overly shortening, too many cross bridges can render it weaker.
• Finger flexion involves wrist extensor activation to stabilize the wrist, preventing the long finger flexors from simultaneously flexing it.
• Finger extension involves wrist flexor activation so that the long finger extensors can function more effectively.
• Changes in wrist position affect extrinsic muscle length, influencing force exertion (dexterity).
• An appropriate length-tension relationship is crucial for optimal function.
• As grip strength increases, wrist extensors slacken allowing a favorable shortening of the flexors to achieve a strong contraction.
• Greatest interphalangeal flexion force is achieved with ulnar deviation and neutral flexion-extension

Dorsal Digital Expansion aka Extensor Mechanism

• Is a broad, flat aponeurotic band of tissue composed of an extrinsic extensor tendon and sheath posteriorly, and by the tendons of the interosseous and lumbrical muscles anteriorly
• Originates at posterior, medial, and lateral sides of proximal phalanges, D1-5
• Inserts at posterior sides of distal phalanges, D1-5
• The extrinsic tendons (ED and EPL) exert force at the MCP.
• The intrinsic tendons (Lumbricals and Interossei) are extensors for the IP joints, D2-5 only.

Prehension

• The musculoskeletal function of the hand lies in its ability to grip objects with 4 types of prehension (pinch, encircle, push or adhere)
• Categorized into two groups: power and precision.
• Humans have all types because of the opposable thumb.
• Power grip is a forceful act with flexion at all fingers (D1-5), that typically remains isometric and involves a median and ulnar grip.
• The thumb stabilizes the object between the fingers and the palm, and two ulnar fingers flex across toward the thenar eminence.
• Variations of power grips include cylindrical, spherical, hook, and fist grips.
• A power grip results from opening the hand, positioning the fingers, approaching the object, and maintaining a static phase, i.e., isometric contraction.
• Precision grip lacks a static phase and is dynamic/isotonic.
• The object is picked upt by the fingers and thumb, but is not in contact with the palm Sensory surfaces of the digits are used for maximum sensory input to influence delicate adjustments.

History, Observation, and ROM

• When taking a patient history, note the location, MOI, nature, onset, pain/10, quality, referral/radiating symptoms, systemic symptoms, timing, and underlying factors.
• When observing, look for any swan neck or boutonniere deformities.
• Most movement occurs in the midcarpal joint during flexion as less occurs at the radiocarpal joint.
• With extension most movement occurs in the radiocarpal joint, and less occurs at the midcarpal joint.
• Radial deviation- primarily midcarpal joint
• Ulnar Deviation- primarily at the radiocarpal joint.

Clinical Conditions

• All of the following have definitive mid-term outcomes.
• Swan Neck: Deformity of the fingers, occurs only at the palm, palmar flexes, and opposite of the boutonniere joints.
• Boutonniere: Fingers sound French, all sound effects, very one sided, and at the MTP.
• Dupuytren's Contracture: Idiopathic; contracture of the palmar fascia resulting in fixed flexion deformity of the MCP and PIP joints, usually seen in digits 4 & 5 with skin also being adhered to the fascia.
• Not tendon, only the palmar fascia.
• Heberden's nodes are at the DIP and Bouchard's nodes are at the PIP joints and MC with OA.
• Ulnar drift- changes in the MCP and resulting pull on those tendons.
• Seen with RA.
• Radial drift- uncommon

Neural Conditions

• Muscle tone is one of the key indicators.
• Peripheral nerve lesions: Radial, median, and ulnar.
• Visualize to see with ape sweat or not (Radial Nerve) Known Radial Nerve
• C5-T1
• C6-BrachioRadialis
• Triceps
• Know common positions
• Motor and sensory problems
• Radial- ape hands or open hand
• Loss of Extensors
• Loss of extensor leads to flexed wrist and finger posture with inability to extend wrist or fingers
• Active: Froment's Sign
• Loss of the abductor pollicis
• Active - Benedictine hand

Median

• So the bishop bends
• Flex the MCP, and flex the PIP
• Flexon, digits, or LHS thumb joints only.
• Thumb flexors over inner power