thumb
Enable an AI agent to recognise a thumb, record its structure and functional state, and judge which interactions require adaptation, protection or further assessment.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise a thumb, record its structure and functional state, and judge which interactions require adaptation, protection or further assessment.
The thumb (pollex; digitus I of the manus) is the radial-most digital ray of the primate hand, distinguished in humans by two phalanges, a saddle-shaped trapeziometacarpal joint, and thenar musculature that together permit palmar abduction, pronation and opposition to the other digits.
It can be Identify and track the same thumb across observations, images and assessments.; Record demonstrated opposition, movement and contact patterns under documented conditions.; Assess its contribution to a specified pinch, grasp or control operation.; Select interface or tool-use adaptations based on observed reach, contact and tolerance.; Record protective measures and externally established restrictions affecting thumb use.; Flag changes or missing evidence that require qualified assessment before increasing demands..
Distinguishing features
Identify it by first-digit position and attachment within the hand; size or apparent opposability alone does not establish thumb identity.
Distinguish it from a great toe by its attachment to a hand rather than a foot; a transferred toe requires reconstruction history to describe its current role.
Check whether movement brings its pad toward the fingers or palm, while recognising that absent opposition does not rule out an injured or atypical thumb.
Use the typical human pattern of two phalanges and a distinct metacarpal as supporting anatomical evidence, allowing for congenital variation and missing structures.
Distinguish living thumb tissue from a prosthetic replacement or cosmetic extension, recording their relationship when both are present.
Scope
+ Thumb identity, laterality and attachment to a particular hand
+ Present anatomical structures, including congenital variation, injury and reconstruction
+ Thumb movement, opposition, sensation and task-specific control
+ Local tissue condition, symptoms and changes over time
+ Thumb participation in pinch, grasp and interaction with tools or controls
- Whole-hand coordination and the condition of other digits
- Wrist, forearm and proximal limb anatomy except as contextual relationships
- Person-wide disease, treatment plans and clinical diagnoses
- Prosthetic thumbs, robotic grippers and their mechanical specifications
- Gloves, splints, tools and interface controls as independently modelled objects
Characteristics
- Hand attachment and laterality
- Linked hand; left, right, other or unresolved Locates the thumb and prevents observations or restrictions being assigned to the wrong side.
- Anatomical configuration
- Present segments and joints; congenital variation, acquired loss, reconstruction or unresolved Establishes which structures exist without treating typical anatomy as mandatory.
- Joint movement
- Degrees by named joint and movement; active or passive; method and position recorded Separates movement limitations that otherwise look like a single inability to use the thumb.
- Opposition performance
- Named contact targets reached, or score under an explicitly identified protocol Records whether the thumb can position its pad for relevant contacts.
- Pinch performance
- Force in N with pinch type, instrument, posture and symptom response Supports task comparisons while preserving the role of the opposing fingers and test conditions.
- Sensory response
- Response by thumb region and named sensory test; reported, observed or unassessed Records sensory limitations relevant to contact control and unnoticed harm.
- Local tissue condition
- Skin, nail and deeper-tissue observations with location, time and assessment method Makes local changes and vulnerable contact surfaces visible.
- Symptoms during use
- Symptom type, location, severity under a named scale, provoking activity and duration Distinguishes available movement from movement the person can comfortably sustain.
- Task participation
- Linked task and contact role; independent, adapted, assisted, unable or unassessed Connects thumb capability to actual activity rather than inferring it from anatomy alone.
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.thumb-artifact
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Thumb identity and configuration Establishes which thumb is being modelled and which anatomical structures it contains.
Thumb identity must survive differences in appearance, congenital anatomy and acquired structural change.
Hand attachment
Locates the digit within a particular hand and resolves ambiguous identity.
First-digit identification
Records the evidence that this structure is the hand's thumb and identifies its side.
- Which hand and side does this thumb belong to, and what establishes its first-digit identity? definition
- Does atypical anatomy or reconstruction make the boundary between thumb, another digit and replacement uncertain? boundary
Structural configuration
Describes present thumb segments, joints and structural history.
Present segments and joints
Records actual anatomy and separates observed structures from presumed typical anatomy.
- Which thumb segments and joints are present, absent, fused, duplicated or reconstructed? definition
- Which observations or records establish whether this configuration is congenital, acquired or reconstructed? provenance
Thumb motion and opposition Captures joint movement and the ability to position the thumb for contact.
A thumb may be identifiable yet unable to reach, rotate or oppose as a particular task requires.
Joint-specific motion
Separates movement at the thumb base, metacarpophalangeal joint and interphalangeal joint where present.
Available movement
Records movement by joint, direction and assessment conditions.
- What active or professionally assessed passive movement is recorded at each present thumb joint? measurement
- Which posture, method, symptoms or compensating hand movements affected the measurement? provenance
Opposition and contact reach
Records thumb-pad positioning relative to the fingers, palm and task targets.
Reachable contact targets
Distinguishes touching a target from achieving the contact orientation needed for use.
- Which finger or palm targets can the thumb reach, and which thumb surface makes contact? measurement
- Does the required contact depend on assistance or compensating movement elsewhere in the hand? boundary
Thumb contact and control Connects thumb sensation and force control to pinch and grasp.
Reach alone cannot establish whether thumb contact is sensed, controlled or sustained.
Thumb sensation
Locates sensory observations on the thumb's contact and non-contact surfaces.
Regional sensory response
Records sensory evidence without inferring a nerve diagnosis from symptoms alone.
- What sensory responses or reported alterations are recorded at the pad, tip and other specified thumb regions? measurement
- Were these responses self-reported or assessed using a named method, and when? provenance
Pinch and grasp contribution
Records thumb performance as one participant in a coordinated hand action.
Task-specific contact control
Captures force, slip, release and symptom response for a specified contact pattern.
- For the specified pinch or grasp, what force, contact stability and controlled release were demonstrated? measurement
- Which opposing digits, object properties and hand posture contributed to that result? boundary
Thumb condition and change Records local tissue observations, symptoms and their trajectory.
Thumb use must account for changing contact surfaces and symptoms as well as established capability.
Thumb tissue observations
Locates observations at the nail, tip, pad, joints and base.
Local tissue state
Captures visible or assessed abnormalities while keeping interpretation separate from observation.
- Where are skin breaks, swelling, nail changes, colour changes or other tissue observations located? measurement
- Which observations have been directly assessed, and which remain reports or uncertain image interpretations? provenance
Symptoms and trajectory
Relates thumb symptoms and functional changes to time and activity.
Change from thumb baseline
Records onset, persistence and departure from the person's previous thumb state.
- What changed in thumb pain, sensation, movement or usable contact, and over what interval? measurement
- What activity or event preceded the change, and is that association reported or independently documented? provenance
Thumb use and protection Connects recorded capability to task demands, adaptations and established restrictions.
An agent needs task-specific grounds for proposing thumb use and clear limits on what the evidence permits.
Task demand fit
Compares a task's thumb reach, contact, force and repetition demands with demonstrated performance.
Thumb task compatibility
Records whether a particular interaction is achievable and what adaptation it needs.
- What thumb position, contact surface, force and repetition does the proposed task require? measurement
- Which demonstrated adaptation makes the task achievable within recorded tolerance and restrictions? action
Protection and assessment limits
Records protective arrangements and the authority behind limits on thumb loading or movement.
Supported use boundaries
Separates demonstrated capability from permission to increase demands or alter protective arrangements.
- What current restrictions or protective measures apply specifically to this thumb, and who established them? provenance
- What missing assessment or unresolved change prevents a justified decision about the proposed thumb use? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Typical biphalangeal human thumb
- Triphalangeal thumb (congenital extra phalanx)
- Hypoplastic or aplastic thumb, including floating thumb (Blauth types)
- Duplicated thumb / preaxial polydactyly (Wassel types)
- Trigger thumb (stenosing tenosynovitis of flexor pollicis longus)
- Hitchhiker's thumb (hypermobile interphalangeal joint)
- Nonhuman primate thumb (vestigial to fully opposable)
- Surgically reconstructed thumb (index pollicization or toe-to-thumb transfer)
- Which of these kinds and varieties hold for the sense of thumb this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q83360 - Item for the anatomical thumb.
- Terminologia Anatomica - pollex; digitus I (manus) - Official Latin name; TA2 numbering should be taken from the current FIPAT release rather than remembered TA98 codes.
- MeSH - D013932 - Heading Thumb.
- SNOMED CT - 76505004 - Thumb structure (body structure).
- Which of these identifiers and schemes hold for the sense of thumb this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Terminologia Anatomica 2 - FIPAT / International Federation of Associations of Anatomists (anatomical nomenclature).
- ISO 7250-1 - International Organization for Standardization (anthropometric landmarks including thumb/hand measures).
- AMA Guides to the Evaluation of Permanent Impairment - American Medical Association (thumb loss is scored as a large fraction of hand function).
- ICD-10 S60-S69 (thumb as a coded laterality-specific body region for injury) - World Health Organization.
- Which of these standards and regulation hold for the sense of thumb this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Precision pinch and power grip in tool use, writing, feeding and object manipulation.
- Clinical tests of median-nerve and thenar function (opposition, palmar abduction, pulp pinch, Kapandji score).
- Forensic and civil identification via thumbprints.
- Reconstructive hand surgery: pollicization of the index finger and microvascular toe-to-thumb transfer.
- Occupational and sports injury clinics (skier's thumb, basal joint pain, trigger thumb, vibration-tool use).
- Anthropometric design of gloves, hand tools, controls and touchscreen targets.
- Which of these real-world use hold for the sense of thumb this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Phalanx count of the thumb ray (typical human) - 2 - count
- Interphalangeal flexion range of motion - 0-80 - degree
- Metacarpophalangeal flexion range of motion - 0-55 - degree
- Carpometacarpal palmar abduction - 0-45 - degree
- Kapandji opposition score - 0-10 - score
- Pulp static two-point discrimination - 2-5 - mm
- Which of these typical measurements hold for the sense of thumb this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Ulnar collateral ligament rupture at the thumb metacarpophalangeal joint (skier's thumb / gamekeeper's thumb), with pinch instability.
- Trapeziometacarpal (basal) osteoarthritis, a common cause of pain and weakened pinch in older adults.
- Trigger thumb from stenosis of the flexor pollicis longus sheath at the A1 pulley.
- Bennett and Rolando fractures of the first metacarpal base; traumatic amputation (thumb loss is functionally costly).
- Congenital hypoplasia, aplasia or duplication requiring reconstruction or pollicization.
- Median-nerve palsy with loss of opposition and thenar atrophy.
- Closed-space pulp infection (felon) and paronychia, which threaten the terminal tuft and flexor sheath.
- Which of these failure modes and hazards hold for the sense of thumb this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Whether the thumb is counted as a 'finger' differs by language and legal phrasing (English often separates 'thumb' from 'fingers'; many other languages treat it as digit I among five).
- Common names: Latin pollex, French pouce, German Daumen, Japanese oyayubi ('parent finger').
- Population frequency of hitchhiker's (distally hypermobile) thumb varies.
- Counting and pointing gestures start on the thumb in some cultures and on the index finger in others.
- Which of these regional variation hold for the sense of thumb this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Fingers (digits II-V) - Those rays normally have three phalanges and no saddle trapeziometacarpal joint capable of true opposition.
- Thenar eminence - The thenar is the palmar muscle mass at the base of the first ray, not the digit itself.
- Hallux (great toe) - Serial homologue with two phalanges, but in humans it lacks a saddle carpometatarsal joint and cannot oppose the other toes.
- Giant panda 'thumb' - An enlarged radial sesamoid used as a false digit; it is not a phalangeal ray.
- First metacarpal - The proximal bone of the thumb ray; the named digit in clinical speech is the phalangeal portion distal to the metacarpophalangeal joint, though the whole first ray is often treated as the thumb.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of thumb this model covers, and on what evidence? provenance
Sources
- Thumb (Encyclopædia article), Wikipedia / Wikimedia Foundation - Common-name identity, two-phalanx structure, opposition, and distinction from other digits.
- thumb (Q83360), Wikidata / Wikimedia Foundation - Stable public identifier and cross-links into anatomical nomenclatures.
- Gray's Anatomy: The Anatomical Basis of Clinical Practice, Elsevier - Osteology of the first ray, trapeziometacarpal saddle joint, thenar muscles, and opposition.
- Terminologia Anatomica 2, FIPAT / International Federation of Associations of Anatomists - Official Latin term pollex / digitus I as the anatomical name of the thumb.
- Cotation clinique de l'opposition et de la contre-opposition du pouce, Annales de Chirurgie de la Main (Masson/Elsevier), 1986 - Kapandji 0-10 clinical score used to measure thumb opposition.
- ISO 7250-1: Basic human body measurements for technological design - Part 1, International Organization for Standardization - Standardised anthropometric landmarks and hand/thumb dimensions for design.
What the second pass must settle
- Does the registry intend thumb to cover humans only, other animals' first digits, or a broader functional category?
- Where should ownership fall between thumb and hand models for the first metacarpal, thumb-base joint and shared muscles or tendons?
- How should congenital duplication, transferred digits and mixed biological-prosthetic reconstructions preserve registry identity?
- Which validated movement, opposition, sensation and pinch protocols should be supported, and when are their results comparable?
- Which authoritative criteria should govern escalation for changes in thumb condition, and how should population and clinical context modify them?