DiagnosticTree/Antecubital
{
"model": "bayesian_lr_scoring",
"version": "2.0",
"region": "Antecubital",
"description": "Probabilistic scoring model for antecubital (anterior elbow) pain. Scope per Travell & Simons: the two muscles whose TrP referral reaches the antecubital space — Brachialis (Vol.1 Ch.31, essential zone thumb base/dorsal web, antecubital spillover) and Biceps Brachii (Vol.1 Ch.30, essential zone anterior shoulder, antecubital spillover). Both are non-bold in the regional overview; equal priors. LRs are deliberately asymmetric: pathognomonic features carry strong positive LRs when present but only mild negative LRs when absent, because a TrP's signature feature is highly specific yet NOT mandatory — gating on it would lose sensitivity for atypical presentations. High-sensitivity shared features (antecubital spillover, loaded-flexion aggravation) carry small LRs so they keep both muscles in contention without dominating the ranking.",
"thresholds": {
"early_exit_posterior": 0.8,
"early_exit_gap": 0.45,
"pairwise_trigger": 0.18
},
"muscles": {
"brachialis": {
"label": "Brachialis",
"prior": 0.5,
"page": "Muscle:Brachialis",
"subtitle": "Thumb base / dorsal web pain with antecubital spillover; active thumb hurts, active elbow does not; weakness equal in pronation and supination",
"key_trp_note": "The brachialis is the essential antecubital pain generator. Its TrPs refer to the dorsum of the thumb CMC joint and dorsal web (essential zone) with spillover to the antecubital space. Almost always co-involved with biceps brachii in elbow-flexion overload; in the tennis-elbow sequence the supinator is the primary TrP with brachialis and biceps secondary. A lateral-border TrP may entrap the radial sensory nerve, adding dorsal-thumb dysesthesia — relieved by TrP inactivation. Examine the distal belly by displacing the biceps medially."
},
"biceps": {
"label": "Biceps Brachii",
"prior": 0.5,
"page": "Muscle:Biceps_Brachii",
"subtitle": "Anterior-shoulder-dominant superficial ache with antecubital spillover; can lie on affected side and reach behind back; weakness worse in supination; positive Biceps-extension Test",
"key_trp_note": "Biceps TrPs refer a superficial ache to the anterior shoulder/anterior deltoid, with antecubital pain only as mild downward spillover — so biceps is rarely the sole cause of an antecubital chief complaint. Infraspinatus is the key TrP source most likely to drive satellite biceps TrPs and should be addressed first for durable relief. As a three-joint muscle, range-of-motion testing is unreliable unless the muscle is lengthened across shoulder, elbow, and radioulnar joints together (Biceps-extension Test)."
}
},
"questions": [
{
"id": "q_antecubital_present",
"text": "Is pain felt in or around the antecubital space (the crease at the front of the elbow)?",
"sublabel": "HIGH SENSITIVITY screen. Antecubital pain is a spillover zone for both elbow flexors, so a 'yes' keeps both muscles in contention rather than discriminating between them. A 'no' gently lowers both (the complaint may belong to an adjacent region — anterior shoulder, lateral elbow, or neck).",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — antecubital / anterior-elbow pain is part of the picture",
"lr": {
"brachialis": 1.6,
"biceps": 1.4
}
},
{
"id": "no",
"label": "No — no antecubital component",
"lr": {
"brachialis": 0.6,
"biceps": 0.7
}
}
]
},
{
"id": "q_loaded_flexion",
"text": "Is the pain provoked by sustained or repeated elbow flexion under load — carrying with the elbow bent, holding tools at elbow height, lifting, or instrument playing?",
"sublabel": "HIGH SENSITIVITY. Both elbow flexors are overloaded by sustained loaded flexion, so this keeps both in the race. Absence only mildly lowers both — many real TrP cases are activated by other mechanisms (overstretch, immobilisation).",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — loaded elbow flexion is an aggravator",
"lr": {
"brachialis": 1.8,
"biceps": 1.7
}
},
{
"id": "no",
"label": "No — not clearly related to loaded flexion",
"lr": {
"brachialis": 0.7,
"biceps": 0.7
}
}
]
},
{
"id": "q_thumb_zone",
"text": "Is pain or deep aching felt at the BASE OF THE THUMB or the dorsal web of the thumb (with or without tingling on the dorsum of the thumb)?",
"sublabel": "HIGH SPECIFICITY for brachialis — the dorsal thumb CMC and web are its essential referral zone, and the biceps does not refer to the thumb. PRESENT is a strong positive for brachialis. ABSENT is only a mild argument against brachialis (atypical brachialis cases may not show the full thumb pattern), so sensitivity is preserved.",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — thumb-base or dorsal-web pain present",
"lr": {
"brachialis": 7.0,
"biceps": 0.6
}
},
{
"id": "no",
"label": "No — no thumb involvement",
"lr": {
"brachialis": 0.55,
"biceps": 1.4
}
}
]
},
{
"id": "q_thumb_elbow_dissoc",
"text": "Does ACTIVE movement of the THUMB reproduce the pain while ACTIVE flexion/extension of the ELBOW does NOT?",
"sublabel": "HIGH SPECIFICITY (near-pathognomonic) for brachialis — the dissociation that redirects attention from the thumb to the arm. PRESENT is decisive for brachialis. ABSENT lowers brachialis only mildly: the dissociation is not always elicitable, and its absence must not rule brachialis out.",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — thumb movement hurts, elbow movement does not",
"lr": {
"brachialis": 8.0,
"biceps": 0.5
}
},
{
"id": "no",
"label": "No — elbow movement is painful, or thumb is not differentially worse",
"lr": {
"brachialis": 0.55,
"biceps": 1.3
}
}
]
},
{
"id": "q_anterior_shoulder_dominant",
"text": "Is the DOMINANT complaint a superficial ache over the ANTERIOR SHOULDER / anterior deltoid, with antecubital discomfort only a secondary spillover?",
"sublabel": "HIGH SPECIFICITY for biceps — the anterior shoulder is its essential referral zone, whereas antecubital is only spillover. PRESENT strongly favours biceps. ABSENT lowers biceps only mildly, since biceps can present with the antecubital spillover more prominent in some cases.",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — anterior shoulder ache dominates; antecubital is secondary",
"lr": {
"biceps": 7.0,
"brachialis": 0.55
}
},
{
"id": "no",
"label": "No — the antecubital/forearm component dominates, not the shoulder",
"lr": {
"biceps": 0.55,
"brachialis": 1.5
}
}
]
},
{
"id": "q_overhead_reach",
"text": "Is there pain or weakness on raising the hand above shoulder level (reaching overhead), or snapping/grating at the front of the shoulder on arm elevation?",
"sublabel": "HIGH SENSITIVITY for biceps — common in biceps TrP presentations (the long-head tendon and three-joint span), but not specific. Mild LRs so it supports biceps without overriding the discriminating features.",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — overhead reach is painful/weak, or anterior shoulder snapping",
"lr": {
"biceps": 2.2,
"brachialis": 0.8
}
},
{
"id": "no",
"label": "No — overhead reach is not a feature",
"lr": {
"biceps": 0.7,
"brachialis": 1.1
}
}
]
},
{
"id": "q_pronation_supination_weakness",
"text": "Comparing elbow-flexion strength with the forearm SUPINATED versus PRONATED (elbow extended): how does the weakness behave?",
"sublabel": "HIGH SPECIFICITY discriminator grounded in anatomy. The brachialis attaches to the ulna, so its strength is unaffected by forearm rotation (equal weakness both ways). The biceps wraps the radius in pronation, so it is weaker in supination-position testing. This is one of the strongest mechanical separators of the two muscles.",
"type": "choice",
"answers": [
{
"id": "equal_both",
"label": "EQUAL weakness in both positions — pronation makes no difference",
"sublabel": "Points to brachialis (ulnar attachment, rotation-independent)",
"lr": {
"brachialis": 6.0,
"biceps": 0.4
}
},
{
"id": "worse_supinated",
"label": "WORSE in supination — pronating the forearm reduces the weakness/pain",
"sublabel": "Points to biceps (radius wrap unloads it in pronation)",
"lr": {
"brachialis": 0.4,
"biceps": 6.0
}
},
{
"id": "not_tested_unclear",
"label": "Not tested or unclear",
"sublabel": "No information — leaves both unchanged",
"lr": {
"brachialis": 1.0,
"biceps": 1.0
}
}
]
},
{
"id": "q_passive_extension",
"text": "Does PASSIVE full elbow extension increase the thumb-base / antecubital pain?",
"sublabel": "SPECIFICITY support for brachialis (passive extension stretches it and reproduces its referred pain). Moderate positive LR; absence is only mildly negative because the few-degree restriction is subtle and easily missed.",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — passive elbow extension reproduces/increases the pain",
"lr": {
"brachialis": 3.0,
"biceps": 1.1
}
},
{
"id": "no",
"label": "No — passive extension does not reproduce it",
"lr": {
"brachialis": 0.7,
"biceps": 1.0
}
}
]
},
{
"id": "q_biceps_extension_test",
"text": "On the Biceps-extension Test (arm abducted ~45°, elbow extended, forearm pronated, arm moved into extension without medial rotation): does the ELBOW FLEX to compensate as the arm is extended?",
"sublabel": "HIGH SPECIFICITY for biceps — compensatory elbow flexion indicates a shortened, TrP-bearing biceps and is the purpose-built test for this three-joint muscle. PRESENT strongly favours biceps; ABSENT lowers it only mildly (the test requires correct technique and the shortening may be mild).",
"type": "binary",
"answers": [
{
"id": "yes",
"label": "Yes — elbow flexes to compensate (positive test)",
"lr": {
"biceps": 6.0,
"brachialis": 0.7
}
},
{
"id": "no",
"label": "No / not performed — no compensatory elbow flexion",
"lr": {
"biceps": 0.7,
"brachialis": 1.1
}
}
]
},
{
"id": "q_sidelying_behindback",
"text": "Can the patient lie comfortably on the AFFECTED side AND reach behind the waistline without pain?",
"sublabel": "SPECIFICITY support that separates biceps from an infraspinatus source of anterior-shoulder pain (infraspinatus prevents both). Within this 2-muscle model it gently supports biceps when the anterior shoulder is involved, and flags infraspinatus screening when negative. Mild LRs.",
"type": "choice",
"answers": [
{
"id": "yes_both",
"label": "Yes — can lie on the affected side and reach behind the back",
"sublabel": "Consistent with biceps; argues against an infraspinatus source",
"lr": {
"biceps": 2.0,
"brachialis": 1.0
}
},
{
"id": "no_either",
"label": "No — cannot lie on that side and/or cannot reach behind the back",
"sublabel": "Screen infraspinatus (separate region) — points away from a pure biceps picture",
"lr": {
"biceps": 0.5,
"brachialis": 0.9
}
},
{
"id": "na",
"label": "Not applicable — no shoulder component",
"sublabel": "Neutral",
"lr": {
"biceps": 1.0,
"brachialis": 1.0
}
}
]
}
],
"pairwise": [
{
"id": "pw_brachialis_biceps",
"pair": [
"brachialis",
"biceps"
],
"text": "Tiebreaker — Brachialis vs Biceps Brachii",
"question": "Taking the single most distressing site of pain: is it at the THUMB BASE / dorsal web (with the antecubital fossa secondary), or over the ANTERIOR SHOULDER (with the antecubital fossa secondary)?",
"answers": [
{
"id": "thumb_dominant",
"label": "Thumb base / dorsal web is the dominant site",
"lr": {
"brachialis": 5.0,
"biceps": 0.25
}
},
{
"id": "shoulder_dominant",
"label": "Anterior shoulder is the dominant site",
"lr": {
"brachialis": 0.25,
"biceps": 5.0
}
},
{
"id": "antecubital_only",
"label": "Neither — pain is confined to the antecubital fossa itself",
"sublabel": "Re-examine both elbow flexors directly; consider lateral-elbow and cervical sources outside this region",
"lr": {
"brachialis": 1.2,
"biceps": 1.0
}
}
]
}
],
"treatment_dag": {
"edges": [
{
"from": "brachialis",
"to": "biceps",
"type": "functional_unit",
"label": "Brachialis and biceps brachii are synergistic elbow flexors almost always involved together — examine and treat both in the same session"
},
{
"from": "biceps",
"to": "brachialis",
"type": "functional_unit",
"label": "Biceps TrPs drive early secondary brachialis TrPs — treat concurrently; spray and stretch the brachialis after the biceps"
}
],
"edge_type_labels": {
"key_satellite": "Treat first — key TrP driving satellites",
"functional_unit": "Treat concurrently in the same session",
"secondary_load": "Treat after primary resolves",
"antagonist_risk": "⚠ Treat in alternating cycles — reactive activation risk"
}
},
"region_label": "Antecubital (Anterior Elbow) Pain",
"red_flags": {
"emergency": [
{
"id": "rf-e1",
"label": "Vascular compromise — brachial artery injury (elbow dislocation / supracondylar fracture)",
"question": "Anterior elbow pain after a fall, dislocation, or supracondylar fracture with a COLD, PALE, or PULSELESS hand, expanding antecubital swelling/haematoma, or new median/anterior interosseous nerve signs? The brachial artery lies in the antecubital fossa and is at risk with posterior elbow dislocation and (especially in children) supracondylar fracture. Check distal pulses and perfusion immediately — an absent pulse or ischaemia needs emergent reduction and vascular/orthopaedic care to avoid limb loss and Volkmann's contracture."
},
{
"id": "rf-e2",
"label": "Acute compartment syndrome of the forearm",
"question": "Severe escalating forearm pain out of proportion to findings, pain on PASSIVE finger extension/stretch, a tense swollen volar compartment, or recent fracture/crush/reperfusion/tight cast? Pallor, pulselessness, and paralysis are LATE — fasciotomy within about 6 hours is limb-saving."
},
{
"id": "rf-e3",
"label": "Necrotising fasciitis",
"question": "Rapidly spreading erythema, pain grossly out of proportion to findings, skin blistering or dusky discolouration, crepitus, or rapid systemic deterioration? A surgical emergency needing immediate debridement and broad-spectrum antibiotics."
},
{
"id": "rf-e4",
"label": "Septic arthritis of the elbow",
"question": "Hot, red, exquisitely tender elbow with marked pain on the slightest passive movement and an effusion, especially with fever? Urgent aspiration (Gram stain, culture, crystals) distinguishes it from an acute gout/CPPD flare; treat as infection (drainage + antibiotics) until excluded."
},
{
"id": "rf-e5",
"label": "Bacteraemia / systemic sepsis",
"question": "Fever, rigors, tachycardia, or malaise with a hot, spreading, tender swelling around the elbow? Systemic toxicity is never myofascial — investigate and treat for sepsis."
},
{
"id": "rf-e6",
"label": "Osteomyelitis",
"question": "Deep, constant, night-prominent bone pain with local warmth/swelling or fever, on a background of recent infection, open wound, or immunocompromise? Needs imaging, inflammatory markers, and specialist referral."
},
{
"id": "rf-e7",
"label": "Acute coronary syndrome / cardiac ischaemia",
"question": "Anterior or medial arm pain reaching the elbow/forearm with chest pressure, breathlessness, sweating, or nausea, especially on exertion or with cardiac risk factors? Cardiac pain can radiate to the anteromedial arm; relief by musculoskeletal treatment does NOT exclude it — establish cardiac status independently and urgently."
}
],
"urgent": [
{
"id": "rf-u1",
"label": "Distal biceps tendon rupture",
"question": "Sudden anterior elbow pain (often a 'pop') during a forceful eccentric load — lifting or catching a heavy object — then weakness of elbow flexion and especially SUPINATION, antecubital bruising, and a retracted muscle belly ('reverse Popeye')? A positive hook test (the examiner cannot hook a finger under the distal biceps tendon) confirms it. Acute complete ruptures need prompt surgical reattachment, ideally within about 2–3 weeks before the tendon retracts and scars."
},
{
"id": "rf-u2",
"label": "Fracture about the elbow (radial head, supracondylar, coronoid)",
"question": "Anterior elbow pain, swelling, and restricted/painful movement after a fall on the outstretched hand? The radial head fracture is the commonest adult elbow fracture and is often subtle — the fat-pad (sail) sign may be the only clue. Supracondylar fractures predominate in children with a high neurovascular complication rate. Marked effusion, inability to fully extend, or bony tenderness warrants radiographs and orthopaedic referral; check distal neurovascular status."
},
{
"id": "rf-u3",
"label": "Pronator teres syndrome / proximal median nerve entrapment",
"question": "Anterior forearm/elbow ache worse on resisted PRONATION, with median-territory paraesthesia that INCLUDES the thenar eminence (unlike carpal tunnel) and a positive Tinel over the proximal pronator teres? Consider the antecubital sibling sites: lacertus fibrosus (worse on resisted elbow flexion in supination), the ligament of Struthers (worse on supination + elbow extension, possible reduced radial pulse), and the FDS sublimis bridge (worse on resisted middle-finger PIP flexion). Progressive motor/sensory deficit warrants nerve studies and surgical release."
},
{
"id": "rf-u4",
"label": "Anterior interosseous nerve (AIN) syndrome",
"question": "Anterior forearm/cubital-fossa pain with WEAKNESS but NO sensory loss — specifically an inability to flex the tips of the thumb and index finger to make a normal 'OK' sign (the pinch flattens)? The anterior interosseous nerve is the pure-motor median branch to flexor pollicis longus, flexor digitorum profundus (index/middle), and pronator quadratus. Often a transient neuritis, but compression and trauma occur; needs electrodiagnostic confirmation and timely specialist assessment as motor recovery is the concern."
},
{
"id": "rf-u5",
"label": "Elbow dislocation (post-reduction instability) / coronoid fracture",
"question": "A history of elbow dislocation (often a posterolateral rotatory mechanism on a fall) with persistent anterior pain, apprehension, or a sense of instability? Even after reduction, an associated coronoid or radial-head fracture can cause ongoing instability; large coronoid fractures need fixation. Post-reduction films and ligament-stability assessment are required, with orthopaedic referral for any fracture or instability."
},
{
"id": "rf-u6",
"label": "Stress fracture",
"question": "Focal BONY (not muscular) tenderness with a history of repetitive loading or a sudden change in training/occupational load, pain worsening with activity and easing with rest? Image and offload if suspected."
}
]
},
"broad_differential": [
{
"condition": "Lateral / medial epicondylitis",
"confidence": "uncommon",
"mimics": "Elbow pain provoked by grip and loading",
"distinguishing_feature": "Point tenderness at the epicondyle; positive Mills'/Cozen's (lateral) or resisted wrist flexion (medial). Frequently coexists with supinator/brachioradialis TrPs.",
"action": "Examine the relevant forearm muscles for TrPs; myofascial source is common and first-line."
},
{
"condition": "Radial tunnel / posterior interosseous nerve entrapment",
"confidence": "uncommon",
"mimics": "Deep aching just lateral to the antecubital region",
"distinguishing_feature": "Pain 4–5 cm distal to the lateral epicondyle (over the mobile wad), worse on resisted middle-finger extension and supination; pain WITHOUT weakness or paraesthesia (contrast PIN compression syndrome, which has true extensor weakness).",
"action": "If TrP treatment fails, refer for nerve conduction studies (often normal in radial tunnel)."
},
{
"condition": "Cubital tunnel syndrome (ulnar nerve)",
"confidence": "uncommon",
"mimics": "Elbow pain with hand symptoms",
"distinguishing_feature": "MEDIAL location; paraesthesia in the ring and little fingers; positive Tinel's at the medial epicondyle — not an anterior/antecubital pattern.",
"action": "Refer for electrodiagnostic assessment; structural compression is not addressed by TrP work."
},
{
"condition": "Cervical radiculopathy (C5/C6)",
"confidence": "uncommon",
"mimics": "Arm pain in a C5/C6 distribution",
"distinguishing_feature": "Dermatomal sensory deficit, reflex change, or true myotomal weakness — absent in pure TrP pain. TrPs commonly coexist and may be the dominant pain source.",
"action": "Neurological examination with Spurling's; image if a focal deficit is present. Treat coexisting TrPs concurrently."
},
{
"condition": "Elbow osteoarthritis (with anterior osteophytes / intra-articular loose body)",
"confidence": "uncommon",
"mimics": "Activity-related elbow ache, stiffness, and end-range anterior pain",
"distinguishing_feature": "Pain at the extremes of motion — anterior pain at maximal FLEXION from coronoid/radial-fossa osteophytes — typically sparing the mid-range, with crepitus and a flexion contracture; an osteophyte can fracture to form a LOOSE BODY causing mechanical locking, catching, or a painful block. Radiographic joint-space change (often preserved until late); pain is not position-specific to a muscle.",
"action": "Radiographs/CT for osteophytes and loose bodies; joint examination before any injection in the fossa. NSAIDs, activity modification; arthroscopic/open debridement or loose-body removal for mechanical symptoms."
},
{
"condition": "Distal biceps tendinopathy",
"confidence": "uncommon",
"mimics": "Anterior elbow pain on lifting and twisting",
"distinguishing_feature": "Activity-related pain at the distal biceps insertion on the radial tuberosity, reproduced by resisted elbow flexion and resisted supination, with tendon tenderness but NO retraction and a NEGATIVE hook test (distinguishing it from rupture). Often coexists with — and may be driven by — biceps TrP taut-band tension.",
"action": "Resisted flexion/supination testing and hook test to exclude rupture; ultrasound for tendinosis/partial tear. Inactivate biceps TrPs first and reassess; relative rest and eccentric loading."
},
{
"condition": "Proximal bicipital (long head) tendinopathy",
"confidence": "uncommon",
"mimics": "Anterior shoulder / bicipital-groove pain spilling toward the arm",
"distinguishing_feature": "Tenderness localised to the long-head tendon and bicipital groove, positive Yergason's/Speed's; often coexists with biceps TrPs and may be driven by their sustained taut-band tension. A shoulder-region source rather than a true antecubital one.",
"action": "Inactivate biceps TrPs first and reassess; persistent tendon signs may warrant sheath injection at the groove."
},
{
"condition": "Bicipitoradial (cubital) bursitis",
"confidence": "uncommon",
"mimics": "Deep anterior elbow pain and fullness",
"distinguishing_feature": "Pain and sometimes a palpable fullness DEEP in the antecubital fossa from inflammation of the bicipitoradial bursa (between the distal biceps tendon and the radial tuberosity), worse on resisted supination/pronation as the tendon compresses the bursa; can occasionally irritate the radial nerve. Anterior — distinct from the posterior olecranon bursa.",
"action": "Ultrasound/MRI to confirm the bursa and exclude a mass; assess for radial nerve irritation. Activity modification, NSAIDs, image-guided aspiration/corticosteroid; excision if refractory."
},
{
"condition": "Brachialis strain / tendinopathy",
"confidence": "uncommon",
"mimics": "Deep anterior elbow pain",
"distinguishing_feature": "Deep anterior elbow pain from overload of the brachialis (prime elbow flexor on the floor of the fossa), worse on resisted elbow flexion with the forearm PRONATED (which favours brachialis over biceps), often after heavy/repetitive lifting or climbing. A brachialis TrP refers to the thumb base and is reproduced by deep palpation (displace biceps medially); overload can irritate the radial sensory nerve at the lateral border.",
"action": "Resisted flexion testing in pronation; relative rest and graded loading. Treat coexisting brachialis TrPs; consider radial sensory irritation if dorsal-thumb dysesthesia appears."
},
{
"condition": "Gout / crystal arthropathy (CPPD) of the elbow",
"confidence": "uncommon",
"mimics": "Acute or recurrent anterior elbow pain and swelling",
"distinguishing_feature": "A subacute or episodic hot, swollen, exquisitely tender elbow with rapid onset — the elbow is involved in 20–30% of gout patients; CPPD is the other crystal cause. Aspiration shows negatively birefringent monosodium urate crystals. A truly hot, red, febrile joint must be treated as SEPTIC until aspiration excludes it.",
"action": "Joint aspiration for crystals and culture (mandatory to exclude sepsis); serum urate. Acute flare: NSAIDs/colchicine/short steroid; chronic: urate-lowering therapy. Treat TrPs only once an active crystal/infective process is excluded."
},
{
"condition": "Rheumatoid / inflammatory arthritis",
"confidence": "uncommon",
"mimics": "Anterior elbow pain, swelling, and stiffness",
"distinguishing_feature": "Persistent synovitic pain with boggy swelling, prolonged morning stiffness, and usually a symmetrical multi-joint pattern with systemic features (fatigue, nodules); the elbow is a common site in established RA. TrP pain lacks synovitis, effusion, and systemic features.",
"action": "Inflammatory markers, rheumatoid serology, rheumatology referral; radiographs for erosions. Treat the underlying disease (DMARDs); address TrPs adjunctively."
},
{
"condition": "Anterior capsule strain (hyperextension injury)",
"confidence": "uncommon",
"mimics": "Diffuse anterior elbow pain after a hyperextension event",
"distinguishing_feature": "Diffuse anterior elbow pain and tenderness following hyperextension (a fall, a blocked tackle), worse on terminal extension as the anterior capsule is stretched, without focal tendon-insertion tenderness, mechanical locking, or neurological signs. Usually self-limiting.",
"action": "Exclude fracture/dislocation and biceps rupture; relative rest, NSAIDs, graded return to extension load. Persistent end-range pain warrants imaging for occult osteochondral injury or loose body."
},
{
"condition": "Tenosynovitis (incl. de Quervain's if thumb-dominant)",
"confidence": "uncommon",
"mimics": "Thumb-base or radial pain",
"distinguishing_feature": "Localised tendon-sheath tenderness and swelling; positive Finkelstein's for de Quervain's — brachialis TrP referral to the thumb base gives no Finkelstein's sign.",
"action": "Examine the first dorsal compartment; differentiate from brachialis referral."
},
{
"condition": "Aseptic (olecranon) bursitis",
"confidence": "uncommon",
"mimics": "Elbow swelling and discomfort",
"distinguishing_feature": "Fluctuant POSTERIOR swelling over the olecranon; not an anterior/antecubital muscle pattern. If hot/red/febrile, treat as septic (emergency).",
"action": "Aspirate if the diagnosis is unclear; exclude septic bursitis."
},
{
"condition": "Enthesitis",
"confidence": "atypical",
"mimics": "Tenderness at a tendon/ligament insertion",
"distinguishing_feature": "Insertional tenderness, potentially part of a spondyloarthropathy; consider if multiple entheses or other inflammatory features.",
"action": "Screen for inflammatory arthropathy if multifocal."
},
{
"condition": "Periostitis",
"confidence": "atypical",
"mimics": "Surface bone tenderness with loading",
"distinguishing_feature": "Tenderness over the periosteum with a repetitive-loading history; bony rather than muscular tenderness. Overlaps with stress fracture.",
"action": "Relative rest and imaging if persistent."
},
{
"condition": "Apophysitis",
"confidence": "atypical",
"mimics": "Traction pain at an apophysis (skeletally immature patient)",
"distinguishing_feature": "Adolescent; tenderness at a traction apophysis aggravated by the attached muscle's loading.",
"action": "Activity modification; imaging if uncertain."
},
{
"condition": "Myositis ossificans",
"confidence": "rare",
"mimics": "Persistent firm painful mass after trauma to the arm",
"distinguishing_feature": "Hardening palpable mass weeks after a significant blow/haematoma; radiographic ossification within muscle.",
"action": "Imaging; avoid aggressive massage of the mass; specialist referral."
},
{
"condition": "Chondromalacia (articular cartilage softening)",
"confidence": "rare",
"mimics": "Activity-related joint ache with crepitus",
"distinguishing_feature": "Joint-line symptoms with crepitus on loaded movement; an articular rather than muscular source.",
"action": "Joint assessment and imaging if persistent."
},
{
"condition": "Adhesive capsulitis",
"confidence": "rare",
"mimics": "Painful global restriction referred from the shoulder",
"distinguishing_feature": "Global passive and active restriction of the shoulder capsule; an adjacent-region condition that can refer toward the arm.",
"action": "Assess the shoulder capsular pattern; manage as a shoulder problem."
},
{
"condition": "Subacromial impingement",
"confidence": "rare",
"mimics": "Anterior shoulder pain spilling toward the arm",
"distinguishing_feature": "Painful abduction arc and positive impingement signs at the shoulder; an adjacent-region source.",
"action": "Shoulder examination; treat at the shoulder if confirmed."
},
{
"condition": "Charcot (neuropathic) joint",
"confidence": "rare",
"mimics": "Swollen joint with surprisingly little pain",
"distinguishing_feature": "Marked joint destruction/swelling disproportionate to the (often reduced) pain, on a background of neuropathy (e.g. diabetes).",
"action": "Imaging and management of the underlying neuropathy; specialist referral."
}
]
}