12-phase flow (12)

1. 1FRAME
   OA is a CLINICAL diagnosis in the typical patient (age ≥45, activity-related pain, ≤30 min stiffness, no systemic inflammatory features) — imaging NOT required; Kellgren–Lawrence grade is a structural anchor, not a diagnostic gate (NICE NG226 2022; ACR/AF 2019 Kolasinski PMID 31908163). Scope: knee, hip, hand (incl. erosive hand OA), with/without inflammatory component
   inputs: age, morning_stiffness_duration
   advance: Phenotype scope set and clinical-vs-imaging frame established
2. 2ENTRY
   Activity-related knee/hip/hand pain (worse with use, better with rest); short morning stiffness / post-rest gelling; bony enlargement (Heberden/Bouchard/1st-CMC); incidental KL osteophytes; or an explicit OA-vs-inflammatory differentiation request (ACR/AF 2019; Altman 1986 PMID 3741515)
   inputs: age, joint_distribution
   advance: Engine entered via a recognised OA trigger
3. 3CONTEXT
   Capture age, sex, BMI, occupational/recreational joint load, prior joint injury, function/QoL targets, AND the comorbidity inventory that GATES pharmacotherapy: CKD stage (eGFR CKD-EPI 2021 race-neutral), cardiovascular disease/HF/HTN, PUD/GI-bleed history, concurrent anticoagulant/antiplatelet, current analgesic regimen (ACR/AF 2019; OARSI 2019 PMID 31278997)
   inputs: age, bmi, morning_stiffness_duration, ckd_stage, cardiovascular_disease, peptic_ulcer_or_gi_bleed, anticoagulant_or_antiplatelet
   actions: calc.ckd_epi_2021
   advance: Risk profile + comorbidity gating matrix inputs captured
4. 4RED_FLAGS
   NOT an OA pathway, escalate: acute hot swollen joint + fever = septic arthritis → STAT arthrocentesis + empiric cover; rapidly destructive / atypical age or onset; true mechanical locking (loose body / displaced meniscal tear); inflammatory pattern (prolonged stiffness, symmetric small-joint synovitis, constitutional symptoms) → re-route to inflammatory/crystal engines (ACR/AF 2019; EULAR)
   inputs: hot_swollen_joint_with_fever, constitutional_symptoms
   actions: workup.acute_monoarthritis, panel.synovial, panel.inflammation
   advance: Septic / inflammatory / mechanical-block mimics screened and escalated if present
5. 5INITIAL_WORKUP
   Usually NONE — OA is diagnosed clinically (NICE NG226 2022). Selective only: ESR/CRP + RF/anti-CCP to EXCLUDE inflammatory arthritis when the pattern is atypical; eGFR (CKD-EPI 2021) BEFORE any oral NSAID; synovial fluid analysis if an effusion is aspirated (OA = non-inflammatory, WBC <2000, no crystals). Do not order radiographs to confirm typical OA (NICE NG226 2022)
   inputs: esr_crp, synovial_fluid_analysis
   actions: workup.osteoarthritis, panel.inflammation, panel.renal, panel.synovial, calc.ckd_epi_2021
   advance: Inflammatory mimic excluded clinically/serologically; NSAID-eligibility eGFR known
6. 6BRANCHING_WORKUP
   Phenotype-specific only when indicated: weight-bearing radiograph → Kellgren–Lawrence grade ONLY if atypical / pre-surgical / diagnostically uncertain (KL ≥2 = definite osteophyte + JSN; structural anchor, not a treatment gate); knee-pain branch for mechanical/effusion features; erosive hand OA → central "gull-wing" erosions of DIP/PIP (ACR/AF 2019; NICE NG226 2022)
   inputs: plain_radiograph_kl_grade
   actions: workup.knee_pain, calc.kl_grade
   advance: Phenotype confirmed; KL grade obtained only where it would change management
7. 7DIFFERENTIAL
   MECE terminal differential — OA vs rheumatoid arthritis (symmetric MCP/wrist synovitis, stiffness >60 min, RF/anti-CCP+, ESR/CRP↑) vs gout/CPPD (acute hot monoarthritis, podagra, synovial crystals) vs psoriatic/reactive arthritis vs septic arthritis vs avascular necrosis vs referred/neuropathic pain vs secondary OA (haemochromatosis, alkaptonuria). Named pivots: morning-stiffness duration, joint distribution, inflammatory markers, constitutional symptoms (Altman 1986 PMID 3741515)
   inputs: joint_distribution, morning_stiffness_duration, rf_anti_ccp
   advance: Terminal diagnosis assigned (clinical criteria + selective serology + named pivots)
8. 8RISK_STRATIFICATION
   WOMAC pain/function severity (calc.womac_oa_index) for treatment intensity; KL grade as structural context; eGFR-driven oral-NSAID eligibility tier; function-limiting refractory disease despite optimised conservative therapy = arthroplasty-referral threshold (Skou NEJM 2015 PMID 26488691)
   inputs: function_and_refractoriness, ckd_stage
   actions: calc.womac_oa_index, calc.kl_grade, calc.ckd_epi_2021
   advance: Severity tier + NSAID-eligibility tier + surgical-candidacy flag documented
9. 9TREATMENT
   Core non-pharm is FIRST-LINE for every phenotype: structured patient education/self-management + structured land-based exercise (knee pain SMD −0.49, Fransen Cochrane 2015 PMID 25569281) + weight loss ≥5–10% if BMI ≥25 (IDEA Messier JAMA 2013 PMID 24065013) + assistive devices/bracing/hand orthoses. THEN topical NSAID (strong first-line drug, knee & hand — ACR/AF 2019; OARSI Level 1A). THEN oral NSAID at the LOWEST effective dose, comorbidity-gated by the encoded matrix (eGFR <30 avoid; CVD prefer naproxen; PUD/anticoagulant → COX-2 + PPI). Adjuncts: duloxetine (centralised/multi-joint/NSAID-limited — Chappell PMID 20602715), intra-articular glucocorticoid (short-term knee relief, NNTB 8, Jüni Cochrane 2015 PMID 26490760; interval-capped — 2017 McAlindon JAMA cartilage-volume signal PMID 28510679), acetaminophen (weak adjunct only). AVOID glucosamine/chondroitin (GAIT PMID 16495392), intra-articular hyaluronic acid (Rutjes PMID 22868835), oral/transdermal opioids (ACR/AF 2019 / OARSI strong against)
   inputs: bmi, ckd_stage, cardiovascular_disease, peptic_ulcer_or_gi_bleed, anticoagulant_or_antiplatelet
   actions: calc.ckd_epi_2021, calc.womac_oa_index
   advance: Core non-pharm engaged + comorbidity-appropriate pharmacotherapy selected (or surgical pathway entered)
10. 10DISPOSITION
    Outpatient throughout — OA is not an admitting diagnosis. Orthopaedic referral for total knee/hip arthroplasty when conservative therapy is exhausted AND pain/function is refractory and life-limiting (Skou NEJM 2015 PMID 26488691); admit only for a complication (septic joint, post-injection sepsis, surgical pathway)
    inputs: function_and_refractoriness
    advance: Care level set; surgical referral placed if threshold met
11. 11MONITORING
    Track pain/function trajectory (WOMAC), exercise & weight-loss adherence; on oral NSAID surveil renal function (eGFR), BP, and GI symptoms; cap intra-articular glucocorticoid frequency (effect decays by 13–26 wk, repeated scheduled injection → cartilage loss — McAlindon JAMA 2017 PMID 28510679); reassess weight (1 kg loss reduces knee load ~4 kg/step) (ACR/AF 2019; OARSI 2019 PMID 31278997)
    inputs: ckd_stage, function_and_refractoriness
    actions: calc.womac_oa_index, calc.ckd_epi_2021, panel.renal
    advance: Response and drug-safety surveillance plan running
12. 12FOLLOWUP
    Chronic self-management with periodic reassessment; deprescribe analgesics that lack benefit (especially opioids — ACR/AF 2019 against); maintain exercise + weight; re-refer to orthopaedics if progressive functional decline; revisit surgical timing using shared decision-making (benefit vs serious-AE trade-off — Skou NEJM 2015 PMID 26488691)
    inputs: function_and_refractoriness
    advance: Long-term self-management + deprescribing + surgical-timing plan booked