msk.knee-pain.core.v1PRODUCTION

msk.knee-pain.core.v1

Knee pain evaluation (Ottawa knee → OA / internal derangement / crystal / septic)

rheumatologyacutesubacutechronicadult

Hard-required inputs

0 / 10

Care setting:

Encounter flow

12/12 authored

Canonical 12-phase frame with authored status for this dossier.

Current phase

Frame

Detailed

Knee pain is a SYNDROME, not a diagnosis. Two-gate frame: GATE 1 acute trauma → Ottawa Knee Rule decides film vs no film (pooled sens ~98%, spec ~43%, LR− ~0.12 — Kazemi PMID 37215241); GATE 2 phenotype the knee (OA / meniscus / ACL / MCL-PCL / PFP / crystal / septic / referred hip / bursitis-tendinopathy). Population adult; settings ED + outpatient

Inputs

Actions

Advance rule

Set

Advance when

Acute-vs-non-acute and trauma-vs-atraumatic frame established

Patient inputs (18)

age*demographic • CONTEXT

Age ≥55 is an Ottawa Knee Rule criterion; age also shifts the pre-test prior — young/sports → ACL/meniscus/PFP; older → degenerative meniscus/OA; very old + minimal trauma → fragility fracture (Stiell JAMA 1996; Kazemi PMID 37215241)

trauma_mechanism*symptom • CONTEXT

Pivot/deceleration → ACL; valgus contact → MCL; dashboard/posterior force → PCL; hyperextension+dislocation → vascular; twisting with weight-bearing → meniscus — sets the §5.5.2 mechanism prior

immediate_effusion_haemarthrosis*symptom • CONTEXT

Effusion within 0–4 h (haemarthrosis) → high prior for ACL tear / osteochondral fracture / patellar dislocation; slow effusion (12–24 h) → meniscal (Frobell NEJM 2010 PMID 20660401)

ckd_stage*history • CONTEXT

not present

eGFR (CKD-EPI 2021 race-neutral) gates oral NSAID and colchicine dose: avoid NSAID if eGFR <30; reduce colchicine in CKD

cardiovascular_disease*history • CONTEXT

not present

Established CVD/HF/uncontrolled HTN → prefer naproxen or avoid oral NSAID; prefer topical NSAID/acetaminophen

anticoagulant_or_antiplatelet*medication • CONTEXT

not present

Anticoagulant raises NSAID GI-bleed risk AND raises traumatic haemarthrosis risk (lower threshold to image / aspirate)

weight_bearing_4_steps*symptom • RED_FLAGS

Inability to take 4 weight-bearing steps both at injury and in ED is an Ottawa Knee Rule criterion (Stiell JAMA 1996; Kazemi PMID 37215241)

active_knee_flexion_90*symptom • RED_FLAGS

Inability to flex the knee to 90° is an Ottawa Knee Rule criterion

extensor_mechanism_intact*symptom • RED_FLAGS

Inability to actively extend / straight-leg-raise = quadriceps or patellar tendon rupture (palpable gap, patella alta/baja) — a cannot-miss not captured by Ottawa imaging alone

fever_or_systemic_illness*symptom • RED_FLAGS

Fever + monoarticular hot knee = septic arthritis until arthrocentesis excludes it; co-exists with crystal disease (Margaretten JAMA 2007 PMID 17405973)

mechanical_block_to_extensionsymptom • BRANCHING_WORKUP

True locked knee (fixed loss of terminal extension) = displaced bucket-handle meniscal tear or loose body — early surgical referral (AAOS meniscal CPG 2024 PMID 40674138)

knee_mriimaging • BRANCHING_WORKUP

not present

MRI when internal derangement (ACL/meniscus/cartilage) suspected and would change management; not first-line for acute Ottawa triage

sexdemographic • CONTEXT

Female sex raises PFP and non-contact ACL priors; male contact-sport raises ACL/multiligament prior

peptic_ulcer_or_gi_bleedhistory • CONTEXT

not present

PUD / prior GI bleed → COX-2 + PPI or avoid NSAID; informs the comorbidity matrix

tense_effusion_for_aspirationhistory • INITIAL_WORKUP

not present

Tense / painful effusion → diagnostic + therapeutic arthrocentesis (cell count, crystals, Gram/culture)

synovial_fluid_analysislab • INITIAL_WORKUP

Synovial WBC / %PMN / crystals / Gram — the decisive septic-vs-crystal-vs-inflammatory pivot (Margaretten JAMA 2007 PMID 17405973)

knee_radiographimaging • INITIAL_WORKUP

not present

Plain films when Ottawa-positive: fracture, effusion, lipohaemarthrosis (occult fracture), Segond fragment (ACL), chondrocalcinosis (CPPD) (Stiell JAMA 1996)

activity_demand_and_instabilitysymptom • RISK_STRATIFICATION

Functional instability + pivoting-sport / occupational demand drives the ACL shared decision (early reconstruction vs rehab-first) (Frobell NEJM 2010 PMID 20660401)

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (7)

7 need judgement

informationallife_threateningseptic_arthritis_suspicion
Acute hot swollen knee + fever / immunocompromise / prosthetic joint / synovial WBC high — septic arthritis until arthrocentesis excludes it; route to id.osteomyelitis-septic-arthritis.v1 above the treatment threshold (Margaretten JAMA 2007 PMID 17405973; Carpenter Acad Emerg Med 2011 PMID 21843213)
Trigger could not be auto-evaluated — needs clinician judgement.
informationallife_threateningknee_dislocation_vascular_injury
Knee dislocation / multiligament injury / absent or asymmetric distal pulses / ABI <0.9 — popliteal artery injury (limb-threatening)
Trigger could not be auto-evaluated — needs clinician judgement.
informationalsevereextensor_mechanism_rupture
Cannot actively extend the knee / perform straight-leg-raise + palpable gap (quadriceps or patellar tendon rupture) — a cannot-miss not captured by the Ottawa imaging gate alone
Trigger could not be auto-evaluated — needs clinician judgement.
informationalseveretrue_locked_knee_displaced_meniscus
Fixed mechanical block to terminal extension (true locked knee) — displaced bucket-handle meniscal tear or loose body (AAOS meniscal CPG 2024 PMID 40674138)
Trigger could not be auto-evaluated — needs clinician judgement.
informationalmoderateottawa_positive_fracture_screen
Acute knee trauma with ANY Ottawa criterion (age ≥55, isolated patellar tenderness, fibular-head tenderness, cannot flex 90°, cannot bear weight 4 steps) — radiograph indicated (Stiell JAMA 1996; Kazemi PMID 37215241)
Trigger could not be auto-evaluated — needs clinician judgement.
informationalmoderateacl_rupture_activity_based_shared_decision
Confirmed ACL rupture (pivot trauma, immediate haemarthrosis, +Lachman/pivot-shift/Lever-sign) — activity-based shared decision between structured rehab and early reconstruction (Frobell NEJM 2010 PMID 20660401)
Trigger could not be auto-evaluated — needs clinician judgement.
informationalmoderateoral_nsaid_contraindicated_by_comorbidity
eGFR <30 (CKD-EPI 2021), established CVD/HF/uncontrolled HTN, active PUD/recent GI bleed, or concurrent anticoagulant — oral NSAID gated OFF
Trigger could not be auto-evaluated — needs clinician judgement.

Workflow calculators

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RED_FLAGSrequiredDrives screening

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Recommended regimen

Knee pain — phenotype routing + symptomatic analgesia (comorbidity-gated) (Stiell JAMA 1996; AAOS CPGs; JOSPT 2019 PMID 31475628; Frobell NEJM 2010 PMID 20660401)

axis: knee_pain_phenotype_routed_analgesiastep 1 - Step 1 — Exclude/escalate the cannot-miss (no analgesia masks these)

Selected step "Step 1 — Exclude/escalate the cannot-miss (no analgesia masks these)" — Every knee-pain presentation before symptomatic treatment

emergent arthrocentesis + empiric IV antibiotics + orthopaedic washout (septic arthritis)
first line
emergency_procedure
triggers: fever_plus_hot_monoarticular_knee, synovial_WBC_high, gram_stain_positive
Septic arthritis is limb/life-threatening; synovial WBC >50K LR 7.7, >100K LR 28 (Margaretten JAMA 2007 PMID 17405973). Empiric anti-staph cover after cultures; do NOT delay for imaging
knee radiograph per Ottawa Knee Rule
first line
imaging_decision_rule
triggers: ottawa_positive, age_>=55, isolated_patellar_tenderness, fibular_head_tenderness, cannot_flex_90, cannot_bear_weight_4_steps
Pooled sens ~98% (95% CI 96–99), LR− ~0.12 → safely omit films if all 5 negative, ~49% reduction (Kazemi PMID 37215241; Emparanza PMID 11574791)
vascular assessment (pulses + ABI ± CT angiography) for knee dislocation/multiligament
first line
emergency_assessment
triggers: knee_dislocation, multiligament_injury, absent_distal_pulses, high_energy_trauma
Popliteal artery injury accompanies up to ~⅓ of knee dislocations — limb-threatening; serial exam + ABI, CTA if ABI <0.9 (vascular surgery)

outpatient playbook — drug actions (4)

1. phenotype routing (OA → osteoarthritis engine; crystal → gout engine)
n/a • n/a • at diagnosis
trigger: Phenotype assigned
Definitive management lives in the phenotype engine; carryover joint-line/effusion/eGFR/synovial data
2. exercise therapy first (PFP / stable degenerative meniscus)
supervised hip+knee strengthening program • n/a • ≥6 weeks
trigger: Patellofemoral pain or stable degenerative meniscus without locking
JOSPT 2019 strongly recommends exercise therapy first for PFP; injection NOT recommended (PMID 31475628)
3. acetaminophen / topical diclofenac
acetaminophen 1000 mg PO q6h PRN; topical diclofenac 1% gel QID • PO/topical • PRN / QID
trigger: Symptomatic relief, comorbidity-gated
Systemic-sparing first-line; matrix-gated by eGFR/CVD/PUD/anticoagulant
4. short-course oral NSAID (naproxen / ibuprofen)
naproxen 250–500 mg BID OR ibuprofen 400 mg TID • PO • lowest effective dose
trigger: Inadequate topical response AND comorbidity matrix permits
Lowest dose/shortest duration; gated off in CKD/CVD/PUD/anticoagulant (PRECISION PMID 27959716)

Auto-drafted A&P note

outpatient

Subjective

- Possible entry pathways: Acute knee injury (twist / fall / direct blow) — trauma triage gate (Ottawa Knee Rule, Stiell Ann Emerg Med 1995 / JAMA 1996; Kazemi meta-analysis PMID 37215241); Mechanical locking / catching / giving-way — internal derangement (meniscus / ACL / loose body) (AAOS meniscal CPG 2024 PMID 40674138); Acute hot, swollen, painful knee ± fever — septic vs crystal monoarthritis (Margaretten JAMA 2007 PMID 17405973).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Knee pain evaluation (Ottawa knee → OA / internal derangement / crystal / septic)** (msk.knee-pain.core.v1).
Phenotype framing: MECE terminal differential by pivot: OSTEOARTHRITIS (chronic, activity-related, age ≥45, KL osteophytes — route msk.osteoarthritis.core.v1) vs MENISCAL TEAR (twist, joint-line tenderness, +McMurray/Thessaly) vs ACL RUPTURE (pivot trauma, immediate haemarthrosis, +Lachman/pivot-shift) vs MCL/PCL/MULTILIGAMENT (valgus / posterior-force / dislocation — vascular screen) vs PATELLOFEMORAL PAIN (insidious anterior pain, loading-aggravated, JOSPT 2019 PMID 31475628) vs CRYSTAL (acute hot joint, MSU/CPP crystals — route msk.gout-acute.core.v1) vs SEPTIC ARTHRITIS (fever, synovial WBC ladder — Margaretten PMID 17405973) vs REFERRED HIP / L3 radicular (hip exam reproduces pain) vs BURSITIS / TENDINOPATHY (prepatellar/pes anserine/patellar tendon). Named pivots: trauma mechanism, effusion timing, joint-line vs anterior vs diffuse pain, synovial analysis, hip exam
Scope: Knee pain is a SYNDROME, not a diagnosis. Two-gate frame: GATE 1 acute trauma → Ottawa Knee Rule decides film vs no film (pooled sens ~98%, spec ~43%, LR− ~0.12 — Kazemi PMID 37215241); GATE 2 phenotype the knee (OA / meniscus / ACL / MCL-PCL / PFP / crystal / septic / referred hip / bursitis-tendinopathy). Population adult; settings ED + outpatient

No severity triggers fired against current inputs.

Plan

Regimen axis: **Knee pain — phenotype routing + symptomatic analgesia (comorbidity-gated) (Stiell JAMA 1996; AAOS CPGs; JOSPT 2019 PMID 31475628; Frobell NEJM 2010 PMID 20660401)** — step "Step 1 — Exclude/escalate the cannot-miss (no analgesia masks these)".
1. emergent arthrocentesis + empiric IV antibiotics + orthopaedic washout (septic arthritis) (emergency_procedure, first line) — Septic arthritis is limb/life-threatening; synovial WBC >50K LR 7.7, >100K LR 28 (Margaretten JAMA 2007 PMID 17405973). Empiric anti-staph cover after cultures; do NOT delay for imaging
2. knee radiograph per Ottawa Knee Rule (imaging_decision_rule, first line) — Pooled sens ~98% (95% CI 96–99), LR− ~0.12 → safely omit films if all 5 negative, ~49% reduction (Kazemi PMID 37215241; Emparanza PMID 11574791)
3. vascular assessment (pulses + ABI ± CT angiography) for knee dislocation/multiligament (emergency_assessment, first line) — Popliteal artery injury accompanies up to ~⅓ of knee dislocations — limb-threatening; serial exam + ABI, CTA if ABI <0.9 (vascular surgery)

Setting playbook (outpatient) — Phenotype subacute/chronic knee pain (OA / meniscus / ACL / PFP / crystal / referred hip / bursitis-tendinopathy), route to the correct engine or rehab/surgical pathway, and deliver comorbidity-appropriate analgesia (AAOS CPGs; JOSPT 2019 PMID 31475628; Frobell NEJM 2010 PMID 20660401)
4. phenotype routing (OA → osteoarthritis engine; crystal → gout engine) n/a n/a at diagnosis — Phenotype assigned (Definitive management lives in the phenotype engine; carryover joint-line/effusion/eGFR/synovial data)
5. exercise therapy first (PFP / stable degenerative meniscus) supervised hip+knee strengthening program n/a ≥6 weeks — Patellofemoral pain or stable degenerative meniscus without locking (JOSPT 2019 strongly recommends exercise therapy first for PFP; injection NOT recommended (PMID 31475628))
6. acetaminophen / topical diclofenac acetaminophen 1000 mg PO q6h PRN; topical diclofenac 1% gel QID PO/topical PRN / QID — Symptomatic relief, comorbidity-gated (Systemic-sparing first-line; matrix-gated by eGFR/CVD/PUD/anticoagulant)
7. short-course oral NSAID (naproxen / ibuprofen) naproxen 250–500 mg BID OR ibuprofen 400 mg TID PO lowest effective dose — Inadequate topical response AND comorbidity matrix permits (Lowest dose/shortest duration; gated off in CKD/CVD/PUD/anticoagulant (PRECISION PMID 27959716))

Non-pharmacologic actions:
- Sports-medicine/orthopaedic referral for ACL rupture — shared decision rehab-first vs early reconstruction (Frobell NEJM 2010 PMID 20660401; AAOS ACL CPG 2022)
- Surgical referral for true locked knee / displaced bucket-handle meniscal tear (AAOS CPG 2024 PMID 40674138)
- Physiotherapy for PFP (hip+knee strengthening), foot orthoses, patellar taping (JOSPT 2019 PMID 31475628)
- Counsel on post-traumatic OA risk (~50% at 10–20 yr after ACL/meniscus injury) regardless of surgical choice (Lohmander Am J Sports Med 2007 PMID 17761605)
- Examine and, if positive, route hip pathology (referred pain)

AVOID / contraindication checks:
- Matrix:oral_NSAID|eGFR<30(CKD EPI 2021)=>AVOID_oral_NSAID;use_acetaminophen_or_topical_NSAID
- Matrix:oral_NSAID|eGFR_30_59=>lowest_dose_shortest_duration_monitor_eGFR_and_BP
- Matrix:oral_NSAID|established_CVD_or_HF_or_uncontrolled_HTN=>prefer_topical_or_acetaminophen;if_unavoidable_naproxen_lowest_dose (PRECISION Nissen NEJM 2016 PMID 27959716)
- Matrix:oral_NSAID|PUD_or_prior_GI_bleed=>avoid_or_COX2_selective_plus_PPI
- Matrix:oral_NSAID|concurrent_anticoagulant_or_antiplatelet=>prefer_topical_NSAID_or_acetaminophen;anticoagulant_also_lowers_threshold_to_image_and_aspirate_haemarthrosis
- Matrix:colchicine|severe_CKD_or_strong_CYP3A4_PGP_inhibitor=>reduce_or_avoid_dose (crystal flare bridge only)
- Matrix:topical_NSAID|any_systemic_comorbidity=>preferred_systemic_sparing_first_line_for_localised_knee_pain
- Matrix:oral_NSAID|pregnancy=>AVOID_esp_3rd_trimester(ductus_arteriosus_closure_oligohydramnios);prefer_acetaminophen;short_topical_2nd_choice_<20wk_only
- Matrix:colchicine_or_systemic_steroid|pregnancy_or_lactation=>colchicine_compatible_low_dose;prednisone_lowest_effective_short_course;acetaminophen_first_line_analgesic_in_pregnancy_and_lactation
- Matrix:patient|paediatric_or_adolescent=>engine_population_is_adult;in_a_skeletally_immature_or_adolescent_knee_actively_exclude_SLIPPED_CAPITAL_FEMORAL_EPIPHYSIS_and_physeal/avulsion_fracture(referred_hip_pain)_before_treating_as_soft_tissue;route msk.fracture triage.core.v1
- Matrix:oral_NSAID|geriatric=>STOPP/START_avoid_or_minimise_oral_NSAID(fall/renal/GI/CV+anticoagulant_DDI);prefer_topical_NSAID/acetaminophen;deprescribe_chronic_NSAID
- Matrix:oral_NSAID|race neutral_eGFR=>use_CKD EPI_2021(race free)_to_set_the_eGFR_gate (no race coefficient)
- Deprescribe:taper and stop analgesia once phenotype specific therapy controls pain (avoid chronic NSAID/opioid carryover)
- Intra articular steroid only after septic arthritis excluded by synovial gram culture (Margaretten JAMA 2007 PMID 17405973; Carpenter PMID 21843213)
- Do not mask cannot miss with analgesia (septic / extensor rupture / dislocation vascular / compartment screened first)
- No chronic opioids for undifferentiated knee pain (phenotype route instead; flag central sensitisation → msk.fibromyalgia.core.v1)

Monitoring

Regimen monitoring:
- septic arthritis serial exam inflammatory markers and washout response (Margaretten JAMA 2007 PMID 17405973)
- acl rehab first track instability quadriceps KOOS convert to delayed reconstruction if unstable (Frobell BMJ 2013 PMID 23349407)
- eGFR BP GI symptoms on oral NSAID (CKD-EPI 2021)
- WOMAC pain function if OA phenotype (route msk.osteoarthritis.core.v1)
- post aspiration or injection reaccumulation and infection signs

Setting (outpatient) monitoring:
- ACL rehab-first: instability episodes, quadriceps strength, KOOS — convert to delayed reconstruction if unstable (Frobell BMJ 2013 PMID 23349407)
- PFP/OA: pain/function (WOMAC) trajectory + exercise adherence
- eGFR, BP, GI symptoms while on oral NSAID (CKD-EPI 2021)
- Re-evaluate diagnosis if no improvement at 6 weeks of phenotype-specific therapy

Follow-up plan: Phenotype-specific: ACL — re-evaluate need for delayed reconstruction by activity/instability; counsel on post-traumatic OA risk (~50% at 10–20 yr after ACL/meniscus injury — Lohmander Am J Sports Med 2007 PMID 17761605) regardless of surgical choice. Meniscus — recovery expectations, OA-risk counselling, preserve meniscal tissue if operated (AAOS CPG 2024 PMID 40674138). PFP — long-term exercise maintenance (relapsing course — JOSPT 2019 PMID 31475628). OA — route msk.osteoarthritis.core.v1 chronic pathway. Return precautions: fever + hot joint, locking, recurrent giving-way, inability to extend
- Close-out criterion: Long-term phenotype plan + OA-risk counselling + return precautions booked

Monitoring phase: Septic: serial exam, inflammatory markers, repeat aspiration/washout response. ACL rehab-first: track instability episodes, quadriceps strength, KOOS — convert to delayed reconstruction if functional instability persists (Frobell BMJ 2013 PMID 23349407). PFP/OA: pain/function trajectory (WOMAC), exercise adherence. On oral NSAID: surveil eGFR, BP, GI symptoms (CKD-EPI 2021). Post-injection / post-aspiration: re-accumulation, infection signs

Disposition

Current setting: outpatient — Phenotype subacute/chronic knee pain (OA / meniscus / ACL / PFP / crystal / referred hip / bursitis-tendinopathy), route to the correct engine or rehab/surgical pathway, and deliver comorbidity-appropriate analgesia (AAOS CPGs; JOSPT 2019 PMID 31475628; Frobell NEJM 2010 PMID 20660401)

Disposition criteria:
- Continue outpatient phenotype-specific care if improving
- Refer to ortho/sports-med for surgical phenotypes (locked meniscus, unstable ACL, refractory)
- Route OA phenotype to msk.osteoarthritis.core.v1 and crystal to msk.gout-acute.core.v1

Escalation triggers (move to higher acuity):
- New fever + hot effused knee → ED arthrocentesis (septic arthritis — Margaretten JAMA 2007 PMID 17405973)
- New true locking / inability to extend → urgent surgical referral (displaced meniscus / loose body)
- Recurrent giving-way despite rehab → orthopaedic ACL reconstruction discussion
- Refractory PFP/OA despite optimised conservative therapy → specialist / arthroplasty pathway (route msk.osteoarthritis.core.v1)

Patient Action Plan

**Knee pain self-management + safety-net plan**
Personalised values: phenotype_diagnosis, rehab_or_surgical_plan, analgesic_plan, comorbid_CKD_CVD_PUD, activity_goal.

**Stable — improving with the agreed plan** (green):
Triggers:
- Pain manageable with simple analgesia / topical gel
- Doing the prescribed exercise/rehab program
- No locking, giving-way, fever, or new swelling
Actions:
- Keep doing your rehabilitation exercises — for kneecap pain and many ACL/meniscus injuries this is the main treatment (JOSPT 2019; Frobell NEJM 2010)
- Use topical anti-inflammatory gel or paracetamol rather than anti-inflammatory tablets when possible, especially if you have kidney/heart/stomach problems
- Build activity back gradually as comfort allows
- Keep your follow-up appointment to confirm the diagnosis and recheck progress

**Flare or not improving** (yellow):
Triggers:
- Pain or swelling worsening or not improving after a few weeks of the plan
- Knee feels unstable or gives way occasionally
- Difficulty with stairs / squatting increasing
Actions:
- Relative rest and ice; continue gentle range-of-motion within comfort
- Optimise simple analgesia; only add an anti-inflammatory tablet at the lowest dose if your kidney/heart/stomach history allows (ask first)
- Contact your clinician to review the plan and consider imaging or specialist referral
- If a sports/ACL injury, ask whether the rehab vs surgery plan should be revisited
Contact provider when:
- No improvement within ~6 weeks of the agreed plan
- Repeated giving-way or the knee locking briefly
- Side effects from medication (stomach pain, ankle swelling, BP rise)

**Possible emergency — seek urgent care now** (red):
Triggers:
- Hot, very swollen, painful knee with fever (possible joint infection)
- Cannot straighten or lift the leg / locked knee that will not move (tendon rupture or trapped cartilage)
- Knee that came out of joint, a cold/pale/numb lower leg, or severe calf tightness after injury
- Cannot bear any weight after an injury
Actions:
- A hot swollen knee with fever — go to the emergency department now (this needs joint fluid testing to exclude infection — Margaretten JAMA 2007)
- Unable to straighten/lift the leg or a locked knee — urgent assessment for tendon rupture or a trapped meniscus
- Dislocated knee or cold/numb/pale lower leg — call emergency services immediately (possible artery injury)
Contact provider when:
- Always seek emergency care for fever + a hot swollen joint, a dislocated knee, or a cold/numb leg

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Acute hot swollen knee + fever / immunocompromise / prosthetic joint / synovial WBC high — septic arthritis until arthrocentesis excludes it; route to id.osteomyelitis-septic-arthritis.v1 above the treatment threshold (Margaretten JAMA 2007 PMID 17405973; Carpenter Acad Emerg Med 2011 PMID 21843213)
- [LIFE_THREATENING] Knee dislocation / multiligament injury / absent or asymmetric distal pulses / ABI <0.9 — popliteal artery injury (limb-threatening)
- [SEVERE] Cannot actively extend the knee / perform straight-leg-raise + palpable gap (quadriceps or patellar tendon rupture) — a cannot-miss not captured by the Ottawa imaging gate alone

Citations

- Ottawa Knee Rule (Stiell et al, Ann Emerg Med 1995 / JAMA 1996; pooled meta-analysis Kazemi Arch Acad Emerg Med 2023) + AAOS Acute Isolated Meniscal Pathology CPG 2024 + AAOS ACL CPG 2022 + JOSPT 2019 Patellofemoral Pain CPG + Margaretten JAMA Rational Clinical Examination (septic arthritis) 2007 + Carpenter Acad Emerg Med 2011 evidence-based diagnostics (septic-arthritis interval LRs, conditional host-dependence, T_test/T_treat thresholds) [PMID:37215241](https://pubmed.ncbi.nlm.nih.gov/37215241/)
- Cited evidence (PMID 11574791) [PMID:11574791](https://pubmed.ncbi.nlm.nih.gov/11574791/)
- Cited evidence (PMID 12827123) [PMID:12827123](https://pubmed.ncbi.nlm.nih.gov/12827123/)
- Cited evidence (PMID 20378739) [PMID:20378739](https://pubmed.ncbi.nlm.nih.gov/20378739/)
- Cited evidence (PMID 32567156) [PMID:32567156](https://pubmed.ncbi.nlm.nih.gov/32567156/)

Last reconciled with current guidelines: 2026-05-22.

References

Ottawa Knee Rule (Stiell et al, Ann Emerg Med 1995 / JAMA 1996; pooled meta-analysis Kazemi Arch Acad Emerg Med 2023) + AAOS Acute Isolated Meniscal Pathology CPG 2024 + AAOS ACL CPG 2022 + JOSPT 2019 Patellofemoral Pain CPG + Margaretten JAMA Rational Clinical Examination (septic arthritis) 2007 + Carpenter Acad Emerg Med 2011 evidence-based diagnostics (septic-arthritis interval LRs, conditional host-dependence, T_test/T_treat thresholds) — PMID:37215241
Cited evidence (PMID 11574791) — PMID:11574791
Cited evidence (PMID 12827123) — PMID:12827123
Cited evidence (PMID 20378739) — PMID:20378739
Cited evidence (PMID 32567156) — PMID:32567156