When to refer a knee injury: a guide for GPs and physios
A desk reference for an adult with an acute knee injury: who needs an X-ray, who needs same-day care, and who needs an orthopaedic review. Children are covered only where stated.
Send any suspected knee dislocation, hot swollen joint or cold foot the same day. Rapid swelling after a twisting injury means a structural injury until proven otherwise.
Who needs an X-ray: the Ottawa knee rule
After an acute knee injury in an adult, an X-ray is needed only if any of these is present:
- age 55 or over
- isolated tenderness at the head of the fibula
- isolated tenderness of the patella
- unable to flex the knee to 90°
- unable to take 4 weight-bearing steps both right after the injury and when seen; limping counts as bearing weight
| Study | Sensitivity | Specificity |
|---|---|---|
| Validation, Canada, 1,096 adults | 100% | not reported |
| Bachmann review, 4,249 adults | 98.5% | 48.6% |
| Sims meta-analysis, 7,385 patients | 99% | 49% |
The rule is good at ruling a fracture out, not at ruling one in. It has no Indian validation study, and it was not studied in children.
The Pittsburgh knee rule is an alternative. In one multicentre comparison of 934 patients in the USA, Pittsburgh had sensitivity 99% and specificity 60%, against 97% and 27% for Ottawa.
Imaging
The American College of Radiology Appropriateness Criteria for acute knee trauma, 2020, say:
- radiographs are the first test
- CT helps plan complex tibial plateau and distal femur fractures
- MRI is the study of choice for internal derangement and bone bruising
An MRI is not needed before referral. If one is already done, send the images and the report.
Orthopaedic review soon
Acute haemarthrosis
Rapid swelling within hours of a twisting injury means a serious structural injury until proven otherwise.
| Group | Finding |
|---|---|
| 106 sportsmen, 1993, men only | ACL partly or completely torn in 67% |
| 117 children aged 9 to 14 | 70% had a serious injury; 39% had a normal X-ray but a serious injury on MRI |
Also refer soon
- suspected ACL tear: a pop, rapid swelling, giving way, or a positive Lachman test
- suspected first-time patellar dislocation
- a child or teenager with a swollen knee after injury, even with a normal X-ray
Bedside ACL tests
From a 2022 meta-analysis:
| Test | Sensitivity | Specificity |
|---|---|---|
| Lachman | 81% | 85% |
| Anterior drawer | 83% | 85% |
| Pivot shift | 55% | 94% |
| Lever sign | 83% | 91% |
Lachman is less accurate after the acute phase: sensitivity 70%, specificity 77%. A normal test does not rule out a tear in a swollen, guarded knee. Re-examine or refer.
Routine referral
- pain or giving way that persists despite good physiotherapy, or recurrent giving way
- catching or intermittent locking, without a locked knee
- an older adult with a degenerative meniscus tear on MRI and no locking: the ESSKA meniscus consensus defines degenerative tears as those in people over 35 with no significant trauma, and favours physiotherapy first
Sending a patient
Call Aggarwal Clinic on +91 98768 24676. Send reports and X-ray images by WhatsApp to +91 84477 30708.
Aggarwal Clinic, 1-E, The Mall, Patiala. Dr Aditya Aggarwal, orthopaedic surgeon.
References
- Ottawa knee rule: derivation, validation and reviews: PMID 7574120, PMID 8594242, PMID 14734335, PMID 32222797
- Ottawa and Pittsburgh rules compared: PMID 9656942
- ACR Appropriateness Criteria, acute trauma to the knee, 2020: PMID 32370956
- Knee dislocation: vascular and nerve injury, systematic review: PMID 24554457
- Hot swollen joint in adults, BSR/BHPR/BOA/RCGP/BSAC guideline, 2006: PMID 16829534
- Acute haemarthrosis: adults and children: PMID 8245089, PMID 24753236
- Bedside ACL tests, meta-analyses: PMID 35150292, PMID 16715828
- Degenerative meniscus tears, ESSKA consensus: PMID 28210788
For healthcare professionals. Not medical advice for individual patients. Last reviewed 26 October 2026.