What should be checked before relying on a WPI figure?
Check maximum medical improvement, the body area, objective findings, the NSW Guideline chapter and any NSW modification before relying on a percentage.
Can this page calculate your percentage?
No. WPI depends on an assessor, maximum medical improvement, objective findings and the NSW Guidelines. This page is general information only.
Permanent impairment assessment
How permanent impairment is assessed for Total knee replacement, hemiarthroplasty and replacement scoring
Knee replacement WPI is a scoring exercise. The corrected NSW table looks at pain, ROM, anteroposterior stability, mediolateral stability and deductions for flexion contracture, extension lag and alignment. The operation name alone does not set the WPI.
What injuries can happen to this body part?
- Total knee replacement after traumatic arthritis, tibial plateau fracture, meniscus/cartilage loss or osteoarthritis aggravation
- Knee hemiarthroplasty where the corrected NSW knee replacement scoring method applies
- Residual pain, stiffness, instability, extension lag, flexion contracture or malalignment after replacement
Symptoms and findings that matter
- Pain category and whether it occurs with walking, stairs or continually
- ROM score, with 1 point per 5 degrees to a maximum of 25 points
- Anteroposterior and mediolateral stability
- Flexion contracture, extension lag and alignment deductions
- Comparison with the unaffected limb where constitutional alignment is relevant
What investigations are usually relevant?
- Treating specialist report and final impairment assessment at maximum medical improvement
- Imaging, pathology, audiology, ophthalmology, respiratory, nerve or functional testing that fits the body system
- Operative reports, discharge summaries, rehabilitation records and objective clinical measurements where relevant
How WPI is assessed for this body part
- Knee replacement WPI is a scoring exercise. The corrected NSW table looks at pain, ROM, anteroposterior stability, mediolateral stability and deductions for flexion contracture, extension lag and alignment. The operation name alone does not set the WPI.
- Assessment source: NSW Guidelines Chapter 3 paragraph 3.29 and corrected Table 17-35 for knee replacement scoring. The local source verifies the scoring elements and deductions, but not every final conversion threshold.
- The assessor should explain maximum medical improvement, the body-system chapter, the method selected, any NSW modification, and why the objective findings fit that method.
How movement affects the assessment
- Knee flexion affects stairs, kneeling, squatting and low chairs.
- Extension lag and flexion contracture can reduce the score after replacement and affect standing/walking efficiency.
NSW corrected knee replacement scoring elements
Pain, ROM and stabilityThe corrected NSW Table 17-35 scores pain, ROM, anteroposterior stability and mediolateral stability before deductions.
ROM scoreAdd 1 point for each 5 degrees of knee motion, to a maximum of 25 points, under the corrected NSW table.
Flexion contracture deductionDeduct 2, 5, 10 or 20 points for flexion contracture from 5-9, 10-15, 16-20 or more than 20 degrees.
Extension lag deductionDeduct 5, 10 or 15 points for extension lag below 10, 10-20, or more than 20 degrees.
Alignment deductionAlignment deductions apply for varus or out-of-range valgus; constitutional variation should be checked against the unaffected limb.
NSW patello-femoral rules
Isolated patello-femoral joint replacementAssess the knee in the usual way and combine with 9% WPI (22% lower extremity impairment) where the NSW criteria apply.
Direct front-of-knee injury or translocationPatello-femoral arthritis rows should be used only where the NSW history criteria are met.
Crepitus timingPatello-femoral crepitus needs to be present at least one year after injury before it is used in the limited NSW context.
No double countPatello-femoral osteoarthritis is not an additional impairment when arthritis of the knee joint itself is being assessed.
NSW lower limb global rules
Most specific method firstUse the method that most specifically addresses the lower limb impairment where possible, rather than a broad fallback label.
Highest valid assessmentWhere more than one valid lower limb method applies, the NSW Guidelines generally require the assessment that gives the highest valid rating, unless a specific rule prevents it.
Do not exceed amputation valueA lower limb part or region cannot exceed the applicable amputation value. The whole lower limb maximum is 40% WPI, except where a specific gait table gives WPI directly.
Gait derangement is last resortGait derangement should be used only as a last resort and cannot be combined with other lower extremity assessment methods.
Permanent walking aid onlyIf a walking aid is relied on, the evidence should show permanent use, not a temporary aid during treatment or recovery.
ROM reliabilityROM can be unreliable where effort, pain behaviour or inconsistency affects measurement. The opposite side should be compared where relevant.
Arthritis needs imagingArthritis/cartilage loss must be radiologically assessed. Pain, crepitus or a broad MRI comment is not enough by itself.
Lower limb ROM and consistency rules
Use ROM only where validROM should be used only where the measurements are consistent and clinically reliable.
Same joint planesMultiple valid planes within the same lower limb joint are added, not combined, under the NSW lower limb method.
Opposite side comparisonIf the opposite side has reduced average mobility, the assessor should explain whether baseline deduction or comparison is needed.
Knee varus/valgus with arthritisVarus or valgus deformity due to compartment arthritis is not combined with ROM; both are calculated and the greater valid value is used.
NSW gait derangement limits
Last resort onlyUse gait derangement only where no more specific lower limb method adequately assesses the impairment.
No combinationDo not combine gait derangement with another lower extremity method such as ROM, arthritis, muscle atrophy, nerve impairment or replacement scoring.
Pathological supportThe gait finding should be supported by objective pathology and examination findings, not only subjective walking difficulty.
Trendelenburg deletionNSW deletes the Trendelenburg item in AMA5 Table 17-5 because it is considered insufficiently reliable.
Practical WPI examples
- A knee replacement with good alignment and stability can score differently from one with severe pain, instability or extension lag.
- A patello-femoral replacement is not assessed as a generic total knee replacement; NSW has a separate patello-femoral rule.
- A poor functional result must be supported by clinical findings and the corrected scoring table, not only by the worker being unhappy with surgery.
Evidence checklist
- A clear diagnosis and the body area being assessed
- Records showing the condition has reached maximum medical improvement, if that is the issue
- Specialist reports, imaging reports and treating notes relied on by the assessor
- Objective findings on examination, not only symptoms described by the injured person
- A work and treatment chronology explaining the injury, treatment, surgery and recovery path
- Any previous injury, degeneration, congenital issue or non-work cause that needs apportionment considered
- Operation report
- Post-operative X-rays
- Orthopaedic review
- ROM and stability measurements
- Physiotherapy notes
- Alignment comments
- Work capacity certificates
What usually does not increase WPI
- Assuming a scan result automatically gives a WPI percentage
- Confusing pain, disability or inability to work with permanent impairment
- Ignoring maximum medical improvement before arranging an assessment
- Using an AMA5 table without checking whether the NSW Guidelines modify or replace it
- Double counting the same impairment through two methods when the Guidelines require one method
- Assuming every knee replacement has the same WPI
- Missing extension lag or alignment deductions
- Adding gait derangement to the replacement result
Assessment source
Assessment source: Assessment source: NSW Guidelines Chapter 3 paragraph 3.29 and corrected Table 17-35 for knee replacement scoring. The local source verifies the scoring elements and deductions, but not every final conversion threshold.
This section is source-backed general information. It is not a WPI assessment and is not legal advice.
- SIRA NSW Workers Compensation Guidelines for the Evaluation of Permanent Impairment: Source for the NSW assessment framework, MMI, AMA5 adoption, NSW modifications and exclusions.
- SIRA lower extremity chapter: Source for NSW lower extremity assessment rules, gait derangement limits and NSW-modified lower limb tables.
Related injury and claim pages
Need a practical claim check?
If an impairment percentage, medical assessment or insurer decision is affecting your NSW injury claim, send the decision or report for a practical review. This is general information only and does not guarantee any result.
Request a free claim checkAssessment scope for Joint Replacement WPI Assessment
The assessment scope for Joint Replacement WPI Assessment should be stated precisely before any percentage is considered. The file should identify whether that label describes the primary diagnosed condition, a symptom of another injury, a regional overview or one component of a broader impairment. Findings from another body area or diagnosis should not be transferred without explanation. The report should connect the stated condition to the correct NSW Guideline chapter, objective findings, treatment history and any permitted combination or apportionment method. This distinction is particularly important where similar page labels cover different clinical questions.
- Confirm the diagnosis and body area being assessed as Joint Replacement
- Separate condition-specific findings from overlapping symptoms or injuries in another body area
- Check that the selected NSW Guideline chapter and method match the condition actually assessed
- Explain any combination, apportionment or exclusion rather than relying on the page label alone
Clinical boundary for this WPI guide
A joint-replacement enquiry must start by naming the replaced joint; a hip, knee or ankle replacement is not assessed by transferring findings from another joint. The prosthesis, operation, revision history and current function should be matched to the body-system method that applies to that joint. This overview is useful when the file contains more than one replacement or an unclear label, but the final report should use joint-specific examination and records.
- Identify each replaced joint, side, procedure and revision date
- Use examination and imaging relevant to that particular prosthesis
- Do not transfer knee-replacement findings to a hip or ankle replacement
- Check whether gait or another joint is a consequence, separate impairment or overlap
Start with maximum medical improvement
Permanent impairment should generally be assessed when the condition is stable and unlikely to change substantially in the next year. Treatment, surgery and rehabilitation history may affect whether the timing is appropriate.
Use the NSW Guidelines first
The NSW Guidelines adopt AMA5 in many areas, but NSW modifications prevail. Do not assume an AMA5 table applies without checking the NSW chapter and any public SIRA clarification.
Keep the assessment practical
A useful assessment file separates diagnosis, objective findings, surgery history, work capacity issues, apportionment questions and the body-area method used by the assessor.
Ask about an impairment issueDocuments and records
Injury evidence to organise early
The useful records depend on how the injury happened, when symptoms were recorded and how treatment or work capacity changed.
- Date, location and short description of the injury event
- Medical certificates, reports, scans, treatment records or hospital documents
- Employer, insurer, police, incident or venue records where relevant
- Photos, witness details, dashcam or other supporting material if available
- Income, superannuation, work capacity or leave records where relevant
- Letters, emails, claim numbers and decisions already received
Common questions
Injury evidence questions
Short general answers only. The right next step depends on the facts, dates and documents.
Is WPI the same as being unable to work?
No. WPI is a medical impairment measure. Work capacity, weekly payments, damages, treatment disputes and TPD issues are separate questions, although the evidence may overlap.
Does pain alone create a WPI percentage?
Not by itself. NSW workers compensation excludes AMA5 Chapter 18 on pain. Chronic pain is assessed through the underlying diagnosed condition where the Guidelines permit it.
Can secondary psychological symptoms be added to physical WPI?
In NSW workers compensation, secondary psychiatric or psychological impairment is not assessed as permanent impairment. Primary psychological impairment is assessed separately and is not combined with physical WPI.
Injury pathway enquiry
Not sure which claim type matches the injury?
Start with how the injury happened, what medical records exist and how work or daily activity has changed. The same injury can sit in different pathways.