Knee instability
ACL, PCL, MCL and LCL injury after a motor accident
Knee ligament WPI depends on permanent objectively measured laxity, not the MRI or reconstruction name. Each cruciate and collateral injury must be identified, and the special clause 6.98 rule applies only to its stated mild combined-laxity scenario.
Motor accident injury
How can this injury happen?
Car or passenger collision
Dashboard loading can injure the PCL, while twisting or cabin intrusion can injure ACL and collateral ligaments.
Motorcycle accident
A planted foot, valgus/varus force or hyperextension during a fall can injure one or several ligaments.
Pedestrian or cyclist impact
Bumper impact can create collateral force, with the fall adding cruciate or meniscus injury.
Injuries that can occur
- ACL or PCL partial/complete rupture
- MCL or LCL partial/complete rupture
- posterolateral corner or multiligament injury
- associated meniscus, cartilage or tibial plateau injury
- post-reconstruction stiffness or instability
Symptoms and functional problems
- giving way during turning or uneven ground
- swelling and loss of confidence loading the knee
- difficulty pivoting, stairs or physical work
- restricted flexion or extension after reconstruction
Seek urgent medical assessment
Knee dislocation, absent pulse, major neurological loss or suspected multiligament vascular injury requires emergency assessment.
Clinical evidence
What findings matter?
The assessor should document which ligament is injured and the residual grade of laxity using reproducible clinical testing. MRI and operative reports identify anatomy but do not replace current stability findings.
| Record or examination | What it may establish | What it cannot prove alone |
|---|---|---|
| Lachman, drawer and stress testing | Records ACL, PCL, MCL or LCL laxity and endpoints. | Subjective giving way does not establish the Table 64 category. |
| MRI and operative report | Shows rupture, associated meniscus/cartilage injury and reconstruction. | Graft presence or tear label is not WPI. |
| Active ROM and functional testing | Records post-operative stiffness and practical stability. | Do not rate the same loss under both ROM and diagnosis methods. |
Movement in daily life
How movement affects real activities
Ligament injury affects stable direction change and loading. Flexion and extension remain relevant after reconstruction, but measured laxity may be the more specific residual method.
Flexion and extension
Sitting, stairs, kneeling and stable walking.
Table 41 is used only where permanent ROM loss is the valid specific impairment.
Cruciate stability
Stopping, changing direction and controlling forward/backward tibial movement.
Objective ACL or PCL laxity may use the applicable Table 64 row.
Collateral stability
Side-to-side control on uneven ground and during impact loading.
Objective MCL or LCL laxity is assessed separately where the table and clause apply.
Threshold injury is a separate question: a verified partial or complete ligament rupture is excluded from the soft tissue definition. Sprain without rupture may be threshold.
Part 6 permanent impairment
How is CTP WPI assessed?
Diagnosis-based estimates use Table 64 and its footnotes. Clause 6.98 expressly states that mild collateral and mild cruciate laxity are each assessed at 3% WPI and then combined to 6% WPI. That verified example must not be extrapolated to other grades.
Measurement rules that apply
- Clauses 6.69 and 6.70 require the method that most specifically addresses the lower-limb impairment. Gait should not replace a joint, nerve, fracture or replacement method that can be applied reliably.
- Clause 6.84 requires active range of motion, a goniometer where clinically indicated and consistent repetitions when reliability is uncertain. Passive movement may inform the examination but does not set the impairment value.
- Clause 6.85 says only the most severe deficit in one direction or axis from the same lower-limb ROM table is rated. Deficits from separate tables may be combined only as the Guidelines permit.
| Method | CTP source | When it is relevant | Important limit |
|---|---|---|---|
| Diagnosis-based ligament laxity | Clauses 6.94-6.98; Table 64 | Permanent objectively measured cruciate or collateral laxity. | Exact rows beyond clause 6.98 require readable AMA4. |
| Mild collateral plus cruciate rule | Clause 6.98 | Both mild collateral and mild cruciate laxity are present. | 3% WPI each, combined to 6% WPI only in that stated scenario. |
| Knee ROM | Table 41; clauses 6.84-6.85 | Separate permanent post-operative movement loss. | Avoid duplication with the diagnosis-based result. |
- Identify each ligament and severity.
- Assess a separate meniscus or tibial plateau injury under clause 6.71.
- Use Table 6.5 before combining methods.
What cannot be combined?
- ROM and ligament method for the same consequence
- gait with any other lower-limb evaluation
- unverified extrapolation from clause 6.98 to moderate or severe laxity
What does not establish WPI by itself?
- MRI rupture
- reconstruction surgery
- subjective instability
- brace use alone
Motor accident examples
PCL dashboard injury with mild MCL laxity
Clause 6.98 applies only if the residual findings meet mild collateral plus mild cruciate laxity; each is 3% WPI and the stated combined result is 6%.
ACL reconstruction with stable knee but flexion loss
The operation does not set WPI. The assessor identifies whether ROM is the valid residual method.
Claim file preparation
Evidence checklist
Practical next steps
What should you do next with a knee ligament injury claim?
Start with the insurer's most recent written decision and identify what is actually disputed: treatment, weekly payments or work capacity, threshold injury, permanent impairment, causation, or damages. These are separate questions and may require different evidence and review procedures. Record the date of the decision and every review deadline shown before gathering further material.
- 01
Preserve the claim and the decision under review
Keep the claim number, accident date, insurer letter, certificate of fitness and any internal review or Personal Injury Commission correspondence together. Do not assume that a treatment approval or payment of statutory benefits decides fault, damages eligibility or WPI.
- 02
Obtain evidence that answers the disputed issue
For this injury, the useful starting material includes MRI and operative reconstruction report and dated Lachman, drawer and varus/valgus stress findings. Clinical testing may include Lachman, drawer and stress testing and MRI and operative report. Ask the treating practitioner to record the diagnosis, accident causation, objective findings, treatment response and current functional limits rather than symptoms alone.
- 03
Use the correct review process
Compare the insurer's reasons with the records it relied on. A threshold-injury decision, treatment refusal, weekly-payment decision and WPI assessment do not all follow the same review process. The decision letter should identify available internal review or dispute steps and the applicable deadline.
If the decision, medical material or deadline is unclear, send the key documents for a focused review before lodging a broad objection. See the CTP disputes guide or contact NSW CTP Claim. Advice depends on the facts, evidence and current law; a review cannot guarantee a claim outcome.
Assessment source
Knee ligament WPI source
Assessment source: Motor Accident Guidelines v10.1 clauses 6.68-6.75, 6.84-6.98; AMA4 Tables 41 and 64, Table 6.5 and Table 6.4.
Threshold injury: Verified partial or complete ligament rupture is excluded from soft tissue injury; sprain without rupture may be threshold.
What the assessor checks
- objective laxity method
- clause 6.98 mild combined-laxity rule
- separate injury assessment
- ROM alternative
What does not establish the result by itself
- MRI
- reconstruction
- giving way
- brace
Official sources
Related NSW CTP guides
Free claim check
Review the medical evidence and insurer decision together
Send the accident date, insurer letter, scans or reports and any deadline shown. NSW CTP Claim is a specialised service of Stephen Young Lawyers. Legal services are provided by Stephen Young Lawyers.
Frequently asked questions
- Does ACL reconstruction have fixed WPI?
- No. The permanent residual laxity, movement or other valid method determines WPI.
- What does clause 6.98 say?
- Where both mild collateral and mild cruciate laxity are present, each is 3% WPI and the Guidelines state a combined total of 6% WPI.
- Can that 3% rule be used for every ligament tear?
- No. It is limited to the stated mild-laxity scenario and must not be extrapolated.
- Is an MRI enough to show permanent laxity?
- No. Current objective stability findings are required.
- Can meniscus impairment be added?
- A separate meniscus injury may be assessed separately, subject to Table 6.5 and no double counting.