Lower limb measurement
Leg length discrepancy after a motor accident
A true leg length discrepancy can follow fracture shortening, malunion or surgery. It must be distinguished from apparent shortening caused by pelvic tilt, joint contracture or posture, and it is measured under the modified CTP Table 35 method.
Motor accident injury
How can this injury happen?
Car or passenger collision
Femur, tibia, pelvis or hip fracture may heal with shortening or altered alignment after a collision.
Motorcycle accident
High-energy motorcycle fractures can shorten the femur or tibia despite fixation.
Pedestrian or cyclist impact
Pedestrian impact may cause long-bone or pelvic fracture with later anatomical discrepancy.
Injuries that can occur
- femoral or tibial shortening after fracture
- malunion or bone loss
- hip or pelvic reconstruction affecting limb length
- joint contracture causing apparent rather than true shortening
Symptoms and functional problems
- uneven stance or pelvic tilt
- difficulty prolonged walking or standing
- shoe-lift use and asymmetric loading
- secondary hip, knee or back symptoms
Seek urgent medical assessment
New shortening with deformity after trauma, loss of circulation or inability to weight-bear requires urgent assessment.
Clinical evidence
What findings matter?
Clauses 6.76 and 6.77 require true anatomical measurement. The examiner measures from the anterior superior iliac spine to the medial malleolus; CT measurement is preferred when available, unless a fixed deformity makes it inappropriate.
| Record or examination | What it may establish | What it cannot prove alone |
|---|---|---|
| Clinical tape measurement | Measures true length from ASIS to medial malleolus on both sides. | Pelvic tilt or poor landmarks can make a single measurement unreliable. |
| CT scanogram or equivalent imaging | Provides preferred anatomical measurement where available. | It may be unsuitable where fixed deformity prevents a valid comparison. |
| Standing alignment and joint examination | Separates true shortening from apparent discrepancy due to contracture or posture. | A limp or shoe lift does not prove the centimetre difference. |
Movement in daily life
How movement affects real activities
Leg length affects level standing, stride symmetry and energy use. The discrepancy method measures anatomical shortening; it does not rate every consequence of an altered gait again.
Standing alignment
Level pelvis and balanced weight bearing.
Block testing may inform function but the Part 6 anatomical measurement controls.
Stride and clearance
Efficient walking and avoiding toe catch.
Gait observation supports context but cannot be added if gait is used as a separate method.
Hip, knee and ankle position
Compensation for true or apparent shortening.
Fixed joint deformity must be identified before relying on CT or tape comparison.
Threshold injury is a separate question: the underlying fracture or structural injury may be non-threshold. The measured discrepancy is a WPI method, not the threshold classification test.
Part 6 permanent impairment
How is CTP WPI assessed?
Clauses 6.76 and 6.77 modify AMA4 Table 35. The Guidelines reproduce higher values of 0, 3, 5, 7 and 8% WPI, corresponding to 0, 9, 14, 19 and 20% lower-extremity impairment, across the table bands. The centimetre bands must still be read from Table 35.
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 |
|---|---|---|---|
| True leg length discrepancy | Clauses 6.76-6.77; modified AMA4 Table 35 | Reproducible anatomical shortening after accident injury. | Use the Table 35 centimetre band; do not infer a band from appearance. |
| CT measurement | Clause 6.76 | Preferred measurement where available and valid. | Fixed deformity may make CT comparison inappropriate. |
| Conversion values | Clause 6.77 | Modified values: 0/3/5/7/8% WPI and 0/9/14/19/20% LEI. | These values do not identify the centimetre band without Table 35. |
- Confirm true rather than apparent discrepancy.
- Use reproducible bilateral measurement.
- Do not add gait for the same lower-limb impairment.
What cannot be combined?
- gait derangement with the leg-length method
- separate symptoms already represented by the discrepancy
- apparent pelvic tilt as though it were anatomical shortening
What does not establish WPI by itself?
- limp
- pelvic tilt
- shoe lift
- one undocumented tape measurement
Motor accident examples
Femoral fracture with measured shortening
The reproducible anatomical difference is matched to the Table 35 centimetre band, then the clause 6.77 modified value is used.
Apparent short leg from hip contracture
The assessor must separate joint-position effect from true bony shortening before using Table 35.
Claim file preparation
Evidence checklist
Assessment source
Leg length WPI source
Assessment source: Motor Accident Guidelines v10.1 clauses 6.76-6.77; modified AMA4 Table 35 and Guidelines Table 6.4.
Threshold injury: Threshold status follows the underlying accident-related structural injury; leg length is assessed separately for WPI.
What the assessor checks
- true-length method
- CT preference
- modified WPI values
- modified LEI values
What does not establish the result by itself
- limp
- pelvic tilt
- shoe lift
- unrepeated measure
Official sources
Related NSW CTP guides
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Frequently asked questions
- How is true leg length measured?
- Clause 6.76 uses the distance from the anterior superior iliac spine to the medial malleolus, with CT preferred when available and valid.
- What values did the Guidelines modify?
- Clause 6.77 states 0, 3, 5, 7 and 8% WPI, corresponding to 0, 9, 14, 19 and 20% lower-extremity impairment.
- Does a limp prove leg shortening?
- No. A limp can have many causes and does not measure anatomical length.
- Can gait be added?
- No. Gait cannot be combined with another lower-limb evaluation.
- Is a shoe lift enough evidence?
- No. It may support management, but reproducible clinical or imaging measurement is required.