Start clinically
Deformity analysis begins with the whole patient rather than the radiograph.
Assess:
- pain and functional limitation
- gait
- limb-length discrepancy
- coronal alignment
- sagittal alignment
- rotational profile
- joint range above and below the deformity
- neurovascular status
- scars, infection history and soft tissues
A deformity that is radiographically impressive may be well compensated; a smaller deformity near a joint can be clinically important.
Limb length
Clinical methods include block testing while standing and tape measurements when appropriate. Imaging options include calibrated full-length radiographs or CT-based techniques in selected cases.
Distinguish:
- true shortening
- apparent shortening due to pelvic obliquity or contracture
Coronal plane
Use a standing long-leg alignment radiograph when possible.
Key concepts:
- mechanical axis of femur
- mechanical axis of tibia
- overall hip-knee-ankle relationship
- joint-orientation angles
The aim is to localise the deformity rather than simply label the limb as varus or valgus.
Sagittal plane
A true lateral view is needed. Assess procurvatum/recurvatum, flexion contracture and compensatory changes at adjacent joints.
Rotation
Rotation is primarily a clinical diagnosis. CT rotational profiling may be useful when surgical correction is contemplated or clinical measurements are uncertain.
CORA
The centre of rotation of angulation is identified from the intersection of proximal and distal anatomical or mechanical axes. Osteotomy planning considers:
- level of CORA
- angulation
- translation
- rotation
- length
The centre of rotation of angulation is the intersection of the proximal and distal mechanical or anatomical axes of the deformed bone.
An osteotomy performed at the CORA can correct angulation without translation. If the osteotomy is away from the CORA, translation is required to maintain axis alignment.
Principle
Correct the deformity that causes abnormal joint loading or functional impairment, not merely the number on an X-ray.
Describe before treating
Deformity should be described in:
- coronal plane
- sagittal plane
- axial/rotational plane
- length
Then determine:
- apex
- level
- whether it is bone or joint based
- whether it is uniapical or multiapical
- whether there is translation
- whether adjacent joints compensate
Mechanical and anatomical axes
In the lower limb, the mechanical axis runs from femoral head centre to ankle centre. The normal knee lies close to this line.
Anatomical and mechanical axes differ, particularly in the femur. Correct interpretation of long-leg weight-bearing radiographs therefore requires knowing which axis is being measured.
Joint orientation angles
Deformity analysis uses standard joint-orientation angles to determine whether abnormal alignment arises from:
- distal femur
- proximal tibia
- joint-line pathology
- combinations
The exact numerical reference range matters less in an oral answer than showing a consistent, reproducible method.
Rotation and length
Long-leg AP radiographs do not define rotational deformity adequately. Clinical rotational profile and CT rotational assessment may be required.
Length discrepancy should be separated into:
- true bony shortening
- apparent shortening from contracture or pelvic obliquity
Planning correction
Consider:
- acute versus gradual correction
- soft-tissue tolerance
- neurovascular risk
- joint contracture
- bone quality
- size of lengthening
- patient age and goals
Gradual correction with external fixation can address complex multiplanar deformity and length, while osteotomy with internal fixation may suit simpler corrections.
FRCS synthesis
The sequence is: define the deformity → localise it → identify the CORA → choose correction level → anticipate translation/rotation/length effects.