How do you diagnose a torsional profile of limbs for rotational deformity?

Assessment of Torsional Profile for Rotational Deformity

The torsional profile is assessed through clinical examination measuring specific rotational angles at the hip, knee, and foot, followed by CT imaging without IV contrast when surgical correction is being considered, as CT provides the gold standard for quantifying femoral and tibial torsion. 1, 2

Clinical Examination Components

The clinical torsional profile consists of systematic measurement of:

• Femoral anteversion: Measured with the patient prone, hip extended, and knee flexed to 90 degrees. The examiner rotates the thigh to position the greater trochanter parallel to the examination table, then measures the angle of the lower leg from vertical. Normal values range from 5°-9° in adults. 2

• Tibial torsion: Assessed with the patient sitting, knee flexed to 90 degrees. The thigh-foot angle is measured by comparing the axis of the foot to the axis of the thigh. Normal values range from 26°-28° of external rotation. 2

• Foot progression angle: Observed during gait, measuring the angle between the long axis of the foot and the line of progression. This integrates the combined rotational profile of the entire limb. 3

Imaging Assessment

CT Without IV Contrast - The Gold Standard

CT without IV contrast is the definitive imaging modality for measuring component rotation and torsional deformities. 1, 4

• Femoral torsion measurement: Two validated methods exist - the Hernandez method and the Weiner method, with the Weiner method showing less variability. 2 Measurements compare the femoral neck axis to the posterior femoral condylar axis. 2

• Tibial torsion measurement: The bimalleolar method compares the axis through the malleoli to the posterior tibial plateau or tibial tubercle. 2

• 3D reconstruction techniques: Modern CT software allows 3D measurement methods that are equivalent to conventional 2D measurements and facilitate surgical planning. 2

When to Order CT Imaging

CT should be obtained when:

• Clinical examination suggests torsional deformity requiring surgical correction 2
• Persistent severe tibial torsion beyond 15° medial or 30° lateral after age 8 years 5
• Persistent severe femoral anteversion exceeding 50° after age 8 years, with medial rotation >85° and lateral rotation <10° 5
• Preoperative planning for derotational osteotomy is needed 2

Critical Thresholds for Intervention

Side-to-Side Comparison

The maximal acceptable side-to-side difference in asymptomatic adults is 12-13° for femoral torsion and 12° for tibial torsion. 2 Differences exceeding these thresholds indicate clinically significant rotational malalignment that may warrant surgical correction.

Absolute Values Requiring Consideration for Surgery

• Tibial torsion: Medial torsion beyond 15° or lateral torsion beyond 30° after age 8 years 5
• Femoral anteversion: Greater than 50° after age 8 years, particularly when medial hip rotation exceeds 85° and lateral rotation is less than 10° 5

Important Clinical Pitfalls

Do not rely solely on anatomic torsion measurements to predict gait patterns or functional outcomes. 3 The correlation between femoral torsion and hip rotation during gait is weak (R²=0.22), while tibial torsion correlates more strongly with knee rotation (R²=0.71). 3 This occurs because:

• Compensatory mechanisms, especially at the hip, significantly influence the resulting gait pattern 3
• The foot progression angle correlates more strongly with tibial torsion than femoral torsion 3
• Pelvic range of motion increases with femoral anteversion as a compensatory mechanism 3

Three-dimensional instrumented gait analysis should be performed before surgical correction of rotational malalignment to understand the functional impact and compensatory patterns. 3

Radiographic Limitations

Plain radiographs have limited value for assessing torsional deformities:

• Standard AP and lateral views cannot measure axial plane rotation 1
• Radiographs are useful for assessing associated coronal plane deformities (varus/valgus) but not torsion 1, 6
• The American Academy of Orthopaedic Surgeons advises against relying solely on simple measurements for complex deformities including torsional components 7