Rotational Profile of the Lower Extremity in Achondroplasia : Computed Tomographi

c Examination of 25 patients

Hae-Ryong Song, M.D., Keny Swapnil.M M.S ,Jong-Won Chung, M.D.

Department of Orthopedic SurgeryKorea University Guro Hospital, Seoul, Korea

Deformities of Lower Extremity in Achondroplasia

• Coxa vara

• Genu varum

• Heel varus

Evaluation of combined deformity necessary when

performing osteotomies for correction of the

deformities

Computed Tomography

• More accurate method for measuring rotational deformity of lower extremity

• No report about rotational profile of lower extremity in achondroplasia by CT scans, as well as clinical methods and plain radiographs

Materials

• 25 patients with achondroplasia

12 females, 13 males

Age 6~37 (mean 15.6)

13 children, 12 adults

• All patients diagnosed with gene mutation analysis between December, 2000 and January, 2004

Methods

• Measure of bilateral torsion of the acetabulum, femur and tibia in 50 limbs

• Using 2 multi detector-row CT scanners (LightSpeed Plus; General Electric Medical Systems, Milwaukee, WI

SOMATOM Sensation 16, Siemens, Forchheim, Germany)

• 5.5mm slice thickness

CT Scans

Acetabular Anteversion

• Axial CT scans

At the level of the center of the hip joint

Line connecting the posterior ischia

Line connecting the posterior and anterior margins of the acetabulum

At the center of the hip joint

Femoral Torsion

Proximal reference line : the line joining the center of the head and the neck

Distal reference line : the line tangent to the most posterior points of the femoral condyle

The angle between proximal and distal reference lines

Proximal Femur Section showing the greater trochanter, femoral neck, femoral head, and acetabulum

Distal Femur Section showing the largest medial and lateral femoral condyles

Tibial Torsion

Ellipse tibial condyle

Proximal reference line : The estimiated long axis of the tibial condyle

Distal reference line : The axis through the centers of medial and lateral malleoli

Proximal tibia Section immediately below the joint line showing the entire anterior and posterior border of proximal tibial condyle

Distal tibia Section immediately above the joint line showing medial and lateral malleoli

External rotation deformity

Ext. Rotational deformity-retroversion of left hip

Left

Left

Measurements

• By three examiners for interobserver variation

Two orthopaedic surgeons

One radiologist

• Intraobserver variation

Measurement repeated one month later

Statistics

• SPSS 9.0 standard statistical version

• Calculation of percentage agreement and intra- and inter-observer difference

Intraclass correlation coefficient (ICC)

ICC > 0.75 excellent

ICC 0.40~0.75 fair

ICC < 0.40 poor agreement

Results

• Mean angle of acetabular anteversion 21.5±6.4° in adults 13.6±7.5° in children Excellent ICC values

• Mean angle of femoral torsion 30.5±20.1° in adults 27.1±20.8° in children Excellent ICC values

• Mean angle of tibial torsion 22.5±10.8° in adults 21.6±10.6° in children Fair to good ICC values

Results-Summary

• The femoral anteversion decreases during growth in normal children

• The femoral anteversion in achondroplasia was more than the normal values (age matched peers ) regardless of age

• No compensation of the increased femoral anteversion by the tibial torsion during growth in patients with achondroplasia

• No significant difference between children and adults

Results- Summary

• No difference in Acetabular torsion compared to normal value (age matched peers ) regardless of age

• Acetabular torsion in achondroplasia had no change during growth

• No significant difference between children and adults

Conclusion

• Increased femoral anteversion and decreased tibial external torsion in children and adults with achondroplasia

• No increase or decrease of femoral and tibial torsion during growth

• The increased femoral torsion was not compensated by the tibial torsion during growth

• The torsional deformity should be evaluated carefully before surgery and treated during correction of angular deformities

Thank you for your attention