Rotational Profile of the Lower Extremity in Achondroplasia : Computed Tomographic Examination of 25 patients Hae-Ryong Song, M.D., Keny Swapnil.M M.S, Jong-Won Chung, M.D. Department of Orthopedic Surgery Korea 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

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

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