Differences in lower limb bone mineral density in children with anisomelia

Background. Lower limb discrepancy (anisomelia) can be caused by many different factors leading to shortening (90% of cases) or lengthening of a limb (10% cases). This article present the results of densitometric tests performed on patients treated for lower limb discrepancy in the Department of Orthopedic of the Silesian Academy of Medicine in the years 1997-1998.
Material and methods. Our research involved 57 patients, 31 girls and 26 boys. The Ilizarov technique was used to lengthen 33 femurs and 24 tibias. The average discrepancy was 45 mm (48 mm in the femurs and 42 mm in the tibias), and the patients average age was 13,8 years (range 7-26). The test were performed with a DPX apparatus by the Lumar Corporation. The bone mineral density (BMD) was measured in the area of the shortened limb segment and compared to the results of the analogous measurement of the opposite limb. The height of the measurement frame was 50 mm, and the width was equal to the width of the bone. The measurement field was located in each case at a distance of 3-4 cm (on the respective bone) from the line of the knee joint, in order to eliminate additional density caused by growth cartilage and the imposition of the patella. The repeatability of the tests was assured by a support maintaining constant internal limb rotation of 400.
Results. A difference in BMD between the shorter limb and the opposite limb was found in 47 children (82,5%). The average was 16,5%, whereas it was higher in the shorter femurs (19,1%, range 4,5 - 68,5%) than in the tibia (14%, 5,2 - 59,8%). A greater degree of demineralization was found in the girls (23,5%) than in the boys (20%). No correlation was found between the etiology of the shortening and the degree of calcification.
Conclusions. The results of these tests may have great significance in the case of densitometric monitoring of regenerated bone being formed in the course of lower limb by the Ilizarow method.