Background: Tibial valgus, a known complication of leg lengthening with external fixation techniques, has been related to the stability of the bone-fixator system and, in particular, to pin loosening. A hydroxyapatite coating has been reported to enhance the quality of the bone-pin interface. The aim of this study was to compare the prevalence of axial deformity after tibial lengthening with hydroxyapatite-coated external fixation pins with the prevalence after tibial lengthening with uncoated pins.

Methods: We conducted a prospective study of thirty-four symmetrical tibial lengthening procedures in seventeen pathologically short patients. One limb of each patient was lengthened with use of hydroxyapatite-coated pins and the other, with standard uncoated pins; the sides of the operations were randomly selected. The bone angle in the frontal plane was measured before the operation and at the end of the fixation period, and the difference between these measurements was compared between the lengthening procedures performed with coated pins and those performed with uncoated pins.

Results: The mean valgus deviation of the tibia was 6.5° in the group treated with hydroxyapatite-coated pins and 12.5° in the group treated with uncoated pins (p = 0.023). With the numbers available, other factors previously related to the development of valgus deformity did not differ significantly between the two groups.

Conclusion: Tibiae that are lengthened with the use of hydroxyapatite-coated external fixation pins are less prone to axial deviation in the frontal plane than are those treated with uncoated pins.

Level of Evidence: Therapeutic study, Level I-1a (randomized controlled trial [significant difference]). See Instructions to Authors for a complete description of levels of evidence.