Analysis of corticalization using the pixel value ratio for fixator removal in tibial lengthening

Abstract

Background It is important to define callus maturation and corticalization during distraction osteogenesis. Quantitative methods such as ultrasound and Q-computed tomography are sensitive but expensive. The pixel value ratio (PVR) obtained using a PACS (picture archiving and communication system) is a simple and cost-effective investigation tool. Recently, the issue of whether the PVR is correlated with quantitative methods has been studied. We investigated whether serial PVR is a useful technique for predicting corticalization in each callus segment of the regenerate, and can act as a guide for fixator removal in tibial lengthening without intramedullary nailing. Methods A retrospective analysis of 30 tibial segments in 18 patients was performed. The mean age of the patients was 18 years (range 5-48 years). There were 6 male patients and 12 female patients, of whom 8 patients were skeletally mature. Indications for limb lengthening were achondroplasia (8 patients), limb length discrepancy (4 patients), and miscellaneous (6 patients). The interobserver variability of the PVR was measured at each callus segment of the regenerate. Serial PVR at each callus segment was classified according to the callus pathway. Results The mean interobserver correlation coefficient at the regenerate was high in the posterior callus segment (0.92), the lateral callus segment (0.90), and the medial callus segment (0.70). However, there was low mean interobserver variability in the anterior callus segment (0.49) at the regenerate. A PVR of 1 at the regenerate was achieved first at the lateral callus segment, second at the posterior, third at the medial callus segment, and last at the anterior callus segment. There was no fracture at the regenerate or wire breakage in patients who began fixator removal and full weight bearing when the PVR was 1 in the three callus segments at the regenerate. Conclusions In tibial lengthening without nailing, serial measurement of the PVR is a reliable and cost-effective technique to assess the maturity of the callus, especially in the lateral and posterior callus segments, and assessment of the cortical pixel value can safely provide guidelines for fixator removal.