Abstract
The regenerative potential of bone is enormous, and it is possible to lengthen limbs by bone distraction. However, there remains a major risk of fracture after lengthening the bone. Previous studies have described how the pixel value ratio may be used for determining the time for frame removal.
The aim of this study was to investigate the intrarater and the interrater reliability of pixel value scores from radiographs in tibial lengthening prior to frame removal. Moreover, the study aimed to determine the overall number of X- rays obtained during circular frame treatment.
Retrospective study. Patients treated with tibial lengthening by a circular frame at Aalborg University Hospital from January 1st 2000 to December 31st 2017 and a minimum of 12 months after frame removal were included. The bone was divided in proximal-, regenerate- and distal bone zone. These 3 zones were in AP x-ray divided in an anterior and posterior zone and in sagittal X-ray medial and lateral zone producing 6 zones in which the pixel value was measured. Pixel value ratio was calculated as: (Proximal pixel value+Distal pixel value)/2/Regenerate pixel value. Interrater correlations were calculated from measurements obtained by an orthopaedic registrar and an orthopaedic specialist. Intrarater correlation was calculated from repeated measurements obtained by an orthopaedic specialist.
Mean duration of circular frame treatment was: 6 (+-3) months. Median number of x-ray controls during frame treatment were: 9 (+-4). Out of 90 tibial lengthening it was only possible to measure pixel value in all six areas of interest on 20 lengthening prior to frame removal. Major reasons for inability to obtain measurements were metal hardware crossing the areas of bone interest on x-rays. The mean (95 % confidence intervals) pixel ratios values were: 1) lateral: 0.96 (0.93–1.00); 2) medial: 0.95 (0.92–0.99); 3) anterior: 0.94 (0.90–0.97); 4) posterior: 0.96 (0.93–0.99). The mean (95 % confidence intervals) inter ratter ICC estimates were: 1) lateral: 0.8 (0.5–0.9); 2) medial: 0.8 (0.4–0.9); 3) anterior: 0.4 (−0.5–0.8); 4) posterior: 0.6 (0.1–0.9). The mean (95 % confidence intervals) intra ratter ICC estimates were: 1) lateral: 1.0 (0.9–1.0); 2) medial: 1.0 (1.0–1.0); 3) anterior: 0.9 (0.9–1.0); 4) posterior: 1.0 (1.0–1.0). Out of the 20 lengthening examined one fracture occurred in the bone regenerate after frame removal.
Prospective studies are warranted to determine whether the pixel value ratio can be used as an indicator for frame removal.
