Assessment of relative uptake by mandibular condyles in a "normal" population

Hyperplasia of the mandibular condyle is self-limiting, but can lead to facial asymmetry, malocclusion, pain, and dysfunction of the temporomandibular joint (TMJ). Bone scintigraphy, particularly with single photon emission computed tomography (SPECT), is effective in assessing relative condylar uptake, but we know of no standardised methods or values. Our aim, therefore was to validate the values currently used to measure relative condylar uptake in our population. Between December 2015 and June 2018 44 patients had skull SPECT (15 male and 29 female patients, whose ages ranged from 4-33 years). They were having bone scans (hydroxydiphosphonate (HDP) -^99MTc, 740 MBq ev) for unrelated reasons and had no known abnormalities of the head, facial asymmetry, or symptoms of the TMJ. Two research workers measured the relative uptake between the condyles using the summed transaxial images. The Hospital Ethics Committee approved the investigation. The maximum difference in condylar uptake was 8.33% with research worker 1 and 8.77% with research worker 2, and the mean (SD) differences were 3.03 (0.17) % and 3.29 (0.18) %, respectively. Data were tested for normality, and the t test and one-way ANOVA were used to assess the significance of differences. None was found in total counts either between sexes or age groups, and there were none between the total counts measured by the two research workers. We conclude that our results are within the published ranges, and the variation in condylar uptake was less than 5% in 37/44 patients, and in none was it 9% or more. When the results indicate less than 10%, but there is a high clinical suspicion of active hyperplasia, surgeons should use their clinical judgement to decide whether condylar surgery is required.