SLR - November 2019 - Josephine P. Lyons
Reference: Knapik DM, Sahejmeet SG, Jones JA, Cooperman DR, Liu RW. Incidence and Fusion of Os Trigonum in a Healthy Pediatric Population. J Pediatr Orthop. 2019 Oct; 139(9):718-721Scientific Literature Review
Reviewed By: Josephine P. Lyons, DPM
Residency Program: Ascension Wisconsin – Milwaukee, WI
Podiatric Relevance: The os trigonum is a common finding radiographically in children and some adults. The incidence of symptoms with this pathology is variable. Prior studies have examined incidence rates in symptomatic patients, but no prior study addressed the incidence rate in asymptomatic pediatric patients. This study further asks the average age of appearance, the age of fusion, and the incidence of fusion in this asymptomatic population using radiographic analysis.
Methods: This is a prognostic level II study, retrospectively performed on serial radiographs of 261 children. A total of 2620 radiographs of the left foot in children (starting age 0.25 to 7 years) were reviewed from the Bolton-Brush collection. These radiographs were performed approximately 80 years ago, then digitized and optimized, and reviewed by two authors separately. Interrelator reliability (IR) was measured and intraclass correlation coefficients (ICC) were tested between radiographs. A minimum of four annual radiographs per subject was necessary for inclusion. Skeletal maturity was assessed from the ossification of the calcaneus.
Results: Of the 261 patients, os trigonum was present in 37 subjects, each with an average of 10 radiographs available for review. Average age of presentation was 9.1±1.8y in females and 10.4±2.0y in males. Overall incidence rate in asymptomatic feet was 18 percent. There was no significant difference in incidence between males and females. Ossicle fusion occurred in 70 percent of subjects by a mean age of 9.5±1.6y in females and 11.2±1.6y in males. Fusion occurred at calcaneal ossification stage two (apophysis covers >50 percent without a plantar edge) and stage three (complete plantar extension of apophysis). IR and ICC measurements were found to be excellent, rated 0.901 at a 95 percent confidence interval.
Conclusions: The incidence rate of 18 percent for asymptomatic feet falls within previously found incidence rates of 2-26 percent. The average age of appearance and average age to fusion is slightly earlier in females to males, which is consistent with prior research findings. The study also found that there was approximately 12 months between initial appearance to fusion. They postulate that this is because the os trigonum is not a separate ossicle, but in fact a cartilaginous extension of the talus, completing ossification comparative to skeletal maturity. As such, since fusion was observed at calcaneal stages 2-3, they recommend that a child with a symptomatic os trigonum at a calcaneal stage four is unlikely to fuse independently. Further recommendations are that a child with symptomatic os trigonum should be treated conservatively for 12 months, since this is the average time to fusion. Some limitations to the study are radiographs were only of the left foot, missed visits could not be recouped and the selected population was of narrow range.