Purpose or Case Report: Subperiosteal new bone formation (SPNBF) is a physiological phenomenon during normal osseous development which also has pathological causes, including healing fractures. Distinguishing between physiological and pathological SPNBF in cases of suspected physical abuse is critical. It has been reported from analogue radiographs that SPNBF above 2 mm in infants over 4 months of age should raise the suspicion of pathology. We sought to refine this using higher resolution modern digital imaging, given the implications for both clinical and medicolegal practice in cases of suspected physical abuse.
Methods & Materials: Postmortem radiographic skeletal surveys in ten male and ten female infants in monthly groups between 0-12 months were recruited from three centres. Cases of asymmetric patient positioning were excluded. Where SPNBF was visualised, thickness was independently measured by two readers at both the medial and lateral mid-diaphyseal points of upper (Reader 1) or lower (Reader 2) limbs, utilising digital callipers on radiology workstations.
Results: We retrieved 212 surveys of which 27 were excluded. SPNBF was visualised in 116 of 2,220 bones (62 skeletal surveys) and was visualised more often in infants aged 0–6 months (60.5%) versus 6–12 months (39.5%). The highest prevalence was 3–4 months (18.3%), followed by 1–2 months (14.0%), and overall more common in males. SPNBF was visualised most often in the tibia, and least in the radius. The maximum and average thicknesses of physiological SPNBF by bone, respectively, were: femur, 2.60 mm and 1.21 mm; tibia, 2.60 mm and 1.02 mm; humerus, 1.90 mm and 0.94 mm; fibula, 1.6 mm and 0.89 mm; ulna 1.20 mm and 0.77 mm; and radius 1.10 mm and 0.73 mm. Bilateral SPNBF was most often in the tibia, and least often in the radius.
Conclusions: This study expands upon previous research by evaluating a larger cohort, excluding asymmetric positioning and using digital callipers to measure SPNBF on diagnostic monitors. New parameters for physiological SPNBF have been set. It is visualised: up to 12 months; most commonly in the tibia, as well as bilaterally; and maximum thickness 2.60 mm in the femur and tibia, above which should raise the suspicion of pathology.