Histopathological Features of Ossified Keloids and Their Association With Recurrence: The Role of Inflammation and Foreign Bodies

Heterotopic ossification within keloid tissue is an uncommon but clinically relevant phenomenon. However, its histopathological characteristics and etiological mechanisms remain poorly understood. To investigate the histological features of ossified keloids and assess potential contributing factors, with a focus on chronic inflammation and foreign body reaction. We retrospectively analyzed 39 histologically confirmed ossified keloids and compared them with two non-ossified control cohorts: a frequency-matched group (n = 78) adjusted for age, sex, and anatomical site, and a broader institutional cohort (n = 345). Histological assessment included evaluation of inflammatory cell infiltration and identification of foreign materials such as hair shafts and suture remnants. Group comparisons were performed using Fisher's exact test. Multivariable logistic regression analysis was also performed to identify independent determinants of ossification, including age, sex, anatomical site, etiology, disease duration, and the presence of foreign bodies. Inflammatory cell infiltration was frequently observed across all groups without significant differences. However, foreign materials were detected significantly more often in ossified keloids (66.7%) than in both the matched (15.4%) and total non-ossified cohorts (8.1%) (p < 0.001). Logistic regression revealed that the presence of foreign bodies was independently associated with ossification (OR = 14.4, 95% CI: 6.1-33.8, p < 0.001), while female sex and acne/folliculitis etiology were also significant predictors. Ossified keloids exhibit characteristic features of active bone formation, including lamellar bone and osteoblast-like cells in the deep dermis, and are frequently associated with embedded foreign materials. These findings suggest that chronic inflammation and foreign body reaction may play key roles in ectopic ossification. Our multivariable analysis further indicates that host-related factors, such as sex and etiology, also contribute to this process, underscoring that foreign bodies alone are not sufficient. Combined with prior evidence indicating increased recurrence rates in ossified keloids, these histological features may serve as prognostic markers and inform surgical management strategies.