Palmar cortical ridges on hand CT: Normal but misleading cortical adaptations and a potential diagnostic pitfall.

PURPOSE: To conduct the first large-scale, population-level CT evaluation of palmar cortical ridges. This study aimed to characterize their prevalence, anatomic distribution, and morphologic features, and analyze associations with demographic factors.

METHODS

This retrospective, single-center study included 459 consecutive patients (279 men, 180 women; mean age, 40.1 ± 17.3 years) who underwent hand CT between 2022 and 2024 for various clinical indications. Twelve-digit phalanx sites (2nd-5th digits; proximal, middle, distal phalanges) were evaluated for the presence, laterality, and severity of palmar ridges. Associations with age, sex, and side were assessed using chi-square tests, and multivariable logistic regression models were used to assess the independent association of age and sex with ridge presence. Interobserver agreement was evaluated using intraclass correlation coefficients (ICCs).

RESULTS

Palmar ridges were consistently identified in the proximal and, to a lesser extent, middle phalanges, most commonly at the 4th (84.3%) and 3rd (74.7%) proximal phalanges. No ridges were observed in any distal phalanx. Ridge prevalence and prominence increased progressively with age (p < 0.001) and were significantly higher in women (p < 0.001). Bilateral involvement predominated (up to 94.8% at the 4th digit-proximal phalanx), and when unilateral, ulnar orientation was more frequent than radial. Interobserver reliability was excellent (ICCs = 0.83-0.94).

CONCLUSION

Our findings indicate that palmar cortical ridges follow a predictable, age-related, and digit-specific distribution, representing physiological enthesis-related cortical adaptations rather than signs of pathology. Recognizing these cortical adaptations - particularly at the proximal phalanges of the 3rd and 4th digits - is essential to avoid diagnostic confusion with periosteal reaction or early arthropathy, thereby improving the accuracy of hand CT interpretation.