Penlight versus Smartphone: Diagnostic Efficacy of Transillumination

Background: The purpose of this study was to compare the diagnostic accuracy of a smartphone flashlight to a conventional penlight with regards to transillumination of simulated soft tissue masses of the hand and wrist. Methods: Eight participants performed transillumination assessments in a fresh frozen cadaver upper extremity model. Spheres measuring 9.5 mm were used to simulate fluid-filled or solid soft tissue masses. Two spheres were placed on the volar aspect and two on the dorsal aspect of the wrist. These were then evaluated with either a smartphone flashlight or penlight. Participants noted whether each sphere did or did not transilluminate. Each participant performed two evaluations at an interval of 3 weeks. Results: The overall sensitivity, specificity and accuracy of the smartphone were 100%, 44% and 72%, respectively. The overall sensitivity, specificity and accuracy of the penlight were 100%, 75% and 88%, respectively. The difference in accuracy between the smartphone group and penlight group was statistically significant (p = 0.029). The kappa value, indicating intra-observer agreement, for the smartphone group and penlight group was 0.76 and 0.76, respectively. Conclusion: In conclusion, transillumination with a penlight is a viable adjunct to the examination of soft tissue masses of the hand and wrist. The use of a smartphone flashlight, while convenient, is less accurate than a penlight and can lead the examiners to misinterpret the composition of soft tissue masses. Level of Evidence: Level IV (Diagnostic).