4.5-Gram Monofilament Sensation Beneath Both First Metatarsal Heads Indicates Protective Foot Sensation in Diabetic Patients

Abstract

Background: Loss of protective plantar foot sensation is the major cause of diabetic foot ulcerations and ultimate limb loss. Identification of patients without protective sensation can reduce the risk of unrecognized foot injury. The current recommended screening protocol requires 10-g monofilament testing of ten foot sites with use of a forced-choice paradigm. The objective of the present study was to determine whether testing of fewer than ten sites could provide accuracy comparable with that obtained by testing all ten sites. Methods: A cross-sectional comparative study of plantar sensory levels in diabetic subjects with and without plantar ulceration was conducted in a tertiary-care teaching hospital setting. We examined forty-seven diabetic subjects with a history of foot ulceration and forty-five diabetic subjects with no history of foot ulceration. Plantar sensory threshold values at five sites on the sole of each foot were measured with a quasi-continuous range of applied forces, and receiver operating characteristic analysis techniques were applied. Results: Screening on the basis of only the maximum force threshold for the left and right first metatarsal head sites provided comparable or better performance at high levels of sensitivity than did either the mean or the maximum force threshold across all ten sites. A sensory threshold of 4.5 g for both the left and right first metatarsal head sites predicted the risk of ulceration with a sensitivity of 100% and a specificity of 67%. Conclusions: Testing of diabetic patients for protective sensation may be simplified to testing under both first metatarsal heads with a 4.5-g monofilament. If a patient cannot sense the application of a 4.5-g monofilament under either first metatarsal head, he or she probably has lost protective sensation and should be considered to be at risk for undetected injury. Level of Evidence: Diagnostic study, Level II-1 (development of diagnostic criteria on the basis of consecutive patients [with universally applied reference "gold" standard]).