A topographical and physiological exploration of C-tactile afferents and their response to menthol and histamine

Unmyelinated tactile (CT) afferents are abundant in arm hairy skin and have been suggested to signal features of social affective touch. Here we recorded from unmyelinated low-threshold mechanosensitive afferents in the peroneal and radial nerves, with the most distal receptive fields located on the proximal phalanx of the third finger for the superficial branch of the radial nerve, and near the lateral malleolus for the peroneal nerve. We found that the physiological properties with regard to conduction velocity and mechanical threshold, as well as their tuning to brush velocity, were similar in CT units across the antebrachial (n=27), radial (n=8) and peroneal nerves (n=4). Moreover, we found that while CT afferents are readily found during microneurography of the arm nerves, they appear to be much more sparse in the lower leg compared to C nociceptors. We continued to explore CT afferents with regard to their chemical sensitivity and found that they could not be activated by topical application to their receptive field of either the cooling agent menthol or the pruritogen histamine. In light of previous studies showing the combined effects that temperature and mechanical stimuli have on these neurons, these findings add to the growing body of research suggesting that CT afferents constitute a unique class of sensory afferents with highly specialized mechanisms for transducing gentle touch.

Extension-Block Pinning for Unstable Dorsal Proximal Interphalangeal Joint Fracture-Dislocations: A Simple, Percutaneous Technique With Reproducible Outcomes

Background: Proximal interphalangeal (PIP) joint fracture-dislocations can be technically challenging injuries to treat, and no technique has proven to be superior nor lead to predictably good outcomes. We describe our experience of treating unstable dorsal fracture-dislocations of the PIP joint with extension-block pinning (EBP) at our institution over a 22-year period. Methods: In all, 23 patients with 24 unstable dorsal fracture-dislocations of the PIP joint treated with EBP between January 1998 and October 2020 were identified. All patients underwent closed reduction of the PIP joint and insertion of a Kirschner wire into the proximal phalanx, creating a mechanical block. Range of motion and joint congruity were assessed at final clinic follow-up. Long-term function was assessed via completion of a Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) questionnaire. Spearman’s correlation coefficient was utilized to assess if any association existed between treatment delay, pin-in-body days, or amount of articular surface involved and QuickDASH score. Results: Mean range of motion at final follow-up was 83.3° and 22 of 24 PIP joints demonstrated a congruent reduction. In all, 15 of the 23 patients completed the QuickDASH questionnaire at a median long-term follow-up of 57.5 months (range: 3-157 months). Average QuickDASH score was 18.8, indicating minimal long-term disability. No statistically significant associations were found between treatment delay, pin-in-body days, or amount of articular surface involved and QuickDASH score. Conclusions: EBP offers a simple and innovative method to treat a complex injury of the PIP joint. It is technically straightforward and cheap, and produces excellent functional outcomes with minimal long-term disability.

Reliability of coronal plane rotation measurements in the medial column of the foot: a cadaveric study

Objective: To assess interobserver reliability of previously described coronal plane rotation measurements of medial column bones and to assess their ability to accurately quantify changes in rotational profile. Methods: Two cadaveric below-knee specimens were implanted with pins in each bone of the medial column. Weight-bearing computed tomography (CT) scans were acquired in a simulated standing position under neutral, supinated, and pronated conditions. For each specimen and condition, 2 observers measured the coronal plane rotation of the navicular, medial cuneiform, first metatarsal base, shaft, and head, and proximal phalanx of the hallux as previously described. The rotation of each pin was measured relative to the ground in the coronal plane for each condition. These measurements were defined as benchmarks for the rotational profile of each bone. The correlation between these benchmarks and direct bone measurements was then assessed. Intraclass correlation coeficiente was used to assess interobserver reliability. Pearson’s coefficient was used to evaluate correlations. Results: The interobserver reliability of direct bone measurements ranged from 0.98 to 0.99. Correlations between pin rotation and direct measurements ranged from ρ=0.87 to 0.99 across the neutral, supinated, and pronated conditions. Conclusion: Coronal plane rotation measurements of medial column bones described in this study are reliable tools. Level of Evidence III; Case-Control Study.