Description

The aim of this project is to use neurophysiological assessment to gain a better understanding of what is actually measured by S2PD (static two-point discrimination). A neurophysiological examination can objectively measure any remaining function in an injured digital nerve. Using this method, axons responsible for pressure, vibration, and touch that are still able to conduct an action potential, are assessed.

The response can be measured both as the amplitude of the summed action potentials from the nerve's axons and as the area, which corresponds to the area under the curve formed by the recorded action potentials. The area is a somewhat more precise measurement method, as it includes all axons, both those with low and high conduction velocities. Amplitude measurements may give falsely low values if nerves with poorer degrees of myelination are included in the measurement. Amplitude is measured in µV and area in µV/ms.

The method currently used to assess discriminative sensation, S2PD, is influenced by many external factors, such as the clinician's level of experience, the patient's desire to give the correct answer, language barriers, and similar issues. Furthermore, this examination method does not clarify what is actually being measured beyond the patient's subjective discriminative sensation.

If neurophysiological assessment is used as a complement to S2PD and can provide an objective measurement tool with high reliability and reproducibility, it could become an important addition to the clinical arsenal for follow-up after nerve injury. Such knowledge would make it easier to clinically evaluate, understand, and monitor the healing process of the injured nerve. It would also facilitate the assessment and systematic follow-up of treatment outcomes.

The investigators also believe that patients would benefit from being able to follow nerve healing in a more objective manner, which could help motivate continued training and rehabilitation (such as tactile stimulation, mirror therapy, desensitization, etc.).

Participants will be identified through the national quality register for hand surgery (HAKIR), and will be invited to attend an examination at the Hand Surgery Outpatient Clinic at Sodersjukhuset by phone (postal invitation if no response). If the response rate is low, patients will be contacted by phone one additional time.

The visit, which is estimated to last approximately 60 minutes, will include assessment using static two-point discrimination (S2PD) and neurophysiological examination of the injured finger as well as the corresponding finger on the contralateral, uninjured hand. Sensory assessment with S2PD will be performed on the fingertip pulp, radially or ulnarly, using a discriminator. Sensory thresholds, measured in millimetres, will be recorded in the study protocol.

Finger temperature will be measured using an infrared thermometer (Testo 826-T2), and, if necessary, the fingers will be warmed (using a water bath or heating pad) to a target temperature of a minimum of 32 °C. The hands will then be gently abraded using a preparation gel (NuPrep). Conductive gel (Ten20) will be applied to the electrodes.

A recording electrode will be placed volarly over the wrist, a ground electrode in the palm, and a stimulating electrode on the finger (digits II, III, or IV). Electrical stimulation will be delivered in an orthodromic direction, from the finger toward the wrist. The stimulus intensity will be gradually increased as long as the recorded amplitude continues to rise, up to a maximum of 20% above the intensity at which no further increase in amplitude is observed. This approach ensures inclusion of all excitable axons in the recording, regardless of individual firing thresholds.