Second Harmonic Generation Microscopy as a Novel Intraoperative Assessment of Rat Median Nerve Injury

PURPOSE

Nerves that are functionally injured but appear macroscopically intact pose the biggest clinical dilemma. Second Harmonic Generation (SHG) Microscopy may provide a real-time assessment of nerve damage, with the ultimate goal of allowing surgeons to accurately quantify the degree of nerve damage present. The aim of this study was to demonstrate the utility of SHG microscopy to detect nerve damage in vivo in an animal model.

METHODS

Ten Sprague-Dawley rats were anesthetized and prepared for surgery. After surgical exposure and using a custom-made stretch applicator, the right median nerves were stretched by 20%, corresponding to a high strain injury, and held for 5 minutes. The left median nerve served as a sham control (SC), only being placed in the applicator for 5 minutes with no stretch. A nerve stimulator was used to assess the amount of stimulation required to induce a flicker and contraction of the paw. Nerves were then imaged using a multiphoton laser scanning microscope.

RESULTS

Immediately after injury (day 0), SHG images of SC median nerves exhibited parallel collagen fibers with linear, organized alignment. In comparison with SC nerves, high strain nerves demonstrated artifacts indicative of nerve damage consisting of wavy, undulating fibers with crossing fibers and tears, as well as a decrease in the linear organization, which correlated with an increase in the mean stimulation required to induce a flicker and contraction of the paw.

CONCLUSIONS

Second Harmonic Generation microscopy may provide the ability to detect an acute neural stretch injury in the rat median nerve. Epineurial collagen disorganization correlated with the stimulation required for nerve function.

CLINICAL RELEVANCE

In the future, SHG may provide the ability to visualize nerve damage intraoperatively, allowing for better clinical decision-making. However, this is currently a research tool and requires further validation before translating to the clinical setting.

An Analysis of Profundus Tendon Repairs After Distal Phalanx Amputation in a Cadaveric Model of Little Finger Superficialis Deficiency

PURPOSE

The flexor digitorum superficialis tendon to the little finger (FDS-5) has been observed to have a higher degree of functional and structural variation than the FDS of other digits. FDS-5-deficient individuals necessarily rely on the flexor digitorum profundus tendon to the little finger (FDP-5) for flexion in their little fingers. FDS-5 deficient patients who experience a considerable injury to their FDP-5 are therefore at a risk of losing substantial little finger flexion. The purpose of this study was to evaluate the degree of flexion of the little finger at the metacarpophalangeal and proximal interphalangeal (PIP) joints in a cadaveric model of FDS-5 deficiency following amputation of the distal phalanx.

METHODS

Ten fresh-frozen cadaveric upper extremities with no prior trauma were used. Loads were applied to the FDP-5. Flexion at the PIP and metacarpophalangeal joints was measured in degrees with a goniometer. Little finger flexion testing was conducted under 5 different conditions: "baseline," "FDS-deficient," "no repair," "bone anchor" repair, and "A4 pulley" repair.

RESULTS

The results were as follows: (1) no significant differences in the flexion between baseline and FDS-deficient conditions; (2) a significant decline in PIP flexion in the no repair condition after FDP-5 division compared with the FDS-deficient condition; (3) a significant restoration in PIP flexion in both surgical repair groups compared with the no repair group; and (4) no significant differences in PIP flexion between the A4 pulley and bone anchor groups.

CONCLUSIONS

The bone anchor repair and the A4 pulley repair demonstrate similar abilities to restore flexion of the little finger at the PIP joint to baseline levels in this cadaveric model.

CLINICAL RELEVANCE

A clinical protocol is yet to be established for the surgical treatment in FDS-5-deficient patients requiring amputation of the distal phalanx of the little finger. This study aims to address this area of uncertainty by comparing the little finger flexion after 2 different approaches to profundus tendon reattachment that may be applicable in this clinical scenario.