Digital Nerve Injury: Assessment and Treatment

Undertreated digital nerve injuries may result in sensory deficits and pain. Early recognition and treatment will optimize outcomes, and providers should maintain a high index of suspicion when assessing patients with open wounds. Acute, sharp lacerations may be amenable to direct repair while avulsion injuries or delayed repairs require adequate resection and bridging with nerve autograft, processed nerve allograft, or conduits. Conduits are most appropriate for gaps less than 15 mm, and processed nerve allografts have demonstrated reliable outcomes across longer gaps.

Biomechanical Testing of a Novel Device for Sutureless Nerve Repair

Suboptimal nerve end alignment achieved with conventional nerve repair techniques may contribute to poor clinical outcomes. In this study, we introduce Nerve Tape®, a novel nerve repair device that integrates flexible columns of Nitinol microhooks within a biologic backing to entubulate, align, and secure approximated nerve ends. This study compares the repair strength of Nerve Tape with that of conventional microsuture repairs. Thirty small (2 mm) and 30 large (7 mm) diameter human cadaveric nerves were transected and repaired utilizing Nerve Tape or appropriate microsuture technique. Biomechanical testing was performed using a horizontal tensile tester. The repaired nerves were loaded until failure at a distraction rate of 40 mm/min, and the maximum failure load was determined. In the small nerve groups, the load-to-failure for Nerve Tape repairs (2.33 ± 0.66 N) was significantly higher than for suture repairs (1.22 ± 0.52 N; p < 0.05). In the large nerve groups, no significant difference in load-to-failure was found between Nerve Tape (7.45 ± 2.66 N) and suture repairs (5.82 ± 1.59 N: p = 0.12). Suture repairs tended to fail by rupture, whereas Nerve Tape failures resulted from microhook pullout. Nerve Tape is a novel nerve coaptation device that provides mechanical repair strength equal or greater to clinically relevant microsuture repairs.

The Use of a Lumbrical Muscle Flap for Treatment of Chronic Tenocutaneous Fistula

Tenocutaneous fistulas after trauma or open release of the A1 pulley provide a unique reconstructive challenge. We describe the use of a lumbrical muscle turnover flap as a novel technique for managing these wounds and present its successful use in a patient with a tenocutaneous fistula after A1 pulley release of the middle finger. This flap provides a simple, local reconstructive option in patients with an array of palmar wounds that have failed conservative management.

Tendon Adhesions: A Novel Method of Objectively Measuring Adhesions by Assessing Tendon Glide Through a Soft Tissue Envelope in a Rat Model

PURPOSE

To develop a rat model of extra-synovial tendon adhesions that will enable accurate testing of scar barriers and adhesion inhibiting treatments to facilitate future research.

METHODS

Thirty-six 6-month-old male Sprague-Dawley rats were randomized to one of the 3 groups of 12. In Group A, the middle one-third portion of the left Achilles tendon was excised. In Group B, the tendon and soft tissue bed was abraded with steel wool. In Group C, a silk suture was sewn along the tendon. The right hind limbs served as controls. At 4 weeks, biomechanical testing was performed on the bilateral hind limbs. The Achilles tendon was cut at the gastrocnemius-tendon junction proximal to the "adhesion zone" (or analogous level in the control limb). The calcaneal insertion of the Achilles was attached to a tensiometer. The force needed to pull the tendon out of its soft tissue envelope at a fixed rate was measured.

RESULTS

Three rats were excluded because of complications during data collection. Pair-wise comparison testing was performed, comparing the mean peak force to pull the Achilles tendon from its soft tissue envelope in 33 control limbs and the contralateral limb from each group. The average peak force for the cut tendon group (A) was 20.1 N, 18.8 N in the steel wool group (B), and 21.1 N in the suture group (C). The average peak force in the control limbs was 15.6 N. There was a significant difference noted in peak forces between the control limbs and each experimental group.

CONCLUSIONS

A consistent and statistically increased force was necessary to pull a rodent Achilles tendon from an adhesion-induced tissue bed compared with controls. No statistical difference was detected between experimental groups.

CLINICAL RELEVANCE

Our study demonstrates an objective method of biomechanical tendon adhesion assessment in a rat model.

Fixation for metacarpal neck fracture: a biomechanical study

BACKGROUND

There is no robust evidence of the best operative treatment for displaced unstable metacarpal neck fractures. Numerous constructs are used in the fixation of metacarpal neck fractures. Currently, two common methods are dorsal locking plate and K-wire fixation. A new metacarpal sled fixation system for metacarpal neck fracture was designed to provide fracture stability but limit dissection and avoid exposed hardware. The purpose of this study was to compare the biomechanical integrity of the metacarpal sled versus standard locking plate fixation and retrograde K-wire fixation in a simulated porcine metacarpal fracture model.

METHODS

Transverse metacarpal neck fractures were created in 30 porcine second metacarpals. The specimens were randomly fixed with locking plates, metacarpal sleds, or retrograde K-wires. Constructs were then loaded to failure in three-point bending. Stiffness and peak load were measured from the load-to-failure deflection curve. Data were analyzed via ANOVA, followed by Tukey-Kramer's post hoc pairwise comparison.

RESULTS

The K-wire group had the highest initial stiffness followed by the sled group and then the plate group. Statistical difference was only found between K-wires and plate. Peak load for the K-wire group was lowest, followed by sled, and then by plate. A statistically significant difference was observed between the peak loads of the K-wires and plate, as well as the sled and plate. However, a difference in peak load was not detected between the K-wires and sled.

CONCLUSIONS

For transverse metacarpal neck fractures, a metacarpal sled construct provides similar fixation to K-wires with limited dissection and without exposed hardware or the potential for soft tissue tethering. The new low profile construct using a minimally invasive technique would be suitable for unstable metacarpal neck fractures.

Reattachment of flexor digitorum profundus avulsion: biomechanical performance of 3 techniques

PURPOSE

To investigate whether inclusion of the volar plate in repair of flexor digitorum profundus avulsions increases the strength of the repair and resists gapping.

METHODS

Cadaveric fingers (n = 18) were divided into 3 equal groups. The first technique involved 2 micro-suture anchors only (A). The second used only volar plate repair (VP). The third group was a hybrid, combining a micro-suture anchor with volar plate augmentation (AVP). Specimens were loaded cyclically to simulate passive motion rehabilitation before being loaded to failure. Clinical failure was defined as 3 mm of gapping, and physical failure as the highest load associated with hardware failure, suture breakage, anchor pullout, or volar plate avulsion.

RESULTS

Gapping throughout cycling was significantly greater for the A group than VP and AVP with no difference detected between VP and AVP groups. Gapping exceeded 3 mm during cycling of 3 A specimens, but in none of the VP or AVP specimens. Load at clinical and physical failure for A was significantly lower than for VP and AVP, whereas no difference was detected between VP and AVP.

CONCLUSIONS

In this cadaveric model, incorporating the volar plate conferred a significant advantage in strength, increasing the mean load to physical failure by approximately 100 N.

CLINICAL RELEVANCE

According to previous biomechanical studies, current reconstructive strategies for flexor digitorum profundus zone I avulsions are not strong enough to withstand active motion rehabilitation. We demonstrated the potential use of volar plate augmentation and the prospective advantageous increase in strength in this cadaveric model. In vivo performance and effects on digital motion are not known.

Range of motion effects of distal pole scaphoid excision and triquetral excision after radioscapholunate fusion: a cadaver study

PURPOSE

Radioscapholunate (RSL) fusion is an effective surgical procedure for the treatment of isolated radiocarpal arthritis. Although functional wrist motion is typically preserved through the midcarpal joint, many patients are still frustrated by postoperative limitations. The purpose of this study was to evaluate motion of cadaver wrists after simulated RSL fusion with excision of the distal pole of the scaphoid and the triquetrum.

METHODS

Ten fresh-frozen cadaver upper extremities were mounted on a custom testing apparatus after isolation of the flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis longus, and extensor carpi ulnaris tendons. Sequential loading of these tendons resulted in flexion, extension, radial, and ulnar deviation. We subsequently measured range of motion with the use of digital photography. All specimens were tested in 4 states: intact (normal), RSL fusion (simulated), RSL fusion with distal scaphoid pole excision, and RSL fusion with distal scaphoid pole and triquetrum excision. The results were statistically analyzed using a repeated measures analysis of variance.

RESULTS

Range of motion decreased to 39% to 46% of normal for flexion and extension and 65% to 71% of normal for radial and ulnar deviation after simulated RSL fusion. The addition of distal pole of scaphoid excision resulted in flexion and extension returning to 72% to 79% of normal, and radial and ulnar deviation returning to 84% to 89% of normal. Excision of the triquetrum further increased flexion and extension to 87% to 97% of normal, and radial and ulnar deviation to 119% to 137% of normal.

CONCLUSIONS

The combination of triquetral and distal scaphoid pole excision after RSL fusion improves wrist motion to levels close to normal in the cadaver model.

Biomechanical comparison of the holding strength of a peek-optima circular plate versus a stainless steel oblique T-plate for radioscapholunate arthrodesis

PURPOSE

Radioscapholunate arthrodesis is an accepted treatment for posttraumatic radiocarpal arthritis that preserves some wrist motion. Good results are dependent on secure fixation while avoiding hardware-related side effects. A small radiolucent countersunk circular plate placed over the radiocarpal joint may offer a low-profile technique for achieving secure fixation of the radioscapholunate joint. The purpose of this study was to compare the biomechanical performance of this circular plate, when applied in this manner, to that of a more conventional fixation technique such as a 3.5-mm T-plate.

METHODS

Ten pairs of fresh-frozen cadaveric wrists were amputated 7 cm proximal to the radiocarpal joint. One wrist from each pair was fixed with a T-plate (DePuy, Inc., Warsaw, IN), and the contralateral wrist was fixed with a circular plate (Xpode plate; TriMed, Inc., Valencia, CA). The radius and scaphoid-lunate complex were each rigidly held and mounted into a materials testing machine. Translational forces to mimic extension and flexion movements were applied cyclically for 40 cycles, followed by failure testing in extension.

RESULTS

Cyclic tests revealed no statistically significant differences between the 2 fixation plates although resistance to flexion motion was higher than resistance to extension motion. The average load at failure was no different between the T-plate and circular plate. However, a ratio of the failure loads (T-plate to circular plate) demonstrated a 58% higher load for the circular plate.

CONCLUSIONS

A countersunk circular plate provides similar biomechanical performance to the T-plate for radioscapholunate arthrodesis.

Comparative analysis of biomechanical performance of available "nerve glues"

PURPOSE

To compare a variety of potentially useful artificial and biological sealants applied to sutured nerve repairs to decrease gapping at the repaired site.

METHODS

Fifty-seven fresh-frozen cadaveric nerve specimens were transected and repaired with two 8-0 nylon epineural sutures placed 180 degrees apart. The specimens were divided into 5 groups. Four groups received augmentation of the repair with application of either autologous fibrin glue, Tisseel fibrin glue, Evicel fibrin glue, or DuraSeal polyethylene glycol-based hydrogel sealant, and the fifth group had no glue. Each nerve construct was mounted in a servohydraulic materials testing machine and stretched at a constant 5 mm/min displacement rate until failure. A noncontact video analysis permitted normalization of stretch within the repair region. Statistical analysis was performed via analysis of variance followed by Tukey-Kramer post hoc pairwise comparison when indicated.

RESULTS

Resistance to gapping as measured through normalized stiffness (N/mm/mm) was greater for the Tisseel group, Evicel group, and DuraSeal group versus the no-glue group only. The stiffness of the autologous group approached significance versus the no-glue group. There were no significant differences in stiffness between any of the nerve glue groups. There was no statistical difference for the peak load at failure between any of the groups.

CONCLUSIONS

Avoidance of gapping at the nerve repair site is crucial in achieving successful nerve regeneration. Commercially available tissue sealants (Tisseel, Evicel, and DuraSeal), when used to augment 2-suture nerve repairs, as in our protocol, help prevent this initial gapping. None of the tissue sealants tested, however, increased the ultimate load to complete failure of the repair.

Analysis of relative motion splint in the treatment of zone VI extensor tendon injuries

PURPOSE

Early protected motion after extensor tendon repair is desirable. The low-profile relative motion splint, described previously by Merritt et al, holds the affected digit in 15 degrees of extension relative to the uninjured digits to allow less-cumbersome early protected motion versus dynamic splinting. Although early clinical results have been favorable, formal biomechanic testing of this approach is lacking. We used an in vitro model to assess the effect of the low-profile relative motion splint on the biomechanics of zone VI extensor tendons by measuring tendon elongation with and without the splint. Tendon elongation also was measured after transection and repair of extensor tendons in zone VI with and without splint protection.

METHODS

Ten fresh-frozen cadeveric upper extremities were prepared and mounted on a testing apparatus with the wrist in 25 degrees of extension. Alternating applications of extension and flexion loads to the tendons induced a full range of motion for 25 cycles. Differential variable reluctance transducers were applied to zone VI of the index, middle, and ring extensor tendons. Measurements of intact tendon microelongation (or strain) were obtained with and without the relative motion splint. The middle finger extensor tendon then was transected (in zone VI) and was repaired immediately. Measurements were repeated with and without splint protection. Elongation ratios were calculated and analyzed statistically.

RESULTS

For the intact tendon of the middle finger splinting reduced the elongation by 1% in extension, by 2% in flexion, and by 3% in neutral position. After the transection and repair of this same tendon, the splint reduced the elongation by 5% in extension, by 7% in flexion, and by 6% in neutral position. Cycling without splint protection caused permanent stretching at the repair site. Reapplication of the splint decreased elongation at the repair site by 2% in extension, by 3% in flexion, and by 3% in neutral position.

CONCLUSIONS

The relative motion splint reduces the effective strain on intact and repaired zone VI middle finger extensor tendons and supports its clinical use.

When speech conflicts with seeing: young children's understanding of informational priority

In a series of investigations we found that children between 3 and 5 years of age judged that an utterance (such as, "There's milk in the jug") would be ignored by a listener who had previously seen something contradictory (orange juice in the jug). However, children judged that the listener would believe the message "There's milk in the jug" when he had not previously seen inside. In these various conditions, child participants had not seen for themselves what was inside the jug, so it was impossible for their own directly perceived knowledge to contaminate their judgments of what the protagonist believed. Under these conditions, even many false-belief failers did not assume that the listener would believe whatever they themselves thought was true. Moreover, the results of control conditions suggested that children's success could not be attributed to low-level strategies. These results seem to indicate an early understanding of how people prioritize information, with the consequence that they acknowledge that one and the same message would be believed in one context but not in another.

Contamination in reasoning about false belief: an instance of realist bias in adults but not children

Children aged around 5 and 9 years and adults were presented with stories and videos about a protagonist who heard a message purporting to provide factual information. Observing subjects knew whether the message was true or false. In some cases, this message contradicted the listener's existing belief based on what he or she had seen previously. Subjects judged whether the listener would believe or disbelieve the message. Child subjects frequently judged that a contradicting message would be disbelieved, irrespective of whether they (the child subjects) knew it to be true or false. In contrast, adult subjects made judgements that were contaminated by their own privileged knowledge of the truth. For three different scenarios, adult subjects judged more frequently that the message would be believed if they (but not the listener protagonist) knew it to be true, than if they thought it was false.