Craig Howard

Functional assessment in the rat by ground reaction forces.

Although the rat sciatic nerve model is used extensively in the investigation of repair techniques, and a variety of evaluation methods utilized to assess the results, a means to measure directly and accurately the return of function in these animals is absent. Histologic, histomorphometric, and electrophysiologic methods can be reliable indicators of nerve regeneration but do not correlate to functional recovery. The purposes of this study were to develop apparatus to continuously measure ground reaction forces (GRF) and use GRF parameters in the assessment of gait parameters in normal rats preoperatively and following peripheral nerve severance and repair. Three neurorrhaphy methods: direct sciatic nerve repair, direct tibial nerve repair and double sciatic nerve repair simulating autograft, as well as a non-repaired tibial nerve transection were evaluated. The testing apparatus was designed to measure the spontaneous and voluntary effort of the rat with objective data. Three orthogonal components - vertical, craniocaudal (braking and propulsion), and mediolateral - of the ground reaction force were measured. Preoperative data showed that vertical forces were comparable among the four limbs but propulsion and braking forces displayed significant differences. At 12 weeks, functional recovery was most evident in the direct tibial nerve repair group and absent in the non-repaired tibial defect group. Direct sciatic nerve repairs and sciatic nerve grafts resulted in lesser degrees of improvement. Results indicated that the propulsive force is the optimal GRF parameter for evaluating recovery of useful function.

Ulnar coronoid process anatomy : Possible implications for elbow instability

Ulnar coronoid process fractures are relatively uncommon injuries usually occurring with elbow dislocations and contributing to elbow instability. Recent evidence suggests coronoid tip fractures have a role in the instability. We sought to quantify the capsular and brachialis attachments of the ulnar coronoid process to better understand why instability occurs. We prepared eight fresh-frozen cadaveric specimens to ascertain the specific attachment locations. After dissection, we isolated and resected the proximal ulna, including the coronoid process and its soft tissue attachments. We then embedded, sectioned, and stained the specimens. The average distance from the tip of the coronoid to the proximal capsule was 2.36 ± 0.39 mm. The average distance from the tip of the coronoid to the proximal brachialis insertion was10.13 ± 1.6 mm. Most coronoid tip fractures included disruption of the anterior capsule, which potentially explains why instability can be associated with these fractures.

Absorbable versus nonabsorbable suture for microneurorrhaphy.

The results of epineural microneurorrhaphy with use of 10/0 monofilament absorbable (Vicryl and Dexon) and nonabsorbable ( Dermalon , Ethilon, and Prolene) microsuture were compared in 150 isogeneic male Sprague-Dawley rats. After sciatic nerve transection and epineural repair, the animals were observed clinically and reexplored before death at intervals from 2 days to 20 weeks. Half of the animals were randomly selected for electrodiagnostic studies at 6, 12, and 20 weeks before sacrificed. We found no significant clinical, electrodiagnostic, or histologic differences affecting axonal regeneration that were attributable to any of the suture types used. All sutures incited moderate zones of localized inflammation acutely. After dissolution, the absorbable group was essentially free of inflammation, whereas the nonabsorbable sutures persisted in small local granulomas. A possible advantage may be suggested in the use of monofilament absorbable sutures for microneural repairs in certain situations.

Biomechanical comparison of femoral fixation devices for anterior cruciate ligament reconstruction using a novel testing method

BACKGROUND A novel biomechanical test method was implemented to compare the mechanical performance of two femoral fixation anchors (AperFix(r), Cayenne Medical, Scottsdale, AZ, USA or the AppianFx(r), KFx Medical, Carlsbad, CA, USA) that were utilized in anterior cruciate ligament reconstruction. METHODS Anterior cruciate ligament reconstructions were performed in 20 porcine femurs by using bovine extensor tendon grafts secured with 9 mm femoral anchors (AperFix(r) or AppianFx(r)). 10 specimens were tested for each anchor type. Infrared position sensors determined the repair construct displacements during conditioning (20 cycles at 5-50 N at 0.25 Hz), cyclic loading (1500 cycles at 50-200 N at 1 Hz), and ultimate loading (150 mm/min). Outcomes included tendon elongation, anchor displacement, stiffness, maximum load, yield load, and load at 5mm of anchor displacement. It was hypothesized that there would be no differences in the outcomes of these two devices. Independent measure t-tests compared the performance of the devices (p<0.05). FINDINGS The performance of the two anchors was comparable during the cyclic loading. During ultimate loading, a statistically higher yield load (p<0.01) and a load at 5mm of anchor displacement (p<0.01) were demonstrated for the AppianFx(r) as compared to AperFix(r). Maximum load and stiffness were not significantly different. INTERPRETATION Given the good clinical track record of the AperFix(r), the comparable, and in some cases superior, the biomechanical data presented here for the AppianFx(r) are encouraging for their clinical implementation. This study also introduced a novel test method that directly tracks the relevant construct displacements during cyclic and ultimate loading tests of the anterior cruciate ligament reconstructions.

Energy Absorbed by Longitudinally Splitting a Tibialis Anterior Allograft: Implications for Double-Bundle Anterior Cruciate Ligament Reconstruction

PURPOSE Split tibialis anterior (TA) allografts have been proposed as a source for double-bundle anterior cruciate ligament reconstruction. We sought to determine whether longitudinally splitting a TA tendon leads to a change in the mechanical properties of the tendon. METHODS Seven cadaveric matched pairs of TA tendons were procured. One member of each pair was longitudinally pierced in its midportion and then bluntly split, creating 2 longitudinally divided grafts. The other member of the pair remained intact. Each tendon was then frozen into thermoelectrically cooled clamps and loaded to failure on an MTS machine (MTS Systems, Eden Prairie, MN) at a displacement of 1 mm/s. The area under the force-versus-displacement curve was calculated as an indicator of energy absorbed by the tendon before failure. The energy absorbed by the intact tendon was then compared with the summed energy absorbed by the 2 specimens obtained by splitting the sibling specimen. RESULTS Energy absorbed by the intact tendon was 10,300 +/- 3,433 Nmm, whereas total energy absorbed by the 2 longitudinally split tendons was 10,530 +/- 2,095 Nmm (P = .78). CONCLUSIONS Longitudinal splitting of a TA allograft by the technique described does not significantly affect the grafts ability to absorb energy. CLINICAL RELEVANCE The splitting technique described can safely be used to create 2 grafts if surgeons wish to use a TA graft for a double-bundle anterior cruciate ligament reconstruction or for reconstruction by use of fixation devices requiring 2 looped tendon grafts.

PERIPHERAL NERVE REPAIR USING NON NEURAL SHEATHS AND CONDUITS

The purpose of this study was to evaluate and compare peripheral nerve regeneration following the use of alternative non neural materials to traditional direct repair techniques and autologous nerve graft. Autologous vein and synthetic polytetrafluoroethylene (PTFE) segments were used to repair standardized defects of the tibial nerve in rabbits. The materials served as sheaths for direct primary repairs and as conduits to bridge a gap in the nerve. Evaluations performed at five months revealed that direct primary repairs ensheathed by vein segments produced a significantly greater number of axons regenerating across the repair site, whereas PTFE, either as a sheath or conduit, failed to improve axonal regeneration. Also, vein conduits used to bridge nerve gaps was less effective than traditional nerve grafts.