Robert K. Zahn

Biomechanical evaluation of flexor tendon repair using barbed suture material: a comparative ex vivo study.

PURPOSE Barbed suture material for tendon repair opens up the possibility of a knotless reconstruction due to an increased suture-tendon interaction. The aim of this study was to compare the tensile strength of a knotted technique with a monofilament polydioxane suture to that of a knotless technique with a barbed suture material, by using a multistrand, modified Kirchmayr-Kessler tenorrhaphy. METHODS Sixty human flexor digitorum tendons were randomized into 4 groups. A modified, knotted, multistrand Kirchmayr-Kessler technique with an absorbable, monofilament polydioxane suture was compared with a modified, knotless, multistrand Kirchmayr-Kessler technique with an absorbable, unidirectional barbed glycolic-carbonate suture. Tendons were distracted to failure. Mode of failure and load to failure were recorded. RESULTS The knotless 2-strand Kirchmayr-Kessler barbed suture shows a significantly lower tensile strength than the knotted 2-strand polydioxane suture (p < .001). The comparison of the maximum tensile strength of the knotless (glycolic-carbonate) technique with that of the knotted (polydioxane) 4-strand technique resulted in no significant difference in either technique utilized (p = .737). The tensile strength of the 4-strand technique was greater than that of the corresponding 2-strand technique (p < .001). CONCLUSIONS The 2-strand Kirchmayr-Kessler barbed suture proved to be insufficient and significantly weaker than the 2-strand polydioxane suture, and therefore it cannot be recommended. With the knotless 4-strand Kirchmayr-Kessler technique, the barbed suture material has the potential to be used in flexor tendon surgery, but it has no advantage over the 4-strand polydioxane suture.

A contoured locking plate for distal fibular fractures in osteoporotic bone: A biomechanical cadaver study

OBJECTIVE Fixation of ankle fractures in elderly patients is associated with reduced stability conditioned by osteoporotic bone. Therefore, fixation with implants providing improved biomechanical features could allow a more functional treatment, diminish implant failure and avoid consequences of immobilisation. MATERIALS AND METHODS In the actual study, we evaluated a lateral conventional contoured plate with a locking contoured plate stabilising experimentally induced distal fibular fractures in human cadavers from elderly. Ankle fractures were induced by the supination-external rotation mechanism according to Lauge-Hansen. Stage II fractures (AO 44-B1) were fixed with the 2 contoured plates and a torque to failure test was performed. Bone mineral density (BMD) was measured by quantitative computed tomography to correlate the parameters of the biomechanical experiments with bone quality. RESULTS The locking plate showed a higher torque to failure, angle at failure, and maximal torque compared to the conventional plate. In contrast to the nonlocking system, fixation with the locking plate was independent of BMD. CONCLUSION Fixation of distal fibular fractures in osteoporotic bone with the contoured locking plate may be advantageous as compared to the nonlocking contoured plate. The locking plate with improved biomechanical attributes may allow a more functional treatment, reduce complications and consequences of immobilisation.

Reduced ictogenic potential of 4-aminopyridine in the perirhinal and entorhinal cortex of kainate-treated chronic epileptic rats

We investigated the potential of 4-AP (50-100 microM) to induce seizure-like events (SLEs) in combined entorhinal cortex-hippocampal slices from Sprague Dawley rats which developed spontaneous limbic seizures following kainic acid induced status epilepticus. Slices from control rats (n=8) displayed SLEs in the entorhinal and perirhinal cortex upon application of 50 or 100 microM 4-AP. By contrast, 4-AP failed to induce SLEs in slices from chronic epileptic rats (n=13) except for one slice from one rat. This animal displayed only minor cell loss in layer III of the entorhinal cortex, in contrast to the other epileptic rats for which layer III neuronal loss was extensive. In all slices from epileptic rats, 4-AP induced recurrent epileptiform discharges similar to the interictal activity observed in control rats. Combined application of 4-AP (100 microM) and bicuculline methiodide (30 microM) induced frequent and prolonged recurrent epileptiform discharges in both control and chronic epileptic rats. 4-AP at 50-100 microM likely affects potassium channels containing Kv1.4, Kv1.5, Kv3.1 or Kv3.2 subunits. Real-time PCR revealed no significant downregulation of Kv1.4, Kv1.5, Kv3.1 or Kv3.2 in the subiculum, entorhinal and perirhinal cortex from chronic epileptic rats compared to controls. However, the expression of Kv3.4, responding to 4-AP in mM range, was significantly reduced. Using sub-unit-specific antibodies, the real-time PCR findings were confirmed by immunocytochemistry. We suggest that after chronic epilepsy, reorganization in the entorhinal cortex is accompanied by adaptations in homeostatic plasticity with anticonvulsant consequences.

RNA editing of Kv1.1 channels may account for reduced ictogenic potential of 4-aminopyridine in chronic epileptic rats.

In rat brain slices, the Kv channel blocker 4‐aminopyridine (4‐AP) induces seizure‐like events. This effect is absent in slices from chronic epileptic rats generated using the kainic acid model. The reason for this phenomenon remained elusive as an altered expression level of Kv channels was ruled out as a mechanism. We recently described that the Ile400Val RNA editing of Kv1.1 generates 4‐AP–insensitive Kv1 channels (Kv1.1I400V). We therefore hypothesized that altered RNA editing levels account for the reduced ictogenic potency of 4‐AP in chronic epileptic rats. We found fourfold increased RNA editing ratios in the entorhinal cortex of chronic epileptic animals compared to healthy control animals. Electrophysiologic recordings in Xenopus oocytes revealed that the observed increased Kv1.1I400V editing level can in fact lead to significant loss of 4‐AP sensitivity. Our data suggest that altered Kv1.1I400V RNA editing contributes to the reduced ictogenic potential of 4‐AP in chronic epileptic rats.

Tensile Strength of Flexor Tendon Repair Using Barbed Suture Material in a Dynamic Ex Vivo Model

The purpose of this study was to compare two sutures; a knotted polydioxane with a knotless barbed in a 4-strand Kirchmayr-Kessler suture technique. Human flexor digitorum tendons were separated into four groups. Group 1 – polydioxane; Group 2 - barbed suture; Group 3 and 4 – same as group 1 and 2 with an additional peripheral running suture. In each group the repaired tendons were subjected to linear and cyclical loads. No difference in maximum tensile strength after linear and cyclical force could be detected between the knotted polydioxane suture and the knotless barbed suture. On linear force tests an additional circumferential repair increased the maximum tensile strength of both sutures. Cyclical force loading did not lead to a reduction of maximum strength. Following linear and cyclical loading the 4-strand barbed suture achieved maximum tensile strengths comparable to the 4-strand repair using the polydioxane suture. Barbed suture repair may offer the advantage of knotless suture techniques.

Glutamine induces epileptiform discharges in superficial layers of the medial entorhinal cortex from pilocarpine-treated chronic epileptic rats in vitro

Purpose:  Glutamine (GLN) is a precursor for synthesis of glutamate and γ‐aminobutyric acid (GABA) and has been found in the cerebrospinal fluid (CSF) at mean concentrations of 0.6 mM. Experiments on slices are usually performed in artificial CSF (aCSF) kept free of amino acids. Therefore, the role of glutamine, particularly in tissue of epileptic animals, remains elusive.

Reduced ictogenic potential of 4-aminopyridine in the hippocampal region in the pilocarpine model of epilepsy

It was previously shown that the ictogenic potential of 4-aminopyridine (4-AP) was reduced in the parahippocampal region of kainate treated chronic epileptic rats. In the actual study we investigated the potential of 4-aminopyridine (50 and 100μM) to induce seizure like events (SLEs) in combined entorhinal cortex hippocampal slices from Wistar rats following pilocarpine induced status epilepticus. The potential of 4-AP to induce SLEs in the entorhinal cortex was reduced in the latent period and in slices of chronic epileptic animals with a high seizure incidence in vivo (>2seizures/24h). 4-AP induced SLEs in slices from animals with a low incidence of seizures in vivo (<2seizures/24h) in a similar manner as compared to controls. The hippocampal formation displayed no SLEs, instead short recurrent epileptiform discharges (REDs) were evoked by application of 4-AP in areas CA3 and CA1. The incidence of REDs was largest in slices from control animals. This study shows that the reduced ictogenic potential of 4-AP is not restricted to kainate treated chronic epileptic animals as it can be found in the pilocarpine model as well. The underlying mechanisms may relate to altered expression and editing of voltage gated potassium channels.

Subfascial directionality of perforators of the distal lower extremity: an anatomic study regarding selection of perforators for 180-degree propeller flaps.

BackgroundThe 180-degree propeller flaps allow closure of soft-tissue defects of the distal lower extremity. In addition to twist, the pedicle is often subject to additional kinking which increases proportionally to the angle at which the perforator pierces through the fascia. This study evaluates the directionality of the perforators at the fascial level to guide in the selection process of the best perforator. Material and MethodsPerforators were identified in the lower extremities of 16 fresh cadavers. The angle of fascial perforation was measured. Perforators were grouped according to source vessel and location. Results were analyzed statistically regarding angle of fascial perforation along the source vessel and region. ResultsA total of 324 perforators were identified. Distal perforators pierced the fascia at a significantly greater angle than in the proximal and middle segment of the peroneal and anterior tibial vessels (P < 0.005). Perforators originating from the posterior tibial artery pierced the fascia at less acute angles distally. When grouped according to the region of the perforators, no significant difference was found between perforators from all source vessels in the proximal region of the distal lower extremity. Even distally, perforators from the posterior tibial artery traveled almost perpendicular (P < 0.005). ConclusionPerforators traveling in a near perpendicular manner are ideal to serve as a pedicle for 180-degree propeller flaps as solely the twist has to be distributed along the vessel. The posterior tibial artery was the source to perforators with the most constant, near-perpendicular course, predisposing them for use in 180-degree propeller flaps.

Reconstruction of pressure sores with perforator-based propeller flaps.

Perforator flaps have been successfully used for reconstruction of pressure sores. Although V-Y advancement flaps approximate debrided wound edges, perforator-based propeller flaps allow rotation of healthy tissue into the defect. Perforator-based propeller flaps were planned in 13 patients. Seven pressure sores were over the sacrum, five over the ischial tuberosity, and one on the tip of the scapula. Three patients were paraplegic, six were bedridden, and five were ambulatory. In three patients, no perforators were found. In 10 patients, propeller flaps were transferred. In two patients, total flap necrosis occurred, which was reconstructed with local advancement flaps. In two cases, a wound dehiscence occurred and had to be revised. One hematoma required evacuation. No further complications were noted. No recurrence at the flap site occurred. Local perforator flaps allow closure of pressure sores without harvesting muscle. The propeller version has the added benefit of transferring tissue from a distant site, avoiding reapproximation of original wound edges. Twisting of the pedicle may cause torsion and venous obstruction. This can be avoided by dissecting a pedicle of at least 3 cm. Propeller flaps are a safe option for soft tissue reconstruction of pressure sores.

A Locking Contoured Plate for Distal Fibular Fractures: Mechanical Evaluation in an Osteoporotic Bone Model Using Screws of Different Length

Osteoporotic bone with poor mechanical capacity provides limited stability after fixation of ankle fractures. Stabilization with an implant providing increased fixation strength in osteoporotic bone could reduce failure rates of fixation and allow a more functional treatment. The purpose of this study was to evaluate a locking contoured plate for fixation of distal fibular fractures in comparison with a conventional contoured plate in an osteoporotic bone model. Eighty cylinders of osteoporotic bone surrogates were fixed with the two plates. We performed torque-to-failure and cyclic testing experiments using screws of different length with a Zwick/Roell testing machine. The locking system showed higher torque-to-failure and maximum torque levels as compared with the conventional plate in torque-to-failure experiments and torsional cyclic testing. The locking contoured plate provides improved fixation strength in the osteoporotic bone model. The locking system may be appropriate for fixation of distal fibular fractures, especially in osteoporotic bone with poor mechanical capacity.