Comparison of continuous and interrupted suture techniques in microvascular anastomosis.

We evaluated the efficacy of the continuous suture technique (CST) in arteries and veins with varying external diameters (ED). In study 1 a direct end-to-end anastomosis was performed in 5 groups of animals (n = 15 in each group): group 1, rabbit carotid artery (ED, 1.8-2.0 mm); group 2, rabbit femoral artery (ED, 1.4-1.6 mm); group 3, rat femoral artery (ED, 0.7-0.9 mm); group 4, rabbit femoral vein (ED, 2.0-2.2 mm); and group 5, rat femoral vein (ED, 1.0-1.2 mm). In study 2 a graft from the femoral vein was interposed into the carotid artery, with a ratio of the diameter of graft to artery of 1.3:1 in the rats (group 6, n = 12) and 1:1 in the rabbits (group 7, n = 12). In each animal the vessel on one side was repaired using CST and the opposite vessel using the interrupted suture technique. Vessel samples were harvested 1, 2, and 4 weeks after anastomosis. The CST significantly reduced anastomosis time by up to 47% in arteries and 41% in veins. Bleeding time and blood loss were also significantly reduced with CST. Similar results were found in study 2. The total thrombosis rate was 8%, but no significant patency difference was noted between the CST and the interrupted suture technique in any vessel category. We conclude that the CST is a reliable and time-saving procedure in microvascular anastomosis of arteries with diameters greater than 0.7 mm and of veins with diameters greater than 1.0 mm.

S-nitroso-N-acetylcysteine protects skeletal muscle against reperfusion injury.

The effects of a nitric oxide (NO) donor on microcirculation and contractile function of reperfused skeletal muscle were studied. Rat cremaster muscles underwent 5 hours of ischemia and 90 minutes of reperfusion and were divided into two groups systemically infused with S-nitroso-N-acetylcysteine (SNAC, 100 nmol/min) and phosphate-buffered saline (PBS), respectively. The results showed that the vessels in the SNAC group had more rapid and complete recovery than that in controls. A significant difference was found from 10 to 40 minutes and at 90 minutes in 10-20-microm arterioles, from 10 to 90 minutes in 20-40-microm arterioles, and at 10 and 90 minutes in 40-70-microm arteries. When compared to controls, SNAC-treated muscles showed larger fluorescein filling areas at 15, 30, 60, and 90 minutes and greater isometric tetanic contractile forces in response to stimulation frequencies of 40, 70, 100, and 120 Hz. The data indicate that supplementation of exogenous NO could effectively improve microcirculation and contractile function of skeletal muscle during early reperfusion.

Effects of S-nitroso-N-acetylcysteine on contractile function of reperfused skeletal muscle.

The ultimate goal of replantation and microsurgical reconstructive operations is to regain or improve impaired function of the tissue. However, the data related to the influence of NO on tissue function are limited. This study evaluated the effects of the NO donor S-nitroso-N-acetylcysteine (SNAC) on contractile function of skeletal muscle during reperfusion. Forty-nine rats were divided into six groups. The extensor digitorum longus (EDL) muscles in groups I and II were not subjected to ischemia-reperfusion but were treated with a low (100 nmol/min) or high (1 mumol/min) dose of SNAC. In groups III-V, the EDL underwent 3 h of ischemia and 3 h of reperfusion and was also treated with low (100 nmol/min) or high doses (1 or 5 mumol/min) of SNAC. Group VI was a phosphate-buffered saline (PBS)-treated control group. Twenty additional animals were used to document systemic effects of SNAC and PBS only. SNAC or PBS was infused for 6.5 h, beginning 30 min before ischemia and continuing throughout the duration of reperfusion. Contractile testing compared the maximal twitch force, isometric tetanic contractile forces, fatigue, and fatigue half time of the experimental EDL and the contralateral nontreated EDL. The findings indicate that 1) SNAC does not influence contractile function of EDL muscle not subjected to ischemia-reperfusion, 2) SNAC significantly protects the contractile function of ischemic skeletal muscle against reperfusion injury in the early reperfusion period, and 3) the protective role of SNAC is critically dosage dependent; protection is lost at higher doses. The conclusion from this study is that supplementation with exogenous NO exerts a protective effect on the tissue against reperfusion injury.

Antithrombotic potencies of enoxaparin in microvascular surgery: influence of dose and administration methods on patency rate of crushed arterial anastomoses.

This study evaluated the influence of the dose and administration methods of enoxaparin, a low-molecular-weight heparin, on the patency rate of crushed rat femoral arteries following anastomosis. An impact crush with a 25-kg magnitude was applied to a 2-mm segment of 100 rat femoral arteries, followed by anastomosis. The arteries were divided into five groups: group 1 received systemic enoxaparin alone with a relatively high dose (45 IU) twice a day for 3 days; groups 2 and 3 received topical irrigation with a lower (15 IU/mL) concentration and a higher (45 IU/mL) concentration, respectively; group 4 received systemic and topical application at a lower (15 IU) dose and concentration (15 IU/mL); and group 5 received systemic and topical application at a higher (45 IU) dose and concentration (45 IU/mL). The results of this study demonstrate the following: (1) topical irrigation with enoxaparin at a concentration of 45 IU/mL-three times higher than that recommended for clinical use adjusted by body weight (15 IU/mL)-is effective for antithrombotic action; (2) a combination of systemic and local application does not offer additional benefit in the patency rate when compared to local irrigation alone; (3) systemic administration alone does not prevent thrombus formation; and (4) enoxaparin is potentially useful to enhance the patency rate in compromised microvessels.

Assessment of ischemia and reperfusion injury.

Direct videomicroscopy of the rat cremaster muscle microcirculation supplemented by animal models of replantation, vascular crushing, and muscle function after injury and recovery were used to investigate the occurrence of reperfusion failure. It is evident that failure of blood reflow may be induced by multiple factors that can be grouped into categories of ischemia, intimal damage, and systemic or local responses, which are referred to as the no reflow triad. The components comprising the 3 sides of the no reflow triad can interact with one another in an intricate manner, and any single factor or combination of factors is capable of triggering the events leading to reperfusion failure. The pronounced regional nature of reperfusion injury and the direct relationship between the severity of the observed vascular alterations and increasing duration of ischemia have been documented. The dynamic changes and histopathology of the microcirculation included constriction of the arteries, swelling of endothelial and leukocytes, and erythrocyte rouleaux formation during ischemia. As ischemia duration was lengthened, the degree of these changes increased correspondingly. The changes on reperfusion were disruption of blood flow patterns, vortex formation, regional stasis, adhesion and migration of leukocytes, focal hemorrhage, edema, vasospasm, and platelet aggregation. The deleterious effects of systemic acidosis, interstitial hemorrhage, denervation, and prolonged venous occlusion were subsequently documented. The application of information gained from this series of laboratory experiments has resulted in continued improvement in the success rate in clinical microvascular surgery.

Meniscal fixation with an absorbable staple. An experimental study in dogs.

An absorbable staple for meniscal fixation was developed and evaluated in an in vivo canine study. The staple consisted of two rigid barbed legs, made of a copolymer of polyglycolic acid and polylactic acid, connected by a flexible suture made of the same absorbable material. The staple was developed for arthroscopic use, eliminating the risk of nerve or vascular injuries associated with suture fixation. Eighty-two mongrel dogs underwent meniscal repair in this study, which was performed in two sequential parts. An incision was made in the medial meniscus at the peripheral third and was fixed with either the staple or with a single 3-0 PDS suture. The animals from the first part of the study, in which the biocompatibility of a prototype staple design, was evaluated were sacrificed at 3 days, 2 weeks, 6 weeks, 3 months, and 9 months. Those from the second part of the study, in which an improved staple design of the same material, was evaluated were sacrificed at 6 weeks, 4 months, and 1 year. The operated menisci were either examined histologically or were mechanically tested for tensile strength. Absorption of the staple began by 3 months and was almost complete by 1 year. Mechanically, the staple provided greater tensile strength augmentation of the meniscus than suture fixation for up to 4 months. In the long term, there was no difference between the staple and suture in enhancement of healing.

Tumor necrosis factor promotes motor functional recovery in crushed peripheral nerve.

The potential benefits of tumor necrosis factor pretreatment in promoting motor functional recovery of peripheral nerve following low load crush injury were examined. Using a specially designed crush device, rat sciatic nerve was subjected to a low load crush injury of 2-h duration. Recombinant murine tumor necrosis factor and saline were intraperitoneally injected into the experimental and control animals, respectively, prior to nerve crushing. Subsequent motor function was evaluated at intervals by measurement of the sciatic functional index. There was significantly (P < 0.05 to < 0.01) more rapid recovery in the tumor necrosis factor pretreated group as compared to the controls between day 14 and day 28. The sciatic functional index in the tumor necrosis factor group improved to -69.3 +/- 5.3 at day 14 and to nearly normal at day 21. In contrast, the sciatic functional index in the control group was -95.5 +/- 3.1% at day 14 and did not approach normal until day 42. Histological results paralleled the functional findings. The results suggest that tumor necrosis factor pretreatment has the potential to attenuate neurostructural damage and promote motor functional recovery in rat peripheral nerve.

Functional effects of lymphotoxin on crushed peripheral nerve.

The effect of lymphotoxin (LT) on the functional recovery of crushed peripheral nerves was studied. Using a specially designed compression device, a 5 mm segment of the right sciatic nerve of rats was subjected to a 100 g crush load with a 2 hr duration. The rats in the experimental and control groups received two doses of LT (20 micrograms/kg each) or the same volume of saline, respectively, administered intraperitoneously 24 hr and 1 hr before the procedure. Walking track tests and histologic examinations were performed at intervals up to 56 days after the crush. Motor functional recovery in the LT pretreated group started at day 7 while the crushed limb in the control group remained totally dysfunctional. The sciatic functional index improved faster in the LT group than in the control group during the second week after the crush and reached a significant difference (P < 0.05) at day 18. Subsequently, both groups had a similar evolution. Histologic results paralleled the functional findings. In conclusion, LT can promote motor functional recovery of crushed rat peripheral nerve in the early stage of regeneration.

Efficacy of recombinant human manganese superoxide dismutase compared to allopurinol in protection of ischemic skeletal muscle against "no-reflow".

A growing body of experimental data indicates that the "no-reflow" phenomenon is a type of reperfusion injury in skeletal muscle which may, in part, be mediated by oxygen free radicals, and thus may be attenuated by using agents that scavenge or inhibit formation of these reactive oxygen metabolites. This study was undertaken to assess the efficacy of recombinant human manganese superoxide dismutase (rhMnSOD) in reducing reperfusion injury in skeletal muscle. The specific advantage of this agent over other SOD types is a much longer plasma half-life (5 to 7 hr), allowing better equilibration between extra- and intracellular compartments. The rat cremaster model was used to study "no-reflow" in skeletal muscle. Reperfusion injury in the muscle was assessed by fluorescein dye perfusion, myocyte creatine phosphokinase (CPK) release, and contractile function in response to electrical field stimulation. Compared with untreated saline control animals, those treated with rhMnSOD after 5 hr of cremasteric ischemia, had a significantly higher percentage area of blood reflow (78 percent +/- 6 percent of normal), a greater percentage tetanic (66 percent +/- 9 percent of normal) and twitch (56 percent +/- 9 percent of normal) contractile strength, and less CPK release (21.5 percent higher than pre-reperfusion baseline CPK levels) (p < 0.05). Untreated saline control CPK release (21.5 percent higher than the prereperfusion level. Animals treated with allopurinol also had a significantly higher percentage twitch contraction (47 percent +/- 14 percent of normal) and a lower CPK release (11.1 percent of the prereperfusion value) 45 min after reperfusion than untreated saline controls.(ABSTRACT TRUNCATED AT 250 WORDS)

A model of cortical window healing in the rabbit.

A rabbit femur cortical window model was developed to study the time-dependent mechanical and radiographic changes with various treatments of surgically created windows. In the present experiment the time-dependent differences in torsional whole bone strength between femora treated with window replacement and those treated without replacement were evaluated. The 3.175 mm diameter windows were surgically created with a power trephine at the lateral femoral isthmus unilaterally, with the contralateral femur serving as a paired control. In one group of animals the window was reconstructed by replacement of the excised cortical plug while in the other group the window was left unreplaced. Each group was divided into three subgroups sacrificed at 3, 6, and 9 weeks postoperatively. Lateral radiographs were obtained immediately prior to sacrifice. After sacrifice bilateral femora were harvested and loaded to failure on a torsional testing apparatus to obtain values for ultimate torque, maximum angle of deformation, and energy capacity expressed as percent of paired control. Replacement resulted in significantly greater whole bone strength (P < .041), and strength increased significantly with time (P < .006). Radiographic appearance correlated significantly with both treatment and time, but not strength. The model was sensitive to both treatment-dependent and time-dependent effects, demonstrating potential for evaluation of other cortical window treatments.

An electromyographic study of arm muscles during climbing.

Upper extremity muscle injuries from rock climbing are common. Knowledge of the activity of specific muscles during climbing may allow the development of training programs to reduce these injuries. This study evaluated the electrical activity of the first interosseous (IN), brachioradialis (BR), flexor digitorum superficialis (FD), and biceps brachii (BB) muscles in seven climbers by integrated electromyography (IEMG) during finger-tip pull-ups. The climbers, with forearms pronated, performed three consecutive pull-ups. Each pull-up consisted of: (1) hanging using four fingers of each hand, (2) pull-up to maximum elbow flexion, (3) slow return to starting position. The IEMG during maximum voluntary contraction (MVC) was obtained for each muscle separately, and the IEMG was normalized to MVC. During hanging, FD showed the highest normalized IEMG (0.64 +/- 0.20). During pull-up, the highest IEMG was produced by FD (0.69 +/- 0.25) and BR (0.67 +/- 0.19), while BB showed only 0.33 +/- 0.12 and IN 0.09 +/- 0.06. During lowering, FD again had the highest IEMG (0.74 +/- 0.24), while the EMG from BR was decreased to 0.42 +/- 0.14 and BB to 0.15 +/- 0.15. BR and BB showed an abrupt peak in EMG during pull-up and lowering, as opposed to FD which remained constantly highly activated, which suggests that FD does not contribute to elbow flexion even though it crosses the elbow joint. The high activation of FD and BR may explain their elevated incidence of injury during climbing. Thus, a reduction in climbing-related muscle injuries may be achieved by a training program that emphasizes conditioning of the BR and FD muscles.

The effect of heparin after microsurgical repair in traumatically damaged arteries.

A main consideration of microvascular surgery is the avoidance of thrombosis. This traditionally involves the avoidance of thrombogenic trauma, the establishment of normal blood flow and full vessel diameter, as well as the use of anticoagulants, such as heparin, as an antithrombotic measure. In the present study we assessed the effectiveness of heparin in maintaining patency in the femoral arteries of rats which have undergone a crush injury with damage to the intima and media layers of the wall. To accomplish this, the animals were treated with heparin 150 units or 300 units twice daily following microvascular repair using standard microsurgical techniques. Control animals received no treatment. The results of this study indicate that the number of patencies in experimentally-injured femoral arteries did not improve significantly following heparin treatment, although pharmacological doses of heparin (300 units twice daily) were associated with a somewhat lower rate of occlusions. We conclude that heparin appears unable to significantly prevent clotting in vessels which have experienced severe trauma to the intima and media layers.

Microvascular anastomoses in growing vessels: a long-term evaluation of nonabsorbable suture materials.

Diametric growth at the anastomotic site, following microvascular anastomoses in pediatric patients, remains a problem, when nonabsorbable suture material is used. This study investigated the long-term effects of femoral artery anastomoses with nonabsorbable sutures in 20 growing rats with a mean weight of 101 g. The right femoral artery was anastomosed with 10-0 polypropylene monofilament suture and the left with identical nylon suture, using 5 to 6 interrupted sutures for each end-to-end anastomosis. At a 6-month harvest, the mean body weight had increased by 729 percent and the diameter of the femoral artery by 240 percent. The patency rate at the anastomotic sites was 97.5 percent and the complication rate was 10 percent, including one occlusion and three aneurysm formations at the sites. Angiography, diameter measurement, and histology demonstrated no stenosis or thrombus formation in all animals. Histology also showed normal vessel lumen size and well-organized re-endothelialization, without intimal hyperplasia at the anastomosis sites. With an interrupted suture technique, nonabsorbable sutures do not compromise growth at the anastomosis site or long-term patency of the anastomosed vessels. This study indicates that interrupted nonabsorbable suture materials are able to create excellent long-term results in microvascular anastomoses in rapidly growing hosts.

Would revision arthroplasty be facilitated by extracorporeal shock wave lithotripsy? An evaluation including whole bone strength in dogs.

Extracorporeal shock-wave lithotripsy has been proposed as a modality to facilitate the removal of bone cement during revision arthroplasty; however, concomitant cortical microfractures have been reported. The current study examines the effect on whole bone strength of extracorporeal shock-wave lithotripsy directed at the cement-bone complex. Canine femora were subjected to manual cement extraction or lithotripsy followed by manual cement extraction. Contralateral femora served as controls. Torsional fractures were created, and maximum torque, maximum angular displacement, and energy capacity to failure were determined. Although cement extraction alone reduced mean torque by 6.6% and failed to reduce mean torque angle or mean energy capacity, the combination of lithotripsy and cement extraction reduced mean torque by 7.3%, mean torque angle by 14.3%, and mean energy capacity by 18.3%. No statistical significance was demonstrated between the two groups in torque, angle, or energy capacity. At magnitudes and numbers of shock waves previously shown to significantly reduce cement-bone interface mechanical strength, lithotripsy exposure had a minimal and insignificant effect on whole bone strength.

Graft isometricity in unitunnel anterior cruciate ligament reconstruction: analysis of influential factors using a radiographic model.

A radiographic model was developed to investigate the influence of three surgical variables on the change in attachment point distance (CAPD) of a hypothetical graft using the unitunnel technique of anterior cruciate ligament (ACL) reconstruction. Using three different femoral target points, we tested the hypothesis that varying the angle of knee flexion between 70 degrees and 110 degrees and varying the tibial starting point over a 4-cm range do not result in a significant variation in CAPD. We also tested the hypothesis that the CAPD from 0 degrees to 135 degrees is greater than the CAPD from 0 degrees to 90 degrees. There was a statistically significant correlation (r = 0.8465, P < 0.0001) between radiographically estimated and isometer-measured values of CAPD. The tibial starting point and the femoral target point were found to affect the CAPD significantly (P < 0.005). A more proximal tibial starting point was associated with a lower CAPD. Both the center of the anatomic femoral attachment of the ACL, and a point 1 mm medial to the junction of the roof and lateral wall of the femoral intercondylar notch and 6 mm anterior to its posterior margin, were associated with lower CAPD values than a target point 5 mm superior and posterior to the center of the femoral ACL attachment. The angle of knee flexion did not significantly affect the CAPD. The CAPD [0 degrees-135 degrees] was significantly greater than the CAPD [0 degree-90 degrees] for all combinations of variables (P < 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of 10-0 polypropylene and 10-0 nylon sutures in rat arterial anastomosis.

The selection of suture materials is an important factor in further improving the results of microsurgical operations. In this study, two kinds of nonabsorbable suture materials, 10-0 polypropylene and 10-0 nylon monofilament, were compared in end-to-end anastomosis of 66 femoral arteries of adult rats. Both suture types were of identical size (70 microns needle/28 microns suture) and each artery received eight sutures. The vessels were harvested at various intervals from 2 hr to 180 days postoperatively and were evaluated by pathology, radiology, and tensile strength test. The results show that both sutures are capable of achieving excellent long-term patency (100%) of anastomosed sites. Polypropylene suture was equivalent to nylon in mechanical integrity of the anastomosis sites but was superior in handling, knotting, and biocompatibility. These physical and biological properties of polypropylene sutures may offer the benefits of diminished early and late complications at anastomosis sites and reduced operation time. Enhancement of contrast against surrounding tissue may make polypropylene a superior alternative to nylon sutures for microsurgical use.

Revision arthroplasty facilitated by ultrasonic tool cement removal. An evaluation of whole bone strength in a canine model.

Ultrasonic driven tools have been developed to facilitate the removal of bone cement during revision arthroplasty. The effect on whole bone strength of cement removal by ultrasonic tools was examined in a canine femur model. Paired, fresh-frozen canine femora were divided into two groups. In group A, one femur from each pair was subjected to cement extraction with ultrasonic tools. In group B, one femur from each pair was subjected to manual cement extraction. Contralateral femora from each pair served as controls to determine the strength of intact femora. Torsional fractures were produced using a servocontrolled hydraulic testing machine (Minneapolis Testing System, Minneapolis, MN). Maximum torque, maximum angle, and energy capacity to failure were determined. Results were recorded as a reduction in percent value of the tested specimen versus the contralateral control. When comparing femora with cement removal by ultrasonic tools to the contralateral control femur, there were no statistical differences in ultimate torque (P = .83), maximum angle (P = .89), and energy capacity (P = .74) by analysis of variance. In addition, there were no significant differences between the group with ultrasonic tool cement removal and the group with manual tool removal. The authors conclude that in this canine model, removal of cement with ultrasonically driven tools has no adverse effects on whole bone strength.

The effect of extracorporeal shock wave lithotripsy on the prosthesis interface in cementless arthroplasty. Evaluation in a rabbit model.

The effect of extracorporeal shock wave lithotripsy on interfacial strength between prosthesis and bone in cementless arthroplasty was examined using a rabbit model. Paired femora, each implanted with fiber mesh porous coated titanium implants, were harvested from rabbits 15 weeks after implantation. In group I, one femur from each pair was exposed to lithotripsy treatment consisting of 2,000 shocks at 20 kV. In group II, one femur from each pair was exposed to 2,000 shocks at 26 kV. Contralateral femora from each pair served as controls in both groups. Mechanical pushout tests were conducted on the implants using a 1321 Instron testing machine at a constant rate of 1 mm/minute. Shock waves generated at 20 kV were found to have no significant decrease on either the prosthesis/bone interfacial strength or energy to failure of cementless implants. Shock waves generated at 26 kV produced a mean 17.45% decrease in the prosthesis/bone interfacial strength, which approached statistical significance (P = .062), and a 7.84% mean decrease in the energy to failure (P = .268). However, in four of the seven group II specimens, cortical fractures occurred. These findings suggest that lithotripsy will not aid in the removal of uncemented porous coated devices and lithotripsy inadvertently focused at an uncemented device will not disrupt significantly the prosthesis-bone interface.

Hemodynamic and histological differences in end-to-side anastomoses.

An end-to-side anastomosis is often a necessity in replantation surgery. This study examines the effects of elliptical versus slit arteriotomy and the angle of anastomosis on vessel patency and aneurysm formation. Forty male rats were divided into four groups of ten rats each. The right and left common iliac arteries were selected as a model. The results showed no significant statistical difference in patency rates among our four experimental groups. The end-to-side anastomotic technique of choice uses the elliptical arteriotomy placed at a 90 degrees angle. It provides good visualization and easy suture placement.