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Biomedical subjects

S E Mackinnon

Publications and source records attributed to S E Mackinnon.

At least 73 records · Page 4Linked to original sources
PubMed1997

Quality of life and functional outcome following brachial plexus injury.

Thirty-two patients (3 women, 29 men) participated in a mailed questionnaire survey to evaluate long-term subjective, employment, and functional outcome following surgical treatment for brachial plexus injury. The mean age was 37 years and mean postinjury time was 7 years. The main outcome measures were overall life satisfaction, employment status, and the impact of the brachial plexus injury on life domains. Quality-of-life questions were adapted from the interviewer form of the U.S. General Social Survey. Considering overall life satisfaction, 25 patients (78%) reported at least moderate satisfaction and no patients reported extreme dissatisfaction. Ten patients reported that their injury did affect to a great deal their overall quality of life and slightly more than half the patients were employed at the time of the study. These outcomes were not affected by such patient factors as coverage by workers' compensation, litigation, pain, marital status, number of children, educational status, and the degree of functional recovery. These patient factors also did not alter the impact of the injury on overall life satisfaction. In spite of the devastating nature of these injuries, this patient population for the most part reported good quality of life with employment status predicted within the first year following injury.

Adult↗
PubMed1997

Differences between contractions of fast and slow muscles after nerve grafting.

The nature of reinnervation of fast- and slow-twitch skeletal muscles, as assessed by contractile characteristics, was determined in a rat sciatic-nerve graft model. The isometric contractile function of the fast-twitch plantaris and slow-twitch soleus muscles from hindlimbs of adult male Lewis rats (225 to 250 g) was assessed at 16 weeks after sciatic-nerve grafting. A 3-cm interposition sciatic-nerve graft was performed in the following groups: fresh syngeneic (n = 10), fresh allogeneic (n = 11), 3-week stored allogeneic (n = 9), and freeze-thawed allogeneic (n = 9). A control group consisted of 8 normal unoperated rats. Contractile properties were assessed by stimulating the muscles indirectly via the sciatic nerve. At 16 weeks, soleus and plantaris muscle masses were 40 and 52 percent of controls, while their respective absolute tetanic forces (N) were less than 65 and 45 percent of controls. Analysis of time-dependent contractile parameters showed that the soleus/plantaris ratios for time to peak tension (TTP) and maximum rate of force development (df/dt) were not significantly altered following grafting. However, the ratio for half relaxation time (1/2RT) was significantly reduced from 4.44 +/- 0.62 toward a value of 1 following grafting. In this study, the authors found that, when fast and slow muscles were reinnervated from a common nerve, maintenance of differences in rate of force development supported selective reinnervation, while loss of differences in time of force relaxation supported random reinnervation.

Animals↗
PubMed1997

The effect of ammonium sulfate injection on peripheral nerve.

Local anesthetic drugs with prolonged nerve-block effect would have clinical application for postoperative or neuromatous pain relief. This study evaluated the possibility of peripheral nerve neurotoxicity by injection of 10 percent ammonium sulfate. Both intrafascicular and extrafascicular injection of 10 percent ammonium sulfate were tested in the rat sciatic nerve model. One percent lidocaine HCl, 5 percent phenol, and normal saline were similarly injected for comparison. Using histologic studies and motor function evaluation with walking-track analysis, 10 percent ammonium sulfate was found to be neurotoxic when it is injected intrafascicularly; however, extrafascicular injection of this drug did not cause significant nerve injury. The neurotoxicity of the 10 percent ammonium sulfate solution was intermediate between the neurotoxicity of 0.1 percent lidocaine hydrochloride and the marked neurotoxicity of 5 percent phenol solution.

Ammonium Sulfate↗
PubMed1997

Motor and sensory specificity of host nerve axons influence nerve allograft rejection.

Previous studies have shown both survival and loss of regenerated host axons within nerve allograft segments after withdrawal of Cyclosporin A (CsA) immunosuppression. We hypothesized that the nature of end-organ reinnervation may influence the response of the axon, with survival of axons for appropriate innervation vs degeneration for inappropriate innervation. The rat femoral nerve model was chosen, as it has approximately equal sensory (S) and motor (M) divisions. Four ACI rat peroneal nerve allografts were sutured in straight (right leg: MM and SS) or switched (left leg; MS and SM) orientation in each femoral nerve transection gap in each Lewis rat recipient. Rats received CsA for 8 weeks to allow end-organ reinnervation, after which immunosuppression was discontinued. Rats were killed at various times thereafter, and underwent histologic and morphometric analysis of the graft segment axons. The regenerated axon population in the allograft reflected the nerve of origin: significantly more but smaller fibers when the proximal nerve was sensory and fewer but larger fibers when the proximal nerve was motor. After CsA withdrawal, there was a marked decrease of host axons as part of an ensuing rejection episode. The overall proportional decrease of axons was similar across all nerve orientation groups and, therefore, did not appear to be influenced by the nerve of origin or by the end-organ. However, the sensory proximal groups (SS and SM) contained more mature, noninjured fibers, while the motor proximal groups (MM and MS) contained significantly more degeneration and newly regenerating axons. We conclude that the motor or sensory nerve origin of the host axon, rather than the end-organ, influences axon survival after immunosuppression cessation. It is hypothesized that sensory axons may be more resilient while motor axons are selectively vulnerable to this second injury.

Animals↗
PubMed1997

Plastic surgeons: a gender comparison.

This study surveyed plastic surgeons for the purpose of identifying gender-related differences within the specialty. A confidential 108-item questionnaire was mailed to all female members and candidates of the American Society of Plastic and Reconstructive Surgeons (ASPRS) and to an equal number of male colleagues. The survey was conducted between September of 1992 and October of 1993 using a modified Dillman five-step computerized method. The response rate was 73 percent for women (157 of 216) and 57 percent for men (124 of 216). Of those who responded, 65 percent of women and 89 percent of men were married (p < 0.01). Fifty-two percent of women and 86 percent of men had biologic children (p < 0.001). The majority of surgeons surveyed (97 percent) were in full-time surgical practice. Many women reported delaying childbearing until they had begun full-time practice of plastic surgery (p < 0.001). No significant gender-related differences were noted with respect to medical school rank, training history, advanced degrees, subspecialty practiced, hospital affiliation, or hours worked. Women surgeons in academic practice held lower rank than men and were less likely to be tenured (p < 0.04). Gross annual income was lower for women (p < 0.001). In contrast to men (27 percent), most women (89 percent) perceived sexual discrimination and harassment (p < 0.001). The majority of plastic surgeons were satisfied with their financial situation (80 percent), work (94 percent), and family life (76 percent). Over 90 percent of both women and men were happy with their career choice and would encourage medical students to become surgeons. Plastic surgeons do not differ in training or professional practice characteristics. Discrimination and harassment and unequal promotion and remuneration of women in the university environment are problems that need to be eliminated.

Adult↗
PubMed1997

Treatment of long-standing thoracostoma and bronchopleural fistula without pulmonary resection in high risk patients.

A chronic bronchopleural fistula and a fibrotic postthoracotomy space in a patient with poor functional respiratory reserve is a difficult problem. The classic management of bronchopleural cutaneous fistulas has been with further pulmonary resection to healthy bronchus, repair of the bronchus directly, and a thoracoplasty or myoplasty technique to obliterate the cavity. In a high risk patient, further pulmonary resection and thoracoplasty may be contraindicated. Myoplasty techniques alone without control of the fistula have limited success. In the last 4 years, we have treated six patients with right-sided thoracostomas after a primary open drainage procedure for bronchopleural fistula and empyema. The air leak was controlled with inversion of the sinus tract, fibrin glue, and muscle flap cavity obliteration. An average of two muscle flaps per patient were used, including the contralateral latissimus dorsi muscle. An 83 percent success rate has been achieved with this procedure in patients who otherwise would not be considered surgical candidates. Attention to the details described, including direct suture closure of the bronchial sinus, obliteration of the cavity by local muscle flaps, and avoidance of mechanical positive pressure ventilation, will make extended thoracotomy, pulmonary resection, and thoracoplasty unnecessary in these high risk patients.

Adult↗
PubMed1997

End-to-side neurorrhaphy resulting in limited sensory axonal regeneration in a rat model.

This study evaluated reinnervation of an end-to-side neurorrhaphy and the resultant functional recovery in a rat model. The cut distal posterior tibial nerve was repaired to the side of an intact peroneal nerve. In one group, the epineurium of the peroneal nerve was left intact; in another group, the epineurium was stripped; in the third experimental group, a perineurial slit was created. Evaluations included walking track analysis, nerve conduction studies, muscle mass measurements, retrograde nerve tracing, and histologic evaluation. Walking tracks indicated poor functional recovery. No significant difference in nerve conduction between the experimental and control groups was seen. Gastrocnemius muscle mass measurements revealed no functional recovery in the end-to-side groups. Retrograde nerve tracing revealed minimal staining of motor neurons. However, sensory neuronal staining of the dorsal root ganglia occurred in all groups. Histology revealed minimal myelinated axonal regeneration. These results suggest that predominantly sensory neural regeneration occurs in an end-to-side neurorrhaphy at an end point of 16 weeks.

Anastomosis, Surgical↗
PubMed1997

Spatial pattern of type I collagen expression in injured peripheral nerve.

The authors studied the spatial expression and regulation of messenger RNA for the alpha subunit of collagen type I in crushed rat sciatic nerve to provide a basis for future therapeutic manipulation. Sciatic nerves in 20 male or female adult Lewis rats were crushed for 60 seconds; the unharmed contralateral sciatic nerves served as controls. Twenty-one days after injury the experimental animals were killed and their tissue was harvested. The spatial expression of collagen type I was determined by using in situ hybridization techniques. Quantification of fibroblast number and total signal was performed through computerized morphometry. Collagen upregulation was evident in epineurial and perineurial layers, with the epineurium displaying higher activity. The cells responsible for procollagen type I production were fibroblasts. No activity was seen in the endoneurium. Morphometric findings indicated that collagen upregulation in the epineurium and perineurium occurred at both pretranscriptional and posttranslational levels when compared to controls; a paired t-test analysis confirmed statistical significance for all comparisons between injured and control tissues. Epineurial fibroblasts are responsible for the collagen production associated with crushed peripheral nerve injury in the rat. Regulation occurs pretranscriptionally as well as posttranslationally. It is interesting to speculate that the delivery of agents directed against collagen production (such as neutralizing antibodies to growth factors) into epineurial tissues proximate to the time and location of clinical nerve injury might mitigate later deleterious effects of excess collagen production in axonal regeneration.

Animals↗
PubMed1997

Enhancing nerve regeneration across a silicone tube conduit by using interposed short-segment nerve grafts.

Isolated nerve segments may inherently contain all of the necessary factors required to support regeneration within a silicone tube conduit placed across a nerve gap. Thirty-six adult Lewis rats each weighing approximately 250 g were randomized into three groups. A sciatic nerve gap (13-15 mm in length) was bridged by an empty silicone tube (Group I), a silicone tube containing a short 2-mm interposed nerve segment (Group II), or a nerve autograft (Group III). At 16 weeks postoperatively, no regeneration was observed through the empty silicone tube. In contrast, regeneration across the silicone tube containing the isolated nerve segment was equivalent to that noted through nerve autografts as assessed by histological, electrophysiological, and functional criteria. Thus, an interposed nerve segment will extend the length of successful nerve regeneration through a silicone tube conduit.

Action Potentials↗
PubMed1997

Advances in peripheral nerve repair.

The basic tenets of peripheral nerve repair as outlined in the introduction remain valid. Advances in the field of peripheral nerve repair have become focused on enhancement of the rate, completeness, and accuracy of neural regeneration on a cellular and molecular level. It is hoped that, within the next decade, techniques that have shown promise experimentally will become mainstays of treatment.

Gap Junctions↗
PubMed1996

Do Canadian female surgeons feel discriminated against as women?

OBJECTIVE: To describe female surgeons' perceptions of discrimination against them as women during the selection and training process and in career development and advancement, and to describe trends over time. DESIGN: Population survey of practising Canadian female surgeons. SETTING: Canada. PARTICIPANTS: All 459 female members in good standing of the Royal College of Physicians and Surgeons of Canada or the Corporation professionnelle des médecins du Québec, or both, practising in Canada as of March 1990. Participants completed a survey between March 1990 and May 1992, the response rate was 91% (419/459). OUTCOME MEASURES: Reported levels of discrimination during selection and training and in career development and advancement, institutional policies on maternity leave and job sharing, and the existence of female role models or mentors. RESULTS: Discrimination during the process of selection for residency was reported by 15% (63/413) of the respondents. Just over half of the respondents (206/405) reported male attending staff as being discriminatory during training, and 41% (168/407) reported nursing staff as being discriminatory. Almost half of the respondents (199/408) indicated that discrimination did not hinder their career development or advancement at all, and 29% (118) indicated that it had little effect. Almost two thirds (245/381) reported no maternity leave policies during residency or practice, and 78% (296/379) reported having no job-sharing opportunities. Although 82% (338/413) agreed that female medical students need female role models, 80% (330/415) reported they did not have a female mentor. CONCLUSIONS: Although most of our respondents perceived no discrimination in their selection for residency and reported that discrimination did not hinder their career development or advancement, the perception of discrimination during surgical training suggests that there needs to be a concentrated effort to identify and address problems. Moreover, since few respondents reported having institutional policies on maternity leave and job-sharing or female mentors, these issues need to be examined.

Adult↗
PubMed1996

Cyclosporine A inhibits lymphocyte migration into ovine peripheral nerve allografts.

Lymphocyte migration into nerve allografts was measured to estimate the cyclosporine A (CsA) dose required to suppress rejection. Twelve outbred sheep received daily subcutaneous CsA at 0, 5, 10, or 15 mg/kg/day for 2 weeks prior to implantation of multiple heterotopic subcutaneous nerve grafts. Lymphocyte migration was determined after 7 days by an intravenous pulse of autologous 111indium-labeled lymphocytes and subsequent quantitation of gamma radioactivity in nerve tissue (CPM/g, mean +/- SEM). Measurement by radioimmunoassay revealed a dose-dependent increase in blood cyclosporine levels. Lymphocyte migration into autografts (404+/-44) was significantly less than migration into allografts (16,554+/-2,049), in control animals (P < 0.01). A dose-dependent inhibition of lymphocyte migration into nerve allografts was observed with counts of 7,662+/-1,692, 4,083+/-1,112, and 1,561+/-232 in sheep receiving 5, 10, or 15 mg/kg/day of CsA, respectively. Daily CsA administration produced effective blood levels and immunosuppression sufficient to inhibit lymphocyte migration into nerve allografts.

Animals↗
PubMed1996

Peripheral nerve allograft preservation improves regeneration and decreases systemic cyclosporin A requirements.

Peripheral nerve allografting is limited by the need for long-term systemic immunosuppression. The purpose of this study was to determine if nerve allograft preservation reduced the requirements for systemic Cyclosporin A (CsA) immunosuppression. One hundred twenty Lewis rats were randomized to one of seven experimental groups. Group 1 received a 2-cm Lewis posterior tibial nerve autograft. Groups 2-7 received 2-cm ACI posterior tibial nerve allografts. The allograft group was then further subdivided into three groups of two receiving daily subcutaneous injections of 0, 2.5, or 5.0 mg/kg of CsA for 12 weeks. Within each CsA dose, one group received a fresh while the other received a preserved allograft. Preserved grafts were stored in University of Wisconsin solution for 7 days at 5 degrees C prior to implantation. Animals from each group were sacrificed at 6, 12, and 20 weeks postoperatively. Evaluations included histomorphometry, electrophysiology, and serial walking track analysis. Histology revealed varying degrees of nerve regeneration in all groups at 6, 12, and 20 weeks. For a given CsA dose, the group receiving the preserved graft revealed evidence of better nerve regeneration by all histomorphometric parameters including fiber width and density, percentage neural tissue, and total fiber number. There was no statistical difference in walking track analysis between groups at 4 weeks. By 20 weeks, functional recovery statistically poorer than autograft was seen only in the fresh allograft groups receiving 0 or 2.5 mg/kg of CsA. Identical electrophysiologic findings were seen at 20 weeks. These results suggest that nerve graft preservation may decrease systemic immunosuppression requirements while improving functional recovery. As well, storage of nerve grafts is feasible and would facilitate elective surgery and less costly reconstructive repair.

Analysis of Variance↗
PubMed1996

Avoidance of transection of the palmar cutaneous branch of the median nerve in carpal tunnel release.

The course of the palmar cutaneous branch of the median nerve (PCBMN) was studied in 25 fresh cadaveric upper extremities in order to identify its relation to local structures and commonly used incisions for carpal tunnel release. The PCBMN was found to closely underlie the thenar crease (average, 0-2 mm radial to crease; range, 6 mm ulnar to 6 mm radial to thenar crease), suggesting that an incision fashioned in the thenar crease would lead to frequent PCBMN injury. The PCBMN was also found to cross the axis of the ring finger when the axis was determined with the finger flexed into the palm. The axis of the ring finger, as drawn with the ring finger extended, projected in a more ulnar direction. The PCBMN was an average of 9 mm radial to this projection (range, 1-16 mm). An analysis of 100 human volunteer hands demonstrated that the deepest point between the thenar and hypothenar eminencies was a constant landmark in the proximal palm (interthenar depression). The PCBMN traveled an average of 5 mm radial to the interthenar depression (range, 0-12 mm radial). Thenar crease anatomy and ring finger projection were highly variable both in absolute location and configuration, providing a poor basis for incision placement. An incision placed approximately 5 mm ulnar to the interthenar depression, extending in the direction of the third web space, will decrease the incidence of injury to the PCBMN.

Cadaver↗
PubMed1996

Somatosensory evoked potentials fail to diagnose thoracic outlet syndrome.

Somatosensory evoked potentials (SEPs) are used in the diagnosis of thoracic outlet syndrome (TOS), even as an indication for surgery. The purpose of this study was to evaluate the use of SEPs in the diagnosis of TOS. Twenty-one patients (mean age, 37 years) with TOS and 23 control subjects (mean age, 34 years) were included. Somatosensory evoked potentials of median and ulnar nerves were measured bilaterally in patients in both a relaxed and arms-elevated provocative position. A three-way analysis of variance showed no significant difference between the interpeak latencies of the TOS and control groups (p = .352). Significant differences were found in testing positions (p = .0014) and nerve tested (p = .001) in both groups. Therefore, this study suggests that SEPs are not helpful in the diagnosis of TOS.

Adult↗
PubMed1996

Long-term follow-up evaluation of cold sensitivity following nerve injury.

This article reports the long-term follow-up evaluation (mean, 10 years) findings of 50 patients with upper-extremity peripheral nerve injuries. The most common persistent symptom was cold sensitivity (n = 38), and 33 of 38 patients rated its intensity as moderate or severe. Cold sensitivity typically developed within months after initial injury and resolved in only 2 patients. No significant difference in the incidence of cold sensitivity was found between patients with subjectively normal hand sensation (7 of 11) and those who reported abnormal hand sensibility (31 of 37). A cold sensitivity severity score (CSSS) was determined; a significant relationship was found between the CSSS and the patient's subjective rating of cold sensitivity intensity and change in job status or occupation due to injury (p < or = .02). No significant relationships were found between incidence of cold sensitivity and age, mechanism of injury, smoking, or level of nerve injury. A significant relationship was found between cold sensitivity and digital amputation injuries (p < or = .05). Thus, cold sensitivity is a common sequela following nerve injury and does not decrease over time.

Adult↗
PubMed1996

Long-segment nerve allograft regeneration in the sheep model: experimental study and review of the literature.

Experimental work in the field of nerve allotransplantation has dealt with the feasibility of nerve allografts reconstructing nerve gaps. In the majority of studies, the nerve gap studied has been short, and some degree of regeneration has been achieved, even in the untreated allograft. To better approximate clinical nerve-allograft reconstruction, a series of long-segment (8-cm) nerve allografts were performed in the ovine model. Twenty outbred ewes were randomized into two experimental groups with four experimental conditions. Animals received nerve allografts treated under one of the following conditions: fresh nerve autograft, fresh nerve allograft, cold-preserved nerve autograft, or cold-preserved nerve allograft. The nerve grafts were examined and compared at 6 and 10 months, using histological, morphometric, and electro-physiologic analyses. The results of the study demonstrated that, while excellent regeneration occurred across the nerve autograft, the long nerve allograft could not support axonal elongation. Similarly, cold nerve preservation did not enhance regeneration. The sheep animal model allows for investigation of the long nerve gap and may be beneficial in a better correlation of experimental nerve transplantation with clinical conditions.

Animals↗