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Biomedical subjects

M MacMillan

Publications and source records attributed to M MacMillan.

At least 19 recordsLinked to original sources
PubMed2000

The role of amino acid neurotransmitters in the regulation of pituitary gonadotropin release in fish.

Both glutamate and gamma-aminobutyric acid (GABA) are involved in pituitary hormone release in fish. Glutamate serves 2 purposes, both as a neurotransmitter and as a precursor for GABA synthesis. Glutamate can be catabolized to GABA by the actions of 2 distinct but related enzymes, glutamate decarboxylase 65 (GAD65) and GAD67. They derive from 2 different genes that likely arose from an early gene duplication prior to the emergence of teleosts more than 400 million years ago. There is good evidence for the involvement of GABA in luteinizing hormone (LH) release in fish. The mechanism of GABA action to stimulate LH release appears to be a combination of effects on GnRH release, potentiation of gonadotropin hormone-releasing hormone (GnRH) action, and in some cases directly at the LH cell. These actions appear to be dependent on such factors as sex or sex steroid levels, and there may also be species differences. Nevertheless, the stimulatory effects of GABA on LH are present in at least 4 fish species. In contrast, convincing data for the inhibitory effects of GABA on LH release have only been observed in 1 fish species. The sites and mechanisms of action of amino acid neurotransmitters on LH release have yet to be fully characterized. Both 130N-methyl-D-aspartic acid (NMDA) and S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors are likely to have important roles. We suggest that it is a receptor similar to the GABA(A) type which mediates the effects of GABA on LH release in fish, at least partially acting on the GnRH neuron, but likely directly acting at the gonadotroph as well. GABA may also be involved in regulating the release of other pituitary hormones in fish, namely follicle stimulating hormone (FSH = GTH-I), prolactin, and growth hormone. Based on the findings described in this review, a working model for the involvement of glutamate and GABA in the regulation of LH release in teleost fish is proposed.

Animals↗
PubMed1999

Anterior cervical discectomy with freeze-dried fibula allograft. Overview of 317 cases and literature review.

STUDY DESIGN: A retrospective review of 317 patients to determine the efficacy of allogeneic fibula arthrodesis after anterior cervical discectomy. OBJECTIVE: To examine the efficacy of allogeneic fibula as an alternative fusion substrate after anterior cervical discectomy, and to determine the effects of cigarette smoking on the healing of fibula allografts. SUMMARY OF BACKGROUND DATA: The use of autogeneic iliac crest is associated with graft harvest complications in up to 20% of patients. Most studies reporting on the use of allogeneic iliac crest cite a high collapse rate. Few studies exist that note the efficacy of allogeneic fibula in this procedure and the effects of cigarette smoking on fusion rate. METHODS: From 1988 to 1993, 317 patients underwent grafting by the Smith-Robinson technique with allogeneic fibula after anterior cervical discectomy. Patients who described themselves as habitual cigarette smokers or who smoked during the perioperative or postoperative period were categorized as smokers. All patients were immobilized in a rigid cervical orthosis (Philadelphia collar) for at least 10 weeks postoperatively. RESULTS: A minimum of 2 years follow-up was achieved in 289 patients. In all, 162 men and 127 women had a total of 311 levels grafted, and the mean follow-up period was 33 months (range, 24 to 51 months). Of patients who received allogeneic fibula at one level, 90% (242/269) achieved radiologic fusion. The fusion rate was 92% (182/198) among nonsmokers compared with 85% (60/71) among smokers (not a statistically significant difference; P = 0.120). After two-level procedures, 72% (13/18) of the patients showed fusion. The fusion rate was 50% (2/4) among smokers compared with 79% (11/14) among nonsmokers (P = 0.53). When one-level arthrodesis (90%) was compared with two-level arthrodesis (72%), the difference approached statistical significance (P = 0.054). Neither of the two patients, both nonsmokers, who received grafts at three levels achieved fusion. There were no infections, and no grafts collapsed. Two grafts extruded (0.6%), but these were partial and did not require reoperation. Both patients fused and constituted the only patients with more than 10 degrees of angulation in the series. Graft subsidence occurred in 5% (17/311) of the grafts, mostly in the beginning of the series, and was not problematic. This phenomenon was thought to have been caused by overaggressive removal of the cortical endplate. CONCLUSION: Allogeneic fibula is an effective substrate for use in achieving fusion after anterior cervical discectomy. Maximal results are achieved with its use at one level in nonsmokers. Cigarette smoking decreased the fusion rate with allogeneic fibula in the anterior cervical spine, but not by a statistically significant amount.

Cervical Vertebrae↗
PubMed1996

Percutaneous lumbosacral fixation and fusion: anatomic study and two-year experience with a new method.

This anatomic and clinical study describes a transsacral, percutaneous approach for fixation and fusion of the L5-S1 disc. A tunnel is created into the L5-S1 disc from this approach, permitting disc removal, bone grafting, and placement of two nine-millimeter diameter titanium screws into the body of L5. There were no complications referable to screw placement, and eight of nine patients had successful fusion.

Adult↗
PubMed1995

Biomechanical analysis of a new anterior spine implant for post-corpectomy instability.

Corpectomies in the lumbar and thoracic spine are sometimes necessary in the treatment of vertebral tumor, trauma, and degeneration. The resultant defect creates marked instability. Present methods to correct this problem involve spanning the defect with structural bone graft and applying either anterior or posterior instrumentation. Some investigators have designed vertebral replacements that distract and wedge into the corpectomy site. This study investigates a proposed prosthesis with a unique method of fixation: a vertebral replacement is fixed to the bodies above and below by screws that are oriented rostrally and caudally. This fixation prevents cantelever bending of the screws, migration of the implant, and possibly visceral damage by the placement of the device. This study investigates the biomechanical performance of this device in flexion, extension, and axial loading in a calf spine model. In comparison with normal spines, this device restored the biomechanical strength of the spine to at least normal levels in all planes tested. It appears that a device of this design may be useful for the reconstruction of vertebral diseases and may reduce the need for more extensive surgeries.

Animals↗
PubMed1994

Functional assessment for prediction of lifting capacity.

OBJECTIVE: This study investigated the ability to predict maximal functional lifting capacity from peak isometric lumbar extension torque and submaximal lifting mechanics. METHODS: Peak isometric lumbar extension torques were measured on 26 healthy men and women, ages 18 to 39 years. In addition, their lifting mechanics were evaluated while they lifted a submaximal load. Each subject's maximal lifting capacity (kg) then was predicted from the peak torque and submaximal kinetic analysis using a linear regression model. RESULTS: Mean values for the predicted and actual maximum weight the subjects lifted were not significantly different (50.3 +/- 15.6 kg and 48.5 +/- 17.0 kg, respectively, P > or = 0.05). The correlation between predicted and criterion values was high (r = 0.96), and the total error of the prediction was 5.1 kg, which represented 10.5% of the actual maximum value. CONCLUSIONS: This multi-faceted functional assessment model involving biomechanical analysis of a submaximal lift and maximal isometric lumbar extension strength accurately predicted a subject's maximum functional lifting capacity.

Adult↗
PubMed1994

Comparison of lumbar range of motion using three measurement devices in patients with chronic low back pain.

STUDY DESIGN: A correlational design was used to compare the lumbar spine's total sagittal range of motion (ROM) within a chronic low back pain patient population (n = 42) using three different measurement systems. OBJECTIVES: To compare, within a back pain patient population, the relationship of ROM measurements obtained from a motion analysis system (SPINETRAK), a lumbar extension rehabilitation device (MedX), and liquid inclinometers. METHODS: Total lumbar sagittal ROM was determined with each device in each subject as part of patients' standard clinical evaluation. RESULTS: Results indicated that the motion analysis system is significantly correlated with the liquid inclinometers and mildly correlated with the MedX. Inclinometer and MedX ROM measurements are also significantly correlated. To assess individual differences, dependent t tests were performed. Results indicated that the SPINETRAK yielded significantly lower ROM than the inclinometer or the MedX. The MedX and inclinometer measures did not significantly differ. CONCLUSIONS: This report shows that, depending on the device and procedures used, the lumbar sagittal ROM within a chronic low back pain population vary significantly.

Adult↗
PubMed1994

Relationship of the pelvic angle to the sacral angle: measurement of clinical reliability and validity.

There is a need to better document the reliability and validity of assessment measures used in physical therapy. Studies documenting the reliability of measurement of the pelvic angle and its relationship to sacral motion are presently inconclusive. The purpose of this study was twofold. First, we wanted to determine the reliability and validity of a goniometric measurement of the pelvic angle. We also wanted to test the hypothesis that there is a relationship between the pelvic angle and the sacral angle. Intertester and intratester reliability of goniometric pelvic angle measurements of 23 healthy young adults were examined using three different raters. Radiographic measurements of the pelvic and sacral angle using two raters and goniometric measurement of the pelvic angle using a single rater were taken from 15 patients with low back pain who had been referred for X-rays. Intraclass correlation coefficients (ICCs) of intratester reliability for goniometric measurements of the pelvic angle were .93, .96, and .96. The intertester reliability was .95. The ICCs for intratester reliability for radiological measurements were .92 and .95 for the sacral angle and .98 for both measurements of the pelvic angle. Intertester reliability coefficients were .86 and .88, respectively. The Pearson correlation coefficients for the goniometric and radiological measurements of the pelvic angle were .85 and .68. A comparison of the radiological and goniometric measurements of the pelvic angle with the sacral angle demonstrated low average correlations of .43 and .58, respectively. The results indicate a high level of correlation between and within testers for goniometric measurements of the pelvic angle but only a fair correlation between goniometric and radiological measurements of the pelvic angle.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

The aging spine: clinical instability.

Clinical instability of the spine is an intensely controversial subject, and its diagnosis, especially in the aging, is difficult. Yet success in its management rests on accurate diagnosis. Because both clinical presentation and radiographic manifestations are nonspecific, the diagnosis of clinical instability lies in understanding the biomechanics involved, in recognizing the relevant radiographic manifestations, and, most importantly, in correlating those observations with the patient's clinical history and physical examination. Stabilization is the treatment of choice for clinical instability. Strengthening of the dynamic stabilizers, especially early in the course of the disease, may prevent or alleviate the incapacitating symptoms of instability, and further research into this area should be undertaken. Static stabilization by bracing has not proved effective, and spinal fusion carries a high risk of complication. Fusion should be reserved for patients whose diagnosis is clear and whose symptoms are recalcitrant to conservative management. Further understanding of clinical spinal instability in the aging will require more precise definition of terms and better standardization of criteria for its diagnosis, management, and research.

Adolescent↗
PubMed1993

Trunk strength and lumbar paraspinal muscle activity during isometric exercise in chronic low-back pain patients and controls.

The purpose of this study was to describe trunk strength and lumbar paraspinal muscle activity across five angles of flexion during isometric exercise and rest in chronic low-back pain patients and control subjects. High muscle tension as measured by surface integrated electromyography is predicted by a muscle spasm model, and low muscle tension is predicted by a muscle deficiency model. Prior lumbar surgery had no affect on peak torque or maximum surface integrated electromyography data. Both groups produced greater torque and less surface integrated electromyography in more flexed positions. Chronic low-back pain patients exhibited lower peak torque and lower maximum surface integrated electromyography bilaterally during isometric extension effort across all angles. A muscle deficiency model of chronic low back pain was supported by these data and a muscle spasm model was not supported. Discriminant analyses indicated that monitoring maximum surface integrated electromyography of lumbar muscles during isometric effort facilitates classification of chronic low-back pain patients. Future directions are discussed in terms of applying psychophysiologic methods to pain rehabilitation.

Adult↗
PubMed1993

Spinal fixation. Part 1. Principles, basic hardware, and fixation techniques for the cervical spine.

Spinal fixation devices provide stability and restore anatomic alignment in the treatment of fractures, degenerative disease, infection, and tumors and correct congenital deformities such as those seen in scoliosis. The devices provide immediate stability but are not strong enough to withstand prolonged stress and eventually fail, in most cases, if bone fusion does not occur. Bone graft material is often used to promote fusion and to replace bone after resection. Internal fixation is used to maintain position and alignment and to prevent motion as the spine fuses. Plates and rods are attached to the vertebral body or posterior elements with wire, screws, and hooks. Screws and wire can also be used alone as a means of fixation. Surgical techniques and instrumentation have advanced in recent years, and radiologists are exposed to a myriad of devices. They need to be able to identify the various plates, screws, wiring techniques, and grafts used most commonly and to understand their function in the cervical spine for fusions and treatment of fractures and degenerative disease.

Cervical Vertebrae↗
PubMed1993

Spinal fixation. Part 2. Fixation techniques and hardware for the thoracic and lumbosacral spine.

Spinal fixation devices are used in the thoracic and lumbosacral spine to stabilize the spine, reduce deformities and fractures, and replace abnormal vertebrae. A bone fusion is usually attempted along with placement of the instrumentation because in most cases the hardware would eventually fail if it were used alone. The thoracolumbar spine is inherently unstable, and early operative intervention improves mobilization and rehabilitation. In some cases of lumbar spinal pain, surgical intervention is necessary for the treatment of conditions such as herniated disks, spondylolysis with spondylolisthesis, and degenerative disease with scoliosis. Surgical procedures consist of posterior (posterior elements) and anterior (vertebral body) fixation. Radiologists face continual changes in both surgical technique and instrumentation and should be knowledgeable about the devices available and the biomechanical principles that direct their use. They need to work with their surgical colleagues to become familiar with the techniques used at their institutions.

Humans↗
PubMed1993

Spinal fixation. Part 3. Complications of spinal instrumentation.

Spinal fixation devices can be used to form a rigid construct with the spine to replace bone, restore alignment, maintain position, and prevent motion in the treatment of fractures, degenerative disease, neoplasm, and congenital deformities. Because most spinal constructs will eventually fail if bone fusion does not occur, bone graft material is often used along with the implant to promote fusion. Conventional radiographs, obtained in two projections, remain the mainstay of implant evaluation, demonstrating the position of the spinal elements, hardware, graft material, and evidence of complication. Possible complications connected with use of fixation devices include intraoperative soft-tissue injuries, postoperative hematomas, and infection. The components (through incorrect use, malpositioning at surgery, and later dislodgment or fracture) may also contribute to complications such as instability; failure of fusion; or pain, with possible resultant neurologic damage. Bone graft material can migrate or hypertrophy, resulting in impingement on the spinal canal or neural foramen. Radiologists should be familiar with the various spinal fixation devices and techniques to better identify evolving complications.

Adult↗
PubMed1992

Reliability of lumbar isometric torque in patients with chronic low back pain.

In this study, the test-retest reliability of lumbar isometric strength testing in patients with chronic low back pain (CLBP) was assessed. Isometric torque measurements were obtained from 89 patients with CLBP at seven different angles of lumbar flexion. Because previous studies have demonstrated significant strength differences between male and female subjects, separate data analyses were performed for each gender. Results indicated moderate to high reliability for patients with CLBP when tested at individually determined angles of flexion within their idiosyncratic range of motion (ROM) (female subjects: r = .59-.96, P less than .05, SEE = 12.0-24.2 N.m; male subjects: r = .71-.93, P less than .05, SEE = 25.1-62.1 N.m). For comparison with previously published data on asymptomatic controls, an additional set of analyses was conducted for subjects with full lumbar ROM. Similar reliability was demonstrated for this subsample (female subjects: r = .57-.93, P less than .05, SEE = 12.4-27.9 N.m; male subjects: r = .63-.93, P less than .05, SEE = 34.2-44.2 N.m). The authors concluded that isometric lumbar extension torque could be reliably measured in patients with CLBP at multiple positions within the full ROM, although reliability decreased at the most extended positions. The demonstrated reliability will allow researchers to assess treatment effects and group differences without undue concern for artifact attributable to measurement error.

Back Pain↗
PubMed1992

Lumbar iEMG during isotonic exercise: chronic low back pain patients versus controls.

Two studies investigated the use of lumbar integrated electromyography (iEMG) during flexion-extension exercises of the lumbar spine. The first study compared the iEMG fatigue slopes of 12 pain-free controls during a standardized isotonic workout with a heavy weight and a light weight. Results indicated that the slopes of the iEMG across flexion-extension repetition was negative in both conditions, with the heavy weight producing significantly steeper fatigue slopes. In the second study, iEMG was compared from 16 chronic low back pain (CLBP) patients and 12 asymptomatic controls during isotonic exercise. Integrated EMG was recorded during 18 lumbar extension-flexion cycles (3 min) at a standard pace. Each subject exercised at a weight equal to 60% of his maximum isometric torque produced at the most extended position. Results indicated significantly less iEMG was produced by the CLBP group during both concentric and eccentric exertion. For both groups, eccentric exertion produced significantly less iEMG than concentric exertion. The groups showed significantly different iEMG fatigue slopes, with the control group showing declining iEMG by repetition, while the CLBP group showed flatter, slightly increasing iEMG. This occurred for both eccentric and concentric comparisons. A muscle deficiency model of CLBP is supported and results suggest the importance of endurance factors in addition to strength in rehabilitation efforts. Results also suggest the possibility of using this methodology for detecting insincere efforts in lumbar spine assessment.

Adult↗
PubMed1992

Transpedicular screw-rod fixation of the lumbar spine: operative technique and outcome in 104 cases.

A total of 104 patients underwent transpedicular spinal instrumentation using the Cotrel-Dubousset (71 cases) or the Texas Scottish Rite Hospital (33) screw-rod system. Surgery was performed for lumbar vertebral column instability secondary to fractures (28 cases), spondylolisthesis (29), tumors (four), vertebral osteomyelitis (two), or postoperative causes (41). Pseudoarthrodesis due to failure of a prior fusion was present in 37 cases. The 55 men and 49 women (mean age 47 years, range 18 to 87 years) all presented with severe back pain. Signs or symptoms of neural compression were noted in 96 patients. Surgery consisted of neural decompression, internal fixation, and autogenous iliac bone grafting. Spondylolistheses were fused in situ, without reduction; otherwise, major spinal deformities were corrected. A total of 516 pedicle screws were placed. The mean extent of fusion was 2.7 motion segments (range one to six motion segments). A 96% fusion rate was obtained with a mean follow-up period of 20 months. There were no operative deaths. Major complications included one spinal epidural hematoma, three isolated nerve root deficits (two transient, one permanent), and three wound infections (two deep, one superficial). Instrument failure eventually developed in 18 patients; nine were asymptomatic with a solid fusion and did not require further treatment and the other nine were symptomatic or had a pseudoarthrosis and required operative revision. Pedicle screw-rod fixation offers biomechanical advantages compared to other forms of internal fixation for the lumbar spine. It enables short-segment fixation with preservation of lumbar lordosis and adjacent normal motion segments. This technique provides a highly successful method to obtain arthrodesis, even with prior pseudoarthrosis.

Adult↗
PubMed1992

Placenta accreta/percreta/increta: a cause of elevated maternal serum alpha-fetoprotein.

OBJECTIVE: To investigate the relationship between elevated maternal serum alpha-fetoprotein (MSAFP) and abnormal placental adherence (placenta accreta/percreta/increta). METHODS: We reviewed the MSAFP levels of 11 women who had cesarean hysterectomies because of placenta accreta/percreta/increta. The control group consisted of 14 women who delivered by cesarean because of placenta previa but who had no abnormal placental adherence. RESULTS: Five of the 11 women with placenta accreta/percreta/increta had elevated MSAFP, whereas all 14 controls had normal levels. CONCLUSION: These results indicate a significant association between elevated MSAFP and placenta accreta/percreta/increta (P = .017). Patients with an unexplained elevation of MSAFP as well as placenta previa may be at increased risk for abnormal placental adherence.

Female↗
PubMed1991

Influence of antiidiotypic antibody activity on renal transplant outcome.

The presence of cytotoxic HLA antibodies (Ab1) against donor lymphocytes in pretransplant sera is almost always associated with rapid rejection of the renal transplant. We have investigated the possibility that antiidiotypic antibodies (Ab2) to cytotoxic HLA antibodies might modulate the immune response and favorably influence renal allograft outcome. The role of antibodies (Ab3) which potentiate the cytotoxic effect of Ab1 was also studied. Pretransplant sera from 63 patients were tested for inhibitory or potentiating activity in the short antiidiotypic assay. Inhibitory activity was detected in 30 patients and in 28 the transplant survived more than a year. Of patients without antibody activity 11 of 17 had grafts surviving more than one year, and of those showing potentiating activity 11 of 16 were functioning at a year. The difference in transplant survival between the first group and the other two groups was statistically significant (P less than 0.05). There was no significant difference in survival rates between the latter two groups. Potentiating activity is therefore not an independent predictor of transplant failure, whereas the presence of antiidiotypic antibody activity did correlate with improved allograft survival.

Antibodies, Anti-Idiotypic↗