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Biomedical subjects

Robert F McLain

Publications and source records attributed to Robert F McLain.

At least 19 recordsLinked to original sources
PubMed2006

Support and satellite cells within the rabbit dorsal root ganglion: ultrastructure of a perineuronal support cell.

STUDY DESIGN: The membrane, nucleus, and cytoplasmic contents of satellite cells were evaluated using a transmission electron microscope. OBJECTIVE: To delineate satellite cell morphometries. SUMMARY OF BACKGROUND DATA: The role of the satellite support cells associated with the neuronal cell bodies remains poorly understood. Previous research has identified one type of satellite support cells. METHODS: Dorsal root ganglions were excised from 10 adult New Zealand White rabbits. Sections from L2-L5 ganglions were prepared, cut, and analyzed under a transmission electron microscope. RESULTS: A total of 190 neurons and their associated satellite cells were selected for analysis. Three subgroups of satellite cells were identified. The two predominant subgroups consisted of previously described satellite cells. The third subgroup consisted of highly complex and unusual cells. Nineteen satellite cells (4%) did not conform to any previous description of glial cells. Cells were characterized by larger nuclei, with numerous inclusions, and by extensively convoluted reflections of the cellular membrane. These cells were "perched" or "piggy-backed" on top of a convoluted and multilayered cytoplasmic sheet. CONCLUSION: A new type of support cell representing a different cell line or a highly adapted cell with specific functional capacities was identified.

Animals↗
PubMed2006

Stress relaxation at the bone-pedicle screw interface in human bone.

STUDY DESIGN: A biomechanical study using human lumbar vertebra. OBJECTIVES: To assess the effects of stress relaxation on the pullout behavior of the pedicle screw in human bone. SUMMARY OF BACKGROUND DATA: The standard pullout test is widely used to assess screw-holding power; however, the effects of incremental deformation on the pullout behavior of pedicle screws are not known in human bone. A recent study in bovine bone suggests that stress relaxation during incremental pullout significantly reduces failure loads seen in pullout testing. METHODS: Fourteen human lumbar vertebrae were instrumented with pedicle screws and tested with one of two pullout protocols: standard pullout model, a continuous withdrawal, and stress relaxation pullout model, an incremental withdrawal allowing stress relaxation. Peak loads and stiffness were calculated and relaxation data were assessed using the stretched exponential function. RESULTS: Pullout strength and stiffness were significantly lower in the stress relaxation model group (P < 0.05). The characteristic relaxation time decreased and relaxation ratio increased with the increasing deformation level. The pullout and stress relaxation parameters were found to correlate with the bone quality. CONCLUSIONS: The stress relaxation process significantly affects the mechanical and viscoelastic properties of the bone-screw interface in human cadaveric bone. Stress relaxation pullout model might be a better representative of in vivo conditions by introducing the time and incremental deformation into the in vitro biomechanical testing.

Biomechanical Phenomena↗
PubMed2006

The biomechanics of long versus short fixation for thoracolumbar spine fractures.

STUDY DESIGN: Literature review. OBJECTIVE: Provide an overview of biomechanical strengths and weaknesses of long and short fixation constructs applied in thoracolumbar fractures, along with a discussion of specific indications for selecting an instrumentation construct for a given fracture. SUMMARY OF BACKGROUND DATA: Previous clinical and biomechanical studies have shown that segmental spinal instrumentation provides superior torsional, axial, and sagittal stability relative to nonsegmental systems. Multilevel fixation (long constructs) has proven reliable and effective in treating thoracic injuries, with or without anterior reconstruction. Short-segment pedicle instrumentation (short constructs) have proven effective in stabilizing thoracolumbar and lumbar fractures while limiting the disruption of lower lumbar motion segments. Loss of anterior column integrity leads to fixation failure when short constructs are not supplemented with further fixation or an anterior reconstruction. METHODS: Review of the applicable clinical and biomechanical literature. CONCLUSIONS: Long constructs serve well in thoracic and thoracolumbar fractures, while short-segment fixation offers advantages in selected thoracolumbar and lumbar fractures. Anterior column integrity determines the risk of sagittal collapse and kyphosis at the thoracolumbar junction. Recognition of fundamental biomechanical principles is necessary to make either construct work reliably.

Fracture Fixation↗
PubMed2006

Cord and cauda equina injury complicating elective orthopedic surgery.

STUDY DESIGN: Presented is a case series of 3 patients, all of whom developed neurologic deficits due to cord or cauda equina compression during elective extremity surgery. OBJECTIVES: To identify characteristics of presentation that may differentiate cord or cauda equina injury from peripheral nerve palsy following extremity surgery and to establish the value of early decompression in patients with intraoperative injury. SUMMARY OF BACKGROUND DATA: Intraoperative neural injury has been described in association with epidural and spinal anesthesia, with cervical or spinal manipulation in the face of instability, and with ischemic injury suffered during extensive vascular repair. However, it has not been described after uncomplicated elective extremity surgery. METHODS: Retrospective review of a case series. RESULTS: In 1 patient, intraoperative paraplegia occurred after routine shoulder arthroscopy. A second patient underwent elective bilateral total hip replacement and awoke with neurologic deficits in both lower extremities, then went on to develop an acute cauda equina syndrome. The third patient developed a central cord syndrome following an otherwise uncomplicated total hip replacement. Two patients were initially misdiagnosed as peripheral nerve palsies. All 3 patients had preexisting spinal stenosis at the level of neural injury. All underwent routine positioning and anesthetic care but were recognized as having a neural injury early in the recovery period. In only 1 case was the diagnosis of a cord level injury made immediately. All 3 patients were treated with urgent surgical decompression once diagnosed. Following surgery, neurologic symptoms improved in each of the 3 patients allowing early mobilization. CONCLUSIONS: Spontaneous neural injury is rare but can occur to the anesthetized patient. Neurologic examination should be routinely performed in the recovery room; and if significant neurologic deficits are seen, investigative workup should not be delayed. If an intraspinal lesion is identified, immediate decompression may offer favorable results. Neurologic deficits should not be dismissed as peripheral palsies without careful evaluation.

Adult↗
PubMed2006

Axial cyclic behavior of the bone-screw interface.

Screw fixation strength is investigated by using a pullout test. Despite many screw pullout studies, the effects of loading rate on the pullout behavior of pedicle screws are not known. The objective of this study was to assess the effects of loading rate on the pullout stiffness and strength of pedicle screws. Sixty pedicle screws were inserted in foam blocks and pulled out at four different rates: 0.1, 1, 5 and 50 mm/min. Twenty of these 60 screws were cycled non-destructively at four different rates sequentially, i.e., 0.1, 1, 5 and 50 mm/min prior to pullout. Ten additional pedicle screws were inserted in five calf lumbar vertebrae, cycled as in foam group, and pulled out at a rate of either 0.1 or 50 mm/min. The results showed that the stiffness was higher at all rates compared to 0.1 mm/min in foam model but in bone model only 1 and 5 mm/min groups were higher compared to 0.1 mm/min. The pullout strength in 50 mm/min group was higher than that in 0.1 mm/min group in both foam and bone model. The results suggested that loading rate influenced the mechanics of the bone-screw interface. Therefore, a fair comparison between the pullout studies can be achieved under same loading rate conditions. Moreover, the cycling of the pedicle screws in axial direction within a pre-yield region showed an unusual hysteresis curve. Further studies are needed for a better understanding of the mechanics of the screw-bone interface.

Animals↗
PubMed2006

Posterolateral spinal cord decompression in patients with metastasis: an endoscopic assisted approach.

Spinal tumors that are radioresistant or cause bony compression of the spinal cord often require surgical decompression to protect or restore neurological function. Metastatic lesions and primary tumors such as multiple myeloma usually arise in the vertebral body, which can collapse and become unstable, and can compress the anterior columns of the cord. Laminectomy is often ineffective in these patients, and direct anterior decompression through thoracotomy is the widely-accepted solution to the neurological problem. The anterior surgical approach is particularly challenging in the upper thoracic spine. Patients with limited pulmonary reserve due to pneumonectomy or pulmonary metastasis might not tolerate the loss of lung capacity necessitated by either thoracotomy or thoracoscopy. Because posterior instrumentation is usually needed to provide stability following corpectomy and spinal cord decompression, posterolateral approaches to spinal cord decompression have gained favor in recent years. Posterolateral decompression offers advantages over the combined anterior and posterior approach, reducing operative time, morbidity, and hospital stay. Drawbacks to traditional posterolateral decompressions include poor visualization of the tumor immediately anterior to the spinal cord and the need to manipulate the spinal cord to completely remove a tumor adherent to the dura. Endoscopically assisted posterolateral decompression allows decompression of the anterior surface of the spinal cord, the point of pressure in most circumstances. Endoscopic video assistance facilitates vertebrectomy, cord decompression, and anterior reconstruction, all performed through the same posterior incision. Endoscopic assisted spinal cord decompression dramatically reduces morbidity, ICU requirements, and inpatient hospitalization and has proven useful for a variety of metastatic tumors at every level of the spinal column.

Adolescent↗
PubMed2005

Trabecular architecture of lumbar vertebral pedicle.

STUDY DESIGN: Investigation on architecture of lumbar pedicle. OBJECTIVE: To determine morphological properties of pedicular cancellous bone. SUMMARY OF BACKGROUND DATA: Many researchers have been stimulated to study trabecular architecture by improvements in stereological technology. Although the structure of vertebral cancellous bone has been well studied in the literature, no information is available about the architecture of pedicular cancellous bone. METHODS: Eight cadaveric L3 lumbar vertebrae were harvested. After collecting the bone mineral density (BMD) data on the vertebrae, pedicle isthmuses were removed from the vertebral bodies using a reciprocal hand saw. The BMD measurements were done on the dissected pedicle isthmus specimens. All the specimens were then analyzed using a micro-computed tomography unit. Morphologic parameters of trabecular bone were calculated. RESULTS: Bone volume was found as 0.209 +/- 0.046, whereas Tb.Th, Tb.Sp, and Tb.N were found to be 0.201 +/- 0.035 mm, 0.930 +/- 0.123 mm, and 1.098 +/- 0.136 mm(-1), respectively. Connectivity density and structure model index were observed to be 3.135 +/- 0.918 mm(-3), 0.37, whereas degree of anisotropy value was 1.241 +/- 0.093. Vertebral BMD could explain 63% of variance in bone density of a pedicle isthmus. CONCLUSIONS: The structure of the pedicular cancellous bone is somewhat different from that of vertebral body. The trabecular architecture within the pedicle isthmus is isotropic and plate-like. The thickness and number of the trabeculae were greater than those of vertebral trabeculae. Decrease in the bone volume with age is mainly by thinning of the trabeculae and increasing in trabecular spacing, but not by loss of mass.

Adult↗
PubMed2005

Aspiration of osteoprogenitor cells for augmenting spinal fusion: comparison of progenitor cell concentrations from the vertebral body and iliac crest.

BACKGROUND: Successful arthrodesis in challenging clinical scenarios is facilitated when the site is augmented with autograft bone. The iliac crest has long been the preferred source of autograft material, but graft harvest is associated with frequent complications and pain. Connective tissue progenitor cells aspirated from the iliac crest and concentrated with allograft matrix and demineralized bone matrix provide a promising alternative to traditional autograft harvest. The vertebral body, an even larger reservoir of myeloproliferative cells, should provide progenitor cell concentrations similar to those of the iliac crest. METHODS: Twenty-one adults (eleven men and ten women with a mean age of 59 +/- 14 years) undergoing posterior lumbar arthrodesis and pedicle screw instrumentation underwent transpedicular aspiration of connective tissue progenitor cells. Aspirates were obtained from two depths within the vertebral body and were quantified relative to matched, bilateral aspirates from the iliac crest that were obtained from the same patient at the same time. Histochemical analysis was used to determine the prevalence of vertebral progenitor cells relative to the depth of aspiration, the vertebral level, age, and gender, as compared with the iliac crest standard. The cell count, progenitor cell concentration (cells/cc marrow), and progenitor cell prevalence (cells/million cells) were calculated. RESULTS: Aspirates of vertebral marrow demonstrated comparable or greater concentrations of progenitor cells compared with matched controls from the iliac crest. Progenitor cell concentrations were consistently higher than matched controls from the iliac crest (p = 0.05). The concentration of osteogenic progenitor cells was, on the average, 71% higher in the vertebral aspirates than in the paired iliac crest samples (p = 0.05). With the numbers available, there were no significant differences relative to vertebral body level, the side aspirated, the depth of aspiration, or gender. An age-related decline in cellularity was suggested for the iliac crest aspirates. CONCLUSIONS: The vertebral body is a suitable site for aspiration of bone marrow for graft augmentation during spinal arthrodesis.

Aged↗
PubMed2005

Comparison of spinal and general anesthesia in lumbar laminectomy surgery: a case-controlled analysis of 400 patients.

OBJECT: Despite a history of safety and efficacy, spinal anesthesia is rarely used in lumbar surgery. Application of regional anesthetics is widely preferred for lower-extremity surgery, but general anesthesia is used almost exclusively in spine surgery, despite evidence that spinal anesthesia is as safe and may offer some advantages. METHODS: In this case-controlled study the authors analyzed outcomes obtained in 400 patients in whom either spinal anesthesia or general anesthesia was induced to perform a lumbar decompression. Patients were matched for anesthesia-related class, preoperative diagnosis, surgical procedure, and perioperative protocols. All aspects of surgery, recovery, postanesthesia care, and pain management were uniform irrespective of the anesthetic type. Case complexity was equivalent. An independent observer performed analysis of the data. Data from the intraoperative period through hospital discharge were collected and compared. Two hundred consecutive patients meeting inclusion criteria were included in each group. Patients were treated for either lumbar stenosis or herniated nucleus pulposus. Demographically, both groups were well matched. Anesthetic and operative times were longer for patients receiving a general anesthetic (p < 0.05), in whom more nausea and greater requirements for antiemetics and pain medication were also present during recovery (p < 0.05). Overall complication rates and, specifically, the incidences of urinary retention were significantly lower in spinal anesthesia--induced patients (p < 0.05). There were no neural injuries in either group, and the incidence of spinal headache was lower in patients receiving a spinal anesthetic (1.5% compared with 3%). CONCLUSIONS: Spinal anesthesia was as safe and effective as general anethesia for patients undergoing lumbar laminectomy. Potential advantages of spinal anesthsia include a shorter anesthesia duration, decreased nausea, antiemetic and analgesic requirements, and fewer complications. Successful surgery can be performed using either anesthesia type.

Adult↗
PubMed2005

The behavior of thoracic trabecular bone during flexion.

Thoracic compression fractures are often described as anterior wedge fractures. Although the radiographic signs of these fractures are easily identified, the mechanism of the trabecular failure is not well understood. The current study addressed this mechanism in the lower thoracic spine by measuring the trabecular strain. Trabecular strain was measured in six human thoracic cadaver spines during 1) compressive and 2) flexural loading. The strains were measured at incremental loads using a texture correlation. They were analyzed by global contour plots and regional analysis of the T11 vertebrae. Specimens loaded under only compression exhibited uniform strains in the vertebral body. During flexion, however, the strains were concentrated in the anterosuperior margin of the vertebral body and the compressive and shear strain magnitudes in this region were significantly increased. These results demonstrate that the flexural position places the lower thoracic spine at greater risk of anterior compression fracture as seen clinically.

Aged↗
PubMed2004

Complications associated with lumbar laminectomy: a comparison of spinal versus general anesthesia.

STUDY DESIGN: A case-controlled, comparative study of 400 patients undergoing lumbar surgery, treated with either spinal or general anesthesia. An independent observer analyzed outcomes. OBJECTIVES: To determine the rate and type, of perioperative complications associated with each anesthetic method among lumbar surgery patients. SUMMARY OF BACKGROUND DATA: Spinal anesthesia is infrequently used for spinal procedures. While complications associated with spinal anesthesia are rare, some authors have suggested that spinal anesthesia may exacerbate existing neurologic disease and have recommended against its use in lumbar disc surgery. Others have found the technique safe and effective. General anesthesia may be preferred because it is seen as the routine accepted practice, because of greater patient acceptance and the ability to perform longer operations, or because of a general sense that general anesthesia is "safer" in these procedures. METHODS: Patients treated between 1994 and 1998 were matched for anesthetic class, preoperative diagnosis, surgical procedure, and perioperative protocols. All patients were treated according to a uniform protocol and recovered in the same perianesthetic environment. Data from the intraoperative period through hospital discharge were collected and compared. RESULTS: A total of 200 patients were included in each group. Overall complication rates and time to discharge were significantly lower in spinal anesthetic patients. Total anesthetic and operative times were significantly longer for general anesthetic patients, and perioperative heart rate and mean arterial pressures were elevated compared with those in spinal anesthetic patients. Nausea, requirements for antiemetic medication, and the incidence of urinary retention were significantly increased among general anesthesia patients. Spinal anesthesia patients had fewer spinal headaches compared with the general anesthetic group, but statistical significance was not obtained. CONCLUSIONS: For patients undergoing decompressive lumbar surgery, spinal anesthesia is at least comparable to general anesthetic with respect to complications. Specific advantages to spinal anesthesia include decreased nausea and antiemetic requirements, reduced analgesic requirements, and reduced overall complication rate.

Anesthesia, General↗
PubMed2004

Spinal surgery in patients with Parkinson's disease: construct failure and progressive deformity.

STUDY DESIGN: Retrospective case series review of patients with Parkinson's disease undergoing elective spine surgery at a single tertiary referral center. OBJECTIVES: To assess the rate of complications of spine surgery in the population with Parkinson's disease and characterize the causes of failure and special needs of this unique population. SUMMARY OF BACKGROUND DATA: Patients with Parkinson's disease experience a combination of poor bone quality and a severe neuromuscular disorder. There is little information in the literature about outcomes of spine surgery in this population. Preliminary review suggests that these patients have a high rate of instrument-related complications that has not been reported previously. METHODS: A computerized search using diagnostic and procedural codes identified 14 patients with Parkinson's disease who underwent spine surgery from January 1993 through December 2000. Their charts and radiographs were reviewed, and those not examined within twelve months were invited for follow-up review. The remaining patients were being followed on a regular basis by their spine surgeon, the Movement Disorders Clinic, or both and were seen and examined during their routine follow-up observation. INDICATIONS AND EXTENT OF INDEX SURGERY VARIED: Complications, revisions, and radiographic evidence of loosening were assessed. Causes of failure were sought with respect to surgical and clinical factors. All patients underwent surgical care by a fellowship-trained spine surgeon. RESULTS: The mean follow-up period from index procedure was 66.8 months; the median follow-up period was 38 months. Of 14 patients, 12 (86%) required additional surgery, undergoing a total of 31 reoperations. Eleven patients (79%) underwent 22 additional procedures at the same or adjacent level for instability, including four patients (29%) who had hardware failure or pullout, necessitating 10 reoperations. The one other patient who required additional surgery had a successful index procedure but underwent another operation to address instability at a remote spinal segment. Of five patients whose index procedure involved only one spinal level, three (60%) required additional procedures, all at that level. Two patients (14%) developed wound infections during the course of treatment but not as the cause of initial treatment failure. The primary mechanisms of failure were relentless kyphosis or segmental instability at the operated-on or adjacent levels. CONCLUSION: Patients with Parkinson's disease undergoing spine surgery in a single tertiary referral center had a very high reoperation rate associated with technical complications. Patients should be appropriately counseled regarding the increased risk of operative complications and closely followed for incipient failure.

Aged↗
PubMed2004

Functional outcomes after surgery for spinal fractures: return to work and activity.

OBJECT OF STUDY: The literature regarding surgical treatment's impact on patient function after spinal fracture is sparse. Some authors have speculated that operative injury--the dissection of paraspinous muscle tissue, damage to spinal motion segments, implantation of spinal devices--may impair functional recovery in spine trauma patients. Nonoperative care has produced satisfactory results in some hands, but results are difficult to reproduce, treatment is resource-intensive, and functional outcomes are poorly documented. This study reports return to work and functional recovery in a 5-year follow-up of severely injured patients treated with segmental spinal instrumentation. MATERIALS AND METHODS: Seventy consecutive patients treated with Cotrel Dubousset instrumentation for unstable thoracic, thoracolumbar, and lumbar spine fractures were followed-up. All had high-energy trauma and were admitted directly to a level 1 university trauma center; 38% were polytraumatized; and 56% had neurologic injuries. Indications for surgery included: (1) segmental instability; (2) incomplete or progressive neurologic injuries with residual spinal canal compromise; (3) concomitant injuries precluding cast treatment; and (4) polytrauma. Two patients died and six were lost to follow-up, leaving 62 (91%) for assessment at a mean 5-year follow-up (range 2-8 y). Clinical outcome has been reported. Functional recovery was assessed based on return to work, level of work, and level of daily activity. RESULTS: Despite the severity of spinal and concomitant injuries, 70% of patients returned to full-time work and another 8% were considered capable: 54% to their previous level of employment without restrictions and 16% to full-time, but lighter, jobs. Twenty-two percent were working part-time or not at all, and 8% were unemployed despite unrestricted functional status. Work status correlated directly with neurologic impairment (P < 0.00005) and was not related to level of injury, hardware failure, extent of surgical dissection, or construct pattern. Of patients with limitations, 18% were limited by pain and 27% by neurologic injury. CONCLUSION: Neurologic injury had a greater impact on functional outcome than any other variable. Patients limited by pain were more often impaired by residual radicular and neuropathic symptoms than by back pain. Impairment was not related to the extent of either the surgical incision or the instrumentation. Patients with persistent back pain generally had an identifiable and correctable mechanical problem-sagittal imbalance, pseudarthrosis, or persistent instability--as the underlying cause. Our series of trauma patients was predominantly young and male. Among this cohort, individual characteristics of occupation (often physical laborers and craftsmen) and judgment (criminal convictions and incarceration) may have restricted opportunities for re-employment in 40% of the entire study group.

Adolescent↗
PubMed2004

Stress relaxation of bone significantly affects the pull-out behavior of pedicle screws.

The initial fixation strength of pedicle screws is commonly tested using a standard pull-out test with load applied at a constant rate. This method overlooks the cyclic nature of in situ loading responsible for clinical failure. This study was undertaken to determine the effects of stress relaxation properties at the bone-screw interface on screw fixation strength. Pedicle screws were inserted into calf lumbar vertebrae using a paired testing array. After embedding and mounting in a custom fixture, axial pull-out tests were performed at the rates of 1, 5, and 25 mm/min. For each vertebra, one screw was pulled at a continuous rate. The other screw was pulled at increments of 0.5 mm, at the same rate, with 1000 s pause between increments. Peak load, energy-to-failure, displacement-to-failure, and stiffness were calculated for each screw pull-out test. Two-way ANOVA showed that the standard pull-out method yielded significantly higher peak loads (p < 0.05) at faster pull-out rates and higher stiffnesses (p < 0.05) at all rates compared to the stress relaxation pull-out protocol. These results suggest that the stress relaxation properties of bone significantly affect the pull-out behavior of pedicle screws, reducing the peak load and stiffness values observed during testing. This mode of testing may provide a better biomechanical model of screw pull-out failure and a more accurate estimate of initial fixation strength.

Animals↗