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Biomedical subjects

M A Asher

Publications and source records attributed to M A Asher.

At least 37 records · Page 2Linked to original sources
PubMed1994

The effects of implant stiffness on the bypassed bone mineral density and facet fusion stiffness of the canine spine.

STUDY DESIGN: Effects of spinal implant stiffness and removal/retention on bypassed bone mineral density and column/fusion stiffness were studied in dogs. METHODS: After facet fusion and bicortical peripedicle screw placement, one group of eight dogs received 6.35 mm and another 4.76 mm rod instrumentation at L3-L5. At 12 weeks, four in each group had implants removed. Bone mineral density was analyzed by dual energy x-ray absorptiometry at 1 to 24 weeks. Axial compressive stiffness of the L3-L5 construct, spinal column, fused facets, and instrumentation were measured. Percent load through the vertebral column was predicted. RESULTS: Five observations were made for this canine model. First, stiffer implants resulted in more bypassed bone mineral loss at 6 and 12 weeks, plateauing and not different at 24 weeks. Second, after implant removal, a significant and similar rebound in bone mineral density occurred. Third, 4.76 mm rod instrumentation (initially 71% load through column) resulted in stiffer posterior fusions and vertebral columns than 6.35 mm rod instrumentation (initially 57% load through column). Fourth, marked stiffening of the anterior-middle columns (apparently disks) occurred. Fifth, percent load borne by the vertebral column increased with time. CONCLUSIONS: There appears to be a range of percent load through the vertebral column that creates optimum fusion/column stiffening while limiting bone stress shielding effects. The 6.35 mm rod constructs were predicted to allow greater than 70% axial load through the adult human thoracic/lumbar spine, implying biologic responses similar to 4.76 mm rods in dogs.

Absorptiometry, Photon↗
PubMed1993

The effect of a stiff spinal implant and its loosening on bone mineral content in canines.

A canine spine surgery model was used to study bone mineral loss induced in vertebrae bypassed by stiff implants. Loosening of implants was measured, and a determination was made as to the effect of loosening on the degree of bone mineral loss. Sixteen dogs were implanted with a rigid screw-rod construct and randomized to one of four groups depending on the motion segments immobilized. No fusions were performed. Bone mineral was studied by DEXA at baseline, and postoperatively at 3, 6, and 9 months. Loosening measurements were made at the implant-implant interface and the implant-bone interface at 9 months postoperatively. Results show that bone mineral loss occurred uniformly at 3 months postoperatively in vertebrae spanned by the implants, with the average bone mineral density at 3 months representing 81% of baseline. When the implant remained secure, bone mineral loss persisted at 6 and 9 months but did not worsen. When the implants loosened, there was recovery of bone mineral to the baseline level by 9 months postoperative.

Absorptiometry, Photon↗
PubMed1991

Survivorship analysis of VSP spine instrumentation in the treatment of thoracolumbar and lumbar burst fractures.

We used survivorship analysis to study 21 burst fractures that were treated with posterior VSP spine implant and fusion, each of which was over two motion segments. There were two treatment classes: 1) eight patients whose surgery included anterior bone grafting (augmentation), seven of which were done by the transpedicular approach; and 2) 13 patients whose surgery did not include anterior bone. Eight patients, seven of whom were in the second group, met at least one of the failure criteria. Life table calculations showed 100% implant survival through 22 months in the group treated with anterior bone augmentation, while the nonaugmented group showed 92% survival at 6 months, 68% survival at 9 months, 60% survival at 13 months, and 50% survival at 19 months. Statistical comparisons of the two groups resulted in P-values of 0.05 (Breslow) and 0.04 (Mantel-Cox). Based on this method of analysis, VSP instrumentation and two-level fusion is suitable surgical treatment for many burst fractures, but high failure rates may result if anterior bone augmentation is not performed.

Actuarial Analysis↗
PubMed1991

The effect of a stiff spinal implant on the bone-mineral content of the lumbar spine in dogs.

The response of canine lumbar vertebral bone to the application of a stiff transpedicular screw-plate implant from the third to the fifth lumbar vertebra, without arthrodesis, was investigated. Five groups of six dogs each were studied: dogs that had not had an operation (control group); dogs that had had a sham operation, with survival periods of three and six months; and dogs that had received an implant, with survival periods of three and six months. The results were the same in specimens from the control group and the group that had had a sham operation. In the groups that had received an implant, dual-photon absorptiometry revealed an insignificant decrease in bone-mineral content at the bypassed fourth lumbar segment (17 per cent at three months and 12 per cent at six months). When the data for the three and six-month intervals were pooled, the mean decrease in bone-mineral content of 14 per cent was significant. Histomorphic study yielded similar results; the mean decrease in bone-mineral content for the pooled three and six-month specimens was significant (16 per cent). Losses were similar for the ventral and dorsal columns. Histomorphometric analysis also showed a significant (13 per cent) loss of bone-mineral content at the adjacent caudad (sixth lumbar) vertebra for the pooled three and six-month groups. The results of the methods of analysis of loss of bone-mineral content correlated strongly. Under these experimental conditions, a stiff spinal implant caused loss of bone-mineral content of the bypassed vertebral segment, although the loss was less than anticipated and did not increase between three and six months.

Absorptiometry, Photon↗
PubMed1989

Fatal cardiac tamponade resulting from a central venous catheter: a case for open-chest cardiac resuscitation.

A computer Medline search has failed to reveal any cases of cardiac tamponade secondary to central venous catheter placement in spinal deformity patients. It has become apparent that this complication should be thought of more frequently, however. The anatomic variation of spinal deformity patients may contribute to this problem. Spine deformity patients have abnormal chest-wall compliance secondary to their deformity, and abnormal position of their intrathoracic organs. This may alter the effectiveness of closed-chest cardiac resuscitation in this patient population.

Bone Nails↗
PubMed1988

Scoliosis evaluation.

The office evaluation of the patient with suspected or confirmed scoliosis is directed toward establishing the etiology (if a known one exists), defining the configuration and magnitude of the deformity, making an estimate of the likely outcome for the patient based on existing knowledge of the natural history of the patient's deformity, and selecting management options. The evaluation tools needed are the patient interview, physical examination, frequently diagnostic radiology, and sometimes other laboratory studies.

Adolescent↗
PubMed1987

The effect of Harrington rod contouring on lumbar lordosis.

The effect of Harrington rod sagittal plane contouring, or lack of it, on total lumbar, segmental lumbar, and lumbosacral lordosis was studied retrospectively in a series of 36 patients operated on for idiopathic scoliosis. Regardless of contouring, there was a decrease in total lumbar lordosis and lordosis above L4, with an increase in lordosis below L5. Although not statistically significant, patients with contoured rods had less loss of segmental (L1-4) lordosis and less increase in segmental lumbosacral lordosis (L4-S1) than the noncontoured group. Although helpful, additional steps beyond concave rod contouring appear to be necessary to consistently preserve lumbar lordosis.

Adolescent↗
PubMed1987

Excision of symptomatic coalition of the middle facet of the talocalcaneal joint.

From 1977 through 1984, nine patients who had ten persistently symptomatic coalitions of the middle facet of the talocalcaneal joint were treated with excision of the coalition and an autogenous free fat graft. Evaluation revealed five excellent, three good, one fair, and one poor result, with an average length of follow-up of forty-two months after surgery. The patient (one foot) with the fair result initially had a poor result until revision, at which time incomplete resection was documented. The patient (one foot) with the poor result initially had a fair result, but it deteriorated forty months postoperatively. Incomplete resection at the time of the initial operation was documented at the time of the second operation. Functional testing of these patients revealed results that were comparable with the results that have been reported after resection of calcaneonavicular coalition. [corrected]

Adipose Tissue↗
PubMed1986

Screening for congenital dislocation of the hip, scoliosis, and other abnormalities affecting the musculoskeletal system.

The three main conditions affecting the musculoskeletal system currently being screened for are spina bifida cystica, congenital dislocation of the hip, and scoliosis. The techniques of screening are different for each: amniotic fluid analysis for spina bifida cystica, a manual physical examination for congenital dislocation of the hip, and a visual examination for scoliosis. Properly time amniotic fluid analysis for alpha-fetoprotein is both a sensitive and specific test for neural tube defects. However, because of the low incidence of spina bifida cystica, this examination is justified only in high-risk pregnancies. Maternal serum screening has not achieved widespread acceptance because of its lack of sensitivity and the low and apparently falling incidence of the deformity. The neonatal manual examination for congenital dislocation of the hip is now well established and widely practiced. Almost all agree that the incidence of persistent congenital dislocation of the hip has been lowered as a result. However, the examination lacks both sensitivity and specificity because of intrinsic difficulties with the examination and the occurrence of late onset subluxation and dislocation. It is becoming apparent that congenital dislocation of the hip is a dynamic problem in the peri- and early neonatal period. Repeated careful evaluation of the hips during infancy is necessary to make the diagnosis as early as possible. To further enhance early detection, it may be necessary to consider obtaining an anteroposterior pelvis radiograph at age 4 to 6 months in babies at high risk. The visual evaluation for scoliosis is a very sensitive test but lacks specificity. Efforts are now being made to quantify visual screening techniques and thus decrease the numbers of false-positive examinations.

Adolescent↗
PubMed1986

Anthropometric studies of the human sacrum relating to dorsal transsacral implant designs.

The sacrum offers several possibilities for fixation that, when combined, appear to provide a secure foundation for a dorsally-placed, transsacrally-fixed implant. The dorsal sacral landmarks, particularly the first and second dorsal foramina, are readily identifiable and relate in a consistent manner both qualitatively and quantitatively to the major mass of sacral bone, which is located ventrally to the vital structures of the sacrum. The authors have utilized these findings in the design of a new implant for direct sacral fixation.

Anthropometry↗
PubMed1983

The top view for analysis of scoliosis progression.

Using computerized spinal analysis, a new top view was developed that displays the spine as if the observer were above and looking down on the patient. Serial top views were obtained of 12 patients with idiopathic scoliosis. In five patients with clinically stable curves, the top views showed no change. One patient with an enlarging rib hump was seen on the top view to have progressive kyphosis but stable scoliosis. Six patients with progressive scoliosis all demonstrated collapse of the thoracic curve in the anteroposterior direction. Five of these six patients had associated lumbar curves. Three lumbar curves demonstrated collapse in the anteroposterior direction similar to the collapse of the thoracic curves, and the other two curves appeared elongated in the anteroposterior direction.

Adolescent↗
PubMed1982

A clinical study of the differences between the scoliotic angles measured on posteroanterior and anteroposterior radiographs.

The scoliotic angles of 128 curves in seventy-eight patients were measured on paired anteroposterior and posteroanterior upright radiographs that had been made on the same day. The association between the difference in the measured angles and the various clinical and curve parameters was examined. The angles on the anteroposterior and posteroanterior radiographs were highly correlated (r = 0.96). The angles on the posteroanterior radiographs were larger than those on the anteroposterior radiographs by a mean of 2.4 degrees for the thoracic curves and 1.7 degrees for the lumbar curves. Only the thoracolumbar scoliotic angles measured essentially the same on the two radiographic projections. The magnitude of the difference between the two measured angles was not correlated with the age of the patient, the direction of the curve, the magnitude of the curve, or the degree of deformity in the sagittal plane.

Adolescent↗
PubMed1981

A method for minimizing the radiation exposure from scoliosis radiographs.

The radiation exposure resulting from standard scoliosis radiographs was determined for eighteen adolescent girls. The risk of inducing breast cancer was estimated from the skin-exposure doses. The average skin exposure to the breasts was 59.6 millirads (0.59 mGy) for the anteroposterior radiograph. Assuming a total of twenty-two anteroposterior radiographs during a course of treatment, the cumulative exposure would result in a 1.35% relative increase in the risk of development of breast cancer. By utilizing collimation of the x-ray beam and proper selection of grids, films, and screens, the radiation risk of scoliosis radiographs is minimized.

Adolescent↗
PubMed1980

Dorso-lumbar spine fractures: recumbent vs. operative treatment.

Internal fixation of fractures of the dorsal-lumbar spine with early ambulation is evaluated in this study of 100 patients with 106 fractures: 34 being treated by recumbency, 13 with Meurig-Williams plates, and 59 with Harrington rods. Fracture reduction in the recumbent group was 14 per cent unsatisfactory, 82 percent satisfactory, and only one case anatomical. Following plating, 38 per cent were unsatisfactory and 61 per cent satisfactory. Harrington rod reduction and internal fixation resulted in 67 per cent anatomical, 31 per cent satisfactory, and 2 per cent unsatisfactory. neurologic improvement in partial lesions was 53 per cent with Harrington rods and 44 per cent with recumbent treatment. For paraplegic patients the time required for wheelchair ambulation was reduced from 10.5 weeks with recumbent treatment to 5.3 weeks with Harrington instrumentation. Ambulatory candidate rehabilitation time was decreased from 7.1 weeks to 2.5 weeks. Complications were reduced from 18 per cent in the recumbent group to 7 per cent in the Harrington rod group. By using the three above-three below, rod long-fuse short approach rather than the two above-two below with fusion over the length of the rods technique, the number of anatomical reductions was increased from 70 per cent to 82 per cent and the length of the fusion decreased from 4.8 levels to 1.4 levels.

Adolescent↗
PubMed1977

Orthopedic screening: especially congenital dislocation of the hip and spinal deformity.

Effective techniques exist for the early detection of congenital dislocation of the hip and of scoliosis, as well as related spinal deformities, allowing correction and prevention of serious permanent deformities. Future developments seem likely to make prenatal detection of spina bifida cystica possible and also may point the way toward means of decreasing the incidence of disabling low back pain and of osteoarthritis of the major joints of the lower extremity.

Child↗
PubMed1977

A longitudinal study of the radiolucent line at the bone-cement interface following total joint-replacement procedures.

After 100 consecutive total hip arthroplasties, a radiolucent line at the bone-cement interface as seen on serial roentgenograms was on the acetabular side in fifty-nine hips and on the femoral side, in three. Similarly, after seventy-five consecutive non-hinged knee-replacement arthroplasties, a radiolucent line was found at the bone-cement interface beneath the polyethylene component more frequently in knees in which the more constrained geometric implant was used (forty-two of fity-nine) than in knees in which the less constrained polycentric and modular prostheses were used (three of sixteen). The presence of a lucent line at the bone-cement interface in these joints did not signify looseness or failure of the arthroplasty.

Bone Cements↗