Biomedical subjects

D G Lewallen

Publications and source records attributed to D G Lewallen.

50 records · Page 3Linked to original sources

PubMed1992

Removal of broken distal interlocking screws.

Existing techniques for removing broken distal interlocking screws can involve trephine over-cutting of the screws, which requires bone exposure and creates larger stress risers by enlarging the original screw hole. We present a technique for removal of these screws that takes advantage of both the design of interlocking screws and the bone quality in the area of their placement. In this technique, a guide-wire "punch" is used to drive the screws through the medial cortex and soft tissue for removal through a small medial incision.

Bone Screws↗

PubMed1991

Quantitative CT for the evaluation of bone healing.

Quantitative computed tomography (QCT) was used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks and imaged with QCT. Invasive techniques were used to determine (1) the torsional properties of the bone; (2) the local stiffness properties and calcium content within the bone; and (3) histologically determined new bone formation and porosity. QCT was strongly associated with the maximum torque (R2 = 0.44) and torsional stiffness (R2 = 0.69) of the healing bone. QCT had strong correlations with the local stiffness (R2 = 0.64), calcium content (R2 = 0.61), new bone (R2 = 0.84), and porosity (R2 = 0.84) of healing tissues.

Animals↗

PubMed1991

The determination of bone fracture properties by dual-energy X-ray absorptiometry and single-photon absorptiometry: a comparative study.

Dual-energy X-ray absorptiometry (DEXA) and single-photon absorptiometry (SPA) were used to quantitate the structural strength and local material properties of healing tibial osteotomies in 32 dogs. Dogs were divided into four equal groups, euthanatized at either 2, 4, 8, or 12 weeks, and imaged with DEXA and SPA. Invasive techniques were used to determine (1) the torsional properties of the bone, (2) the local stiffness properties and calcium content within the bone, and (3) new bone formation and porosity by histology. There were no differences between SPA and DEXA in their associations with the torsional properties of bone. SPA and DEXA had strong correlations with the ultimate torque (R2 = 0.76, 0.51) and the torsional stiffness (R2 = 0.68, 0.53) of bone. SPA and DEXA of periosteal callus, endosteal callus, and cortical bone had similar associations with indentation stiffness, calcium content, new bone formation, and porosity. SPA of gap tissue had significantly stronger associations with these four parameters than DEXA (P less than 0.05). Correlation coefficients (R2) with these local material properties ranged as high as 0.82 for SPA with new bone formation in the gap tissue and 0.73 for DEXA with indentation stiffness of periosteal callus.

Absorptiometry, Photon↗

PubMed1991

Primary total knee arthroplasty in patients with psoriasis.

Between 1976 and 1988, 50 primary total knee arthroplasties were performed on 34 patients with psoriasis vulgaris. The skin lesions were graded for severity in all patients and the extent of affected body surface was mapped. All patients received peri-operative antibiotics. Only one deep infection, with Staphylococcus aureus, occurred 25 months after operation. The average length of follow-up was nearly four and a half years, being to a minimum of two years or until failure of the arthroplasty. There appears to be no increased risk of deep infection in patient with psoriasis vulgaris undergoing primary total knee arthroplasty.

Adult↗

PubMed1991

Use of bipolar endoprosthesis and bone grafting for acetabular reconstruction.

Reconstruction operations for severe acetabular defects using bone grafting and a bipolar hemiarthroplasty retrospectively reviewed in 81 hips between 1983 and 1985. The most common indication was failed total hip arthroplasty. Bone grafts consisted of cancellous bone, bone blocks, and wafer-type grafts used singly or in combination. The follow-up period was 12 to 36 months postoperatively (mean, 16 months). There were 22 perioperative complications (27%) and 13 postoperative complications (16.7%). A majority of hips showed some graft resorption and component migration that worsened with time. There were four graft failures with subluxation of the component, one prosthesis dislocation, and one component disassembly. Ten hips had revision (13.3%) for a variety of reasons. Nevertheless, clinically, most patients (83%) believed the procedure had improved their condition. Reconstruction for severe acetabular defects can be achieved successfully using this technique, but long-term follow-up evaluation is needed to fully assess the role of this procedure in relation to other available options.

Acetabulum↗

PubMed1990

Effects of retinacular release and tibial tubercle elevation in patellofemoral degenerative joint disease.

Release of the patellar retinaculum and tibial tubercle elevation have both been advocated for the treatment of patellofemoral degeneration. Questions remain, however, regarding the magnitude and predictability of such effects in diseased joints. Using cadaver knee joints exhibiting a range of patellofemoral cartilage degeneration, we investigated the effects on joint contact pressures on release of the patellar retinaculum, followed by tibial tubercle elevations of 1.25 and 2.5 cm. Retinacular release failed to alter the joint-loading parameters significantly. Tibial tubercle elevation reduced the patello-femoral joint contact area and contact force, but failed to cause a consistent change in contact pressure. Tibial tubercle elevation also caused a migration of the joint contact area superolaterally on the retropatellar surface. This migration occurred in conjunction with ventral tilting of the inferior pole of the patella as the tubercle was elevated, suggesting that significant changes in joint kinematics may result from this procedure.

Aged↗

PubMed1990

Total hip arthroplasty after fracture of the acetabulum. Long-term results.

We made a retrospective study of 55 primary total hip arthroplasties in 53 patients with a history of previous acetabular fracture. The mean follow-up was 7.5 years and the average age at fracture was 48.7 years. The incidence of radiographic femoral loosening (29.4%), symptomatic loosening (15.7%), and femoral revision (7.8%) were similar to those previously reported at 10 years for routine arthroplasties by Stauffer (1982). On the acetabular side, the incidence of radiographic loosening (52.9%), symptomatic loosening (27.5%), and revision (13.7%) were four to five times higher. We conclude that a history of prior acetabular fracture has a significant adverse impact on the long-term outcome of any subsequent total hip arthroplasty.

Acetabulum↗

PubMed1990

Quantification of bone healing. Comparison of QCT, SPA, MRI, and DEXA in dog osteotomies.

Four noninvasive imaging modalities were used to quantitatively evaluate and compare tibial osteotomy healing in dogs. Quantitative computed tomography (QCT), magnetic resonance imaging (MRI), single-photon absorptiometry (SPA), and dual-energy x-ray absorptiometry (DEXA) were the four techniques examined. Bilateral tibial osteotomies were performed in 32 dogs divided into four groups. The osteotomies were stabilized with a 2-mm gap using unilateral external skeletal fixation. Dogs were anesthetized, imaged with the four noninvasive techniques, and killed at 2-12 weeks. Invasive techniques were used to determine: 1) the torsional properties of the bone; and 2) the local stiffness properties and calcium content within the bone. The techniques which had the strongest associations with the torsional properties of the osteotomies were QCT, SPA and DEXA. Generally, QCT and SPA had marginally stronger correlations than DEXA; but, overall, there were no differences between the techniques. MRI had the poorest associations with the torsional properties of the osteotomies. Generally, QCT had the strongest correlations with local material properties, such as indentation stiffness and calcium content. SPA had the second strongest correlations with calcium content and had the third strongest correlations with indentation stiffness behind DEXA. DEXA had the third strongest correlations for calcium content. With the exception of some of the correlations with indentation stiffness, MRI had the poorest associations with the local parameters studied.

Absorptiometry, Photon↗

PubMed1990

The effects of physiologic dynamic compression on bone healing under external fixation.

The effects of early physiologic dynamic compression on fracture healing were studied in the dog. Transverse midtibial osteotomies were performed bilaterally and stabilized with a relatively rigid external fixation system in a neutralization mode (800 microns) to prevent compression of the osteotomy ends during weight bearing. On the 15th day, one osteotomy in each animal was subjected to dynamic compression through weight bearing by release of the fixator-telescoping mechanism (axial dynamization), while the other side remained unchanged as the control. Analysis of sequential roentgenograms showed that the callus distribution was more symmetric on the dynamic compression side. The two sides showed no significant differences in quantitative technetium-99 bone scans or in osteotomy-site blood flow. There were no statistical differences in new bone formation, bone porosity, or maximum torque between sides. The fixation had maintained the initially created osteotomy gap on the control side and tended to unite through a gap-healing mechanism. The dynamic compression side showed reduction in gap size and union by more of a contact-healing mechanism. There were no statistical differences in the rate of pin loosening, but its distribution according to pin location was significantly different between the two sides.

Animals↗

PubMed1989

The effect of rigidity on fracture healing in external fixation.

Knowledge of the basic biomechanics of external fixation is necessary to obtain the full benefits of the technique for bone fracture treatment. The rigidity of external fixation, including pin-bone interface stresses, is discussed and bone healing and remodeling under different fixation stiffnesses and fracture gap conditions are described. The rigidity of fixation ultimately depends on the biomechanical characteristics of the fracture, the accuracy of reduction, and the amount of physiologic loading. Comparative experiments using a canine tibial fracture model have suggested that fixation rigidity is important in early bone healing and in the prevention of pin loosening. Bone union can be achieved under external fixation through different pathways, ranging from callus-free gap healing under a rigid neutralization configuration to direct-contact healing with periosteal new bone formation under axially dynamized stable fixation. Cortical reconstruction by secondary osteons seems to be important for the ultimate strength of the bone union.

Animals↗

PubMed1989

Prediction of properties of fracture callus by measurement of mineral density using micro-bone densitometry.

UNLABELLED: An experiment was designed to determine whether the material properties of fracture callus can be predicted by the measurement of mineral density. Rat tibiae that had a closed fracture were used to obtain uniform specimens of fracture callus at sequential stages of healing. An in vitro indentation test was done and tissue was biopsied, using a trephine, to determine the hardness and calcium content of a standardized area of callus tissue. The hardness of the callus was correlated with the mineral density of the local tissue, which initially had been measured non-invasively with single-photon-based micro-bone densitometry. The progress of differentiation and remodeling of callus was determined by comparative planimetric and microradiographic analyses of tissue. Determinations of density showed a linear correlation with concentrations of a hydroxyapatite equivalent solution (r = 0.997, p less than 0.001), with the ash weight of control specimens of cortical-trabecular bone (r = 0.998, p less than 0.001), and with the calcium content (micrograms per cubic millimeter) of the fracture callus (r = 0.854, p less than 0.001). The hardness of the callus had a non-linear relationship (r = 0.959, p less than 0.005) with the mineral density per volume of tissue, as measured by micro-bone densitometry. CLINICAL RELEVANCE: The appearance of fracture callus on conventional radiographs is an important clinical finding in the assessment of fracture-healing. It is, however, an unreliable predictor of the strength of the union of the fracture. Three-dimensional imaging and quantification of bone mineral provide additional data about the quality and geometry of fracture callus. Our study showed that mineral content per unit of volume is a good index of hardness of the fracture callus. Thus, quantitative imaging may be useful clinically for monitoring fracture-healing.

Animals↗

PubMed1988

Epidemiology of diaphyseal and distal femoral fractures in Rochester, Minnesota, 1965-1984.

Over the 20-year period from 1965 to 1984, 370 residents of Rochester, Minnesota experienced 402 femoral fractures exclusive of the hip, giving an overall incidence rate of 37.1 per 100,000 person-years (95% confidence interval, 33.4-40.8). Of these, 54 were subtrochanteric and 210 were diaphyseal, while 123 involved the distal femur and 15 were at unspecified femoral sites. Fifty-eight percent of these fractures were caused by severe trauma. The incidence of femoral fractures due to severe trauma was greatest in young patients, especially for diaphyseal fractures, and showed a male excess. One-third of the fractures were associated with moderate trauma and were responsible for the rising incidence rates with age at all three fracture sites. These increases were greater in women. Eighty percent of patients 35 years of age or older with fractures due to moderate trauma had prior evidence of generalized osteopenia or a condition likely to cause localized osteopenia in the fractured femur. These data confirmed similar findings from Sweden, providing evidence for a relationship between osteoporosis and femoral fractures distal to the hip.

Adolescent↗

PubMed1984

Comparison of the effects of compression plates and external fixators on early bone-healing.

We used two mechanically dissimilar devices, compression bone-plates and unilateral-frame external fixators, in a standard canine osteotomy model; both methods were highly successful in achieving mature bone union. Bone union was studied by histological, physiological, and biomechanical means. At 120 days after injury, union was biomechanically less mature on the external fixator side. These tibiae had less intracortical new-bone formation (p less than 0.01), more bone resorption (p less than 0.045), and more bone porosity (p less than 0.04) when compared with paired tibiae that had been treated with compression plates. This higher level of bone turnover on the external fixator side was accompanied by an increase in blood flow (measured by clearance of 85Sr) (p less than 0.04). At the osteotomy site, pre-experimental or unlabeled bone and porosity were greater on the external fixator side and endosteal new-bone formation was greater on the plated side. Since the in vitro stiffness of the external fixator was less in all modes tested (compression, distraction, torsion, and anteroposterior bending) except lateral bending, it may be that the rigidity of the fixation is an important factor in early bone-remodeling of a healing osteotomy.

Animals↗

PubMed1984

Polycentric total knee arthroplasty. A ten-year follow-up study.

After review of the first 209 polycentric total knee arthroplasties (in 159 patients) performed at the Mayo Clinic between July 1970 and November 1971, we found that the calculated probability of the arthroplasty remaining successful ten years postoperatively was 66 per cent. Actual results showed 42 per cent of the arthroplasties to be successful in patients who were still alive at review; another 24 per cent were successful but were in patients who had died or were lost to follow-up before ten years postoperatively. In 34 per cent failure occurred, which we defined as reoperation for any reason, unacceptable pain, or loss of function. The most common causes of failure were instability or ligament laxity (13 per cent), loosening of a component (7 per cent), infection (3 per cent), and patellofemoral joint pain (4 per cent). Prior knee surgery significantly decreased the probability of success, as did axial malalignment of the prosthetic components at operation.

Adult↗