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Biomedical subjects

H K Dunn

Publications and source records attributed to H K Dunn.

At least 19 recordsLinked to original sources
PubMed2001

Total hip arthroplasty in young adults after failed triple innominate osteotomy.

This study compared the results of total hip arthroplasty (THA) in 11 patients with 13 hips who underwent THA after a failed triple innominate osteotomy (TIO) with an age-matched and sex-matched group of patients who underwent THA without prior TIO. The average age at the time of THA was 37 years (range, 16-50 years). The average follow-up of the patients who underwent THA for failed TIO was 36 months and for the control group was 28 months. One hip in each group underwent revision for dislocation. At final follow-up, the average Harris hip score in the study group was 76, whereas in the control group it was 88 (P <.05). The pain component of the Harris hip score in the study group averaged 32, whereas in the control group it averaged 40 (P <.05). Functional scores between the 2 groups were similar. Radiographically, there was no difference between the 2 groups. Estimated blood loss for the hips performed for failed TIO averaged 721 mL, whereas in the control group the estimated blood loss averaged 448 mL (P <.05). There was no difference in operative time. The results of this study indicated that although the radiographic results of THA after TIO are equivalent to THA without prior TIO, clinical results in terms of pain relief and the technical difficulty of THA are not equivalent to results in young adult patients who undergo THA without prior TIO.

Adolescent↗
PubMed2001

Triple innominate osteotomy in young adults for the treatment of acetabular dysplasia: a 9-year follow-up study.

Fifty patients who underwent 60 triple innominate osteotomies were reviewed radiographically and clinically using a modified Harris hip score (HHS). Average patient age was 26 years (range: 13-48 years). At average 9-year follow-up (range: 5-14 years), 12 (20%) hips had been converted to total hip arthroplasty (THA) and 4 (7%) hips had incapacitating pain. Sixteen (27%) hips were considered failures. Average modified HHS at final follow-up was 67 (range: 28-91). Forty-nine (98%) of 50 patients reported they would recommend the procedure to others in the same situation. Radiographically, there was significant improvement in the center-to-edge angle of Wiberg and the acetabular angle of Sharp. There also was a statistically significant relationship between failure of the osteotomy and severity of preexisting hip arthrosis as measured by the Tonnis criteria. The results demonstrate triple innominate osteotomy was effective in eliminating pain, but the fact that 27% of hips required or will require THA indicates results may deteriorate with time.

Acetabulum↗
PubMed1997

Cementless femoral revision arthroplasty. 2- to 5-year results with a modular titanium alloy stem.

Seventy-five consecutive cementless femoral revision arthroplasties were performed, using a modular titanium alloy stem (S-ROM, Joint Medical Products, Stamford, CT). Sixty-six hips were available for complete follow-up evaluation at 2 to 5 years (average, 3.4 years). Independent clinical analysis compared pre- with postoperative modified Harris hip scores and examined patient satisfaction. Independent radiographic analysis was also undertaken. There were two rerevisions, both for hematogenous sepsis. Of the rest, clinical scores improved from a preoperative value of 44 to a postoperative value of 83. Eighty-nine percent of patients were satisfied or very satisfied with the results of surgery. Fifty-two stems had solid bony ingrowth, seven were stabilized by fibrous tissue, and five were radiographically loose. Five-year survival, with rerevision as endpoint, was 96.4%.

Adult↗
PubMed1997

Analysis of particles in acetabular components from patients with osteolysis.

Acetabular polyethylene components were quantitatively analyzed for the presence of third body particles from 38 consecutively retrieved components. Backscattered electron imaging and correlated energy dispersive x-ray analysis were used for the assessments. Retrievals were divided into 4 groups based on methods of fixation and metal alloy types: 8 hydroxyapatite coated, 6 cobalt chrome porous coated, 17 titanium porous coated, and 7 cemented implants were evaluated. The backscattered electron imaging data showed that the components from the hydroxyapatite coated implants had larger particles than did the components from the cemented group. The hydroxyapatite group had 51 +/- 52 particles per mm2. The cobalt chrome alloy group had 10 +/- 9 particles per mm2, and the titanium alloy group had 9 +/- 16 particles per mm2. The cemented group had 5 +/- 4 particles per mm2. The difference between the cement group and the hydroxyapatite group was statistically significant. The elemental analysis showed that 70% of the particles in the hydroxyapatite group had calcium and phosphorus elements. Third body particles likely contribute to particulate generation. The results suggest that the hydroxyapatite coated components have the potential for producing greater amounts of particulate debris. Continued analysis of retrieved components for the presence of the third body particles is required.

Acetabulum↗
PubMed1996

Inability of energy dispersive X-ray analysis to identify particulate polyethylene.

There are limitations to all techniques used to identify particulate polyethylene in histological specimens. The goal of our study was to determine if remnant metal elements used during the catalytic production of ultra high molecular weight polyethylene, could be used as markers for particulate polyethylene detection in histological specimens. It was hypothesized that these catalyst elements could be detected in polyethylene using energy dispersive X-ray elemental analysis. Six samples from five different companies were evaluated. These included virgin polymer powder, polyethylene bar stock, and artificial joint components. Five specimens from each of the six samples were analyzed with energy dispersive X-ray elemental analysis. After elemental analysis was completed, only 2 of 30 specimens were positive for the catalyst elements. In the remaining 28 specimens, catalyst elements were not detected. Our investigation demonstrates that energy dispersive X-ray elemental analysis is not currently a feasible method of particulate polyethylene detection. Additional techniques will need to be developed to accurately identify particulate polyethylene in histological specimens.

Beryllium↗
PubMed1994

Biomechanical evaluation of the stability of thoracolumbar burst fractures.

STUDY DESIGN: The decision to treat thoracolumbar burst fractures in neurologically intact patients either surgically or nonoperatively depends largely on whether the fracture is clinically stable. This study evaluated the relative contributions of the anterior, middle, and posterior columns to spinal stability by way of in vitro experimentation and supplemental analysis of patients with nonoperatively treated burst fractures. METHODS: An L1 burst fracture model was used to evaluate the contribution of the three columns of the spine to resisting imposed flexion deforming forces. Six spines were tested to a gross bending flexion angle of 25 degrees. Changes in vertebral motion across the site of injury were measured and compared. In addition, a summary of our recent clinical experience with nonoperatively treated burst fractures is presented and correlated with the study's laboratory findings. RESULTS: T12-L2 motion measurements after vertebral and ligamentous disruption revealed a statistically significant increase in motion upon anterior and added posterior column compromise, but not for added middle column disruption. Review of the clinical series revealed that burst fractures with anterior and middle column compromise but an intact posterior column were stable and healed satisfactorily. CONCLUSIONS: The data suggest that the condition of the posterior column, not the middle column, is a better indicator of burst fracture stability. It is proposed that the classic burst fracture (anterior and middle column compromise) is a stable injury that, in the absence of neurologic deficit, can be managed nonoperatively.

Adult↗
PubMed1994

Distraction and compression loads enhance spine torsional stiffness.

We have assessed the degree to which compression and distraction forces applied to the spine of the magnitude achievable through instrumentation systems increase torsional stiffness, thereby possibly enhancing the environment for arthrodesis. A functional relationship between spine torsional stiffness and axial compression and distraction forces is described. To establish this relationship whole human thoracolumbar spines as well as individual motion segments were tested in torsion under a variety of axial loading conditions consistent with forces applied clinically. These studies indicate that applying axial loads to the whole thoracolumbar spine through the action of compression or distraction increases the stiffness of the spine in torsion. Compression and distraction forces increased the torsional stiffness of thoracic segments, but only compression forces were found to significantly increase the stiffness of lumbar segments. The soft tissue structures of both the anterior and the posterior columns have the ability to increase torsional stiffness with axial loading.

Adult↗
PubMed1991

A new method for assessing relative dynamic motion of vertebral bodies during cyclic loading in vitro.

A new experimental technique for measuring generalized three-dimensional motion of vertebral bodies during cyclic loading in vitro is presented. The system consists of an orthogonal array of three lasers mounted rigidly to one vertebra, and a set of three mutually orthogonal charge-coupled devices mounted rigidly to an adjacent vertebra. Each laser strikes a corresponding charge-coupled device screen. The mathematical model of the system is reduced to a linear set of equations with consequent matrix algebra allowing fast real-time data reduction during cyclic movements of the spine. The range and accuracy of the system is well suited for studying thoracolumbar motion segments. Distinct advantages of the system include miniaturization of the components, the elimination of the need for mechanical linkages between the bodies, and a high degree of accuracy which is not dependent on viewing volume as found in photogrammetric systems. More generally, the spectrum of potential applications of systems of this type to the real-time measurement of the relative motion of two bodies is extremely broad.

Equipment Design↗
PubMed1989

Initial effect of collarless stem stiffness on femoral bone strain.

Stress shielding resulting from a stiffness mismatch between bone and femoral prosthesis stems (leading to bone resorption in the proximal femur) is believed to contribute to failure in total hip arthroplasty. In this study, strains were measured under compressive femoral head loads both in the intact femur and after implanting first a collarless steel stem and then a geometrically identical fiber-reinforced polymer composite stem 64% less stiff. Decreasing stem stiffness would be expected increase load transfer from the stem to the proximal medial femur, decreasing the degree of stress shielding. The authors found that proximal medial bone strains were significantly lower with either the steel or composite stem implanted than in the intact case. However, there were no significant differences in strain patterns between the steel and composite stem cases. This apparent insensitivity to prosthesis stiffness may result from factors related to implant geometry and fit.

Adult↗
PubMed1986

Anterior spine stabilization and decompression for thoracolumbar injuries.

In a series of patients with thoracolumbar spine injuries, anterior spinal canal decompression resulted in better neurologic recovery than did previously reported posterior instrumentation or nonoperative treatment. The technique allows stabilization over a much shorter segment of the spine than posterior instrumentation and therefore is indicated for fractures at L2 and below and in all patients with burst fractures and neurologic compromise.

Adolescent↗
PubMed1985

Computerized tomographic determination of vertebral density after total hip arthroplasty.

Computerized tomography (CT) provides the capability to determine vertebral bone density with a high degree of accuracy and precision, detecting density changes as small as 5% in serial testing. In this pilot study, CT was used to determine the effects of total hip arthroplasty and its consequent alterations in physical activity levels on the vertebral bone density of 13 postoperative patients. Vertebral bone density was also evaluated in six preoperative patients with degenerative joint disease of the hip and five control patients. The preoperative group and controls were then compared with the postoperative patients, who were divided into two groups--those who had achieved good activity levels and those whose levels of activity remained poor. CT measurement of bone density in the central bodies of T12, L1, and L2 showed that the preoperative group was similar to controls. This suggests that patients accept total hip arthroplasty rather than endure significant activity limitations for extended periods of time. When activity level was restored by arthroplasty, vertebral bone density was preserved. If the patient continued at a poor activity level postoperation, significant loss of bone density occurred secondary to disuse.

Aged↗
PubMed1985

Strength of stainless steel surgical wire in various fixation modes.

Although wire is a commonly used fixation device in orthopedics, little is known about the effects of fastening methods and configurations on the strength of wiring systems. Three sizes of stainless steel surgical wire were tested in noncyclic tensile loading. Load failure levels increased with enlarging wire diameter. Fastening twists were stronger than knots or the ASIF bend technique. The failure mode for twists was untwisting. More than two twists gave no additional strength to the system. Two commercial wire tightening devices gave stronger and more reproducible twists than did ordinary pliers. The addition of a tension equalizing loop opposite the fastening loop weakened the wire system by 10%-15%. The combination of two single wire loops was stronger than a continuous double loop of wire. The results from this study are intended to help the orthopedic surgeon optimize the use of wire.

Fracture Fixation, Internal↗
PubMed1984

A new method for continuous intraoperative measurement of Harrington rod loading patterns.

A new method has been developed for continuous intra-operative monitoring of bone and implant loading patterns in the operative correction of scoliosis using the Harrington distraction rod. The method incorporates a strain gauge instrumented, distal Harrington hook and similarly equipped Harrington operating instruments (outrigger and distractor). These latter instruments are used to calibrate the hook's response to bone loads under existing operative conditions. Alternative methods of monitoring loading patterns were explored and rejected because they were noncontinuous, more difficult to use, altered the mechanics of the system, or required more expensive components. The method established is being used to avoid bone rupture or rod damage while gaining maximum spinal correction and to determine the effect of auxiliary implant components on loading patterns.

Biomedical Engineering↗
PubMed1984

Anterior stabilization of thoracolumbar injuries.

A new implant system has been designed to rigidly fix the spine anteriorly at a single level above and below the injury site for treatment of severe thoracolumbar fractures. The primary system consists of two rods rigidly linked by vertebral body bridges. These bridges are secured to each vertebra at two points: one posterolaterally on the body with a vertebral body screw and the other more anterolaterally with a vertebral body staple. This implant system has been used in 48 consecutive thoracolumbar injuries. There have been three late failures to attain spine fusion, but in no patient has there been loss of vertebral column alignment or spinal canal decompression. There have been no major catastrophes with the system. There have been one deep- and two superficial-wound infections, all of which have been successfully treated and resolved.

Adolescent↗
PubMed1984

Pelvic osteotomy: an alternative to total hip replacement in the young adult.

For the young adult patient with a painful hip in whom there is acetabular dysplasia, innominate osteotomy is not only an alternative to total hip replacement, but rather it is the procedure of choice. If the prerequisites for a Steel or a Chiari osteotomy are met and if the procedures are adequately carried out, satisfactory relief of pain and return to function can be expected. The length of the satisfactory result is unknown as yet because an insufficient number of patients have been followed over a long enough period to determine the life expectancy of these procedures. It would appear, however, that it is going to be more than 10 years, which is certainly longer than one could expect for the current generation of cemented total joint replacements to last. Cementless total joint replacements are so new that a comparison cannot be made, but intuitively, a procedure that can leave the patient with his own tissue is the procedure of choice. Certainly, in a well-executed Steel or Chiari osteotomy, later reconstruction or total joint replacement will not be compromised.

Acetabulum↗
PubMed1983

Simultaneous quantitation of knee ligament forces.

An apparatus and experimental technique have been developed which allow the simultaneous quantitation of human cadaver knee ligament forces with the knee in various positions and subjected to various loads. The methodology permits all the major ligaments of the knee to be kept intact, thus preserving much of their normal relative load-bearing function. A novel measurement technique was employed for ligament force measurement. Strain gauges were placed at the ligamentous insertions and origins either on cortical bone or the cancellous/cortical transition. Gauge output was subsequently calibrated quantitatively by cutting the ligaments and subjecting them to known loads. The gauging technique was thermally stable, and the method as a whole yielded reproducible relative ligament force data when knee positions and loads were repeated for a given knee specimen. Three fresh human cadaver knee specimens have been subjected to testing thus far with gauges at six ligamentous sites. Initial evaluation of the data indicate that ligamentous loading patterns were quite different from those reported in the literature as determined by other methods.

Humans↗
PubMed1980

Mechanical properties of some fibre reinforced polymer composites after implantation as fracture fixation plates.

Continuous fibre reinforced composite bone plates made from graphite/polysulphone and glass/epoxy laminates were implanted for 16 weeks on osteotomized canine femurs and for 12 months on intact femurs. After sacrifice, the plates were removed and tested in four point bending for stiffness and strength. There were no significant differences in properties between control and implanted plates in the 16 week study. Both the glass/epoxy and the graphite/polysulphone systems showed deterioration after implantation for 12 months.

Animals↗