Biomedical subjects

D M Estok

Publications and source records attributed to D M Estok.

13 recordsLinked to original sources

PubMed2001

An electronic database for outcome studies that includes digital radiographs.

We report on acquisition of key data from the clinical medical record, surgical data, radiologic studies, and patient surveys for a novel digital total hip arthroplasty (THA) registry that includes electronic capture of digital radiographic images into a database on an internet platform for query. We now have the ability to collect demographic and operative data, including the operative note, discharge summary, surgery data, and Digital Imaging Communications in Medicine (DICOM) radiology images. Steps are being completed to assemble office encounters, hospital procedural codes, and implant bar codes. Two examples include a THA surgery record and a THA outcome study with plain radiograph set. Analysis of such data could suggest ways to improve clinical practice.

Arthroplasty, Replacement, Hip↗

PubMed2001

Larger diameter femoral heads used in conjunction with a highly cross-linked ultra-high molecular weight polyethylene: a new concept.

The design of femoral and acetabular components of metal-on-polyethylene total hip arthroplasty implants has been dominated by the limitations of the wear properties of ultra-high molecular weight polyethylene (UHMWPE). As a result, the commonest femoral head diameters used range from 22 to 32 mm, the latter producing maximal volumetric wear. Cross-linking has been shown to improve significantly the wear resistance of acetabular components when tested in vitro against conventional femoral head sizes (22-32 mm). We expanded the study of the wear behavior of 1 type of electron-beam cross-linked UHMWPE with femoral head diameters ranging from 22 to 46 mm. The simulated gait studies showed that wear was independent of head size for the range of femoral head sizes studied. Even for the 46-mm femoral head, wear was reduced significantly using criteria of gravimetric and geometric measurements and morphologic appearance of the machining marks out to 11 million cycles of simulated gait.

Acetabulum↗

PubMed2000

20-year experience with cemented primary and conversion total hip arthroplasty using so-called second-generation cementing techniques in patients aged 50 years or younger.

We present the 20-year experience of 47 hips in 40 patients aged 50 years or younger with cemented primary total hip arthroplasty using second-generation femoral cementing techniques. Average follow-up duration in the 23 patients living at least 17 years was 18.2 years. Overall, 18 hips (38%) had components revised or removed for any reason, at an average duration of 12.6 years. Every revision or reoperation involved removing the acetabular component. Of these 18 acetabular components, 15 (32%) were revised for aseptic loosening. Eleven additional acetabular components were loose by radiographic criteria at final follow-up, yielding prevalence of aseptic acetabular loosening (55%). Four femoral components (8%) were revised for osteolysis without loosening, and 3 (6%) were revised for aseptic loosening. Femoral osteolysis, with or without component loosening, led to revision in 5 ( 11%) hips compared with 6% for aseptic loosening alone. Osteolysis was the primary problem leading to acetabular and femoral component revision in this series of people < or = 50 years old over the first 20 years after the index operation.

Adult↗

PubMed2000

A stem design change to reduce peak cement strains at the tip of cemented total hip arthroplasty.

A series of 3-dimensional finite element models was created to assess different designs of the tip of the stems of cemented femoral components of total hip arthroplasty that would decrease the peak axial tensile cement strains developed near the tip. Features of stem design that would facilitate positioning the femoral component in a neutral position centered in uniform cement mantle of adequate thickness also were evaluated. These studies showed that a stem that had a narrow tip profile that would accept an externally applied polymethyl methacrylate centralizer shaped similar to a napkin ring and had a gradual transition zone to join the body of the implant achieved these objectives. Such a combination resulted in the reduction of the peak axial strains to less than half the magnitude of the peak strains around a conventional tip (830 vs 1,868 microstrain). The reduction in peak axial strains was to one third the magnitude of the strains developed adjacent to a stem with a hole drilled into the tip to accept the commonly used fin-type polymethyl methacrylate centralizer (830 vs 2,466 microstrain). These goals were achieved because a stem that is designed to accept a napkin ring-style centralizer i) has a lower bending stiffness at the tip of the implant, ii) allows room for a thicker cement mantle, and iii) avoids creating a stress riser adjacent to the edge of the drill hole. The peak cement strains adjacent to a stem of this design are well below the endurance limit of cement as long as the transition zone where the narrow tip meets the body of the implant is gradual.

Biomechanical Phenomena↗

PubMed1998

Analysis of the kinematics of different hip simulators used to study wear of candidate materials for the articulation of total hip arthroplasties.

We developed an analytical technique to determine the paths traced by specific points on the femoral head against the acetabulum in the human hip joint during gait. The purpose of the study was to apply this technique to the mechanical hip simulators chosen to conduct wear tests on polymeric acetabular liners used in total hip replacements. These simulators differ from one another in the type of motion produced, apart from other variables such as type of lubricant and head position. Due to the variation in the kinematics between the machines, the paths traced by the points on the femoral head against the acetabular liner ranged from simple linear traces to figure-8 loops and quasi-elliptical paths during a single simulator cycle. The distances traveled by these points during the same period also varied appreciably among the different hip simulator designs. These results are important when combined with other studies that have shown that kinematics can play an important role in the outcome of in vitro wear experiments. The kinematic differences quantified in this study can partially explain the substantial differences in wear data reported from different simulator designs and also underscore the usefulness of the technique described in this study in judging the results from different hip simulator experiments.

Acetabulum↗

PubMed1998

Average 12-year outcome of a chrome-cobalt, beaded, bony ingrowth acetabular component.

Seventy-two hips (67 patients) were reconstructed with the Acetabular Reconstruction Component (ARC, Howmedica, Rutherford, NJ), a chrome-cobalt component with sintered ingrowth beads and peripheral flanges for screw fixation. All the materials used in the ARC (metal, porous layer, and polyethylene) are identical to those used in the Porous Coated Anatomic (PCA) acetabular component (Howmedica), but the design is different. To determine the importance of design features alone, clinical results obtained with the 2 different designs made of identical materials were compared. The average follow-up period for patients with the ARC was 12 years (range, 10-13.3 years). Seven patients (7 hips) with the ARC died prior to the minimum 10-year follow-up period, none having undergone revision procedures. Overall, 3 acetabular components (4%) in 3 patients were revised, at an average of 8.5 years (range, 7.6-9.3 years) from the index operation. The reasons for revision were aseptic loosening, third-body polyethylene wear observed during a revision for femoral lysis, and acetabular component malposition and recurrent dislocation. The total incidence of acetabular aseptic loosening was 4% (3 of 72 hips). Pelvic osteolysis occurred in 3 cases (4%). In contrast, the incidence of acetabular revision of the PCA acetabular component at follow-up periods of 2-10 years is reported to be as high as 11% (range, 3-11%). Rates of aseptic loosening are as high as 30% (range, 3-30%) at substantially shorter follow-up periods, and the incidence of pelvic osteolysis associated with the PCA component is also as high as 30% (range, 5-30%). These differences may reflect differences in design between the 2 acetabular components, as the materials used were identical. In this, the longest reported average follow-up study of a successful cementless acetabular component, the aseptic loosening rate of 4% contrasts with the 42% rate at similar follow-up duration for cemented acetabular components placed by the same surgeon in patients of similar age.

Acetabulum↗

PubMed1998

Total hip arthroplasty with use of second-generation cementing techniques. An eighteen-year-average follow-up study.

In this report, we present the results of a further follow-up of a series of 140 consecutive patients (161 hips) who had had a primary total hip arthroplasty with insertion of a bead-blasted monoblock femoral component with use of so-called second-generation cementing techniques. The average age of the patients at the time of the arthroplasty was sixty-one years (range, twenty-one to eighty-five years). Sixty-seven patients (seventy-seven hips) died less than seventeen years after the index operation. The remaining seventy-three patients (eighty-four hips) were followed for an average of eighteen years (range, seventeen to twenty years). No patient was lost to follow-up. In the entire group of 161 hips, over the twenty-year span of the study, eight femoral components (5 percent) and twenty-eight acetabular components (17 percent) had been revised because of aseptic loosening. Of the seventy-seven hips in the sixty-seven patients who died, four had been revised because of aseptic loosening of the acetabular component only; one, because of aseptic loosening of the femoral component only; and one, because of aseptic loosening of both components. Of the eighty-four hips in the seventy-three patients who were alive at least seventeen years after the index arthroplasty, twenty-four hips (29 percent) in twenty-one patients had had revision of one or both components for any reason. Twenty-three acetabular components (27 percent) and six femoral components (7 percent) had been revised because of aseptic loosening. An additional two hips (2 percent) in two patients were loose according to radiographic criteria but had not been revised. Of the sixty-five all-polyethylene acetabular components that had been inserted with cement and were in patients who were alive at least seventeen years postoperatively, fifteen (23 percent) had been revised because of aseptic loosening. An additional seventeen cups (26 percent) were loose according to radiographic criteria. Thus, a total of thirty-two cups (49 percent) had been revised because of loosening or were loose but had not been revised at the time of the latest follow-up. The femoral components that had been inserted with use of second-generation cementing techniques fared better than did the acetabular components that had been inserted with these techniques during the same time-period. We found that assessment of all postoperative radiographs rather than only those that had been made immediately postoperatively increased the accuracy of the grading of the cement around the femoral component. Subsequent radiographs frequently had been made at different projections, which revealed new findings, consisting primarily of previously undetected voids, areas of thin cement, and defects in the cement mantle. Thus, we now use all available radiographs to determine the grade of the cement.

Adult↗

PubMed1998

Follow-up of intertrochanteric osteotomy of the hip during a 25-year period.

In 1984, in reporting follow-up on 67 hips in 61 patients who underwent intertrochanteric osteotomies for osteoarthritis of the hip, we found that between 12 and 15 years after osteotomy, 34% (23) of the 67 hips remained functional and the remainder had been converted to an arthroplasty. We now report on the fate of those osteotomies over a 25-year period. Ten patients with 10 osteotomies did not require an arthroplasty, having died without requiring conversion to total hip arthroplasty at an average of 18.3 years after osteotomy (range: 11 to 24.1 years). Two others were living at an average of 25.2 years after osteotomy without requiring conversion. Thus, for 18% of the hips, no further hip surgery was performed. For the remaining 55 hips in 49 patients, the osteotomy had served for an average of 9.8 years (range: 1.3 to 26.1 years) before requiring arthroplasty. The cumulative probability of osteotomy survival was 57.8% (standard error: 6.0%) at 10 years, 20.0% (standard error: 4.9%) at 20 years, and 5.7% (standard error: 2.9%) at 25 years by Kaplan-Meier survivorship analysis.

Adult↗

PubMed1997

Factors affecting cement strains near the tip of a cemented femoral component.

A generic three-dimensional finite-element model of the upper half of the femur containing a cemented femoral stem of a total hip arthroplasty was developed to study those factors influencing cement strains near the tip of a cemented femoral component. This generic model was verified through another three-dimensional finite-element model that had been created based on the precise geometry of a cadaver femur implanted with a contemporary cemented femoral component. This cadaveric femoral reconstruction had been created with strain gauges embedded in the cement mantle and was then loaded under conditions simulating single leg stance and stairclimbing. By use of the cement strains measured experimentally in the cadaver femur, and comparison of them with those obtained from the finite-element model of that cadaver femur, it was possible to establish proper material properties, boundary conditions, and loading conditions for the generic model. The generic model was then modified parametrically to determine those factors that influence the strains occurring within the cement mantle near the tip of a cemented femoral component. These models suggest that the single factor that most adversely influenced peak strains at or near the tip of the prosthesis was a thin cement mantle. This effect was present both when the cement mantle was reduced in thickness and when a similar effect occurred by virtue of a varus or valgus placement of the stem. Factors that decreased the peak cement strains near the tip of the femoral stem included a more flexible stem and thicker cement mantles. This effect of a more flexible stem could be obtained by changing the modulus of the metal implant by uniformly reducing the thickness of the stem, or by tapering the stem within the same bone geometry. Thicker cement mantles reduced both the axial and the shear strains occurring at the tip of the prosthesis. The presence or absence of a hole in the tip of the prosthesis per se, as for a centralizer, had no significant effect on the peak cement strains seen around the tip of the prosthesis; however, truncating the tip of the prosthesis from a hemisphere to a flat profile, which resulted in a sharp corner at the tip of the prosthesis, produced a 35% increase in cement strains at the tip as a result of a stress concentration effect. Thus, the common way of modifying the tip to have a hole for a centralizer, which involved truncating the tip, increased the cement strains occurring near the tip of the prosthesis.

Bone Cements↗

PubMed1996

Loci of movement of selected points on the femoral head during normal gait. Three-dimensional computer simulation.

Wear of ultrahigh-molecular-weight polyethylene and the subsequent lytic response to the particulate wear debris are the dominant problems in total joint arthroplasty surgery. Wear testing apparatus can play a vital role in the in vitro evaluation of the many factors involved in wear, such as head size, surface roughness, materials for the head, and new materials for the socket. Wear of ultrahigh-molecular-weight polyethylene may be influenced by the wear path. For the related polymer, high-density polyethylene, the wear path is critical to wear magnitude. What is the actual path taken by a single point (or by multiple representative points) on the femoral head of a total hip arthroplasty as it passes through the gait cycle? The goal of this computer simulation study was to trace the paths of specific points on the femoral head as they moved against the polyethylene cup during a single cycle of normal gait to illustrate the motions occurring at the intraarticular surface of the hip joint. This study also yielded unusual data on the "distance traversed" by these points during a single gait cycle. It was found that there was not one path, but rather there were many, and the paths varied widely in both shape and length depending on the location on the femoral head. Moreover, the differences in excursion and direction at different sites during the loaded phase were great. In addition, distances traveled by different points on the femoral head of any given size varied by a factor greater than 2. Most of the points traced quasielliptical paths. This automatically means that the paths of neighboring points cross each other, creating multidirectional shear forces on the acetabular cup surface which may be important in the localization and extent of wear. The plots of traces of the points derived from this study can serve as benchmarks for the ability of hip simulators to reproduce the actual distances and paths of travel of individual points on the femoral head.

Computer Simulation↗

PubMed1995

Total hip arthroplasty with use of so-called second-generation cementing techniques. A fifteen-year-average follow-up study.

One hundred and forty-nine patients (162 hips) had a standard primary total hip arthroplasty with a grit-blasted femoral component and use of so-called second-generation cementing techniques. No patient was lost to follow up. Fifty-one patients (sixty hips) died within fourteen years after the index operation. The remaining ninety patients (102 hips) were followed for a minimum of fourteen years. Of the fifty-one patients (sixty hips) who died within fourteen years, three patients (three hips; 5 per cent) had had a revision: one, because of aseptic loosening of the acetabular component; one, because of aseptic loosening of the femoral component; and one because of aseptic loosening of both components. Of the ninety patients (102 hips) who were alive fourteen years or more (average duration of follow-up, fifteen years) after the arthroplasty, one patient (two hips; 2 per cent) had a revision because of bilateral aseptic loosening of the femoral component. In seven patients (seven hips; 7 per cent), the femoral component loose according to radiographic criteria but was not revised. For the entire group of 162 hips, four femoral components (2 per cent) were revised because of aseptic loosening. In contrast, the rate of aseptic loosening of the acetabular component was higher and continued to increase. Of the eighty-one hips with an all-polyethylene acetabular component in the patients who were alive at fourteen years or more, eight (10 per cent) had a revision because of aseptic loosening. In addition, twenty-eight (42 per cent) of the sixty-seven all-polyethylene acetabular components that were in place after fourteen years or more, and for which there were current radiographs, were loose. Femoral components implanted with the use of second-generation cementing techniques appear to have fared much better than acetabular components that were inserted with similar techniques in this series of patients. A thin (less than one-millimeter) mantle of cement around the femoral component and defects in the mantle of cement were associated with increased loosening of the femoral component.

Adult↗

PubMed1994

Long-term results of cemented femoral revision surgery using second-generation techniques. An average 11.7-year follow-up evaluation.

From a group of 43 hips in 41 patients, previously reported at an average of six years of follow-up evaluation, in whom second-generation cementing techniques were used during femoral revision hip surgery, 38 hips in 36 patients were rereviewed at an average follow-up period of 11.7 years (range, 118-172 months). The average age of the patients at the time of revision surgery was 52.8 years. Only four femoral components (10.5%) required rerevision for aseptic loosening. Of those not rerevised, the average Harris hip score at the time of follow-up evaluation was 81. Four additional hips (10.5%) had radiographic evidence of definite femoral component loosening. The survival of 90% of the implants of cemented femoral revision surgery and the 79% incidence of well-fixed femoral components for more than 11.7 years is attributed to the improved cementing techniques and modern stem design.

Adult↗

PubMed1991

Technique to detect migration of femoral components of total hip arthroplasties on conventional radiographs.

Critical to the evaluation of patients with painful total hip arthroplasties and to the assessment of the efficacy of fixation of new prosthetic designs and/or new insertion techniques is the ability to detect migration of the femoral components. The authors present a simple and effective technique using plain radiography that can detect migration of 1 mm with a high degree of accuracy.

Equipment Failure↗