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Biomedical subjects

L D Dorr

Publications and source records attributed to L D Dorr.

At least 19 recordsLinked to original sources
PubMed2001

Matched-pair analysis of all-polyethylene versus metal-backed tibial components.

Forty-eight matched pairs of osteoarthritic knees from patients who underwent primary total knee arthroplasty with a round-on-round, Apollo Knee System were studied to evaluate the outcome between all-polyethylene and metal-backed tibial components. Patients were matched for patient factors, preoperative deformities, cruciate salvage or sacrifice, and surgical technique. At the last follow-up (average, 38.4 months), there was no statistically significant difference in terms of knee scores, patient self-assessment, and radiographic outcomes. No component required revision, and no revisions were pending. Maintenance of these results over time would project into better long-term success for all-polyethylene tibial components because of the amount of wear and osteolysis with current modular metal-backed tibial components. We advocate the use of a more cost-effective all-polyethylene tibial component in elderly patients (>70 years old) who are not likely to need the versatility of exchange of a modular polyethylene insert because of wear.

Adult↗
PubMed2001

Technical factors for success with metal ring acetabular reconstruction.

Sixty-four hips in 62 patients were revised with a Mueller ring (28 hips), Ganz ring (18 hips), and Burch-Schneider cage (18 hips) under the direction of a single surgeon. A polyethylene cup was cemented into the metal support of all hips. Average follow-up was 4.6 years (range, 2.0-6.7 years). Six rings were revised because of aseptic loosening, and 5 others were radiographically loose, for a mechanical failure rate of 11 of 64 (17%). Acetabular metal ring supports failed by migration when defects of > or =60% of the superior weight-bearing bone were filled by only cement or particulate graft. At the time of surgery, the superior rim of the metal support should be against host-bone for 60% of its support, and if not, the use of bulk allograft, rather than particulate graft, is required. Dislocation was the second failure mechanism identified, and this occurred in 15 hips (23%), with reoperation required in 5 hips (8%). A constrained liner should be used in patients with nonunion of the trochanter and preoperative abductor weakness that grades fair/minus or worse as measured by the side-lying abduction test.

Acetabulum↗
PubMed2001

Comparison of preoperative radiographs and intraoperative findings of fixation of hemispheric porous-coated sockets.

BACKGROUND: The radiographic criteria for identification of loose cementless acetabular components have not been well established. The purpose of this study was to compare the radiographic appearance of a hemispheric porous-coated cementless cup fixed with screws with the intraoperative findings with regard to the fixation status. METHODS: The quality of the cup fixation was evaluated at fifty-two hip revisions that were performed, for reasons other than infection, at an average of 89.9 months (range, 33.8 to 150.1 months) after the primary operations. The fixation status at the revision surgery was compared with the findings on sequential anteroposterior and lateral radiographs of these sockets. Sequential radiographs of an additional 100 total hip replacements that had not required a reoperation and that had been followed for an average of 121 months were also measured. RESULTS: Loosening of the socket was radiographically identified by (1) radiolucent lines that initially appeared after two years, (2) progression of radiolucent lines after two years, (3) radiolucent lines in all three zones, (4) radiolucent lines 2 mm or wider in any zone, or (5) migration. The sensitivity of these criteria was 94%, and the specificity was 100%. The criteria had a positive predictive value of 100% and a negative predictive value of 97%. CONCLUSIONS: The most predictive radiographic findings for early diagnosis of loosening of a hemispheric porous-coated cup were progression of radiolucent lines more than two years after the operation and any new radiolucent line of 1 mm or wider that appeared more than two years postoperatively. Sequential anteroposterior and lateral radiographs are necessary to assess the time of onset and progression of radiolucent lines in order to identify loose hemispheric porous-coated cups accurately.

Acetabulum↗
PubMed2001

The unstable total hip arthroplasty: the role of postoperative bracing.

Control of the unstable THA can be problematic, but conservative management with casting and bracing can assist the patient in gaining stability, both externally and internally. The application of such appliances does not negatively affect the ultimate function of the hip and can prevent further surgical intervention.

Adult↗
PubMed2001

Mobile-bearing knee replacement: concepts and results.

In summary, if TKRs are to be performed in patients who are younger and more active than those who had the initial procedures in the 1970s and 1980s, better wear performance is imperative for long-term durability, especially if surgeons continue to consider the versatility associated with modular knee-replacement systems to be a necessity. At least with some designs, including the Oxford knee and the LCS knee, the results after a minimum follow-up of 10 years are comparable with the best results after arthroplasty with fixed-bearing designs in terms of wear, loosening, and osteolysis (Table 7). As with fixed-bearing designs, there are additional challenges in terms of optimizing bearing-surface conformity and improving kinematics. Improvements in future designs of mobile-bearing total knee replacements should include better control of bearing mobility patterns to reduce the prevalence of the abnormal kinematic motions that have been observed in fluoroscopic evaluations.

Adult↗
PubMed2000

Radiographic anatomic structure of the arthritic acetabulum and its influence on total hip arthroplasty.

Acetabular bone structure is not the same in all patients and can be defined by the radiolucent triangle superior to the acetabulum. Of 132 hips, 81 had an isosceles triangular shape, which was named type A acetabulum. Forty-six hips had an extension of the triangle into the teardrop, which created a thickened medial wall and was named type B. Five hips had a right-angle triangle, which was found only with congenital disease of the hip and was named type C. The density of the superior acetabular bone in the triangle could be normally radiolucent (stage I), have vertical and transverse trabeculae throughout the triangle (stage II), or have the triangle filled with bone and cysts (stage III). The relationship between progressive radiolucent lines and acetabular type showed that type A3 (thin medial wall with dense triangle bone) had the highest incidence of progressive radiolucent lines (P < .05).

Acetabulum↗
PubMed2000

The effect of diaphyseal biologic fixation on clinical results and fixation of the APR-II stem.

This study evaluated the effect of a grit-blasted diaphyseal surface on noncemented fixation of the Anatomic Porous Replacement II stem (APR-II, Sulzer Medica Orthopaedics, Austin, TX) for improvement of clinical results and fixation. A total of 107 consecutive total hip arthroplasties with the APR-II stem, which has proximal porous coating and a diaphyseal grit-blasted surface, were performed without cement, and 99 were studied at average 4 years. Of these hips, 37 had hydroxyapatite sprayed onto the proximal porous coating, but because there were no statistical differences for performance in any category, all stems were considered as 1 group. Clinical results were measured by the Harris hip score. Radiographic measurements of fixation, osteolysis, and bone remodeling were studied by reference to Gruen zones. Of hips, 99% had a good or excellent result by Harris hip score, with an average pain score of 42.3. Of hips, 98% had >40 points, with no patient reporting thigh pain after 3 years. There were no radiolucent lines in 94% of stems, and 100% had proximal bone ingrowth fixation. Distal cortical hypertrophy associated with tip fixation occurred in 49%, whereas proximal stress shielding was present in 43% of hips. Comparison of these clinical and radiographic results with our previous experience of bone ingrowth implants (smooth stem) suggests that bone ingrowth proximally with ongrowth in the diaphysis of the femoral stem provides better clinical and radiographic results.

Arthroplasty, Replacement, Hip↗
PubMed2000

Functional comparison of posterior cruciate retention and substitution knee replacement.

Thirty-eight matched pairs of osteoarthritic knees from patients who underwent primary total knee replacements with minimum 2 years of followup were studied to compare the functional outcome between a cruciate retention and posterior stabilized design with essentially identical articulation surfaces. Patients were matched for age, weight, gender, diagnosis, activity, deformity of the knee, type of tibial component, and duration of followup. The patients were evaluated functionally by three methods: the Knee Society scoring system; a self-administered questionnaire; and an activity rating based on distance walked. In addition, in vivo fluoroscopic examination was performed in 10 cruciate retention and 10 posterior stabilized knees to determine the functional knee kinematics. Results showed that by patient self-assessment, functional improvement was achieved in 35 (92%) cruciate retention knees and 36 (95%) posterior stabilized knees. There was no statistically significant difference between the two groups in the clinical evaluations. Fluoroscopic kinematics showed that the posterior stabilized knee experienced anteroposterior femorotibial translation more similar to the normal knee during normal gait and deep knee bend. These clinically equivalent results are not in agreement with the predicted better functional results of cruciate retained knees as determined by gait studies.

Aged↗
PubMed2000

Radiographic comparison of diaphyseal grit blasted with smooth surface stems by matched pair analysis.

A matched pair comparison of two groups of 42 patients who had a total hip arthroplasty with uncemented fixation of the femoral stem with proximal porous coating and distal grit blasting were compared with a stem of identical design except with diaphyseal smooth surfaces. Radiographic analysis was done to determine differences in fixation and bone remodeling at the 2-year followup, and these results were compared with clinical results. The method used for measuring cortical thickness was semiquantitative, with measurements done at 15 1-cm increments beginning at 3 cm distal to the midlesser trochanter. This study determined whether, with an identical stem design, diaphyseal biologic fixation, rather than mechanical fixation, would provide better fixation without significant stress shielding differences. Seven percent of grit blasted stems had radiolucent lines in Gruen Zones 3 to 5, compared with 79% of smooth stems. The smooth stem was on average one size larger so the stress shielding was not different between matched pairs. There was a distinct pattern of adaptive remodeling that occurred in the femur with both stem surfaces. Bone loss was greatest in the proximal medial and proximal posterior bone and occurred along the entire anterior cortex. Bone thickening occurred in the distal medial and posterior cortices and extended below the tip of the prosthesis.

Adult↗
PubMed2000

Total hip arthroplasty with use of the Metasul metal-on-metal articulation. Four to seven-year results.

BACKGROUND: Total hip replacements with a metal-on-metal articulation were commonly used until the mid-1970s; most were then abandoned in favor of hip replacement with a metal-on-polyethylene articulation. The reason for this change was primarily early cup loosening, which was more prevalent with these metal-on-metal designs than it was with metal-on-polyethylene designs. In the late 1980s, a metal-on-metal design with improved clearance (adequate space between the femoral head and the acetabular articulation surface to allow fluid film lubrication and clearance of any debris from within this joint), metal hardness, and reproducible surfaces was introduced by Sulzer Orthopedics in Switzerland. Orthopaedic surgeons were interested in this Metasul articulation because the contribution of polyethylene wear particles to the failure of total hip replacements had become evident. This study was undertaken to review the clinical performance of this implant and to determine if early acetabular loosening or revision and wear and osteolysis were prevalent. METHODS: Between 1991 and 1994, seventy patients (seventy hips) had a total hip replacement with the Metasul metal-on-metal articulation and a cemented Weber cup. Nine patients died less than four years after the replacement; none of these deaths were related to the operation. Five patients were not available for radiographic evaluation, but they were contacted and it was known that the hip was not painful and had not been revised. Fifty-six patients (fifty-six hips) had complete clinical and radiographic data four to 6.8 years after the operation, and they made up the study group. The patients were evaluated with use of the Harris hip score, a patient-self-assessment form, and radiographs. RESULTS: At an average of 5.2 years (range, four to 6.8 years) after the operation, the average total Harris hip score for the fifty-three patients who did not have a revision was 89.6 points (range, 62 to 100 points). The average Harris pain score was 41.0 points (range, 30 to 44 points), and the average Harris limp score was 9.4 points (range, 5 to 11 points). One patient had revision of a loose cup, but there were no other loose acetabular components in the series. Two patients had revision of the acetabular component because of dislocation. No patient had a loose or revised femoral component. Therefore, the mechanical failure rate was one (2 percent) of fifty-six patients. Thirty-six of forty-seven patients who completed the patient-self-assessment form rated their result as excellent; seven, as very good; two, as good; one, as fair; and one, as poor. Wear could not be measured on radiographs because of the metal-on-metal articulation. No hip had radiographic evidence of acetabular osteolysis and two hips had calcar resorption, but there was no other radiographic evidence of focal osteolysis. CONCLUSIONS: Our four to seven-year experience with this articulation surface indicates that the clinical results are similar to those of total hip replacements with a metal-on-polyethylene articulation. We believe that the Metasul articulation may have a role in reducing the wear that occurs with total hip replacement. The Metasul articulation appears to be particularly indicated for more active patients. A historical comparison with the reports in the literature of which we are aware indicated that the hips in our study had a lower rate of acetabular revision and loosening than did those with previous metal-on-metal designs and that they had no more acetabular loosening or osteolysis than did those with metal-on-polyethylene articulations followed for an average of five years.

Adult↗
PubMed2000

The bearing surface in total hip arthroplasty: evolution or revolution.

Highly cross-linked polyethylenes represent a new class of polyethylenes that demonstrate dramatic improvements of wear characteristics in laboratory tests. Cross-linked polyethylenes can be manufactured by a number of methods, all of which lead to some changes in the physical properties of the polyethylene. The very limited clinical information about cross-linked polyethylenes available has been favorable. Cross-linked polyethylenes appear to hold promise as an alternative to conventional polyethylene and to hard-on-hard bearing surfaces, but much more clinical information will be required before they can be recommended for routine clinical use.

Biomechanical Phenomena↗
PubMed1999

Effect of stem stiffness and bone stiffness on bone remodeling in cemented total hip replacement.

The hypothesis in this study is that the stem stiffness-to-bone stiffness ratio influences the incidence and type of bone remodeling and fixation with cemented total hip arthroplasty. Ninety-one patients with 99 hips had cemented stems using 3 different anatomic porous replacement designs. The APR I and APR II titanium stems with proximal porous coating on the proximal one fourth of the stem were cemented into 49 and 35 patients. The APR II-C stem, which is a cobalt-chrome stem only for cemented fixation, was cemented into 15 patients. These 3 different stem designs were used to study different metals as well as different stem shapes. The average follow-up was 4.3 years (range, 2-10 years) with all hips having 2 years' follow-up and 42 hips at least 5 years' follow-up. Bone remodeling was measured as stress shielding, calcar resorption, and distal hypertrophy on anteroposterior and lateral radiographs of the hip. Stress shielding was measured by the 4 grades described by Engh. A stem stiffness-to-femoral bone stiffness ratio was calculated from the plain radiographs with the stem stiffness known from the manufacturer and the bone stiffness calculated using measurements of the outer and inner diameters of the femur. There was no statistical difference for bone remodeling and fixation between the 3 stem shapes or 2 metal types used in these hips. No stem was loose, and only 10 had radiolucent lines. Stress shielding was statistically related to stem stiffness but was more strongly related to the axial stiffness ratio, mediolateral bending stiffness ratio, anteroposterior stiffness ratio, and torsional stiffness ratio. Stress shielding grade 3 and 4 was present in 20% of hips with a torsional stiffness ratio < 0.33, in 38% of hips with a torsional stiffness ratio of 0.34 to 0.5, and in 70% of hips with a torsional stiffness ratio > 0.5. Five-year results showed no statistical change in stress shielding, calcar resorption, and distal hypertrophy from the 2-year observations. The stem stiffness-to-bone stiffness ratio influenced bone remodeling but not fixation of these cemented stems.

Adult↗
PubMed1999

Medial protrusio technique for placement of a porous-coated, hemispherical acetabular component without cement in a total hip arthroplasty in patients who have acetabular dysplasia.

Twenty-four hip replacements were performed with use of a medial protrusio technique to stabilize the fit of a hemispherical metal shell in the acetabulum in nineteen patients who had dysplasia of the hip. All of the hips were followed for a minimum of five years (average, seven years; range, five to thirteen years). Six of the hips were type I, seven were type II, eight were type III, and three were type IV according to the criteria of Crowe et al. The acetabular cup was implanted with the medial aspect of its dome beyond the Kohler line (drawn from the ischium along the ilioischial line) in all hips. An autogenous graft sculpted from the femoral head was used to cover 15 to 30 percent of the superolateral portion of the cup in one type-I hip, four type-III hips, and one type-IV hip. The need for these six bone grafts could have been avoided by reaming two to three millimeters more medially or by allowing 20 percent of the superolateral portion of the cup to be uncovered. Sixty to 84 percent of each bone graft was resorbed, effectively leaving the superolateral portion of the cup uncovered. The amount of the surface of the cup that was beyond the Kohler line averaged 41 percent for the six type-I hips, 43 percent for the seven type-II hips, 41 percent for six of the type-III hips, and 44 percent for one of the type-IV hips. Crossing of the ilioischial and iliopubic lines was noted on the radiographs of two type-III and two type-IV hips. Radiographs of two type-I hips and one type-II hip showed 7 to 17 percent of the surface of the dome of the cup through the internal pelvic wall (beyond the iliopubic line). None of the twenty-four metal shells were revised. A reoperation was performed on two hips to exchange a worn polyethylene insert, and three femoral components that had been fixed without cement were revised because of mechanical loosening. Wear averaged 0.26 millimeter per year in the fourteen hips that had a titanium femoral head and 0.09 millimeter per year in the nine hips that had a cobalt-chromium femoral head. The remaining hip had a ceramic femoral head, and the wear rate was 0.09 millimeter per year. The medial protrusio technique is a predictable, reproducible method for obtaining fixation of a porous-coated, hemispherical acetabular component in a dysplastic acetabulum. The technique permits the use of a porous-coated (bone-ingrowth) component; avoids the use of support bone graft and thereby reduces the operative time; facilitates rehabilitation by permitting earlier weight-bearing of the hip; and permits the use of a modular bearing surface, which may allow future exchange of only this surface rather than revision of the entire acetabular component because of excessive wear.

Acetabulum↗