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Biomedical subjects

A A McBeath

Publications and source records attributed to A A McBeath.

14 recordsLinked to original sources
PubMed1992

Fixation stability of femoral components in a canine hip replacement model.

A canine hip replacement model was used to compare fixation stability in cemented and cementless femoral components. Parameters of comparison were the load-induced positional changes of each prosthesis relative to its proximal femoral cortex, hereafter called relative displacements. Identical femoral components, with the proximal third of their stem porous-coated, were implanted in the right femurs of 10 large, mixed-breed dogs. Five were tightly fit to allow porous ingrowth, and five were cemented into the medullary canal. Four months after implantation, all femurs were harvested. A prosthesis was implanted in the left (normal) femur of each dog ex vivo with fixation identical to the contralateral limb to simulate acute postoperative fixation. Eddy current transducers measured relative displacements under application of static loads, serially applied in the axial, mediolateral, and craniocaudal directions. Thereafter, the femurs were transversely sectioned and morphologically analyzed to correlate bony apposition at the implant surface with relative displacements. We observed no difference in relative displacements between acute and 4-month-cemented groups (e.g., 0.0059 +/- 0.0021 vs. 0.0060 +/- 0.0048 mm, respectively, for 100-N axial loading measured at midstem). With cementless implantation, relative displacements of the acute group were significantly larger (p = 0.007) than those of the 4-month group (e.g., 0.236 +/- 0.257 vs. 0.097 +/- 0.129 mm, respectively, for 100-N axial loading measured at midstem). Cementless components implanted for 4 months were not significantly different than cemented components, but a trend suggested that they were still not as stable as cemented components, particularly for craniocaudal loads. Relative displacements of the 4-month, porous ingrowth group were approximately proportional to the percentage of bony apposition raised to the -1.44 power (r = 0.94).

Animals↗
PubMed1992

Determination of bone mineral density by dual x-ray absorptiometry in patients with uncemented total hip arthroplasty.

Bone remodeling is an expected sequela with total hip arthroplasty (THA). Although there are several methods of estimating bone response in THA patients from radiographs, there are no accurate and generally accepted methods for quantitative determinations in vivo. In this study, we describe an application of dual x-ray absorptiometry (DXA) for measuring bone mineral content and bone mineral density in the proximal femur following THA. DXA is a noninvasive technique with minimal radiation exposure (< 5 mrem). Various aspects of measurement error (accuracy and reliability) of this application of DXA were determined in a series of studies reported here. Accuracy error (how similar are the measured and actual values) was < 1% determined in bone phantoms of four densities. Precision error (how reproducible are the measurements) was also < 1% at all four densities in the phantoms and was only slightly elevated (0.9-1.5%) in repeated measurements of implanted cadaver femora. Precision error in vivo, determined both from multiple replicates on five patients and from duplicate scans on 30 patients, was further elevated but remained < 5%. Contributions to precision error, rotation of the leg, and interoperator variability were assessed; none was found to elevate precision error appreciably. We suggest that DXA is a feasible method for quantifying bone response following THA, and will allow discrimination of small changes (> 5%) not previously measurable.

Absorptiometry, Photon↗
PubMed1991

Canine intersegmental hip joint forces and moments before and after cemented total hip replacement.

Intersegmental forces and moments (i.e. resultant free body forces and moments computed at the joint centers) were studied in canine hindlimbs before and after cemented total hip replacement (THR). Five large, adult, mixed-breed dogs were selected. Their gait was recorded (while leash-walked) before surgery using high-speed cinematography and a force plate. Cemented total hip replacement was unilaterally performed on each dog. Gait was again recorded at one and four months after surgery. Segmental properties (mass, center of mass, and mass moment of inertia) of the hindlimbs were experimentally determined, and an inverse dynamics approach was used to compute intersegmental forces and moments in the sagittal plane. Significant reductions in intersegmental joint forces and moments were observed in the operated hindlimb one month after surgery, although kinematic gait parameters were unaltered. Decreases of 77.0% for vertical forces, 61.9% for craniocaudal forces, and 66.2% for extension moments were determined. Four months after surgery, the joint forces and moments had returned to their preoperative values. This experiment demonstrates that the dynamics of normal walking can be restored in a canine model by four months after THR. It also shows that kinetic (rather than kinematic) parameters are more descriptive of antalgic gait in the canine.

Animals↗
PubMed1990

Femoral strain adaptation after total hip replacement: a comparison of cemented and porous ingrowth components in canines.

The purpose of this study was to investigate if experimental strain analysis is predictive of femoral adaptation after total hip replacement (THR). Ten large adult dogs underwent unilateral THR with identical implants. Five implants were press fit for porous ingrowth fixation, and five were cemented. Four months after surgery femora were harvested. Strain gauge rosettes were applied to the femora at eight proximal locations. Femora were compressively loaded on the head of the femur or femoral component. Strain data represented three conditions: preoperative, acutely postoperative, and four-month postoperative. The unoperated femur of each dog was used to simulate preoperative and acutely postoperative behavior of the contralateral implanted femur. Strains from each condition were compared. Transverse femoral sections were obtained through the levels of the strain gauges. Fine detailed radiographs were used to quantify morphological changes. Results showed cemented and uncemented implantations produce similar trends but different amounts of bone adaptation. Adaptations were generally consistent in direction with strain perturbations caused by implantation, but the extent of adaptation did not strongly correlate with the magnitude of perturbations. Also, there was no consistent trend towards normalization of altered strains. Results suggest that strain perturbations after THR may be mechanical triggers for morphological changes, but caution is required when predicting the extent of these changes or the autoregulatory role of strain.

Adaptation, Physiological↗
PubMed1990

K-edge digital subtraction arthrography of the painful hip prosthesis: a feasibility study.

K-edge energy subtraction radiography is a method for detecting the presence of iodinated contrast material by subtracting two digital radiographs produced by X-ray beams with energies above and below the iodine K edge. We performed a feasibility study on the application of K-edge energy digital subtraction arthrography (KEDSA) to painful hip prostheses. During arthrography, loosening of the prosthesis is implied if contrast material is seen dissecting around the prosthesis, an often difficult detection task because of adjacent prosthesis metal or cement. In conventional arthrography a preliminary mask image is thus used from which films obtained after injection of iodinated contrast material are subtracted. Movement by the patient during this process may preclude subsequent subtraction. With KEDSA, since multiple image pairs may be obtained after the injection of contrast material, the problem of patient motion is virtually eliminated. A conventional X-ray tube operating between 55 and 65 kVp was alternately filtered by iodine and cerium filters to produce the KEDSA images. The apparatus was capable of producing a subtracted image within 3 sec. The technique was applied to phantoms and to six patients immediately after hip arthrography that had been positive for prosthesis loosening. Although of lower spatial resolution, the KEDSA images were, in all cases, positive for loosening in a pattern consistent with the conventional arthrographic images. KEDSA was shown to be successful in detecting extraarticular contrast material. During a single study, subtraction in various imaging planes as well as postexercise subtraction imaging can be accomplished-techniques not heretofore possible in routine subtraction arthrography.

Aged↗
PubMed1979

Femoral component loosening after total hip arthroplasty.

To determine the long-term durability of total hip arthroplasty and to identify factors responsible for femoral component loosening, 106 total hip arthroplasties were reviewed in patients with a minimum postoperative period of 3 years. Seventy-four had Charnley-Müller prostheses and 32 had Charnley prostheses. Femoral component loosening occurred in 16 of 106 hips. Not all loose components were symptomatic. The femoral component at risk was the femoral Charnley-Müller type that had been inserted in varus position in a functioning active heavy patient who previously had had a femoral head prosthesis.

Body Weight↗
PubMedDate not supplied

Phemister bone graft for osteonecrosis post renal transplant.

Avascular necrosis of the femoral head is an unfortunate sequela of renal transplantation. The necessary exogenous steroids are felt to be the cause of the necrosis. The case histories of three patients with bilateral disease are presented. All 6 hips were initially treated with a Phemister bone graft. According to the classification of Marcus, et al., one hip was Stage 3, three hips were Stage 4, and two hips were Stage 5 at the time of grafting. Four of these hips have had minimal further collapse and have been functionally satisfactory for the patients. One femoral head has had marked collapse but is pain free. One femoral head has had marked collapse with pain sufficient to necessitate a total hip replacement. The two heads with marked collapse were both Stage 5 at the time of surgery. The Phemister bone graft is presented as a possible treatment for this problem, especially when the disease is treated before femoral head collapse occurs.

Adolescent↗
PubMedDate not supplied

Knee synovectomy for rheumatoid arthritis.

Twenty-one patients with rheumatoid arthritis had 33 knees treated with synovectomy. They were followed for an average of 5 2/3 years postoperatively. At follow-up, patients with 58% of the knees had less pain, 15% more pain, 54% were satisfied, 39% had palpable synovitis, but all had lesser synovitis postoperatively, and 53% showed radiographic progression of disease. Motion was not lost. There were no significant complications. Better results can be anticipated in those patients whose knees show little or no destruction radiographically and no significant deformity at the time of operation. However, beneficial results can occur even in those with more advanced changes. Even though quality of results tends to diminish with time, the procedure offers sufficient benefits to continue its use.

Arthritis, Rheumatoid↗