Biomedical subjects

Mauricio Silva

Publications and source records attributed to Mauricio Silva.

18 recordsLinked to original sources

PubMed2005

In vivo wear of bilateral total hip replacements: conventional versus crosslinked polyethylene.

Crosslinked polyethylene (PE) was developed to reduce volumetric wear in prosthetic joints. Hip simulator studies have shown promising results but there is as yet limited clinical data. We identified three patients with bilateral total hip replacements who received a crosslinked PE liner (Marathon, DePuy, Warsaw, IN, USA) on one side and a conventional PE insert (Enduron, DePuy) on the contralateral side. As an assessment of in vivo PE wear, linear head penetration was measured on standardized radiographs using a validated computer-assisted technique. In all the three cases, a marked reduction of more than 70% in volumetric wear was found in association with Marathon crosslinked PE. These case reports support the efficacy of this type of crosslinked PE in a selected group that allows direct comparison of the two different materials without the influence of patient-related factors such as activity, gender, weight, or others.

Adult↗

PubMed2005

Activity sampling in the assessment of patients with total joint arthroplasty.

Quantitative assessment of patient activity is important in evaluating the outcomes of joint prostheses, and such methods are gaining popularity. The single greatest impediment to quantitative activity assessment is patient compliance. How many days of sampling are necessary to provide reliable and accurate estimates of walking activity? The current study analyzes how well sampling for 4 consecutive days of activity compares to assessing activity for 7 or more days with the same pedometer in 131 patients with either a total hip or total knee prosthesis. The mean steps per day obtained throughout the full-length sampling (7-123 days) was strongly correlated to the one obtained from the random consecutive 4-day sample (r2 = 0.94, P < .001) with only 5 outliers. The 4-day activity assessment gave an underestimation of 4.7% (P = .5). The number of outliers increased with fewer days of sampling. Monitoring activity for 4 consecutive days yields a quantitative assessment that is within 5% of a sampling of 7 or more days.

Adult↗

PubMed2005

Metal-on-metal total hip replacement.

Metal-on-metal bearings have wear rates that are 20 to 100 times lower than metal-on-conventional polyethylene. The amount of wear generally is the same order of magnitude for the head and the cup. There is an initial run-in period of higher wear followed by lower, steady-state wear. Wear rate is a function of the interplay of material(s), macrogeometry, microgeometry, and the resultant type and amount of lubrication. The wear resistance and clinical performance of a metal-on-metal bearing are more sensitive to macrogeometry and lubrication than a metal-on-polyethylene bearing. Metal wear particles are nanometers in linear dimension. They are much smaller and more numerous than the submicron polyethylene wear particles, but the volume of periprosthetic inflammatory tissue is less. Osteolysis seems to be relatively rare. Little is known about the systemic distribution of metal particles and ions. The significance of systemic distribution also is not known. The levels of serum and urine Co and Cr ions are elevated in patients with metal-on-metal bearings, but the long-term, steady-state levels are not much higher than those from corrosion of modular femoral components. Because of the elevated levels of Co and Cr ions, there is a greater risk of delayed type hypersensitivity. There also is concern about the potential for malignant degeneration secondary to prolonged exposure to these elements. The available data are insufficient to address this concern. Rigorous long-term studies are needed. It will take decades of close clinical observation to determine if the benefits of metal-on-metal bearings outweigh the associated risks.

Animals↗

PubMed2005

Optimizing patient selection and outcomes with total hip resurfacing.

UNLABELLED: Short-term failures of total hip resurfacing have been related to specific characteristics of the proximal femur. A radiographic arthritic hip grading scale was used to assess four characteristics of the proximal femur: bone density, shape, biomechanics, and focal bone defects. Hips with no unfavorable characteristics were Grade A, hips with one unfavorable characteristic were Grade B, hips with two unfavorable characteristics were Grade C, hips with three unfavorable characteristics were Grade D, and hips with four unfavorable characteristics were Grade F. One hundred forty-seven consecutive hips were treated with metal-on-metal resurfacing by a single surgeon. There were no femoral neck fractures. Of the 91 hips eligible for a minimum 2 year followup, 90% were Grades A or B, 10% were Grade C, and none were Grades D or F. With a minimum 2-year followup, arthritic hip grading was associated with preoperative Harris hip score, occurrence of mild to moderate postoperative pain, preoperative and postoperative range of motion, preoperative and postoperative hip center of rotation, preoperative and postoperative horizontal femoral offset, preoperative and postoperative limb length discrepancy, and acetabular radiolucencies. Hips with a lesser degree of secondary arthritic changes have a higher arthritic hip grade and better outcomes with total hip resurfacing. Relatively strict selection criteria for resurfacing were associated with a low occurrence of short-term failures. LEVEL OF EVIDENCE: Prognostic study, Level II (retrospective study). See the Guidelines for Authors for a complete description of levels of evidence.

Adult↗

PubMed2005

Long-term results of primary total knee replacement in patients with hemophilia.

BACKGROUND: The outcome of total knee replacement in patients with hemophilia has been variable. Several authors have suggested a relationship between high rates of late infection following total knee replacement in patients with hemophilia and a positive HIV status. The objective of this study was to evaluate the results of primary total knee replacements performed in a large group of hemophilic patients at a single institution by the same primary surgeon. METHODS: The results of ninety primary total knee replacements performed in sixty-eight hemophilic patients between 1975 and 2001 were reviewed retrospectively. The HIV status and the CD4 count at the time of the surgery were recorded for fifty-three patients (seventy-one knees). Knee Society clinical and functional scores were determined for twenty-nine patients (thirty-eight knees) who were available for follow-up. Prosthetic survival was calculated with use of Kaplan-Meier survivorship analysis. RESULTS: The overall prevalence of infection was 16%. Twelve knees required removal of components, and the reason for the removal was late infection in nine of them. The prevalence of infection in HIV-positive and HIV-negative patients was 17% and 13%, respectively (p = 0.5). When component removal for any reason, survival free of infection at any point, and mechanical failure were considered to be the end points, the ten-year survival rates were 83%, 77%, and 96%, respectively. The Knee Society clinical score was excellent or good for 80% of the knees, and the Knee Society functional score was excellent or good for 97% of the knees. CONCLUSIONS: Despite the anatomical challenges, the mechanical survival of total knee replacements in patients with hemophilia is quite good. However, the prevalence of infection after the total knee replacements was high. The prevention of late infection would substantially improve the long-term outcome of total knee replacements in this patient population.

Adult↗

PubMed2005

The relationship between activity and ions in patients with metal-on-metal bearing hip prostheses.

BACKGROUND: Total hip replacements with metal-on-metal bearings are frequently implanted in young, active patients. The relationship between patient activity and cobalt and chromium ion levels has not been investigated, to our knowledge. METHODS: Seven patients with well-functioning metal-on-metal bearing hip prostheses and one control subject (no implants), all with normal renal function, were monitored during a two-week-long activity protocol. Lower-extremity activity was continuously assessed with use of a computerized, two-dimensional accelerometer. During the first week, the subjects were requested to limit physical activity. The subjects then completed an hour-long treadmill test followed by a week in which they were encouraged to be as physically active as practically possible. Serum levels of cobalt and chromium ions and urine levels of chromium were assessed at ten time-points during these two weeks. RESULTS: Regardless of activity, the serum ion levels for a given patient were essentially constant and no correlation was found between patient activity and serum levels of cobalt or chromium, or urine levels of chromium. A mean increase in activity of 28% during the week of high-intensity activity was associated with a mean decrease of 2.7% in the serum cobalt level and a mean increase of 2.0% in the serum chromium level. During the treadmill test, a mean increase in activity of 1621% was associated with a mean increase of 3.0% in the serum cobalt level and a mean increase of 0.8% in the serum chromium level. These results fall within the variability for the measurement accuracy of these tests. CONCLUSIONS: For these patients, serum cobalt and chromium ion levels were not acutely affected by patient activity. Periodic measurements of serum ion levels could be used to monitor the tribologic (lubrication, friction, and wear) performance of a metal-on-metal bearing without adjusting for patient activity. Additional research is needed into the kinetics of ion production, transport, and excretion.

Adult↗

PubMed2005

The effects of lower-extremity total joint replacement for arthritis on obesity.

Total hip or knee replacement patients who are overweight or obese often consider their disabling joint disease a cause for their increased weight. This prospective study investigated weight change in 100 patients after successful total joint replacement to determine whether surgical treatment of hip or knee arthritis leads to weight reduction. Postoperatively, both hip and knee replacement patients gained weight, with no difference in weight gain between hip and knee replacement patients. Younger hip patients gained a significant amount of weight. Patients a with normal body mass index and obese patients did not lose weight, while overweight patients gained a significant amount of weight after surgery. These findings demonstrate successful treatment of lower-extremity arthritis does not lead to weight loss, and obesity should be treated as an independent disease that is not the result of inactivity from arthritis.

Adult↗

PubMed2004

Neuromuscular electrical stimulation enhances fracture healing: results of an animal model.

Neuromuscular electrical stimulation (NMES) could simulate physiological muscle functions known to be associated with the normal bone healing process. The object of the present study was to evaluate the effect of NMES on fracture healing, using an animal model. Thirty rabbits received unilateral, transverse, mid-tibial, 3-mm gapped osteotomies that were stabilized with double-bar external fixators. The femoral vein was ligated to induce venous stasis. From the fourth post-operative day, the study group was treated with 1 h daily of NMES for four weeks, while the control group was treated without NMES. For NMES, two surface electrodes were used: one above the patellar tendon and another around the lateral thigh. Callus area and mineral content at the osteotomy gap were measured, biweekly, using computerized tomographic examinations. Biomechanical properties of healing were evaluated with a torsion test, eight weeks after the index operation. Osteotomies treated with NMES exhibited 31% (p=0.01) higher mineral content and 27% (p=0.009) larger callus area than control osteotomies at eight weeks. The maximum torque, torsional stiffness, angular displacement at maximum torque, and energy required to failure of specimens in the study group were 62% (p=0.006), 29% (p=0.03), 34.6% (p=0.008), and 124% (p<0.0001) higher, respectively, than those in the control group at eight weeks. The results of the present study demonstrated that the use of NMES can enhance callus development and mineralization, with the consequent improvement in biomechanical properties of the healing bone.

Animals↗

PubMed2004

The biomechanical results of total hip resurfacing arthroplasty.

BACKGROUND: With the advent of more wear-resistant bearings, there is renewed interest in resurfacing total hip arthroplasty. However, there is a paucity of information on the biomechanical results of this type of arthroplasty compared with those of contemporary total hip arthroplasty. METHODS: Using standardized radiographs, we measured and compared the biomechanical parameters that affect the hip joint reactive forces in fifty hips that had a metal-metal surface replacement with those parameters in forty hips that had a contemporary cementless total hip replacement performed during the same time-period by the same surgeon. RESULTS: On the average, the arthritic hips that were treated with metal-metal surface replacement had had a more valgus preoperative neck-shaft angle and less horizontal femoral offset than the normal, contralateral hips (p = 0.0003). After both the metal-metal surface replacements and the cementless total hip replacements, the hip center of rotation was medialized by approximately 6 mm. Both procedures were associated with an average increase in limb length of approximately 3 or 4 mm. After the metal-metal surface replacements, the horizontal femoral offset was essentially equal to the preoperative value, but both values averaged about 8 mm less than those on the normal, contralateral side (p < 0.00001). In the hips with a conventional total hip replacement, the horizontal femoral offset increased an average of 9.5 mm compared with the preoperative value and was an average of 5 mm more than that for the normal, contralateral hip (p = 0.001). CONCLUSIONS: The biomechanical results of total hip resurfacing depend on the preoperative anatomy of the proximal part of the femur. Limb lengthening of 1 cm can be achieved, but horizontal femoral offset is essentially unchanged by hip resurfacing. Horizontal femoral offset can be increased reliably with a contemporary total hip replacement. Arthritic hips of limbs that are more than 1 cm shorter than the contralateral limb or that have a comparatively low horizontal femoral offset may be better served by a contemporary total hip replacement. These biomechanical limitations should be considered in the selection of hips for resurfacing. LEVEL OF EVIDENCE: Therapeutic study, Level III-1 (case-control study). See Instructions to Authors for a complete description of levels of evidence.

Adult↗

PubMed2004

Short-term in vivo wear of cross-linked polyethylene.

BACKGROUND: Cross-linked polyethylene was developed to reduce volumetric wear in prosthetic joints. Hip simulator studies have shown promising results with regard to wear reduction. This study evaluated the short-term in vivo wear of a moderately cross-linked polyethylene. METHODS: Linear head penetration, as an assessment of in vivo polyethylene wear, was measured in two groups of patients after total hip replacement. Twenty-four hips received a conventional polyethylene insert and thirty-four, a cross-linked polyethylene liner; both inserts were manufactured by the same company. Linear and volumetric wear rates were measured on radiographs with use of a validated computer-assisted technique and were adjusted for patient-related factors. Patient activity was assessed by a computerized two-dimensional accelerometer worn on the ankle. RESULTS: Patients with a conventional polyethylene insert showed a mean linear wear rate of 0.13 mm per year and a mean volumetric wear rate of 87.6 mm(3) per year. The group with a cross-linked polyethylene liner showed a mean linear wear rate of 0.02 mm per year and a mean volumetric wear rate of 17.0 mm(3) per year. Wear in the group with cross-linked polyethylene was 81% lower than that in the group with conventional polyethylene (p < 0.00001). Accounting for differences in patient activity, the adjusted wear rates per million cycles for a patient weight of 70 kg were 53 mm(3) per million cycles for conventional polyethylene and 15 mm(3) per million cycles for cross-linked polyethylene, a 72% reduction (p = 0.0002). No factor, other than the type of polyethylene, was found to influence the difference in wear rates between the two groups. CONCLUSIONS: The results of this study are promising. The in vivo wear reduction with this cross-linked polyethylene is consistent with the predictions of hip simulator studies.

Adult↗

PubMed2004

Bearing surface options for total hip replacement in young patients.

Encouraging results and new implant developments have allowed total hip replacement to be performed in increasingly younger and more active patients. In young patients, however, outcomes are not comparable to those seen in older patients. The inflammatory reaction to polyethylene wear particles is one of the main causes of aseptic loosening and subsequent revision surgery and can limit the longevity of an arthroplasty in young and active patients. The wear resistance of polyethylene has been improved by cross-linking; however, greater degrees of cross-linking are associated with progressive decreases in other material properties, which theoretically increase the risk of component failure from very high or localized stresses. Ceramic femoral heads have been associated with lower in vivo polyethylene wear rates, which have been variable and up to 50% lower than with metallic heads. Metal-on-metal bearings have been reintroduced with improved materials, design, and manufacturing, although theoretical concerns remain regarding long-term exposure to metal particles and ions. Improved ceramic-on-ceramic bearings also are available and have the lowest wear rates. They offer a very small risk of in vivo fracture; however, they are the most expensive bearing option and wear rate is more sensitive to implant position. Long-term clinical studies are needed to show a reduction in revision surgery associated with the use of this current generation of bearings. The use of any of these bearings has specific benefits and risks that should be considered on a patient-by-patient basis.

Arthroplasty, Replacement, Hip↗

PubMed2003

Knee strength after total knee arthroplasty.

Fifty-two knees in normal healthy subjects and 32 knees more than 2 years after total knee arthroplasty (TKA) were evaluated. Average isometric extension peak torque values in TKA patients were reduced by up to 30.7% (P=.01). Isometric flexion peak torque values in patients with TKA were, on average, 32.2% lower than those from control subjects throughout the motion arc (P=.004). Knee Society Functional Scores were positively correlated to the average isometric extension peak torque (r=0.57; P=.004) and negatively correlated to the average isometric hamstring to quadriceps (H/Q) ratio (r=-0.78, P<.0001). Relatively greater quadriceps strength was associated with a better functional score. Older TKA patients (>/=70 years) generated lower isometric extension peak torque values in terminal extension than younger TKA patients (>24.2%; P=.05). Higher body mass index (BMI) was associated with relative quadriceps weakness (r=0.44; P=.007). These results suggest that more thorough rehabilitation after TKA would improve functional outcomes.

Aged↗

PubMed2003

Surface damage on open box posterior-stabilized polyethylene tibial inserts.

Twenty retrieved Scorpio posterior-stabilized implants were available for analysis. The mean implantation time was 22 months (range, 2 days-42 months). Favorable types and amounts of surface damage were seen on the tibiofemoral and backsides of these modular PE liners that had been packaged in an inert environment and then sterilized by gamma irradiation. Delamination represented only 0.1% of the total surface damage. Off-axis loading (varus malalignment) was associated with tibial component loosening but there was no evidence of peripheral damage of PE caused by edge loading. With this open-box design, hyperextension marks on the anterior aspect of the posterior-stabilized post from femoral component impingement occurred in 11 of 20 cases and was related to sagittal component positioning: excess tibial slope or increased tibial slope combined with a flexed femoral component. Unique coarse abrasions occurred in 16 of 20 cases and were the result of cement extrusion into the open box, especially with varus malalignment. These observations provide guidance for optimizing the surgical technique and the design of posterior-stabilized total knee components.

Adult↗

PubMed2003

Effect of intermittent pneumatic soft-tissue compression on fracture-healing in an animal model.

BACKGROUND: The fracture-healing process is closely related to blood supply. Intermittent pneumatic compression of the surrounding soft tissue may alter blood flow and, therefore, modify the healing process. The object of the present study was to evaluate the effect of intermittent pneumatic compression on fracture-healing in an animal model. METHODS: Unilateral, transverse, mid-tibial osteotomies with a 3-mm gap were performed in thirty rabbits. The osteotomy site was stabilized with a double-bar external fixator. The femoral vein was ligated to induce venous stasis. Beginning on the fourth postoperative day, fifteen rabbits were treated with intermittent pneumatic compression with use of four rubber balloons, two around the distal part of the calf and two around the midpart of the calf, for one hour daily for four weeks (the study group) and fifteen rabbits were not treated with intermittent pneumatic compression (the control group). Peripheral computerized tomographic examination was performed biweekly to measure callus area and mineral content at the fracture gap. At eight weeks, the rabbits were killed, and the biomechanical properties of the healing fractures were evaluated with a torsional test. RESULTS: An increase in callus area and mineral content at the osteotomy gap was observed in the study group, compared with the values in the control group, starting four weeks after the index procedure. At six weeks, the rabbits treated with intermittent pneumatic compression exhibited, on the average, a 32.2% larger callus area (p = 0.035) and a 49.7% higher mineral content (p = 0.01) at the osteotomy site compared with the values in the control group. The torsional stiffness, maximum torque, angular displacement at maximum torque, and energy required to failure of specimens in the study group were an average of 27.0% (p = 0.05), 61.5% (p = 0.0001), 35.4% (p = 0.0003), and 110.8% (p = 0.0001) higher, respectively, than those in the control group at eight weeks. CONCLUSIONS: Intermittent pneumatic compression enhanced callus mineralization and development and it improved the biomechanical properties of a healing osteotomy site in the rabbit tibia.

Animals↗

PubMed2002

Effect of repeated irrigation and debridement on fracture healing in an animal model.

The initial management of open fractures often requires repeated irrigation and debridement of the open wound and stabilization of the fracture. However, washing out the fracture hematoma could delay the early healing process of stable fractures. Because delayed union and non-union are serious complications, the effect of repeated irrigation and debridement on the fracture healing process was investigated. Twenty-four rabbits received unilateral, transverse. mid-tibial open osteotomies with a 3 mm gap. The osteotomy site was thoroughly irrigated and stabilized with double-bar external fixators. The osteotomy sites in the study groups underwent repeat irrigation and debridement on either the third day (Group II), the fourth day (Group III), or consecutively on the first and second days (Group IV) after the index procedure. The bone healing was assessed with weekly radiographs and peripheral quantitative computerized tomographs. In Group I (control), all osteotomies healed radiographically before the tenth week. In Group II, five out of six osteotomies healed radiographically before the tenth week. In Group III, only two of five osteotomies healed before the tenth week. In Group IV, none of the osteotomies had healed by week fifteen. All of the non-healed osteotomies exhibited atrophic non-unions at fifteen weeks. Compared to the control group at the tenth week, the average bone mineral content at the osteotomy site and the area of high mineral density callus (> or = 890 mg/cm3) were significantly lower in Groups III (63%, p = 0.002 and 95%, p = 0.05, respectively) and IV (99%, p < 0.001 and 100%, p = 0.05, respectively). The results of this study suggest that repeated irrigation and debridement, associated with persistent rigid immobilization, may contribute to the development of delayed unions or atrophic non-unions.

Animals↗

PubMed2002

Average patient walking activity approaches 2 million cycles per year: pedometers under-record walking activity.

A two-dimensional accelerometer worn on the ankle (step activity monitor [SAM]; Prosthetic Research Study, Seattle, WA) has been proved to be highly accurate for assessing walking activity. The walking activity of 33 patients with well-functioning total hip arthroplasties was measured continuously during daily life, simultaneously with a pedometer and a SAM. The SAM recorded an average of 1.9 million cycles/y. The pedometer under-recorded an average of 34% cycles per day compared with the SAM (P=.0007), but the 2 measures were highly correlated (r=0.66; P=.001). No difference was seen in the number of gait cycles per day between men and women. The previously reported difference in average walking activity between men and women is due to greater under-recording of the pedometer in women, especially those with a body mass index > or =27. The pedometer is more reliable in quantifying the walking activity of men, less obese women, and patients with >1 million gait cycles/y.

Aged↗

PubMed2002

Results of direct exchange or debridement of the infected total knee arthroplasty.

In this literature review, 30 reports provided outcome data on 37 direct exchange arthroplasties, 530 open debridements, and 23 arthroscopic debridements. The average followup was approximately 4 years, but the range was broad (range, 0.02-14 years). Infection was controlled in 33 of the 37 infected total knee arthroplasties (89.2%) treated by direct exchange arthroplasty, in only 173 of the 530 infected total knee arthroplasties (32.6%) treated by open debridement and retention of the prosthetic components, and in 12 of the 23 infected total knee arthroplasties (52.2%) treated by arthroscopic debridement. There was wide variability in associated antibiotic therapy. Factors associated with successful direct exchange included infections by gram-positive organisms, absence of sinus formation, use of antibiotic-impregnated bone cement for the new prosthesis, and 12 weeks of antibiotic therapy. Direct exchange arthroplasty failed in four of 37 knees; two were in patients with rheumatoid arthritis who were taking corticosteroids. Factors associated with successful debridements included those done within 4 months of the index procedure, or in patients with less than 4 weeks of symptoms, antibiotic sensitive gram-positive organisms, well-fixed components with no radiologic evidence of osteitis, and in young healthy patients. Factors associated with the failed debridements included postoperative drainage for more than 2 weeks, sinus tracts present at the time of the debridement, a hinged prosthesis, and an immunocompromised host. Direct exchange can be successful with a sensitive organism in a healthy host with prolonged antibiotic therapy. Debridement can be successful in early infections in a healthy host.

Anti-Bacterial Agents↗

PubMedDate not supplied

Hemophilic arthropathy.

The most common clinical manifestation of hemophilia is arthropathy secondary to recurrent hemarthroses and chronic synovitis. Joint-surface erosions secondary to chronic synovitis often occur in early childhood and progress to advanced arthropathy by late adolescence. The knee, elbow, ankle, hip, and shoulder are the most commonly involved joints. Management of hemophilic arthropathy has advanced with the development of purified clotting factor concentrates and procedures to prevent chronic synovitis. Radiosynovectomy using beta particle-emitting radiocolloids has been effective in dramatically reducing the frequency of hemarthroses and resolving chronic synovitis. The most common surgical procedures used to manage hemophilic arthropathy are synovectomy, joint debridement, fusion, and joint arthroplasty. Late infection and arthrofibrosis complicate joint arthroplasty more often in these patients than in patients with other forms of arthritis. The high incidence of late infection may relate to frequent intravenous self-infusion of clotting factor combined with immune suppression. Despite the medical and surgical complexities of hemophilic arthropathy, orthopaedic procedures have a high incidence of patient satisfaction.

Autoantibodies↗