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Thomas P Schmalzried

Publications and source records attributed to Thomas P Schmalzried.

At least 19 recordsLinked to original sources
PubMed2006

The infected hip: telltale signs and treatment options.

The diagnosis of deep infection after total hip arthroplasty may not be obvious. Mild pain may be the only symptom. Normal radiographs do not exclude infection. Screening blood tests include the erythrocyte sedimentation rate and the C-reactive protein. If either test is elevated with a painful total hip, aspiration of the joint is efficacious. Aspiration remains the cornerstone for the diagnosis and treatment of infection. Intraoperative frozen sections can also be of value in the diagnosis of infection; however, this method is dependent on tissue sampling. A 2-stage revision remains the criterion standard for treatment. An antibiotic-impregnated cement spacer can deliver a high concentration of antibiotic to the infected space, maintain soft tissue tension, and provide better function than a resection arthroplasty. Direct exchange is rarely indicated today.

Anti-Bacterial Agents↗
PubMed2006

The optimal metal-metal arthroplasty is still a total hip arthroplasty: in opposition.

The longevity of any hip arthroplasty in an individual patient cannot be predicted with certainty so revisability of the arthroplasty remains an issue. As the occurrence of loosening and osteolysis decreases, then fatigue failure of femoral stems, complications of modular connections, and infection will become relatively more common modes of failure. Metal-metal hip resurfacing conserves bone stock, which provides better options for revision surgery. Hip resurfacing favors early intervention and has demonstrated excellent outcomes in young active males, the group historically at increased risk for failure of a conventional total hip arthroplasty. The best balance of the benefit-risk ratio for hip resurfacing is in those patients at increased risk for failure of a conventional total hip arthroplasty.

Arthroplasty, Replacement, Hip↗
PubMed2006

Hip resurfacing arthroplasty.

Hip resurfacing arthroplasty is a type of hip replacement that involves capping the femoral head and preserving bone of the proximal femur. Metal-on-metal surface replacements have been manufactured since the early 1990s. Recent studies indicate excellent clinical results with low failure rates at 1- to 5-year follow-up. Although these early results are encouraging, resurfacing devices must be used with caution because less is known about their long-term safety and efficacy. The best candidates for resurfacing are patients younger than age 60 years with good bone stock. The surgical approach is similar to that for standard total hip replacements, but with slightly more dissection because the femoral head must be preserved and displaced to visualize the acetabulum. To reduce complications, resurfacing arthroplasty should be performed by surgeons who have received training specifically in this technique.

Arthroplasty, Replacement, Hip↗
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 resurfacing arthroplasty: no way under the sun!--in opposition.

The functional demands and the longevity of hip arthroplasty patients are increasing. High volumetric wear and osteolysis limit the durability of metal-ultra high molecular weight polyethylene resurfacing. Cemented femoral hemiresurfacing components (no acetabular component) do not develop osteolysis and rarely loosen. Consistent long-term fixation has been demonstrated with hemispherical cementless acetabular components. Metal-metal bearings have demonstrated low wear and rare osteolysis over 3 decades of use. These facts form foundation for total hip resurfacing with metal-metal bearings.

Arthroplasty, Replacement, Hip↗
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

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↗
PubMed2005

Preoperative templating and biomechanics in total hip arthroplasty.

Preoperative templating is an essential ingredient of a successful hip arthroplasty. The socket template is positioned first to establish the center of rotation of the reconstruction. For femoral templating, a surgeon should not only consider the part inside the bone (the size of the component), but should also consider the part outside the bone, which determines limb length and biomechanical parameters such as theabductor muscle and joint reaction forces. Medializing the hip center of rotation and increasing the horizontal femoral offset can improve clinical outcomes and reduce polyethylene wear. Modern modular systems allow limb length adjustment and biomechanical improvement for a range of patients.

Arthroplasty, Replacement, Hip↗
PubMed2004

How I choose a bearing surface for my patients.

There is insufficient clinical data to demonstrate the overall superiority of any one bearing couple for all total hip cases. It is therefore reasonable to individualize the choice of bearing surface. The fundamental exercise in choosing a bearing surface is maximizing the benefit to risk ratio. There are at least 3 perspectives to consider: the patient's, the surgeon's, and that of the health care delivery system. The following question should be addressed on a patient-by-patient basis: what available bearing is most likely to meet the needs of this patient, with an acceptable risk of revision surgery during his or her lifetime, is accepted in my community, and is there a means to pay for it?

Arthroplasty, Replacement, Hip↗
PubMed2004

Patient factors and wear in total hip arthroplasty.

Polyethylene wear in vivo is multifactorial including numerous patient factors, such as gender, age, and activity. There are limitations in the clinical assessment of some of these factors and, for this reason, surrogate variables are used. For example, patient age and diagnosis frequently are used as surrogates for patient activity. The most variable and difficult factor to quantify is the frequency and intensity of use of the prosthesis during the service life of the arthroplasty. The clinical evaluation of patients with a total hip arthroplasty would be enhanced by a standardized assessment of the frequency and intensity of patient activity as it relates to the use of the prosthesis.

Adolescent↗
PubMed2004

Total resurfacing for osteonecrosis of the hip.

With the resurgence of metal-on-metal bearings, there is renewed interest in total hip resurfacing. A cementless acetabular component used for resurfacing with a wall thickness of fewer than 5 mm is comparable in size to acetabular components used for total hip replacement. The fixation of a porous-ingrowth acetabular component used for resurfacing has been shown to be reliable and durable. There are few clinical reports of total hip resurfacing that stratify results by diagnosis. However, available evidence indicates that the pain relief, function, and activity after total hip resurfacing for osteonecrosis are superior to the results reported for hemiresurfacing and similar to the results of total hip replacement. Femoral-side failure is the main issue occurring with total resurfacing for osteonecrosis, and the femoral side failure rate is higher than that of hemiresurfacing. There are no simple guidelines for the extent of femoral head necrosis that are compatible with successful resurfacing. Refined patient selection and surgical technique can improve the outcomes and durability of total hip resurfacing for osteonecrosis.

Adult↗
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↗