Biomedical subjects

Kenneth B Mathis

Publications and source records attributed to Kenneth B Mathis.

8 recordsLinked to original sources

PubMed2006

Does neck/liner impingement increase wear of ultrahigh-molecular-weight polyethylene liners?

We explore the hypothesis that repetitive impingement increases wear of ultrahigh-molecular-weight polyethylene inserts. During revision total hip arthroplasty, 113 acetabular components were retrieved and examined for impingement, backside wear, and articular wear. Sixty percent of acetabular liners showed evidence of prosthetic impingement, with moderate or severe damage to the rim in 32%. Moderate or severe backside damage was present in 31%. Backside wear was found in 61% (22/36) of liners exhibiting impingement vs 16% (12/73) of liners without impingement (P < .0001). The average articular wear rate of liners with moderate/severe impingement damage was 159 +/- 42 mm(3)/y, compared with 70 +/- 21 mm(3)/y for liners with no/mild impingement damage (P = .02). Repetitive impingement frequently occurs after total hip arthroplasty and leads to a multitude of adverse events, including motion between the liner and the acetabular shell.

Acetabulum↗

PubMed2006

The John Insall Award: Patient expectations affect satisfaction with total knee arthroplasty.

Satisfaction with the outcome of total knee arthroplasty is highly variable, with a small but significant percentage of patients reporting dissatisfaction with the procedure. The purpose of this study was to determine which factors contribute to patient satisfaction with total knee replacement (TKR), and their relative importance. At a minimum of 1 year post unilateral primary TKR, 253 patients completed a self-administered, validated "Knee Function Questionnaire," which examined each patient's participation in a broad range of activities involving the knee, their level of satisfaction, and the extent to which TKR had fulfilled their expectations. The association between function, expectation and satisfaction was examined using univariate and multivariate logistic regression. Seventy-five percent of patients were either "satisfied" or "very satisfied" with their knee replacement, while 14% were "dissatisfied" or "very dissatisfied." Satisfaction correlated significantly (p < 0.001) with age less than 60, absence of residual symptoms, fulfillment of expectations, and absence of functional impairment. Satisfaction with TKR is primarily determined by patients' expectations, and not their absolute level of function. Real improvements in the outcome of TKA must address prevention of residual pain, stiffness and swelling, and each patient's preoperative concept of the likely outcome of these procedures.

Adult↗

PubMed2005

Cracking and impingement in ultra-high-molecular-weight polyethylene acetabular liners.

The purpose of this study was to determine the prevalence of crack formation in conventional ultra-high-molecular-weight polyethylene cups and its association with rim impingement, oxidation, and time in situ. One hundred twenty acetabular cups were retrieved during revision total hip arthroplasty. In 40% (48/120) of the retrieved specimens, multiple subsurface cracks of several millimeters in length were revealed by transillumination. In 5 specimens, full thickness cracks led to fragmentation of the liner before revision. Thirty-eight (32%) liners had regions of moderate to severe impingement damage to the rim; cracks were initiated at the site of impingement in all but 1 liner (P < .0001). Cracks commonly occur in conventional ultra-high-molecular-weight polyethylene liners, often after neck impingement and almost always in association with oxidation of the polymer.

Acetabulum↗

PubMed2005

Does total knee replacement restore normal knee function?

Despite the advanced age of many patients having total knee arthroplasty, previous attempts to quantify patient function postoperatively have not allowed for normal deterioration of musculoskeletal function that occurs with aging. We determined the effects of aging on knee function, thereby providing a realistic level of normal, healthy knee function for patients and surgeons after total knee arthroplasties. A self-administered, validated knee function questionnaire consisting of 55 scaled multiple choice questions was used in this study. Responses were collected from 243 patients at least 1 year after they had total knee arthroplasties, and from 257 individuals (age- and gender-matched) who had no previous history of knee disorders. Many of these latter subjects reported that they could do most of the activities cited in the questionnaire without symptoms attributable to their knees. However, knee symptoms were experienced more frequently during activities that placed greater loads on the extremity. There was no difference in the knee function of men and women, and both groups had continuous deterioration in knee function with increasing age. There were large differences in the functional capacity to do activities involving the knee between the group of patients who had total knee arthroplasties and the age- and gender-matched patients with no previous knee disorders. Overall, 52% of the patients who had total knee arthroplasties reported some degree of limitation in doing functional activities, versus 22% of subjects with no previous knee disorders. Two groups of activities were identified: activities in which the patients and control subjects had essentially similar knee function (swimming, golfing, and stationary biking), and activities in which the function scores of the control group exceeded the scores of the patients who had total knee arthroplasties (kneeling, squatting, moving laterally, turning and cutting, carrying loads, stretching, leg strengthening, tennis, dancing, gardening, and sexual activity). Our data show that many of the limitations reported by patients after total knee arthroplasties are shared by individuals with no previous knee disorders. However, only approximately 40% of the functional deficit present after a total knee arthroplasty seems to be attributable to the normal physiologic effects of aging. Patients who had total knee replacements still experienced substantial functional impairment compared with their age- and gender-matched peers, especially when doing biomechanically demanding activities. This suggests that significant improvements in the procedure and prosthetic designs are needed to restore normal knee function after a total knee arthroplasty.

Adult↗

PubMed2005

Surface damage of patellar components used in total knee arthroplasty.

BACKGROUND: Patellofemoral complications are a common cause of failure of total knee replacement. In this study, we examined eighty-five patellar components that had been retrieved for a variety of reasons after a mean of 71.9 months in vivo. The objective of this study was to identify factors contributing to surface damage of patellar components in total knee replacements. METHODS: The retrieved patellar components were of three primary designs: dome-shaped, sombrero-shaped, and pseudo-anatomic. Five zones on each specimen were evaluated for five different types of damage (creep, pitting, delamination, abrasion, and burnishing). The severity of the damage was assigned a score of 0 to 4, with 0 indicating no damage and 4 indicating extreme damage. The extent of the damage was also assigned a score of 0 to 4, with 0 indicating 0% and 4 indicating 76% to 100%. An asymmetry ratio was calculated for each damage pattern to evaluate the uniformity of the distribution of the damage across each component. RESULTS: Eighty-six percent of the components had a damage score of > or =4 (product of the extent and severity scores) for at least one damage mechanism (creep for 38% of the components, pitting for 47%, delamination for 26%, abrasion for 49%, and burnishing for 76%). Components that had been in situ for more than two years had significantly more severe creep, delamination, and burnishing than components that had been in place for less than two years. Metal-backed designs had more severe damage than all-polyethylene components. Factors that reduced the occurrence and severity of polyethylene damage were a congruent patellar design (a non-dome-shaped component) and the use of an asymmetric femoral component. CONCLUSIONS: Damage to the patellar component was a common finding, particularly when the implant had been retrieved more than two years after implantation. Moreover, delamination was frequently found on the patellar components, as has been observed by others who examined retrieved tibial inserts. The results of this study suggest that the use of congruent patellar components may reduce damage.

Adult↗

PubMed2003

Extraarticular abrasive wear in cemented and cementless total knee arthroplasty.

In this study, we examine the contributions of periprosthetic impingement to a seldom recognized source of PE damage resulting in gouging, abrasion, and severe localized damage in cemented and cementless total knee replacement. One hundred sixty two tibial components of 34 different designs in a retrieval collection were examined. The presence and location of abrasive wear to the nonarticulating edges of the insert were measured, with representative specimens examined using SEM. Significant abrasive wear was observed in 35% of the retrievals with cemented femoral components and 25% from noncemented components. Within the group of worn inserts, abrasive scars were seen with a frequency of 75% on the extreme medial edge, 20% on the extreme lateral edge, 26% on the posteromedial edge, and 16% on the posterolateral edge. The role of extraarticular impingement in this damage mode was confirmed by examination of retrieved femoral components with overhanging cement or embedded osteophytes. In the majority of cases, this complication may be avoided by careful removal of excess cement and extracortical osteophytes.

Adult↗

PubMed2003

Computer simulation: how can it help the surgeon optimize implant position?

Component placement critically affects the performance and longevity of total hip replacements (THRs). Because of limitations of observation and anatomic orientation imposed by the operative site, selection of the correct size, and position of the acetabular and femoral components is best done through preoperative planning. Currently, this is done by comparing two-dimensional templates of prosthetic components with clinical radiographs; however, this method has the inherent limitation that AP and lateral radiographs each provide one projection of the pelvis and the femur. Computer technology makes it possible to observe implantation of the femoral and acetabular components in three dimensions. This approach allows surgeons to template with superior accuracy, while providing an intimate view of the fit of the components in the implantation site. Additionally, computer routines can predict the functional outcome of a preoperative plan before its implementation. Restoration of leg length, center of rotation, ROM of the joint during various activities, and points of bony and prosthetic impingement can be analyzed preoperatively by the surgeon. This is a valuable tool for surgical navigation and surgeon training. With emerging technologic advances in surgical technique, computer-based preoperative planning tools should prove all the more essential to reliable component placement.

Arthroplasty, Replacement, Hip↗

PubMed2002

What functional activities are important to patients with knee replacements?

There is interest in quantifying the patient's function and mobility after joint replacement. The current study identified activities important to patients having total knee replacement and the prevalence of limitations to participation in these activities. A Total Knee Function Questionnaire consisting of 55 questions addressing the patient's participation in various activities was developed, validated, and mailed to 367 patients at least 1 year after knee replacement. Patients were asked the frequency with which they did each activity, the activity's importance to them, and the extent to which their participation was limited by their knee replacement. The questionnaire was returned by 176 patients, 40% men and 60% women, with an average age of 70.5 years. The most prevalent activities were stretching exercises (73%), leg strengthening exercises (70%), kneeling (58%), and gardening (57%). The activities most important to the patients were stretching exercises (56%), kneeling (52%), and gardening (50%); those most difficult were squatting (75%), kneeling (72%), and gardening (54%). The current study showed a high correlation between the importance of activities and frequency of patient participation confirming that knee replacement successfully restores a significant degree of function. However, after knee replacement, improvements in knee function still are needed to allow patients to do all activities that they consider important.

Activities of Daily Living↗