Biomedical subjects

Michael A Conditt

Publications and source records attributed to Michael A Conditt.

17 recordsLinked to original sources

PubMed2006

Posterior cruciate ligament substitution is not essential for excellent postoperative outcomes in total knee arthroplasty.

The study compared postoperative range of motion (ROM) and functional outcome of total knee arthroplasty (TKA) with a posterior cruciate ligament (PCL)-substituting knee prosthesis compared with an ultracongruent PCL-sacrificing design. Two hundred nine patients underwent primary TKA. Posterior stabilized design (121) and highly conforming, PCL-sacrificing, ultracongruent design (88) TKAs were reviewed. Surgeon, surgical approach, and a hyperflexion postoperative rehabilitation protocol were the same. Results showed significant improvement in knee flexion, ROM, Knee Score, and Function Score within each group. Postoperative mean total ROM was slightly higher with the posterior stabilized design. The 2 groups were the same postoperatively in the improvement in ROM, Knee Score, Function Score, satisfaction level, among other activity metrics. There was no clear evidence proving superiority and the need for posterior stabilization in PCL-sacrificing TKA.

Aged↗

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

Interaction of visual and proprioceptive feedback during adaptation of human reaching movements.

People tend to make straight and smooth hand movements when reaching for an object. These trajectory features are resistant to perturbation, and both proprioceptive as well as visual feedback may guide the adaptive updating of motor commands enforcing this regularity. How is information from the two senses combined to generate a coherent internal representation of how the arm moves? Here we show that eliminating visual feedback of hand-path deviations from the straight-line reach (constraining visual feedback of motion within a virtual, "visual channel") prevents compensation of initial direction errors induced by perturbations. Because adaptive reduction in direction errors occurred with proprioception alone, proprioceptive and visual information are not combined in this reaching task using a fixed, linear weighting scheme as reported for static tasks not requiring arm motion. A computer model can explain these findings, assuming that proprioceptive estimates of initial limb posture are used to select motor commands for a desired reach and visual feedback of hand-path errors brings proprioceptive estimates into registration with a visuocentric representation of limb position relative to its target. Simulations demonstrate that initial configuration estimation errors lead to movement direction errors as observed experimentally. Registration improves movement accuracy when veridical visual feedback is provided but is not invoked when hand-path errors are eliminated. However, the visual channel did not exclude adjustment of terminal movement features maximizing hand-path smoothness. Thus visual and proprioceptive feedback may be combined in fundamentally different ways during trajectory control and final position regulation of reaching movements.

Adaptation, Physiological↗

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↗

PubMed2005

Backside wear of polyethylene tibial inserts: mechanism and magnitude of material loss.

BACKGROUND: Wear of the underside of modular tibial inserts (backside wear) in total knee replacements has been reported by several authors. Although, for some implant designs, this phenomenon seems to contribute to osteolysis, the actual volume of material lost through wear of the backside surface has not been quantified. This study describes the results of computerized measurements of tibial inserts of one design known to be associated with a high prevalence of backside wear in situ. METHODS: A series of retrieved total knee components of one design were examined. The duration of implantation of the retrieved components ranged from thirty-six to 146 months. Laser surface profilometry and computer-aided design software were used to develop individual three-dimensional models of each worn, retrieved tibial insert to compare with scanned unused inserts. Volumetric subtraction of both models revealed the material lost because of backside wear. RESULTS: Worn and unworn areas on the backside surface were easily identified by stereomicroscopy and laser profilometry. The computer reconstructions showed that, in all retrievals, all unworn surfaces on the nonarticulating surface lay in one plane. The average volume (and standard deviation) of the material lost because of backside wear was 925 +/- 637 mm(3) (range, 197 to 2720 mm(3)). On the basis of the time in situ for each implant, the average volumetric wear rate was 138 +/- 95 mm(3)/yr. CONCLUSIONS: The predicted volume of material removed because of backside wear is substantial and may be sufficient to induce osteolysis. Our results suggest that peg-like protrusions are not generated by the extrusion of polyethylene into screw-holes within the base-plate but by abrasion of the underside of the bearing insert, leaving the protruding pegs as the only remnants of the original surface.

Aged↗

PubMed2004

The PCL significantly affects the functional outcome of total knee arthroplasty.

This study tests the hypothesis that patients receiving a posterior cruciate ligament (PCL)-retaining prosthesis have no difference in functional outcome compared to those receiving a cruciate-sacrificing, posterior-stabilized (PS) design. Forty-nine patients underwent a total knee arthroplasty (TKA), performed by a single surgeon using the same implant design with either a PCL-retaining or a PS tibial insert. Each patient completed a self-administered, validated Total Knee Function Questionnaire as well as the SF-36. At 1-year follow-up, each patient's range of motion and Knee Society knee score were measured. There were no statistically significant differences between the 2 groups using the traditional measures of function following total knee replacement, including overall satisfaction with surgery. However, the TKFQ revealed that patients with PS knees reported greater functional limitations in squatting, kneeling, and gardening. Our results suggest that with the specific implant used in this study, substitution for the PCL with a spine and cam mechanism may not fully restore the functional capacity of the intact PCL, particularly in high-demand activities that involve deep flexion.

Aged↗

PubMed2004

The optimal strategy for stable tibial fixation in revision total knee arthroplasty.

In revision total knee arthroplasty, the optimal strategy for stabilizing the tibial component in the face of proximal defects remains controversial. The stability of a revision tibial prosthesis was measured using a mechanical surrogate of the revision tibia, while varying the defect treatment proximally and the cortical engagement distally. An offset axial load in combination with an axial torque were applied to each specimen to simulate the stance phase of gait. It was found that, in revision total knee arthroplasty, the mechanical stability of tibial fixation is increased by the addition of a canal filling stem, especially in the presence of poor proximal bone. Proximal tibial coverage, even with a custom-fitted tibial component, adds little additional stability to a tibial tray stabilized by intramedullary engagement of a canal-filling stem.

Arthroplasty, Replacement, Knee↗

PubMed2004

Factors affecting the severity of backside wear of modular tibial inserts.

BACKGROUND: The use of modular tibial components in total knee arthroplasty introduces a possible source of polyethylene wear at the nonarticulating (backside) surface. However, it is not known whether this phenomenon is an incidental finding observed in unique specimens or is a feature common to all modular components. The purpose of this study was to determine the type and severity of backside wear in retrieved tibial inserts of several common total knee designs. METHODS: One hundred and twenty-four polyethylene tibial inserts of twelve different designs were retrieved at revision total knee replacements after implantation periods ranging from zero to 180 months. Each insert was visually inspected with use of a stereomicroscope for seven different modes of surface damage in four quadrants defining the backside surface. RESULTS: Pitting, burnishing, and measurable polyethylene protrusions were observed on the backside of polyethylene inserts of implant designs with a variety of different capture mechanisms. Across all implant designs, pitting was observed in 90% of the retrieved specimens; burnishing, in 77%; and protrusion, in 61%. Overall, implants of the IB-II (Insall-Burstein-II) design (Zimmer) exhibited the most severe burnishing, whereas those of the Duracon design (Howmedica) had the most severe pitting. Severe protrusions were noted with inserts of one design (AMK [Anatomic Modular Knee]; DePuy). A longer time in situ was associated with larger polyethylene protrusions, but the severity of pitting and burnishing did not increase with increasing duration of implantation. CONCLUSIONS: Moderate-to-severe wear of the nonarticulating surface of the tibial insert was frequently observed in all designs of knee prostheses, independent of the capture mechanism. These results indicate that new designs of modular tibial components are needed to prevent the generation of polyethylene wear debris through backside wear of total knee replacements.

Humans↗

PubMed2004

Backside wear of modular ultra-high molecular weight polyethylene tibial inserts.

BACKGROUND: The capture mechanisms of modular tibial total knee components may allow relative micromotion between the insert and the base-plate, leading to wear at the nonarticulating (backside) surface. Although retrieved components often display laxity in the capture mechanism in the unloaded condition, the magnitude of the relative motion that actually occurs under physiologic conditions has not been determined. This study was performed to assess the impact of different modes of knee-loading on the relative micromotion between the insert and the base-plate and the relationship between the duration that the implant had been in situ and the severity of backside wear. METHODS: Twenty-one posterior-stabilized total knee replacements of one common design (Insall-Burstein II) were retrieved at one to 100 months after implantation. The extent and severity of backside wear was graded with use of stereomicroscopy. All components were soaked in a bath (of physiologic saline solution at 37 degrees C for four days prior to reassembly. The relative micromotion between the insert and the base-plate of each specimen was measured in vitro in two different conditions: with no axial load and with a combination of loads and torques simulating the stance phase of gait. RESULTS: The capture mechanism laxity between the insert and the tibial base-plate in the unloaded condition was approximately eight times larger than the micromotion measured during simulated gait. The capture mechanism laxity allowed a mean (and standard deviation) of 618 +/- 226 micro m of total relative micromotion compared with 103 +/- 54 micro m of relative micromotion during the gait cycle. Under both loading conditions, the predominant direction of interface motion was medial-lateral. No correlation was found between the magnitude of capture mechanism laxity and the relative micromotion measured during simulated gait (p = 0.11). Larger polyethylene protrusions on the backside surface did not correlate with less micromotion (p = 0.48) or with capture mechanism laxity (p = 0.06). CONCLUSIONS: For the implant design that was studied, capture mechanism laxity between the modular insert and the base-plate in the unloaded condition was an order of magnitude larger than and not indicative of the micromotion that occurred during simulated physiologic loading. In addition, polyethylene protrusions into the screw-holes of tibial base-plates did not seat or lock the insert in place and reduce relative motion. CLINICAL RELEVANCE: While some clearance between the insert and the base-plate is required to allow assembly of modular tibial components at the time of surgery, the amount of relative interface motion during a functional activity such as normal gait, which can produce potentially damaging wear debris, is unknown. However, the compressive forces applied to the articular surface during a functional activity may substantially reduce micromotion between the insert and the base-plate relative to the unloaded condition.

Adult↗

PubMed2003

Mechanical alignment of tibial stems in revision total knee arthroplasty.

This multicenter, retrospective study evaluates the radiographic results of achieving optimal tibial alignment in revision total knee arthroplasty (TKA) using a single modular CoCr cemented or cementless stemmed implant design. Stem size and length also were evaluated. The hundred ninety-nine revision TKAs were performed between January 1993 and January 1996 by 13 experienced revision knee surgeons. The cases were subdivided into 5 comparative groups: (1) cemented stems, (2) 140-mm length canal-filling stems, (3) 140-mm length non-canal-filling stems, (4) 95-mm length canal-filling stems, and (5) 95-mm length non-canal-filling stems. The anteroposterior (AP) tibial alignment angle was measured. The canal-filling ratio (CFR) was determined by dividing the stem diameter by the endosteal diameter at the stem tip. Overall, the ability to achieve tibial alignment in the AP plane was more predictable when canal-filling (CFR >/= 0.85) cementless stems were used. This was further enhanced when long canal-filling cementless stems were selected. The least-predictable results and the highest probability of varus malalignment were achieved with cemented stems.

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

Components of laxity in interference fit fixation of quadrupled hamstring grafts.

We tested in vitro 15 Poly-L-lactic acid and 14 titanium interference screws in male human cadaver tibia-hamstring constructs. Elongation of the graft, displacement of the screw in the tibial tunnel, and slippage at the graft/screw interface were measured as outcomes with an infrared optical system. All constructs failed by slippage of the graft past the interference screw. On average, graft slippage accounted for 92% of total construct laxity at 5mm total construct elongation, whereas permanent stretching of the midsubstance of the graft accounted for only 8%. Movement of the interference screw in the tibial canal was minimal, averaging 0.01 (0-0.5) mm at construct failure. Inadequacy of isolated tibial interference screw fixation of soft tissue grafts may be overcome if early failure at the graft/screw interface is prevented.

Adult↗

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↗