Operating Room Airborne Microbial Load: Nonscrubbed Staff Apparel Matters.

BACKGROUND: Infection is a leading cause of total joint arthroplasty failure. In previous studies, we found correlations between the level of contamination, concentrations of airborne particles, and the number of staff present. In this study, we focused on the apparel of nonscrubbed operating room (OR) staff to elucidate their contribution to the airborne microbial load. METHODS: We compared hospital-laundered scrubs to disposable coveralls using 2 methods. (1) Participants entered an isolation chamber with a controlled environment and completed tasks for 1 hour wearing both the approved and alternative OR attire. Settle plates collected viable contaminants that were shed by the participants during testing. (2) Lab members conducted standardized maneuvers in a functional OR that simulated typical movements of the nurse, anesthesiologist, implant representative, and entering/exiting staff. An airborne particle counter and settle plates were positioned throughout the OR. After 1 hour, the staff changed apparel and repeated the test. Each session of both phases consisted of 2 tests by the same individuals on the same day. RESULTS: There was approximately a 10-fold difference in the settlement rate of viable particles between groups when employing the isolation chamber. The settle rate for scrubs was 5,519 ± 1,381 colony forming units (CFUs)/m2/h, while the settle rate for coveralls was 505 ± 55 CFUs/m2/h (P = .008). During testing in the OR, 218.7 ± 35 CFUs/m2/h were captured for scrubs, compared with 50.5 ± 13 CFUs/m2/h for the coverall (P < .01). The concentration of airborne particles collected for scrubs was 4,952.1 ± 495 particles/m3 and 1,065 ± 53 particles/m3 for the coveralls (P < .01). This was a 77% and 79% reduction for both measures, respectively. CONCLUSIONS: The open nature of standard scrubs allows contaminated particles to escape into the OR environment, whereas the one-piece design of the coveralls restricts pathways of escape. The results of this study may be helpful when developing hospital infection prevention policies.

Wearing a Surgical Vest With a Sterile Surgical Helmet System Decreases Contamination of the Surgical Field.

BACKGROUND: Sterile surgical helmet systems are frequently utilized in total knee arthroplasty procedures to protect the surgeon while maintaining a comfortable working environment. However, common helmet systems pressurize the space between the surgical gown and the surgeon's skin. In gowns with a back seam, this may allow contaminated skin particles to escape into the surgical field. By measuring bacterial colony-forming units (CFUs), this study sought to determine if occlusion of the open back seam reduced the risk of potential contamination. METHODS: First, qualitative analysis depicting airflow variations between gown configurations was performed using the Schlieren Spherical Mirror imaging system. Each gown configuration consisted of a sterile surgical helmet and one of 3 gown configurations: a standard gown with rear-tied closure, a standard gown with a surgical vest, and a zippered Toga-style gown. Next, a surgeon then performed simulated surgical activities for 60 minutes within a 1.4 m3 isolation chamber with work surfaces and controllable filtered air exchanges. During each procedure, contaminated particles were collected on sets of agar settle plates positioned directly behind the surgeon. Upon completion, the agar plates were incubated in a biolab, and the number of bacterial and fungal CFUs was counted. The experimental procedure was repeated 12 times for each gown configuration, with sterilization of the chamber between runs. Contamination rates were expressed as CFUs/m2/h. RESULTS: The mean contamination rate measured with the standard gown was 331.7 ± 52.0 CFU/m2/h. After the addition of a surgical vest, this rate decreased by 45% to 182.2 ± 30.8 CFU/m2/h (P = .02). Similarly, with the Toga-style gown, contamination rates dropped by 49% to 170.5 ± 41.9 CFU/m2/h (P = .01). CONCLUSIONS: When used in conjunction with surgical helmet systems, conventional surgical gowns do not prevent potential contamination of the surgical field. We recommend that staff within the surgical field cover the back seam of standard gowns with a vest or don a zippered Toga-style gown.

Self-administered transcranial direct current stimulation treatment of knee osteoarthritis alters pain-related fNIRS connectivity networks.

Significance: Knee osteoarthritis (OA) is a disease that causes chronic pain in the elderly population. Currently, OA is mainly treated pharmacologically with analgesics, although research has shown that neuromodulation via transcranial direct current stimulation (tDCS) may be beneficial in reducing pain in clinical settings. However, no studies have reported the effects of home-based self-administered tDCS on functional brain networks in older adults with knee OA. Aim: We used functional near-infrared spectroscopy (fNIRS) to investigate the functional connectivity effects of tDCS on underlying pain processing mechanisms at the central nervous level in older adults with knee OA. Approach: Pain-related brain connectivity networks were extracted using fNIRS at baseline and for three consecutive weeks of treatment from 120 subjects randomly assigned to two groups undergoing active tDCS and sham tDCS. Results: Our results showed that the tDCS intervention significantly modulated pain-related connectivity correlation only in the group receiving active treatment. We also found that only the active treatment group showed a significantly reduced number and strength of functional connections evoked during nociception in the prefrontal cortex, primary motor (M1), and primary somatosensory (S1) cortices. To our knowledge, this is the first study in which the effect of tDCS on pain-related connectivity networks is investigated using fNIRS. Conclusions: fNIRS-based functional connectivity can be effectively used to investigate neural circuits of pain at the cortical level in association with nonpharmacological, self-administered tDCS treatment.

Feasibility, Acceptability, and Efficacy of Home-Based Transcranial Direct Current Stimulation on Pain in Older Adults with Alzheimer's Disease and Related Dementias: A Randomized Sham-Controlled Pilot Clinical Trial.

Although transcranial direct current stimulation (tDCS) is emerging as a convenient pain relief modality for several chronic pain conditions, its feasibility, acceptability, and preliminary efficacy on pain in patients with Alzheimer's disease and related dementias (ADRD) have not been investigated. The purpose of this pilot study was to assess the feasibility, acceptability, and preliminary efficacy of 5, 20-min home-based tDCS sessions on chronic pain in older adults with ADRD. We randomly assigned 40 participants to active (n = 20) or sham (n = 20) tDCS. Clinical pain intensity was assessed using a numeric rating scale (NRS) with patients and a proxy measure (MOBID-2) with caregivers. We observed significant reductions of pain intensity for patients in the active tDCS group as reflected by both pain measures (NRS: Cohen's d = 0.69, p-value = 0.02); MOBID-2: Cohen's d = 1.12, p-value = 0.001). Moreover, we found home-based tDCS was feasible and acceptable intervention approach for pain in ADRD. These findings suggest the need for large-scale randomized controlled studies with larger samples and extended versions of tDCS to relieve chronic pain on the long-term for individuals with ADRD.

Efficacy of Home-Based Transcranial Direct Current Stimulation on Experimental Pain Sensitivity in Older Adults with Knee Osteoarthritis: A Randomized, Sham-Controlled Clinical Trial.

Although transcranial direct current stimulation (tDCS) is encouraging regarding clinical pain intensity for individuals with knee osteoarthritis, very few studies have explored its impact on experimental pain sensitivity, which may hinder our understanding of underlying therapeutic mechanisms. The purpose of this study was to assess the efficacy of 15 home-based tDCS sessions on experimental pain sensitivity and explore its relationships with clinical pain intensity. We randomly assigned 120 participants to active tDCS (n = 60) and sham tDCS (n = 60). Quantitative sensory testing (QST) was used, including heat pain threshold and tolerance, pressure pain threshold, and conditioned pain modulation. Patients in the active tDCS group exhibited reduced experimental pain sensitivity as reflected by all QST measures at the end of treatment. Furthermore, correlations were observed between changes in clinical pain intensity and experimental pain sensitivity. These findings warrant further studies on tDCS and experimental pain sensitivity in patients with knee osteoarthritis and exploring the magnitude and sustainability of effects on a longer term.

Self-administered transcranial direct current stimulation for pain in older adults with knee osteoarthritis: A randomized controlled study.

BACKGROUND: Knee osteoarthritis (OA) is a leading cause of pain in older adults. Previous studies indicated clinic-based transcranial direct current stimulation (tDCS) was effective to reduce pain in various populations, but no published studies have reported the efficacy of home-based self-administered tDCS in older adults with knee OA using a randomized clinical study. OBJECTIVE: The purpose of this study was to evaluate the efficacy and feasibility of tDCS on clinical pain intensity in adults with knee OA pain. METHODS: One hundred twenty participants aged 50-85 years with knee OA pain were randomly assigned to receive fifteen daily sessions of 2 mA tDCS for 20 min (n = 60) or sham tDCS (n = 60) over 3 weeks with remote supervision via telehealth. Clinical pain intensity was measured by the Numeric Rating Scale and Western Ontario and McMaster Universities Osteoarthritis Index. Also, we collected data on the tDCS experience via a questionnaire. RESULTS: Participants (68% female) had a mean age of 66 years. Active tDCS significantly reduced pain intensity compared to sham tDCS after completion of the fifteen daily sessions (Cohen's d = 1.20; p-value < 0.0001). Participants showed high levels of satisfaction with their tDCS experience, and there have been no adverse events. CONCLUSION: We demonstrated that home-based self-administered tDCS was feasible and reduced clinical pain intensity in older adults with knee OA, which can increase its accessibility. Future studies with multi-site randomized controlled trials are needed to validate our findings. TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT04016272.

Contemporary Robotic Systems in Total Knee Arthroplasty: A Review of Accuracy and Outcomes.

The success of total knee arthroplasty (TKA) depends on restoration of the stability and biomechanical efficiency of the native knee. The emergence of robotic surgical technologies has greatly increased the precision and reproducibility. We discuss contemporary robotic TKA systems by reviewing the features of the individual platforms, their accuracy, and the clinical outcomes. While early results suggest significant gains in patient outcomes, long-term evidence is still awaited from multicenter prospective clinical trials. Moreover, advances in this technology are needed to address knee laxity while individualizing the functional performance of each patient's new joint.

Functional Near-Infrared Spectroscopy to Assess Central Pain Responses in a Nonpharmacologic Treatment Trial of Osteoarthritis.

BACKGROUND AND PURPOSE: Knee osteoarthritis (OA) is a common source of pain in older adults. Although OA-induced pain can be relieved with analgesics and anti-inflammatory drugs, the current opioid epidemic is fostering the exploration of nonpharmacologic strategies for pain mitigation. Amongs these, transcranial direct current stimulation (tDCS) and mindfulness-based meditation (MBM) hold potential for pain-relief efficacy due to their neuromodulatory effects of the central nervous system, which is known to play a fundamental role in pain perception and processing. METHODS: In this double-blind study, we used functional near-infrared spectroscopy (fNIRS) to investigate the effects of tDCS combined with MBM on underlying pain processing mechanisms at the central nervous level in older adults with knee OA. Nineteen subjects were randomly assigned to two groups undergoing a 10-day active tDCS and MBM regimen and a sham tDCS and MBM regimen, respectively. RESULTS: Our results showed that the neuromodulatory intervention significantly relieved pain only in the group receiving active treatment. We also found that only the active treatment group showed a significant increase in oxyhemoglobin activation of the superior motor and somatosensory cortices colocated to the placement of the tDCS anodal electrode. To our knowledge, this is the first study in which the combined effect of tDCS and MBM is investigated using fNIRS. CONCLUSION: In conclusion, fNIRS can be effectively used to investigate neural mechanisms of pain at the cortical level in association with nonpharmacological, self-administered treatments.

Changes in Experimental Pain Sensitivity from Using Home-Based Remotely Supervised Transcranial Direct Current Stimulation in Older Adults with Knee Osteoarthritis.

OBJECTIVE: The present study examined the effects of home-based remotely supervised transcranial direct current stimulation on quantitative sensory testing measurements in older adults with knee osteoarthritis. Participants were hypothesized to experience improved pain measurements over time. DESIGN: Open-label, single-arm trial. SETTING: Southeast Texas between March and November 2018 at a nursing school and participant homes. SUBJECTS: Older adults (aged 50-85 years) with self-reported unilateral or bilateral knee osteoarthritis pain who met eligibility criteria set by the American College of Rheumatology. METHODS: The intervention was applied with a constant current intensity for 20 minutes every weekday for two weeks (10 total sessions). Quantitative measures of pain were collected three times over 10 days (days 1, 5, and 10) and included heat threshold and tolerance, pressure pain threshold, punctate mechanical pain, pain, and conditioned pain modulation. Analyses used nonparametric tests to evaluate differences between day 1 and day 10. Generalized linear mixed models were then used to evaluate change across all three time points for each measure. Bayesian inference was used to provide the posterior probability of longitudinal effects. RESULTS: Nonparametric tests found improvements in seven measures, and longitudinal models supported improvements in 10 measures, with some nonlinear effects. CONCLUSIONS: The home-based, remotely supervised intervention improved quantitative measurements of pain in older adults with knee osteoarthritis. This study contributes to the growing body of literature supporting home-based noninvasive stimulation interventions.

Feasibility and efficacy of remotely supervised cranial electrical stimulation for pain in older adults with knee osteoarthritis: A randomized controlled pilot study.

Cranial electrical stimulation (CES) is a noninvasive brain stimulation technique that has been shown to improve pain. However, few studies have investigated the potential benefits associated with remotely supervised CES in older adults with knee osteoarthritis (OA). The aim of this study was to examine the feasibility and preliminary efficacy of remotely supervised CES via secure videoconferencing software on clinical pain severity, experimental pain sensitivity, and pain-related cortical response in older adults with knee OA. Thirty participants with symptomatic knee OA pain were randomly assigned to receive 10 daily sessions (60 min each) of remotely supervised CES (n = 15) or sham CES (n = 15) over two weeks. We measured clinical pain severity via a Numeric Rating Scale, experimental pain sensitivity (e.g., heat pain sensitivity, pressure pain sensitivity, and conditioned pain modulation) using quantitative sensory testing, and pain-related cortical response via functional near-infrared spectroscopy imaging. We also measured participant satisfaction with treatment using the Client Satisfaction Questionnaire. Active CES significantly reduced scores on the Numeric Rating Scale and increased heat pain threshold, pressure pain thresholds, and conditioned pain modulation. We also found significant changes in pain-related cortical hemodynamic activity after CES. Participants tolerated CES well without serious adverse effects and were satisfied with the treatment. Our findings demonstrate promising clinical efficacy of remotely supervised CES for older adults with knee OA.

Does the combination of erythropoietin and tapered oral corticosteroids improve recovery following iatrogenic nerve injury?

INTRODUCTION: The reported prognosis for recovery after peripheral nerve injury is remarkably poor. Deficits may persist for years, resulting in significant functional disability. Both corticosteroids and Erythropoietin have been investigated as neuroprotective agents; however, their efficacy in total hip and knee arthroplasty is not known. The purpose of this study was to evaluate the effect of systemically-administered Erythropoietin and tapered oral corticosteroids on the recovery of postoperative nerve palsies in the setting of total hip and knee arthroplasty. METHODS: Eleven patients sustaining postoperative peripheral nerve injuries after total hip or knee arthroplasty were treated acutely with Erythropoietin and tapered oral steroids. Motor and sensory function was assessed clinically pre- and postoperatively until complete motor recovery or for a minimum of 1 year. RESULTS: Motor loss was complete in seven (64%) patients and partial in four (36%). Seven (64%) patients' symptoms affected the common peroneal nerve distribution and four (36%) had concomitant tibial nerve involvement. Eight (73%) patients experienced full motor recovery at an average of 39 days (range: 3-133 days), and three (27%) had near-complete motor recovery. At final follow up, no patient required assistive devices for ambulation. CONCLUSIONS: Administration of Erythropoietin coupled with oral tapered steroids for patients sustaining iatrogenic nerve injuries in total hip and knee arthroplasty demonstrated faster and more complete recovery of motor and sensory function compared to previous reports in the literature. This study highlights the importance of further investigation to define the role of each in the setting of acute postoperative nerve palsies. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Preformed articulating knee spacers in 2-stage total knee revision arthroplasty: minimum 2-year follow-up.

Two-stage revision arthroplasty using articulating spacers for the treatment of infected total knee arthroplasty (TKA) is a successful management technique. Our purpose was to report our results using preformed, commercially available articulating spacers made of gentamicin-impregnated cement. Thirty-three patients with infected primary or revision TKAs were treated with these spacers using a 2-stage revision technique. In most cases, the spacers were modified intraoperatively by adding a stem of reinforced antibiotic-impregnated acrylic cement. Successful eradication was achieved in 30 of 33 cases at a minimum 2-year follow-up interval. Two patients required a second spacer before successful revision TKA. No spacer fractures or dislocations occurred in this series. No adverse soft tissue effects were noted from the use of this type of articulating spacer.

Constrained cups appear incapable of meeting the demands of revision THA.

BACKGROUND: Failure rates of constrained cups for treating recurrent dislocation in revision THA range from 40% to 100%. Although constrained liners are intended to stabilize the hip by mechanically preventing dislocation, the resulting loss of range of motion may lead to impingement and, ultimately, implant failure. QUESTIONS/PURPOSES: We therefore documented the mechanisms of failure of constrained acetabular cups in revision THA and determined the type and severity of damage (wear, fracture, and impingement) that occurs in situ. METHODS: We retrieved 57 constrained components of four different designs at revision THA and examined for the presence of rim impingement, oxidation, cracks within the liner, backside wear, pitting, scratching, abrasion, burnishing, and the presence of embedded particles. Articular wear was calculated from the volume of the concave articular bearing surface, which was measured using the fluid displacement method. RESULTS: Failure of the locking ring was responsible for 51% of failures, whereas 28% of revisions were the result of acetabular cup loosening, 6% backside wear, and 22% infection. Impingement damage of the rim of the polyethylene liner was seen in all retrievals with moderate or severe damage in 54%. The average volumetric wear rate of the articular surface was 95 mm(3)/year. CONCLUSIONS: Failure of the locking liner ring and loosening of the acetabular cup are the primary causes of mechanical failure with constrained liners; polyethylene is an inadequate material for restricting motion of the hip to prevent instability. The durability of these devices is unlikely to improve unless the mechanical demands are modified through increased range of motion leading to less frequent rim impingement.

The optimal skin incision for minimally invasive total hip arthroplasty performed via the anterolateral approach.

Twelve total hip arthroplasty procedures were performed in fresh cadaveric specimens via the anterolateral approach using straight 9-cm incisions placed in 2 different locations with respect to anatomical landmarks. During each procedure, the forces applied to the wound edges by each of the hip instruments and the pressures and strains generated along the wound edges were measured. Pressures ranging from 40 to 190 kPa were developed between the retractors and the wound edges during acetabular reaming and femoral rasping. The resulting strain along the wound edges averaged 28% during acetabular reaming and 34% during femoral broaching (P < .0001). Maximum strains were recorded at the ends of each incision and averaged 58% and 61%, respectively (P < .0001). These results were independent of the anatomical placement of the skin incision. In total hip arthroplasty, the mechanical trauma associated with the procedure is primarily determined by the surgical approach to the hip and the properties of the subcutaneous tissues, and not the anatomical location of the skin incision itself.

Initial results of managing severe bone loss in infected total joint arthroplasty using customized articulating spacers.

Twenty-three cases of infected total joint arthroplasty with substantial bone loss were treated with a cement spacer, which was customized intraoperatively to achieve joint stability and to allow motion. All but one of the patients were ambulatory with the spacer in place. Spacer dislocation occurred in 1 hip patient (9%) and in none of the knee patients. Articulating antibiotic-impregnated spacers with intraoperative customization is our preferred treatment of cases of infected total joint arthroplasty even in the presence of bone loss.

Towards the reduction of medication errors in orthopedics and spinal surgery: outcomes using a pharmacist-led approach.

STUDY DESIGN: Evaluation of medication ordering errors discovered on an orthopedic/spinal in-patient hospital unit and efforts initiated to reduce them. OBJECTIVE.: In this study the authors aimed to assess the frequency of medication ordering errors and to examine the impact of local measures set forth to reduce their occurrence. SUMMARY OF BACKGROUND DATA: Since the release of the 2000 Institute of Health report: "To Err is Human"; in-hospital medical errors have been recognized as being unacceptably high; the consequence being preventable death rates estimated near 125,000 patients per year. The most common of errors are those involving medications. METHODS: The study consisted of 2 parts. In part 1, the charts from 82 consecutive patients admitted to the Orthopedic/Spine Surgical Unit were assessed to determine the frequency, type, and potential severity of medication ordering errors. Several programs to reduce such errors were subsequently instituted and included: improved chart surveillance by pharmacists, a newly developed medication/history form given to and reviewed with patients before surgery, in-service education of preoperative nursing staff, patient database form changes, and requests for patients to bring their medications on admission. Part 2, including 87 patients, assessed the impact of these measures. RESULTS: In part 1, medication errors were detected in 62% of orders overall. Of these, 43% were found to be of moderate or high potential for harm. After the institution of the above measures (part 2), overall errors were reduced by 31%; moderate/high risk potential harm was reduced by 64%; and errors of omission were detected twice as often. CONCLUSION: Medication errors in ordering are common in orthopedics. We found in part 1 that a chart review and patient interview by the pharmacy team can detect and correct these before reaching the patient. Furthermore, we found in part 2 that the risk could be further reduced by the implementation of pharmacist-led: patient education, education of preoperative nursing personnel, improvement of forms used for data collection, and having the patients bring all of their medications on admission.

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.

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.

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.

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.