Association of volunteer-administered home care with reduced emergency room visits and hospitalization among older adults with chronic conditions: A propensity-score-matched cohort study.

OBJECTIVES: The objective of this study was to examine the association of receiving care from a volunteer-administered outreach program with emergency room utilization and hospitalization among older people with chronic conditions in Hong Kong. METHODS: Volunteers consisting of retired healthcare professionals, university students, and openly recruited citizens received training to provide home care services to hospital-discharged older Chinese adults aged 65+ with chronic conditions who were identified as high-risk patients of hospital admission and referred by public healthcare providers. Several home visits were made to enhance the patients' self-care capacity. For comparison, a 4:1-propensity score matching based on age, sex, the month of discharge, length of stay for the index episode, and 14 common chronic conditions was conducted to select a comparison group from a territory-wide inpatient database. Poisson regression was used to compare emergency room utilization and the number of hospitalized days. RESULTS: In total, 775 patients were analyzed, including 155 home care recipients and 620 extracted from the inpatient database as a matched comparison with similar baseline characteristics. Regression analysis showed that home care recipients had 21% fewer overall emergency room visits [95% confidence interval (CI): 3%-35%], 22% fewer such visits which led to hospitalization (95% CI: 1%-39%) and 22% fewer overall hospitalized days (95% CI: 16%-28%). Nevertheless, the number of hospitalized days admitted through the emergency room was 10% higher among home care recipients (95% CI: 0%-20%). CONCLUSIONS: Volunteer-administered home care might be effective in reducing emergency room visits and non-acute hospitalization, as well as early detection of acute problems warranting tertiary care. Further randomized studies are needed to substantiate this finding.

Differential Impacts of Multimorbidity on COVID-19 Severity across the Socioeconomic Ladder in Hong Kong: A Syndemic Perspective.

The severity of COVID-19 infections could be exacerbated by the epidemic of chronic diseases and underlying inequalities in social determinants of health. Nonetheless, there is scanty evidence in regions with a relatively well-controlled outbreak. This study examined the socioeconomic patterning of COVID-19 severity and its effect modification with multimorbidity in Hong Kong. 3074 local COVID-19 cases diagnosed from 5 July to 31 October 2020 were analyzed and followed up until 30 November 2020. Data on residential addresses, socio-demographic background, COVID-19 clinical conditions, and pre-existing chronic diseases of confirmed cases were retrieved from the Centre for Health Protection and the Hospital Authority. Results showed that, despite an independent adverse impact of multimorbidity on COVID-19 severity (aOR = 2.35 [95% CI = 1.72-3.19]), it varied across the socioeconomic ladder, with no significant risk among those living in the wealthiest areas (aOR = 0.80 [0.32-2.02]). Also, no significant association of the area-level income-poverty rate with severe COVID-19 was observed. In conclusion, the socioeconomic patterning of severe COVID-19 was mild in Hong Kong. Nonetheless, socioeconomic position interacted with multimorbidity to determine COVID-19 severity with a mitigated risk among the socioeconomically advantaged. Plausible explanations include the underlying socioeconomic inequalities in chronic disease management and the equity impact of the public-private dual-track healthcare system.

Does Low Dose Angiotensin Converting Enzyme Inhibitor Prevent Pneumonia in Older People With Neurologic Dysphagia--A Randomized Placebo-Controlled Trial.

OBJECTIVE: To examine if angiotensin converting enzyme inhibitor reduces the risk of pneumonia in older patients on tube-feeding because of dysphagia from cerebrovascular diseases. DESIGN: Randomized placebo-controlled trial. SETTING: Acute and subacute geriatrics units, speech therapists' clinic, and nursing home. PARTICIPANTS: Older patients on tube-feeding for >2 weeks because of dysphagia secondary to cerebrovascular diseases. INTERVENTION: Participants were randomized to lisinopril 2.5 mg or placebo once daily for 26 weeks. MEASUREMENTS: Participants were followed up at weeks 12 and 26. The primary outcome was the incidence rate of pneumonia as determined by pneumonic changes on x-ray and clinical criteria. The secondary outcomes were mortality rate and swallowing ability as defined by the Royal Brisbane Hospital Outcome Measure for Swallowing at week 12. RESULTS: A total of 93 older patients were randomized. In interim analysis, 71 completed the trial, whereas 15 had dropped out. Among those who had completed the trial, odds ratio (OR) for death was significantly higher in the intervention group (unadjusted OR 2.94, P = .030; fully adjusted OR 7.79, P = .018). There was no difference in the incidence of pneumonia or fatal pneumonia in the 2 groups. The intervention group had a marginally better swallowing function at week 12 (Royal Brisbane Hospital Outcome Measure for Swallowing score: 4.2 ± 1.5 in intervention group, 3.5 ± 1.5 in placebo group, P = .053). As a result of the interim finding on mortality, the trial was prematurely terminated with 7 participants still in the trial. CONCLUSIONS: Low dose lisinopril given to older tube-fed patients with neurologic dysphagia resulted in increased mortality, although swallowing function showed marginal improvement. ACE inhibitors did not prevent pneumonia in older patients with neurologic dysphagia and might increase mortality.

The synergistic effect of functional status and comorbidity burden on mortality: a 16-year survival analysis.

OBJECTIVES: The relationship between disability and comorbidity on mortality is widely perceived as additive in clinical models of frailty. DESIGN: National data were retrospectively extracted from medical records of community hospital. DATA SOURCES: There were of 12,804 acutely-disabled patients admitted for inpatient rehabilitation in Singapore rehabilitation community hospitals from 1996 through 2005 were followed up for death till 31 December 2011. OUTCOME MEASURE: Cox proportional-hazards regression to assess the interaction of comorbidity and disability at discharge on all-cause mortality. RESULTS: During a median follow-up of 10.9 years, there were 8,565 deaths (66.9%). The mean age was 73.0 (standard deviation: 11.5) years. Independent risk factors of mortality were higher comorbidity (p<0.001), severity of disability at discharge (p<0.001), being widowed (adjusted hazard ratio [aHR]: 1.38, 95% confidence interval [CI]:1.25-1.53), low socioeconomic status (aHR:1.40, 95%CI:1.29-1.53), discharge to nursing home (aHR:1.14, 95%CI:1.05-1.22) and re-admission into acute care (aHR:1.54, 95%CI:1.45-1.65). In the main effects model, those with high comorbidity had an aHR = 2.41 (95%CI:2.13-2.72) whereas those with total disability had an aHR = 2.28 (95%CI:2.12-2.46). In the interaction model, synergistic interaction existed between comorbidity and disability (p<0.001) where those with high comorbidity and total disability had much higher aHR = 6.57 (95%CI:5.15-8.37). CONCLUSIONS: Patients with greater comorbidity and disability at discharge, discharge to nursing home or re-admission into acute care, lower socioeconomic status and being widowed had higher mortality risk. Our results identified predictive variables of mortality that map well onto the frailty cascade model. Increasing comorbidity and disability interacted synergistically to increase mortality risk.

Development and validation of a clinical risk score for predicting drug-resistant bacterial pneumonia in older Chinese patients.

BACKGROUND AND OBJECTIVE: Health care-associated pneumonia (HCAP) and drug-resistant bacterial pneumonia may not share identical risk factors. We have shown that bronchiectasis, recent hospitalization and severe pneumonia (confusion, blood urea level, respiratory rate, low blood pressure and 65 year old (CURB-65) score ≥ 3) were independent predictors of pneumonia caused by potentially drug-resistant (PDR) pathogens. This study aimed to develop and validate a clinical risk score for predicting drug-resistant bacterial pneumonia in older patients. METHODS: We derived a risk score by assigning a weighting to each of these risk factors as follows: 14, bronchiectasis; 5, recent hospitalization; 2, severe pneumonia. A 0.5 point was defined for the presence of other risk factors for HCAP. We compared the areas under the receiver-operating characteristics curve (AUROC) of our risk score and the HCAP definition in predicting PDR pathogens in two cohorts of older patients hospitalized with non-nosocomial pneumonia. RESULTS: The derivation and validation cohorts consisted of 354 and 96 patients with bacterial pneumonia, respectively. PDR pathogens were isolated in 48 and 21 patients in the derivation and validation cohorts, respectively. The AUROCs of our risk score and the HCAP definition were 0.751 and 0.650, respectively, in the derivation cohort, and were 0.782 and 0.671, respectively, in the validation cohort. The differences between our risk score and the HCAP definition reached statistical significance. A score ≥ 2.5 had the best balance between sensitivity and specificity. CONCLUSIONS: Our risk score outperformed the HCAP definition to predict pneumonia caused by PDR pathogens. A history of bronchiectasis or recent hospitalization is the major indication of starting empirical broad-spectrum antibiotics.

A new model for end-of-life care in nursing homes.

OBJECTIVES: This study aimed to promote quality end-of-life (EOL) care for nursing home residents, through the establishment of advance care plan (ACP) and introduction of a new care pathway. This pathway bypassed the emergency room (ER) and acute medical wards by facilitating direct clinical admission to an extended-care facility. DESIGN: An audit on a new clinical initiative that entailed the Community Geriatrics Outreach Service, ER, acute medical wards, and an extended-care facility during winter months in Hong Kong. METHODS: The participants were older nursing home residents enrolled in an EOL program. We monitored the ratio of clinical to emergency admissions, ACP compliance rate, average length of stay (ALOS) in both acute hospital and an extended-care facility, and mortality rates. RESULTS: A total of 76 patients were hospitalized from January to March 2013. Of them, 30 (39%) were directly admitted to the extended-care facility, either through the liaison of Community Geriatrics Outreach Service (group A, 19/76, 25%) or transferred from the ER (group B, 11/76, 14%). The remaining 46 patients (group C, 61%) were admitted via the ER to acute medical wards following the usual pathway, followed by transfer to an extended-care facility if indicated. The ACP compliance rate was nearly 100%. In the extended-care unit, groups A and C had similar ALOS of 11.8 and 11.1 days, respectively, whereas group B had a shorter stay of 7.6 days. The ALOS of group C in acute medical wards was 3.5 days. The in-hospital mortality rates were comparable in groups A and C of 26% and 28%, respectively, whereas group B had a lower mortality rate of 18%. CONCLUSIONS: Nearly 40% of EOL patients could be managed entirely in an extended-care setting without compromising the quality of care and survival. A greater number of patients may benefit from the EOL program by improving the collaboration between community outreach services and ER; and extending hours for direct clinical admission to an extended-care facility.

Predictors of viral pneumonia: the need for viral testing in all patients hospitalized for nursing home-acquired pneumonia.

AIM: Community-acquired pneumonia (CAP) is presumed to be bacterial in origin and empirical antibiotics are almost always given on admission. However, early detection of viral infection is also very important for hospital infection control and timely use of antiviral agents. The present study aimed to compare patients with viral and bacterial pneumonia, and identify independent predictors of viral pneumonia. METHODS: A prospective cohort study was carried out in a tertiary teaching hospital in a 1-year period. Older patients (aged ≥ 65 years) were recruited if they were admitted for CAP confirmed by chest radiographs. RESULTS: A cohort of 488 patients was analyzed. Infective causes were found in 137 (28.1%) patients. Bacterial, viral and mixed infections were detected in 86 (17.6%), 41 (8.4%) and 10 (2.0%) patients, respectively. Bacteriology was established mostly by sputum culture and virology by nasopharyngeal aspirate (NPA) viral culture. The commonest bacterial isolates were Haemophilus influenzae (31), Pseudomonas aeruginosa (15), Mycobacterium tuberculosis (14), Klebsiella spp. (9) and Streptococcus pneumoniae (6). Influenza A virus (28, 8 were pandemic 2009 A/H1N1 subtype) and respiratory syncytial virus (16) were the most frequent viral causes. Independent predictors of viral pneumonia included nursing home residence (RR 3.056, P = 0.009) and absence of leukocytosis (RR 0.425, P = 0.026). CONCLUSIONS: All nursing home residents hospitalized for CAP should undergo NPA viral testing because of infection control, early antiviral treatment and discharge planning. We suggest that empirical antiviral agents might be considered for nursing home residents hospitalized for CAP if outbreaks of influenza-like illness are reported in nursing homes.

Role of atypical pathogens in nursing home-acquired pneumonia.

OBJECTIVES: No international consensus has been reached on the empirical use of antibiotics with atypical coverage in nursing home-acquired pneumonia (NHAP). Aspiration is an important cause of NHAP, but it may not require antimicrobial treatment. This study aimed to investigate the prevalence and clinical characteristics of AP infections and review the need for empirical antibiotics with atypical coverage in NHAP. DESIGN: A prospective cohort study. SETTING: Four nursing homes with a total number of 772 residents. PARTICIPANTS: Patients were aged ≥ 65 years, hospitalized for NHAP, which was defined as the presence of respiratory symptoms and abnormal chest radiographs, from April 2006 to March 2007. MEASUREMENTS: Demographics, clinical parameters, and investigation results were recorded. Microbial investigations comprised sputum routine and mycobacterial cultures, blood and urine cultures, serology, and nasopharyngeal aspirate viral culture and polymerase chain reaction tests. Suspected aspiration pneumonitis was arbitrarily defined as NHAP without pathogens identified. RESULTS: After excluding lone bacteriuria, 108 episodes of NHAP in 94 patients were included. Twelve APs were detected in 11 patients. There was no clinical feature to distinguish between infections caused by APs and other pathogens. The commonest APs were Mycoplasma pneumoniae (6) and Chlamydophila pneumoniae (3). No Legionella pneumophila was detected by urinary antigen test. None of the patients with AP infection received antibiotics indicated for AP infections. However, AP infections did not result in mortality. No pathogen was isolated in 31.5% of cases. Patients without pathogens isolated were less likely to have purulent sputum and crepitations on chest auscultation, compared with those with pneumonia caused by identified pathogens. CONCLUSIONS: Atypical pathogens (APs) were not associated with mortality even in cases where the prescribed antibiotics did not cover APs. NHAP may not necessarily be treated with empirical antibiotics covering APs.

Should nursing home-acquired pneumonia be treated as nosocomial pneumonia?

OBJECTIVES: It is contentious whether nursing home-acquired pneumonia (NHAP) should be treated as community-acquired pneumonia (CAP) or health care-associated pneumonia. This study aimed to compare NHAP with CAP, and to examine whether multidrug-resistant (MDR) bacteria were significantly more common in NHAP than CAP. DESIGN: A prospective, observational cohort study SETTING: The medical unit of a tertiary teaching hospital PARTICIPANTS: Patients 65 years and older, hospitalized for CAP and NHAP confirmed by radiographs from October 2009 to September 2010 MEASUREMENTS: Demographic characteristics, Katz score, Charlson comorbidity index (CCI), pneumonia severity (CURB score), microbiology, and clinical outcomes were measured. RESULTS: A total of 488 patients were recruited and 116 (23.8%) patients were nursing home residents. Compared with patients with CAP, patients with NHAP were older and had more comorbidities and higher functional dependence level. A larger proportion of patients with NHAP had severe pneumonia (CURB ≥2) than patients with CAP (30.2% vs 20.7%, P = .034). Similar percentages of patients had identified infective causes in the CAP and NHAP groups (27.7% vs 29.3%, P = .734). Viral infection accounted for more than half (55.9%) of NHAP, whereas bacterial infection was the most frequent (69.9%) cause of CAP. MDR bacteria were found in 6 patients of all study subjects. Nursing home residence and history of MDR bacterial infection were risk factors for MDR bacterial pneumonia, which had more severe pneumonia (CURB ≥2). Logistic regression analysis was limited by the small number of patients with MDR bacterial pneumonia. CONCLUSION: In both CAP and NHAP, MDR bacterial infections were uncommon. Most cases of NHAP were caused by unknown etiology or viral pathogens. We suggest that NHAP should not be treated as nosocomial infection. The empirical treatment of broad-spectrum antibiotics in NHAP should be reserved for patients with severe pneumonia or at high risk of MDR bacterial infection.

Predictors of in-hospital mortality of older patients admitted for community-acquired pneumonia.

BACKGROUND: there were a few studies on the case mortality of pneumonia in older people, of which results were conflicting. OBJECTIVES: this study aimed to identify risk factors associated with in-hospital mortality in older patients admitted for community-acquired pneumonia (CAP). DESIGN: a prospective cohort study. SETTING: hospital sample. SUBJECTS: during the 1-year study period (from October 2009 to September 2010), 488 older patients aged 65 or above were recruited. METHODS: demographic characteristics, medical illnesses (Charlson's comorbidity index (CCI)), premorbid functional status (Katz's index) and baseline blood tests were recorded. The outcome was in-hospital mortality. RESULTS: in this cohort of patients, the mean age was 81.0 years (±7.9) and 282 (57.8%) were male. Nursing home residents accounted for 23.8% (116/488) of study subjects. The median CCI was 2 (inter-quartile range (IQR): 1-3); 60 (12.3%) patients succumbed during hospital stay. Logistic regression showed that comorbidities, mid-arm circumference, serum albumin level and severity of pneumonia (Confusion, blood Urea nitrogen, Respiratory rate and low Blood pressure (CURB) score) were independent predictors of in-hospital mortality of pneumonia. CONCLUSION: in keeping with previous studies, CURB score and comorbidities were the most significant independent predictors of mortality of CAP in older patients. Our study concluded that nutritional status was also an important factor affecting their survival. This study failed to demonstrate functional status as a predictor of mortality due to limitation of Katz's index.

Mobile-bearing knees reduce rotational asymmetric wear.

Polyethylene wear of bearing components is the most common long-term complication in total knee arthroplasty. One would anticipate differing kinematics would generate different wear patterns (including wear type, degree, and symmetry) on the articulating surface of mobile-bearing and fixed-bearing inserts. Because mobile-bearing designs facilitate movement of the insert relative to the tray when the knee rotates, we hypothesized mobile-bearing designs would reduce the incidence of rotational asymmetric wear. We examined 51 worn tibial inserts, including 15 from mobile-bearing rotating-platform posterior-cruciate-sacrificing dished prostheses and 36 from fixed-bearing posterior-cruciate-retaining flat prostheses, which were retrieved at revision surgery with an average implantation time of 115 months. We divided wear types into low-grade wear (burnishing, abrasion, and cold flow) and high-grade wear (scratching, pitting, metal embedding, and delamination) to assess wear degree of polyethylene. To assess symmetry of wear, the insert surface was divided into medial and lateral sides and each side was further divided into three equal zones along the anteroposterior direction. Low-grade wear was more common in mobile-bearing knees, whereas high-grade wear was more common in fixed-bearing knees. We identified no internal/external rotational asymmetric wear or anteroposterior asymmetric wear in mobile-bearing knees.

Preparation of UHMWPE particles and establishment of inverted macrophage cell model to investigate wear particles induced bioactivites.

Total joint replacement surgery has been widely applied to patients with severe osteoarthritis. Aseptic loosening induced by wear particles generated during joint movement is the major reason causing the failure of joint implants. Interaction of ultra-high molecular weight polyethylene (UHMWPE) wear particles with macrophages stimulates the release of inflammatory cytokines and leads to bone resorption and osteolysis. Effect of UHMWPE particle size and shape on the bioactivities remains unclear due to the lack of particles with controlled morphology as well as adequate in-vitro cell culture models for further investigations. We have developed a micro-cutting procedure to generate UHMWPE particles with desired sizes and shapes by rubbing UHMWPE with microfabricated surfaces. A narrow distribution and sterility of the generated particles was achieved. An inverted cell culturing apparatus and procedures were created and the contact between particles and macrophage cells was observed. No significant difference of the cell proliferations under normal and inverted positions further demonstrates the feasibility of the system. This newly developed platform can assist in the further understanding of the mechanism and therapy strategies of osteolysis induced by polyethylene particles.

Long-term results of total condylar knee arthroplasty.

From 1979 to 1984, 126 consecutive Total Condylar (Howmedica, Rutherford, NJ) knee arthroplasties were performed at a hospital in Taiwan, of which 64 knees were available for evaluation. The patients' average weight was 58 kg. The average Hospital for Special Surgery knee score at the latest follow-up was 86 points. Using revision for mechanical failure as an end point, the 20-year overall survival was 91.9%. The survival for the all-polyethylene tibial component was 96.4% and for the metal-backed tibial component was 88.4%. The difference was statistically significant (P < .001). We recommend the use of the more cost-effective and durable all-polyethylene tibial component for a primary cemented total knee arthroplasty, particularly in Asians with a relatively low weight and who are relatively inactive, especially in elderly people.

A randomized, controlled trial of an intensive community nurse-supported discharge program in preventing hospital readmissions of older patients with chronic lung disease.

OBJECTIVES: To evaluate the effectiveness of an intensive community nurse (CN)-supported discharge program in preventing hospital readmissions of older patients with chronic lung disease (CLD). DESIGN: Randomized, controlled trial. SETTING: Two acute hospitals in the same health region in Hong Kong. PARTICIPANTS: One hundred fifty-seven hospitalized patients aged 60 and older with a primary diagnosis of CLD and at least one hospital admission in the previous 6 months. INTERVENTION: CNs made home visits within 7 days of discharge, then weekly for 4 weeks and monthly until 6 months. CNs coordinated closely with a geriatric or respiratory specialist in hospital. Subjects had telephone access to CNs during normal working hours from Monday to Saturday. MEASUREMENTS: The primary outcome was the rate of unplanned readmission within 6 months. The secondary outcomes were the rate of unplanned readmission within 28 days, number of unplanned readmissions, hospital bed days, accident and emergency room attendance, functional and psychosocial status, and caregiver burden. RESULTS: One hundred forty hospitalized patients completed the trial. Intervention group subjects had a higher rate of unplanned readmission within 6 months than control group subjects (76% vs 62%, P=.080, chi2 test). There was no significant group difference in any of the secondary outcomes except that intervention group subjects did better on social handicap scores. CONCLUSION: There was no evidence that an intensive CN-supported discharge program can prevent hospital readmissions in older patients with CLD.

Long-term results of low contact stress mobile-bearing total knee replacements.

Five hundred ninety-eight consecutive primary low contact stress total knee replacements were done in 502 patients between 1985 and 1990. Clinical review was available for 495 knees (406 patients), 228 knees with meniscal-bearing prostheses and 267 knees with rotating-platform prostheses. The average followup was 12 years (range, 10-15 years). The average postoperative knee and functional scores were 87 points and 75 points, respectively. The average postoperative range of motion was 110 degrees. Fifty-six knees (11%) required revision for excessive wear of the tibial insert (41), dislocation (10), patellar polyethylene breakage (one), component loosening (one patellar, one tibial), and infection (two). During revision, osteolysis (20 knees), patellar polyethylene failure (33), and femoral component fracture (one) were seen. The overall survivorship was 88.1% at 15 years using Kaplan-Meier analysis. The survival rate was 83% for the meniscal-bearing prostheses and 92.1% for the rotating-platform prostheses. The Low Contact Stress mobile-bearing knee prosthesis has no superiority over that of fixed-bearing knees, especially for the meniscal-bearing design in prevention of polyethylene failure or revision. Based on the results of this study, the use of the LCS meniscal-bearing prosthesis does not appear to be justified.

Late dislocation of rotating platform in New Jersey Low-Contact Stress knee prosthesis.

Five patients with late rotational dislocation of the rotating platform bearing in the New Jersey Low-Contact Stress total knee arthroplasty are reported. The prostheses had functioned well for 8 to 12 years before failure. Preoperative radiographs showed asymmetric femorotibial joint spaces. Entrapment of the dislocated bearing in three patients and spontaneous reduction of the dislocated bearing in another two patients were seen at revision. Femorotibial ligamentous instability was found after reduction. The retrieved polyethylene bearings showed advanced wear and cold flow deformities and the thickness was reduced. The revision arthroplasty was accomplished by replacement with a thicker bearing element. Progressive femorotibial ligament laxity and reduction of the thickness of polyethylene with wearing break down the originally well-balanced soft tissue tension of the knee. The rotational degree of the rotating platform bearing is unrestricted, which may result in late dislocation. Polyethylene wear is unavoidable in knee prostheses using metal contact with polyethylene even with a mobile-bearing design. Efforts to reduce polyethylene wear are mandatory.

Osteolysis in failed total knee arthroplasty: a comparison of mobile-bearing and fixed-bearing knees.

BACKGROUND: Osteolysis is an important complication associated with total knee arthroplasty. The purpose of this study was to compare the prevalence of osteolysis after failed total knee arthroplasty with a mobile-bearing prosthesis and after failed arthroplasty with a fixed-bearing prosthesis. METHODS: Eighty revision total knee arthroplasties performed between 1995 and 1998 were included in this study. All had radiographic evidence of advanced polyethylene wear. The mobile-bearing group consisted of thirty-four knees with a Low Contact Stress implant, and the fixed-bearing group included forty-six knees. The average time (and standard deviation) from the primary operation to the revision was 102.8 +/- 26.5 months in the mobile-bearing group and 96.0 +/- 30.1 months in the fixed-bearing group. The prerevision radiographs and operative findings were reviewed. RESULTS: The prevalence of osteolysis was significantly higher in the mobile-bearing group (47%; sixteen of thirty-four knees) than in the fixed-bearing group (13%; six of forty-six knees) (p = 0.003). The distal part of the femur was involved in thirteen knees in the mobile-bearing group and in four knees in the fixed-bearing group. Seventeen knees had osteolysis in the posterior aspect of the femoral condyle, which was the most common site of osteolysis; however, twelve of them had no evidence of osteolysis on prerevision radiographs. CONCLUSIONS: The prevalence of osteolysis was higher in the knees with a mobile-bearing prosthesis than in those with a fixed-bearing prosthesis. The osteolysis was predominantly on the femoral side, adjacent to the posterior aspect of the condyle. Radiographic evaluation of osteolysis in the distal part of the femur may not be reliable and usually leads to an underestimation of the degree of osteolysis.

Particle size and morphology of UHMWPE wear debris in failed total knee arthroplasties--a comparison between mobile bearing and fixed bearing knees.

Osteolysis induced by ultrahigh molecular weight polyethylene wear debris has been recognized as the major cause of long-term failure in total joint arthroplasties. In a previous study, the prevalence of intraoperatively identified osteolysis during primary revision surgery was much higher in mobile bearing knee replacements (47%) than in fixed bearing knee replacements (13%). We postulated that mobile bearing knee implants tend to produce smaller sized particles. In our current study, we compared the particle size and morphology of polyethylene wear debris between failed mobile bearing and fixed bearing knees. Tissue specimens from interfacial and lytic regions were extracted during revision surgery of 10 mobile bearing knees (all of the low contact stress (LCS) design) and 17 fixed bearing knees (10 of the porous-coated anatomic (PCA) and 7 of the Miller/Galante design). Polyethylene particles were isolated from the tissue specimens and examined using both scanning electron microscopy and light-scattering analyses. The LCS mobile bearing knees produced smaller particulate debris (mean equivalent spherical diameter: 0.58 microm in LCS, 1.17 microm in PCA and 5.23 microm in M/G) and more granular debris (mean value: 93% in LCS, 77% in PCA and 15% in M/G).