The Contact Area and Pressure Distribution Pattern of the Knee: A Study of Normal and Osteoarthrotic Knee Joints

Seven knees were studied to determine the contact area and pressure distribution of the tibiofemoral joint, under various loads and at 0° flexion, using the casting method and special sensor sheets. At a load of 1000N (Newton) the contact area of the knee was 11.5 × lCmm² with menisci and 5.2 × lCmm² without menisci, and the menisci occupied 70 per cent of the total contact area. Peak pressure at 1000N was 3MPa (Mega Pascal) with the menisci and 6MPa without them. the high pressure areas were located on the lateral meniscus as well as on the uncovered part of the articular cartilage of the lateral compartment, and on the uncovered cartilage in the medial compartment. After removal of the menisci the contact area decreased to below one half that of the intact knee and the contact pressure considerably increased. These facts imply that the menisci have load bearing and load spreading functions.

The contact areas were also measured in two osteoarthrotic knees and they were significantly larger than those in normal knees. in these arthrotic knees the menisci seemed to play a less significant role in transmission of weight than in the normal knees.     

Time of admission and mortality after hip fracture: a detailed look at the weekend effect in a nationwide study of 55,211 hip fracture patients in Norway

Background and purpose — There are numerous studies on the weekend effect for hip fracture patients, with conflicting results. We analyzed time of admission and discharge, and the association with mortality and length of hospital stay in more detail.

Patients and methods — We used data from 61,211 surgically treated hip fractures in 55,211 patients, admitted to Norwegian hospitals 2008–2014. All patients were aged 50 years or older. Data were analyzed with Cox and Poisson regression.

Results — Mortality within 30 days did not differ substantially by day of admission, although admissions on Sundays and holidays had a slightly increased mortality. The hazard ratios were 1.1 (95% confidence interval [CI] 0.97–1.2) for Sundays, and 1.2 (CI 0.98–1.4) for holidays, relative to Mondays. For patients admitted between 6:00 am and 7:00 am the hazard ratio was 1.4 (CI 1.1–1.8) relative to patients admitted between 2:00?pm and 3:00?pm. Discharges during weekends and holidays were associated with a substantial higher mortality than weekday discharges. Patients admitted from Friday to Sunday generally stayed in hospital for a shorter time than patients admitted during other days.

Interpretation — Our results indicate that the discussion on weekday versus weekend admission effects might have distracted attention from other important factors, such as time of day of admission, and day of discharge from hospital treatment.     

Re-revision Knee Arthroplasty in a Tertiary Center: Infection and Multiple Previous Surgeries Were Associated With Poor Early Clinical and Functional Outcomes

BackgroundThe incidence of re-revision knee arthroplasty (re-revision KA) is increasing and associated with high complication and failure rates. The aim of this study was to investigate re-revision rates, complications, and patient-reported outcomes following re-revision KA and factors associated with poor outcome.MethodsThis was a retrospective cohort study of 206 patients (250 knees) undergoing re-revision KA at a major revision center from 2015 to 2018. The mean follow-up was 26 months (range, 0 to 61) and mean age at re-revision KA was 69 years (range, 31 to 91 years). The main indications for surgery were prosthetic joint infection (PJI) (n = 171/250, 68.4%) and aseptic loosening (n = 25/250, 10.0%). We compared re-revision rates, joint function, and complications for aseptic and infective indications. Logistic regressions were performed to identify risk factors for further reoperation.ResultsThe estimated re-revision rates at 2 years were 28.7% (95% confidence interval [CI]: 22.7-35.9) and at 4 years were 42.0% (95% CI: 32.8-52.6). Mean Oxford Knee Score was 26 points (range, 1 to 48). Mean EuroQoL-5D-5L utility was 0.539 (range, -0.511 to 1.000). Multivariable analyses demonstrated that PJI (Odds Ratio [OR] 2.39, 95% CI 1.06-5.40, P = .036), greater number of previous surgeries (OR 1.18, 95% CI 1.04-1.33, P = .008), and higher Elixhauser score (OR 1.06, 95% CI 1.01-1.13, P = .045) were independently associated to further surgery.ConclusionRe-revision KA carried a high risk of early failure. Multiple revised joints and patients with more comorbidities had worse function. Patients undergoing re-revision KA for PJI should be counseled to expect higher failure rates and complications than patients who have aseptic indications.     

Comorbidities Have a Greater Impact Than Age Alone in the Outcomes of Octogenarian Total Knee Arthroplasty

Background

Increasing age and various comorbidities are known risk factors for complications after total knee arthroplasty (TKA), but data on the impact of total comorbidity burden is scarce. We investigated the effect of age and total comorbidity burden on outcomes after primary TKA in octogenarians (OGs).

Seventeen to Twenty Years of Follow-Up of the Low Contact Stress Rotating-Platform Total Knee Arthroplasty With a Cementless Tibia in All Cases

Background

Total knee arthroplasty designs can be categorized by bearing design and fixation method. The mobile-bearing concept was developed with the aim of increasing longevity and improving function by reduced polyethylene wear and closer replication of physiological knee motion. Cementless fixation has the goal of achieving a long-lasting “biological” fixation between prosthesis and bone.

In a Bundled Payment Model,the Costs Associated With Total Joint Replacement in Those Aged Older Than 80 Years Are Significantly Greater

BackgroundThe number of octogenarians requiring a total hip arthroplasty (THA) and/or total knee arthroplasty (TKA) will rise disproportionally in the coming decade. Although outcomes are comparable with younger patients, management of these older patients involves higher medical complexity at a greater expense to the hospital system. The purpose of this study was to compare the cost of care for primary THA and TKA in our bundled care patients aged ≥80 years to those aged 65-80 years.MethodsA retrospective review of primary TKA (n = 641) and THA (n = 1225) cases from 2013 to 2017 was performed. Patient demographic and admission cost data were collected. Patients were grouped based on surgery type (ie, elective or nonelective THA/TKA) and age group (ie, older [≥80 years old] or younger [65-80 years old]). Multivariate regression analyses were used to account for demographic differences.ResultsElective primary THA in the older cohort (n = 157) cost 24.5% more than the younger cohort (n = 1025) (P < .0001). Elective primary TKA cases in the older cohort (n = 87) cost 17.0% more than the younger cohort’s (n = 554) (P < .0001). For nonelective THA cases, the older cohort’s (n = 29) episodes cost 39.1% more than the younger cohort (n = 14) (P < .0001). When comparing the <80 elective THA cohort (n = 1025) to the ≥90 cohort (n = 10), the cost difference swelled to 58.7% (P < .0001).ConclusionAlthough primary THA and TKA in ≥80-year-old patients yield similar outcomes, this study demonstrates that the additional measures required to care for older patients and ensure successful outcomes cost significantly more. Consideration should be given to age as a factor in determining reimbursement in a bundled payment system to reduce the incentive to restrict care to elderly patients.