Is a shortened length of stay and increased rate of discharge to home associated with a low readmission rate and cost-effectiveness after primary total knee arthroplasty?

BACKGROUND: It is controversial whether shortening the average length of hospital stay and increasing discharge from a rehabilitation facility to home with either health care or outpatient physical therapy is safe and cost-effective. METHODS: We computed the average length of hospital stay; the rate of discharge to a rehabilitation facility, home with health care, or home with outpatient physical therapy; the all-cause readmission rate within 30 days of discharge per year; and cost savings for 2328 consecutive patients treated with a unilateral primary total knee replacement between 2009 and 2014. RESULTS: The average length of hospital stay per year shortened from 2.0 to 1.3 days (P < .0001); the rate of discharge per year to a rehabilitation facility decreased from 41% to 1% and increased from 9% to 53% to home with outpatient physical therapy (P < .0001); and the rate of readmission within 30 days per year did not change (P = .38). The cost savings averaged $3245 per patient. CONCLUSIONS: A shorter length of hospital stay and an increased rate of discharge to home was not associated with an increased rate of readmission within 30 days and was cost-effective. LEVEL OF EVIDENCE: Level IV, Therapeutic study.

Accuracy evaluation of a lower-cost and four higher-cost laser scanners.

Knowing the accuracy of laser scanners is imperative to select the best scanner to generate bone models. However, errors stated by manufacturers may not apply to bones. The three objectives of this study were to determine: 1) whether the overall error stated by the manufacturers of five laser scanners was different from the root mean squared error (RMSE) computed by scanning a gage block; 2) the repeatability of 3D models generated by the laser scanners when scanning a complex freeform surface such as a distal femur and whether this differed from the repeatability when scanning a gage block; 3) whether the errors for one lower-cost laser scanner are comparable to those of four higher-cost laser scanners. The RMSEs in scanning the gage block were 2 to 52µm lower than the overall errors stated by the manufacturers. The repeatability in scanning the bovine femur 10 times was significantly worse than that in scanning the gage block 10 times. The precision of the lower-cost laser scanner was comparable to that of the higher-cost laser scanners, but the bias was an order of magnitude greater. The contributions of this study are that 1) the overall errors stated by the manufacturers are an upper bound when simple geometric objects like a gage block are scanned, 2) the repeatability is worse on average three times when scanning a complex freeform surface compared to scanning the gage block, and 3) the main difference between the lower-cost and the higher-cost laser scanners is the bias.

Assessment of the radii of the medial and lateral femoral condyles in varus and valgus knees with osteoarthritis.

BACKGROUND: Understanding the relationship between the radii of the medial and lateral femoral condyles in varus and valgus knees is important for aligning the femoral component and for restoring kinematics in total knee arthroplasty. The purpose of this study was to test the hypothesis that the asymmetry between the radii of the medial and lateral femoral condyles in varus and valgus knees with osteoarthritis is small enough to be clinically unimportant. METHODS: A magnetic resonance imaging scan was obtained with use of a biplanar, rotational alignment protocol in a consecutive series of subjects with end-stage osteoarthritis prior to total knee arthroplasty. The alignment protocol oriented the scanning plane so that both condyles were imaged in a plane perpendicular to the primary femoral axis of the knee about which the tibia flexes and extends. The study included 155 varus knees and forty-four valgus knees. Radii were calculated from the area of the best-fit circle overlaid from 10 degrees to 160 degrees on the subchondral corticocancellous bone interface of the medial and lateral femoral condyles. The radius of a condyle was the average of the radii on four adjacent images that showed the femoral condyle with the largest curvature. RESULTS: In the 155 varus knees, the radius of the lateral condyle was an average of 0.1 mm larger than that of the medial condyle (p = 0.003). In the forty-four valgus knees, the radius of the lateral condyle was an average of 0.2 mm larger than that of the medial condyle (p < 0.006). There was a strong association between the radii of the medial and lateral femoral condyles in both the varus (r(2) = 0.9210) and the valgus (r(2) = 0.9129) knees. CONCLUSIONS: As determined by imaging of the femoral condyles perpendicular to the primary femoral axis of the knee, the asymmetry between the radii of the medial and lateral femoral condyles in varus and valgus knees with end-stage osteoarthritis was < or =0.2 mm, which is small enough to be considered clinically unimportant when aligning a total knee prosthesis.