In vivo determination of condylar lift-off and screw-home in a mobile-bearing total knee arthroplasty.

Twenty subjects implanted with the low-contact stress (LCS) cruciate-sacrificing, mobile-bearing total knee arthroplasty underwent dynamic videofluoroscopy during in vivo weight-bearing conditions using a 3-dimensional computer-aided design (CAD) interactive modeling method. Ninety percent of the subjects demonstrated significant lift-off during stance phase of gait. Condylar lift-off was present at both the medial and the lateral condyles. The maximal medial lift-off was 2.12 mm, whereas the greatest lateral lift-off was 3.53 mm. The maximal positive screw-home was 9.6 degrees, whereas the maximal negative or reverse screw-home was 6.2 degrees. The average screw-home rotation was positive 0.5 degrees. In 50% of patients, medial condylar translation was unexpectedly greater than lateral condylar motion. Condylar lift-off and screw-home motion are significant kinematic functions in this rotationally unconstrained total condylar knee arthroplasty.

Relationship between mortality rates and hospital patient volume for Medicare patients undergoing major orthopaedic surgery of the hip, knee, spine, and femur.

This study examines the relationship between mortality rates and hospital patient volume for major orthopaedic surgery. All Medicare patients from fiscal years 1993 and 1994 in diagnosis-related groups (DRGs) 209, 210, and 214 were included, covering hip and knee arthroplasty, other hip and femur procedures, and spine procedures. Within DRG 209, five procedures were studied in more detail: total hip arthroplasty, partial hip arthroplasty, revision total hip arthroplasty, total knee arthroplasty, and revision total knee arthroplasty. Higher-volume hospitals had lower mortality rates, both in-house and in-house plus 30-day, for each of the DRGs studied and for each of the individual procedures within DRG 209. Age and sex were examined as potential causes of the differences in mortality rates, but no attempt was made to adjust for comorbidities or orthopaedic degree of difficulty. Results for 1995 are included in an appendix.