W.A. Hodge

Making Sense of Knee Arthroplasty Kinematics: News You Can Use

Many groups are reporting results of in vivo studies of knee replacement motions. Despite this growing abundance of data, it may be difficult for the practicing orthopaedist to glean usable information from these highly technical studies. This paper summarizes key study findings related to implant design and surgical strategy. A number of important issues are explored: surgical technique, range of motion, patterns of knee motion, polyethylene wear, and functional knee strength.⇓,⇓ Fig 1: Knee prostheses with a flat tibial insert and a femoral component with a large distal radius can exhibit posterior femoral translation with knee flexion1. However, achieving this pattern of motion appears to depend on surgical technique. Many knee replacements with the same or similar designs exhibit different patterns of motion2-9. (Reprinted, with permission, from: Nozaki H, Banks SA, Suguro T, Hodge WA. Observations of femoral rollback in cruciate-retaining knee arthroplasty. Clin Orthop. 2002;404:310.) Fig 2: Figs. 2-A and 2-B Patterns of anteroposterior translations during a stair-climbing activity in two groups of patients who were operated on by two different surgeons using the same design of knee arthroplasty1. There were no differences between groups in terms of clinical or demographic factors, preoperative disease, implant alignment, or postoperative clinical and functional outcomes. Each line represents the group mean, plus or minus one standard deviation. The open circles indicate flexion ranges at which there were significant differences between the two groups. The anterior-posterior midpoint of the tibial plateau is 0 on the vertical axis. Fig. 2-A Medial tibiofemoral contact was significantly more posterior in Group 1 throughout most of the flexion arc. Fig. 2-B Lateral tibiofemoral contact was significantly more posterior in Group 1 from 50° to 90° of flexion. (Reprinted, with permission, from: Nozaki H, Banks SA, Suguro T, Hodge WA. Observations …

New cementless fixation in hip arthroplasty: a radiostereometric analysis

Introduction Scyon Orthopaedics AG developed a new mode of cementless fixation of the femoral component that provides immediate and permanent anchorage by monocortical locking screws. The aim of this study was to evaluate the stability of the Scyon total hip replacement (THR) stem in-vivo. Methods A total of 15 patients, with an average age of 50 years had surgery between 2008 and 2011. Each patient received a Scyon THR. Standard questionnaires were completed at each follow-up visit for evaluation of functional outcomes. RSA, patient reported outcomes, and plain radiographic follow-up were obtained at 6 months, 1 year, 2 years, and 5 years postoperatively. Results The median ± standard error (SE) stem subsidence (negative y-translation) was 0.07 ± 0.07 mm at 1 year, 0.05 ± 0.04 mm at 2 years and 0.04 ± 0.13 mm at 5 years. The median ± SE stem rotation (y-rotation) was 0.1 ± 0.21 degrees at 1 year, 0.51 ± 0.31 degrees at 2 years and 0.60 ± 0.37 degrees at 5 years. Plain radiographs showed bone on-growth onto medial aspect of the stem. Median HHS improved from 55 preoperatively to 93 at 1 year and 97 at 5 years. The median UCLA Activity Score improved from 4 preoperatively to 6 at 1 year and 5 years. Conclusions RSA results indicate that the Scyon stem with its 5 monocortical locking screws is stable at 5 years. Immediate surgical fixation of the stem and bony on-growth onto the femoral component may ultimately decrease the rate of aseptic stem loosening in these THR patients.