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Friday, February 25, 2005

New tool for evaluating TKA results described

A new tool for evaluating the results of total knee arthroplasty (TKA) is explained in poster exhibit P116. Researchers developed a new weight-bearing axial radiographic view and scoring system that can be used in analyzing the patellofemoral joint after TKA.

Patellofemoral evaluation after TKA is not addressed by most knee scoring systems. Patellar radiographic assessment after TKA is obtained with static, unloaded views that may not reproduce the in vivo patellofemoral kinematics. Investigators wanted to develop and validate new, reliable and reproducible clinical and radiographic assessment tools for comprehensive evaluation of results in TKA.

Beginning with an axial Merchant radiographic view, researchers maintained the relationships between the X-ray source, the angle of incidence on the joint and the cassette position but positioned the standing patient in a semi-squatted position (knee bent at 45 angle). This altered the muscle involvement from the standing view.

Researchers confirmed the quality of the view on a cadaveric knee model with multiple markers. They also developed a new Patella Scoring System, which ranges from 0 to 100 points and considers anterior knee pain, crepitus, stair performance and quadriceps strength. Any radiographic abnormalities are calculated as deductions.

The radiographic assessment and scoring systems were then tested with 69 patients (100 posterior-stabilized TKAs). Safety, reproducibility and clinical reliability were measured; intra- and inter-observer variability was assessed by comparing the results of two different investigators.

The modified Merchant view showed significant patellofemoral tracking changes in 68 percent of patients. In 21 knees (15 patients) bone-implant contact was observed under load. The new scoring system had a significantly higher correlation between excellent-good clinical outcomes and excellent patellofemoral performance than either the Knee Society or Lysholm scores (p=0.022; p=0.014).

Using a multivariate regression analysis, researchers did not find a correlation between clinical outcomes and radiographic tilt, subluxation or height. Bone-implant contact, however, did show higher incidence of pain, particularly when associated with asymmetric patellar resection.

Researchers included Andrea Baldini, MD; John Anderson, MD; Pierpaolo Cerulli Mariani, MD; James Kalyvas, BhS; Piergiuseppe Zampetti, MD; Helene Pavlov, MD; and Thomas Sculco, MD-all of New York City.

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