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Saturday, March 18, 2000

Finds condyle bearing surface positions in TKA

A study using lateral radiographs of 20 subjects with total knee arthroscopy (TKA) determined that the medial and lateral condyle bearing surface positions for subjects having a posterior stabilized (PS) and posterior cruciate retaining (PCR) TKA are posterior while subjects are seated. However, while kneeling the subjects with a PCR TKA are statistically more anterior than subjects having a PS TKA.

Researchers of the study, presented in scientific exhibit 48, hypothesize that while in a kneeling position, the posterior cruciate ligament has less resistance to the anterior thrust of the femur relative to the tibia than in a PS TKA where this force is absorbed in the cam and post mechanism.

Each subject was clinically successful (HSS>90), without having any pain or ligamentous laxity. The 2-D radiographic images were converted into 3-D using a fully automated computer model-fitting technique. The medial and lateral femorotibial contact points for each subject were determined during kneeling and seated positions. A location anterior of the midline of the tibia in the sagittal plane was denoted as positive and posterior as negative.

In a seated position, the femorotibial contact points were, on average, posterior for both TKA groups (PCR: medial = -2.4 mm and lateral = -3.4 mm; PS: medial = -5.1 mm and lateral = -8.9 mm). In a kneeling position, the bearing surface positions were shifted anterior for both groups (PCR: medial = 0.9 mm and lateral = -0.8 mm; PS: medial = -5.6 mm and lateral = -8.3 mm). A statistical analysis comparing the kinematic data for subjects having a PS or PCR TKA revealed that the relative contact positions are statistically different during kneeling (medial, p=0.002, lateral, p=0.0004), but not while seated (medial, p=0.2, lateral, p=0.08).

The researchers are Richard D. Scott, MD, department of orthopaedic surgery, Harvard Medical School; and David Yasgur, MD; and from the Rocky Mountain Musculoskeletal Research Laboratory, Denver, Colo., Richard D. Komistek, PhD, president, executive director, Douglas A. Dennis, MD, chairman, medical director, and Dylan T. Anderson, research engineer.

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2000 Academy News March 18 Index C

Last modified 24/February/2000 by IS