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Three-Dimensional Tibiofemoral Articular Contact Kinematics of a Cruciate-Retaining Total Knee Arthroplasty

¹ Massachusetts General Hospital, 55 Fruit Street, GRJ 1215, Boston, MA 02114. E-mail address for G. Li: gli1{at}partners.org
² 6080 Falls Road, Suite 203, Baltimore, MD 21209
³ P.O. Box 708, 1800 West Center Street, Warsaw, IN 46581
⁴ Massachusetts General Hospital, Yawkey Center for Outpatient Care, 32 Fruit Street, YAW-3-3B, Boston, MA 02114

Investigation performed at the Bioengineering Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital/Harvard Medical School, Boston, Massachusetts

NOTE: The authors thank Dr. Louis DeFrate, Ramprasad Papannagari, and Elizabeth DeSouza for their technical assistance.

In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from Zimmer. In addition, one or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Zimmer). Also, a commercial entity (Zimmer) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Methods: Nine osteoarthritic patients who were managed with a single design of a posterior cruciate ligament-retaining total knee implant were investigated with the use of an innovative dual orthogonal fluoroscopic imaging system. The position of the components during in vivo weight-bearing flexion was measured from full extension to maximum flexion in 15° intervals. Tibiofemoral articular contact was determined by the overlap of the tibiofemoral articular surfaces. The centroid of the surface intersection was used to report the point of contact location. The average tibiofemoral contact points on both the medial and lateral tibial component surfaces were reported as a function of flexion.

Results: The average maximum weight-bearing flexion angle was 113.3° ± 13.1° (range, 96° to 138°). In the anteroposterior direction, the contact location was relatively constant in the medial compartment and moved posteriorly by 5.6 mm in the lateral compartment as the knee flexed from full extension to 90° of flexion. The range of the contact location in the mediolateral direction was 3.7 mm in the medial compartment and 4.8 mm in the lateral compartment. For both compartments, posterior translation of the contact point was significant from 90° to maximum flexion, but the contact point at maximum flexion was not observed to reach the posterior edge of the polyethylene tibial insert articular surface.

Conclusions: While the minimum anteroposterior translation of the contact point on the medial side might be interpreted as a medial pivot rotation during knee flexion, the contact point did move in the mediolateral direction with flexion. Beyond 90°, both medial and lateral contact points were shown to move posteriorly but stopped before reaching the posterior edge of the polyethylene tibial insert articular surface. It seemed that the current component design did not allow the femoral condyle to roll off the polyethylene edge at high degrees of flexion because of the geometry at the posterior lip.

Clinical Relevance: These three-dimensional tibiofemoral contact data may provide new insight for determining polyethylene tibial insert wear patterns in vivo and for designing the articulating surfaces by accounting for contact location in both the anteroposterior and mediolateral directions.

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