Tibiofemoral contact points relative to flexion angle measured with MRI Per Wretenberg a,b , Dan K. Ramsey b, * , Gunnar N emeth a,b a Department of Orthopaedic Surgery, Karolinska Hospital, S-171 76 Stockholm, Sweden b Department of Surgical Sciences, Section for Orthopaedics, Karolinska Institute, S-171 76 Stockholm, Sweden Received 28 January 2002; accepted 14 May 2002 Abstract Objective. To determine whether knee flexion influenced bony contact movements during flexion. Design. Accurate three-dimensional (3D) measurements of tibiofemoral bony contact points in vivo was performed using magnetic resonance imaging technology at 0°, 30° and 60° of flexion. Background. Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bone, and provides precise 3D co-ordinates. Methods. Magnetic resonance imaging recordings were made from the right knee of 16 subjects with no history of knee dys- function at 0°, 30° and 60° of flexion. Joint contact movements were reported as changes of the contact point’s position on the medial and lateral tibial condyle with respect to a fixed reference point for each flexion angle. Results. The dominant motion of the centroid of the contact area was posterior with a concomitant inferior and lateral dis- placement when flexing from 0–30°. Increased flexion to 60° the contact points moved slightly anterior, superior and continued laterally. Comparing movements between the medial and lateral compartments, larger displacement magnitudes were observed laterally. Additionally, tibial rotations of 3–5° were noted relative to the femur. Conclusion. Based on magnetic resonance imaging co-ordinates and the rotated anatomical reference frame, the geometric equations to derive the contact point between the tibiofemoral articulating surfaces is a viable means to investigate tibiofemoral bony contact movement. Relevance Contact areas and pressure distributions have been reported using cadaveric specimens but interpretation of the results is limited. Other investigations have been restricted to sagittal plane movement. Using kinematic magnetic resonance imaging, accurate non- invasive 3D recordings of the normal knee at increments of flexion are possible. The normative baseline date can be compared against that of the pathological knee, such as cruciate ligament injury or the status of post-operative meniscectomy in order to examine skeletal joint motion and stability. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Magnetic resonance imaging; MRI; Tibiofemoral contact points; Tibiofemoral kinematics; Three-dimensional tibiofemoral kinematics; Knee kinematics 1. Introduction Information about movement of the contact points between the femoral and tibial condyles is of importance in understanding the basic kinematics of the normal knee. To date it remains unclear whether the location of the instant center of rotation or changes in the position of the tibiofemoral contact points is more clinically rel- evant when examining skeletal joint motion, joint de- generation, and stability. Using three-dimensional (3D) in vivo baseline data of the normal knee, kinematics can be compared against that of the pathological knee, such as cruciate ligament injury or the status of post-opera- tive meniscectomy in order to examine skeletal joint motion and stability. * Corresponding author. Address: MotorikLab Q6: 101 77, Astrid Lindgren Children’s Hospital, Karolinska Hospital, S-171 77 Stock- holm, Sweden. E-mail address: dan.ramsey@kbh.ki.se (D.K. Ramsey). 0268-0033/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0268-0033(02)00036-0 Clinical Biomechanics 17 (2002) 477–485 www.elsevier.com/locate/clinbiomech