Kinematic Determinants of Anterior Knee Pain in Cerebral Palsy: A Case-Control Study  Frances T. Sheehan, PhD, Anna Babushkina, MD, Katharine E. Alter, MD  Archives of Physical Medicine and Rehabilitation  Volume 93, Issue 8, Pages 1431-1440 (August 2012) DOI: 10.1016/j.apmr.2012.03.022 Copyright © 2012 American Congress of Rehabilitation Medicine Terms and Conditions

Fig 1 Experimental setup. Subjects were placed supine within the MR bore. A coil holder stabilized 2 flexible coils medial and lateral to the knee and provided medial-lateral support for the knee. A cushion wedge was placed under the knee and adjusted so that each subject could select his/her own terminal extension angle, which the subject could reach repeatedly and comfortably. An auditory metronome (played through a pair of headphones) provided guidance for the repeated movement (2 beats per cycle at 35 cycles/min). Archives of Physical Medicine and Rehabilitation 2012 93, 1431-1440DOI: (10.1016/j.apmr.2012.03.022) Copyright © 2012 American Congress of Rehabilitation Medicine Terms and Conditions

Fig 2 Three-dimensional PF translations and rotations. The exact directions associated with the 3 movement directions (positive directions: medial, superior, and anterior) are based on establishing a 3-dimensional coordinate system, but can be approximated in 2 dimensions using the anatomic landmarks from which the coordinate system is established.31 The Po was selected to be the most posterior point on the patella at its midsection in the superior-inferior direction. The Fo was selected to be the deepest point within the femoral sulcus at the level of the femoral epicondylar width. The PF displacements were derived by defining how the patellar origin moved relative to the femoral origin. The rotations are based on an xyz-body fixed Cardan rotation sequence,54 but can be approximated using anatomic lines (positive rotations: medial tilt, flexion, and varus rotation). The tibial coordinate system was defined in a similar manner, with the tibial origin being the center of the patellar tendon insertion into the tibia, and tibiofemoral internal rotation being positive. Abbreviations: Fo, femoral origin; Po, patellar origin. Archives of Physical Medicine and Rehabilitation 2012 93, 1431-1440DOI: (10.1016/j.apmr.2012.03.022) Copyright © 2012 American Congress of Rehabilitation Medicine Terms and Conditions

Fig 3 Comparison of PF kinematics between the CP subgroups. Double arrow lines with 2 asterisks (**) above denote the ranges where there are significant differences between subgroups. The control cohort is represented by a solid line with 1 SD range shown in a shaded area. The CP subgroups without AKP and with pain (CP_noPain and CP_pain) are represented by solid lines with a hollow square symbol and single asterisk, respectively. One SD bar provided every 5°. Abbreviations: CP_noPain cohort, all knees within the CP cohort without chronic AKP; CP_pain cohort, all knees within the CP cohort with chronic AKP >6 mos; Disp, displacement; I/S, inferior/superior; L/M, lateral/medial; P/A, posterior/anterior; rot, rotation. Archives of Physical Medicine and Rehabilitation 2012 93, 1431-1440DOI: (10.1016/j.apmr.2012.03.022) Copyright © 2012 American Congress of Rehabilitation Medicine Terms and Conditions

Fig 4 Discriminant analysis. PF superior displacement versus PF extension. The participants with CP and AKP (CP_pain) are represented by circular symbols. The participants with CP and no AKP (CP_noPain) are represented by square symbols. The average value of PF superior displacement and extension for the control cohort is represented by a star with lines extending the width and height of the graph. Abbreviations: AK, anterior knee; Disp, displacement. Archives of Physical Medicine and Rehabilitation 2012 93, 1431-1440DOI: (10.1016/j.apmr.2012.03.022) Copyright © 2012 American Congress of Rehabilitation Medicine Terms and Conditions

Fig 5 Visual description of PF extension and patella alta at 20° of knee extension, during active extension. The knee angle was defined as 180°– Θ. The top row represents a single participant with CP and AKP. This participant had the most severe alta of the entire CP cohort. (A) The CPC MR anatomic image. The PF superior displacement and extension is visually approximated on the image. Patellar extension can be approximated by its 2-dimensional counterpart (the angle between the vector bisecting the anterior and posterior edges of the distal femur and the vector delineating the posterior edge of the patella). The patellar superior position is the superior displacement of the patellar origin relative to the femoral origin (see fig 2) in the femoral coordinate system. (B) A 3-dimensional model of the knee joint for this same individual at 20° knee extension. The patella is not shown so that the contact between the patellar cartilage and femoral shaft can be seen. (C) A CPC MR image for a single control subject with the third highest level of patellar superior position of all the control subjects. (D) A CPC MR image from an otherwise healthy patient with PFPS from a previous study.24 Of all the patients with PFPS in this previous study, this subject had the second highest level of patella alta. Abbreviations: PFflex, patellofemoral flexion (rotation about the medial-lateral axis); PFSI, patellofemoral superior-inferior displacement. Archives of Physical Medicine and Rehabilitation 2012 93, 1431-1440DOI: (10.1016/j.apmr.2012.03.022) Copyright © 2012 American Congress of Rehabilitation Medicine Terms and Conditions