The position of the center of the mass from the knee center correlates closely with the knee adduction moment in patients with knee osteoarthritis

s / Osteoarthritis and Cartilage 21 (2013) S63–S312 S104 178 THE POSITION OF THE CENTER OF THE MASS FROM THE KNEE CENTER CORRELATES CLOSELY WITH THE KNEE ADDUCTION MOMENT IN PATIENTS WITH KNEE OSTEOARTHRITIS N. Takeda y,z, R. Niki x, T. Kobayashi y, T. Ino k, M. Yamanaka y, T. Majima y. yHokkaido Univ., Sapporo, Japan; zHokuto Hosp., Obihiro, Japan; xObihiro Kousei Hosp., Obihiro, Japan; kHakodate Orthopedic Clinic, Hakodate, Japan Purpose: The external knee adduction moment (KAM) has been demonstrated to be a risk factor for the progression of knee osteoarthritis. The KAM can be changed by the relative position of the knee center, the center of pressure (COP), and the center of the mass (COM) during walking. Few previous gait analysis studies have examined whether the distance from the COM to the knee center are variables that influence the KAM or its relationship with the kinematics of the trunk and lower limbs. Therefore, the objective of this study was to clarify the relationships among the KAM, COM and other kinematic variables. Methods: Nineteen subjects with knee osteoarthritis, eighteen females and one male, with an average age of 70.9 years (range: 5079 years) were recruited from the university hospital. The study was approved by the institutional board, and all subjects gave their written informed consent for their participation. All subjects had a radiograph taken while standing on one foot. The femorotibial joint in all radiographs was evaluated using the Kellgren and Lawrence scale (K/L). Two subjects had a K/L score of 2, nine had a K/L of 3, five had a K/L of 4. The knees with more symptoms were investigated. The average femorotibial angle (FTA) was 178.9 (range: 174 -187 ). Gait data were collected with a six camera motion analysis system and two force plates that were time synchronized and sampled at 120 Hz and 1200 Hz, respectively. Modified Helen Hays marker sets with 31 retroreflective markers were attached. The subjects were instructed to walk on a 10 m walkway at a selfselected speed. A total of three trials with clean, single force plate strikes from the study limb were collected. The external first peak knee adduction moment in the stance phase (1st KAM), COM, the distance from the COM to the center of the knee in the frontal plane (COM-K), lateral trunk tilt, lateral pelvic tilt, adduction angle at the hip joints, toeout angle of the foot, gait width and the gait speed were analyzed. The external moment was calculated with OrthoTrak. The kinetic data were calculated using the Matlab R2009b software program. All angles were reported during the stance phase of the gait for the affected limb at the first peak knee adduction moment. Values for each gait variable were obtained by averaging them across the trials. We used Pearson correlation coefficients to examine the relationships among the 1st KAM, FTA, COM-K, trunk tilt angle, pelvic tilt angle, hip adduction angle, leg heel angle, heel floor angle and toe-out angle. We used a multiple regression analysis to evaluate the amount of variance in the 1st KAM explained by FTA, COM-K, pelvic tilt angle and toe-out angle. Results: The 1st KAM was significantly correlated with the COM-K (r1⁄40.64, p1⁄40.014) and the pelvic tilt angle (r1⁄4-0.458, p1⁄40.043). The COM-K was also significantly correlated with the trunk tilt angle (r1⁄4-0.46, p1⁄40.040) and hip adductor angle (r1⁄4-0.60, p1⁄40.005). In a multiple regression analysis, the COM-K and pelvic tilt angle were independently correlated with the 1st KAM (R2 1⁄40.445). Conclusions: The 1st KAMwas more closely correlated with the COM-K thanwith the foot-related variables. Modifications to the position of the COM, including the pelvic tilt, trunk tilt, and hip adduction are important to reduce the 1st KAM for patients with knee osteoarthritis. The factors associated with the 1st knee adduction moment as determined by a multivariate analysis. Predictor variables b-coefficient Standard error p value COM-K 0.0050 0.002 0.006 Pelvic tilt 0.042 0.015 0.014 Femorotibial angle -0.011 0.009 0.232 Toe-out angle 0.009 0.006 0.133 179 CHANGES TO ROTATIONAL LOADING AFTER ACL INJURY AND RECONSTRUCTION DURING STANDING TARGET MATCHING A.S. Lanier y,z, K. Manal y,z, T.S. Buchanan y,z. yUniv. of Delaware, Newark, DE, USA; zDelaware Rehabilitation Inst., Newark, DE, USA Purpose: Nearly half of patients with anterior cruciate ligament injury will eventually get osteoarthritis (OA). Frontal plane knee measures are commonly used to explain the high incidence of OA but rotational loading may also be a contributing factor. Transverse knee moment (TKM) can help understand rotational instability common after ACL injury and correlates to cartilage loss. Measuring transverse knee moment during tasks that require dynamic rotational loading, such as a run cut maneuver, post ACL injury and reconstruction risks re-injury. Our lab uses a standing target matching protocol that safely evaluates rotational loading as it requires sub-maximal forces. In standing target matching subjects generate controlled shear forces to control a cursor. Our goal was to use standing target matching to understand rotational loading in ACL deficient (ACL-d) and reconstructed (ACL-r) subjects. We hypothesized that TKM measured during standing target matching would be greater in ACL-d subjects than healthy subjects and similar between healthy and ACL-r subjects. Methods: This study included 8 healthy, 8 ACL-d and 8 ACL-r subjects, all of similar age, mass and BMI. Reconstruction types included cadaveric allograft or hamstrings autograft. ACL-d subjects were testedwithin 6 months of injury. ACL-r subjects were tested 6 months to 1 year of surgery. For the standing target matching subjects stood barefoot on 2 force plates (OR-6 AMTI, Watertown, MA, USA), each limb on a force plate. Subjects controlled a cursor presented on a screen in front of them. The cursor was controlled by shear forces generated by a single limb. The goal of standing target matching was to create the forces to place the cursor on a location on the screen designated with a target. Shear direction controlled the cursor's movement in that direction if subjects created shear in the anterior/posterior direction the cursor moved towards the top/bottom of the screen, respectively, and AP shear forces moved the cursor left and right. 18 targets were presented at 20 increments around a circle; target position order was randomized. Target position from the center of the screen was 50% of the minimum shear MVC of the anterior, posterior, medial, and lateral directions. Cursor size was based on weight distribution; requiring even distribution of body weight. Standard motion capture techniques were used to collect kinematic and GRF data during target matching. Results: ACL-d and ACL-r limbs have significantly larger TKM when compared to limbs of healthy subjects when matching targets (Figure 1). The ACL-d limbs have greater internal rotation moment (designated as a positive TKM) at 5 target positions which require medial shear forces (140 -220 ). Figure 1. Avg. TKM SE normalized to mass*height: ACL-d (left), ACL-r (right) & healthy subjects. * p<0.05. Conclusion: ACL-d patients have increased TKM which persists after reconstruction. These findings support our first hypothesis but do not support our second hypothesis. Increased moments occur at target positions requiringmedial shear force. Previous research using standing target matching found poor muscular control post injury. After injury there is poor proprioception in transverse and sagittal planes. Poor control and reduced proprioception are creating increased rotational loading which presents itself strongly at medial target positions. Higher rotational loading occurs at medial target positions; producing medial shear force may be dangerous when patients return to sport. Athletes experience medial shear force multiple times during a single game which also contributes to valgus collapse, a contributor to noncontact