$502 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) Poster Presentations

The effect of changing anthropometric parameters of the model was analyzed, and the results showed that the coordinates of the attachment points of the ligaments on femur and tibia are the most affecting parameters. Thus it appears that this approach could be practicable providing that an adequate data base of knee joint morphology was available. The potential of the available imaging techniques (NMR, CT scan) will be exploited and will permit an advancement of the model on a statistical basis.

5218 Mo-Tu, no. 12 (P57) Alteration in knee alignment and muscle activation pattern during walking after frequent cutting training P.-Y. Lee 1 , C.-'~ Yang 2, W.-L. Chen 3 . 1Department efPhysical Medicine and Rehabilitation, Cheng Ching Hospital, Taichung, Taiwan, 2Department of Orthopedics, National Cheng Kung University, Tainan, Taiwan, 3Department of Physical Therapy, National Cheng Kung University, Tainan, Taiwan

Cutting maneuvers have been suggested as the commonest mechanism of non-contact knee injuries. While transverse plane moments have been widely proposed to play an important role in cutting mechanism, no studies have directly investigated the effect of long-term cutting training on the rotational alignment of knee joint or on alteration in the EMG pattern of daily walking. Purpose: To examine the differences in knee alignment and the EMG patterns of normal walking process between collegiate basketball players and the sedentary controls. Methods: 14 collegiate basketball players were recruited to take CT scans for alignment evaluation (Knee Version, KV, the static external rotated angle of the tibia relative to the femur). Seven of these basketball players without any knee pain history were arranged for further EMG analysis with their cutting legs in comparison of the non-dominant legs from 12 sedentary controls during walking. Results: The cutting legs of basketball subjects demonstrated significantly smaller KV in comparison with their non-cutting legs (p<0.05). Basketball group exhibited significantly lower vastus lateralis (VL) activities during most of the stance phase and significantly lower hamstrings lateralis (HL) activities at late stance during walking. Discussion and Conclusion: Basketball players undergoing long-term cutting training have demonstrated apparent knee internal rotational alignment in their cutting legs. Significantly decreased VL activation found in basketball group during walking has suggested the increased efficiency of VL after cutting training. Furthermore, significantly lower muscle activities found in knee external rotators (VL and HL) at late stance phase implied lower demands for basketball subjects to work against the popltieus, the primary internal rotator that plays an important role in the cutting tasks and in the process of knee unlocking at late stance of daily walking. Our results clearly demonstrated the effect of cutting training on the efficiency of popliteus and VL.

6042 Mo-Tu, no. 13 (P57) MRI-based modeling of changes in knee positioning and cartilage contact related to injury and weightbearing P.J. Barrance, D.L. Benoit, J. Twomey, T.S. Buchanan. Center for Biomedical Engineering Research, University of Delaware, Newark, Delaware, USA

Introduction: Injury to the knee can alter tibiofemoral joint positioning and contact surface loading, and such changes may influence the development of osteoarthritis. Assessment of the importance of these effects requires precise measurements during weightbearing. We used MRI and computer modeling to compare joint positioning and cartilage contact areas in injured and healthy knees in high and low weightbearing conditions. Methods: Two males with healthy knees (41.5 ± 4.9 yr) and two males who had sustained complete unilateral anterior cruciate ligament tears (42.5 ±4.9 yr) were scanned bilaterally. The inclination of the table of the scanner (Upright MRI, Fonar Corporation) was changed, varying the fraction of body weight supported. A series of sagittal images was acquired for each of the eight knees in conditions of minimal weightbearing (table 200 from horizontal) and high weightbearing (table 50 from vertical). Scans were performed at 200 knee flexion, measured by goniometer. Distal femoral and proximal tibial bone surfaces, as well as medial/lateral compartment cartilage surfaces, were digitized and projected into 3D. Centers of contact were calculated for regions of tibial cartilage that lay within 2 mm of femoral cartilage. Anatomical axes were assigned in one scan of each subject and transferred to the remaining three scans using surface matching. Positioning and contact points were calculated relative to those axes. Results: Between low and high weightbearing, anterior tibial translation (8 knees, 4.4 ±2.5 mm), internal tibial rotation (7 knees, 1.7 ±2.6°), and pos- terior migration of the medial (6 knees, 1.5 ± 1.6 mm) and lateral (7 knees, 2.3 ± 2.4 mm) tibial contact points were observed. The greatest anterior posi- tioning relative to the contralateral knee during high weightbearing was seen in an injured subject (6.8mm); also, that injured knee exhibited the highest

positioning change (8.3 mm) and posterior contact migration (medial: 3.8 mm, lateral: 5.3 mm) between low and high weightbearing. Discussion: Using weightbearing MRI combined with computer modeling, we measured injury-related changes to tibiofemoral joint positioning and cartilage contact.

5426 Mo-Tu, no. 14 (P57) influence of achilles tendinopathy on lower extremity joint stiffness strategies during single-legged hopping

S. Arya 1 , S. Solnik 2, K. Kulig 1 . 1Department of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, USA, 2University School of Physical Education, Wroclaw, Poland

Introduction: The purpose of this study was to determine lower extremity joint stiffness strategies in persons with Achilles tendinopathy during single- legged hopping. Understanding inter-segmental limb dynamics in the presence of tendinopathy has important implications for the study of joint stability and control. We hypothesized that individuals with Achilles tendinopathy will alter joint stiffness strategies during hopping. Methods: Two groups of subjects participated. Subjects in the chronic Achilles tendinopathy group (n =4) and a healthy control group (n=4) performed 20 single-legged hops at a self-selected frequency. 3-D kinematics (VICON Motion System, 120 Hz), and ground reaction forces (AMTI force plate, 1560 Hz) were collected. Joint torsional stiffness (A Moment/A Angle) during the stance phase of hopping was calculated for ankle and knee joints and normalized to body weight. Leg stiffness was calculated as the ratio of peak ground reaction force to maximum change in leg length during stance and normalized to body weight. Response Surface Methodology (RSM) was used to determine the interaction of ankle joint torsional stiffness (KA) and knee joint torsional stiffness (KK) to lower extremity stiffness (KL) by fitting the data to a 2nd order regression model. Results and Discussion: The coefficient of determination values (R 2) for the healthy and tendinopathy groups were 0.84 and 0.72 respectively. The coefficients of non-linear terms obtained for the healthy group were 1.95 and -4.27 for KA and K K respectively. For the tendinopathy group, the coefficient values were 4.31 (KA) and 2.94 (KK). This indicates that knee stiffness strategy varied between groups. The healthy group maximized knee stiffness whereas the tendinopathy group minimized knee stiffness during hopping. Conclusion: Modulation of knee stiffness strategy to optimize lower extremity stiffness in the tendinopathy group suggests a neuromuscular adaptation to chronic tissue pathology. The implications of this study to joint stability warrants further investigation.

4809 Mo-Tu, no. 15 (P57) Subchondral bone density pattern in the normal canine carpal joint

J. Maierl 1 , A. Kaiser 1 , P. B6ttcher 2, H.-G. Liebich 1 , U. Matis 3. 1Institute of Veterinary Anatomy, Ludwig-Maximilians-University, Munich, Germany, 2Department of Small Animal Medicine, University of Leipzig, Leipzig, Germany, 3 Clinic of Veterinary Surgery, Ludwig-Maximilians-University, Munich, Germany

Severe injuries, such as hyperextension injuries and slab and chip fractures, are commonly seen in the carpal joints of racing and working dogs. They typically involve the radial und accessory carpal bones. To date, little is known about the normal loading pattern in the canine carpal joint. Therefore, the objective of this novel study was to determine the long-term loading pattern in 120 normal carpal joints of 60 medium- to large-breed dogs using Computertomography-Osteoabsorptiometry (CTOAM, MiJller-Gerbl 1998). Individual computed-tomographic datasets were matched onto a refer- ence template joint surface using automatic mutual information-based image registration (B6ttcher et al 2004). This allowed for quantitative topographic comparisons of subchondral bone density among and between dogs. It also allowed for computing and visualizing the 3D-topographic mean bone density. Areas of high bone density, which correlated to regions of high stress, were very consistent among the joints. In the antebrachiocarpal joint, areas with high bone density were identified dorsomedially. In the midcarpal and car- pometacarpal joints, they were equally distributed over the joint surfaces; this was because of the very limited range of motion in these joints. With increasing age, the subchondral bone density also increased, and areas of high bone density became more demarcated. Regions of high bone density coincided with typical sites of cartilage damage or fractures. There were no differences between male and female dogs or between right and left carpal joints. These findings are attributable to normal hyperextension of the canine carpal joint, which is intensified by a larger load during walking or trotting. The resulting compressive and shear forces, located mainly on the dorsal aspects of the joint surfaces, may cause chip fractures, which are characteristically seen after jumping or falling from great heights.