Track 2. Musculoskeletal Mechanics-Joint ISB Track

6483 We-Th, no. 93 (P57) Experimental evaluation of biological samples impact response F. Varga 1 , M. Dr2ik 2, M. Handl 3, J. Chlpik 2, E. Filov~ 1,4, E. Amler 1,4. 1Department of Biophysics, Charles University, 2nd Medical Faculty, Prague, Czech Republic, 2International Laser Centre, Bratislava, Slovakia, 3Orthopaedic Clinic, Charles University, University Hospital Motel, Prague, Czech Republic, 4Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czech Repubfic

Introduction: In addition to conventional static and dynamic mechanical test- ing, the impact response of load-bearing biological materials is an essential part of the material characterization. Therefore, the drop-weight testing proce- dures have been developed for basic mechanical parameters determination of bioelements at both tensioned and compressed conditions. Material and Methods: The method is based on rapid increase of the loading force during the shock pulse developed by impact of drop-weight. Tensile force is usually applied on tendon specimens, causing subsequent elongation up to their failure and compressive forces are applied on cartilage specimens. Both, the Laser Doppler Vibrometer and piezoaccelerometer are used to read the impact process dynamics. By measuring the time-dependent signal of the drop- weight velocity or alternatively its deceleration during the impact, the required information on the loading force, drop-weight energy and specimen elongation vs. time can be extracted. Such information allows us to evaluate stress-strain diagrams and Young's modulus vs. strain relation. Results: Pilot studies examined biomechanical properties of knee anterior cruciate ligament (ACL) and its most frequent substitutes. The tensioned strands of the original ACL showed mean maximum stress 41.3 MPa; patellar- tendon-bone 40.6MPa; gracilis tendon 95.1 MPa and the semitendinosus 88.7 MPa. Preliminary tests of joint cartilages have been accomplished as well, proving "hardening" of cartilage with more rapid loading, when compared with conventional static and dynamic tests. Conclusions: The experiments realized have confirmed the proposed ap- proach as effective with high information yield. Moreover, the experimental problems with small biological samples handling were simply solved. Acknowledgments: This research is supported by the grants of the Science Foundation of the Charles University (GAUK No. 200040), Prague and The Internal Grant Agency of the Ministry of Health of the Czech Republic NR 8122-3/2004.

4707 We-Th, no. 94 (P57) The kinematics of knee joint in different injury degrees of posterior cruciate ligament at full extension C.-H. Wu 1 , C.-K. Cheng 1 , J.-J. Liau 2. 1Institute efBiemedical Engineering, National Yang Ming University; Taipei, Taiwan, 2School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan

Previous studies have defined the function of posterior cruciate ligament (PCL) is the primary restraint to tibial posterior translation. But very little information is known about the kinematics of knee in different PCL-deficient degrees. In current study, the influence of the isolated PCL injury on knee's kinematics at full extension was evaluated with a finite element model. A non-linear three-dimensional finite element model of the human knee joint consisting two bones with articular cartilage layers, menisci, and four main ligaments was constructed to investigate the kinematic response of the knee joint under 100 N of posterior tibial force in different strength of PCL at full extension. The boundary conditions were selected to fix all freedoms on the top of femur, and assure unconstraint on the bottom of tibia except flexion-extension. Partial PCL injury was simulated by reducing the elastic modulus of the PCL in the model. At full extension under drawer, the posterior displacement was 3.63 mm in the lateral compartment of normal PCL knee, which significant coupled with tibial external rotation of 4.05 °. Rupture of the PCL led to increase the sagittal laxity in the medial compartment of the knee, which resulted in tibial internal rotation about 3.01 °. Without PCL rupture, all degrees of PCL injury un-affect the total laxity of knee at full extension under a posterior tibial force, but the degrees of tibial external rotation were significant decreased in severe PCL injury knee. Therefore, the degree of PCL-deficient is difficult to be diagnosed from the kinematics of knee at full extension except for PCL rupture patients

6241 We-Th, no. 95 (P57) Experimental study of different arthroscopic rotator cuff repair techniques C. Ohman 1 , M. Baleani 1 , A. Marinelli 2, G. Giavaresi 3, A. Toni 1 . 1Laboratorio Tecnologia Medica, Istituti Ortopedici Rizzoli, Bologna, Italy, 2 Sezione-B Chirurgia Ortopedico-Traumatologica, Istituti Ortopedici Rizzoli, Bologna, Italy, 3 Laboratorio Chirurgia Sperimentale, Istituti Ortopedici Rizzoli, Bologna, Italy

Retears of arthroscopic rotator cuff repairs still occur. Further improvements of the surgical technique are thus needed. The objective of this study was

2.8 Tendons and Ligaments - Mechanics of Normal Tissue $497

to determine the mechanical performance of different arthroscopic repair tech- niques. All tests were performed in-vitro using sheep humera and infraspinatus tendons. Firstly, the strengths of four different grasping techniques were compared: Simple stitch(SS), Mattress, modified Mason-Allen, and simple stitch closed over a horizontal Ioop(SS+HL). The SS+HL was developed as an alternative to the modified Mason-Allen, the golden standard in open surgery. Secondly, the pull-out strength of two different anchors(SuperRevo ® and Twinfix TM) was tested. Finally, the strength and stiffness of the whole repair were assessed, comparing two different grasping techniques: 2SS and 2SS+HL, two different sutures(Ethibond ® and Herculine TM) and the two different anchors previously tested. The strength of the SS+HL(224 N±45) was more than twice the strengths of the Mattress(86 N±15) and SS(71 N±14). No significant difference was found between the SS+HL and the modified Mason-Allen(226 N±44). The pull-out strength of the SuperRevo ® anchor(674 N±196) was significantly greater than that of the TwinfixmM(448 N±116). The results for the whole repair showed that the strength of the 2SS+HL(290 N±58) was more than twice the one of the 2SS(115N±35), regardless of anchor type. A strength reduction was found in the 2SS+HL repair shifting from Herculine TM (290N±58) to Ethibond ® (169N±19). Also the stiffness depended on the suture type but neither on the anchor nor the stitch. The results show that SS+HL could be a potential substitute to the Modified Mason-Allen. The SuperRevo ® showed higher pull-out strength than Twinfix TM in healthy bone. Nevertheless, both anchors have pull-out strengths larger than the strength of the best grasping technique. The use of the 2SS+HL instead of 2SS should increase the strength of the repair. The suture stiffness seems important for the whole repair stiffness. This could be important since a higher stiffness might prevent the gap-formation between tendon and bone.

6578 We-Th, no. 96 (P57) Three-dimensional in vivo knee joint laxity under torsional loading

A. Hemmerich 1 , W. van der Merwe 2, C.L. Vaughan 1 . 1Human Biology, University of Cape Town, South Africa, 2Sports Science Orthopaedics Clinic, Cape Town, South Africa

Excessive knee joint laxity is often used as an indicator of joint injury such as rupture of the anterior cruciate ligament (ACL). Although the ACL has been shown to contribute to rotational stability [1,3], clinical assessment devices are currently limited to anterior-posterior drawer measurements. The objective of this work was to design a non-invasive procedure whereby in vive knee joint kinematics could be evaluated in 3D using magnetic resonance imaging (MRI) to view the underlying bone and soft tissues. An MRI compatible jig is securely fastened to the frame of the open MR magnet and has been designed to administer a torque in the transverse plane while the subject's knee is imaged. The magnitude of the rotational torque is measured using a strain gauge instrument. Additional rotation in the coronal and sagittal planes (up to 150 of abduction-adduction and 800 of flexion) is permitted. When the predetermined torque is reached, the foot is clamped in place and the strain gauge is disconnected prior to imaging, thereby preventing image distortion. The 3D Tl-weighted sequence of the commercial 0.2 T MRI generates approximately 40 contiguous slices of less than 2 mm thickness (256 256 matrix). This 3D image volume is acquired in less than 5 minutes. Segment coordinate systems are defined for the femur and tibia based on the 3D positions of easily identifiable landmarks on the MR images. 3D rotations and translations resulting from the applied torque are calculated based on the method of Grood and Suntay [2]. This unique methodology, which enables us to measure kinematics of the non-weight-bearing knee joint in vive, is non- invasive, eliminates soft tissue artefact during 3D measurements, and permits soft tissue visualization which is beneficial in clinical assessment.

References Georgoulis AD, et al. (2003). Am J Sports Med. 31: 75-79. Grood ES, Suntay WJ. (1983). J Biomech Eng. 105: 136-144. Scopp JM, et al. (2004). Arthroscopy 20: 294-299.

5919 We-Th, no. 97 (P57) In vivo analysis of the role of ACL in controlling antero-medial instabilities of the knee S. Zaffagnini, S. Bignozzi, S. Martinelli, N. Lopomo. Rizzoli Institutes, Lab. Biomeccanica, Bologna, Italy

The treatment of ACL lesion combined with torn MCL is a controversial issue. This residual laxity might cause the loosening over time of the ACL graft and cause failure of the reconstruction. The aim of this study was, to evaluate in- vive if the degree of instability was higher in combined ACL+MCL injury with respect to isolated ACL rupture, and if a single ACL reconstruction was capable of restoring all the residual knee laxities in isolated ACL or ACL+MCL injuries.