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T-11 Remedial Surgery May Cause Sizable Effects Also at Unintended Sites Due to Epimuscular Myofascial Force Transmission
Oral and Poster Presentations / Journal of Biomechanics 43S1 (2010) S23–S74
[3] Gordon MY et al. Characterization and clinical application of human CD34+ stem/progenitor cell populations mobilized into the blood by granulocyte colony-stimulating factor. Stem Cells 2006;24–7:1822–30. [4] Nordsletten L. A method for intramedullary fixation of fractures and segmental grafts in the rat tibia. Scandinavian journal of laboratory animal science 1992;19:75.
The Clinical Trial obtained approval from London Ethics Committee in June 2009 (REC: 09/H70718/4; EudraCT: 2006–004521–28). Patient recruitment to be started in May 2010. T-9 Evaluating the Mechanical Properties of a Tendon Graft, Using Digital Image Correlation (DIC) Technique W. Cheung1 , J. Mahmud2 , S. Evans2 , C. Holt2 , M. Snow1 , B. Wang3 , M. Chizari3,4 . 1 The Royal Orthopaedic Hospital, UK; 2 Cardiff University, UK; 3 Aberdeen University, UK; 4 Brunel University, UK Accurate measurement of the biomechanical properties of tendon grafts such as stiffness, Young’s modulus and ultimate strength has important implications in the surgical repair of anterior cruciate ligament injuries. However, the mechanical behaviour of the tendon is complex and difficult to model. The data from the grip-to-grip displacement reported by the standard testing machines may not be an accurate way to determine the mechanical properties of tendon. The goal of this study was to verify the biomechanical property of an anterior cruciate ligament model tendon graft using the experimental data obtained from the standard tensile loading testing machines with a non-invasive digital imaging correlation (DIC) method. In this study the in vitro mechanical properties of the 10 bovine digital flexor tendon constructs was determined. Each construct consisted of a synthetic foam block where the tendon was doubled over an Endo-button loop and fixed with a round head Arthrex® interference screw. The diameter of the tunnel and interference screw was the same as the diameter of the doubled tendon. The samples were secured and tested in a custom-made apparatus that was mounted in a LOS (Losenhausen, Maschinenbau AG Dusseldorf) uniaxial testing machine. Samples were pre-conditioned and cyclically loaded. A final tensile load to failure was applied to the failure. Experimental measurements were carried out using a DIC system, including two cameras and Vic3D (Limess GmbH, Pforzheim, Germany) software. The technique utilizes two similarly speckled images, which were captured by a solid state video camera, to represent the states of the object before and after deformation. By analyzing any pair of consecutive speckle images with the DIC technique, displacements between the corresponding load levels, incremental displacements and strain of the speckled pattern were obtained. At the beginning of the test, the contour was uniform with same displacement in axial direction, for both limbs of the tendon which verifies that the sample stretched fairly uniformly. By increasing the load the result of displacement in different limbs was slightly different. This meant that there was a relative motion between the limbs and can be concluded that the fixation force is not equal for both strand in the tunnel. At the maximum load, the maximum vertical strain was 0.42 and the shear strain was 0.26. Our results have shown that DIC provides a novel and reliable technique for assessing the biomechanical properties of a tendon graft. This in turn may help clinicians to accurately determine the mechanical properties of tendon grafts used in surgical repair such as a single bundle and a double bundle anterior cruciate ligament repair.
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T-10 Intermuscular Myofascial Connections of FCU Contribute to Wrist Flexion Torque in the Spastic Arm of Cerebral Palsy Patients M. de Bruin1 , M.J.C. Smeulders1 , M. Kreulen1,2 . 1 Reconstructive and Hand Surgery, Academic Medical Center, The Netherlands; 2 Red Cross Hospital, Beverwijk, The Netherlands The flexor carpi ulnaris muscle (FCU) is thought to be the strongest forearm muscle and is held responsible for the flexion and ulnar deviation deformity of the wrist in cerebral palsy. Recent studies revealed an important role of fascia in muscle performance [1,2]. It is thought that myofascial connections play a substantial role in the functioning of the spastic arm in cerebral palsy [2]. The hypothesis was that both tenotomy of the FCU and subsequent dissection of the fascia affect the flexion torque at the wrist. Eleven patients having a transposition of the tendon of the FCU were included. Under general anesthesia without administration of muscle relaxants, the FCU was percutaneously stimulated with supramaximal electrical pulses through two skin electrodes that were placed on the cubital tunnel of the elbow. The surgeon fixated the forearm in neutral position and assured that the hand was not blocked dorsally. A force transducer was placed on the volar side of the distal tubercle of os metacarpale III. The palmar crest of the hand was assumed to be the volar projection of the wrist flexion axis. The moment arm was the distance of the impact point of the force transducer to this palmar crest. Isometric wrist torque was measured under three conditions: before tenotomy, after tenotomy of the distal tendon, and after subsequent dissection of the fascia around the FCU up until approximately halfway the muscle belly. Each session consisted of three trials that were averaged. Change of torque was expressed as a percentage relative to the torque before tenotomy. After tenotomy, the wrist flexion torque decreased on average to 85%. After dissection of the FCU from surrounding structures, the torque decreased to 71%. The 14% difference between the after tenotomy and after dissection conditions was significant (p < 0.05). In these patients, dissection of the FCU resulted in 14% decrease of wrist torque and thus affected the FCU muscle function. The myofascial connections of spastic muscles may play a role in the development of deformities in the spastic arm of cerebral palsy patients and should not be overlooked in planning surgical intervention. Reference(s) [1] Maas H, Meijer HJ, Huijing PA. Intermuscular interaction between synergists in rat originates from both intermuscular and extramuscular myofascial force transmission. Cells Tissues Organs 181(1):38–50, 2005. [2] Yucesoy CA and Huijing PA. Substantial effects of epimuscular myofascial force transmission on muscular mechanics have major implications on spastic muscle and remedial surgery. Journal of Electromyography and Kinesiology 17(6):664–679, 2007.
T-11 Remedial Surgery May Cause Sizable Effects Also at Unintended Sites Due to Epimuscular Myofascial Force Transmission F. Ates1 , P.A. Huijing2 , C.A. Yucesoy1 . 1 Bo˘gazici ¸ University, Turkey; 2 Vrije Universiteit, The Netherlands Epimuscular myofascial force transmission (EMFT ) has been shown to cause (1) unequal forces being exerted at muscle’s origin and insertion, (2) condition dependent length-force characteristics and (3) length changes of a target muscle to affect forces of neighbouring muscles [e.g., 1]. These effects may have implications for remedial surgery. For conditions characterized by EMFT i.e., muscle with intact connections to its neighbouring muscular and nonmuscular structures, we aimed to assess how effects of muscle lengthening surgery (an integral intervention including dissection to reach the target muscle and its subsequent aponeurotomy) be affected.
S64
Oral and Poster Presentations / Journal of Biomechanics 43S1 (2010) S23–S74
Effects of aponeurotomy per se were studied by extending our finite element model of rat extensor digitorum longus (EDL) muscle [2]. For one of the two epimuscularly connected muscles, aponeurotomy was modeled (target muscle) whereas, the other muscle was left intact (non-targeted synergistic muscle). Compared to a modeled control case with no intervention, aponeurotomy caused distal forces of the target muscle to decrease substantially (by 32.8% at low and 14.2% at high length). Other results were (1) proximally an even more pronounced force reduction (by 42.8% at low and 31.4% at high length) for the target muscle and (2) also a decreased distal force of the non-targeted synergistic muscle (by 4.41% at low and 10.59% at high length). The latter was explained by accompanying altered sarcomere length distributions that cause a force reduction (quantified by decreased fiber direction stresses minimally by 3.02% and maximally by 58.12%). A set of model based hypotheses were tested experimentally for rat muscles within the anterior crural compartment: An integral intervention aimed at EDL lengthening causes: (i) reduction of EDL forces at both high and low muscle lengths, (ii) more pronounced force reduction at the proximal EDL tendon and (iii) force decreases also for its synergistic tibialis anterior and extensor hallicus longus muscles (TA+EHL). Our first hypothesis was confirmed only in part (no significant effect at low lengths). However, experimental results did confirm our second and third hypotheses: such intervention causes a more pronounced EDL force decrease proximally (by 35.9%) than distally (by 26.9%) and also force decreases for the synergistic TA+EHL (by 11.88% at high and by 7.93% at low lengths). Our results suggest that major effects of EMFT should be taken into account in designing surgical interventions: (1) For poly-articular muscles, interventions cause differential mechanical effects at the muscle’s origin and insertion site. While yielding a desired effect at the target joint this may even cause an unfavorable effect at nontargeted joints spanned by that muscle. (2) Such aponeurotomies may cause “weakening” of not only the target muscle but also its non-targeted synergists. Reference(s) [1] Yucesoy CA, Koopman BH, Baan GC, Grootenboer HJ and Huijing PA, “Effects of inter- and extramuscular myofascial force transmission on adjacent synergistic muscles: assessment by experiments and finiteelement modelling”, J Biomech. 36(12), 1797–767 (2003). [2] Yucesoy CA, Koopman BH, Huijing PA and Grootenboer HJ, “Threedimensional finite element modeling of skeletal muscle using a twodomain approach: linked fiber-matrix mesh model”, J Biomech. 35(9), 1253–62 (2002).
T-12 Is Myofascial Force Transmission Compensating for the Harvested Hamstrings in Anterior Cruciate Ligament Reconstruction? M. Karahan1 , F. Ates2 , O. Bas¸ cı ¸ 1 , U. Akgun ¨ 3 , C.A. Yucesoy2 . 1 Marmara 2 University, Turkey; Bo˘gazici ¸ University, Turkey; 3 Acıbadem University, Turkey Semitendinosus and Gracilis muscles’ distal tendons are harvested to be used in anterior cruciate ligament reconstruction surgery. A substantial damage is created in the force transmission capacity of the muscle-tendon unit and the expected outcome postoperatively is loss of knee flexion torque. However, not all studies have agreed on the loss of such function. Some studies have argued that there is no difference between preoperative and the postoperative functions of the Semitendinosus and Gracilis muscles [1]. Studies that have not limited themselves with maximum flexion torque alone have shown that the maximum flexion torque has not decreased but only the functioning angle has decreased and flexion capacity is dramatically reduced postoperatively [2]. In a study comparing three groups (intact knee, only semitendinosus harvested, semitendinosus and gracilis harvested) it has been shown that increasing tendon harvesting is correlated with lower
functioning angle and lower active knee flexion [3]. Varying results have been shown on the tendon regeneration capacity and the volume of the semitendinosus muscle postoperatively. There is no consistency in these studies and there is no explanation to the presence of inconsistencies due to the fact that there is not enough information on the postoperative status of the hamstring muscles. We believe that the reasons could be (1) there is not enough research or information on the acute phase postoperatively, (2) the function of the muscles are tried to be investigated through indirect methods such as isokinetic testing methods or magnetic resonance imaging and (3) the expectations are shaped according to the classical perspective rather than the emerging myofascial force transmission theories. Recently, muscular force transmission channels were shown not to be limited to myotendinous junctions: direct collageneous linkages between the epimysia of adjacent muscles, as well as an integral system of collagen reinforced tissues supporting neurovascular tracts and compartmental boundaries provide mechanical connections of muscle to its surroundings additional to its insertion and origin. Due to epimuscular myofascial force transmission [e.g., 4] occurring via this pathway, a muscle may transmit the force it has produced also through a neighboring muscle’s tendon. This may explain the postoperative muscle power retention in the knee with the residual hamstring. Reference(s) [1] Lipscomb AB, Johnston RK, Snyder RB, Warburton MJ and Gilbert PP, Evaluation of hamstring strength following use of semitendinosus and gracilis tendons to reconstruct the anterior cruciate ligament. Am J Sports Med. 10, 340–342 (1982). [2] Ohkoshi Y, Inoue C, Yamane S, Hashimoto T and Ishida R, Changes in muscle strength properties caused by harvesting of autogenous semitendinosus tendon for reconstruction of contralateral anterior cruciate ligament. Arthroscopy. 14, 580–584 (1998). [3] Adachi N, Ochi M, Uchio Y, Sakai Y, Kuriwaka M and Fujihara A, Harvesting hamstring tendons for ACL reconstruction influences postoperative hamstring muscle performance. Arch Orthop Trauma Surg. 123, 460–465 (2003). [4] Yucesoy CA, Koopman BH, Baan GC, Grootenboer HJ and Huijing PA, Effects of inter- and extramuscular myofascial force transmission on adjacent synergistic muscles: assessment by experiments and finiteelement modelling. J Biomech. 36, 1797–767 (2003).
T-13 Effects of Scar Tissue Formation Following Tendon Transfer on Muscular Force Transmission in the Rat H. Maas1 , M.J. Ritt2 , P.A. Huijing1 . 1 VU University, The Netherlands; 2 VU University Medical Center, The Netherlands To improve active wrist extension in patients with obstetrical brachial plexus injury, transposition of flexor carpi ulnaris (FCU) tendon onto extensor carpi radialis muscle (ECR, longus and/or brevis) is performed. However, results after recovery can be surprisingly variable (an increase in wrist extension between 0° and 100°; Ritt, unpublished observations). This may be explained by interindividual differences in neural response and/or in tissue adaptation. The goal of this study was to quantify to what extent scar tissue formation following a FCU-to-ECR tendon transfer affects the biomechanical characteristics of the transferred FCU. As there are severe limitations of studying tendon transfers in humans (e.g., it is not possible to perform a second surgery for experimental measurements), we used an animal model. Under aseptic conditions and with the rats (n = 8) deeply anesthetized, FCU was transferred to the cut distal tendons of ECR. Five weeks postoperatively, FCU muscle function was evaluated in situ. Using indwelling electrodes, wrist movements upon excitation of FCU were observed prior to and after severing the new FCU insertion. Subsequently, the distal FCU tendon was connected to a force transducer for measurement of isometric length-force characteristics. Data were collected (1) with minimally disrupted
[3] Gordon MY et al. Characterization and clinical application of human CD34+ stem/progenitor cell populations mobilized into the blood by granulocyte colony-stimulating factor. Stem Cells 2006;24–7:1822–30. [4] Nordsletten L. A method for intramedullary fixation of fractures and segmental grafts in the rat tibia. Scandinavian journal of laboratory animal science 1992;19:75.
The Clinical Trial obtained approval from London Ethics Committee in June 2009 (REC: 09/H70718/4; EudraCT: 2006–004521–28). Patient recruitment to be started in May 2010. T-9 Evaluating the Mechanical Properties of a Tendon Graft, Using Digital Image Correlation (DIC) Technique W. Cheung1 , J. Mahmud2 , S. Evans2 , C. Holt2 , M. Snow1 , B. Wang3 , M. Chizari3,4 . 1 The Royal Orthopaedic Hospital, UK; 2 Cardiff University, UK; 3 Aberdeen University, UK; 4 Brunel University, UK Accurate measurement of the biomechanical properties of tendon grafts such as stiffness, Young’s modulus and ultimate strength has important implications in the surgical repair of anterior cruciate ligament injuries. However, the mechanical behaviour of the tendon is complex and difficult to model. The data from the grip-to-grip displacement reported by the standard testing machines may not be an accurate way to determine the mechanical properties of tendon. The goal of this study was to verify the biomechanical property of an anterior cruciate ligament model tendon graft using the experimental data obtained from the standard tensile loading testing machines with a non-invasive digital imaging correlation (DIC) method. In this study the in vitro mechanical properties of the 10 bovine digital flexor tendon constructs was determined. Each construct consisted of a synthetic foam block where the tendon was doubled over an Endo-button loop and fixed with a round head Arthrex® interference screw. The diameter of the tunnel and interference screw was the same as the diameter of the doubled tendon. The samples were secured and tested in a custom-made apparatus that was mounted in a LOS (Losenhausen, Maschinenbau AG Dusseldorf) uniaxial testing machine. Samples were pre-conditioned and cyclically loaded. A final tensile load to failure was applied to the failure. Experimental measurements were carried out using a DIC system, including two cameras and Vic3D (Limess GmbH, Pforzheim, Germany) software. The technique utilizes two similarly speckled images, which were captured by a solid state video camera, to represent the states of the object before and after deformation. By analyzing any pair of consecutive speckle images with the DIC technique, displacements between the corresponding load levels, incremental displacements and strain of the speckled pattern were obtained. At the beginning of the test, the contour was uniform with same displacement in axial direction, for both limbs of the tendon which verifies that the sample stretched fairly uniformly. By increasing the load the result of displacement in different limbs was slightly different. This meant that there was a relative motion between the limbs and can be concluded that the fixation force is not equal for both strand in the tunnel. At the maximum load, the maximum vertical strain was 0.42 and the shear strain was 0.26. Our results have shown that DIC provides a novel and reliable technique for assessing the biomechanical properties of a tendon graft. This in turn may help clinicians to accurately determine the mechanical properties of tendon grafts used in surgical repair such as a single bundle and a double bundle anterior cruciate ligament repair.
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T-10 Intermuscular Myofascial Connections of FCU Contribute to Wrist Flexion Torque in the Spastic Arm of Cerebral Palsy Patients M. de Bruin1 , M.J.C. Smeulders1 , M. Kreulen1,2 . 1 Reconstructive and Hand Surgery, Academic Medical Center, The Netherlands; 2 Red Cross Hospital, Beverwijk, The Netherlands The flexor carpi ulnaris muscle (FCU) is thought to be the strongest forearm muscle and is held responsible for the flexion and ulnar deviation deformity of the wrist in cerebral palsy. Recent studies revealed an important role of fascia in muscle performance [1,2]. It is thought that myofascial connections play a substantial role in the functioning of the spastic arm in cerebral palsy [2]. The hypothesis was that both tenotomy of the FCU and subsequent dissection of the fascia affect the flexion torque at the wrist. Eleven patients having a transposition of the tendon of the FCU were included. Under general anesthesia without administration of muscle relaxants, the FCU was percutaneously stimulated with supramaximal electrical pulses through two skin electrodes that were placed on the cubital tunnel of the elbow. The surgeon fixated the forearm in neutral position and assured that the hand was not blocked dorsally. A force transducer was placed on the volar side of the distal tubercle of os metacarpale III. The palmar crest of the hand was assumed to be the volar projection of the wrist flexion axis. The moment arm was the distance of the impact point of the force transducer to this palmar crest. Isometric wrist torque was measured under three conditions: before tenotomy, after tenotomy of the distal tendon, and after subsequent dissection of the fascia around the FCU up until approximately halfway the muscle belly. Each session consisted of three trials that were averaged. Change of torque was expressed as a percentage relative to the torque before tenotomy. After tenotomy, the wrist flexion torque decreased on average to 85%. After dissection of the FCU from surrounding structures, the torque decreased to 71%. The 14% difference between the after tenotomy and after dissection conditions was significant (p < 0.05). In these patients, dissection of the FCU resulted in 14% decrease of wrist torque and thus affected the FCU muscle function. The myofascial connections of spastic muscles may play a role in the development of deformities in the spastic arm of cerebral palsy patients and should not be overlooked in planning surgical intervention. Reference(s) [1] Maas H, Meijer HJ, Huijing PA. Intermuscular interaction between synergists in rat originates from both intermuscular and extramuscular myofascial force transmission. Cells Tissues Organs 181(1):38–50, 2005. [2] Yucesoy CA and Huijing PA. Substantial effects of epimuscular myofascial force transmission on muscular mechanics have major implications on spastic muscle and remedial surgery. Journal of Electromyography and Kinesiology 17(6):664–679, 2007.
T-11 Remedial Surgery May Cause Sizable Effects Also at Unintended Sites Due to Epimuscular Myofascial Force Transmission F. Ates1 , P.A. Huijing2 , C.A. Yucesoy1 . 1 Bo˘gazici ¸ University, Turkey; 2 Vrije Universiteit, The Netherlands Epimuscular myofascial force transmission (EMFT ) has been shown to cause (1) unequal forces being exerted at muscle’s origin and insertion, (2) condition dependent length-force characteristics and (3) length changes of a target muscle to affect forces of neighbouring muscles [e.g., 1]. These effects may have implications for remedial surgery. For conditions characterized by EMFT i.e., muscle with intact connections to its neighbouring muscular and nonmuscular structures, we aimed to assess how effects of muscle lengthening surgery (an integral intervention including dissection to reach the target muscle and its subsequent aponeurotomy) be affected.
S64
Oral and Poster Presentations / Journal of Biomechanics 43S1 (2010) S23–S74
Effects of aponeurotomy per se were studied by extending our finite element model of rat extensor digitorum longus (EDL) muscle [2]. For one of the two epimuscularly connected muscles, aponeurotomy was modeled (target muscle) whereas, the other muscle was left intact (non-targeted synergistic muscle). Compared to a modeled control case with no intervention, aponeurotomy caused distal forces of the target muscle to decrease substantially (by 32.8% at low and 14.2% at high length). Other results were (1) proximally an even more pronounced force reduction (by 42.8% at low and 31.4% at high length) for the target muscle and (2) also a decreased distal force of the non-targeted synergistic muscle (by 4.41% at low and 10.59% at high length). The latter was explained by accompanying altered sarcomere length distributions that cause a force reduction (quantified by decreased fiber direction stresses minimally by 3.02% and maximally by 58.12%). A set of model based hypotheses were tested experimentally for rat muscles within the anterior crural compartment: An integral intervention aimed at EDL lengthening causes: (i) reduction of EDL forces at both high and low muscle lengths, (ii) more pronounced force reduction at the proximal EDL tendon and (iii) force decreases also for its synergistic tibialis anterior and extensor hallicus longus muscles (TA+EHL). Our first hypothesis was confirmed only in part (no significant effect at low lengths). However, experimental results did confirm our second and third hypotheses: such intervention causes a more pronounced EDL force decrease proximally (by 35.9%) than distally (by 26.9%) and also force decreases for the synergistic TA+EHL (by 11.88% at high and by 7.93% at low lengths). Our results suggest that major effects of EMFT should be taken into account in designing surgical interventions: (1) For poly-articular muscles, interventions cause differential mechanical effects at the muscle’s origin and insertion site. While yielding a desired effect at the target joint this may even cause an unfavorable effect at nontargeted joints spanned by that muscle. (2) Such aponeurotomies may cause “weakening” of not only the target muscle but also its non-targeted synergists. Reference(s) [1] Yucesoy CA, Koopman BH, Baan GC, Grootenboer HJ and Huijing PA, “Effects of inter- and extramuscular myofascial force transmission on adjacent synergistic muscles: assessment by experiments and finiteelement modelling”, J Biomech. 36(12), 1797–767 (2003). [2] Yucesoy CA, Koopman BH, Huijing PA and Grootenboer HJ, “Threedimensional finite element modeling of skeletal muscle using a twodomain approach: linked fiber-matrix mesh model”, J Biomech. 35(9), 1253–62 (2002).
T-12 Is Myofascial Force Transmission Compensating for the Harvested Hamstrings in Anterior Cruciate Ligament Reconstruction? M. Karahan1 , F. Ates2 , O. Bas¸ cı ¸ 1 , U. Akgun ¨ 3 , C.A. Yucesoy2 . 1 Marmara 2 University, Turkey; Bo˘gazici ¸ University, Turkey; 3 Acıbadem University, Turkey Semitendinosus and Gracilis muscles’ distal tendons are harvested to be used in anterior cruciate ligament reconstruction surgery. A substantial damage is created in the force transmission capacity of the muscle-tendon unit and the expected outcome postoperatively is loss of knee flexion torque. However, not all studies have agreed on the loss of such function. Some studies have argued that there is no difference between preoperative and the postoperative functions of the Semitendinosus and Gracilis muscles [1]. Studies that have not limited themselves with maximum flexion torque alone have shown that the maximum flexion torque has not decreased but only the functioning angle has decreased and flexion capacity is dramatically reduced postoperatively [2]. In a study comparing three groups (intact knee, only semitendinosus harvested, semitendinosus and gracilis harvested) it has been shown that increasing tendon harvesting is correlated with lower
functioning angle and lower active knee flexion [3]. Varying results have been shown on the tendon regeneration capacity and the volume of the semitendinosus muscle postoperatively. There is no consistency in these studies and there is no explanation to the presence of inconsistencies due to the fact that there is not enough information on the postoperative status of the hamstring muscles. We believe that the reasons could be (1) there is not enough research or information on the acute phase postoperatively, (2) the function of the muscles are tried to be investigated through indirect methods such as isokinetic testing methods or magnetic resonance imaging and (3) the expectations are shaped according to the classical perspective rather than the emerging myofascial force transmission theories. Recently, muscular force transmission channels were shown not to be limited to myotendinous junctions: direct collageneous linkages between the epimysia of adjacent muscles, as well as an integral system of collagen reinforced tissues supporting neurovascular tracts and compartmental boundaries provide mechanical connections of muscle to its surroundings additional to its insertion and origin. Due to epimuscular myofascial force transmission [e.g., 4] occurring via this pathway, a muscle may transmit the force it has produced also through a neighboring muscle’s tendon. This may explain the postoperative muscle power retention in the knee with the residual hamstring. Reference(s) [1] Lipscomb AB, Johnston RK, Snyder RB, Warburton MJ and Gilbert PP, Evaluation of hamstring strength following use of semitendinosus and gracilis tendons to reconstruct the anterior cruciate ligament. Am J Sports Med. 10, 340–342 (1982). [2] Ohkoshi Y, Inoue C, Yamane S, Hashimoto T and Ishida R, Changes in muscle strength properties caused by harvesting of autogenous semitendinosus tendon for reconstruction of contralateral anterior cruciate ligament. Arthroscopy. 14, 580–584 (1998). [3] Adachi N, Ochi M, Uchio Y, Sakai Y, Kuriwaka M and Fujihara A, Harvesting hamstring tendons for ACL reconstruction influences postoperative hamstring muscle performance. Arch Orthop Trauma Surg. 123, 460–465 (2003). [4] Yucesoy CA, Koopman BH, Baan GC, Grootenboer HJ and Huijing PA, Effects of inter- and extramuscular myofascial force transmission on adjacent synergistic muscles: assessment by experiments and finiteelement modelling. J Biomech. 36, 1797–767 (2003).
T-13 Effects of Scar Tissue Formation Following Tendon Transfer on Muscular Force Transmission in the Rat H. Maas1 , M.J. Ritt2 , P.A. Huijing1 . 1 VU University, The Netherlands; 2 VU University Medical Center, The Netherlands To improve active wrist extension in patients with obstetrical brachial plexus injury, transposition of flexor carpi ulnaris (FCU) tendon onto extensor carpi radialis muscle (ECR, longus and/or brevis) is performed. However, results after recovery can be surprisingly variable (an increase in wrist extension between 0° and 100°; Ritt, unpublished observations). This may be explained by interindividual differences in neural response and/or in tissue adaptation. The goal of this study was to quantify to what extent scar tissue formation following a FCU-to-ECR tendon transfer affects the biomechanical characteristics of the transferred FCU. As there are severe limitations of studying tendon transfers in humans (e.g., it is not possible to perform a second surgery for experimental measurements), we used an animal model. Under aseptic conditions and with the rats (n = 8) deeply anesthetized, FCU was transferred to the cut distal tendons of ECR. Five weeks postoperatively, FCU muscle function was evaluated in situ. Using indwelling electrodes, wrist movements upon excitation of FCU were observed prior to and after severing the new FCU insertion. Subsequently, the distal FCU tendon was connected to a force transducer for measurement of isometric length-force characteristics. Data were collected (1) with minimally disrupted