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 non-

targeted 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 finite-

element modelling”, J Biomech. 36(12), 1797–767 (2003).

[2] Yucesoy CA, Koopman BH, Huijing PA and Grootenboer HJ, “Three-

dimensional finite element modeling of skeletal muscle using a two-

domain 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. Bascı1, U. Akgun3, C.A. Yucesoy2. 1Marmara

University, Turkey; 2Bogazici University, Turkey; 3Acıbadem 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 finite-

element 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. 1VU University, The Netherlands;2VU 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