Electromyographic analysis in the reconstruction of anterior cruciate ligament: a new control and prevention method.

Gian Nicola Bisciotti⁽¹⁾
Rossano Bertocco
Pier Paolo Ribolla
Jean Marcel Sagnol ⁽¹⁾

1. Facoltà di Scienze dello Sport, Università Claude Bernard, Lione (F).

.

Summary

In this study ten subjects, whose age, weight and height were respectively 25 + 3 years (mean + standard deviation), 71.1 + 6.5 kg and 179.7 + 4.2 cm were taken into account after they had been fully informed about the purposes of the research. They were all accustomed to sporting activity and had reported an isolated or associated breakage of anterior cruciate ligament (ACL), surgically treated through arthroscopy.

Each subject was asked to perform a series of 6 maximal isometric leg contractions at the height of the thigh with an articular angle standardized at 90°, both with the injured limb as well as with the sane counterpart, during which we recorded the value of the maximal isometric force as well as the electromyographic superficial signal (EMG) of the Vastus Medialis Obliquus (VMO) and of the Vastus Lateralis (VL). The deficiency of the force in the injured limb was equal to 30.27 + 21.655 (p< 0.005), the EMG VMO/VL Ratio of the sane limb and of the injured limb were equal to, respectively, 1.12 + 0.08 and 0.95 + 0.04, the difference proved to be statistically significant (p<0.006). The results show that following an operation to reconstruct the ACL, there is a greater contractile deficiency in the VMO compared to that of the VL, which shows up in a modification of the EMG Ratio, which in turn is a sign of an alteration in the patterns of the neuromuscular activation.

Key words: Electromyography , Anterior Cruciate Ligament, Vastus Medialis, Vastus Lateralis, Functional Deficiency.

Introduction

An important aspect within the diagnosis of articular injury is a careful evaluation of the changes in the functional response of the muscles directly involved in the main movements of the joints.

In the context of a functional evaluation following an injury, the muscular dysfunction can show up as an altered pattern of muscular recruitment in the injured limb in regards to that of its sane counterpart¹. This alteration within the strategy of the neuromuscular response, which can be seen in the injured limb, proofs a change in the neural input of the muscles involved in the specific movement. The surface electromyography (EMG) can represent a method of clinic investigation to underline a possible alteration in the muscular recruitment strategy or a "compensatory" recruitment pattern in the injured limb in comparison to health one^{1 15}. The changes in the pattern of the neuromuscular activation and the following physiological mechanisms of adjustment of the muscular response, which can be seen by means of EMG, can be used successfully (in our opinion) for diagnostic purposes, especially if we consider the good reproducibility of this kind of study ^{3 66 47}. The aim of this study is in fact to set out an EMG research protocol to be used for diagnostic purposes within articular injuries based on the alteration of the neuromuscular activation, which can be monitored in the injured limb in contrast to the sane counterpart in the specific case of the reconstruction of anterior cruciate ligament (ACL), following an isolated or an associated injury of the ligament and evaluating the available data concerning the rehabilitation therapy carried out and the possible risk of traumatic relapse (giving way)

For a better understanding of this matter, we believe it to be important to briefly clarify certain aspects directly related to the field of study in question.

The possible causes of damage to muscular tissue.

Damage to the muscular fibre can be caused by a single muscular contraction or as the culminating effect of a series of contractions ². However the mechanism which appears to be a main correlating factor in the possible damaging of muscular fibre seems to be an eccentric type of contraction ^{1 14 26 52}. The reason that there is higher incidence of traumas on a muscular level registered during situations of eccentric contractions is probably due to the fact that more force is produced in such a contraction than in a concentric or isometric activation ^{57 26}. In fact in an eccentric contraction carried out at a velocity 90° s^-1 the muscular region registers a force three times greater than the one registered at the same velocity during a concentric contraction ⁴³. Moreover, during an eccentric contraction, the passive elements of the connective tissues of the muscle undergoing extension produce a greater force ¹⁸. Referring mainly to this datum, we must stressed that even the purely mechanical phenomenon of elongation can play an important role in bringing on an injury, since this can take place in a muscle which is active during the stretching phase or in a muscular region which is passive during the extension phase ²⁷. During an eccentric contraction, in fact, the muscle undergoes a ‘overstretching’ phenomenon which, as such, can cause damage at the insertion of the tendon, at the muscle-tendon joint, or on a muscular region made more fragile by a vascular deficiency ⁴³. It is interesting to note that the bi-articular muscles are the ones mainly exposed to traumatic injuries because, through their eccentric contraction, they have to control the articular range of more articulations⁷.

The different typology of the muscular fibres also gives a different incidence of traumatic injuries. Compared to the ST fibres, the FT fibres are in fact more exposed to structural damage probably due to their greater contractile capacity, which is turned into a greater production of force and contraction velocity ^{24 22}. Moreover, the muscles which show a high percentage of FT are generally more superficial ⁴¹ and usually affect two or more articulations. Both these factors create a predisposition towards structural damage^{7 26}. It is also interesting to note that a traumatic injury is mainly localized in the muscular-tendon joint, which proofs that there is a greater mechanical stress in the final portion of the muscular fibre ^{26 27 42 53 58 59}.

Finally, we must underline the particular metabolic conditions connected to an eccentric contraction. Since in an eccentric contraction the muscular vascularisation is interrupted, the work carried out is anaerobic and creates an increase of the local temperature and an acidosis state, as well as an evident cellular anoxia. These metabolic situations create an increase in muscular fragility and a possible cellular necrosis on a muscular level and of the connective support⁴³.

The alteration in the cellular functioning of the muscular tissue following a traumatic injury.

In consequence of an injury it is possible to register a series of effects on a muscular level that can be fundamentally connected to a degeneration of the muscular fibres, characterized by myofibrillar destruction together with damage, both on a mitochondrial level and of the sarcoplasmatic reticulum⁹. Moreover, in this condition of ultra structural muscular alteration there can be a sarcolema discontinuity¹⁰. Its loss of sarcolemma integrity with the damage to the sarcoplasmatic reticulum can cause a rise of the intracellular concentration of Ca⁺⁺. The resulting alteration in the capacity to pump Ca⁺⁺ from the sarcoplasm causes a parallel Ca⁺⁺ homeostasis alteration, which would result in an uncontrolled contraction of the sarcomeres² This uncontrolled contraction of the muscular fibres can persist even in the absence of a potential action able to depolarises the fibres, until the intracellular concentration of Ca⁺⁺ remains high and the availability of ATP is sufficiently adequate ^{2 60}. The mechanical forces, caused by this chain of events and persisting on a myofibrillar level after a traumatic injury, can cause an expansion of the affected myofibrillar region ². If the damage suffered by the muscular tissue is severe, the clinical symptoms are manifested by a more or less painful symptomatology, both in passive extension and in active contraction²⁶, swelling, inflammation or oedema in the muscular tissue itself ²⁵, a reduction in the force capacity of the muscular region in question and an alteration of the proprioceptive schemes.^{26 32 42 44 53 58}

Nevertheless is important to note that in many cases, after an appropriate period of rehabilitation, the duration of which depending obviously on the severity of the trauma suffered, the contractile characteristics and thus the capacity of the muscular region in question to generate force, can return within normal limit²⁶. Moreover during the period of rehabilitation and after the muscle could be at a greater risk of suffering further injuries than it would in a situation of complete physiological normality¹⁷.

The alteration of the neuromuscular activation pattern following a traumatic injury.

The surface electromyography (EMG) is usually used in clinical and functional examinations as an instrumental methodology apt for giving information regarding the patterns of neuromuscular activation in the muscular regions in question^{6 33 36 37}. The electromyographic signals obtainable by using the surface electromyography depends every instant on the number of active motor units (MU), on their discharge frequency, on their degree of synchronisation and on their action potential⁶. A traumatic injury suffered on a muscular level can cause an alteration of the EMG signal and in particular of the Force/EMG Ratio (F/EMG Ratio) of the injured limb in contrast to that registered in its healthy counterpart during a muscular contraction¹⁷ . This alteration of the EMG signal can be caused mainly by two types of mechanisms, the first is connected to the sensation of pain felt during the contraction itself. The nociceptive reaction can in fact be responsible for an alteration of the responses of the multiple motoneurons pool, whose activation is conditioned by the anatomical location of the muscular injury suffered and by the intensity of the pain felt^{17 31 55}. The second mechanism which can cause an alteration of the F/EMG Ratio is not necessary linked to the sensation of pain felt by the patient. In fact, in certain cases the severity of the injury and the consequent functional limitation linked to this do not necessarily bring about a sensation of pain of the same severity¹⁷. In the field of this particular clinical condition the alteration of the F/EMG Ratio of the injured limb compared to its healthy counterpart can be attributed to an increased number of motor neurons being recruited to compensate the force deficiency of the injured muscular region¹⁷. This particular kind of compensatory mechanism can affect the MU belonging to a region of the same muscular group not directly affected by the traumatic injury or it can involve the MU belonging to the other synergic muscular groups, which are able to carry out the same kind of biomechanical activity^{17 23 51}.

Muscular pain concomitant with an isolated or associate ACL injury

An isolated or associate ACL injury, which has to be surgically reconstructed by means of arthroscopyc technique using patellar tendon or semitendinous or gracilis tendon, can cause an evident amyotrophia of the thigh muscles²⁹. Muscular hypotrophy involves both the flexor muscles and the extensor ones even of the muscular damage suffered by extensor muscles seems much greater⁴⁶ . The associated injury of the internal meniscus seems to worsen the dynamic function deficiency in flexion while injuries of the external meniscus worsen the overall dynamic function in extension⁴⁶. The loss of muscle tone, observable above all in the femoral quadriceps causes a loss of the contractile capacity during a muscular contraction carried out following isokinetic and isometric methods^{46 68}. The loss of force in the extensor muscles in patients that have undergone surgery to reconstruct the ACL, seems to be linked to the velocity of contraction called for and it becomes particularly evident when muscles contraction takes place at a low velocity²⁸. The hypotrophy and the consequent loss of force affects above all the Vastus Medialis Obliquus (VMO)⁶⁵ and could cause an alteration of the EMG Ratio Vastus Medialis Obliquus / Vastus Lateralis (VMO/VL Ratio) thus weakening the dynamic neuromuscular activation pattern¹⁷.

MATERIALS AND METHODS

Subjects

In this study ten subjects were taken into account whose age, weight and height were respectively 25 ± 3 years (average ± standard deviation), 71.1 ± 6.5 kg and 179.7 ± 4.2 cm. All the subjects took part in some kind of sports activity (table 1) and had suffered an isolated or associated injury of the ACL treated surgically by means of an arthroscopyc reconstruction (table 2). All the subjects, during the test period continued their normal physiotherapy rehabilitation activities. None of the subjects showed symptoms of muscular or neuromuscular problems apart from the one described above. When the test was carried out the subjects were in their 60° ± 7° post- operative day and had completely recuperated the articular mobility of the injured limb. Moreover all the subjects had been informed of the aim of the study and of the possible risks involved.

Protocol

Determination test for the EMG registration on a maximal isometric contraction.

Each subject asked to carry out 6 maximal isometric contractions for limb of the leg extensor muscles at the height of the thigh in open kinetic chain. The contractions lasted 5’’ with a standardized articular angle of the knee of 90°^{17 64}. The value of maximal isometric force (MIF) was registered by means of a strain gauge (Globusitalia, Treviso, Italy, Mod. Ergometer, sample rate 100 Hz, non linearity hysteresis and repeatability 0.02% of R.O, temperature compensated 0° to 50°, charge scale 0-300 kg). At the same time as the MIF was being registered a surface electromyography was carried out on the Vastus Medialis Oblique (VMO) and the Vastus lateralis (VL) of each limb. The electrodes (Neuro Line Disposable Neurology Elecrodes, Type 720-00-S Qty/Menge 25) were placed on both limbs in conformity with the positions indicated by Perotto and coll.⁴⁵. The registration of the EMG (IEMG) was carried out with a pair of bipolar electrodes positioned on the abdominal muscles 20 mm apart. The signal given by the electromyography apparatus (Ergo system EMG by Globusitalia, Treviso, Italy, 2000 Hz sample ratebandWith 25-500 Hz, sensibility 0,48 microV.) and by the strain gauge were synchronised and analysed using a programme designed specifically for this purpose (Ergometer Total Rehabilitation, Globus Italia).

The following values were thus calculated:

1. the maximal isometric force (MIF) given by the highest value of force reached on the force reached on the force —time scale after 900 ms of isometric contraction^{39 54}. This value was calculated for both limbs.

2. the difference of percentage of the MIF registered for each limb (D%F).

3. the integral of electromyography activity relative to the VMO and the VL (ò VMO, ò VL) both of the injured limb and the healthy one.

4. the electromyographic Ratio between VMO and VL (VMO/VL Ratio) obtained by using the relation between VMO and VL integrals of electromyographic activity. This value was calculated on both limbs.

4. the Ratio between the isometric force value and the total electromyographic activity (F/EMG Ratio) calculated by using the relation between the force integral with the sum of the integral of electromyographic activity of the VMO and the VL. This value was calculated on both limbs.

5. the difference of percentage between the sum of electromyographic surface of the VMO and VL registered for the healthy limb and the injured limb (D%ò VMO+ò VL).

6. the percentage difference between the electromyographic surface of the VMO of the healthy limb and the injured limb (D%ò VMO).

7. the percentage difference between the electromyographic surface of the VL of the healthy limb and the injured one (D%ò VL).

STATISTICS

Ordinary statistical indexes such as average, standard deviation and variance were calculated for each single variable and situation.

With Wilkoxon’s non parametric test the injured and the healthy limbs were compared and the the differences between the average values of the MIF, ò VMO, ò VL, VMO/VL Ratio and the F/EMG Ratio were recorded.

The percentage difference between the sum of the ò VMO and the ò VL of the healthy and of the injured limb (D% ò VMO+ò VL) was correlated with the percentage difference of the force recorded in the two limbs (D% F) using the Spearman’s rank order correlation coefficient.

Moreover, using again the Spearman’s rank order correlation coefficient the following values were correlated whether D%F with the difference between the values of the ò VMO (D% ò VMO) and the ò VL (D% ò VL) of both the healthy and the injured limb, or the values of the D% ò VMO and of the D% ò VL.

The level of statistical significance was fixed at p<00.5.

RESULTS

The MIF values recorded on the healthy and on the injured limb were equal to, respectively 681.90 ± 49.17 and 704.41 ± 174.83 N. The difference between the two values (D% F), equal to 30.27 ± 21.65%, resulted statistically significant (p<0.005).

The ò VMO values of the healthy and of the injured limb were respectively 1.82 ± 0.66 and 0.92 ± 0.39 mV· s. The difference equal to the 43.86 ± 27.93% resulted statistically significant (p<0.005).

The ò VL values of the healthy and of the injured limb were respectively 1.60 ± 0.42 and 0.98 ± 0.43 mV · s. The difference equal to 34.04 ± 12.25% resulted statistically significant (p<0.01).

The difference between the ò VMO and the ò VL values of the healthy limb, equal to 10.69 ± 6.58%, was statistically significant (p<0.01).

The difference between the ò VL and the ò VMO values of the injured limb, equal to 5.01 ± 3.65%, resulted statistically significant (p<0.05).

The VMO/VL Ratio between the healthy and the injured limb, equal respectively to 1.12 ± 0.08 and 0.95 ± 0.04, resulted statistically significant (p<0.006).

The F/EMG Ratio of the healthy and the injured limb equal respectively to 1071.30 ± 346.43 and 1308.80 + 310.54 [ N · s] · [ mV ·s] ^-1, is not resulted statistically significant.

The D % ò VMO + ò VL resulted positively correlated to the D%F (r = 0.80, p<0.004).

The D% ò VMO resulted positively correlated to the D%F (r = 0.97, p<0.001).

The D%ò VL resulted positively correlated to the D% F (r = 0.80, p<0.004).

The relation between the D%ò VMO and D% ò VL resulted statistically significant (r = 0.84, p<0.002).

DISCUSSION

After a surgical reconstruction of an isolated or associated injury of the ACL, the main causes of the knee’s instability are hypo-tonus and hypo-trophy of the femoral quadriceps, in particular of the VMO, which has suffered hypo-functioning consequent to the operation and is the most damaged

muscular region.^{8 48} It is also important to remember that VMO is the muscular district chiefly injured when the knee ligament apparatus is damaged³⁵. The VMO plays an important mechanical role in many sporting motions. In most movements directly connected with sports activities that involve running, the VMO carries out an important mechanical function, being particularly active when the athlete touches the ground after jumping^{11 12}, walks or runs laterally⁶⁷. It is the most important power generator during the push-off phases in speed-skating⁴ and also it is the most important force generator during isokinetic leg extensions at the height of the thigh³⁴. Finally during eccentric contractions the VMO is also much more active than the VL¹⁹. In addition to these considerations, in the functional ambit it is important to note that the VMO is the muscular region of the thigh that shows the greater signs of fatigue during the various movements carried out in sports activity that require an intense and prolonged muscular activity, both to healthy³⁸ and to injured subjects⁶¹ (suffering patellar pathology). Due to the fatigue phenomenon of the leg extensor muscles, the VMO presents a more important reflex response time in comparison to the VL, on the contrary in consequence to fatigue phenomenon the VL presents a quicker reflex response time⁶³. Given the importance of the VMO in the stability of the knee articulation, one of the main causes of distortion traumas, particularly in team sport activities (football, basketball, rugby) may be its fatigue.

In healthy subjects the physiological value of the EGM VMO/VL Ratio is usually considered equal to 1^{30 40 67}. Nevertheless, some studies record VMO/VL Ratio values between 1e 1.2^{13 66}, while others underline that the VMO/VL Ratio value is always extremely individualised⁶²and dependent on the articular angle²⁰. This study has collected data in line with the latest bibliography. The VMO/VL Ratio values recorded were, in fact, 1.12 ± 0.08 in the healthy limb and 0.95 ± 0.04 in the injured counterpart. The alteration in the VMO/VL Ratio value in the injured limb was related to a diminution of the surface IEMG both of the VMO (-43.86 ± 27.93%, p<0.005) and of the VL (-34.04 ± 12.25%, p<0.01), and to a parallel diminution of the MIF value (-30.27 ± 26.3%, p<0.005). Moreover, our results are in the line with the studies carried out on the force reduction¹⁶ and on the EMG signal ⁶¹ in subjects who showed the results of knee articular injuries.

The EMG signal is better recorded during an isometric contraction than during a dynamic movement. It is important to note that the absence of movement (or reduced movement and however only to onset phase of movement) of the muscles recorded in comparison to the surface electrodes , as in this study, eliminates a condition which would seriously compromise the reliability of the EMG signal^{49 50}. Moreover, in an isometric contraction, the EMG signal gives a linear relationship with the intensity of the force produced, whereas in a dynamic contraction the Force/EMG Ratio is curvilinear and is given by the sum of two indexes: the first corresponding to the spatial recruitment of MU and the second to the MU temporal recruitment⁶.

In this study the linearity between the EMG signal and the production of isometric force is evident and the relationship between DF% and ò VMO + ò VL shows a strong positive correlation (r = 0.80, p<0.004). It is very important to note that, since the relationships between DF% and ò VMO and between DF% and ò VL gives respectively a correlation index equal to 0.97 (p<0.001) and 0.80 (p<0.004), the loss of force in the injured limb is probably caused more by the diminution of the contractile capacity of the VMO in comparison to the VL. This datum is further confirmed by the significant statistical change in the VMO/VL Ratio of the healthy limb in comparison to the injured limb (1.12 ± 0.08 versus 0.95 ± 0.04, p<0.006). However, as the relation between D% ò VMO and D% ò VL is statistically significant (r 0 0.84, p<0.002), the reconstruction of the ACL, VL and VMO is always followed by functional suffering of VL and VMO but more intense in the VMO. Moreover, as the F/EMG Ratio of both limbs does not show variations statistically significant, we hypothesis that the diminution in force in the injured limb is caused not by a deficit within the expression of the contractile force produced, but just by the deficit within the UM spatial recruitment.

Literature has extensively reported the EMG Ratio variations between VMO and VL in the various knee articulation pathologies, giving particular attention to the subjects affected by patellar syndrome^{5 16 56}.Nevertheless, there are no studies backed by electromyographic researches which link muscular injuries mainly to the VMO after ACL reconstruction. In this particular context, the EMG research supplies the information needed to quantify, in an objective way, the muscular deficit caused by the hypo-functional period following the operation^{8 46 48 68}. For diagnostic and preventive purposes the comparison of the VMO/VL Ratio of the healthy and of the injured limb is very important too. The alteration of this latter causes a simultaneous alteration of the neuromuscular activation patterns which, in final analysis, may expose the neo- ligament to the risk of relapsing traumas, especially at the end of the rehabilitation period when the subject starts again to perform a sporting activity^{17 21}.

The simple reacquisition of force in the injured limb, tested through isometric, isotonic or isokinetic methodologies, does not ensure a parallel restoration of the neuromuscular activation patterns as these may be substantially different, since the forces recorded result equal just thanks to the compensating mechanisms of the muscles¹⁷. In an arthro-muscular context, a simultaneous dynamometric and electromyographic evaluation allows us to work with data much more complete and reliable.

Table 1: Subjects distribution in function of the practiced sport

Table 2: Subjects distribution in function to the suffered injury.

Abstract

Nel presente studio sono stati considerati 10 soggetti la cui età, peso ed altezza erano rispettivamente 25 ± 3 anni (media ± deviazione standard), 71.1 ± 6.5 kg, 179.7 ± 4.2 cm, tutti praticanti attività sportiva ed aventi subito una rottura isolata od associata del legamento crociato anteriore (LCA), trattata chirurgicamente tramite ricostruzione artroscopia

Ad ogni soggetto è stato richiesto di effettuare una serie di 6 contrazioni isometriche massimali della gamba sulla coscia con angolo articolare standardizzato a 90°, sia con l’arto leso che con il controlaterale sano, durante le quali è stato registrato, sia il valore di massima forza isometrica, sia il segnale elettromiografico di superficie del Vasto Mediale Obliquo (VMO), che dal Vasto Laterale (VL). Il deficit di forza a carico dell’arto leso è stato pari a al 30.27 ± 21.65% (p<0.005), la Ratio EMG VMO/VL dell’arto sano e dell’arto leso è stata pari rispettivamente a 1.12 ± 0.08 e 0.95 ± 0.04, la differenza è risultata statisticamente significativa (p< 0.006). I risultati mostrano come in seguito ad intervento ricostruttivo del LCA, si verifichi un deficit contrattile maggiore a carico del VMO rispetto al VL, che si traduce in una modificazione della Ratio EMG che è a sua volta indice di un’alterazione dei pattern di attivazione neuromuscolare.

A questo proposito è importante ricordare che una delle principali cause d’instabilità del ginocchio conseguente all’intervento ricostruttivo del LCA, in seguito ad una sua rottura isolata od associata, è costituita dall’ ipotonia e dall’ipotrofia del quadricipite femorale, ed in particolar modo del VMO, conseguente al periodo di ipofunzionalità successivo all’atto operatorio

Poter quindi comparare la Ratio VMO/VL dell’arto sano nei confronti del controlaterale leso appare soprattutto interessante a fini diagnostici e preventivi, un’alterazione di quest’ultima comporta infatti una contemporanea alterazione dei patterns di attivazione neuromuscolare che potrebbe, in ultima analisi, esporre il neo-legamento al rischio di recidiva traumatica, soprattutto nella fase in cui il soggetto praticante un’attività sportiva, alla fine del periodo riabilitativo, si riavvicini attivamente a quest’ultima. La semplice riacquisizione di forza dell’arto leso nei confronti del controlaterale sano, testabile attraverso modalità isometriche, isotoniche od isocinetiche, infatti non garantisce, a nostro parere, un parallelo ripristino dei patterns di attivazione neuromuscolare, che potrebbero essere comunque sostanzialmente diversi, anche in presenza di un’eguale espressione di forza, grazie a dei meccanismi muscolari di compenso. Una contemporanea valutazione dinamometria ed elettromiografia, permetterebbe invece di poter disporre di un quadro valutativo della situazione artro-muscolare sicuramente più completo ed attendibile.

Parole chiave: Elettromiografia , Legamento Crociato Anteriore, Vasto Mediale, Vasto laterale, Deficit Funzionale.

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