Isokinetic assessment of the flexor-extensor balance of the knee in athletes with total rupture of the anterior cruciate ligament

Avaliação isocinética do equilíbrio flexo-extensor do joelho nos atletas com ruptura total do ligamento cruzado anterior

ORIGINAL ARTICLES

ISOKINETIC ASSESSMENT OF THE FLEXOR-EXTENSOR BALANCE OF THE KNEE IN ATHLETES WITH TOTAL RUPTURE OF THE ANTERIOR CRUCIATE LIGAMENT

Antonio Sérgio A. P. Terreri, Marco A. Ambrósio, André Pedrinelli, Roberto F.M. Albuquerque, Felix Andrusaitis, Júlia Maria D. Greve, João G. Carazzato and Marco Martins Amatuzzi

RHCFAP/2958

TERRERI, A . S. A . P. et al. - Isokinetic assessment of the flexor-extensor balance of the knee in athletes with total rupture of the anterior cruciate ligament. Rev. Hosp. Clín. Fac. Med. S. Paulo 54 (2): 35-38, 1999.

SUMMARY: The purpose of this study was to assess the flexor-extensor group of muscles of the knee in young athletes diagnosed with a total rupture of the anterior cruciate ligament (ACL). Eighteen knees of 18 athletes (14 men and 4 women) with an average age of 21.6 years (range 16-32 years) were assessed with a Cybex 6000 model isokinetic apparatus. The average interval between occurrence of the injury and assessment was 10.2 months (range 2 - 48 months). There was an associated meniscal injury in eight of the knees. Athletes with any other kind of associated injury, limitation, or blockage of the movement of the joint, significant pain during the exam, or interval between injury and exam of less than two months were excluded from the study. The parameters studied were the peak torque-velocity and flexor-extensor relationships at the constant angular velocities of 60°/sec and 240°/sec. Previous warming-up was done by means of an ergometric bicycle and adaptation with 3 submaximal repetitions. The contra-lateral side, which presented no injury, was used as control.

Peak torque (PT) at the constant velocity of 60°/sec was greater than that at 240°/sec for knees with and without injuries. However, there was no significant difference between the injured and uninjured sides at 60°/sec or at 240°/sec.

The average value for the flexor-extensor relationship at 60°/sec on the injured was 60% (( 6), compared to 57% (( 10) on the contra-lateral side. At 240°/sec, the average value was 75% ((10) on the injured side, and 65% ((12) on the contra-lateral side.

In conclusion, despite the complete rupture of the ACL of one knee, the average values for the flexor-extensor relationship were similar on the injured and uninjured sides at the velocity of 60°/sec. As the velocity increased, an increase in the values for the flexor-extensor relationship of the knee also occurred, indicating a tendency of the performance of the flexor muscle group to approach that of the extensor muscle group, and this tendency was more pronounced on the side of the injury.

DESCRIPTORS: Isokinetic assessment. Knee. Anterior cruciate ligament. Sport. Muscular strength and balancy.

Agonistic-antagonistic functional equilibrium is an important parameter in sports performance. Injuries of the static stabilizing mechanisms, such as those of the ligament complex, may also harm the dynamic stabilizing function or muscle/tendon segment. Athletes with injuries of the ligaments, such as a partial or total rupture of the anterior cruciate ligament (ACL) due primarily to twisting, often become restricted in their physical activities. Once such athletes are injured by situations involving pain, edema, muscular hypotrophy, instability, and limitations of the movement of the joint, their sporting activity becomes limited, and they develop muscular imbalance, which may then lead to a disproportion between the agonistic -antagonistic muscles^1,2,4,5.

The isokinetic apparatus is a dynamometer with a computerized system, which is used both for the assessment of muscular equilibrium and for rehabilitation of the injuries of the locomotive apparatus. This assessment is made by comparing the right muscular group ith the left, as well as by determining the agonistic and antagonistic balance relationship. The individual makes a muscular effort, and the machine permits arcs of movement at a constant angular velocity, regardless of the degree of effort made. The assessor determines the velocity in degrees per second. Angular velocities vary between 30°/sec and 300°/sec and may be considered slow (<180°/sec) or rapid (³180°/sec). The parameters for analysis by isokinetic assessment include peak torque (PT), which is the result of the effort multiplied by the distance measured in newton-meters (N); the muscular work undertaken (joule); and the power, which is the work done divided by time (watt).

In the present study, the equilibrium of forces of the flexor-extensor muscle group of the knee in young athletes with a complete rupture of the ACL was assessed using an isokinetic apparatus.

MATERIALS AND METHODS

At the "Grupo de Medicina Esportiva" and in the laboratory of the "Área de Estudos do Movimento of the Instituto de Ortopedia e Traumatologia do Hospital das Clínicas da Universidade de São Paulo", 18 knees of 18 athletes (14 men and 4 women) with a complete injury of the ACL were assessed with a Cybex 6000 model isokinetic apparatus between January 1997 and March 1998 (Figure 1). The injuries occurred in a variety of sports: soccer (8), judo (4), basketball (2), handball (1), volleyball (1), rowing (1), "capoeira" (an Afro-Brazilian martial art-dance) (1).

1 - Isokinetic assessment of knee with Cybex 6000

The average age of the athletes was 21.6 years (range 16-32 years), and right side was injured in 13 of the athletes. The average time lapse between the occurrence of the injury and the isokinetic assessment was 10.2 months (range 2-48 months).

The athletes were all properly enrolled with sporting federations and had been participating actively in training sessions and competitions up to the time of the injury. The majority reported having received some previous conservative treatment in some other health service. Some even reported having resumed some kind of sporting activity.

The diagnosis of the total rupture of the ACL was based on positive Lachman and pivot shift tests and surgical findings. The test with the Cybex apparatus was undertaken as a pre-operative assessment for the reconstruction of the ACL a patellar tendon autograft. There was associated meniscal injury in eight of the knees. Athletes with any other type of associated injury, limitation or blockage of the range of the motion of the joint, considerable pain during the exam, or time since the occurrence of the injury of less than 2 months were excluded from the study.

The parameters studied were the peak torque (PT) and the flexor-extensor relationship of the maximum torque, which is the calculation of the maximum torque of the hamstrings divided by that of the quadriceps. The constant angular velocities established were 60/sec (3 concentric repetitions) and 240/sec (20 concentric repetitions). Guidance was given as to the warm-up preparation prior to the examination with the use of the ergometric bicycle (5 minutes), stretching, and the performance of 3 submaximal isokinetic repetitions. Each athlete, placed in a sitting position with stabilizers for the trunk and with thigh and shin pads, made extension and flexion movements ranging between 0º and 90º. The uninjured contra-lateral knee was used as control.

The average, standard deviation, and Student's t test were used for the statistical assessment of the comparison between the injured and uninjured sides with significance at p<0.05.

RESULTS

Tables 1 and 2 show the values of the maximum effort represented by the peak torque at the constant angular velocities of 60°/sec and 240°/sec, for both the flexor and the extensor groups of the knees with and without injury.

At the velocity of 60°/sec, the average values of PT for both the flexors and the extensors were lower on the side with the injury, but this difference was not significant.

At the velocity of 240°/sec, average values of PT were lower for the extensors, but slightly higher for flexors, on the side with the injury. However, these values were not significantly different from the control values.

Greater values of PT occurred at the angular velocity of 60º/sec than at 240º/sec for both the injured and uninjured sides.

The average value for the flexor-extensor relationship at 60º/sec on the side with the injury (60%) was slightly greater than that for the side without the injury (57%), but was not significantly different. At 240°/sec, there was a significant difference in the flexor-extensor relationship for the injured side (75%) compared with the uninjured side (65%) (p< 0.01). It was noted that the greater the angular velocity, the smaller was the difference in PT values between the flexors and the extensors, indicating a tendency on the part of the flexor muscle group to approximate to that of the extensor muscle group at higher angular velocities.

The values for peak torque for the flexor and the extensor groups are used to calculate the flexor-extensor relationship, given as a percentage, permitting a quantitative assessment of the degree of equilibrium between the agonistic and the antagonistic musele groups (Table 3).

DISCUSSION

This study describes objectively and precisely determined values for the degree of muscular equilibrium prior to the reconstruction of the ligaments of young, competitive athletes who had a total rupture of the ACL. The average lapse of 10 months between the occurrence of the injury and the examination was a relatively short time in terms of the evolution of chronic injuries. Because of the study's inclusion criteria, the assessment was independent of the effects of pain and limitations of range of motion or joint blocking factors. The meniscal injury in 8 knees did not impede the examination.

Proper execution of the assessment requires adequate prior explanation, warm-up, stretching, and submaximal repetitions. Also important is the correct positioning of the fulcrum. The axis for the movement of the knee should be the same as that of the axis of the machine. Attention to these details ensures the reliability of the data obtained.

Reports regarding the flexor-extensor relationship in knees with no injury normally vary between 55% and 77%^2,3. Stafford & Grana⁶ wrote that dominant knees with no injury in American football players had flexor-extensor relationships of 67% and 82% at the velocities of 90º/sec and 300º/sec, respectively. The difference between the dominant and non-dominant sides was not significant. Harilainen et al. showed that patients with ACL deficiency with an average time of lapse from injury to evaluation of 2.7 years had flexor-extensor relationships of 66% and 82% at the velocities of 60º/sec and 180º/sec, respectively. They found similar PT values for injured and uninjured sides at velocities of 60º/sec and 240º/sec. There was a slight, non-significant tendency for lower PT values on the side of the injury, except for the flexors at 240º/sec. On the other hand, some studies show that there is deficit in the muscle strength of the knee with insufficiency of ACL^4,7. These authors found a significant difference in the flexor-extensor relationship between injured and uninjured knees at 240°/sec, due to a lower value for the quadriceps and a greater one for the hamstrings in the side with the injury. However, at 60º/sec, they found no difference between injured and uninjured sides. On the other hand, at the velocity of 240º/sec, the quadriceps on the injured side exerted a significantly lower maximum torque than that exerted by the hamstrings. However, these values are within the normal range^2,3,6.

These studies show that the higher the angular velocity, the smaller the PT achieved, for both the extensors (quadriceps) and the flexors (hamstrings), regardless of whether the knee had a total rupture of the ACL. They also show that the values for flexor-extensor relationship are greater when the angular velocity increases.

The absolute values of the moment of effort (torque) are lower, because the time necessary for the neurological activity on the muscle fiber is reduced due to the greater angular velocity. Therefore, in measurements of increasing velocity, the flexor-extensor relationship tends to increase as the flexors tend to become equal in strength to the extensors. However, there are reports that even rehabilitated subjects with ACL insufficiency who have attained adequate degrees of muscular balance can experience episodes of instability and of perpetuation of instability in knees. ^3,4.

For athletes who must undergo reconstruction of the ACL to achieve a stable knee for participation in competitive sports, testing with the isokinetic apparatus provides pre- and post-operative quantitative assessment of the muscular equilibrium. Isokinetic testing should be conside red for athletes diagnosed with total rupture of the ACL if there is nothing impeding the examination, such as pain, blockages, or limitation of the range of motion of the joint.

CONCLUSION

We observed that peak torque at the angular velocity of 60°/sec was greater than that at 240°/sec regardless of the presence of the ACL injury. There was no significant difference between the side with and without the injury at either 60°/sec or 240°/sec.

The values for the flexor-extensor relationship were similar at the velocity of 60°/sec on both the injured and uninjured sides. As the velocity increased to 240°/sec, the values for the flexor-extensor relationship increased, with a more pronounced tendency on the injured side for the performance of the flexor muscle group to approximate that of the extensor muscle group.

RESUMO

RHCFAP/2958

TERRERI, A. S. A . P. - Avaliação isocinética do equilíbrio flexo-extensor do joelho nos atletas com ruptura total do ligamento cruzado anterior. Rev. Hosp. Clín. Fac. Med. S. Paulo 54 (2): 35 - 38, 1999.

O objetivo desse estudo foi avaliar o grupo muscular flexo-extensor do joelho de esportistas jovens que tiveram diagnóstico de ruptura completa do ligamento cruzado anterior (LCA). Dezoito joelhos de 18 atletas (14 homens e 4 mulheres) com idade média de 21,6 anos (16 - 32) foram avaliados com aparelho isocinético modelo Cybex 6000. O intervalo médio entre a lesão e a avaliação foi de 10,2 meses (2 - 48). Houve lesão meniscal associada em oito joelhos. Demais atletas com outro tipo de lesão associada, limitação ou bloqueio da amplitude articular, dor importante durante o exame e tempo de lesão com menos de dois meses foram excluídos do estudo. O parâmetro estudado foi o pico de torque (PT) e a relação flexo-extensora do PT nas velocidades angulares constantes de 60º/seg e 240º/seg . Foi realizado um aquecimento prévio com bicicleta ergométrica e adaptação com três repetições submáximas. O lado contra-lateral, que não apresentava lesão, foi usado como controle.

O PT na velocidade constante de 60°/seg foi maior do que na velocidade de 240°/seg, seja nos joelhos com ou sem lesão. Não houve diferença significante entre o lado com e sem lesão, tanto a 60°/seg como a 240°/seg.

O valor médio da relação flexo-extensora do PT na velocidade de 60º/seg no lado com lesão foi de 60 % (± 6) e no lado contra-lateral 57 % (±10). A 240º/seg no lado com lesão foi de 75 % (± 10) e no contra-lateral foi de 65 % (± 12).

Como conclusões observou-se que os valores do equilíbrio flexo-extensor foram semelhantes na velocidade de 60º/seg, apesar da ruptura completa do LCA. À medida que ocorreu aumento da velocidade, ocorreu também um aumento da relação flexo-extensora do joelho, indicando leve tendência do grupo muscular flexor se aproximar do extensor, mais pronunciada no lado com lesão.

DESCRITORES: Avaliação isocinética. Joelho. Ligamento cruzado anterior. Esporte. Força e equilíbrio muscular.

Received for publication on the 05/10/98

Study undertaken at the "Grupo de Medicina Esportiva" and at "Área de Estudos do Movimento" of the LIM-41 - IOT HCFMUSP "Departamento de Ortopedia e Traumatologia da Faculdade de Medicina da Universidade de São Paulo".

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Publication Dates

• Publication in this collection
  31 Aug 2000
• Date of issue
  Apr 1999

History

• Received
  05 Oct 1988