Effects of Hamstring Training in Different Modes on Stabilizing Knee Joints With Anterior Drawer Laxity
Condition: Knee Instability
Study type: Interventional

Summary: 
      Question: To investigate how different modes of thigh muscles strengthening exercises
      emphasizing the knee internal rotators can be as effective as possible in improving the
      static stability and agility of the knees with anterior drawer laxity.

      Design: Randomized controlled clinical trial.

      Participants and Interventions:

      Young men with anterior drawer laxity of the knee were randomly assigned to three
      experimental groups in different strengthening modes: plate-loaded squat press (SP),
      plate-loaded kneeling leg curl with internal rotation (KLCIR), and kneeling leg curl (KLC).
      The control group with stable knees received no training.

      Outcome measures: static and dynamic knee stability, isokinetic strength. The purpose of this
      paper was to find out an optimal solution to the enhancement of the static and dynamic knee
      stability to a great extent.

      Key words: anterior cruciate ligament; agility; knee stability; hamstring; knee internal
      rotator
    

Detailed description: 
      INTRODUCTION Anterior cruciate ligament (ACL) injuries are commonly seen among athletes,
      which eventually makes more or less devastating impacts on their performances. Although ACL
      injuries may result from the knee collision, 70% of them are due to noncontact movements,
      including abrupt brakes, changing directions at high speed (i.e. sidestep cuttings and
      crossover cuttings). In doing so, one must at first have his or her axial foot fixed on the
      ground to absorb the momentum oriented from the original direction. Insufficient eccentric
      muscles or ligament strength are likely to trigger muscle and ligament injuries.

      It is generally agreed that the risk of ligament injuries can be reduced by strengthening a
      specific muscle group by which the dynamic stability of the joint is able to be enhanced and
      the static stability provided by the ligament can also be compensated. Traditionally, the
      strengthening exercise of ACL rehabilitation has been putting an emphasis on the hamstring
      and quadriceps with an attempt to decrease the anterior drawer instability as well as the
      shearing force of ACL. Nonetheless, from the aforementioned pathomechanism of ACL injuries,
      the knee rotators should be valued as they are supposed to . The internal rotators of the
      knee joint (semitendinosus, semimembranosus and gracilis) are highly related to ACL
      injuries5. However, the knee rotator strength is often neglected and even sacrificed as an
      autograft for the ACL reconstruction .

      Modifications can be made in progressive resistance exercise for strengthening knee internal
      rotators. In this current study, 20 subjects with anterior drawer laxity were randomly
      assigned to three groups adopting different training modes: plate-loaded squat press (SP),
      plate-loaded kneeling leg curl with internal rotation (KLCIR), and plate-loaded kneeling leg
      curl (KLC). Static stability, dynamic stability, and isokinetic strength were measured. The
      purpose of this paper was to find out an optimal solution to the enhancement of the static
      and dynamic knee stability to a great extent.

      MATERIALS AND METHODS Subjects The research program was approved by the Human Subject
      Committee in Taipei Physical Education College. Knee joint laxity was surveyed by a KT-2000
      test (MED Metric Co., San Diego, USA) in the Department of Physical Education and Health at
      Taipei Physical Education College. The anterior drawer laxity of the knee joint in this study
      was defined as anterior displacement over 3 mm discrepancy between bilateral knee joints by a
      KT-2000 test under 20-pound force. According to this criterion, Dale M. et al. demonstrated
      that 85% (33/39) of this population have complete ACL tears and 15% (6/39) have partial tear.
      One hundred and seventy-three students were tested and 30 met the criterion, including 22
      males and 8 females, although no obvious trauma history was available in some of them. Two
      males were excluded due to other causes that might affect muscle strength or knee stability
      such as lower limbs fracture and arthritis. Besides, eight female students were eliminated to
      avoid possible gender difference. Twenty male students were included in the experimental
      group. Another 8 male students with stable knees without any medical history of knee injuries
      were included in the control group. The participants in both experimental and control groups
      lived a sedentary lifestyle. Stable knees were defined as a discrepancy less than 1.5mm
      between bilateral knees by a KT-2000 test under 20-pound force.

      Flow Path Twenty subjects in the experimental group were randomly assigned into three groups:
      SP (n=7), KLCIR (n=7) and KLC (n=6). Eight control subjects neither received any training nor
      was engaged in body-building on their own during the training period. Every subject was asked
      to fill in basic information, including age, body height, and body weight. Before the
      experiments, the flow path was explained to each subject who had already signed an
      informed-consent form.

      The experimental procedure was divided into three phases. The first and the third phases were
      the tests before and after training respectively, including KT-2000, agility, and isokinetic
      strength assessment. The second phase was the training phase.

      Static Stability (Laxity) The KT-2000 knee ligament arthrometer (MED Metric Co., San Diego,
      USA) is designed to assess the anterior drawer laxity of the knee joint. The discrepancy of
      anterior displacement between the sound side and the lesion side had been reported and
      applied in evaluating the static stability of the knee, and it was also used as one of the
      references for the ACL reconstruction surgery. In this current study, a discrepancy less than
      1.5mm was normally accepted when 20-pound anterior traction force was exerted on the tibia
      with the knee joint in 20° flexion. In contrast, ACL laxity was defined as a discrepancy over
      3mm, which was highly related to ACL injury.

      Dynamic Stability (Agility) Dynamic knee stability was assessed by agility, which was
      measured by a 6-meter left-and-right shuttle run. A good dynamic knee stability is necessary
      for changing the movement direction. Each subject started running from the midline to the
      left terminal and then stepped on the square with his left foot. Then, the subject used the
      left leg as the axis and turned around to the right side. The subject then ran to the right
      terminal. Once the front foot was crossing the midline, this was the first round for testing
      the agility of left knee. The subject kept running to the right terminal without stopping on
      the midline, stepping on the square with his right foot, turning around to the left side, and
      running toward the left terminal. This was the first round of right knee test as the
      subject's front foot crossed the midline. Whenever the front foot crossed the midline, a
      timer was clocked. The time interval in seconds between the 1st and the 2nd time clocked was
      the 1st measure of the left knee agility, and the time interval between the 2nd and the 3rd
      was the 1st measure of the right knee agility, and so forth. There were five-round tests for
      the agility of right and left knees respectively. Three raters were assigned respectively at
      the midline, right and left terminals. Single-blind method was adopted. That is, all the
      three raters did not know which group the subject was assigned to. The square at the right or
      left terminal ends was 10 inches wide and 3 meters away from the midline. It would be
      recognized as a qualified round if the plantar surface of the foot ever contacted any part of
      the square; otherwise, the subject would be asked to repeat the whole set consisting of five
      rounds. Three sets were collected and averaged. The rest interval between each set should be
      long enough for the examinee to feel relaxed before the next set. The subject was asked to
      run as fast as possible. The average time difference of 3 sets between the affected and the
      sound side was regarded as the dynamic stability of the affected side. The greater the
      difference was, the poorer the dynamic stability or the agility would be. A practice session
      was given prior to the actual beginning of the study to avoid learning effect.

      Prior to the study, intrarater test-retest reliability was established. Nine subjects,
      including four in the experimental groups and five in the control group, took the agility
      exam twice in separated days. The intraclass correlation coefficient was 0.78.

      Isokinetic Strength Cybex NORM (Cybex International, Inc, Ronkonkoma, New York, U.S.A.) was
      employed to evaluate isokinetic muscle strength before and after training. Tests were
      conducted in two different motion modes which included the flexor/extensor and the internal
      /external rotator. In the former, the range of motion was set in the range of 0-90°. Maximal
      concentric force had been performed for five times at the angular velocity of 60°, 120° and
      180° per second, respectively. Peak torque was taken to represent muscle strength. Only
      smooth and similar curves with a peak torque which was no less than 90% of the maximum would
      be taken. The assessment of isokinetic strength of internal/external rotator was generally
      similar to flexor/extensor. The ankle joint was fixed into 30° dorsiflexion with an
      air-stirrup ankle brace (Aircast, Summit, NJ) to limit unnecessary inversion/eversion
      movement, which might affect measurement of knee joint rotation. In addition, the knee and
      hip joints were kept in 90°, and the range of motion of knee rotation was set in the range
      between 25° internally and 35° externally.

      Training Modes Three training modes were chosen. (Ⅰ) SP (or called angled leg presses); (Ⅱ)
      KLCIR; (Ⅲ) KLC. The training phase had been lasting for 6 weeks in which none dropped out.
      Each subject had to accomplish three training workouts weekly under supervision by licensed
      athletic trainers. A workout contained five sets for each lower limb, which were composed of
      20 (repetitions)×60% (1RM), 15×65% , 12×70% , 8×75% and 20×60% with a two-minute resting
      interval between each set. During the six-week rehabilitation course, they were not allowed
      to involve in any other regular fitness activities or sports.

      Data Analysis Data are expressed as mean±SEM. SPSS version 12.0 Windows was used for
      statistic analysis. Nonparametric analysis, including Kruskal-Wallis Test, Wilcoxon Test and
      Mann-Whitney test, was applied. Significance was defined as P<0.05. Intrarater reliability
      was assessed with intraclass correlation coefficient.
    

Intervention name(s): plate-loaded kneeling leg curl with internal rotation; plate-loaded squat press; plate-loaded kneeling leg curl
Intervention type(s): Other; Other; Other
Intervention description(s): The participant was instructed to point toes toward medial side as knee flexing. This is an open-kinetic chain (OKC) exercise and medial hamstring was emphasized.; The subject was instructed to position his back properly against the backrest on a machine, with the feet slightly apart. He was instructed to place his feet higher on the foot plate and draw his two knees as close as possible while the knees flexed so that medial hamstring would supposedly bear more tension in the course of knee flexion. This is a closed-kinetic chain (CKC) exercise and was expected to strengthen the quadriceps and hamstring with medial hamstring emphasized.; An open-kinetic chain (OKC) exercise was intended to strengthen the hamstring muscle without lateralization emphasized.
Other intervention name(s): angled leg presses
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: anterior cruciate ligament; agility; knee stability; hamstring; knee internal rotator