The effect of joint velocity on the contribution of the antagonist musculature to knee stiffness and laxity

The electromyographic (EMG) coactivation patterns of the knee flexors and extensors when acting as antagonists were studied as a function of limb velocity to assess their contribution to joint stiffness and laxity. Normalized antagonist coactivation patterns developed from surface EMG recordings from the hamstrings and quadriceps during maximal effort isokinetic extension and flexion, respectively, demonstrated characteristic variations as the joint velocity increased from 15 deg/sec up to 240 deg/sec. The two-tailed t-test (P less than 0.01) was performed on the data obtained from eight normal knees. The results indicate that both hamstrings and quadriceps demonstrate a significant increase (greater than 100%) in their antagonist coactivation pattern during the final 40 degrees of fast extension and flexion movements, respectively, as limb velocity increases. A minor decrease in antagonist activity of the hamstrings (24%) and quadriceps (8%) was evident during the initial phase of the extension and flexion movements, respectively, as joint velocity increased. We concluded that as limb velocity is increased, there is a substantial reflexive (unintentional) increase in the contribution of the antagonist musculature to joint stiffness and reduction of laxity. The results also suggest that strength training of the hamstrings (rather than quadriceps) should be considered as a modality for conservative treatment of ACL deficiencies, as well as an adjunct to surgical reconstruction. Such training can also reduce the risk of high performance athletes in a reflexive manner by increasing joint stiffness.     

Mechanisms responsible for the age-associated increase in coactivation of antagonist muscles

Age alters the control of voluntary movement. A frequently observed adaptation is the increased agonist and antagonist muscle coactivation. Here we examine the evidence for spinal circuits mediating this change in motor behavior and propose the hypothesis that cortical mechanisms also contribute to this age-associated change in muscle coactivation.     

Muscular fatigue, maximum strength an stress reactions of the shoulder musculature in paraplegics.

In paraplegic patients, shoulder complaints attributable to muscle dysbalances arising from the particular daily form of exercise are often observed. The goal of therapy is to correct these imbalances through muscular training, whereby eccentric exercise might offer advantages due to lower fatigue with concurrent higher maximum strength. This study therefore examines muscle fatigue, maximum strength, and suitability for paraplegics of eccentric exercise of the shoulder. Muscle fatigue, isokinetic peak torque, and EMG activity were determined eccentric (Ecc) and concentric (Con) in 41 paraplegic subjects (13 early rehabilitants; 16 trained in wheelchair sports; 12 untrained). Serum CK, myoglobin, and subjective pain were collected for one week after exercise. In eccentric exercise, there was less muscle fatigue in all groups. Highest Ecc/Con peak torque ratio was found in trained subjects in all movements, followed by the untrained and the early rehabilitants. EMG-activity was lower in eccentric compared to concentric exercise (Ecc/Con ratio <1). CK and myoglobin concentrations, like pain symptoms, showed a marked increase after exercise. It is concluded that the Ecc/Con strength patterns among paraplegics are altered. Eccentric exercise offers advantages on the basis of lower muscular fatigue independent of training status and lesion time and higher maximum strength with increasing duration of paraplegia and additional athletic training. However, due to structural damage and subjective pain eccentric exercise can only be recommended with reservations in therapy and training.     

Interaction between age and gait velocity in the amplitude and timing of antagonist muscle coactivation

Old adults execute single-joint voluntary movements with heightened antagonist muscle coactivation and altered timing between agonist and antagonist muscles. It is less clear if old adults adopt similar strategies during the most common form of activity of daily living, gait, and if age and gait velocity interact. We compared antagonist muscle activation amplitude and onset, offset, and activation duration of the vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius lateralis from surface EMG in 17 young (age 19–25) and 17 old adults (age 71–85) while walking at 1.2, 1.5, and 1.8 m/s. All participants were healthy and highly mobile. The activation level of the four muscles when each acted as the antagonist was, on the average, 83% higher in old vs young adults (for each muscle p < 0.05). In two of four muscles this activation increased with gait velocity in young but not in old adults. The inter-burst interval between TA and GL was two-fold (83 ms) longer in young vs old adults and at higher gait velocities it became 14% (24 ms) shorter in young but 51% (31 ms) longer in old adults (interaction, p = 0.015). It is concluded that there is an interaction between age and gait velocity in the amplitude and timing of antagonist muscle coactivation.     

The arcuate ligament revisited: role of the posterolateral structures in providing static stability in the knee joint

Purpose

To determine the involvement of the posterolateral structures including the lateral collateral ligament, the popliteus muscle–tendon unit, the arcuate ligament (popliteofibular ligament, fabellofibular ligament, popliteomeniscal fascicles, capsular arm of short head of the biceps femoris and anterolateral ligament) and the posterior cruciate ligament in providing restraint to excessive recurvatum, tibial posterior translation and external tibial rotation at 90° of flexion.

Methods

Ten fresh-frozen cadaveric knees were tested with dial test, posterior drawer test and recurvatum test. The values were collected, using a surgical navigation system, on intact knees, following a serial section of the posterolateral corner (lateral collateral ligament, arcuate ligament and popliteus muscle–tendon unit), followed by the additional section of the posterior cruciate ligament.

Results

The mean tibial external rotation, recurvatum and posterior drawer were, respectively, measured at 9° ± 4°, 2° ± 3° and 9 ± 1 mm on intact knees. These values increase to 12° ± 5°, 3° ± 2° and 9 ± 1 mm after cutting the lateral collateral ligament; 17° ± 6° (p < 0.05), 3° ± 2° and 10 ± 1 mm after sectioning the arcuate ligament; 18° ± 7°, 3° ± 2° and 10 ± 1 mm after sectioning the popliteus muscle–tendon unit and 27° ± 6° (p < 0.05), 5° ± 3° (p < 0.05) and 28 ± 2 mm (p < 0.05) after the additional section of the posterior cruciate ligament.

Conclusion

Among the different structures of the posterolateral corner, only the arcuate ligament has a significant role in restricting excessive primary and coupled external rotation. The popliteus muscle–tendon unit is not a primary static stabilizer to tibial external rotation at 90° of knee flexion. The posterior cruciate ligament is the primary restraint to excessive recurvatum and posterior tibial translation. The posterior cruciate ligament and the arcuate ligament have predominant role for the posterolateral stability of the knee. The functional restoration of these ligaments is an important part of the surgical treatment of posterolateral ligamentous injuries.     

The effect of the squat exercise on knee stability

Past studies have produced conflicting results as to the effect of squat exercises on knee stability. One hundred male and female college students were measured using a knee ligament arthrometer on nine tests of knee stability. Over an 8-wk training program, full or half squats did not consistently affect knee stability compared to non-squatting controls. To measure the effect of long-term squat training 27 male powerlifters (14 Elite or Master Class) and 28 male weightlifters (8 Elite or Master Class) were measured on the same tests. Powerlifters were significantly tighter than controls on the anterior drawer at 90 degrees of knee flexion. Both powerlifters and weightlifters were significantly tighter than controls on the quadriceps active drawer at 90 degrees of knee flexion. Data on powerlifters and weightlifters were also analyzed by years of experience and skill level. No effect of squat training on knee stability was demonstrated in any of the groups tested.     

Muscular tension significantly affects stability in standing posture

BackgroundMuscular co-contraction is a strategy commonly used by elders with the aim to increase stability. However, co-contraction leads to stiffness which in turns reduces stability. Some literature seems to suggest an opposite approach and to point out relaxation as a way to improve stability. Teaching relaxation is therefore becoming the aim of many studies letting unclear whether tension or relaxation are the most effective muscular strategy to improve stability. Relaxation is a misleading concept in our society. It is often confused with rest, while it should be addressed during stressing tasks, where it should aim to reduce energetic costs and increase stability. The inability to relax can be related to sub-optimal neuro-motor control, which can lead to increased stresses.Research questionThe objective of the study is to investigate the effect of voluntary muscle contraction and relaxation over the stability of human standing posture, answering two specific research questions:(1) Does the muscular tension have an impact on stability of standing posture?(2) Could this impact be estimated by using a minimally invasive procedure?MethodsBy using a force plate, we analysed the displacement of the center of pressure of 30 volunteers during state of tension and relaxation in comparison with a control state, and with open and closed eyes.ResultsWe found that tension significantly reduced the stability of subjects (15 out of 16 parameters, p < 0.003).SignificanceOur results show that daily situations of stress can lead to decreased stability. Such a loss might actually increase the risk of chronic joint overload or fall. Finally, breathing has direct effect over the management of pain and stress, and the results reported here point out the need to explicitly explore the troubling fact that a large portion of population might not be able to properly breath.     

Sensorimotor control of knee stability. A review

Traditionally, the concept of joint stability considered the displacement (or subluxation) of two bones relative to each other as the measurement index, and attributed the preservation of such stability in its physiologic range to the various ligaments associated with the joint. Although the ligaments are indeed the major restraints of any joint, the significant contribution of the musculature toward joint stability had been grossly overlooked or neglected until the last 15 years. The value and importance of muscular activity in that role becomes immediately apparent if one performs even a superficial functional comparison of muscles and ligaments. Ligaments are passive viscoelastic structures, whereas muscles are dynamic viscoelastic organs. The viscoelastic effects of the ligaments are activated and applied strictly upon the geometric and kinematic configuration of the joint traversing through its range of motion according to fixed force-displacement relationships. The musculature, however, can apply passive viscoelastic effects to the joint when not active (passive tone) and variable dynamic viscoelastic effects when contracting under voluntary or reflexive control, and at any desirable point in the range of motion and in response to joint speed, external load, gravity, pain, and so forth, while executing the functional objective of the movement set by the individual. Preservation of joint stability cannot be ascribed to the ligaments alone, but should be considered as a synergistic function in which bones, joint capsules, ligaments, muscles, tendons, and sensory receptors and their spinal and cortical neural projects and connections function in harmony. The objective of this report is to first review the anatomy and physiology of the various mechanoreceptors and their neural pathways about the joint, and describe some of the current concepts of the reflex arcs elicited by such receptors, with special emphasis on biomechanical outcomes relative to stability. The role of the musculature in maintaining stability while controlling joint motion is then reviewed, with data obtained from experiments performed on humans and animals. Finally, some clinical findings from patients with anterior cruciate ligament deficiency using a brace that simulates the ligament-muscle functions is described.     

The synergistic action of the anterior cruciate ligament and thigh muscles in maintaining joint stability

The synergistic action of the ACL and the thigh muscles in maintaining joint stability was studied experimentally. The EMG from the quadriceps and hamstring muscle groups was recorded and analyzed in three separate experimental procedures in which the knee was stressed. The test revealed that direct stress of the ACL has a moderate inhibitory effect on the quadriceps, but simultaneously it directly excites the hamstrings. Similar responses were also obtained in patients with ACL damage during loaded knee extension with tibia subluxation, indicating that an alternative reflex arc unrelated to ACL receptors was available to maintain joint integrity. The antagonist muscles (hamstrings) were clearly demonstrated to assume the role of joint stabilizers in the patient who has a deficient ACL. The importance of an appropriate muscle-conditioning rehabilitation program in such a patient is substantiated.     

The role of the high tibial osteotomy in the unstable knee

High tibial osteotomy is an accepted treatment option for knee arthrosis in association with coronal malalignment. However, the effect of this procedure on the sagittal balance of the knee has until recently been largely ignored. Basic science research over the past several years and some small clinical series have introduced a "novel" concept whereby the sagittal balance of a ligament deficient knee can be restored to some degree by altering the posterior tibial slope. This review summarizes the available evidence supporting the role of selective high tibial osteotomy in the treatment of both the acute and chronic ligament deficient knee.     

浮膝损伤中膝关节稳定性的恢复与重建

目的 探讨浮膝损伤中骨和韧带等稳定装置的恢复与重建的方法和疗效. 方法 对2000年1月-2006年1月我院收治的38例浮膝损伤合并急性膝关节不稳患者的治疗方法进行总结,评定术后疗效. 结果 38例患者术后均得到随访,时间1～4年,平均1.5年,骨折均愈合.术后伤口感染3例,内固定松动2例,前交叉韧带松弛1例,骨关节炎2例.按照改良美国特种外科医院(Hospital for Special Surgery,HSS)系统评价膝关节功能:优良32例,中上5例,下中1例,优良率占84%. 结论 浮膝损伤治疗中不仅仅要重视骨结构连续性的重建,更要重视韧带、半月板、关节囊、肌肉等稳定结构的恢复.     

Cross-training effects of a proprioceptive neuromuscular facilitation exercise programme on knee musculature

ObjectivesTo examine the cross-training effects of a proprioceptive neuromuscular facilitation training (PNF) program on peak torque and endurance.DesignFactorial design.ParticipantsTwenty-three males were assigned to a PNF group (n=12) or a control group (n=11).InterventionsThe PNF program included training of the knee extensor and flexor muscles for a period of 8 weeks, exercising three times a week. PNF training included performance of knee movements through range of motion against manual resistance.Main outcome measuresIsokinetic torque and fatigue of the knee flexors and extensors at 60, 180 and 300° s⁻¹ were assessed prior to and immediately after the training period.ResultsAnalysis of variance designs indicated that the PNF group demonstrated significant gains (9.9%) in knee extension torque of the contralateral leg. In contrast, no cross-training effects on peak flexion torque was observed.ConclusionsCross-training effects after PNF exercise were restricted to the knee extensor muscles. Such effects may be important when the aim of a rehabilitation program is to improve the knee extensor muscle function of an immobilized contralateral leg.     

Knee stability in orthotic knee braces

The ability of six commercially available orthotic knee braces to stabilize ligamentous injuries of the knee was evaluated using fresh cadaver specimens. Anterior, valgus, and rotational forces were applied to the intact knee, after the anterior cruciate and medial collateral ligaments were cut, and after application of the knee braces. Bony displacement was measured using half pins and an external fixator applied to the tibia and femur. There was a significant difference in brace performance, most likely due to differences in brace design. Of the six braces tested, the 3D 3-Way Brace provided the greatest knee stability.     

The effect of proprioceptive knee bracing on knee stability after anterior cruciate ligament reconstruction

BackgroundInjury to the anterior cruciate ligament (ACL) is common among young athletes and can impact knee stability and control. Wearing proprioceptive knee braces can improve knee control and may reduce the risk factors associated with injury and re-injury, although the effect of such braces after ACL reconstruction (ACLR) is unclear.Research questionThis study aimed to determine the effect of proprioceptive knee bracing on knee control and subjective rating of participants post ACLR during three dynamic tasks.MethodsFifteen participants 2–10 years post ACLR performed a slow step down, single leg drop jump, and pivot turn jump with and without a proprioceptive knee brace. Knee kinematics in the sagittal (flexion – extension), coronal (abduction – adduction), and transverse (internal – external rotation) planes were collected using a 3D infrared system. Paired t-tests were performed to explore differences in knee angles and angular velocities between the no brace and brace conditions during the three tasks. After each task, subjective ratings regarding ease of the task were recorded.ResultsThe brace reduced the peak knee external rotation angle and range of motion in the transverse plane during the pivot turn jump task, and significantly increased the maximum knee flexion angular velocity during the single leg drop jump task. The majority of participants reported that tasks were easier to perform with the proprioceptive brace than without.SignificanceThis study confirms that proprioceptive knee braces can significantly influence knee kinematics during dynamic tasks post ACLR. The observed effects were clinically relevant.