Dynamic Knee Stability Research Articles

Specificity of muscle action after anterior cruciate ligament injury

Neuromuscular control is believed to be a critical factor in dynamic knee stability. The purpose of this study was to evaluate voluntary muscle control in anterior cruciate ligament deficient (ACL-D) and uninjured people. Twenty athletes of similar age participated in this study. Subjects performed a target-matching protocol that required them to produce isometric moments about the knee with fine control in flexion, extension, varus, and valgus (i.e., loads were generated in the plane perpendicular to the long axis of the shank). Electromyographic data were collected from 10 muscles that span the knee. A specificity index was calculated for each muscle to describe how fine-tuned (specific) its muscle activity pattern was with respect to its principal direction of action in the load plane. Diminished specificity of muscle action was observed in 8 of 10 muscles in the ACL-D subjects’ involved knees when compared with the activity patterns from their uninvolved knees and those from the uninjured subjects’ knees. The vastus lateralis muscle was especially affected. Increased and more global co-contraction was also observed in the ACL-D limbs. The alterations in muscle firing patterns observed in this study are consistent with diminished neuromuscular control.

Dynamic knee stability after anterior cruciate ligament rupture.

A functional classification scheme has been devised to study knee stabilization strategies after anterior cruciate ligament rupture. A screening examination can determine which patients may be candidates for nonsurgical treatment (potential copers). A rehabilitation program that includes support surface perturbations can improve the potential coper's ability to stabilize the knee. Biomechanical, electromyographic, and clinical data support the classification scheme and perturbation training for improving dynamic knee stability.

THE EFFECT OF MUSCLE RECRUITMENT STRATEGIES ON KNEE STABILITY AFTER ACUTE ACL RUPTURE

Patients with acute anterior cruciate ligament (ACL) rupture can be categorized by their potential for dynamic knee stability (potential copers = good potential, non-copers = poor potential). Demonstrated differences between these groups in walking and jogging suggest differences in knee stabilization strategies; however, muscle recruitment has not been compared. Recent studies show that lower-functioning subjects with ACL rupture recruit their quadriceps first in response to a mechanically applied, anterior-directed force on the tibia. Quadriceps contraction may induce anterior tibial translation, potentially destabilizing the ACL deficient knee. PURPOSE To differentiate the knee stabilization strategies of potential copers and non-copers by examining lower extremity muscle recruitment in response to a postural disturbance. METHODS Nineteen subjects with ACL rupture (9 potential copers, 10 non-copers) and 10 highly active people without lower extremity injury participated in the study. Subjects stood in unilateral stance (ACL deficient subjects = injured leg; uninjured subjects = randomly assigned leg) on a custom-built platform that was manually triggered to translate horizontally in an anterior direction (40 cm/s, 5.8 cm). Surface electromyography was collected from the lateral hamstrings, quadriceps, and gastrocnemius muscles. Approximately 2 seconds of data were collected before and after the random application of platform movement. Ten trials were collected. Subjects maintained unilateral stance during data acquisition. The threshold for muscle onset was when muscle activity exceeded 2 times the average level of activity in the 100 ms prior to platform movement. Muscle recruitment was ordered by onset during the interval from 60–180 ms after platform translation. RESULTS The majority of potential copers (7/9) and uninjured subjects (8/10) recruited the hamstrings, whereas the quadriceps was recruited first by most non-copers (6/10). CONCLUSIONS Recruitment of the quadriceps first in response to an anterior-directed destabilization of posture is a strategy adopted by those with poor potential for dynamic knee stability and gives insight into why their knee stabilization strategy fails.

Development of dynamic knee stability after acute ACL injury

Recently, a training program that includes perturbation of support surfaces has been shown to allow most active individuals with ACL injury who pass a screening examination to successfully return to high level activities. The purpose of this study was to identify the effect of this rehabilitation program on involved side muscle activation during walking in subjects with acute ACL rupture and to determine if the activation changes were coincident with improved function. Nine subjects with an acute, unilateral ACL injury or rupture of an ACL graft, who met the screening examination criteria, received ten sessions of rehabilitation that included perturbation training. Motion analysis of five self-paced walking trials were performed before and after training. Electromyographic (EMG) data were collected during stance. After training during walking, the vastus lateralis (VL) integral of activity increased, and relationships between muscles were significantly altered. During walking, VL activation variables were dependent on lateral hamstrings (LH) and/or the soleus (SOL) activation, while no relationships were found before training. Function improved after training, and all subjects returned to their pre-injury activities without experiencing instability. The relationships formed between muscles post-training suggests that perturbation training enhances dynamic knee stability by inducing a well-coordinated strategy among muscles that affect tibial translation.

Dynamic knee stability: current theory and implications for clinicians and scientists.

We will discuss the mechanisms by which dynamic knee stability may be achieved and relate this to issues that interest clinicians and scientists concerned with dynamic knee stability. Emphasis is placed on the neurophysiologic evidence and theory related to neuromuscular control. Specific topics discussed include the ensemble firing of peripheral mechanoreceptors, the potential for muscle stiffness modulation via force and length feedback, postural control synergies, motor programs, and the neural control of gait. Factors related to answering the difficult question of whether or not knee ligament injuries can be prevented during athletic activities are discussed. Prevention programs that train athletes to perform their sport skills in a safe fashion are put forth as the most promising prospect for injury prevention. Methods of assessing neuromuscular function are reviewed critically and the need for future research in this area is emphasized. We conclude with a brief review of the literature regarding neuromuscular training programs.

Hop tests as predictors of dynamic knee stability.

Single leg hop tests are commonly used as physical performance measures of function and are also commonly used to evaluate progress in knee rehabilitation programs, particularly for individuals recovering from anterior cruciate ligament injury or reconstructive surgery. While there is some evidence that hop tests may show promise as a predictive measure for identifying individuals who are at risk for recurrent dynamic instability, further work is needed to clearly define the role of hop test measurements for this purpose. The purposes of this clinical commentary are to review the research that has been done to establish hop tests as a physical performance measure of function, to discuss neuromuscular and biomechanical considerations related to hop performance and dynamic knee stability, to discuss existing evidence that supports the potential for hop tests as a predictor of dynamic knee stability, and to discuss considerations for future studies that are designed to more clearly define the role of hop tests in predicting dynamic knee stability.

Biomechanical evidence supporting a differential response to acute ACL injury

Objective. To describe movement patterns in people with complete anterior cruciate ligament rupture objectively identified as good candidates for non-operative management of the injury. Design. Involved side kinematics and kinetics were compared to the uninvolved side and to uninjured subjects. Background. High-level athletes with anterior cruciate ligament rupture and poor dynamic stability (non-copers) have movement alterations, including less knee flexion and a decreased internal knee extensor moment during loading response, that are not seen in those with excellent knee stability (copers). Our screening exam can identify people with good rehabilitation potential for non-operative management of anterior cruciate ligament injury (potential copers), but the movement strategies of these individuals are unknown. Methods. Sagittal plane kinematics and kinetics during the stance phase of walking and jogging were collected from 11 subjects who had an acute anterior cruciate ligament rupture and met the criteria of the screening exam, and were compared to 10 uninjured subjects, who we studied previously. Variables were those in which non-copers differed from uninjured subjects. Results. The potential copers flexed their involved knee less than uninjured subjects and their uninvolved side during walking. Potential copers, compared to uninjured subjects, also had a lower vertical ground reaction force during loading response, a lower knee support moment, and an increased ankle support moment during walking. In jogging, the involved knee angle at initial contact was more extended compared to uninjured subjects, and the amount of knee flexion was less than the uninvolved side. No differences in kinetics were present during jogging. Conclusions. This study provides evidence that the potential copers identified by the screening examination have movement patterns that are consistent with people who have more knee stability than non-copers. Relevance Although potential copers have developed some characteristics of a successful stabilization strategy, the presence of kinematic alterations indicates that they may benefit from training programs designed to enhance dynamic knee stability.

Neuromuscular and Hormonal Factors Associated With Knee Injuries in Female Athletes

Female athletes who participate in jumping and cutting sports are 4 to 6 times more likely to sustain a serious knee injury than male athletes participating in the same sports. More than 30,000 serious knee injuries are projected to occur in female intercollegiate and high school athletics in the US each year. The majority of these injuries occur by non-contact mechanisms, most often during landing from a jump or making a lateral pivot while running. Knee instability, due possibly to decreased neuromuscular strength and coordination or increased ligamentous laxity, may underlie the increased incidence of knee injury in females. Neuromuscular training can significantly increase dynamic knee stability in female athletes. Female sex hormones (i.e. estrogen, progesterone and relaxin) fluctuate radically during the menstrual cycle and are reported to increase ligamentous laxity and decrease neuromuscular performance and, thus, are a possible cause of decreases in both passive and active knee stability in female athletes. Oral contraceptives stabilise hormone levels during the menstrual cycle and may function to either passively or actively stabilise the knee joint. The long term objective of clinicians and researchers should be to determine the factors that make women more susceptible than men to knee ligament injury and to develop treatment modalities to aid in the prevention of these injuries. The immediate objectives of this review are to examine how female and male athletes differ in neuromuscular and ligamentous control of the lower extremity. The review will examine the effects of neuromuscular training on knee stability. The effects of female hormone levels and oral contraceptives on neuromuscular control of the female athletes' knee will also be discussed.

REHABILITATION COMPLICATIONS FOLLOWING KNEE SURGERY

When pain and effusion have been minimized and patients assume appropriate knee posture at rest and during exercise, the extent of postinjury or postoperative quadriceps femoris neuromuscular inhibition and avoidance during locomotion is reduced. Restoring normal lower-extremity ROM and musculotendinous extensibility (with consideration for biarticular muscles) is foundational to the implementation of an exercise program that integrates the trunk, hip, and ankle muscles into dynamic knee-stabilization challenges while addressing isolated quadriceps femoris deficiencies. Cardiovascular conditioning should be addressed as early as feasible. Although programs generally address anaerobic and aerobic energy systems, increasing patients' fatigue resistance, as evidenced by prolonged maintenance of appropriate functional exercise techniques and body control without verbalized discomfort or observed movement-avoidance patterns, ensures therapists that neuromuscular responsiveness for dynamic knee stabilization is improving.

Fatigue after eccentric quadriceps femoris work produces earlier gastrocnemius and delayed quadriceps femoris activation during crossover cutting among normal athletic women.

Athletic women are at greater risk of anterior cruciate ligament (ACL) injury than men. Twenty, healthy, athletic women were evaluated for the effect of preferred stance limb isokinetic quadriceps femoris and hamstring fatigue from eccentric work compared with controls on the activation onset of vastus medialis, rectus femoris, vastus lateralis, the medial hamstrings, biceps femoris, and gastrocnemius muscles. Following 3 weeks of crossover cut training, subjects were tested for fatigue effects (5 subjects/week, 3 conditions, 1 condition/day, order effect controlled) on muscle activation onsets prior to crossover cut landing heelstrike (mixed model, ANOVA, P < 0.05). Fatigue from eccentric quadriceps femoris work produced delayed vastus medialis (P = 0.03), rectus femoris (P = 0.007), and vastus lateralis (P = 0.03) activation onsets compared with control, but did not differ compared to hamstring fatigue. Neither hamstring nor quadriceps femoris fatigue produced differences (P > 0.05) in medial hamstring or biceps femoris activation onsets compared to control. Quadriceps femoris fatigue from eccentric work produced earlier gastrocnemius activation onsets (P = 0.048) than control, but did not differ for hamstring fatigue. The gastrocnemius appears to provide synergistic and compensatory dynamic knee stabilization in closed kinetic chain function during quadriceps femoris fatigue. This finding in a normal group at high risk of ACL injury while performing a maneuver with a high ACL injury risk supports gastrocnemius inclusion in knee rehabilitation and conditioning programs and suggests the need for comparative evaluations of knee injured/reconstructed subjects.

Management of complete traumatic anterior cruciate ligament tears in the skeletally immature patient: Current concepts and review of the literature

Once considered extremely rare, complete traumatic tears of the anterior cruciate ligament (ACL) in skeletally immature patients with open physes are now being diagnosed with increasing frequency. Concomitant subsequent meniscal injuries develop in a significant number of these patients. Nonoperative treatment, primary surgical repair of the torn ACL, or extraarticular stabilization procedures have not been reported to restore dynamic knee stability or prevent further meniscal damage. Transphyseal bone plugs from a patellar tendon graft fixed with suture or interference screws have not been reported in patients with significant growth potential and cannot be recommended. Soft-tissue autografts placed through transphyseal tunnels have been reported to give good functional results and minimize potential for growth disturbance.

Microbiological assay on microtitre plates of folate in serum and red cells.

To develop a simple microbiological assay for serum and red cell folates on 96-well microtitre plates, suitable for use in routine clinical diagnosis. Use of a chloramphenicol resistant organism (NCIB 10463) saved time by avoiding aseptic precautions. Use of plate sealers facilitated mixing. Evaluation of assay performance included estimations of folate recovery, assay reproducibility, and response to reduced folate. Results obtained on sera (193) and red cell folates (150) were compared with those obtained using a traditional microbiological assay. Good recovery of folic acid added to serum and also good interassay and intra-assay precision were obtained with both serum (CV% of less than 5) and red cell folate pools (CV% of less than 5). Equimolar assay responses were obtained with folic acid, 5-formyltetrahydrofolate (L-form), and 5-methyltetrahydrofolate (L-form). The microassay correlated well with a traditional assay for estimation of folate in both serum (n = 193, r = 0.975) and red cells (n = 150, r = 0.96). This assay is more compact and less time consuming than the traditional assay. It is extremely economical and is easy to perform in a routine clinical laboratory.

Rehabilitation of the anterior cruciate ligament in the athlete.

Recent medical advances in diagnosis, surgical technique, bracing and postoperative rehabilitation have greatly improved subjective and objective results following anterior cruciate ligament surgery. A team approach involving patient, therapist, athletic trainer, and surgeon is vital to a successful outcome. Surgical rationale and postoperative rehabilitation should be based on sound scientific data, recognising the need for static and dynamic knee stability. The rehabilitation programme should incorporate principles which enhances the well-being of the musculoskeletal system, avoiding potential problems such as periarticular contractures, disuse atrophy, negative cartilage changes, and cardiopulmonary deconditioning. This article is an attempt to summarise the scientific data and principles, and describe a rehabilitation programme which adheres to the data and principles outlined.

Balance in lower limb child amputees.

Postural stability of five unilateral above-knee amputee children was measured when wearing the SACH and the experimental Child Amputee Prosthetic Project (CAPP) prosthetic foot. Excursions of the centre of pressure of the supportive forces were recorded via force platform during sustained weight-shifting forward, backward, left, right, and during normal standing. Visual proprioception effects on upright stance were also demonstrated with these child amputees. Total base of support did not differ for the two types of prosthetic feet, but the functional base of support for SACH foot was significantly larger than CAPP. Fluctuations of centre of pressure about a mean position in normal standing were less when children used CAPP foot. Focusing on a static target had no effect on postural stability in either anterior-posterior or lateral direction for CAPP foot conditions, but lack of visual target had a deleterious effect on lateral stability when SACH foot was worn. Balance is one of the most difficult problems for a lower limb amputee (Hellebrandt et al, 1950; Moncur, 1969; Murdoch, 1969). The absence of part or all of a lower limb reduces the amount of proprioceptive information about the surfaces on which the foot is resting and the precise location of the prosthetic limb. While limited data have been reported on the balance and stability characteristics of adult amputees (Fernie and Holliday, 1978; Hellebrandt et al, 1950), information about balance of child amputees is almost non-existent. We have found only one report of the postural stability characteristics of a child amputee; Shambes and Waterland (1970) studied an 11-year-old quadrilateral amputee who had congenital Lisfranc amputations of both lower limbs, long above-elbow amputation of the left upper limb, and medium below-elbow amputation of the right upper limb. The purpose of this study was to detail the postural stability characteristics for lower limb child amputees. In addition, the conventional SACH prosthetic foot was compared with the experimental Child Amputee Prosthetic Project (CAPP) foot for various postural tasks. The SACH foot (Fig. la) is usually constructed with a moulded polyurethane material which incorporates a heel cushion to allow some compression of the heel during heel strike in walking to simulate plantar flexion of a normal foot. The CAPP foot (Fig. lb) is an experimental prosthesis undergoing development at the UCLA Child Amputee Prosthetic Project. It is designed to provide more knee stability during early stance phase during walking and also to respond to torsional loads occurring in the stance phase of walking. The heel projection of the CAPP foot is non-weight bearing and deflects upward at heelstrike. With the ground reaction forces shifted more anteriorly on the supporting foot there is an expected increase in dynamic knee stability during the stance phase of walking. While additional research is being conducted on the dynamic characteristics of the CAPP foot, the present study provides some preliminary information about the postural stability of child amputees using the experimental CAPP foot, as well as providing a comparison with the conventional SACH foot.