Effect of knee musculature on anterior cruciate ligament strain in vivo

Squatting is a commonly prescribed exercise following reconstruction of the anterior cruciate ligament (ACL). The objective of this paper was to measure the in vivo strain patterns of the normal ACL and the load at the knee for the simple squat and for squatting with a “sport cord”. A sport cord is a large elastic rubber tube used for added resistance. Strain patterns were deduced using displacement data from a Hall Effect Strain Transducer (HEST), while joint loads were determined by a mathematical model with inputs from a force plate and electrogoniometers. ACL strain for the free squat in one subject had a maximum of 2% at a knee angle of 10° and was slack for knee angles >17°. In squatting with a sport cord, peak strain was 1% at 10° and was slack at knee angles >14°. Since these peak strains are low, squatting appears to be a safe exercise for conservative rehabilitation of ACL reconstruction patients. In addition, the sport cord is a recommended augmentation to the activity. We believe that the decrease in strain with the sport cord results from added joint stiffness due to greater compressive forces at the tibiofemoral joint. This greater compressive force results from the approximately 10% increase in quadriceps activity. From shear force data predicted by the mathematical model, the maximum anterior drawer force for free squatting (50 N) was considerably less than for sport cord squatting (430 N). Therefore, the value of shear force at the tibiofemoral joint only partially determines the load placed on the ACL.     

Inflammatory and healing environment in synovial fluid after anterior cruciate ligament reconstruction: Granulocytes and endogenous opioids as new targets of postoperative pain

BackgroundBiological processes after anterior cruciate ligament reconstruction (ACLR) is crucial for recovery. However, alterations in the of synovial fluid cell population during the acute phase following ACLR and the relationship between these cells and postoperative pain is unclear. The goal of this study was to reveal alterations in synovial fluid cell population during the acute phase following ACLR and relationship between postoperative pain and proportion of synovial fluid cells.MethodsSynovial fluids were obtained from all patients (n = 50) before surgery and from patients who showed hydrarthrosis at days 4 (n = 25), and 21 (n = 42) post-surgery. The cell population was analyzed by flow cytometry. IL1β, IL8, and met-enkephalin in synovial fluid were quantitated by enzyme-linked immunosorbent assay. Patients answered numerical rating scale (NRS) questionnaire at 4 days and approximately 4 weeks postoperatively.ResultsThe granulocyte population was significantly higher at 4 days after surgery than at any other time points. The population of macrophages was 3.2 times and 7.7 times as high as at surgery on days 4 and 21, respectively. T cell population was significantly higher 21 days after surgery compared to 4 days after surgery. All NRS 4 weeks after surgery showed a significant negative correlation with the granulocyte population in synovial fluid 4 days after surgery. Granulocyte population in synovial fluid significantly correlated with the levels of IL1β and IL8. Postoperative pain at rest tended to decrease with an increase in met-enkephalin concentration 4 days after ACLR.ConclusionsSynovial fluid after ACLR had an inflammatory environment at early time points and a healing environment in the subsequent phase about concerning to the cellular composition. A proportion of synovial fluid cells and endogenous opioids affected postoperative pain.     

Knee stability and muscle coordination in patients with anterior cruciate ligament injuries: An electromyographic approach

We present findings on the way in which to use electromyographic (EMG) measurements from muscles acting on the knee in planning rehabilitation of subjects after rupture of anterior cruciate ligament (ACL). ACL subjects demonstrated an earlier recruitment and a tendency to prolonged activity in muscles around the deficient knee as compared with a control group. Especially the hamstring lateralis and the gastrocnemius medialis (GM) muscles showed an earlier EMG onset and a longer EMG burst duration. The clinical relevance of the EMG findings was assessed by comparing the muscle coordination and relative levels of activity between a functionally excellent/good and a functionally poor ACL patient group. Significant differences between the two groups were noted in EMG onset and burst duration of the GM muscle. A rehabilitation program based on the EMG findings from the GM muscle was designed. In this program, the ACL subjects with poor stability were trained to change the EMG activity of the gastrocnemius muscles according to the recruitment pattern of the good/excellent ACL-group. We were able to train the subjects to change their muscle recruitment and to improve their knee stability. The stability of the knee joint depends on the stiffness of the muscles and ligaments around and within the knee. We discuss the importance of the gastrocnemius muscles with regard to knee joint stiffness.     

Kinematic motion of the anterior cruciate ligament deficient knee during functionally high and low demanding tasks

The purpose of this study was to determine whether mechanical adaptations were present in patients with anterior cruciate ligament (ACL)-deficient knees during high-demand activities. Twenty-two subjects with unilateral ACL deficiency (11 males and 11 females, 19.6 months after injury) performed five different activities at a comfortable speed (level walking, ascending and descending steps, jogging, jogging to a 90-degree side cutting toward the opposite direction of the tested side). Three-dimensional knee kinematics for the ACL-deficient knees and uninjured contralateral knees were evaluated using the Point Cluster Technique. There was no significant difference in knee flexion angle, but an offset toward the knee in less valgus and more external tibial rotation was observed in the ACL-deficient knee. The tendency was more obvious in high demand motions, and a significant difference was clearly observed in the side cutting motions. These motion patterns, with the knee in less valgus and more external tibial rotation, are proposed to be an adaptive movement to avoid pivot shift dynamically, and reveal evidence in support of a dynamic adaptive motion occurring in ACL-deficient knees.     

Quantifying in vivo laxity in the anterior cruciate ligament and individual knee joint structures

A custom knee loading apparatus (KLA), when used in conjunction with magnetic resonance imaging, enables in vivo measurement of the gross anterior laxity of the knee joint. A numerical model was applied to the KLA to understand the contribution of the individual joint structures and to estimate the stiffness of the anterior-cruciate ligament (ACL). The model was evaluated with a cadaveric study using an in situ knee loading apparatus and an ElectroForce test system. A constrained optimization solution technique was able to predict the restraining forces within the soft-tissue structures and joint contact. The numerical model presented here allowed in vivo prediction of the material stiffness parameters of the ACL in response to applied anterior loading. Promising results were obtained for in vivo load sharing within the structures. The numerical model overestimated the ACL forces by 27.61–92.71%. This study presents a novel approach to estimate ligament stiffness and provides the basis to develop a robust and accurate measure of in vivo knee joint laxity.     

Effect of posterior cruciate ligament creep on muscular co-activation around knee: A pilot study

The effect of posterior cruciate ligament (PCL) on muscle co-activation (MCO) is not known though MCO has been extensively studied. The purpose of the study was to investigate the effect of PCL creep on MCO and on joint moment around the knee. Twelve males and twelve females volunteered for this study. PCL creep was estimated via tibial posterior displacement which was elicited by a 20 kg dumbbell hanged on horizontal shank near patella for 10 min. Electromyography activity from both rectus femoris and biceps femoris as well as muscle strength on the right thigh was recorded synchronically during knee isokinetic flexion–extension performance in speed of 60 deg/s as well as 120 deg/s on a dynamometer before and after PCL creep. A one-way ANOVA with repeated measures was used to evaluate the effect of creep, gender and speed. The results showed that significant tibial posterior displacement was found (p = 0.01) in both male and female groups. No significant increase of joint moment was found in flexion as well as in extension phase in both female and male groups. There was a significant effect of speed (p = 0.036) on joint moment in extension phase. Co-activation index (CI) decreased significantly (p = 0.049) in extension phase with a significant effect of gender (p ⩽ 0.001). It was concluded that creep developed in PCL due to static posterior load on the proximal tibia could significantly elicit the increase of the activation of agonist muscles but with no compensation from the antagonist in flexion as well as in extension phase. The creep significantly elicited the decrease of the antagonist–agonist CI in extension phase. MCO in females was reduced significantly in extension phase. It was suggested that PCL creep might be one of risk factors to the knee injury in sports activity.     

1998 Basmajian Student Award Paper: Movement patterns after anterior cruciate ligament injury: a comparison of patients who compensate well for the injury and those who require operative stabilization

The purpose of this study was to describe kinematic and kinetic differences between a group of ACL deficient subjects who were grouped according to functional ability. Sixteen patients with complete ACL rupture were studied; eight subjects had instability with activities of daily living (non-copers) and eight subjects had returned to all pre-injury activity without limitation (copers). Three-dimensional joint kinematics and kinetics were collected from the knee and ankle during walking, jogging and going up and over a step. Results showed that both groups mitigated the force with which they contacted the floor but non-copers consistently demonstrated less knee flexion in the involved limb. The copers used joint kinematics similar to those of their uninvolved knees and similar to knee motions reported in uninjured subjects. The reduced knee motion in the involved knee of the non-copers did not correlate directly with quadriceps femoris muscle weakness.

The data suggest that the non-copers utilize a stabilization strategy which stiffens the knee joint which not only is unsuccessful but may lead to excessive joint contact forces which have the potential to damage articular structures. The copers use a strategy which permits normal knee kinematics and bodes well for joint integrity.     

The effects of knee joint kinematics on anterior cruciate ligament injury and articular cartilage damage

This study determined which knee joint motions lead to anterior cruciate ligament (ACL) rupture with the knee at 25° of flexion. The knee was subjected to internal and external rotations, as well as varus and valgus motions. A failure locus representing the relationship between these motions and ACL rupture was established using finite element simulations. This study also considered possible concomitant injuries to the tibial articular cartilage prior to ACL injury. The posterolateral bundle of the ACL demonstrated higher rupture susceptibility than the anteromedial bundle. The average varus angular displacement required for ACL failure was 46.6% lower compared to the average valgus angular displacement. Femoral external rotation decreased the frontal plane angle required for ACL failure by 27.5% compared to internal rotation. Tibial articular cartilage damage initiated prior to ACL failure in all valgus simulations. The results from this investigation agreed well with other experimental and analytical investigations. This study provides a greater understanding of the various knee joint motion combinations leading to ACL injury and articular cartilage damage.     

Quantitation of estrogen receptors and relaxin binding in human anterior cruciate ligament fibroblasts

Summary The significantly higher incidence of anterior cruciate ligament (ACL) injuries in collegiate women compared with men may result from relative ligament laxity. Differences in estrogen and relaxin activity, similar to that seen in pregnancy, may account for this. We quantified estrogen receptors by flow cytometry and relaxin receptors by radioligand binding assay in human ACL cells and compared the presence of these receptors in males and females. ACL stumps were harvested from seven males and eight females with acute ACL injuries. The tissue was placed in M199 cell culture medium. Outgrowth cultures were obtained, and passage 2 cells were used for all studies. Estrogen receptor determination was performed using flow cytometry. Relaxin binding was performed in ACL cells derived from five female and male patients using I¹²⁵-labeled relaxin. Estrogen receptors were identified by flow cytometry in 4 to 10% of ACL cells. Mean fluorescence of cells expressing estrogen receptors was approximately twice that of controls, with no significant differences between males and females. Relaxin studies showed low-level binding of I¹²⁵-relaxin-labeled ACL cells. Relaxin binding was present in four out of five female ACL cells versus one out of five male ACL cells.     

Age-related changes of elements in human anterior cruciate ligaments and ligamenta capitum femorum

To elucidate compositional changes of human ligaments by aging, the content of elements in anterior cruciate ligaments (ACLs) and ligamenta capitum femorum (LCFs) was analyzed by inductively coupled plasma-atomic emission spectrometry. The subjects consisted of 11 men and 7 women, ranging from 59 to 91 yr of age. With regard to the content of elements, the content of sulfur and iron was significantly higher in the LCFs than in the ACLs. It was found in the ACLs that the content of sulfur decreased gradually with aging, whereas the content of calcium, phosphorus, and magnesium increased progressively with aging. On the other hand, it was found in the LCFs that the content of magnesium decreased gradually with aging, whereas the content of phosphorus increased progressively with aging. The common finding that the content of phosphorus increased with aging, but the content of iron decreased, was obtained in the ACL and LCF. Regarding sexual difference, it was found in both the ACLs and LCFs that the content of phosphorus was higher in women’s ligaments than in men’s.     

Mechanical stretch increases CCN2/CTGF expression in anterior cruciate ligament-derived cells

Anterior cruciate ligament (ACL)-to-bone interface serves to minimize the stress concentrations that would arise between two different tissues. Mechanical stretch plays an important role in maintaining cell-specific features by inducing CCN family 2/connective tissue growth factor (CCN2/CTGF). We previously reported that cyclic tensile strain (CTS) stimulates α1(I) collagen (COL1A1) expression in human ACL-derived cells. However, the biological function and stress-related response of CCN2/CTGF were still unclear in ACL fibroblasts. In the present study, CCN2/CTGF was observed in ACL-to-bone interface, but was not in the midsubstance region by immunohistochemical analyses. CTS treatments induced higher increase of CCN2/CTGF expression and secretion in interface cells compared with midsubstance cells. COL1A1 expression was not influenced by CCN2/CTGF treatment in interface cells despite CCN2/CTGF stimulated COL1A1 expression in midsubstance cells. However, CCN2/CTGF stimulated the proliferation of interface cells. Our results suggest that distinct biological function of stretch-induced CCN2/CTGF might regulate region-specific phenotypes of ACL-derived cells.     

应用无内固定装置技术双束双隧道重建前交叉韧带疗效分析

目的：探讨应用无内固定装置技术双束双隧道重建前交叉韧带（ACL）的治疗效果。方法：2006年1月至2008年1月,我科应用无内固定装置技术双束重建ACL损伤患者33例,男31例,女2例。患者排除手术禁忌后,分别在关节镜下采用双股半腱肌腱重建前内侧束,双股股薄肌腱重建后外侧束。韧带采用无内固定装置固定,股骨端行悬吊固定,胫骨端行拴桩固定。术后1~3周内指导患者在支具保护下进行康复训练,并逐渐提高训练强度。结果：术后切口均一期愈合,无并发症。病例随访时间24~48个月,平均36个月。术后12月时：Lysholm评分由术前的52.2±2.5,升至96.4±7.2分,IKDC评分55.3±3.7分,升至94.1±5.3分,其中A级19例,B级：11例。术前与术后Lysholm评分及IKDC评分有显著差别（P〉0.05）。结论：采用无内固定装置双束ACL重建方法能够较好的平衡患者前内侧束和后外侧束张力,并有利于保留ACL韧带残余结构、节约经费,具有令人满意的临床效果。     

ACL对膝关节胫骨内、外旋转稳定性控制作用的初步研究

目的:研究正常人前交叉韧带(Anterior Cruciate Ligament,ACL)对膝关节内、外旋转稳定性的控制作用;探讨膝关节ACL多纤维束动态力学特性。方法:采集5例新鲜正常成年男性左侧膝关节标本,评估标本完整性后,向ACL胫骨止点中心做斜行骨隧道,游离ACL胫骨侧止点,以象限法平均分为4区:1.后内区、2.后外区、3.前外区、4.前内区;将4区的附着纤维束分别连接至自制膝关节交叉韧带测力计传感器上,并固定于自主发明的通用生物关节自由度动态应力加载系统。对股内侧、股中间肌股直肌联合肌腱、股外侧肌群分别施以1.25N:1.5N:1N的负荷。分别在膝关节屈曲0°、30°、60°、90°位将ACL各纤维束张紧并系统平衡后,利用扭距传感器测量胫骨做内、外旋转时ACL的受力情况。结果:膝关节屈伸过程中,1区纤维束对膝关节内、外旋转稳定性的控制作用较小。2区纤维胫骨外旋时受力最大,并在屈膝30°时达最大(16.97±1.45N)。3区纤维束时对胫骨内、外旋控制作用相当,并在屈膝60°时最大,分别为10.67 1.34N和16.45 1.34N。4区纤维束对胫骨内旋稳定的控制明显大于胫骨外旋,在屈膝90°时作用最大,为11.67 2.25N。结论:膝关节在屈膝不同角度内、外旋转时,每一纤维束的受力是不同的且不断变化的。膝关节屈伸过程中ACL控制胫骨内、外旋转稳定性的最重要作用纤维束集中在胫骨止点的前内侧和后外侧。ACL后外侧纤维束(2区)对膝关节外旋稳定性控制作用最为重要,且以屈膝30°时控制作用最强。前内侧纤维束(4区)对膝关节内旋稳定性的控制最为重要,并且以屈膝90°控制作用最强。前外侧纤维束(3区)对膝关节的内旋和外旋相当,并且在屈膝60°对膝关节内、外旋转稳定性控制最强。     

Overrepresentation of the COL3A1 AA genotype in Polish skiers with anterior cruciate ligament injury

Although various intrinsic and extrinsic risk factors for anterior cruciate ligament (ACL) rupture have been identified, the exact aetiology of the injury is not yet fully understood. Type III collagen is an important factor in the repair of connective tissue, and certain gene polymorphisms may impair the tensile strength. The aim of this study was to examine the association of the COL3A1 rs1800255 polymorphism with ACL rupture in Polish male recreational skiers. A total of 321 male Polish recreational skiers were recruited for this study; 138 had surgically diagnosed primary ACL ruptures (ACL-injured group) and 183 were apparently healthy male skiers (control group – CON) who had no self-reported history of ligament or tendon injury. Both groups had a comparable level of exposure to ACL injury. Genomic DNA was extracted from the oral epithelial cells. All samples were genotyped on a real-time polymerase chain reaction instrument. The genotype distribution in the ACL-injured group was significantly different than in CON (respectively: AA=10.1 vs 2.2%, AG=22.5 vs 36.1, GG=67.4 vs 61.8%; p=0.0087). The AA vs AG+GG genotype of COL3A1 (odds ratio (OR)=5.05; 95% confidence interval (CI), 1.62-15.71, p=0.003) was significantly overrepresented in the ACL-injured group compared with CON. The frequency of the A allele was higher in the ACL-injured group (21.4%) compared with CON (20.2%), but the difference was not statistically significant (p=0.72). This study revealed an association between the COL3A1 rs1800255 polymorphism and ACL ruptures in Polish skiers.     

关节镜下多种移植物联合重建膝关节前、后交叉韧带

目的：评估关节镜下膝关节前交叉韧带（ACL）与后交叉韧带（PCL）同时重建的技术和临床效果。方法：自2003年6月～2009年10月,27例病人（28膝）经MRJ检查及关节镜检查证实ACL和PCL均断裂,其中9膝伴内侧副韧带损伤（MCL）,8膝伴后外侧角损伤（PLC）,5膝伴内侧半月板破裂,4膝伴外侧半月板损伤。27例患者于伤后3～10周在关节镜下行膝关节前、后交叉韧带联合重建。结果：本组术后早期均未发生严重并发症。术后随访12-88个月,平均（42．67±3．34）个月,Lysholm膝关节功能评分为78-93分,平均（86．67±5．21）分。国际膝关节文件编制委员会（mDC）综合评定由术前显著异常（D级）28膝,改进为随访时正常（A级）9膝、接近正常（B级）16膝、异常（C级）3膝。结论：关节镜下膝关节前交叉韧带（ACL）与后交叉韧带（PCL）同时重建创伤小、手术操作精细,术后膝关节功能恢复满意。     

Assessment of standing balance deficits in people who have undergone anterior cruciate ligament reconstruction using traditional and modern analysis methods

Modern methods of assessing standing balance such as wavelet and entropy analysis could provide insight into postural control mechanisms in clinical populations. The aim of this study was to examine what effect anterior cruciate ligament reconstruction (ACLR) has on traditional and modern measures of balance. Ninety subjects, 45 who had undergone ACLR and 45 matched controls, performed single leg static standing balance tests on their surgical or matched limb on a Nintendo Wii Balance Board. Data were analysed in the anterior–posterior axis of movement, which is known to be affected by ACLR. The traditional measures of path velocity, amplitude and standard deviation were calculated in this plane. Additionally, sample entropy and discrete wavelet transform derived assessment of path velocity in four distinct frequency bands related to (1) spinal reflexive loops and muscle activity, (2) cerebellar, (3) vestibular, and (4) visual mechanisms of postural control were derived. The ACLR group had significantly increased values in all traditional measures and all four frequency bands. No significant difference was observed for sample entropy. This indicated that whilst postural sway was amplified in the ACLR group, the overall mechanism used by the patient group to maintain balance was similar to that of the control group. In conclusion, modern methods of signal analysis may provide additional insight into standing balance mechanisms in clinical populations. Future research is required to determine if these results provide important and unique information which is of benefit to clinicians.     

Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

The purposes of this study were to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury, and to quantify the corresponding in situ joint contact mechanics. Experiments were performed in the anterior cruciate ligament (ACL) transected knee of the cat and the corresponding, intact contralateral knee, 16 weeks following intervention. Cartilage thickness, stiffness, effective Young’s modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral joint were obtained in situ using Fuji Pressensor film, and comparisons between experimental and contralateral joint were made for corresponding loading conditions. Total joint contact area and peak pressure were increased and decreased significantly (=0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stiffness were increased and decreased significantly (=0.01), respectively, in the experimental compared to the contralateral joint in the four femoral and patellar test locations. Articular cartilage material properties (effective Young’s modulus and permeability) were the same in the ACL-transected and intact joints. These results demonstrate for the first time the effect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corroborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of cartilage properties and joint surface geometry from the experimental animals. We conclude that the joint contact mechanics in the ACL-transected cat change within 16 weeks of experimental intervention.     

Altered biomechanical strategies and medio-lateral control of the knee represent incomplete recovery of individuals with injury during single leg hop

Anterior cruciate ligament (ACL) injury can result in failure to return to pre-injury activity levels and future osteoarthritis predisposition. Single leg hop is used in late rehabilitation to evaluate recovery and inform treatment but biomechanical understanding of this activity is insufficient.