前交叉韧带不同断裂程度对髌骨内外侧关节面的生物力学影响

目的:探讨前交叉韧带(ACL)完全断裂和部分断裂对髌骨内外侧关节面生物力学的影响.方法:10例新鲜正常成人膝关节标本作为ACL完整组,在200N轴向载荷下,测试膝关节0°、30°、60°、90°髌骨内外侧关节面应变,测试完毕后随机将标本造模成前内侧束(AMB)切断组和后外侧束(PLB)切断组,各5例,在上述条件下测试,再将ACL中下1/3全切作为全切组进行测试.结果:膝伸直0°位各组应变无显著性差异(P＞0.05),膝屈曲30°、60°、90°各组间均有显著性差异(P＜0.05),其应变变化趋势为ACL完整组＞PLB切断组＞AMB切断组＞全切组.且髌骨内侧面应变小于髌骨外侧面应变(P＜0.05).结论:ACL完全断裂,在不同栽荷和角度下,对髌骨内外侧关节面的应变均有影响.ACL部分断裂在膝关节屈曲30°、60°、90°位可引起髌骨内外侧生物力学改变.ACL完全断裂,髌骨外侧应变高于髌骨内侧应变,其意义尚需进一步探讨.     

前交叉韧带不同断裂程度对内侧半月板后角生物力学特性的影响

目的:探讨前交叉韧带(ACL)断裂对内侧半月板后角的生物力学特性影响.方法:12例新鲜正常成人膝关节标本作为ACL完整组,在200N轴向载荷下,测试膝关节0°、30°、60°、90°内侧半月板后角应变,测试完毕后随机将标本造模成前内侧束(AMB)断裂组和后外侧束(PLB)断裂组,各6例,在上述条件下测试,再将标本的ACL中下1/3全部切断作为全断组进行测试.结果:膝伸直0°、屈曲30°,全断组后角应变大于其它各组(p＜0.01),PLB断裂组后角应变大于完整组、AMB断裂组(p＜0.01),AMB断裂组与完整组无显著性差异(p＞0.05);膝屈曲60°,全断组后角应变大于PLB断裂组、完整组(p＜0.05).与AMB断裂组无显著性差异(p＞0.05),AMB断裂组后角应变大于PLB断裂组、完整组(p＜0.05),PLB断裂组与完整组无显著性差异(p＞0.05);膝90°,全断组后角应变大于其它各组(p＜0.05),完整组、AMB断裂组、PLB断裂组组间均无显著性差异(p＞0.05).结论:(1)ACL完全断裂,在膝关节各角度对内侧半月板后角应变均有较大影响,为ACL完全断裂早期修复提供了理论依据.(2)AMB断裂在膝屈曲位(60°)引起内侧半月板后角生物力学改变;PLB断裂在膝0°、30°引起内侧半月板后角生物力学变化,其意义尚需进一步探讨.     

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。     

关节镜下前交叉韧带重建术后翻修的临床研究(附14例报告)

目的:探讨关节镜下前交叉韧带(ACL)重建术后翻修手术的开展方式和临床效果。方法:我院2009年1月~2012年9月共收治ACL重建后失稳需翻修的患者14例,均给予关节镜下检查以及翻修手术,术后对患者的治疗情况采用Lysholm评分、Tegner评分、KT-2000及IKDC进行综合评价。结果:患者的KT-2000检查中术前屈曲30°为5.2mm,屈曲90°为3.3mm,术后屈曲30°为3.0mm,屈曲90°为1.6mm;IKDC评分术前为(50±5)分,术后为(72±8)分;Lysholm评分术前为(51±15)分,术后为(77±19)分;Tegner评分术前为(2.6±0.6)分,术后为(4.8±1.2)分。手术前后对比均有显著差异,具有统计学意义(P0.05),表明术后患者的膝关节功能明显增强。结论:对ACL重建术失败患者给予术后的翻修可以有效改善患者膝关节功能。     

后交叉韧带断裂对外侧半月板生物力学的影响

目的:探讨后交叉韧带(Posterior cruciate ligament,PCL)损伤后对外侧半月板各部位生物力学特性的影响,为PCL断裂后外侧半月板损伤的防治避免骨性关节炎提供力学理论依据.方法:自愿捐献新鲜成年男性正常膝关节标本共10具,年龄21～36岁,平均32.3岁,为非对称性,左、右膝关节各5具.置于自制运动夹具上并通过电子试验机连续轴向加载0～800N负荷模拟膝关节的受力,采用压力感受器分别测定PCL完整组及PCL断裂组外侧半月板前角体部和后角于屈膝0、30、60及90°时应变值.结果:膝关节0°位,在PCL完整时,前角、体部和后角的应变均为负值,为压应变,当PCL完全切断时,前角、体部应变在各种载荷下较完整时均出现负向减小,而后角的应变却出现负向增大.膝关节30°、60°、90°位,PCL完整时前角、体部的应变为正值,是拉应变,且随载荷和角度的增大而增大,后角的应变是负值,为压应变,且随载荷和角度的增大而负向增大,PCL断裂组应变值明显大于完整组.不同角度不同载荷下两组差异均有统计学意义(P＜0.05).结论:PCL断裂会对外侧半月板产生显著的生物力学影响,这也为伤后避免膝关节屈曲负重和早期重建PCL保护半月板功能避免骨性关节炎提供了力学理论依据.     

股四头肌腱双束重建前交叉韧带的生物力学特性研究

目的:探讨股四头肌腱的生物力学特性,为其能否应用于临床前交叉韧带(ACL)重建提供实验依据.方法:取32例新鲜尸体的1cm宽股四头肌腱,按其解剖结构分为两柬:股直肌、股内、外侧肌腱舍为A束,股中问肌腱为B束,用游标卡尺测量两束的宽度及厚度,然后将两束置于电子万能试验机上分别测其生物力学指标.结果:A 束厚度为4.39±1.72mm,宽度为8.19±1.18mm,生物力学强度为685.67±227.09N,抗拉强度为17.00±3.48Mpa;B束厚度为3.06±1.47mm,宽度为7.10±2.03mm,生物力学强度为435.04±205.80N,抗拉强度为13.16±4.02Mpa.A束生物力学强度与ACL比较,差异有统计学意义(p<0.05);B束生物力学强度与ACL比较,差异有统计学意义(p<0.05).结论:股四头肌腱的生物力学性能不能满足ACL双束重建的要求,其在临床上应用于ACL双束重建的价值有待于进一步的深入研究.

Abstract：

Objective: To investigate the biomechanics of the quadrieeps tendon and to provide theoretical basis for double-bundle reeonstruction of anterior cruciate iigament(ACL). Methods: 32 quadriceps tendons (width lena) taken from fresh cadaver were dissected into 2 bundles according to the anatomy, one bundle including rectus femoris, vastus medialis and vastus lateralis was named A bundle and the other was named B bundle. The width and thickness of the A and B bundle were detected respectively with a Vernier caliper and the biomechanics were determined by WDW-30 election universal testing machine. Results: The thickness, width, ultimate load and ultimate tensile strength of bundle A were 4.39± 1.72mm, 8.19± 1.18mm, 685.67± 227.09 N and 17.00± 3.48 Mpa respectively, while for bundle B,which were 3.06± 1.47 ram, 7.10± 2.03mm: 435.04±205.80 N and 13.16± 4.02 Mpa. There was difference between bundle A and the ACL (p<0.05). Conclusion: The ultimate load ofbundle A was much lower than the the ACL and bundle Bwas also lower than the ACL.     

双源CT测量前交叉韧带单束重建术后隧道位置的临床研究

目的:应用双源CT(Dual-source computer tomography,DSCT)测量前交叉韧带(Anterior cruciate ligament,ACL)单束重建术后胫骨、股骨隧道位置,并对隧道位置进行评价。方法:对2013年1月至2014年6月我科收治的92例(男64例,女28例,平均年龄31.2岁)ACL单束重建患者术后膝关节进行双源CT三维重建,应用Adobe Photoshop CS6软件圈画隧道中心并采用Lorenz法测量胫骨隧道中心点相对位置百分比(Tx,Ty),采用Bernard四格表法测量股骨隧道中心点相对位置百分比(Fx,Fy)。结果:Tx平均为(54.54±3.42)%,Ty平均为(39.58±6.72)%,Fx平均为(28.98±6.51)%,Fy平均为(28.04±8.70)%。男、女性及左、右膝之间Tx、Ty、Fx、Fy的差异均无统计学意义(P0.05)。结论:双源CT能够清晰,三维显示ACL术后隧道,可以用来评估隧道位置,为改进前交叉韧带损伤后的手术方式及个体化解剖重建提供帮助。     

全膝关节置换术假体的三维有限元生物力学分析

分析基于MRI图像数据建立的膝关节有限元模型,并采用人工膝关节置换术对假体进行匹配,通过有限元法对匹配假体接触关节表面进行应力变化分析,为人工关节假体进一步研究提供理论依据。采用MRI对1名正常男性青年双膝关节进行扫描并获取二维图像数据,根据MRI扫描数据建立膝关节三维模型;根据实际假体模型经过逆向工程技术建立膝置换假体模型,在截骨的膝关节三维模型上装配置换假体,最终构建三维有限元模型,并进行相关的生物力学分析。进行置换术后膝关节在垂直受力的0°~90°屈曲运动中,相对于胫骨,内股骨滚动并向后方发生了滑动外旋;膝关节在90°~120°范围內侧髁向内后方滑动,并且外侧髁向上抬离处于内旋状态。在屈曲运动过程中,膝关节随着度数增加,聚乙烯垫片内侧后方出现应力集中情况,约为120°时垫片后缘产生较大的应力峰值;基于MRI图像扫描并通过有限元法建立膝关节三维模型,用于膝关节置换后生物力学分析,为进一步人工关节假体研究提供相应理论依据。     

数字化导航技术在人工全膝关节置换中的初步应用研究

目的:探讨数字化导航技术在人工全膝关节置换术中应用的可行性及初步临床应用。方法:对我院2013年6月至2014年6月行单侧全膝关节置换术的80例患者,按照抽签法随机分为数字化导航组40例及传统手术组40例,导航组术前设计个性化定制导航模板,术中应用导航模板截骨,传统组应用厂家器械截骨。分别测量两组患者手术前后的髋-膝-踝角、冠状面股骨和胫骨截骨面与机械轴夹角、矢状面股骨和胫骨截骨面与外旋和后倾夹角,记录每一例患者手术时间及术中出血量并进行对比。结果:数字化导航组患者的手术时间及术中出血量均少于传统手术组,差异具有统计学意义(P0.05)。与传统手术组比较,数字化导航组术后冠状面FFC角及FTC角平均偏差角度较小,差异具有统计学意义(P0.05)。与传统手术组比较,数字化导航组术后矢状面LFC角及LTC角平均偏差角度较小,差异具有统计学意义(P0.05)。结论:数字化导航技术在人工膝关节置换术中具有快速、个性化及精确性高等优点,值得临床推广应用。     

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.     

Tibio-femoral joint contact in healthy and osteoarthritic knees during quasi-static squat: A bi-planar X-ray analysis

The aim of this study was to quantify the tibio-femoral contact point (CP) locations in healthy and osteoarthritic (OA) subjects during a weight-bearing squat using stand-alone biplanar X-ray images.Ten healthy and 9 severe OA subjects performed quasi-static squats. Bi-planar X-ray images were recorded at 0°, 15°, 30°, 45°, and 70° of knee flexion. A reconstruction/registration process was used to create 3D models of tibia, fibula, and femur from bi-planar X-rays and to measure their positions at each posture. A weighted centroid of proximity algorithm was used to calculate the tibio-femoral CP locations. The accuracy of the reconstruction/registration process in measuring the quasi-static kinematics and the contact parameters was evaluated in a validation study.The quasi-static kinematics data revealed that in OA knees, adduction angles were greater (p<0.01), and the femur was located more medially relative to the tibia (p<0.01). Similarly, the average CP locations on the medial and lateral tibial plateaus of the OA patients were shifted (6.5±0.7 mm; p<0.01) and (9.6±3.1 mm; p<0.01) medially compared to the healthy group. From 0° to 70° flexion, CPs moved 8.1±5.3 mm and 8.9±5.3 mm posteriorly on the medial and lateral plateaus of healthy knees; while in OA joints CPs moved 10.1±8.4 mm and 3.6±2.8 mm posteriorly. The average minimum tibio-femoral bone-to-bone distances of the OA joints were lower in both compartments (p<0.01).The CPs in the OA joints were located more medially and displayed a higher ratio of medial to lateral posterior translations compared to healthy joints.     

Predictive mathematical modeling of knee static laxity after ACL reconstruction: in vivo analysis

Previous studies did not take into consideration such large variety of surgery variables which describe the performed anterior cruciate ligament (ACL) reconstruction and the interaction among them in the definition of postoperative outcome. Seventeen patients who underwent navigated Single Bundle plus Lateral Plasty ACL reconstruction were enrolled in the study. Static laxity was evaluated as the value of anterior/posterior displacement at 30° and at 90° of flexion, internal/external rotation at 30° and 90° of knee flexion, varus/valgus test at 0° and 30° of flexion. The evaluated surgical variables were analyzed through a multivariate analysis defining the following models: AP30_estimate, AP90_estimate, IE30_estimate, IE90_estimate, VV0_estimate, VV30_estimate. Surgical variables has been defined as the angles between the tibial tunnel and the three planes, the lengths of the tunnel and the relationship between native footprints and tunnels. An analogous characterization was performed for the femoral side. Performance and significance of the defined models have been quantified by the correlation ratio (η²) and the corresponding p-value (*p < 0.050). The analyzed models resulted to be statistically significant (p < 0.05) for prediction of postoperative static laxity values. The only exception was the AP90_estimate model. The η² ranged from 0.568 (IE90_estimate) to 0.995 (IE30_estimate). The orientation of the tibial tunnel resulted to be the most important surgical variable for the performed laxity estimation. Mathematical models for postoperative knee laxity is a useful tool to evaluate the effects of different surgical variables on the postoperative outcome.     

Role of gastrocnemius activation in knee joint biomechanics: gastrocnemius acts as an ACL antagonist

Gastrocnemius is a premier muscle crossing the knee, but its role in knee biomechanics and on the anterior cruciate ligament (ACL) remains less clear when compared to hamstrings and quadriceps. The effect of changes in gastrocnemius force at late stance when it peaks on the knee joint response and ACL force was initially investigated using a lower extremity musculoskeletal model driven by gait kinematics—kinetics. The tibiofemoral joint under isolated isometric contraction of gastrocnemius was subsequently analyzed at different force levels and flexion angles (0°–90°). Changes in gastrocnemius force at late stance markedly influenced hamstrings forces. Gastrocnemius acted as ACL antagonist by substantially increasing its force. Simulations under isolated contraction of gastrocnemius confirmed this role at all flexion angles, in particular, at extreme knee flexion angles (0° and 90°). Constraint on varus/valgus rotations substantially decreased this effect. Although hamstrings and gastrocnemius are both knee joint flexors, they play opposite roles in respectively protecting or loading ACL. Although the quadriceps is also recognized as antagonist of ACL, at larger joint flexion and in contrast to quadriceps, activity in gastrocnemius substantially increased ACL forces (anteromedial bundle). The fact that gastrocnemius is an antagonist of ACL should help in effective prevention and management of ACL injuries.     

Suture augmentation following ACL injury to restore the function of the ACL, MCL, and medial meniscus in the goat stifle joint

Functional tissue engineering (FTE) approaches have shown promise in healing an injured anterior cruciate ligament (ACL) of the knee. Nevertheless, additional mechanical augmentation is needed to maintain joint stability and appropriate loading of the joint while the ACL heals. The objective of this study was to quantitatively evaluate how mechanical augmentation using sutures restores the joint kinematics as well as the distribution of loading among the ACL, medial collateral ligament, and medial meniscus (MM) in response to externally applied loads. Eight goat stifle joints were tested on a robotic/universal force-moment sensor testing system under two loading conditions: (1) a 67N anterior tibial load (ATL) and (2) a 67N ATL with 100N axial compression. For each joint, four experimental conditions were tested at 30°, 60°, and 90° of flexion: the (1) intact and (2) ACL-deficient joint, as well as following (3) suture repair of the transected ACL, and (4) augmentation using sutures passed from the femur to the tibia. Under the 67N ATL, suture augmentation could restore the anterior tibial translation (ATT) to within 3mm of the intact joint (p>0.05), representing a 54-76% improvement over suture repair (p<0.05). With the additional axial compression, the ATT and in-situ forces of the sutures following suture augmentation remained 2-3 times closer to normal (p<0.05). Also, the in-situ forces in the MM were 58-73% lower (p<0.05). Thus, suture augmentation may be helpful in combination with FTE approaches for ACL healing by providing the needed initial joint stability while lowering the loads on the MM.     

The effect on patellofemoral joint stability of selective cutting of lateral retinacular and capsular structures

Patient selection for lateral retinacular release (LRR) and its efficacy are controversial. Iatrogenic medial subluxation can occur with inappropriate LRR. The aim of this study was to determine the reduction in patellofemoral stability with progressively more extensive LRR. The force required to displace the patella 10 mm medially and laterally in nine cadaveric knees was measured with and without loading of the quadriceps and iliotibial band. The knee was tested intact, then after progressive release beginning proximal to the patella (PR), the mid-level between the proximal and distal limit of the patella (MR) where the fibres are more transverse, then distally till Gerdy's tubercle (DR) and finally the joint capsule (CR). Both medial and lateral stability decreased with progressive releases, larger for the medial. The MR caused a significant reduction of lateral stability between 30° and 90° of knee flexion. There was an 8% reduction in medial stability at 0° flexion with a complete LRR (DR). A comparable reduction in medial stability in the loaded knee at 20° and 30° flexion was obtained with MR alone, with no further reduction after DR. A capsular release caused a further reduction in medial stability at 0° and 20° and this was marked in the unloaded knee. In extension, the main lateral restraint was the joint capsule. At 30° flexion, the transverse fibres were the main contributor to the lateral restraint.     

Mechanisms of anterior-posterior stability of the knee joint under load-bearing

The anterior-posterior (AP) stability of the knee is an important aspect of functional performance. Studies have shown that the stability increases when compressive loads are applied, as indicated by reduced laxity, but the mechanism has not been fully explained. A test rig was designed which applied combinations of AP shear and compressive forces, and measured the AP displacements relative to the neutral position. Five knees were evaluated at compressive loads of 0, 250, 500, and 750 N, with the knee at 15° flexion. At each load, three cycles of shear force at ±100 N were applied. For the intact knee under load, the posterior tibial displacement was close to zero, due to the upward slope of the anterior medial tibial surface. The soft tissues were then resected in sequence to determine their role in AP laxity. After anterior cruciate ligament (ACL) resection, the anterior tibial displacement increased significantly even under load, highlighting its importance in stability. Meniscal resection further increased displacement but also the vertical displacement increased, implying the meniscus was providing a buffering effect. The PCL had no effect on any of the displacements under load. Plowing cartilage deformation and surface friction were negligible. This work highlighted the particular importance of the upward slope of the anterior medial tibial surface and the ACL to AP knee stability under load. The results are relevant to the design of total knees which reproduce anatomic knee stability behavior.     

The effects of femoral graft placement on in vivo knee kinematics after anterior cruciate ligament reconstruction

Achieving anatomical graft placement remains a concern in Anterior Cruciate Ligament (ACL) reconstruction. The purpose of this study was to quantify the effect of femoral graft placement on the ability of ACL reconstruction to restore normal knee kinematics under in vivo loading conditions. Two different groups of patients were studied: one in which the femoral tunnel was placed near the anterior and proximal border of the ACL (anteroproximal group, n=12) and another where the femoral tunnel was placed near the center of the ACL (anatomic group, n=10) MR imaging and biplanar fluoroscopy were used to measure in vivo kinematics in these patients during a quasi-static lunge. Patients with anteroproximal graft placement had up to 3.4mm more anterior tibial translation, 1.1mm more medial tibial translation and 3.7° more internal tibial rotation compared to the contralateral side. Patients with anatomic graft placement had motion that more closely replicated that of the intact knee, with anterior tibial translation within 0.8mm, medial tibial translation within 0.5mm, and internal tibial rotation within 1°. Grafts placed anteroproximally on the femur likely provide insufficient restraint to these motions due to a more vertical orientation. Anatomical femoral placement of the graft is more likely to reproduce normal ACL orientation, resulting in a more stable knee. Therefore, achieving anatomical graft placement on the femur is crucial to restoring normal knee function and may decrease the rates of joint degeneration after ACL reconstruction.     

Effect of hip joint angle on concentric knee extension torque

This study tested the hypothesis that the effect of hip joint angle on concentric knee extension torque depends on knee joint angle during a single knee extension task. Twelve men performed concentric knee extensions in fully extended and 80° flexed hip positions with maximal effort. The angular velocities were set at 30° s⁻¹ and 180° s⁻¹. The peak torque and torques attained at 30°, 50°, 70° and 90° (anatomical position = 0°) of the knee joint were compared between the two hip positions. Muscle activations of the vastus lateralis, medialis, rectus femoris and biceps femoris were determined using surface electromyography. The peak torque was significantly greater in the flexed than in the extended hip position irrespective of angular velocity. The torques at 70° and 90° of the knee joint at both angular velocities and at 50° at 180° s⁻¹ were significantly greater in the flexed than in the extended hip position, whereas corresponding differences were not found at 30° (at either angular velocity) and 50° (at 30° s⁻¹) of the knee joint. No effect of hip position on muscle activation was observed in any muscle. These results supported our hypothesis and may be related to the force–length and force–velocity characteristics of the rectus femoris.     

EMG-angle relationship of the hamstring muscles during maximum knee flexion.

The aim of the present study was to investigate the EMG-joint angle relationship during voluntary contraction with maximum effort and the differences in activity among three hamstring muscles during knee flexion. Ten healthy subjects performed maximum voluntary isometric and isokinetic knee flexion. The isometric tests were performed for 5 s at knee angles of 60 and 90 degrees. The isokinetic test, which consisted of knee flexion from 0 to 120 degrees in the prone position, was performed at an angular velocity of 30 degrees /s (0.523 rad/s). The knee flexion torque was measured using a KIN-COM isokinetic dynamometer. The individual EMG activity of the hamstrings, i.e. the semitendinosus, semimembranosus, long head of the biceps femoris and short head of the biceps femoris muscles, was detected using a bipolar fine wire electrode. With isometric testing, the knee flexion torque at 60 degrees knee flexion was greater than that at 90 degrees. The mean peak isokinetic torque occurred from 15 to 30 degrees knee flexion angle and then the torque decreased as the knee angle increased (p<0.01). The EMG activity of the hamstring muscles varied with the change in knee flexion angle except for the short head of the biceps femoris muscle under isometric condition. With isometric contraction, the integrated EMGs of the semitendinosus and semimembranosus muscles at a knee flexion angle of 60 degrees were significantly lower than that at 90 degrees. During maximum isokinetic contraction, the integrated EMGs of the semitendinosus, semimembranosus and short head of the biceps femoris muscles increased significantly as the knee angle increased from 0 to 105 degrees of knee flexion (p<0.05). On the other hand, the integrated EMG of the long head of the biceps femoris muscle at a knee angle of 60 degrees was significantly greater than that at 90 degrees knee flexion with isometric testing (p<0.01). During maximum isokinetic contraction, the integrated EMG was the greatest at a knee angle between 15 and 30 degrees, and then significantly decreased as the knee angle increased from 30 to 120 degrees (p<0.01). These results demonstrate that the EMG activity of hamstring muscles during maximum isometric and isokinetic knee flexion varies with change in muscle length or joint angle, and that the activity of the long head of the biceps femoris muscle differs considerably from the other three heads of hamstrings.