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束：股直肌、股内、外侧肌腱合为A束,股中间肌腱为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。     

Successful embryo transfer in Tianzhu white yak using standard protocol

The present study was carried out to investigate the efficiency of superovulation, oestrus synchroni-zation, and embryo recovery in Tianzhu white yaks and also to confirm the pregnancy rate of black yaks, to which embryos collected from white yaks were transplanted. Forty-seven yaks were selected from different experiment groups, including 10 Tianzhu white female yaks (donor, group A) and 37 black female yaks (recipient, groups B and C). Superovulation of the donor was induced by the application procedure of CIDR-B FSH PG. Oestrus synchronization of recipients was induced using two meth-ods: group B was given the same treatment as group A, except that the follicle-stimulating hormone (FSH) injection was not administered, whereas group C was injected with cloprostenol only once when corpus luteum (corpora lutea) was (were) palpated. The results showed that the oestrous rates in group A were higher (80%) than those in group B (60%) and group C (44.5%). As for the efficiency of su-perovulation, it was indicated that the mean numbers (±SD) of total corpora lutea, follicles, viable (transferable), and degenerated embryos were 4.75 ± 2.19, 1.13 ± 0.83, 2.50 ± 1.31, and 1.38 ± 0.92, re-spectively. The mean embryo recovery rates were 55.6%. All together, 18 viable embryos of Tianzhu white yak were obtained and 12 of them were transplanted to 10 recipients. The pregnancy rate was 50% and the delivery rate was 40%.     

An in vitro and finite element study of load redistribution in the midfoot

A good knowledge of midfoot biomechanics is important in understanding the biomechanics of the entire foot,but it has never been investigated thoroughly in the literature.This study carried out in vitro experiments and finite element analysis to investigate the midfoot biomechanics.A foot-ankle finite element model simulating the mid-stance phase of the normal gait was developed and the model validated in in vitro experimental tests.Experiments used seven in vitro samples of fresh human cadavers.The simulation found that the first principal stress peaks of all midfoot bones occurred at the navicular bone and that the tensile force of the spring ligament was greater than that of any other ligament.The experiments showed that the longitudinal strain acting on the medial cuneiform bone was-26.2±10.8μ-strain,and the navicular strain was-240.0±169.1μ-strain along the longitudinal direction and 65.1±25.8μ-strain along the transverse direction.The anatomical position and the spring ligament both result in higher shear stress in the navicular bone.The load from the ankle joint to five branches of the forefoot is redistributed among the cuneiforms and cuboid bones.Further studies on the mechanism of loading redistribution will be helpful in understanding the biomechanics of the entire foot.     

以光合效率度量天然白桦种群生态位初探

In terms of photosynthetic efficiency,which demonstrates the space-time function of plant,niche width of B. Platyphylla population was described.First,on the basis of net photosynthetic amount in certain time,the niche width of a birch was calculated.Then,the realized niche and rudimental niche of B. Platyphylla seedlings,young trees and adult trees were discussed.Finally, the dynamic of niche under special conditions was studied.     

A new method of preparing fiber-optic DNA biosensor and its array for gene detection

A new method of preparing fiber-optic DNA biosensor and its array for the simultaneous detection of multiple genes is described. The optical fibers were first treated with poly-l-lysine, and then were made into fiber-optic DNA biosensors by adsorbing and immobilizing the oligonucleotide probe on its end. By assembling the fiber-optic DNA biosensors in a bundle in which each fiber carried a different DNA probe, the fiber-optic DNA biosensor array was well prepared. Hybridization of fluorescent- labeled cDNA of p53 gene, N-ras gene and Rb1 gene to the DNA array was monitored by CCD camera. A good result was achieved.     

Zonal distribution and population biology of Ilyoplax frater (Brachyura:Ocypodoidea:Dotillidae) in a coastal mudflat of Pakistan

<正> Zonal distribution and population biology of Ilyoplax frater were studied in a mangrove mudflat area of Pakistan.The crabs were collected from Korangi creek through transect and quadrat method from low tide level to high tide level. Twotransects were delimited in a mangrove area of Korangi creek (24°79'N/ 67°20'E). On each transect, three 0.25 m quadrats weresampled at three tidal levels on a monthly basis during low tide periods from March 2001 to February 2002. A total of 1124 crabswere obtained, of which 482 were males and 642 were females. Density of crabs varied between 0 and 90 /m". The density andsize distribution varied and showed significant differences from low to high tide level, and were positively correlated with thepercent moisture, percent organic matter and sediment grain size. The carapace width (CW) ranged from 2.5 to 11.5 mm for maleand 2.5 to 11.0 mm for female and was not significantly different. The overall sex ratio did not differ significantly from the expected1:1 throughout the year in small crabs but was significantly different in adult crabs (x~2= 49.73) with more male crabs. Sizefrequency distribution showed recruitment of juvenile crabs ( 4 mm) nearly throughout the year except during June and July.Presence of ovigerous females in all months with seasonal peaks in September, October, December and May indicates seasonalcontinuous breeding. Weight of egg mass increases with weight of ovigerous females and show positive linear relationship. Theestimated mean diameter of egg was 2.83±0.25μm, and the average number of eggs was 3065±902     

Study of the Antifungal Ability of Bacillus subtilis Strain PY-1 in Vitro and Identification of its Antifungal Substance （Iturin A）

A Bacillus strain,denoted as PY-1,was isolated from the vascular bundle of cotton.Biochemical,physiological and 16S rDNA sequence analysis proved that it should belong to Bacillus subtilis.The PY-1strain showed strong ability against many common plant fungal pathogens in vitro.The antibiotics producedby this strain were stable in neutral and basic conditions,and not sensitive to high temperature.From theculture broth of PY-1 strain,five antifungal compounds were isolated by acidic precipitation,methanolextraction,gel filtration and reverse-phase HPLC.Advanced identification was performed by mass spec-trometry and nuclear magnetic resonance spectroscopy.These five antifungal compounds were proved to bethe isomers of iturin A:A2,A3,A4,A6 and A7.In fast atom bombardment mass spectrometry/mass spec-trometry collision-induced dissociation spectra,fragmentation ions from two prior linear acylium ions wereobserved,and the prior ion,Tyr-Asn-Gln-Pro-Asn-Ser-βAA-Asn-CO~ ,was first reported.     

Changes of microcirculation in healthy volunteers and patients with septic shock in Xining

Objective: The purpose of this study is to investigate the characteristic of microcirculation in healthy volunteers and patients with septic shock in both Xining(2 260 m) and Nanjing(10 m). Methods: A total of 62 cases, 33 healthy volunteers, 22 cases in Xining,(2 260 m above sea level) and 11 cases in Nanjing(10 m above sea level); and 29 septic shock, 13 cases in Xining and 16 cases in Nanjing were collected. The total vessel density(TVD), perfused vessel density(PVD), proportion of perfused vessel(PPV) and microcirculation flow index(MFI) of both healthy volunteers and septic shock had been investigated by using sidestream dark field(SDF). Analyzed and managed the image data by using AVA3.0 software. Results: In the healthy volunteers in Xining area(22 cases),the volume of TVD(15.59 ± 2.58 mm/mm~2), PVD(15.58 ± 2.58 mm/mm~2) and PPV(96.60% ± 4.63%) were significant higher than the volume of TVD(10.0 ± 2.10 mm/mm~2), PVD(10.81 ± 2.38 mm/mm~2) and PPV(84.24% ± 8.00%) of the volunteers(11 cases) in Nanjing(11 cases). But the MFI(2.17 ± 0.31) of the healthy volunteers in the Xining was significant lower(P0.05) than the MFI(3.21 ± 0.34) in the healthy volunteers of Nanjing. In the septic shock group(13 cases) in the Xining, the volume of TVD(5.44 ± 1.94 mm/mm~2), PVD(4.18 ± 1.61 mm/mm~2), PPV(42.14%± 5.38%) and MFI(1.05 ± 0.32) compared with the volume of the healthy volunteers in Xining, the TVD(15.59 ± 2.58 mm/mm~2), PVD(5.58 ± 2.58 mm/mm~2), PPV(96.60% ± 4.63%) and MFI(2.17 ± 0.30) were significant lower(P0.05). In the healthy volunteers compare with septic shock group in Nanjing area, the TVD(6.80±1.72 vs 10.00±2.10, P0.05), PVD(5.86±1.58 vs10.81±2.38,P0.05), PPV(45.42±4.86 vs 84.24±4.86, P0.05), MFI(1.28±0.28 vs 3.21±0.34 P0.05), there was significant decreased. In the septic shock group in the Xining compared with the septic shock in Nanjing, there was no significant difference. 10 of 13 patients with septic shock were survived in Xining. 13 of 16 patients with septic shock were survived in Nanjing. Conclusion: The changes of physiological and pathophysiological characteristic in microcirculation induced by hypoxia would be useful for clinical treatment of septic shock at high altitude.     

Serological identification and molecular characterization of B (A) 02 subtype in patients and blood donors from Eastern China

This study was designed to identify the rare?type?ABO?blood?groups, B(A) 02, from Eastern China. Three samples with discordant serological results during routine blood type identification and four samples from one sample’ family were selected. All of them were detected by serological method. The exon 6 and 7 of the ABO genes were amplified by PCR and sequenced. They were typed as AsubB by serology and as BO by genotype. In AsubB samples, nt 700C>G mutation was detected in B gene, which was previously defined as B(A)02 alleles. In these seven samples, six showed B(A)02/O01 and one showed B(A)02/O02.B(A)02 allele was found to be more common in this study than B(A)04 which is considered to be more frequent than B(A)02. The careful identification of rare blood types is important for the safety of clinical blood transfusion.     

Effects of Irradiance and Temperature on the Photosynthesis and Vegetative Propagation of Caulerpa serrulata

The photosynthetic oxygen evolution of Caulerpa serrulata was determined with oxygen electrodes. The effects of light and temperature on the growth and regeneration of fragmented C. serrulata thalli were analyzed. The regenerating rate and establishment of different sizes and portions of C. serrulata were studied. The results showed that the light saturation point of C. serrulata was 200 μmol photons/m2 per s and the optimum growth temperature was 25-30℃. Under these conditions, the maximum photosynthetic oxygen evolution rate was 15.1:±0.29 mg O2/mg Chl a/h, the growth rate and elongation rate reached the highest values, 4.67±0.09 mg FW/d and 0.78±0.01 mm/d, respectively. The fragmented C. serrulata thalli was regenerated at 20-35℃ and survived at 15℃ and 200 μmnol photons/m2 per s. A different survival rate was detected according to fragment size. All of these results indicated that C. serrulata was a candidate to become an invasive species if introduced into a new place. Therefore, we should pay more attention to C. serrulata for its potential threat to marine ecosystem when it is sold for aquarium use.     

Anatomy and Biomechanical Properties of the Plantar Aponeurosis: A Cadaveric Study

Objectives

To explore the anatomy of the plantar aponeurosis (PA) and its biomechanical effects on the first metatarsophalangeal (MTP) joint and foot arch.

Methods

Anatomic parameters (length, width and thickness of each central PA bundle and the main body of the central part) were measured in 8 cadaveric specimens. The ratios of the length and width of each bundle to the length and width of the central part were used to describe these bundles. Six cadaveric specimens were used to measure the range of motion of the first MTP joint before and after releasing the first bundle of the PA. Another 6 specimens were used to evaluate simulated static weight-bearing. Changes in foot arch height and plantar pressure were measured before and after dividing the first bundle.

Results

The average width and thickness of the origin of the central part at the calcaneal tubercle were 15.45 mm and 2.79 mm respectively. The ratio of the length of each bundle to the length of the central part was (from medial to lateral) 0.29, 0.30, 0.28, 0.25, and 0.27, respectively. Similarly, the ratio of the widths was 0.26, 0.25, 0.23, 0.19 and 0.17. The thickness of each bundle at the bifurcation of the PA into bundles was (from medial to lateral) 1.26 mm, 1.04 mm, 0.91 mm, 0.84 mm and 0.72 mm. The average dorsiflexion of the first MTP joint increased 10.16° after the first bundle was divided. Marked acute changes in the foot arch height and the plantar pressure were not observed after division.

Conclusions

The first PA bundle was not the longest, widest, or the thickest bundle. Releasing the first bundle increased the range of motion of the first MTP joint, but did not acutely change foot arch height or plantar pressure during static load testing.     

Calibration of hyperelastic material properties of the human lumbar intervertebral disc under fast dynamic compressive loads

Under fast dynamic loading conditions (e.g. high-energy impact), the load rate dependency of the intervertebral disc (IVD) material properties may play a crucial role in the biomechanics of spinal trauma. However, most finite element models (FEM) of dynamic spinal trauma uses material properties derived from quasi-static experiments, thus neglecting this load rate dependency. The aim of this study was to identify hyperelastic material properties that ensure a more biofidelic simulation of the IVD under a fast dynamic compressive load. A hyperelastic material law based on a first-order Mooney-Rivlin formulation was implemented in a detailed FEM of a L2-L3 functional spinal unit (FSU) to represent the mechanical behavior of the IVD. Bony structures were modeled using an elasto-plastic Johnson-Cook material law that simulates bone fracture while ligaments were governed by a viscoelastic material law. To mimic experimental studies performed in fast dynamic compression, a compressive loading velocity of 1 m/s was applied to the superior half of L2, while the inferior half of L3 was fixed. An exploratory technique was used to simulate dynamic compression of the FSU using 34 sets of hyperelastic material constants randomly selected using an optimal Latin hypercube algorithm and a set of material constants derived from quasi-static experiments. Selection or rejection of the sets of material constants was based on compressive stiffness and failure parameters criteria measured experimentally. The two simulations performed with calibrated hyperelastic constants resulted in nonlinear load-displacement curves with compressive stiffness (7335 and 7079 N/mm), load (12,488 and 12,473 N), displacement (1.95 and 2.09 mm) and energy at failure (13.5 and 14.7 J) in agreement with experimental results (6551 ± 2017 N/mm, 12,411 ± 829 N, 2.1 ± 0.2 mm and 13.0 ± 1.5 J respectively). The fracture pattern and location also agreed with experimental results. The simulation performed with constants derived from quasi-static experiments showed a failure energy (13.2 J) and a fracture pattern and location in agreement with experimental results, but a compressive stiffness (1580 N/mm), a failure load (5976 N) and a displacement to failure (4.8 mm) outside the experimental corridors. The proposed method offers an innovative way to calibrate the hyperelastic material properties of the IVD and to offer a more realistic simulation of the FSU in fast dynamic compression.     

A modeling study of partial ACL injury: simulated KT-2000 arthrometer tests

A partial ACL injury may involve different levels of fiber disruption, orfibers may sustain microscopic changes in their structure without gross disruption, resulting in a change in ligament function. The effect of partial ACL tears on the mechanical and functional stability of the knee has not been well documented, in part because of diagnostic difficulties. A computer model of the knee in the sagittal plane was used in this study to simulate tests using the KT-2000 Knee Arthrometer, which quantifies Lachman's test for ACL injury. A variety of partial ACL anterior and posterior bundle injuries were simulated. Anterior and posterior bundle injuries were subdivided into four different simulated injury levels: mild (one-half tear of the bundle), moderate (complete tear of the bundle), severe (complete tear of the bundle and tear of one-half of the other bundle), and more severe (severe injury plus an additional elongation of the other bundle represented by 5% increases of its initial strain). Force-displacement results obtained from simulated KT-2000 knee arthrometer tests depended on the level of injury. Mild and moderate injuries produced only small change in the anterior tibial translation--at different force levels. Severe injury produced increased anterior tibial translation depending on which bundle was completely ruptured. The compliance index defined as the ratio of the displacement and the force within 68 N and 90 N anterior drawer forces, the stiffness, and the rate of change of stiffness of the anterior force-displacement were found to be better at predicting partial ACL ruptures than simple differences in anterior tibial translation. It was possible in the model results to discriminate knees with various levels of partial ACL injuries using the first and second derivatives of the force-displacement curve.     

Comparison of viscoelastic, structural, and material properties of double-looped anterior cruciate ligament grafts made from bovine digital extensor and human hamstring tendons

Due to ready availability, decreased cost, and freedom from transmissible diseases in humans such as hepatitis and AIDS, it would be advantageous to use tendon grafts from farm animals as a substitute for human tendon grafts in in vitro experiments aimed at improving the outcome of anterior cruciate ligament (ACL) reconstructive surgery. Thus the objective of this study was to determine whether an anterior cruciate ligament (ACL) graft composed of two loops of bovine common digital extensor tendon has the same viscoelastic, structural, and material properties as a graft composed of a double loop of semitendinosus and gracilis tendons from humans. To satisfy this objective, grafts were constructed from each tissue source. The cross-sectional area was measured using an area micrometer, and each graft was then pulled using a materials testing system while submerged in a saline bath. Using two groups of tendon grafts (n = 10), viscoelastic tests were conducted over a three-day period during which a constant displacement load relaxation test was followed by a constant amplitude, cyclic load creep test (first day), a constant load creep test (second day), and an incremental cyclic load creep test (third day). Load-to-failure tests were performed on two different groups of grafts (n = 8). When the viscoelastic behavior was compared, there were no significant differences in the rate of load decay or the final load (relaxation test) and rates of displacement increase or final displacements (creep tests) (p > 0.115). To compare both the structural and material properties in the toe region (i.e., < 250 N) of the load-elongation curve, the tangent stiffness and modulus functions were computed from parameters used in an exponential model fit to the load (stress)-elongation (strain) data. Although one of the two parameters in the functions was different statistically, this difference translated into a difference of only 0.03 mm in displacement at 250 N of load. In the linear region (i.e., 50-75 percent of ultimate load) of the load-elongation curve, the linear stiffness of the two graft types compared closely (444 N/mm for bovine and 418 N/mm for human) (p = 0.341). At failure, the ultimate loads (2901 N and 2914 N for bovine and human, respectively) and the ultimate stresses (71.8 MPa and 65.6 MPa for bovine and human, respectively) were not significantly different (p > 0.261). The theoretical effect of any differences in properties between these two grafts on the results of two types of in vitro experiments (i.e., effect of surgical variables on knee laxity and structural properties of fixation devices) are discussed. Despite some statistical differences in the properties evaluated, these differences do not translate into important effects on the dependent variables of interest in the experiments. Thus the bovine tendon graft can be substituted for the human tendon graft in both types of experiments.     

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。     

Estimation of in vivo ACL force changes in response to increased weightbearing

Accurate knowledge of in vivo anterior cruciate ligament (ACL) forces is instrumental for understanding normal ACL function and improving surgical ACL reconstruction techniques. The objective of this study was to estimate the change in ACL forces under in vivo loading conditions using a noninvasive technique. A combination of magnetic resonance and dual fluoroscopic imaging system was used to determine ACL in vivo elongation during controlled weightbearing at discrete flexion angles, and a robotic testing system was utilized to determine the ACL force-elongation data in vitro. The in vivo ACL elongation data were mapped to the in vitro ACL force-elongation curve to estimate the change in in vivo ACL forces in response to full body weightbearing using a weighted mean statistical method. The data demonstrated that by assuming that there was no tension in the ACL under zero weightbearing, the changes in in vivo ACL force caused by full body weightbearing were 131.4 ± 16.8 N at 15 deg, 106.7 ± 11.2 N at 30 deg, and 34.6 ± 4.5 N at 45 deg of flexion. However, when the assumed tension in the ACL under zero weightbearing was over 20 N, the change in the estimated ACL force in response to the full body weightbearing approached an asymptotic value. With an assumed ACL tension of 40 N under zero weightbearing, the full body weight caused an ACL force increase in 202.7 ± 27.6 N at 15 deg, 184.9 ± 22.5 N at 30 deg, and 98.6 ± 11.7 N at 45 deg of flexion. The in vivo ACL forces were dependent on the flexion angle with higher force changes at low flexion angles. Under full body weightbearing, the ACL may experience less than 250 N. These data may provide a valuable insight into the biomechanical behavior of the ACL under in vivo loading conditions.     

油桐尺蠖幼虫龄期的划分

通过对油桐尺蠖Buzura suppressaria Guene幼虫实际蜕皮次数的观察和头壳宽度的测量,确定幼虫龄期为7龄。1～7龄幼虫头壳宽(mm)分别为:0.2905±0.0101,0.4627±0.0213,0.6884±0.03,1.124±0.0407,1.7826±0.0457,2.6772±0.078,3.8401±0.0567。经统计分析得到其龄期y与幼虫头壳宽度x的关系式为y=0.1917e0.436x。     

Effect of the intra-abdominal pressure and the center of segmental body mass on the lumbar spine mechanics - a computational parametric study

Determination of physiological loads in human lumbar spine is critical for understanding the mechanisms of lumbar diseases and for designing surgical treatments. Computational models have been used widely to estimate the physiological loads of the spine during simulated functional activities. However, various assumptions on physiological factors such as the intra-abdominal pressure (IAP), centers of mass (COMs) of the upper body and lumbar segments, and vertebral centers of rotation (CORs) have been made in modeling techniques. Systematic knowledge of how these assumptions will affect the predicted spinal biomechanics is important for improving the simulation accuracy. In this paper, we developed a 3D subject-specific numerical model of the lumbosacral spine including T12 and 90 muscles. The effects of the IAP magnitude and COMs locations on the COR of each motion segment and on the joint/muscle forces were investigated using a global convergence optimization procedure when the subject was in a weight bearing standing position. The data indicated that the line connecting the CORs showed a smaller curvature than the lordosis of the lumbar spine in standing posture when the IAP was 0?kPa and the COMs were 10?mm anterior to the geometric center of the T12 vertebra. Increasing the IAP from 0 kPa to 10 kPa shifted the location of CORs toward the posterior direction (from 1.4?±?8.9 mm anterior to intervertebral disc (IVD) centers to 40.5?±?3.1 mm posterior to the IVD centers) and reduced the average joint force (from 0.78?±?0.11 Body weight (BW) to 0.31?±?0.07 BW) and overall muscle force (from 349.3?±?57.7 N to 221.5?±?84.2 N). Anterior movement of the COMs from -30 mm to 70 mm relative to the geometric center of T12 vertebra caused an anterior shift of the CORs (from 25.1?±?8.3 mm posterior to IVD centers to 7.8?±?6.2 mm anterior to IVD centers) and increases of average joint forces (from 0.78?±?0.1 BW to 0.93?±?0.1 BW) and muscle force (from 348.9?±?47.7 N to 452.9?±?58.6 N). Therefore, it is important to consider the IAP and correct COMs in order to accurately simulate human spine biomechanics. The method and results of this study could be useful for designing prevention strategies of spinal injuries and recurrences, and for enhancing rehabilitation efficiency.     

The importance of quadriceps and hamstring muscle loading on knee kinematics and in-situ forces in the ACL

This study investigated the effect of hamstring co-contraction with quadriceps on the kinematics of the human knee joint and the in-situ forces in the anterior cruciate ligament (ACL) during a simulated isometric extension motion of the knee. Cadaveric human knee specimens (n = 10) were tested using the robotic universal force moment sensor (UFS) system and measurements of knee kinematics and in-situ forces in the ACL were based on reference positions on the path of passive flexion/extension motion of the knee. With an isolated 200 N quadriceps load, the knee underwent anterior and lateral tibial translation as well as internal tibial rotation with respect to the femur. Both translation and rotation increased when the knee was flexed from full extension to 30 of flexion; with further flexion, these motion decreased. The addition of 80 N antagonistic hamstrings load significantly reduced both anterior and lateral tibial translation as well as internal tibial rotation at knee flexion angles tested except at full extension. At 30 of flexion, the anterior tibial translation, lateral tibial translation, and internal tibial rotation were significantly reduced by 18, 46, and 30%, respectively (p<0.05). The in-situ forces in the ACL under the quadriceps load were found to increase from 27.8+/-9.3 N at full extension to a maximum of 44.9+/-13.8 N at 15 of flexion and then decrease to 10 N beyond 60 of flexion. The in-situ force at 15 was significantly higher than that at other flexion angles (p<0.05). The addition of the hamstring load of 80 N significantly reduced the in-situ forces in the ACL at 15, 30 and 60 of flexion by 30, 43, and 44%, respectively (p<0.05). These data demonstrate that maximum knee motion may not necessarily correspond to the highest in-situ forces in the ACL. The data also suggest that hamstring co-contraction with quadriceps is effective in reducing excessive forces in the ACL particularly between 15 and 60 of knee flexion.