Effect of knee flexion angle on active joint stiffness

AIM: The purpose of this study was to determine if active joint stiffness measured during maximum voluntary knee extension contractions was affected by knee flexion angle. METHODS: Eighteen subjects volunteered (11 male, seven female). A stretch was imposed on isometric knee contractions performed at 30 degrees, 50 degrees, 70 degrees, 90 degrees, and 110 degrees of knee flexion. Active joint stiffness was computed from the increase in torque relative to the change in knee flexion angle for the first 50 ms of the stretch (approximately 1.5 degrees ) and corrected for effects of gravitational component due to leg mass and passive tension. RESULTS: There was a plateau in knee extension torque between 70 degrees and 90 degrees with lower values at all other angles (P < 0.05). Peak active joint stiffness occurred at 70 degrees with lower values (P < 0.05) at all other angles except 50 degrees. Stiffness at 70 degrees (441.1 +/- 189.9 Nm rad-1) was 49% higher than at 30 degrees and 45% higher than at 110 degrees. CONCLUSION: Active joint stiffness was dependent on knee flexion angle. Peak joint stiffness during maximal contractions occurred at, or prior to, the optimal angle for torque production for all subjects.     

Lower extremity kinematics and ground reaction forces after prophylactic lace-up ankle bracing

CONTEXT: Long-term effects of ankle bracing on lower extremity kinematics and kinetics are unknown. Ankle motion restriction may negatively affect the body's ability to attenuate ground reaction forces (GRFs). OBJECTIVE: To evaluate the immediate and long-term effects of ankle bracing on lower extremity kinematics and GRFs during a jump landing. DESIGN: Experimental mixed model (2 [group] x 2 [brace] x 2 [time]) with repeated measures. SETTING: Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 37 healthy subjects were assigned randomly to either the intervention (n = 11 men, 8 women; age = 19.63 +/- 0.72 years, height = 176.05 +/- 10.58 cm, mass = 71.50 +/- 13.15 kg) or control group (n = 11 men, 7 women; age = 19.94 +/- 1.44 years, height = 179.15 +/- 8.81 cm, mass = 74.10 +/- 10.33 kg). INTERVENTION(S): The intervention group wore braces on both ankles and the control group did not wear braces during all recreational activities for an 8-week period. MAIN OUTCOME MEASURE(S): Initial ground contact angles, maximum joint angles, time to reach maximum joint angles, and joint range of motion for sagittal-plane knee and ankle motion were measured during a jump-landing task. Peak vertical GRF and the time to reach peak vertical GRF were assessed also. RESULTS: While participants were wearing the brace, ankle plantar flexion at initial ground contact (brace = 35 degrees +/- 13 degrees , no brace = 38 degrees +/- 15 degrees , P = .024), maximum dorsiflexion (brace = 21 degrees +/- 7 degrees , no brace = 22 degrees +/- 6 degrees , P = .04), dorsiflexion range of motion (brace = 56 degrees +/- 14 degrees , no brace = 59 degrees +/- 16 degrees , P = .001), and knee flexion range of motion (brace = 79 degrees +/- 16 degrees , no brace = 82 degrees +/- 16 degrees , P = .036) decreased, whereas knee flexion at initial ground contact increased (brace = 12 degrees +/- 9 degrees , no brace = 9 degrees +/- 9 degrees , P = .0001). Wearing the brace for 8 weeks did not affect any of the outcome measures, and the brace caused no changes in vertical GRFs (P > .05). CONCLUSIONS: Although ankle sagittal-plane motion was restricted with the brace, knee flexion upon landing increased and peak vertical GRF did not change. The type of lace-up brace used in this study appeared to restrict ankle motion without increasing knee extension or vertical GRFs and without changing kinematics or kinetics over time.     

Bilateral medial tibiofemoral joint stiffness in full extension and 20 degrees of knee flexion

CONTEXT: The valgus stress test is used clinically to assess injury to the medial knee structures in 2 positions: full extension and some degree of flexion. The amount of flexion used to "isolate" the medial collateral ligament is not consistent in the literature, but most studies have shown that stiffness of the ligaments was consistent between the limbs. OBJECTIVE: To determine (1) if the stiffness of the medial knee structures was the same bilaterally, and (2) if the stiffness was different in full extension compared with 20 degrees of knee flexion. DESIGN: Criterion standard, before-after design. SETTING: University research laboratory. PATIENTS OR OTHER PARTICIPANTS: Both knees of 45 healthy and active volunteers (26 females, 19 males; age = 23.2 +/- 3.96 years, height = 170.6 +/- 7.75 cm, mass = 74.2 +/- 15.14 kg) were studied. INTERVENTION(S): A valgus force of 60 N was applied to the lateral aspect of both knees in full extension and in 20 degrees of flexion. MAIN OUTCOME MEASURE(S): The slope of the force-strain line of the medial knee during a valgus force was calculated using the LigMaster arthrometer. RESULTS: Slope means in full extension were 16.1 +/- 3.3 (right knee) and 15.8 +/- 3.1(left knee). Means for 20 degrees of flexion were 12.2 +/- 3.1 (right) and 11.7 +/- 2.8 (left). Stiffness was greater when the knee was in full extension versus 20 degrees of flexion (t(44) = 12.04, P < .001). No difference was noted between the slopes of the 2 knees in extension (t(44) = 0.74, P = .46) or in flexion (t(44) = 1.2, P = .27). CONCLUSIONS: These findings support the use of the contralateral knee as a control. Further, the valgus stress test should be performed in full extension and in some degree of flexion to assess the different restraining structures of the medial tibiofemoral joint.     

In vivo knee laxity in flexion and extension: a radiographic study in 30 older healthy subjects

In order to determine how "tight" a total knee prosthesis should be implanted, it is important to know the amount of laxity in a healthy knee. The objective of this study was to determine knee laxity in extension and flexion in healthy, non-arthritic knees of subjects similar in age to patients undergoing a total knee arthroplasty and to provide guidelines for the orthopaedic surgeon in his attempt to restore the stability of an osteoarthritic knee to normal. Thirty healthy subjects (15 male, 15 female), mean age 62 (SD 6.4) years, were included in the study. For each subject one, randomly selected, knee was stressed in extension and in 70 degrees flexion (15 Nm). Varus and valgus laxity were measured on radiographs. The passive range of motion and active flexion was assessed. Mean valgus laxity in extension was 2.3 degrees (SD 0.9, range 0.2 degrees -4.1 degrees ). In extension mean varus laxity was 2.8 degrees (SD 1.3, range 0.6 degrees -5.4 degrees ). In flexion, mean valgus laxity was 2.5 degrees (SD 1.5, range 0.0 degrees -6.0 degrees ) and mean varus laxity was 3.1 degrees (SD 2.0, range 0.1 degrees -7.0 degrees ). Varus and valgus knee laxity in extension and in flexion were comparable. This study shows that the normal knee in this age group has an inherent degree of varus-valgus laxity. Whether the results of the present study can be used to optimise the total knee arthroplasty implantation technique requires further investigation.     

Biomechanics of passive knee joint in drawer: load transmission in intact and ACL-deficient joints

A non-linear 3D finite element model of the passive human tibiofemoral knee joint consisting of two bony structures and their articular cartilage layers, menisci, and four principal ligaments was used to investigate the detailed response of the unconstrained joint under up to 100 N posterior femoral force at different flexion angles from 0 to 90 degrees. The analysis was repeated after the transection of the anterior cruciate ligament (ACL). The boundary conditions were selected to assure a stable and unconstrained response of the joint throughout the range of motion. The results indicated the ACL as the primary structure to resist the drawer load throughout the range of flexion considered and that the joint primary and coupled laxities substantially increased in its absence. At full extension under drawer, forces in collateral ligaments increased significantly resulting in larger overall contact forces as the ACL was transected. In the ACL-deficient joint, such large forces in collateral ligaments, however, diminished as flexion angle varied from 0 to 90 degrees. At full extension or flexion angles up to approximately 30 degrees, the medial meniscus and adjacent medial tibial and femoral cartilage layers were subjected to substantially larger loads and stresses following the transection of the ACL. Adequate consideration of such couplings is important in avoiding further damage to joint structures subsequent to an injury and restoring adequate function following injuries to primary components.     

伤科手法治疗腰椎间盘突出症的运动学研究

为探索中医手法治疗腰椎间盘突出症的运动学规律和机制,选取上海交通大学附属瑞金医院魏氏伤科手法中的经典“悬足压膝”和“腰部提拉”手法动作作为研究对象。对10名健康青年男性施加手法动作,并通过三维运动捕捉系统采集手法作用时受试者的5次运动学数据,定义人体相对关节坐标系,并通过Visual3D软件建立人体三维运动模型。计算下肢髋关节、膝关节和踝关节的相对运动角度,并分解对应得到各关节的屈曲/伸展、外展/内收、轴向旋转运动,处理计算得到关节的平均运动角度和轨迹规律。统计各运动数据,分析运动的左右侧差异。结果表明,右侧髋关节的平均被动屈曲角度可达137.33°,被动伸展角度可达30.86°,这与解剖学上髋关节的被动最大角度以及其与膝关节位置相关的理论相一致,也验证了髋关节的极限屈曲/伸展角度与膝关节的位置有关,从而说明魏氏手法的运动学作用机理在于促进髋关节被动运动达到可达最大程度。同时发现,部分关节运动角度针对下肢惯用侧存在统计学上的左右侧差异(P<0.05)。该研究为手法的研究和定量评估提供新的研究方法。     

全膝关节置换后关节后方复合松解的可行性评价

背景：临床对于膝骨关节炎患者可以实施全膝关节置换治疗,为提高修复效果,促进功能恢复,要采取有效措施改善置换过程中的关节间隙以及置换后的关节活动度。 目的：探讨全膝关节置换后行关节后方复合松解的有效性及可行性。 方法：从两家三甲医院2009年12月至2013年12月收治的行单侧全膝关节置换的膝骨关节炎患者中选择118例进行研究,随机分为对照组和观察组,每组59例。在患者全膝关节置换过程中完成截骨之后,对照组行常规后髁增生骨清理,观察组行关节后方复合松解。观察两组患者置换后伸、屈膝间隙情况和主动屈膝90°和120°所需时间,记录3个月随访时的膝关节功能美国纽约特种外科医院评分以及最大屈膝角度,并进行比较。 结果与结论：经统计和比较,两组患者在屈膝间隙方面差异无显著性意义(P > 0.05);但在伸膝间隙、主动屈膝90°、120°所需时间以及最大屈膝角度方面,两组差异均有显著性意义,观察组优于对照组(P均< 0.05)。比较置换后3个月两组患者的膝关节功能美国纽约特种外科医院评分,可得观察组的各项指标得分以及总分均显著高于对照组,差异均有显著性意义(P均 < 0.05)。表明全膝关节置换后行关节后方复合松解具有一定的有效性和可行性,可以有效改善置换过程中伸膝间隙以及置换后膝关节活动度,但对置换过程中屈膝间隙方面无明显影响。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

In vivo measurement of fascicle length and pennation angle of the human biceps femoris muscle

The purpose of this investigation was to measure in vivo fascicle length (L(fas)) and pennation angle (PA) of the long head of the biceps femoris muscle (BF(lh) m.) at different hip and knee angles while the muscle was relaxed using ultrasonography (US). Data were collected from 18 healthy females (23.0 +/- 1.8 years). To validate the measurements of the L(fas) and PA, the US measurements on cadavers (n = 5), embalmed with the hip and knee in anatomical position, were compared to actual fiber lengths and PA from the dissected muscles. US images from volunteer subjects were recorded when the hip joint was positioned at 0 degrees, 45 degrees and 90 degrees of hip flexion, and at each hip position, the knee joint was placed at 0 degrees, 45 degrees and 90 degrees from full extension. The images were digitized to measure L(fas) and PA. Results showed no significant differences between US and direct measurements of the L(fas) and PA on the cadaver BF(lh) m. (p > 0.05). L(fas) and PA changed significantly between the different hip and knee positions in volunteer subjects (p < 0.05). Changes in the L(fas) and PA are more sensitive to changes in hip position with the knee position constant than to changes in knee position with the hip position constant. This difference may be related to the larger muscle moment arm at the hip resulting in greater excursion of the muscle with changing hip position. Based on the changes in L(fas) with changing joint positions, BF(lh) sarcomere length was estimated to occupy a portion of the ascending limb, the plateau and descending limb of the length-tension relationship over the range of motion studied. US scanning is valid and reliable for measuring L(fas) and PA of the BF(lh) m. An understanding of the dynamic nature of muscle architecture will assist in determining effective and efficient clinical evaluation and rehabilitation techniques.     

Internal/external rotation moment arms of muscles at the knee: moment arms for the normal knee and the ACL-deficient knee

Knowledge of the three-dimensional balance of loads at the knee joint is required to adequately assess the treatment and rehabilitation of the malfunctioning knee. This report focuses upon the moment arms for the knee in internal/external (IE) rotation motion. It augments prior work that defined flexion/extension moment arms. Muscle excursions and angular motion of the lower leg during IE rotation were measured in 17 fresh-frozen hemi-pelvis specimens. Moment arms were calculated as the derivatives of excursion with respect to the angle. Rotational motion was performed for the normal and anterior cruciate ligament (ACL)-deficient knee. Of the 13 muscles measured at the knee, seven were significant contributors to IE rotation: the biceps femoris long and short head externally rotate opposite the gracilis, sartorious, semimembranosis, semitendonosus and popliteus, functioning as internal rotators. Moment arm magnitudes were greatest with the knee in a flexed position (internal [external] rotators peaked at 70° [90°] flexion). At 30° flexion, the IE rotation moment arm minima and maxima were 10.1–11.6, 6.8–9.0, 6.0–15.7, 8.2–14.1 and 0.0–10.4 mm for the semimembranosis, semitendonosus, gracilis, sartorius and popliteus, and 14.7–27.9 and 18.5–31.5 mm for the biceps femoris short and long, respectively. Moment arms for the ACL-deficient condition were significantly changed only at extremes of flexion–extension.     

Does joint line elevation after revision knee arthroplasty affect tibio-femoral kinematics,contact pressure or collateral ligament lengths? An in vitro analysis

Introduction

Correct restoration of the joint line is generally considered as crucial when performing total knee arthroplasty (TKA). During revision knee arthroplasty however, elevation of the joint line occurs frequently. The general belief is that this negatively affects the clinical outcome, but the reasons are still not well understood.

Material and methods

In this cadaveric in vitro study the biomechanical consequences of joint line elevation were investigated using a previously validated cadaver model simulating active deep knee squats and passive flexion-extension cycles. Knee specimens were sequentially tested after total knee arthroplasty with joint line restoration and after 4 mm joint line elevation.

Results

The tibia rotated internally with increasing knee flexion during both passive and squatting motion (range: 17° and 7° respectively). Joint line elevation of 4 mm did not make a statistically significant difference. During passive motion, the tibia tended to become slightly more adducted with increasing knee flexion (range: 2°), while it went into slighlty less adduction during squatting (range: –2°). Neither of both trends was influenced by joint line elevation. Also anteroposterior translation of the femoral condyle centres was not affected by joint line elevation, although there was a tendency for a small posterior shift (of about 3 mm) during squatting after joint line elevation. In terms of kinetics, ligaments lengths and length changes, tibiofemoral contact pressures and quadriceps forces all showed the same patterns before and joint line elevation. No statistically significant changes could be detected.

Conclusions

Our study suggests that joint line elevation by 4 mm in revision total knee arthroplasty does not cause significant kinematic and kinetic differences during passive flexion/extension movement and squatting in the tibio-femoral joint, nor does it affect the elongation patterns of collateral ligaments. Therefore, clinical problems after joint line elevation are probably situated in the patello-femoral joint or caused by joint line elevation of more than 4 mm.     

Collegiate Football Players Display More Active Cervical Spine Mobility Than High School Football Players

OBJECTIVES: To compare the active cervical spine range of motion and resting cervical spine alignment (sagittal plane) of collegiate and high school football players using the Cervical Range of Motion (CROM) Measurement System and to identify normative values for these populations. DESIGN AND SETTING: A 2 x 7 factorial design for main effects was used to evaluate the influence of level of play (college, high school) on the cervical spine range of motion of football players. Data were collected during preparticipation physical examinations. SUBJECTS: A convenience sample of 189 unimpaired collegiate (n = 70, age = 19.5 +/- 1.5 years) and high school (n = 119, age = 15.7 +/- 1.4 years) football players participated. MEASUREMENTS: Subjects were measured for active cervical spine range of motion using the CROM system and the manufacturer's recommended measurement techniques. RESULTS: Collegiate football players had increased active cervical spine range of motion for flexion, extension, left cervical rotation, and left lateral flexion (overall mean increase = 4.3 +/- 2 degrees ) compared with high school players. Collegiate players also assumed a more flexed resting sagittal-plane cervical spine posture (P =.001). CONCLUSIONS: Collegiate players generally displayed greater active cervical spine range of motion than high school players. The increased resting sagittal-plane cervical spine flexion alignment we report among the collegiate players suggests a change in the natural cervical spine lordosis, possibly due to a neutral-zone shift associated with combined increases in lower cervical spine flexion and upper cervical spine extension as an adaptation to football training or playing. Further study using radiographic or magnetic resonance imaging techniques is warranted. The CROM system is a useful tool for identifying aggregate hypomobile or hypermobile active cervical spine mobility among football players that might otherwise remain unrecognized during standard preparticipation physical examinations. In combination with manual segmental assessments of passive accessory intervertebral movements, CROM enables early identification of players with impaired or excessive cervical spine mobility, thus facilitating proactive injury-prevention intervention.     

枕颈部三维运动范围的测量

目的：研究枕颈部正常的三维运动范围，为枕颈部不稳分析和治疗提供生物力学基础。方法：运用脊柱三维运动测量分析系统，对１１具成人新鲜枕颈部标本的三维运动范围进行测试。结果：寰枕关节的前屈、后伸、左／右侧屈、左／右轴向旋转运动范围分别是：１１．７°、９．６°、２．８°／２．７°、６．９°／５．４°；寰枢关节分别为：８．９°、５．９°、３．４°／４．２°、３７．５°／３８．７°；寰枢关节中性区为２７．４°，占主运动范围的７１．７％；枕颈部与脊柱其它部位相比，主运动时伴有更明显的藕合运动，屈伸、侧屈时伴有比主运动范围更大的藕合旋转运动，分别为１０．５°、１４．３°。结论：脊柱三维测试分析系统不仅能对枕颈部的三维运动范围进行精确的测量，且能反映枕颈部三维运动的特点。     

Fast voluntary trunk flexion movements in standing: primary movements and associated postural adjustments

Movement patterns were studied during fast voluntary forward flexions of the trunk from an erect standing position. Three healthy subjects performed three series of six consecutive trunk flexions at maximum velocity and with successively increasing amplitude, covering a major part of the range of motion (range for all subjects: 13-97 degrees). Angular displacements of the trunk, hip, knee and ankle were measured together with the tilt of the pelvis and the flexion of the spine using a Selspot optoelectronic system. Trunk flexion was the result of a simultaneous forward pelvic tilt and flexion of the spine. For trunk movements up to 55 degrees, spine flexion dominated the movement, whereas for larger movements a major part of the amplitude was caused by pelvic tilt. During flexion of the trunk a simultaneous hip flexion and ankle extension was seen. At the knee there was an initial flexion and a subsequent extension. The net amplitude of the knee flexion showed a negative correlation with net trunk flexion amplitude for movements up to 50 degrees, whereas for larger amplitudes the correlation was positive. Time from onset of the trunk movement to peak knee flexion showed a weak correlation to net trunk flexion amplitude (r = 0.34) whereas the corresponding correlation was higher for pelvic tilt, spine flexion, hip flexion, ankle extension, and knee extension (r = 0.60-0.91). Each successive trial during a series of trunk movements was started from an increasing degree of knee flexion. This gradual adaptation was also present when successive trunk flexions were performed with constant movement amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contrasting roles of inertial and muscle moments at knee and ankle during paw-shake response

Intralimb kinetics of the paw-shake response (PSR) were studied in four spinal, adult cats. Using rigid body equations of motion to determine the dynamic interactions between limb segments, knee and ankle joint kinetics were calculated for the steady-state cycles as defined in the preceding paper. Hindlimb motion was filmed (200 frames/s) to obtain knee and ankle kinematics. Responses of flexors and extensors at both joints were recorded synchronously with cinefilm. Ankle and knee joint kinematics were determined from 51 steady-state cycles of 16 PSRs. Average maximum displacements, velocities, and accelerations were substantially greater for the ankle than for the knee joint. Knee and ankle motions were out of phase in the first part of the cycle; knee extension occurred simultaneously with ankle flexion. In the second part of the cycle, motions at the two joints were sequential; rapid knee flexion, accompanied by negligible ankle displacement, preceded rapid ankle extension with minimal knee displacement. At the ankle joint, peak net moments tending to cause flexion and extension were similar in magnitude and determined primarily by muscle moments. Moments due to leg angular acceleration contributed significantly to an extensor peak in the net moment near the end of the cycle. Other inertial and gravitational moments were small. At the knee joint, net moments tending to cause flexion and extension were also similar, but smaller than those at the ankle. The knee muscle moments, however, were large and counteracted large inertial moments due to paw angular acceleration. Also, moments due to leg angular acceleration and knee linear acceleration were substantial and opposite in effect. Other inertial and the gravitational moments were negligible. Muscle moments slowed and reversed joint motions, and active muscle force components of muscle moments were derived from lengthening of active musculotendinous units. Segmental interactions, in which proximal segment motion augmented distal segment velocity, increased the effectiveness of PSR steady-state cycles by facilitating the generation of extremely large paw linear accelerations. Limb oscillations during PSR steady-state result from interactions between muscle synergies and motion-dependent limb dynamics. At the ankle, muscle activity functioned to control paw acceleration, whereas at the knee, muscle activity functioned to control leg and paw inertial interactions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Angle- and velocity-specific alterations in torque and semg activity of the quadriceps and hamstrings during isokinetic extension-flexion movements

The purpose of this study was to investigate the effect of movement velocity (100 degrees, 200 degrees , 300 degrees s(-1), and 400 degrees s(-1)) and joint position (0 degrees - 15 degrees [L0], 25 degrees - 40 degees [L25], 55 degrees - 70 degrees [L55], and 75 degrees - 90 degrees [L75]) on peak torque (PT) parameters and surface electromyography (SEMG) of the knee-joint muscles during reciprocal isokinetic extension and flexion movements. Thirteen subjects (age = 22.7 +/- 2.1 years, mean height = 161.1 +/- 6.6 cm, mean weight = 63.5 +/- 5.8 kg) participated in the study. Bipolar surface electrodes were placed over the vastus medialis, vastus lateralis, biceps femoris, and medial hamstrings for determination of the root mean square (SEMGrms) and median frequency (SEMGmf) of the SEMG. Peak torque, angle of peak torque (PTang), percentage of peak torque (PTper), SEMGrms, and SEMGmf were analyzed using separate repeated measures analysis of variance (ANOVA). The following main results, significant at p < or = 0.05 or better, were found: The PTang was influenced by movement velocity (in extension there was a decrease in PTang moving from 300 degrees x s(-1) to 400 degrees x s(-1) and inflexion there was an increase in PTang moving from 300 degrees x s(-1) to 400 degrees x s(-1)). Secondly, a greater percentage of peak torque (PTper) was maintained during knee flexion than knee extension. And thirdly, both the quadriceps and hamstrings exhibited changing amplitudes and spectral frequencies based on joint position and movement velocity. There was a trend of decreasing SEMGrms for the quadriceps as the knee moved into extension, and a lower SEMGmf during early (L75) and end stages of knee extension (L0). For the hamstrings, SEMGrms was lowest at the more shortened position (L75) and highest near the mid-position (L25); the lowest SEMGmf occurred at the more lengthened position (L0) and the highest occurred at the more shortened position (L75). Finally, velocity influenced hamstrings and quadriceps muscle amplitude such that SEMGrms was highest at the slower velocities and lowest at the higher velocities. Velocity had no impact on quadriceps spectral properties (p > 0.05), but had a cyclic effect on hamstrings spectral properties. Changes in amplitude and frequency spectrum in tested muscles could be explained, in part, by neural drive to these muscles. Data support the hypothesis of lower activation levels of the quadriceps muscle in the extended position espoused by several authors as a way to protect the knee-joint in the knee-extended position.     

Relationships between early postoperative gait biomechanical factors and patient-reported outcome measures 6 months after total knee arthroplasty

BackgroundThis study was focused on the gait parameters of the knee extensor and hip abductor muscle groups, which are believed to contribute to knee joint function improvement in early postoperative TKA. The associations between patient-reported outcome measures (PROMs) 6 months after total knee arthroplasty (TKA) and the early postoperative internal knee extension moment, knee extension negative joint power, and internal hip abduction moment while walking were investigated.MethodsTwenty-one patients who underwent primary TKA for knee osteoarthritis were included. Three weeks after TKA, gait at a comfortable speed was measured by three-dimensional motion analysis. The lower limb joint angle, internal joint moment, and joint power parameters on the operated side while standing were calculated. The PROMs 6 months after TKA were assessed using the Japanese Knee Osteoarthritis Measure (JKOM). The relationship between each gait biomechanical parameter and the JKOM was determined.ResultsThe maximum internal knee extension moment and maximum knee extension negative joint power during the early stance showed moderate negative correlations with the JKOM scores. The maximum internal hip abduction moment was not correlated with the JKOM scores. The maximum internal hip extension moment during the early stance and internal hip flexion moment during the late stance showed moderate negative correlations with the total JKOM scores.ConclusionThe early postoperative internal knee extension moment, maximum knee extension negative joint power, and internal hip extension and flexion moment are associated with patient PROMs 6 months after TKA.     

Selection of muscles for initiation of planar,three-joint arm movements with different final orientations of the hand

Muscle activities and joint rotations were examined at the shoulder, elbow, and wrist joints for pointing movements to targets in the horizontal plane. In such movements, multiple arm configurations are possible for a given target location. Thus, starting from the same initial configuration and for the same target location in space, the joint excursions could be varied. When no constraints were placed on the final orientation of the hand, the choice of muscles initially activated at the wrist joint was consistent with a function to resist inertial effects of proximal segment motion on the wrist joint. When subjects were asked to produce different final orientations of the hand for the same target location, the initial choice of muscles at the three joints was preserved in most trials, whether wrist flexion or extension was required to reach the final hand orientation. The relative onset times of muscle activity at the different joints were also not correlated with wrist excursion. This suggests a predetermined initial selection of muscles that is related to target location, not to joint angular excursion. The fact that the required final hand orientation was nevertheless achieved suggests that the planning of these pointing movements is not a unitary process, but is comprised of two components: a fixed initial muscle selection for a given target location in space, and a selection appropriate for the required joint excursions.     

基于静态磁共振图像构建髌股关节准动态三维运动模型

目的　创建基于多屈膝角度静态膝关节磁共振图像,构建完整屈伸膝过程的髌股关节准动态三维模型的方法。 方法　选择1名健康成年男性,年龄30岁,体重65 kg,身高172 cm,对其右膝关节分别在0°、30°、60°、90°、120°5个屈膝角度进行MRI扫描,并将扫描结果以Dicom格式导入Mimics软件中,提取髌骨、股骨轮廓,重建五个屈膝角度的静态髌股关节三维模型,再将上述五个静态模型导入逆向工程软件Rapidform中进行同一坐标系的配准,利用三次样条插值算法,将离散静态髌股关节模型配准为动态三维运动模型。据此动态三维模型计算髌骨运动轨迹并与既往文献结果对比以验证模型的准确性。 结果　基于静态核磁共振图像可以快速构建准确而无辐射的髌股关节准动态三维运动模型,以此动态模型计算出的髌骨运动轨迹和髌股关节旋转轴与既往文献结果相一致。 结论　本方法成功构建了包含屈膝0°到120°间的完整髌股关节运动过程,在屈膝过程中,随着屈膝角度的增加,髌骨相对于股骨滑车不断俯屈,同时轻度的外倾和外旋。     

Increase in range of knee motion to obtain floor sitting after high tibial osteotomy for osteoarthritis

In order to obtain better range of motion in knees with osteoarthritis, medial and lateral parapatellar retinaculo-capsular release operations were performed at the time of high tibial osteotomy, with fixation using dual plating on medial compartmental knee osteoarthritis (29 knees) or spontaneous osteonecrosis of the medial femoral condyle (15 knees). At removal of the blade plate, 1 to 2 years after the initial osteotomy, the same release procedures were performed together with resection of adhesive soft tissue and resection of osteophytes, which were obstacles to full flexion. A grading system (Grade 0-3) was proposed to evaluate the duration (min) of formal floor sitting. After these procedures, the patients were able to sit on the floor with 155-165 degrees of flexion for more than 30 min (Grade 3) in 20 knees, for 10-29 min (Grade 2) in seven, for less than 10 min (Grade 1) in nine and were unable to sit on the floor (Grade 0) in eight knees. Maximum knee flexion and total range of motion were 142+/-8.4 degrees and 137+/-11 degrees before and 152+/-6.6 degrees and 151+/-7.4 degrees after surgery, respectively. The American Knee Society Knee Score and Function Score were 61+/-17 and 46+/-16 before, and 97+/-5 (P<0.0001) and 91+/-13 (P<0.0001) after surgery at the final follow-up, respectively. The femoro-tibial angle in standing with one leg was 183+/-6 degrees (3 degrees of anatomical varus angulation) before and 170+/-3 degrees (P<0.0001) (10 degrees of anatomical valgus angulation) after surgery.     

连续疲劳干预对膝关节主被动生物力学特性的影响

目的 探究连续疲劳干预对膝关节主被动生物力学特性的影响。方法 招募27位健康大学生在等速力量测试系统上进行疲劳实验。疲劳实验包括3个疲劳周期,每个疲劳周期至少30次股四头肌连续等长收缩。对比不同疲劳周期的最大被动力矩、平均最大自主收缩（maximum voluntary contraction,MVC）力矩、股外侧肌和股二头肌肌电积分值以及协同收缩指数（co-contraction index,CI）。结果 疲劳周期3后,最大被动力矩显著下降（P<0.05）。疲劳周期1、2、3过程内平均MVC力矩、股外侧肌和股二头肌肌电积分值都显著下降（P<0.05）,然而二者CI全程无显著变化（P>0.05）。结论 股四头肌等长收缩训练剂量为90次的连续疲劳干预会显著影响膝关节主被动生物力学特性。疲劳干预后,膝关节抵抗被动屈伸能力下降。并且随着疲劳干预进程,股四头肌主动收缩能力下降,股四头肌和腘绳肌肌肉激活也下降,但二者肌群协同收缩水平不变。这种温和的肌群协同收缩模式有益于保持良性膝关节力学加载环境。研究结果有助于理解疲劳后膝关节主被动生物力学特性。