A planar model of the knee joint to characterize the knee extensor mechanism

A simple planar static model of the knee joint was developed to calculate effective moment arms for the quadriceps muscle. A pathway for the instantaneous center of rotation was chosen that gives realistic orientations of the femur relative to the tibia. Using the model, nonlinear force and moment equilibrium equations were solved at one degree increments for knee flexion angles from 0 (full extension) to 90 degrees, yielding patellar orientation, patellofemoral contact force and patellar ligament force and direction with respect to both the tibial insertion point and the tibiofemoral contact point. The computer-derived results from this two-dimensional model agree with results from more complex models developed previously from experimentally obtained data. Due to our model's simplicity, however, the operation of the patellar mechanism as a lever as well as a spacer is clearly illustrated. Specifically, the thickness of the patella was found to increase the effective moment arm significantly only at flexions below 35 degrees even though the actual moment arm exhibited an increase throughout the flexion range. Lengthening either the patella or the patellar ligament altered the force transmitted from the quadriceps to the patellar ligament, significantly increasing the effective moment arm at flexions greater than 25 degrees. We conclude that the levering action of the patella is an essential mechanism of knee joint operation at moderate to high flexion angles.     

全膝关节置换术治疗骨关节炎

目的 探讨人工全膝关节置换术治疗骨关节病的临床疗效。方法 对31例人工全膝关节置换术进行临床分析和总结,并应用HSS膝关节评分系统进行分析。结果 手术优良率为93．6％,患者术后在疼痛、功能及关节活动度等方面都有明显改善。结论 全膝关节置换术是治疗骨关节病的有效方法。     

Modeling of the knee joint load in rehabilitative knee extension exercises under water

A biomechanical and hydrodynamic theoretical model has been developed in order to calculate the knee joint load during underwater knee extension exercises. The hydrodynamic force has been evaluated within the framework of a strip-theory approach, when a blunt rectangular resistive device is applied proximally to the shank to increase its frontal area. Analytical expressions of the patellar tendon force (F(PT)), the axial (phi(n)) and the shear (phi(t)) component of the tibiofemoral joint load have been derived as a function of joint angle (theta), angular velocity (theta ), angular acceleration (theta ), resistive device density, length (L(x)), width (L(z)) and thickness, and average hydrodynamic drag and added mass coefficients. An inverse dynamic problem has been solved, assuming for theta and theta a dependence on theta consistent with the experimental kinematic data available in the literature. The results highlight that the characteristics of the resistive device and the level of muscular activation can be adjusted reciprocally in order to control the peak value of F(PT), phi(n) and phi(t), and the position of these peaks within the joint range of motion (ROM). No anterior cruciate ligament (ACL) stress is observed (phi(t)>0) over the whole ROM, independent of the level of muscular activation, for a light resistive device with L(x) < or = 0.3 m and L(z) < or = 0.4 m. This work highlights that aquatic exercises can be usefully and safely implemented in the rehabilitation program following ACL surgery, and whenever it is important to avoid excessive shear joint forces that constrain the tibial plateau anterior translation with respect to the femur.     

Partitioning of knee joint internal forces in gait is dictated by the knee adduction angle and not by the knee adduction moment

Medial knee osteoarthritis is a debilitating disease. Surgical and conservative interventions are performed to manage its progression via reduction of load on the medial compartment or equivalently its surrogate measure, the external adduction moment. However, some studies have questioned a correlation between the medial load and adduction moment. Using a musculoskeletal model of the lower extremity driven by kinematics–kinetics of asymptomatic subjects at gait midstance, we aim here to quantify the relative effects of changes in the knee adduction angle versus changes in the adduction moment on the joint response and medial/lateral load partitioning. The reference adduction rotation of 1.6° is altered by ±1.5° to 3.1° and 0.1° or the knee reference adduction moment of 17 N m is varied by ±50% to 25.5 N m and 8.5 N m. Quadriceps, hamstrings and tibiofemoral contact forces substantially increased as adduction angle dropped and diminished as it increased. The medial/lateral ratio of contact forces slightly altered by changes in the adduction moment but a larger adduction rotation hugely increased this ratio from 8.8 to a 90 while in contrast a smaller adduction rotation yielded a more uniform distribution. If the aim in an intervention is to diminish the medial contact force and medial/lateral load ratio, a drop of 1.5° in adduction angle is much more effective (causing respectively 12% and 80% decreases) than a reduction of 50% in the adduction moment (causing respectively 4% and 13% decreases). Substantial role of changes in adduction angle is due to the associated alterations in joint nonlinear passive resistance. These findings explain the poor correlation between knee adduction moment and tibiofemoral compartment loading during gait suggesting that the internal load partitioning is dictated by the joint adduction angle.     

Effect of knee position on hip and knee torques during the barbell squat

Some recommendations suggest keeping the shank as vertical as possible during the barbell squat, thus keeping the knees from moving past the toes. This study examined joint kinetics occurring when forward displacement of the knees is restricted vs. when such movement is not restricted. Seven weight-trained men (mean +/- SD; age = 27.9 +/- 5.2 years) were videotaped while performing 2 variations of parallel barbell squats (barbell load = body weight). Either the knees were permitted to move anteriorly past the toes (unrestricted) or a wooden barrier prevented the knees from moving anteriorly past the toes (restricted). Differences resulted between static knee and hip torques for both types of squat as well as when both squat variations were compared with each other (p < 0.05). For the unrestricted squat, knee torque (N.m; mean +/- SD) = 150.1 +/- 50.8 and hip torque = 28.2 +/- 65.0. For the restricted squat, knee torque = 117.3 +/- 34.2 and hip torque = 302.7 +/- 71.2. Restricted squats also produced more anterior lean of the trunk and shank and a greater internal angle at the knees and ankles. The squat technique used can affect the distribution of forces between the knees and hips and on the kinematic properties of the exercise. PRACTICAL APPLICATIONS: Although restricting forward movement of the knees may minimize stress on the knees, it is likely that forces are inappropriately transferred to the hips and low-back region. Thus, appropriate joint loading during this exercise may require the knees to move slightly past the toes.     

Arthroscopic surgery of the knee.

In the first 1000 arthroscopic operations performed by one surgeon 136 patients had two or more procedures, making a total of 1168 during the 1000 operations. The indications for operation were internal mechanical derangements in 565 patients, anterior knee pain in 246, disorders of the synovium in 77, ligament injuries in 63, and degenerative joint disease in 49. Complications included fracture of instruments in the knee in five patients, haemarthrosis in 10, deep vein thrombosis in three, and synovial fistula in one. In no patient was the wound infected. A total of 26 different operations was performed.     

Down on one knee: soft tissue knee injuries across the lifespan

Joint injury is a potent risk factor for osteoarthritis, the most important musculoskeletal disease affecting humankind. Yet the population incidence of soft tissue knee injury is not well documented. Using health-care register data from Sweden, Peat and colleagues report that soft tissue knee injuries are common, peak in adolescence and early adulthood, have a second spike in women who are 35 to 49 years old, and continue throughout the lifespan. The study highlights the need for more knowledge on the natural history of knee injuries, their impact on knee osteoarthritis development and progression, and the potential for prevention programs to reduce the incidence of these injuries.Joint injury is a potent risk factor for osteoarthritis (OA), the most important musculoskeletal disease affecting humankind. Although evidence is mounting that knee joint injury rates are high and increasing, it is also perhaps the lowest hanging fruit for primary OA prevention; several randomized clinical trials have shown that knee injuries can be dramatically reduced with relatively straightforward interventions. Yet outside of anterior cruciate ligament (ACL) injury and despite its potential public health impact, the population incidence of soft tissue knee injury requiring medical attention is not well documented: we have not known the extent or the nature of the problem, until now.In a recent issue of Arthritis Research & Therapy, Peat and colleagues [1] provided population-wide estimates of clinically diagnosed soft tissue knee injuries across all ages on the basis of an entire region of Sweden (approximately 1.3 million people). The opportunity to report and classify all clinically diagnosed knee injuries across the lifespan arises from unique and detailed health-care registries typical to Scandinavian countries. This overcomes weaknesses of previous epidemiological evaluations of knee injuries, which are limited to specific health-care settings, subgroups of people, and specific injury types. Of note, the findings of Peat and colleagues [1] have convergent validity - largely agreeing with previous reports of incidence for specific injury types and subgroups where data overlap.What emerges is that population exposure to soft tissue knee injury is a common problem; the annual incidences for males and females are 766 and 676 per 100,000 persons per year, respectively. This is approximately 10 times higher than ACL injuries alone. If these ‘less catastrophic’ but more common injuries are a risk for OA development (as risk factor studies measuring self-reported injury suggest [2]), then this study may be uncovering and detailing critical new exposure data. They are clearly more numerous though more difficult to accurately diagnose. This study begins to shed light on this challenge.Also revealed is new information on age and gender differences. The incidence of soft tissue knee injuries peaks in adolescence and early adulthood and is likely sports-related, matching seasonal fluctuations in popular sports in Sweden. The rates after this period decline over the lifespan with a notable exception: females from 35 to 49 experience a second peak. This is intriguing and the reasons are not clear, although the authors propose that the previously reported link between parity/child-bearing and knee OA may be mediated by injury. Although the reasons remain obscure, the finding is compelling and may help elucidate the consistently reported, but unexplained, higher prevalence of knee OA in females.Peat and colleagues [1] show that, although incidence rates are highest in the second and third decades of life, considerable rates of contusion, collateral ligament sprain, and other soft tissue strains continue into middle and old age. These injuries coincide with the age of onset of knee OA symptoms and illustrate the challenge of differentiating what is truly an injury from what is part of a previously latent or degenerative process or both. This also applies to meniscal injuries. Surgeries for meniscal tears peak in the mid to late 40s [3–5]. In contrast, Peat and colleagues [1] report a high incidence of meniscal tears in adolescents and young adults. As acknowledged by the authors, less severe injuries such as meniscal tears likely suffer from some misclassification. However, the relationship between diagnosis and surgery for meniscal tears requires further investigation.The high injury incidence among adolescents and young adults, together with the known risk of OA incidence from ACL and meniscal injuries, provides further impetus for implementing knee injury prevention programs, for which there is a strong body of level 1 evidence [6–11]. Efficacy has been demonstrated primarily in the sports team setting, implemented as novel 10- to 15-minute team warm-ups consisting of neuromuscular exercises to train athletes to land, decelerate, and push off with better lower limb alignment and improved trunk control, balance, and proprioception. The reported risk reductions range from 41% to 88% [7,8,11]. Given the age and frequency at which these injuries most often occur and their potential sequelae, perhaps targeting injury prevention programs to physical education classes in public schools could address a growing public health problem.The study by Peat and colleagues highlights several areas for further study. Knowledge is needed on the natural history of knee injuries in the development of knee OA as well as the potential for prevention programs to reduce the incidence. The spike of injuries in females between 35 and 49 requires confirmation and further investigation as to its causes, prevention, and potential role in OA development or progression. The same is true for injuries that occur in middle and older age, often coinciding with a time when knee OA has been diagnosed. Further clarity is needed around meniscal injury: what is traumatic injury and what is degenerative knee disease? There is still much to discover about the different knee injury types throughout the lifespan and the initiation and progression of knee OA. The study by Peat and colleagues [1] provides a good platform for this to be pursued.     

The effects of antagonist moment on the resultant knee joint moment during isokinetic testing of the knee extensors

The purpose of this study was to examine the effects of moment of antagonistic muscle on the resultant joint moment during isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum eccentric and concentric knee extension and flexion efforts on a Biodex dynamometer at 0.52 rad · s⁻¹ (30° · s⁻¹). Electromyographic (EMG) activity of vastus medialis and biceps femoris (hamstrings) was also recorded. The antagonistic moment of the hamstrings was determined by recording the integrated EMG (iEMG)/moment relationship at different levels of muscle effort. The iEMG/moment curves were fitted using second-degree polynomials. The polynomials were then used to predict the antagonistic moment exerted by the hamstrings from the antagonist iEMG. The antagonistic moment had a maximum of 42.92 Nm and 28.97 Nm under concentric and eccentric conditions respectively; paired t-tests indicated that this was a significant difference (P < 0.05). These results indicate that the resultant joint moment of knee extensors is the result of both agonist and antagonist muscle activation. The greater antagonist muscle activity under concentric activation conditions may be partly responsible for the lower resultant joint concentric moment of knee extensors compared with the corresponding eccentric activation. The antagonist moment significantly affects comparisons between the isokinetic moments and agonist EMG and in vitro force measurements under different testing (muscle action and angular velocity) conditions. Accepted: 25 February 1997