vendex and Joint-Diseases

Less invasive dissection of the extensor apparatus, one of the aspects of minimally invasive surgical (MIS) TKA, might result in less reduction of postoperative quadriceps strength. However, it is unclear whether MIS is associated with less strength reduction.. We asked whether knee strength (extensor or flexor torque) would be greater in patients having a MIS TKA compared with patients having a standard TKA and whether knee scores, alignment, ROM, tourniquet and operating times, and hospital length of stay were improved.. We prospectively recruited 52 patients awaiting MIS or standard TKA, matched for age, weight, height, BMI, sex, and surgically treated side, but not randomized. Isokinetic tests were performed preoperatively and postoperatively to obtain peak values of extensor and flexor torque. Postoperative-to-preoperative ratios and the extensor-flexor torque ratio also were calculated.. Mean baseline extensor torques were 57 Nm and 53 Nm for MIS and standard TKAs, respectively. At 8 weeks postoperatively, absolute values of the mean postoperative knee extensor torque also were similar: 47 and 45 Nm for patients with MIS and standard TKAs, respectively. The postoperative-to-preoperative ratios were 0.8 for extensor and flexor torque in both groups. The extensor-flexor torque ratios were similar between groups.. Our data suggest a less invasive dissection of the extensor apparatus involved in MIS TKA does not enhance postoperative quadriceps strength.. Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Topics: Aged; Arthroplasty, Replacement, Knee; Biomechanical Phenomena; Female; Humans; Joint Diseases; Knee Joint; Male; Middle Aged; Minimally Invasive Surgical Procedures; Torque

The purpose of this study was to compare the knee extensor mechanics in persons with and without patella alta. Thirteen subjects with patella alta and 14 subjects with normal patellar position participated in the study. Sagittal and axial MR images of the knee were acquired at 0 degrees , 20 degrees , 40 degrees , and 60 degrees of knee flexion. Measurements of actual moment arm, patellar ligament/quadriceps tendon force ratio, quadriceps effective moment arm, and joint reaction force/quadriceps force ratio were obtained. There were no differences between groups in terms of actual moment arm. However, subjects with patella alta had significantly larger patellar ligament/quadriceps tendon force ratios (1.04+/-0.02 vs. 0.92+/-0.02) and quadriceps effective moment arms (4.40+/-0.09 vs. 4.00+/-0.09 cm) when averaged across the range of knee flexion angles tested. There was no difference in the joint reaction force/quadriceps force ratio between groups. The observed differences in knee extensor mechanics suggest that individuals with patella alta have a more efficient knee extensor mechanism and would be expected to generate similar joint reaction forces per unit quadriceps force compared to subjects with normal patellar position. Therefore, persons with patella alta may experience less patellofemoral joint reaction force to overcome the same knee flexion moment in the range of 0 degrees -60 degrees of knee flexion.

Topics: Adult; Biomechanical Phenomena; Female; Humans; Image Interpretation, Computer-Assisted; Joint Diseases; Knee Joint; Magnetic Resonance Imaging; Male; Muscle Contraction; Muscle, Skeletal; Patella; Postural Balance; Range of Motion, Articular; Stress, Mechanical; Torque

To determine if persons with patella alta exhibit elevated patellofemoral joint stress compared to pain-free controls during normal and fast walking speeds.. Twenty-four subjects (13 patella alta, 11 pain-free controls) participated.. Sagittal and axial magnetic resonance images of the knee were obtained to quantify subject specific knee extensor mechanics and patellofemoral joint contact area. Instrumented gait analysis was used to quantify knee joint kinematics and kinetics. MRI and gait data were used as input variables into a model of patellofemoral joint stress. Analysis of variance with repeated measures was used to compare group differences and group x gait speed interactions for each dependent variable during stance.. During normal speed gait there were no group differences in peak knee flexion angle, knee extensor moment, joint reaction force, or stress. However, the patella alta group had significantly less contact area. During fast speed gait there were no group differences in peak knee flexion angle, knee extensor moment, or joint reaction force. However, the patella alta group demonstrated significantly less contact area and significantly greater stress compared to controls.. Persons with patella alta demonstrated greater calculated patellofemoral stress during fast walking. This was the result of reductions in contact area as joint reaction forces were similar between groups.. Persons with patella alta may be predisposed to patellofemoral dysfunction through elevations in joint stress. Therefore, treatments aimed at increasing the load-bearing surface area between the patella and femur, such as bracing, may be beneficial in this patient population.

Topics: Adult; Female; Femur; Gait; Humans; Image Interpretation, Computer-Assisted; Joint Diseases; Knee Joint; Magnetic Resonance Imaging; Male; Models, Biological; Patella; Physical Exertion; Torque; Walking

Joint mechanical impedance, which describes the instantaneous relationship between kinematic perturbations and the resulting torque response, plays an important role in the way humans ambulate, interact with the environment, and respond to disturbances. Recent studies have quantified how the stiffness component of mechanical impedance varies during walking. However, the extent to which humans can voluntarily regulate leg joint stiffness is not yet known. Our study sought to quantify the accuracy and precision of the neuromotor system to voluntarily regulate ankle joint stiffness while seated, and compare these data to the well-known abilities to regulate ankle joint torque and position. We tested individuals' ability to to regulate these quantities at three different magnitudes: 20%, 40%, and 60% of a maximum value. Our results showed that subjects were able to voluntarily regulate ankle joint stiffness, and that the normalized accuracy and precision of stiffness regulation were not different than those of position or torque for targets at magnitudes of 20% of a maximum value. However, the accuracy and precision of stiffness regulation were statistically different than those of position and torque for targets at magnitudes of 40% of the maximum values. At moderate targets, the similarity of the ability to regulate ankle joint stiffness when compared to the abilities to regulate joint torque and position highlights the importance of a comprehensive description of lower-limb biomechanics that includes consideration of joint mechanical impedance, in addition to the common descriptions of joint torque and position.

Topics: Adult; Ankle Joint; Biomechanical Phenomena; Female; Humans; Joint Diseases; Male; Middle Aged; Models, Biological; Neuromuscular Junction; Torque; Walking; Young Adult

The ability to rise from a chair is a basic functional task that is frequently compromised in individuals diagnosed with orthopedic disorders in the low back and hip. There is no published literature that describes how this task is altered by sacroiliac joint dysfunction (SIJD).. The objective of this study was to compare lower extremity biomechanics and the onset of muscle activity when rising from a chair in subjects with SIJD and in healthy persons.. Six women with unilateral SIJD and six age-matched healthy controls performed a sit-to-stand task while we measured kinematics, kinetics, and muscle activity.. Subjects stood up at a preferred speed from a seated position on an armless and backless adjustable stool. We measured kinematics with a 10-camera motion capture system, ground reaction forces for each leg with force plates, and muscle activity with surface electromyography. Joint angles and torques were calculated using inverse dynamics. Leg-loading rate was quantified as the average slope of vertical ground reaction (VGRF) force during the 500-millisecond interval preceding maximal knee extension.. Between-leg differences in loading rates and peak VGRFs were significantly greater for the SIJD group than for the control group. Maximal hip angles were significantly less for the SIJD group (p=.001). Peak hip moment in the SIJD group was significantly greater in the unaffected leg (0.75±0.22 N⋅m/kg) than in the affected leg (0.47±0.29 N⋅m/kg, p=.005). There were no between-leg or between-group differences for peak knee or ankle moments. The onset of activity in the latissimus dorsi muscle on the affected side was delayed and the erector spinae muscles were activated earlier in the SIJD group than in the control group.. Subjects with SIJD have a greater VGRF on the unaffected leg, generate a greater peak hip moment in the unaffected leg, use a smaller range of motion at the hip joint of the affected leg, and delay the onset of a key muscle on the affected side when rising from a seated position.

Topics: Adult; Biomechanical Phenomena; Female; Humans; Joint Diseases; Lower Extremity; Movement; Posture; Range of Motion, Articular; Sacroiliac Joint; Torque

In clinical practice, clubfeet feel stiffer compared to healthy feet. Furthermore, the clinical impression is that stiffer clubfeet have a higher tendency to relapse. Until now, no objective measure has been available to determine the stiffness of clubfeet. The goal of the current project was to objectively quantify ankle and subtalar joint stiffness in clubfeet patients and to compare this stiffness between clubfeet patients and healthy controls using a newly developed measurement device.. The newly developed Torque-Displacement-Handpiece in combination with an adjusted Abduction Dorsiflexion Mechanism clubfoot-brace, made it possible to move a foot over two rotational axis, while continuously capturing the applied torque and the achieved angulation. Based on this information, stiffness of the ankle and subtalar joint were assessed for 11 clubfoot patients with 17 clubfeet and 11 healthy subjects with 22 healthy feet.. With the Torque-Displacement-Handpiece measuring device it was possible to measure torque, angulation and stiffness in a reliable and precise manner. Clubfoot patients showed less angulation and a higher stiffness for measurements over the ADM subtalar axis compared to controls. After adjusting for shoe size, the stiffness for measurements over the ADM tibiotalar axis was also significantly higher in clubfeet than controls.. Overall, these results indicate that clubfoot patients have a higher ankle and subtalar joint stiffness in the affected joint compared to healthy controls. In the future, the Torque-Displacement-Handpiece could be used to monitor stiffness of clubfeet during treatment, and as such, play a potential role in the early detection of relapsing clubfeet.

Topics: Ankle; Ankle Joint; Braces; Child; Child, Preschool; Clubfoot; Female; Foot; Humans; Joint Diseases; Male; Orthopedics; Recurrence; Subtalar Joint; Torque; Treatment Outcome

This paper describes a novel model structure and identification method for the time-varying, intrinsic stiffness of human ankle joint during imposed walking (IW) movements. The model structure is based on the superposition of a large signal, linear, time-invariant (LTI) model and a small signal linear-parameter varying (LPV) model. The methodology is based on a two-step algorithm; the LTI model is first estimated using data from an unperturbed IW trial. Then, the LPV model is identified using data from a perturbed IW trial with the output predictions of the LTI model removed from the measured torque. Experimental results demonstrate that the method accurately tracks the continuous-time variation of normal ankle intrinsic stiffness when the joint position changes during the IW movement. Intrinsic stiffness gain decreases from full plantarflexion to near the mid-point of plantarflexion and then increases substantially as the ankle is dosriflexed.

Topics: Algorithms; Ankle; Ankle Joint; Biomechanical Phenomena; Computer Simulation; Female; Humans; Imaging, Three-Dimensional; Joint Diseases; Linear Models; Male; Monitoring, Ambulatory; Reproducibility of Results; Torque; Walking

This paper describes a novel method for the identification of Hammerstein systems with time-varying (TV) static nonlinearities and time invariant (TI) linear elements. This paper develops a linear parameter varying (LPV) state-space representation for such systems and presents a subspace identification technique that gives individual estimates of the Hammerstein components. The identification method is validated using simulated data of a TV model of ankle joint reflex stiffness where the threshold and gain of the model change as nonlinear functions of an exogenous signal. Pilot experiment of TV reflex EMG response identification in normal ankle joint during an imposed walking task demonstrate systematic changes in the reflex nonlinearity with the trajectory of joint position.

Topics: Adult; Algorithms; Ankle; Ankle Joint; Biomechanical Phenomena; Computer Simulation; Electromyography; Humans; Joint Diseases; Linear Models; Male; Pilot Projects; Reflex, Stretch; Software; Time Factors; Torque

During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step toward our ultimate goal of quantifying knee stiffness during gait.

Topics: Adult; Biomechanical Phenomena; Electromyography; Humans; Joint Diseases; Knee Joint; Male; Models, Biological; Muscle, Skeletal; Reproducibility of Results; Signal Processing, Computer-Assisted; Torque

We have previously shown that abduction angular perturbations applied to the knee consistently elicit reflex responses in knee joint musculature. Although a stabilizing role for such reflexes is widely proposed, there are as of yet no studies quantifying the contribution of these reflex responses to joint stiffness. In this study, we estimate the mechanical contributions of muscle contractions elicited by mechanical excitation of periarticular tissue receptors to medial-lateral knee joint stiffness. We hypothesize that these reflex muscle contractions will significantly increase knee joint stiffness in the adduction/abduction direction and enhance the overall stability of the knee. To assess medial-lateral joint stiffness, we applied an abducting positional deflection to the fully extended knee using a servomotor and recorded the torque response using a six degree-of-freedom load-cell. EMG activity was also recorded in both relaxed and preactivated quadriceps and hamstrings muscles with surface electrodes. A simple, linear, second-order, delayed model was used to describe the knee joint dynamics in the medial/lateral direction. Our data indicate that excitation of reflexes from periarticular tissue afferents results in a significant increase of the joint's adduction-abduction stiffness. Similar to muscle stretch reflex action, which is modulated with background activation, these reflexes also show dependence on muscle activation. The potential significance of this reflex stiffness during functional tasks was also discussed. We conclude that reflex activation of knee muscles is sufficient to enhance joint stabilization in the adduction/abduction direction, where knee medial-lateral loading arises frequently during many activities.

Topics: Adult; Electromyography; Humans; Joint Diseases; Male; Muscle Contraction; Postural Balance; Reflex, Stretch; Time Factors; Torque; Weight-Bearing

In children with obstetric brachial plexus palsy (OBPP) who develop an internal rotation deformity of the shoulder, release of subscapularis improves the range of external rotation of the shoulder and the strength of supination of the forearm. We studied the strength of supination in 35 healthy adult volunteers at 45 degrees of both internal and external rotation. The mean and maximum torques were greater in external than internal rotation by 8.7% and 7.5%, respectively. This was highly significant (p < 0.0001). The increased strength of supination in external rotation is probably because the maximum power of biceps, particularly the long head, may be exerted in this position. In children the difference may be even greater due to anatomical differences causing the dramatic increases in the strength of supination after surgery for OBPP. In adults our findings suggest that the supination exercises which are undertaken after injury or surgery to the forearm or wrist should be performed in external rotation.

Topics: Adult; Brachial Plexus Neuropathies; Female; Forearm; Humans; Joint Diseases; Male; Middle Aged; Muscle, Skeletal; Range of Motion, Articular; Rotation; Shoulder Joint; Supination; Torque

The aim of this study was to evaluate and compare muscular activation in sitting and standing in patients with patellofemoral pain syndrome and healthy controls. Eleven women with patellofemoral pain syndrome and nine healthy controls were evaluated regarding: (a) muscle performance in sitting compared to standing-knee extensor torque was registered in sitting with a Kin Com dynamometer and in standing with a force plate, and quadriceps muscle activity was registered with EMG in both sitting and standing; and (b) ability to maximally voluntarily activate during sitting isometric knee extension. Maximally tolerated single-twitch electrical stimulation was superimposed on 20, 40, 60, 80 and 100% of maximal voluntary activation. Additional torque from the single twitch was documented. Five patients and all nine controls were tested twice (tests a and b) with 2 days between tests, and high reproducibility could be demonstrated. A significantly higher torque during sitting compared with standing was found in both patients and controls, but with a significant correlation between sitting and standing torque values. No significant difference was found between patients and controls. Single-twitch electrical stimulation superimposed on maximal voluntary activation resulted in increased torque in two of the nine controls compared to 10 of the 11 patients. The average increased torque in the patients were significantly higher than in the controls and estimated to 18%. It was concluded that sitting isometric measurements are representative of the ability to produce standing isometric knee torque. A moderate degree of inhibition was demonstrated during sitting strength measurements in the patients (not studied in standing).

Topics: Adolescent; Adult; Electric Stimulation; Electromyography; Female; Femur; Humans; Isometric Contraction; Joint Diseases; Knee Joint; Muscle Contraction; Muscle, Skeletal; Pain; Patella; Posture; Reproducibility of Results; Syndrome; Torque; Weight-Bearing