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Additional file 1. Example of muscle synergies in one of the participants. Activation coefficients and weight vectors obtained from a representative healthy subject of the sample population considering two different task conditions: eyes open and eyes closed conditions

INTRODUCTION: Proprioception is one of the most significant factors in balance, joint stability, coordination and injury prevention. It includes a wide set of neural input that bring information from peripheral mechanoreceptors, located within joints, muscles and tendons, to central nervous system. Generally, proprioception is defined as the ability to sense position of a joint in the space. Total knee arthroplasty (TKA) is the gold standard procedure to treatments of severe gonarthrosis, which aims to alleviate the pain, restore the locomotor function and increase patient satisfaction. Even if osteoarthritis has already altered proprioception abilities, the TKA procedure can furtherly affect proprioceptors. Some studies demonstrated that TKA slightly improved the kinaesthesia and balance. Other researchers, differently, did not observe any improvement. The aim of this study is to evaluate proprioception and postural control in subject with TKA, before and after the surgery, using Delos Postural Proprioceptive System (DPPS; Delos, Turin, Italy). METHODS: A cohort of 8 subjects (5 women and 3 men) were involved in the study. Subjects were aged 66.5±4.9, had primary knee osteoarthritis, and were scheduled for TKA. DPPS was used to assess proprioception and postural control before and after the surgery. The two tests considered to evaluate postural and proprioceptive control were stabilometric test and static Riva test. The parameters taken into account for these tests were the Stability Index (SI; percentage score where 100% is a theorical task performed with maximum stability), Autonomy (AU; percentage score based on hands support during tasks) and Postural Instability (PI; score in degree based on movement of trunk). RESULTS: The SI measured during the single stance test improved from 56.1%±27.5 to 73.3%±15.7 with opened eyes and decreased from 37.7%±10.2 to 34.5%±13.1 with closed eyes in the operated limb. PI measured during the double stance test increased of 0.07° with opened eyes and decreased of 0.13° with closed eyes. AU improved from 66.6% to 86.6% with open eyes and has maintained almost the same value with closed eyes (from 47.08% to 47.12%). CONCLUSION: In TKA, mechanoceptors of the knee are sacrificed, this should result in a drop of the proprioceptive information with respect to healthy knee, and consequently there is a decreased of balance and increased of risk of falls. The proprioceptive system are more stimulate during instability situation, for example in poorly lighting places or in restricted movement condition. The reduction of pain and the restoration of limb alignment are probably the main reason of the several improvement of SI and AU during open eyes task, whereas the lack or ineffectiveness of the proprioceptive system, could be the cause of failure improvement of closed eyes task too. Double stance task did not show relevant variations between pre and post surgery, due to influences of non-operated limbs and low numbers of subjects.

Purpose: The computerized Animated Activity Questionnaire (AAQ) for assessing activity limitations in hip and knee osteoarthritis (HKOA) consists of video animations from which patients can choose the animation that best matches their own performance. The AAQ has demonstrated good validity and reliability. Application of the AAQ in international studies, requires good cross-cultural validity, i.e., minimal Differential Item Functioning (DIF) across countries. The aim of this study was to evaluate cross-cultural validity. Methods: Patients in 7 European countries patients completed the AAQ on a computer. Ordinal logistic regression analysis was used to evaluate DIF across languages (Dutch versus 6 other languages). DIF is defined as follows: If a patient in a country has the same level of activity limitation as a patient in the Netherlands (the reference country in which the AAQ is developed), they should score the same on each item of the AAQ. If there is a statistical significant difference between countries, there is DIF. We used frequently described criteria in literature to assess DIF between countries. Criteria for non-uniform DIF were set as a statistical significance (p

Background: The Animated Activity Questionnaire (AAQ) measures activity limitations in hip and knee osteoarthritis (HKOA), and demonstrated good validity and reliability [1]. The AAQ shows stylized video animations of different levels of activity performance. Patients are asked to choose which video best matches their own performance. Accordingly, for international studies, the AAQ should show minimal Differential Item Functioning (DIF) across countries, which means that patients from different countries with the same level of activity limitations should have the same score on each item. Objectives: To evaluate cross-cultural validity of the AAQ. Methods: In 7 European countries patients were asked to complete the AAQ. An example of an item of the AAQ is shown on: http://kmin-vumc.nl/-14-0.html. Ordinal logistic regression was used to evaluate DIF across languages (Dutch versus 6 other languages). As a criterion for uniform DIF we used an odds ratio outside the interval 0.53-1.89. An significant interaction term (p-value

After total knee arthroplasty, changes in articular surface geometry, soft tissue treatment, and component alignment can alter normal lower limb function. The guided motion bi-cruciate substituting prosthesis was designed specifically to restore physiological knee joint motion. We determined whether this design could in vivo normal kinematics and kinetics, not only at the replaced knee, but also throughout both lower limbs. Sixteen patients (4 male, 12 female, mean age of 68.2 years with a range from 58 to 79 years) with primary knee osteoarthritis were implanted with the bi-cruciate substituting prosthesis. At 6-month follow-up, knee joint kinematics was assessed by video-fluoroscopy during stair-climbing, chair-rising/sitting, and step-up/down. Lower limb overall function was also assessed on the same day by standard gait analysis with simultaneous electromyography during level walking. By video-fluoroscopy, mean anteroposterior translations between femoral and tibial components during the three motor tasks were 9.7 +/- 3.0, 10 +/- 2.6, and 6.9 +/- 3.5 mm on the medial compartment, and 14.3 +/- 3.5, 18.5 +/- 3.0, and 13.9 +/- 3.8 mm on the lateral compartment, respectively. Axial rotation ranged from 5.6 degrees to 26.2 degrees. Gait analysis revealed restoration of nearly normal walking patterns in most patients. This rare combination of measurements, i.e., accurate rotation-translation at the replaced knee and complete locomotion patterns at both lower limb joints, suggested that bi-cruciate substituting arthroplasty can restore physiological knee motion and normal overall function.

The effect of specific exercise therapy programs on the management of balance and walking disorders in multiple sclerosis (MS) patients have not been fully explained yet. Reproducible measurement systems are especially required to show their efficacy. The aim of the present case series study was to explore the feasibility of an aerobic treadmill rehabilitation protocol (endurance training protocol) and its effects on walking parameters, muscular activity and postural balance. An adequate instrumental measure set was adopted to provide evidence of minimal motor dysfunction, not quantifiable by means of standard clinical examination.Three minimally impaired MS patients were enrolled. The patients underwent endurance training on a treadmill for four weeks. Posturographic assessment, energy cost measurement and gait analysis by basography and surface electromyography recordings were used as outcome measures.Energy cost during treadmill walking was generally reduced in the three patients after exercise. Indexes of both sway path and sway area used for postural stability measurement were reduced after exercise in two patients, particularly with eyes closed. Minor changes were observed in gait pattern in terms of foot placement. Muscular activity pattern tended to normalize after training.The aerobic treadmill exercise is feasible, safe and it may improve early anomalies of posture and gait in early MS patients. In the context of an impairment oriented rehabilitation approach, the set of instrumental measurements proposed seems to be able to identify subclinical anomalies in a very low degree of functional involvement on an individual basis.

An evaluation of total hip replacement patients requires objective criteria that allow for the measurement of any changes in the biomechanics of the prosthesis and the effects of these changes on clinical findings. An evaluation of loading and joint movement during walking in these patients has been dealt with by many authors. In this study 15 patients who had undergone total hip replacement for coxarthrosis primary or secondary to congenital dysplasia were examined by kinematic and kinetic gait analysis, clinical evaluation, and radiographic evaluation of the position of the neocenter of prosthetic joint rotation. The patients with prostheses in congenital dysplasia presented with a pattern of walking that was significantly modified. In agreement with what is reported in the literature proximal positioning had less influence on gait parameters as compared to lateral dislocation. Furthermore, changes in positioning observed did not seem to have negative effects on joint loading, measured indirectly by the calculation of joint moments.

In recent years research into joint physiology and biomechanics of movement has employed high-technology instruments to quantify the parameters which determine whether the behavior of a joint or kinematic chain is normal or pathologic. Motion analysis, featuring evaluation of both kinematics and the foot-ground reaction, enables us to measure the temporal and quantitative events of normal and pathologic gaits. The use of motion analysis in the study of flat foot has confirmed the ability to discriminate between "normal" and pathologic. Analysis of these themes has enabled us to follow the temporal evolution of the quantitative parameters both before and after treatment, which can be either surgical or conservative. Evaluation of the kinematic changes and the foot-ground reaction also provides information about the quality and effectiveness of the corrective treatment. For instance, the change in the subtalar alignment following application of an endo-orthotic implant can be targeted for validation by motion analysis. All of the joints comprised in the kinematic chain of the lower limb work together to achieve a symmetrical, rhythmic, and most of all harmonic gait.