Anatomical study of paratenons and fascia lata connections in the posteromedial knee region.

INTRODUCTION: In the last decade, fascia research increased significantly in various aspects such as anatomical and biomechanical features related to epimuscular force transmission. METHODS: The present anatomic study focuses on macroscopic observations of the potential gracilis and semitendinosus paratenons, as well as fascial surroundings connections in the posteromedial knee region on 17 lower-limbs dissections. RESULTS: The gracilis and semitendinosus expansions and paratenons were observed in all specimen and further connections with the fascia lata and crural fascia were demonstrated. Contrary to the previously described expansions connected to the tendons, we observed that the expansions were the edges of the paratenon tunnel and that the paratenon structure surrounded the overall muscle. Both paratenons of gracilis and semitendinosus were connected to the crural fascia and, respectively, to the sartorius fascia (part of the fascia lata), to the semimembranosus and the fascia lata. Furthermore, numerous connections between the fascia lata and the neighboring structures in the posteromedial knee region are described. DISCUSSION-CONCLUSION: The present study describes for the first time gracilis and semitendinosus paratenons and other surrounding fascial connections. Such macroscopic observations may represent a new basis for further characterization of the myofascial pathway of epimuscular force transmission in the knee region.

The biomechanical role of the lacertus fibrosus of the biceps brachii Muscle.

PURPOSE: The lacertus fibrosus (LF) is involved in various surgeries. However, the biomechanical contribution of the LF remains unclear. The aim of this study was to determine the role of the lacertus fibrosus on the elbow and forearm kinematics and on the biceps brachii muscle lever arms. METHODS: This biomechanical study was performed on seven fresh-frozen upper limbs of cadavers. Elbow flexion, forearm supination, and biceps brachii muscle lever arms were analyzed in the intact conditions (I) and after superficial (R) and deep part (R2) of the lacertus fibrosus release, respectively. RESULTS: Elbow flexion shows a significant difference (p < 0.0001) between I, R, R2. Abduction/adduction shows a significant difference between I-R (p < 0.0001) and I-R2 (p < 0.0001). Supination does not show a significant difference in mean maximum amplitude, but between 40 and 70%, there are significant differences. There is a significant mean decrease of lever arm in flexion (28%) and supination (50%) after superficial and deep part of the lacertus fibrosus release. CONCLUSION: The results of this study show that the lacertus fibrosus increases the lever arm during flexion and supination. It limits the flexion and abduction of the elbow and supination of the forearm. Lacertus fibrosus maintains the rhythmicity between the elbow flexion and supination of the forearm. LEVEL OF EVIDENCE: Basic science study, biomechanics.

Joint contact areas after radial head arthroplasty: a comparative study of 3 prostheses.

BACKGROUND: Contact stresses of radial head prostheses remain a concern, potentially leading to early capitellar cartilage wear and erosion. In particular, point contact or edge loading could have a detrimental effect. The purpose of this study was to compare 3 different types of radial head prostheses in terms of joint contact areas with each other and with the native situation. The hypothesis was that the joint contact areas would be lower after monopolar arthroplasty. METHODS: Seven fresh-frozen cadaveric upper limbs were used. Radiocapitellar contact areas of a monopolar design, a straight-neck bipolar design, and an angled-neck bipolar design were compared with each other and with the native joint. After standardized preparation, polysiloxane was injected into the loaded radiocapitellar joint to create a cast from which the joint contact area was measured. Measurements were performed at 3 angles of elbow flexion and in 3 different forearm positions. RESULTS: In the native elbow, contact areas were highest in supination. Elbow flexion had no significant effect on native and prosthetic joint contact areas. Contact areas were decreased for all types of arthroplasties compared with the native joint (from 11% to 53%). No significant contact area difference was found between the 3 designs. However, bipolar prostheses showed lateral subluxation in neutral forearm rotation, resulting in a significant decrease in the contact areas from pronation to the neutral position. CONCLUSIONS: All types of radial head prostheses tested showed a significant decrease in radiocapitellar contact area compared with the native joint. Bipolar designs led to subluxation of the radial head, further decreasing radiocapitellar contact.

Metatarsal arch deformation and forefoot kinematics during gait in asymptomatic subjects.

This study aimed to investigate both foot arch-shaped architecture and forefoot kinematics during gait. Using a dedicated three-compartment forefoot subdivision, we studied asymptomatic subjects and quantified disorders related to the metatarsal arch. Foot motion and arch shape were measured in 30 healthy subjects with a motion-capture system and force plates. Kinematic results were expressed using a novel model, which anatomically divides the forefoot into three parts. This model integrated the medial longitudinal arch angle and the metatarsal arch height and width. During the first part of stance phase, the medial longitudinal arch flattens and all foot segments move toward dorsiflexion. During terminal stance and preswing phase, medial longitudinal and metatarsal arch restoration was noted with plantarflexion of all segments, an eversion and abduction of the medial forefoot, and an inversion and adduction of the lateral forefoot. Kinematics obtained with the proposed forefoot model corroborates metatarsal arch restoration in late stance. This observation supports the fact that foot architecture is supple until midstance and subsequently creates a rigid lever arm with restored arches to support propulsion. This study's results and methods highlight the potential of the three-compartment model for use in clinical decision-making.

Pregnancy and pelvic girdle pain: Analysis of pelvic belt on pain.

AIMS AND OBJECTIVES: To analyse pain and functional capacity in women with pelvic girdle pain and to evaluate the effect of pelvic belt on these parameters. Two types of belts were to compare. BACKGROUND: Pelvic girdle pain is very common during pregnancy. To prevent and relieve pelvic pain, women can use a set of techniques and tools such as a pelvic belt. While scientific evidence is lacking, commercial industries suggest the effectiveness of pelvic belts. DESIGN: Randomised control trial. METHODS: Forty-six pregnant women with pelvic girdle pain were evaluated. Pain analysis included a quantitative and a qualitative assessment. A daily activities questionnaire was used for functional capacity evaluation. Women were tested at two times during the pregnancy for a longitudinal evaluation, and they used one of the two belt models during their pregnancy. RESULTS: Pelvic pain started between the 14th-21st week of pregnancy. Pain intensity was 60 ± 20 mm. Daily activities could increase pain. The use of belts reduced pain. The intensity of pain decreased by 20 mm on a visual analogue scale. The daily activities were also easier. However, all these conclusions are valid only if pregnant women used belts regularly on short periods. CONCLUSIONS: The belts appear to be interesting tools to reduce pelvic pain and improve comfort of pregnant women. This effect might be explained by an analgesic effect with proprioceptive and biomechanical effect. The different types of belts could have differential effects on global, sacroiliac joint and back pain during pregnancy, but this hypothesis requires confirmation. RELEVANCE TO CLINICAL PRACTICE: Relevant for patient: to use an easy and validated tool. Relevant for clinical practice: to suggest a tool scientifically validated for patient. Relevant to economic issues: belts decrease pelvic pain and increase comfort of pregnant women. Sick leave could decrease.

Pregnancy and Pelvic Girdle PainAnalysis of Center of Pressure During Gait.

BACKGROUND: A woman's body undergoes many changes during pregnancy, and it adapts by developing compensatory strategies, which can be sources of pain. We sought to analyze the effects of pregnancy and pelvic girdle pain (PGP) on center of pressure (COP) parameters during gait at different speeds. METHODS: Sixty-one healthy pregnant women, 66 women with PGP between 18 and 27 weeks of pregnancy, and 22 healthy nonpregnant women walked at different velocities (slow, preferential, and fast) on a walkway with built-in pressure sensors. An analysis of variance was performed to determine the effects of gait speed and group on COP parameters. RESULTS: In healthy pregnant women and women with PGP, COP parameters were significantly modified compared with those in nonpregnant women (P < .01). Support time was increased regardless of gait speed, and anteroposterior COP displacement was significantly decreased for women with PGP compared with healthy pregnant women. In addition, mediolateral COP displacement was significantly decreased in pregnant women compared with nongravid women. CONCLUSIONS: Gait speed influenced COP displacement and velocity parameters, and gait velocity potentiated the effect of pregnancy on the different parameters. Pelvic girdle pain had an influence on COP anteroposterior length only. With COP parameters being only slightly modified by PGP, the gait of pregnant women with PGP was similar to that of healthy pregnant women but differed from that of nonpregnant women.

Pregnancy-related changes in center of pressure during gait.

PURPOSE: Physical and hormonal modifications occuring during the pregnancy, can lead to an increase in postural instability and to a higher risk of falls during gait. The first objective was to describe the center of pressure (COP) during late pregnancy at different gait velocity. Comparison of nulliparous women with postpartum women were conducted in order to investigate the effects of pregnancy. The second objective was to analyse COP variability between pregnant and non-pregnant women in order to investigate the effects of pregnancy on gait variability. METHODS: Fifty-eight pregnant women in the last four months of pregnancy, nine postpartum women and twenty-three healthy non-pregnant women performed gait trials at three different speeds: preferred, slow and fast. RESULTS: In the last four months of pregnancy gait velocity decreased. During the pregnancy, gait velocity decreased by 22%, stopover time increased by 6-12%, COP excursion XY decreased by 5% and COP velocity decreased by 16% and 20% along the anteroposterior and transverse axes, respectively. After delivery, gait velocity increased by 3% but remained a lower compared to non-pregnant women (-12%). Intra-individual variability was greater for non-pregnant than pregnant women. CONCLUSIONS: COP parameters were influenced by pregnancy. This suggests that pregnant women establish very specific and individual strategies with the aim of maintaining stability during gait.

Plantar Pressure During Gait in Pregnant Women.

BACKGROUND: During pregnancy, physical and hormonal modifications occur. Morphologic alterations of the feet are found. These observations can induce alterations in plantar pressure. This study sought to investigate plantar pressures during gait in the last 4 months of pregnancy and in the postpartum period. A comparison with nulliparous women was conducted to investigate plantar pressure modifications during pregnancy. METHODS: Fifty-eight women in the last 4 months of pregnancy, nine postpartum women, and 23 healthy nonpregnant women (control group) performed gait trials on an electronic walkway at preferred speeds. The results for the three groups were compared using analysis of variance. RESULTS: During pregnancy, peak pressure and contact area decreased for the forefoot and rearfoot. These parameters increased significantly for the midfoot. The gait strategy seemed to be lateralization of gait with an increased contact area of the lateral midfoot and both reduced pressure and a later peak time on the medial forefoot. In the postpartum group, footprint parameters were modified compared with the pregnant group, indicating a trend toward partial return to control values, although differences persisted between the postpartum and control groups. CONCLUSIONS: Pregnant women had altered plantar pressures during gait. These findings could define a specific pattern of gait footprints in late pregnancy because plantar pressures had characteristics that could maintain a stable and safe gait.

A novel method for in-vivo evaluation of finger kinematics including definition of healthy motion patterns.

BACKGROUND: Despite recent progress in motion capture technology, such as stereophotogrammetry based on the tracking of markers set on the subject, it remains challenging to develop a complete protocol for in-vivo functional evaluation of the hand. The current practical problems regarding small anatomical segments, such as the fingers, are mainly due to the high concentration of markers in a relatively reduced volume. METHODS: This paper proposes a novel procedure for hand functional analysis by analysing finger behaviour along the main displacement plane simultaneously with combined motions. The objective was two-fold. For one thing, a novel data collection protocol was implemented, which includes specific setting of the motion capture system and the development of finger marker clusters. The second purpose of this study was to create a reference database of a healthy sample for further clinical investigation. Twenty healthy volunteers took part in the study. Analytical motions (flexion/extension and abduction/adduction) of all five fingers were recorded. FINDINGS: Results showed good correspondence with the literature. Specific kinematic behaviour of each analysed joint is reported. Statistically significant differences were found between the right and left sides of the subjects for the flexion/extension movement only, between the finger joints and between the fingers for all movements. No significant difference was found between genders. A validation protocol was performed, which proved the validity of the presented methodology. INTERPRETATION: The protocol appears suitable for further use in motion analysis and for musculoskeletal modelling of the hand. It will also be considered for clinical application.

Temporal and spatial parameters of gait during pregnancy.

PURPOSE: The objective of this study was to describe spatial and temporal parameters during gait in pregnant women, and to compare it with women in post-partum and with a control group. METHODS: To investigate alteration in natural locomotion, we used an electronic walkway (GAITRite system). Fifty-eight pregnant women (four last months of pregnancy), nine post-partum women and twenty-three healthy nulligravidae women participated in this study. The women performed the motor task at three different speeds: preferred, fast and slow. Spatial and temporal parameters for pregnant and non-pregnant were compared. RESULTS: In pregnant women, gait speed, step length and cadence were reduced. Consequently, cycle time was longer. The gait cycle was modified by an increase of stance phase and a decrease of swing phase. As a result, an increase of double support and a decrease of single support phases were observed. Step width increased by 15%. CONCLUSIONS: The pattern of gait displayed significant modifications during pregnancy as compared to nulliparous women. These changes favour a more stable and safe gait. After childbirth, women kept some characteristics of gait in pregnancy during 8 months.

Head-trunk kinematics during high-velocity-low-amplitude manipulation of the cervical spine in asymptomatic subjects: helical axis computation and anatomic motion modeling.

OBJECTIVE: This study aimed to analyze the in vivo 3-dimensional kinematics of the head during cervical manipulation including helical axis (HA) computation and anatomic motion representation. METHODS: Twelve asymptomatic volunteers were included in this study. An osteopathic practitioner performed 1 to 3 manipulations (high-velocity and low-amplitude [HVLA] multiple component technique) of the cervical spine (between C2 and C5) with the patient in the sitting position. During manipulation, head motion was collected using an optoelectronic system and expressed relative to the thorax. Motion data were processed to analyze primary and coupled motions and HA parameters. Anatomic motion representation including HA was obtained. RESULTS: During manipulation, average maximal range of motion was 39° (SD, 6°), 21° (SD, 7°), and 8° (SD, 5°) for lateral bending (LB), axial rotation (AR), and flexion extension, respectively. For the impulse period, magnitude averaged of 8° (SD, 2°), 5° (SD, 2°), and 3° (SD, 2°), for LB, AR, and flexion extension, respectively. Mean impulse velocity was 139°/s (SD, 39°/s). Concerning AR/LB ratios, an average of 0.6 (SD, 0.3) was observed for global motion, premanipulation positioning, and impulse. Mean HA was mostly located ipsilateral to the impulse side and displayed an oblique orientation. CONCLUSION: This study demonstrated limited range of AR during cervical spine manipulation and provided new perspectives for the development of visualization tools, which might be helpful for practitioners and for the analysis of cervical manipulation using HA computation and anatomic representation of motion.

Femoral curvature variability in modern humans using three-dimensional quadric surface fitting.

INTRODUCTION: This study analysed femoral curvature in a population from Belgium in conjunction with other morphological characteristics by the use of three-dimensional (3D) quadric surfaces (QS) modelled from the bone surface. METHODS: 3D models were created from computed tomography data of 75 femoral modern human bones. Anatomical landmarks (ALs) were palpated in specific bony areas of the femur (shaft, condyles, neck and head). QS were then created from the surface vertices which enclose these ALs. The diaphyseal shaft was divided into five QS shapes to analyse curvature in different parts of the shaft. RESULTS: Femoral bending differs in different parts of the diaphyseal shaft. The greatest degree of curvature was found in the distal shaft (mean 4.5° range 0.2°-10°) followed by the proximal (mean 4.4° range 1.5°-10.2°), proximal intermediate (mean 3.7° range 0.9°-7.9°) and distal intermediate (mean 1.8° range 0.2°-5.6°) shaft sections. The proximal and distal angles were significantly more bowed than the intermediate proximal and the intermediate distal angle. There was no significant difference between the proximal and distal angle. No significant correlations were found between morphological characteristics and femoral curvature. An extremely large variability of femoral curvature with several bones displaying very high or low degrees of femoral curvature was also found. CONCLUSION: 3D QS fitting enables the creation of accurate models which can discriminate between different patterns in similar curvatures and demonstrates there is a clear difference between curvature in different parts of the shaft.

Effect of anatomical landmark perturbation on mean helical axis parameters of in vivo upper costovertebral joints.

The literature concerning quantification of costovertebral joint (CVJ) motion under in vivo conditions is scarce. Most papers concerning this topic are related to ex vivo loading conditions. In vivo protocols are available from the literature to determine rib and vertebra kinematics but new developments are needed to improve data processing concerning CVJ behaviour obtained from discrete breathing positions showing limiting ranges-of-motion and sensitive to noise. Data from previous work were used to implement a method analyzing mean helical axis (MHA) and pivot point parameters of the CVJ complexes. Several levels of noises were estimated within Monte-Carlo simulations to optimize MHA results. MHA parameters were then used to transform and define a CVJ-specific local coordinate system. This study proposes an improvement for CVJ kinematics processing and description from in vivo data obtained from computed tomography. This methodology emphasizes the possibility to work with variability of MHA parameters using Monte-Carlo procedures on anatomical landmark coordinates and to define a local coordinate system from this particular joint behaviour. Results from the CVJ joint model are closer to a hinge joint (secondary motions inferior to 3°) when anatomical frames are expressed from MHA orientation. MHA orientation and position data obtained from the proposed method are relevant according to angular dispersion obtained (from 7.5° to 13.9°) and therefore relevant to define behaviour of CVJ.

Interchangeability of the Wii Balance Board for Bipedal Balance Assessment.

BACKGROUND: Since 2010, an increasing interest in more portable and flexible hardware for balance and posture assessment led to previously published studies determining whether or not the Wii Balance Board could be used to assess balance and posture, both scientifically and clinically. However, no previous studies aimed at comparing results from different Wii Balance Boards for clinical balance evaluation exist. OBJECTIVE: The objective of this crossover study is to assess the interchangeability of the Wii Balance Board. METHODS: A total of 6 subjects participated in the study and their balance was assessed using 4 different Wii Balance Boards. Trials were recorded simultaneously with Wii Balance Boards and with a laboratory force plate. Nine relevant clinical parameters were derived from center of pressure displacement data obtained from Wii Balance Board and force plate systems. Intraclass correlation coefficients (ICC), F tests, and Friedman tests were computed to assess the agreement between trials and to compare the Wii Balance Board and force plate results. RESULTS: Excellent correlations were found between the Wii Balance Board and force plate (mean ρ =.83). With the exception of 2 parameters, strong to excellent agreements were found for the 7 remaining parameters (ICC=.96). No significant differences were found between trials recorded with different Wii Balance Boards. CONCLUSIONS: Our results indicate that for most of the parameters analyzed, balance and posture assessed with one Wii Balance Board were statistically similar to results obtained from another. Furthermore, the good correlation between the Wii Balance Board and force plate results shows that Wii Balance Boards can be reliably used for scientific assessment using most of the parameters analyzed in this study. These results also suggest that the Wii Balance Board could be used in multicenter studies and therefore, would allow for the creation of larger populations for clinical studies. TRIAL REGISTRATION: Ethical Committee of the Erasme Hospital (CCB B406201215142).

Physiologically corrected coupled motion during gait analysis using a model-based approach.

Gait analysis is used in daily clinics for patients' evaluation and follow-up. Stereophotogrammetric devices are the most used tool to perform these analyses. Although these devices are accurate results must be analyzed carefully due to relatively poor reproducibility. One of the major issues is related to skin displacement artifacts. Motion representation is recognized reliable for the main plane of motion displacement, but secondary motions, or combined, are less reliable because of the above artifacts. Model-based approach (MBA) combining accurate joint kinematics and motion data was previously developed based on a double-step registration method. This study presents an extensive validation of this MBA method by comparing results with a conventional motion representation model. Thirty five healthy subjects participated to this study. Gait motion data were obtained from a stereophotogrammetric system. Plug-in Gait model (PiG) and MBA were applied to raw data, results were then compared. Range-of-motion, were computed for pelvis, hip, knee and ankle joints. Differences between PiG and MBA were then computed. Paired-sample t-tests were used to compare both methods. Normalized root-mean square errors were also computed. Shapes of the curves were compared using coefficient of multiple correlations. The MBA and PiG approaches shows similar results for the main plane of motion displacement but statistically significative discrepancies appear for the combined motions. MBA appear to be usable in applications (such as musculoskeletal modeling) requesting better approximations of the joints-of-interest thanks to the integration of validated joint mechanisms.

The effect of humerus diaphyseal shortening on brachial plexus tension: a cadaver study.

PURPOSE: To assess the extent to which diaphyseal shortening of the humerus can allow direct suture in case of rupture or transection injuries of the brachial plexus. METHODS: The use of 3 fresh cadaver specimens allowed for the study of 6 brachial plexuses. Distance measurements were made between reference points placed on the clavicle and on different parts of the plexus. Those measurements were repeated after shortening the humerus by 2, 4, and 6 cm. RESULTS: None of the dissected plexuses had classic anatomy. A humeral shortening of 6 cm allowed for a statistically significant reduction of length between the supraclavicular part of the plexus and the terminal branches, which did not exceed 17 mm on average. The difference of length was much greater for the specimen in which the musculocutaneous nerve did not pierce the coracobrachialis muscle proximally. CONCLUSIONS: In clinical situations, nerve defects are usually larger than the gain observed when doing a 6-cm humeral shortening. Moreover, this procedure implies a large dissection, a functional loss of certain muscles, and a risk of humeral nonunion. CLINICAL RELEVANCE: In the absence of extensive nerve dissection, the observed change of length is insufficient in the most brachial plexus disruptions to allow for a direct suture instead of long nerve grafts.

Kinematics of the upper cervical spine during high velocity-low amplitude manipulation. Analysis of intra- and inter-operator reliability for pre-manipulation positioning and impulse displacements.

To date, kinematics data analyzing continuous 3D motion of upper cervical spine (UCS) manipulation is lacking. This in vitro study aims at investigating inter- and intra-operator reliability of kinematics during high velocity low amplitude manipulation of the UCS. Three fresh specimens were used. Restricted dissection was realized to attach technical clusters to each bone (skull to C2). Motion data was obtained using an optoelectronic system during manipulation. Kinematics data were integrated into specific-subject 3D models to provide anatomical motion representation during thrust manipulation. The reliability of manipulation kinematics was assessed for three practitioners performing two sessions of three repetitions on two separate days. For pre-manipulation positioning, average UCS ROM (SD) were 10° (5°), 22° (5°) and 14° (4°) for lateral bending, axial rotation and flexion-extension, respectively. For the impulse phase, average axial rotation magnitude ranged from 7° to 12°. Reliability analysis showed average RMS up to 8° for pre-manipulation positioning and up to 5° for the impulse phase. As compared to physiological ROM, this study supports the limited angular displacement during manipulation for UCS motion components, especially for axial rotation. Kinematics reliability confirms intra- and inter-operator consistency although pre-manipulation positioning reliability is slightly lower between practitioners and sessions.

What is the Safest Sprint Starting Position for American Football Players?

The main objective of this study was to perform a biomechanical analysis of three different sprint start patterns to determine the safest position in term of neck injury and Sport-Related Concussion (SRC). The second objective was to collect data on the learning process effect between football players and non-players. Three different sprint initial positions adopted by football players were studied (i.e., 4-, 3- and 2-point positions). Twenty five young healthy males, including 12 football players, participated to this study. A stereophotogrammetric system (i.e., Vicon) was used to record motion patterns and body segments positions. Various measurements related to head and trunk orientation, and player field-of-view were obtained (e.g., head height, trunk bending, time to reach upright position, head speed (vertical direction) and body speed (horizontal direction)). Learning process was found to have no influence on studied parameters. Head redress is also delayed when adopting a 4-point position leading to a reduce field-of-view during the start and increasing therefore the probability of collision. Concerning the three different positions, the 4-point position seems to be the more dangerous because leading to higher kinetic energy than the 2- and 3-point start positions. This study proposes a first biomechanical approach to understand risk/benefit balance for athletes for those three different start positions. Results suggested that the 4-point position is the most risky for football players. Key pointsMotion analysis and biomechanical analysis of the initial start position of the sprint could be used to increase the safety of the football players.Analysis of kinematic and trajectory of the head and the time to reach the upright position could be used to determine whether or not a player can return to play after concussion.A balance needs to be found between player's safety (2-point start) and speed (4-point start).

Determination of repeatability of kinect sensor.

BACKGROUND: The Kinect™ (Microsoft™, Redmond, WA) sensor, originally developed for gaming purposes, may have interesting possibilities for other fields such as posture and motion assessment. The ability of the Kinect sensor to perform biomechanical measurements has previously been studied and shows promising results. However, interday repeatability of the device is still not known. MATERIALS AND METHODS: This study assessed the intra- and interday repeatability of the Kinect sensor compared with a standard stereophotogrammetric device during posture assessment for measuring segment lengths. Forty subjects took part in the study. Five motionless captures were performed in one session to assess posture. Data were simultaneously recorded with both devices. RESULTS: Similar intraclass correlations coefficient (ICC) values were found for intraday (ICC=0.94 for the Kinect device and 0.98 for the stereophotogrammetric device) and interday (ICC=0.88 and 0.87, respectively) repeatability. CONCLUSIONS: Results of this study suggest that a cost-effective, easy-to-use, and portable single markerless camera offers the same repeatability during posture assessment as an expensive, time-consuming, and nontransportable marker-based device.

Motion representation of the long fingers: a proposal for the definitions of new anatomical frames.

Despite the availability of the International Society of Biomechanics (ISB) recommendations for the orientation of anatomical frames, no consensus exists about motion representations related to finger kinematics. This paper proposes novel anatomical frames for motion representation of the phalangeal segments of the long fingers. A three-dimensional model of a human forefinger was acquired from a non-pathological fresh-frozen hand. Medical imaging was used to collect phalangeal discrete positions. Data processing was performed using a customized software interface ("lhpFusionBox") to create a specimen-specific model and to reconstruct the discrete motion path. Five examiners virtually palpated two sets of landmarks. These markers were then used to build anatomical frames following two methods: a reference method following ISB recommendations and a newly-developed method based on the mean helical axis (HA). Motion representations were obtained and compared between examiners. Virtual palpation precision was around 1mm, which is comparable to results from the literature. The comparison of the two methods showed that the helical axis method seemed more reproducible between examiners especially for secondary, or accessory, motions. Computed Root Mean Square distances comparing methods showed that the ISB method displayed a variability 10 times higher than the HA method. The HA method seems to be suitable for finger motion representation using discrete positions from medical imaging. Further investigations are required before being able to use the methodology with continuous tracking of markers set on the subject's hand.