Aplicaciones clínicas de las pruebas biomecánicas: mitos y realidades / No disponible

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Fracaso de la osteosíntesis mandibular. Consideraciones biomecánicas y tratamiento. A propósito de dos casos clínicos / Mandibular osteosynthesis failure. Biomechanical and therapeutic considerations. Two clinical cases

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Evaluación de la marcha con bastones en pacientes con lesión medular incompleta / Assessment of walking on crutches in patients with incomplete spinal cord injury

Objetivo. Determinar las aportaciones que suponen el empleo de técnicas de análisis biomecánico a la hora de recomendar la marcha con uno o dos bastones en personas con lesión medular incompleta. Material y métodos. Se efectuó el análisis cinemático de la marcha en 12 pacientes con lesión medular incompleta de más de un año de evolución y capacidad funcional para caminar con un bastón. Los pacientes caminaron a velocidad libre en un pasillo de 10 m con uno y con dos bastones. Se utilizó un equipo que permite realizar un análisis cinemático en 3 D basado en marcadores activos. Los parámetros analizados fueron los temporo-espaciales y los articulares (máximos, mínimos y rango articular a lo largo del ciclo). Resultados. Caminando con dos bastones la duración del ciclo es mayor (p = 0,010) y la frecuencia de ciclos/minuto es menor (p = 0,014). Respecto a los parámetros articulares, en la marcha con dos bastones el pico de valor máximo (p = 0,036) y el mínimo de basculación anterior pélvica (p = 0,038), así como el recorrido articular de rotación pélvica (p = 0,006) son mayores, y el valor mínimo de flexión de cadera es menor (p = 0,022). Conclusión. A pesar de la mayor seguridad ofrecida para los lesionados medulares que pueden caminar con un bastón, el hacerlo con dos puede constituir una marcha más costosa. Las técnicas de análisis biomecánico constituyen un elemento de soporte a la hora de recomendar una ayuda técnica para la marcha (AU)

Objective. To determine the differences in gait kinematic parameters of people with incomplete spinal cord injury while walking with one or two crutches. Material and methods. Twelve patients with incomplete spinal cord injury whose injury occurred at least one year ago with functional capacity for walking with one crutch were kinetically analyzed. The patients walked at free rate in a 10 m hallway with one or two crutches. A system was used that allowed for kinematic analysis in 3 D based on active markers. The parameters analyzed were time-space and joint values (maximum, minimum and range of movement during the cycle). Results. When walking with two crutches, the stride time is greater (p = 0.021) and the stride/minute is less (p = 0.014). Regarding joint parameters of walking with two crutches, the maximum value peak (p = 0.036) and the minimum of anterior pelvic tilt (p = 0.038) and the joint range of the pelvic rotation (p = 0.006) are greater and the minimum value of hip flexion is less (p = 0.022). Conclusion. In spite of the greater safety offered for the patients suffering spinal cord injuries, for those who can walk with one crutch, the use of 2 crutches can make walking more difficult. Biomechanical analysis techniques are a supportive element when recommending technical help for walking (AU)

El patrón de movimiento en el swing de golf en jóvenes promesas / No disponible

Introducción: El swing de golf es una destreza que podríamoscatalogar de golpeo de velocidad donde el objetivo esque la cara del palo alcance la máxima velocidad en el momentodel impacto.Objetivos: Analizar la secuencia temporal del swing degolf y determinar su patrón de movimiento.Métodos: Se han analizado biomecánicamente 10 golpeosde 4 jugadores promesas, mediante el sistema de fotogrametría3D Vicon Oxford Metrics® de captura automática.Resultados: En primer lugar se ha podido comprobar quelos valores absolutos de velocidades lineales eran mayoresen los chicos que en las chicas. El análisis de las 2 fases delswing indica que la fase de aceleración downswing presentauna variabilidad menor que el backswing. El análisis de la secuenciatemporal de máximos alcanzados en las velocidadeslineales de los segmentos muestra que sus acciones siguenun orden diferente en función del sexo. La secuencia en loschicos empieza por el movimiento de caderas y sigue conel codo izquierdo, el hombro izquierdo y el palo; en las chicas,las caderas y el codo izquierdo actúan simultáneamenteseguidos del hombro izquierdo y del palo. En cambio, lassecuencias de velocidades angulares encontradas seguíanen ambos sexos el mismo orden: primero el giro de caderas,luego el giro de hombros y por último la aceleracióndel palo. Esta secuencia de acciones se encontraba más separadaen el tiempo en los hombres que en las mujeres.Conclusiones: Se hallaron los patrones del movimientomediante fórmulas discriminantes en ambos sexos, capacesde predecir si el golpeo sería “bueno” o “malo” siguiendoel criterio de rendimiento marcado en la velocidad de la cabezadel palo

Introduction: The golf swing is a skill that could be classifiedas high velocity hitting in which the main goal is thatthe head of the golf club reaches its maximum velocity atthe moment of impact.Aims: To analyze the timing sequence of the golf swingand to identify the movement pattern of this skill.Methods: Ten golf swings executed by four young playerswere biomechanically analyzed. Automatic capture with ViconOxford Metrics® was used.Results: The absolute values of the linear velocities werehigher in men than in women. In the interval analysis, thedownswing showed less variation than the backswing.Analysis of the maximum speed timing sequence revealed adifferent order depending on gender. In men, the sequencestarted with the hip movement, followed by the left elbow,left shoulder and the club head. In women, the hips and leftelbow moved simultaneously, followed by the left shoulderand the club head. In contrast, the angular velocity sequencesfollowed the same order in both genders: first the hipturn, then the shoulder turn, and finally the golf club headacceleration. These key events were more separated in thetime line in men than in women.Conclusions: Movement patterns were found throughdiscriminatory formulae in both genders, which were ableto predict whether the golf swing was “good” or “bad”, taking the club head speed as the performance criterion (AU)

Síndrome de los isquiotibiales acortados / Shortened hamstring syndrome

La falta de flexibilidad en los músculos isquiotibiales condiciona una disminución de la movilidad pelviana que lleva invariablemente al cambio biomecánico en la distribución de presiones en la columna vertebral. La incidencia del síndrome de los isquiotibiales acortados es mayor en varones y puede tener relación con lesiones musculares, alteraciones articulares, actividad deportiva y estilo de vida. Muchos de los actuales estudios se centran en los beneficios de entrenamiento de la flexibilidad, actuando en los mecanismos involucrados en ellos mediante la aplicación de programas de estiramientos, con el objetivo de incrementar la longitud musculotendinosa(AU)

Lack of flexibility in the hamstring muscle conditions a decrease of pelvic mobility. Thisinvariably leads to biomechanical changes in the distribution of pressures in the spine.The incidence of the shortened hamstrings syndrome is greater in men and can beassociated to muscles injuries, joint alterations, sport activity and style of life.Many of the present investigations are focused on the benefits of training flexibility, actingon the mechanisms involved in such through the application of stretching programs,in order to increase the muscle tendinuos length(AU)

Measurement of vertebral kinematics using noninvasive image matching method-validation and application.

STUDY DESIGN: In vitro and in vivo laboratory study. OBJECTIVE: To validate a dual fluoroscopic image matching technique for measurement of in vivo spine kinematics. SUMMARY OF BACKGROUND DATA: Accurate knowledge of the spinal structural functions is critical to understand the biomechanical factors that affect spinal pathology. Many studies have investigated vertebral motion both in vitro and in vivo. However, determination of in vivo motion of the vertebrae under physiologic loading conditions remains a challenge in biomedical engineering because of the limitations of current technology and the complicated anatomy of the spine. METHODS: In in vitro validation, an ovine spine was moved to a known distance in a known speed by an MTS machine. The dual fluoroscopic system was used to capture the spine motion and reproduce the moving distance and speed. In in vivo validation, a living subject moved the spine in various positions under weightbearing. The fluoroscopes were used to reproduce the in vivo spine positions 5 times. The standard deviations in translation and orientation of the 5 measurements were used to evaluate the repeatability of technique. RESULTS: The translation positions of the ovine spine could be determined with a mean accuracy less than 0.40 mm for the image matching technique using magnetic resonance image-based vertebral models. The spine speed could be reproduced within an accuracy of 0.2 mm/s. The repeatability of the method in reproducing in vivo human spine 6DOF kinematics was less than 0.3 mm in translation and less than 0.7 degrees in orientation. CONCLUSION: The image matching technique was accurate and repeatable for noninvasive measurement of spine vertebral motion. The technique could be a useful tool for determination of vertebral positions and orientations before and after surgical treatment of spinal pathology to evaluate and improve the efficacy of the various surgical methods in restoring normal spine function.

Should the instructions issued to the subject in traditional static posturography be standardised?

The postural ability of a subject is usually evaluated through the observation of the centre of pressure parameters obtained through posturography. These parameters are known to be sensitive to various factors and standards have consequently been proposed for data acquisition and analysis. A factor usually not taken into due consideration but likely to influence the postural exam is the kind of standing posture (e.g. natural or immobile) a subject is instructed to maintain. This study aimed at investigating whether instructions issued in a traditional static posturographic test influence its outcome and hence should be considered in the standardisation of the posturography protocols. Two groups of young healthy subjects were each issued one of two common instructions, "stand quietly" or "stand as still as possible", by means of projected instructions. Differences between the two groups were investigated for commonly calculated centre of pressure parameters. All these parameters, but the mean frequency, were significantly different, with variations in the range between 8% (mean velocity) and 71% (confidence circle area). These results suggest that instructions given to the subjects strongly influence the outcome of posturography and should, hence, be standardised.

New extensometer to measure in vivo uniaxial mechanical properties of human skin.

Biomechanical properties of skin are important for clinical decision making as well as clinical intervention. Measuring these properties in vivo is critical for estimating dimensional behaviour of skin flap or graft after harvest. However, existing methodologies and devices often suffer from lack of standardisation and unwanted peripheral force contribution due to the deformation of surrounding tissues during measurement. This naturally leads to measurement inaccuracies and lack of reproducibility. In order to improve the measurement accuracy, a new portable extensometer, which measures the non-invasive in vivo biomechanical properties of skin, has been designed and constructed. This design incorporates three pads that attach to the skin, including a C-shaped pad to shield the force sensor from peripheral forces. Such design produces data that are significantly closer to in vitro measurements. The results have been verified by finite element analysis, and experiments on rubber sheets and pig skins. This device can be used to obtain biomechanical properties of skin that will aid doctors in measuring skin elasticity and surgical planning, especially in skin flap surgery.

The reliability of knee joint position testing using electrogoniometry.

BACKGROUND: The current investigation examined the inter- and intra-tester reliability of knee joint angle measurements using a flexible Penny and Giles Biometric electrogoniometer. The clinical utility of electrogoniometry was also addressed. METHODS: The first study examined the inter- and intra-tester reliability of measurements of knee joint angles in supine, sitting and standing in 35 healthy adults. The second study evaluated inter-tester and intra-tester reliability of knee joint angle measurements in standing and after walking 10 metres in 20 healthy adults, using an enhanced measurement protocol with a more detailed electrogoniometer attachment procedure. Both inter-tester reliability studies involved two testers. RESULTS: In the first study, inter-tester reliability (ICC[2,10]) ranged from 0.58-0.71 in supine, 0.68-0.79 in sitting and 0.57-0.80 in standing. The standard error of measurement between testers was less than 3.55 degrees and the limits of agreement ranged from -12.51 degrees to 12.21 degrees . Reliability coefficients for intra-tester reliability (ICC[3,10]) ranged from 0.75-0.76 in supine, 0.86-0.87 in sitting and 0.87-0.88 in standing. The standard error of measurement for repeated measures by the same tester was less than 1.7 degrees and the limits of agreement ranged from -8.13 degrees to 7.90 degrees . The second study showed that using a more detailed electrogoniometer attachment protocol reduced the error of measurement between testers to 0.5 degrees . CONCLUSION: Using a standardised protocol, reliable measures of knee joint angles can be gained in standing, supine and sitting by using a flexible goniometer.

Validation of hamstrings musculoskeletal modeling by calculating peak hamstrings length at different hip angles.

Accurate estimates of hamstrings lengths are useful, for example, to facilitate planning for surgical lengthening of the hamstrings in patients with cerebral palsy. In this study, three models used to estimate hamstrings length (M1: Delp, M2: Klein Horsman, M3: Hawkins and Hull) were evaluated. This was done by determining whether the estimated peak semitendinosus, semimembranosus and biceps femoris long head lengths, as measured in eight healthy subjects, were constant over a range of hip and knee angles. The estimated peak hamstrings length depended on the model that was used, even with length normalized to length in anatomical position. M3 estimated shorter peak lengths than M1 and M2, showing that more advanced models (M1 and M2) are more similar. Peak hamstrings length showed a systematic dependence on hip angle for biceps femoris in M2 and for semitendinosus in M3, indicating that either the length was not correctly estimated, or that the specific muscle did not limit the movement. Considerable differences were found between subjects. Large inter-individual differences indicate that modeling results for individual subjects should be interpreted with caution. Testing the accuracy of modeling techniques using in vivo data, as performed in this study, can provide important insights into the value and limitations of musculoskeletal models.

Gesture as an important factor in 3D kinematic assessment of the knee.

Contradictions exist between studies of the 3D kinematics of the knee. We hypothesize that they are in part due to differences in the gesture performed by the subjects during kinematic assessment. The purpose of this study is to evaluate the impact of gesture variations on knee kinematics. Seventeen healthy male subjects performed 20-s series of knee-bends in a knee-bend standardizing structure. All series differed regarding either foot rotation, knee excursion, or hip rotation. 3D knee kinematics were recorded using optical position sensors mounted on a skin-motion-reducing harness. Kinematic comparisons were made between a gesture of reference (the standard gesture) and every other gesture. Analyses were performed on average differences. Differences of up to 15 degrees of tibial rotation were found for gestures involving different foot rotation. Gestures involving different knee excursion brought on differences of more than 4 degrees of tibial rotation while hip rotation induced more than 5 degrees of tibial rotation. It is hereby demonstrated that gesture differences can have a dramatic impact on measured knee kinematics. Hence gesture performance needs to be carefully monitored during 3D kinematic assessment of the weight-bearing human knee.

An easily reproducible and biomechanically standardized model to investigate bone healing in rats, using external fixation.

Abstract We have established a new small animal model to investigate the process of bone regeneration. A total of 42 male Sprague-Dawley rats received an osteotomy of the left femur, stabilized with a custom-made external fixator. The fixation method was chosen to create an easily reproducible, biomechanically well-defined model with minimized interference of the implant with the healing zone. At 14 or 56 days post-operation, the animals were sacrificed and examined biomechanically, histologically and radiologically. Radiologically, the femurs of all animals were anatomically positioned directly post-operation and remained in that position throughout the examination period. At 14 days post-operation, a typical periosteal callus formation could be observed both histologically and radiologically. At 56 days post-operation, the osteotomy was almost completely bridged by periosteal callus and the biomechanical competence of the bones was fully restored. Relative to the intact contralateral femur, the torsional stiffness median was 130.3% (interquartile range 118.9-157.7%) and the maximum torsional failure moment median was 135.6% (interquartile range 69.5-208.7%). As this model provides standardized conditions, it is suitable for a wide range of investigations and is particularly valuable for investigations of locally applied therapies, such as osteoconductive materials or osteoinductive factors.

Assessment of mild hindlimb lameness during over ground locomotion using linear discriminant analysis of inertial sensor data.

REASONS FOR PERFORMING STUDY: Hindlimb lameness is common and can be difficult to diagnose or quantify in evaluating response to nerve blocks. An objective measure of lameness can also be used to evaluate the effectiveness of the treatment's contribution to evidence-based medicine. The inertial sensor system can be used to capture 6 degree of freedom movement during over ground locomotion and here was used to quantify tuber coxae movement in nonlame and lame horses. HYPOTHESIS: Tuber coxae movement is useful for discriminating between nonlame and lame horses. OBJECTIVES: To measure left and right tuber coxae movement in lame and nonlame horses during over ground locomotion and to implement a linear discriminant analysis to discriminate between lame and nonlame horses. METHODS: Two inertial sensors were attached to the skin over left and right tuber coxae of 21 horses (9 mildly and 12 not lame). Horses were trotted on a hard surface. A total of 1021 strides were collected. For each stride 34 features were extracted from the dorsoventral and craniocaudal movement and used in 2 different classification scenarios (lame vs. nonlame or left lame, right lame and nonlame) using linear discriminant analysis. RESULTS: Six degree of freedom inertial sensors were successfully used to collect kinematic data continuously from left and right tuber coxae in horses during over ground locomotion. These data were used for an automated classification of lameness. In the first scenario, a sensitivity of 89% was achieved with a specificity of 75%. In the second scenario, all horses could be correctly assigned to the correct class in a simple 3 class reclassification test. POTENTIAL RELEVANCE: A mobile system that reliably detects and quantifies hindlimb lameness in horses during unconstrained locomotion could be a valuable tool to perform an evidence-based assessment of lameness in horses in a clinical setting, e.g. before and after nerve blocks or before and after surgery.

Estimating mandibular motion based on chin surface targets during speech.

PURPOSE: The movement of the jaw during speech and chewing has frequently been studied by tracking surface landmarks on the chin. However, the extent to which chin motions accurately represent those of the underlying mandible remains in question. In this investigation, the movements of a pellet attached to the incisor of the mandible were compared with those of pellets attached to different regions of the chin. METHOD: Ten healthy talkers served as participants. Three speaking contexts were recorded from each participant: word, sentence, and paragraph. Chin position errors were estimated by computing the standard distance between the mandibular incisor pellet and the chin pellets. RESULTS: Relative to the underlying mandible, chin pellets moved with an average absolute and relative error of 0.81 mm and 7.30%, respectively. The movements of chin and mandibular pellets were tightly coupled in time. CONCLUSION: The chin tracking errors observed in this investigation are considered acceptable for descriptive studies of oromotor behavior, particularly in situations where mandibular placements are not practical (e.g., young children or edentulous adults). The observed amount of error, however, may not be tolerable for fine-grained analyses of mandibular biomechanics. Several guidelines are provided for minimizing error associated with tracking surface landmarks on the chin.

The reliability of three-dimensional scapular attitudes in healthy people and people with shoulder impingement syndrome.

BACKGROUND: Abnormal scapular displacements during arm elevation have been observed in people with shoulder impingement syndrome. These abnormal scapular displacements were evaluated using different methods and instruments allowing a 3-dimensional representation of the scapular kinematics. The validity and the intrasession reliability have been shown for the majority of these methods for healthy people. However, the intersession reliability on healthy people and people with impaired shoulders is not well documented. This measurement property needs to be assessed before using such methods in longitudinal comparative studies. The objective of this study is to evaluate the intra and intersession reliability of 3-dimensional scapular attitudes measured at different arm positions in healthy people and to explore the same measurement properties in people with shoulder impingement syndrome using the Optotrak Probing System. METHODS: Three-dimensional scapular attitudes were measured twice (test and retest interspaced by one week) on fifteen healthy subjects (mean age 37.3 years) and eight subjects with subacromial shoulder impingement syndrome (mean age 46.1 years) in three arm positions (arm at rest, 70 degrees of humerothoracic flexion and 90 degrees of humerothoracic abduction) using the Optotrak Probing System. Two different methods of calculation of 3-dimensional scapular attitudes were used: relative to the position of the scapula at rest and relative to the trunk. Intraclass correlation coefficient (ICC) and standard error of measure (SEM) were used to estimate intra and intersession reliability. RESULTS: For both groups, the reliability of the three-dimensional scapular attitudes for elevation positions was very good during the same session (ICCs from 0.84 to 0.99; SEM from 0.6 degrees to 1.9 degrees ) and good to very good between sessions (ICCs from 0.62 to 0.97; SEM from 1.2 degrees to 4.2 degrees ) when using the method of calculation relative to the trunk. Higher levels of intersession reliability were found for the method of calculation relative to the trunk in anterior-posterior tilting at 70 degrees of flexion compared to the method of calculation relative to the scapula at rest. CONCLUSION: The estimation of three-dimensional scapular attitudes using the method of calculation relative to the trunk is reproducible in the three arm positions evaluated and can be used to document the scapular behavior.

Investigation of clinician agreement in evaluating movement quality during unilateral lower extremity functional tasks: a comparison of 2 rating methods.

STUDY DESIGN: Nonexperimental. OBJECTIVES: To determine interrater and intrarater agreement for 2 methods of evaluating movement quality during 2 lower extremity functional tasks, and to descriptively compare levels of agreement between the 2 methods. BACKGROUND: Clinicians typically use observational analysis to evaluate movement quality during functional tasks, but the extent of agreement is unknown. METHODS AND MEASURES: Twenty-five uninjured subjects performed 3 trials of unilateral squat and lateral step-down tasks. Three clinicians evaluated the trunk, pelvis, and hips for coronal plane and transverse plane movement deviations. Two rating methods were used: assessment of the entire movement ("overall method") and rating each segment individually ("specific method"). Movement deviation severity was rated using basic clinical guidelines and ratings were repeated from videotape. Percent agreement and weighted kappa coefficients were calculated between rater pairs and rating sessions. Generalized kappa coefficients were calculated across raters. RESULTS: Interrater and intrarater percent agreement were higher using the overall method. Interrater weighted kappa coefficients were similar between rating methods (overall method, 0-0.55; specific method, 0.23-0.53). Intrarater weighted kappa coefficients were higher for the specific method (0.38-0.68) compared to the overall method (0.13-0.50). Generalized kappa coefficients were also higher for specific method compared to the overall method (unilateral squat, 0.19 and 0.01, respectively; lateral step-down, 0.22 and 0.18, respectively) and 95% confidence intervals remained above zero. CONCLUSIONS: Rating movement at body segments appears to result in agreement among raters that is better than chance. Neither rating method produced high agreement, indicating a need to develop more explicit criteria for rating movement deviation severity.

Diferencias de sexo durante la amortiguación de caídas en tests de salto / Gender differences during landings after jumping

Objetivo: Analizar, en una población de aspirantes al ingreso en una Facultad de Ciencias del Deporte, la cinética de la batida, vuelo y amortiguación de sus saltos y estudiar las diferencias entre los subgrupos de hombres y mujeres. Metodología: Se analizaron los saltos de 180 sujetos, 132 eran hombres (edad= 19.8+/-3.0 años) y 48 mujeres (edad = 19.6+/-3.3 años). Se utilizó una plataforma de fuerzas Quattro Jump de Kistler. Se analizaron las fuerzas de reacción verticales y la posición del centro de gravedad en un salto con contramovimiento. Resultados: Los hombres lograron mayores alturas del centro de gravedad en el vuelo (hombres = 35.77+/-4.55 cm, mujeres = 26.08+/- 3.33 cm; p<0.001) y mayores segundos picos de fuerza en la amortiguación (F2) (hombres = 7.41+/-2.20 BW, mujeres = 5.72+/-1.82 BW; p<0.001) (BW = veces el peso corporal). Las mujeres mostraron un mayor recorrido del centro de gravedad durante la amortiguación (hombres = 10.21+/-2.26%, mujeres =10.84+/-2.21%; p<0.05). Los valores obtenidos en F2 en el conjunto de la población estudiada han sido superiores a los registrados por otros autores en alturas de caídas mayores, en las que el objetivo era lograr la máxima amortiguación. Conclusiones: Los resultados de este estudio justifican la necesidad de intervenciones profilácticas para enseñar a amortiguar correctamente las caídas de saltos. El mayor valor obtenido en F2 por los hombres podría ser debido a que caían desde mayor altura que las mujeres y al mayor recorrido del centro de gravedad registrado por las mujeres que les protegía de valores altos en F2

Purpose: To analyse, in a population of applicants to a Faculty of Sports Sciences, the kinetics of the push off, flight and Lansing phases in a jump test, and to study the differences between men and women. Methodology: The jumps of 180 applicants to a faculty of Sports Sciences (132 men, mean age: 19.8+/-3.0 years, and 48 women, mean age: 19.6+/-3.3 years) were recorded with a Quattro Jump Kistler force plate. Vertical ground reaction forces and the position of the centre of gravity in a counter movement jump were analysed. Results: The men´s group reached higher heights of the centre gravity during the flight phase (men= 35.77+/-4.55 cm, women = 26.08+/-3.33 cm; p<0.001) and greater vertical forces in the second peak of the landing phase (F2) (men = 7.41+/-2.20 BW, women = 5.72+/-1.82 BW; p<0.001) (BW = body weight). Women showed greater vertical displacement of the centre of gravity during the landing phase (men = 10.21+/-2.26% of subject´s height, women = 10.84+/-2.21%; p<0.05). The values of F2 in the population studied have been greater than those found in other studies performed with higher landing heights, but with the aim of maximal softening. Conclusion: The results of the present study support the necessity of prophylactic interventions to teach proper landing techniques among specific populations. The greater values of F2 in the men´s group could have be caused by the higher landing heights and the shorter vertical displacement of the centre of gravity during the landing phase, compared to the women´s group

High-viscosity cement significantly enhances uniformity of cement filling in vertebroplasty: an experimental model and study on cement leakage.

STUDY DESIGN: Experimental study using a laboratory leakage model. OBJECTIVE: To examine the working hypothesis that high-viscosity cements will spread uniformly, thus significantly reducing the risk of leakage. SUMMARY OF BACKGROUND DATA: In vertebroplasty, forces that govern the flow of bone cement in the trabecular bone skeleton are an essential determinant of the uniformity of cement filling. Extraosseous cement leakage has been reported to be a major complication of this procedure. Leakage occurs due to the presence of a path of least resistance caused by irregularities in the trabecular bone or shell structure. Ideally, cement uniformly infiltrates the trabecular bone skeleton and does not favor specific paths. Cement viscosity is believed to affect the infiltration forces and flow during the procedure. Clinically, altering the time between cement mixing and delivery modifies the viscosity of bone cement. METHODS: An experimental model of the leakage phenomenon of vertebroplasty was developed. A path, simulating a blood vessel, was created in the model to perturb the forces underlying cement flow and to favor leakage. Cement of varying viscosities was injected in the model, and, thereafter, the filling pattern, cement mass that has leaked, time at which leakage occurred, and injection pressure were measured. RESULTS: A strong relationship was found between the uniformity of the filling pattern and the elapsed time from cement mixing and viscosity, respectively. Specifically, 3 distinct cement leakage patterns were observed: immediate leakage was observed when cement was injected 5-7 minutes following mixing. The cement was of a low viscosity and more than 50% of the total cement injected leaked. Moderate leakage was observed when injection occurred 7-10 minutes following mixing. Less than 10% of the cement leaked, and the viscosity was at a transient state between the low viscosity of immediate leakage and a higher viscosity, doughy cement. Cement leakage ceased completely when cement was delivered after 10 minutes. The viscosity of the cement in this case was high, and the cement was of a dough-like consistency. CONCLUSIONS: High-viscosity cement seems to stabilize cement flow. However, the forces required for the delivery of high-viscosity cement may approach or exceed the human physical limit of injection forces. Although the working time of the cement is about 17 minutes, it may not be manually injectable with a standard syringe and cannula after 10 minutes, at which time cement leakage ceased completely.