RESUMEN
Back discomfort, lower extremity loading and unbalanced positions may inhibit workers from standing for industrial stationary work. Two forward-leaning supports were compared to unsupported standing during an extreme reach with 30° trunk flexion under varied light load conditions in the outstretched hands. A total of 11 males from the university participated (mean age 30 years [SD = 5]). Link segment modelling showed a 25-30% reduction in the L4/L5 bilateral hip external moments when using a chest-height support. Ribcage expansion with maximal inspiration remained unchanged with an average 85 N of compression force, and low back discomfort remained tolerable for this difficult reach. Leaning against a work table had no influence on L4/L5 moments or back discomfort because contact was at the pelvis; the external moment at the hips decreased by 6%. Postural stability was improved with little migration of the centre of pressure under both supports. Only the chest support showed potential to influence work positioning and prevent back injuries; further study is needed on support forces and usability.
Asunto(s)
Fenómenos Biomecánicos/fisiología , Postura/fisiología , Equipos de Seguridad , Análisis y Desempeño de Tareas , Adulto , Brazo/fisiología , Dolor de Espalda/etiología , Dolor de Espalda/fisiopatología , Dolor de Espalda/prevención & control , Voluntarios Sanos , Cadera/fisiología , Humanos , Masculino , Tórax/fisiología , Torso/fisiología , Soporte de PesoRESUMEN
The advent of haptic simulation systems for orthopaedic surgery procedures has provided surgeons with an excellent tool for training and preoperative planning purposes. This is especially true for procedures involving the drilling of bone, which require a great amount of adroitness and experience due to difficulties arising from vibration and drill bit breakage. One of the potential difficulties with the drilling of bone is the lack of consistent material evacuation from the drill's flutes as the material tends to clog. This clogging leads to significant increases in force and torque experienced by the surgeon. Clogging was observed for feed rates greater than 0.5 mm/s and spindle speeds less than 2500 rpm. The drilling simulation systems that have been created to date do not address the issue of drill flute clogging. This paper presents force and torque prediction models that account for this phenomenon. The two coefficients of friction required by these models were determined via a set of calibration experiments. The accuracy of both models was evaluated by an additional set of validation experiments resulting in average R² regression correlation values of 0.9546 and 0.9209 for the force and torque prediction models, respectively. The resulting models can be adopted by haptic simulation systems to provide a more realistic tactile output.
Asunto(s)
Simulación por Computador , Procedimientos Ortopédicos , Animales , Fenómenos Biomecánicos , Huesos/fisiología , Bovinos , Procedimientos Ortopédicos/instrumentación , TorqueRESUMEN
Few experimental studies have examined surgical drilling in human bone, and no studies have inquired into this aspect for a popular commercially-available artificial bone used in biomechanical studies. Sixteen fresh-frozen human femurs and five artificial femurs were obtained. Cortical specimens were mounted into a clamping system equipped with a thrust force and torque transducer. Using a CNC machine, unicortical holes were drilled in each specimen at 1000 rpm, 1250 rpm, and 1500 rpm with a 3.2 mm diameter surgical drill bit. Feed rate was 120 mm/min. Statistical significance was set at p < 0.05. Force at increasing spindle speed (1000 rpm, 1250 rpm, and 1500 rpm), respectively, showed a range for human femurs (198.4 ± 14.2 N, 180.6 ± 14.0 N, and 176.3 ± 11.2 N) and artificial femurs (87.2 ± 19.3 N, 82.2 ± 11.2 N, and 75.7 ± 8.8 N). For human femurs, force at 1000 rpm was greater than at other speeds (p ≤ 0.018). For artificial femurs, there was no speed effect on force (p ≥ 0.991). Torque at increasing spindle speed (1000 rpm, 1250 rpm, and 1500 rpm), respectively, showed a range for human femurs (186.3 ± 16.9 N·mm, 157.8 ± 16.1 N·mm, and 140.2 ± 16.4 N·mm) and artificial femurs (67.2 ± 8.4 N·mm, 61.0 ± 2.9 N·mm, and 53.3 ± 2.9 N·mm). For human femurs, torque at 1000 rpm was greater than at other speeds (p < 0.001). For artificial femurs, there was no difference in torque for 1000 rpm versus higher speeds (p ≥ 0.228), and there was only a borderline difference between the higher speeds (p = 0.046). Concerning human versus artificial femurs, their behavior was different at every speed (force, p ≤ 0.001; torque, p < 0.001). For human specimens at 1500 rpm, force and torque were linearly correlated with standardized bone mineral density (sBMD) and the T-score used to clinically categorize bone quality (R ≥ 0.56), but there was poor correlation with age at all speeds (R ≤ 0.37). These artificial bones fail to replicate force and torque in human cortical bone during surgical drilling. To date, this is the largest series of human long bones biomechanically tested for surgical drilling.
Asunto(s)
Órganos Artificiales , Fémur/cirugía , Torque , Adulto , Factores de Edad , Anciano , Anciano de 80 o más Años , Animales , Miembros Artificiales , Fenómenos Biomecánicos , Bovinos , Femenino , Humanos , Masculino , Persona de Mediana Edad , PorcinosRESUMEN
No trunk support (NTS) was compared to a lower trunk support (LTS) of leaning against a worktable and a dynamic upper trunk support (UTS) using postural kinematics, trunk extensor muscle activity and subjective rating of both comfort and effort. Ten females completed 3 repetitions where they lifted 0 and 5 kg load from a symmetrical position at hip-height to a 45° asymmetric position at: i) hip-height and ii) shoulder-height. Human motion capture showed trunk flexion decreased by 12° ± 10 with trunk support with hip-height reach. The table blocked axial rotation of the pelvis which was compensated by an additional 8° ± 6 rotation of the thoracic segment. Surface EMG of the lumbar erector spinae, contralateral to reach, showed the UTS to be almost twice as effective as the LTS with shoulder-height reach with a 30% ± 18 reduction. With hip-height reach, UTS resulted in a smaller reduction equal to 23% ± 27 while the LTS had no effect. Further investigation is needed to determine optimal performance parameters for trunk support with complex, dynamic trunk postures and whether altered kinematics arising from LTS have higher risk of upper back discomfort.
Asunto(s)
Músculo Esquelético/fisiología , Postura/fisiología , Equipos de Seguridad , Torso/fisiología , Adulto , Fenómenos Biomecánicos/fisiología , Electromiografía , Femenino , Humanos , Elevación , Contracción Muscular/fisiología , Rotación , Adulto JovenRESUMEN
Two forward-placed supports with different heights are investigated using human motion capture and EMG. Ten male participants stood in 10 degrees increments of trunk flexion between 0 and 40 degrees for three conditions; leaning on a desk adjusted to the height of the pelvis, leaning on a prototype support at the height of the sternum and with no external support. Low back and hip extensor muscle activity was reduced by an average 60% with leaning against the prototype compared to the no-support condition whereas leaning on a desk produced no significant change in muscle activity. Supported conditions resulted in greater forward displacement of the trunk by at least two-fold compared to no-support representing a longer reach distance. No adverse changes in kinematics indicate that either support blocked segmental flexion of the pelvis, lumbar spine or thoracic spine. These findings suggest that leaning against a higher-placed trunk support could be beneficial for tasks requiring forward flexion.