RESUMEN
During acupuncture treatments, acupuncture needles are manipulated to elicit the characteristic "de qi" reaction widely viewed as essential to acupuncture's therapeutic effect. De qi has a biomechanical component, "needle grasp," which we have quantified by measuring the force necessary to pull an acupuncture needle out of the skin (pullout force) in 60 human subjects. We hypothesized that pullout force is greater with both bidirectional needle rotation (BI) and unidirectional rotation (UNI) than no rotation (NO). Acupuncture needles were inserted, manipulated, and pulled out by using a computer-controlled acupuncture needling instrument at eight acupuncture points and eight control points. We found 167 and 52% increases in mean pullout force with UNI and BI, respectively, compared with NO (repeated-measures ANOVA, P < 0.001). Pullout force was on average 18% greater at acupuncture points than at control points (P < 0.001). Needle grasp is therefore a measurable biomechanical phenomenon associated with acupuncture needle manipulation.
Asunto(s)
Acupuntura , Acupuntura/instrumentación , Acupuntura/métodos , Puntos de Acupuntura , Adulto , Fenómenos Biomecánicos , Diseño de Equipo , Femenino , Humanos , Masculino , Persona de Mediana Edad , Agujas , RotaciónRESUMEN
Increasing femoral rollback in flexion is thought to reduce patellofemoral contact load in total knee arthroplasty (TKA). The objectives of this study were to quantify the dependence of patellar load on rollback and to assess the effectiveness of posterior cruciate ligament (PCL)-retaining, PCL-sacrificing, and PCL-substituting TKA types in generating rollback. Nine cadaver knees were tested in simulated squatting. Six TKAs that were expected to produce varying amounts of femoral rollback were evaluated: PCL-retaining TKA, PCL-sacrificing TKA, a commercially available PCL-substituting TKA, and 3 modified PCL-substituting TKAs in which the anteroposterior position of the tibial post was varied. Kinematics, quadriceps loads, and patellofemoral contact loads were recorded. Significant differences in rollback were observed in the 30 degrees to 90 degrees flexion range. PCL-sacrificing TKAs generated the least rollback. PCL-retaining TKAs produced greater rollback but had the most variability. PCL-substituting TKAs produced the greatest and most reproducible rollback. Moving the tibial post posteriorly further increased rollback. Increased rollback correlated with reduced patellar load (-2.2%/mm). Reductions in patellar load of 17.6% were observed. Quadriceps loads were reduced by increasing rollback but to a smaller degree (-0.9%/mm). Rollback primarily affects patellar load rather than quadriceps load or efficiency.
Asunto(s)
Artroplastia de Reemplazo de Rodilla , Fémur/fisiología , Rótula/fisiología , Ligamento Cruzado Posterior/fisiología , Adulto , Anciano , Análisis de Varianza , Fenómenos Biomecánicos , Cadáver , Humanos , Persona de Mediana Edad , Análisis de Regresión , Soporte de PesoRESUMEN
The mechanism of action of acupuncture remains largely unknown. The reaction to acupuncture needling known as 'de qi', widely viewed as essential to the therapeutic effect of acupuncture, may be a key to understanding its mechanism of action. De qi includes a characteristic needling sensation, perceived by the patient, and 'needle grasp' perceived by the acupuncturist. During needle grasp, the acupuncturist feels pulling and increased resistance to further movement of the inserted needle. We hypothesize that 1) needle grasp is due to mechanical coupling between the needle and connective tissue with winding of tissue around the needle during needle rotation and 2) needle manipulation transmits a mechanical signal to connective tissue cells via mechanotransduction. Such a mechanism may explain local and remote, as well as long-term effects of acupuncture.
Asunto(s)
Terapia por Acupuntura , Tejido Conectivo/fisiología , Transducción de Señal , Animales , Comunicación Autocrina , Colágeno/ultraestructura , Tejido Conectivo/anatomía & histología , Tejido Conectivo/inervación , Técnicas de Cultivo , Fibroblastos/citología , Humanos , Mecanorreceptores/fisiología , Modelos Biológicos , Agujas , Manejo del Dolor , Comunicación Paracrina , Ratas , Piel , Estrés Mecánico , TorqueRESUMEN
In cementless total hip arthroplasty, increased femoral stem flexibility and decreased fracture propensity are desirable characteristics. The slotting and tapering of the stem have been introduced to achieve this. These features should not, however, be allowed to interfere with the ability of the distal stem to provide initial mechanical stability, especially under rotation. This study was done to investigate the ability of slotted and tapered stem designs to reduce stiffness and insertion force while still maintaining adequate torsional strength. The torsional strength, maximum insertion force, and insertional work of straight, slotted, and taper stems were measured by inserting each type into rigid polyurethane foam and torque testing to failure. Bending stiffness of each stem design was calculated using numerical methods. When compared to a straight stem, a unislot stem has similar torsional strength, maximum insertional force, and work of insertion. The bending stiffness is decreased by 19% to 82% depending on the bending direction. A trislot design decreased torque strength by 29%, maximal insertion force by 36%, and work by 11%. Bending stiffness was decreased by 74% and was not dependent on bending direction. A 0.5-mm taper decreased torque strength by 11% and insertional work by 14%. No difference was seen in maximum insertional force. We conclude that the design features studied (slots and taper) are effective in decreasing stem stiffness and reducing fracture propensity.
Asunto(s)
Prótesis de Cadera , Análisis de Varianza , Artroplastia de Reemplazo de Cadera , Fémur , Humanos , Ensayo de Materiales , Diseño de Prótesis , Falla de Prótesis , Estrés Mecánico , TorqueRESUMEN
Provocative growth hormone (GH) testing using oral clonidine, a central alpha2-adrenergic agonist, is routinely performed by many pediatric endocrinologists worldwide. However, there is no clear consensus on the appropriate length of time over which serial blood samples for GH should be obtained for diagnosing GH deficiency. Retrospective analysis of data from oral clonidine GH stimulation testing performed at our center on 66 consecutive patients (42 males), aged 2 to 18 years, was performed to evaluate the clinical utility of obtaining GH samples at 0, 60, 90 and 120 min. In 29 of 30 patients, the presence of a normal GH response was demonstrated by the time of the 90 min sample. It is therefore concluded that serial GH sampling to 90 min is the preferred duration when screening for GH deficiency with clonidine.
Asunto(s)
Agonistas alfa-Adrenérgicos , Clonidina , Hormona de Crecimiento Humana/sangre , Administración Oral , Adolescente , Niño , Preescolar , Femenino , Hormona de Crecimiento Humana/deficiencia , Humanos , Masculino , Enfermedades Metabólicas/diagnóstico , Valores de Referencia , Estudios Retrospectivos , Factores de TiempoRESUMEN
Adequate bone cement pressurization is critical in obtaining optimal femoral cement mantles during total hip arthroplasty. Pressurization can be generated during insertion of the femoral stem into the cement-filled canal. This may be clinically useful in augmenting conventional cement gun pressurization. Two factors, which were expected to influence the amount of insertion-induced pressurization, are the cement's cure state (viscosity) at the time of insertion and the femoral stem profile. This study evaluated the effect of these factors on cement pressurization during stem insertion. Femoral stems were inserted at a controlled rate into a reusable, simulated femoral canal. Intramedullary pressures were monitored at four locations along the canal's medial midline. The intrusion factor quantity, which accounts for pressure magnitude, duration of pressurization, and cement viscosity, was developed to quantify pressurization. Stem insertion into late cure stage (high viscosity) cement resulted in significantly higher intramedullary pressures (as much as 187% higher) and intrusion factors (as much as 43% higher) as compared with early stage (low viscosity) cement. The highest pressures and intrusion factors were found in the distal canal. A tapered stem profile resulted in significantly higher pressures (as much as 65%) and higher intrusion factors (as much as 63%) than a straight stem.
Asunto(s)
Artroplastia de Reemplazo de Cadera , Cementos para Huesos , Prótesis de Cadera , Humanos , Presión , Diseño de Prótesis , ViscosidadRESUMEN
The Vermont knee laxity device (VKLD) was developed to evaluate anterior-posterior (A-P) displacement of the tibia relative to the femur (A-P laxity) during weightbearing and non-weightbearing conditions. The purposes of this study were to determine the repeatability and reliability of the VKLD measurements of A-P laxity and to compare them with two devices currently in clinical use: the KT-1000 knee arthrometer and planar stress radiography. Two independent examiners tested six subjects with no history of knee injury. A-P laxity was measured on three separate days with the KT-1000 and the VKLD. With the VKLD, A-P laxity was measured in the weightbearing and non-weightbearing conditions. In addition, one examiner measured A P laxity in each subject on each day using a planar stress radiography technique. Similar A-P laxity values were obtained with the KT-1000 and the VKLD; however, the planar stress radiography technique measured less A-P laxity compared to the VKLD (9.2+/-2.2 mm versus 13.3+/-2.9 mm, P = 0.0004). None of the three devices showed significant differences in measuring A-P laxity between days. During weightbearing, A-P laxity was reduced by 65-70% compared to the non-weightbearing condition (P = 0.0001). Future investigations will use the VKLD to study subjects that have suffered injury to the anterior and posterior cruciate ligaments.
Asunto(s)
Equipos y Suministros , Fémur/fisiología , Rodilla/fisiología , Tibia/fisiología , Soporte de Peso , Adolescente , Adulto , Femenino , Humanos , MasculinoRESUMEN
Knee arthrodesis using an intramedullary nail has gained acceptance as treatment in difficult cases such as infection after total knee arthroplasty (TKA), neuropathic joint, and obesity. A retrospective review of 22 cases treated at our institution using an intramedullary nail for knee arthrodesis was performed. Deep infection after primary (11) or revision (6) TKA was the most common indication for this procedure. A long intramedullary nail was used in 3 cases, a long nail with a proximal interlocking screw was used in 6 cases, and a customized nail with a valgus bend and a proximal interlocking screw was used in 11 cases. A modular knee fusion nail was used in 1 case. Successful fusion occurred in all cases, although 4 patients required additional surgery. Average operative blood loss was 748 mL, and average time to union was 7 months. Shortening of the extremity averaged 3.2 cm. Tibiofemoral alignment was improved by using a customized valgus nail (average, 3.1 valgus; range, 1-5) when compared with a straight nail (average, 0.2 valgus; range, 3 varus to 3 valgus). No patient developed infection in the hip or ankle region as a result of the long intramedullary nail. Intramedullary nailing is an excellent technique for knee arthrodesis in difficult cases. A customized proximal interlocking nail with 5 degrees to 7 degrees of valgus and 5 degrees of anterior angulation improves tibiofemoral alignment and is straightforward to insert or extract should it be necessary. Stability and pain relief are rapid, and the fusion rate is maximized.
Asunto(s)
Artrodesis/métodos , Clavos Ortopédicos , Articulación de la Rodilla/cirugía , Adulto , Anciano , Anciano de 80 o más Años , Pérdida de Sangre Quirúrgica , Femenino , Humanos , Masculino , Persona de Mediana Edad , Reoperación , Estudios Retrospectivos , Resultado del TratamientoRESUMEN
The traditional understanding of knee kinematics holds that no single fixed axis of rotation exists in the knee. In contrast, a recent hypothesis suggests that knee kinematics are better described simply as two simultaneous rotations occurring about fixed axes. Knee flexion and extension occurs about an optimal flexion axis fixed in the femur, whereas tibial internal and external rotations occur about a longitudinal rotation axis fixed in the tibia. No other translations or rotations exist. This hypothesis has been tested. Tibiofemoral kinematics were measured for 15 cadaveric knees undergoing a realistic loadbearing activity (simulated squatting). An optimization technique was used to identify the locations of the optimal flexion and longitudinal rotation axes such that simultaneous rotations about them could best represent the measured kinematics. The optimal flexion axis was compared with the transepicondylar axis defined by bony landmarks. The longitudinal rotation axis was found to pass through the medial joint compartment. The optimal flexion axis passed through the centers of the posterior femoral condyles. No significant difference was found between the optimal flexion and transepicondylar axes. To an average accuracy of better than 3.4 mm in translation, and 2.9 degrees in orientation, knee kinematics were represented successfully by simple rotations about the optimal flexion and longitudinal rotation axes. The optimal flexion axis is fixed in the femur and can be considered the true flexion axis of the knee. The transepicondylar axis axis, which is identified easily by palpation, closely approximates the optimal flexion axis.
Asunto(s)
Articulación de la Rodilla/fisiología , Adulto , Anciano , Fenómenos Biomecánicos , Fémur/fisiología , Humanos , Técnicas In Vitro , Persona de Mediana Edad , Rotación , Tibia/fisiología , Soporte de PesoRESUMEN
Knee joint kinematics after total knee arthroplasty (TKA) are not well understood. This study measured knee kinematics before and after TKA in six cadaveric specimens. Different tibial surface contours (standard, flat, and dished) and slopes (10 degrees and 15 degrees) with the posterior cruciate ligament (PCL) intact as well as a posterior-stabilized design were studied. The anteroposterior and proximal-distal displacements of the tibia relative to the femur were measured during active knee extension. For the standard design, it was possible to restore the normal position of the tibia relative to the femur at 90 degrees of flexion to within 2 mm; however, restoration of the tibiofemoral position was not achieved with the knee in the extended position. At 90 degrees of flexion, all of the TKA components resulted in a posteriorly positioned tibia compared with the normal knee. The standard, flat, and dished components shifted the tibia into a proximal position compared with the normal knee, while the 15 degrees and posterior-stabilized components shifted the tibia distally. With the knee in the extended position, the standard, flat, dished, and posterior-stabilized designs placed the tibia posteriorly and proximally compared with the normal position of the tibia relative to the femur. The 10 degrees and 15 degrees sloped components placed the tibia in a more anterior position. Of the PCL-retaining designs tested, the 10 degrees sloped tibial component produced the closest to normal knee kinematics. Overall, normal kinematic behavior of the knee was not restored after TKA.