ABSTRACT
Objetivo. El uso del cemento óseo esta muy extendido en COT, existiendo multitud de estudios experimentales que lo avalan. La mayoría de los ensayos mecánicos están realizados en seco, lo que cuestiona la extrapolación de los resultados a la clínica. El objetivo de este estudio es evaluar si las propiedades mecánicas del polimetilmetacrilato (PMMA) obtenidas en series previas en seco, se mantienen en un medio fisiológico. Material y método. Se ha diseñado un estudio experimental para evaluar este aspecto, utilizando PMMA con antibiótico (vancomicina). Cuatro grupos fueron definidos en función del medio estudiado (seco o líquido) y de la realización de un acondicionamiento previo en suero fisiológico (una semana o un mes). Se hicieron estudios de desgaste y resistencia a flexión según las normativas ISO y ASTM, valorando el desgaste, el coeficiente de fricción, la resistencia a la rotura y el modulo de Young. Las muestras fueron analizadas mediante microscopía electrónica. Resultados. Las muestras ensayadas en medio líquido presentaron menores valores de desgaste, así como menor resistencia a flexión, obteniéndose significación en el desgaste. El tipo de desgaste se modificó de un desgaste abrasivo a uno adhesivo en aquellas muestras estudiadas en medio líquido. El tiempo de acondicionamiento proporcionó menores valores de desgaste (p < 0,05). Conclusiones. Se recomienda precaución a la hora de extrapolar los resultados de los estudios sobre PMMA en seco dado el diferente comportamiento mecánico del cemento en un medio líquido mucho más cercano a la situación clínica real, como es el suero fisiológico (AU)
Purpose. The use of bone cement is widespread in orthopaedic surgery. Most of the mechanical tests are performed in dry medium, making it difficult to extrapolate the results. The objective of this study is to assess if the mechanical properties of polymethylmethacrylate (PMMA), obtained in previous reports, are still present in a liquid medium. Material and method. An experimental study was designed with antibiotic (vancomycin) loaded PMMA. Four groups were defined according to the medium (dry or liquid) and the pre-conditioning in liquid medium (one week or one month). Wear and flexural strength tests were performed according to ASTM and ISO standards. Volumetric wear, friction coefficient, tensile strength, and Young's modulus were analyzed. All samples were examined by scanning electron microscopy (AU)
Subject(s)
Humans , Male , Female , Joint Instability/diagnosis , Joint Instability/therapy , Implants, Experimental/standards , Implants, Experimental , Proprioception , Proprioception/physiology , Proprioception/radiation effects , Biomechanical Phenomena , Biomechanical Phenomena/physiology , Biomechanical Phenomena/radiation effects , Neuromuscular Blocking Agents/metabolism , Neuromuscular Blocking Agents/pharmacokinetics , Neuromuscular Diseases/complications , Neuromuscular Diseases/diagnosis , Neuromuscular Diseases/therapyABSTRACT
PURPOSE: As long as the neuromuscular stabilizers are intact, a lesion of the scapholunate ligament may or may not progress to a carpal instability. The mechanisms by which the muscles compensate this defect are not very well known. We designed an experimental study with the aim of clarifying these mechanisms. MATERIAL AND METHOD: Using 10 fresh wrists, with no pre-existing lesions, we studied the movements of the scaphoid, triquetrum and capitate produced by the isometrical loading of the muscles which move the wrist, each of them isolated or combined, before and after cutting off the scapholunate ligaments. To do this, we placed sensors in each of these bones and used the Fastrack system to record these movements. RESULTS: The simultaneous loading of the muscles of the wrist produce rotational movements in flexion and supination of the proximal carpal row. After cutting off the scapholunate ligaments, the scaphoid rotates in pronation and flexion, while the triquetrum rotates in pronation and extension. In this situation of a scapholunate lesion, the muscles that worsen the carpal dexasation are the extensor carpi ulnaris and flexor carpi ulnaris. On the other hand, the isolated loading of the radial muscles reduce the scapholunate diastasis, thus improving the carpal alignment. CONCLUSION: In dynamic scapholunate instabilities, isometric contraction of the ulnar carpal muscles must be avoided, as it promotes the scapholunate diastasis. The rest of the muscles have the opposite effect, stabilizing the carpus when primary stabilizers have failed.
Subject(s)
Carpal Joints , Joint Instability/physiopathology , Lunate Bone , Muscle, Skeletal/physiopathology , Scaphoid Bone , Wrist Joint , Aged , Aged, 80 and over , Cadaver , Female , Humans , Ligaments, Articular/physiopathology , MaleABSTRACT
OBJECTIVE: To evaluate, experimentally in cadavers, the effect of the motor muscles in the wrist in the kinetic behaviour of the carpal, under axial load, and the wrist in a neutral position. MATERIAL AND METHOD: The changes in the spatial orientation of the carpal bones were recorded with a movement trajectory gauge that functions with electromagnetic fields. A total of 30 fresh cadaver wrists were used, in which the principal motor tendons were isolated and subjected to loads proportional to the area of the physiological section of each muscle. The experiment was performed under isometric load conditions of all the tendons, and separately from each tendon. RESULTS: The simultaneous load of all the tendons studied caused a three-dimensional change of the carpal bones. The flexor carpi radialis led to supination of the scaphoids and pronation of the pyramidal. Conversely, the isolated load of the flexor carpi ulnaris, abductor pollicis longus and the extensor carpi radialis longus, caused a supination movement of the 2 carpal rows. Only the extensor carpi ulnaris led to a marked pronation of the carpal. COMMENTS AND CONCLUSIONS: The forearm muscles, as well as the movements of the wrist, cause pronation/supination/supination, flexion/extension and radial/cubital inclination movements. It is proposed that the most important movements in the dynamic stabilisation of the carpal are the intercarpal pronation and supination movements provoked by these muscles. Depending on the carpal injury mechanism or instability, the stimulating of one muscle group or the other may be beneficial.
Subject(s)
Carpal Joints/physiology , Muscle, Skeletal/physiology , Tendons/physiology , Aged , Aged, 80 and over , Biomechanical Phenomena , Cadaver , Female , Humans , Male , Middle Aged , Posture/physiology , Weight-Bearing/physiologyABSTRACT
Ten cadaveric forearms were tested using a wrist testing apparatus specifically designed to investigate the mechanisms of muscle stabilization of the wrist. The specimens were set in a jig allowing the distal row to migrate proximally and rotate around the axis of pronosupination. The extensor carpi ulnaris (ECU) was loaded with specific weights. Reactive rotations of the scaphoid, triquetrum, and capitate were measured by an electromagnetic motion tracking device. Loading the ECU caused pronation of both proximal and distal rows. After sectioning its sheath, the overall direction of the movement remained unchanged, but there was a 40% and 50% decrease of the pronation power over the distal and proximal carpal row, respectively. In addition to stabilizing the distal radiolunar joint, the ECU is an important structure that contributes to the dynamic stability of the wrist. Furthermore, its sheath plays a crucial role in maintaining the effect of the ECU muscle on the carpus.
