Assessment of the function and resistance of sternoclavicular ligaments: A biomechanical study in cadavers.

BACKGROUND: Few biomechanical studies have assessed the resistance of the ligamentous structures of the sternoclavicular joint, and none have reproduced the physiological movements of the joint. Determining the structures that are injured in sternoclavicular dislocations is important for the surgical planning of acute or chronic ligament reconstruction. METHODS: Forty-eight joints from 24 human cadavers were studied, and they were divided into 4 groups of 12 joints each (retraction, protraction, depression and elevation). Biomechanical testing assessed primary and secondary failures. The mechanical resistance parameters between movements that occurred on the same plane (depression versus elevation, protraction versus retraction) were compared. RESULTS: The posterior sternoclavicular ligament was the most injured structure during the protraction test, but it was not injured during retraction. The anterior sternoclavicular ligament was the most affected structure during retraction and depression. The costoclavicular ligament was the most affected structure during elevation. Joint resistance was significantly greater during protraction movements when compared to retraction (P<0.05). CONCLUSION: The anterior sternoclavicular ligament was the most affected structure during retraction and depression movements. During protraction, lesions of the posterior sternoclavicular ligament were most frequent during elevation, and the costoclavicular ligament was the most frequently injured ligament. The resistance of the sternoclavicular joint was significantly greater during protraction movement when compared to retraction. LEVEL OF EVIDENCE: IV, basic science, biomechanics, cadaver model.

Experimental determination of bone cortex holding power of orthopedic screw.

Cylindrical specimens of bone measuring 15 mm in diameter were obtained from the lateral cortical layer of 10 pairs of femurs and tibias. A central hole 3.2 mm in diameter was drilled in each specimen. The hole was tapped, and a 4.5 mm cortical bone screw was inserted from the outer surface. The montage was submitted to push-out testing up to a complete strip of the bone threads. The cortical thickness and rupture load were measured, and the shear stress was calculated. The results were grouped according to the bone segment from which the specimen was obtained. The results showed that bone cortex screw holding power is dependent on the bone site. Additionally, the diaphyseal cortical bone tissue is both quantitatively and qualitatively more resistant to screw extraction than the metaphyseal tissue.

[Interpretation of the quantitative data of the computerized baropodometry in normal subjects]. / Interpretação das variáveis quantitativas da baropodometria computadorizada em indivíduos normais.

The present work intended to test the validity of the quantitative datas provided by computerized baropodometry based in three comparisons: between static vertical force on the three regions of the foot and weight, between vertical force on the three regions of the foot during gait and weight, and between peak plantar pressure on the three regions of the foot and weight. It was used body weight because the calibration of the equipment is done in relation to the body weight of the patient. It was selected ten volunteers without foot pain complaints, age between 27-54 years old, 6 women and 4 men. The equipment used was the FSCAN version 1.821 (Teckscan, Boston MA), with new insoles. At the static assessment, the correlation between vertical force and weight was statistically significant only to the midfoot. At the assessment during gait the correlation between vertical force and weight was statistically significant for all regions of the foot and the correlation between peak plantar pressure and weight was statistically significant only to the midfoot. The clinical interpretation of the quantitative data provided by this exam must be done with caution due to uncount variables that are involved.

[Mechanical study of stiffness in LIM-41 external fixator assemblages submitted to torsion strain]. / Estudo mecânico da rigidez nas montagens do fixador externo LIM-41 submetidas a esforços de torção.

The mechanical stiffness of LIM-41 external fixator assemlages submitted to torsional strain was studied. A condition of unstable fracture was reproduced. The authors evaluated the effect of of Schanz pin configurations, defined as "distal", "standard" and "proximal", and of the distance, 20 mm, 40 mm or 60 mm between the external fixator and the element employed to simulate bone. The authors conclude that stiffer LIM-41 assemblages are obtained if the "standard" or "proximal" configurations are employed, on which some pins are placed near the fracture simulation site, and if the external fixator body is fitted closer to the bone simulating element, having the former variable greater influence over the stiffness coefficient.