Marc Garcia-Elias

Flexor tendon forces: In vivo measurements

S-shaped force transducers were developed for measurement of the forces along intact tendons. After calibration, the transducers were applied to the flexor pollicis longus and flexor digitorum superficialis and profundus tendons of the index finger in five patients operated on for treatment of carpal tunnel syndrome. The tendon forces generated during passive and active motion of the wrist and fingers were recorded. For pinch function, the amount of the applied load was measured with a special pinch meter. Tendon forces in the range of 0.1 to 0.6 kgf were measured during passive mobilization of the wrist. Tendon forces up to 0.9 kgf were present during passive mobilization of the fingers. Tendon forces up to 3.5 kgf were present during active unresisted finger motion. Tendon forces up to 12.0 kgf were recorded during tip pinch, with a mean applied pinch force of 3.5 kgf. These results have potential application in determining the amount of force that a tendon repair would have to resist during passive as well as active postsurgical mobilizations.

Effect on force transmission across the carpus in procedures used to treat Kienböck's disease

A simplified two-dimensional articulating force analysis (rigid body spring model) examined how different surgical procedures used for treating Kienböcks disease modify the force distribution across the carpus. A two-dimensional model of a carpus was loaded through the metacarpals by forces of up to 143 Newtons. The resulting intercarpal displacement and joint loadings were calculated for the intact wrist and for different simulated surgical procedures. The predicted total amount of force transmitted through the radio-lunate joint of the intact wrist averaged a 32% of the total radio-ulno-carpal joint load. Limited intercarpal fusions were found to reduce compressive loading at the radio-lunate joint by no more than 15% of the original load. Capitate shortening was successful in relieving radio-lunate forces, however, it dramatically overloaded the adjacent scapho-trapezial and triquetral-hamate joints. By contrast, a 4 mm lengthening of the ulna (or shortening of the radius) resulted in a 45% reduction of radio-lunate load with only moderate changes in force at the midcarpal and radio-scaphoid joints. On the basis of this study, radial shortening or ulnar lengthening significantly unload the lunate and are rationale procedures in the treatment of Kienböcks disease. Limitations regarding direct clinical application of this mathematical model are also discussed.

Wrist kinematics after limited intercarpal arthrodesis

Two limited intercarpal fusions, scapho-trapezial-trapezoidal and scapho-capitate, were simulated in six fresh human cadaver wrists by means of two Herbert screws. By use of a biplanar radiographic measurement system, the relative kinematic behavior of selected carpal bones, before and after the simulated limited fusions could be analyzed. Both scapho-trapezial-trapezoidal and scapho-capitate fusions produced a similar reduction in global range of motion and comparable effects on the relative intracarpal motion. In both fusions, a significant reduction in relative motion at the lunocapitate joint was recorded. The scaphoid, being fused to the distal carpal row, was shown to lose its role in the adaptative mechanism that allows preservation of articular congruency to the always changing space between the distal carpal row and the radius. After both types of fusion, increased sliding motion of the lunate on the radius was found. These kinematic changes are likely to enhance shear stresses on the lunate and tension on the surrounding ligaments, potentially diminishing long-term functional results.

Reliability of carpal angle determinations

The radioscaphoid, radiolunate, and radiocapitate angles of nine lateral projections of the wrist (three in flexion, three in extension, and three in neutral position) of three fresh cadaver specimens were measured. Seven orthopedic surgeons (six hand surgeons and one orthopedic surgeon) made the measurements with a standard goniometer using both the axial and tangential methods of angle determination. The overall standard deviation for all measurements was 5.2 degrees, and no significant difference in variability between axial and tangential methods was found. By comparing the same angles from different wrist positions, the amount of flexion-extension motion of the capitate, scaphoid, and lunate with respect to the radius was estimated. To assess the accuracy of such a method of carpal motion determination, a more accurate stereoradiographic method of analysis of carpal kinematics was utilized. The overall estimated error of this standard goniometric method of carpal motion determination averaged 7.4 degrees.

Stability of the transverse carpal arch: An experimental study

The mechanical characteristics of the transverse carpal arch were studied using fresh-frozen human cadaveric wrists. Tensile properties of the ligaments involved in this structure were also analyzed. The flexor retinaculum did not prove to be a major factor in the maintenance of the carpal arch since its division only reduced the global transverse carpal arch stiffness an average of 7.5%. On the contrary, the transverse intercarpal ligaments connecting the bones of the distal carpal row were shown to have an essential role in providing stability to the carpal tunnel.

Extensor mechanism of the fingers. I. A quantitative geometric study

A close-range stereophotogrammetric measurement system was used to determine the three-dimensional geometric characteristics of the extensor assembly in seven human finger specimens and five finger configurations. The numerical data obtained showed that, although changes in length of the different bundles are small, their spatial orientation varies considerably from one to another position. This information should help to improve the accuracy of models derived to understand the extensor assembly behavior in normal and pathological conditions.

Axial loading induces rotation of the proximal carpal row bones around unique screw-displacement axes

The changes in carpal bone alignment secondary to the application of an axial compressive load through the major wrist motor tendons while the wrist is kept in neutral position (isometric loading) have been investigated on 13 fresh cadaver specimens using a biplanar radiographic method of kinematic analysis. The scaphoid, lunate and triquetrum rotate an average of 5.1, 4.2, and 3.8 degrees, respectively, around different screw displacement axes, all implying flexion, radial deviation and supination. Based on these findings, a new interpretation of the mechanism by which the wrist remains stable under physiologic loads is provided.

Extensor mechanism of the fingers. II. Tensile properties of components

Seven fresh human finger specimens have been studied to determine the differences in structural stiffness between different components of the extensor assembly. Differences were found to be significant, ranging from an average of 275 N/mm for the proximal and distal segments of the central band to an average of 40 N/mm for the central-to-lateral intercrossing fascicles. The terminal tendon of the lateral band was shown to be as stiff as the middle segment of the central band.

Lateral closing wedge osteotomy for treatment of Kienböck's disease. A clinical and biomechanical study of the optimum correcting angle.

A retrospective clinical analysis of 20 patients who underwent a lateral closing wedge osteotomy of the radius as an adjuvant procedure to a radial recession in the treatment of Kienböcks disease is reported. The functional outcome is compared to the results of a simplified two-dimensional articulating force analysis (Rigid Body Spring Model) based on radiographs of the wrist of the same patients taken before and after surgery. At an average follow-up of 39 months, wrist function was excellent in 4 patients, good in 9, moderate in 6, and poor in one patient. A significant positive correlation between functional improvement and percent reduction of the calculated peak pressure at the radiolunate interval was found. This was maximal in patients with wedge osteotomies between 5 and 10 degrees.

The “Four-Leaf Clover” Treatment Algorithm: A Practical Approach to Manage Disorders of the Distal Radioulnar Joint

Most symptomatic distal radioulnar joint (DRUJ) conditions result from derangements to several structures that may include the length, shape, and/or orientation of the articulating surfaces; the cartilage of the DRUJ and/or ulnocarpal joint; the DRUJ and/or ulnocarpal joint ligaments; and the extensor carpi ulnaris and/or pronator quadratus muscle. Once a complete diagnosis is made, often only one of these components is addressed, which results in suboptimal clinical outcomes. In this article, we present a treatment algorithm (the Four-Leaf Clover algorithm) to guide treatment of DRUJ pathology. The Four-Leaf Clover principle is a guiding algorithm, not a document forcing the surgeon to adopt one particular treatment. Its purpose is to provide treating physicians with a checklist that helps ensure that they do not miss any of the different components that need to be addressed for a complete treatment. Using the treatment algorithm, we should achieve satisfactory resolution of patients symptoms after addressing the particular components in a stepwise approach.