Tenascin-X deficiency and Ehlers-Danlos syndrome: a case report and review of the literature.

Tenascin-X is a large extracellular matrix glycoprotein that is widely distributed within connective tissues and is associated with an autosomal recessive type of Ehlers-Danlos syndrome (EDS). Tenascin-X represents the first EDS susceptibility gene that does not code for a fibrillar collagen or collagen-processing enzyme. We describe a paediatric case of tenascin-X deficiency and review the literature.

Right versus left symmetry of ulnar variance. A radiographic assessment.

One hundred skeletally mature healthy volunteers underwent standardized bilateral posteroanterior radiographs in unloaded (static) and loaded (dynamic) conditions to determine the symmetry of ulnar variance. The mean age was 32 +/- 9 years (range, 19-61 years), with 58 women and 42 men. Ulnar variance was measured to the closest 0.5 mm using the method of perpendiculars. Three separate measurements were made of each radiograph in a blinded fashion by the same investigator. An intraobserver standard deviation of 0.21 was used to calculate a 95% tolerance interval of 0.7 mm (rounded up to 1 mm) as a measure of significance. The average static ulnar variance was -0.13 +/- 1.5 mm on the left and -0.29 +/- 1.6 mm on the right. The average dynamic ulnar variance was 0.93 +/- 1.5 mm on the left and 0.82 +/- 1.5 mm on the right. When compared individually, there was a greater than or equal to 1 mm side to side difference in 37% of volunteers under static and 38% under dynamic conditions. There were no significant correlations between ulnar variance measurements and patient age, gender, race, or handedness. Use of the normal wrist radiograph as a baseline for static radial length measurements is valid in only 63% of cases.

In situ calibration of miniature sensors implanted into the anterior cruciate ligament part I: strain measurements.

The goals of this study were to (a) evaluate the differential variable reluctance transducer as an instrument for measuring tissue strain in the anteromedial band of the anterior cruciate ligament, (b) develop a series of calibration curves (for simple states of knee loading) from which resultant force in the ligament could be estimated from measured strain levels in the anteromedial band of the ligament, and (c) study the effects of knee flexion angle and mode of applied loading on output from the transducer. Thirteen fresh-frozen cadaveric knee specimens underwent mechanical isolation of a bone cap containing the tibial insertion of the anterior cruciate ligament and attachment of a load cell to measure resultant force in the ligament. The transducer (with barbed prongs) was inserted into the anteromedial band of the anterior cruciate ligament to record local elongation of the instrumented fibers as resultant force was generated in the ligament. A series of calibration curves (anteromedial bundle strain versus resultant force in the anterior cruciate ligament) were determined at selected knee flexion angles as external loads were applied to the knee. During passive knee extension, strain readings did not always follow the pattern of resultant force in the ligament; erratic strain readings were often measured beyond 20 degrees of flexion, where the anteromedial band was slack. For anterior tibial loading, the anteromedial band was a more active contributor to resultant ligament force beyond 45 degrees of flexion and was less active near full extension; mean resultant forces in the range of 150-200 N produced strain levels on the order of 3-4%. The anteromedial band was also active during application of internal tibial torque; mean resultant forces on the order of 180-220 N produced strains on the order of 2%. Resultant forces generated by varus moment were relatively low, and the anteromedial band was not always strained. Mean coefficients of variation for resultant force in the ligament (five repeated measurements) ranged between 0.038 and 0.111. Mean coefficients of variation for five repeated placements of the strain transducer in the same site ranged from 0.209 to 0.342. Insertion and removal of this transducer at the anteromedial band produced observable damage to the ligament. In our study, repeatable measurements were possible only if both prongs of the transducer were sutured to the ligament fibers.

In situ calibration of miniature sensors implanted into the anterior cruciate ligament part II: force probe measurements.

The arthroscopically implantable force probe transducer, which measures the effects of local ligament fiber tension, was inserted into the anteromedial band of the anterior cruciate ligament after measurements with the differential variable reluctance transducer were completed in Part I of this study. The overall goals in Part II remained the same, with additional experiments included to determine the sensitivity of output voltage from the transducer to medial-lateral placement of the device within the anteromedial band and to depth of placement within a given insertion hole. Calibration curves of output voltage from the arthroscopically implantable force probe transducer versus resultant force in the ligament were generated during a separate series of knee-loading experiments identical to those performed in Part I. The output voltage for a given probe placement was highly sensitive to the depth of implantation into the anteromedial band. When the probe was completely buried within the ligament, voltage outputs were often sporadic or absent even though surface fibers had clearly developed tension. When the probe was only partially inserted into the hole, such that the end of the probe was slightly proud to the surface, voltage output was significantly higher as the device measured tension in the superficial fibers. Voltage outputs for proud placement were always significantly higher than corresponding voltages for deep placements for all test conditions. With proud placements, voltage outputs were not sensitive to small deviations in medial-lateral position within the anteromedial band. Mean coefficients of variation for output voltage (four repeated placements of the probe into the same central hole) ranged from 0.156 to 0.359 (deep and proud insertions). Output voltage from the probe generally followed the pattern of resultant force in the ligament during passive knee extension. For anterior tibial loading, the contribution of deep fibers to resultant force did not depend on the knee flexion angle at which the test was conducted; the contribution of superficial fibers was greatest beyond 45 degrees of flexion and least at full extension. The contributions of the anteromedial band to resultant force in the ligament were not significantly different between the three modes of loading (anterior tibial force, internal tibia torque, and varus moment) at either 0 or 10 degrees of flexion; this was true for both superficial and deep fibers. We found it necessary to secure the probe within the insertion site using a suture (for both deep and proud placements) to obtain repeatable readings. Puncturing the anteromedial band clearly produced tissue damage; the insertion hole often produced a permanent plane of cleavage in the anteromedial band. However, this tissue damage did not alter the overall ability of the ligament to generate resultant force.