Correlation of radiographic measurements with biomechanical test results.

The refracture of bone after the removal of an internal fixation device is not common, but it can be a serious complication. The development of a simple radiographic tool to determine the condition of a healing bone would be of clinical importance. As a basis to developing this tool, it was important to determine whether a correlation exists between radiographic results and the stiffness index of bones during fracture healing. This experimental investigation in beagles showed that at 24 weeks after a unilateral femoral osteotomy, plain radiographs could be used to determine the stiffness index of healing bone. The results showed the cortex to callus ratio (the thickness of the cortex, including the periosteal callus, normalized by the thickness of the cortex of the bone not surgically treated) correlated positively with the stiffness index of the bones. This measurement might be useful in the clinical assessment of fracture healing. From a clinical point of view, caution is recommended after the removal of fracture plates when the cortex to callus ratio is low because such a low ratio may be associated with a low stiffness index of the healing bone. This information allows clinicians to adapt the postoperative regimen accordingly.

Structural disorders at the insertion of the supraspinatus tendon. Relation to tensile strength.

We examined macroscopically and microscopically 55 cadaver rotator-cuff tendons attached to their humeral heads to determine the distance between the edge of the articular cartilage and the tendon insertion of the supraspinatus (the width of the sulcus) and the score of regressive changes at the sulcus. In 33 specimens we measured the tensile strength. The width of the sulcus was correlated with the score of regressive changes and with the ultimate tensile strength of the supraspinatus tendon. The width of the sulcus correlated positively with the score of regressive changes (r = 0.66, p < 0.0001), but there was a negative correlation between the latter and the ultimate tensile strength (r = -0.81, p = 0.001) and between the width of the sulcus and the ultimate tensile strength (r = -0.74, p = 0.004). We believe that the width of the sulcus is a simple and useful clinical indicator of the integrity and the tensile strength of the supraspinatus tendon.

Degeneration at the insertion weakens the tensile strength of the supraspinatus tendon: a comparative mechanical and histologic study of the bone-tendon complex.

The purpose of this investigation was to determine the relationship between the degree of degeneration at the supraspinatus insertion, the tensile strength, and the site of failure of this tendon. Thirty-three fresh cadaveric shoulders (average age: 62 years; range: 39-83 years) were examined. A tensile load to failure was applied at a constant crosshead speed of 25.4 mm/min to a 10 mm wide strip of the supraspinatus tendon that remained attached to the bone. Preexisting degenerative changes at the insertion were assessed and scored histologically and compared with the ultimate tensile stress. Twenty tendons failed at the insertion (the insertion group), and 11 failed in the midsubstance (the midsubstance group). The histologic score of degeneration for the insertion group was significantly higher than that for the midsubstance group (p = 0.0026). There was a negative correlation between the ultimate tensile stress at the insertion and the degeneration score for the insertion group (r = -0.60; p = 0.013). Histologic observations revealed that disruptions of tendon fibers were located mostly in the articular half of the tendon and that they enlarged during mechanical testing in 90% of the specimens of the insertion group. It seems that degenerative changes at the supraspinatus insertion reduce the tensile strength of the tendon and constitute a primary pathogenetic factor of rotator cuff tear.