Abstract: An orthopedic fixation device and method are disclosed using circular rod stock and circular positive threaded fixation pins. The fixation pins are held in place relative to the fixation surface and relative to the rod by dual sectioned clamps which can be added to the rod at any time without regard to whether there are other clamps already in place at other locations along the rod. The clamps are held in place by a locking bolt which has a hole in a shank which allows the fixation pin to be inserted through the hole and into the fixation surface. The locking bolt contains a washer having a circular divot positioned in mating relationship with the inserted fixation pin. When the bolt is tightened, the clamp sections are forced together to grip the rod and also the divot portion of the washer is forced into contact with the fixation pin, thereby effectively reducing the circumference of the bolt hole which in turn provides three points of friction contact for maintaining the structure in rigid relationship.

Abstract: A method for detecting the absence of a pressure differential across a cryogenic refrigerator includes the following steps. At least one measurement of load in the refrigerator is taken during both a warmstroke and a coldstroke of a refrigeration cycle. These measurements are then compared to determine whether the differential load across the cryogenic refrigerator has been lost. A system for performing this method includes a compressor that circulates compressed gas through a compressed gas line routed through a cryogenic refrigerator. Within the refrigerator, a displacer is driven through a refrigeration cycle by a motor. A means for measuring the load on the motor is provided, and an electronic module monitors the load measurements to detect a loss of differential pressure across the refrigerator by comparing the load on the motor during the warmstroke to the load on the motor during the coldstroke.