[0008] In accordance with the present invention, a bone fixation apparatus and method are provided that substantially integrates the mechanism for advancing a non-invasive pin to an external pin positioner so as to simplify the apparatus and make the entire apparatus less unwieldily to use. More particularly, the positioner has a pin holder which includes a pin advance assembly integrated therewith. In this manner, the present fixation apparatus avoids the use of an applicator gun or the like so that the positioner is directly gripped by the user for orienting the pins in position for being advanced into engagement with the bone.
[0009] The pin holder is preferably formed as a compact housing or module having a through opening which allows the user to manually push the pin at the projecting proximal end thereof in an advancing direction toward the bone for engaging the distal end of the pin therewith. The preferred bone fixation apparatus has a ratcheting mechanism that can operate in the pin holder housing including cam and stop or locking surfaces with the cam surfaces allowing the pin to be ratcheted as the user pushes the pin in the advancing direction and with the stop surfaces automatically engaging, as by a bias force as applied thereto, upon removal of the manual pushing force on the pin so as to keep the pin in the advanced position thereof. To this end, the present bone fixation apparatus allows a user to employ the fingers on the same hand that is gripping the positioner for pushing the pins carried by the pin holders of the positioner in the advancing direction, thus providing one-handed operation of the apparatus herein. Further, the manual pushing of the pin into engagement with the bone allows the user to accurately feel whether the pin is properly engaged with the bone with their finger pushing on the pin.
[0012] Other arrangements are also contemplated such as by providing cam threads on the bone pin shaft to allow it to be either linearly advanced as by ratcheting with the shaft threads snapping past the threads on the holder, or the pin can be rotated into engagement with the bone, albeit with the pin including an appropriately configured bone engaging end to accommodate rotation on the bone surface. Similarly, in lieu of direct linear pushing of the pins in their initial stage of quick advance toward the bone, there could be a threaded driver to accomplish the same purpose. The threaded driver can utilize a larger pitch than the fine adjustment screw device so that larger advancing movements are obtained with each turn of the driver. In yet another alternative, a pinion gear can be provided in the pin holder with the gear mating with teeth or threads provided on the bone pin so that turning of the gear shaft causes the bone pin to advance. In each instance, it is preferred that the advancing mechanism be integrated with the holder, and thus stay with the pin positioner during the healing process, and preferably provide for high resolution of the engagement forces between the bone and pin to the user so that they have optimized tactile feedback as to the proper anatomical placement of the pin on the bone and the engagement forces therebetween.
[0013] Another form of the present invention relates to enhancing the stiffness of a bone fixation system that employs the non-invasive bone pins herein, i.e. pins which are not intended to penetrate deep into the bone material, such as beyond the bone cortex, and certainly not to be driven all the way through the bone, as in certain prior fixation systems. In the present system, the rigidity and stability of the system having a pair of fixators fixed along a bone is optimized by pins supported thereby advanced into gripping engagement with the bone by the position of rod mounts for the connecting rods extending between the fixators. The positions of the rod mounts are at a predetermined angular spacing so that with the rods received thereby, there is a separation of the rods from a generally coplanar relation with the bone that is substantially optimized to provide stability to the interconnected fixators.
[0014] In one form, the angular spacing of the rod mounts about the pin positioner is approximately 80 degrees. While the most preferred angular spacing between the rods would be 90 degrees in terms of system stability, it is clear that the 80 degree spacing contemplated herein is significantly improved over the prior non-invasive Ballier bone fixators which had a relatively unstable spacing of approximately 50 degrees between the connecting rods thereof. To keep the weight of the fixators and the entire system to a minimum, the rod mounts each include flexible receptacles and an independent clamping member for each of the receptacles for clamping on the receptacles and fixing the rods therein. By the provision of independent clamping members for each of the receptacles, the size of the clamping mechanism is significantly reduced as compared to the single large plate that would otherwise be required as employed with the Ballier fixators earlier described. In this way, the clamping rods can have the desired stable separation without requiring an increase in the weight of the fixators.
[0015] In another form of the invention, the fixation apparatus includes a pair of pin positioners having arcuately configured bodies. An adjustable connection is provided between the bodies to allow the pins supported thereby to be angularly shifted about a bone for obtaining different angles of pin-to-bone orientation. This provides the bone fixation apparatus with significant flexiblity in terms of where the pins engage the bone so as to allow pin orientations that cause the minimum amount of interference with surrounding nerves, blood vessels, muscles and the like. To this end, it is preferred that pin holders in the form of modules carrying one or multiple bone pins be releasably connected to one of the ends of each of the positioner bodies. With the modular form, a user can interchange the modules on the positioner bodies depending on the number of bone pins needed at the angle of orientation selected for the bone pin or pins for the bone surface to be engaged thereby.