Without limiting the scope of the disclosure, its background is described in connection with external fixation devices and specifically tools used for the adjustment of external fixator struts or other connection rods.
Generally, external fixation devices are commonly used in a variety of surgical procedures including limb lengthening and deformity correction. The process involves a rigid framework comprising several rings that are placed externally around the limb and attached to bone segments using wires and half pins inserted into the bone segments and connected to the related sections of the external rigid framework. The opposite rings of the rigid framework are interconnected by either threaded or telescopic rods directly or in conjunction with uni-planar or multi-planar hinges, which allow the surgeon to adjust position of the rings relative to each other longitudinally, rotationally, horizontally or angularly over a period of time.
For example, in limb lengthening, the bone is surgically divided into two segments and wires and half pins are inserted into bone segments above and below the surgical bone cut and attached to rings of a rigid framework interconnected by struts or threaded and telescopic connection rods. The rigid framework is used to gradually push the two bone segments apart longitudinally over a period of time (e.g., one millimeter a day). This allows the bone to gradually form in the gap between bone segments created by this distraction technique. Once the desired amount of lengthening is achieved (e.g., 5-6 cm), the external apparatus is stabilized into a fixed position and left on the bone segments until complete mineralization of the newly formed bone (e.g., 3-6 months, depending on the nature of pathology and amount of lengthening).
Similarly, in deformity correction, the bone is surgically divided into two segments (usually at the apex of the deformity) and wires and half pins are inserted into bone segments above and below the surgical bone cut and attached to rings of a rigid framework. Opposite rings of the rigid framework are connected together by threaded rods with attached uni-planar or multi-planar hinges that are used to gradually push the two bone segments apart angularly over a period of time.
One common fixation device is a circular metal structure known as the Ilizarov Apparatus. The Ilizarov apparatus, when used for limb lengthening or deformity correction, consists of several rings or arches that are placed externally around the limb and attached to surgically separated bone segments using wires and half pins. For limb lengthening, the opposite rings are interconnected directly by three or four threaded or telescopic rods that are regularly adjusted in length and allowed for gradual separation of bone segments longitudinally. For angular deformity correction, the opposite rings of the Ilizarov apparatus are connected by a pair of hinges that provide an axis of rotation for bone segments and one angular distractor that gradually pushes two rings and associated bone segments apart.
Another common external fixation device is the Taylor Spatial Frame, which is a hexapod type of the external fixation device based on a Stewart platform but shares many components and features of the Ilizarov apparatus. The Taylor Spatial Frame consists of two external fixation rings attached to bone segments by wires and half pins and connected together by 6 telescopic struts with multi-planar hinges located at both ends of the strut. Each strut may be lengthened or shortened as necessary to either pull two interconnected ring segments towards each other or push them apart. Adjustment of strut length allows manipulating with bone segments acutely or gradually in 6 axes (e.g., lengthening/shortening external/internal rotation, anterior/posterior horizontal translation, medial/lateral horizontal translation, anterior/posterior angular translation, and medial/lateral angular translation) to perform limb lengthening and correct angular, translational and rotational deformities simultaneously.
An amount of an external fixator strut or connection rod length adjustment depends on the amount of bone segment separation to produce a reliable distraction regenerate. Generally, for limb lengthening and deformity correction the optimal daily amount of bone segment separation was determined as 1 mm divided into at least 4 increments per day. Therefore in cases with limb lengthening using 3-4 parallel threaded or telescopic rods or deformity correction using one threaded or telescopic rod (e.g., Ilizarov apparatus), the length of each rod is adjusted ¼ of a millimeter four times a day producing a total length increase of 1 mm per day. It has also been suggested that smaller movements using a high frequency rate of distraction (e.g., a rate of distraction of from 1/60 to 1/1440 of a millimeter 60 to 1440 times a day) prevents soft tissue damage and produces even better results.
In cases with limb lengthening and deformity correction using six struts (e.g., Taylor Spatial Frame), the amount of daily strut length adjustment is calculated by special software. Once the apparatus is attached to the bone segments, numerous parameters such as rings diameter, initial strut length, strut location and so forth are entered into the software to characterize one ring position relative to another ring and position of bone segments relative to each other and to the rings. After calculation of the total amount of each strut length adjustment, the software provides a tabled instruction (“prescription”) on the amount of each strut length adjustment that should be achieved per each increment including strut number, the exact amount of adjustment necessary and the time to make the adjustment. In most of the cases with deformity correction, the struts are adjusted in different directions (shortening/lengthening) and in the different amounts.
External fixator strut (or other connection threaded or telescopic rod) length adjustments are usually made by the patient (parents) either by turning the adjustment knob of the struts or telescopic rods manually or by turning the nuts of the threaded rods with a regular (e.g., open end) wrench. This way of strut length adjustment is time consuming (e.g., due to loosening and retightening of the threaded rod nuts before and after each adjustment), does not provide precise length adjustment (e.g., due to difficulty to monitor small amounts of adjustments) and creates overall frame instability during adjustments (e.g., due to dimensional clearance between connection elements). Furthermore, the prescription for length adjustments can be complicated, and human errors are prone to occur during the course of a complicated prescription. Additionally, existing adjustment processes do not include any feedback to the doctors or patient to confirm the desired adjustments have been properly and accurately made.