1. Alberto Bencivenga MD, DCh, PhD, Facharzt für Chirurgie (M. Chir.) (Tübingen) Specialista in Chirurgia (M. Chir.) (Florence) Specialista in Chirurgia addominale (M. Abdominal Surg.) (Florence) Specialista in Urologia (M. Urol.) (Florence) Professor Emeritus of General Surgery, Somali National University Professor Emeritus of Orthopaedic Surgery, University of Nairobi CONSULTANT GENERAL AND TRAUMA SURGEON INTERNAL FIXATION IN HAND BONES: DETAILS OF SURGICAL TECHNIQUE NOT FOUND IN TEXTBOOKS

3. This short paper will try to explain why this can happen, and how to minimise this risk. Everyone knows that when tightening screws placed in drill holes eccentrically placed far from the fracture line when plating a diaphysis, the head of each eccentrically placed screw glides into the centre of its plate hole and toward the fracture line, thus causing a degree of interfragmentary compression along the transversal fracture line of a shaft fracture 1, 2, 3. Everyone also knows that, in order to achieve a reliable compression along the cortex opposite to the position of the plate, one has to “ load ” the plate, meaning that one has to bend the plate in its centre, just above the fracture, so that the centre of the bend is elevated in respect to the bone shaft, in such a way that the elasticity of the metal also compresses the far cortex. As we all know, these principles usually work very well in a femoral shaft. If we were to mathematically describe what happens in these cases, at the end of the procedure, within the system ‘ plate-fracture-screws ’ (that is, how much interfragmentary compression we finally produce), we would see that this compression is mainly a function of the thickness of the plate (because the thickness of the plate determines the length of the gliding path toward the centre of the plate, inside the plate holes).

4. However, near the eccentricity of the screw holes within the plate holes, the amount of loading given to the plate will also influence the achieved interfragmentary compression (because after tightening all the screws home, the rectification of the plate can distract the fracture ends and this distraction will be very significant when the plate thickness is minimal, as it happens in the small implants used in long hand bones). The thickness of the small-fragment-set plates used in hand surgery is unfortunately insufficient to secure a gliding distance of the screw heads capable of causing a sufficient interfragmentary pressure and the rectification of the “ loaded ” plate - hardly meaningful in the femur or the tibia - can produce a significant distraction of the fracture ends 3 [Fig. 1]. These are the facts responsible for the annoyingly high percentage of non union of fractures of hand bones, recorded by some surgeons.

5. Fig. 1: The rectification of a loaded plate after tightening the screws may cause a distraction of the fracture line, when using small-fragment-set plates.

9. However, this method, published by us in 1974 , is difficult and unreliable when one of the fracture segments is too small, when the fracture is too oblique or when its margins are too friable, rounded or irregular. Therefore, because of the need of having an increased stability of the system while pre-compressing, we designed a much more stable pre-compressing device, originally meant for the trapezio-metacarpal fusion 6 , which, with the ingenuity and the geniality of Robert Mathys Sen. developed into a very effective and easy to use tool [Fig. 4 and 5]). Ever since then, we have been systematically using this instrument in every transversal shaft fracture, in order to always obtain a strong interfragmentary compression, before performing the actual internal fixation and it has never let us down. The instrument is mounted on two (occasionally 4) Kirschner wires, ideally with a thread at their tips. It is very easy to use, and it will always secure a more than sufficient interfragmentary compression. An added advantage in using this instrument is that, with it in place, there will be no need to use cumbersome bone holding forceps, for which there is hardly enough space in a finger.

14. Fig. 6, 7, 8, 9: after positioning the first metacarpal on the trapezium, a strong pre-compression is obtained before fixing the fusion with an AO small-fragment-set T-plate .

16. Fig. 11-12: After pre-compressing a transversal fracture this is plated (look in the pictures at your left side how big is the compression given, as it is shown by the change of shape of the pre-compressor )

17. When compressing an oblique fracture with a lag screw in a situation in which one needs to support this fixation with a neutralisation plate (even if the density of hand bone tissue is so high that a lag screw is almost always absolutely sufficient), one has to place the plate screws adjacent to the fracture line in such a way as not to decrease the effect of the lag screw, but, possibly, to increase it and always after placing the screws for the most peripheral plate holes. If one positions the screws for the plate holes adjacent to the fracture line along the hole diameter which is roughly perpendicular to the oblique fracture, one adds a compressing vector along the oblique fracture line. In any case, in choosing where to place the screws for the plate holes adjacent to the oblique fracture line, one has to always keep in mind the general rules that govern the positioning of a lag screw 2 , and place these screws in such a way that the vector they create does not fall outside the useful angle. The skilful application of these new vectors must always increase the overall interfragmentary compression both in the direction of the bone shaft axis and within the oblique fracture line, so that the overall stability of the system is enhanced.

20. Fig. 13: Perforator used to create an indentation in the bone surface where the drill bit will be inserted, in order to avoid it slipping away

21. Fig. 14: New screws with a thread on their heads that engages into the threaded holes of the new plates (enlarged). Impossible with these screws to put the plate in tension by positioning the screws eccentrically inside the plate holes!

24. Fig. 15: Here is the use of our pre-compressor as a plate tension device (in the insert is sketched the shape of the modified Kirschner wire used as a hook for the plate).