Alberto BencivengaMD, 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 UniversityProfessor 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

A B S T R A C T

The small dimensions of the plates and screws used in hand surgery rarely permit the reliable interfragmentary compression necessary for an undisturbed primary healing of diaphyseal fractures, without the risk of a delayed union or a non union. It is therefore necessary to always create a sufficient interfragmentary pre-compression, even before fixing the plates. This article, based upon the author’s 30 years of experience in hand surgery, explains the reasons for the unreliability of securing an adequate interfragmentary compression in hand bones by blindly applying the conventional techniques used in large bones, like femur or tibia, and describes how to produce the adequate pre-compression between the fracture ends necessary to always secure optimal results, when performing internal fixations in hand bones.

KEY WORDS: Plating in the hand skeleton. Compression and precompression, Avoiding non-union.

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).

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.

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.

When we started being interested in this surgery, at the end of the sixties and the beginning of the seventies, while we had the privilege of working under Heim3 as his deputy, we immediately realised that the crucial difficulty in plating hand bones was how to always secure a sufficient interfragmentary compression. We therefore started using an improvised system to systematically precompress transverse shaft fractures [Fig. 2] before fixing the plate, which always gave us excellent results4. Later on, in order to try to avoid the geometrical tendency to twist under compression stress of the cumbersome contraption we improvised at the beginning of our hand surgical experience, and after seeing how the bending of the wires under stress would angulate the fracture ends, we thought of obtaining this necessary strong interfragmentary compression by placing the plate on the bone in such a way as to form a triangle in which the plate is the base and the two fracture fragments are the other two sides, like the section of a roof on a supporting transversal beam. If two screws are inserted and tightened at the two plate ends, by forcing the fracture segments into alignment, the plate will be put in tension [Fig. 3].

Fig. 2: Improvised pre-compressor (1970). The available holes let through only too thin Kirschner wires with the result of the wires being twisted and bent so that the geometrical plane formed by the system becomes slanting.

Fig. 3: By forcing the realignment of the two fracture segments with a plate fixed with its most peripheral screws only, the plate is put in tension and a substantial interfragmentary compression is achieved.

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 fusion6, 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.

Fig. 4: The prototype of our pre-compres-sor. Its use shown in a dry bone.

Fig. 5: The final version of our pre-compressor or mini-compressor-distractor, of-fered by two manufac-turers (Synthes® and Aesculap®)

An other “trick” is to drill the screw holes in the bone always before loading the mini-plate in order to avoid placing these drill holes, through the curved (loaded) plate, too close to the fracture line and so cause a distraction when the plate is rectified by the tightening home of the screws, as already said [Fig. 1]. This rectification is maximised if one tightens the screws close to the fracture after tightening the screws for the two plate ends.

In the small dimensions we are working within the hand, the wrong positioning of the screws inside the plate holes can have other unexpected mechanical consequences. For example, in a very oblique fracture where the interfragmentary compression is obtained with a lag screw, a neutralisation plate with screws placed in a not ideal position inside the plate holes adjacent to the oblique fracture line can reduce the dynamic vector caused by the lag screw(s) and distract the fracture line.

This and other examples tell us that, in the order of dimensions of hand bones and implants, the careful and correct placing of our plate screws is always crucial. If, in placing these screws, we constantly keep in mind that we must strive to keep a correct direction of the vector caused by these screws, common sense will always guide us in increasing the final interfragmentary compression.

In summary, the main guideline to optimise our chances of success with this surgery is to always secure a sufficient pre-compression, to always drill the screw holes before removing the pre-compressor with a straight (not yet loaded) plate, in order to increase the final interfragmentary compression, because this way the screw holes will be placed at the maximal distance possible from the fracture line, compatible with the plate.

To better drive home the utility of this instrument, Fig 6-10 show the operation picture sequence of a trapezio-metacarpal fusion (rizarthrodesis) and its final result (the picture were taken with the prototype of the instrument, whose final shape is shown in Fig. 5). The patient has a full active opposition before removing the skin sutures. Fig. 11 and 12 show the use of the instrument in a transverse fracture.

An added bonus is that this instrument is also very useful in neglected fractures with overlapping of the fragments or with shortening, where one has to distract and we have often used it also in corrective surgery at the lower end of the radius, because its construction is very sturdy. The instrument, initiaslly produced by Synthes, is available also in Aesculap’s catalogue.

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.

Fig. 10: The op-position is full even before re-moving the skin sutures

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)

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 screw2, 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.

One must always remember that a wrongly placed screw, in the small dimensions of hand bones can easily jeopardise the interfragmentary compression and so pave the way for a delayed union or a non-unionThis way of positioning the screws close to the fracture is useful when one

has a slightly oblique fracture, where the right sequence of the operation steps would be to 1, reduce and axially pre-compress the fracture, 2, place the screw holes for the most peripheral plate holes using a not

yet contoured plate, 3, contour (load) the plate to compress the opposite cortex and fix it with

the two most peripheral screws for which you have prepared the drill holes in the bone, 4, drill the screw holes adjacent to the fracture line also eccentrically and

along the hole diameter perpendicular to the fracture line in order to additionally compress this line by creating a new vector perpendicular to it and at either side of it;5, remove the pre-compressing device.

A last observation must be made here: after just emphasising the importance of a correct placing of the screw hole inside the borders of a relatively small plate hole, anyone who has enough experience with such surgery will point out that, after drilling a hole, one often discovers that this hole is not where one wanted it because it is extremely easy for the drill bit to slip away when starting to drill. Since the positioning of the screws inside the holes of these thin plates is crucial and can make the difference between causing a compression or causing a distraction, it is strongly advised to always use a hand perforator [Fig. 13] to create a small indentation on the bone cortex exactly where the screw hole has to be, so that the drill bit will engage itself firmly inside this indentation without slipping away and thus without introducing an undesired and unplanned vector into the system. If all of this is important in the old traditional small-fragment plate and screw systems, it becomes essential when we use the new lock plate system recently introduced by the AO [Fig. 14], in order to avoid bad results. In this new system, there is a thread around the screw heads and along the internal surface of the plate holes that locks the screws inside the plate holes, so that the end result is a sort of rigid system with no possibility of any movement between plate and screws, as it happens in an external clamp fixation, in which the screws sit in a position perfectly perpendicular to the plate. This system is incredibly stable and does not require a perfect contouring of the plate, but it has a big additional built-in risk to cause a non-union in transverse fractures if it is used without an adequate pre-compression. This is because the drill guide used to place the screws perfectly perpendicular to the plate makes no allowance for a gliding path along which the head of the screw can travel when being tightened home, so that no fracture compression can be caused with these plates, exploiting the eccentricity of the screws within the plate holes. One could say that our pre-compressing device is for these plates what Müller’s plate tensioning device was for the round hole plates used at the beginning of the AO experience, before the introduction of the dynamic compression holes.

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

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!

An other risk with this system is that, if one does not use the ad hoc designed drill bit guide perfectly screwed into the plate hole, the screw holes in the bone do not end up being placed perfectly perpendicular to the plate so that, when the thread of the screw head engages into the thread of the screw hole - if it does! - it forces the surface of the plate surrounding the actual screw hole to move into a position perpendicular to the screw and this will twist the plate and completely disrupt the reduction. Obviously, this is why this new system, that proved to be so successful in long oblique fractures or in comminuted fractures, keeps on giving delayed unions or non-unions in transverse fractures 6, a fact that can be absolutely avoided by the systematic application of an adequate pre-compression. To increase the versatility of our pre-compressor above

described, we have thought of adding to it a simple ancillary element that we improvised with a 2 mm Kirschner wire, at the end of which, with a small file, we created a sort of a hook that can engage the last plate hole. If one fixes the other side of the mini-compressor to the bone shaft with a threaded Kirschner wire [Fig. 15], one repeats exactly the function of the AO plate

tensioning device we have for the large femoral or tibial plates and so one can put the miniplate in a lot of tension which will mean to put the transverse fracture line in a very stabilizing compression. Eventually, an additional instrument could be produced to put these new locking plates under tension. This should consist of one gadget repeating the shape of the threaded screw head at the end of a cylindrical shaft, to be inserted into one of the holes of our pre-compressing device. If one screws the base of this ancillary tool into the last screw hole of the plate, inserts its cylindrical shaft into our pre-compressing device and fixes the system at the other side to the bone as said before, one can put the plate in tension with the absolute certainty that no additional, unwanted shearing force is applied to the it.

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).

Keeping in mind these simple tricks and guidelines, disturbing complications can be avoided when performing internal fixation in hand bone fractures and one can confidently enlarge the indication for open reduction and internal fixation in these lesions, with the assurance of serving our patients much better 7. In a recently published monographic book on internal fixation in hand bones, based upon 212 consecutive cases operated on by us in Switzerland, Somalia, Kenya and Italy, we did not observe a single case of non union or delayed union 8, which proves that these small tricks and guidelines are effective and useful, particularly when one wants to maximise the functional results in cases of multiple fractures of the same hand [Fig. 16].

Fig. 16 This patient had at the same side also a 1st degree compound fracture of radius and ulna. He resumed his work as a high ranking civil servant just 3 weeks after the operation, with a full hand function. Had he been a surgeon or a pianist, every-body would have been easily convinced that we have to learn this kind of surgery, if we want to always offer an ideal treat-ment to our patients.

REFERENCES

1) M. E. Müller, M. Allgöwer, H. Willenegger: “TECHNIQUE OF INTERNAL FIXATION OF FRACTURES”, Springer-Verlag, Berlin-Heidelberg-New York, 1965;2) M. E. Müller, M. Allgöwer, H. Willenegger: “MANUAL DER OSTEO-SYNTHESE”, Springer-Verlag, Berlin-Heidelberg-New York, 1969;3) U. Heim, K. M. Pfeiffer: “PERIPHERE OSTEOSYNTHESEN”, Springer-Verlag, Berlin-Heidelberg-New York, 1972;4) A. Bencivenga: “SURGICAL TREATMENT OF HAND FRACTURES BY MEANS OF RIGID INTERNAL FIXATION. EXPERIENCE IN A DEVELOPING COUNTRY."Report at the XXV Annual Conference of the Association of Surgeons of East Africa, Dar-es-Salaam, 4-8.12.1974;5) A. Bencivenga: “EINE NEUE TECHNIK ZUR DRUCK-OSTEO-SYNTHESE IM BEREICH DES HANDSKELETTS”, Chirurg, 45, 327, 1974;6) A. Bencivenga: “COMPRESSION-FUSION OF THE FIRST CARPO-METACARPAL JOINT (RIZARTHRODESIS) IN THE TREATMENT OF DISABILITY ARISING FROM NEGLECTED BENNETT’s FRACTURE. A NEW SURGICAL TECHNIQUE”, Injury, 1977, 8, 182;7) T. Rüedi: personal communication;8) A. Bencivenga: “OSTEOSINTESI NELLE OSSA DELLA MANO”, Timeo Editore, Bologna, 2002.

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