a new plate for internal fixation—the dynamic compression plate (dcp)

Injury 40 INJURY: THE BRITISH JOURNAL OF ACCIDENT SURGERY July 1970

A NEW PLATE FOR INTERNAL FIXATION THE DYNAMIC COMPRESSION PLATE (DCP) M. ALLGOWER, S. PERREN, and P. MATTER

Surgical Department, University of Basle, and Laboratory for Experimental Surgery, Davos, Switzerland

A system of internal fixation of fractures is presented in which two new principles are introduced simultaneously. Titanium is adopted as the material for the plates and screws by virtue of its corrosion resistance and because its elasticity is nearer to that of bone than is that of stainless steel. The second new principle is the provision of sloping cylindrical oval holes in the plate, so that driving home the spherical-headed screws applies compression without the need for a separate compressor.

COMPRESSION fixation of fractures and osteotomies has become increasingly popular in recent years. Danis (1947) was the first to design a rigid longitudinal compression system, which in his experience led to the healing of fractures of forearm bones and of the tibia without visible callus (' primary bone healing'). Mtiller (1961) has designed a compressor which is removed after the plate had been fixed to the compressed frag- ments. The use of rigid plates of various sizes combined with the removable compressor has become known as the ' A O ' or 'AS1F ' compression-plate technique. It should be emphasized, however, that compression in internal fixation is not con- fined to the use of plates, nor is compression always applied in the long axis of the bone. Wherever long and comminuted fractures are bridged by plates, compression is primarily exerted by lag screws crossing the fracture planes.

A mechanical analysis of the elastic deformation in the system ' plate-on-bone' shows that a compression of 60-140 kilogram-force exerted by the plate results in an elastic deformation of bone in the range of 10-20 la. Therefore shortening of the compressed bone segment will result in total abolition of the applied compression. This would even occur if the compressed interface of the osteotomy were resorbed by a thickness of a single cell layer. Experiments performed with plates fitted with strain gauges, implanted in animals, proved that no such resorption is induced by compression (Perren, Huggler, Russenberger, Straumann, Miiller, and Allg6wer, 1969;

Perren, Huggler, Russenberger, Allg6wer, Mathys, Schenk, Willenegger, and Mtiller, 1969). On the contrary, the osteotomy surfaces held together by such compression forces unite directly by a process of simultaneous bone resorption and osteogenesis in the axial direction. One observes only a gradual decrease of the initial ' compression load ' over a period of 4 months until a new equilibrium near zero pressure is reached. The decrease in compression is paralleled by the increase in longitudinal Haversian remodelling of the bone cortex. The usefulness of this type of compression plate has been evaluated in various experiments using dogs (Anderson, 1965; Schenk and Willenegger, 1967; Olerud and Danckwardt-Lilliestr6m, 1968; Rhinelander, 1968) and sheep (Perren, Huggler, Russenberger, Allg6wer, and others, t969). It has been successfully used in fractures and non-union in clinical cases (Anderson, 1965; Mtiller, Allg6wer, and Willenegger, 1965).

The rigid AO (ASIF) compression plate with accurately fitting screws and a separate compressor has some disadvantages : - -

1. After removal of the compressor there is an unpredictable change of forces in the osteotomy. Very small displacements of a closely fitting screw in relation to the screw-hole will result in large pressure changes.

2. Applying a separate compressor requires a rather wide exposure.

3. The removal of physiological stress from the bone beneath a rigidly fixed plate occasionally

Volume 2 Number I ALLG()WER ET AL. : NEW PLATE FOR INTERNAL FIXATION

leads to such osteoporosis in the subjacent cortex that fatigue fracture through the porotic area may ensue (though rarely), sometimes after removal of the plate.

4. The close conical fit between screw-head and plate countersink holds the screw exactly perpendicular to the plate. This makes it difficult to adapt the position of the screw to any obliquity of the fracture plane.

5. A considerable amount of stress is transmitted from the tightly fitting screws to the plate,

41

2. The countersink part of the screw-head was made spherical to fit the cylindrical shape of the screw-hole. This allows optimal positioning of the screws relative to the fracture plane because the screw does not necessarily have to be perpendicular to the plate.

3. The third and probably most ' hypothetical ' change was the one in the Young's modulus of the metal, which was decreased so that more functional stress should be transmitted to the bone. To provide the desired elastic properties

A B C

Fig. 1.--The new screw-hole, which compresses the osteotomy (or fracture) when the screw is driven home, offers adequate stability and prevents any locking effect. A, Shows how a ball (screw) is guided along a sloping cylinder (screw-hole). Any movement downward will result in a horizontal displacement. No sideways movement is possible. The position aimed at is the intersection of the two cylinders. This position offers maximal stability without any locking effect. In the horizontal cylinder displacement towards the osteotomy is possible. B, Projection of the cylinders into the screw-hole, and the ball-shaped screw. C, Actual shape of the hole with the slot necessary for the screw neck and thread. (Reproduced by courtesy of Acta orthop, scand., fi'om Perren, Russenberger, and others, 1969.)

especially at the end holes and this may increase its tendency to corrosion.

To avoid these disadvantages, three alterations seemed to be indicated as long as rigidity was maintained. These were : - -

1. Change of the original conical screw-hole into a slotted hole which would permit rigid fixation without interfering with the axial compression of the bone by physiological stresses. At the same time the slotted hole was provided with a slope to displace the plate when the screw was driven home, thus providing compression without the need for a separate compressor. The actual shape of this slotted hole is shown in Fig. 1. It consists of a geometrical figure formed by two hemicylinders intersecting at an obtuse angle. The screw entering this hole will first be guided by the sloping cylinder. A movement of the underlying bone towards the other fragment will result. The effect will be first to close and then to compress the fracture. The horizontal cylinder will, in addition, allow the screw to move a little further towards the fracture. This is to prevent any tendency to obstruct the closure of the fracture during the operation as well as any ' locking act ion ' of the screw under weight- bearing conditions. The need for an external compressor is thus eliminated but it can still be used in special cases.

100

Kp

0 ,

days

218 516

Fig. 2.--Average pressure decay of interfrag- mentary pressure recordings in a group of transverse tibial osteotomies in sheep, fixed by DCP. (kp, kilogram-force.)

and excellent corrosion resistance titanium was chosen.

Other shapes of compression holes, and plates with slots have been used before. They do not seem optimal from a mechanical standpoint. Eggers' ingenious plate (Eggers, 1948) did not regularly function as hoped, because by the absence of a proper countersink fitting between the screw and the plate, adequate stability was difficult to achieve, especially in relation to torsion and shear. Bagby's modified Colison plate (Bagby, 1958) with its incongruous contact between the screw-head and the screw-hole was also unsatisfactory. The DCP plates were tested

42 INJURY" THE BRITISH JOURNAL OF ACCIDENT SURGERY Injury July 1970

as to their ability to maintain initial compression load in the osteotomized tibia, as had been done before with the conventional A O (ASIF) compression plate (Perren, Russenberger, Steinemann, Miiller, and Allg6wer, 1969). Fig. 2 shows the

decreases progressively after an initial, somewhat steeper drop.

In those animals which were observed for 4 months, pressure continued to decrease gradually until it approached zero with no sudden pressure

, (~ , ::~...' . i~ ~, ~ ~,

Fig. 3.--Histology of a transverse tibial osteotomy 16 weeks after stable internal fixation with two DCP gauge plates. (Reproduced by courtesy of Acta orthop, scand., fi'om Perren, Russenberger, and others, 1969.)

@ ®

Fig. 5.--The drill guides used for the applica- tion of DCP. 'Load guide' (on the right of the illustration) with eccentric hole, placing the screw on the slope of the screw-hole and 'neutral guide' placing the screw near the end of the slope, thus increasing compression to some extent when the screw is driven home.

average pressure decrease in an experiment on eight tibiae of sheep over a period of 2 months. As with the conventional steel plate, the pressure

? 7? . . . . : . " ....

Fig. 4.--Dynamic compression plate with cancellous and cortical screw made of commer- cially pure titanium.

Table /.--SUMMARY OF CASES RECEIVING D C P PLATE

Fresh Fractures (327) Tibia 227 Femur 38 Forearm 31 Humerus 22 Pelvis 8 Clavicle 1

Cases of Non-union (20) Uninfected 16 Infected 4

Total 347

drop at any point. If at any t ime one cell layer's thickness of bone material had been removed at the pressure points (osteotomy surface or screw sites), the pressure would have dropped to zero immediately, as the whole shortening of the bone in response to the pressure, as measured by a strain gauge plate, was only 10-20 ~1.

Histology showed the osteotomies to be bridged directly by new osteones (Fig. 3). The cortex was undergoing extensive Haversian remodelling. The D C P plate thus clearly fulfils the function of giving sufficient rigidity to allow primary healing of cortical bone.

The experimental findings with the strain gauge moni tored D C P plate being satisfactory, a model for clinical use was worked out. The overall shape of the plate as seen in Fig. 4 corresponds to that of the A S I F plate. The cross- section of the dynamic compression plate is

Volume 2 Number I ALLGOWER ET AL. : NEW PLATE FOR INTERNAL FIXATION 43

slightly larger than the steel plate. This is to allow for the somewhat smaller tensile strength of t i tanium when compared with AISI 316 steel. The screw-seat has been designed as illustrated in Figs. 5 and 6 in order to combine : - -

a. Compression of the fracture when the screw is driven home.

b. F i rm precision fit of the spherical screw- head in the hemicylindrical screw-hole at all times.

c. Prevention of any ' l ock ing ef fec t ' of the screw under axial compression.

Up to now, 327 fresh fractures and 20 cases of non-union have been operated on, using the D C P plates (Table 1). The first 60 consecutive

patients operated on between January, 1966, and February, 1967, were followed through to the

A

B C

Fig. 6.--Compression fixation by the DCP. Compression is obtained by the ' spherical gliding principle '. The spherically countersink screw head is congruous with the hemicylindrical sloping screw-hole and approximates the bone ends when driven home.

A B

Fig. 7.--A, Tibial fracture sustained I0 years after a spiral fracture which had been fixed by cerclage wiring. There was a complete avascular zone at the fracture site. After fixation with a DCP, primary bone healing occurred in 4 months. B, Primary bone healing at 22 weeks.


removal of the plate, with histological examina- tion of the tissue surrounding the plate. These have previously been reported in detail (All- g6wer, Ehrsam, Ganz, Matter, and Perren,

/

f l

1969). The results were very gratifying. No infection occurred and no secondary operat ion was required, except for the removal of the plate. The t i tanium was well tolerated, al though in some

A B

Fig. 8.--A, Pelvic fracture in a 28-year-old male after a traffic accident. B, Result 56 weeks after stable internal fixation with a DCP.

A B C Fig. 9.--A, Non-union after inadequate fixation of a forearm fracture. B, Radiographs taken after

1½ months. C, Radiographs taken at 8 months showing bony union practically completed. No external fixation was used at any time.

Volume 2 Number I A L L G ( J W E R ET AL. ~ N E W PLATE FOR I N T E R N A L F I X A T I O N 45

cases metal deposits were found in the tissues surrounding the plate but this hardly provoked any inflammatory reaction. The complete series of 347 cases confirmed the results obtained in the first 'clinical pilot study '. It will be detailed elsewhere (Matter, 1971). Five clinical cases are now briefly reported.

Fig. 7A shows a fresh tibial fracture sustained 10 years after a spiral fracture which had been fixed by cerclage wiring. There was a complete avascular zone at the fracture site. After fixation

58-year-old female and the result after 24 weeks (partial weight-bearing at 10 weeks and full weight-bearing at 20 weeks).

DISCUSSION The question arises whether it is possible to

avoid the disadvantages of the rigid compression

A B Fig. 10.--A, Avascular non-union of the distal humerus after repeated operations. 13, Radiograph

2 years after rigid fixation by DCP in combination with a cancellous autograft. (Two nuts have remained in place from previous operations!)

with a DCP, primary bone healing occurred in 4 months (Fig. 7B). In the pelvic fracture shown in Fig. 8 the DCP plate enabled the fracture to be very effectively compressed without extensive exposure. It healed promptly. Fig. 9 shows a non-union of a forearm fracture after inadequate stabilization by short plates. Rapid healing occurred after fixation by DCP plates. No external fixation was used at any time after the second operation. Active mobilization was encouraged immediately after operation.

Fig. 10 shows severely osteoporotic avascular non-union in a 63-year-old female after repeated operations using various implants in combination with cancellous bone-grafts. Rigid fixation by a DCP in combination with a new cancellous autograft finally resulted in union and good recovery of function.

Fig. 11 demonstrates a comminuted fracture of the upper end of the tibia fixed by a DCP in a

plate fixation mentioned above, without losing the advantages of successful neutralization and compression of the fracture. In osteotomized tibiae of sheep fixed with the DCP plates we have indeed been able to show that the rate of pressure fall is identical to that observed with the conventional ASIF plates. This is good evidence that the stability is in fact well maintained. Results in the clinical series confirm this point.

The next question is whether we have really reduced the above-mentioned drawbacks of the rigid compression plates. It is obvious that the exposure required when using a DCP plate is diminished. There are indications that ' biologi- cally ' the DCP plate is also better tolerated. Cortical bone in the plated area seems more solid and more homogeneous radiologically when using DCP plates than with ordinary ASIF plates. On removal of the plate the site of the plate is distinctly better vascularized. Patients also


complained of less discomfort in lower leg fractures, but this point is clearly very difficult to quantitate.

DCP plates have been used successfully to obtain primary bone healing in rabbits (Rahn,

namely complete immobility of the fracture site and functional loading of the fractured bone cortex.

From the experimental as well as from the clinical viewpoint, the DCP plate seems to offer

?

A B

Fig. I 1.--A, Compound tibial fracture from a traffic accident. B, Radiograph of bony union after 24 weeks. No external fixation was used at any time.

Gallinaro, Baltensperger, and Perren, 1970), where earlier attempts to study this type of fracture healing had been unsuccessful (Geiser, 1963). The fact that in such a difficult long bone as the brittle rabbit tibia stable fixation through- out the healing period was maintained in the face of immediate full weight-bearing, is vely good proof of the adequate 'b iomechanical ' design in the DCP.

Since we introduced two changes simultaneously----configuration of the screw-hole and change from stainless steel to ti tanium--we are not quite sure which factor has played the greater role. It is felt very definitely that the biomechani- cal design of the plate is more important than the metal. Titanium however seems to be surprisingly well tolerated and the increased deformability of the DCP plates made from pure titanium certainly did not compromise the results. Therefore if titanium of adequate strength is used, two elements of internal fixation which are most desirable can be combined--

some distinct advantages over previous compression plates.

REFERENCES ALLGt)WER, M., EHRSAM, R., GANZ, R., MATTER, P.,

and PERREN, S. M. (1969), 'Clinical Experience with a New Compression Plate "DCP" ', Acta orthop, scand., Suppl. 125, 45.

ANDERSON, L. D. 0965), ' Compression Plate Fixa- tion and the Effect of Different Types of Internal Fixation on Fracture Healing ', J. Bone Jt Surg., 47A, 191.

BAGBY, G. W. 0958), ' The Effect of Compression on the Rate of Fracture Healing using a Special Plate ', Am. J. Surg., 95, 761.

DANIS, R. (1947), Thdorie et Pratique de l'Ost6o- synthdse. Paris: Masson.

EGGERS, G. W. N. (1948), ' Internal Contact Splint ', J. Bone ,It Surg., 30A, 40.

GEISER, M. (1963), Beitriige zur Biologie der Knochen- bruchheilung. Stuttgart : Enke.

HUTZSCHENREUTER, P., PERREN, S. M., STEINEMANN, S., GERET, V., and KLEBL, M. (1969), ' Some Effects of Rigidity of Internal Fixation on the Healing Pattern of Osteotomies ', In/ury, 1, 77.

MATTER, P. (1971), in preparation.

Volume 2 Number 1 ALLGOWER ET AL." NEW PLATE FOR INTERNAL FIXATION 47

MOLLER, M. E. (1961), ' Principes d'Ost6osynth~se ', Heir. chir. Acta, 28, 198.

- - - ALLGOWER, M., and WILLENEGGER, H. (1965), Technique of b~ternal Fixation of Fractures. Berlin: Springer.

OLERUO, S., and DANCKWARDT-LILLIESTR6M, G. (1968), 'F rac tu re Healing in Compression Osteo- synthesis in the Dog ', J. Bone Jt Surg., 50B, 844.

PERREN, S. M., HUGGLER, A., RUSSENBERGER, M., STRAUMANN, F., MOLLER, M. E., and ALLGOWER, M. (1969), ' A Method of Measuring the Change in Compression applied to Living Cortical Bone ', Acta orthop, scand., Suppl. 125, 7.

ALLGOWER, M., MATHYS, R., SCHENK, R., WILLENEGGER, H., and MULLER, M. E. (1969), ' T h e Reaction of Cortical Bone to Com- pression ', Ibid., Suppl. 125, 19.

- - - RUSSENBERGER, M., STEINEMANN, S., MOLLER,

M. E., and ALLGOWER, M. (1969), ' A Dynamic Compression Plate ', Acta orthop, scand., Suppl. 125, 31.

RAHN, B., GALLINARO, P., BALTENSPERGER, A., and PERREN, S. M. (1970), ' Primary Healing of Osteoto- mies in Rabbits using New Compression Plates ', Ibid., in the press.

RHINELANDER, F. W. (1968), ' T h e Normal Micro- circulation of Diaphyseal Cortex and its Response to Fracture ', J. Bone Jt Surg., 50A, 784.

SCHENK, R., and WILLENEGGER, H. 0967), ' Morpho- logical Findings in Primary Fracture Healing ', Syrup. biol. hung., 7, 75.

WILLENEGGER, H., SCHENK, R., and STRAUMANN, F. (1962), ' Methodik und vorl~.ufige Ergebnisse experimenteller Untersuchungen fiber die Heilvor- g~inge bei stabiler Osteosyntbese an Schaftfrak- turen ', Arch. klin. Chir., 301, 180.

Requests for reprints should be addressed to:--Professor M. Allg6wer, Chirurgische Universit~.tklinik, Btlrgerspital, Basle, Switzerland.

ABSTRACTS

B O N E R E P A I R A N D I M P L A N T S

Bone Repair and Fracture Healing This is one of the most easily understandable

accounts of the process of bone repair, and brings the subject up to date with a well balanced review of the literature. Each phase of the process is fully discussed and clearly defined, yet Dr. Sevitt manages to convey the continuity of the events taking place.

He begins with the histogenesis of repair and mentions possible control factors. Bone induction and osteogenesis from pre-existing embryologically determined cells are dealt with as the two concepts of histogenesis. Osteoclasts are given an active role rather than that of relatively passive onlookers to the process of bone resorption.

Primary union and the factors necessary for its development are discussed. Union without callus is an essentially radiological rather than biological event, and not necessarily synonymous with primary union.

It is of particular interest to see the usual form of bone union described under its correct title of secondary repair, and to see it take its logical place in the general discussion.

The usual form of bone union is divided into two stages.

Stage I a. Local haemorrhage, necrosis, and inflammation. b. Proliferation of granulation tissue. c. Formation of new bone and cartilage around the

fracture gap.

Stage 11 d. Union of the fracture gap. e. Remodelling of callus and original bone struc-

ture. What the surgeon often calls ' union ', is described

more accurately as provisional union which is Stage I above. The point is made that Stage II may not occur until the fractured limb has become functionally normal.

The routes to union (secondary repair) by direct ossification and ossification after fibrous union and finally remodelling are described. Delayed union is dealt with as a failure of ossification after fibrous union.

The profuse illustrations appear to have lost a certain amount of impact in reproduction as mono- chrome, but nevertheless help to underline points made in the text.

SEvt'rT, S. (1970), ' B o n e Repair and Fracture Healing ', Br. J. Hosp. Med., 3, 693.

Effect of Corrosion on Tissue Almost all the metals used in surgical implants

(alloys and the elements composing them), also several that are under consideration for future use, were tested by implantation in rabbit 's muscle for 6 months. The intensity of the tissue reaction was assessed by the thickness of the fibrous tissue pseudo- membrane that developed around the implant and by the degree of vascularity and cellular infiltration in severe instances. The authors had on a previous occasion measured the quantities of chemical deriva- tives in the tissues around implants. Nickel, iron, chromium, cobalt, and molybdenum were amongst those that produced bad reactions but most stainless steels and most of the cobalt alloys were moderately good. Titanium and its alloys were mostly good. Of alloys not hitherto used in surgery, one or two nickel alloys and most zirconium alloys ought to prove good. The authors point out, however, that they have paid no attention to the mechanical and physical properties of the metals.

This is valuable confirmation of a tissue reaction already known in man and also valuable confirmation and supplementation of relative toxicities arrived at by tissue-culture experiments many years ago. This test could be, and ought to be done on any newly introduced metal before being used surgically. The only experiment nearer to real-life conditions that remains to be done is a study of the reaction in bone.

LAING, P. G., FERGUSON, A. B., jun., and HODGE, E. S. (1967), 'Tissue Reaction in Rabbit Muscle exposed to Metallic Implants, J. biomed. Mater. Res., 1, 135.

a new plate for internal fixation—the dynamic compression plate (dcp)

Documents