D. Wolter:

I. Unidirectional locking screw technology

Locking screw technology signifies a frictional connection between two parts, which is characterised by the fact that the contact surfaces of the two parts are connected firmly and without movement with one another. Stresses or forces are transmitted from one part to the other without substantial loss. The pioneer and inventor of plate internal fixation, Carl Hansmann from St. Georg General Hospital, Hamburg, was already thinking of this in his 1886 article when he designed the contact site between the screw head and plate to be areal.



 
Carl Hansmann in part of a painting by Johannes Grützke. The painting hangs in the lecture hall of the Berufsgenossenschaftliches Unfall-Krankenhaus [Professional Cooperative Trauma Hospital ], Hamburg. See also Johannes Grützke "Das Wandbild [The Mural]", Merlin Verlag, ISBN 3-87536-208-X.

   

Hansmann C (1886) A new method of fixing the fragments in complicated fractures. Verh Dtsch Ges Chir 15:134

    


According to the current state of knowledge, Paul Reinhold from Paris should be regarded as a pioneer of unidirectional locking screw technology. He was the first to propose a locking-screw plate-screw-connection according to the “thread-in-thread“ principle. A patent application followed in Paris in 1931.



See also: Wolter D, Jürgens Ch, Wenzl M, Schümann U, Seide K (1998, 2001) Titanium internal fixator systems with multidirectionally angle-stable screw position, Trauma Berufskrankenh 2001 · (Suppl 4): p425-p428, Springer Verlag 2001

The Collin company manufactured the implant and included it in its catalogue (1935).



 

It is thanks to the art historian, Prof. Benedicte Savoy, that we know more today about the career of Paul Reinhold. She also discovered the illustration of the implant in the Collin catalogue. She found out the following details of his curriculum vitae from her researches in Paris:


Paul Reinhold

• Born on 28.2.1894 in Reims as the youngest of five siblings

• Father was a commercial traveller

• Baccalaureate on 24.6.1910 in Paris

• Medical studies in Paris financed by scholarships

• War-wounded in 1917

• Doctorate in 1924




We have to thank Paul Reinhold for the fact that we apply the advantages of locking screw technology to the construction of the new generation of locking-screw implants today. Some companies have adopted Reinhold‘s construction in their unidirectional implants without acknowledging this pioneer. Heinz Kuderna, Vienna, designed an unidirectional locking-screw plate in 1981 without knowing of Reinhold. The prototype was manufactured by Matthys. This implant, where the bone thread is identical to the thread in the plate hole, did not come into clinical use. H. Kuderna is not the only one who has thought of unidirectional angular stability after P. Reinhold. However, the time was not yet ripe for this solution. Problems with materials, difficulties in finding the constructive solution to this angular stability and a lack of knowledge about the flow of forces prevented its successful clinical use sooner.

 



II. Multidirectional locking screw technology


Chance led to the first multidirectional locking-screw implant. In the operative management of patients with fractures of the thoraco-lumbar spine, I observed that, when anterior stabilisation was carried out with a bone block and plate, individual screws loosened and migrated following mobilisation of the patient. In order to avoid protrusion of the screws, I arranged for a metal cover to be screwed on when such a plate was used. This meant it was no longer possible for the bone screw to protrude. At the same time, I observed that the screw head was locked firmly in any direction by the cover plate. This marked the birth of the first plate internal fixator (1983). It was and is used for posterior stabilisation of unstable fractures of the thoraco-lumbar spine. I also applied the compression plate fixator principle to femoral implants. The implant thickness, necessitated by its construction, prevented its use when soft tissue cover was limited.

A locking-screw implant should meet the following requirements:

1. Screw direction can be chosen freely

2. Additional components are unnecessary

3. Solution that is not limited to one bone

4. Suitable material

5. Builds on experience from plate and nail implantation in previous decades

6. Easy and safe to handle


The development of the titanium internal fixator implants with thread forming in the screw hole (tifix®)


The “ideal” way of locking the screw head emerged from theoretical considerations and practical investigations (1993, 1995, 1998, 2001, 2004). The tifix screw head has a thread that locks in the plate hole through reshaping processes due to differences in material hardness and design. The connection demonstrates high strength. The screw position varies from 0°— 40°.



First generation tifix®

Any screw angle of up to about 40° can be obtained by using a thread former for the plate hole.


Second generation tifix®

Any screw angle of up to about 15° can be obtained by direct material reshaping in the wall of the hole. Larger angles are obtained through the additional use of a special thread former.


The first tifix® generation demonstrates slight friction during material reshaping. This is markedly reduced in the second generation as the material is now pressed into the wall of the hole during the reshaping process. The material quantities with this blocking principle are similar to the abrasion quantities of conventional steel implants. (Jessel M, Wolter D, Schümann U, Seide K, Weidtmann A (1999) Abrasion investigations in steel and titanium implants for internal fixation Trauma Berufskrankh 1:326-331, Springer, Berlin, Heidelberg, New York) The tifix® system is thus an locking screw plate system with a free choice of multidirectional screw position. Locking screw technology signifies a frictional connection. This effective principle also allows implants to be of smaller dimensions than before and nevertheless achieve a greater loading capacity. The flow of forces and thus the loading of the individual screws vary according to our own observations. The flow of forces through the screw next to the fracture line is greatest and is about half, it is about one-third with the next screw and the remaining screws bear the rest. Locking screw technology leads to optimal areal transmission of forces in the area of contact between the bone and screw and plate or nail. This avoids overloading of bone or implant. The multidirectional screw positioning makes work easier for the surgeon and the effect is reinforced by the optimal biomechanical position and by the greater screw lengths. The result is that the longest possible tifix® screw is the most effective. For biomechanical reasons, the plate holes should be filled with at least 2-3 locking screws on either side. Remaining plate holes can also be filled by conventional screws (e.g. to bring a fragment closer and fix it). The same principle is also applicable with medullary nailing. Metal removal is easily carried out. (Wolter D, Schümann U, Seide K (1999) Universal Titanium Internal Fixator, Trauma Berufskrankh (1999) 1:307-319, Springer, Berlin, Heidelberg, New York)