Implants and Instruments

8.1 General Remarks

Significant technical improvements to implants and instruments have been achieved. The dimensions and designs have been adapted to the anatomy of the hand.

They have slender profiles and can be used for different bone shapes and fracture types. The rounded edges cause minimal trauma. With the introduction of titanium, allergenic components have largely disappeared.

Self-tapping screws in all sizes are the norm today. Thread-tapping instruments are a thing of the past.

8.2 Fixed-Angle Locking Fixation

Note

The development of fixed-angle locking fixation has contributed greatly to the safety of postoperative loading.

This requires a stable connection between screw and plate. Different options are provided by the industry:

Unidirectional fixed-angle locking fixation
Multidirectional fixed-angle rigid fixation by means of locking

Unidirectional connection The thread of the screw head and the thread of the plate hole are identical. Tightening the screw in the hole produces a firm connection between screw and plate. With this kind of connection, the direction of the screw and plate is predetermined; it therefore is called a unidirectional connection ( ▶ Fig. 8.1).

Fig. 8.1 Methodical placement of unidirectional fixed-angle locking screws. (a) The unidirectional drill guide is fixed in the plate. (b) The hole is drilled with the diameter of the screw core. (c) The fixed-angle locking screw is tightened until the screw head is countersunk in the plate.

Multidirectional connection by means of locking Locking is based on two different technical methods, both of which lead to a stable connection through plastic deformation of the thread of the screw and the plate hole. One method locks the thread of the screw head in the plate hole through a reshaping process due to differences in material hardness and design. The other method uses a jamming mechanism between one lip of the plate and the head-thread of the screw while locking ( ▶ Fig. 8.2). The multidirectional locking method allows variance when placing the fixed-angle locking screws up to an angle of 20° between screw and plate ( ▶ Fig. 8.3).

Fig. 8.2 Fixed-angle locking plate holes. (a) Unidirectional with precisely defined thread. (b) Multidirectional, threaded lip for locking.

Fig. 8.3 (a,b) Conical variant for placing multidirectional fixed-angle locking screws.

Advantages and disadvantages Fixed-angle locking fixation allows the components to become ever smaller in size, which is naturally an advantage given the delicacy of the hand and finger structures. Nevertheless, fixed-angle locking plates are thicker than standard implants.

Because fixed-angle fixation is rigid, implant placement outside the tension band side is possible. Sensitive gliding structures, especially the extensor tendons, are less traumatized, thereby minimizing the feared adhesions.

A further advantage is preservation of periosteal perfusion, as the stability of the fixation is based on the principle of rigid internal fixator stability and not on friction between the plate and the bone surface ( ▶ Fig. 8.4).

Fig. 8.4 The stability of plate fixation is based on two different principles. (a) Friction principle: Stability is achieved by friction between the plate and the bone surface. (b) Fixed-angle locking principle: This corresponds to an internal fixator; that is, stability is achieved by a rigid construction between plate and screw. An advantage is that perfusion of the periosteum is not affected because of the gap between plate and bone surface.

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