Once the classification has been established, recognition of the key type will facilitate the ideal treatment options (see Table 1).
Radial key type
Radial key type fractures are best treated with radial oriented plates (see Fig. 13a–c). These plates have a longer radial and shorter ulnar border and are the mirror image of the ulnar oriented watershed plates.
These radial plates can be mounted very far distally, thereby grasping fragments that cannot be reached by watershed plates. The main disadvantage of this type of plate is the potential damage to the flexor tendons, depending on the plate position. In addition, the plate needs to be removed after fracture healing. A good method for treating single styloid fractures without depression of the articular surface are K-wire guided, cannulated, double headed screws, especially if the surgery is done with arthroscopic assistance (see Fig. 13d).
Access Primarily from the palmar side. Radial mounted plates in the first extensor compartment are being replaced by polyaxially locking plates with two rows that can also grasp these fragments from the palmar side.
Palmar key type fractures
Similarly, palmar plates should be used to treat palmar key type fractures. In the case of a palmar key fragment, one must differentiate between the fragment sites, if it is only ulnarly (see Fig. 14), if there is a rim fragment (see Fig. 15) or if it also extends to the radial side (see Fig. 16).
Access palmar approach.
Palmar ulnar type
The so-called Watershade plates are optimal for ulnar sided palmar fragments as they can be mounted very far ulnarly as well as distally (see Fig. 14c). They therefore do not compromise the flexor tendons on the radial side. In addition, special plates for isolated stabilization of the lunate facet are available. These very narrow plates minimize contact to the flexor tendons but can only be used for limited indications (see Fig. 14d).
Palmar rim fragment
If the palmar fragments are too small to be adequately stabilized by a single plate, alternatives such as small hook plates (see Fig. 15c), screws (see Fig. 15d) and special plates with attached hooks can be used to grasp these rim fragments, thereby increasing stability and preventing palmar dislocation.
Palmar radio ulnar type
If the palmar fragment extends as far as the radial aspect, a wider distal plate has to be used to incorporate these fragments.
Special plates are available with two separated arms (see Fig. 16d). The space between the two arms is intended for the flexor pollicis longus tendon. Theoretically, the tendon runs in this space and pressure on the tendon is reduced to a minimum. The Soong concept can be neglected when using these implants. Alternatively, special frame plates, mounted far distally, can be used. However, an early plate removal has to be planned if they are placed distally to the Watershed line (see Fig. 16c).
Once the palmar fragments have been stabilized, an inspection for any remaining palmar instability must be performed as an accessory ligamentous lesion is likely. In this case, the carpus requires temporary transfixation to the radius in a neutral position with one or two K-wires to prevent secondary dislocation. These K-wires have to be removed after 6 weeks, when the cast is removed.
Dorsal key type fractures
Dorsal key type fractures should be treated from the dorsal side especially if the dorsal fragment cannot be correctly reduced from the palmar side and are too small for fixation from the palmar side (see Fig. 17d). If the fracture also includes palmar fragments, then a combined palmar and dorsal approach is necessary (see Fig. 17c).
The dorsal approach can be done selectively over the dislocated dorsal key fragment, especially if the fragment is dorso-ulnar. In this case, small buttress plates are useful. The irritation to the extensor tendons is the main disadvantage in all dorsal stabilizations. However, the use of advanced low-profile plates is recommended, as they can significantly reduce this problem [49, 50] (see Fig. 17d).
A palmar plate may also be used if the isolated, large dorsal key fragment can be reduced indirectly and the palmar screws ensure secure fixation. These are mostly ulnar-dorsal sigmoid notch fragments and large enough to be grasped from the palmar side.
Access dorsal limited or dorsal wide exposure depending on the fracture type. In limited situations indirect reduction from palmar with palmar plate fixation.
Central key type fractures
Central depressions of the articular surface are sometimes difficult to detect. If the depression is centrally confined and the palmar and dorsal cortical bone remain intact, then CT scans are best to determine the extent of depression. Arthroscopically assisted procedures are the best choice for treating these fragments.
Occasionally indirect reduction under X-ray intensifier with palmar plating using polyaxially angle stable plates including two distal rows to support the articular surface is feasible. The depressed area is corrected by a hole drilled into the palmar cortical bone. If the cortical bones fracture in a tulip-like fashion under the central depression, then a dorsal approach generally offers the best access to the radiocarpal joint. In this case, dorsal plating is a good choice. K-wires are optional (see Fig. 18c, d).
Access dorsal limited or dorsal wide exposure depending on the fracture type. In selected situations indirect reduction from palmar and palmar plate fixation.
Distal shear fractures
Distal shear fractures are comparable to a ligamentous radiocarpal dislocation. In this case, the shear fragments have no contact to the intact radius shaft. The articular surface fractures with small fragments occur very far distally and include the palmar and dorsal ligamentous insertions. These fragments are very difficult to stabilize, therefore plates which can be placed very far distally are necessary. Frame plates with a dorsal or palmar approach or single screws depending on the type of fracture can be used (see Fig. 19c, d). If sufficient stabilization cannot be achieved, then temporary fixation of the carpus is necessary. Sometimes, spanning plates are used.
Access Depending on the direction of dislocation, palmar or dorsal access is chosen.
Three-part fractures are usually accessed by a palmar approach. Particular attention must be paid to correctly reduce the sigmoid notch, as it is not visible in this approach. Occasionally, an additional dorsal approach is necessary. Watershade plates stabilize these fractures best and reduce the risk of tendon damage (Fig. 20).
Access palmar approach (limited dorsal approach).
The entire articular surface breaks into separate pieces and has no contact to the radius shaft. A comminution zone appears in the metaphyseal area. The articular surface looks like floating ice. As long as the fragments are identifiable, they can be treated individually and fracture specific. Polyaxially, angle stable plates including many holes with two rows are the best option. In the first row, the screws are positioned under the palmar part of the articular surface and in the second row under the dorsal part. Preferably the biggest fragments should be grasped by screws, but if that is not possible then the screws should be placed in a randomized grid-like fashion under the articular surface.
A palmar as well as dorsal access is sometimes useful when double plating is necessary (see Fig. 21c, d). If stability cannot be achieved, then an alternative such as spanning plates or external fixation should be used (see Fig. 22c, d).
Approach Both dorsal and palmar approaches have to be used, depending on the dislocation and fragments of the fracture.