"Mother and baby plate": a strategy to improve stability in proximal fractures of the ulna

Abstract

Introduction: Proximal ulna fractures with a large zone of comminution, such as in the context of Monteggia injuries, require mechanically strong osteosyntheses as they occur in regions with high physiological joint load. Consequently, implant failure and pseudarthrosis are critical and devastating complications, especially with the background of mainly young patients being affected. An effective solution could be provided by adding a small second plate 90° angulated to the standard dorsal plate in the area of non-union. Thus, this study investigates whether, from a biomechanical point of view, the use of such a mini or baby plate is worthwhile.

Materials and methods: Comminuted fractures distal to the coronoid process, equivalent to Jupiter type IIb fractures, are generated on artificial Sawbones^® of the ulna and stabilized using two different plate osteosyntheses: in the first group, a dorsal locking compression olecranon plate is used (LCP group). In the second group, a small, ulnar 5-hole olecranon plate is added as a baby plate in addition to the mother plate at the level of the fracture zone (MBP group). Dynamic biomechanical loading in degrees of flexion from 0° to 90° is carried out to determine yield load, stiffness, displacement, and changes in fracture gap width as well as bending of the dorsal plate.

Results: The "mother-baby-plate" osteosynthesis had a significantly higher yield load (p < 0.01) and stiffness (p = 0.01) than the LCP group. This correlates with the increased movement of the proximal fracture element during cyclic testing for the LCP group compared to the MBP group as measured by an optical metrology system.

Conclusions: Here, we show evidence that the addition of a small plate to the standard plate is highly effective in increasing the biomechanical stability in severe fractures equivalent to Jupiter type IIb. As it hopefully minimizes complications like pseudarthrosis and implant failure and as the additional preparatory effort leading to compromised blood supply is regarded to be negligible, this justifies and highly advises the use of a mother-baby-plate system.

Keywords: Biomechanical; Double-plate; Fracture; Monteggia; Mother–baby; Plate; Ulna.

Fig. 1

Complications like implant failure of the dorsal angle-stable plates (A) are seen in comminuted proximal ulna fractures. Here the case of non-union and subsequent plate breakage is presented. As a rescue operation, a mother–baby-plate osteosynthesis was performed (B)

Fig. 2

In group 1, the comminuted ulna fracture was stabilized with a standard dorsal plate osteosynthesis (a + b). In group 2, additionally a baby-plate (5-hole ulna plate) was attached at the ulnar side with 4 screws (c + d)

Fig. 3

The biomechanical tension loading was performed in 0°, 30°, 60° and 90° flexion of the elbow by a deflection roll

Fig. 4

Biomechanics of plate osteosyntheses of the two groups LCP and MBP indicate a significant difference in yield load (a, p < 0.01) and stiffness at yield load (b, p = 0.01). c Biomechanical testing of the displacement of LCP versus MBP in different flexion angles. No significant difference in displacement between LCP and MBP was observed

Fig. 5

a Overview of marker points analyzed by the optical system. b A significant higher displacement of the analyzed points on the proximal fracture element could be detected for the LCP plate alone in comparison to the mother–baby-plate group (MBP) for P1 (p < 0.01), P2 (p = 0.02) and P3 (p = 0.03). c The displacement of points on the LCP plate is significantly higher for the LCP group compared to the MBP group for P8 (p = 0.03) and P9 (p = 0.01). There is no significant difference for P10. d Compared to the MBP group, the LCP group shows a higher movement of both fracture elements, as the proximal fracture gap distance D1 decreases and the distal fracture gap distance D3 increases, although no significant difference could be found