Fractures of the splint bones: The importance of soft tissue attachments

Abstract

Splint bone fractures are common and a variety of management options have been reported in the literature, ranging from rest to invasive treatments such as osteosynthesis or complete removal of the fourth metatarsal bone. There are no general recommendations for the treatment of splint bone fractures, because this is dependent on type, location and age of the fracture, as well as involvement of the cannon bone, adjacent joints and soft tissue structures. Anatomy textbooks generally focus on the bones and joints, but the soft tissues that stabilise the splint bones are not described in detail. However, a detailed knowledge of the soft tissues is not only helpful for the treatment (decision making and surgical anatomy) of splint bone fractures, but also to understand the pathogenesis of fractures sustained without external trauma. Jackson et al. (2005) examined the soft tissue structures related to the splint bones of the foreand hindlimb macroand microscopically. Unfortunately their paper is written in German, but there is a summary in English and 13 figures in colour nicely illustrating the anatomy of the relevant soft tissue structures (Figs 1 and 2). Their findings were that the connection of the splint bone to the cannon bone established through the metacarpal/metatarsal interosseus ligament is very variable between horses, between limbs and within limbs ranging from osseous union to a proper ligamentous structure. They also identified a ligament-like structure originating from the distal end of the splint bone and inserting in a fan shaped manner to the dorsolateral and dorsomedial aspect of the condyles of distal metacarpus (MC) III and metatarsus (MT) III, respectively. But possibly more relevant in regard to treatment of splint bone fractures is the palmar metacarpal/plantar metatarsal fascia that runs from the medial to the lateral splint bone embracing the flexor tendons and the suspensory ligament at the palmar and plantar aspect of MC III and MT III, respectively. In the hindlimb the fascia emanates from the tarsal fascia and is particularly strong in the proximal third of the splint bones (2 mm). Thus, forces acting on the MT IV are not only transmitted by the long lateral collateral ligament and the long plantar ligament, but also by the other soft tissue structures described above. The aim of the study of Sherlock and Archer (2008) was to produce information that could be helpful in estimating a prognosis and selecting the appropriate treatment for open fractures of the fourth metatarsal bone. Using a retrospective study design they reviewed 53 cases from 6 equine hospitals in England and compared surgical vs. conservative treatment. They hypothesised that: 1) conservative management is an appropriate treatment option for many open comminuted