Low Transcondylar Fractures of the Distal Humerus

Introduction

Distal humerus fractures in adults consist of a variety of fracture patterns involving a specific anatomic region. As a result of pattern variation, different surgical procedures must be considered for optimal results. Controversy exists regarding the surgical approach, plate fixation configuration, whether to do internal fixation or elbow replacement, and soft tissue management. The patient's age, bone quality, fracture comminution, comorbidities, and expectations must be assessed when choosing the surgical procedure. Distal humerus anatomy is complex and precise. Fixation is challenged by the lack of distal bone stock, articular involvement, and subchondral lesions. For these reasons, fractures of the distal humerus require a fair number of elements to be considered in the decision making process for the best surgical strategy for each individual. This chapter provides an overview of this lesion.

Relevant Anatomy

The distal humerus is composed of the medial and lateral columns, lateral epicondyles, and the articular surface. Fractures occurring proximal to the lateral columns are termed fractures of the distal third of the humeral shaft. The lateral column diverges distally from the humeral shaft at approximately 20 degrees laterally, covering the posterior aspect of the capitellum with cortical bone, allowing for both posterior and lateral plate fixation. The medial column diverges 45 degrees medially toward the articular segment of the trochlea, allowing lateral plate fixation only. The integrity of the columns is crucial because these structures are responsible for connecting the diaphysis with the articular surface. Lateral epicondyles have a number of tendon attachments that contribute to rotational deformity. Reconstruction of distal humeral fractures is primarily based on reestablishing the triangular-shaped anatomy comprised by the columns and the articular surface. The central area of this triangle is a weak, thin layer of bone containing the radial, coronoid, and olecranon fossa. There is no possibility of fixation in this anatomic region. The articular surface extends distal to the lateral epicondyles and is tilted 45 degrees forward, with 6 degrees of valgus and 5 degrees of external rotation. The trochlea is shaped like an asymmetric pulley connected to the capitellum laterally, which is shaped like a sphere. When these surfaces are compromised, fixation is difficult due to this complex shape and absence of subchondral bone.

Epidemiology

Distal humerus fractures account for 2% of the total fractures in adults and one third of the fractures involving the humerus, with an incidence of 5.7 per 100,000 persons per year. The fractures exhibit a bimodal distribution with respect to age and gender, with peaks of incidence in males of age 12 to 19 years and females aged 80 years and over. The fractures in the younger population are caused by high-energy trauma events such as sports-related injuries and motor vehicle accidents, whereas in the elderly, simple falls from their own height often cause this injury. As life expectancy increases, the incidence of fragility fractures is similarly increasing. In these cases, surgeons are facing complex fractures with comminution and osteoporotic bone. Early mobilization with stable fixation is crucial for independent elderly patients, and plate design and configuration have evolved to address this matter. Elbow arthroplasty is now being considered as a primary procedure for a select group of elderly patients with distal humerus fractures.

Classification

The most widely used classification system is the AO (Arbeitsgemeinschaft für Osteosynthesefragen) classification, in which fractures are divided into three distinctive groups: extraarticular (type A), partial articular (type B), and complete intraarticular (type C). These groups are then subclassified according to the fracture line and fragments. This comprehensive classification system is based on the anatomic description of the fracture lines involving the distal humerus. This classification is easily reproduced, although oversimplified for partial articular coronal fractures where other classification systems might be more appropriate. There is substantial interobserver agreement regarding the three main types of fractures, but only moderate agreement regarding the subclassified types of fractures. Jupiter and Mehne described a different classification system based on the surgical anatomy—that is, the longitudinal medial and lateral columns. In this system, fractures are grouped into intraarticular, extraarticular, intracapsular, and extracapsular fractures. These groups are then subdivided depending on whether the fracture line is high, low, medial, or lateral according to the fracture pattern, with an overall fair interobserver agreement. Three-dimensional computed tomography (CT) significantly increases intraobserver and interobserver agreement for any classification system of distal humerus fractures. A three-dimensional CT scan aids in the understanding of fragment size and location in complex articular fractures.

We propose a simple classification system as an introduction to the following chapters on distal humerus fractures. In this system, fractures are first classified as extraarticular or intraarticular. Extraarticular fractures are subclassified as either (1) transcondylar (transverse fractures through the condyles at or below the olecranon fossa), (2) supracondylar, or (3) epicondyle avulsion fractures. Intraarticular fractures are subclassified as (1) intercondylar (fractures of the columns with articular involvement) or (2) purely articular (isolated fractures of the capitellum and articular shear fractures of the distal humerus). Hence, there are five distinct fracture patterns that will be discussed in separate chapters of this edition.