Distal Clavicle Fractures

Introduction

Distal clavicle fractures, also known as lateral clavicle fractures, account for approximately 25% of all clavicle fractures, the second most common subset after midshaft fractures. This fracture is unique because of its high potential for nonunion, potential effects on scapulothoracic motion, and cosmetic deformity. Distal clavicle fractures have a predilection for elderly and middle-aged individuals, due to an overall decrease in bone mineral density. The outcome for nonoperative treatment of distal clavicle fractures is largely dependent on the location of the fracture and the integrity of the coracoclavicular (CC) ligaments. These two factors are the primary determinants of displacement, stability, and operative versus nonoperative treatment.

Relevant Anatomy/Pathoanatomy

The cross-sectional area of the clavicle enlarges laterally, as the bone transitions from the thick cortices of the middle third to the thinner cortices with cancellous bone in the lateral third. Bone mineral density is greater in the medial aspect of the distal clavicle (at the conoid tubercle and intertubercle space) as compared with the more lateral aspect. These factors make the lateral region more prone to fracture, especially in an osteoporotic population. The subclavian artery and vein, which lie posteroinferiorly to the clavicle, are, on average, 63 and 76 mm from the distal clavicle, respectively.

The surrounding ligamentous and capsular anatomy is of paramount importance in influencing displacement of these fractures. The four acromioclavicular (AC) ligaments, confluent with the joint capsule itself, act primarily to prevent anterior-posterior instability of the distal clavicle. The superior AC ligament has been shown to provide rotational stability of the distal clavicle. The CC ligaments prevent vertical displacement of the distal clavicle. The posteromedial, conoid ligament thickens at its clavicular end, attaching 4.6 cm from the AC joint. The trapezoid ligament attaches anterolaterally on the undersurface of the distal clavicle, 2.5 cm from the AC joint. ^, One can evaluate for injury to the CC ligaments radiographically by measuring the CC interspace; a measurement exceeding 1.3 cm indicates injury.

Both muscular forces and gravity exacerbate fracture displacement. The pectoralis major, trapezius, anterior deltoid, and sternocleidomastoid (SCM) muscles all originate from the clavicle. The SCM and trapezius displace the proximal fragment superiorly and posteriorly, while the weight of the arm displaces the lateral fragment inferiorly and medially.