Key points

Introduction

Most humeral shaft fractures are caused by a traumatic event. Nontraumatic upper extremity fractures related to throwing motions are reported less frequently in the literature, and controversy exists surrounding the cause and mechanism of injury. Throwing is a complex motion that involves multiple muscle groups and forces acting synergistically and antagonistically on the humerus. The primary movements about the shoulder include shoulder abduction, horizontal adduction, and external and internal rotation. The primary movements about the elbow joint include flexion, internal and external rotation, extension, and joint compression. Simultaneous kinematic changes at the shoulder and elbow contribute to the torsional forces inflicted on the humerus throughout the throwing phase.

The action of throwing can be broken down into 6 phases: wind-up, stride, arm cocking, arm acceleration, and follow-through ( Fig. 1 ). Historically, thrower’s fractures have primarily occurred during the cocking and acceleration phases of the throwing action. The activities of various muscle groups have been cited as principal factors contributing to throwers’ fractures. The antagonistic actions of the deltoid muscle and the coracobrachialis muscle during throwing were originally implicated in humeral shaft fractures in previous case studies. Furthermore, Hennigan and colleagues attributed the occurrence of fracture during the deceleration phase of throwing to eccentric muscular contraction. However, most thrower’s fractures are spiral in nature and located distal to the insertion of these muscle groups.

Phases of throwing. Thrower’s fractures primarily occur during the cocking and acceleration phases of the throwing action.

( From Hamilton CD, Glousman RE, Jobe FW, et al. Dynamic stability of the elbow: electromyographic analysis of the flexor pronator group and the extensor group in pitchers with valgus instability. J Shoulder Elbow Surg 1996;5(5):349; with permission.)

During throwing, the elbow and shoulder are brought into extreme external rotation with subsequent valgus positioning of the elbow, greatest in the late cocking phase. During early acceleration there is a transition from external rotation to internal rotation at the shoulder and extension at the elbow whereby the greatest amount of torsional force in the distal humerus is experienced. Recent kinematic studies have highlighted the differential rotational force occurring proximally and distally, resulting in a midshaft torque experienced greatest during maximal external rotation. This torque occurs because the internal rotators of the shoulder and the humerus, primarily the subscapularis, latissimus dorsi, and pectoral major, initiate the internal rotation about the shoulder and proximal humerus before the distal humerus, thus allowing the distal humerus to continue to externally rotate momentarily with respect to the proximal humerus, secondary to a combination of the forearm, hand, and throwing object momentum at the transition of late cocking and early acceleration.

These rotational forces at the distal humerus are most consistent with mid to distal third spiral humerus fractures with concomitant medial butterfly fracture fragments. Kaplan and colleagues also found that, in conjunction with the torsional force on the humerus, improper and uncoordinated throwing techniques, especially over time, can contribute to the likelihood of nontraumatic humeral fractures during a throwing motion, particularly during irregularly occurring athletic outings.

Radial nerve palsies associated with humeral shaft fractures occur with an overall incidence of 5% to 11%, and increase in probability with more distal and spiral patterned fractures. This finding is consistent with the incidence of radial nerve palsies associated specifically with thrower’s fractures reported in the literature. Holstein-Lewis fractures are classically described as distal third spiral humerus fractures with concomitant radial nerve palsy. Although some thrower’s fractures overlap with Holstein-Lewis fractures with respect to fracture pattern and location, most are involved at the middle and distal third junction with a corresponding butterfly fragment.

The goal of this case report is not only to discuss and review throwers’ fractures in cases seen by the authors and in the literature but also to highlight the existence of prodromal symptoms that may suggest an underlying preceding stress fracture. Early identification of these symptoms and appropriately managing and counseling patients may prevent debilitation and extension into a thrower’s fracture.

Introduction

Most humeral shaft fractures are caused by a traumatic event. Nontraumatic upper extremity fractures related to throwing motions are reported less frequently in the literature, and controversy exists surrounding the cause and mechanism of injury. Throwing is a complex motion that involves multiple muscle groups and forces acting synergistically and antagonistically on the humerus. The primary movements about the shoulder include shoulder abduction, horizontal adduction, and external and internal rotation. The primary movements about the elbow joint include flexion, internal and external rotation, extension, and joint compression. Simultaneous kinematic changes at the shoulder and elbow contribute to the torsional forces inflicted on the humerus throughout the throwing phase.

The action of throwing can be broken down into 6 phases: wind-up, stride, arm cocking, arm acceleration, and follow-through ( Fig. 1 ). Historically, thrower’s fractures have primarily occurred during the cocking and acceleration phases of the throwing action. The activities of various muscle groups have been cited as principal factors contributing to throwers’ fractures. The antagonistic actions of the deltoid muscle and the coracobrachialis muscle during throwing were originally implicated in humeral shaft fractures in previous case studies. Furthermore, Hennigan and colleagues attributed the occurrence of fracture during the deceleration phase of throwing to eccentric muscular contraction. However, most thrower’s fractures are spiral in nature and located distal to the insertion of these muscle groups.

Phases of throwing. Thrower’s fractures primarily occur during the cocking and acceleration phases of the throwing action.

( From Hamilton CD, Glousman RE, Jobe FW, et al. Dynamic stability of the elbow: electromyographic analysis of the flexor pronator group and the extensor group in pitchers with valgus instability. J Shoulder Elbow Surg 1996;5(5):349; with permission.)

During throwing, the elbow and shoulder are brought into extreme external rotation with subsequent valgus positioning of the elbow, greatest in the late cocking phase. During early acceleration there is a transition from external rotation to internal rotation at the shoulder and extension at the elbow whereby the greatest amount of torsional force in the distal humerus is experienced. Recent kinematic studies have highlighted the differential rotational force occurring proximally and distally, resulting in a midshaft torque experienced greatest during maximal external rotation. This torque occurs because the internal rotators of the shoulder and the humerus, primarily the subscapularis, latissimus dorsi, and pectoral major, initiate the internal rotation about the shoulder and proximal humerus before the distal humerus, thus allowing the distal humerus to continue to externally rotate momentarily with respect to the proximal humerus, secondary to a combination of the forearm, hand, and throwing object momentum at the transition of late cocking and early acceleration.

These rotational forces at the distal humerus are most consistent with mid to distal third spiral humerus fractures with concomitant medial butterfly fracture fragments. Kaplan and colleagues also found that, in conjunction with the torsional force on the humerus, improper and uncoordinated throwing techniques, especially over time, can contribute to the likelihood of nontraumatic humeral fractures during a throwing motion, particularly during irregularly occurring athletic outings.

Radial nerve palsies associated with humeral shaft fractures occur with an overall incidence of 5% to 11%, and increase in probability with more distal and spiral patterned fractures. This finding is consistent with the incidence of radial nerve palsies associated specifically with thrower’s fractures reported in the literature. Holstein-Lewis fractures are classically described as distal third spiral humerus fractures with concomitant radial nerve palsy. Although some thrower’s fractures overlap with Holstein-Lewis fractures with respect to fracture pattern and location, most are involved at the middle and distal third junction with a corresponding butterfly fragment.

The goal of this case report is not only to discuss and review throwers’ fractures in cases seen by the authors and in the literature but also to highlight the existence of prodromal symptoms that may suggest an underlying preceding stress fracture. Early identification of these symptoms and appropriately managing and counseling patients may prevent debilitation and extension into a thrower’s fracture.