title: Classification of Olecranon Stress Fractures in Baseball Players.
abstract: BACKGROUND
  Although the onset mechanism of an olecranon stress fracture (OSF) due to a throwing disorder is believed to involve valgus extension overload, olecranon posteromedial impingement, or triceps traction force, this issue is still debated in the literature.
  
  
  OBJECTIVE
  To establish a classification system for the different types of OSFs to improve diagnosis and clarify the onset mechanism.
  
  
  METHODS
  Case series; Level of evidence, 4.
  
  
  METHODS
  A total of 200 baseball players (198 male, 2 female; mean age, 16.1 years; age range, 13-27 years) who were diagnosed with an OSF from January 1987 to July 2012 were studied. Combined disorders as well as the direction and form of the fracture line were analyzed on plain radiographs, computed tomography, and magnetic resonance imaging. Furthermore, the presence or absence of ulnar collateral ligament (UCL) injuries and avulsion fractures of the lower pole of the medial epicondyle was determined by imaging findings to calculate the combined percentage of OSFs. In addition, the prevalence of OSFs was evaluated among patients who were evaluated between April 2008 and March 2011 for throwing elbow disorders.
  
  
  RESULTS
  There were 5 types of OSFs identified in the new classification system: physeal, classic, transitional, sclerotic, and distal. The physeal type was further separated into stages 1 to 4 based on severity. The mean age for each type identified was as follows: physeal, 14.1 years; classic, 18.6 years; transitional, 16.9 years; sclerotic, 18.0 years; and distal, 19.6 years. A concomitant UCL injury and/or medial epicondyle avulsion fracture was diagnosed in 71% to 95% of cases, depending on the OSF type. Among baseball-related elbow disorders, the incidence of OSFs was 5.4%.
  
  
  CONCLUSIONS
  This study presents a new classification system for the different types of OSFs based on the origin and direction of the fracture plane. This new system was strongly influenced by the age at symptom onset. Such information is essential for successful open reduction and internal fixation by ensuring that fixation pressure is perpendicular to the fracture plane, which will avoid the recurrence of stress fractures. In addition, the prevalence of UCL injuries suggests that it is a major risk factor for the development of OSFs.
authors.affiliation: Sports Medical Center, Keiyu Orthopaedic Hospital, Gunma, Japan furu719@nifty.com.
authors.forename: Kozo
authors.initials: K
authors.lastname: Furushima
authors.affiliation: Sports Medical Center, Keiyu Orthopaedic Hospital, Gunma, Japan.
authors.forename: Yoshiyasu
authors.initials: Y
authors.lastname: Itoh
authors.affiliation: Sports Medical Center, Keiyu Orthopaedic Hospital, Gunma, Japan.
authors.forename: Shohei
authors.initials: S
authors.lastname: Iwabu
authors.affiliation: Sports Medical Center, Keiyu Orthopaedic Hospital, Gunma, Japan.
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Sports Medical Center, Keiyu Orthopaedic Hospital, Gunma, Japan.
authors.forename: Ryuji
authors.initials: R
authors.lastname: Koga
authors.affiliation: Sports Medical Center, Keiyu Orthopaedic Hospital, Gunma, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Shimizu
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001484:Baseball / Q000293:injuries*; D017885:Collateral Ligaments / Q000000981:diagnostic imaging / Q000293:injuries / Q000473:pathology; D003952:Diagnostic Imaging; D004551:Elbow Joint / Q000000981:diagnostic imaging / Q000473:pathology; D004838:Epiphyses / Q000000981:diagnostic imaging / Q000293:injuries / Q000473:pathology; D005260:Female; D015775:Fractures, Stress / Q000145:classification* / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008297:Male; D056740:Olecranon Process / Q000000981:diagnostic imaging / Q000293:injuries* / Q000473:pathology; D011859:Radiography; D012189:Retrospective Studies; D055815:Young Adult; D000092464:Elbow Injuries
keywords: baseball; classification; mechanism of injury; olecranon stress fracture; ulnar collateral ligament injury