• Laurent Audigé, Damian Griffin, Mohit Bhandari, James Kellam, and Thomas P Rüedi.
• AO Clinical Investigation and Documentation, AO Center, Davos Platz, Switzerland. laurent.audige@aofoundation.org
• Clin. Orthop. Relat. Res. 2005 Sep 1;438:221-32.

UnlabelledA prospective observational study was done in 41 trauma centers. Four hundred sixteen patients with tibial shaft fractures were treated operatively and followed up for at least 6 months. Fifty-two (13%) cases of delayed healing or nonunion were reported. In such nonrandomized observational studies, multiple interrelationships exist between prognostic factors and patient outcomes. We used path analyses to investigate prognostic factors associated with the occurrence of delayed healing or nonunion. The most important factors were identified using multivariate regression analyses, and interrelationships between factors were illustrated using a path diagram. Fractures with open injuries less than and greater than 5 cm were 3.6 and 5.7 times as likely, respectively, to have delayed healing or nonunion as fractures with no skin injuries. The Müller-AO classification of fractures did not provide additional prognostic information. The risk of healing problems was doubled for fractures of the distal shaft and for fractures showing a postoperative diastasis. Treatment options showed an indirect effect on outcome with the occurrence of diastasis. A model for predicting delayed healing or nonunion is proposed. We encourage the use of path analysis in orthopaedics as a powerful visual technique to interpret data from observational studies.Level Of EvidencePrognostic study, Level II-1 (retrospective study). See the Guidelines for Authors for a complete description of levels of evidence.

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