We applied the technique of path analysis to investigate the effect of potential prognostic factors, including injury characteristics and treatment choices, on the risk of delayed healing or non-union after operative treatment of tibial shaft fractures.

Data were collected in a prospective observational study of 41 Swiss hospitals over two years, and analysed by regression models and path analysis. Path analysis is a technique to visualize the most important associations between clinical factors and outcome in a ‘causal path diagram’ that summarises the most likely cause and effect relationships.

Factors having a direct relationship with the occurrence of delayed healing or non-union included open fracture (RR 6.7), distal shaft location (RR 2.2), and initial treatment with an external fixator (RR 2.8). There were many other significant inter-relationships within the final diagram. For example, the choice of treatment was related to factors such as fracture aetiology, AO classification, location and skin injury. Fracture classification was not associated with delayed healing and non-union after adjustment for other factors including treatment choice.

The association of hypothesised risk factors, such as soft tissue injury and fracture location, with delayed healing or non-union was confirmed and measured. This study suggested that the use of an external fixator had a direct, negative effect on outcome, and that the use of nails or plates might contribute to delayed healing or non-union by their association with post-operative diastasis. These observations support this first use of path analysis in orthopaedics as a powerful technique to interpret data from an observational study.