Plain X-ray is insufficient for correct diagnosis of tibial shaft spiral fractures: a prospective trial

The results show that based on plain X-rays only it was not possible to rule out accompanying PM fractures in tibial shaft fractures with certainty. Although increased awareness led to a significant improvement in sensitivity (0.17 vs. 0.56), it was still not possible to achieve the required reliability for responsible patient treatment.

There are several studies indicating high incidences of additional PM fractures in tibial shaft fractures (25–50%) [11,12,13]. A large meta-analysis on PM fractures in tibial shaft fractures identified an incidence rate of 70% when utilizing CT or MRI, however, half of these were occult on plain X-ray (Fig. 1) [12].

Fig. 1figure 1

The figures show an example of the X-ray and CT images of a patient with a tibial shaft spiral fracture type A with fracture of the posterior malleolus. CT images were not available for the examiners. Additional screw osteosynthesis of the posterior malleolus was performed in this patient

No study has dealt with the reliability of X-ray in identifying these fractures and investigated the impact of previous knowledge, awareness, specialization and level of training on diagnostic accuracy. The present study closes this gap in the literature and shows that plain X-ray imaging is not sufficient to ensure a reliable diagnosis of tibia shaft fractures with a high risk of associated PM fractures—regardless of the examiner. Even with advanced awareness of additional PM fractures, 20% (5/25) of the additional PM fractures in tibial shaft spiral fractures—especially in type A fractures [1]—were not recognized preoperatively. This is clinically highly relevant as treatment of any fracture relies on a correct and complete diagnosis, which could not be achieved with plain X-ray diagnostics only.

Fractures with a high risk of PM involvement are primarily spiral fractures and fractures in the distal third of the tibia [1, 2, 4]. Both Marchand et. al. as well as Fisher et al. demonstrated this in similar studies. While Fisher et. al. identified spiral fractures, fractures in the distal third and fractures with an angle > 45° as independent risk factors for additional PM fractures, Marchand et. al. use the ratio of fracture length to distance to tibial plafond to identify fractures with a low risk of joint involvement (negative predictive value of 100% with ratio < 0.224) [2, 4].

Bouche et. al. compared the detection rates of PM fractures in bimalleolar fractures on plain X-ray or CT in a retrospective study. In this study, both, the plain X-rays and the CT scans, were evaluated by 2 surgeons for the presence of a PM fracture twice with an interval of 6 weeks. Similar to the present study, significantly fewer PM fractures were detected on X-rays (35/60 in X-ray vs. 53/60 in CT) and the interrater-reliability on plain X-rays was in a comparable range with a kappa of 0.39 (0.292 in our study). These results support the present results of the current study in that PM fractures cannot be excluded with certainty in the plain X-ray. However, compared to the present study, the study refers to ankle fractures and there were fewer examiners (2 vs. 8) [13].

Furthermore, there is further evidence that the size of the fragments in PM fractures cannot be adequately judged on plain X-rays and that there is poor interrater reliability for these fractures (in plain X-rays) [8, 14]. According to Solan/Sakellariou CT imaging is mandatory for the assessment of PM fractures and even for fractures that are only suspicious for an involvement of the PM [15].

There are no standardized treatment guidelines for fractures of the PM, however, the size of the PM has been a classic indication of internal fixation. Recent studies suggest that other fracture factors may be more important clinically [6, 16, 17]. A meta-analysis on ankle fractures found that fracture displacement, congruency of the articular surface, and residual tibiotalar subluxation were more relevant for the outcome of PM fractures than the fragment’s size [16]. Preoperative cross-sectional imaging is required for a precise assessment of these factors. Despite the increasing number of publications on PM fractures, there is no consensus on therapy yet [17].

In the patient population of the present study, in which preoperative CT imaging was available for all patients, all PM fractures large enough for screw osteosynthesis were fixated internally. Of these fractures, there were 2/17 fractures requiring surgical fixation that would not have been recognized preoperatively by all 8 experienced examiners in their daily routine (see Table 1 #3 and #10).

In addition, the presence of a fracture of the posterior malleolus is essential for surgical planning as the insertion of an intramedullary nail can result in secondary dislocation of the posterior malleolus. To avoid this, it must either be fixed with screw osteosynthesis beforehand or plate osteosynthesis must be used instead of the intramedullary nailing.

Despite the known accumulation of PM fractures in tibial shaft spiral fractures type A and distal tibial fractures, the indication and planning of the surgery are usually carried out without CT imaging on the basis of plain X-rays. Therefore it can be assumed that the PM fractures that are overlooked and not treated in everyday care occur even more frequently here than in ankle fractures, where preoperative CT scans are more common. Due to the ongoing trend towards earlier mobilization and weight bearing in recent years, the reliable detection and surgical fixation of additional PM fractures is becoming increasingly important [18,19,20,21]. While an non-displaced additional PM fracture may heal adequately within 6 weeks of non-weight bearing, the risk of secondary dislocation of undetected fractures increases significantly with immediate full weight bearing.

The present study has some limitations. There are previous publications demonstrating the coincidence of PM fractures in tibial shaft fractures, so the “no awareness” group maybe had some awareness for PM fractures [2, 22,23,24,25]. The limited sample size of 50 patients can potentially affect the generalizability of the results and may raise concerns about the study's statistical power. However, despite the modest number of patients, the findings demonstrated statistical significance, supporting the validity of the conclusions drawn from the study. Moreover, a post hoc power analysis for the primary outcome (correct diagnosis of accompanying PM fractures in plain X-rays) revealed a power of over 80%, which further strengthens the reliability of the results. Additionally, the screening of patients for inclusion and exclusion criteria may introduce a selection bias. To avoid this potential bias, the screening process was independently performed by a specialist in trauma surgery and a specialist in radiology. Another possible limitation is the variability in the indication for surgery among different surgeons, as there is no consistent definition of which PM fragments can be grasped with screw osteosynthesis.

However, in our opinion, these limitations do not affect the key statement, that plain X-ray imaging is not sufficient for comprehensive diagnosis of accompanying PM fractures in tibial shaft fractures.

The strengths of the study are its prospective design, the inclusion of radiologists and trauma surgeons, and the comparison of different levels of training. In conjunction with the incidences of fractures of the posterior malleolus in tibial shaft fractures described in the literature, we recommend preoperative CT imaging for all tibial shaft spiral fractures—especially with a fracture path in the AP X-ray extending from proximal-lateral to distal-medial (type A)—and all tibial fractures in the distal third.

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