This study highlighted an 11.4% risk of ACS occurrence during the treatment of tibial shaft fractures. Higher distance from the talar dome to the centre of the tibial fracture, associated tibial plateau or pilon fracture, closed fracture and polytrauma were individually confirmed by the multivariable regression analysis as significantly associated with ACS.
Reported incidence rates of ACS in the treatment of tibial shaft fractures range from 3 to 11.5% and seem to be stable over the past decades [5,6,7,8, 16]. Our results fall within this range. In this aspect, our study population represents a rather usual cohort of tibial shaft fracture patients. We did not find any clinical records suspect of late ACS sequellae in the charts of patients that were not diagnosed with ACS, and every patient who underwent fasciotomy had pathological ICP values before fasciotomy, and/or presented muscle bulging or suffering at the time of fasciotomy.
Some ACS developed during or after surgery (external or definitive internal fixation) and the surgical procedure may therefore be partly responsible for these occurrences. However, we believe that surgery only represents an aggravating factor, and that the initial fracture with soft tissue injury is the primary factor for the occurrence of ACS. Indeed, after the initial injury, there may be a certain period of soft tissue vulnerability to further surgical aggression, as recently postulated .
In the univariate analysis, patients younger than 45 years were about three times as likely to present with ACS than patients over 45 years. However, the multivariable analysis did not confirm this association as statistically significant. Young age is the most consistently observed independent predictor of ACS occurrence throughout the literature [5, 7, 8, 18, 26]. The reasons for ACS occurring more often in younger individuals are thought to be that younger patients tend to have bulkier muscle and thicker, less yielding fasciae [5, 18]. Thus, any increase in intra-compartmental volume is more likely to lead to a rapid rise in ICP and to ACS.
The univariate analysis showed a trend for male patients to be more likely to develop ACS, but statistical significance was not reached in the multivariable analysis. Literature on this subject is contradictory, with some reports showing male sex to be a risk factor for ACS , and some others failing to highlight an association between gender and ACS occurrence [5, 7, 8].
This study failed to point out an association between high-energy trauma and development of ACS, although there was a statistically significant association in the univariate analysis. The literature is controversial on this topic, as one study showed an association between high-energy trauma and ACS occurrence  while others did not [5, 7, 18]. Indeed, retrospective determination of the amount of energy released during initial trauma might be unreliable, as chart review may not provide a good representation of the detailed mechanism of injury (for example, type of sports injury, vehicle speed, etc.) . In this perspective, our retrospective attempt to differentiate between low and high-energy mechanism by classifying trauma into “fall from own height” and “other” makes any conclusion about energy of the injury weak.
Interestingly, differentiation between isolated trauma and polytrauma seems to be better in determining possible association with ACS development, as polytrauma was found to be associated with ACS occurrence in the multivariable analysis. This differentiation did not use the Injury Severity Score (ISS) [27, 28], but rather relied on a subjective appreciation of the extension of trauma: the fractured leg (tibia and/or fibula) was either an isolated injury or associated to other musculoskeletal, thoraco-abdominal, spine or cranio-cerebral injuries. This subjective appreciation can be quickly performed by the treating surgeon during the initial survey of any trauma patient and is probably more reliable than any anamnestic investigation in determining the potential risk of ACS occurrence. Furthermore, it does not rely on an a posteriori ISS determination, which is usually performed several hours after the trauma [27, 28]. However, to mitigate this statement, it is important to note that despite an increase in high-energy trauma as a causative injury and an improved survival rate among severe polytrauma patients noted over the past decades [29, 30], ACS rates following tibial shaft fractures do not seem to have increased during the same period [5,6,7,8, 16].
Despite older reports recognizing open fractures as positively associated with the occurrence of ACS in tibial shaft fractures, with an incidence of ACS directly proportional to the severity of the open fracture [4, 17], our results are more in line with recent publications having not found any association between open fractures and ACS development [5, 7, 8]. Our results even show that open fractures might have a protective effect against ACS development. Importantly, these findings must not lead clinicians to be wrongly reassured by an open fracture, assuming that the wound would relieve the pressure inside the muscle compartments, as ACS may still develop in these occurrences [5,6,7,8]. In fact, skin wounds in the vicinity of a fracture should be recognized as a direct sign of increased amount of underlying fascial and muscle injury and must not be underestimated by the treating physician .
Although the first level of the AO/OTA classification (42-A, B and C) is supposed to reflect the amount of energy delivered to the bone and surrounding soft tissues to produce the fracture , this parameter did not reach statistical significance in the multivariable analysis. There was nevertheless a distinctive trend for higher-grade fractures to develop ACS, with 14 of 159 42-A fractures (8.8%), 12 of 89 42-B (13.5%) and 5 of 25 42-C (20%). Another study found similar results several years ago . Thus, this radiographic parameter should be used with caution in evaluating the potential risk for ACS to occur. The incidence of ACS in the setting of 42-A fractures should not be underestimated or discarded, and the index of suspicion should remain high.
The presence of an associated non-contiguous tibial plateau or pilon fracture was highlighted in this study. It represents a red flag and an indicator of a high amount of energy transmitted to the injured limb, causing increased skeletal lesions (associated non-contiguous tibial plateau or pilon fracture) and extensive soft tissue damage potentially leading to the development of ACS. Similar results were recently published, where the presence of a non-contiguous tibial fracture or knee dislocation was a predictor of ACS development after tibial plateau fractures . However, this finding is statistically weak, due to low numbers of events (three in the group without ACS and two in the group with ACS) leading to extended CIs.
The most powerful factor highlighted by this study in predicting occurrence of ACS during the treatment of tibial shaft fractures is the distance between the talar dome and the centre of the tibial fracture. In other words, the more proximal the tibial fracture is, the more likely ACS will occur. A previous study found that the incidence of ACS was higher with tibial plateau fractures than with tibial shaft or pilon fractures, but there were no specific results presented on fracture localization within the tibial shaft . This factor has been specifically evaluated only once in the literature, and no influence of the localization of the fracture within the tibial shaft (proximal vs. middle vs. distal third) on the development of ACS could be demonstrated . Our finding is new and may be explained by the fact that a fracture occurring at a location surrounded by a bulkier muscle mass (proximal diaphysis) may lead to more energy transmitted to the soft tissues, thus to the potential development of ACS. This observation may be useful when clinical findings are difficult to assess (doubtful clinical signs, obtunded, sedated or intubated patients). However, the design of the present study did not allow calculating this distance as a ratio relative to the total length of the tibia, which could have been an interesting element to generalize the use of this finding. This could be the aim of a further study on this topic.
One of our initial hypotheses, postulating that higher fracture displacement would be associated to higher-energy trauma and more extended soft tissue damages leading to ACS, could not be confirmed by this study. No association between angulation, translation or over-riding at the fracture site and occurrence of ACS could be demonstrated. As per institutional policy, grossly deformed limbs are aligned by gentle traction and rotational control before any radiographs are taken, in order to protect vascularization and to relieve soft tissue suffering of the injured limb as soon as possible. Thus, radiographs may not reflect the initial deformity and this makes any conclusion about fracture displacement weak.
Additionally, neither the presence or absence of an associated fibular fracture nor the distance between the tibial fracture and the fibular fracture when present showed an association with ACS development. This is in line with previously published data .
Despite being one of the largest series to date analyzing the association between key demographic, injury-related, clinical and radiographic parameters in tibial shaft fracture patients and the development of ACS, this study suffers several limitations: 1) the retrospective attempt to differentiate between low and high-energy trauma on chart review makes any conclusions about mechanism or energy of the injury weak; 2) ICP measurements, which would have been the gold standard to diagnose or exclude ACS, were performed only on a subset of patients, thus introducing the possibility of false positive or false negative diagnosis; however, we did not find any clinical records suspect of late ACS sequellae in the charts of patients that were not diagnosed with ACS, and every patient who underwent fasciotomy had pathological ICP values before fasciotomy, and/or presented muscle bulging or suffering at the time of fasciotomy; 3) radiographic analysis was performed on one occasion only thus not quantifying intra-observer variability and measurement imprecision; however, inter-observer reliability assessment performed on 10.3% of the cases showed almost perfect agreement for all measurements, except for over-riding which had substantial or good agreement: this may validate the entire radiographic measurement process performed by an observer with 2 years of experience in orthopedic radiographic interpretation and measurements, as the observer who took part in the inter-observer reliability assessment had more than 15 years of experience in the field; 4) the most powerful factor highlighted by this study in predicting occurrence of ACS during the treatment of tibial shaft fractures, namely the distance between the talar dome and the centre of the tibial fracture, was measured as a distance rather than as a ratio relative to the total length of the tibia; the design of the present study did not allow such a measurement, and this ratio determination could be the aim of a further study in order to generalize the use of this finding; 5) and finally, proximal tibiofibular dislocation, which has been recently shown to be possibly associated with a higher rate of ACS (29%) in both tibial plateau and tibial shaft fractures, was not investigated in the present study .