Background
The specific structural integrity of motor–tendon units of both the upper and lower extremity is crucial for efficient usage and dexterity of the limbs [
1]. These units are grouped within compartments with sturdy fasciae. Any traumatic impact to the integrity of the compartments may cause devastating impairment [
2‐
4]. The acute compartment syndrome (ACS) is not easy to diagnose and failure to adequately intervene on time may entail fatal lesions, such as “Volkmann contractures”, which summarizes the culmination of the ACS-associated pathophysiological cascade [
5]. Since ACS embodies a pathology with varying symptoms, it is even more challenging and difficult to diagnose the former entity in young children and infants [
6,
7]. As risk factors for developing compartment syndrome in pediatric patients, Mortensen et al. detected male gender, high-energy trauma, open fractures, and concurrent humerus and forearm fractures [
8].
Despite the principal knowledge of the danger of ACS development, Broom et al. stated that the diagnosis of pediatric compartment syndrome may be delayed for more than 24 h from the onset and clinical symptoms may be obscured [
6]. Due to the benefit of earliest possible ACS treatment, identifying parameters which help to raise early suspicion for compartment syndrome is of utmost importance. In the current clinical approach, the diagnosis is based on clinical testing and invasive measurement of compartment pressures in ambiguous cases.
However, clinical symptoms are variable and accuracy of the clinical examination is not satisfying. The positive predictive value of clinical findings is low. Ulmer et al. concluded a value of 11% to 15% [
9]. Whereas, the negative predictive value was high up to 98%. They argue that the absence of clinical findings of an acute compartment syndrome is reliable to exclude one. Recently, Lorange et al. supported the weakness of the clinical examination in a meta-analysis. They conclude that the positive predictive value for diagnosing ACS of clinical findings (21%) combined with the invasive pressure measurement (25%) reaches the probability of 68% [
10]. To date, invasive pressure measurement of the muscle compartment is accepted as an additional examination. However, its accuracy and reliability are questioned [
11]. Though, invasive monitoring may not be suitable for pediatric patients because of patient compliance and ethical reasons. In addition, cases of imminent ACS need a thorough monitoring over time by repeated examinations. Hence, a research focus on non-invasive measures to reliably monitor compartment pathophysiology is of upmost clinical importance. In this context, measurements have to be correlated with clinical symptoms [
12‐
14].
Ultrasound-based measurements of cross-section views of muscle compartments and correlation of the latter to the intrinsic compartment pressure by pressure-related ultrasound (PrUS) might be a method to non-invasively monitor compartment physiology [
14,
15]. Initial in vitro and in vivo studies seem to find promising data [
15,
16]. Therefore, the aim of the presented study is to determine the muscle compartment elasticity as a resulting quantitative value of intra-compartmental swelling and increasing pressure after pediatric trauma in cases of diaphyseal forearm shaft fractures. The authors hypothesize the feasibility of the aforementioned novel and potentially reliable method to measure the increasing muscle compartment swelling after trauma non-invasively and to objectify the observer’s examination in cases without developing an associated ACS.
Discussion
Changes in muscle compartment pressure conditions after trauma or surgical interventions have its importance to exclude ACS [
21]. The history and clinical findings of the patient may lead to an awareness of potential ACS with the well-known yellow and red flags [
3,
4]. In toddlers and infants, the risk to develop an ACS is well described and often recognized with a delay of hours [
6,
8]. The clinical findings are heterogenous and may mask the potentially life threatening pathology. Invasive needle compartment pressure measurement is still used to prove or exclude the diagnosis of ACS, even if it is painful and the results are questioned regarding their reliability [
7,
11]. Hence, the physicians´ clinical findings have to be supported by objective measurements and parameters to indicate or to forgo the need for fasciotomy. To date, there is a need for a non-invasive method monitoring the muscle compartments in suspected cases. Numerous scientific groups went different pathways to detect either the increasing intra-compartmental pressure or the decreasing perfusion pressure of the muscle tissue non-invasively [
12‐
14].
PrUS is a novel and non-invasive approach to objectify the clinical findings of the physician’s palpation. Hereby, the muscle compartment elasticity is correlated with the compressibility. Several publications revealed a close and reliable correlation between the decreasing amount of the compartment compressibility and increasing intra-compartmental pressures [
16,
17,
20,
22].
“Pressure related ultrasound” examines the overall compartment cavity with the fascial and bony borders. Nowak et al. collated this methodology as a method based on “strain elastography” [
15]. As PRUS calculates a relative value of “relative elasticity” (RE in %) of the entire compartment, this method is a quantitative technique. Though, PRUS provides information on the overall compartment elasticity, compressibility and stiffness independently of the tissue heterogeneity and density, shear modulus of the soft tissue, and the ultrasound velocity within the compartment.
Recently, Anwander et al. investigated the reliability of a dual sensor approach in healthy volunteers [
23]. Based on the methodology of PrUS, they demonstrated a significant and reliable approach to detect changes of a compression ratio (corresponding to RE) in 60 cases. In addition, the advantage of the application of P1 (10 mmHg) compared to P1 (0 mmHg) as the starting point of measurement was demonstrated.
It is still unknown, whether PrUS has the potential to differentiate beginning changes of muscle compartment pressure conditions after trauma and surgical interventions thereby an early recognition of an imminent ACS. This could be evidence for the use of PrUS in monitoring children at risk developing an ACS.
The presented results in 25 pediatric cases suffering a forearm shaft fracture affirm this potential diagnostic benefit of PrUS. The RE grade 3 resulted in a significant difference compared with the control group. Surprisingly, even the category grade 0 without any clinically recognized soft-tissue changes by the observer resulted in a substantial difference compared with the unaffected healthy limb. The statistical analysis of the clinical findings and the measured RE (%) resulted in a low correlation (rs = 0.474). These findings affirm that the clinical examination alone is not reliable and predictive to detect or monitor soft-tissue changes of the forearm in pediatric trauma. However, this observation may show evidence for a potentially precise method for monitoring the muscle compartment pressure condition non-invasively, particularly if invasive pressure measurements can be avoided.
The RE ratio of the injured vs. healthy limb also showed an obvious change according to the increasing swelling. However, based on our results, it remains uncertain whether the RE ratio is able to delimit an imminent compartment syndrome (ICS) of an ACS by a clear cut off level. Hence, this was not the aim of our study and has therefore to be investigated in the following studies including patients developing an ACS over the clinical course. This novel method based on pressure measurement combined with the ultrasound is to determine the dimensions of the muscle compartment related to the clinical finding of the physicians’ palpation [
17,
20].
Hence, the compressibility of the soft-tissue envelope by the observer can be objectified. Moreover, the specific anatomy of the examined compartment can be identified and differentiated by the observer. It remains to be seen whether further developments in this methodology of PrUS may help to estimate and to monitor potential ACS in toddler and infants.
There are important limitations to be delineated regarding the presented study. First, the number of children in the subgroups is limited. Further prospective studies are needed to determine the value of the resulting RE and of the RE ratio of the injured vs. healthy limb. The main limitation is the classification of the soft-tissue swelling in grade 0–3. The collation of the compartment elasticity in the described graduation by a single observer has a limited value. As the presented ultrasound-based methodology is novel, the study investigated its feasibility. However, further studies are needed to prove the presented concept as a novelty to monitor the increasing pressure as well as the decreasing compressibility in suspected cases of ACS by repeated measurements.
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