Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims?

original article Wien Klin Wochenschr https://doi.org/10.1007/s00508-020-01631-y Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? Jure Aljinović · Igor Barišić · Ana Poljičanin · Sandra Kuzmičić · Katarina Vukojević · Dijana Gugić Bokun · Tonko Vlak Received: 4 July 2019 / Accepted: 3 March 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020 Summary Background Whiplash injury of the cervical spine is the most common injury after a car accident and in 25% of patients it progresses into chronic neck pain. Aim of the study To investigate the difference in neck muscle stiffness using shear wave ultrasound elastography between subjects who suffered an uncomplicated whiplash injury and a control group. Possible recognition of patients who insist on physical therapy in order to support their false whiplash injury claims. Methods This study included 75 whiplash injury patients and 75 control subjects. Trapezius, splenius capitis and sternocleidomastoid muscles were examined by ultrasound shear wave elastography. Results Increased muscle stiffness was noticed in trapezius muscle bilaterally in the whiplash group when compared to the control group (p < 0.001; J. Aljinović and I. Barišić equally contributed to this paper as first authors. J. Aljinović () · A. Poljičanin · S. Kuzmičić · T. Vlak Institute of Physical and Rehabilitation Medicine with Rheumatology, University Hospital of Split, Šoltanska 1, 21000 Split, Croatia [email protected] I. Barišić Clinical Department of Diagnostic and Interventional Radiology, University Hospital of Split, Split, Croatia K. Vukojević Department of Anatomy, Histology and Embryology, University of Split School of Medicine, Split, Croatia D. Gugić Bokun Clinical Department of Pathology, Forensic Medicine and Cytology, University Hospital of Split, Split, Croatia J. Aljinović · A. Poljičanin Department of Health Studies, University of Split, Split, Croatia K right 57.47 ± 13.82 kPa vs. 87.84 ± 23.23 kPa; left 54.4 ± 12.68 kPa vs. 87.21 ± 26.47 kPa). Muscle stiffness in splenius capitis and sternocleidomastoid muscles was not suitable for analysis because of asymmetrical data distribution. Patients with less than 76 kPa of muscle stiffness in trapezius muscle are unlikely to belong in whiplash injury group (sensitivity 90% for right and 97% for left trapezius muscle, specificity 72% and 73%, respectively). Conclusion Patients measuring below 76 kPa of muscle stiffness in the trapezius muscle might have no whiplash injury. Further follow-up of the patients measuring higher than cut-off value might be beneficial for detecting patients with prolonged neck muscle spasm that can lead to chronic cervical pain syndrome. Keywords Elastography · Ultrasound · Trapezius · Shear wave · Neck pain Introduction Whiplash injury and whiplash-associated disorder are the most common injuries resulting from a car accident [1]. Recovery usually occurs within 3 months of the accident [2, 3]. Although most of the people recover completely, in about 25% of the cases medium to severe chronic neck pain develops [3]. Negative predictive factors for complete recovery reported in the literature are high initial neck pain intensity [4], high neck disability index score, development of posttraumatic stress syndrome and pain catastrophizing [5]. Some preaccident factors, such as high psychological distress, female gender, low educational level, and being unemployed, sick-listed or receiving social assistance were also reported as possible predictive factors for developing chronic neck pain after whiplash Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? original article injury [6]. Poor coping strategies were one of the proposed mechanisms in those patients. In the study by Ritchie et al. regarding whiplash injury it was proposed that a tool named clinical prediction rule (CPR) could be used in predicting outcomes, such as developing either disability after whiplash injury or full recovery [2]. It consists of eight domains: initial neck disability index (NDI), initial neck pain on visual analogue scale (VAS), cold pain threshold, range of neck movement, age, gender, presence of headache and posttraumatic stress disorder (PTSD). This tool is still not in use in clinical practice and all of the eight domains are undergoing a validation procedure. The mechanism of pain after whiplash injury is still unexplained, but the strain of muscles and ligaments followed by reactive spasm is believed to be the main cause. Usually only plain radiographs of the cervical spine are performed in patients involved in car accidents. A radiograph can detect cervical spine straightening and prior intervertebral osteochondrosis and radiograph can exclude fractures of the cervical vertebra. So far little is known about the status of muscle injury or reactive spasm, both of which are not detectable on plain radiographs and their involvement in the chronic pain development is not defined. Ultrasound examination with shear wave elastography (SWE) is a relatively new radiological method that can access structural changes in different tissues including muscles [7]. This method can measure the level of muscle stiffness (elasticity) and permits both qualitative and quantitative evaluation of the elasticity properties of soft tissues and their alteration in traumatic lesions and degenerative pathology. The SWE method uses a combination of the radiation force induced in a tissue by an ultrasonic beam and the ultrafast imaging sequence capable of catching the propagation of the resulting shear waves in real time. It is worth mentioning that the ultrasound SWE is harmless for both the patient and the medical practitioner. Within a given region of interest (ROI), defined by an electronic cursor positioned by the radiologist, values for the maximum tissue stiffness, mean stiffness and standard deviation (SD) are produced. Areas of stiffness within a muscle can thus be clearly mapped. This reproducible, quantitative information is not available with standard elastography and yet it can aid both the diagnosis and rehabilitation evaluation of acute musculoskeletal injuries or chronic myofascial pain [8]. The problem of this radiological method is the lack of standardization of applied pressure onto the tissue during the examination. Also, there are no standardized values available in the literature for normal stiffness of the examined muscles with only one paper has been published, which addressed passive muscle stiffness in young children [9]. Two papers were published in adults: one addressing quantitative estimation of muscle shear elastic modulus of the upper trapezius muscle with supersonic shear imaging during arm po- sitioning [10] and the other quantifying cervical and axioscapular muscle stiffness using SWE [11]. In the CPR tool, the level of muscle stiffness is not included as one of the domains for outcome prediction. The literature research produced no papers that would refer on muscle stiffness as a possible predictive factor for prolonged pain. The circulus vitiosus that bonds muscle stiffness and pain appears to be an important factor for development of chronic pain sensation. It was hypothesized that some people who did not sustain a true whiplash injury after a car accident are going to physical therapy in order to attempt false insurance claims. We believe those patients would have normal muscle stiffness measurements and no clinical signs, such as radiculopathy or limitation of neck movement. In order to test this presumption, we needed to obtain basic data of muscle stiffness in healthy people and whiplash injury patients. Until now the only verification of injury status was the patient’s own pain perception measured by VAS. That measure is highly subjective and sometimes exaggerated. By measurement of passive neck muscle stiffness in a whiplash injury using SWE we would have a quantifiable measure that can objectively inform us of the true postinjury muscle tone. This study aimed to investigate the difference in muscle stiffness between two groups: subjects who suffered whiplash injury examined by a specialist of physical medicine and rehabilitation (PMR) and a control group of healthy people. We also sought to compare the possible differences in pain perception as reported by the patients themselves versus pain estimation by an experienced physician during clinical examination. Additionally, we compared muscle stiffness values in subjects who took analgesics or/and myorelaxant drugs after the whiplash injury with the muscle stiffness values measured in subjects who did not take the aforementioned drugs. Ultimately, we aimed to establish which muscles were most affected by prolonged spasm in the first 3 months after whiplash injury. The three biggest muscles of the neck region that usually suffer strains and sprains after uncontrolled movement of the neck were analyzed: posteriorly located trapezius muscle, anteriorly located sternocleidomastoid muscle and laterally located splenius capitis muscle. Materials and methods This prospective study was conducted at the Institute of Physical and Rehabilitation Medicine and Clinical Department of Diagnostic and Interventional Radiology in University Hospital Split, Croatia. It was approved by the Ethical Committee of the University Hospital Split. Patients and healthy control subjects were informed about the study design and goals and informed consent was obtained in written form. Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? K original article Fig. 1 Position of ultrasound probe for analyzing neck muscles. a Trapezius muscle; b Splenius capitis muscle; c Sternocleidomastoid muscle The study was designed to evaluate ultrasound SWE as a diagnostic method in the quantification of the neck muscle stiffness in patients who were involved in a car accident and suffered a whiplash injury. Only patients that were examined by PMR specialist within 90 days from the car accident and diagnosed as having a whiplash injury were included in the study (Quebec Task Force classification grade 1: pain in the neck alone, grade 2: pain and decrease of movement in the neck or point tenderness, grade 3: additional neurological signs such as decreased or absent deep tendon reflex and/or muscle weakness and/or sensory defect) [12]. Exclusion criteria for this study were: Quebec Task Force classification grade 4 with sustained fracture of cervical vertebrae [12], bone fractures of any other location sustained in accident and whiplash injury in any other type of vehicle other than the automobile. This study was conducted during 8 months from August 2017 through April 2018, and 93 patients were examined with the diagnosis of whiplash injury. From this number only 75 patients were included in the K study as 8 patients had exclusion criteria while 10 patients refused to participate. The control group was formed from 75 randomly selected healthy volunteers, with no prior muscular injuries reported. Participants were age and gender matched between control and whiplash groups. Whiplash injury group had 75 patients of which 32 were men and 43 women (43% vs. 57%). Mean age of the patients was 43.1 ± 13.5 years (mean ± SD). There were 75 people in the control group, 34 men and 41 women (45% vs. 55%), with the mean age of 46.5 ± 16.3 years. Data collected from the medical documentation and from the interviews with patients included age and sex, date of the car accident, driver or passenger status, seat belt usage, concomitant analgesics and myorelaxant usage, and evaluation of the cervical spine radiographs. For the use of analgesics the answers available to the patients were: yes, no and sometimes, while for the myorelaxant use at any time from the accident, they had only yes or no choices. Radiographs of the cervical spine were analyzed and either a normal X-ray, a straightening of the cervical Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? original article lordosis or a prior intervertebral osteochondrosis were noted. This was followed by a clinical examination and evaluation of the level of pain in the neck region by VAS (values from 0–10) completed by the physician and the patient. Before any physical therapy procedures all of the patients and control subjects were examined by the same experienced musculoskeletal radiologist on the same ultrasound machine. The radiologist involved in this study subspecializes in ultrasound and has 20 years of experience in musculoskeletal radiology. In his everyday practice he uses SWE for breast tissue and for supraspinatus and Achilles tendon examinations. The radiologist was blinded to whether the analyzed individual was in the whiplash or the control group. A multi-frequency linear probe (2–10 MHz; Aixplorer Supersonic Ultrasound system, Aix en Provence, France) was used for the ultrasound examination with SWE and measurement of difference in muscle stiffness. This machine was previously validated for SWE ultrasound in liver fibrosis staging [13]. Tissue stiffness was measured by a physical quantity called Young’s modulus and expressed in pressure units (kilopascals [kPa]). We have used absolute elasticity values ranging from 0–300 kPa. Examination was done on the preselected muscles: trapezius, splenius capitis and sternocleidomastoid muscles, on both sides of the neck. Two ROI were picked in each muscle at the thickest part of the muscle (without the fascia) and three measurements were made in each muscle for every ROI. The mean value from those six values was used for statistical analysis. Furthermore, these measurements where used to calculate intrarater reliability. Standardization of the SWE examination was done by using minimal pressure of the ultrasound probe against the skin to prevent tissue from deforming and thus inadvertently increasing the stiffness. All patient body postures for different muscles were also standardized as follows: trapezius muscle was examined in the seated position with the relaxed shoulder girdle and the arms in supination resting on the thighs. The head was slightly flexed forward. The ultrasound probe was positioned in the upper part of trapezius muscle at the thickest part of the muscle in midpoint from the shoulder and head (Figs. 1a and 2). The splenius capitis muscle was examined in the same seated position with the probe located in the upper lateral part of the neck with 45° inclination (Fig. 1b). In this position the splenius capitis muscle is located nearest to the skin with the trapezius muscle below and sternocleidomastoid muscle above. Only the sternocleidomastoid muscle was examined with the subject lying in the supine position with the chin-up and the probe located in the middle of lateral side of the neck on the thickest portion of the muscle (Fig. 1c). Data distribution of elastography measures in each of the muscles analyzed was tested by Shapiro–Wilk test. The difference between VAS pain scale reported Fig. 2 Optimal positioning of the ultrasound probe over trapezius muscle during SWE. (drawing) by the patient and by the physician was tested with t-test for independent samples. The difference of elastography values of the left and right trapezius muscle in the same person and between control and whiplash group was tested with 2-way ANOVA test. Results of the 2-way ANOVA test were later analyzed by post hoc Tuckey HSD test. Correlation between X-ray, VAS reported by patient and physician, use of analgesics or myorelaxant drugs and muscle tension was tested with Spearman’s r test. For sensitivity and specificity of SWE the receiver operating characteristic curve (ROC) analysis was performed. All statistical analyses except correlation were done in GraphPad Prism 8.0 software (GraphPad Software, La Jolla, CA, USA). Correlation analysis was done in Past3 Software (Øyvind Hammer, Natural History Museum, University of Oslo, Norway). Results In the control group the values for stiffness of analyzed muscles obtained by elastography were for the trapezius muscles 57.5 ± 13.8 kPa for the right and 54.4 ± 12.7 kPa for the left one; the splenius muscles 26.7 ± 8.7 kPa for the right and 25.9 ± 7.4 kPa for the left one and for the sternocleidomastoid muscles Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? K original article Fig. 3 Elastography values of trapezius muscles in healthy people and whiplash injury patients. Ctr control group, Whp whiplash group, r right, l left, ****p < 0.0001 21.4 ± 4.9 kPa for the right and 21.2 ± 4.1 kPa for the left one. In whiplash injury group elastography values for trapezius muscles were 87.8 ± 23.3 kPa for the right and 87.2 ± 26.7 kPa for the left one. Splenius muscles showed mean values of 39.6 ± 23.5 kPa for the right and 43.9 ± 22.3 kPa for the left one; sternocleidomastoid muscles had mean values of 34.7 ± 21.8 kPa for the right muscle and 31.2 ± 15.9 kPa for the left muscle. On further statistical analysis only trapezius muscles had normal distribution of data both in whiplash and control group. Splenius capitis muscles and sternocleidomastoid muscles had asymmetrical data distribution and therefore were not included in further statistical analysis. We have found that both trapezius muscles had more stiffness in the whiplash group when compared with control group and the difference was significant (2-way ANOVA, f = 185.82, p < 0.001; right 57.47 ± 13.82 kPa vs. 87.84 ± 23.23 kPa, p < 0.001; left 54.4 ± 12.68 kPa vs. 87.21 ± 26.47 kPa, p < 0.001, Fig. 3). The results show that there is no difference in the level of tension between trapezius muscles of left and right side within the whiplash injury group and within the control group (f = 0.64, p = 0.425, left vs. right whiplash group 87.21 ± 26.47 vs. 87.84 ± 23.23 kPa; control group 54.4 ± 12.68 vs. 57.47 ± 13.82 kPa). Mean time elapsed from the car accident was 36.4 ± 17.9 days with the minimum of 10 days and the maximum of 85 days. Patients reported higher intensity of pain in the cervical region on VAS then estimated by the experienced physician after clinical examination and palpation of tested muscles (doctor vs. patient 5.7 ± 1.5 vs. 4.3 ± 1.7, t = –5.4, p < 0.001). Radiographs of the cervical spine were normal in 28 patients, 29 had straightening of the cervical spine, while 14 had previous intervertebral osteochondrosis together with straightening of the spine. Four patients were not X-rayed. There was no difference in muscle tension in patients with normal X-rays (group 1), cervical spine lordosis straightening (group 2) or intervertebral osteochondrosis (group 3) both between left and right side and within the group or between groups (right side: group 1: 91.1 ± 26.3 kPa; group 2: 83.13 ± 21.6 kPa; group 3: 87.6 ± 21.5 kPa; left side: group 1: 87.91 ± 25.1 kPa; group 2: 80.54 ± 25.5 kPa; group 3: 91.35 ± 27.8 kPa). Of the patients 57 (76%) were driving at the time of the accident while 18 (24%) were passengers in the car. Fig. 4 Elastography values of trapezius muscles 1, 2 and 3 months after the whiplash injury. R right, L left. Horizontal bar time from injury in days, vertical bar trapezius stiffness in kPa. * p < 0.05 K Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? original article Table 1 Specificity and sensitivity of shear wave elastography in whiplash injury of the neck vs. control healthy population Test Cut-off (kPa) AUC (fraction) (95% CI) Sensitivity (%), (95%CI) Specificity (%) (95%CI) LR+, (95%CI) LR– (95%CI) Tension in right trapezius 76 0.8745 (0.82–0.93) 90.67 (81.97–95.41) 73.33 (62.37–82.02) 3.39 (2.17–5.3) 0.12 (0.05–0.28) Tension in left trapezius 75.6 0.8589 (0.79–0.92) 97.33 (90.73–99.53) 72 (60.96–80.90) 3.47 (2.32–5.21) 0.03 (0.005–0.15) AUC area under ROC curve, LR+ positive likelihood ratio, LR– negative likelihood ratio, kPa kilopascal, CI Confidence interval Table 2 Intrarater variability of elastography measurements in analyzed muscles Elastography of muscle ICC coefficient 95% CI Trapezius R 0.975 [0.9291, 0.9932] Trapezius L 0.9337 [0.8211, 0.9815] Splenius capitis R 0.9759 [0.9315, 0.9934] Splenius capitis L 0.9331 [0.8195, 0.9813] Sternocleidomastoid R 0.8685 [0.6706, 0.9621] Sternocleidomastoid L 0.886 [0.7089, 0.9674] R right, L left, ICC inter-class correlation, CI Confidence interval Only three patients stated they had not fastened the seat belt (4% of whiplash injury group), while others stated they had fastened it. Most of the patients took analgesics on demand (48 patients, 64%), 17 patients took analgesics regularly (23%) and 10 patients did not take any analgesics at all (13%). There was no statistically significant difference in trapezius muscle stiffness between patients who took analgesics and the ones who did not (right side: no analgesics vs. analgesics group, 96.2 ± 26.46 kPa vs. 86.56 ± 22.8 kPa, t = 1.1, p = 0.295; left side 85.36 ± 26.7 kPa vs. 87.5 ± 26.66 kPa, t = –0.22, p = 0.828). Although almost always prescribed by the physicians at emergency departments, less than half of the patients took a myorelaxant agent like diazepam (33 patients, 44%). There was no significant difference in muscle stiffness between patients who took a myorelaxant agent and the ones that did not (right side: no myorelaxant vs. myorelaxant group 88.92 ± 22.4 kPa vs. 86.46 ± 24.57 kPa, t = 0.45, p = 0.654; left side 82.62 ± 28.19 kPa vs. 93.06 ± 23.93 kPa, t = –1.73, p = 0.087). The correlation between level of muscle tension and VAS reported by patients was tested and no statistical significance was noted. Patient’s age and trapezius tension did not show any correlation (right r = –0.01, p = 0.91, left r = 0.02, p = 0.06). Upon dividing whiplash injury patients into three groups regarding time elapsed from the accident (group 1: <30 days, group 2: 30–60 days and group 3: 60–90 days) we have found statistically significant increase of right trapezius stiffness in group 3 vs. both groups 1 and 2 (Fig. 3; group 1 vs. group 3: MD; –24.14, CI –46.6 to –1.7, p = 0.02, group 2 vs. group 3: MD; –23.66, CI –47.8 to 0.46, p = 0.03). Left trapezius tension showed no significant differences between groups (Fig. 4). We calculated the sensitivity and specificity of SWE measurements of trapezius muscle stiffness in determining into which group the analyzed person belongs to. Our data showed that people who had less than 76 kPa of muscle stiffness in the trapezius muscle were unlikely to belong to the whiplash injury group with calculated sensitivity of 90.6% (95% CI; 81.97–95.41) for right and 97.3% (95% CI; 90.73–99.53) for left trapezius muscle (Table 1). The specificity of SWE in detecting if the analyzed person in fact belongs to the whiplash injury group is lower: 73.3% for right trapezius (95% CI; 62.37–82.02) and 72% for left trapezius muscle (95% CI; 60.96–80.90) (Table 1). Intrarater variability was assessed by interclass correlation coefficient (ICC) using the model 3.1 of Shrout and Fleiss [14]. For all muscles ICC was above 0.85 which indicates good and excellent reliability (Table 2). Discussion The current presumption is that sudden and extreme acceleration-deceleration movement of the neck causes a painful response of the neck muscles through nociceptors which subsides within 3 weeks following the injury by neck rest and medication [15]. In some patients who present with no new injuries (either of bones, facet joints, spinal cord, intervertebral discs, or nerve roots) functional disorders like spasms and cramps can persist longer than 3 weeks. These patients were our targeted population. In this study patients with whiplash injury had more stiffness in all of the analyzed muscles than control group as detected by SWE. Trapezius muscle proved to be the ideal muscle for detection of muscle stiffness because it displayed normal data distribution and statistically significant difference in whiplash versus control group. Splenius and sternocleidomastoid muscles dis- Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? K original article played highly asymmetric data distribution and thus were neither suitable for relevant statistical analyses nor referencing in the routine clinical practice. There was no significant difference in the level of muscle stiffness between right and left trapezius muscle in whiplash group, therefore we conclude that the force suffered in a car accident symmetrically affects both sides of the neck. All but three patients in whiplash group fastened the seat belt so the group was homogeneous. For this study the ethics committee of the local institution allowed only inquiries about the driver vs. passenger status, usage of the seat belt and type of vehicle involved in the accident. Additional questions, such as the responsibility of the patient for the car crash, or the mechanics of it (i.e. velocity, site of impact) were not allowed due to legislative issues and open court cases. This fact limited our ability to explain extremely high values of trapezius muscle stiffness in few patients who presumably suffered a high velocity or side impact. After analyzing the data, we determined that most of the patients were referred to physical therapy because of the pain and stiffness in cervical muscles. Mean stiffness of trapezius muscles in whiplash injury patients was more than 30 kPa higher than in control group. Some patients with lesser pain levels might not have been referred to a PMR specialist and have self-treated their pain at home which we perceive as a study flaw. We presume that the difference between stiffness in trapezius muscle between whiplash and control group would be smaller if these milder cases were included. On the other hand, some patients might have aggravated their symptoms because of possible insurance issues in the aftermath of the car accident. Whilst gathering patients who were referred to a PMR specialist with the diagnosis of neck whiplash injury ten people refused to participate in this study. We hypothesize that if there indeed were some simulants they would have been in this excluded set therefore we can presume that the studied whiplash injury group consisted of correctly diagnosed patients with an objectively and clinically relevant condition. Whiplash injury patients reported stronger pain on VAS scale then was estimated by experienced PMR specialist after an examination. In both groups mean VAS of pain was above 4 which suggests a need for pain treatment either with analgesics or physical therapy or both (VAS patient vs. VAS medical doctor 5.7 ± 1.5 vs. 4.3 ± 1.7). A meta-analysis in 2013 showed that initial pain reporting by patients of more than 5.5 on VAS scale is a risk factor for poor recovery [16], therefore most of our patients can be regarded as high-risk patients for chronic pain development. The shortcoming of this study is that there exists no validated questionnaire with which a physician would estimate and grade the pain of the patient. We have therefore used an experienced PMR specialist’s estimation of pain severity elicited during an examina- K tion of the patient through indirect signs such as facial grinning, occurrence of palpable myogelosis, tenderness during palpation, and painful limitation of movement. All PMR specialists who were involved in this estimation had examined and diagnosed more than 100 whiplash patients prior to this study. Patients with whiplash injury usually wear soft neck collars and use medicament treatment (analgesics or myorelaxant agents). We did not find any significant difference in trapezius muscle stiffness in subjects who took analgesics or myorelaxant agent and the ones who did not. Also, the level of muscle stiffness did not differ between patients who took analgesics regularly compared to patients who took analgesics on an as-needed basis. The same result was obtained for myorelaxant drugs. These results suggest that effects of drugs are temporary and that the dosage of these medications should be on an as-needed scheme. This is in agreement with Curatolo’s findings from 2016, who concluded, upon searching the available literature that there was a lack of evidence for long-term benefits of nonsteroidal anti-inflammatory drugs (NSAID) in chronic whiplash injury [17]. Curatolo also stressed possible gastrointestinal and renal side effects and advised their use in the acute posttraumatic phase. As for diazepam, which was used both as myorelaxant and antidepressive in half of the patients in this study, we have found no longterm effect on level of stiffness. The literature shows that diazepam may be helpful in conditions such as hyperalgesia, sleep disorder associated with pain, or depression connected to whiplash injury [17]. A paper from Australia showed that 1 out of 10 people with whiplash injury have had opioids in the treatment of whiplash-associated pain [18]. Recently opioid use became controversial in many conditions due to lack of evidence of long-term benefits and possible development of drug dependence. Since the aspect of different drugs and their separate influence on muscle stiffness was not of special interest in this study, NSAIDs, paracetamol and/or opioid drugs were jointly taken into account, that is as one group of analgesics. As for radiological procedures and their role in quantifying muscle spasm, radiographs were first to be analyzed since all but 4 patients had them. It is a common belief in the wider medical community that cervical lordosis straightening as portrayed on radiographs is connected to prolonged muscle spasm of the cervical region; however, this hypothesis was disproved in studies by Helliwell et al. and Beltsios et al. where the authors concluded that the alterations in normal cervical lordosis in patients with neck injury must be considered coincidental since cervical lordosis straightening appears in healthy individuals likewise [19, 20]. This is in agreement with our results since we have found no difference in the trapezius muscle stiffness between groups with normal X-ray findings, cervical lordosis straightening and previous intervertebral osteochondrosis. This suggests that Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? original article radiographs of the cervical spine alone are not an adequate tool to either hypothesize or objectify which patients have more tension in their cervical region post-injury. In 2007 Grob et al. measured global curvature of the spine from C2 to C7 and each segmental angle in more than 50 patients with degenerative neck pain and healthy individuals and concluded that no significant difference between the two groups could be found in relation to the global curvature, the segmental angles, or the incidence of straight spine or kyphotic deformity [21]. Incidence of cervical kyphosis in neck whiplash injury in comparison to normal population is not known and neither did we examine the segmental cervical kyphosis in our study, which leaves an interesting niche of questions and opportunities that should encourage future investigations. No correlation was found between age and level of muscle stiffness in a patient. In the group of patients for whom the time elapsed from the accident was between 60 and 90 days only the right trapezius showed increased tension compared to other groups with less time elapsed from the accident. We can only hypothesize about the possible reason(s). Maybe those patients suffered a more complex mechanics and stronger forces during the accident or they might be the group from which individuals developing chronicity of the cervical neck pain will be derived. Another question arises: why only the right trapezius muscle had increased tension within the 60–90 days group? Could it be because of the seat belt design which restraints movements of left shoulder more efficiently during an accident therefore acceleration-deceleration forces are lesser on the left side in car drivers? Could it be that the left hand is usually holding on to the steering wheel therefore having a protective role during impact while the right one is more mobile due to the manual gearbox? We must also take into account that sometimes position of radiologist during assessment of muscle stiffness could differ from side to side but we tried to minimize this by using revolving chairs and by positioning patients as described in the “Material and methods section”. Further research in patients with uncomplicated whiplash injury is required to standardize muscle stiffness values in different age and population groups; however, it is clear that patients with whiplash injury have higher values of muscle stiffness in trapezius muscle and some of them could probably be in need of PMR specialist for treatment of prolonged muscle stiffness. Upon statistical analysis of trapezius muscle stiffness measurements by SWE in whiplash and control groups, we have demonstrated a high sensitivity of this method. Therefore, we are able to claim, with more than 90% probability that the patient with muscle stiffness below 76 kPa is not in the whiplash injury group. Specificity of this method is somewhat lower (around 70%) meaning we correctly position a person in the whiplash injury group in 7 out of 10 cases, if they measure above 76 kPa of trapezius muscle stiffness as determined by SWE. Ultrasound SWE is the only method that can objectively quantify muscle stiffness, while all other methods are subjective. We believe that elastography should be a part of the standardized examination in whiplash injury patients in order to quantify the level of neck muscle stiffness. This measurement would be useful for patient follow-up and unbiased evaluation of response to physical therapy procedures. Among numerous advantages of elastography the most prominent ones are that it is not time consuming and it is not harmful for the patient or the examiner. Furthermore, elastography can easily detect patients who have prolonged muscle spasm and therefore should be selected and subjected to early physical therapy in order to prevent development of chronic neck pain. The clinical prediction tool is reported in scientific papers that addresses prognosis of whiplash injury and it consists of eight different predictor variables. Some of them, like older age and initially higher levels of neck disability index, have shown positive predictive value for developing moderate disability; however, stiffness of the muscles in the neck region, especially the trapezius, has not been included as a clinical prediction tool variable and we as authors believe it should be considered as a strong candidate as this is a quantitative variable and it is easily obtainable by SWE when performed by an experienced radiologist. Although there have been reports of positive effect of low-frequency electric stimulation on erector spinae muscle and far-infrared irradiation of cervical muscles, quantitative measures on decrease of spasm are not currently known [22]. Further research is needed on the effect of other physical therapy modalities such as exercise [23], ultrasound, paraffin and transcutaneous electric nerve stimulation (TENS) on whiplash-associated disorders as already suggested by other authors [24] and we likewise propose that quantifying muscle stiffness of trapezius muscle by SWE before and after these procedures could show us which treatment is the best for decreasing muscle stiffness. The major limitation of this study is that interrater reliability of the SWE could not be calculated because there was only one experienced musculoskeletal radiologist for the SWE employed in our institution. The examination was standardized in a way that two ROIs were picked in each muscle at the thickest part of the muscle (without the fascia) and three measurements were made in each muscle for every ROI and that the mean value from those six values was used for statistical analysis. Furthermore, these measurements where used to calculate intrarater reliability. Standardization of the pressure during SWE examination was done by using minimal pressure of the ultrasound probe against the skin to prevent tissue from deforming and thus inadvertently increasing muscle stiffness. Can measuring passive neck muscle stiffness in whiplash injury patients help detect false whiplash claims? K original article Conclusion Increased muscle stiffness was noticed in trapezius muscle bilaterally in the whiplash group when compared to the control group (p < 0.001; right 57.47 ± 13.82 vs. 87.84 ± 23.23; left 54.4 ± 12.68 vs. 87.21 ± 26.47 kPa). Muscle stiffness in splenius capitis and sternocleidomastoid muscles was not suitable for analysis because of asymmetrical data distribution. Patients with less than 76 kPa of muscle stiffness in trapezius muscle are unlikely to belong in whiplash injury group (sensitivity 90% for right and 97% for left trapezius muscle, specificity 72% and 73%, respectively). Further research on this subject could conclude whether stratification of patients after uncomplicated whiplash injury can be made with ultrasound SWE of trapezius muscle stiffness. Further follow-up of the patients measuring higher than cutoff value might be beneficial for detecting patients with prolonged neck muscle spasm that can lead to chronic cervical pain syndrome. Acknowledgements The authors would like to acknowledge Professor Goran Kardum, PhD, for statistical analysis, Ana Krnić, MD and Benjamin Benzon, MD, PhD for their help with the study design, and Renato Igrec MD for drawing the ultrasound probe positioning. Conflict of interest J. Aljinović, I. Barišić, A. Poljičanin, S. Kuzmičić, K. Vukojević, D. Gugić Bokun, and T. 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