The clinical situation in patients with chronic low back pain (CLBP) varies considerably, from minor distress to total disablement. In more severe cases the demand for therapy is pressing both for the patient and the physician. For most patients with persistent unspecific pain for months and even years, a large number of non-specific treatments are proposed. Although some patients may benefit to an acceptable degree from these measures, many still experience unbearable pain after having tried all conservative methods, including psychological treatment. In such situations the possible value of spinal fusion may be discussed. However, only two out of five randomized studies have reported the results following fusion surgery for CLBP to be better than after conservative treatment [1, 2, 3, 4, 5]. One possible reason for the modest results of fusion surgery is the lack of a description of specified symptoms that might be related to a painful segment/disc, making patient selection more or less a matter of chance . In the randomized studies mentioned above, the patients’ back symptoms were described simply as “chronic low back pain” in three of the studies [2, 3, 4], as “back pain more pronounced than leg pain and no signs of nerve root compression” in the forth study , and as “low back pain” in the fifth study .
Our intention was to analyse in more detail the clinical symptoms and signs presented pre-operatively by those patients within the CLBP group who showed substantial relief from their back pain following fusion surgery, with the aim of possibly finding a pain pattern indicating segmental, discogenic pain.
2 Material and methods
2.1 Number of patients and pain duration
The material includes 40 consecutive patients, 35 women and 5 men, mean age 41 years (range 24–61), with a history of disabling low back pain for a mean of 7.7 years (range 2–36). All 40 patients were on sick leave and had been so for a mean of 4.0 years (range 1–15). All attempts at using conservative treatment methods, including long periods of physical therapy, had been unsuccessful.
2.2 Patient selection
Our intention was to find patients with symptoms from a presumed painful disc. According to our previous clinical experience, patients with more centrally located back pain had often reported a good outcome following fusion surgery. We therefore selected patients describing their back pain as located in proximity of the spine, and not in larger areas. Some, but not all of the patients had diffuse non-radicular pain radiation of varying extension down one or both legs. All patients were carefully examined radiologically by plain X-ray, CT scan or MRI in order to exclude those with specific reasons for their pain, e.g. disc herniation, stenosis, spondylolisthesis, etc.
2.3 Surgical procedure
All patients underwent monosegmental fusion without internal fixation. The presumptive painful level was chosen according to the signs at clinical examination and the results from intradiscal injection of local anaesthetic in at least two discs, blinded for the patients. Operations were performed regardless of whether or not various degenerative findings were present radiologically, and regardless of previous surgery or minor psycho-social problems. Posterior lumbar interbody fusion (PLIF) was performed using microsurgical technique. The operations were carried out between November 1987 and June 1988. Surgibone (calf bone) was used as transplant, which at that time was said to be equally effective as autologous bone [7, 8]. Two patients underwent surgery at the L3–L4 level, 15 at the L4–L5 level and 23 at the L5–S1 level.
2.4 Questionnaire concerning symptoms
Before surgery all 40 patients completed a detailed questionnaire concerning various aspects of their symptoms, Table 1. The responses of those patients who showed much improvement at the 2-year follow-up, according to their own assessments and that of the independent examiner (see below), were analysed in order to determine if there was a pattern of symptoms indicating segmental, discogenic pain. These patients were also compared with those who did not show improvement following the operation.
2.5 Evaluation of outcome
In addition to the global assessments made by the patients, outcome was evaluated retrospectively by an independent observer (neurologist Henrik Weber (HW), Oslo, Norway). He also checked the list of names in the operation record during the period in question, ensuring that the patients had been operated on consecutively. The pre-operative state of the patients was recorded based on data from the hospital records and was confirmed by means of the patients’ own report, including duration of pain, drug consumption, pain-provoking and alleviating factors, psycho-social state and the effect of conservative therapy. The patients were asked by HW to describe the state of their spine pre- as well as post-operatively by using one of the following expressions: good, rather good, fair, inferior, poor or miserable.
In order to create an “over-all” assessment, four factors were assessed, scored using a VAS scale and summarized numerically by HW. These comprised: (a) the consumption of analgesics; (b) the history of illness, signs and symptoms of the patient including the mobility and state of the spine, neurological deficits, and function of the urinary bladder; (c) back pain intensity (VAS 0–100); and (d) results of the Roland-Morris Disability Questionnaire reduced from 24 to 20 questions. According to the degree of severity regarding factors a and b, respectively, HW marked a point on a VAS scale. Similarly, the functional state of the patient as recorded by the Roland-Morris Questionnaire was transformed to a VAS scale according to the number of positive answers. The VAS scores for factors b, c and d were regarded by HW as being more reliable in describing the disability state of the patient, and these values were therefore multiplied by three. The total sum of all four values constituted the “over-all” assessment. Differences between pre- and post-operative values were classified by HW as follows: much improved (50–100% improvement), somewhat improved (20–49%), unchanged (±19%) or deteriorated (less than−19%).
All patients were examined by HW at one year after surgery. At two years 34 patients were examined and four were interviewed by telephone. At that time one patient had been diagnosed as having breast cancer with spinal metastases that induced new symptoms, and was therefore excluded. Another patient did not participate. At 4 years 15 patients were examined by HW and 23 were interviewed by telephone. At follow-up the patients were asked for their own opinions regarding the effect of the operation using one of the following descriptions: much improved, somewhat improved, unchanged or deteriorated.
The patients underwent a final follow-up 18 years postoperatively that comprised a questionnaire, the Balanced Inventory for Spinal Disorders, BIS [9, 10, 11], including assessment of their back and leg pain, their physical, social and mental condition, use of analgesics, work situation, and a general statement concerning whether their current situation was much better, somewhat better, unchanged, somewhat worse or much worse compared with the situation before surgery.
2.6 Pre-operative clinical examination
The clinical examination included inspection of posture, whether kyphosis or exaggerated lordosis was present, the patient’s ability to perform flexion and extension of the lumbar spine, and a routine neurological examination including motor, sensory and reflex analysis. Interspinal palpation of the lumbar spine was performed and any distinct interspinal tenderness was noted. A tapping test was developed and performed with the patient lying on his/her side in a slight foetal position. The base of a tuning fork was placed against the respective spinal process and tapped in a longitudinal direction, thereby producing a percussion of the respective process, and the reaction of the patient was noted.
2.7 Post-operative radiological examination
2.8 Previous surgery
Prior to treatment at our clinic, 13 of the 40 patients had undergone surgical procedures for their back problems. Seven patients had undergone a decompression procedure, one patient a decompression and fusion, four patients had had three previous operations each, and one patient had undergone five operations including decompression and fusion procedures. Altogether, the 13 patients had undergone 26 previous operations.
3.1 Clinical results
The patients’ own opinions regarding their clinical situation before operation and at 1, 2 and 4 years post-operatively are shown in Table 2. The patients’ opinions regarding changes in their clinical condition at 1, 2 and 4 years post-operatively are shown in Table 3 in comparison with the opinions of HW.
At 18 years after surgery 19 patients assessed their back pain to be completely disappeared or much better than before surgery, eight patients as somewhat better, two as unchanged, three as somewhat worse and three as much worse. Three patients did not respond.
At 2 years after surgery 27 of the patients were much improved according to HW’s assessment (Table 3). These patients then comprise a group in which pre-operative symptoms and clinical signs may be analysed with the aim of possibly revealing symptoms and signs of prognostic significance. This “good outcome group” consisted of 23 women and 4 men, mean age 41 years. They had had on average 6.7 years of back pain and had been on sick leave on average 3.5 years before the operation.
At the 2-years follow-up 6 patients were assessed by HW as unchanged and one as deteriorated (Table 3). The symptoms of these seven patients (the “poor outcome group”) were then compared with those in the “good outcome group”. Another four patients were somewhat better at 2 years and, for clarity, were not analysed further.
3.1.1 Back pain, VAS
The VAS values for back pain of each patient prior to surgery and at 2 years after surgery are plotted in Fig. 1. At 18 years after surgery the back pain VAS in the “good outcome group” (see below) was 15 (median) and in the “poor outcome group” (see below) 80 (median).
3.1.2 Functional state
The functional state of the patients as reflected by the Roland-Morris Questionnaire before and up to 18 years post-operatively is shown in Fig. 2.
3.1.3 Sick leave
Before surgery all 40 patients were on sick leave and had been so for a mean of 4.0 years. At two years after surgery the independent examiner (HW) noted 16 patients to be in full work and a further 5 patients to work part time, all these patients belonging to the “good outcome group” (see below).
Among the 19 patients assessing themselves as much better at 18 years (see Section 3.1) 5 patients had pension due to age and 7 early pension, one patient worked full time and 6 patients part time.
3.1.4 Medical consumption
The independent examiner (HW) categorized the patients’ use of analgesics as: overuse, maximal use, moderate, slight or no use. Before surgery the number of patients in the respective levels were 12, 10, 8, 8 and 2. At two years after surgery the respective figures were 1, 6, 2, 4 and 25.
3.2 Analysis of pre-operative symptoms
3.2.1 Analysis of patient groups resulting from the independent examiners assessment
188.8.131.52 The “good outcome group”
When analysing the patients’ responses to the questionnaire that was filled in at the time of the operation (Table 1), it emerged that 23 of the 27 patients in the “good outcome group” had reported a sudden onset of back pain, 25 patients had pain in both their back and their legs, with diffuse localization of the leg pain suggesting referred pain. The origin of the back pain was felt to be in the midline of the spine by 24 of the 27 patients, whereas three patients felt back pain in a larger area. The character of the back pain was dull and aching in 26 of the 27 patients, and 23 patients also had a stabbing, knife-like pain, also in the midline, in connection with an abrupt side step, stumbling, coughing or sneezing, and 23 experienced such pain when driving on a bumpy road. The dull, aching pain was provoked most by sitting and standing, while walking felt reasonably good, and lying down, often in a specially chosen favourite position, felt best. Regarding their back pain, the best time of day was in the morning (16 patients), and the best position for relief of the back pain was lying on their side in a slight foetal position (19 patients).
Pain radiating down the legs was found in 25 of the 27 patients; 11 had radiation in both legs, seven in the right leg and seven in the left leg. The radiation was diffuse, pseudoradicular and extended to the toes in 23 of the 27 patients. There was no dermatomal pattern in the leg pain distribution to indicate which segment was responsible for the pain (Fig. 3). The character of the leg pain was mostly aching (18 patients), but shooting sensations were also common (10 patients). Subjective numbness was very common (25 patients), but tingling (13 patients) and the sensations of pins-and-needles also occurred (13 patients). A majority of the patients also described bladder dysfunction, generally symptoms of frequency (17 patients).
184.108.40.206 The “poor outcome group”
Patients belonging to the “poor outcome group” did not differ from the patients in the “good outcome group” with respect to the character of the back pain, its being provoked mostly by sitting and standing, and morning being the best time of day. These patients also had diffuse leg pain extending to the toes and five had bladder dysfunction with frequency. However, only three had had a sudden onset of their back pain. The most obvious difference seen between the groups was the origin of the back pain reported by the patients. Among the seven in the “poor outcome group” only two localized it to the midline compared to 24 of the 27 patients in the “good outcome group”.
3.2.2 Pre-operative symptoms of prognostic value
When various pre-operative symptoms were analysed and related to the patients’ paired assessments of perceived back pain situation at study start and on the follow-up occasion two years after surgery, two specified symptoms clearly emerged; (a) the patient’s report of back pain origin in the midline of the spine and (b) the presence of stabbing pain upon sudden movements. Among the 23 patients reporting both these symptoms 18 assessed their back situation two years after surgery to be good (8 + 5) or rather good (4 + 1), altogether 78% (Fig. 4A), whereas among those reporting only one or lacking these symptoms 5 out of 15 patients assessed their back situation as good (2 + 2) or rather good (1), together 33% (Fig. 4B), a statistically significant difference (χ2 = 7.67, p < 0.01). Among the 23 patients reporting both midline origin of the back pain and presence of stabbing pain at sudden movements, 21 assessed themselves as improved two years after surgery (Fig. 5) as against 9 out of 15 among those with one or none of these symptoms (Fig. 5). The difference between the groups is statistically significant (χ2 =5.35, p < 0.05).
Among the patients who had a sudden onset of their back problems 68% belonged to the good/rather good group at 2 years against 40% among those without a sudden onset (no statistically significant difference). Various other back symptom details, the presence and various extension of leg pain or the presence or not of bladder disturbance did not show prognostic significance.
3.3 Pre-operative clinical signs
Most of the 27 patients with a good outcome had normal posture, although 10 showed slight lumbar kyphosis. Muscle tenderness was not an outstanding sign. The back pain was aggravated upon bending backwards while standing in 20 of the 27 patients compared to only two patients when bending forward, and five patients when bending both backwards and forward. There were no motor or sensory disturbances and no reflex abnormalities. A true Lasegue sign was never present. Interspinal tenderness was found at the level later chosen for fusion in 16 patients and at an adjacent level in 10 patients, and it differed by two levels in one patient. Pressure in the area of interspinal tenderness provoked the deep back pain. All 27 patients in the “good outcome group” showed sensitivity to the tapping test around the suspected pain origin, and this test also provoked the deep back pain.
Up until the 2-year follow-up, eleven of the patients were reoperated due to defective bony healing, six of them belonging to the “good outcome group” and thus showing a good outcome after re-operation. Five of the seven patients in the “bad outcome group” were re-operated but without improvement.
We have previously discussed the need for a better analysis and description of the symptoms that might indicate a painful segment/disc . The present study is an attempt in that direction despite some weaknesses, one being the retrospective analysis of outcome although the symptoms and signs were recorded pre-operatively. The independent observer, Henrik Weber, was, however, an experienced researcher [14, 15] and was well aware of the difficulties concerning assessments of clinical outcome. Further, his assessments were in good accord with the patients’ own opinion concerning the effect of surgery (Table 3). It is previously found that the patients’ global assessment is a valid description of the overall effect of treatment for CLBP . At two years after surgery 27 of our patients assessed themselves as much better, so also the independent examiner, this improvement being fairly stable also for as long as 18 years. Whether this change is causal to surgery or not cannot be decided from this our pilot study, but the change is real and these patients therefore worth studying concerning pre-operative symptoms of possible prognostic importance.
Few previous studies have dealt with symptoms and signs that might be related more specifically to a painful disc. This state, discogenic pain, is reported by some to be reliably revealed by concordant pain reaction at discography [17, 18, 19, 20, 21], but others are in disagreement [22, 23, 24]. When using this test procedure Schwarzer et al.  were unable to differentiate patients with discogenic pain clinically from other patients within the CLBP population. In contrast to our findings, they found that patients with central lumbar pain were unlikely to suffer from discogenic pain. Young et al. , who also used concordant pain reaction at discography as an indicator of a painful disc, described centralization of back pain during repeated testing and pain when rising from sitting as symptoms related to a painful disc. Contrary to our findings Ohnmeiss et al.  described specific pain projection areas in the leg/s during discography as shown in pain drawings, as being related to specified lumbar discs (see Fig. 3). They also described discogenic pain as being mainly burning in character, which also contrasts to our findings. The only previous study describing many of the symptoms and signs we found in our CLBP patients who improved by fusion surgery is that of Lettin , published more than 40 years ago. He also described a sudden onset of the back pain in his patients, increasing pain when standing and sitting, aggravated pain (but not stabbing) while coughing and sneezing, pain and paraesthesia in the legs, and midline tenderness.
Logically, provocative discography would be the most suitable test for pinpointing a painful disc, and several reports defend this opinion [17, 18, 19, 20, 21, 28, 29, 30, 31] while others do not [22, 23, 24, 31, 32]. In fusion surgery in patients suffering from non-specific CLBP Madan et al.  and Carragee et al.  did not find pain reaction at discography to be a reliable method for pinpointing a presumed painful disc. However, if a more homogeneous population of patients within the CLBP group could be selected, truly representing patients with discogenic pain, the pain reaction at discography might be a possible selection instrument for indication of the proper disc. At present there is no validated method for pinpointing a painful disc [33, 34]. The discoblock we used has been compared with the pain reaction at discography and found to be a better selection instrument , although it is not validated. Nor has the use of temporary external fixation proven to be of value for selecting the proper disc . It could therefore be said that the method we used, discoblock, may be as good or as bad as any other method.
If a model patient representing segmental, discogenic pain were to be established based on our analysis of the preoperative symptoms and signs of the patients showing much improvement 2 years after surgery, the most important would be: back pain originating in the midline of the spine, being aching in character, with provocation of stabbing pain in the same area with sudden movements. Besides, in most patients the back pain should be combined with diffuse pain radiation down one or both legs, even to the toes, often with paraesthesia and also bladder dysfunction with frequency.
Our observation in the present study that CLBP patients showing a good outcome two years after fusion surgery present with a fairly uniform pattern of symptoms and signs does not rule out the possibility that patients with divergent symptoms and signs may also benefit from a fusion operation. This, however, must then be analysed in a similar way.
One weakness of our study is the use of Surgibone (calf bone) as transplant without internal fixation. This resulted in many cases of defective bony healing. Re-operation of patients in the “good outcome group” using autologous bone resulted in bony healing, and most of these patients had a good outcome. Patients in the “poor outcome group” who were subjected to re-operations without success differed somewhat from the “good outcome group” regarding their back symptoms. There may have been reasons other than discogenic pain for their complaints, alternative, segment selection may have been wrong.
Patients within the CLBP group reporting (1) back pain origin in the midline and (2) with provocation of stabbing pain in that area at sudden movements, and also (3) showing localized interspinal tenderness in the same area with provocation of the deep back pain by pressure and by tapping a neighbouring spinous process, may benefit from fusion surgery. Our results are previously described in a preliminary report .
Specified symptoms related to a painful segment/disc are not previously reported.
We analysed symptoms of patients with back pain relief following fusion operation.
A symptom triad emerged: dominating aching midline pain, stabbing at sudden movements.
Most patients also had diffuse leg pain radiation and often bladder frequency.
Our results may improve selection of patients suitable for fusion surgery.
Fritzell P, Hägg O, Wessberg P, Nordwall A. 2001 Volvo award winner in clinical studies: lumbar fusion versus nonsurgical treatment for chronic low back pain. Spine 2001;26:2521–34. PubMedGoogle Scholar
Brox JI, Sörensen R, Friis A, Nygaard Ö, Indahl A, Keller A, Ingebrigtsen T, Eriksen H, Holm I, Koller AK, Riise R, Reikerås O. Randomized clinical trial of lumbar instrumented fusion and cognitive intervention and exercises in patients with chronic low back pain and disc degeneration. Spine 2003;28: 1913–21. CrossrefPubMedGoogle Scholar
Fairbank J, Frost H, Wilson-MacDonald J, Yu L-M, Barker K, Collins R. Randomised controlled trial to compare surgical stabilisation of the lumbar spine with an intensive rehabilitation programme for patients with chronic low back pain: the MRC spine stabilisation trial. BMJ 2005;330:1233–9. PubMedCrossrefGoogle Scholar
Brox JI, Reikerås O, Nygaard Ö, Sörensen R, Indahl A, Holm I, Keller A, Ingebrigtsen T, Grundnes O, Lange JE, Friis A. Lumbar instrumented fusion compared with cognitive intervention and exercises in patients with chronic back pain after previous surgery for disc herniation: a prospective randomized controlled study. Pain 2006;122:145–55. CrossrefPubMedGoogle Scholar
Ohtori S, Koshi T, Yamashita M, Yamashita M, Yamauchi K, Inoue G, Suzuki M, Orita S, Eguchi Y, Ochiai N, Kishida S, Takaso M, Kuniyoshi K, Aoki Y, Ishikawa T, Arai G, Miyagi M, Kamoda H, Suzuki M, Nakamura J, Toyone T, Takahashi K. Surgical versus nonsurgical treatment of selected patients with discogenic low back pain. Spine 2011;36:347–54. CrossrefPubMedWeb of ScienceGoogle Scholar
Svensson E, Schillberg B, Kling A-M, Nyström B. The balanced inventory for spinal disorders. The validity of a disease specific questionnaire for evaluation of outcomes in patients with various spinal disorders. Spine 2009;34:1976–83. Google Scholar
Svensson E, Schillberg B, Kling A-M, Nyström B. Reliability of the Balanced inventory for spinal disorders, a questionnaire for evaluation of outcomes in patients with various spinal disorders. J Spinal Disord Tech 2012;25: 196–204. CrossrefPubMedWeb of ScienceGoogle Scholar
Svensson E, Schillberg B, Zhao X, Nyström B. Responsiveness of the Balanced Inventory for Spinal Disorders. A questionnaire for evaluation of outcomes in patients with various spinal disorders. J Spine Neurosurg 2015;4:2, http://dx.doi.org/10.4172/2325-9701.1000184.
Enblom M, Hansson J, Moström U, Nyström B. Benläkningskontroll efter fusionskirurgi i ländryggen. Datortomografi med tunna snitt och låg stråldos. Swed Soc Med Radiol Förhandlingar 1995;32:76–80. Google Scholar
Enblom M, Moström U, Hansson J, Nyström B. Assessment of fusion in the lumbar spine with thin slice low dose CT. Ups J Med Sci 1998;54(Suppl.):52–3. Google Scholar
Amundsen T, Weber H, Nordal HJ, Magnaes B, Abdelnoor M, Lilleas F. Lumbar spinal stenosis: conservative or surgical management?: a prospective 10-year study. Spine 2000;25:1424–35. CrossrefPubMedGoogle Scholar
Hägg O, Fritzell P, Odén A, Nordwall A. Simplifying outcome measurement. Evaluation of instruments for measuring outcome after fusion surgery for chronic low back pain. Spine 2002;27:1213–22. CrossrefPubMedGoogle Scholar
Colhoun E, McCall IW, Williams L, Cassar Pullicino VN. Provocation discography as a guide to planning operations in the spine. J Bone Joint Surg Br 1988;70-B:267–71. Google Scholar
Schwarzer AC, Aprill CN, Derby R, Fortin J, Kine G, Bogduk N. The relative contributions of the disc and zygapophyseal joint in chronic low back pain. Spine 1994;19:801–6. PubMedCrossrefGoogle Scholar
Schwarzer AC, Aprill CN, Derby R, Fortin J, Kine G, Bogduk N. The prevalence and clinical features of internal disc disruption in patients with chronic low back pain. Spine 1995;20:1878–83. PubMedCrossrefGoogle Scholar
Zdeblick TA. Discogenic back pain. In: Rothman RH, Simeone FA, editors. The spine. Philadelphia: WB Saunders; 1999. p. 749–65 [Chapter 28]. Google Scholar
Madan S, Gundanna M, Harley JM, Boeree NR, Sampson M. Does provocative discography screening of discogenic back pain improve surgical outcome? J Spinal Disord Tech 2002;15:245–51. CrossrefPubMedGoogle Scholar
Carragee EJ, Lincoln T, Parmar VS, Alamin T. A gold standard evaluation of the “discogenic pain” diagnosis as determined by provocative discography. Spine 2006;31:2115–23. Web of ScienceCrossrefPubMedGoogle Scholar
Lee CK, Vessa P, Lee JK. Chronic disabling low back pain syndrome caused by internal disc derangements. The results of disc excision and posterior lumbar interbody fusion. Spine 1995;20:356–61. PubMedCrossrefGoogle Scholar
Hancock MJ, Maher CG, Latimer J, Spindler MF, McAuley JH, Laslett M, Bogduk N. Systematic review of tests to identify the disc, SIJ or facet joint as the source of low back pain. Eur Spine J 2007;16:1539–50. PubMedCrossrefWeb of ScienceGoogle Scholar
Willems PC, Staal JB, Walenkamp GHIM, de Bie RA. Spinal fusion for chronic low back pain: systematic review on the accuracy of tests for patient selection. Spine J 2013;13:99–109. CrossrefPubMedWeb of ScienceGoogle Scholar
Ohtori S, Kinoshita T, Yamashita M, Inoue G, Yamauchi K, Kosci T, Suzuki M, Orita S, Eguchi Y, Nakamura S, Yamagata M, Takaso M, Ochiai N, Kishida S, Aoki Y, Takahashi K. Results of surgery for discogenic low back pain. A randomized study using discography versus discoblock for diagnosis. Spine 2009;34:1345–8. PubMedCrossrefGoogle Scholar
Elmans L, Willems PC, Anderson PG, van Limbeek J, de Kleuver M, van der Schaaf D. Temporary external transpedicular fixation of the lumbosacral spine. A prospective, longitudinal study in 330 patients. Spine 2005;30:2813–6. PubMedCrossrefGoogle Scholar
Nyström B. Lumbal segmentell smärta I. Anamnestiska uppgifter och kliniska fynd. Hygiea 1989;98:253. Google Scholar
About the article
Published Online: 2017-12-29
Conflict of interest: The authors have no conflict of interest.
Ethical issues: The patients gave their informed consent to the study. Ethical Boards did not exist at the time this study was undertaken.
Citation Information: Scandinavian Journal of Pain, Volume 16, Issue 1, Pages 213–220, ISSN (Online) 1877-8879, ISSN (Print) 1877-8860, DOI: https://doi.org/10.1016/j.sjpain.2016.10.007.
© 2016 Scandinavian Association for the Study of Pain. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. BY-NC-ND 4.0