Predictors for a negative surgical outcome in patients with disc degenerative disease (DDD)

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Predictors for a negative surgical

outcome in patients with disc

degenerative disease (DDD)

Martin Näslund

THE SWEDISH SCHOOL OF SPORT

AND HEALTH SCIENCES

Master Degree Project 8:2015

Master program in Sports Science

Supervisor: Eva Kosek

Examiner: Karin Söderlund

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Abstract

Aim

The aim of this study was to identify predictive factors for negative treatment outcome defined as high disability ratings in patients undergoing spine surgery for disc degenerative disease (DDD)

Method

Patients were consecutively recruited from a waiting list for surgery at Stockholm Spine Center. The analysed cohort consisted of 212 patients (109 women and 103 men, 25-65 years old). They all had radiologically demonstrated degenerative changes in the lumbar spine at one or both of the two lower levels (L4/L5 and/or L5/S1). All subjects gave their written informed consent to participate. The patients completed validated self-assessment questionnaires regarding anxiety and depression (HAD), catastrophizing (CSQ), kinesiophobia (TSK), and disability (ODI). Pain intensity ratings were performed separately for the back and the legs using the visual analogue scale (VAS). Pressure pain thresholds were assessed at eight different body sites with pressure algometry. The participants were assessed shortly before surgery and the questionnaires were mailed to the patients at one year follow up. The primary outcome variable was ODI at one year; the secondary outcome was change in ODI.

Results

Following surgery, there were statistically significant improvements regarding all the self-reported symptoms, including the outcome measure ODI. A higher value on ODI and higher ratings of leg pain preoperatively were found to predict a higher ODI score postoperatively.

Conclusion

We found reduced pain intensity ratings in the back and leg, reduced ratings of anxiety, depression, catastrophizing and kinesiophobia as well as reduced disability ratings following surgery compared to baseline. Furthermore, we found two

predictors for postoperative disability, namely preoperative leg pain and disability, i.e., high leg pain and high disability ratings before surgery predicted high disability

ratings following surgery. Our data stress the importance of pain analysis and diagnostics before surgery and indicate that pain drawings could be an initial tool to see if pain location is consistent with the radiological findings.

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Sammanfattning

Syfte och frågeställningar

Syftet med denna studie var att identifiera förutsägande faktorer för ett negativt behandlingsutfall för ryggkirurgi hos patienter med väl karaktäriserad ländryggsmärta på degenerativ basis (segmentell rörelsesmärta (SRS)).

Metod

Försökspersoner rekryterades från en väntelista på Stockholm Spine Center. Den analyserade kohorten bestod av 212 patienter (109 kvinnor och 103 män, 25-65 år gamla). Alla hade radiologiskt påvisade degenerativa förändringar i ländryggen på en eller två av de nedre ländryggsnivåerna(L4/L5 och/eller L5/S1). Alla deltagare gav sitt skriftliga samtycke till deltagande. Patienterna fyllde i validerade

självskattningsformulär gällande ångest och depression (HAD), katastroftänkande (CSQ), rörelserädsla (TSK) och funktionsförmåga (ODI). Smärtintensitet skattades separat för rygg och ben genom användande av visuell analog skala. Tryckömhet mättes på åtta olika lokalisationer på kroppen med hjälp av tryckalgometri.

Patienterna fyllde i formulären just innan operationen och formulären mailades sedan hem till patienterna för en ett-års uppföljning. Det primära effektmåttet var ODI efter ett år och det sekundära effektmåttet var förändring i ODI.

Resultat

Patienterna uppvisade statistiskt signifikanta resultat gällande alla självskattade formulär efter operationen, inklusive effektmåttet ODI. Ett högt värde på ODI och högt skattad bensmärta innan operation visades predicera ett högre postoperativt värde på ODI.

Slutsats

Vi fann minskad smärtintensitet i rygg och ben, sänkta skattningar gällande ångest, depression, katastroftankar och rörelserädsla såväl som ökning av funktionsförmåga vid skattning efter operation i jämförelse med utgångsvärdet. Vidare fann vi två prediktorer för nedsatt funktionsförmåga postoperativt, nämligen preoperativ bensmärta och nedsatt funktion preoperativt dvs. högt skattad bensmärta och lågt skattad funktion före operationen predicerade lågt skattad funktion efter operationen. Våra data stödjer vikten av smärtanalys och smärtdiagnostik vid kirurgiska

bedömningar och indikerar att smärtritningar skulle kunna vara ett hjälpmedel för att se om smärtutbredningen motsvarar de radiologiska fynden.

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1. Background

1.1 Low back pain

Low back pain is a common condition in the population and approximately 84 percent of the population are affected during their life time, although the cause of the pain might vary (Willems 2014). In the literature, low back pain is described as pain, muscle tension or stiffness, with or without leg pain (Koes, Van Tulder & Thomas 2006). Low back pain is divided into two main categories, specific or non-specific. Whereas non-specific low back pain is defined by a lack of a specific cause, which means that the origin of the pain is unknown, specific low back pain involves a specific pathophysiological mechanism, such as fracture or tumour (Koes et al 2006; Sahu 2014). Approximately ninety percent of all patients suffering from low back pain are classified as having non-specific low back pain (Koes et al 2006)

Patients who suffer from non specific low back pain have a relatively good prognosis for recovery, approximately eighty-ninety percent show full recovery within 6 weeks from the onset of pain (Van Tulder, Becker, Bekkering, Breen Del Real & Hutchinson 2006). After the initial 6 weeks, entitled as the acute phase, the potential for recovery decreases and patients are at higher risk of developing a chronic state which is defined as duration of pain from the same area, lasting longer than 12 weeks (Van Tulder 2006). Even if the pain diminishes within the acute phase, the patient is more likely to develop a similar condition further on in their life (Statens beredning för medicinsk utvärdering 2000). Recent studies have supported that non-specific chronic low back pain could, to some extent derive, from hypersensitivity in the central nervous system, which affects the immune system and through a bi-directional communication, creates a painful (Miyagi, Millecamps, Ohtori, Takahashi & Stone 2014).

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1.2 Disc degeneration

The cause of low back pain is difficult to determine since there is typically only a weak correlation to magnetic resonance imaging (MRI) findings such as modic changes and disc degeneration (Sahu 2014; Berg, Hellum, Gjertsen, Neckelmann & Johnsen 2013). However, disc degeneration is prevalent and has been reported in approximately 40% of all patients suffering from low back pain (Binch, Cole, Breakwell, Micheal, Chiverton, Cross & Le Maitre 2014) and the presence of disc degeneration reaches up to eighty five percent within the group of patients suffering from chronic low back pain (Willems 2014). Disc degeneration has been associated with multiple potential causes such as genetic factors, smoking, ageing and physical loading. For a long time, physical loading was considered a major cause of disc degeneration, but research findings during the last twenty years have proven a much stronger correlation to genetic factors (Burgmeier, Hsu 2014).

Disc degeneration is in most cases asymptomatic and forms a natural part of ageing. About ninety percent of the population above fifty years of age have incipient disc degeneration (Pelle, Peacock, Schmidt, Kampfschulte, Scholten & Russo 2014). Given the poor correlation between radiological changes and symptoms, it is hard to tell the difference between a painful degenerative disc from an asymptomatic

degenerative disc by radiological exams. Therefore, an accurate clinical assessment is always needed to evaluate if there is an agreement between the radiological findings and the patient’s symptoms (Iatridis, Nicoll, Michalek, Walter & Gupta 2013). One possible cause of pain has been proposed to be the ingrowth of nociceptive nerve endings into the degenerated disc creating the painful condition, the previous view has rather been that compression of the disc is the main reason for pain in degenerated discs (Binch et al 2014). Burke et al has shown that patients with pain deriving from a disc, i.e. disc degenerative disease (DDD), have more nociceptive nerve endings in the end plate and in the nucleus pulposus than a population with asymptomatic disc degeneration (Burke, Watson, Mccormack, Dowling, Walsh & Fitzpatrick 2002).

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1.3 Disability

Even if a person has radiological findings of disc degeneration that matches the clinical assessment it does not necessarily mean that a dysfunction is present. Several components decide whether the person develops symptoms and functional limitations from the condition. It has been shown that reduced selfefficacy (Oesch, Hilfiker, Kool, Bachmann & Hagen 2010), psycho-social factors such as stress, anxiety and

depression (Patrick, Emanski & Knaub 2014) and also general health status and psychiatric comorbidity are important prognostic factors for developing lingering pain conditions (Menezes Costa, Maher, Hancook, McAuley, Herbert & Costa 2012). It is noticeable that patients with chronic low back pain often score high on psychological symptoms in addition to the intensity and duration of pain. Also, about fifty percent of people with chronic low back pain obtain complementary psychological treatments beside a physical rehabilitation (Cramer, Haller, Lauche & Dobos 2012).

Many patients end up in a situation where they avoid activities and relationships important to them due to fear of pain or an expectation that the situation will deteriorate if they provoke the pain, this can be seen as an example of how

psychological factors affect the functional ability (Wand & O’connell 2008). It has been shown that low back pain leads to more years of impairment than any other condition in terms of sick leave. Beside a great suffering for the individual and his/hers family, the condition also has a large impact on society in the form of costly job absenteeism and a large health care consumption (Statens beredning för medicinsk utvärdering 2003).

1.4 Treatment

1.4.1 The bio-psycho-social model

The bio-psycho-social model is an accepted basis for the treatment of chronic low back pain. It has been shown that, in addition to biological factors, social and

psychological factors have a great impact on chronic pain conditions. This complexity creates a need for a more concerted effort. In team-based rehabilitation, with so-called

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4 multimodal teams, treatment is usually based on the bio-psycho-social model with a holistic approach to the patient's situation in mind and various professionals working together to achieve a good treatment result. Studies have shown that multimodal rehabilitation is an effective intervention regarding pain reduction, functionality and return to work in long-term follow-ups (Von der Hoeh, Voelker, Gulow, Uhle, Przkora & Heyde 2014).

1.4.2 Conservative treatment

Most of the patients suffering from low back pain are treated without a surgical intervention. They normally undergo training led by a physiotherapist, receive analgesic medicine, manual treatment and indicative advice (Machado, Maher, Herbert, Clare & McAuley 2010). Consensus is currently lacking regarding which training method that is most effective in treating non-specific low back pain as well as DDD. There is no clear answer whether it is more effective with specific and isolated training of specific abdominal muscles rather than general trunk stabilization training to accomplishing reduced pain (Searle, Spink, Ho & Chuter 2015). Research has shown that kinesiophobia (fear of movement) and fear of burdening the body predicts worse results of treatment interventions in the rehabilitation of patients with chronic low back pain (Havakeshian & Mannion 2013). Given that chronic pain often is in fact a multifactorial illness there is a need to make a detailed examination of the patients overall problems, in addition to the physical examination, to be able to make an adequate treatment plan (Ghamkhar & Kahlaee 2015).

1.4.3 Surgical treatment

In the group of patients with treatment-resistant low back pain and a radiologically proven disc degeneration matching their symptoms, there is a possibility of surgery using two different techniques, fusion or disc replacement (Willems 2014). With the insertion of a disc implant the movement in the joint is preserved, an artificial disc replaces the original, while the fusion technique creates joint immobility by fusing the two segments. Both methods have been proved to be successful in reducing disability and pain intensity in long-term follow-ups of patients with DDD (Sköld C, Tropp H,

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5 Berg S 2013). Although most patients who undergo surgery will be improved, there are always patients where the results are not as positive. Despite the fact that more than 70% of DDD patients benefit from surgery, still approximately 30% are only slightly improved, unchanged or even worse (www.SweSpine.se, cited may 18 2015). Therefore selection of patients likely to profit from spinal surgery is a most

challenging task (Don & Carragee 2008).

Patient selection

The number of patients suffering from chronic pain located to the lumbar spine is growing in the general population. It is a great source of suffering for the individual and a significant burden for society in terms of sick leave and health care costs (Willems 2014). The ability to correctly diagnose the underlying causes of pain has improved in the medical care but the difficulty of choosing which treatment is preferable persists (Iatridis et al 2013). Surgical treatments, for people with

segmentally defined degenerative changes in the lumbar spine, are today performed with good results (Berg, Tullberg & Branth 2009). However, surgical treatments are costly and there is always a risk of surgical complications. Therefore, there is a great clinical need to improve the rational of patient selection and to identify patients with a higher risk of negative treatment outcome. These patients may profit better from non-surgical treatments or may need additional treatments in order to benefit from surgery.

1.5 Aim, research questions and hypothesis

The main purpose of this study was to identify predictive factors for negative treatment outcome defined as high disability ratings one year following surgery for disc degenerative disease (DDD) (fusion or disc replacement). We hypothesized that high ratings of pain intensity, depression, anxiety, catastrophizing and kinesiophobia as well as increased pain sensitivity as assessed by pressure algometry would be associated with poor treatment outcome i.e. a low value on ODI.

The research question was to examine whether any of the questionnaires and scales used in this study (see below) and/or pressure pain algometry performed before surgery could predict a negative outcome of surgery as assessed by the ODI at one

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6 year postoperatively or by the change between ratings in ODI between the two

measurements.

2 Method

2.1 Participants

212 patients, 109 women, 103 men, age 25 - 65 years, were included in the study. They all had radiologically demonstrated degenerative changes in the lumbar spine (L4/L5 and/or L5/S1). The patients were recruited from the waiting list for surgical treatment (fusion surgery or disc replacement) at Stockholm Spine Center. The exclusion criteria consisted of:

1) Patients who previously had undergone lumbar surgery.

2) Lack of knowledge in the Swedish language to such a degree that the patient was not able to complete self-assessment forms.

3) Patients with other prominent types of pain, such as pain due to osteoarthritis in other joints, arthritis, fibromyalgia.

4) Patients with neurological diseases (multiple sclerosis, Parkinson's disease, polyneuropathy, stroke etc.).

5) Patients with other morbidity that prevented participation in the study.

In addition the patients were also included in two other studies, the results of which will be presented elsewhere. The first is a genetic study primarily designed to assess the impact of genetic factors on symptoms and treatment outcome following surgery in DDD patients. The second is a study assessing the relationship between

radiological changes, symptoms and treatment outcome. An orthopaedic surgeon graded the degenerative changes by viewing MRI and the aim was to relate them to the degree of symptoms and, at follow ups, to treatment outcome.

2.2 Research design

The study was designed as an observational study using a quantitative longitudinal design.

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2.3 Procedure and data collection

All subjects found eligible by the orthopaedic surgeons were contacted by a nurse, responsible for gathering research material. The nurse gave information about the study and made sure that all patients took part of the written information regarding the study and that they signed the informed consent. In connection with the admission to the department before surgery the subjects completed the validated self-assessment questionnaires, which tool approximately 45-60 minutes. The assessed parameters consisted of anxiety and depression (hospital anxiety and depression scale, HADS) (Bjelland, Dahl, Haug & Neckelmann 2002), the subscales of catastrophizing in the coping strategy questionnaire (CSQ) (Monticone, Ferrante, Giorgi, Galandra, Rocca & Foti 2014), kinesiophobia (Tampa scale for kinesiophobia, TSK) (Rusu, Kreddig, Hallner, Hulsebusch & Hasenbring 2014), and disability (Oswestry Disability Index, ODI) (Fairbank & Pynsent 2000). Pain intensity ratings were performed separately for the back and the legs using the visual analogue scale (VAS) (Boonstra, Schiphorst, Reneman, Posthumus & Stewart 2008). Pressure pain thresholds (PPTs) (Kosek, Ekholm & Nordemar 1993) were assessed using a pressure algometer (Somedic Sales AB), with the probe area of 1cm2 and the rate of pressure increase of approximately 50 kPa/s. The PPT test was performed, by the nurse, in connection with the

questionnaires. The subjects were examined in a sitting position. The pressure algometer was applied manually with gradually increasing pressure and the subjects were instructed to push a button as soon as the pressure sensation turned into pain. The PPTs were assessed bilaterally at m. supraspinatus, at the elbow, at the gluteal muscle and at the medial knee pad, once per site and the average was calculated and used for further analysis. One year following surgery, the same battery of

questionnaires was mailed to the patients. The primary outcome variable was ODI at one year. The ODI questionnaire has sufficient validity and reliability to be applied in a clinical population with low back problems (Davidson & Keating 2002).

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Ethical Considerations

The study was approved by the ethical committee. The study was an observational study with no influence on clinical treatment. Pressure algometry does not inflict any injury and is only associated with very brief pain experience. Therefore we do not see any major ethical issues regarding this study.

2.4 Statistical analysis

A multiple linear regression model with stepwise analysis was performed twice, with both postopertive ODI and change in ODI as dependent variable. Stastica 12 (Statsoft Inc, (USA) was used to perform the statistical analysis. Possible preoperative risk variables as HAD, CSQ, TSK, VAS back and leg, PPT and ODI were entered. In the first analysis the ODI value at one year follow up was as the dependent variable and in the second analysis the change in ODI was chosen as the dependent variable (i.e., ODI pre- ODI post). Students Paired t-test was used to assess differences between ratings of anxiety, depression, catastrophizing, kinesiophobia and disability before and one year following surgery. In accordance with previous studies we chose to use parametric tests for these analyses. Given the large number of participants no formal assessment of normal distribution was performed. Paired–Sample Wilcoxon Signed Rank Test was used for comparisons of VAS ratings. Given that our patient cohort had overall low ratings of anxiety/depression, we also chose to perform a post-hoc analysis where patients with HAD-D and HAD-A, respectively, with a sum between 11-21 (probable and manifest depression or anxiety disorder) constituted one group and patients with a score between 0-7 (no risk) and 8-10 (mild or possible depression or anxiety) were placed in the other group. We did not substitute for missing data, instead subjects with incomplete data were omitted from that particular analysis. The significance level was set to p≤0.05.

3. Results

Of the 212 included patients, 26 were missed to follow-up, so the analysed cohort consists of 186 patients.

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3.1 Effects of surgery

There were statistically significant decreases in the ratings of anxiety (HAD-A: p < 0.0001), depression (HAD-D: p < 0.0001), catastrophizing (CSQ: p < 0.0001), kinesiophobia (TSK: p < 0.0001) and disability (ODI: p < 0.0001) at one year following surgery compared to before surgery (Table 1).

Table 1: Descriptive data for the cohort of 212 (of which 26 were missed to follow-up) patients participating in the study, means and standard deviations of ratings before surgery (pre) and at one-year follow surgery (post). Occasional missing data explain differences in the number of patients. VAS = Visual analogue scale, HADD-D = HAD Depression, HADS-A = HAD Anxiety, CSQ = coping strategy questionnaire, TSK = Tampa scale for kinesiophobia, ODI = Oswestry disability index.

Mean N Std. Deviation Pair 1 preVASback 59,21 183 20,22 postVASback 15,22 183 18,13 Pair 2 preVASleg 30,16 182 27,17 postVASleg 11,29 182 18,23 Pair 3 preHAD-D 5,33 177 3,78 postHAD-D 2,84 177 3,40 Pair 4 preHAD-A 6,08 177 4,11 postHAD-A 3,84 177 4,00 Pair 5 preCSQ 2,63 143 1,24 postCSQ 1,12 143 1,20 Pair 6 preTSK 36,91 161 8,37 postTSK 30,82 161 7,69 Pair 7 preODI 37,20 186 12,14 postODI 13,26 186 12,92

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10 The results showed that surgery improved ratings of anxiety and depression. Our findings indicate that surgery had beneficial effects on the psychological symptoms. The post hoc analysis of HAD A and D respectively, divided into the two groups, HAD low (0-10) and HAD high (11-21), all showed statistically significant

improvements (p < 0,0001) between baseline and the one-year follow up (Table 2).

Table 2 shows the means and standard deviations for the groups HAD D low (n=156), HAD D high (n=21), HAD A low (n=151) and HAD A high (n=26). All differences between pre- and post surgery were statistically significant p < 0.0001.

Mean N Std. Deviation

Pair 1

PreHAD Depression Low 4,40 156 2,97

PostHAD Depression Low

2,35 156 2,92

Pair 2

PreHAD Depression High 12,24 21 0,94

PostHAD Depression High

6,52 21 4,40

Pair 3 PreHAD Anxiety Low 4,83 151 2,83

PostHAD Anxiety Low 2,88 151 3,14

Pair 4 PreHAD Anxiety High 13,35 26 2,51

PostHAD Anxiety High 9,38 26 4,00

3.2 Factors predicting post ODI

The multiple linear regression analysis with one-year ODI as a dependent variable showed that VAS leg pain was the preoperative value with the highest association, p = 0.01, followed by the factor baseline ODI, p = 0.03. No other factors turned out to have a statistically significant effect (Table 3).

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11 Table 3: Multiple linear regression model with ODI at one-year follow up as a

dependent variable.

N=169

Regression Summary for one year ODI as dependent

p-value

Intercept 0,74

Gender 0,61

PreOp- VASpain back (mm) 0,22

PreOp- VAS pain leg(mm) 0,01

PreOp-HADDepression 0,67

PreOp-HADAnxiety 0,21

PreOp-CSQAverage 0,36

PreOp-TSKTotal 0,44

PreOp- Pressure pain thresholds 0,37

PreOp-ODI 0,03

3.3 Factors predicting change in ODI

In order to assess the influence of the various factors on the degree of reductions in disability following surgery, we also performed a multiple linear regression analysis with the change in ODI as the dependent variable. We found that the baseline ODI was the preoperative value with the highest association, p < 0.0001, i.e. high ratings of disability predicted a higher degree of reduction in disability following surgery, followed by the factor preoperative VAS leg pain p = 0.01. No other factors turned out to have a statistically significant effect (Table 4).

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12 Table 4: Multiple linear regression model with change in ODI as a dependent variable.

N=169

Regression Summary for Delta ODI as Dependent

p-value

Intercept 0,74

Gender 0,61

PreOp-VAS pain back (mm) 0,22

PreOp-VAS pain leg (mm) 0,01

PreOp-HADDepression 0,69

PreOp-HADAnxiety 0,21

PreOp-CSQAverage 0,36

PreOp-TSKTotal 0,44

PreOp-Pressure pain thresholds 0,37

PreOp-ODI 0,00

4. Discussion

Surgery has been reported to be an effective intervention for the treatment of pain and disability due to disc degenerative disease (DDD) (Berg et al 2009;

www.SweSpine.se ). In accordance with this, we found statistically significant improvements regarding all of the self-reported symptoms in this study, i.e., reduced back and leg pain, anxiety, depression, catastrophizing, kinesiophobia and disability at the one year follow-up compared to baseline. The improvements in depression and anxiety ratings were not limited to patients with low preoperative ratings, i.e., 0-10 signifying no or mild/possible depression or anxiety, but were also seen in the group of patients who rated 11-21, i.e., probable and manifest depression or anxiety disorder. Interesting, especially since high ratings of anxiety and depression have been

associated with a poorer outcome of surgery (Don et al 2008). The two regression analysis, one with the postoperative ODI as the dependent factor and the other with the change in ODI as the dependent factor both identified high ratings of VAS leg pain for negative outcome. In the regression analysis with postoperative ODI as the dependent factor we also found that high preoperative ODI ratings was a statistically

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13 significant predictor for high postoperative ODI ratings while high preoperative ODI ratings were a predictor for a larger change in ODI in the analysis.

As stated above, two factors emerged as being statistically significant predictors for disability as assessed by ODI at one year following surgery for DDD. The most significant factor was high ratings of leg pain before surgery. Since patients with nerve root compression or a diagnosis of neuropathic pain were excluded from the study, the radiating leg pain is most likely explained as referred pain from the back or as pain due to a higher degree of central sensitization. There is also a risk that patients could be misdiagnosed, i.e. not having pain due to the disc degeneration, but rather pain due to other causes, for example myalgia, i.e., pain symptoms that just happen to coincide with radiological findings of disc degeneration. The latter is not unlikely given the weak correlation between radiological findings and symptoms (Berg et al 2013). Patients with other prominent painful conditions and patients diagnosed with fibromyalgia were excluded but there is still a wide spectrum of pain mechanisms which could explain symptoms beside the DDD. Our results would suggest that a thorough pain analysis as a part of the surgical examination is of great value to improve the surgical outcome. Moreover, high estimates on ODI before surgery predicted, as expected, a high value also after surgery, signifying that more severely disabled patients tended to retain a higher disability also following surgery. Our results suggest that the ability to cope with the symptoms of DDD, retaining a good function, are important for the outcome of surgery and raise the question whether presurgical interventions aiming at improving function could improve surgical outcome. However, we saw that more severely disabled patients also had a greater improvement on ODI than patients with lower preoperative ratings on ODI. This is probably explained by a ceiling effect for patients with low ratings of disability since they had less potential for improvement due to their already low ODI ratings. Further supporting our findings from the first regression analysis are the results showing that high ratings of leg pain predicted lesser improvement of function following surgery, i.e., low change in ODI.

Our patient cohort had high average back pain ratings before surgery (approx. 60 mm on a 100 mm VAS) and the pain was significantly reduced following surgery (average 15 mm), corresponding to a 75% reduction of back pain intensity. Similar to back

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14 pain, we also saw reductions of leg pain from an average of 30 mm before surgery to 11 mm one year following surgery, corresponding to a 63% pain reduction. The results indicate significant pain reductions in the back as well as the leg, despite the fact that leg pain was a negative predictor. In this study we did not see any

statistically significant predictive effects of preoperative anxiety and depression, catastrophizing or kinesiophobia on postoperative ODI or change in ODI. High ratings of anxiety and depression have previously been associated with a poorer outcome of surgery (George & Beneciuk 2015) and catastrophizing as well as kinesiophobia have been reported to be negative predictors of treatment outcome in chronic pain patients (Mannion & Elfering 2006). However, in our study it appears as if the surgical treatment of DDD, in addition to the reduction of pain and disability also lead to reduced psychological symptoms. Although no definite conclusions regarding causality can be drawn, it is reasonable to assume that the reductions of DDD symptoms such as pain lead to the improvements in mood. Also it seems likely that by reducing the pain, fear of movement was alleviated.

Methodological considerations

PPT, which is used in this study, is an established method with good reliability over time and a strength in this study is that the measurements were made by the same person. Well validated forms were chosen to evaluate the factors important for patients with DDD and we refrained from substituting missing data.

Furthermore, these patients are well characterized and therefore constitute a relatively homogeneous population which is a strength in a mechanistic study. The study is conducted at a highly specialized clinic, which ensures that the difference between the surgeons is relatively small. SSC has very good results regarding DDD - surgery, i.e. variability due to technically deficient surgery is minimal. Therefore, the cohort is suitable for studying other parameters of interest.

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4.1 Limitations

In order to reduce heterogenicity, rigorous inclusion and exclusion criteria were applied in this study, for example patients with previous low back surgery and patients with other painful co-morbidities were excluded. Thus the present results cannot automatically be generalized to any clinical population of DDD patients.

5. Conclusion

In conclusion we found reduced pain intensity ratings in the back and leg, reduced ratings of anxiety, depression, catastrophizing and kinesiophobia as well as reduced disability following surgery compared to baseline. Furthermore, we found two predictors for postoperative function, namely preoperative leg pain intensity and function, i.e., high leg pain and low function before surgery predicted lower function following surgery. Our data stress the importance of pain analysis and diagnostics before surgery and suggest the use of pain drawings as an initial tool to see if the localization of pain is consistent with what would be expected from the radiological findings. Further studies are needed to see if a more specific preoperative pain assessment could be developed to improve presurgical assessments and thus patient selection for DDD surgery. Also, it would be interesting to study if interventions aiming at reducing disability before surgery would be beneficial for the treatment outcome following surgery.

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6. Acknowledgements

I would like to express great gratitude to my supervisor Professor Eva Kosek for her invaluable guidance and generosity with her great knowledge throughout this master project. Great gratitude is also directed to MD, PhD Martin Skeppholm, for his enthusiastic approach to science and for taking the time out of his busy schedule to help me with the statistical analysis. Also, a special thanks to my employer,

Stockholm Spine Center for giving me the opportunity to develop in my professional role.

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Predictors for a negative surgical outcome in patients with disc degenerative disease (DDD)