Rehabilitation following surgery: Clinical and psychological predictors of activity
limitations
Short running title: Activity limitations after surgery.
Rachael Powell1, Marie Johnston2, W Cairns Smith3, Peter M King4, W Alastair
Chambers5, Lorna McKee6, Julie Bruce7.
1
School of Psychological Sciences and Manchester Centre for Health Psychology, University
of Manchester, Manchester, UK.
2
Health Psychology, University of Aberdeen, Aberdeen, UK.
3
School of Medicine and Dentistry, University of Aberdeen, Aberdeen, UK.
4
Department of Surgery, Aberdeen Royal Infirmary, Aberdeen, UK.
5
Department of Anaesthesia, Aberdeen Royal Infirmary, Aberdeen, UK.
6
Health Services Research Unit, Division of Applied Health Sciences, University of
Aberdeen, Aberdeen, UK.
7
Warwick Clinical Trials Unit, Division of Health Sciences, Warwick Medical School, The
University of Warwick, Coventry, UK.
Corresponding author:
Dr Rachael Powell
School of Psychological Sciences and Manchester Centre for Health Psychology,
University of Manchester,
Coupland 1 Building,
Oxford Road,
Manchester, M13 9PL
UK
Telephone: +44 121 204 4188
Email: rachael.powell@manchester.ac.uk
1
Abstract
Purpose/Objective: Activity limitations following surgery are common and patients may
have an extended period of pain and rehabilitation. Inguinal hernia surgery is a common
elective procedure. This study incorporated fear avoidance models in investigating cognitive
and emotional variables as potential risk factors for activity limitations at 4 months after
inguinal hernia surgery.
Research Design/Method: This was a prospective cohort study, predicting activity
limitations 4 months postoperatively (T3) from measures taken before surgery (T1) and 1
week after surgery (T2). The sample size at T1 was 135; response rates were 89% and 84%
at T2 and T3 respectively. Questionnaires included measures of catastrophizing, fear of
movement, depression, anxiety, optimism, perceived control over pain, pain and activity
limitations. Biomedical and surgical variables were recorded. Predictors of T3 activity
limitations from T1 and T2 were examined in hierarchical multiple regression equations.
Results: Over half of participants (57.7%) reported activity limitations due to their hernia at
4 months after surgery. Higher levels of activity limitation were significantly predicted by
older age, higher pre-operative activity limitations, higher pre-operative anxiety, and more
severe post-operative pain and depression scores.
Conclusions/Implications: Interventions to reduce pre-operative anxiety and post-operative
depression may lead to reduced 4-month activity limitations. However, the additional
variance explained by psychological variables was low (ΔR2 = 0.05). Our models, which
included biomedical and surgical variables, accounted for less than 50% of the variance in
activity limitations overall therefore further investigation of psychological variables,
particularly cognitions related specifically to activity behavior, would be merited.
2
Keywords
Hernia surgery; inguinal hernia; activity limitations; functional limitations; depression; fear
avoidance.
Impact

It has previously been demonstrated that some people experience delayed recovery
and persisting activity limitations after hernia repair surgery, but little research has
been conducted which incorporates psychological models in predicting such
limitations.

This study has identified pre-operative anxiety and post-operative depression as
independent predictors of activity limitations four months after hernia surgery after
accounting for pain, previous activity limitations and biological and surgical
variables.

Rehabilitation interventions targeting pre-operative anxiety and depressed mood in
the acute postoperative period might assist in promoting postoperative rehabilitation
and reduce activity limitations after hernia surgery. Nevertheless, the models utilized
in the present study left much variance in activity limitations to be accounted for. A
worthy direction for further research would be to investigate beliefs about activity.
3
Introduction
Chronic post-surgical pain after hernia surgery has been associated with functional
limitations and in this paper we investigate predictors of persistent limitations in order to
inform rehabilitation programs. In 2009-2010, over 71,000 surgical repairs were completed
for inguinal hernia in England alone; 93% of these were in men (The NHS Information
Centre, 2010). Rutkow and Robbins (1993) reported that approximately 680,000 hernia
repair operations were performed annually in the USA. However, a significant proportion of
patients experience activity limitations and chronic post-surgical pain following hernia
surgery, defined as pain persisting for at least three months (International Association for the
Study of Pain Subcommittee on Taxonomy, 1986). In a review of 40 studies, Poobalan et al.
(2003) found that prevalence of chronic pain after inguinal hernia surgery ranged from 0 to
54% depending upon the method and timing of assessment.
Courtney, Duffy, Serpell and O’Dwyer (2002) followed up people with severe pain three
months after hernia surgery and found that 71% still experienced pain two and a half years
later. This persistent pain was reported to be disabling and to interfere with activities
including walking and sleeping at all levels of severity, although the impact was greatest in
those reporting severe pain. Bay-Nielsen et al. (2001) found 29% of patients reported pain
one year after inguinal hernia surgery and for 11% this pain affected their work or leisure
activity. As will be discussed below, psychological factors have been demonstrated to
predict disablement in various health contexts. Psychological factors likely to be important
include fear, anxiety and catastrophizing (as encompassed within fear-avoidance models),
depression, control cognitions and optimism.
Fear avoidance models could have important implications for individuals in the recovery and
rehabilitation phase after surgery. These models suggest that the association between pain
4
and activity limitation is mediated by psychological variables (Kori, Miller, & Todd, 1990;
Lethem, Slade, Troup, & Bentley, 1983; Philips, 1987). It is proposed that people who avoid
activity that causes pain do not reduce their fear of pain through exposure to the pain
stimulus. Reduced activity may then lead to physical consequences such as loss of muscle
strength (Bortz, 1984). Thus, pain, activity and fear avoidance are linked in a negative spiral.
People who catastrophize about pain, defined as those who have ‘an exaggerated negative
orientation toward noxious stimuli’ (Sullivan, Bishop, & Pivik, 1995) are proposed to be
more likely to experience pain-related fear and anxiety, to avoid activities that are associated
with pain and thus to experience higher levels of disability (Leeuw et al., 2007; Vlaeyen,
Kole-Snijders, Boeren, & van Eek, 1995). Archer et al. (2011) found that post-operative, but
not pre-operative, fear of movement predicted post-operative disability in people undergoing
spinal surgery.
Negative emotions more generally have been demonstrated to predict slower recovery of
activity. Negative affect was found to predict activity limitations in people recovering from
stroke (Powell, Johnston, & Johnston, 2008) and may also be relevant when recovering from
surgery. Higher levels of depression predicted worse activity limitations after coronary artery
bypass graft surgery (Kendel et al., 2010). Depression measured before surgery predicted
activity limitations two months after surgery, and depression two months after surgery
predicted activity limitations at one year after surgery. Seebach et al. (2012) found that
negative affect and depression measured six weeks after discharge following spinal surgery
predicted disability at three months post-discharge.
From a fear-avoidance perspective, it is likely that someone who perceives pain as
controllable or manageable would be less anxious and fearful about activities that might lead
to pain. Pain ‘coping efficacy’ has been associated with increased physical functioning at six
5
months after knee replacement surgery (Engel, Hamilton, Potter, & Zautra, 2004). It is,
therefore, important to consider the role of perceptions of control over pain when
investigating return to physical activity and function after surgery.
Moving from pain-specific cognitions to a more general perspective, Scheier and Carver
(1985) argue that generalized expectancies (optimism) are important because situations that
people encounter may require complex solutions with multiple components rather than a
specific behavior. Thus, generalized expectancies may be important in predicting response to
a novel situation, where a person has no experience on which to base specific expectancies.
For many, the process of surgery, recovery and rehabilitation is a novel experience, and there
are a range of activity behaviors that an individual must regain. Optimism has predicted
return to normal activity after coronary artery bypass surgery (Scheier et al., 1989) and
recovery after various elective operations (Peters et al., 2007).
There is emerging evidence that psychological factors contribute to activity recovery after
elective surgery. This prospective study aimed to investigate predictors of activity recovery
at four months after inguinal hernia repair surgery in order to determine whether a model
incorporating psychological constructs alongside biological factors might improve our
understanding of activity limitation during the rehabilitation period and to identify
opportunities for intervention. In particular, we wanted to examine the impact of pre- and
post-operative cognitive and emotional factors on activity recovery, independently of the
impact of pain.
We hypothesized that activity limitations at four months after surgery would be predicted by
higher anxiety, depression, catastrophizing and fear of movement and lower optimism,
perceptions of control over pain, and coping with pain by increasing activity.
6
Methods
Design
The study design was a prospective cohort study of people undergoing inguinal hernia
surgery. Clinical and questionnaire data were collected at three time points: before surgery
(Time 1,T1), one week after surgery (Time 2, T2) and four months after surgery (Time 3,
T3). Questionnaires included measures of pain and emotion and cognitive variables which
were used to predict T3 activity limitations.
Participants
People undergoing inguinal hernia surgery at two hospitals in North East Scotland between
December 2006 and March 2008 were invited to take part. Recruitment packs were sent to
355 patients by hospital administrative staff approximately two weeks before surgery. This
study was approved by Grampian Research Ethics Committee and NHS Grampian Research
and Development.
Measures
Activity Limitations
SF-36 Physical Functioning Subscale (SF-36 PF); Version 2, Acute Form (Ware, Kosinski, &
Dewey, 2000) (All time points)
The SF-36 is ‘the most widely-used health status questionnaire in the world’ (Ware et al.,
2000, p6) and has received substantial psychometric evaluation since it was published in
1988 (Ware, 1988). The physical functioning subscale asks participants to indicate the extent
to which their health limits them on ten activities e.g. ‘Vigorous activities such as running,
lifting heavy objects, participating in strenuous sports’, ‘lifting or carrying groceries’ and
‘bathing or dressing yourself’. Participants indicate whether they are limited a lot, limited a
7
little or not limited at all for each item. The standard scoring procedures were followed,
yielding scores on a scale from 0 to 100, where higher scores indicate fewer limitations.
Pollard, Johnston and Dieppe (2006) classified SF-36 items according to the ICF definitions
of impairment, activity limitations and participation (World Health Organisation, 2001). In
the SF-36 PF subscale, all items were found to assess activity limitations with three items
also assessing participation (details in personal communication from Pollard, 2010). The SF36 PF subscale has been used to assess postoperative activity recovery (e.g. Engel et al.,
2004; Kendel et al., 2010). In the present data set, Cronbach’s alpha for SF-36 PF was 0.87,
0.89 and 0.88 for T1, T2 and T3 respectively. SF-36 PF was the primary outcome measure in
all multiple regression analyses.
Hernia Physical Functioning (Hernia PF) (All time points)
The SF-36 PF detects all-cause activity limitation. In order to describe the activity limitation
experienced by participants which they attributed specifically to their hernia, the Hernia PF
measure was devised: a 10-item scale based on the SF-36 PF. Participants were asked to
what extent they were limited by their hernia for the same activities as described by the SF36 PF. The response scale and scoring method described for the SF-36 PF were followed.
Cronbach’s alpha = 0.87, 0.88, 0.82 for T1, T2 and T3 respectively. This measure was used
descriptively and as an outcome measure for secondary, exploratory analyses.
Emotional and cognitive variable measures
Anxiety and Depression: Hospital Anxiety and Depression Scale (HADS) (Zigmond & Snaith,
1983) (T1 and T2)
The HADS was designed to assess anxiety and depression without being confounded by
somatic symptoms indicating physical disorders. The scale contains 14 items, seven to assess
depression and seven for anxiety. Good psychometric properties have been reported
8
(Johnston, Pollard, & Hennessey, 2000; Moorey et al., 1991; Zigmond & Snaith, 1983).
Higher scores indicate higher anxiety or depression. In the present sample, the scales had
acceptable internal consistency: Cronbach’s alphas were 0.87, 0.82 for Anxiety and 0.80,
0.79 for Depression at T1 and T2 respectively.
Fear of Movement: Tampa Scale for Kinesiophobia (TSK-11) (Woby, Roach, Urmston, &
Watson, 2005) (T1 and T2)
The TSK was developed to assess pain-related fear, and the impact of that fear on movement.
Woby et al. (2005) reduced the original TSK (Miller, Kori, & Todd, 1991) to an 11-item
scale and demonstrated that its psychometric properties were similar to the original 17-item
scale. As some people with a hernia experience little or no pain the scale was split into the
eight items that do not assume the person to have pain (e.g. ‘Pain always means I have
injured my body’) and the remaining three items that assume the individual is experiencing
pain (e.g. ‘I wouldn’t have this much pain if there weren’t something potentially dangerous
going on in my body’). All participants were asked to complete the eight items that do not
assume pain; participants who were painfree were directed to skip the three items that assume
pain. The reliabilities of the full, 11-item measure and the shortened, 8-item measure were
compared: at T1 Cronbach’s alpha = 0.77 and 0.79; at T2 Cronbach’s alpha = 0.76 and 0.82
respectively. The correlation between the 11- and 8-item scales was extremely high at both
time points (r=0.97 (T1), r=0.97 (T2), p<0.001 each time). The 8-item measure was used in
all analyses.1 Higher scores indicate greater fear of movement.
Catastrophizing: from Pain Coping Strategies Questionnaire (CSQ) (Rosenstiel & Keefe,
1983) (T1 and T2)
1
A sensitivity analysis was conducted, entering the full TSK-11 scores into the Stage 3 multiple regression with
primary outcome SF-36 PF). Findings were similar with both measures.
9
The CSQ includes a 6-item subscale assessing Catastrophizing when feeling pain, e.g. ‘It is
terrible and I feel it is never going to get any better’. Items were scored on a scale from 0
(never do that) to 6 (always do that). In the present data set, Catastrophizing yielded
Cronbach’s alphas of 0.73 and 0.91. However, the data were highly skewed (T1 skew = 2.15,
kurtosis = 5.2; T2 skew = 3.8; kurtosis = 17.9), with skew persisting after transformation.
Inspection of the data showed that high numbers of participants scored 0 (62 of 117 preoperatively; 55 of 113 post-operatively). A bivariate Catastrophizing score was therefore
calculated: participants who scored 0 were allocated 0 (non-catastrophizers), all other scores
were allocated 1 (catastrophizers). The split was placed between scores of 0 and 1 on logical
grounds as this separated those who responded ‘never do that’ to all items of catastrophizing
from those who reported any degree of catastrophizing.
Increasing Activity, Control, Ability to Decrease Pain (CSQ) (Rosenstiel & Keefe, 1983) (T1
and T2)
In addition to the Catastrophizing sub-scale, the other sub-scales of the ‘Helplessness’
dimension of the CSQ questionnaire were used: Increasing Activity, Control of Pain and
Ability to Decrease Pain. The Increasing Activity subscale consisted of 6 items assessing
various activities as responses to feeling pain, e.g. ‘I do anything to get my mind off the
pain’. Items were scored on a scale from 0 (never do that) to 6 (always do that). Higher
scores indicate greater use of increasing activity as a pain coping strategy. In the present data
set, Increasing Activity produced Cronbach’s alphas of 0.80 and 0.73 at T1 and T2
respectively. Control of Pain consists of a single item: ‘On an average day, how much
control do you feel you have over your pain?’ with responses on a scale from 0 (no control)
to 6 (complete control). Ability to Decrease Pain is also measured with a single item: ‘On an
average day, how much are you able to decrease your pain?’ with responses from 0 (can’t
decrease it at all) to 6 (can decrease it completely).
10
Optimism: Life Orientation Test (LOT, Scheier & Carver, 1985) (T1 and T2)
Scheier and Carver (1985) designed the LOT to measure dispositional optimism. The fulllength scales consists of 8 items but items 4 and 8 may be used on their own (Johnston,
Wright, & Weinman, 1995); these two items were used in the present study: 1:‘I always look
on the bright side’ and 2: ‘I hardly ever expect things to go my way’. Responses are given on
5-point scales from ‘I agree a lot’ to ‘I disagree a lot’. Item 2 was reverse-scored and the two
items were summed such that high scores indicate greater optimism. Correlations between
the two items were r=0.30 and r=0.35 (p<0.001) for both correlations), T1 and T2
respectively.
Pain
McGill Pain Questionnaire (MPQ, Melzack, 1975) (T1 & T2)
Psychometric properties of the MPQ were demonstrated by Melzack (1975). The present
study used the measure Number of Words Counted (NWC) in analysis. NWC is derived by
asking participants to select words that describe their pain from a list of 78 descriptors.
Descriptors are divided into 20 subclasses; participants can only select a single word from
any category therefore pain scores range from 0 to 20, with higher scores indicating greater
pain.
Use of painkiller medication (T2).
Participants were asked whether they were taking pain-killer medication (Yes/No).
Surgical variables
11
Medical records were checked to confirm the type of surgery (open or laparoscopic, primary
or recurrent), surgery duration and anesthetic used during the procedure (general, local or
both). The type of mesh was also recorded and categorized as ‘lightweight’ or ‘standard
weight’. At T3, participants reported retrospectively whether or not they had experienced
any complications after surgery. The following time period data were recorded: a)
Completion of T1 questionnaire to operation; b) Operation to T2 questionnaire; c) Operation
to T3 questionnaire; d) Nights in hospital post-operatively.
Individual biological baseline measures
Participants reported their age, height and weight at T1. Height and weight were used to
calculate Body Mass Index (BMI).
Procedure
The recruitment packs sent to participants two weeks pre-operatively included an information
sheet, consent form and the pre-operative, T1 questionnaire. Participants also received a prepaid envelope with which to return the completed consent form and questionnaire to the
research team. On sending out packs, administrative staff recorded the non-identifiable
details of location of surgery (right, left, bi-lateral), gender, year of birth and age. A
researcher posted follow-up questionnaires at one week (T2) and four months (T3) after the
surgery date. Reminder questionnaires were posted two weeks after the first mailing for T2
and T3 questionnaires.
Statistical Analysis
In the event of missing data, following the instructions of the SF-36 manual (Ware et al.,
2000), if participants answered at least 50% of the items in a scale, the average score across
completed items in that scale for that respondent were calculated. If less than 50% of the
12
items were answered, the score for the scale was recorded as ‘missing’; otherwise, the mean
of the remaining items was substituted for each missing item. This rule was followed across
all measures except for the HADS where the scale’s publishers recommend substituting the
mean of the remaining items if no more than 20% of data are missing (GL Assessment, 20072010). Final regression models using available data were compared with models using only
those participants with complete data (with item substitution where appropriate). Data were
checked statistically (Z>3.29) and visually for univariate outliers and skew as recommended
by Tabachnick and Fidell (2007); Mahalanobis distances were used to check for multivariate
outliers (Tabachnick & Fidell, 2007). Where appropriate, scales were subjected to log
transformation. Multicollinearity of independent variables was assessed by examining the
correlations between variables. This was a particularly pertinent issue as some independent
variables were likely to be related and, following Tabachnick and Fidell’s (2007)
recommendations, if two variables had a correlation greater than 0.70 we would not include
both items. The variable with the lowest tolerance in regression would be removed and the
regression model repeated. Bivariate analyses were non-parametric because skew persisted
for some measures (NWC and T3 Activity Limitations). Mann-Whitney U was used to
compare activity limitations at T1 and at T3.
Regression analyses were conducted to identify a) T1 predictors of T3 activity limitations
(primary outcome measure: SF-36 PF; secondary outcome measure: Hernia PF) and b) T2
predictors of T3 activity limitations (primary outcome measure: SF-36 PF, secondary
outcome measure: Hernia PF.). For both a) and b), analyses were conducted in three stages:
Stage 1: Spearman’s rho, Mann-Whitney U or χ2 were performed to identify associations
between risk factors (at either T1 or T2) and outcome (T3 activity limitations). Predictors
associated with outcomes at p<0.2 were carried forward to Stage 2 (Bendel & Afifi, 1977).
Stage 2: Variables were grouped:
13
Group 1: Surgical variables: surgery type (open/laparoscopic); recurrent/primary hernia;
mesh type (standard/lightweight); uni/bilateral hernia; anesthetic (local/no local); surgery
duration; presence of complications; timings (from T1 to operation, operation to T3 as
relevant).
Group 2: Individual biological and behavioral variables: age; BMI; Pain (T1 or T2);
Activity limitations (T1 or T2 using either SF-36 or Hernia PF to match outcome measure);
painkiller use (T2).
Group 3: Emotional and Cognitive Variables: Anxiety, Depression, CSQ Catastrophizing,
CSQ Increased Behavioral Activities, CSQ Control, CSQ Ability to Decrease Pain, Optimism
(each at T1 or T2 as appropriate).
Multiple regressions were carried out for each group. Variables significantly predicting the
outcome at p<0.2 were carried forward to Stage 3.
Stage 3: Only independent variables that predicted risk factors at p<0.2 in Stage 2 were
entered into hierarchical multiple regression equations. Pain at T1/T2 was always entered into
the Stage 3 regression because it is an important potential confounding variable (Hosmer &
Lemeshow, 2000). Surgical variables (Group 1) were entered first, then biological and
behavioral measures (Group 2). Emotional and cognitive variables (Group 3) were entered in
steps three and four respectively. At this final stage, the significance level p<0.05 was used.
Results
Response Rates
The pre-operative questionnaire was completed by 140 respondents (39.4%). There were no
significant differences between respondents and non-respondents for hospital location,
location of surgery (right/left/bilateral) or gender. A trend was observed for age: nonrespondents were slightly younger (mean age: 52.0 years compared with 62.1 years for
respondents, t(353)=1.89, p=0.06). Five of these pre-operative questionnaires were
14
completed after surgery; these responses were excluded leaving a total of 135 eligible
participants. Seven participants were unavailable for follow-up: two did not return their
contact details on the consent forms and five participants’ operations were cancelled or
postponed beyond the study timeframe. Questionnaires were returned by 120 participants at
T2 and 114 at T3 (88.9% and 84.4% of the total sample of 135 respectively).
Descriptive Statistics
The majority of participants (126) were male; six were female; three did not respond to this
item. The mean age of participants was 61.5 years (SD=12.0) and mean BMI was 25.7
(SD=3.26). An open repair was conducted for 84.6% participants; 15.4% had laparoscopic
surgery. Most operations (91.0%) were primary repairs using standard mesh (78.0%) and
were unilateral (92.6%) Most procedures were conducted using both general and local
anesthesia (77.7%); the use of general anesthesia only was reported for 8.5% and local only
for 13.8% of procedures. Most participants (84.1%) did not report complications resulting
from surgery. The median time from T1 questionnaire completion to the operation was 13
days (IQR: 6, 23); from operation date to T2 questionnaire completion was 9 days (IQR: 8,
11); from operation date to T3 questionnaire completion was 127 days (18.1 weeks; IQR:
125, 132 days). The median number of nights spent in hospital post-operatively was 0 (IQR:
0,1).
Across all measures in the analysis, 42 data points were imputed at T1, 26 at T2 and 15 at T3.
As not all missing data could be imputed, the sample sizes used in the final regressions were
101 and 92 (for T1 data predicting T3 activity limitations and T2 predicting T3 activity
limitations respectively2. Scales log-transformed were: Pain, Anxiety, Depression (all time
2
Complete data were available for 67 participants and sensitivity analyses were conducted of the final
regressions using the data from these participants only. In the T2 regression, there were changes in variables
reaching significance (Pain and Depression reached significance with available data (p=.046, p=.050) but not
15
points) and SF-36 PF (T1 and T3; transformation worsened this distributions at T2). The
time periods T1 to operation and operation to T3 and post-operative hospital stay were also
transformed. The direction of effect of scales was maintained after transformation.
Following transformation, the SF-36 PF still displayed signs of skew. Therefore, all
exploratory analyses were carried out using non-parametric analyses (Spearman’s rho and
Mann-Whitney U). On conducting multiple regression equations, the distributions of
residuals were inspected to assess any impact of skewed measures on these equations, and to
check the assumptions of linearity and homoscedasticity.
Table 1 about here
Table 1 displays descriptive statistics for questionnaire measures (non-transformed).
Participants reported being significantly less limited in their activity four months postoperatively than preoperatively (Z=6.15, p<0.01, SF-36 PF; Z=7.62, p<0.01, Hernia PF).
Activity limitations
Pre-operatively, 109 of 129 participants who completed these items (84.5%) reported some
degree of activity limitation due to their hernia (scores <100 on Hernia PF). At one week
after surgery, 108 of 110 (98.2%) and, at four months, 64 of 111 participants (57.7%)
reported some degree of limitation due to their hernia. On the SF-36 PF measure, 114 of 131
(87.0%) participants reported some degree of limitation at T1, 114 of 118 (96.6%) at T2, and
79 of 112 at T3 (49.8%).
Predicting Activity Limitations
with complete data, while CSQ Decrease Pain was significant with complete data (p = .025) but not available
data. However, inspection of beta estimates, 95% CIs and visual inspection of scatter plots of estimates using
complete and available data did not identify major deviations from a linear relationship using the two methods.
Findings using the larger, ‘available’ dataset are therefore reported.
16
Predicting SF-36 Physical Functioning T3 from T1 measures.
In bivariate equations, variables found to predict SF-36 PF were: Surgical variables: mesh
type and unilateral/bilateral surgery. Individual biological and behavioral variables: age,
BMI, Pain, SF-36 PF. Emotional and cognitive variables: Anxiety, Depression, Fear of
Movement, CSQ Control and Optimism (see Tables 2 & 3). The variables from the Stage 2
group regressions that maintained significance at p<0.2 and were entered into the Stage 3
hierarchical multiple regression equations were mesh type, unilateral/bilateral surgery, age,
BMI, SF-36 PF, Anxiety and Fear of Movement. Pain did not reach this level of significance
β=0.06, p=0.46), but as per the analysis plan was forced into the final multiple regression. .
Tables 2 & 3 about here
In the final, stage 3 regression, younger age, higher baseline physical functioning and lower
anxiety predicted higher activity levels at four months after surgery (T3) (Table 4; β=-0.21,
p=0.02; β=0.50, p<0.01; β=-0.24, p=0.01).
Table 4 about here
Predicting SF-36 PF T3 from T2 measures.
The bivariate T2 predictors of SF-36 PF at T3 carried forward to the group multiple
regression equations were as follows (see Tables 2 & 3). Surgical predictors: mesh type and
unilateral/bilateral surgery. Individual biological and behavioral variables: age, BMI, T2
Pain, T2 SF-36 PF and T2 painkiller use. Cognitive and emotional variables: Anxiety,
Depression, Fear of Movement, CSQ Control T2, CSQ Decrease Pain T2 and Optimism T2.
From Stage 2 group multiple regressions, the variables to be continued to the final
hierarchical multiple regression equation were: mesh type, unilateral/bilateral surgery, age,
17
BMI, SF-36 PF T2, Pain T2 and Painkiller use. When examining the cognitive and emotional
variables for multicollinearity, CSQ Control and CSQ Decrease Pain were found to correlate
at r>0.7 (r=0.74). CSQ Control had the lower tolerance level and was therefore removed from
the group regression. The cognitive and emotional variables that met the criteria to be taken
forward from the Stage 2 group multiple regression equation were Depression and CSQ
Decrease Pain. All other variables failed to meet the criterion for inclusion at Stage 3.
The final hierarchical multiple regression equation showed that older participants were less
active than younger participants, and those with higher levels of post-operative pain were less
active at four months (β=-0.51, p<0.01; β=-0.19, p=0.046 respectively) (Table 5). CSQ
Decrease Pain did not reach significance (β=0.14, p=0.12) but higher levels of depression at
T2 marginally significantly predicted being more limited in activity at 4 months after hernia
repair surgery (β=-0.20, p=0.050).
Table 5 about here
Predicting Hernia PF T3 from T1 and T2 measures
Bivariate predictors of Hernia PF T3 are shown in Tables 2 and 3. In Stage 2 group
regressions, the surgical group variables that significantly predicted Hernia PF T3 at p<0.02
were anesthetic and mesh type. In the T1 individual biological and behavioral variables
group, BMI and Hernia PF T1 reached the p<0.2 criterion; T1 Pain did not (β=0.004, p=0.97)
but as per the analysis plan was forced into the final multiple regression. None of the T1
emotional and cognitive variables met the p<0.2 criterion in the group regression. In the
final, hierarchical regression for T1 variables, only Hernia PF at T1 was a significant
predictor of T3 Hernia PF (β=0.46, p<0.01). As an individual variable, anesthetic also
reached significance such that individuals who received no local anesthesia were more active
18
(β=-0.22, p=0.02) but Model 1, containing anesthetic, was not significant (ΔF = 0.05, p=0.11)
(Table 6).
Table 6 about here
In T2 group regressions, BMI, T2 Hernia PF and Taking Painkiller all maintained
significance at p<0.2 in the individual biological and behavioral variable group. T2 Pain did
not meet this criterion (β=-0.04, p=0.69) but was forced into the Stage 3 equation as per the
planned analyses. When examining the cognitive and emotional variables for
multicollinearity, CSQ Control and CSQ Decrease Pain were found to correlate at r>0.7
(r=0.72). CSQ Control had the lower tolerance level and was therefore removed from the
group regression. The cognitive and emotional variable that met the criterion to be taken
forward from the Stage 2 group multiple regression equation was CSQ Decrease Pain. In the
final hierarchical equation, only T2 Hernia PF significantly predicted T3 Hernia PF (β=0.24,
p=0.048) (Table 7).
Table 7 about here
Discussion
We used a prospective cohort study design to investigate the contribution of psychological
and clinical variables in predicting activity limitations persisting 4 months after inguinal
hernia repair surgery. We found that, at four months after surgery, 58% of participants
continued to report some degree of activity limitation due to their hernia (50% on more
general SF-36 measure of limitations), although levels of activity had increased from before
surgery. A bias may have occurred such that participants who were more limited were more
likely to respond at four months. However, if the more conservative full sample denominator
19
is considered (135 participants), it is still the case that almost half of the sample report being
limited because of their hernia at four months post-operatively (47.4%).
Pre-operative predictors of activity limitations (when controlling for concurrent pain) were
being older, having a greater degree of pre-existing activity limitations and higher anxiety
levels. Post-operative predictors were older age and more depressed mood (marginally
significant, p=0.050). Depression predicting later activity limitations is consistent with
previous research (Kendel et al., 2010 (a surgical context); Powell et al., 2008 (recovery from
stroke)). Only post-operative depression score was predictive – pre-operative depression
was not. In participants undergoing surgery on the spine, Seebach et al. (2012) found that
post-operative depression (at six weeks) predicted disability at 3 months but pre-operative
depression did not. In contrast, Kendel et al. (2010) found depressive symptoms measured
pre-operatively predicted activity limitations 2 months post-operatively in individuals
undergoing coronary surgery.
It might be that the role of depression differs according to the type of surgery. In the case of
hernia surgery, individuals may be generally in a good state of health, with low levels of pain
and the ability to perform many normal activities. After surgery, these individuals are likely
to then experience acute postoperative pain and activity limitation. We assessed depression
using the Hospital Anxiety and Depression Scale which asks participants how they have been
feeling in the past week. Our post-operative questionnaire was presented one week after
surgery, thus individuals were asked to report how they felt in the immediate post-operative
period. It may be that it is how a person feels at the start of the recovery process that is
important in predicting the recovery of activity, rather than how they feel at a time when the
impact of the surgery on the individual is, as yet, unknown.
20
Pre-operative anxiety was a significant predictor of 4-month activity limitation. There is
good evidence that higher anxiety before surgery predicts worse post-operative pain, with
evidence for its impact on other recovery variables being less clear (Munafò & Stevenson
2001). The present study showed post-operative pain to predict 4-month activity limitations;
it may be that anxiety impacted on 4-month activity limitation by increasing post-operative
pain. In a systematic review and meta-analysis, Johnston and Vögele (1993) demonstrated
that pre-operative preparation techniques designed to reduce anxiety, such as relaxation and
procedural information, reduced post-operative pain and also lead to improvements on other
health outcomes. The present findings suggest that such interventions may yield benefits for
regaining activity in the longer term, as well as in the shorter-term recovery after hernia
surgery.
As predicted by biomedical models such as the WHO ICIDH model (World Health
Organisation, 1980)3, post-operative pain appeared to influence activity limitations at four
months after surgery. The presented analyses do not test a second model: that post-operative
pain predicts 4-month pain, and it is this 4-month pain that affects 4-month activity
limitations. However, in a parallel study with this data set, we found that pain at four months
was predicted by lower pre-operative optimism and lower perceptions of control over pain
post-operatively rather than post-operative pain (Powell et al., 2011). Future research could
usefully examine two mediational models of activity limitation, with either post-operative
pain, or 4-month pain tested as a mediator in a predictive relationship between psychological
variables and recovery of activity after surgery.
In both models, the impact of psychological variables on 4-month activity limitations was a
‘small’ effect (Cohen, 1992). In the context of rehabilitation after hernia repair surgery,
3
The WHO ICIDH model (1980) has been replaced by the ICF model which has a biopsychosocial framework
(WHO, 2001). However, the ICF model makes no predictions and so cannot be used as a predictive model.
21
behavior-specific cognitions could be better at predicting activity outcome than the more
general and pain-related constructs that are encompassed within fear avoidance models, and
the broad construct of optimism. Social Cognitive Theory (Bandura, 1977, 1982) emphasizes
the importance of control cognitions – self efficacy – in determining behavior. People who
are more confident that they can perform a behavior are more likely to persist with attempts
to do so. While it is not inconsistent with this model that someone with higher perceptions of
control over their pain would be more likely to persist with an activity, a more sensitive
approach to predicting activity would be to ask people about their self-efficacy to do that
activity, rather than their self-efficacy in controlling their pain.
Avoidance of activity after surgery is not necessarily driven by fear or by focusing on the
negative consequences of pain. People may believe (appropriately or inappropriately) that
avoiding activity will facilitate and promote more effective tissue and wound healing. In
qualitative interviews conducted with people as they progressed through the experience of
anticipating and recovering from hernia surgery, we found that participants tended not to be
overly concerned about experiences of pain – they regarded pain as a natural consequence of
surgery rather than something of which to be fearful (Powell, McKee, King & Bruce, 2013).
Pain was sometimes regarded as a marker of when they were doing too much, but the extent
to which individuals returned to activity seemed to be associated with the extent to which
they perceived the risk that activity could lead to damage at the hernia site. At four months
after surgery, we found a dissociation between pain and activity, with some individuals still
limiting activity despite being pain-free to ensure that the hernia site was protected, rather
than out of pain-related fear or a desire to avoid pain (Powell et al. 2013). These findings
suggest that a focus on thoughts and beliefs about activities might be a better predictor of
activity outcome in this context than a measure of fearfulness.
22
It has been proposed that combining a biomedical model with a model focused on beliefs
about behavior, such as the Theory of Planned Behavior (Ajzen, 1991), will lead to better
prediction of activity limitations than the biomedical model alone (Johnston, 1996). The
combined model has been found to account for more variance in activity limitations in people
with pain, awaiting joint replacement surgery, than can pain severity alone (Dixon, Johnston,
Rowley, & Pollard, 2008). Similar findings were seen following surgery (Quinn et al., 2012)
and also in community residents (Dixon, Johnston, Elliott, & Hannaford, 2012). With a focus
on beliefs about behavior, rather than beliefs and concerns about pain, this may be a useful
model in future research investigating psychological risk factors for poor recovery of activity
after surgery.
While much variance in activity limitations outcome has yet to be accounted for, from current
findings there may be value in attempting to identify those individuals who may be at greatest
risk of experiencing functional limitations after surgery. As discussed above, pre-operative
preparation may be beneficial for those experiencing pre-operative anxiety. Few centers
currently implement prolonged treatment or rehabilitation after hospital discharge for minor
surgical procedures such as inguinal hernia repair. Older patients with depressed mood might
benefit from postoperative rehabilitation to facilitate return to functional activity.
Interventions could be targeted to reduce pre-operative anxiety post-operative depressed
mood, for example by using brief cognitive behavioral therapy methods (Westbrook,
Kennerley & Kirk 2007).
Exploratory analyses were conducted with ‘Hernia PF’ as the outcome measure: an as yet
unvalidated measure designed to assess activity limitations the participant believes to be
specifically due to the hernia rather than all-cause activity limitation. The only variables to
significantly predict activity limitations due to the hernia at 4-months were activity
23
limitations pre-operatively and immediately after surgery. Further research on the measure is
needed to understand this finding. For example, participants were asked to rate to what
extent they were limited ‘by their hernia’; it is unclear whether participants interpreted this as
their original, pre-operative hernia, or took a broader view, incorporating the surgical and
recovery processes when considering the hernia’s impact on activity limitations.
Limitations
Our response rate was not high at 39.4%. This might be expected from a postal survey
attempting to sample people just as they are preparing to undergo surgery, many of whom are
of working age. However, this does limit the extent to which results may be generalized.
The comparative analyses between responders and non-responders were encouraging, with
the only difference between the groups being a trend effect for non-participants to be
younger.
Our findings were also limited by the low internal consistency of the optimism measure. We
used a brief version of the LOT because of questionnaire length; a fuller questionnaire may
be more valuable in this context. It was not possible to use the catastrophizing measure as the
authors intended; instead of using it as a continuous independent variable we were obliged to
convert this to a binary measure because of the floor effect. The lack of findings for
‘catastrophizing’ may result from this unusual way of operationalizing the construct which
may have resulted in reduced sensitivity. However, it may be that, in the context of hernia or
post-operative pain, individuals actually tend not to catastrophize, or to catastrophize only at
low levels. Our qualitative interviews with individuals undergoing hernia surgery suggested
that pain or discomfort was accepted as a natural and expected consequence of having a
hernia or having had surgery (Powell et al. 2013). As such, it may be that these individuals
24
catastrophize less in this situation than in contexts where pain is more severe or unexplained,
and where the expected timeline for duration of pain is uncertain.
Nevertheless, although many studies have reported the incidence of chronic pain after hernia
repair surgery, few studies have investigated the risk factors associated with postoperative
activity limitations. While activity limitations had reduced at four months compared with
before surgery, a large proportion of participants had persistent activity limitations due to the
hernia suggesting that further rehabilitation strategies and treatments are necessary to
optimize outcomes beyond the immediate short-term. This study explored psychological
predictors in a longitudinal approach, adjusting for pain intensity. The rigorous
epidemiological design used standardized measures and had a low attrition rate at four
months (84% completion).
Conclusions
Although inguinal hernia surgery is a very common elective procedure, often considered
relatively ‘minor’, we found that activity limitations were experienced by up to 58% of
participants at four months after surgery. While postoperative pain and surgical factors
explained some variance in activity limitations, much variance remained unaccounted for,
leaving scope for further research into beliefs about the behavior under investigation. There
was some evidence that pre-operative anxiety and depressed mood immediately following
surgery predicted poorer activity levels at four months and it may be possible to design
interventions to minimize these effects. There is also scope for testing alternate rehabilitation
strategies to improve and expedite functional recovery.
25
Acknowledgements
This research was funded by a research fellowship to RP at the University of Aberdeen from
the Chief Scientist Office of the Scottish Government Health Directorates. JB was funded by
an MRC Special Training Fellowship. We are grateful to the consultant surgeons and
administrative staff at Aberdeen Royal Infirmary and Dr Gray’s Hospital, Elgin for their
support; we are particularly grateful to Professor Zygmunt Krukowski at Aberdeen Royal
Infirmary for his advice and support.
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Table 1
Data from questionnaire measures (non-transformed data)
T1
T2
Median
n
(IQR)
Median
(IQR)
T3
n
Median
n
(IQR)
Pain
4 (1, 7)
135 5(2, 9)
120 --------------
SF-36 PF
80 (70, 95)
131 50 (35, 70)
118 95 (85, 100) 112
Hernia PF
85 (70, 95)
129 50 (30, 66.3)
110 95 (90,100)
Anxiety
3 (1, 6)
135 3 (1, 6)
118 --------------- ----
Depression
2 (1, 4)
135 3 (1, 6)
118 --------------- ----
Fear of Movement
18 (15, 20)
131 18 (15, 21)
118 --------------- ----
CSQ Increasing Activity
11.5 (6, 17)
118 14 (9, 17.5)
113 --------------- ----
CSQ Control
4 (3, 5)
123 4 (3, 5)
115 --------------- ----
CSQ Ability to decrease pain
4 (3, 5)
120 4 (3, 5)
106 --------------- ----
Optimism
6 (5, 8)
130 6 (5, 8)
117 --------------- ----
%Y %N
53.0
%Y %N
Catastrophizing
47.0
117 51.3 48.7
Taking painkillers
------- ------- ----
57.8 42.2
%Y
----
111
%N
113 ------ ------ ---116 ------ ------ ----
Y = Yes, N = No, PF = Physical Functioning.
32
Table 2
Correlations between predictor variables and Four-month (T3) activity limitations
measures
SF-36 PF T3 (tr)
Hernia PF T3 (tr)
rs
p
rs
p
Duration
0.08
0.45
0.03
0.79
T1 to operation (tr)
0.10
0.28
0.05
0.61
Operation to T3 (tr)
-0.09
0.33
-0.15
0.13
Age
-0.35
<0.01
-0.03
0.78
BMI
-0.17
0.08
-0.17
0.09
Pain T1 (tr)
-0.12
0.20a
-0.21
0.03
SF36 PF T1 (tr)
0.58
<0.01
0.35
<0.01
Hernia PF T1 (tr)
0.41
<0.01
0.45
<0.01
Anxiety T1 (tr)
-0.26
0.01
-0.24
0.01
Depression T1 (tr)
-0.29
<0.01
-0.26
0.01
Fear of Movement T1
-0.29
<0.01
-0.23
0.02
CSQ Increasing Activity T1
0.03
0.77
0.01
0.93
CSQ Control T1
0.23
0.02
0.25
0.01
CSQ Decrease Pain T1
0.12
0.24
0.17
0.09
Optimism T1
0.20
0.04
0.19
0.05
Pain (T2 (tr))
-0.27
0.01
-0.30
<0.01
SF36 PF T2
0.34
<0.01
0.35
<0.01
Hernia PF T2
0.31
<0.01
0.43
<0.01
Anxiety T2 (tr)
-0.22
0.02
-0.22
0.03
Depression T2 (tr)
-0.31
<0.01
-0.22
0.03
Fear of Movement T2
-0.18
0.07
-0.26
0.01
CSQ Increasing Activity T2
-0.07
0.47
-0.10
0.32
CSQ Control T2
0.25
0.01
0.34
<0.01
CSQ Decrease PainT2
0.23
0.03
0.22
0.03
Optimism T2
0.15
0.12
0.05
0.60
Note. tr = transformed; PF = Physical Functioning. Italicization and bold type indicate
significance at p<0.2.a: p=0.197.
33
Table 3
Bivariate predictors of Activity Limitations at T3: Mann-Whitney U (p)
SF36 PF T3 (tr)
Type of surgery
U
Z
919.5
0.93
629.5
Hernia PF T3 (tr)
p
U
Z
p
0.35
966.0
1.44
0.15
0.74
0.46
612.0
0.64
0.52
1309.0
2.27
0.02
1211.5
1.69
0.09
481.0
1.39
0.16
478.5
1.46
0.15
465.0
-0.47
0.64
347.5
-1.70
0.09
672.5
-1.06
0.29
653.5
-1.19
0.24
1141.0
-0.53
0.60
1088.5
-0.75
0.46
1046.5
-1.73
0.08
1163.0
0.79
0.43
948.0
-2.37
0.02
904.0
-2.64
0.01
(0 = open, 1 = laparoscopic)
Primary/recurrent surgery
(0 = primary, 1 = recurrent)
Type of mesh
(0 = standard, 1 = lightweight)
Uni-/Bilateral
(0 = uni-, 1 = bilateral)
Anesthetic
(0 = no local, 1 = local)
Complication
(0 = no complication, 1 = complication)
Catastrophizing T1
(0 = no catastrophizing, 1 = catastrophizing)
Catastrophizing T2
(0 = no catastrophizing, 1 = catastrophizing)
Painkillers T2
(0 = no painkillers, 1 = painkillers)
Note. tr = transformed; PF = Physical Functioning. Italicization and bold type indicate
significance at p<0.2.
34
Table 4
Hierarchical regression equation. Independent variables: T1 variables, baseline measures
and surgical variables. Dependent variable: T3 Activity Limitations (SF-36 PF).
T3 SF-36 Physical Functioning (tr)
Model 1
Model 2
Model 3
β
p
β
p
β
p
Mesh type
0.20
0.05
0.10
0.22
0.11
0.18
Uni/bilateral surgery
0.11
0.26
-0.03
0.75
0.02
0.84
Age
-0.19
0.03
-0.21
0.02
BMI
-0.15
0.07
-0.13
0.12
SF-36 PF (T1, tr)
0.54
<0.01
0.50
<0.01
Pain (T1, tr)
0.09
0.30
0.17
0.06
-0.24
0.01
0.00
1.00
Anxiety (T1, tr)
Fear of Movement (T1)
ΔR2
0.05
0.37
0.05
ΔF
2.59 (p=0.08)
14.91 (p<0.01)
4.14 (p=0.02)
Note. Model 3: F = 10.07, Adj R2 =0.42, N=101, p<0.001. PF = Physical Functioning; tr =
transformed.
35
Table 5
Hierarchical regression equation. Independent variables: T2 variables, baseline measures
and surgical variables. Dependent variable: T3 Activity Limitations (SF-36 PF).
T3 SF-36 Physical Functioning (tr)
Model 1
Model 2
Model 3
β
p
β
p
β
p
Mesh type
0.26
0.02
0.15
0.11
0.13
0.14
Uni/bilateral surgery
0.09
0.41
0.05
0.56
0.09
0.32
Age
-0.51
<0.01
-0.52
<0.01
BMI
-0.12
0.19
-0.09
0.30
SF36 PF (T2)
0.08
0.44
0.00
0.97
Pain (T2, tr)
-0.25
0.01
-0.19
0.05a
Taking painkiller
-0.18
0.05
-0.11
0.24
-0.20
0.05b
0.14
0.12
Depression (T2, tr)
CSQ Decrease Pain (T2)
ΔR2
0.08
0.33
0.05
ΔF
3.60 (p=0.03)
9.44 (p<0.01)
3.57 (p=0.03)
Note. Model 3: F=7.61, Adj R2=0.40, N=92, p<0.001. PF = Physical Functioning;
tr = transformed.
a:
p=0.046; b: p=0.050.
36
Table 6
Hierarchical regression equation. Independent variables: T1 variables, baseline measures
and surgical variables. Dependent variable: T3 Activity Limitations (Hernia PF).
T3 Hernia Physical Functioning (tr)
Model 1
β
Model 2
β
p
p
Mesh type
0.14
0.16
0.14
0.12
Anesthetic
-0.17
0.09
-0.22
0.02
-0.14
0.14
Hernia PF (T1, tr)
0.48
<0.01
Pain (T1, tr)
0.04
0.66
BMI
ΔR2
0.05
0.22
ΔF
2.29 (p=0.11)
9.70 (p<0.01)
Note. Model 2: F = 6.98, Adj R2 =0.23, N=101, p<0.001. PF = Physical Functioning; tr =
transformed.
37
Table 7
Hierarchical regression equation. Independent variables: T2 variables, baseline measures
and surgical variables. Dependent variable: T3 Activity Limitations (Hernia PF).
T3 Hernia Physical Functioning (tr)
Model 1
Model 2
Model 3
β
p
β
p
β
p
Mesh type
0.25
0.02
0.13
0.25
0.11
0.30
Anesthetic
-0.16
0.12
-0.15
0.16
-0.17
0.11
-0.13
0.22
-0.14
0.18
0.24
0.05
0.24
0.05a
Pain (T2, tr)
-0.06
0.62
-0.02
0.87
Taking painkiller
-0.14
0.21
-0.08
0.47
0.17
0.13
BMI
Hernia PF (T2)
CSQ Decrease Pain (T2)
ΔR2
0.08
0.12
0.02
ΔF
3.67 (p=0.03)
3.00 (p=0.02)
2.41 (p=0.13)
Note. Model 3: F=3.25, Adj R2=0.16, p=0.01 N=87. PF = Physical Functioning; tr =
transformed; a: p=0.048.
38