Chronic pain after open inguinal hernia repair: expertise-based randomized clinical trial of heavyweight or lightweight mesh

 
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BJS, 2021, 108, 138–144
                                                                                                                                  DOI: 10.1093/bjs/znaa049
                                                                                                         Advance Access Publication Date: 28 December 2020
                                                                                                                               Randomized Clinical Trial

Chronic pain after open inguinal hernia repair:
expertise-based randomized clinical trial of heavyweight
or lightweight mesh
M. Rutegård1,2, M. Lindqvist1, J. Svensson1,3, P. Nordin4 and M. M. Haapamäki                  1,
                                                                                                   *

                                                                                                                                                              Downloaded from https://academic.oup.com/bjs/article/108/2/138/6053676 by guest on 16 September 2021
1
  Department of Surgical and Perioperative Sciences, Surgery, Umeå University, Umeå, Sweden
2
  Wallenberg Centre for Molecular Medicine, Umeå University, Umeå, Sweden
3
  Department of Statistics, Umeå School of Business, Economics and Statistics, Umeå University, Umeå, Sweden
4
  Department of Surgical and Perioperative Sciences, Surgery, Östersund Research Unit, Umeå University, Östersund, Sweden

*Correspondence to: Department of Surgical and Perioperative Sciences, Surgery, Umeå University, SE-901 85 Umeå, Sweden (e-mail: markku.haapamaki@umu.se)

Abstract
Background: There is a shortage of high-quality studies regarding choice of mesh in open anterior inguinal hernia repair in relation
to long-term chronic pain. The authors hypothesized that heavyweight compared with lightweight mesh causes increased postoper-
ative pain.
Methods: An RCT was undertaken between 2007 and 2009 at two sites in Sweden. Men aged 25 years or older with an inguinal hernia
evaluated in the outpatient clinic were randomized in an unblinded fashion to heavyweight or lightweight mesh for open anterior in-
guinal hernia repair. Data on pain affecting daily activities, as measured by the Short-Form Inguinal Pain Questionnaire 9–12 years af-
ter surgery, were collected as the primary outcome. Differences between groups were evaluated by generalized odds and numbers
needed to treat.
Results: A total of 412 patients were randomized; 363 were analysed with 320 questionnaires sent out. A total of 271 questionnaires
(84.7 per cent) were returned; of these, 121 and 150 patients were in the heavyweight and lightweight mesh groups respectively. Pain
affecting daily activities was more pronounced in patients randomized to heavyweight versus lightweight mesh (generalized odds
1.33, 95 per cent c.i. 1.10 to 1.61). This translated into a number needed to treat of 7.06 (95 per cent c.i. 4.28 to 21.44). Two reoperations
for recurrence were noted in the heavyweight mesh group, and one in the lightweight mesh group.
Conclusion: A large-pore lightweight mesh causes significantly less pain affecting daily activities a decade after open anterior ingui-
nal hernia repair. Registration number: NCT00451893 (http://www.clinicaltrials.gov).

Introduction                                                                        compared with heavyweight mesh at 6 months after inguinal
                                                                                    hernia repair. However, results are conflicting, as other stud-
Inguinal hernia is the most common type of hernia in men, with
                                                                                    ies14,15 evaluating pain 3–5 years after surgery did not show such
a lifetime risk of 27 per cent1. Therefore, with estimated 20 mil-
                                                                                    differences. Unfortunately, there are very limited long-term data
lion inguinal repairs performed each year2, each improvement in
                                                                                    addressing this topic from RCTs.
surgical technique translates into substantial public health bene-
                                                                                       The purpose of this study was to evaluate the long-term im-
fits.
                                                                                    pact of heavyweight or lightweight mesh on chronic pain, dis-
    Mesh repairs have become standard practice for inguinal her-
                                                                                    comfort, and recurrence rates a decade after open anterior
nias3,4, as recurrence rates are lower than those associated with
                                                                                    inguinal hernia repair. It was hypothesized that the lightweight
classical tissue repair5. Because recurrence rates are now low, the
                                                                                    mesh group would have less pain and discomfort than the heavy-
focus of technical improvements has shifted to outcomes such as
                                                                                    weight mesh group, whereas recurrence rates would be similar in
chronic postoperative pain, which affects up to 30 per cent of all                  the two groups.
patients after inguinal hernia repair6–8. Chronic postoperative
pain is classified by the ICD-11 as pain lasting more than 3
months after surgery9. This pain is often neuropathic in charac-                    Methods
ter, believed to be caused by tissue and nerve trauma induced by                    This was a follow-up study of a previous expertise-based, paral-
surgical dissection, as well as inflammation and a foreign body                     lel-group RCT16, carried out at the regional centres Umeå
reaction owing to the suture material and mesh10,11.                                University Hospital and Östersund Hospital, Sweden. In this
    Some studies12,13 have reported that the use of lightweight                     study, men aged at least 25 years with a symptomatic unilateral
mesh is associated with decreased postoperative chronic pain                        inguinal hernia were randomized (1 : 1) to a group of surgeons

Received: June 26, 2020. Revised: September 8, 2020. Accepted: September 20, 2020
C The Author(s) 2020. Published by Oxford University Press on behalf of BJS Society Ltd.
V
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Rutegård et al.   |   139

that use either heavyweight (90 g/m2, BardTM Flatmesh; Davol) or        Study measures
lightweight (28 g/m2, ULTRAPROTM; Ethicon) mesh. The age crite-         The exposure of the study was the type of mesh used for the pri-
rion was chosen to ensure a fully grown patient and acceptance          mary inguinal hernia repair, either heavyweight or lightweight.
of local anaesthesia. Patient exclusion criteria were: femoral her-     The main outcome was the occurrence of chronic pain 9–12 years
nias, unwillingness to participate, refusal of local anaesthesia,       after open anterior inguinal hernia repair with the standardized
bleeding disorders, and concurrent use of anticoagulation ther-         Lichtenstein technique. The primary outcome, the first item of
apy. The study was expertise-based, meaning that surgeons used          the sf-IPQ, comprises a seven-grade ordinal scale measuring the
the type of mesh they personally preferred, minimizing the prob-        impact of pain in the groin on different daily activities, whereas
ability of differential expertise bias17. The two groups of surgeons’   the McCarthy visual analogue scale, which ranges from 0 to 150
surgical experience was evaluated. Surgical trainees were               mm, measures the mean intensity of pain during the past week.
allowed to participate provided they had reached surgical inde-         Other secondary outcomes evaluated were patient-reported
pendence for primary inguinal hernia repair, for which a mini-          awareness of a groin lump (yes or no), perception of foreign mate-
mum of 20 unsupervised inguinal hernia repairs was required.            rial in the groin (yes or no), loss of skin sensation in the operated

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The study group attested that the groups of surgeons for each in-       groin (yes or no), other discomfort or pain located in the groin
tervention arm were sufficiently similar in terms of surgical ex-       (yes or no), and the patient’s impression of groin symptoms com-
perience. Specification of surgeon groups can be found in Table         pared with before surgery (better, no change or worse) as well as
S1. Randomization was stratified by centre and performed at the         overall satisfaction with the surgery (completely satisfied, mostly
outpatient clinic, after consent for surgery had been obtained.         satisfied, mostly unsatisfied or completely unsatisfied).
The randomization did not include stratification for preoperative       Reoperations for recurrences and patient-perceived recurrences
pain, and blinding of patients and surgeons was not achieved.           were also compared between mesh groups. The questionnaire
The random allocation sequence was computer-generated by a              consisted of a total of 10 questions covering the outcomes of the
                                                                        present study.
statistician by means of a random number technique. Allocation
was obtained for each patient from a central web-based server           Statistical analysis
(https://www.norrlandskirurgi.se). The program concealed the al-
                                                                        The analysis was performed using the intention-to-treat princi-
location sequence.
                                                                        ple. As some of the variables had a skewed distribution, the
    A standardized manual for carrying out the operation was dis-
                                                                        results are reported as median (i.q.r.). Categorical variables are
tributed and used by all participating surgeons. Additionally, sur-
                                                                        presented as frequencies with percentages, and were analysed
geons had to undertake two operations under supervision before
                                                                        using Fisher’s exact test. The Mann–Whitney U test was used
being accepted to participate in the study. This report of long-
                                                                        to evaluate differences between mesh groups in the ordinal sf-
term results is written according to the CONSORT 2010 guide-            IPQ and McCarthy pain scales. The primary outcome, sf-IPQ
line18.                                                                 grade, was also analysed using generalized Wilcoxon–Mann–
    All patients provided informed consent to participate in the        Whitney odds (WMW odds)22,23, providing data on the odds of
present study, which was conducted according to the latest revi-        shifting from one response level to the next as a function of
sion of Declaration of Helsinki and approved by the ethical review      mesh allocation. This analysis was also used to derive num-
board at Umeå University.                                              bers needed to treat. A sensitivity analysis using ordinal re-
                                                                        gression was undertaken to evaluate the impact of adherence
Study design                                                            bias and chance confounding, using the following co-variables:
Of 412 patients randomized, 363 were analysed in the original           age, BMI (less than 25, 25–30, or over 30 kg/m2), hernia type
trial. These patients were cross-checked against the Swedish pop-       (indirect, direct or combined), preoperative McCarthy pain
ulation registry, using the national personal registration num-         score (0 to 150) and ASA grade (I, II or III). All tests were two-
ber19, 9–12 years after the inguinal hernia repair, to exclude those    sided, and P < 0.050 was considered significant. For illustrative
                                                                        purposes, a box plot was used for the McCarthy pain scale dis-
who had died. Information about the follow-up study and ques-
                                                                        tribution at follow-up.
tionnaires were sent out to the remaining 320 patients, and a re-
                                                                            According to the power calculation for the original trial16,
search nurse contacted all patients who could be reached by
                                                                        some 240 patients in total were needed to demonstrate a reduc-
telephone and asked if they were willing to take part in the pre-
                                                                        tion in the proportion of patients reporting pain from 30 to 15 per
sent follow-up study. The questionnaire consisted of the first
                                                                        cent, with 80 per cent statistical power. Before the questionnaires
item of the Short-Form Inguinal Pain Questionnaire (sf-IPQ)20, the
                                                                        were sent out, it was assumed that this number of patients could
McCarthy visual analogue scale21, and a set of study-specific
                                                                        be included and the present study was therefore considered feasi-
questions. The data were inserted and matched into a Microsoft
       R
                                                                        ble.
AccessV database (version 14; Microsoft, Redmond, Washington,                                                    R
                                                                                                                 V
                                                                            Data analysis was done in Stata release 15 (StataCorp,
USA) together with the baseline data from the previous study,           College Station, Texas, USA) and R version 3.6.3 (R Foundation for
and double-checked for errors. Linkage was also made to the na-         Statistical Computing, Vienna, Austria).
tional Swedish Hernia Register to obtain data on reoperations for
recurrence or chronic pain. Baseline data collected for the previ-
ous study included patient age, BMI, preoperative pain measured         Results
with the McCarthy pain scale during normal activity, patient-           All operations were performed during 2007–2009 with open ante-
reported preoperative regular pain medication, hernia type, ASA         rior inguinal hernia repair according to Lichtenstein using local
fitness grade, operated side, duration of operation, study centre,      anaesthesia24. Some 320 of 363 patients from the earlier analysis
and information on surgical experience of the two groups of sur-        were alive by the end of March 2018. Of these, 271 (84.9 per cent)
geons participating in the study.                                       consented to participate and returned questionnaires: 121
140   |   BJS, 2021, Vol. 108, No. 2

                                                   Assessed for eligibility
                                                         n = 858

              Enrolment
                                                                                    Excluded n = 446
                                                                                    • Did not meet inclusion criteria n = 152
                                                                                    • Met exclusion criteria or declined to participate n = 294
                                                         Randomized
                                                           n = 412
              Allocation

                                  Heavyweight mesh group n = 206                     Lightweight mesh group n = 206
                                  • Operation n = 197                                • Operation n = 194
                                  • Declined surgery n = 9                           • Declined surgery n = 12

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              in previous study
                  Follow-up

                                  Lost to follow-up n = 15                                   Lost to follow-up n = 4
                                  • Operation in non-participating hospital n = 2            • Operation in non-participating hospital n = 0
                                  • Declined follow-up n = 13                                • Declined follow-up n = 4
              in previous study

                                   Analysed n = 178                                  Analysed n = 185
                   Analysis

                                   Excluded from analysis n = 4                      Excluded from analysis n = 5
                                   • Erroneously included n = 4                      • Erroneously included n = 4
                                   • Operated by non-expert n = 0                    • Operated by non-expert n = 1
              Follow-up

                                  Lost to follow-up n = 57                           Lost to follow-up n = 35
                                  • Patient died n = 29                              • Patient died n = 14
                                  • Questionnaire not returned n = 28                • Questionnaire not returned n = 21
              Analysis

                                              Analysed                                           Analysed
                                               n = 121                                            n = 150

Fig. 1 CONSORT diagram showing patients included in long-term follow-up

patients in the heavyweight mesh group and 150 in the light-                         mesh group included more patients on regular pain medication
weight mesh group (Fig. 1). The questionnaire was answered be-                       before surgery (8.0 versus 4.1 per cent). Operating time was
tween 19 April and 20 September 2018. There were more deaths                         slightly shorter in the heavyweight group, with a median of 68.5
during the postoperative follow-up in the heavyweight mesh                           (i.q.r. 60.0–80.0)) min, compared with 74.5 (61.5–90.0) min in the
group than in the lightweight mesh group (29 of 178 versus 14 of                     lightweight group.
185; P ¼ 0.014).
   Baseline data collected in conjunction with the inclusion of                      Chronic pain
patients in the original study are shown for the group participat-                   The impact of pain on daily activities was measured using the
ing in this follow-up study in Table 1. Study groups were compara-                   seven-grade sf-IPQ scale, and a statistically significant differ-
ble concerning age, BMI, hernia type, ASA grade, and McCarthy                        ence in favour of the lightweight mesh was evident (P ¼ 0.003)
preoperative pain score during normal activity. The lightweight                      (Table 2). In the heavyweight group, the proportion of patients
Rutegård et al.    |   141

Table 1 Baseline characteristics of 271 men who participated in the follow-up study a decade after surgery, stratified by type of mesh
in open anterior inguinal hernia repair

                                                                        Heavyweight mesh (n ¼ 121)                                    Lightweight mesh (n ¼ 150)

Age (years)*                                                                  61.1 (52.9–66.4)                                              61.3 (53.7–67.4)
BMI (kg/m2)*                                                                  25.5 (23.3–27.2)                                              25.1 (23.5–26.9)
Preoperative McCarthy pain score*†                                               18 (5–43)                                                     23 (5–50)
Preoperative regular pain medication
  No                                                                              108 (89.3)                                                   130 (86.7)
  Yes                                                                              5 (4.1)                                                      12 (8.0)
  Not classified                                                                   8 (6.6)                                                       8 (5.3)
Hernia type
  Indirect                                                                        67 (55.4)                                                     84 (56.0)
  Direct                                                                          45 (37.2)                                                     48 (32.0)
  Combined                                                                         9 (7.4)                                                      16 (10.7)
  Not classified                                                                    0 (0)                                                        2 (1.3)

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ASA fitness grade
  I                                                                               72 (59.5)                                                     98 (65.3)
  II                                                                              43 (35.5)                                                     47 (31.3)
  III                                                                              6 (5.0)                                                       5 (3.3)

Operated side
  Left                                                                            55 (45.5)                                                     63 (42.0)
  Right                                                                           66 (54.5)                                                     87 (58.0)
Centre
  Umeå                                                                          57 (47.1)                                                     68 (45.3)
  Östersund                                                                     64 (52.9)                                                     82 (54.7)
Duration of operation (min)*                                                  68.5 (60.0–80.0)                                              74.5 (61.5–90.0)

Values in parentheses are percentages unless indicated otherwise; *values are median (i.q.r.). Percentages may not add up owing to rounding. †Measured during
normal activity.

Table 2 Proportion of patients in pain categories of the first item of the Short-Form Inguinal Pain Questionnaire, 9–12 years after open
anterior inguinal hernia repair

sf-IPQ grade20                                  Description                             Heavyweight mesh (n ¼ 121)                    Lightweight mesh (n ¼ 150)

1                                 No pain                                                          89 (73.6)                                   132 (88.0)
2                                 Pain present but can easily be ig-                               18 (14.9)                                     8 (5.3)
                                    nored
3                                 Pain present, cannot be ignored,                                  7 (5.8)                                      5 (3.3)
                                    but does not interfere with
                                    daily activities
4                                 Pain present, cannot be ignored,                                  3 (2.5)                                      3 (2.0)
                                    interferes with concentration
                                    on chores and daily activities
5                                 Pain present, cannot be ignored,                                  1 (0.8)                                      1 (0.7)
                                    interferes with most activities
6                                 Pain present, cannot be ignored,                                  1 (0.8)                                       0 (0)
                                    necessitates bed rest
7                                 Pain present, cannot be ignored,                                  1 (0.8)                                       0 (0)
                                    prompt medical advice sought
Missing response                                                                                    1 (0.8)                                      1 (0.7)

Values in parentheses are percentages. The first item of the Short-Form Inguinal Pain Questionnaire (sf-IPQ) measures the impact of pain in the groin on different
daily activities, estimated as the worst pain felt in the operated groin during the past week. P ¼ 0.003 for global difference between mesh groups (Mann–Whitney U
test). The sf-IPQ grade was used as a continuous numerical test value for each patient in the calculation.

who were pain-free was 89 of 121 (73.6 per cent) compared                           to the next higher with use of heavyweight mesh. This trans-
with 132 of 150 (88.0 per cent) in the lightweight group,                           lated to a number needed to treat of 7.06 (95 per cent c.i. 4.28
whereas easily ignored pain was reported by 18 of 121 (14.9                         to 21.44). In the ordinal regression sensitivity analysis, the
per cent) and 8 of 150 (5.3 per cent) respectively. The propor-                     results of unadjusted (odds ratio (OR) 2.63, 95 per cent c.i. 1.38
tion of patients with pain that could not be ignored but did                        to 5.02) and adjusted (OR 2.41, 1.18 to 4.90) analyses were sim-
not interfere with activities was 7 of 121 (5.8 per cent) and 5                     ilar.
of 150 (3.3 per cent) in the heavyweight and lightweight groups                         The McCarthy postoperative pain scale values were slightly
respectively.                                                                       higher in the heavyweight mesh group (112 patients) with a me-
   With the lightweight group as the reference category, a gen-                     dian value of 4 (95 per cent c.i. 3 to 5), compared with 3 (3 to 4) in
eralized WMW odds of 1.33 (95 per cent c.i. 1.10 to 1.61;                           the lightweight group (132 patients) (Fig. 2). However, this trend
P ¼ 0.004) was derived for a shift from a lower sf-IPQ category                     did not reach statistical significance (P ¼ 0.099).
142    |               BJS, 2021, Vol. 108, No. 2

Groin symptoms                                                                          Some 83.0 per cent of all patients were completely satisfied with
There was a statistically significant difference regarding the per-                  the surgery, 15.6 per cent were mostly satisfied, whereas 1.5 per
ception of foreign material in the groin, favouring the lightweight                  cent were either mostly or completely unsatisfied. There was no
mesh (P ¼ 0.006) (Table 3). There were no significant differences in                 statistically significant difference between the groups (Table 5).
awareness of a groin lump, loss of sensation, or other pain and
discomfort.
                                                                                     Recurrence
   Some 95.1 per cent of all patients rated their groin symptoms                     Rates of patient-reported recurrence in the heavyweight and
as better than before surgery, 4.5 per cent deemed that their                        lightweight groups were 5.8 per cent (7 of 121) and 2.1 per cent
symptoms were the same as before, whereas 0.4 per cent reck-                         (3 of 145) respectively. This difference was not statistically signifi-
oned that the symptoms were worse. No significant differences                        cant (P ¼ 0.193). According to the Swedish Hernia Register, reoper-
could be discerned between the study groups (Table 4).                               ation was undertaken for only three recurrences in the cohort of
                                                                                     271 patients, two in the heavyweight group and one in the light-
                                                                                     weight group; the latter was operated on using a polytetrafluoro-
                       150                                                           ethylene mesh that was not intended for the study, which

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                                                                                     constituted a protocol violation.

                                                                                     Discussion
                                                                                     In this long-term follow-up of an RCT comparing the use of
                                                                                     heavyweight and lightweight mesh in open anterior inguinal her-
                                                                                     nia repair in adult men, there was a difference in pain affecting
                                                                                     daily activities as well as in the perception of foreign material 9–
                                                                                     12 years after surgery, favouring the lightweight mesh; this trans-
                       100
                                                                                     lated into a number needed to treat of 7.06 regarding chronic
                                                                                     pain. However, there were no statistically significant differences
      VAS score (mm)

                                                                                     between mesh groups in other groin symptoms, pain measured
                                                                                     by the McCarthy pain scale, satisfaction or symptoms after oper-
                                                                                     ation compared with before surgery. Regardless of mesh type
                                                                                     used, the great majority of patients experienced significant im-
                                                                                     provement in symptoms and satisfaction with the inguinal her-
                                                                                     nia repair. Only three patents underwent reoperation for hernia
                                                                                     recurrence in the decade after inguinal hernia repair.
                        50                                                              The strengths of this study include that it was an expertise-
                                                                                     based RCT, minimizing the possibility of selection bias as well as
                                                                                     bias related to surgeon experience. The operating techniques
                                                                                     were standardized and the surgical performance was controlled
                                                                                     at the start of the study. There was also an excellent response
                                                                                     rate, with 84.7 per cent of patients returning questionnaires.

                                                                                     Table 4 Assessment of symptoms 9–12 years after surgery,
                                                                                     compared with situation perceived before surgery, stratified by
                                                                                     type of mesh
                         0
                                     HWT                LWT                                         Heavyweight mesh (n ¼ 121)        Lightweight mesh (n ¼ 150)

Fig. 2 Pain assessed with the McCarthy visual analogue scale according               Worse            1 of 121 (0.8; 0.2, 4.5)             0 of 147 (0; 0, 2.0)
to type of mesh                                                                      No change        6 of 121 (5.0; 1.8, 10.5)          6 of 147 (4.1; 1.5, 8.7)
Pain was measured on a visual analogue scale (VAS) from 0 to 150 mm. Bold            Better         114 of 121 (94.2; 88.4, 97.6)     141 of 147 (95.9; 91.3, 98.5)
horizontal lines represent median value, boxes indicate i.q.r., and whiskers
indicate the adjacent values which are the highest value not greater than the        Values in parentheses are percentages, with 95 per cent Chopper–Pearson
75th percentile þ1.5 i.q.r.. Outliers are marked with a dot. HWT, heavyweight        confidence interval. Data were missing for some patients. P ¼ 0.125 for global
mesh group; LWT, lightweight mesh group.                                             difference between mesh groups (Fisher’s exact test).

Table 3 Global assessment of groin symptoms 9–12 years after surgery, stratified by type of mesh

                                                          Heavyweight mesh (n ¼ 121)                         Lightweight mesh (n ¼ 150)                         P*

Perception of foreign material in                                16 of 104 (15.4)                                   6 of 134 (4.5)                            0.006
  groin
Awareness of a groin lump                                         9 of 106 (8.5)                                    7 of 141 (5.0)                            0.303
Loss of skin sensation in groin                                  18 of 105 (17.1)                                  21 of 138 (15.2)                           0.726
Discomfort in groin                                              16 of 101 (15.8)                                  16 of 140 (11.4)                           0.341
Patient-perceived recurrence                                      7 of 121 (5.8)                                    3 of 145 (2.1)                            0.193

Values in parentheses are percentages. Data were missing for some patients. *Fisher’s exact test.
Rutegård et al.   |     143

Table 5 Assessment of patient satisfaction 9–12 years after surgery, stratified by type of mesh

                                                                Heavyweight mesh (n ¼ 121)                                           Lightweight mesh (n ¼ 150)

Completely unsatisfied                                             2 of 121 (1.7; 0.2, 5.8)                                               0 of 149 (0; 0, 2.0)
Mostly unsatisfied                                                  1 of 121 (0.8; 0, 4.5)                                               1 of 149 (0.7; 0, 3.7)
Mostly satisfied                                                 23 of 121 (19.0; 12.9, 27.0)                                         19 of 149 (12.8; 7.8, 19.2)
Completely satisfied                                             95 of 121 (78.5; 70.1, 85.5)                                        129 of 149 (86.6; 80.0, 91.6)

Values in parentheses are percentages with 95 per cent Chopper–Pearson confidence interval. Data were missing for one patient. P ¼ 0.653 for global difference
between mesh groups (Fisher’s exact test).

Moreover, validated questionnaires were used along with modern                          The sf-IPQ analysis provided evidence favouring the light-
statistical modelling, and sensitivity analyses were used to cor-                   weight mesh in this trial, but this was not corroborated using the

                                                                                                                                                                       Downloaded from https://academic.oup.com/bjs/article/108/2/138/6053676 by guest on 16 September 2021
roborate the trial findings.                                                        McCarthy pain scale. Both variables measure pain, although in a
    Although missing values were frequent in the study, every                       different manner. One can speculate that the discordance might
questionnaire item reached an response percentage exceeding 83                      be explained by the seeming difficulty patients had in responding
per cent. The variables with the highest degree of completeness                     to the McCarthy pain scale item, as the response rate was lower
were the first item of the sf-IPQ scale, as well as the questions on                (99.3 versus 90.0 per cent) and some patients seemed to answer
satisfaction and comparisons before and after surgery, all with                     the question incorrectly. The authors suspect a common error at
rates rounding up to at least 99 per cent. The questions are sim-                   the lower end of the McCarthy scale, which indicates the absence
ple and easy to understand, whereas more complicated questions                      of pain. Some patients seemed to have interpreted the location
might lead to omission of the question completely.                                  immediately above the centre of the sentence ‘no pain sensation’
    This study was carried out on men with a primary inguinal                       to indicate the absence of pain. This gives a measure of 5–10 mm
hernia. Therefore, no general conclusion can be made for other                      on the pain scale instead of the presumed 0 mm, whereas most
types of inguinal hernia and other patient groups, such as chil-                    patients were in fact pain-free. This is a likely source of non-
dren and women. However, the authors believe the hypothesis                         differential misclassification in the McCarthy pain scale variable,
that less foreign material in the wound causes less inflammation,                   probably causing bias towards the null. It is also of note that no
and hence less chronic pain, should apply to most circumstances                     differences between groups could be ascertained in the second-
in which mesh is used for hernia repair. There is, however, a ca-                   ary comparison of groin symptoms before and after surgery; al-
veat regarding the relationship between pore size and mesh                          though this could be interpreted as contradicting the main result,
weight that necessitates comment; this trial was conducted in an                    the finding might be explained by the fact that this question was
era when heavier meshes also signified a smaller pore size, which                   not validated formally and gives no measure of how much better
is not always true with modern mesh types. Therefore, caution                       the situation became after surgery, and also that a considerable
must be taken to not extrapolate the study findings to all types of                 time span had passed since the inguinal hernia repair.
                                                                                        The current trend in inguinal surgery in Sweden is the increas-
heavyweight mesh.
                                                                                    ing use of lightweight meshes28, which is also recommended by
    In the original trial with short-term results16, there were sta-
                                                                                    the European Hernia Society guidelines29. The present findings
tistically significant differences regarding awareness of a groin
                                                                                    further support this recommendation, when considering the
lump and discomfort in the groin 12 months after surgery. A de-
                                                                                    long-term reductions in chronic pain.
cade after surgery the differences in these specific symptoms had
levelled out and were no longer significant. There was no statisti-
cally significant difference in the rate of reoperation for hernia re-              Acknowledgements
currence, although a few more patients in the heavyweight group
                                                                                    The authors thank research nurse A. Karhu and secretary L.
reported subjective experiences of recurrence (5.8 versus 2.1 per
                                                                                    Häggkvist for assisting with data collection. This study was
cent); yet only two patients in this group underwent reoperation
                                                                                    funded by Västerbotten County Council, the VISARE NORR Fund,
for recurrence. The high rate of subjective recurrences might be
                                                                                    and the Knut and Alice Wallenberg Foundation.
explained by the increased rates of foreign material and groin
lump awareness; they did not represent true recurrences.                            Disclosure. The authors declare no conflict of interest.
Nevertheless, the present results are in line with those of previ-
ous studies25,26 suggesting that lightweight meshes are as good
as heavyweight meshes in preventing recurrence after open ante-
                                                                                    Supplementary material
rior mesh inguinal hernia repair, provided that an appropriate                      Supplementary material is available at BJS online.
surgical technique is employed. A recent well conducted trial27 of
laparoscopic totally extraperitoneal repairs showed that a heavy-
weight mesh was superior to a lightweight mesh, both in terms of                    References
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