Surgical correction of an inguinal hernia in adults is one of the most common operations with an annual rate of 2,800 per 1 million people in the United States.  The operation often is performed on an outpatient basis and with little intra- and postoperative morbidity. Postoperatively, pain may persist for 1 to several weeks, and the consequences of pain may include an extended convalescence period. [2–4] In addition, some patients may develop chronic disabling pain. [5–7]
We have critically reviewed the literature for the role of anesthesiologic and surgical factors in acute postherniorrhaphy pain. We also have reviewed data on the etiology and incidence of chronic postherniorrhaphy pain. Data from pediatric herniorrhaphy have not been included in this review. In the assessment of different anesthesiologic or surgical treatments with respect to their effects on acute postherniorrhaphy pain, only well-designed randomized studies have been included, whereas several studies have been excluded because of improper randomization or blinding, insufficient data presentation or interpretation, lack of information on anesthetic and analgesic technique, and so on. [8–15]
Effects of Anesthetic and Analgesic Technique
Choice of Anesthetic Technique
The choice of anesthetic technique, primarily general anesthesia (GA), spinal or epidural anesthesia (SA or EA), and inguinal field block (IFB, to be discussed) depends on considerations about safety, economy, and postoperative analgesia.  Despite herniorrhaphy being a common operation and often performed in elderly and high-risk patients, only two randomized studies provide reliable data to compare different techniques. Tverskoy et al. compared inhalational GA, GA plus incisional bupivacaine (GA+), and SA for open hernia repair of unspecified type in 36 patients.  Pain scores were significantly higher in the GA group than in both other groups during rest and mobilization after 24 and 48 h, but not after 10 days, and the SA group had higher mobilization pain scores than the GA+ group after 24 and 48 h, but not after 10 days. In addition, wound tenderness was significantly lower in the GA+ group than in both other groups for 10 days, and there was a longer time to first analgesic in the GA+ group. Teasdale et al. compared GA (intravenous + inhalational) with IFB with lidocaine in 103 patients undergoing open herniorrhaphy, but found no differences in pain after 6 and 24 h and 1 week postoperatively.  However, at 6 h the patients in the IFB group were able to mobilize to a greater extent, and there was significantly less nausea, vomiting, headache, and sore throat for the first 24 h.
Inguinal Field Block (conduction blockade of the iliohypogastrical and ilioinguinal nerves at the level of the iliac crest, often combined with incisional infiltration). In four placebo-controlled studies, IFB supplementary to GA reduced pain scores for the first 30 min to approximately 6 h [19–22] and reduced the use of analgesics. [19–21] In patients operated during spinal anesthesia with or without IFB, pain and analgesic use were decreased for the first 48 h in the IFB group.  No differences in pain scores during the first 24 h or use of additional analgesics were observed when GA was supplemented with either IFB or wound instillation of local anesthetic. 
Incisional Analgesics-Local Anesthetic. Although incisional administration of local anesthetics has been demonstrated to be effective on postoperative pain in several types of operations,  only three randomized studies with nontreatment or placebo control groups are available regarding herniorrhaphy patients. One compared GA with and without wound bupivacaine infiltration and found less pain in the incisional bupivacaine group (see previous discussion). One placebo-controlled study of incisional bupivacaine infiltration showed less pain during rest, mobilization, and cough and a decreased use of analgesics in the bupivacaine group during the first 6 h.  Another placebo-controlled study showed that lidocaine sprayed on the wound surfaces decreased pain during rest but not during mobilization; in addition, meperidine use was reduced in the lidocaine group.  Although different local anesthetic techniques apparently are effective, the site of local anesthetic application also may be important. In one study, subfascial injection of lidocaine was more effective to reduce pain scores at rest, cough, and mobilization and to delay request for analgesics compared with subcutaneous administration, suggesting that the local anesthetic should be administered into the muscle and subfascial layers. 
Different agents have been added to local anesthetics to enhance their action. However, placebo-controlled studies on the addition of dextran (to delay absorption) or triamcinolone (to reduce tissue inflammation) to the local anesthetic solution for infiltration anesthesia have not demonstrated prolonged analgesia or reduced need for analgesics.
The choice of local anesthetic should logically be a long-acting drug, although in the only comparative study, no difference was demonstrated between bupivacaine and ropivacaine. 
Incisional Analgesics-NSAID, Opioid. Local administration of nonsteroidal antiinflammatory drugs (NSAID) has been studied with intrawound administration of ketorolac or piroxicam gel. Intrawound administration of ketorolac was as effective as intramuscular or intravenous ketorolac, but was more effective than oral ketorolac, [32,33] and was as effective as incisional bupivacaine.  The use of preoperative piroxicam gel reduced pain (0–4 h) and morphine consumption (24 h) compared with saline and was as effective as an IFB block. 
The demonstration of an increased number of opioid receptors on peripheral nerve terminals in the postinflammatory state has led to the concept of peripheral opioid treatment.  This approach may be effective in arthroscopic procedures. However, in the only herniorrhaphy study comparing intravenous versus intrawound versus subcutaneous administration of morphine, 5 mg, no differences in pain or analgesic requirements could be demonstrated, although supplementary morphine use was reduced in all three groups compared with a placebo group. 
Systemic Analgesics-NSAID, Opioids. Systemic NSAID reduced postherniorrhaphy pain and use of additional analgesics in four placebo-controlled studies. [32,33,35,36] The effect of acetyl salicylic acid may be less because an analgesic effect was demonstrated in only one of two studies. [22,36] Only one placebo-controlled study of the effect of systemic morphine administration on postherniorrhaphy pain is available; it shows a higher use of supplementary morphine in the placebo group but without significant differences in pain scores. 
Cryoanalgesia. In a study in 36 patients, cryoanalgesia of the ilioinguinal nerve had no significant effect on pain scores or on use of supplemental analgesics. 
Preemptive Analgesia. Experimental studies have demonstrated that administration of analgesics before surgical trauma can decrease or even abolish posttraumatic sensitization in the spinal cord and on secondary hyperalgesia.  It was therefore hypothesized that preemptive analgesia, i.e., pain treatment before the nociceptive stimulus, would reduce intensity and duration of postoperative pain.  Two double-blind, randomized studies comparing pre- and postincisional subcutaneous and subfascial infiltration with lidocaine or bupivacaine conflict. One study showed delayed request for additional analgesics in the preincisional group, but with similar pain scores,  whereas the other study, with prolonged and repeated observation up to 1 week, could not demonstrate differences in pain scores or use of or time to first request of analgesics between pre- and postincisional groups.  In other surgical procedures, preemptive analgesia with nerve blocks, opioids, or NSAID also has had questionable efficacy. [39,42,43]
Multimodal Analgesia. A combination of analgesics, with a potential reduction of side effects, has been demonstrated to improve analgesia in gynecologic, thoracic, and abdominal surgery.  In hernia surgery, few systematic studies of such multimodal analgesia are available, although combinations of analgesics often are used in clinical practice. The use of incisional ketorolac and bupivacaine was not more effective than bupivacaine or ketorolac alone.  Likewise, the combination of IFB and oral acetyl salicylic acid and papaveretum did not improve analgesia compared with IFB administered alone, although both were better than oral analgesia alone or placebo. 
Effects of Surgical Technique
The primary surgical techniques are the open procedures, i.e., simple anulorrhaphy, a duplication of the muscle and fascia layers (Bassini, McVay, Shouldice techniques), or tension-free implantation of prosthetic material (Lichtenstein, mesh plug techniques) to reinforce the posterior wall of the inguinal canal, with or without an extirpation of the hernial sac. In addition to these techniques, the laparoscopic approach with implantation of prosthetic material has received increased interest. Postoperative pain and duration and quality of convalescence may depend on choice of surgical technique, as summarized in Table 2and Table 3.
Open Repair Techniques. In a randomized study in 209 herniorrhaphies, patients with a Lichtenstein mesh repair used about 50% less analgesic postoperatively compared with those receiving a Shouldice repair.  Pain was not scored, and more patients in the Lichtenstein group received local infiltration anesthesia, which may have influenced the results. In a randomized study in 105 patients, nonligation of the hernia sac resulted in less pain 2 and 6 weeks postoperatively compared with ligation. 
Laparoscopic Versus Open Repair. Eleven prospective randomized studies have compared the laparoscopic transabdominal approach [3,47–55] or the preperitoneal approach [55,56] with different open techniques, primarily Lichtenstein mesh or Shouldice technique (Table 2). In one study, the observation period included only the immediate recovery period; patients with the open repair used less opioid, probably because they received an inguinal field block.  Another study found improved performance tests in the laparoscopic repair group compared with the Lichtenstein group, probably as a result of less pain, although pain was not assessed.  In the remaining studies, laparoscopic repair resulted in significantly reduced pain in five studies [3,47,52,55,56] and significantly reduced use of analgesics in six studies. [3,47–49,52,53] However, in general, little information is given on intra- and postoperative pain management, and additional data are needed with optimized analgesic regimens in the open repair groups.
Late and Chronic Postherniorrhaphy Pain
Some patients may experience a long-lasting (> 4 weeks) pain state with allodynia or hyperalgesia in the groin or in the inner aspects of the thighs, which may severely impair level of function and quality of life. [5–7,57,58] The incidence of this condition varies from 0% to 8% after open repair [47–49,51,57–61] and from 0% to 10% after laparoscopic repair. [47–49,51,57,60] In most patients, the condition resolves spontaneously within 4–6 months, but in some, it may progress to a chronic, disabling state of pain. The exact incidence of chronic pain is unknown because of the lack of well- performed and complete prospective follow-up studies. In a recent survey, in 315 of 883 patients (240 were lost to follow up and 308 refused participation), the incidence of moderate-to-severe episodic pain 1 year postoperatively was 12%. 
The proposed cause of chronic pain is damage to one the sensory nerves (iliohypogastric and ilioinguinal nerves and the genital branch of the genitofemoral nerve) during dissection under open hernia repair. [5–7] During the laparoscopic procedure entrapment of nerves by the metal staples used to affix the prosthetic material has been proposed,  but only rarely documented, as the cause. [60,63,64]
Both preservation or routine division of the genital branch of the genitofemoral nerve have been advocated to prevent pain. [7,57,58,65] Therapeutically, repeated local anesthetic blocks, alone or in combination with glucocorticoids or cryoanalgesia are recommended, whereas different surgical approaches should be restricted to cases, refractory to local anesthetic or multimodal pain therapy. [5–7,57,58,66] However, no prospective, controlled studies exist on prevention or therapy of chronic postherniorrhaphy pain.
With 2,800 hernia repairs per million people per year in the United States and with an average convalescence period between 2–3 weeks (see data from randomized studies in Table 3) the socioeconomic impact of postherniorrhaphy convalescence is large. No study is available to elucidate the exact factors responsible for the length of postherniorrhaphy convalescence, and recommendations vary tremendously in the literature, ranging from a few days [67,68] up to 16 weeks. [69,70] Recommendations are not based on valid scientific data regarding the influence of pain or the risk of recurrence. The patient's experience of pain combined with restrictions caused traditional practice are probably the main factors to determine the duration of convalescence.  Early return to normal activities within days or weeks has not been demonstrated to increase the risk of recurrence,  and in the only randomized study to date, no difference in recurrence rate was found between two groups of naval officers who had either 3 weeks or 3 months leave from full physical activity. 
Except from short-term studies, no randomized clinical trials have examined the effect of different analgesic techniques on postherniorrhaphy convalescence. Teasdale et al. showed that patients who had IFB were ambulatory before patients receiving general anesthesia.  Nehra et al. showed better mobilization scores 6 h, but not 24 h, postoperatively after supplementary IFB plus oral analgesics compared with oral analgesics administered alone or with placebo. 
The influence of surgical technique on convalescence has been studied in nine randomized studies (Table 3). Only one study compared open techniques (Lichtenstein versus Shouldice) and found no difference in absence from work.  Of the eight studies comparing laparoscopic repair versus different open repair techniques (Table 3), a significantly shorter absence from work after laparoscopic repair was demonstrated only in three studies. [3,51,53] The median or mean time off work varied between 9 and 31 days in laparoscopic groups and between 10 and 48 days in the open groups. This pronounced interstudy variability in duration of convalescence probably reflects differences in traditions and recommendations for sick leave rather than the effect of surgical technique. Interpretation of convalescence data are further hindered by the role of personal motivation, insurance status, and physical workload. [72,73]
- Inguinal field block and incisional local anesthetics decrease early (< 6 h) postherniorrhaphy pain scores and use of additional analgesics. The finding of extended analgesia (up to 48 h) needs further documentation.
- Local (intrawound) NSAID or morphine administration may not confer any important analgesic advantage over systemic use.
- Systemic NSAID administration reduces postherniorrhaphy pain and need for additional analgesics.
- Timing of analgesic treatment (preemptive analgesia) has probably no clinically important effect on postherniorrhaphy pain or on analgesic requirements.
- No open repair technique has convincingly been demonstrated to be superior to another with respect to postoperative pain.
- Laparoscopic herniorrhaphy results in less pain and shorter convalescence than open repair.
- The relationship between postherniorrhaphy pain, effective analgesia, and length of convalescence needs further evaluation.
- The incidence, pathogenesis, and management of late, chronic postherniorrhaphy pain need to be evaluated in well-designed studies with complete follow-up evaluation.
Despite postherniorrhaphy pain being common and probably of importance for convalescence, good scientific data on the incidence, duration, management, and socioeconomic implications of acute and chronic postherniorrhaphy pain are lacking.
To improve early postherniorrhaphy pain therapy, systematic studies on the topographic origin of pain and sensation from the wound components (skin, subcutaneous tissue, muscle fascia, and so on) and a systematic description of the intensity and duration of pain at rest and during mobilization after the various surgical techniques are required. From an anesthesiologic point of view, the multimodal analgesic approach may be most relevant, and there is a need for further well-controlled studies of multimodal analgesic management of postherniorrhaphy pain.
Development of long-acting, slow-release preparations with incorporation of local anesthetics or opioids in liposomes or microspheres, so far only tested in experimental pain models, deserves increased attention. [74,75]
Although pain retards postherniorrhaphy convalescence, this has not been sufficiently elucidated with scientific data, and a systematic description of convalescence and its relationship to pain, age, surgical technique, traditional practice, work load, insurance status, and risk of recurrence and the socioeconomic consequences of changes in pain management and surgical technique is needed. Future studies should evaluate the effect of laparoscopic versus open techniques on convalescence in well-defined patient populations, including occupational and insurance data. In addition, brief absence from work and physical activity (probably only a few days) should be a standard recommendation in patients with limited, light, or moderate work load and physical activities. Only by such a strategy can true differential effects of various analgesic and surgical techniques on duration and quality of postherniorrhaphy convalescence be evaluated, and such data are mandatory if new surgical techniques are introduced. For example, potential benefits of laparoscopic hernia repair should be weighed against the extra cost associated with this technique, ranging from 281–973 dollars. [3,47,49,51] In addition, convalescence recommendations in patients with heavy work load or strenuous physical activity need to be reevaluated, based on good scientific data, and related to the duration of pain.
Well-designed, prospective and complete scientific data are required to evaluate the incidence of chronic pain after different surgical techniques and to provide recommendations for rational therapy.
To solve these important questions, with major socioeconomic implications, anesthesiologists and surgeons should collaborate to integrate their knowledge on surgical, anesthetic and analgesic, and socioeconomic factors in future research.