The effect of intravenous magnesium sulfate infusion on sensory spinal block and postoperative pain score in abdominal hysterectomy

AIM

The aim of this study was to investigate the effect of i.v. infusion of magnesium sulphate during spinal anesthesia on duration of spinal block and postoperative pain.

METHODS

Forty ASA physical status I and status II, aged between 18 and 65, female patients undergoing abdominal hysterectomy under spinal anesthesia were enrolled in this study. Patients in the magnesium group (Group M, n = 20) received magnesium sulphate 65 mg kg(-1) infusion in 250 mL 5% dextrose at 3.5 mL/min rate, and control group (Group C, n = 20) received at the same volume of saline during operation in a double-blind randomized manner. Duration of sensory and motor block, systolic, diastolic, and mean arterial blood pressures, heart rates, pain scores (VAS values), and side effects were recorded for each patient. Blood and CSF samples were taken for analysis of magnesium concentrations.

RESULTS

Regression of sensorial block was longer in Group M when compared with that in Group C (175 ± 39 versus 136 ± 32 min) (P < 0.01). The VAS scores were lower in Group M than those in Group C at the 2 time points postoperatively (P < 0.01).

CONCLUSION

65 mg kg(-1) of magnesium sulphate i.v. infusion under spinal anesthesia prolongs spinal sensorial block duration and decreases pain VAS scores without complication in patients undergoing abdominal hysterectomy.

Comparative effects of vasectomy surgery and buprenorphine treatment on faecal corticosterone concentrations and behaviour assessed by manual and automated analysis methods in C57 and C3H mice

Establishing effective cage-side pain assessment methods is essential if post-surgical pain is to be controlled effectively in laboratory animals. Changes to overall activity levels are the most common methods of assessment, but may not be the most appropriate for establishing the analgesic properties of drugs, especially in mice, due their high activity levels. Use of drugs that can affect activity (e.g. opioids) is also a problem. The relative merits of both manual and automated behaviour data collection methods was determined in two inbred mouse strains undergoing vasectomy following treatment with one of 2 buprenorphine dose rates. Body weights and the effects of surgery and buprenorphine on faecal corticosterone were also measured.

Surgery caused abnormal behaviour and reduced activity levels, but high dose buprenorphine caused such large-scale increases in activity in controls that we could not establish analgesic effects in surgery groups. Only pain-specific behaviour scoring using the manual approach was effective in showing 0.05 mg/kg buprenorphine alleviated post-vasectomy pain. The C57 mice also responded better to buprenorphine than C3H mice, indicating they were either less painful, or more responsive to its analgesic effects. C3H mice were more susceptible to the confounding effects of buprenorphine irrespective of whether data were collected manually or via the automated approach. Faecal corticosterone levels, although variable, were higher in untreated surgery mice than in control groups, also indicating the presence of pain or distress.

Pain-specific scoring was superior to activity monitoring for assessing the analgesic properties of buprenorphine in vasectomised mice. Buprenorphine (0.01 mg/kg), in these strains of male mice, for this procedure, provided inadequate analgesia and although 0.05 mg/kg was more effective, not completely so. The findings support the recommendation that analgesic dose rates should be adjusted in relation to the potential severity of the surgical procedure, the mouse strain, and the individual animals' response.

[First experience of monoport laparoscopic surgery in the treatment of kidney diseases]

The results of research on the effectiveness of monoport laparoscopic surgery for kidney disease are presented. Operations using LESS method (Laparo-Endoscopic Single-Site Surgery) were performed in 21 patients, including 14 nephrectomies and 7 cyst resections. In five cases, nephrectomy was performed due to terminal hydronephrosis, in two cases--due to presence of arteriolosclerotic kidney, in seven cases--due to renal cell carcinoma (T1a-bN0M0). "Pain DETECT" questionnaire was used for assessment of pain symptom. Maximum longitudinal size of a removed organ was 14 cm, the average volume of intraoperative blood loss--80 ml. Duration of monoport laparoscopic radical nephrectomies ranged from 125 to 230 min (mean duration, 164 min). The time for renal cyst resection ranged from 40 to 120 minutes. Moderate intensity pain was observed in all patients but only at the first day after surgery. The average hospital stay was 4 days. The length of postoperative skin scar varied from 2.5 to 6.0 cm. Early and late postoperative complications were not observed. During follow-up period 6 to 8 months, tumor or cyst recurrence were not registered.

Does body mass index and position of impacted lower third molar affect the postoperative pain intensity?

The main objective of this study was to determine to which extent body mass index and position of impacted lower third molar was affecting the pain intensity in the first seven postoperative days. The study was conducted following the extraction of the lower third molar in 108 patients. Depending on the type of information given to each particular patient, the patients were divided in two groups: the test group where patients were given detailed standard written and verbal instructions and the control group which received only standard written instructions about treatment after surgery. Using canonical discriminant analysis we investigated the influence of body mass index and the position of impacted lower third molar on postoperative pain intensity in two groups of patients. Results of this study showed that the body mass index or the tooth position did not have influence on intensity of postoperative pain. The body mass index and the position of impacted lower third molar do not affect the postoperative pain intensity.

Evaluation of leukemia inhibitory factor (LIF) in a rat model of postoperative pain

Postoperative pain remains a significant problem despite optimal treatment with current pharmaceutical agents. In an effort to provide better postoperative pain control, there is a need to understand the factors that contribute to the development of pain after surgery. Leukemia inhibitory factor (LIF) is a pleiotropic cytokine released from tissues after injury. We hypothesized that LIF expression in skin, muscle, and dorsal root ganglion (DRG) would increase after plantar incision. The mRNA and protein expression of LIF and LIF receptor (LIF-R) were measured after plantar incision in the rat. Pain behaviors, immunohistochemistry, and C-fiber heat responses to LIF were also studied. LIF expression increased after incision in skin and muscle, and LIF-R was present in large and small DRG neurons. LIF administration to the hindpaw increased pain behaviors, a process that was reversed by anti-LIF. However, LIF and anti-LIF treatment at the time of incision did not augment or ameliorate pain behaviors. LIF treatment activated the second messenger system, JAK-STAT3, in cultured DRG neurons, but failed to alter spontaneous activity or heat responses in C-fiber nociceptors. In conclusion, LIF is not a target for postoperative analgesia; LIF may be important for skin and muscle repair and regeneration after incision.

PERSPECTIVE

This article highlights an incision pain model for the study of factors involved in nociception. The study demonstrates that LIF in is an unlikely target for novel early postoperative analgesics.

Prevention of scar tissue formation in spinal surgery: state of the art and review of the literature

Recurrent radicular pain after lumbar micro-discectomy may lead to reduced quality of life of the patient. Lumbar epidural fibrosis is believed to be one of the mechanisms involved in the genesis of the pain. The use of absorbable gel temporarily separating disc remnants, muscle or bone structures from the nerve roots could reduce the amount of scar tissue surrounding the nerve, reduce tethering and therefore pain, improve outcomes and facilitate revision surgery. The author reviews the literature on prevention techniques for lumbar epidural fibrosis. The most recent studies on new compounds are encouraging in terms of safety and clinical efficacy.

[Pasha-Cath in the treatment of neuropathic pain: case report]

In neuropathic pain, the nerve fibers themselves may be damaged, dysfunctional or injured. A 49-year-old female patient experienced radiating right anterior arm pain following an operation on the same arm. Visual analogue scale (VAS) score was 10. Tramadol, gabapentin and amitriptyline were started as medical treatment. In view of the persisting complaints, epidural pulsed radiofrequency with Pasha-Cath was scheduled. After 2 years, VAS remained at 1-2. It was concluded that epidural pulsed radiofrequency with Pasha-Cath is an alternative and effective choice of treatment in neuropathic pain when the medical treatment alone is not sufficient.

Consequences of persistent pain after lung cancer surgery: a nationwide questionnaire study

BACKGROUND

post-thoracotomy pain syndrome (PTPS) and its social consequences have been inconsistently investigated as most studies were either small sized, focused on a limited number of risk factors or included heterogeneous surgical procedures. The current objectives were to obtain detailed information on the consequences of PTPS after thoracotomy and video-assisted thoracic surgery (VATS) from homogenous unselected nationwide data, and to suggest mechanisms for the development of PTPS.

METHODS

data from 1327 patients were collected using a prospective national database and combined with a detailed questionnaire.

RESULTS

the response rate was 81.5%, resulting in 546 patients without prior thoracic surgery for the final analysis. Follow-up was 22 months (range 12-36). PTPS occurred in 33% thoracotomy patients and 25% VATS patients. Clinically relevant pain was present in 11-18% of the patients and severe pain in 4-12% depending on the level of physical activity. In PTPS patients, 64% also had pain from other locations on the body. Perceived sensory changes in the thoracic area were present in 63% of PTPS patients vs. 25% in pain-free patients (P<0.001). When comparing VATS with thoracotomy, no consistent differences in the prevalence, distribution of pain, sensory changes or effect of pain on daily activities were observed although clinically relevant and severe pain was reduced after VATS.

CONCLUSIONS

this nationwide study corroborates that PTPS is a clinically relevant problem influencing daily activities a long time after thoracotomy and VATS. Nerve injury and increased pain responsiveness may explain the majority of symptoms, the prevalence and distribution of pain including perceived sensory sensations.

[Complications of tongue base reduction with radiofrequency tissue ablation on obstructive sleep apnea hypopnea syndrome]

OBJECTIVE

To investigate the complications of tongue base reduction with radiofrequency tissue ablation on patients with obstructive sleep apnea hypopnea syndrome (OSAHS) and find out the effective prevention strategies.

METHODS

One hundred and ninety three OSAHS patients diagnosed by polysomnography were received tongue base reduction with radiofrequency tissue ablation between March 2008 and December 2009. The intraoperative and postoperative complications including bleeding, hematoma of tongue base, abscess of tongue base, altered taste, tongue numbness, deviation of tongue extension movement, dysfunctions of pronunciation and swallowing as well as the managements were analyzed retrospectively.

RESULTS

No perioperative complications occurred. There were 186 cases with postoperative pain (96.4%), 155 cases with submandibular edema (80.3%). Nocturnal sudden cardiac death was encountered in 1 case and secondary bleeding in 1 case. There was no ulceration of tongue base mucose, hematoma or abscess of tongue base, altered taste, tongue numbness, tongue deviations, speech, swallowing and taste disorder after operation. The scale of postoperative pain claimed by patients was ranged between mild to moderate. Diclofenac suppository had analgesic effect for these patients. The quantity of bleeding in patient with secondary hemorrhage was so little that after proper treatment the bleeding was stopped and never happened again. Patient with nocturnal sudden cardiac death occurred at thirty-seven hours after operation, because of swelling and pain of tongue base aggravated sleep apnea and night hypoxemia inducing fatal arrhythmia.

CONCLUSIONS

Postoperative pain and submandibular edema were 2 most common postoperative complications which can be easily controlled by antibiotics, Glucocorticoids and Diclofenac suppository. For those severe OSAHS patients accompanied by cardiopulmonary diseases, the tongue base reduction with radiofrequency tissue ablation can induce nocturnal sudden cardiac death. It is important to pay more attention on arrhythmias at night in severe OSAHS patients.

Evidence for a role of endocannabinoids, astrocytes and p38 phosphorylation in the resolution of postoperative pain

BACKGROUND

An alarming portion of patients develop persistent or chronic pain following surgical procedures, but the mechanisms underlying the transition from acute to chronic pain states are not fully understood. In general, endocannabinoids (ECBs) inhibit nociceptive processing by stimulating cannabinoid receptors type 1 (CB(1)) and type 2 (CB(2)). We have previously shown that intrathecal administration of a CB(2) receptor agonist reverses both surgical incision-induced behavioral hypersensitivity and associated over-expression of spinal glial markers. We therefore hypothesized that endocannabinoid signaling promotes the resolution of acute postoperative pain by modulating pro-inflammatory signaling in spinal cord glial cells.

METHODOLOGY/PRINCIPAL FINDINGS

To test this hypothesis, rats receiving paw incision surgery were used as a model of acute postoperative pain that spontaneously resolves. We first characterized the concentration of ECBs and localization of CB(1) and CB(2) receptors in the spinal cord following paw incision. We then administered concomitant CB(1) and CB(2) receptor antagonists/inverse agonists (AM281 and AM630, 1 mg x kg(-1) each, i.p.) during the acute phase of paw incision-induced mechanical allodynia and evaluated the expression of glial cell markers and phosphorylated p38 (a MAPK associated with inflammation) in the lumbar dorsal horn. Dual blockade of CB(1) and CB(2) receptor signaling prevented the resolution of postoperative allodynia and resulted in persistent over-expression of spinal Glial Fibrillary Acidic Protein (GFAP, an astrocytic marker) and phospho-p38 in astrocytes. We provide evidence for the functional significance of these astrocytic changes by demonstrating that intrathecal administration of propentofylline (50 microg, i.t.) attenuated both persistent behavioral hypersensitivity and over-expression of GFAP and phospho-p38 in antagonist-treated animals.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate that endocannabinoid signaling via CB(1) and CB(2) receptors is necessary for the resolution of paw incision-induced behavioral hypersensitivity and for the limitation of pro-inflammatory signaling in astrocytes following surgical insult. Our findings suggest that therapeutic strategies designed to enhance endocannabinoid signaling may prevent patients from developing persistent or chronic pain states following surgery.

Effects of ketamine added to ropivacaine in pediatric caudal block

OBJECTIVES

We aimed to determine the hemodynamic effects and postoperative pain control quality of ropivacaine and ketamine addition to ropivacaine in children undergoing inguinal hernia repair with caudal anesthesia.

METHODS

A total of 45 patients (1-4 years) scheduled to undergo inguinal hernia repair were studied. Anesthesia was induced with sevoflurane in O2/N2O and vecuronium was administered to facilitate endotracheal intubation. Anesthesia was maintained with sevoflurane in O2/N2O. Patients were randomly divided into three groups. Following endotracheal intubation, we administered 2 mg/kg 0.2% ropivacaine to Group R; 0.5 mg/kg ketamine to Group K; and 2 mg/kg 0.2% ropivacaine plus 0.5 mg/kg ketamine to Group R+K caudally. Pain levels were evaluated via modified CHEOPS, and sedation levels were assessed by the Wilson Sedation Scale.

RESULTS

At the postoperative 45th minute (min), the CHEOPS score was significantly higher in Group R compared to Group K and Group R+K (p<0.05). This score was significantly higher in Group R than in Group R+K at the postoperative 60th min (p<0.05). The effective analgesic period was significantly higher in Group K (852+/-309 min) and Group R+K (1032+/-270 min) than in Group R (435.5+/-273 min) (p<0.05). The analgesic requirement in the first 24 hours postoperatively was lower in Group R+K than the other groups. Sedation scores were below 2 in all groups. There were no significant differences between groups regarding adverse events.

CONCLUSION

The results of the present study indicate that caudal ropivacaine, ketamine and ropivacaine plus ketamine provided effective postoperative analgesia. Additionally, ketamine combined with ropivacaine lengthened the duration of analgesia while lowering analgesic requirements.

Utility of pathologic evaluation following removal of explanted orthopaedic internal fixation hardware

This report questions the cost and effectiveness of routinely sending explanted hardware to pathology for evaluation. Forty-six consecutive patients who had symptomatic hardware removed were enrolled in this study. Pathology reports following hardware removal were obtained, and charts were reviewed for these patients. The pathology department was contacted for related departmental procedure codes, and hospital billing records were obtained regarding the cost of the procedure. In all cases, the pathology reports gave the gross diagnosis of "hardware" and the gross description included the measurements of the internal fixation hardware removed. In no case did the report alter the plan of the attending physician. The healthcare system may benefit by subspecialty review of the current practice of sending internal fixation devices to pathology for evaluation. We recommend a single radiographic view along with proper documentation in the postoperative report to confirm the removal of internal fixation hardware in lieu of pathologic evaluation.

Redo kyphoplasty with vertebroplasty technique: a case report and review of the literature

Osteoporosis is a metabolic disorder which may result in devastating medical problems if not treated appropriately. However, even in the best treated patients fractures may occur. The most devastating fractures are spine and hip. Traditionally, treating fractures of the spine consisted of bed rest, opioid analgesic medications, and bracing. This resulted in increased risk of side-effects from medication, myocardial infarction, pulmonary embolism, pneumonia, admissions to nursing homes, and death. Vertebroplasty and kyphoplasty techniques were developed to decrease the detrimental effects of "conservative care" by decreasing or eliminating the pain and stabilizing the fracture. The safety and efficacy of vertebroplasty and kyphoplasty are similar with several biased opinions in the literature which denotes conflict. Choosing one technique over the other is a physician and/or facility performed preference. There are a small percentage of patients that either vertebroplasty or kyphoplasty does not help. Possibilities could be that not enough cement was used, an adjacent level fracture has occurred, or worsening fracture around the previously treated fracture is causing the pain. For the latter, a repeat vertebral augmentation could be medically necessary. Due to technical constraints, placing an additional kyphoplasty after one has already been accomplished may be technically dangerous and a simpler less costly vertebroplasty technique may be beneficial. This is a case report and review of the literature on the treatment of repeat vertebral augmentation after a previously treated vertebral fracture with kyphoplasty technique. To this date, this is the first article published regarding the use of vertebroplasty technique over a kyphoplasty treated patient. In this case report, a redo vertebroplasty was performed over a previously treated kyphoplasty or vertebroplasty. This procedure can give a patient significant pain relief when they are suffering with pain after a previously treated fracture.

Effect of intraarticular injection of lornoxicam on the articular cartilage & synovium in rat

BACKGROUND & OBJECTIVE

Intraarticular (i.a) drug application is consider to be a new therapeutic approach for the treatment of postoperative pain after arthroscopic knee surgery without any systemic adverse effects. Lornoxicam, a nonsteroid anti-inflammatory drug is a short acting agent, and its anti-inflammatory and analgesic activity may be effective in the postoperative pain management in minor surgery. In this study, the effects of intraarticular administration of lornoxicam on the synovium and articular cartilage in the rat knee joint were investigated.

METHODS

Lornoxicam (0.25 ml) was given as an injection into the right knee joint and 0.25 ml of 0.9 per cent saline solution by injection into the left knee joint as a control in 25 rats. Groups of five rats were sacrificed by a lethal injection of ketamine 1st, 2nd, 7th, 14th and 21st days after lornoxicam administration. Knee joints were detached, fixed in 10 per cent buffered formalin and decalcified. Serial sections of 5 microm were stained with haematoxylin-eosin and evaluated for the presence of inflammation in the articular, periarticular regions and synovium. Inflammatory changes in the joints were graded according to a five-point scale, histologically.

RESULTS

There were no significant differences in inflammation and cartilage degeneration, between control and lornoxicam applied knees. Grade 3 inflammatory changes occurred only in one knee in lornoxicam group, at 24 h after injection. No pathological changes were observed in both groups at any time point.

INTERPRETATION & CONCLUSION

Lornoxicam did not show significant effect on inflammation on rat synovia in knee joint. Further studies including in human need to be done before any recommendations are made for i.a. administration of lornoxicam.

Preponderance of sensory versus sympathetic nerve fibers and increased cellularity in the infrapatellar fat pad in anterior knee pain patients after primary arthroplasty

Sensory nerve fibers transmit pain perception and secrete pro-inflammatory substance P (SP). Sympathetic nerve fibers secrete anti-inflammatory norepinephrine and endogenous opioids, which inhibit pain perception in a bidirectional crosstalk with sensory fibers. In patients with anterior knee pain after primary arthroplasty of the knee (AKP), this study investigated in parallel the innervation of the infrapatellar fat pad by sensory and sympathetic nerve fibers. A total of 32 patients with osteoarthritis (OA) of the knee (n = 10), AKP after primary knee joint replacement (n = 7), and OA of the hip (n = 15) were included. Sensory nerve fibers were semiquantitatively detected by immunohistochemistry against SP, and sympathetic nerve fibers were stained with an antibody against tyrosine hydroxylase. Cellular density of the tissue was investigated by counting cell nuclei. The density of sympathetic nerve fibers in the fat tissue was similar in knee OA as compared to AKP. In the fat tissue, density of sensory substance P-positive nerve fibers was higher in AKP than in knee OA, which was not observed in the fibrosis capsule of the fat pad. The preponderance of sensory over sympathetic nerve fibers was accompanied by an increased cellular density in fat tissue in patients with AKP compared to knee OA. A positive correlation existed between cellularity and sensory nerve fiber density in fat tissue. This study revealed a preponderance of sensory over sympathetic innervation in the infrapatellar fat pad in AKP after primary arthroplasty of the knee, which possibly leads to aggravation and continuation of AKP and local inflammation.

Novel biomechanical quantification methodology for lumbar intraforaminal spinal nerve adhesion in a laminectomy and disc injury rat model

Spinal nerve fibrosis following injury or surgical intervention may play an important role in the pathophysiology of chronic back pain. In this current study, we demonstrate the role of biomechanical quantification of lumbar intraforaminal spinal nerve adhesion and tethering in the analysis of the post-laminectomy condition and describe a direct methodology to make this measurement. Twenty age-matched Sprague-Dawley male rats were divided into operative and non-operative (control) groups. Operative animals underwent a bilateral L5-L6 laminectomy with right-side L5-6 disc injury, a post-laminectomy pain model previously published by this lab. At eight weeks, animals were sacrificed and the strength of adhesion of the L5 intraforaminal spinal nerve to surrounding structures was quantified using a novel biomechanical methodology. Operative animals were found to have a significantly greater load to displace the intact right L5 spinal nerve through the intervertebral foramen when compared to control animals. The findings show that the post-laminectomy condition creates quantifiable fibrosis of the spinal nerve to surrounding structures and supports the conclusion that this fibrosis may play a role in the post-laminectomy pain syndrome.

Mid-term results of stapled hemorrhoidopexy for third- and fourth-degree hemorrhoids--correlation with the histological features of the resected tissue

BACKGROUND

Stapled hemorrhoidopexy is used to remove a circumferential strip of mucosa and submucosa about 4 cm above the dentate line, in order to restore the correct anatomical relationships of the anal canal structures. We evaluated the histological features of the resected tissue obtained after stapled hemorrhoidopexy with correlation to the short-term and mid-term results.

METHODS

This retrospective study evaluated 234 cases of stapled hemorrhoidopexy. Data concerning postoperative bleeding, anal pain, incontinence, stenosis, and recurrence of hemorrhoids were collected from hospital and outpatient clinic records. Histologic slides were examined for the type of epithelium, presence of muscle fibers, nerve endings, and degree of vascular ectasia.

RESULTS

Some 52% of the biopsies revealed on the surface a combination of glandular with squamous epithelium, meaning a stapling line at the level of the transitional zone/dentate line. Smooth muscle fibers were more frequent as the stapling line approached the level of the dentate line/transitional zone (p = 0.0028). Internal sphincter fibers were present in 36% of the cases, yet there were no cases of anal incontinence. Inclusion of merely squamous epithelium in the resected tissue correlated with severe postoperative pain persisting one week after surgery (p < 0.0001), whereas the concurrent presence of squamous and glandular epithelium correlated only with severe pain on the first postoperative day (p = 0.018). Nerve endings were more frequent in patients with anal pain one week after surgery (p = 0.02). The rate of recurrence of symptoms was 3%, which did not correlate with any of the histological parameters tested.

CONCLUSIONS

Though stapled hemorrhoidopexy is performed according to well-established technical guidelines, it is too difficult to be standardized.

Behavioral alterations and severity of pain in cats recovering at home following elective ovariohysterectomy or castration

OBJECTIVE

To identify behavioral alterations in client-owned cats recovering at home following elective ovariohysterectomy or castration and determine owner perceptions regarding severity of postoperative pain.

DESIGN

Cohort study. Animals-145 cats undergoing elective ovariohysterectomy (n = 80) or castration (65) at 4 veterinary clinics in Finland.

PROCEDURES

Owners were asked to complete a questionnaire on their cats' behavior during the 3 days after surgery. Owners were also asked to indicate their perceptions of the severity of postoperative pain during these days by use of a 100-mm visual analog scale.

RESULTS

Owners consistently indicated that there were changes in their cats' behavior, with the most commonly reported alterations being a decrease in overall activity level, an increase in the amount of time spent sleeping, a decrease in playfulness, and altered way of movement. Changes (ie, either an increase or decrease) in aggressive behavior were rare. Median pain score the day of surgery was 15.0 mm for male cats and 25.0 mm for female cats. Behavior score was significantly associated with day of observation, type of surgery (ovariohysterectomy vs castration), owner-assigned pain score, and veterinary clinic.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that behavioral alterations can be detected for several days after surgery in cats recovering at home following ovariohysterectomy or castration and emphasized owner concerns about the existence of postoperative pain.

Characterization of a model of persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR)

Various surgical procedures, e.g. thoracotomy and inguinal hernia repair, frequently evoke persistent pain lasting for many months following the initial surgery. The essential prolonged tissue retraction required during such surgeries may account for the persistence and high incidence of postoperative pain in these patient populations. This study describes a new rat model of persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR), akin to a clinical procedure. Under anaesthesia, skin and superficial muscle of the medial thigh were incised and a small pair of retractors inserted. This tissue was retracted for 1h causing potential stretch of the saphenous nerve. SMIR surgery evoked persistent significant mechanical hypersensitivity to von Frey stimulation of the plantar ipsilateral hindpaw, compared to either pre-surgery responses or concurrent responses of sham-operated rats. SMIR-evoked mechanical hypersensitivity was observed by postoperative day 3, most prominent between postoperative days 10 and 13, persisted until at least postoperative day 22 and had dissipated by postoperative day 32. Overall, mechanical sensitivity of the SMIR contralateral paw and the sham ipsilateral paw did not significantly change from pre-surgery responses. SMIR did not evoke significant heat hyperalgesia or cold allodynia. Light microscopy of saphenous nerve sections did not show degeneration or oedema in the saphenous nerve at, or proximally or distally to, the surgical site. In addition, very little to no degeneration was detected with ATF3 staining in DRG from SMIR-operated rats. These data suggest that prolonged retraction of superficial tissue evokes a persistent pain syndrome that is not driven by neuronal damage.

Cutaneous endothelin-A receptors elevate post-incisional pain

The contribution of endothelin-1 (ET-1), acting via endothelin-A receptors (ET(A)), on post-incisional pain was examined in a rat model of incision through the hairy skin of the lumbar dorsum. Post-incisional mechanical hyperesthesia was evaluated by cutaneous trunci muscle reflexes (CTMR) of subcutaneous muscles responding to stimulation with von Frey filaments near the wound (primary responses) and at a distance, especially on the contralateral dorsum (secondary responses, involving spinal circuits). The role of ET(A) was determined by pre-incisional, subcutaneous injection of the selective receptor antagonist BQ-123 at the incision site, 15 min or 24h before surgery. Control incisions showed both primary tactile allodynia and hyperalgesia, and a weaker secondary hyperesthesia, peaking 3-4h after surgery and lasting at least 24h. Primary allodynia, but not hyperalgesia, was dose-dependently suppressed by 15 min pre-incisional BQ-123. In contrast, both secondary allodynia and hyperalgesia were inhibited by local BQ-123. The suppression of primary allodynia by local antagonist disappeared in 24h, but that of secondary hyperesthesia remained strong for at least 24h. Systemically delivered BQ-123 was without effect on any post-incisional hyperesthesia, and if the antagonist was locally injected 24h before surgery there was no difference on hyperesthesia compared to vehicle injected at that time. We conclude that ET-1, released from skin by incision, activates nociceptors to cause primary allodynia and to sensitize spinal circuits through central sensitization. Blockade of ET(A) in the immediate peri-operative period prevents the later development of central sensitization.

Persistent pain in patients following scoliosis surgery

Chronic or persistent pain is increasingly recognised as a consequence of surgery in a number of different disciplines. The pain often exhibit qualities that differ from the acute post-operative pain and may represent changes in the central nervous system. There is lack of information regarding the incidence of persistent pain in patients following spinal surgery for scoliosis. This study aims to estimate the incidence of persistent pain following spinal surgery for scoliosis in a group of mainly adolescent patients. Questionnaires were distributed to consecutive patients attending the outpatient clinic of a hospital with specialist services in paediatric orthopaedics and spinal surgery. One hundred and five patients out of 122 eligible patients completed the survey. Fifty-two percent had ongoing pain upon hospital discharge either in the primary surgical site and/or in the iliac bone graft site. Approximately 10 and 7% of all patients had back and pelvic pain persisting beyond 12 months, respectively. A small proportion described elements of neuropathic pain. There was a trend suggesting that those who experienced more severe post-operative pain were more likely to develop persistent pain. These data are consistent with those reports that implicate surgery as the trigger for chronic pain.

From marrow oedema to osteonecrosis: common paths in the development of post-transplant bone pain

Osteonecrosis, the calcineurin-inhibitor-induced pain syndrome and transient marrow oedema may occur after renal transplantation, are generally painful and can be diagnosed by X-ray, radionuclide scan or magnetic resonance imaging. They share features of increased intraosseous pressure, compromised vascular supply, marrow oedema and the development of a 'bone compartment syndrome'. Glucocorticoid dosage is the most commonly implicated risk factor for osteonecrosis. Mechanisms may include the differentiation of mesenchymal stem cells to adipocytes causing increased intraosseous pressure and collapse of marrow sinusoids, as well as increased osteoblast and osteocyte apoptosis. Some of these effects may be ameliorated by lipid lowering drugs. Calcineurin-inhibitors, particularly cyclosporine, may increase the risk of osteonecrosis because of vasoconstrictive effects and sirolimus may influence the development of osteonecrosis by potentiating the effects of calcineurin inhibitors or by influencing the lipid profile. For osteonecrosis, early stages are generally managed conservatively or with core decompression sometimes accompanied by bone grafting and more recently the injection of bone morphogenic protein. The use of iloprost to improve blood flow and bisphosphonates and RANK-ligand inhibition to reduce osteoclastic resorption of remaining trabecular structures are as yet unproven strategies. Unfortunately, the rate of total hip arthroplasty remains high. For the calcineurin-inhibitor-induced pain syndrome and transient marrow oedema, calcium channel blockers, the reduction or withdrawal of calcineurin-inhibitors and core decompression have been used. Although a lack of randomized controlled trials makes management decisions difficult, early recognition of these bone pain syndromes affords the best opportunity for avoiding prolonged pain or joint replacement surgery.

Spinal glial activation contributes to postoperative mechanical hypersensitivity in the rat

The activation of spinal cord microglia and astrocytes after peripheral nerve injury or inflammation contributes to behavioral hypersensitivity. The contribution of spinal cord glia to mechanical hypersensitivity after hind paw incision has not been investigated previously. Male Sprague-Dawley rats underwent a unilateral plantar hind paw incision, and the development of mechanical hypersensitivity was assessed by using von Frey filaments. The activation of spinal cord microglia and astrocytes was measured 1, 2, 3, and 5 days after hind paw incision by using immunohistochemistry. The glial activation inhibitor, fluorocitrate, was administered intrathecally 24 hours after hind paw incision to determine glial involvement in mechanical hypersensitivity. Hind paw incision induced an activation of spinal astrocytes ipsilateral to incision within 24 hours. Both microglia and astrocytes reached a maximum activation 3 days after hind paw incision. Fluorocitrate produced a dose-dependent reduction in mechanical hypersensitivity when administered 24 hours after hind paw incision. Spinal cord glial activation contributes to the mechanical hypersensitivity that develops after hind paw incision.

PERSPECTIVE

Hind paw incision produces mechanical hypersensitivity that can be alleviated with the inhibition of spinal cord glia. Our results suggest that the activation of spinal cord astrocytes within 24 hours of incision contributes to mechanical hypersensitivity. Therefore, spinal cord astrocytes might represent a novel target for the treatment of postoperative pain.