Incidence and severity of complications due to

THEKNE-01681; No of Pages 5 The Knee xxx (2012) xxx–xxx

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The Knee

Incidence and severity of complications due to femoral nerve blocks performed for knee surgery Benjamin Widmer a, Sébastien Lustig a, b,⁎, Corey J. Scholes a, Allen Molloy c, Sean P.M. Leo a, d, Myles R.J. Coolican a, David A. Parker a a

Sydney Orthopaedic Research Institute, Chatswood, NSW, Australia Albert Trillat Center, Lyon Nord University Hospital, Lyon, France Anesthesiology, Royal North Shore Hospital, St Leonards, NSW, Australia d Singapore Armed Forces, Army Medical Services, Singapore b c

a r t i c l e

i n f o

Article history: Received 9 March 2012 Received in revised form 1 November 2012 Accepted 12 November 2012 Available online xxxx Keywords: Complications Femoral nerve block Knee

a b s t r a c t Background: While single shot femoral nerve blocks and indwelling femoral nerve catheters provide significant peri-operative analgesia, there are small but serious risks of neurovascular complications. We aimed to determine the incidence and characterise the nature of neural complications arising from femoral nerve blocks performed for knee surgery. Methods: One thousand eight hundred and two patients receiving a femoral nerve block for knee surgery during the study period were screened. Patients with possible neurological symptoms were evaluated with a detailed physical examination and self-report questionnaires. Also measures of depression, anxiety and tension/stress were collected. Results: In the patients screened, an incidence of 1.94% was found. Of the 24 patients available for testing, 4 had bilateral symptoms following bilateral nerve blocks. All had sensory abnormalities in the distribution of the femoral nerve. The incidence was significantly higher in females (females=2.5%, males=0.83% p=0.01) and in patients receiving a single shot block (single shot= 2.66%, femoral catheter=0.93, p=0.01). Conclusions: The incidence of neurological complication after FNB was higher in this series than typically reported and the symptoms significantly influenced the quality of life in the affected cases. The decision to include a femoral nerve block in the peri-operative analgesic regimen should be made on an individual basis considering the risks and benefits. Level of evidence: Therapeutic level IV. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Knee surgery often results in considerable peri-operative pain which often hinders rehabilitation and recovery. Multimodal peri-operative analgesia benefits patients by allowing them to participate comfortably in early peri-operative rehabilitation [1,2]. Peri-operative pain management is a critical aspect of total knee arthroplasty (TKA), as effective treatment has been correlated with improved patient satisfaction, better short term outcomes, and decreased length of hospital stay [3,4]. Numerous analgesia techniques have been employed to meet often competing demands, with each presenting risks and benefits. A key priority is to minimise systemic narcotic usage to reduce the incidence of known adverse reactions including tiredness, nausea, respiratory depression, decreased intestinal motility and urinary retention. Epidural analgesia is associated with various well documented risks [5–7], ⁎ Corresponding author at: Level 1, The Gallery 445 Victoria Avenue, Chatswood, NSW, 2067, Australia. Tel.: +61 2 9904 7182; fax: +61 2 9410 0666. E-mail address: [email protected] (S. Lustig).

the most important being probably to considerably slow mobilisation. Femoral nerve block (FNB) in combination with oral and parenteral analgesia has been used to provide effective post-surgical analgesia [8–12]. FNB has been generally described as safe and effective [13–15], and single-shot FNB has been shown to improve analgesia and reduce morphine requirements postoperatively [9,16]. A randomised controlled trial demonstrated more rapid ambulation and decreased post-operative narcotic requirements with FNB when compared with local anaesthetic infiltration via an intra-articular catheter [11]. The use of continuous femoral nerve sheath catheters was initially thought to be problematic due to variable accuracy of catheter position, analgesic benefits and bacterial colonisation [10,14,17]. However a high-volume centre reported a complication rate of only 0.3% with indwelling regional blockade catheters [12]. While these studies have documented improved analgesia, various neuromuscular complications have been encountered [18]. Falls due to quadriceps weakness have been associated with wound dehiscence or even peri-prosthetic fractures in patients undergoing TKA with FNB [19–21], although there are a number of other causes of iatrogenic

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Please cite this article as: Widmer B, et al, Incidence and severity of complications due to femoral nerve blocks performed for knee surgery, Knee (2012), http://dx.doi.org/10.1016/j.knee.2012.11.002

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B. Widmer et al. / The Knee xxx (2012) xxx–xxx

femoral nerve injury [22,23]. Inflammation and infection have also been associated with indwelling peri-neural catheters, with an infection rate ranging from 0.2% to 3.2% [24–26]. These reports primarily refer to local complications within the distribution of the involved peripheral nerve. A more comprehensive evaluation of the possible consequences of these injuries including neuropathic pain, mood alterations, and resultant decreased quality of life has not been reported in the literature. To address this, a retrospective review of all patients with complications after peri-operative FNB was undertaken. The aims of this study were to determine the incidence of neurological complications following femoral nerve blocks in patients undergoing knee surgery, and to characterise the nature of these complications and their effects on patients' quality of life. 2. Materials and methods Records from all cases of knee surgery performed in our institution by two fellowship-trained knee surgeons (DP and MC) between January 2003 and June 2009 were evaluated. A cohort of 1802 patients was identified, all having had regional anaesthesia involving the femoral nerve. From this cohort, patients reporting neurological symptoms in the distribution of the femoral nerve during routine follow-up visits were selected. Patient selection was on the basis of peripheral neurological symptoms in the distribution of the femoral nerve, occurred in the post-operative period and related to regional anaesthesia. Surgical and anaesthetic details of the procedure were obtained from the selected patient records, with particular attention to pre-operative regional anaesthesia involving the femoral nerve. Over the study period, various techniques were utilised by the five anaesthetists, but on each occasion a nerve stimulator or an ultrasound was used to identify the nerve. Patients were sedated but awake and block administered prior to surgery with ropivacaine (0.75% with infusion of 0.2% 5–8 ml/h for indwelling catheters). Once identified, the patients were then contacted by phone and invited to participate in the study. This was performed in accordance with a protocol approved by the Institutional Ethics Committee. After providing written consent, patients initially underwent a detailed history and physical examination. All patients were interviewed and examined by one of the senior surgeons. The mean follow-up between surgery and physical examination was 24 months (range 3 to 65 months). Patients were asked if their symptoms were improving, stable, worsening or resolved. For patients who reported resolution of symptoms, the approximate time from surgery to complete resolution of symptoms was recorded. A physical examination of both lower limbs included deep tendon reflexes at the patellar and Achilles tendons, motor examination with manual muscle testing (MMT), and sensory examination consisting of a combination of Von Frey's monofilament and a camel's-hair brush to evaluate touch and allodynia. Patients were further evaluated with a range of self-report measures for the assessment of neuropathic pain and subjective instruments for neuropathic pain and mental health. The Douleur Neuropathique 4 (DN4) was used to discriminate between somatic and neuropathic pains and the Neuropathic Pain Symptom Inventory (NPSI) was employed to characterise the type of neuropathic pain. The Depression Anxiety Stress Scales (DASS) which is a 42-item self-report instrument designed to measure the three related emotional states of depression, anxiety and tension/stress, was used to assess the patients' broader mental health. DASS results were interpreted on the basis of the summation of scores for each negative emotional state, and the scores were then divided into categories ranging from normal to extremely severe [27]. Statistical analyses were performed using Minitab statistical software (version 16. Minitab Inc, USA). Bivariate analysis was performed with chi-square testing to establish odds ratios for complication rates between groups as defined by sex and intervention (i.e. indwelling

catheter or single shot block). A-priori alpha was set at 5%. Kruskal– Wallis one way analysis of variance and post hoc analysis were utilised to determine any differences between groups for subjective scores. 3. Results From the 1802 nerve blocks or catheters performed during the study period, 31 patients (35 limbs) reported neurological symptoms involving the femoral nerve distribution, resulting in an incidence of 1.94% (Table 1). The affected patients numbered 7 males and 24 females with a mean age of 50.3 yrs (21–82 yrs), weight of 80.6 kg (47–107 kg) and mean surgery tourniquet time of 66 min (33–144 min). Neurological symptoms were most common following ACL reconstruction (4%) and primary unicompartmental knee replacement (2.2%), followed by primary total knee replacement (1.2%). One patient with symptoms was identified for each of the revisions of total knee replacement, high tibial osteotomy and patellofemoral reconstruction (Table 2). An additional patient was identified with symptoms following an open reduction and internal fixation of the proximal tibia and distal femur. All patients with neurological symptoms had undergone a femoral nerve block and there were no patients who had a femoral neuralgia in the absence of a femoral nerve block. The incidence of complications following single-shot FNB (2.66%) was significantly higher (p = 0.01) than that in catheter FNB (0.93%), with an odds ratio of 2.91 (95% CI: 1.26–6.7). Similarly, the incidence of complications for females (2.5%) was significantly higher (p = 0.01) than that for males (0.83%), with an odds ratio of 3.0 (95% CI: 1.3–7.1). There was no association between tourniquet time and neurological symptom. Of the 31 patients sustaining neurologic complications, 24 patients (28 knees, 77%) agreed to participate in the follow-up evaluation. Five patients declined to participate, one patient could not be contacted and one was deceased due to unrelated pathology. The average duration of symptoms was 25 months (range 3–65 months). 42% of patients described their symptoms as static, 42% reported gradual improvement in their symptoms and 16% felt that their symptoms had resolved. No patients reported worsening of symptoms. After physical examination, all patients' demonstrated grade five motor strength and normal deep tendon reflexes in both lower limbs. Sensory testing identified hypoaesthesia in 46% of patients, hyperaesthesia in 25% and both abnormalities in different areas of the same patient in 18%. In addition, 2 patients (7%) were asymptomatic following recovery from hypoaesthesia and one patient (3.6%) was identified with loss of sensation to the stimuli applied in this study. Electromyography (EMG) and nerve conduction studies were not utilised on any patient. All patients denied neurological symptoms prior to their femoral nerve block. NPSI data indicated that tingling was the most common symptom reported (86%), with stabbing pain the least common (25%) (Fig. 1). A one-way ANOVA revealed no significant differences in intensity between symptoms (df = 9, H = 14.4, p = 0.11) (Fig. 2). Of particular note, was the high frequency reported for evoked pain by pressure (Fig. 1), with a relatively high average intensity (Fig. 2). Similarly, the dimensions of neuropathic pain displayed varying frequency within the sample, with paraesthesia and dysaesthesia being the most common (Fig. 3). No significant differences in pain intensity were observed (df = 4, H = 7.5, p = 0.11) (Fig. 4). At the time of review, 71% of the sample had a DN4 score of greater or equal to four (suggestive of neuropathic pain) and 14% had a score of three. On further questioning, these patients reported that their symptoms had improved since the time of surgery (5–65 months ago) and they previously had positive symptoms, which would have made their score 4 or higher. The DASS results displayed no significant differences in average severity (H = 1.3, df = 2, p = 0.53) between depression, anxiety or stress scores (Fig. 5). The large variance observed in the average severity is explained by the varying incidence of symptoms reported. Specifically, 46% of the sample indicated no negative emotional state, while 16%, 12.5% and 25% indicated one, two or three emotional states respectively (Fig. 6). Analysis of the incidence of symptoms revealed that moderate depression was most common, followed by moderate stress, with anxiety evenly distributed between mild, moderate and severe (Fig. 6).

4. Discussion The aim of peri-operative analgesia is to control intense nociceptive input while allowing active rehabilitation of a mobile joint. Ideally analgesia should commence prior to or during the procedure to limit the development of hypersensitivity in afferent pathways [28,29].

Table 1 Global incidence of reported neurological symptoms involving the femoral nerve distribution.

Nerve blocks or catheter Limbs affected Incidence a

Total

One shot FNB

Catheter

p

1802 35 1.9%

1051 28 2.7%

751 7 0.9%

0.01a

Significant difference between one shot FNB and catheter.



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Table 2 Surgery performed and neurological symptoms involving the femoral nerve. Total

Primary TKA ACL reconstruction UKA Revision TKA HTO PFR Other Total

Neurological symptoms involving the FN

One shot FNB

Catheter

One shot FNB

Catheter

Total

498 297 152 19 76 2 7 1051

689 2 28 29 3 0 0 751

10 12 3 0 1 1 1 28

4 1 1 1 0 0 0 7

14 13 4 1 1 1 1 35

FN: femoral nerve; FNB: femoral nerve block; TKA: total knee arthroplasty; ACL: anterior cruciate ligament; UKA: unicompartmental knee arthroplasty; HTO: high tibial osteotomy; PFR: patella femoral replacement.

In an effort to reduce patients' systemic opioid exposure, multiple regional and local adjuncts have been advocated. Single shot femoral nerve block has been widely reported as safe and effective [9,10,12,14,16,17]. However, complications including infections, falls, postoperative paraesthesias and neuropathic pain have been reported [19–21,30]. The main finding of this study is that the incidence of neurological complication after FNB was higher in this series than typically reported, with influence on the quality of life in the affected cases. Reported rates of nerve injuries following peripheral nerve blocks vary from 0.3% to 2.07%, and the incidence in this study of 1.94% is at the upper end of this range [12,30–32]. Standard clinical guidance also indicates recovery from neurological symptoms to be predictable, and that new onset neurological symptoms experienced by patients after peripheral nerve block resolve after 6 months, with most resolving within the first 6–12 weeks [31,32]. While long-term postoperative neuropathy has been rarely studied, an incidence of 0.22% has been previously reported [33]. In contrast, the data reported here indicate an average duration of neurologic symptoms of over two years. While this differs from conventional thinking, the majority of reports to date are found in the anaesthetic literature. Consequently this finding likely reflects the longer follow-up period used by surgeons compared to that of anaesthetists. The characteristics of these patients suffering from persistent neurological symptoms were significant in both sex and procedural technique. The odds ratio showed a significant female predominance to an extent that has not been previously reported in the literature. The results also showed that neurological complications were more likely to arise in patients who underwent single shot blocks rather than indwelling femoral nerve catheters. The possibility that the higher

Fig. 1. Incidence of symptoms reported in patients assessed with NPSI. (EP—evoked pain).

Fig. 2. Intensity of NPSI symptoms reported by responders. (EP—evoked pain). Error bars represent inter-quartile ranges.

pressure developed by infusion during the single shot technique has been entertained, but it has not been proven. The low, continuous pressure of indwelling catheter techniques may have resulted in fewer complications. However the use of continuous femoral sheath catheters is not without risk and has been associated with complications such as variable accuracy of catheter position and procedural site infection [10,14,17]. While femoral nerve blocks have been effective in providing pain relief, it is important to be cognisant of the potential neurological complications that may occur with its use. When neurological complications do occur, they are also likely to be more persistent and to affect patients' sense of general well-being and their emotional state. Prior studies have not rigorously assessed the characteristics of patients' post nerve-block pain, so we employed a validated, clinician administered questionnaire (DN4) to identify neuropathic pain and differentiate it from somatic pain. The DN4 questionnaire comprises 10 items with each item equally weighted, and a score of four or higher carries with it a sensitivity of 83% and specificity of 90% for neuropathic pain [34]. Twenty of our patients at the time of evaluation had a score of four or greater, indicating the presence of neuropathic pain after the procedure, rather than somatic or simple paraesthetic symptoms. To quantify the dimensions of pain within this neuropathic presentation, patients completed the NPSI. This inventory includes ten descriptors and two temporal items based on common neuropathic symptoms and can discriminate and quantify the symptoms experienced by patients into five distinct dimensions of neuropathic pain syndromes [35]. Attal et al. noted that the pathophysiological nature of neuropathic pain remains poorly understood and grouping patients as a single entity may result in therapeutic failure [36]. The results of our study did not identify any predominant pain dimension associated with post-nerve block neuropathic pain. This supports prior work concluding that symptoms alone are poor discriminators for the specific aetiology of peripheral nerve trauma [36]. More studies need to be

Fig. 3. Incidence of NPSI symptom sub-scales.


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Fig. 4. Average intensity of NPSI symptom sub-scales. Error bars represent inter-quartile ranges.

conducted to understand the correlations of different pain dimensions with specific neuropathic aetiologies. The final evaluation involved the degree to which their neurological symptoms manifest in their emotional states. To this end patients were given the DASS questionnaire consisting of 42 questions aggregated into three groups for the assessment of depression, anxiety and stress. This assessment revealed that 54% of the participants exhibited negative emotional states affecting patients with neurological complications. Normative mean DASS scores in a general population study for depression (5.55), anxiety (3.56) and stress (8.04) were lower in all three categories than those reported by our patients (6, 7, 10.5) respectively [37]. Two explanations exist for this finding. The persistence of neurological symptoms may have adversely affected the patients' sense of well-being. However, it is also possible that patients who were experiencing negative emotional states prior to surgery and nerve block are predisposed to developing prolonged symptoms from any neurological injury should it occur. Without the use of preoperative psychometric inventories in this retrospective study, it is difficult to ascertain the efficacy of this explanation with any certainty. This disease process would benefit from a prospective study, in which patients were provided with both pre- and postprocedure neurologic and psychometric evaluations. This would then allow a thorough within-subject analysis in patients suffering complications. Finally, the tests of neuropathic pain and mood need to be seen in the context of the finding that neuropathic pain can occur after knee surgery without femoral nerve block [36,37]. Inevitably, there were some limitations to this retrospective study. The anaesthetists involved in this study used different techniques when administering the femoral nerve block according to the clinical requirements of each case. Variables included the level of sedation, technique (ultrasound, nerve stimulator, or both), and the type and concentration of local anaesthetic agent, as well as tourniquet time. We acknowledge that these factors may have an effect on the

Fig. 6. Incidence of negative emotional symptoms detected by DASS.

incidence of neurological complications. However, the intention of this study is not to critique specific techniques of administering femoral nerve block, but rather to analyse the incidence of neurological complications from femoral nerve blocks in general. While the incidence of neurological complications could potentially be reduced with the use of techniques such as ultrasound guidance, we have observed that even with the use of these adjuvants, some patients still developed neurological complications. It would seem that these techniques may allow anaesthetists to avoid direct injury to the nerve, but not to completely eliminate the type of complications seen in this study. Finally, only patients with significant and persistent symptoms were detected. Hence, it is possible that an under estimation of the incidence of femoral nerve trauma associated with femoral nerve blocks was established. 5. Conclusion The provision of appropriate perioperative pain relief continues to evolve with a constant need to balance the effectiveness of available modalities of pain relief against potential complications. Neurologic complications following femoral nerve block for knee surgery have been described as infrequent and transient, but we have identified both an increased incidence and longer duration of symptoms. Femoral nerve block is an effective procedure for post-operative analgesia, but the associated potential complications must be weighed carefully against the benefit. Whether to employ femoral nerve block as part of a perioperative analgesia protocol should be decided collectively by patient, anaesthetist and surgeon. Conflict of interest

Fig. 5. Average severity of negative emotional symptoms detected by DASS. Error bars represent interquartile ranges.

Benjamin WIDMER MD No conflict of interest Sébastien LUSTIG MD, PhD Paid consultant for Tonier SA and Depuy SA Corey J. SCHOLES PhD No conflict of interest Allen MOLLOY MD No conflict of interest Sean P.M. LEO MD No conflict of interest Myles COOLICAN FRACS Institutional and Research support from Zimmer David A. PARKER FRACS



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