Pain control after primary total knee replacement. A prospective randomised controlled trial of local infiltration versus single shot femoral nerve block
Introduction
TKR is a painful procedure. Studies have shown that reducing post-operative pain reduces length of stay [2], [3]. However there are a large variety of modalities employed and a limited evidence base upon which to base any conclusions as to the optimum [1].
Femoral nerve block (FNB) has been described as an effective method for managing pain following TKR [3] and has been standard practice at our institution for the past five years. FNB leads to an improvement in pain control on the day of surgery as well as a reduction in opioid analgesia and antiemetic use post operatively [4]. FNB has been found to facilitate early ambulation and range of knee movement post-operatively and has been hypothesised to lead to a decrease in the incidence of deep vein thrombosis and pulmonary emboli in patients who have undergone TKR. Further to this, administration of FNB has led to a reduced hospital stay when compared with patients in a placebo group injected with saline [3].
However, the use of FNB has its own costs, with regards to equipment and training, particularly if an ultrasound machine is used to ensure correct placement of the infiltrate. The procedure also prolongs the time spent in the anaesthetic room. An unpleasant numbness of a large portion of the lower extremity is a common experience following femoral nerve block administration [5]. Other adverse events include decreased quadriceps function in the early post-operative period, which can result in incidents of falls. A study of 1018 patients reported 12 incidents of falls following FNB for TKR, with three patients being re-operated on as a result of this. A further consequence of weakened quadriceps is the hindrance to attempts of early rehabilitative physiotherapy. Cases of post-operative femoral neuritis which could be secondary to an FNB have also been documented, as well as, rarely, femoral nerve palsy [6]. A paper looking at major complications from regional anaesthesia in France documented that more than half of patients documented to sustain nerve injury, reported residual symptoms six months following the anaesthetic incident [7].
In recent years there has been more use of intra-articular infiltration using a variety of constituents in controlling post-operative pain. A number of studies have found this technique to be safe and effective in comparison to a placebo [8], [9], [10], [11] and a number of authors suggest that it is superior to other interventions [5], [12]. A recent meta-analysis summarised the evidence [1]. To our knowledge the technique of LIA has never been directly compared to single shot FNB. The present study was designed to compare these two interventions.
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Patients and methods
The study was approved by the regional ethics committee on 15 March 2012 (ref: 12/NW/0153). It was registered with controlled-trials.com, identifier: ISRCTN42045594.
All patients scheduled to undergo primary TKR under the care of three consultants were approached and asked to take part in the study. All implants were a cemented Nexgen CR. The inclusion criterion was any patient undergoing a primary TKR. Exclusion criteria included patients that lacked capacity to consent to the study, patients
Results
Fifty patients were initially consented for the study. Two patients were excluded after randomisation as described above. Eight patients were excluded before randomisation. Four required a general anaesthetic, two changed their mind, one had diamorphine put into the spinal and one anaesthetist refused to take part.
The primary outcome measure analysed was pain score at 4 h post operatively. The mean (SD) pain score was 6.8 (3.2) for the FNB group and 2.1 (2.6) for the LIA group. This difference
Discussion
Optimising control of post-operative pain after TKR allows early mobilisation and reduces hospital stay [2], [3]. A variety of means are used, often in combination. A recent meta-analysis has shown the benefit of local infiltration of anaesthetic in conjunction with femoral nerve block [1]. We are not aware of a study that has directly compared single shot femoral nerve block with local infiltration. Our local policy was to give a single shot femoral nerve block at induction followed by PCA,
Conflict of interest statement
None of the authors nor their institutions have any conflicts of interest in relation to the above study.
Acknowledgements
The authors acknowledge the statistical advice of Dr Anna Hart of the University of Lancaster.
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