Intrathecal Diamorphine Versus Femoral Nerve Block in Primary Total Knee Arthroplasty

Randomised, Observer Blinded, Controlled Trial of Intrathecal Diamorphine Versus Femoral Nerve Block for Post-operative Analgesia Following Primary Total Knee Arthroplasty

Primary total knee arthroplasty (TKA) is commonly associated with moderate to severe early post-operative pain. The primary aim of this study was to investigate the impact of either a single-shot femoral nerve block (FNB) or intrathecal diamorphine (ID) on post-operative pain after TKA

The Null Hypothesis is that there is no difference in the post operative pain relief provided for TKA by a single-shot femoral nerve block (FNB) as compared to intrathecal diamorphine (ID).

In 2008, the Prospect Working Group, a multidisciplinary expert panel, published their consensus guidelines on the relative merits of different anaesthetic and analgesic techniques for TKA based on a review of the available published literature up to 2005. These guidelines supported the use of general anaesthesia combined with a femoral nerve block for surgery and postoperative analgesia, or alternatively spinal anaesthesia with local anaesthetic combined with spinal morphine. The preference for femoral nerve block in favour of intrathecal opiates was as a consequence of the greater potential for side effects with the latter technique. The authors conceded that there were a lack of well-conducted studies on this subject, graded their recommendations as level D (expert opinion), and concluded further research was needed. Consequently there has been debate around the conclusions drawn and clinicians have not universally accepted the recommendations.

Most researchers to date have focused on short-term outcomes such as static pain scores and/or opiate consumption. It is also important however to investigate dynamic pain scores, patient reported outcomes, the attainment of rehabilitation goals, length of stay and longer term functional outcomes. In addition, the use of the total pain relief score (TOTPAR) as described by Cooper and Beaver, assesses the cumulative response to treatment. This is a well validated area under the time-analgesic effect curve (AUC) derivation for pain relief which is commonly used by meta-analyses of analgesic interventions. The aim of this study is to investigate all these endpoints in patients receiving a single-shot femoral nerve block (FNB) for TKA as compared to intrathecal diamorphine (ID), a more commonly used spinal opiate in United Kingdom anaesthetic practice.

Inclusion Criteria:

• Adult patients scheduled for primary unilateral Total Knee Arthroplasty

Exclusion Criteria:

• Uni-compartmental surgery, bilateral surgery, contra-indication to spinal anaesthesia or peripheral nerve block (anticoagulation, hydrocephalus, raised intracranial pressure), allergy to local anaesthetics or diamorphine, malignant hyperthermia or other concerns over general anaesthesia, chronic opiate use and chronic pain medication use (e.g. gabapentin, pregabalin, amitriptyline).