Our aim is to investigate which components of the quadriceps femoris muscle are affected following an ACB with different volumes (10, 20 and 30 ml) of 1% lignocaine evaluated by electromyography. Both a placebo treatment (20ml saline) and the femoral nerve block (20ml lignocaine 1%) as an active comparative will be used for model control. Further, we want to investigate the effect of volume on motor block. This will be evaluated by measuring the Maximum Voluntary Isometric Contraction (MVIC) of the quadriceps femoris muscle.
The ACB has a well-proven analgesic effect after TKA, but we do not know which nerves that are affected by the block. Aside being a motor nerve, the nerve to the vastus medialis of the quadriceps femoris muscle, contains the second largest sensory contribution from the femoral nerve. It is probable that some of the analgesic effect of the ACB arises from blocking this nerve. Even though the ACB is mainly a sensory nerve block, a study in healthy volunteers showed a small decline by 8% in quadriceps muscle strength(10). It is speculated that the decline in muscle strength was caused by the spread of local anesthetic to the nerve supplying the vastus medialis of the quadriceps femoris muscle. Three out of eleven of the volunteers experienced an even larger decline of 25 % in quadriceps muscle strength. It has been argued that this decline likely was caused by a proximal spread of the local anesthetic to the femoral triangle thereby resulting in an affection of the femoral nerve. In this study, a volume of 30 ml of local anesthetic was used. We do not know the optimal volume for the ACB and we find it relevant to investigate to what extent and which parts of the quadriceps muscle gets affected when different volumes of a local anesthetic are injected into the adductor canal. Selective affection of the different components of the femoral quadriceps muscle can be assessed by non-invasive EMG recordings. Further, the quadriceps femoris muscle strength will be evaluated by measuring the MVIC following the different volumes. The EMG recordings will be voluntary (vEMG) measured during MVIC and stimulated (sEMG). sEMG is measured during transcutaneous electrical stimulation of the femoral nerve.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Rigshospitalet
Copenhagen, Denmark
Difference between ACB-groups, one hour post-block, in amplitude of the rectified vEMG signal from the vastus medialis, expressed as percentage of the pre-block value.
vEMG=voluntary electromyography
Time frame: one hour post-block
• Difference between ACB-groups, one hour post-block, in amplitude of the rectified vEMG signal from the vastus lateralis, expressed as percentage of the pre-block value.
vEMG=voluntary electromyography
Time frame: one hour post block
• Difference between groups, one hour post-block, in MVIC expressed as percentage of the pre-block value
MVIC=maximum voluntary isometric contraction. (Quadriceps femoris muscle)
Time frame: one hour post-block
• Difference between ACB-groups, one hour post-block, in amplitude of the rectified sEMG signal from the vastus medialis, expressed as percentage of the pre-block value.
sEMG= stimulated Electromyography
Time frame: one hour post-block
• Difference between ACB-groups, one hour post-block, in amplitude of the rectified sEMG signal from the vastus lateralis, expressed as percentage of the pre-block value.
sEMG= stimulated Electromyography
Time frame: one hour post-block
• Association between volume and MVIC. MVIC expressed as a percentage of the pre-block value.
Time frame: one hour post-block
Difference in proportions between ACB-groups having an affection of both the saphenous nerve and the vastus medialis (but no other components of the quadriceps femoris muscle), one hour post block evaluated by EMG
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Masking
DOUBLE
Enrollment
20
For each subject a series of 5 voluntary EMG recordings during MVIC will be made to estab-lish the variability of the EMG recordings. This will be done prior to the blocks on each day resulting in 300 EMG recordings from the vastus medialis and 300 recordings from the vastus lateralis. From this variability we will establish a cut-off point (how large a decline in EMG amplitude is "synonymous" with affection of the nerve?). After the cut-off point has been established the EMG data will be presented in dichotomous form: affected/not affected
Time frame: one hour post-block