Adductor canal nerve blocks are traditionally used for pain management for procedures of the medial ankle. These regional anaesthesia blocks numb the saphenous nerve. Doctors noticed that adductor canal block was usually accompanied by numbness of the knee, so this sparked an interest in using this particular block for knee surgery.
Prior to the millenium, it was common in USA orthopaedic clinics to keep knee patients (eg cruciate ligament, knee replacement) in hospital for three days for rehab, continuing their pain relief from the operating room via anaesthetic agent delivered via an indwelling epidural cathether. This reduced the amount of pain medication taken by mouth, keeping patients more alert and co-operative and reducing nausea and other side effects of pain medication.
Pressure from hospital management around the time of the millennium to send patients home early from knee surgery rather than retaining them in hospital for rehabilitation during this time triggered a change in practice to the insertion of a femoral nerve catheter, with discharge after only one day. This allowed full use of the good leg but had the disadvantage of blocking or reducing strength of the quadriceps muscle of the operated leg, a muscle which is essential for proper rehab as it is responsible for straightening the leg, and giving the patient confidence to stand up and to walk. The quadriceps muscle has a peculiar response to pain and seems to shut itself down, initially becoming inhibited (quads inhibition) but later actually decreasing in bulk (quads atrophy), and failure to use the quads in normal movement after surgery can lead to adhesions in the knee which can further hamper rehabilitation.
A couple of years ago, interest turned to using a resident adductor canal catheter instead of a femoral nerve catheter because it does not have this dulling effect on the quadriceps muscle, but it still helps greatly with reducing knee pain. The patient can control the pain via a pump that delivers a fixed amount of long-acting anaesthetic agent per hour to the area. The catheters are very easy to remove once they are no longer needed.
The researchers looked at -
The strength of the quads was significantly better with the adductor canal block than with the femoral nerve block. The degree of pain relief may not be as great as for the femoral nerve block, and in particular the back of the knee where for example a meniscus procedure may still give some pain, but patients can get going earlier on their rehabilitation.
The indices used to measure pain were essentially similar with the two blocks.
An ultrasound probe used mid-thigh (about three handsbreadths above the patella) to identify the key structures of the adductor canal - the sartorius muscle which forms the roof of the canal, the vastus medialis part of the quadricep muscle which forms the medial part of the canal, and the adductor canal. Under direct vision with the ultrasound image, the catheter is threaded into the adductor canal, and a bolus of anaesthetic agent delivered, which can be seen to bulge out that area.