| 3.5 | Proximal sciatic nerve blocks |
Proximal sciatic nerve blocks target the nerve where it emerges from the lower pelvis. Here, various means of access are possible. In most patients, the two branches of the sciatic nerve - the tibial nerve and the common peroneal nerve - are still united in the gluteal region or, at least, are located very close together. It is also of clinical relevance that proximal sciatic nerve blocks reach the posterior femoral cutaneous nerve. For that reason, to achieve full analgesia of the leg, it is sensible to combine the proximal sciatic nerve block with a lumbar plexus block (psoas or femoral).
Parasacral approach (according to Mansour)
Anatomical landmarks
Posterior superior iliac spine, ischial tuberosity, (greater trochanter)
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Block technique
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The parasacral block targets the sciatic nerve at its most proximal point where it induces fast and full anaesthesia. The block is performed with the patient seated or in the lateral recumbent position.We prefer the lateral recumbent position, given that, in combination with the psoas compartment block, the technique is especially suited for complex surgical interventions on the leg, and avoids the inconvenience of repositioning and re-draping of the patient between the two procedures. The side to be blocked is upward, the lumbar spine shows a kyphosis and the hip flexed to facilitate orientation. The posterior superior iliac spine and the ischial tuberosity are marked. From the posterior superior iliac spine, the palpating finger follows the tuberosity until no more bony structures are encountered. Here, approximately 5 - 7 cm caudad to the posterior superior iliac spine, the puncture site is marked. After disinfection and deep infiltration of the puncture channel, a stimulation needle of 80 -120 mm in length is advanced sagittally in the direction of the tuberosity until a stimulatory response is elicited from the peroneal or tibial part of the sciatic nerve.
The amplitude is reduced accordingly down to the threshold current and 20 to 40 ml of local anaesthetic are injected. If no primary stimulatory response is achieved or bony resistance encountered, the insertion direction is corrected to the caudolateral (around to midline between greater trochanter and ischial tuberosity). Here, there will be no problems placing an indwelling catheter. Whilst contractions of the gluteal muscles are of no value, a stimulation of the ischiocrural muscle group is a promising response.
Indications
Surgical interventions on the dorsal thigh, lower leg (not in the supply area of the saphenous nerve), whole foot, pain management. In combination with psoas compartment block/femoral nerve block for operations on the whole leg below the hip.
Contraindications
No specific
Side effects/complications
Vessel puncture (inferior gluteal artery)
Transgluteal approach (according to Labat)
Anatomical landmarks
Posterior superior iliac spine, greater trochanter, sacral hiatus, ischial tuberosity
Block technique
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The patient is placed in the lateral recumbent position, with the leg to be blocked uppermost. The other leg is extended. The upper leg is bent approx. 30-40º at the hip joint and approx. 90º at the knee joint. The upper knee should rest on the table. The uppermost foot must not be "hooked behind" the calf of the bottom leg.
In this position, the greater trochanter and the posterior superior iliac spine at the dorsal end of the iliac crest should be identified by touch and a mark is made at each point. A line is drawn perpendicularly from the midpoint of the line connecting these two marked points to the medial and the puncture site is marked at a point 4 to 5 cm along this line. To check this location, the connecting line between the greater trochanter and the sacral hiatus is halved. As a rule, this point is the same or in the direct vicinity as the previously marked puncture site.
After disinfection and local anaesthetising of the puncture site, a puncture perpendicular to the skin surface is made with the stimulation needle (Stimuplex® D, 80 mm). Advancing the needle results at first in contractions of the gluteal musculature by means of direct stimulation. Upon bone contact, the needle should be withdrawn and advanced after correcting the direction. Contact with the sciatic nerve is encountered at a depth of 5 to 8 cm. Contractions of the calf musculature with plantar or dorsal flexion of the foot are triggered until a stimulation current of 0.2 - 0.3 mA is reached.
Indications
Surgical interventions on the dorsal thigh, lower leg (not in the supply area of the saphenous nerve), whole foot, pain management. In combination with psoas compartment block/femoral nerve block for operations on the whole leg below the hip.
Contraindications
No specific
Side effects/complications
Vessel puncture (inferior gluteal artery)
Anterior approach (according to Meier)
The anterior approach to the sciatic nerve is advantageous in patients who cannot be reasonably placed in the lateral recumbent position due to pain or their condition.
Anatomical landmarks
Posterior superior iliac spine, symphysis, greater trochanter
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Block technique
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The patient is supine on his back, with the leg in a neutral position, not rotated outwardly like in the femoral nerve block. The line connecting the anterior superior iliac spine and the symphysis is marked. A parallel to this line is drawn to the greater trochanter.
The length of the first line (between the anterior superior iliac spine and the symphysis) is divided into thirds. A perpendicular line is drawn from the medial third point to the distal. This perpendicular line intersects the second guideline. This puncture is made at the point of intersection.
Use finger of one hand to feel along the muscle compartment between the rectus femoris muscle and the vastus medialis and/or the sartorius muscle, taking the femur as a counter point. By doing so, the neurovascular bundle is forced to the medial. The puncture is made lateral to this, thereby minimising the risk of hitting a vessel. Insert the stimulation needle (Stimuplex® D 120 mm) into the skin at a 75-85° angle, guiding it in a dorsocranial direction. Stimulation of parts of the femoral nerve is possible in the superficial areas. At a depth of 6-10 cm, you reach the dorsal thigh compartment. The sciatic nerve is encountered by advancing the needle a bit further. The tip of the needle is positioned correctly when plantar flexion (tibial part) and dorsal flexion (peroneal part) are elicited.
Indications
Surgical interventions on the dorsal thigh, lower leg (not in the supply area of the saphenous nerve), whole foot, pain management. In combination with psoas block/femoral nerve block for operations on the whole leg below the hip.
Contraindications
No specific
Side effects/complications
Vessel puncture (femoral artery, profunda femoris artery)
Neural injury (femoral nerve or its branches)
Subtrochanteric approach (according to Guardini)
As with the anterior approach to the sciatic nerve, the subtrochanteric approach offers the advantage that it does not require painful repositioning of the patient, for example secondary to trauma or fractures. Another even greater advantage over the anterior approach, we believe, is the low puncture depth into the nerves and the fact that no vulnerable structures are located in or along the puncture channel.
Anatomical landmarks
Greater trochanter, ischial tuberosity
Block technique
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The patient is supine, with the leg in a neutral position or rotated slightly inwards. Padding placed under the lower leg and pelvis helps facilitate puncture, but is not imperative. By passive rotation of the hip joint, it is possible to palpate and mark the greater trochanter, even in adipose patients. The puncture site is located approx. 2 cm inferior and 4 cm distal to the greater trochanter. The direction of insertion is horizontal and slightly cranial to the ischial tuberosity. Needles of between 80 and 120 mm in length are employed. The anticipated distance to the nerve can usually be judged very accurately in advance by measuring the horizontal distance from the greater trochanter to the sartorius muscle compartment. If the femur is encountered during puncture, the insertion point must be changed to the dorsal. Should stimulation at a reasonable depth fail to achieve the desired response, a correction of the insertion direction a little to the ventral will often help along with shifting the accentuation of inward rotation of the hip. Placement of a pain catheter should pose no problems.
Alternative technique
The leg to be anaesthetised is placed on the table with the knee bend. About 2 - 3 cm distal to the midpoint between greater trochanter and ischial tuberosity is where the puncture site is marked. The insertion is now made in the cranial and slightily medial direction.
Indications
Surgical interventions on the dorsal thigh, lower leg (not in the supply area of the saphenous nerve), whole foot, pain management. In combination with psoas block/femoral nerve block for operations on the whole leg below the hip.
Contraindications
Relative: Status secondary to total ipsilateral hip replacement
Side effects/complications
No specific
Indications for proximal sciatic blocks
In combination with a femoral nerve block or psoas block:
The proximal sciatic block is indicated in operations on the lower extremity, also with application of a tourniquet at the thigh.
Isolated proximal sciatic nerve block (rare):
Surgical interventions on the lower leg and foot (not in the supply area of the saphenous nerve).
The catheter technique (proximal sciatic catheter) is especially suited for operations known to have high postoperative analgesia requirements, such as revision osteotomies of the toes, synovectomies of the foot, amputations of the toes and anterior foot.
Contraindications
There are no specific contraindications for proximal sciatic blocks. The general contraindications that apply are listed at the end of this chapter.
Side effects/complications
There are no specific side effects of the proximal sciatic blocks. The general side effects associated with this technique are summarised at the end of the chapter.
