HUMAN SPINAL ARACHNOID SLEEVES AND ITS POSSIBLE RELATION WITH TRANSIENT NEUROLOGICAL SYNDROME AFTER SPINAL ANAESTHESIA

commonly experienced when the saphenous nerve is left unanaesthetised for ankle and foot surgery in spite of a functioning sciatic nerve block that innervates the vast tissue of the foot. It is experienced likewise when the sural nerve is left unanaesthetised for lateral ankle surgery or just the removal of a fibular plate. Performing rescue blocks for breast lumpectomies, mastectomies and axillary lymph node dissections with nerve blocks of the lateral or anterior cutaneous branches of the intercostal nerves, despite wound infiltration by the surgeon, provides this experience also. Regional anaesthesia of the cutaneous nerves of the superficial cervical plexus for medial clavicular fracture repair, or for shoulder surgery where the incision includes the skin more medial than covered by the interscalene nerve block, will also show the intensity of pain from cutaneous nerves. Additional anaesthesia of the intercostobrachial nerve after elbow surgery, the superior cluneal nerves, the subcostal nerve or the iliohypogastric nerve after hip surgery, and the medial femoral cutaneous nerve or saphenous nerve for anteromedial knee surgery or anterior tibial surgery respectively, are all instances where the analgesic effect of cutaneous nerve blocks can be the defining cause of having comfortable patients postoperatively, with less hours spent in the postoperative care unit. One possible explanation for the effect of cutaneous nerve blocks is that, what have been labelled cutaneous nerves, contrary to the immediate intuition, may innervate the periosteum where no muscles cover the skeleton e.g., the saphenous nerve for the anterior tibia and the superficial cervical plexus for the clavicle. Additionally some cutaneous nerves may innervate joint capsules, e.g. the saphenous nerve at the medial ankle and the medial femoral cutaneous nerve at the medial knee. However, as mentioned above, even in cases where no deeper tissue is innervated, as with the lateral cutaneous branches of the intercostal nerves in breast surgery, the intensity of postoperative pain solely originating from cutaneous nerves can be easily observed. It is particularly recognizable when pain is resolved completely after the performance of a cutaneous rescue block postoperatively. While cutaneous nerves have a part in mediating acute postoperative pain, they are the most frequent cause of postsurgical chronic neuropathic pain. The inescapable neurectomies of the surgical incisions, or the unintentional trauma by the surgical tools, consistently produce a procedure-dependent ratio of patients with chronic neuropathic symptoms such as disabling allodynia and hyperalgesia in the involved cutaneous areas Historically, regional anaesthesia of the involved cutaneous nerves had only little relevance in the treatment of these chronic conditions. However, the increasing accessibility to non-neurodestructive technologies, such as percutaneous cryoneurolysis, in conjunction with improving point-of-care ultrasound equipment and the continuously ongoing scientific work into the anatomy of cutaneous nerves, changes this. Ultra-selective diagnostic nerve blocks of cutaneous nerve branches play an indispensable role in the treatment of these patients. Even in the absence of the ability to offer an interventional treatment, the diagnosis of cutaneous nerves as the cause of chronic pain has a significant potential to avoid improper secondary or tertiary surgical procedures when the pain is erroneously believed to have a different origin and a surgical solution. The importance of cutaneous nerves in chronic postsurgical neuropathic pain should be of little dispute. Knowledge of the anatomy and ultrasonographic appearance of cutaneous nerves is essential to interventional treatments and help patients avoid unnecessary surgery. However, whether or not cutaneous nerve blocks should be of relevance to the regional anaesthetist in regard to acute postoperative pain, depends on the objective of the postoperative pain treatment. If future improvements towards opioid-free, painless, fast track procedures are an ambition, then cutaneous nerves and knowledge of cutaneous nerve blocks seem like an unavoidably part that equation.