Terminal latency index in the carpal tunnel syndrome.

From: www.wheelessonline.com 

– Anatomy:    

– LFCN, as its name suggests, is purely sensory;    
– it arises from L2 and L3, travels downward lateral to the psoas muscle, crosses the iliacus muscle (deep to fascia), passes either thru or underneath the lateral aspect of the inguinal ligament, and finally travels onto innervate the lateral thigh;
– it divides into anterior and posterior branches and supplies skin on lateral aspect of thigh;
– in the study by Hospodar et al (JTO 1999), the course of the nerve was variable, but was most commonly found at 10-15 mm from the ASIS and as far medially as 46 mm from the ASIS;
– in no specimen did the nerve pass lateral to the ASIS (eventhough historically the nerve is thought to pass lateral to the ASIS in 10% of population);
– in all specimens the nerve passed underneath the ilioginal ligament and anterior to the iliacus muscle; 

– Meralgia Paresthetica: 

– entrapment syndrome of the lateral femoral cutaneous nerve causing burning, numbness, and paresthesias down the proximal-lateral aspect of the thigh;
– may be idiopathic, be a result of trauma, previous operations, and in some cases may arise from Perthes Disease abduction splints;
– in idiopathic cases, the nerve may be encased in bone by the growing apophysis of the anterior superior iliac spine, or may be entrapped in fascia either proximal or distal to the ASIS;    
– diagnosis is made by:           
– reproduction of the pain by deep palpation just below the anterior superior iliac spine and by hip extension;           
– relief of pain by localized injection of lidocaine;    
– treatment: when diagnosis is not in doubt and the symptoms are severe, consider operative decompression at the site of constriction;