Fig 4. Case illustration of a 63 year patient (number 8, Table 1) in whom blocking a nerve had no pain relieving effect, but nerve surgery had.

Following the current selection algorithm, this patient would not have been operated. The patient had complaints befitting ankle arthrosis. An isolated subtalar arthrodesis was performed by placing compression screws. Immediate postoperative, the patient had severe neuropathic pain with allodynia in the sural nerve area limiting the walking distance to around 150 meters. Conservative treatment failed. A: At inspection 38 months after the onset of the pain, a scar of the screw placement was seen around 4 centimetres below the lateral malleolus. Percussion in the scarred damaged area provoked irradiating painful sensations in the sural nerve area. The sural nerve was blocked three times in 4 weeks (with a 2-week interval between injections) consisting of two single-blind injections with a volume of 4 cc. lidocaine 1% and one with placebo. There was no effect of the lidocaine injections and following saline injection the pain increased temporarily. B: At surgery, the sural nerve was identified in undamaged area (1^st incision) and dissected free subcutaneously. A second incision was made and the sural nerve was followed distally towards the scar. Subsequently, a third incision was made over the scar and a damaged sural nerve was identified. C: The damaged sural nerve was cut and the abnormal looking nerve tissue was resected. Pathological examination of the abnormal tissue showed traumatic neuroma. The resection plane of the proximal stump showed normal myelinated fibers and fascicles. D: The proximal stump of the sural nerve was loosely buried in fat proximal to the ankle joint. Postoperatively, his pain decreased significantly. The area with allodynia disappeared and became hypesthetic. The patient could walk again for at least one hour.