Randomised control trial of the effectiveness of metatarsal block versus ultrasound-guided ankle block in osseous first ray surgery

V. Roberts, M. Attwal, F. Fombon, M. Bhatia

Introduction: Osseous first ray surgery is a common day case procedure. Patients are often given regional blocks as an adjunct to general anaesthesia. We sought to find if there is a difference between ultrasound guided ankle block and metatarsal block in this group of patients, in providing effective post-operative analgesia.

Methods: After ethical approval was granted and power analysis performed, 25 patients were recruited into each arm of the study. These patients were having either an osteotomy or arthrodesis. All patients had standardised general anaesthesia and received 20mls of 0.5% chirocaine for the blockade. The cohort having the ankle block had infiltration under ultrasound guidance in the anaesthetic room; and the cohort receiving the metatarsal block had infiltration at the end of the procedure. The timings of both the anaesthesia and the operation were recorded for each patient. Patients scored their pain level at 2, 6 and 24 hours. The amount of post-operative analgesia used in the first 24 hours was also recorded by the research nurse. All patients were discharged home with a standardised prescription of analgesia.

Results: Analysis of the pain scores showed that there was no difference between the two blocks at any measured time period. Nor was there a difference in the analgesic requirement in the first 24 hours. There was, however, a difference in the time taken for the whole procedure: with the ankle block taking an average of ten minutes more.

Conclusion: We conclude that metatarsal blocks are as effective as ultrasound guided ankle blocks in providing analgesia after osseous first ray surgery with a smaller potential for morbidity. Metatarsal blocks may also be a more efficient use of time.