Introduction

Percutaneous radiofrequency lesioning of the lateral branches of the sacroiliac joint has become a recognised method of treating chronic pain arising from this joint. Due to the large and varied innervation from the S1-3 lateral branches success has been achieved with large lesions that has a high chance of covering these nerves. Such lesions require specialised and expensive equipment and the NIMBUS needle is a large 17G electrode with expandable tines at the tip. It is compatible with all standard radiofrequency probes and it produces a large lesion at the tip. It has been in use in the USA in over 100 cases and we describe its use in the UK

Aim: To measure contact pressures in vivo in patients with unicompartmental arthritis fitted with osteoarthrosis (OA) braces to see if the arthritic side of the joint is unloaded.

Method: A thin flexible sensor (TekScan) was manoeuvered arthroscopically into the medial compartment of the knee joint under local anaesthesia in patients with unicompartmental OA of the knee undergoing either therapeutic or diagnostic arthroscopy. All 15 patients had been fitted with a brace before the arthroscopy. Measurements were made within the compartment of double leg stance and single leg stance. Ground reaction force using a load cell was measured for 14 patients and the knee sensor data were normalised relative to this. Recordings were then repeated with the patients with different commercially available braces.

Results: The first two groups of patients showed significant reductions in pressures. Normalised knee sensor forces were reduced to 68%(Sd 22%) and 61%(Sd31%). In the last group of patients, reductions in pressure recordings were less between no-brace and brace. Three patients produced low signals suggesting incorrect sensor replacement.

Conclusions:

Significant unloading of the osteoarthritic compartment could be observed by applying manually a valgus force to the knee.