How ultrasound can be used to minimise the need for big surgical incisions

Introduction

Ultrasound lends itself well to intra-operative use because it provides real-time imaging, is portable, and can be applied intraoperatively to image soft tissues but also the surface of bone. It can therefore be used intra-operatively to facilitate minimally invasive surgical procedures.

Technique

Intra-operative use requires the transducer to be sterile. A small amount of ultrasound gel (which does not need to be sterile) should be applied to the surface of the transducer. This should then be enclosed by the gloved surgeon using a sterile covering such as an arthroscopic camera sleeve, sterile ultrasound transducer sleeve, or, in some occasions, a sterile glove. A glove provides the least robust sterile barrier and hence is only useful for standing procedures where the lead hangs down away from the surgical field. In open surgical fields, there is usually sufficient blood for adequate contact, but this can be supplemented with sterile saline (in open wounds), or surgical spirit (alcohol) when the transducer is applied to intact skin within the sterile field. In most situations a linear high frequency (~10MHz) transducer is used because most ultrasound guided surgery is superficial. Wireless transducers are also useful for intra-operative use and have the advantage of lacking a lead which also needs to be enclosed in a sterile covering. Good awareness by the theatre staff of ultrasound machine operation is helpful to optimise image quality and for image storage during the procedure.

Indications

1. Pre-surgical planning Ultrasound evaluation of the surgical area is helpful to optimise the surgical approach and hence minimise the size of any incision. This can be done prior to the induction of general anaesthesia or else after the area has been prepared for aseptic surgery.
2. Identifying bony fragments and foreign bodies Bony fragments or foreign bodies that require removal can be hard to locate within tissues or fibrinous material inside a joint. Ultrasound can be used either pre-operatively, when the location of the foreign body/bony fragment is marked on the skin, or intra-operatively to help guide instruments in real-time, or locate them when they have moved or when they have not been visible (eg during arthroscopy).
3. Optimising instrument placement – examples will be given showing:

a. Introduction of the arthroscope in unfamiliar locations. When the cavity being accessed is not one for which there are already established portals – such as acquired synovial cavities or areas of fluid collection within tissues. Ultrasound can also be helpful for less easily accessed synovial cavities – such as the caudal pouch of the medial femorotibial joint.

b. Distant debridement Ultrasound can provide real-time guidance of instruments placed through small incisions to guide them to a more distant site while avoiding important structures.

c. Improving fasciotomy techniques for proximal suspensory ligament surgery The fasciotomy performed as part of the neurectomy and fasciotomy procedure for the management of proximal suspensory desmitis in the hindlimb requires the introduction of surgical scissors or a fasciotome through the surgical incision and accurately placed at the proximal limit of the metatarsal fascia. Iatrogenic damage to the suspensory ligament has been reported after this procedure [1] and an experimental study suggested the fasciotome required, although did not eliminate, the risk of this damage [2]. The use of concurrent ultrasound using a transversely orientated transducer immediately distal to the incision helps to reduce this risk further by ensuring the instrument is cutting the plantar fascia without entering the adjacent suspensory ligament.

d. Transection of tendons and ligaments This can be achieved minimally invasively through a small incision with the help of intra-operative ultrasound – such as the accessory ligament of the deep digital flexor tendon [3], the palmar annular ligament [4], medial patellar ligament, and tenotomy of the distal limb tendons (eg superficial and deep digital flexor and extensor tendons). e. Implant placement and removal Drains and transphyseal screw placement can be performed minimally invasively with the concurrent use of ultrasound. Removal of bone screws can also be facilitated by identifying the screw head ultrasonographically.