USE OF PIEZOELECTRIC BONE SCALPEL IN HAND AND RECONSTRUCTIVE MICROSURGERY

INTRODUCTION

Cutting bony tissues, traditionally performed by electric or power driven reciprocating or oscillating saws, not only generates substantial heat – which can interfere with normal bone healing process – but can also damage underlying soft tissues (blood vessels, nerves) and cause permanent functional impairment. The saw is controlled exclusively by the surgeon’s experience and dexterity and does not stop when it comes into contact with tissues of different density. Some authors speculate that the actual rate of soft tissue damage in such procedures is higher than that reported in the literature (12). For these reasons it is important to perform osteotomies with instruments which only cut bone, thus preserving adjacent soft tissues. Such an instrument would increase the applicability of the method, as well as enhance the safety and quality of the surgical procedure.

Ultrasound has been used in industry for cutting hard substance ever since the early 1950s (8). Soon afterwards it was introduced into medicine and first used in 1957 in oral surgery, for cutting dento-osseous structures (15). In 1972 it was used in thoracic surgery (13). At present ultrasound technology is used in almost every hospital for surgical aspiration in laparoscopic surgery, fragmentation of kidney stones and soft tissue dissection by harmonic scalpel (2, 3, 5, 16, 18, 19).

Recently ultrasound in the form of the piezoelectric bone scalpel has been introduced in maxillofacial and craniofacial surgery for osteotomies of viscero- and neurocranial bones of reduced thickness (osteotomies of orbital walls, mandibular osteotomies and craniotomies) (12).

We report the use of a piezoelectric bone scalpel for cutting bones of larger thickness (metacarpal, fibula, rib and rib cartilage) where high precision is required to protect underlying neurovascular bundles.

In this way – for the first time, to our knowledge – the field of application of this machine/instrument has been enlarged to include hand and reconstructive microsurgery taking advantage of its principal qualities, namely precision and safety during osteotomy when a significant risk of damaging soft tissues is present. 

MATERIALS AND METHODS

In our Department for Plastic and Reconstructive Surgery at Cattinara University Hospital in Trieste (Italy) we started to use the ultrasound machine at the beginning of 2008, initially for debridement of chronic wounds and ulcers, taking advantage of its mechanic-vibratory, cavitation and thermal energy permitting elimination of fibrinous and necrotic materials from the wound bed and thus reducing bacterial load while preserving viable tissues.

Later we expanded its use to include head and neck reconstruction (osteotomies of nasal bones and mandible).

However, here we present only three cases where piezoelectric bone scalpel has been successfully used in an innovative way for osteotomies of larger diameter bones (metacarpal, fibula, rib and rib cartilage), proving its great applicability in hand and reconstructive microsurgery.

Our osteotomies were performed using an ultrasound-activated device produced by Genera^® (Italia Medica, Milano, Italy). The device consists of a console and piezoelectric hand-piece with changeable tips (Fig. 1, 2, 3).

It operates in continuous mode, activating the tip, which is made of titanium and fixed to a hand-piece, a piezoelectric transducer vibrating at a frequency of 26 kHz and making transversal movements of 15–30 μm from peak to peak. The vibrating tip is continuously irrigated and cooled by cold saline solution with the help of a peristaltic pump. Tip vibration changes the cooling solution into an aerosol which, in addition to cooling, also cleans bone detritus and blood from the operating field. Another feature offered by the vibrating tip and the cooling liquid is “cavitation” – the production of microscopic bubbles of saline which increase the mechanical effects (cutting) of piezoelectric bone scalpel. The ultrasound energy force on Genera^® Ultrasonic console is set to 90W. In our experience, compared with other similar devices, such force is necessary for cutting bones of larger thickness. The Genera console offers two independent channels, permitting greater reliability. Because of such specific characteristics the osteotomy line is made by the precise and controled progressive micro-fracturing and dispersing of bony tissue. Furthermore, cavitations created by vibrations augment the mechanic effects of the device and stimulate the process of repair. Injury to the soft tissues is avoided by special software and microprocessors which limit the bone scalpel’s action only to bone but also by its precise, progressive and controlled cutting action, which lets the surgeon “feel” when the bone has been thoroughly cut (12, 17).

Case 1

A 35-year-old woman presented after having sustained open fractures of the 3^rd and 4^th metacarpal bones and incomplete amputation of the 5^th finger with extensive contusion of soft tissues on the dorsum of the right hand while hit by a rock when climbing in French Alps. Her primary treatment was performed in France and consisted of primary debridement, bone fixation of the 3^rd and 4^th metacarpal by plate and screws and secondary amputation of the 5^th finger, which presented non curable venous insufficiency at the level of proximal phalanx. The amputation stump was covered by necrotic masses and required shortening. Our operative plan was elimination of all necrotic tissues on the dorsum of the hand with aesthetic amputation of the 5^th ray proximal to the head of the metacarpal and simultaneous cover of the dorsum of the hand by a reversed radial forearm island flap. Since intact palmar arches are necessary for such a reconstruction we opted for a precise method of oblique cutting the neck of the 5^th metacarpal by Genera^® Ultrasonic, providing necessary protection of the neurovascular bundles. Amputation with osteotomy regularized the aesthetic profile of the hand, permitted flap coverage and shortened postoperative rehabilitation (Fig. 4, 5, 6).

Case 2

A 74-year-old woman was diagnosed with carcinoma of the left body of the mandible involving oral mucosa. She was offered radical tumour excision with ipsilateral neck dissection and reconstruction with a free osteo-cutaneous fibular flap, which she accepted. While the ENT surgical team was performing the oncologic part of the procedure, the plastic surgery team was harvesting the fibular free flap. Both proximal and distal osteotomies of the fibular bone were performed by using Genera^® Ultrasonic in a progressive, controlled and precise manner. Due to the substantial bone thickness the cutting time compared to cutting with an oscillating saw was about 30% longer, but since no protection of the peroneal artery with bone retractors was necessary when performing distal osteotomy – as would be usual when using an oscillating saw – fibula harvesting took no longer than usual.

Case 3

A 45-year-old woman underwent an operation for breast cancer by modified radical mastectomy with simultaneous autologous reconstruction by a DIEAP free flap. The microsurgical anastomosis was planned to ipsilateral internal mammary vessels. We planned to remove part of the 3^rd rib cartilage to gain access to the recipient vessels. Harvesting of ribs/rib cartilages usually requires special instruments and can easily cause pneumothorax or bleeding, either from intercostals or internal mammary vessels or their branches. Cutting the rib cartilage at the level of sterno-costal joint and 4 cm laterally by Genera piezoelectric scalpel permits easy and fast removal of the rib cartilage/rib with complete preservation of the intact recipient vessels which are required for problem-free microvascular anastomosis (see Fig. 3). 

RESULTS

All three reconstructive surgical procedures using Genera^® Ultrasonic to perform osteotomies were completed successfully, with no complication either to bony structures/cartilage or soft tissues. Blood vessels or neurovascular pedicles remained untouched and functioning, resulting in free or pedicled flap transfer with no vascular complications and consequently no (partial or total) flap loss. The patient undergoing aesthetic amputation of the 5^th ray amputation presented no sensory loss, and the patient undergoing mandible reconstruction by free fibula flap showed primary bone healing at X-ray and CT-scan controls three months after the operation.

Cutting thick bones (>10mm) by Genera^® Ultrasonic takes 20–30% more time than is the case with a conventional oscillating saw. We believe the precision of the cut and preservation of underlying soft tissues more than compensate for this slight increase in time spent.

Learning to use the Genera^® Ultrasonic is easy and quick. It only takes a few minutes to understand the function of the device and a few more to be able to use it correctly and safely. 

DISCUSSION

Ultrasound technology has found many applications in medicine (2, 3, 5, 16–18, 19).

The machine that we are using is, in a simplified way, just a tool to produce ultrasound, but at the same time its specific characteristics can be modified as required: the tips of the bone scalpel are interchangeable, offering different length and shapes as needed; furthermore, the frequency of vibration as well as the power of the machine can be regulated. The increased power level (90W) seems to be necessary for cutting thicker bones (such as the fibula or metacarpal in our case). At the same time this increased power only produces a moderated quantity of heat at the tip of the bone scalpel, reducing osteonecrosis at the cutting surface to a minimum (4).

The effects on bony tissue of cutting bones by ultrasound energy have been extensively analysed in the literature (1, 6, 9–11, 14). They include a less smooth cutting surface compared to that produced when cutting with a conventional electrical saw. However, the major advantages of cutting by ultrasound are the absence of microfractures, only modest heating at cutting surface and the creation of cavitations.

These features prevent structural alterations (necrosis) of bony tissue – as proven by histology and electron   microscopy – and facilitate bone healing after bone fixation.

The possibilities for use of the Genera^® Ultrasonic are numerous. It has been widely used for treatment of chronic skin ulcers and in cranio-maxillo-facial surgery for cutting cranial and facial bones (thickness <10mm). In our department we have used it (other than for debridement of venous, arterial and combined lower extremity ulcers) for the removal of a nasal bone invaded by a local recurrence of basocellular carcinoma (primarily operated elsewhere) because we wanted to preserve untouched the underlying nasal mucosa which appeared on CT-scan not to be involved. In this case the ultrasound technology was applied to cut bone of moderate thickness.

In the three case reports presented the osteotomized bone was much thicker. To our knowledge reports of cases of this sort have not been published before and extend the use of piezoelectric bone scalpel to new fields – hand surgery and reconstructive microsurgery – where precision of cutting and protection of neurovascular structures is of paramount importance. In fact, in the patient with soft tissue necrosis on the dorsum of the hand and amputation of the 5^th finger after being hit by a rock while climbing in the Alps (Case 1), the osteotomy proximal to the metacarpal head (aesthetic amputation of the 5^th ray) was neat (see Fig. 5) and the neurovascular bundle remained untouched. Integrity of the palmar vascular arches made it possible for us to harvest the distally based radial forearm flap for easy and fast coverage of the exposed metacarpal fractures and extensor tendons.

Selectivity of bone scalpel for bony tissues has been confirmed during harvesting of the osteocutaneous fibular flap for reconstruction of the mandible and oral mucosa after demolition by oncology surgeons. It has been possible to cut the fibula, a bone of important diameter, twice, proximally and distally, with no risk of lesion of damaging the vascular pedicle. Sculpturing fibula with multiple osteotomies into a new hemi-mandible, or a double-barrel fibula, are particularly good indications for the use of Genera^® Ultrasonic, since the bone can be cut precisely for effective and stable bone fixation with reconstructive plate or mini plates while preserving the integrity of peroneal vessels which, together with a perfect microvascular anastomosis, is critical for survival of the flap.

The mechanism of irrigation in the phase of osteotomy during which the liquid is vaporized combines efficient washing and cooling of bone surfaces, thus reducing the risk of overheating the bone and soft tissues and subsequent complications, namely necrosis, vascular thrombosis and non-union. Clinically we have not observed any of these features in tissues adjacent to the osteotomy site where heat could have been dissipated (7, 12).

Moreover, the possibility of choosing the appropriate bone scalpel tip from a variety of different length, diameter and form permits differentiated use of this instrument with bony tissues. 

CONCLUSION

Performing osteotomies with the piezoelectric bone scalpel is also possible with larger diameter/thickness of bones. At the same time, adjacent soft tissues are not in danger from cutting or thermal damage, reducing the risk of damaging neurovascular structures – which is of primary importance in hand and reconstructive microsurgery. These features contribute to the safety and easy execution of the procedure.

The resulting bony cut is precise and permits immediate and safe bone fixation.

Osteotomy of bones of >1cm thickness takes 20–30% longer than when using a conventional oscillating saw, though the increased safety of the procedure more than compensates for this. 

Fabio Toffanetti, M.D.

Department of Plastic Surgery, Cattinara Hospital

Strada di Fiume N°447

34100 Trieste

Italy

E-mail: Toffa772000@yahoo.it