Keywords
hallux valgus - piezoelectric - forefoot - distal linear osteotomy - mini-invasive
Introduction
The term of “hallux valgus” has been introduced by Carl Hueter[1] in 1870 to 1871 to define a static subluxation of the first metatarsophalangeal
(MTP) joint and it is clinically correlated with pain, generally due to bursitis and
shoes conflict and functional limitation. Prevalence estimated for hallux valgus is
23% in adult population between 18 and 65 years old and 35.7% in elderly people[2] and represents a deformity characterized by lateral displacement of the great toe
and medial displacement of the first metatarsophalangeal joint, associated to lateral
displacement of sesamoidal bones.[3]
The surgical correction of deformities of the first ray of the foot presents more
than 130 different well-codified operative techniques.[4] In this article, authors describe the well-codified distal linear osteotomy of the
first metatarsal by Giannini et al[3] using piezoelectric tools.
Piezoelectric and ultrasonic vibrations have been used to cut tissues for three decades.
It is only in the last years that applications have been used for standard clinical
performances. In particular, ultrasounds have been widely used in periodontics with
good results for decontamination of root surfaces, mainly because of its efficiency
for calculus removal,[5] dental extraction techniques, maxillofacial bone surgery, and bone block collection
for autogenous grafting.[6]
[7]
The increasing use of piezosurgery is based on its clinical advantages, such as selective
cutting (avoiding soft tissues damage), precision (due to the micrometric amplitude
of the oscillation), and low-temperature work rates.
Instruments for piezoelectric cutting of bone, developed by Vercellotti in 1988, create
microvibrations caused by the piezoelectric effect, first described by Jean and Marie
Curie in 1880.[8] The passage of an electric current across certain ceramics and crystals deform their
structures, determining expansion and constriction perpendicular to the polarity of
the material.
A frequency of 25 to 29 kHz is usually used because the micromovements created at
this frequency (ranging between 60 and 210 µm) cut selectively mineralized tissues.
Neurovascular structures and other soft tissues are cut at higher frequencies (more
than 50 kHz).[9]
The aim of this study is to describe application of the piezosurgery to the orthopaedic
procedures, in particular, the hallux valgus surgical correction using a traditional
distal linear osteotomy of the first metatarsal and piezosurgical tools, analyzing
and discussing advantages and limits of the technique.
Methods
Instrumentation
The osteotome equipped was the Surgysonic Moto-II model, (Esacrom, Imola, Italy),
a system recently developed for cutting bone with microvibrations. The equipment consisted
of a piezoelectric handpiece and a foot switch that are connected to a main unit ([Figs. 1] and [2]), which supplied power with sterilizable holders for the handpiece and irrigation
fluids. It contained a peristaltic pump for cooling with a jet of saline solution
that discharges from the insert with an adjustable flow of 0 to 60 mL/min and removes
detritus from the cutting area. This allowed a precise cut and a good visual control
of the surgical field. The setting of power and frequency modulation of the device
can be selected on a control panel with a digital display. For the handpiece several
autoclavable tooltips, called “inserts,” are available ([Fig. 3]).
Fig. 1 Main unit, supplying power, and irrigation fluids.
Fig. 2 Sterile piezoelectric handpiece connected to the main unit.
Fig. 3 Autoclavable tooltips, called “inserts.” Tips used in author's case series were a
high efficiency five teeth piezoelectric saw (thickness, 0.27 mm; operative length,
20.3 mm [third one from left]) and a high efficiency flat scalpel shaped on three
edges (thickness, 0.27 mm; operative length, 16.3 mm [second one from left]).
Tips used in authors' case series were a high-efficiency five teeth piezoelectric
saw (thickness, 0.27 mm; operative length, 20.3 mm) and a high-efficiency flat scalpel
shaped on three edges (thickness, 0.27 mm; operative length, 16.3 mm); all tools used
had a double nanostructural finishing surface, that could be used to a maximum power
of 50 W. These tips are microshaped instead of diamond coated, allowing more resistance
and less abrasion.
Distal linear osteotomy used by authors in this article, as described by Giannini
et al[3] in 2013, had been indicated to correct deformities characterized by a mild severity,
with an intermetatarsal (IMT) angle included between 15 degrees and 25 degrees.
Postoperative care is characterized by a functional bandage dressing, aiding the Kirschner
wire (K wire) fixation of the osteotomy for 35 days. Patients were allowed to walk
with complete weightbearing on the day after the surgical operation with the use of
a dedicated footwear with a flat, rigid sole.
Operative Technique
The patients were counselled regarding the surgical procedure and the risk involved,
informed consent were obtained.
Under spinal anesthesia, the patient was placed in supine position, with feet at approximately
3 cm from the end of the operating table and a thigh tourniquet was applied and inflated
for lower limb exsanguination, following the AORN guidelines (tourniquet inflated
intraoperatively to a pressure higher than the limb occlusion pressure).[10]
Stretching of the adductor hallucis tendon at its insertion and lateral capsule release
were permorfed after mini-open approach weaking, using a size-15 scalpel.
Medial approach through less than 1 cm skin incision was performed, performed at the
level of the neck of the first metatarsal ([Fig. 4]). The periosteum around the site of the osteotomy was detached first, from 3 to
5 mm just to allow the insertion of piezoosteotome. Before proceeding to osteomoty,
the site and the direction of the cut could be controlled by intraoperative X-ray.
In selected cases, such as first metatarsophalangeal joints free from early-to-moderate
osteoarthritic processes, it has been possible to work through a mini-invasive approach
without associated articular procedures.
Fig. 4 Medial approach through less than 1-cm skin incision performed at the level of the
neck of the Ist metatarsal bone.
The osteotomy was performed through the subcapital region of the first metatarsal
using a proper tip. Contrary to the osteotomies with oscillating saw, that needs pushing
movement, piezoelectric saw works with gentle sliding movements. The cutting efficiency
is linked to the pressure on bone. With a piezoelectric unit, cutting is due to the
high frequency vibrations of the tip. Excessive pressure prevents vibration, decreases
efficiency, and generates frictional heat. A moderate force (1.5–2 N) is used to allow
the tip to vibrate (as comparison, the axial force during handwriting closely corresponds
to 1 N).[11] A working pressure of 1.5 N has been shown to fulfill the requirements for harmless
intraosseous temperature. Beyond 3 N, cutting efficiency was not improved and thermal
damage was increased.[12]
The cut was made at approximately 15 degrees of inclination in sagittal plane, under
visual control, perpendicular to the axis of the second metatarsal bone ([Fig. 5]). The mediolateral inclination of the osteotomy in transverse plane makes it possible
to lengthen or shorten the metatarsal with lateral displacement of the distal fragment.
So, in this way, if decompression of the first metatarsophalangeal joint is required,
such as in case of slight stiffness, the osteotomy can be inclined up to 20 degrees.
Furthermore, the metatarsal head can be rotated in the axil plane to correct the rotational
component of the pathoanatomy of the deformity.
Fig. 5 Cut was made at approximately 15 degrees of inclination in sagittal plane, under
visual control, perpendicular to the axis of the second metatarsal bone.
A 2-mm K wire was positioned to stabilize the osteotomy, inserted in the distal direction
through the skin incision in a parosteal position along the longitudinal axis of the
toe to its tip, 2 or 3 mm from the medial corner of the nail. The wire was withdrawn
from the tip of the toe until its proximal end reached the osteotomy site. At this
point, the displacement was best achieved using a small grooved lever. With the lever,
authors accessed the osteotomy and the K wire was pushed in a retrograde way through
the osteotomy into the medullary channel. It was firmly driven as far as the base
of the metatarsal bone to improve stability.
If the proximal edge of the osteotomy was prominent, a small resection of bone was
performed.
The head can be manipulated in transverse plane or rotated to modify the distal metatarsal
articular angle. The plantar or dorsal adjustments of the metatarsal head can be obtained
by positioning the K-wire dorsal or plantar in the soft tissues, close to the bone.
Tourniquet was deflated and tourniquet time was recorded. Emostasis was not necessary
in any treated case. The skin was closed, being careful of tension, with interrupted
absorbable no. 3–0 suture.
Postoperative Care
The postoperative care involves an imbricated bandage, the use of a forefoot off-loading
shoe footwear, and progressive-to-full weight bearing for 1 month. The rehabilitative
protocol starts at the removal of K wires at 1 month of follow-up and provides active
and passive mobilization exercises of the first MTP to recovery articularity and function.
Discussion
Piezoelectric techniques were developed in response to the need for great precision
and safety in bone surgery than was available with other manual and motorized instruments.
In orthopaedic surgery, piezoelectric devices allow precise cuts during osteotomies.
Budd et al reported that bone could be cut precisely at an angle, but the system was
less efficient for deep cuts.[13] As the cutting speed decreased the temperature rose, so it was necessary to pause
to allow the system to cool down. In devices used by authors, the peristaltic pump
with a jet of saline solution for cooling can be taken in consideration to resolve
this problem. Cavitation effect associated with ultrasonic instrumentations, responsible
of expansion and contraction of microbubbles of gas dissolved in fluids that violently
collapse creating a shock wave.[14] This effect lead to reduction of bony debris at the site of osteotomy that is generally
correlated to longer time of fracture healing. Piezoelectric surgery presents better
results regarding to bone healing and radiographic healing time. Piezosurgery is able
to allow a favorable bone response, linked to the lack of coagulative necrosis due
to heat generation of traditional osteotomy methods and to higher rate of viable bone
cells in site. This can lead to a faster formation of bone callus.
Another important point of discussion is represented by bone saving in the osteotomy
sites.
Shahid et al[15] demonstrated that the mean bone loss during a linear osteotomy on rigid polyurethane
foam blocks (sawbones) was 0.23 g using a 31 mm × 9 mm × 0.51 mm oscillating saw blade
and 0.85 g using a 3 mm × 20 mm burr, corresponding to 0.67 and 3.21 mm of cut thickness,
respectively. In authors' case series, piezoelectric osteotome had 0.27 mm of thickness,
corresponding to real bone loss of 0.3 mm. Anyway different studies in literature,[16]
[17] demonstrate that larger bone loss and larger thickness of the cut may lead to shortening
of the metatarsal and this, in turn, may result in abnormal transfer lesion to lesser
metatarsals due to the change of the biomechanics of the forefoot and the function
of the first ray, requiring further surgery.
Furthermore, piezoelectric surgery is safe, especially in tiny small surgery fields.
It has been shown that a piezoelectric tool directly applied for 5 seconds on a peripheral
nerve with a relatively high working force (1.5 N) did not dissect the nerve but induced
some structural and functional damage.[18] Moreover, blood loss during procedures is reduced by 25 to 30%, due to a better
visibility and to the sparing effect on soft tissues. .
Precision of the cut is enhanced by the micrometric vibrations of the tips, continuous
washing of the osteotomy site, reduced bleeding, and powerful high luminosity LEDs
which improves visibility at the surgical site even in deep locations.
Limitations
Limitations of the piezoelectric instrumentation are the speed of osteotomy and the
costs. Piezobone surgery is usually considered to be slower that traditional burr
and oscillating saw, especially when surgeon is learning this new field of application.
In literature, Spinelli et al showed that the whole operative procedure took 35% longer
with a piezoelectric tool compared with an oscillating saw.[19] A clinical trial is currently ongoing and preliminary results are comparable to
the literature: correction of hallux valgus with SERI (simple, effective, rapid, and
inexpensive).[3] and oscillating saw took approximately 3 minutes, with piezoelectric saw approximately
10 minutes.
Conclusion
In conclusion, piezotechnology allows minimally-invasive and percutaneous surgery,
with reduced trauma on periostium, bone, and soft tissues, reduced healing time of
the osteotomy due to the absence of bony necrosis and debris formation and major precision.
Further development on the piezoelectric percutaneous technologies may include computer-assisted
tools and three-dimensional printed mechanical jigs.
