| |
Info direct
Sulzer Orthopedics Ltd
Monica Fucentese
Erlenauweg 17
CH-3110 Münsingen
Switzerland
Telephone
+41 (0)41-768 36 80
Fax
+41 (0)41-768 16 80
E-mail
monica.fucentese
@sulzer.ch
|
|
Monica
Fucentese
Sulzer Orthopedics
Whether playing soccer
in summertime or skiing in wintertime, the knee is the joint most subject
to sports injuries. One of the possible injuries to the knee is a torn
of the anterior cruciate ligament. As generally is the case with sports
injuries, most patients with torn anterior cruciate ligaments are active
young persons. A complete reconstruction of the ligament is very important
for them, so that they can participate as unhindered as possible in every
athletic as well as professional activity.
..... Removing
a tendon surgically from the patient’s own body and implanting it in place
of the injured ligament is becoming the treatment of choice. Either the
middle third of the patellar tendon or tendons taken from the inner thigh
(semitendinosus and gracilis) can be used. The so-called interference
screws (Fig. 1n) are normally used to secure the “new” cruciate ligament
into place in the bone. These screws settle the graft in the immediate
vicinity of the articulation, in the holes previously drilled into the
femur and into the tibia (Fig. 2n). In highly industrialized countries
like Switzerland or the United States, this operation is carried out annually
about 800 times per million residents.
Completely
degradable
The
latest developments in biotechnology combined with modern manufacturing
technologies have enabled the production of bioresorbable screws which
can be successfully implanted in humans. The Sysorb interference screw
is a product of this technical evolution. It was designed in 1995 with
the help of the orthopaedist Dr. Andreas Stähelin from Basel, Switzerland, and is made of polylactide,
a lactic acid polymer. Lactic acid polymers are metabolized in the human
body to water and CO2 and then eliminated. The speed of this degradation
depends on the polymer structure and on the proportion of L(evorotary)-
and D(extrorotary)-lactides. Pure poly-L-lactide for example, which is
likewise used for interference screws, is partially crystalline and is
degraded only after 2–6 years. Sysorb, on the other hand, consisting of
50% L- and 50% D-lactides (poly-D,L-lactide), is amorphous and is completely
degraded within only one year (Fig. 3n). This time frame of degradation
is long enough to stabilize the tendon transplant during the one-to-two-months
healing period, but markedly shorter than that of the partially crystalline
screw.
Secure
screwing-in guaranteed
The
design and manufacture of the Sysorb screw are adapted to the specific
properties of the material. The screws meet the mechanical requirements
made and are easy to implant. The design of the screw compensates completely
for the lower biomechanical strength of the amorphous, as compared with
a crystalline, material. A special screwdriver has been developed, with
which the screw can be placed securely into the bone (Fig. 4n). The screwdriver
is made in such a way that the torque is applied along the entire length
of the screw as it is screwed in. There are no centrifugal or torsion
forces that could cause the screw to break. Biomechanical studies by Weiler
et al. have shown that of all the bioresorbable screws tested, Sysorb
can stand the greatest torque at failure while being screwed in.
..... The
primary fixation of the transplanted tendon achieved with the bioresorbable
Sysorb is as stable as primary fixation supplied by conventional metallic
interference screws. Several biomechanical studies by Weiler et al. have
shown that the resistance to being pulled out is comparable to that of
metallic interference screws; about 600 N. A cruciate ligament has to
be able to stand forces of about 400 N as a rule.
No second
surgery necessary
In
addition to possessing certain biomechanical properties and degradation
capability, bioresorbable implants have to meet certain biocompatibility
requirements. Among other difficulties, rejection by the body can lead
to severe inflammation, associated with pain. The good biocompatibility
of the Sysorb has been confirmed clearly by extensive clinical experience
acquired over many years. Histological tests show that the bone grows
into the tendon within a short time (Fig. 5n), and that during the degradation
of the Sysorb screw, there is no evidence of inflammation in the bone
tissue (Fig. 6n).
...... A
great advantage of bioresorbable implants, as opposed to metal implants,
is the fact that a second surgery to remove the screws is no longer necessary.
The whole procedure is therefore a lesser strain for the patient, and
costs are lower. In addition, postoperative radiologic examinations such
as MRI (magnetic resonance imaging) or CT (computer tomography) can be
carried out without artefacts. Metal parts, on the other hand, distort
the pictures created by MRI or CT, making their interpretation more difficult.
|
