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BIOLOGICAL
PLATING
A New Concept
To Foster Bone Healing
R
Original Instruments and Implants of the Association for the Study of Internal Fixation—AO ASIF
Early Temporary Porosis Beneath Bone Plates
Is there a correlation between bone loss beneath the plate and
“stress protection”?
Observed patterns of bone
loss beneath a plate do not
correspond to the stress
patterns of the corresponding
bone segment.
Situation under a plate: Under weightbearing conditions, stresses in the bone
(represented by black lines) diminish
towards the plate (shielding effect of
a plate [1]).
Situation under a plate: The area of
observed porosis is sharply defined and
unrelated to the pattern of stress
shielding (as represented at left).
Bone loss in the vicinity of a plate has always been explained on the basis
of Wolff’s law as a reaction of living bone to mechanical unloading of
the plated bone segment (stress protection). Although experiments have
demonstrated that flexible plastic plates do not improve the situation,
the rigidity of a plate is generally still considered the prime factor inducing porosis.
AO ASIF observation
The disturbance of the blood
supply and porosis are
strongly correlated [2].
Disturbance of blood supply demonstrated with disulphine blue as an
indicator of blood perfusion.
A comparative histological section
shows remodelling located in the area
of previous avascularity.
Osteoporosis beneath a plate is the direct result of damage to the blood
supply and not the result of mechanical unloading of the bone [2].
Limited Contact Concept
Reduced vascular damage
Area of disturbed circulation in bone cross section
mm2
Reduction of surface contact
between plate and bone
results in a reduced disturbance of blood supply [3].
20
10
Full Contact
Limited Contact
Histological investigation brings a new understanding of vascular damage
in relation to different contact surfaces and enlightens the etiology
of temporary porosis of bone.
Improved bone consolidation with reduced porosis
Favorable blood perfusion
conditions promote better
bone quality.
Extensive area of bone loss as observed
beneath a full-contact plate.
Reduced area of bone loss (porosis)
as observed beneath a limitedcontact plate.
Besides supplying the energy for the body’s regenerative mechanisms,
an intact blood supply is essential as a defense against infection and as
a medium to reduce early porosis, possible necrosis, and/or sequestration.
Minimal Contact Achieved Without Impaired Implant Strength
Uniform bending and torsional stiffness
Finite Element Analysis grid of the optimized plate viewed
from above
To achieve a uniform stiffness with limited bone contact
along the plate length, CAD/CAE tools and mathematical
analysis are used for a reliable functional design [4].
The Finite Element Analysis of a plate under bending
load conditions (see picture below) shows bending
stresses evenly distributed along the plate.
Improved Mechanical Performance
Plate protected from localized high stresses
Contouring the LC-DCP™: The plate holes preserve their shape.
Conventional plate: Kinks at holes impair the mechanical
performance.
The LC-DCP deforms over a long distance, resulting in an even
stress distribution (exaggerated situation).
Exact contouring is essential for good force transmission
and successful fracture treatment.
When loaded, the uniform stiffness of the LC-DCP
results in an even distribution of stresses over a long
distance along the plate, protecting the plate holes from
localized high stresses. Therefore, the LC-DCP is less
prone to fatigue, especially where plates span a wide
bony defect or in comminuted fractures. In contrast,
a conventional plate deforms mainly at the hole, and
stresses concentrate at the smallest cross section.
Strain
Improved contouring of the plate
The uniform stiffness of the LC-DCP™ enables continuous
curvature, allows a good fit of the screw head in the
plate hole, and preserves the mechanical features of
the plate.
The Material of Biological Choice: AO ASIF Pure Titanium
High corrosion resistance of conventional
implant materials
Fretting effects on conventional implant
materials
tissue
passivelayer
metal
Standard implant materials are protected by a thin passive layer.
Typical congruent zones where fretting occurs between screw
head and plate hole in stainless steel implants [5].
As long as the protective oxide layer on the implant
surface is intact, the material remains passive.
Relative motion between metallic implants leads to
fretting effects, and alloying components can be
released into the tissues.
The conventional implant materials used today are
highly corrosion-resistant and generally well tolerated.
They are protected by a spontaneously forming submicroscopic thin oxide layer on their surface which
prevents the metal from further oxidation and
corrosion. This protective oxide layer is known as
passive film.
In areas where implants are in contact, the protective
oxide layer may be destroyed by relative motion; even
micromotion is enough. In this situation, called
fretting, abrasive action takes place, and fretting
corrosion can occur because the passive film is
disrupted.
Alloying elements less tolerated by the tissues than the
alloy itself can be released during the abrasive process
of mechanical wear. Usual metals used in alloys, like
nickel, chromium, cobalt, aluminum, and vanadium,
can thus find their way into the body tissues. The
ingestion and transport of metallic degradation
products in the body tissues is complex, and different
mechanisms might operate simultaneously depending
on the form in which the metal is released [5]. The
metallic degradation products may be in the form
of wear particles, oxidized compounds, or ionized
species.
Alloying elements with biological activity
toxic and
corroding
increasing
acceptance
Pure titanium is biologically inert
excellent
acceptance
Corrosion resistance
Titanium
Co-Alloys
St Steel
Pt
Ta
Nb
Ag Au
Ni
V
Cu
Co
Mo
Al
Fe
Increasing biocompatibility
Corrosion resistance vs. biocompatibility of some pure metals
and alloys [6].
Pure titanium displays excellent biocompatibility.
The biocompatibility of metallic materials is closely
related to their corrosion resistance and to the transportability of the corrosion products. The extent to
which the wear products from alloys further corrode
in tissues is uncertain, but biological activity of alloying components does occur, and occasional reactions cannot be ruled out.
Nickel is a known allergen, and contact alone can
provoke an allergic reaction (i.e., no particular corrosive process has to take place). Speculations on the
systemic effects of nickel and other metals abound.
Various published and unpublished data from cell
and organ cultures show that nickel and vanadium
have cytotoxic effects at considerably lower concentrations than other metals used in implants [7,8]
(see diagram above).
Tissue impregnated with pure titanium wear particles does not
show adverse reactions.
Pure titanium and its wear products remain passive
and do not affect the tissue.
In contrast to the above-mentioned metals, pure
titanium displays very little biological activity, and its
unmatched tissue tolerance has been scientifically
and clinically demonstrated.
In cases of unstable internal fixation with tissues
stained by abrasion particles, no accompanying
corrosion has been observed [5].
In tissue fluids, the pure titanium mechanical wear
products are practically insoluble and are chemically
non-transportable. Besides this, the body seems to
be saturated with titanium, and this suggests that
no additional soluble titanium can become active [6].
These properties and the extraordinary corrosion
resistance of pure titanium help to explain why
adverse tissue reactions are not observed (inertness).
The AO chose not to add any element
to pure titanium which could cause an
adverse biological response.
AO ASIF Pure Titanium
Broad Clinical Experience
Better Vascularized Tissues
Since 1965, the AO ASIF has gained clinical experience with nearly 5,000 cases treated with AO ASIF
Pure Titanium implants. The outstanding tissue
compatibility of AO ASIF Pure Titanium has been
repeatedly confirmed and is well established;
no documented case of metal sensitivity (allergy)
or adverse tissue reaction has ever been related
to pure titanium implants.*
Today, pure titanium is already the material of choice
for implants to be used in patients suffering from
metal allergy. Furthermore, if it is advantageous to
avoid explantation surgery (e.g., distal humerus),
implants made of inert materials, such as pure
titanium, are ideal.
Well vascularized tissue around AO ASIF Pure Titanium
implants
Clinical experience shows that the tissues which
envelop pure titanium implants are better vascularized and show a reduced tendency towards capsule
formation [9,10,11]. There is better tissue adherence
to the pure titanium plate than when other standard
implant materials are used.
These biologically favorable conditions help to
reduce the spread of bacteria and increase
resistance to infection.
* In cases of prosthetic-related wear, adverse reactions to titanium alloy (Ti-6AI-4V) have indeed been documented. Titanium alloys have different
properties from pure titanium.
It may be mentioned that titanium alloys are often addressed as titanium. This inaccurate expression causes confusion and must be avoided.
Highly Advanced Manufacturing Methods
Pure titanium is a relatively soft metal. In order to
maintain reduction and to withstand anatomical
loads, the implant requires a minimum adequate
strength which depends on the type of implant and
its function.
The strength of pure titanium can easily be
increased by adding alloying elements like
vanadium, aluminum, etc., but this may have
negative effects. Ductility (workability) is reduced,
and the addition of toxic elements compromises
biocompatibility.
To endow pure titanium with a strength that is
similar to that of medium-hard stainless steel while
preserving its ductility, the AO ASIF, its collaborating
laboratories, and its exclusive producers have developed special manufacturing and thermic treatment
methods. With these methods, the required strength
and ductility are achieved without the addition
of alloying elements of proven toxicity such as
vanadium. Thus, the AO can take uncompromised
clinical advantage of the outstanding biocompatibility of pure titanium.
Distinct Mechanical Properties
Ultimate
tensile
strength
N/mm2
Commercially
available
Pure Titanium
AO ASIF
Pure Titanium
900
800
700
600
500
400
300
200
100
0
The diagram shows the range of tensile strength characteristic
of commercially available pure titanium and AO ASIF Pure
Titanium.
Depending on the type of implants and their function, the appropriate strength level is chosen within
this range.
Advantages in Surgical Technique
Compression can be achieved in either
longitudinal direction
A lag screw can be inserted at greater
angulation
40°
40°
LC-DCP hole
Longitudinal cross section of LC-DCP hole and feasible
angulation of a lag screw
The basic spherical gliding principle of the screw in
the DCP ™ hole is now implemented at both ends of
the plate hole in the LC-DCP plate. This enables
compression in either direction along its longitudinal
axis. The redesigned geometry of the hole also adds
more flexibility to the plating technique and eases
handling of complex situations.
With conventional DCP plates, the maximum screw
angulation in the longitudinal axis is about 20
degrees. Greater angulation of the lag screw could
not be achieved without impeding the gliding of the
lag screw in the gliding hole. The LC-DCP hole offers
the possibility of safe insertion of the lag screw up to
40 degrees through the plate in both directions. This
gives the surgeon more possibilities to achieve interfragmental compression through the plate [12,13].
The plate hole can be used for interfragmental
compression of multifragmentary fractures. Due
to the regular hole spacing along the axis of the
plate—no midsection without holes—the surgeon
has more options to reposition a plate of different
length using the same predrilled holes.
To achieve additional interfragmental compression,
correct angulation of the lag screw is required. To
secure a loose fragment through the plate, an angle
greater than 24 degrees (standard plating systems) is
occasionally required.
Implant removal is facilitated
Standard plate cross section
LC-DCP plate trapezoidal cross section reduces the risk of
generating stress risers.
The normally thin bone lamella lining the plate may
impede removal of conventional plates. The frail
lamella is susceptible to damage upon removal and
will act as a stress riser [14] which could eventually
result in refracture of the bone.
Because of the trapezoidal cross section of the
LC-DCP, the bone lamella attached to the plate is
flatter and less fragile, allowing easier plate detachment and reducing the risk of refracture.
References
[1] Cordey, J. and S.M. Perren. “Stress Protection in Femora
Plated by Carbon Fiber and Metallic Plates: Mathematical
Analysis and Experimental Verification.” Biomaterials and
Biomechanics 1983. Eds. P. Ducheyne, G. Van der Perre, and
A.E. Aubert. Amsterdam: Elsevier Science Publisher B.V., 1984.
189-194.
Excerpt—“Bone refracture after plate removal has been attributed to the structural adaptation of bone (loss of bone) to
reduced stress (stress protection). The analysis of the stress pattern in plated bones seems to be a prerequisite for the assertion
that bone loss is stress-related. The strain distribution at the surface of plated human femoral shaft has been analyzed using the
composite beam theory and verified experimentally using strain
gauges. Plates made of carbon, titanium and stainless steel were
investigated. The difference between the reduction of stress
obtained using the less stiff plate materials and that obtained
by using thinner stainless steel plates is astonishingly small. The
reduction of the rigidity of the plate does not result in a proportional improvement of the strain in bone under the combined
axial and flexural load.”
[2] Gautier, E., J. Cordey, R. Mathys, B.A. Rahn, and S.M. Perren.
“Porosity and Remodelling of Plated Bone After Internal Fixation:
Result of Stress Shielding or Vascular Damage?” Biomaterials and
Biomechanics 1983. Eds. P. Ducheyne, G. Van der Perre, and A.E.
Aubert. Amsterdam: Elsevier Science Publisher, 1984. 196-200.
Excerpt—“The bone loss observed in the five months following
plating of cortical bone is mainly due to porosis. The porosis
accompanies the internal remodelling of the diaphyseal bone.
It is not clear whether the porosis is a reaction due to the
mechanical unloading of the bone, or whether, as seems more
probable, it is a temporary stage in the remodelling of necrotic
bone. In an experimental study using sheep, plates of different
bending stiffness and different lower surface structure were fixed
onto the medial aspect of intact tibiae. Changes in blood supply
and bone remodelling were assessed at four, ten and twenty
weeks.
There is no difference in the amount of bone remodelling
between groups with plates made of steel and groups with
similar plates made of polyacetal with a thin metal core. It seems
noteworthy that the extent of the remodelling differs towards
the proximal and the distal ends of the plated bone. A correlation was found between plate contact to bone and the extent
of the vascular damage at four weeks on the one hand, and
between plate contact and the extent of the bone remodelling
area at twenty weeks on the other hand.
The results of the experiment suggest that porosis of the bone
is related to internal remodelling, which in turn is related to
vascular damage due to plate contact.”
[3] Perren, S.M., J. Cordey, B.A. Rahn, E. Gautier, and E.
Schneider. “Early Temporary Porosis of Bone Induced by Internal
Fixation Implants: A Reaction to Necrosis, Not to Stress Protection?” Clinical Orthopaedics and Related Research 232 (1988):
139-151.
Excerpt—“Stabilization of the fracture using implants requires
contact surfaces between implant and bone. Such contact has
been observed to induce bone porosis first seen at one month
after surgery. Bone loss in the vicinity of implants has hitherto
been explained as being induced by mechanical unloading of
the bone (stress protection). Experiments in sheep, dogs, and
rabbits combining intravital staining of blood circulation and
polychrome fluorescent labelling of bone remodelling leads to
the conclusion that early bone porosis in the vicinity of the
implants is the result of internal remodelling of cortical bone and
is induced by necrosis rather than by unloading. This theory is
favored by the evidence that 1) the bone is of a temporary
nature, an intermediate stage in internal bone remodelling; 2)
the pattern of the remodelling zone is closely related to that of
the disturbed circulation, and not to that of unloading; 3) plastic
plates may produce more porosis than steel plates; and 4)
improved blood circulation using modified plates resulted in
reduced porosis. The clinical relevance of these findings is related
first to temporary weakening of the bone, and second to the
possibility of sequestration. Sequestration may be the result of
intensified remodelling activity in the presence of inflammation
or infection.”
[4] Gasser, B., S.M. Perren, and E. Schneider. Parametric
Numerical Design Optimization of Internal Fixation Plates.
Transactions of the 7th Meeting. Aarhus, Denmark: European
Society of Biomechanics, 1990.
Excerpt—“Disturbance of blood supply due to contact between
plate and bone has been made responsible for bone remodelling
in the early postoperative phase. Based on the experience with
the Dynamic Compression Plate (DCP), the design of a new Low
Contact-DCP (LC-DCP) was optmized.
Design optimization is a multiparametrical problem, and the
goal of this study was to identify by mathematical means the
optimal design for a new plate with respect to the following
criteria: a reduced bone/plate contact by means of a lateral recess
in the undersurface of the plate; a symmetrical hole geometry
with an oblique undercut at both ends to increase tilting of lag
screws; a trapezoidal plate cross section to facilitate removal. For
evaluation, particular emphasis has been put on preserving the
continuity of bending and torsional stiffnesses along the plate
and the maintenance of plate strength under different loadings.
Tools and Method: Finite Element Analysis (FEA) to study and
compare geometrical and mechanical properties of different
plate types.
Four load cases (simulated screw load, bending and/or torsion)
were compared with the DCP. The homogeneity of the bending
stiffness was improved by 49%, without reduction of the
strength for any of the load conditions investigated. The area
of the underside of the Low Contact-DCP was reduced to 50%,
compared with the DCP.”
[5] Pohler, O.E.M. “Degradation of Metallic Orthopaedic
Implants.” Biomaterials in Reconstructive Surgery. Ed. L. Rubin.
St. Louis: The C.V. Mosby Co., 1983. 158-227.
Excerpt—“Metal degradation can be evoked through dissolution
and corrosion as well as through the action of mechanical forces.
The latter lead to wear, fatigue, and overload failures. Particularly
detrimental are combinations of mechanical and chemical/
electrochemical attack, which can cause, for example, fretting
corrosion and corrosion fatigue. Orthopaedic implants can suffer
those forms of material destruction through interaction with
the body.
Mechanical and chemical/electrochemical damage should be
distinguished sharply. Through fretting, wear debris and corrosion products are generated, and local and systemic effects
might be considered.
A thorough section of the paper concentrates on the description of the destructive mechanisms found typically on the different implant materials, mainly based on the investigation of
implants for fracture treatment.
In general, the biological tolerance in the in vivo tests is
higher compared to that in culture tests. It is characteristic that
the nickel- and cobalt-containing alloys are very well tolerated
as long as they do not disintegrate. Only when, through fretting
and fretting corrosion, the individual metals are released in
active form, they unfold their specific metabolic effects.”
[9] Rüedi, T.P., S.M. Perren, O. Pohler, and U. Riede. Titan und
Stahl und deren Kombination in Knochenchirurgie. Langenbeck
Arch. Suppl. Chir. Forum, 1975.
Excerpt—“The combined application of titanium plates with
stainless steel screws appeared interesting. Three different combinations of titanium and stainless steel implants were tested in
the animal and on humans. A morphometric evaluation of the
soft tissue (animal) gave similar good results for stainless steel
implants as for the combination of titanium and steel, while
pure titanium gave the best result. Atomic absorption test
(human) showed that in the case of the titanium/steel mixture,
only the stainless steel screws did corrode. Delayed fracture
healing or mechanical instability always gave risk to more metal
deposits in the soft tissue than primary bone healing. The combination of the two metals appears possible and temporarily
without danger.”
[6] Steinemann, S.G. “Corrosion of Surgical Implants—in vivo
and in vitro Tests.” Evaluation of Biomaterials. Eds. G.D. Winter,
J.L. Leray, and K. de Groot. New York: John Wiley & Sons Ltd.,
1980. 1-34.
Excerpt—“In vivo and in vitro corrosion data for pure metals
and alloys for surgical implants are reviewed, and it is shown
that such data can be related to pH shifts and metal ion concentrations in tissue by solving a realistic transport equation.
The results go beyond a symptomatic connection between corrosion and tissue reaction and, with the aid of electrochemical
equilibria, explain conditions for interaction.
But surgical implants are also prone to special forms of corrosion, e.g. crevice attack and fretting, which lead to a drastic
enhancement of local ion concentration and can then induce
toxic reactions.”
[10] Matter, P. and H.B. Burch. Titanium Implants and Limited
Contact DCP-System: Clinical Experience. Bern, Switzerland:
AO-Documentation Center, 1990.
Excerpt—“AO ASIF with its collaborating laboratories has
developed special methods to obtain the required strength for
using pure titanium as an implant material. The first prospectively controlled clinical series of implants made of this material
dates back to 1966 and was reported to be most successful.
Pure titanium became the material of choice for implants to be
used in patients suffering from metal allergy. Today a long-term
and well-documented experience with pure titanium implants
exists which proves that this material fulfills the requirements of
optimal biocompatibility. For this reason it was integrated in the
biological concept of the limited-contact-plating system, which
aims to preserve the biointegrity of the affected area as much
as possible by means of a less aggressive approach to treat the
already damaged bone. Pilot clinics have started to implant
titanium LC-DCP in 1987. Today 271 plates have been
implanted mainly for the treatment of fresh fractures, and 57
plates have so far been removed. The preliminary results are
most favorable. They especially confirm the effects of the
preserved cortical blood flow and the outstanding biocompatibility of the pure titanium.”
[7] Gerber, H.W. and S.M. Perren. “Evaluation of Tissue Compatibility of in-vitro Cultures of Embryonic Bone.” Evaluation of
Biomaterials. Eds. G.D. Winter, J.L. Leray, and K. de Groot. New
York: John Wiley & Sons Ltd., 1980. 307-314.
Excerpt—“Organ-cultured embryonic rat femurs were used
as an experimental model to evaluate metal tolerance.
Using a variety of metal chlorides, individual dose response
curves could be established which are well-suited for statistical
analysis. Miniature solid metal implants serve to determine the
growth inhibition due to the complex corrosion product. The
histological appearance of the tissue at different distances from
the metal is reported. The model seems to be sensitive and
easily standardized.”
[8] Gerber, H.W., M. Bürge, J. Cordey, W.J. Ziegler, and S.M.
Perren. Quantitative Determination of Tissue Tolerance of
Corrosion Products by Organ Culture. Proceedings of the
European Society of Artificial Organs. Vol. 1. Davos,
Switzerland: Laboratory for Experimental Surgery, AO ASIF,
1975. 29-34.
Excerpt—“Surgical implants are manufactured from metals of
good mechanical strength and corrosion resistance. However,
every metal implant releases, in vivo, metal ions into the tissue
permanently. Clinical requirements lead to the search for new
metal alloys, which then necessitates a method of comparative
testing tissue toxicity.”
[11] Simpson, J.P., V. Geret, K. Merritt, and S.A. Brown. Retrieved
Fracture Plates: Implant and Tissue Analysis (NBS SP-601). Eds.
A. Weinstein, D. Gibbons, S. Brown, and W. Ruff. Washington:
National Bureau of Standards, 1980. 423-448.
Excerpt—“A study was undertaken by the AO ASIF to investigate the suitability of different materials for bone plates for
osteosynthesis. A total of 80 plates were retrieved together with
clinical data, histologic data, and chemical analysis. The
materials used were stainless steel 316 LVM, commercially
available pure titanium, titanium (Ti-6AI-4V) alloy, and a cobaltchrome-nickel-tungsten-iron alloy as used in the AO ASIF compression plates and screws. The protocols used and the results
of these first 80 cases are presented. The histologic analysis
revealed the greatest differences occurring in the accumulation
of lymphocytes, macrophages, and giant cells which were
greatest with the cobalt alloy. The quantity of debris in the
tissue was greatest with pure titanium. The chemical analysis
revealed a wide scattering of values and the results are discussed. The examination of plates and screws revealed that
stainless steel suffers fretting corrosion and that the amount
of metal loss is less than on the cobalt alloy, titanium, and
the titanium alloy, although significant corrosion was observed
at the plate screw contact area for the cobalt alloy.
In this paper, a protocol for the evaluation of metal osteosynsthesis plates has been presented along with a scheme for
analyzing tissue responses and obtaining clinical data. The
number of cases presently available for analysis does not permit
any definite conclusions as to the advantages of one of the
alloys tested over another. It is hoped that with the addition of
more cases this will be possible. We recommend that the type of
protocol we have described here be used so that comparison
can be made between different studies.”
[12] Klaue, K. The Dynamic Compression Unit (DCU) for Stable
Internal Fixation of Bone Fractures. Davos, Switzerland: The
Laboratory for Experimental Surgery, AO ASIF.
Excerpt—“In the internal fixation of fractures, compression
between the fragments is often applied by the use of interfragmentary lag screws together with plates. Plate screws may,
in certain circumstances, also function simultaneously as lag
screws. If conventional interfragmentary lagged plate screws are
used in the inclined position, they permit more efficient compression. However, problems may arise, due to the possible
interference of the thread of the screw with the edge of the
plate hole and/or with the bone within the ‘gliding hole.’ To
take advantage of inclined lagged plate screws, the system was
modified to provide more efficient compression. The system
reported here provides symmetrical interfragmentary compression using modified implants. This is achieved by using inclined
shaft screws inserted through longitudinal slots in the plate and
crossing the fracture line. Implantations performed on sheep,
after preliminary investigations in vitro, seem to confirm the
predicted compression effects. Although a high incidence of
excellent reduction was achieved, further investigation will be
required to determine the exact conditions in which the bone
will support the forces applied.”
[13] Klaue, K. and S.M. Perren. Interfragmentary Compression
Using Inclined Lag Screws in Self-Compressing Plate Holes:
Problems and Solutions. Transactions of the 35th Annual
Meeting. Davos, Switzerland: Laboratory for Experimental
Surgery, Orthopaedic Research Society, 1989.
Excerpt—“Fully threaded lag screws, inclined 20° towards the
fracture and inserted through self-compressing plate holes
across the fracture plane, yield only about 49% of their possible
compressive effect along the fracture plane. This loss of compressive effect is due to anchorage observed histologically after
the screw has glided towards the fracture. Modifications of the
plate holes and screws allow full efficiency of the lag screw
compression to be retained. The Dynamic Compression Unit
(DCU) of lag screw and self-compressing plate has been
developed to optimize stabilization using plate screws which
serve simultaneously as lag screws. The term ‘Unit’ was coined
to indicate the combined effect of screw and plate. The combination can be used to function as a tension band; it can
also function as a protecting or buttressing splint. The newly
designed plate holes are elongated and flared. They are
designed to avoid the screw abutting against the inner edge
of the plate hole. With this design, simultaneous compression
along the bone axis (axial compression) as well as along the
screw axis (interfragmentary compression) is achieved with only
one bone screw. After tests in 20 sheep, a first series of more
than 100 DCU plates have been implanted in humans; evaluation awaits their removal.
Conclusions
A substantial improvement of the stabilizing interfragmentary
compression of lag screws used in self-compressing holes has
been achieved. Clinical tests underway will show whether it is
safe to reduce the total number of screws in plate fixation and
so take advantage of the new design.”
[14] Klaue, K. and S.M. Perren. Unconventional Shapes of the
Plate Cross-Section in Internal Fixation: The Trapezoid Plate.
Long Term Study of Bone Reaction in Sheep Tibiae. Davos,
Switzerland: Laboratory for Experimental Surgery, AO ASIF, 1990.
Excerpt—“Plated cortical bone undergoes changes of its
structure and shape. Generally, these changes are explained
on the basis of stress relief. Factors that influence the biological
response of bone to an implant include: implant material
(biocompatibility), contact area between the implant and the
bone (blood supply), and stiffness of the implant (mechanical
load). The goal of the present study was to determine the
biological and mechanical effect of four different plates on the
underlying bone. These plates consisted of: 1) steel plates of
conventional AO dimension and rectangular shape; 2) steel
plates of trapezoidal cross section to reduce area of contact
but similar stiffness; 3) carbon-polysulfone thermoplastic fiber
plates of conventional shape and dimension; 4) thinned conventional steel plates of similar stiffness to the carbon plates.
The carbon fiber composite plates did not reveal any specific
advantage in respect to bone stiffness. There is no correlation
between the stiffness of the plate and the stiffness of the bone
after plate removal. Porosity of cortical bone under the plate
was minimal with the trapezoidal plate. On the other hand,
porosity underneath the polysulfone/carbon plate was markedly
higher and remodelling more intense when compared to the
stainless steel plates.
While the results of the carbon plates were discouraging, the
trapezoidal plates provided not only a better bone structure but
were also easier to remove. The chances to produce stress risers
by defects of the side laminae was minimized in this group as
well. The experiment revealed the mechanical importance of the
intactness of the cortical bone lining the plates. The trapezoidal
plate provides increased bone cross section and increased stiffness of bone when compared to conventional plates.”
Additional Literature
Holzach, P., and P. Matter. “The Comparison of Steel and Titanium Dynamic
Compression Plates Used for Internal Fixation of 256 Fractures of the Tibia.”
120 Injury 10 (1978): 120-123.
Lombardi, A.V., Jr. et al. “Aseptic Loosening in Total Hip Arthroplasty Secondary to
Osteolysis Induced by Wear Debris from Titanium-Alloy Modular Femoral Heads.”
Journal of Bone and Joint Surgery 71-A.9 (October 1989).
Matter, P., M. Schutz, M. Buhler, A Ungersbock, and S. Perren. “[Clinical results with
the limited contact DCP plate of titanium–a prospective study of 504 cases].” [Article
in German] Z Unfallchir Versicherungsmed 1994 Apr.; 87(1):6-13.
McKee, M.D., J.G. Seiler, and J.B. Jupiter. “The application of the limited contact
dynamic compression plate in the upper extremity: an analysis of 114 consecutive
cases.” Injury 1995 Dec.; 26(10):661-6.
Perren, S.M. “Basic Aspects and Scientific Background of Internal Fixation.” Scientific
Bulletins of the AO Group. Davos, Switzerland: Laboratory for Experimental Surgery,
AO ASIF, 1990.
Perren, S.M. “The Biomechanics and Biology of Internal Fixation Using Plates and
Nails.” Orthopedics 12.1 (1989): 21-34.
Pfeiffer, K.M., J. Brennwald, U. Buchler, D. Hanel, J. Jupiter, K. Lowka, J. Mark, and P.
Staehlin. “Implants of pure titanium for internal fixation of the peripheral skeleton.”
Injury 1994 Mar.; 25(2):87-9.
Pfister, U., B.A. Rahn, S.M. Perren, and S. Weller. “Blood Supply and Bone Remodeling
Following Medullary Nailing of Long Bones: Experimental Study in the Sheep Tibia.”
Akt. Traumatol. 9 (1979): 191-195.
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