[Ortho] Re: эндопротезирование или артродез

[Dr. A. Liberson]

AGREE
I would not take this one as an aseptic one! Which makes it more difficult 2
replace
AL
----- Original Message ----- 
From: "Korobushkin Gleb V" <gleb на gelios.net>
To: <ortho на weborto.net>
Sent: Sunday, May 20, 2007 9:39 PM
Subject: Re: [Ortho] эндопротезирование или артродез


> По всем канонах хирургии стопы асептический некроз таранной кости -
> абсолютное противопоказание для эндопротезирования голеностопного сустава.
> С уважением Глеб Коробушкин
>
>
>
>       Foot & Ankle International
>       April 1, 2004
>       277 Renew Paid Title: Challenges in Total Ankle Arthroplasty -
Lowell
> H. Gill, M.D.   (Receive without keywords highlighted)
>       Summary: (view full summary) ABSTRACT - In the past, total ankle
> arthroplasty was largely abandoned due to poor survivorship most often
> caused by loss of bone support. High complication rates were also
reported.
> Despite this...
>
>
> Challenges in Total Ankle Arthroplasty
>
> Lowell H. Gill, M.D. Charlotte, NC
>
> ABSTRACT
>
> In the past, total ankle arthroplasty was largely abandoned due to poor
> survivorship most often caused by loss of bone support. High complication
> rates were also reported. Despite this, there is renewed interest in ankle
> arthroplasty and encouraging results are seen in survivorship with midterm
> follow-up. The procedure, however, remains more challenging than total hip
> or total knee arthroplasty. With the limited soft tissue envelope, wound
> problems are not uncommon. Forces at the ankle are very large and yet the
> surface area for prosthetic support is small. Therefore, fixation can be
> more difficult. The strongest bone can be eccentric at the distal tibia.
The
> tibial prosthesis can, therefore, tend to settle into the softer bone
often
> laterally. Polyethylene needs to be sufficiently thick to maintain its
> integrity but that requires a larger bone resection, which weakens bone
> support. Polyethylene failure or wear leads to the majority of failures in
> hip and knee arthroplasty. There is a need for further basic science
> research in total ankle arthroplasty. The lessons learned from other
> arthroplasty should be considered in ankle arthroplasty design.
>
> Key Words: Agility; Angiosomes; Ankle Arthroplasty; Biomimetic Coatings;
> Bone Support; Buechel-Pappas; Polyethylene; STAR Ankle Arthroplasty
>
> Corresponding Author:
> Lowell H. Gill Gill Orthopaedic Clinic Midtown Medical Plaza 1918 Randolph
> Road, Suite 700 Charlotte, NC 28207
> E-mail: dvenne на gillortho.com
> For information on prices and availability of reprints call 410-494-4994
> X226.
>
> HISTORY
>
> The earliest reports of total ankle arthroplasty were favorable.
Stauffer70
> at the Mayo Clinic reported on 63 total ankles with an average follow-up
of
> 6 months. Of these 63 ankles, 52 were rated excellent, six fair, and five
> poor. In a smaller series with longer follow-up, Lachiewicz et al.46
> reported on 15 total ankle arthroplasties at 39 months postoperatively.
All
> results were excellent or good. Other early series similarly reported
> encouraging results.38,59,79
>
> With longer follow-up, however, the reports became more
> cautious.21,29,30,66,76 The terminology used to report results changed.
The
> word ''excellent'' became rarely used, and instead series often
substituted
> the words ''success'' or ''satisfactory.''76 At times, this only meant
that
> the prostheses were still in place.
>
> In time, virtually all series reported larger numbers of
> failures.35,39 -41,52,60,85 Ultimately, almost all authors abandoned or
> largely abandoned total ankle arthroplasty due to the high failure
> rate.29,35,38,40,41,52,60,85 Bolton-Maggs and associates,11 reporting on
62
> total ankle arthroplasties with the ICLH prosthesis, recommended against
> total ankle arthroplasty. They noted, ''in view of the high complication
> rate and generally poor long-term clinical results, we recommend
arthrodesis
> as the treatment of choice for the painful stiff arthritic ankle,
regardless
> of the underlying pathologic process.'' Years earlier, this same practice
> had reported that their study ''encouraged optimism'' regarding total
ankle
> arthroplasty.38 Newton, another early proponent of total ankle
arthroplasty,
> subsequently also reported fusion as the procedure of choice.60
>
> Design variations seemed to make little difference. Several authors
> recommended against constrained designs because of a high failure
> rate.39,40,85 However, nonconstrained designs failed as well.41,60
>
> Authors who previously performed arthroplasty recommended arthrodesis,
which
> was felt to give more predictable results with fewer
> complications.11,35,41,52,60 Schaap and associates67 reported favorable
> long-term results with an average of 10 years in patients treated with
> arthrodesis. There are additional studies which also show favorable
> long-term results with arthrodesis.54,55 Some authors reported superior
gait
> patterns in the arthrodesis patients, whereas more abnormal kinematics and
> marked muscle weakness were documented following total ankle
arthroplasty.22
> Mazur and associates55 found all patients had favorable gait studies after
> ankle arthrodesis.
>
> Lord,51 a French surgeon who performed the first total ankle in 1970,
> reported disturbances in balance occurring in total ankle arthroplasty
> patients. These balance abnormalities did not exist in total hip
> arthroplasty patients and were much milder in total knee arthroplasty
> patients.51 There was also noted decreased anteroposterior stability
> following laboratory total ankle arthroplasties using a meniscal bearing
> with a flat upper surface.16 Many years later using the Scandinavian Total
> Ankle Replacement (STAR) prosthesis, which employs such a design, Garde
and
> Kofoed26 reported satisfactory stabilometry studies following total ankle
> arthroplasty.
>
> Summarizing the early experience, it should be noted that initially total
> ankle arthroplasty was successful. However, these procedures were
ultimately
> abandoned because of the high failure rates. Today's surgeons should
> therefore still use caution in the optimism with the present designs,
which
> also appear favorable in the early and midterm reports.
>
> COMPLICATIONS AND WOUND HEALING
>
> Total ankle arthroplasty is associated with a high complication
> rate.11,21,22,29,30,35,71 The procedure is technically challenging. There
is
> a risk of fracture of one or both malleoli. Neurovascular structures are
in
> close proximity. Laceration of the posteromedial tendons from saw cuts
using
> the anterior approach can occur. Wound healing problems are not
> unusual.29,65 The vascular supply may be more likely compromised by
arterial
> disease at the level of the ankle. As a result of more constricted
> tethering, the vascular supply of the ankle does not tolerate the
> dislocation28 that is done for total hip arthroplasty nor the marked
> subluxation that is performed at the time of total knee arthroplasty. The
> soft tissue envelope is sparse at the ankle and has minimal flexibility.3
At
> the subcutaneous surface of the tibia where deep fascia is continuous with
> the periosteum, branches of the anterior tibial artery which supply the
skin
> are easily torn by shear forces.74 The dorsalis pedis is absent or
extremely
> attenuated in 12% of cases,3 and this is the main arterial supply to the
> dorsum of the foot.
>
> ANGIOSOMES
>
> An angiosome is a block or three-dimensional area of tissue supplied by a
> specific source artery. The angio-some may include bone, muscle, fascia,
> subcutaneous tissue, and skin. In many areas of the body, such as the
> forearm, there are rich intramuscular anastomoses between different
> angiosomes.74 Four of the five angiosome areas of the leg have blood
supply
> from more than one angiosome. The angiosome supplied by the anterior
tibial
> artery, however, has circulation supported by only one source artery, the
> anterior tibial artery.74 For this reason the anterior compartment leg
> muscles are particularly vulnerable to ischemia. After a vascular insult
to
> the source artery of an angiosome, it is possible for closed or reduced
> caliber connections termed ''chokers'' to open and supply the structures
of
> an adjacent angiosome. However, this process can take 3-10 days, which
> places the structures in an angiosome at risk for necrosis when there is
> only one supply.3,4 The safest incision in the foot and ankle is at the
> junction of two angiosomes.4 In this way both sides of the incision are
> likely to have healthy and independent blood supply. A lateral approach
has
> this advantage. The anterior approach to the ankle, however, divides a
> single angiosome approximately in the middle. The anterior incision is the
> one most commonly used for total ankle arthroplasty. This incision is in
the
> angiosome supplied by the anterior tibial artery and its continuation as
the
> dorsalis pedis. The proximal part of the incision may lie in the anterior
> compartment of the leg where there is greater risk of ischemia. More
> distally at the level of the ankle and foot there are anastamoses to other
> vessels, but at this more distal level there are other risks previously
> outlined.
>
> Either an anterolateral or an anteromedial incision can potentially be at
> risk. For example, if the neurovascular bundle is retracted laterally,
then
> the two medial anastomoses from the anterior tibial to the posterior
tibial
> vessel are likely ligated or injured. In this situation if the lateral
> peroneal anastomoses are vestigial or blocked, then healing is at
> considerable risk. On the other hand, if the surgeon approaches
> anterolaterally and retracts the vascular bundle medially, then the
lateral
> anastomoses are likely interrupted. In this situation if the medial
> anastomoses from the posterior tibial artery are ineffective, then again
the
> anterior incision is at considerable risk.
>
> Summarizing, the anterior angiosome itself has only a single arterial
source
> in the leg. The midline anterior approach is less desirable than the
border
> areas between angiosomes. The anastomoses that do exist are at risk and
> easily injured. Vessel anomaly is common. A suggested plan for the surgeon
> is to use a doppler preoperatively to map out individual precise
> circulations.
>
> SUPPORT
>
> The most frequent complication of total ankle arthroplasty in the past has
> been loss of bone support.
>
>
>
> Fig 1: Talar component subsidence.
>
> Most orthopaedic prostheses depend primarily on bone for support.
> Unfortunately, however, many patients needing prosthetic arthroplasties
have
> weakened or compromised bone. Past experience with total ankle
arthroplasty
> has shown that loss of support is a primary reason for failure (Fig. 1).
>
> Bone Strength
>
> The importance of bone support was recognized early in total ankle
> arthroplasty and attention has focused on the increased risks in patients
> with bone depleted by osteonecrosis, long-term disease, chronic
inactivity,
> or steroid use.59 An early laboratory study38 looked at total ankle
> arthroplasty support by performing total ankle arthroplasties in cadavers
> and subjecting these arthroplasties to physiologic forces. The study found
> failure of the support bone around the prostheses in just a few days.
> Studies of three-dimensional models of talar and tibial components of
> implanted ankle prostheses have shown that by removing the cortical shell
of
> the talus, abnormally increased stresses are placed on the remaining talar
> bone.17 Bone strength at the ankle has been studied and there is marked
> reduction in the bone strength as the sections are taken farther from the
> articular surface. The talar bone was found to be 40% stronger than the
> distal tibial bone, which was noted to be dangerously close to or below
the
> failure point for prosthetic replacement at the ankle (Fig. 2). Distal
> tibial bone strength should equal or exceed 20 MPa.33 The strongest bone
is
> not central nor evenly distributed across the distal tibia, but is in fact
> eccentric, usually posteromedial33 (Fig. 3). Since maximum bone strength
is
> eccentric, and strongest in a specific small area reflecting the
> transmission of the force of heel strike, this can produce a type of pivot
> point which could lead to tibial component subsidence into the weaker
> surrounding bone, which is usually anterolateral (Fig. 4).
>
>
>
> Fig. 2: Minimal amount of strong bone at distal tibia. Arthroplasty
> resection removes best support bone.
>
>
>
> Fig. 3: Minimal Area of maximal bone strength is often eccentric.
>
> Force
>
> Forces at the lower extremity are large due to the principle of leverage,
> which magnifies the force of body weight. Lower extremity forces are
> particularly increased at the ankle.2,69-72 Since the forefoot metatarsal
> pad is a greater distance from the fulcrum at the ankle joint compared to
> the shorter distance from the ankle to hindfoot, this creates a longer
> anterior lever arm at the foot. During ambulation, therefore, the Achilles
> tendon must generate very large tensile forces to overcome the body weight
> on the longer lever arm of the forefoot. This results in very high
> compressive forces at the ankle.
>
> Ankle compressive forces are estimated to be three to five times body
weight
> during normal walking.22,69,72 In one study,22 marked muscle weakness was
> documented in ankle arthroplasty patients. Due to their muscle weakness,
the
> total ankle arthroplasty patients did not or were not able to generate a
> normal compressive load at the ankle. This may be good for prosthesis
> survival, but not advantageous for ambulation. It should
>
>
>
> Fig. 4: Eccentric bone support potentially causes uneven prosthetic
> subsidence.
>
> be noted that the forces at the ankle are large, yet laboratory studies
have
> shown that bone strength is often compromised at this same location.
>
> Surface Area
>
> As the force across the ankle joint cannot be markedly influenced by a
> prosthetic design, the surface area contact between the prosthetic
component
> and resected bone becomes critical for success. Forces are commonly
measured
> in Newtons. One Newton equals the force required to lift 1 kg of mass
> against gravity kg-m/s2). What is critical in prosthetic design is the
> pressure applied by the prosthesis to the bone. Pressure a measure of the
> force per unit area. A Pascal (Pa) equal to 1 N spread over 1 m2 (N/m2).
The
> strength bone is measured in the same units as pressure (Pascals). Thus,
as
> the surface area is increased, the pressure is decreased, and vice versa.
>
> Early total knees were available in only one size. Often the tibial
> component was prone to subsidence (Fig. 5A). Today's tibial components are
> available in multiple sizes allowing better prosthetic support through the
> expansion of support surface area (Fig. 5B).
>
> The actual surface area of the ankle joint is 12 cm,2 which is large
> compared to the hip or knee.70 Much this surface area is in the medial and
> lateral gutters and on the relatively large anteroposterior dome of the
> talus. Depending on the particular design, much of this surface area may
not
> be available for prosthetic support. The talus is a small bone. When the
> dome of the talus resected, this results in approximately one half the
> surface area as that of the upper tibia at the knee. The compressive force
> at the knee is three to four times body weight on a larger surface area,
> whereas at the ankle during ambulation there are compressive forces
>
>
>
> Fig. 5: A, Subsidence of a single-sized tibial total knee component with
> inadequate base plate coverage. B, Newer base plates improve bone coverage
> for better support.
>
>
>
> Fig. 6: Smaller surface area for support at ankle.
>
> of up to 5.5 times body weight on a much smaller surface area. This
greatly
> increases the load per unit area (Fig. 6).
>
> The addition of a keel expands surface area, reduces force per unit area,
> and greatly reduces micromotion.24, 78 The small size of the talus allows
> little room for a keel if one is to preserve sufficient support bone. The
> proximity of the subtalar joint completely prevents the expansion of the
> keel distally and the confines of the narrow talus prevent expansion of
the
> keel medially and laterally.
>
> The force borne across the ankle is often not central nor equally placed
> across the prosthetic support surfaces (Fig. 7). Instead the force is
often
> off-center (i.e., eccentric). The eccentric force across the pros-thesis
> leads to a compressive or intrusive force on one side and an elevation or
> lift-off force on the opposite side.36, 77 (Figs. 4 and 7). Shear forces
> also result which increase the stress in the underlying cancellous bone.7
> Studies in cadaver tibial knee arthroplasties showed that four peripheral
> screws with a central peg best resists the micromotion of the tibial base
> plates which
>
>
>
> Fig. 7: Stresses across prosthetic ankle may be eccentric.
>
> results from eccentric force.77 Another study which included a keel in the
> selection of base plate designs found that a keel consistently best
resists
> eccentric and shear forces. The worst design of the five designs tested
was
> the tibial base plate with no understructure.24 At the ankle because of
the
> anatomic limitations of the talus, it may be impossible to provide either
> four screws plus a central stem or a keel.
>
> In summary, it has already been stated that bone strength at the ankle is
> not evenly distributed but maximal strength is instead eccentric (Fig. 3).
> Forces that result from normal human activity are also often eccentric.
Any
> malalignment (Fig. 8) may aggravate the eccentric distribution of force in
> the bone, which is not evenly strong. The eccentricities may not match. At
> the ankle there is minimal surface area available for the distribution of
> force and it has already been documented that bone strength is often
> marginal if not even inadequate. A total ankle arthroplasty is
>
>
>
> Fig. 8: Malalignment potentially aggravates eccentric force and resultant
> subsidence.
>
> therefore always at risk for failure because of inadequate bone support.
>
> MATERIALS: POLYETHYLENE
>
> Initially polyethylene was thought to be a nearly ideal material for
> arthroplasty. It provides low friction when articulating with metal in
vivo.
> Earlier studies suggested the amount of wear was acceptable and the wear
> particles were thought to be innocuous.38 Wear studies suggested minimal
> wear allowing longevity of 20 years or longer with the available designs.
>
> Clinical observation has proved many of the above assumptions as false and
> the early laboratory studies as misleading.10,61,68 There are numerous
> different patterns of wear and the causes of failure are
> multifactorial49,50,68 (Fig. 9). The magnitude of the polyethylene problem
> is seen clearly in a US report of medical device failures.20 It is
estimated
> that only 1-5% of such failures are actually reported. A study of 1,717
> total hip and 2,769 total knee arthroplasty failures that were reported
> documents the significance of the polyethylene problem. Polyethylene
failure
> was the most common cause of total hip failures and accounted for 68% of
> total knee failures.20 Early laboratory wear studies often utilized
> pin-on-disk or linear track motion, both of which provided misleading and
> overly optimistic predictions.49, 50 Poly-ethylene wear is reduced with
> these types of motion in the laboratory. Clinically, however, the
> crossing-path type of motion, which occurs in vivo, produces greater wear.
> Retrieval studies document the severity of the wear (Fig. 9).
>
> We now know that particulate polyethylene debris may cause osteolysis32,
37
> (Fig. 10). Polyethylene particles in sufficient numbers incite a chronic
> inflamma-tory process which leads to osteolysis.37 Particles of small size
> (less than 15 чm) are phagocytized by
>
>
>
> Fig. 9: Complete wear-through of a tibial polyethylene component.
>
>
>
> Fig. 10: Large area of osteolysis caused by polyethylene wear in less than
7
> years.
>
> macrophages. In response to the phagocytosis of these small sized
particles,
> a cascade of events occurs and the end result is osteolysis. As this
> progresses, the osteolysis leads to aseptic loosening and eventual loss of
> support.32 The yield strength of polyethylene is relatively low, between
13
> and 25 MPa.10, 84 The developers of the Buechel-Pappas (BP) ankle
(Endotech,
> Inc., S. Orange, NJ) present data showing computed surface contact
stresses
> for the BP ankle on polyethylene to be less than 5 MPa, which is well
below
> the yield strength of polyethylene.15 This same report notes contact
> stresses on polyethylene to be 32 MPa for a fixed polyethylene
two-component
> design.15 The lessons learned during the time of round-on-flat
polyethylene
> total knee designs have shown extremely high failure rates in the past in
> part due to excessively high contact stresses on the polyethylene. These
> observations in knee design should be considered in total ankle
arthroplasty
> design.
>
> Thin polyethylene wears faster than thick polyethyl-ene.6, 7 It is
estimated
> that a minimum of 4-6 mm of polyethylene thickness is needed at the hip
and
> 6-8 mm at the knee where there are larger forces and less conformity.
> Optimal thickness at the ankle has not been determined.
>
> Metal backing of polyethylene improves force distribution to the nearby
> cancellous bone and allows in-growth but also requires another 2 mm of
bone
> resection, or decreases the thickness of polyethylene. The metal backing,
> particularly if there is a lack of polishing, causes backside wear of the
> polyethylene. Backside wear can be severe in both hips and knees. This
> underscores the importance of the newer and improved locking mechanisms
for
> polyethylene.
>
> Polyethylene osteolysis was not reported in the early series of total
ankle
> arthroplasty. Early total ankle arthroplasties probably did not last long
> enough for polyethylene failure to become manifest. Also polyethylene
> osteolysis was not widely recognized until after the development of
> cementless fixation. Prior to that time osteolysis was usually thought to
be
> secondary to cement (i.e., ''cement disease''). We now know that cement
> disease is actually particle disease and that particulate debris from a
> variety of different materials, including polyethylene, can contribute to
> bone loss.32 Present design total ankle arthroplasties now show improved
> survival rates and therefore polyethylene problems may become more
apparent
> in total ankle arthroplasty.
>
> Fracture of the mobile polyethylene component had been reported in
separate
> series of STAR (Waldemar Link GmbH & Co., Hamburg, Germany)
> arthroplasties.19,43,80 The typical history is a sudden catastrophic event
> followed by pain and swelling in the involved ankle.43 This has occurred
> rarely and most commonly in physically active people such as hikers.43 The
> phenomenon of edge loading on the polyethylene component of total ankle
> arthroplasties has been reported.80,81,83 This causes excessive wear and
is
> described in a recent review of 200 STAR ankle arthroplasties.83
> Polyethylene failures have also been reported due to excessive wear in the
> BP total ankle.15 Osteolysis has been reported with both the Agility
(DePuy,
> Inc., Warsaw, IN) and STAR prostheses.62,80,83 Although most reports are
of
> radiographic findings, the presumptive etiology is polyethylene osteolysis
> as is commonly seen in hip and knee arthroplasty.
>
> The failures of polyethylene have led to the search for improved
> polyethylenes as well as for alternative bearing surfaces. Past attempts
to
> improve polyethylene include the development of Poly II and Hyalmer.49
Poly
> II included a composit of carbon fibers which were added to reduce creep
> (cold flow) of polyethylene. Hyalmer is polyethylene with altered polymer
> morphology. In clinical usage, however, both ''improvements'' failed in
the
> sense that their performance was inferior. These products have been
> discontinued for total joint usage. Although laboratory tests suggest
> greatly improved wear characteristics with the newer highly cross-linked
> polyethylenes, the effects of this process on fatigue and fracture
> resistance properties of the polyethylene are not yet known.49 It is
> important to remember that past attempts to improve polyethylene have
failed
> to provide superior performance in vivo.50
>
> FIXATION
>
> The early total ankle arthroplasties used polymethyl-methacrylate cement
for
> fixation. This fixation was often lost, however, when the bone support
> failed, which was the most common mode of failure. Virtually all current
> ankle arthroplasty designs employ cementless fixation which potentially
> offers a more permanent long-term bond provided the bone support is not
> lost.
>
> Astudyofcementedstainlesssteelmetalandpolyethy-lene total ankle
> arthroplasties compared with unce-mented ceramic-on-polyethylene total
ankle
> arthroplasties recommended the cementless technique.73 Since the
cementless
> ankles were an average of only 4.1 years postoperative, whereas the
cemented
> ones averaged 8.1 years postoperative, meaningful conclusions regarding
the
> use of cement or cementless technique are not clari-fied in this
comparative
> study.
>
> There is a paucity of laboratory study on cementless fixation in ankle
> arthroplasty. However, recent clinical series which use cementless
fixation
> report successful midterm survivorship.1,13,15,43,44,62,80,81-83 Those
> results are improved compared to earlier series.11,29,35,38-52,60,85
>
> Cementless fixation occurs with on-growth onto the surface of a prosthetic
> component or in-growth into a roughened coating applied to the surface of
a
> prosthesis. In-growth can occur into a roughened surface such as that
> obtained with sintered beads, plasma spray metals, or fiber metals. These
> roughened microsurface treatments are added as an external layer on to the
> surface of the prosthesis.
>
> Osteoconductive coatings may be added also in order to stimulate bone
growth
> at the bone-prosthesis interface. Calcium phosphate ceramics such as
> hydrox-yapatite can be applied to the prosthetic surface with a plasma
spray
> technique. This technique as a line-of-sight process tends to coat the
high
> spots on the outside of the roughened coating and misses the inner surface
> of a three-dimensional microstructure coating.
>
> The newer biomimetic coating techniques involve a precipitation in a
> supersaturated Ca (PO4)2 solution done at low temperatures. As an
immersion
> technique this has the ability to coat more fully the inner geometry of a
> three-dimensional microstructure surface coating applied to a
prosthesis.27
> The potential benefits of bioactive coatings are the improved strength of
> bone prosthetic bonding, an accelerated response of the bone at the
implant
> junction, improved filling of gaps, and the elimination of the fibrous
layer
> that can occur between the prosthesis or cement and bone.
>
> Both laboratory and clinical investigations support the use of
> hydroxyapatite18,75 but the success can vary according to the specific
> prosthetic component treated,27,47,57,63 the specific area of use, and
> whether or not there is a roughened surface treatment.9 For example,
> hydroxyapatite added to a smooth femoral hip arthroplasty component has
> shown long-term success, whereas this same treatment on a smooth
acetabular
> component has shown a much higher failure rate.9,47,57,63 This is another
> example, beside that of polyethylene, of a material transfer phenomenon
> where a material may not behave in the same fashion when transferred to a
> different area. Therefore, success at the ankle would not be necessarily
> assumed simply because of the success on the femoral components of total
hip
> arthroplasties.
>
> In the United States, ankle prosthetic components are sold without
bioactive
> coatings. The Agility total ankle arthroplasty has a porous-coated cobalt
> chrome surface. The BP has a beaded titanium surface for in-growth. The
STAR
> prosthesis in current use in the United States is a titanium porous
coating
> on a cobalt chrome prosthesis without hydroxyapatite or calcium phosphate.
> This prosthesis is made available to selected surgeons who are part of a
> multicentered study.
>
> Bioactive coatings have been added to total ankle arthroplasty components
in
> Europe and Japan. The TNK prosthesis (TNK ankle, Nara, Japan) has a
ceramic
> component coated with hydroxyapatite. Two ankle designs similar to the BP
> sold in Europe, the Alpha-norma OSG ankle (Corin Group Co., Quierschied,
> Germany) and the AES (Ankle Evolution System) (Biomet Merck Valence,
Cedex,
> France) ankle have a double coating surface which includes hydroxyapatite.
> The HINTEGRA ankle (New Deal Co., Vienne, France) has a double-coated
porous
> titanium and hydroxyapatite surface. In the year 2000, the STAR prosthesis
> was made available in Europe using a dual coating of calcium phosphate
which
> is electrochemically bonded onto a titanium porous coating which is
applied
> to the cobalt chrome prosthesis. The advantage of the electrochemical
> application of calcium phosphate is that this process allows better
> distribution of the bioactive surface throughout the interstices of the
> microstructure of the titanium coating since it is an immersion process.
The
> above ankles sold in Europe are examples of the ''second line of defense''
> concept in surface treatment.
>
> In a review of 200 cementless STAR total ankle arthroplasties, Wood noted
> significantly improved radiologic appearance in the newer dual-coated STAR
> prostheses compared with the earlier hydroxyapatite-coated cobalt chrome
> prostheses.81,83 Similarly, Bonnin12 reported improved radiologic
appearance
> on the bioactive coated Salto Total Ankle prosthesis compared to earlier
> Salto ankle arthroplasties without the bioactive coating.12
>
> DESIGN
>
> In speaking of total knee design, John Insall stated that knee
arthroplasty
> design was based more on opinion than scientific study.34 The same may be
> true for ankle arthroplasty. There have been comparatively few laboratory
> studies on the design criteria for total ankle arthroplasty. Falsig and
> associates25 looked at stress transfer to distal tibial trabecular bone
with
> three different generic tibial designs at the ankle as follows: (1) a
> polyethylene tibial component, (2) a metal-backed polyethylene component,
> and (3) a long-stem metal-backed tibial component using a much longer stem
> than is common. With these three designs, an eccentric anterolateral load
of
> 2,100 N (approximately three times body weight) was applied and
compressive
> stresses in the bone were measured. The authors found a 25% reduction in
> trabecular bone stress to 15 N/mm2 by adding metal backing to the
> polyethylene component. Shear stresses were also reduced. The addition of
> the long stem, however, resulted in almost complete reduction of
trabecular
> bone stress in the distal tibial bone since most stress was transferred to
> the long stem. The authors postulated that this situation may lead to
> excessive stress shielding in the distal tibial bone and therefore could
> adversely affect a long-term clinical result.
>
> Based on the few available laboratory studies looking
> atbonestrengthattheankle33 andtotalanklearthroplasty studies17,48 as well
as
> the information available from hip and knee arthroplasty, it appears that
> goals for total ankle arthroplasty may be as outlined in Table 1.
>
> Review of these goals show that some are difficult to achieve or even
> contradictory. Achieving goal 4 (i.e., use thicker polyethylene), for
> example, directly inhibits the ability to achieve goal 1, which is to
> minimize bone removal. Furthermore because of the small size of the distal
> tibia and talus, goals 2 and 3 (maximizing surface area for support and
> stabilization) are very difficult to achieve.
>
> Designs vary considerably in the amount of bone area resurfaced in total
> ankle arthroplasty. Although data are not available providing guidance on
> how much area at the ankle should be resurfaced, from a force distribution
> standpoint it is desirable to maximize the area for resurfacing. On the
> talar side, the STAR maximizes the area of resurfacing by including the
>
>
>
> medial and lateral talar facets in addition to preserving part of the dome
> of the talus. Theoretically this may improve force distribution and
> long-term stability of the talar component.
>
> It has not been determined, however, if it is in fact necessary to
resurface
> the medial and lateral facets. The BP ankle is an on-lay component of the
> superior surface of the talus only with two fins in the talar dome. By not
> resurfacingthemedialandlateraltalarfacets,lesscortical bone is removed
from
> the talus. Saltzman points out that with each additional area resurfaced
> greater operative exposure and more bone removal are required.65 Without
> resurfacing the medial and lateral talar facets, there is a theoretical
> concern of persistent postoperative pain from the nonresurfaced facets.
> However, surgeons experienced in both the STAR and BP total ankles report
> that medial and lateral facet pain has not been a clinical problem with
the
> BP ankle.64,81 Rippstein has found that it is not necessary to resurface
the
> facets.64 With regard to resurfacing of the facets, the trade-off
therefore
> is the potential benefit of increased surface area for stability and
> fixation by including facet resurfacing versus the potential benefit of
> preservation of the strong medial and lateral cortical bone by not
> resurfacing these areas.
>
> Kinematics
>
> Arthroplasty alters normal kinematics at the ankle. Rather than being a
> simple hinge joint, Michelson et al.56 found that the ankle moves ''as a
> complex joint with coupled three-dimensional motions.'' The talus is wedge
> shaped with different radii of curvature on the medial and lateral talar
> domes as well as different radii of curvature anteriorly and posteriorly.5
> Therefore, the ankle joint axis changes continuously throughout the range
of
> motion.53 The axis of motion can vary considerably and may vary among
> different individuals.5,53
>
> With the exception of the HINTEGRA, most current ankle arthroplasty
designs
> do not employ a different radius of curvature on the medial and lateral
> aspects of the talus. In the normal anatomy, there is a slightly smaller
> curvature medially. Theoretically, an arthroplasty with symmetric equal
> curvatures on the medial and lateral aspects of the talar component could
> result in a ligamentous imbalance which is tight medially and loose
> laterally. In arthroplasty designs with a mobile bearing, the flat
geometry
> on the upper side does not reproduce the convex-concave articulation of
the
> talus in the tibial mortis. The normal anatomy, therefore, has more
inherent
> anteroposterior stability. Theoretically, the lack of the convex-concave
> shape in the sagittal plane puts more stress on the ankle ligaments.
Proper
> ligamentous balance and stability therefore may be even more important
> following prosthetic replacement than in the normal ankle, especially in a
> relatively unconstrained prostheses such as the STAR, BP, and HINTEGRA.
> Despite the potential advantage of a more physiologic tensioning of ankle
> ligaments with a truncated talar component, the BP and STAR arthroplasties
> appear to work well in the hands of experienced surgeons.15,45,83
>
> Bearing Surfaces: Fixed vs. Mobile Bearings
>
> Present total ankle arthroplasty designs use a polyethylene-bearing
surface.
> The Agility polyethylene measures from 3.73 mm to 4.7 mm and additional
plus
> 2-mm inserts are available.23 Other popular designs also have relatively
> thin polyethylene when compared to total knee arthroplasty in which 6-8 mm
> is recommended. Since bone cuts must be kept conservative, there is not
> sufficient room remaining to allow two metal components that are a minimum
> of 2-3 mm in thickness each and still allow sufficiently thick
polyethylene.
> A fixed polyethylene-bearing surface may potentially reduce backside wear
if
> there is an effective locking mechanism. The Agility ankle and the Eska
> developed in Germany use a fixed bearing.
>
> A mobile bearing by definition allows backside wear but may be made fully
> conforming, which greatly reduces contact stress in the polyethylene. Most
> newer design total ankle arthroplasties use a mobile bearing. In the
United
> States, mobile bearings are used for the STAR and the BP ankles. In
Europe,
> in addition to the STAR and BP (Wright Cremascoli Ortho S.A.,
Toulon-Cedex,
> France), the HINTEGRA, the AES, the Salto, and the Alpha-norma OSG ankle
all
> use a mobile bearing. An advantage of the mobile bearing concept is that
the
> flat upper surface allows some rotation which reduces stress at the
> prosthesis-bone interface. A potential disadvantage is that the flat
> geometry does not reproduce the convex-concave articulation of the talus
in
> the tibial mortis. Studies that look at ankle stability after prosthetic
> replacement show conflicting results, although some studies document
> increased instability.16,26,51 The BP ankle design may allow better
contact
> at the bearing surface because of its curving geometry under adverse
loading
> conditions, such as tilting due to malalignment or ligament imbalance.81
> Even the mobile bearing STAR design may be prone to edge-loading.81 Fixed
> two-component designs can be prone the problem of edge-loading especially
if
> there is any malalignment. Edge-loading will increase contact stresses in
> the polyethylene.
>
> A review of the three ankle arthroplasty designs in current use in the
> United States follows.
>
> Agility1 (Fig. 11)
>
>   a.. The Agility ankle employs a unique feature of an arthrodesis of the
> distal fibula to the distal tibia at the time of surgery. This expands the
> surface area available for support on the tibial side by utilizing the
> distal fibula for additional support. A nonunion of this important
> arthrodesis, however, risks loss of fixation on the upper side.
>
>
> Fig. 11: Agility ankle prosthesis. The upeer cononent includes a
> polyethylene insert.
>
>   a.. The polyethylene insert into the metal-backed tibial component is
> concave in the sagittal plane. This adds anteroposterior stability.
>   b.. A deliberate mismatch exists between the larger upper tibial
component
> and the smaller lower talar component. This mismatch allows the talus to
> seek its own position and allows freedom from excessive constraint
> protecting bone-prosthesis interfaces.
>   c.. The deliberate mismatch in sizing of components could potentially
> allow increased contact stresses in the polyethylene if any malalignment
or
> ligament imbalance led to ''edge-loading'' of the talar component.
>   d.. The polyethylene component is relatively thin. It does not have the
> expanded surface area for fixation of polyethylene as used in the newer
> locking mechanisms. The locking mechanism relies on a medial and lateral
peg
> only as well as a posterior stop as opposed to a circumferential or
multiple
> fixation point locking mechanism. Without any anterior capture it does not
> circumferentially capture the polyethylene as in many of the newer locking
> mechanisms.
>   e.. The prosthesis resurfaces the tibiotalar surface as well as the
medial
> and lateral facet areas.
>   f.. The talar component requires a relatively aggressive talar cut
leaving
> less talar bone available for support.
>   g.. The early talar design did not take advantage of the entire
available
> surface area for support. A modified newer version partially improves this
> situation.
>   h.. Insertion of the entire prosthesis requires relatively aggressive
bone
> cuts. A distracter used at the time of surgery helps reduce this problem
but
> the amount of bone removal is still substantial.
> Buechel-Pappas Total Ankle8,9 (Fig. 12)
>
>   a.. BP total ankle is a three-component design, which utilizes a mobile
> polyethylene bearing.
>
>
> Fig. 12: Anterior A and lateral B, views of Buechel-Pappas total ankle
> prosthesis.
>
>   a.. The mobile bearing reduces excessive stress transfer to the
> bone-prosthesis interface.
>   b.. There is full conformity between the polyethylene component and the
> tibial and talar components.
>   c.. The prosthesis resurfaces only the tibiotalar area and not the
facets.
>   d.. Because the bearing is mobile, there is automatically backside wear.
>   e.. The tibial component has a short stem. This may potentially protect
> tibial trabecular bone but avoid the excessive stress shielding from an
> overly long stem.
>   f.. The talar component is an on-lay component with two fins for
fixation.
> It preserves most of the talar dome. Since it does not resurface the
medial
> and lateral talar facets it thereby helps preserve talar cortical bone.
>   g.. The flat upper surface of the mobile bearing may reduce
> anteroposterior stability.
> Star30, 31 (Fig. 13)
>
>   a.. This prosthesis also has a mobile bearing polyethy-lene component.
>   b.. The prosthesis resurfaces the tibiotalar articulation and provides a
> hemi-resurfacing of the two facet areas.
>   c.. There are two dowels for tibial component fixation. This presents a
> lower surface area for stress distribution in the distal tibia compared to
> the BP ankle but might also reduce stress shielding from a stem.
>
>
> Fig. 13: The Scandinavian Total Ankle Replacement (STAR) prosthesis.
>
>   a.. Talar bone cuts remove less bone than is commonly removed with the
> Agility ankle.
>   b.. Talar fixation is enhanced by medial and lateral resurfacing which
> expands the surface area for support on the lower side. Therefore, surface
> area for fixation and load distribution is maximized on the talar
component.
> The removal of medial and lateral facets decreases the amount of remaining
> cortical bone.
>   c.. The flat upper surface of the mobile bearing may reduce
> anteroposterior stability.10
> All three ankle arthroplasties have shown acceptable short-term and
midterm
> results in clinical trials.1,13 -15,19,42,43,45,62,80,81, 83 Longer term
> follow-up is not yet available.
>
> SUMMARY
>
> The stimulus for total ankle arthroplasty derives from a partial
> dissatisfaction with ankle arthrodesis49,58,59 as well as success seen
with
> total hip arthroplasty and total knee arthroplasty. Total ankle
arthroplasty
> is more challenging than total hip arthroplasty and total knee
arthroplasty
> due to the limitations of bone strength, the marked limitation of the
> anatomic size of the talus, and the magnified compressive forces
distributed
> across the ankle due to the longer lever arm of the foot. Healing problems
> are also much more common at the ankle. Early total ankle arthroplasties
> were initially successful and reported as ''excellent.'' However, with
> longer follow-up these failed largely due to insufficient bone support.
>
> Bone support at the ankle may be marginal. The strongest bone is often
> eccentric. Forces may also be eccentric causing a compressive force on one
> side of a prosthesis and lift-off force on the contralateral side.
> Malalignment may aggravate eccentric loads on prostheses causing
compressive
> forces on weaker underlying bone. Forces are large at the ankle but the
> surface area for support is small. There is little to no room to provide a
> keel in the talus and a keel has been shown to best resist eccentric
forces.
> Polyethylene has been the primary cause of arthroplasty failure in the hip
> and knee leading to interest in alternative bearing surfaces. Current
ankle
> arthroplasty designs use polyethylene.
>
> Successful design of total ankle arthroplasty has been far more
challenging
> than at the hip or knee. There is a paucity of laboratory studies of ankle
> arthroplasty to help guide appropriate design. Laboratory investigation is
> essential and will hopefully improve the long-term success with this
> procedure and prevent another series of failures.
>
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> total knee components. Clin. Orthop. 205:67 -74, 1986.
> 85.   Wynn, AH; Wilde, AH: Long-term follow-up of the conaxial
> (Beck-Steffee) total ankle arthroplasty. Foot Ankle 13:303 -306, 1992.
>
> ----- Original Message ----- 
> From: "Batal" <orthoforum на weborto.net>
> To: <ortho на weborto.net>
> Sent: Saturday, May 19, 2007 10:49 PM
> Subject: [Ortho] эндопротезирование или артродез
>
>
> >К нам обратился пациент 73 лет с жалобами на боли и деформацию в
> > области левого голеностопного сустава.
> > В анамнезе: в 1980 году перелом обеих лодыжек с вывихом стопы кнаружи.
> > Лечился консервативно: одномоментная репозиция переломовывиха в левом
> > голеностопном суставе с трансартикулярной фиксацией голеностопного
> > сустава спицами Киршнера через пяточную, таранную, большеберцовую
> > кости. Накладывалась гипсовая иммобилизация. Даная манипуляция
> > осложнилась нагноением с развитием гнойного артрита. Были удалены
> > спицы, сустав со слов больного, промывался растворами, но не
> > вскрывался, получал антибиотики.
> >
> > Гнойный процесс был купирован, и рецидива с тех пор не было. Об-но:
> > Левый голеностопный сустав деформирован за счет разрастания костной
> > ткани и отечности мягких тканей. Левая стопа с вальгусной установкой,
> > практически отсутствуют все своды левой стопы (стопа плоская). Полный
> > объем движений в левом голеностопном суставе максимум достигает 15 гр,
> > движения стопы в основном за счет подтарнного сустава. Пальпаторно
> > область голеностопного сустава не столь болезненна, как болезненна
> > область подтаранного сустава и область таранно-ладьевидного сустава.
> > После изучения объективного статуса, анамнеза, рентгенснимков,
> > больному предложен был трехсуставной артродез, так-как мы сочли это
> > наиболее приемлемым в данном случае. Но больной отказывается от данной
> > операции и настаивает на эндопротезировании левого голеностопного
> > сустава. Во первых, наше отделение не имеет опыта в эндопротезиовании
> > голеностопного сустава. Во вторых, нам кажется, что трехсуставное
> > артродезирование в данном случае наиболее подходящее. Причиной тому,
> > на наш взгляд, выраженная деформация левой таранной кости, как
> > следствие аваскулярного некроза, и то, что болит не голеностопный
> > сустав в данном случае (хотя в нем и ограничено движение), а
> > подтранный и таранно-ладьевидный суставы, и то, что эндопротезирование
> > одного голеностопного сустава не решит проблем в подтаранном,
> > ладьевидно-таранном сочленениях. Наши доводы оказались безуспешными, а
> > так как пациент  является ученым, требовал доказательной базы наших
> > умозаключений. Ваше мнение по данному случаю, и мы были бы благодарны,
> > если у кого то есть материал по данной теме или есть ссылки. Заранее
> > благодарны всем, кто примет участие в обсуждении данной темы.
> > Batal
> >
>
>
> --------------------------------------------------------------------------
------
>
>
> > _______________________________________________
> > Ortho mailing list
> > Ortho на weborto.net
> > http://weborto.net:8080/mailman/listinfo/ortho
> >
>


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