- Email: [email protected]
Articular congruency of the Salto Talaris total ankle prosthesis
Accepted Manuscript Title: Articular Congruency of the Salto Talaris Total Ankle Prosthesis Author: Colin H. Morris Jeffrey C. Christensen Randal P. Ching Francis Chan John M. Schuberth PII: DOI: Reference:
S1268-7731(15)00005-3 http://dx.doi.org/doi:10.1016/j.fas.2015.01.003 FAS 789
To appear in:
Foot and Ankle Surgery
Received date: Revised date: Accepted date:
13-11-2014 18-12-2014 8-1-2015
Please cite this article as: Morris CH, Christensen JC, Ching RP, Chan F, Schuberth JM, Articular Congruency of the Salto Talaris Total Ankle Prosthesis, Foot and Ankle Surgery (2015), http://dx.doi.org/10.1016/j.fas.2015.01.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
d
M
an
us
Colin H. Morris1 Jeffrey C. Christensen, DPM2 Randal P. Ching, PhD3 Francis Chan, DPM4 John M. Schuberth, DPM5
cr
ip t
Articular Congruency of the Salto Talaris Total Ankle Prosthesis
te
1.Senior Undergraduate Engineering Student, University of Washington, Seattle, WA. E-mail: [email protected]. 2.Attending Surgeon, Department of Orthopedics Swedish Medical Center, Seattle, WA. Research Director, International Foot & Ankle Foundation. E-mail: [email protected]. 3. Director Applied Biomechanics Laboratory, University of Washington, Seattle, WA. E-mail: [email protected]. 4. Assistant Professor, Department Podiatric Medicine, Surgery & Biomechanics, Western University of Health Sciences, Pomona, CA. E-mail: [email protected]. 5. Chief of Foot & Ankle Service, Kaiser Permanente, San Francisco, CA. E-mail: [email protected].
Ac ce p
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
Address correspondence to: John M. Schuberth, DPM, Department of Orthopedic Surgery, Kaiser Foundation Hospital, French Campus. 450 6th Avenue, San Francisco, CA 94118 E-mail address: [email protected].
1
Page 1 of 17
Articular Congruency of the Salto Talaris Total Ankle Prosthesis
cr
ip t
Highlights The surface contour of polyethylene bearings in total ankle is not well described Semi-constrained prostheses allow for multiple degrees of freedom of motion. Computer simulated imaging of Salto-Talaris prosthesis reveal incongruent surfaces The points of bearing contact will be smaller with incongruent bearing surfaces.
ABSTRACT
us
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68
Background: The Salto-Talaris polyethylene articulating surface was designed to allow, but limit accessory motion. This investigation examines surface characteristics between the
70
polyethylene bearing and anatomic talar component in various positions of function.
71
Methods: A Salto Talaris talar prosthesis and matching polyethylene bearing were scanned to
72
create digital solid body models and manipulated to assess surface contact during simulated
73
gait. With computer micromanipulation of the component positions, the surface intersections
74
were recorded for 15 different alignments.
75
Results: The Salto Talaris has limited contact congruity with four points of contact in
76
dorsiflexion, neutral, and plantarflexion. Lateral and medial translations showed only 2-point
77
contact. The radii of curvatures between the talar component and polyethylene surfaces do not
78
match. There was no sulcus contact yet component separation distance was small, suggesting
79
increased loads.
M
d
te
Ac ce p
80
an
69
81
Conclusion: Surface incongruency was measured based on computer model analysis which
82
raises a concern of increased contact pressures.
83 84 85
Key words: Ankle Arthroplasty; Total Ankle Replacement; Salto-Talaris; Ankle Kinematics
2
Page 2 of 17
85 86 A. 87
INTRODUCTION The Salto Talaris Total Ankle (Tornier, Inc. Stafford, TX) is a semi-constrained prosthesis
89
consisting of two articulating components: a metal tibial base with attached polyethylene
90
insert and a contoured metal talar resurfacing component [1]. There is a lack of peer-reviewed
91
or company generated literature that analyzes mechanical characteristics, testing, and logic
92
behind the designs in the various total ankle systems available in the US [2]. Most of the
93
information available to surgeons comes in the form of clinical outcomes of a particular
94
design years after placement [3-17]. More design particulars and rationale is important to
95
better understand the functional design differences such as conformity and constraint.
an
us
cr
ip t
88
96
The Salto total ankle system (Tornier, Saint-Ismier, France) is three-part mobile bearing
98
design that has been in clinical use in France since 1997 [18]. Similar to the natural talus, the
99
talar component is wider anteriorly and has a conical design with two different radii of
d
M
97
curvature [19]. It maintains a congruent constrained surface between the talar component and
101
polyethylene bearing [18]. Design modifications were necessary to convert to the Salto to a
102
two-part semi-constrained design as the bearing surface was attached to the tibial tray. The
103
obvious design changes involved the attachment mechanism to fix the backside of the
104
polyethylene to the tibial tray. More subtle reengineering was also necessary to the
105
polyethylene articulating surface to make the surface less conforming and allow for rotational
106
and translatory movement (play) [20]. The purpose of this investigation is to analyze and
107
characterize the Salto Talaris articulating interface in various simulated positions of function.
108
This will hopefully provide some insights to the inherent biomechanical characteristics of this
109
device.
110 B.111 112
Ac ce p
te
100
MATERIALS AND METHODS 3
Page 3 of 17
A size 1 right Salto Talaris talar and matching polyethylene components were obtained for
114
investigation and were individually digitally scanned using desktop laser scanner (Next
115
Engine Desktop 3D Scanner Model 2020i, Santa Monica, CA). High-resolution three-
116
dimensional solid models were acquired and imported into a software modeling program
117
(formZ, AutoDesSys, Inc. Columbus, OH) for solid body computer analysis. The constructed
118
3D solid models had 64.7K and 74.5K triangular faces for the polyethylene and talar models
119
respectively [Figure 1]. The prosthetic components were aligned to a Cartesian coordinate
120
grid.
121
Relative component positions were assigned at five degrees dorsiflexed, neutral and 15
122
degrees plantarflexed positions and were based on postoperative radiographic derived motion
123
data from a large series of Salto Talaris placements [21]. For each of the functional positions,
124
the polyethylene component was oriented to simulate five positions of function (internal and
125
external rotation, medial and lateral translation, and neutral positions). Loads simulating one
126
body-weight (750N) were applied to the solid body components with intersection size based
127
on known viscoelastic contact properties of polyethylene [22, 23]. With micro-millimeter
128
manipulation of the component solids, surface contact could be established using Boolean
129
intersection operations within the software program. The shape and location of the surface
130
intersections were recorded for all 15 alignments. Additional relevant kinematic and surface
131
component characteristics were measured and recorded.
cr
us
an
M
d
te
Ac ce p
C. 132
ip t
113
RESULTS
133
Based on high-resolution laser scanning, the features of the talar component articulation are
134
comprised of a flat central sulcus with adjacent raised curved medial and lateral shoulder rails
135
that complete the trochlear shape [Figure 2]. The shoulders have a lateral transverse convexity
136
with a lateral edge radius of 7.143 cm and medial edge radius of 6.431 cm. The sagittal radius
137
of curvature for the talar lateral and medial shoulder rails is 2.114 and 1.714 cm respectively 4
Page 4 of 17
[Figure 3a]. This produces an axis of motion that deviates 82.2 degrees in the frontal plane
139
from the projected tibial axis. The polyethylene sagittal radius is 2.667 cm on the lateral rail
140
surface and 2.462 cm over the medial rail surface. Primary contact does not occur on the apex
141
of the rails, rather the measured contact occurs on the most lateral and medial aspects of the
142
rails. The contour profiles at the contact zone are nearly flat in the transverse plane [Figure
143
3b].
ip t
138
cr
144
Analysis of interference patterns showed marked incongruence between the talar and
146
polyethylene components [Figure 4 a-e]. This loss of conformity allows for secondary motion
147
with an average of 4.37 (range 4.44 to 4.20) millimeters of medial to lateral translation and an
148
average of 17.42 (range 17.3 to 17.65) degrees of transverse plane rotation play in all three
149
positions. Congruency patterns showed two points of rail contact for centered, medial, and
150
lateral displacements for dorsiflexed, neutral and plantarflexed positions. External and internal
151
rotated positions revealed four points of rail contact for dorsiflexed, neutral and plantarflexed
152
positions. While the sulcus did not contact in this analysis, the mean sulcus separation was
153
0.016mm.
D 155
an
M
d
te
Ac ce p
154
us
145
DISCUSSION
156
Inman determined that the talar trochlea has a larger radius of curvature on the lateral as
157
compared to its medial aspect [24]. In his monograph, he concluded that conical shape causes
158
the ankle joint axis to be tilted in the frontal plane on an average of 80 (range 68 to 88)
159
degrees from the tibial axis. Similarly, the results of this investigation confirm a conical
160
shape of the Salto Talaris talar component with an axis deviation of 82.2 degrees from the
161
tibial axis, therefore is consistent with Inman’s work. An anatomic talar design is likely
162
complimentary to implanted ankles that have properly balanced ligament tissues and carries
163
the potential to replicate the original kinematics of the ankle. 5
Page 5 of 17
164 It is the ankle surface contour and associated contact characteristics that define and
166
differentiate any prosthesis. A perfect example of this is the Salto Talaris versus the Salto, a
167
congruent mobile bearing design compared to its cousin two-part design. The talar
168
components appear to be identical however, the polyethylene surface characteristics are vastly
169
different. Ianuzzi and Mkanawire have reported that the Salto Talaris polyethylene insert
170
design allows 5+/- degrees of internal-external rotation, 4+/- degrees of varus-valgus rotation,
171
and two mm of anterior-posterior translation [20]. While the source of their data is unclear,
172
our results confirm potential of ancillary motions of transverse rotation as well as medial-
173
lateral translation. Similar to a mobile bearing design, the Salto Talaris shows three degrees
174
of freedom; however, this motion is possible because of articular incongruity.
an
us
cr
ip t
165
M
175
The articular surface design shows a wide separation of the contact areas, which can help
177
reduce ligament strain and controls frontal plane deforming forces. However, this
178
investigation confirms that the Salto Talaris has an incongruent articular surface. There was a
179
sizable discrepancy in the radius of curvature between the opposing polyethylene and metal
180
surfaces, which translates into a point of contact rather than a line of contact. While, this
181
design feature raises concerns regarding premature polyethylene wear and component failure,
182
recent clinical investigation has not shown the prevalence of early polywear [25]. There have
183
been other total ankle designs in which surface contact characteristics have been evaluated
184
[26-29]. Pappas and associates criticized the Newton ankle due to its incongruent design and
185
potential high pressures [29]. Although abnormal pressures were never measured these
186
conclusions were based on engineering computations and emphasized the importance of
187
congruency in TAR designs. Other investigators have also demonstrated abnormal contact
188
stresses in situations of limited surface area contact [26-28]. However currently there is no
189
clinical evidence that a more congruent TAR design has more favorable wear patterns.
Ac ce p
te
d
176
6
Page 6 of 17
190
Further, more congruent devices may increase the stress between the components and bone
191
[30].
192 There is a paucity of published information in the ankle regarding wear potential of
194
polyethylene in any design. Certainly manufacturers processing of the polyethylene as far as
195
level of crosslinking and other treatments would play a role in wear potential with this
196
particular design. Wear testing results if performed should be made available to surgeons
197
placing this device. The authors acknowledge that adaptive wear could improve surface
198
contact profile which may permit for sulcus loading.
an
199
us
cr
ip t
193
There are limitations of this investigation. This is a computer model of the prosthesis and
201
there could be some inconsistencies in the scanning of the prosthetic design. Furthermore, the
202
study involved solid (non-deformable) bodies that did not reflect the viscoelastic qualities of
203
the polyethylene layer and only evaluated one prosthetic size. In addition, the model analyses
204
were performed using static manual positioning of the TAR components, which may not
205
accurately represent dynamic positioning. The authors consider these results as a preliminary
206
step in understanding the contact effects of this unique prosthetic design. Finite element
207
analysis and laboratory load testing are next logical steps in future investigations to better
208
understand polyethylene surface and subsurface strain patterns of the Salto Talaris prosthesis.
E 210
d
te
Ac ce p
209
M
200
CONCLUSIONS
211
New total ankle designs that come to the US market through the Food and Drug
212
Administration 510K process do not go through a major design evaluation prior to total ankle
213
devices coming to market. Surgeons need to understand the Salto Talaris has an anatomical
214
shape to the talus with an axis deviation similar to the true ankle. This prosthesis has a true
215
semi-constrained design that has three-degrees of freedom of motion. However, the increased 7
Page 7 of 17
te
d
M
an
us
cr
ip t
mobility seen in this device is possible because of an incongruent articular interface.
Ac ce p
216
8
Page 8 of 17
REFERENCES 1. Tornier Salto Talaris Product Insert, 2007. 2. Gill LH. Principles of Joint Arthroplasty as Applied to the Ankle. AAOS Instructional Course Lectures. 2002; 51:117-127.
ip t
3. Anderson T, Montgomery F, Carlsson A. Uncemented STAR total ankle prostheses. Three to eight-year follow-up of fifty-one consecutive ankles. J Bone Joint Surg Am. 2003; 85-A(7):1321-1329.
cr
4. Bolton-Maggs BG, Sudlow RA, Freeman MA. Total Ankle Arthroplasty. A longterm review of the London Hospital Experience. J Bone Joint Surg Br. 1985; 67B(5):785-790.
an
us
5. Bonnin M, Gaudot F, Laurent JR, et al. The Salto total ankle arthroplasty: survivorship and analysis of failures at 7 to 11 years. Clin Orthop Relat Res. 2011; 469(1):225-236. doi:10.1007/s11999-010-14.53-y.
M
6. Buechel FF, Sr., Buechel FF, Jr., Pappas MJ. Eighteen-year evaluation of cementless meniscal bearing total ankle replacements. Instr Course Lect. 2002; 51:143-151.
d
7. Doets HC, Brand R, Nelissen RG. Total ankle arthroplasty in inflammatory joint disease with use of two mobile-bearing designs. J Bone Joint Surg Am. 2006; 88A(6):1272-1284.
te
8. Hintermann B, Valderrabano V, Dereymaeker G, et al. The HINTEGRA ankle: rationale and short-term results of 122 consecutive ankles. Clin Orthop Relat Res. 2004; 424:57-68.
Ac ce p
217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266
9. Knecht SI, Estin M, Callaghan JJ, et al. The Agility total ankle arthroplasty. Seven to sixteen-year follow-up. J Bone Joint Surg Am. 2004; 86-A(6):11611171. 10. Newton SE, 3rd. Total ankle arthroplasty. Clinical study of fifty cases. J Bone Joint Surg Am. 1982;64-A(1):104-111. 11. Pyevich MT, Saltzman CL, Callaghan JJ, et al. Total ankle arthroplasty: a unique design. Two to twelve-year follow-up. J Bone Joint Surg Am. 1998; 80A(10):1410-1420. 12. Rippstein PF, Huber M, Coetzee JC, et al. Total ankle replacement with use of a new three-component implant. J Bone Joint Surg Am. 2011; 93-A(15):1426-1435. doi: 10.2106/JBJS.J.00913 13. Saltzman CL, Mann RA, Ahrens JE, et al. Prospective controlled trial of STAR total ankle replacement versus ankle fusion: initial results. Foot Ankle Int. 2009; 30(7):579-596. doi:10.3113/FAI.2009.0579.
9
Page 9 of 17
14. Schuberth JM, Patel S, Zarutsky E. Perioperative complications of the Agility total ankle replacement in 50 initial, consecutive cases. J Foot Ankle Surg. 2006; 45(3):139-146. 15. Spirt AA, Assal M, Hansen ST, Jr. Complications and failure after total ankle arthroplasty. J Bone Joint Surg Am. 2004; 86-A(6):1172-1178.
ip t
16. Wood PL, Karski MT, Watmough P. Total ankle replacement: the results of 100 mobility total ankle replacements. J Bone Joint Surg Br. 2010; 92-B(7):958-962. doi: 10.1302/0301-620X.92B7.23852.
cr
17. Wood PL, Prem H, Sutton C. Total ankle replacement: medium-term results in 200 Scandinavian total ankle replacements. J Bone Joint Surg Br. 2008; 90(5):605-609. doi: 10.1302/0301-620X.90B5.19677.
us
18. Bonnin M, Judet T, Colombier JA, et al. Midterm results of the Salto Total Ankle Prosthesis. Clin Orthop Relat Res. 2004; 424:6-18.
an
19. Cracchiolo A 3rd, Deorio JK. Design features of current total ankle replacements: implants and instrumentation. J Am Acad Orthop Surg. 2008; 16(9):530-540.
M
20. Ianuzzi A, Mkandawire C. Applications of UHMWPE in Total Ankle Replacements, in Kurtz S (ed): UHMWPE Biomaterials Handbook (2nd ed), Vol 2, p 533. Burlington, MA: Academic Press; 2009.
te
d
21. Schuberth JM, McCourt MJ, Christensen JC. Interval changes in postoperative range of motion of Salto-Talaris total ankle replacement. J Foot Ankle Surg. 2011: 50(5):562-565. doi: 10.1053/j.jfas.2011.05.003. 22. Ho SP, Riester L, R, Drews M, et al. Nanoindentation properties of compressionmoulded ultra-high molecular weight polyethylene. Proc Inst Mech Eng H. 2003; 217(5):357-366.
Ac ce p
267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316
23. Oliver WC, Pharr GM. An improved technique for determing hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res. 1992; 7(6):1564-1583. 24. Inman VT: The Joints of the Ankle. Baltimore, MD: Williams and Wilkins; 1976. 25. Schweitzer KM, Adams SB, Viens NA, et al. Early Prospective Clinical Results of a Modern Fixed-Bearing Total Ankle Arthroplasty. J Bone Joint Surg Am. 2013; 95-A:1002-1011. doi: 10.2106/JBJS.L.00555. 26. Espinosa N, Walti M, Favre P, et al. Misalignment of total ankle components can induce high joint contact pressures. J Bone Joint Surg Am. 2010; 92-A(5):11791187. doi: 10.2106/JBJS.I.00287. 27. Miller MC, Smolinski P, Conti S. Stresses in polyethylene liners in a semiconstrained ankle prostheis. J Biomech Eng. 2004; 126(5):636-640.
10
Page 10 of 17
28. Nicholson JJ, Parks BG, Stroud CC, et al. Joint contact characteristics in agility total ankle arthroplasty. Clin Orthop Relat Res. 2004; 424:125-129. 29. Pappas M, Buechel FF, DePalma AF. Cylindrical total ankle joint replacement: surgical and biomechanical rationale. Clin Orthop Relat Res. 1976; 118:82-92.
te
d
M
an
us
cr
ip t
30. Hodaei M, Farhang K, Maani N. A contact mechanics model for ankle implants with inclusion of surface roughness effects. J Phys D: Appl Phys. 2014; 47:085522. doi:10.1088/0022-3727/47/8/085502.
Ac ce p
317 318 319 320 321 322 323 324 325 326 327 328
11
Page 11 of 17
LEGENDS Figure 1: Constructed wireframe model of the Salto Talaris talar and polyethylene components. Figure 2: The talar design shows a relatively flat sulcus with adjacent rails that define a trochlear shape with transverse plane lateral convexity.
cr
ip t
Figure 3a: Cross sections of talar contact in neutral ankle position with neutral (centered) poly position. The arrows depict the region of contact on the rails. Note the relatively flat areas of contact on the medial and lateral most positions of the rails. 3b): The sagittal cross section through a neutral aligned ankle with a neutral aligned poly depicts a difference of radii of curvatures between the poly and talar components.
te
d
M
an
us
Figure 4: Contact pressures with a translucent polyethylene component in 15 defined positions. The images show the ankle in dorsiflexed, neutral and plantarflexed alignment. For each alignment there are defined deviated polyethylene positions of internal rotation, external rotation, lateral translation, neutral (centered), and medially translation. Note the darker areas depict solid body intersections that are equal to simulated contact at one body weight.
Ac ce p
328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349
12
Page 12 of 17
We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work. [OR] Dr. Christensen is a consultant for Stryker Corporation.
ip t
We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.
cr
We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property.
te
d
M
an
us
We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He/she is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author.
Ac ce p
349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369
13
Page 13 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Figure 1
Page 14 of 17
Ac
ce
pt
ed
M
an
us
cr
i
Figure 2
Page 15 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Figure 3
Page 16 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Figure 4
Page 17 of 17
S1268-7731(15)00005-3 http://dx.doi.org/doi:10.1016/j.fas.2015.01.003 FAS 789
To appear in:
Foot and Ankle Surgery
Received date: Revised date: Accepted date:
13-11-2014 18-12-2014 8-1-2015
Please cite this article as: Morris CH, Christensen JC, Ching RP, Chan F, Schuberth JM, Articular Congruency of the Salto Talaris Total Ankle Prosthesis, Foot and Ankle Surgery (2015), http://dx.doi.org/10.1016/j.fas.2015.01.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
d
M
an
us
Colin H. Morris1 Jeffrey C. Christensen, DPM2 Randal P. Ching, PhD3 Francis Chan, DPM4 John M. Schuberth, DPM5
cr
ip t
Articular Congruency of the Salto Talaris Total Ankle Prosthesis
te
1.Senior Undergraduate Engineering Student, University of Washington, Seattle, WA. E-mail: [email protected]. 2.Attending Surgeon, Department of Orthopedics Swedish Medical Center, Seattle, WA. Research Director, International Foot & Ankle Foundation. E-mail: [email protected]. 3. Director Applied Biomechanics Laboratory, University of Washington, Seattle, WA. E-mail: [email protected]. 4. Assistant Professor, Department Podiatric Medicine, Surgery & Biomechanics, Western University of Health Sciences, Pomona, CA. E-mail: [email protected]. 5. Chief of Foot & Ankle Service, Kaiser Permanente, San Francisco, CA. E-mail: [email protected].
Ac ce p
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
Address correspondence to: John M. Schuberth, DPM, Department of Orthopedic Surgery, Kaiser Foundation Hospital, French Campus. 450 6th Avenue, San Francisco, CA 94118 E-mail address: [email protected].
1
Page 1 of 17
Articular Congruency of the Salto Talaris Total Ankle Prosthesis
cr
ip t
Highlights The surface contour of polyethylene bearings in total ankle is not well described Semi-constrained prostheses allow for multiple degrees of freedom of motion. Computer simulated imaging of Salto-Talaris prosthesis reveal incongruent surfaces The points of bearing contact will be smaller with incongruent bearing surfaces.
ABSTRACT
us
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68
Background: The Salto-Talaris polyethylene articulating surface was designed to allow, but limit accessory motion. This investigation examines surface characteristics between the
70
polyethylene bearing and anatomic talar component in various positions of function.
71
Methods: A Salto Talaris talar prosthesis and matching polyethylene bearing were scanned to
72
create digital solid body models and manipulated to assess surface contact during simulated
73
gait. With computer micromanipulation of the component positions, the surface intersections
74
were recorded for 15 different alignments.
75
Results: The Salto Talaris has limited contact congruity with four points of contact in
76
dorsiflexion, neutral, and plantarflexion. Lateral and medial translations showed only 2-point
77
contact. The radii of curvatures between the talar component and polyethylene surfaces do not
78
match. There was no sulcus contact yet component separation distance was small, suggesting
79
increased loads.
M
d
te
Ac ce p
80
an
69
81
Conclusion: Surface incongruency was measured based on computer model analysis which
82
raises a concern of increased contact pressures.
83 84 85
Key words: Ankle Arthroplasty; Total Ankle Replacement; Salto-Talaris; Ankle Kinematics
2
Page 2 of 17
85 86 A. 87
INTRODUCTION The Salto Talaris Total Ankle (Tornier, Inc. Stafford, TX) is a semi-constrained prosthesis
89
consisting of two articulating components: a metal tibial base with attached polyethylene
90
insert and a contoured metal talar resurfacing component [1]. There is a lack of peer-reviewed
91
or company generated literature that analyzes mechanical characteristics, testing, and logic
92
behind the designs in the various total ankle systems available in the US [2]. Most of the
93
information available to surgeons comes in the form of clinical outcomes of a particular
94
design years after placement [3-17]. More design particulars and rationale is important to
95
better understand the functional design differences such as conformity and constraint.
an
us
cr
ip t
88
96
The Salto total ankle system (Tornier, Saint-Ismier, France) is three-part mobile bearing
98
design that has been in clinical use in France since 1997 [18]. Similar to the natural talus, the
99
talar component is wider anteriorly and has a conical design with two different radii of
d
M
97
curvature [19]. It maintains a congruent constrained surface between the talar component and
101
polyethylene bearing [18]. Design modifications were necessary to convert to the Salto to a
102
two-part semi-constrained design as the bearing surface was attached to the tibial tray. The
103
obvious design changes involved the attachment mechanism to fix the backside of the
104
polyethylene to the tibial tray. More subtle reengineering was also necessary to the
105
polyethylene articulating surface to make the surface less conforming and allow for rotational
106
and translatory movement (play) [20]. The purpose of this investigation is to analyze and
107
characterize the Salto Talaris articulating interface in various simulated positions of function.
108
This will hopefully provide some insights to the inherent biomechanical characteristics of this
109
device.
110 B.111 112
Ac ce p
te
100
MATERIALS AND METHODS 3
Page 3 of 17
A size 1 right Salto Talaris talar and matching polyethylene components were obtained for
114
investigation and were individually digitally scanned using desktop laser scanner (Next
115
Engine Desktop 3D Scanner Model 2020i, Santa Monica, CA). High-resolution three-
116
dimensional solid models were acquired and imported into a software modeling program
117
(formZ, AutoDesSys, Inc. Columbus, OH) for solid body computer analysis. The constructed
118
3D solid models had 64.7K and 74.5K triangular faces for the polyethylene and talar models
119
respectively [Figure 1]. The prosthetic components were aligned to a Cartesian coordinate
120
grid.
121
Relative component positions were assigned at five degrees dorsiflexed, neutral and 15
122
degrees plantarflexed positions and were based on postoperative radiographic derived motion
123
data from a large series of Salto Talaris placements [21]. For each of the functional positions,
124
the polyethylene component was oriented to simulate five positions of function (internal and
125
external rotation, medial and lateral translation, and neutral positions). Loads simulating one
126
body-weight (750N) were applied to the solid body components with intersection size based
127
on known viscoelastic contact properties of polyethylene [22, 23]. With micro-millimeter
128
manipulation of the component solids, surface contact could be established using Boolean
129
intersection operations within the software program. The shape and location of the surface
130
intersections were recorded for all 15 alignments. Additional relevant kinematic and surface
131
component characteristics were measured and recorded.
cr
us
an
M
d
te
Ac ce p
C. 132
ip t
113
RESULTS
133
Based on high-resolution laser scanning, the features of the talar component articulation are
134
comprised of a flat central sulcus with adjacent raised curved medial and lateral shoulder rails
135
that complete the trochlear shape [Figure 2]. The shoulders have a lateral transverse convexity
136
with a lateral edge radius of 7.143 cm and medial edge radius of 6.431 cm. The sagittal radius
137
of curvature for the talar lateral and medial shoulder rails is 2.114 and 1.714 cm respectively 4
Page 4 of 17
[Figure 3a]. This produces an axis of motion that deviates 82.2 degrees in the frontal plane
139
from the projected tibial axis. The polyethylene sagittal radius is 2.667 cm on the lateral rail
140
surface and 2.462 cm over the medial rail surface. Primary contact does not occur on the apex
141
of the rails, rather the measured contact occurs on the most lateral and medial aspects of the
142
rails. The contour profiles at the contact zone are nearly flat in the transverse plane [Figure
143
3b].
ip t
138
cr
144
Analysis of interference patterns showed marked incongruence between the talar and
146
polyethylene components [Figure 4 a-e]. This loss of conformity allows for secondary motion
147
with an average of 4.37 (range 4.44 to 4.20) millimeters of medial to lateral translation and an
148
average of 17.42 (range 17.3 to 17.65) degrees of transverse plane rotation play in all three
149
positions. Congruency patterns showed two points of rail contact for centered, medial, and
150
lateral displacements for dorsiflexed, neutral and plantarflexed positions. External and internal
151
rotated positions revealed four points of rail contact for dorsiflexed, neutral and plantarflexed
152
positions. While the sulcus did not contact in this analysis, the mean sulcus separation was
153
0.016mm.
D 155
an
M
d
te
Ac ce p
154
us
145
DISCUSSION
156
Inman determined that the talar trochlea has a larger radius of curvature on the lateral as
157
compared to its medial aspect [24]. In his monograph, he concluded that conical shape causes
158
the ankle joint axis to be tilted in the frontal plane on an average of 80 (range 68 to 88)
159
degrees from the tibial axis. Similarly, the results of this investigation confirm a conical
160
shape of the Salto Talaris talar component with an axis deviation of 82.2 degrees from the
161
tibial axis, therefore is consistent with Inman’s work. An anatomic talar design is likely
162
complimentary to implanted ankles that have properly balanced ligament tissues and carries
163
the potential to replicate the original kinematics of the ankle. 5
Page 5 of 17
164 It is the ankle surface contour and associated contact characteristics that define and
166
differentiate any prosthesis. A perfect example of this is the Salto Talaris versus the Salto, a
167
congruent mobile bearing design compared to its cousin two-part design. The talar
168
components appear to be identical however, the polyethylene surface characteristics are vastly
169
different. Ianuzzi and Mkanawire have reported that the Salto Talaris polyethylene insert
170
design allows 5+/- degrees of internal-external rotation, 4+/- degrees of varus-valgus rotation,
171
and two mm of anterior-posterior translation [20]. While the source of their data is unclear,
172
our results confirm potential of ancillary motions of transverse rotation as well as medial-
173
lateral translation. Similar to a mobile bearing design, the Salto Talaris shows three degrees
174
of freedom; however, this motion is possible because of articular incongruity.
an
us
cr
ip t
165
M
175
The articular surface design shows a wide separation of the contact areas, which can help
177
reduce ligament strain and controls frontal plane deforming forces. However, this
178
investigation confirms that the Salto Talaris has an incongruent articular surface. There was a
179
sizable discrepancy in the radius of curvature between the opposing polyethylene and metal
180
surfaces, which translates into a point of contact rather than a line of contact. While, this
181
design feature raises concerns regarding premature polyethylene wear and component failure,
182
recent clinical investigation has not shown the prevalence of early polywear [25]. There have
183
been other total ankle designs in which surface contact characteristics have been evaluated
184
[26-29]. Pappas and associates criticized the Newton ankle due to its incongruent design and
185
potential high pressures [29]. Although abnormal pressures were never measured these
186
conclusions were based on engineering computations and emphasized the importance of
187
congruency in TAR designs. Other investigators have also demonstrated abnormal contact
188
stresses in situations of limited surface area contact [26-28]. However currently there is no
189
clinical evidence that a more congruent TAR design has more favorable wear patterns.
Ac ce p
te
d
176
6
Page 6 of 17
190
Further, more congruent devices may increase the stress between the components and bone
191
[30].
192 There is a paucity of published information in the ankle regarding wear potential of
194
polyethylene in any design. Certainly manufacturers processing of the polyethylene as far as
195
level of crosslinking and other treatments would play a role in wear potential with this
196
particular design. Wear testing results if performed should be made available to surgeons
197
placing this device. The authors acknowledge that adaptive wear could improve surface
198
contact profile which may permit for sulcus loading.
an
199
us
cr
ip t
193
There are limitations of this investigation. This is a computer model of the prosthesis and
201
there could be some inconsistencies in the scanning of the prosthetic design. Furthermore, the
202
study involved solid (non-deformable) bodies that did not reflect the viscoelastic qualities of
203
the polyethylene layer and only evaluated one prosthetic size. In addition, the model analyses
204
were performed using static manual positioning of the TAR components, which may not
205
accurately represent dynamic positioning. The authors consider these results as a preliminary
206
step in understanding the contact effects of this unique prosthetic design. Finite element
207
analysis and laboratory load testing are next logical steps in future investigations to better
208
understand polyethylene surface and subsurface strain patterns of the Salto Talaris prosthesis.
E 210
d
te
Ac ce p
209
M
200
CONCLUSIONS
211
New total ankle designs that come to the US market through the Food and Drug
212
Administration 510K process do not go through a major design evaluation prior to total ankle
213
devices coming to market. Surgeons need to understand the Salto Talaris has an anatomical
214
shape to the talus with an axis deviation similar to the true ankle. This prosthesis has a true
215
semi-constrained design that has three-degrees of freedom of motion. However, the increased 7
Page 7 of 17
te
d
M
an
us
cr
ip t
mobility seen in this device is possible because of an incongruent articular interface.
Ac ce p
216
8
Page 8 of 17
REFERENCES 1. Tornier Salto Talaris Product Insert, 2007. 2. Gill LH. Principles of Joint Arthroplasty as Applied to the Ankle. AAOS Instructional Course Lectures. 2002; 51:117-127.
ip t
3. Anderson T, Montgomery F, Carlsson A. Uncemented STAR total ankle prostheses. Three to eight-year follow-up of fifty-one consecutive ankles. J Bone Joint Surg Am. 2003; 85-A(7):1321-1329.
cr
4. Bolton-Maggs BG, Sudlow RA, Freeman MA. Total Ankle Arthroplasty. A longterm review of the London Hospital Experience. J Bone Joint Surg Br. 1985; 67B(5):785-790.
an
us
5. Bonnin M, Gaudot F, Laurent JR, et al. The Salto total ankle arthroplasty: survivorship and analysis of failures at 7 to 11 years. Clin Orthop Relat Res. 2011; 469(1):225-236. doi:10.1007/s11999-010-14.53-y.
M
6. Buechel FF, Sr., Buechel FF, Jr., Pappas MJ. Eighteen-year evaluation of cementless meniscal bearing total ankle replacements. Instr Course Lect. 2002; 51:143-151.
d
7. Doets HC, Brand R, Nelissen RG. Total ankle arthroplasty in inflammatory joint disease with use of two mobile-bearing designs. J Bone Joint Surg Am. 2006; 88A(6):1272-1284.
te
8. Hintermann B, Valderrabano V, Dereymaeker G, et al. The HINTEGRA ankle: rationale and short-term results of 122 consecutive ankles. Clin Orthop Relat Res. 2004; 424:57-68.
Ac ce p
217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266
9. Knecht SI, Estin M, Callaghan JJ, et al. The Agility total ankle arthroplasty. Seven to sixteen-year follow-up. J Bone Joint Surg Am. 2004; 86-A(6):11611171. 10. Newton SE, 3rd. Total ankle arthroplasty. Clinical study of fifty cases. J Bone Joint Surg Am. 1982;64-A(1):104-111. 11. Pyevich MT, Saltzman CL, Callaghan JJ, et al. Total ankle arthroplasty: a unique design. Two to twelve-year follow-up. J Bone Joint Surg Am. 1998; 80A(10):1410-1420. 12. Rippstein PF, Huber M, Coetzee JC, et al. Total ankle replacement with use of a new three-component implant. J Bone Joint Surg Am. 2011; 93-A(15):1426-1435. doi: 10.2106/JBJS.J.00913 13. Saltzman CL, Mann RA, Ahrens JE, et al. Prospective controlled trial of STAR total ankle replacement versus ankle fusion: initial results. Foot Ankle Int. 2009; 30(7):579-596. doi:10.3113/FAI.2009.0579.
9
Page 9 of 17
14. Schuberth JM, Patel S, Zarutsky E. Perioperative complications of the Agility total ankle replacement in 50 initial, consecutive cases. J Foot Ankle Surg. 2006; 45(3):139-146. 15. Spirt AA, Assal M, Hansen ST, Jr. Complications and failure after total ankle arthroplasty. J Bone Joint Surg Am. 2004; 86-A(6):1172-1178.
ip t
16. Wood PL, Karski MT, Watmough P. Total ankle replacement: the results of 100 mobility total ankle replacements. J Bone Joint Surg Br. 2010; 92-B(7):958-962. doi: 10.1302/0301-620X.92B7.23852.
cr
17. Wood PL, Prem H, Sutton C. Total ankle replacement: medium-term results in 200 Scandinavian total ankle replacements. J Bone Joint Surg Br. 2008; 90(5):605-609. doi: 10.1302/0301-620X.90B5.19677.
us
18. Bonnin M, Judet T, Colombier JA, et al. Midterm results of the Salto Total Ankle Prosthesis. Clin Orthop Relat Res. 2004; 424:6-18.
an
19. Cracchiolo A 3rd, Deorio JK. Design features of current total ankle replacements: implants and instrumentation. J Am Acad Orthop Surg. 2008; 16(9):530-540.
M
20. Ianuzzi A, Mkandawire C. Applications of UHMWPE in Total Ankle Replacements, in Kurtz S (ed): UHMWPE Biomaterials Handbook (2nd ed), Vol 2, p 533. Burlington, MA: Academic Press; 2009.
te
d
21. Schuberth JM, McCourt MJ, Christensen JC. Interval changes in postoperative range of motion of Salto-Talaris total ankle replacement. J Foot Ankle Surg. 2011: 50(5):562-565. doi: 10.1053/j.jfas.2011.05.003. 22. Ho SP, Riester L, R, Drews M, et al. Nanoindentation properties of compressionmoulded ultra-high molecular weight polyethylene. Proc Inst Mech Eng H. 2003; 217(5):357-366.
Ac ce p
267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316
23. Oliver WC, Pharr GM. An improved technique for determing hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res. 1992; 7(6):1564-1583. 24. Inman VT: The Joints of the Ankle. Baltimore, MD: Williams and Wilkins; 1976. 25. Schweitzer KM, Adams SB, Viens NA, et al. Early Prospective Clinical Results of a Modern Fixed-Bearing Total Ankle Arthroplasty. J Bone Joint Surg Am. 2013; 95-A:1002-1011. doi: 10.2106/JBJS.L.00555. 26. Espinosa N, Walti M, Favre P, et al. Misalignment of total ankle components can induce high joint contact pressures. J Bone Joint Surg Am. 2010; 92-A(5):11791187. doi: 10.2106/JBJS.I.00287. 27. Miller MC, Smolinski P, Conti S. Stresses in polyethylene liners in a semiconstrained ankle prostheis. J Biomech Eng. 2004; 126(5):636-640.
10
Page 10 of 17
28. Nicholson JJ, Parks BG, Stroud CC, et al. Joint contact characteristics in agility total ankle arthroplasty. Clin Orthop Relat Res. 2004; 424:125-129. 29. Pappas M, Buechel FF, DePalma AF. Cylindrical total ankle joint replacement: surgical and biomechanical rationale. Clin Orthop Relat Res. 1976; 118:82-92.
te
d
M
an
us
cr
ip t
30. Hodaei M, Farhang K, Maani N. A contact mechanics model for ankle implants with inclusion of surface roughness effects. J Phys D: Appl Phys. 2014; 47:085522. doi:10.1088/0022-3727/47/8/085502.
Ac ce p
317 318 319 320 321 322 323 324 325 326 327 328
11
Page 11 of 17
LEGENDS Figure 1: Constructed wireframe model of the Salto Talaris talar and polyethylene components. Figure 2: The talar design shows a relatively flat sulcus with adjacent rails that define a trochlear shape with transverse plane lateral convexity.
cr
ip t
Figure 3a: Cross sections of talar contact in neutral ankle position with neutral (centered) poly position. The arrows depict the region of contact on the rails. Note the relatively flat areas of contact on the medial and lateral most positions of the rails. 3b): The sagittal cross section through a neutral aligned ankle with a neutral aligned poly depicts a difference of radii of curvatures between the poly and talar components.
te
d
M
an
us
Figure 4: Contact pressures with a translucent polyethylene component in 15 defined positions. The images show the ankle in dorsiflexed, neutral and plantarflexed alignment. For each alignment there are defined deviated polyethylene positions of internal rotation, external rotation, lateral translation, neutral (centered), and medially translation. Note the darker areas depict solid body intersections that are equal to simulated contact at one body weight.
Ac ce p
328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349
12
Page 12 of 17
We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work. [OR] Dr. Christensen is a consultant for Stryker Corporation.
ip t
We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.
cr
We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property.
te
d
M
an
us
We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He/she is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author.
Ac ce p
349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369
13
Page 13 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Figure 1
Page 14 of 17
Ac
ce
pt
ed
M
an
us
cr
i
Figure 2
Page 15 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Figure 3
Page 16 of 17
Ac ce p
te
d
M
an
us
cr
ip t
Figure 4
Page 17 of 17