Giddins G

Joyce TJ

\ua9 2018, The Author(s) 2018. Single-piece silicone implants dominate metacarpophalangeal joint arthroplasty. The NeuFlex\uae implant was introduced to improve on the clinical performance of other silicone implants by having a pre-flexed hinge. By visually examining a cohort of 30 explanted NeuFlex\uae metacarpophalangeal joint prostheses we sought to identify the failure modes of these implants. Seven were not fractured, 11 had fractured across the hinge, nine had fractured at the junction of the distal stem and the hinge, and three showed fractures at both the hinge and at the junction of the distal stem and the hinge. These data may prove helpful in identifying how the performance of single-piece silicone implant designs can be improved

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Page 1 of 13  Sites of fractures in explanted NeuFlex metacarpophalangeal silicone prostheses 1 T J Joyce, G Giddins* 2  3 School of Engineering, Newcastle University, Stephenson Building, Claremont Road, Newcastle upon 4 Tyne, NE1 7RU, UK 5 *Orthopaedic Department, Royal United Hospital, Bath, UK 6  7 Corresponding author: T J Joyce, School of Engineering, Newcastle University, Stephenson Building, 8 Claremont Road, Newcastle upon Tyne, NE1 7RU, UK 9 Telephone: 0044 191 208 6214; Fax 0044 191 222 8600 10 Email Thomas.joyce@ncl.ac.uk; twitter handle @metalhip_ncl  11  12 Keywords: NeuFlex; Swanson; Sutter; silicone; retrieval analysis; fracture 13  14 Funding: The authors received no financial support for the research, authorship, and/or publication of 15 this article. 16  17 The authors declared no potential conflicts of interest with respect to the research, authorship, and/or 18 publication of this article. 19   20 Page 2 of 13  Abstract 21 Single-piece silicone implants dominate metacarpophalangeal (MP) joint arthroplasty. The NeuFlex 22 implant was introduced to improve on the clinical performance of other silicone implants by having a 23 pre-flexed hinge. By visually examining a cohort of 30 explanted NeuFlex MP joint prostheses we 24 sought to identify failure modes of these implants. Seven were not fractured, 11 had fractured across 25 the hinge, nine had fractured at the junction of the distal stem and the hinge, and three showed 26 fractures at both the hinge and at the junction of the distal stem and the hinge. This data may prove 27 helpful with identifying how the performance of single-piece silicone implant designs can be improved. 28 Level IV 29  30  31   32 Page 3 of 13  INTRODUCTION 33  34 Single-piece silicone implants dominate finger arthroplasty of the metacarpophalangeal (MP) joint.  35 The Swanson (Wright Medical, Memphis, USA) implant is the market leader 36 (Norwegian_Arthroplasty_Register, 2016).  Known ‘problems’ include fracture (Kimani et al., 2009), 37 primarily at the junction of the distal stem and hinge (Joyce and Unsworth, 2002).  This position of 38 fracture is also seen with the Avanta/Sutter (Sutter Corporation/Avanta, San Diego, USA) single-piece 39 silicone finger implant (Joyce et al., 2003). It is thought to be particularly related to the dominance of 40 subluxing forces in the rheumatoid MP joint (Drayton et al., 2016; Joyce, 2009).  In 1998 the pre-flexed 41 NeuFlex implant was introduced.   The three designs, Swanson, Sutter and NeuFlex, are shown in Fig 42 1.   43 It is recognised that fracture of silicone MP implants is common.  Trail et al. reported that two-thirds of 44 1336 Swanson implants had fractured at 17 years follow-up (Trail et al., 2004).  Goldfarb and Stern 45 reported that 67% of their Swanson implants and 52% of their Sutter implants had fractured at 14 46 years follow-up (Goldfarb and Stern, 2003).  A fractured implant does not necessarily mean a clinical 47 failure but recurrent symptoms are more likely with fractured implants (Trail et al., 2004).   48 Clinically, it has been reported that the NeuFlex MP joint has produced an increased range of motion 49 compared to use of the Swanson implant (Delaney et al., 2005).  This finding was also reported by 50 Escott et al, although their patients implanted with a Swanson implant had better self-reported function 51 and aesthetics (Escott et al., 2010).  While Namdari and Weiss reported 1/29 fractures in their cohort 52 of NeuFlex implants (Namdari and Weiss, 2009), similar fracture rates between the NeuFlex and 53 Swanson designs have been reported (Kimani et al., 2009).  When NeuFlex and Sutter implants were 54 compared in the MP joint, two out of 78 NeuFlex and five out of 78 Sutter implants broke (Pettersson 55 et al., 2006).   56 Page 4 of 13  The aim of this study was to assess the failure of explanted NeuFlex implants and compare the results 57 with established patterns for other one-piece silicone implants. 58  59 METHODS AND MATERIALS 60 NeuFlex MP joint explants were gathered as part of an ongoing retrieval programme.  Following 61 removal the implants were cleaned with a brief immersion in Chlorhexidine for 30 mins and then 62 washed in tap water.  The explants were photographed using a digital camera.  The position of 63 fracture, if any, was noted.  We recorded patient demographics including the patient age, gender, 64 underlying diagnosis, site of surgery and time in situ.  The implants were part of a consecutive series 65 of explants for which patient demographic data were available.   66 Based on the explant results (q.v.), we compared the thickness of the central hinge section of NeuFlex 67 and Sutter/Avanta implants as a thinner section would probably fail quicker, as crack growth 68 resistance is probably key to the longevity of these single-piece, silicone prostheses (ASTM-F1781-15, 69 2015; Hutchinson et al., 1997).  Size 20 and size 40 implants of the NeuFlex and Sutter/Avanta were 70 measured using a Vernier calliper (Mitutoyo, Huddersfield, UK).   71  72 RESULTS 73 Thirty NeuFlex MP joint explants were available for study.  The position of the complete implant 74 fracture, if any, is shown in table 1, alongside patient and other information.  All revision procedures 75 were undertaken for clinical problems i.e. symptomatic joint replacement failure requiring revision 76 surgery after failure of non-operative treatment. 77 Seven explants were not fractured (Fig 2A).  Eleven explants had completely fractured at the hinge 78 (Fig 2B).  A further nine explants had completely fractured at the junction of the distal stem and hinge 79 (Fig 2C).  Three explants had completely fractured at both the hinge and at the distal stem (Fig 2D).  80 Page 5 of 13  We saw a mix of fractured and intact implants in some patients, for example explants 8-11 came from 81 the hand of one patient.  One explant was intact, two had fractured at the distal stem and one had 82 fractured at the hinge.  Separate to this we saw an explant (no. 19) with an incomplete fracture. 83 NeuFlex MP explants ranged in size from 0 to 40.  As might be expected, smaller sizes were retrieved 84 from the smaller fingers of hands, while larger implants tended to come from the index and middle 85 fingers.  The age at revision ranged from 43 to 81 (median 58) years.  The time in situ ranged from 6 86 to 120 (median 58.5) months.  In all but two cases the diagnosis was rheumatoid arthritis.  87 Discolouration of some explants had occurred (Fig 3).  The significance of this is unclear but it could 88 represent some change in material properties of the implant. 89 The size 20 NeuFlex and Sutter/Avanta implants were each measured to have a hinge thickness of 90 1.9 mm and the size 40 implants were each measured to have a hinge thickness of 2.3 mm. 91  92 DISCUSSION 93 As shown in table 1, 11 NeuFlex explants had fractured across the hinge (Fig 2B); this has not 94 previously been reported in vivo.  Fracture at the hinge occurred when three NeuFlex implants were 95 tested in vitro in a finger function simulator (Joyce and Unsworth, 2005).  Nine NeuFlex explants had 96 fractured at the junction of the distal stem and hinge (Fig 2C).  This is similar to the site of implant 97 fracture seen with Swanson implant fractures (Gellman et al., 1997; Trail et al., 2004) and 98 Sutter/Avanta (Joyce et al., 2003) implant fractures.  In vitro tests have shown that Swanson (Joyce 99 and Unsworth, 2000) and Sutter (Joyce et al., 2003) implants fracture at the junction of the distal hinge 100 and stem, in both cases matching clinical experience.   101 Intriguingly, 10% of the cohort fractured at the hinge and at the junction of the distal stem and hinge 102 (Fig 2D).  The authors are not aware of such a failure mode having been reported previously.  That it 103 happened in three explants, and that one of the un-fractured NeuFlex explants (no. 19) also showed 104 substantial damage at both the hinge and the junction of the distal stem and hinge indicates that the 105 Page 6 of 13  failure mode was not an anomaly; of greater note 11 (37%) fractured just at the hinge.  Overall 14 106 (47%) suffered fractures of the implant hinge.  Silicone implant hinge fractures have not previously 107 been reported.  It is unclear whether this occurs before, after or separate to stem fractures.   108 The one incomplete fracture (no. 19) showed that fracture began dorsally.  This matches with the 109 fracture initiation site of silicone MP joint implants seen previously (Joyce, 2009).   110 Discolouration of most explants occurred (Fig 3) likely indicating that the silicone material can change 111 when in the body.  This may affect the material properties of the implants and could therefore be a 112 useful area for future research. 113 We appreciate that fractures would likely have occurred sometime before removal of the implants and 114 therefore time in situ does not equate with time to fracture. 115 Ex vivo analysis of finger implants potentially highlight key areas of failure, thus providing information 116 that could be used to reduce failures by improving future designs.  For example, based on the 117 empirical evidence provided in this paper and by other previous publications (Drayton et al., 2016; 118 Joyce, 2009; Joyce et al., 2003), subluxing forces need to be minimised, to reduce the shear stresses 119 on the implant at both the junction of the distal stem and hinge and probably at the hinge.  In addition, 120 consideration could be given to increasing the thickness of the hinge to reduce the time taken to 121 fracture, although there may be a concomitant increase in stiffness of the implant. 122 With improved designs, patients could achieve more with their replaced joints while increased 123 prosthesis longevity should lead to fewer revision operations.  The latest Norwegian Arthroplasty 124 Register shows that revision MP joint arthroplasties accounted for 42% of all MP joint replacement 125 operations in 2015 (Norwegian_Arthroplasty_Register, 2016).  Therefore revision MP joint arthroplasty 126 is common and opportunities to reduce such operations are substantial. 127 There are limitations on this research.  There is no denominator to show the rate of implant failure.  128 The details of the original operations are unknown; there may have been factors leading to implant 129 failure.  There is no correlation with the biomechanics of the failed joints. 130 Page 7 of 13  This study provides new data on the failure of NeuFlex implants raising questions about their design 131 and its possible link to mechanical failure. 132  133  134 CONFLICT OF INTERESTS 135 None declared 136  137 Funding 138 This research received no specific grant from any funding agency in the public, commercial, or not-for-139 profit sectors. 140   141 Page 8 of 13  REFERENCES 142  143 ASTM-F1781-15. Standard specification for elastomeric flexible hinge finger total joint implants. West 144 Conshohocken, ASTM, 2015. 145 Delaney R, Trail IA, Nuttall D. A comparative study of outcome between the neuflex and swanson 146 metacarpophalangeal joint replacements. J Hand Surg Br. 2005, 30: 3-7. 147 Drayton P, Morgan BW, Davies MC, Giddins GEB, Miles AW. A biomechanical study of the effects of 148 simulated ulnar deviation on silicone finger joint implant failure. J Hand Surg Eur. 2016, 41: 944-7. 149 Escott BG, Ronald K, Judd MGP, Bogoch ER. Neuflex and swanson metacarpophalangeal implants 150 for rheumatoid arthritis: Prospective randomized, controlled clinical trial. J Hand Surg. 2010, 35: 44-51. 151 Gellman H, Stetson W, Brumfield RH, Costigan W, Kuschner SH. Silastic metacarpophalangeal joint 152 arthroplasty in patients with rheumatoid arthritis. Clin Orthop Rel Res. 1997, 342: 16-21. 153 Goldfarb CA, Stern PJ. Metacarpophalangeal joint arthroplasty in rheumatoid arthritis. J Bone Jt Surg. 154 2003, 85A: 1869-78. 155 Hutchinson DT, Savory KM, Bachus KN. Crack-growth properties of various elastomers with potential 156 application in small joint prostheses. J Biomed Mat Res. 1997, 34: 94-9. 157 Joyce TJ. Currently available metacarpophalangeal prostheses: Their designs and prospective 158 considerations. Expert Rev Med Devs. 2004, 1: 193-204. 159 Joyce TJ. Analysis of the mechanism of fracture of silicone metacarpophalangeal prostheses. J Hand 160 Surg Eur. 2009, 34: 18-24. 161 Joyce TJ, Milner RH, Unsworth A. A comparison of ex vivo and in vitro sutter metacarpophalangeal 162 prostheses. J Hand Surg Br. 2003, 28B: 86-91. 163 Joyce TJ, Unsworth A. The design of a finger wear simulator and preliminary results. J Engng Med. 164 2000, 214: 519-26. 165 Joyce TJ, Unsworth A. A literature review of 'failures' of the swanson finger prosthesis in the 166 metacarpophalangeal joint. Hand Surg. 2002, 7: 139-46. 167 Page 9 of 13  Joyce TJ, Unsworth A. Neuflex metacarpophalangeal prostheses tested in vitro. J Engng Med. 2005, 168 219: 105-10. 169 Kimani BM, Trail IA, Hearnden A, Delaney R, Nuttall D. Survivorship of the neuflex silicone implant in 170 mcp joint replacement. J Hand Surg Eur. 2009, 34: 25-8. 171 Namdari S, Weiss A-PC. Anatomically neutral silicone small joint arthroplasty for osteoarthritis. J Hand 172 Surg. 2009, 34: 292-300. 173 Norwegian_Arthroplasty_Register. Nasjonalt register for leddproteser. 2016. 174 http://nrlweb.ihelse.net/eng/Rapporter/Report2016_english.pdf (25 September 2017). 175 Pettersson K, Wagnsjö P, Hulin E. Neuflex compared with sutter prostheses: A blind, prospective, 176 randomised comparison of silastic metacarpophalangeal joint prostheses. Scand J Plas Reconstr Surg 177 Hand Surg. 2006, 40: 284-90. 178 Trail I, Martin J, Nuttall D, Stanley J. Seventeen-year survivorship analysis of silastic 179 metacarpophalangeal joint replacement. J Bone Joint Surg Br. 2004, 86-B: 1002-6. 180 Weiss A-PC, Moore DC, Infantolino C, Crisco JJ, Akelman E, McGovern RD. Metacarpophalangeal 181 joint mechanics after 3 different silicone arthroplasties. J Hand Surg. 2004, 29: 796-803. 182  183   184 Page 10 of 13  Figure legends 185 Figure 1 – different designs of silicone single-piece finger implants.  Top NeuFlex, middle 186 Sutter/Avanta, bottom Swanson.  In all cases the distal stem is to the right.   187 Figure 2 A (top left) – An un-fractured NeuFlex explant (explant 15); B (top right) – A NeuFlex explant 188 (explant 28) showing fracture at the hinge; C (bottom left) – A NeuFlex explant (explant 24) showing 189 fracture at the junction of the distal stem and hinge; D (bottom right) – A NeuFlex explant (explant 13) 190 showing fracture at both the hinge and at the junction of the hinge and the distal stem 191 Figure 3 – Two NeuFlex explants (explant 18 above and explant 13 below) showing discolouration.  192 Note that discolouration of explant 13 has occurred to the entire material and not just the outer 193 surfaces.   194  195  196 Page 11 of 13   197  198  199  200 Page 12 of 13   201 Explant Finger Explant Size Patient age at revision Time in situ (months) Diagnosis Position of fracture 1 Index 30 43 36 RA Hinge and distal stem 2 Little 10 43 36 RA Hinge 3 Middle 30 43 36 RA Hinge 4 Index 40 58 63 RA Distal stem 5 Middle 40 58 63 RA Distal stem 6 Ring 30 58 63 RA Distal stem 7 Little 20 58 63 RA Distal stem 8 Index 30 78 54 RA Distal stem 9 Middle 40 78 54 RA Distal stem 10 Ring 20 78 54 RA No fracture 11 Little 10 78 54 RA Hinge 12 Ring 20 57 78 RA Hinge and distal stem 13 Little 10 57 78 RA Hinge and distal stem 14 Index 30 58 63 RA No fracture 15 Ring 20 58 63 RA No fracture 16 Little 20 58 63 RA No fracture 17 Middle 40 58 63 RA Hinge 18 Middle 40 84 18 OA Distal stem 19 Index 40 84 18 OA No fracture 20 Little 10 73 24 RA No fracture 21 --- 40 70 120 RA Hinge Page 13 of 13  22 Little 10 62 18 RA Hinge 23 Index 40 81 31 RA Distal stem 24 Middle 40 81 31 RA Distal stem 25 Little 20 81 31 RA No fracture 26 Index 30 56 84 RA Hinge 27 Middle 30 56 84 RA Hinge 28 Ring 20 56 84 RA Hinge 29 Little 0 56 84 RA Hinge 30 Index 30 49 6 RA Hinge Table 1 – table of data regarding NeuFlex MP joint explants.  RA = rheumatoid arthritis; OA = 202 osteoarthritis. 203  204 

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Sites of fractures in explanted NeuFlex\uae silicone metacarpophalangeal joint prostheses

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Sites of fractures in explanted NeuFlex\uae silicone metacarpophalangeal joint prostheses

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