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Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study
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Original article
Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study Yuki Kikuchi a , Kotaro Sato a,∗ , Yoshikuni Mimata a , Kenya Murakami a , Gaku Takahashi b , Minoru Doita a a b
Department of Orthopaedic Surgery, Iwate Medical University, 1-1-1, Idaidori, Yahaba-cho, Shiwa-gun, 028-3694 Iwate, Japan Department of Critical Care Medicine, Iwate Medical University, 1-1-1, Idaidori, Yahaba-cho, Shiwa-gun, 028-3694 Iwate, Japan
a r t i c l e
i n f o
Article history: Received 8 March 2019 Accepted 17 December 2019 Available online xxx Keywords: Distal radius fracture Volar locking plate Flexor pollicis longus Tendon rupture Anatomic study
a b s t r a c t Background: The volar locking plate (VLP) system provides stable fixation and is widely used for distal radius fractures. Studies have shown that irritation of the implant prominence is a risk factor for flexor tendon rupture, especially of the flexor pollicis longus (FPL). Contact between VLPs and flexor tendons should be avoided. We aimed to investigate the ulnar facet locking screw locations of various VLPs placed without FPL tendon contact in cadaver wrists. Hypothesis: We hypothesized that ulnar facet locking screws would be in the vicinity of the subchondral bone when the plate is placed in the most distal position without FPL tendon contact. Materials and methods: The study assessed two variable-angles and four fixed locking plates. We placed each plate in six different cadavers, resulting in 36 different plate-cadaver combinations. Plates were placed in the most distal position without FPL tendon contact. We drilled the most ulnar hole (hole A) and the second ulnar hole (hole B) of the distal row. All drilling procedures were performed using a specific jig for each fixed locking plate. For variable-angle locking plates, we drilled with a fixed jig for each plate. We obtained lateral radiographs when the drill penetrated the dorsal cortex and measured the distance between the drill and the articular surface. Results: With regard to hole A, the mean distances between the drill and the center of the articular surface were 2.6–5.2 mm for the four fixed locking plates and 4.9–5.6 mm for the two variable-angle locking plates. With regard to hole B, the mean distances between the drill and the center of the articular surface were 3.8–5.9 mm for the four fixed locking plates and 5.5–5.9 mm for the two variable-angle locking plates. Discussion: When clinicians place a VLP without FPL tendon contact, the distance between the ulnar facet screws and the center of the articular surface is over 3 mm in most cases. Surgeons should select variable-angle drilling for strong articular support when using variable-angle locking plates. Level of evidence: III, diagnostic Level. © 2019 Elsevier Masson SAS. All rights reserved.
1. Introduction The volar locking plate (VLP) has been widely used in patients with unstable distal radius fractures and many clinical studies have warned about implant-related tendon rupture, especially of the flexor pollicis longus (FPL) [1–6]. Previous studies have shown that irritation of the implant prominence is a risk factor for tendon rupture [4,5]. Therefore, surgeons should try to avoid contact between VLPs and flexor tendons
∗ Corresponding author at: Department of Orthopaedic Surgery, Iwate Medical University, 1-1-1, Idaidori, Yahaba-cho, Shiwa-gun, 028-3694 Iwate, Japan. E-mail address: [email protected] (K. Sato).
during surgery. As an index of FPL rupture-related VLP surgery, the volar ridge of the distal radius, known as the watershed line, is widely accepted as the distal limit of VLP placement [1,4,5]. In the last decade, studies have reported modified plate designs, and the screws may provide good subchondral support [7–10]. However, the most appropriate attachment of the plate varies, and the contour of the volar distal radius shows individual differences. To date, biomechanical studies have not considered tendon rupture associated with distal setting of the VLP [7,11–16]. We conducted an anatomical study to investigate the distal limit for safe positioning of commercially available VLPs. We hypothesized that ulnar facet locking screws would be in the vicinity of the subchondral bone when the plate is placed in the most distal position without FPL tendon contact.
https://doi.org/10.1016/j.otsr.2019.12.002 1877-0568/© 2019 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002
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2. Materials and methods The study considered six widely used VLPs with current designs (two variable-angle locking plates and four fixed locking plates). The variable-angle locking plates were VariAx (Stryker; Kalamazoo, MI, USA; launched in 2010) and Variable-angle LCP two-column volar distal radius Plate 2.4 (VA-TCP; Depuy Synthes, West Chester, PA, USA; launched in 2009), while the fixed locking plates were HYBRIX (Mizuho, Tokyo, Japan; launched in 2015), MODE (JAPAN MEDICAL DINAMIC MARKETING INC, MDM, Tokyo, Japan; launched in 2012), Acu-Loc2P (Acumed, Hillsboro, OR, USA; launched in 2011), and DVR (Zimmer Biomet, Warsaw, IN, USA; launched in 2000) (Fig. 1). We performed experiments using nine unpaired human cadaveric right upper limbs (7 male and 2 female specimens; age range, 67–89 years) without severe degenerative changes or wrist fractures. The mean width of the distal radius was 31.2 ± 1.67 mm (range, 29.4–33.6 mm). We fixed all specimens with 10% formalin and preserved them in 50% alcohol for 6 months. The ethics committee at our institution approved this study (No. H28-90). For cadaver preparation, we removed the skin and soft subcutaneous tissue on the forearm to expose the flexor muscle group. We maintained the FPL muscle origin in its anatomical position during the dissection. To confirm the relationship between the FPL and plate prominence, all flexor muscles were cut, except for the FPL. This process was mandatory because if other flexors were retained, it would not be possible to confirm contact between the FPL tendon and the plate. The pronator quadratus (PQ) was removed, as it is detached from the radial border during VLP surgery. Other soft tissues, such as ligaments, joint capsules, and fat tissue, were preserved. Although we used nine specimens, each plate was placed in six different cadavers to avoid loosening of the plates, resulting in 36 different plate-cadaver combinations. To minimize bias associated with the order of fixation, the plate and cadaver were randomly selected. We used the smallest size of each plate to exclude selection bias. Such sizing is common in clinical practice and is appropriate for most Japanese specimens. We placed the plate in the most distal position without FPL tendon contact and with the best fit in the radial-ulnar position (Fig. 2a and b). The second author, an experienced hand specialist, performed all plate placements under direct visualization [17]. First, the plate was fixed with a cortical screw in the oval hole, sufficiently distally to make contact with the FPL tendon, and then was slightly moved sufficiently proximally to relieve the contact during 30◦ wrist extension [18]. Finally, the plate was fixed with a locking screw. Thereafter, the first author confirmed that the plate was not in contact with the FPL tendon and that there was no room to position the plate more distally. These procedures were similarly performed in all formalinfixed specimens. We fixed the plate to the radial cortex thorough
the same cortical screw hole, when fixation was maintained. When the plate could not obtain rigid fixation because of screw loosening, we used another hole and achieved secure fixation. For the measurement, we performed drilling under fluoroscopic guidance. A lateral view was obtained by confirming projection of the pisiform over the distal portion of the scaphoid [4]. Thereafter, the wrist was lifted and an inclined lateral view was obtained for optimal evaluation of the articular surface [19]. A lateral radiograph was taken when the drill was closest to the articular surface. The second author performed all drilling procedures. A specific jig was used for each fixed locking plate. For variable-angle locking plates, drilling was performed with a fixed jig for each plate. As we could insert the drill more accurately and avoid misdirection when compared with screw insertion using a screwdriver, we investigated radiographs of the drill rather than those of the screw. Analyses involved the most ulnar hole and the second ulnar hole of the distal row because these screw holes were used to fix the volar lunate facet, which is most important for supporting longitudinal load [20]. The most ulnar hole of the distal row was considered hole A, and the second ulnar hole was considered hole B (Fig. 3). Hole B was the center hole of the distal row for the VariAx, HYBRIX, MODE, and DVR plates. 3. Measurements On the lateral radiographs, we marked the center of the articular surface, the dorsal halfway point between the center and dorsal edge, and the volar halfway point between the center and volar edge. Thereafter, we drew a line perpendicular to the drill at each point. We then measured the distances between the drill and the center, dorsal halfway point, and volar halfway point as the dc, dd, and dv values, respectively (Fig. 4). All measurements were adjusted using the radiolucent scale on the radiographs. The first author measured the radiographic parameters using a DICOM viewer (Yakami DICOM Tools, Kyoto University, Kyoto, Japan). The mean value of two measurements was used as the final value. Statistical analysis included one-way analysis of variance with the Tukey test. P < 0.05 was considered statistically significant. 4. Results 4.1. Hole A The mean dc values (value ± standard deviation) for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 5.6 ± 1.06 mm, 4.9 ± 0.68 mm, 2.6 ± 1.34 mm, 3.8 ± 1.85 mm, 4.1 ± 1.37 mm, and 5.2 ± 1.51 mm, respectively (Fig. 5). The mean dd values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 6.2 ± 1.32 mm, 4.9 ± 1.19 mm, 3.0 ± 1.33 mm, 4.6 ± 1.77 mm,
Fig. 1. The six plates used in this study. A. VariAx. B. VA-TCP. C. HYBRIX. D. MODE. E. Acu-Loc2P. F. DVR.
Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002
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Fig. 2. Plate placement: a: plate placement viewed from the front. We excised the flexors, except for the flexor pollicis longus (FPL); b: plate placement viewed from the lateral side. We fixed the plate to the cadaver in the most distal position without FPL contact.
Fig. 3. Holes A and B. Hole A is the most ulnar hole of the distal row, and hole B is the second ulnar hole of the distal row.
4.8 ± 1.33 mm, and 6.4 ± 1.70 mm, respectively. The mean dv values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 7.1 ± 0.74 mm, 7.0 ± 0.83 mm, 4.3 ± 1.60 mm, 5.5 ± 1.89 mm, 5.6 ± 1.27 mm, and 6.1 ± 1.59 mm, respectively. The dc value for the HYBRIX was significantly smaller than that for the VariAx (p < 0.05), while its dd values were significantly smaller than those for the VariAx (p < 0.05) and DVR (p < 0.05). The dv values for the HYBRIX were significantly smaller than those for the VariAx (p < 0.05) and VA-TCP (p < 0.05).
(Fig. 6). The mean dd values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 5.9 ± 1.45 mm, 5.4 ± 0.98 mm, 4.5 ± 1.69 mm, 4.1 ± 1.72 mm, 4.3 ± 1.30 mm, and 6.5 ± 2.25 mm, respectively. The mean dv values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 8.2 ± 0.60 mm, 8.0 ± 1.02 mm, 5.6 ± 1.35 mm, 5.6 ± 1.67 mm, 5.1 ± 1.33 mm, and 7.64 ± 2.42 mm, respectively. The dv values for the Acu-Loc2P were significantly smaller than those for the VariAx (p < 0.05).
4.2. Hole B
5. Discussion
The mean dc values for the VariAx, VA-TCP, HYBRIX, MODE, AcuLoc2P, and DVR were 5.9 ± 1.09 mm, 5.5 ± 0.68 mm, 3.8 ± 1.53 mm, 3.8 ± 1.84 mm, 3.6 ± 1.39 mm, and 5.9 ± 2.19 mm, respectively
Most of the plates showed dc, dd, and dv values of more than 3 mm. These results indicate that when clinicians use fixed locking plates for comminution fractures and need to hold them directly
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Fig. 4. A line is drawn perpendicular to the drill from the articular surface to the drill. We measured the distances between the drill and the center, dorsal halfway point, and volar halfway point as the dc, dd, and dv values, respectively. de: dorsal edge; ve: volar edge.
under the articular surface, the plates need to be placed distally and would come into contact with the FPL tendon [9,21]. The variableangle locking system of the VariAx and VA-TCP showed larger values. When using variable-angle locking plates, surgeons should select variable-angle drilling for strong fixation. Screws should be inserted in a more fragment-specific manner and more subchondrally. Kawasaki et al. reported the usefulness of the double-tiered subchondral support procedure with variable angle-locking plates for AO-type C3 fractures [10]. In their method, distal screws supported the central subchondral bone and proximal screws
supported the dorsal subchondral bone; therefore, this method can provide relatively wide articular stability. Although a variableangle locking system can efficiently change the screw location at the dorsal side, the location does not significantly change at the volar side [9,22]. Many severe fractures with lunate facet fragments or volar sharing fractures need to be stabilized at the volar articular surface [21,23–25]. When secure subchondral fixation of the volar fragments is needed, careful consideration is necessary before use of the VariAx and VA-TCP, because distal placement in such a situation could result in high pressure on the FPL tendon [9,21]. The variable-angle LCP volar rim distal radius plate (Depuy Synthes, West Chester, PA, USA) provides an adequate buttress of the lunate facet fragments. However, implant removal is necessary if tendon irritation or interference with wrist motion develops [26,27]. The value for the HYBRIX was smaller than all the values for the VariAx, the dd value for the DVR, and the dv value for the VA-TCP in hole A. Therefore, surgeons may obtain stronger subchondral support with the HYBRIX than with these three plates when attempting to avoid FPL tendon contact. Throughout the measurement, the values for the HYBRIX, MODE, and Acu-Loc2P were smaller than the values for the other three plates; however, the differences were not significant. The smaller values for the HYBRIX, MODE, and AcuLoc2P might be associated with the introduction of these plates after the year 2011 and the fact that they were more recently developed than the other three models. Recent commercially available VLPs are designed to fit the morphology of the distal radius. Many of these plates have a medial extension to fix the lunate facet or a lateral extension to support the lateral rim and radial process [8]. The present study had several limitations. First, the study included small sample sizes of plates and cadavers. Additionally, we used each specimen several times; therefore, the order of plate placement could affect the fixing force associated with plate loosening. However, adjustment of the placement order might have minimized this problem. Second, we used formalin-fixed specimens, which might involve alteration of the muscles and soft tissues’ condition. Additionally, it was not possible to evaluate dynamic problems, such as rubbing of the tendon over the plate with wrist and thumb motion. Matityahu et al. studied contact pressure between fresh frozen cadavers and VLP using pressure sensors [28]. Contact pressure between the FPL and plate showed a 7% increase in wrist extension from 25 to 60◦ in their study. Although we considered only the situation involving wrist extension of 30◦ , the use of fresh cadavers as well as measurement instruments
Fig. 5. Results for hole A. The dc, dd, and dv values indicate the distances between the drill and the center, dorsal halfway point, and volar halfway point, respectively. The upper whisker indicates the maximum value and the lower whisker indicates the minimum value. * p < 0.05.
Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002
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Fig. 6. Results for hole B. * p < 0.05.
would increase the reliability of our results. Third, we excised all flexor muscles around the FPL because it was necessary to confirm the relation between the FPL tendon and plate. This would lead to a change in the position of the FPL and the circumstances might differ from that of patients with normal muscle. Also, we removed the PQ in this study. Ultrasonographic studies showed that the PQ acts as a protective sleeve to prevent attrition of the flexor tendons [29,30]. These reports suggested that the PQ elevates flexor tendons and keeps them away from the plate, meaning that repair of the PQ would be one of the ways to prevent tendon rupture [29,30]. We believed that assessing VLP placement and PQ repair might be meaningful. However, the quality of the repaired PQ would deteriorate as the number of plates placed increased. In addition, repair of the PQ might have potentially lead to variability in the measurements performed in this experimental setting. For this reason, we removed the PQ to obtain accurate measurements in this study. Fourth, all specimens were normal without wrist fractures. Restoration of the volar tilt would affect the results, and this cannot be assessed in a non-fracture model. Fifth, although we placed the plate with the best fit in the radial-ulnar position, the plate may not have been placed absolutely straight on the radius because of the individual differences in the distal radius. This problem might have affected the measurements. Sixth, we analyzed radiographs of the drill instead of those of the screw. The diameter of the screw is greater than that of the drill. Thus, each measurement might be slightly smaller than the measurement of the screw. Finally, we used only six plate designs. Presently, different plates are available depending on the condition of the fracture site. The strength of this study was that we were able to verify the distance between the drill and articular surface in lateral radiographs of VLPs placed without FPL contact, which is usually difficult in clinical settings. In conclusion, the distance between the ulnar facet screws and the articular surface is over 3 mm in most cases when clinicians attempt to place a VLP without FPL tendon contact. When clinicians need to place the locking screw directly under the articular surface, the plate would come into contact with the FPL tendon. Surgeons should select variable-angle drilling for strong articular support when using variable-angle locking plates.
Disclosure of interest The authors declare that they have no competing interest.
Funding sources None. Author contribution Conception and the design of the study: Yoshikuni Mimata, Kenya Murakami, and Minoru Doita. Acquisition of the data and drafting of the manuscript: Kotaro Sato. Analysis the data: Gaku Takahashi. Acknowledgment The authors wish to thank associate professor Jun Yan from the Department of Anatomy of Iwate Medial University for his technical assistance and Professors Jiro Hitomi and Professors Akira Fujimura for their continuous support of this study. References [1] Orbay JL, Touhami A. Current concepts in volar fixed-angle fixation of unstable distal radius fractures. Clin Orthop Relat Res 2006;445:58–67. [2] Cross AW, Schmidt CC. Flexor tendon injuries following locked volar plating of distal radius fractures. J Hand Surg [Am] 2008;33:164–7. [3] White BD, Nydick JA, Karsky D, Williams BD, Hess AV, Stone JD. Incidence and clinical outcomes of tendon rupture following distal radius fracture. J Hand Surg [Am] 2012;37:2035–40. [4] Soong M, Earp BE, Bishop G, Leung A, Blazar P. Volar locking plate implant prominence and flexor tendon rupture. J Bone Joint Surg Am 2011;93:328–35. [5] Kitay A, Swanstrom M, Schreiber JJ, et al. Volar plate position and flexor tendon rupture following distal radius fracture fixation. J Hand Surg [Am] 2013;38:1091–6. [6] Obert L, Rey PB, Uhring J, et al. Fixation of distal radius fractures in adults: a review. Orthop Traumatol Surg Res 2013;99:216–34. [7] Stanbury SJ, Salo A, Elfar JC. Biomechanical analysis of a volar variable-angle locking plate: the effect of capturing a distal radial styloid fragment. J Hand Surg [Am] 2012;37:2488–94. [8] Limthongthang R, Bachoura A, Jacoby SM, Osterman AL. Distal radius volar locking plate design and associated vulnerability of the flexor pollicis longus. J Hand Surg [Am] 2014;39:852–60. [9] Inagaki K, Kawasaki K. Distal radius fractures-Design of locking mechanism in plate system and recent surgical procedures. J Orthop Sci 2016;21:258–62. [10] Kawasaki K, Nemoto T, Inagaki K, Tomita K, Ueno Y. Variable-angle locking plate with or without double-tiered subchondral support procedure in the treatment of intra-articular distal radius fracture. J Orthop Traumatol 2014;15:271–4. [11] Mehling I, Müller LP, Delinsky K, Mehler D, Burkhart KJ, Rommens PM. Number and locations of screw fixation for volar fixed-angle plating of distal radius fractures: biomechanical study. J Hand Surg [Am] 2010;35:885–91.
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[22] Lee SK, Chun YS, Shin HM, Kim SM, Choy WS. Double-tiered subchondral support fixation with optimal distal dorsal cortical distance using a variable-angle volar locking-plate system for distal radius fracture in the elderly. Orthop Traumatol Surg Res 2018;104:883–91. [23] Beck JD, Harness NG, Spencer HT. Volar plate fixation failure for volar shearing distal radius fractures with small lunate facet fragments. J Hand Surg [Am] 2014;39:670–8. [24] O’Shaughnessy MA, Shin AY, Kakar S. Volar marginal rim fracture fixation with volar fragment-specific hook plate fixation. J Hand Surg [Am] 2015;40:1563–70. [25] O’Shaughnessy MA, Shin AY, Kakar S. Stabilization of volar ulnar rim fractures of the distal radius: current techniques and review of the literature. J Wrist Surg 2016;5:113–9. [26] Kachooei AR, Tarabochia M, Jupiter JB. Distal radius volar rim fracture fixation using depuy-synthes volar rim plate. J Wrist Surg 2016;5:2–8. [27] Goorens CK, Geeurickx S, Wernaers P, Staelens B, Scheerlinck T, Goubau J. Midterm follow-up of treating volar marginal rim fractures with variable angle LCP volar rim distal radius plates. J Hand Surg Asian Pac Vol 2017;22: 184–7. [28] Matityahu AM, Lapalme SN, Seth A, Marmor MT, Buckley JM, Lattanza LL. How placement affects force and contact pressure between a volar plate of the distal radius and the flexor pollicus longus tendon: a biomechanical investigation. J Hand Surg Eur Vol 2013;38:144–50. [29] Goorens CK, Van Royen K, Grijseels S, et al. Ultrasonographic evaluation of the distance between the flexor pollicis longus tendon and volar prominence of the plate as a function of volar plate positioning and pronator quadratus repair — A cadaver study. Hand Surg Rehabil 2018;37:171–4. [30] Walch A, Erhard L, Vogels J, Pozzetto M, Gibert N, Locquet V. Ultrasound evaluation of the protector role of the pronator quadratus suture in volar plating. J Ultrasound Med 2019;38:2785–91.
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Original article
Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study Yuki Kikuchi a , Kotaro Sato a,∗ , Yoshikuni Mimata a , Kenya Murakami a , Gaku Takahashi b , Minoru Doita a a b
Department of Orthopaedic Surgery, Iwate Medical University, 1-1-1, Idaidori, Yahaba-cho, Shiwa-gun, 028-3694 Iwate, Japan Department of Critical Care Medicine, Iwate Medical University, 1-1-1, Idaidori, Yahaba-cho, Shiwa-gun, 028-3694 Iwate, Japan
a r t i c l e
i n f o
Article history: Received 8 March 2019 Accepted 17 December 2019 Available online xxx Keywords: Distal radius fracture Volar locking plate Flexor pollicis longus Tendon rupture Anatomic study
a b s t r a c t Background: The volar locking plate (VLP) system provides stable fixation and is widely used for distal radius fractures. Studies have shown that irritation of the implant prominence is a risk factor for flexor tendon rupture, especially of the flexor pollicis longus (FPL). Contact between VLPs and flexor tendons should be avoided. We aimed to investigate the ulnar facet locking screw locations of various VLPs placed without FPL tendon contact in cadaver wrists. Hypothesis: We hypothesized that ulnar facet locking screws would be in the vicinity of the subchondral bone when the plate is placed in the most distal position without FPL tendon contact. Materials and methods: The study assessed two variable-angles and four fixed locking plates. We placed each plate in six different cadavers, resulting in 36 different plate-cadaver combinations. Plates were placed in the most distal position without FPL tendon contact. We drilled the most ulnar hole (hole A) and the second ulnar hole (hole B) of the distal row. All drilling procedures were performed using a specific jig for each fixed locking plate. For variable-angle locking plates, we drilled with a fixed jig for each plate. We obtained lateral radiographs when the drill penetrated the dorsal cortex and measured the distance between the drill and the articular surface. Results: With regard to hole A, the mean distances between the drill and the center of the articular surface were 2.6–5.2 mm for the four fixed locking plates and 4.9–5.6 mm for the two variable-angle locking plates. With regard to hole B, the mean distances between the drill and the center of the articular surface were 3.8–5.9 mm for the four fixed locking plates and 5.5–5.9 mm for the two variable-angle locking plates. Discussion: When clinicians place a VLP without FPL tendon contact, the distance between the ulnar facet screws and the center of the articular surface is over 3 mm in most cases. Surgeons should select variable-angle drilling for strong articular support when using variable-angle locking plates. Level of evidence: III, diagnostic Level. © 2019 Elsevier Masson SAS. All rights reserved.
1. Introduction The volar locking plate (VLP) has been widely used in patients with unstable distal radius fractures and many clinical studies have warned about implant-related tendon rupture, especially of the flexor pollicis longus (FPL) [1–6]. Previous studies have shown that irritation of the implant prominence is a risk factor for tendon rupture [4,5]. Therefore, surgeons should try to avoid contact between VLPs and flexor tendons
∗ Corresponding author at: Department of Orthopaedic Surgery, Iwate Medical University, 1-1-1, Idaidori, Yahaba-cho, Shiwa-gun, 028-3694 Iwate, Japan. E-mail address: [email protected] (K. Sato).
during surgery. As an index of FPL rupture-related VLP surgery, the volar ridge of the distal radius, known as the watershed line, is widely accepted as the distal limit of VLP placement [1,4,5]. In the last decade, studies have reported modified plate designs, and the screws may provide good subchondral support [7–10]. However, the most appropriate attachment of the plate varies, and the contour of the volar distal radius shows individual differences. To date, biomechanical studies have not considered tendon rupture associated with distal setting of the VLP [7,11–16]. We conducted an anatomical study to investigate the distal limit for safe positioning of commercially available VLPs. We hypothesized that ulnar facet locking screws would be in the vicinity of the subchondral bone when the plate is placed in the most distal position without FPL tendon contact.
https://doi.org/10.1016/j.otsr.2019.12.002 1877-0568/© 2019 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002
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2. Materials and methods The study considered six widely used VLPs with current designs (two variable-angle locking plates and four fixed locking plates). The variable-angle locking plates were VariAx (Stryker; Kalamazoo, MI, USA; launched in 2010) and Variable-angle LCP two-column volar distal radius Plate 2.4 (VA-TCP; Depuy Synthes, West Chester, PA, USA; launched in 2009), while the fixed locking plates were HYBRIX (Mizuho, Tokyo, Japan; launched in 2015), MODE (JAPAN MEDICAL DINAMIC MARKETING INC, MDM, Tokyo, Japan; launched in 2012), Acu-Loc2P (Acumed, Hillsboro, OR, USA; launched in 2011), and DVR (Zimmer Biomet, Warsaw, IN, USA; launched in 2000) (Fig. 1). We performed experiments using nine unpaired human cadaveric right upper limbs (7 male and 2 female specimens; age range, 67–89 years) without severe degenerative changes or wrist fractures. The mean width of the distal radius was 31.2 ± 1.67 mm (range, 29.4–33.6 mm). We fixed all specimens with 10% formalin and preserved them in 50% alcohol for 6 months. The ethics committee at our institution approved this study (No. H28-90). For cadaver preparation, we removed the skin and soft subcutaneous tissue on the forearm to expose the flexor muscle group. We maintained the FPL muscle origin in its anatomical position during the dissection. To confirm the relationship between the FPL and plate prominence, all flexor muscles were cut, except for the FPL. This process was mandatory because if other flexors were retained, it would not be possible to confirm contact between the FPL tendon and the plate. The pronator quadratus (PQ) was removed, as it is detached from the radial border during VLP surgery. Other soft tissues, such as ligaments, joint capsules, and fat tissue, were preserved. Although we used nine specimens, each plate was placed in six different cadavers to avoid loosening of the plates, resulting in 36 different plate-cadaver combinations. To minimize bias associated with the order of fixation, the plate and cadaver were randomly selected. We used the smallest size of each plate to exclude selection bias. Such sizing is common in clinical practice and is appropriate for most Japanese specimens. We placed the plate in the most distal position without FPL tendon contact and with the best fit in the radial-ulnar position (Fig. 2a and b). The second author, an experienced hand specialist, performed all plate placements under direct visualization [17]. First, the plate was fixed with a cortical screw in the oval hole, sufficiently distally to make contact with the FPL tendon, and then was slightly moved sufficiently proximally to relieve the contact during 30◦ wrist extension [18]. Finally, the plate was fixed with a locking screw. Thereafter, the first author confirmed that the plate was not in contact with the FPL tendon and that there was no room to position the plate more distally. These procedures were similarly performed in all formalinfixed specimens. We fixed the plate to the radial cortex thorough
the same cortical screw hole, when fixation was maintained. When the plate could not obtain rigid fixation because of screw loosening, we used another hole and achieved secure fixation. For the measurement, we performed drilling under fluoroscopic guidance. A lateral view was obtained by confirming projection of the pisiform over the distal portion of the scaphoid [4]. Thereafter, the wrist was lifted and an inclined lateral view was obtained for optimal evaluation of the articular surface [19]. A lateral radiograph was taken when the drill was closest to the articular surface. The second author performed all drilling procedures. A specific jig was used for each fixed locking plate. For variable-angle locking plates, drilling was performed with a fixed jig for each plate. As we could insert the drill more accurately and avoid misdirection when compared with screw insertion using a screwdriver, we investigated radiographs of the drill rather than those of the screw. Analyses involved the most ulnar hole and the second ulnar hole of the distal row because these screw holes were used to fix the volar lunate facet, which is most important for supporting longitudinal load [20]. The most ulnar hole of the distal row was considered hole A, and the second ulnar hole was considered hole B (Fig. 3). Hole B was the center hole of the distal row for the VariAx, HYBRIX, MODE, and DVR plates. 3. Measurements On the lateral radiographs, we marked the center of the articular surface, the dorsal halfway point between the center and dorsal edge, and the volar halfway point between the center and volar edge. Thereafter, we drew a line perpendicular to the drill at each point. We then measured the distances between the drill and the center, dorsal halfway point, and volar halfway point as the dc, dd, and dv values, respectively (Fig. 4). All measurements were adjusted using the radiolucent scale on the radiographs. The first author measured the radiographic parameters using a DICOM viewer (Yakami DICOM Tools, Kyoto University, Kyoto, Japan). The mean value of two measurements was used as the final value. Statistical analysis included one-way analysis of variance with the Tukey test. P < 0.05 was considered statistically significant. 4. Results 4.1. Hole A The mean dc values (value ± standard deviation) for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 5.6 ± 1.06 mm, 4.9 ± 0.68 mm, 2.6 ± 1.34 mm, 3.8 ± 1.85 mm, 4.1 ± 1.37 mm, and 5.2 ± 1.51 mm, respectively (Fig. 5). The mean dd values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 6.2 ± 1.32 mm, 4.9 ± 1.19 mm, 3.0 ± 1.33 mm, 4.6 ± 1.77 mm,
Fig. 1. The six plates used in this study. A. VariAx. B. VA-TCP. C. HYBRIX. D. MODE. E. Acu-Loc2P. F. DVR.
Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002
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Fig. 2. Plate placement: a: plate placement viewed from the front. We excised the flexors, except for the flexor pollicis longus (FPL); b: plate placement viewed from the lateral side. We fixed the plate to the cadaver in the most distal position without FPL contact.
Fig. 3. Holes A and B. Hole A is the most ulnar hole of the distal row, and hole B is the second ulnar hole of the distal row.
4.8 ± 1.33 mm, and 6.4 ± 1.70 mm, respectively. The mean dv values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 7.1 ± 0.74 mm, 7.0 ± 0.83 mm, 4.3 ± 1.60 mm, 5.5 ± 1.89 mm, 5.6 ± 1.27 mm, and 6.1 ± 1.59 mm, respectively. The dc value for the HYBRIX was significantly smaller than that for the VariAx (p < 0.05), while its dd values were significantly smaller than those for the VariAx (p < 0.05) and DVR (p < 0.05). The dv values for the HYBRIX were significantly smaller than those for the VariAx (p < 0.05) and VA-TCP (p < 0.05).
(Fig. 6). The mean dd values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 5.9 ± 1.45 mm, 5.4 ± 0.98 mm, 4.5 ± 1.69 mm, 4.1 ± 1.72 mm, 4.3 ± 1.30 mm, and 6.5 ± 2.25 mm, respectively. The mean dv values for the VariAx, VA-TCP, HYBRIX, MODE, Acu-Loc2P, and DVR were 8.2 ± 0.60 mm, 8.0 ± 1.02 mm, 5.6 ± 1.35 mm, 5.6 ± 1.67 mm, 5.1 ± 1.33 mm, and 7.64 ± 2.42 mm, respectively. The dv values for the Acu-Loc2P were significantly smaller than those for the VariAx (p < 0.05).
4.2. Hole B
5. Discussion
The mean dc values for the VariAx, VA-TCP, HYBRIX, MODE, AcuLoc2P, and DVR were 5.9 ± 1.09 mm, 5.5 ± 0.68 mm, 3.8 ± 1.53 mm, 3.8 ± 1.84 mm, 3.6 ± 1.39 mm, and 5.9 ± 2.19 mm, respectively
Most of the plates showed dc, dd, and dv values of more than 3 mm. These results indicate that when clinicians use fixed locking plates for comminution fractures and need to hold them directly
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Fig. 4. A line is drawn perpendicular to the drill from the articular surface to the drill. We measured the distances between the drill and the center, dorsal halfway point, and volar halfway point as the dc, dd, and dv values, respectively. de: dorsal edge; ve: volar edge.
under the articular surface, the plates need to be placed distally and would come into contact with the FPL tendon [9,21]. The variableangle locking system of the VariAx and VA-TCP showed larger values. When using variable-angle locking plates, surgeons should select variable-angle drilling for strong fixation. Screws should be inserted in a more fragment-specific manner and more subchondrally. Kawasaki et al. reported the usefulness of the double-tiered subchondral support procedure with variable angle-locking plates for AO-type C3 fractures [10]. In their method, distal screws supported the central subchondral bone and proximal screws
supported the dorsal subchondral bone; therefore, this method can provide relatively wide articular stability. Although a variableangle locking system can efficiently change the screw location at the dorsal side, the location does not significantly change at the volar side [9,22]. Many severe fractures with lunate facet fragments or volar sharing fractures need to be stabilized at the volar articular surface [21,23–25]. When secure subchondral fixation of the volar fragments is needed, careful consideration is necessary before use of the VariAx and VA-TCP, because distal placement in such a situation could result in high pressure on the FPL tendon [9,21]. The variable-angle LCP volar rim distal radius plate (Depuy Synthes, West Chester, PA, USA) provides an adequate buttress of the lunate facet fragments. However, implant removal is necessary if tendon irritation or interference with wrist motion develops [26,27]. The value for the HYBRIX was smaller than all the values for the VariAx, the dd value for the DVR, and the dv value for the VA-TCP in hole A. Therefore, surgeons may obtain stronger subchondral support with the HYBRIX than with these three plates when attempting to avoid FPL tendon contact. Throughout the measurement, the values for the HYBRIX, MODE, and Acu-Loc2P were smaller than the values for the other three plates; however, the differences were not significant. The smaller values for the HYBRIX, MODE, and AcuLoc2P might be associated with the introduction of these plates after the year 2011 and the fact that they were more recently developed than the other three models. Recent commercially available VLPs are designed to fit the morphology of the distal radius. Many of these plates have a medial extension to fix the lunate facet or a lateral extension to support the lateral rim and radial process [8]. The present study had several limitations. First, the study included small sample sizes of plates and cadavers. Additionally, we used each specimen several times; therefore, the order of plate placement could affect the fixing force associated with plate loosening. However, adjustment of the placement order might have minimized this problem. Second, we used formalin-fixed specimens, which might involve alteration of the muscles and soft tissues’ condition. Additionally, it was not possible to evaluate dynamic problems, such as rubbing of the tendon over the plate with wrist and thumb motion. Matityahu et al. studied contact pressure between fresh frozen cadavers and VLP using pressure sensors [28]. Contact pressure between the FPL and plate showed a 7% increase in wrist extension from 25 to 60◦ in their study. Although we considered only the situation involving wrist extension of 30◦ , the use of fresh cadavers as well as measurement instruments
Fig. 5. Results for hole A. The dc, dd, and dv values indicate the distances between the drill and the center, dorsal halfway point, and volar halfway point, respectively. The upper whisker indicates the maximum value and the lower whisker indicates the minimum value. * p < 0.05.
Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002
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Fig. 6. Results for hole B. * p < 0.05.
would increase the reliability of our results. Third, we excised all flexor muscles around the FPL because it was necessary to confirm the relation between the FPL tendon and plate. This would lead to a change in the position of the FPL and the circumstances might differ from that of patients with normal muscle. Also, we removed the PQ in this study. Ultrasonographic studies showed that the PQ acts as a protective sleeve to prevent attrition of the flexor tendons [29,30]. These reports suggested that the PQ elevates flexor tendons and keeps them away from the plate, meaning that repair of the PQ would be one of the ways to prevent tendon rupture [29,30]. We believed that assessing VLP placement and PQ repair might be meaningful. However, the quality of the repaired PQ would deteriorate as the number of plates placed increased. In addition, repair of the PQ might have potentially lead to variability in the measurements performed in this experimental setting. For this reason, we removed the PQ to obtain accurate measurements in this study. Fourth, all specimens were normal without wrist fractures. Restoration of the volar tilt would affect the results, and this cannot be assessed in a non-fracture model. Fifth, although we placed the plate with the best fit in the radial-ulnar position, the plate may not have been placed absolutely straight on the radius because of the individual differences in the distal radius. This problem might have affected the measurements. Sixth, we analyzed radiographs of the drill instead of those of the screw. The diameter of the screw is greater than that of the drill. Thus, each measurement might be slightly smaller than the measurement of the screw. Finally, we used only six plate designs. Presently, different plates are available depending on the condition of the fracture site. The strength of this study was that we were able to verify the distance between the drill and articular surface in lateral radiographs of VLPs placed without FPL contact, which is usually difficult in clinical settings. In conclusion, the distance between the ulnar facet screws and the articular surface is over 3 mm in most cases when clinicians attempt to place a VLP without FPL tendon contact. When clinicians need to place the locking screw directly under the articular surface, the plate would come into contact with the FPL tendon. Surgeons should select variable-angle drilling for strong articular support when using variable-angle locking plates.
Disclosure of interest The authors declare that they have no competing interest.
Funding sources None. Author contribution Conception and the design of the study: Yoshikuni Mimata, Kenya Murakami, and Minoru Doita. Acquisition of the data and drafting of the manuscript: Kotaro Sato. Analysis the data: Gaku Takahashi. Acknowledgment The authors wish to thank associate professor Jun Yan from the Department of Anatomy of Iwate Medial University for his technical assistance and Professors Jiro Hitomi and Professors Akira Fujimura for their continuous support of this study. References [1] Orbay JL, Touhami A. Current concepts in volar fixed-angle fixation of unstable distal radius fractures. Clin Orthop Relat Res 2006;445:58–67. [2] Cross AW, Schmidt CC. Flexor tendon injuries following locked volar plating of distal radius fractures. J Hand Surg [Am] 2008;33:164–7. [3] White BD, Nydick JA, Karsky D, Williams BD, Hess AV, Stone JD. Incidence and clinical outcomes of tendon rupture following distal radius fracture. J Hand Surg [Am] 2012;37:2035–40. [4] Soong M, Earp BE, Bishop G, Leung A, Blazar P. Volar locking plate implant prominence and flexor tendon rupture. J Bone Joint Surg Am 2011;93:328–35. [5] Kitay A, Swanstrom M, Schreiber JJ, et al. Volar plate position and flexor tendon rupture following distal radius fracture fixation. J Hand Surg [Am] 2013;38:1091–6. [6] Obert L, Rey PB, Uhring J, et al. Fixation of distal radius fractures in adults: a review. Orthop Traumatol Surg Res 2013;99:216–34. [7] Stanbury SJ, Salo A, Elfar JC. Biomechanical analysis of a volar variable-angle locking plate: the effect of capturing a distal radial styloid fragment. J Hand Surg [Am] 2012;37:2488–94. [8] Limthongthang R, Bachoura A, Jacoby SM, Osterman AL. Distal radius volar locking plate design and associated vulnerability of the flexor pollicis longus. J Hand Surg [Am] 2014;39:852–60. [9] Inagaki K, Kawasaki K. Distal radius fractures-Design of locking mechanism in plate system and recent surgical procedures. J Orthop Sci 2016;21:258–62. [10] Kawasaki K, Nemoto T, Inagaki K, Tomita K, Ueno Y. Variable-angle locking plate with or without double-tiered subchondral support procedure in the treatment of intra-articular distal radius fracture. J Orthop Traumatol 2014;15:271–4. [11] Mehling I, Müller LP, Delinsky K, Mehler D, Burkhart KJ, Rommens PM. Number and locations of screw fixation for volar fixed-angle plating of distal radius fractures: biomechanical study. J Hand Surg [Am] 2010;35:885–91.
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Please cite this article in press as: Kikuchi Y, et al. Ulnar facet locking screw locations of volar locking plates placed without flexor pollicis longus tendon contact: A cadaver study. Orthop Traumatol Surg Res (2019), https://doi.org/10.1016/j.otsr.2019.12.002