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Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis
Journal of Orthopaedic Science xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original Article
Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis Pormes Suwanno a, 1, Shohei Omokawa b, *, 2, Yasuaki Nakanishi c, 2, Tsutomu Kira c, 2, Yasuhito Tanaka c, 2 a Department of Orthopaedic Surgery and Physical Medicine, Faculty of Medicine, Prince of Songkla University 15 Karnjanavanich Rd., Hat Yai, Songkhla, 90110, Thailand b Department of Hand Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan c Department of Orthopedic Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 June 2019 Received in revised form 7 November 2019 Accepted 17 December 2019 Available online xxx
Background: Of the anatomical reduction and fixation methods used to treat distal radius fracture, nonbridging external fixation has the advantage of enabling early wrist motion. The surgical technique relies on successful placement of the pin in individual fracture fragments. The present study aimed to identify the safe zone of pin insertion for a non-bridging external fixator into the distal radius that avoids metal impingement of extensor tendons. Methods: The width and length of the septal attachments of the extensor retinaculum were measured on axial MR images of 62 wrists. Results: The 2e3 septum was the widest and longest, with a width of 2e7 mm and a location 0e36 mm proximal to the wrist joint. The width of the 1e2 septum was 2e6 mm, and was widest at 10 mm proximal to the joint. The 1e2 septum was triangular-shaped, while the 2e3 septum was oval-shaped. The 3e4 and 4e5 septa had narrow attachments and were adequate for pin insertion (with a pin 1 e2 mm in width) at a position less than 8 mm proximal to the wrist. The width of the 1 R septum (radial to the 1st septum) was 2e6 mm at the radiovolar aspect of the wrist. Conclusions: There were two safe pin insertion sites; the first was safe at the distal aspect only (8e10 mm proximal to the wrist) and included the 1e2, 3e4, and 4e5 septa, while the second was safe from 0 mm to 32e38 mm proximal to the wrist and included the 1 R and the 2e3 septa. The 1 R septum had adequate size for use as a new pin insertion site that aligns in the internervous plane and has minimal risk of superficial radial nerve injury. © 2020 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction Distal radius fractures are common and have a significant impact on health and well-being, especially in paediatric and elderly people (approximately 25% and 18% of all fractures in paediatric and elderly populations, respectively [1]. Recently, many randomised controlled trials have compared functional outcomes after plating versus external fixators [2e6]. Advantages of plate fixation include early recovery (at 3e6 months) in wrist range of motion and grip strength, but these outcomes were not
* Corresponding author. E-mail address: [email protected] (S. Omokawa). 1 Fax: þ66 74 446825. 2 Fax: þ81 744 25 6449.
significantly different at 12 months postoperatively [3]. A longterm study with >5 years of follow-up found that the complication rate (including tendon irritation and rupture that required implant removal) was higher for plates (31%) than for external fixators (17%) [2]. Non-bridging external fixators provide early wrist motion [7] in the setting of anatomical reduction and adequate fixation, and the surgical technique relies on successful placement of the pin in individual fracture fragments. Small 3- to 4-mm threaded pins are used for fixation of distal radius fragments to restore radial height and volar tilt [5]. Wolfe et al. used two distal pins for simple or minimally comminuted extra-articular fractures and suggested that the second pin at the dorsal ulnar corner of the radius had to be placed between the fourth and fifth extensor compartments [8]. Pin placement in the septum of the extensor retinaculum potentially
https://doi.org/10.1016/j.jos.2019.12.005 0949-2658/© 2020 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
2
P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
reduces the risk of abnormal loading and friction to the tendons [9,10], which could help avoid tenosynovitis of the extensor mechanism during the postoperative course of non-bridging external fixation. Knowledge of anatomy in the wrist extensor retinaculum septa would be useful to determine the precise location of pin insertion, but there is no detailed guidance for pinning while taking into consideration the anatomy of the septa. Although Iwamoto et al. measured the size of septal attachment in a cadaveric study [11], advanced imaging technique in living subjects without prior surgery would provide more accurate measurements [12]. In the present study, we reviewed magnetic resonance (MR) images of the area of the distal radius to investigate mapping the septa of extensor tendons between compartments. The purpose of this study was to determine preferred locations and technique for pinning distal fragments using a market-available, non-bridging external fixator.
Then, the volar tilt angle of each scaphoid and lunate fossa, and sigmoid notch angle were measured using sagittal and axial MR images to guide adequate directions of pin insertion from the 2e3 and 4-5 septa. Three blinded examiners independently measured the narrowest width of the septum, the volar tilt angle of each scaphoid and lunate fossa, and the sigmoid notch angle. All observers repeated the measurements on all MR images after a period of 2 months or more from the initial measurements to decrease the recall bias. Intra-observer and inter-observer reliability of the measurements were assessed by calculating interclass correlation coefficient (ICC) values, wherein 0e0.21 indicated slight agreement, 0.21e0.40 indicated fair agreement, 0.41e0.6 indicated moderate agreement, 0.61e0.80 indicated substantial agreement, and 0.81e1.0 indicated almost perfect agreement based on the criteria of Landis and Koch (1977).
2. Methods
3. Results
After approval of the Hand Research Committee, 76 MR images of the wrist were collected from our institutional data with closedlabel identity. Most of the MR images had been performed to investigate ulnar wrist pain. Exclusion criteria were a soft tissue mass in the septal area (e.g., ganglion), severe synovitis, poor signal images with artefacts, and age <10 years. Among the 76 MR images, 14 were excluded. Thus, 62 MR images (29 left wrists, 33 right wrists) were evaluated. There were 23 male and 39 female wrists (mean age 46 years, range 10e83 years). Patient age, height, weight, and body mass index (BMI) at the time of MRI were obtained from the medical records. Five septa were measured in this study, including the 1 R septum (between the first extensor compartment and radial artery), 1-2 septum (between the first and second extensor compartments), 2-3 septum (between the second and third compartments), and 3e4 and 4-5 septa (those attached to the dorsal surface of the distal radius). We measured the narrowest width of the septum between each extensor tendon compartment (defined as the width measured from the outer border of one tendon compartment to the outer border of the neighbouring tendon compartment) and then calculated the length of each septum using serial axial MR images (Fig. 1). The most distal level of the measurement was an axial cut that was closest to the wrist joint, where all five septa were attached to the radius (1e2 mm proximal to the joint line of the lunate fossa). The 2 mm slice cut images were used as a standard format via the Picture Archiving and Communication System/Digital Imaging and Communication in Medicine system [ApolloView Lite, version 4.14.9.12 (1); Anima, Tokyo, Japan], which were measured in millimetres with one decimal (e.g., 3.2 mm) and then summed for calculating the mean (SD) at each level, recorded by Microsoft Excel (2015).
The mean age, height, body weight and BMI of the participants were 52.3 years (SD 15.7 years; range: 24e83 years), 1.61 m (SD 0.085 m; range: 1.43e1.80 m), 58.5 kg (SD 17.0 kg; range 41.0e88.0 kg), and 23.5 kg/m2 (SD 3.51 kg/m2; range: 17.0e37.1 kg/ m2), respectively. Table 1 shows the data and distribution pattern of the septal width of each intercompartment of the distal radius. The 2-3 septum had a consistently wide area from the most distal level to 36 mm proximally (mean width 4.8 mm, range 2.1e7.4 mm). The 12 septum was widest at the most distal area (mean width 4.3 mm, range 2.2e6.1 mm). The septum 1 R was relatively wide (mean width 3.1 mm, range 1.5e5.5 mm). The other two septa (3e4 and 4e5) had narrower septa (0.8e2.5 mm) and were located only at an area 20 mm proximal to the wrist joint. We determined that, morphologically, septa 1e2, 3e4, and 4e5 were triangular, and 2e3 and 1 R septum were oval. Measurement of the volar tilt angle using 28 sagittal MR images revealed that the volar tilt of the scaphoid fossa averaged 10 (SD 6 ), and that of the lunate fossa averaged 7 (SD 6 ) (Fig. 2). The dorsal sigmoid notch angle, measured between the dorsal surface of the radius and a line tangential to the sigmoid notch curve, averaged 91 (SD 11 ). The intra-observer ICC values for the measurements are shown in Table 2. Intra-observer reliability for the measurements was almost perfect for each observer. The inter-observer ICC value for the septa measurements among the three examiners was 0.74 (95% CI 0.62e0.82), indicating substantial agreement. Furthermore, the inter-observer ICC values for the measurements of the volar tilt of the scaphoid, the lunate fossa, and the dorsal sigmoid notch angle were all >0.9, indicating almost perfect agreement of the measurements.
Fig. 1. D indicates the narrowest width of the septum (arrows) between each extensor compartment that was measured in the current study. d indicates the width of the attachment site of the septum.
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
3
Table 1 1 R septum indicates the septum radial to the first extensor compartment. 1e2, 2e3, 3e4, and 4-5 septa represent the respective septa between each extensor set of compartments. Light gray indicates mean septal widths of >3 mm. Dark gray indicates mean narrow septal widths (<1 mm). SD, standard deviation.
Distance from the wrist joint
Width of 1R
Width of 2R
Width of 3R
Width of 4R
Width of 5R
septum
septum
septum
septum
septum
[mm], X ±
[mm], X ±
[mm], X ±
[mm], X ±
[mm], X ±
SD
SD
SD
SD
SD
0mm
1.6 ± 1.2
5.6 ± 1.5
3.5 ± 2.8
2.5 ± 1.5
2.5 ± 1.1
2mm
2.3 ± 1.5
6.1 ± 1.6
3.9 ± 2.1
2.1 ± 1.3
2.3 ± 1.0
4mm
3.3 ± 1.9
5.2 ± 1.7
4.5 ± 1.8
1.9 ± 1.0
2.1 ± 0.9
6mm
4.2 ± 1.4
3.5 ± 1.2
4.9 ± 1.8
1.7 ± 1.4
1.7 ± 0.9
8mm
4.7 ± 1.8
3.1 ± 1.9
5.4 ± 1.4
1.2 ± 1.0
1.6 ± 1.0
10mm
4.4 ± 1.9
2.2 ± 1.6
6.0 ± 1.7
0.8 ± 1.1
1.4 ± 0.9
12mm
5.5 ± 1.7
0.5 ± 0.7
6.0 ± 1.4
0.5 ± 0.7
0.5 ± 0.7
14mm
4.3 ± 1.9
0.8 ± 1.3
6.8 ± 1.2
0.3 ± 0.6
0.8 ± 0.9
16mm
3.7 ± 2.0
0.3 ± 0.7
7.2 ± 1.5
0.1 ± 0.3
0.5 ± 0.8
18mm
3.1 ± 1.2
0.4 ± 0.8
7.3 ± 1.2
0.3 ± 0.8
0.2 ± 0.5
20mm
3.4 ± 1.8
0.3 ± 0.5
7.4 ± 2.1
0.1 ± 0.2
0.3 ± 0.8
22mm
3.1 ± 1.3
0.1 ± 0.4
7.0 ± 2.8
0.2 ± 0.6
0.1 ± 0.4
24mm
2.7 ± 2.3
0
4.4 ± 1.5
0
0
26mm
3.0 ± 1.7
0.2 ± 0.5
6.2 ± 4.3
0.2 ± 0.5
0.1 ± 0.4
28mm
3.4 ± 2.6
0.3 ± 0.6
3.3 ± 4.1
0
0
30mm
2.3 ± 0.2
0.5 ± 0.5
5.1 ± 1.0
0.6 ± 0.6
0.6 ± 0.6
32mm
2.8 ± 2.5
0.2 ± 0.5
2.3 ± 3.0
0
0
34mm
1.5 ± 0.6
0.6 ± 0.7
2.6 ± 2.3
0.2 ± 0.3
0.2 ± 0.3
36mm
0.9 ± 0.5
0
2.8 ± 0.7
0
0
38mm
1.4 ± 0.5
0.5 ± 0.5
2.1 ± 0.0
0
0
Fig. 2. Arrows indicate an adequate direction of pin insertion for the external fixator. VT, volar tilt angle of the lunate and scaphoid fossa of the distal radius; SN, sigmoid notch angle. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Table 2 Intra-observer reliability for the measurements was almost perfect for all observers. Observers
Septal widths (ICC)
95% CI
I II III
0.80 0.89 0.84
0.71e0.87 0.85e0.91 0.76e0.90
4. Discussion Taleisnik et al. in their cadaveric study on wrists, found that the wrist extensor retinaculum consists of supratendinous and intratendinous layers [13]. There are six compartments for the tendons dorsal to the wrist separated by six longitudinal vertical septa, with
each septum originating from the supratendinous retinaculum and inserting into the radius. The current study measured the width of each vertical septum between extensor compartments to identify a safe zone for pin insertion during surgery to repair a distal radius fracture. Inserting pins in the vertical septa would be safe and could avoid pin-related complications because there would be no mechanical friction between the pin and extensor tendons in cases in which the inserted pin is located within the septal structure. We measured the narrowest width of each septum using in vivo MR images, which was different from the location of the measurements conducted by Iwamoto et al. [11](Fig. 1). Based on the current measurements, we found two septal shape patterns: oval and triangular. The oval 2e3 and 1 R septa had relatively larger, safe pin insertion sites from distal to proximal
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
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P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
areas (30 mm proximal to the wrist joint). The triangular septa, observed in the 1e2, 3e4, and 4e5 intercompartmental areas, and only the distal aspect (up to 10 mm proximal to the wrist joint) were safe sites for pin insertion. Fig. 3 shows the patterns and mapping of extensor retinacular septa that could guide surgeons to choose an appropriate pin size for specific septa, depending on the fracture pattern and their favoured instruments. We suggest four surgical tips for non-bridging external fixation surgery. (1) A dorsal-to-volar pin (3 mm diameter) can be inserted into the 2-3 septum (30 mm proximal to the wrist joint) to fix distal fracture fragments. (2) Pin insertion at the 1e2, 3e4, and 4-5 septa should be limited to within 10 mm proximal to the wrist joint. (3) A 3-mm pin can be inserted into the 1-2 septum so long as the pin is located within 10 mm proximal to the wrist joint. (4) The 1 R septum may prove to be a new pin insertion site for external fixation of a distal radius fracture that is located just radial to the first compartment and 2e32 mm proximal to the wrist joint. This site may have the advantage of reducing the risk of superficial radial nerve irritation because it is located on an internervous plane between the radial and median nerves. Several devices are available for non-bridging external fixation, and each device has specific recommendations for clinical use [5,8,14e20]. Wolfe used two pins for distal fragment fixation and noted that the first pin was placed between the wrist extensor tendons (extensor carpi radialis longus and extensor carpi radialis brevis) and a second between the fourth and fifth extensor compartments [8]. Based on the current results, we suggest that the first pin can be placed in the 1 R septum, and the second pin can be inserted from the 2-3 septum to reduce tendon friction [9,10] and nerve irritation [21,22]. Gradl et al. and Jupiter used four pins with an AO multiplanar nonbridging external fixator [5,16,19]. Two pins were used for a radial styloid fragment, one pin for a dorsoulnar fragment, and one pin perpendicular to the articular surface with 1.8- to 2.0-mm K wires. We suggest that, for four-pin insertion, one pin is inserted via the 1 R septum, one pin via the 1-2 septum, and the other two pins via the 2e3 and 4-5 septa. Because the 2-3 septum is wide enough for insertion of large pins (3e5 mm), our recommendation may provide more stable fracture fixation and less tendon irritation (Fig. 3). There are several limitations of this study. First, a retrospective MRI review may include different thicknesses of imaging data.
Fig. 3. There are 5 septa for pinning we suggest for distal pin for non-bridging external fixator for each 2 pins (1 R and 2e3), 3 pins (1 R, 2e3, and 1e2), and 4 pins (1 R, 2e3, 1e2 and 4e5).
Furthermore, most of the patients were Japanese woman, and the general size of their bodies may be smaller than that of other populations. 5. Conclusion Morphologically there were two categories of safe pin insertion sites for non-bridging external fixation. We suggest that intraseptal pin insertion is indispensable to reduce the risk of tendon irritation during surgery for distal radius fracture repair. Conflict of interest statement The authors declare that there is no conflict of interest regarding the publication of this manuscript. References [1] Nellans KW, Kowalski E, Chung KC. The epidemiology of distal radius fractures. Hand Clin 2012 May;28(2):113e25. [2] Williksen JH, Husby T, Hellund JC, Kvernmo HD, Rosales C, Frihagen F. External fixation and adjuvant pins versus volar locking plate fixation in unstable distal radius fractures: a randomized, controlled study with a 5-year follow-up. J Hand Surg Am 2015 Jul;40(7):1333e40. [3] Roh YH, Lee BK, Beak JR, Noh JH, Gong HS, Baek GH. A randomized comparison of volar plate and external fixation for intra-articular distal radius fractures. J Hand Surg Am 2015 Jan;40(1):34e41. [4] Shukla R, Jain RK, Sharma NK, Kumar R. External fixation versus volar locking plate for displaced intra-articular distal radius fractures: a prospective randomized comparative study of the functional outcomes. J Orthop Traumatol 2014 Dec;15(4):265e70. [5] Gradl G, Gradl G, Wendt M, Mittlmeier T, Kundt G, Jupiter JB. Non-bridging external fixation employing multiplanar K- wires versus volar locked plating for dorsally displaced fracture of distal radius. Arch Orthop Trauma Surg 2013 May;133(5):595e602. [6] Wilcke MKT, Abbaszadegan H, Adolphson PY. Wrist function recovers more rapidly after volar locked plating than after external fixation but the outcomes are similar after 1 year. Acta Orthop 2011 Feb;82(1):76e81. [7] Eichenbaum MD, Shin EK. Nonbridging external fixation of distal radius fractures. Hand Clin 2010 Aug;26(3):381e90. [8] Wolfe SW. Distal radius fractures. In: Wolfe SW, editor. Green‘s operative Hand surgery. 7th ed. Churchill Livingstone, Philadelphia: PA Elsevier; 2016. p. 531e87. [9] Sharma P, Maffulli N. Tendon injury and tendinopathy: healing and repair. J Bone Joint Surg Am 2005 Jan;87(1):187e202. [10] Lavagnino M, Wall ME, Little D, Banes AJ, Guilak F, Arnoczky SP. Tendon mechanobiology: current knowledge and future research opportunities. J Orthop Res 2015 Jun;33(6):813e22. [11] Iwamoto A, Morris RP, Andersen C, Patterson RM, Viegas SF. An anatomic and biomechanic study of the wrist extensor retinaculum septa and tendon compartments. J Hand Surg Am 2006 Jul-Aug;31(6):896e903. [12] Ljungquist KL, Agnew SP, Huang JI. Predicting a safe screw length for volar plate fixation of distal radius fractures: lunate depth as a marker for distal radius depth. J Hand Surg Am 2015 May;40(5):940e4. [13] Taleisnik J, Gelberman RH, Miller BW, Szabo RH. The extensor retinaculum of the wrist. J Hand Surg Am 1984 Jul;9(4):495e501. [14] Krishnan J, Wigg AE, Walker RW, Slavotinek J. Intra-articular fractures of the distal radius: a prospective randomized controlled trial comparing static bridging and dynamic non-bridging external fixation. J Hand Surg 2003 Oct;28(5):417e21. [15] Hayes AJ, Duffy PJ, McQueen MM. Bridging and non-bridging external fixation in the treatment of unstable fractures of the distal radius: a retrospective study of 588 patients. Acta Orthop 2008 Aug;79(4):540e7. [16] Krukhaug Y, Ugland S, Lie SA, Hove LM. External fixation of fractures of the distal radius: a randomized comparison of the Hoffman compact II nonbridging fixator and the Dynawrist fixator in 75 patients followed for 1 year. Acta Orthop 2009 Feb;80(1):104e8. [17] Yamako G, Ishii Y, Matsuda Y, Noguchi H, Hara T. Biomechanical characteristics of nonbridging external fixators for distal radius fractures. J Hand Surg Am 2008 Mar;33(3):322e6. [18] Mirza A, Jupiter JB, Reinhart MK, Meyer P. Fractures of the distal radius treated with cross-pin fixation and a nonbridging external fixator, the CPX system: a Preliminary Report. J Hand Surg Am 2009 Apr;34(4):603e16. [19] Gradl G, Jupiter JB, Gierer P, Mittlmeier T. Fracture of the distal radius treated with a nonbridging external fixation technique using multiplanar k-wires. J Hand Surg Am 2005 Sep;30(5):960e8. [20] Windolf M, Schwieger K, Ockert B, Jupiter JB, Gradl G. A novel non-bridging external fixator construct versus volar angular stable plating for the fixation
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx of intra-articular fractures of the distal radius–a biomechanical study. Injury 2010 Feb;41(2):204e9. [21] Hochwald NL, Levine R, Tornetta 3rd P. The risks of Kirschner wire placement in the distal radius: a comparison of techniques. J Hand Surg Am 1997 Jul;22(4):580e4.
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[22] Chen Y, Zheng X, Wang J, Zhu Y, Zhan C. Reliable techniques to avoid damaging the superficial radial nerve due to percutaneous Kirschner wire fixation of the distal radius fracture through the radial styloid process. Surg Radiol Anat 2010 Oct;32(8):711e7.
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
Contents lists available at ScienceDirect
Journal of Orthopaedic Science journal homepage: http://www.elsevier.com/locate/jos
Original Article
Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis Pormes Suwanno a, 1, Shohei Omokawa b, *, 2, Yasuaki Nakanishi c, 2, Tsutomu Kira c, 2, Yasuhito Tanaka c, 2 a Department of Orthopaedic Surgery and Physical Medicine, Faculty of Medicine, Prince of Songkla University 15 Karnjanavanich Rd., Hat Yai, Songkhla, 90110, Thailand b Department of Hand Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan c Department of Orthopedic Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 June 2019 Received in revised form 7 November 2019 Accepted 17 December 2019 Available online xxx
Background: Of the anatomical reduction and fixation methods used to treat distal radius fracture, nonbridging external fixation has the advantage of enabling early wrist motion. The surgical technique relies on successful placement of the pin in individual fracture fragments. The present study aimed to identify the safe zone of pin insertion for a non-bridging external fixator into the distal radius that avoids metal impingement of extensor tendons. Methods: The width and length of the septal attachments of the extensor retinaculum were measured on axial MR images of 62 wrists. Results: The 2e3 septum was the widest and longest, with a width of 2e7 mm and a location 0e36 mm proximal to the wrist joint. The width of the 1e2 septum was 2e6 mm, and was widest at 10 mm proximal to the joint. The 1e2 septum was triangular-shaped, while the 2e3 septum was oval-shaped. The 3e4 and 4e5 septa had narrow attachments and were adequate for pin insertion (with a pin 1 e2 mm in width) at a position less than 8 mm proximal to the wrist. The width of the 1 R septum (radial to the 1st septum) was 2e6 mm at the radiovolar aspect of the wrist. Conclusions: There were two safe pin insertion sites; the first was safe at the distal aspect only (8e10 mm proximal to the wrist) and included the 1e2, 3e4, and 4e5 septa, while the second was safe from 0 mm to 32e38 mm proximal to the wrist and included the 1 R and the 2e3 septa. The 1 R septum had adequate size for use as a new pin insertion site that aligns in the internervous plane and has minimal risk of superficial radial nerve injury. © 2020 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
1. Introduction Distal radius fractures are common and have a significant impact on health and well-being, especially in paediatric and elderly people (approximately 25% and 18% of all fractures in paediatric and elderly populations, respectively [1]. Recently, many randomised controlled trials have compared functional outcomes after plating versus external fixators [2e6]. Advantages of plate fixation include early recovery (at 3e6 months) in wrist range of motion and grip strength, but these outcomes were not
* Corresponding author. E-mail address: [email protected] (S. Omokawa). 1 Fax: þ66 74 446825. 2 Fax: þ81 744 25 6449.
significantly different at 12 months postoperatively [3]. A longterm study with >5 years of follow-up found that the complication rate (including tendon irritation and rupture that required implant removal) was higher for plates (31%) than for external fixators (17%) [2]. Non-bridging external fixators provide early wrist motion [7] in the setting of anatomical reduction and adequate fixation, and the surgical technique relies on successful placement of the pin in individual fracture fragments. Small 3- to 4-mm threaded pins are used for fixation of distal radius fragments to restore radial height and volar tilt [5]. Wolfe et al. used two distal pins for simple or minimally comminuted extra-articular fractures and suggested that the second pin at the dorsal ulnar corner of the radius had to be placed between the fourth and fifth extensor compartments [8]. Pin placement in the septum of the extensor retinaculum potentially
https://doi.org/10.1016/j.jos.2019.12.005 0949-2658/© 2020 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
2
P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
reduces the risk of abnormal loading and friction to the tendons [9,10], which could help avoid tenosynovitis of the extensor mechanism during the postoperative course of non-bridging external fixation. Knowledge of anatomy in the wrist extensor retinaculum septa would be useful to determine the precise location of pin insertion, but there is no detailed guidance for pinning while taking into consideration the anatomy of the septa. Although Iwamoto et al. measured the size of septal attachment in a cadaveric study [11], advanced imaging technique in living subjects without prior surgery would provide more accurate measurements [12]. In the present study, we reviewed magnetic resonance (MR) images of the area of the distal radius to investigate mapping the septa of extensor tendons between compartments. The purpose of this study was to determine preferred locations and technique for pinning distal fragments using a market-available, non-bridging external fixator.
Then, the volar tilt angle of each scaphoid and lunate fossa, and sigmoid notch angle were measured using sagittal and axial MR images to guide adequate directions of pin insertion from the 2e3 and 4-5 septa. Three blinded examiners independently measured the narrowest width of the septum, the volar tilt angle of each scaphoid and lunate fossa, and the sigmoid notch angle. All observers repeated the measurements on all MR images after a period of 2 months or more from the initial measurements to decrease the recall bias. Intra-observer and inter-observer reliability of the measurements were assessed by calculating interclass correlation coefficient (ICC) values, wherein 0e0.21 indicated slight agreement, 0.21e0.40 indicated fair agreement, 0.41e0.6 indicated moderate agreement, 0.61e0.80 indicated substantial agreement, and 0.81e1.0 indicated almost perfect agreement based on the criteria of Landis and Koch (1977).
2. Methods
3. Results
After approval of the Hand Research Committee, 76 MR images of the wrist were collected from our institutional data with closedlabel identity. Most of the MR images had been performed to investigate ulnar wrist pain. Exclusion criteria were a soft tissue mass in the septal area (e.g., ganglion), severe synovitis, poor signal images with artefacts, and age <10 years. Among the 76 MR images, 14 were excluded. Thus, 62 MR images (29 left wrists, 33 right wrists) were evaluated. There were 23 male and 39 female wrists (mean age 46 years, range 10e83 years). Patient age, height, weight, and body mass index (BMI) at the time of MRI were obtained from the medical records. Five septa were measured in this study, including the 1 R septum (between the first extensor compartment and radial artery), 1-2 septum (between the first and second extensor compartments), 2-3 septum (between the second and third compartments), and 3e4 and 4-5 septa (those attached to the dorsal surface of the distal radius). We measured the narrowest width of the septum between each extensor tendon compartment (defined as the width measured from the outer border of one tendon compartment to the outer border of the neighbouring tendon compartment) and then calculated the length of each septum using serial axial MR images (Fig. 1). The most distal level of the measurement was an axial cut that was closest to the wrist joint, where all five septa were attached to the radius (1e2 mm proximal to the joint line of the lunate fossa). The 2 mm slice cut images were used as a standard format via the Picture Archiving and Communication System/Digital Imaging and Communication in Medicine system [ApolloView Lite, version 4.14.9.12 (1); Anima, Tokyo, Japan], which were measured in millimetres with one decimal (e.g., 3.2 mm) and then summed for calculating the mean (SD) at each level, recorded by Microsoft Excel (2015).
The mean age, height, body weight and BMI of the participants were 52.3 years (SD 15.7 years; range: 24e83 years), 1.61 m (SD 0.085 m; range: 1.43e1.80 m), 58.5 kg (SD 17.0 kg; range 41.0e88.0 kg), and 23.5 kg/m2 (SD 3.51 kg/m2; range: 17.0e37.1 kg/ m2), respectively. Table 1 shows the data and distribution pattern of the septal width of each intercompartment of the distal radius. The 2-3 septum had a consistently wide area from the most distal level to 36 mm proximally (mean width 4.8 mm, range 2.1e7.4 mm). The 12 septum was widest at the most distal area (mean width 4.3 mm, range 2.2e6.1 mm). The septum 1 R was relatively wide (mean width 3.1 mm, range 1.5e5.5 mm). The other two septa (3e4 and 4e5) had narrower septa (0.8e2.5 mm) and were located only at an area 20 mm proximal to the wrist joint. We determined that, morphologically, septa 1e2, 3e4, and 4e5 were triangular, and 2e3 and 1 R septum were oval. Measurement of the volar tilt angle using 28 sagittal MR images revealed that the volar tilt of the scaphoid fossa averaged 10 (SD 6 ), and that of the lunate fossa averaged 7 (SD 6 ) (Fig. 2). The dorsal sigmoid notch angle, measured between the dorsal surface of the radius and a line tangential to the sigmoid notch curve, averaged 91 (SD 11 ). The intra-observer ICC values for the measurements are shown in Table 2. Intra-observer reliability for the measurements was almost perfect for each observer. The inter-observer ICC value for the septa measurements among the three examiners was 0.74 (95% CI 0.62e0.82), indicating substantial agreement. Furthermore, the inter-observer ICC values for the measurements of the volar tilt of the scaphoid, the lunate fossa, and the dorsal sigmoid notch angle were all >0.9, indicating almost perfect agreement of the measurements.
Fig. 1. D indicates the narrowest width of the septum (arrows) between each extensor compartment that was measured in the current study. d indicates the width of the attachment site of the septum.
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
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Table 1 1 R septum indicates the septum radial to the first extensor compartment. 1e2, 2e3, 3e4, and 4-5 septa represent the respective septa between each extensor set of compartments. Light gray indicates mean septal widths of >3 mm. Dark gray indicates mean narrow septal widths (<1 mm). SD, standard deviation.
Distance from the wrist joint
Width of 1R
Width of 2R
Width of 3R
Width of 4R
Width of 5R
septum
septum
septum
septum
septum
[mm], X ±
[mm], X ±
[mm], X ±
[mm], X ±
[mm], X ±
SD
SD
SD
SD
SD
0mm
1.6 ± 1.2
5.6 ± 1.5
3.5 ± 2.8
2.5 ± 1.5
2.5 ± 1.1
2mm
2.3 ± 1.5
6.1 ± 1.6
3.9 ± 2.1
2.1 ± 1.3
2.3 ± 1.0
4mm
3.3 ± 1.9
5.2 ± 1.7
4.5 ± 1.8
1.9 ± 1.0
2.1 ± 0.9
6mm
4.2 ± 1.4
3.5 ± 1.2
4.9 ± 1.8
1.7 ± 1.4
1.7 ± 0.9
8mm
4.7 ± 1.8
3.1 ± 1.9
5.4 ± 1.4
1.2 ± 1.0
1.6 ± 1.0
10mm
4.4 ± 1.9
2.2 ± 1.6
6.0 ± 1.7
0.8 ± 1.1
1.4 ± 0.9
12mm
5.5 ± 1.7
0.5 ± 0.7
6.0 ± 1.4
0.5 ± 0.7
0.5 ± 0.7
14mm
4.3 ± 1.9
0.8 ± 1.3
6.8 ± 1.2
0.3 ± 0.6
0.8 ± 0.9
16mm
3.7 ± 2.0
0.3 ± 0.7
7.2 ± 1.5
0.1 ± 0.3
0.5 ± 0.8
18mm
3.1 ± 1.2
0.4 ± 0.8
7.3 ± 1.2
0.3 ± 0.8
0.2 ± 0.5
20mm
3.4 ± 1.8
0.3 ± 0.5
7.4 ± 2.1
0.1 ± 0.2
0.3 ± 0.8
22mm
3.1 ± 1.3
0.1 ± 0.4
7.0 ± 2.8
0.2 ± 0.6
0.1 ± 0.4
24mm
2.7 ± 2.3
0
4.4 ± 1.5
0
0
26mm
3.0 ± 1.7
0.2 ± 0.5
6.2 ± 4.3
0.2 ± 0.5
0.1 ± 0.4
28mm
3.4 ± 2.6
0.3 ± 0.6
3.3 ± 4.1
0
0
30mm
2.3 ± 0.2
0.5 ± 0.5
5.1 ± 1.0
0.6 ± 0.6
0.6 ± 0.6
32mm
2.8 ± 2.5
0.2 ± 0.5
2.3 ± 3.0
0
0
34mm
1.5 ± 0.6
0.6 ± 0.7
2.6 ± 2.3
0.2 ± 0.3
0.2 ± 0.3
36mm
0.9 ± 0.5
0
2.8 ± 0.7
0
0
38mm
1.4 ± 0.5
0.5 ± 0.5
2.1 ± 0.0
0
0
Fig. 2. Arrows indicate an adequate direction of pin insertion for the external fixator. VT, volar tilt angle of the lunate and scaphoid fossa of the distal radius; SN, sigmoid notch angle. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Table 2 Intra-observer reliability for the measurements was almost perfect for all observers. Observers
Septal widths (ICC)
95% CI
I II III
0.80 0.89 0.84
0.71e0.87 0.85e0.91 0.76e0.90
4. Discussion Taleisnik et al. in their cadaveric study on wrists, found that the wrist extensor retinaculum consists of supratendinous and intratendinous layers [13]. There are six compartments for the tendons dorsal to the wrist separated by six longitudinal vertical septa, with
each septum originating from the supratendinous retinaculum and inserting into the radius. The current study measured the width of each vertical septum between extensor compartments to identify a safe zone for pin insertion during surgery to repair a distal radius fracture. Inserting pins in the vertical septa would be safe and could avoid pin-related complications because there would be no mechanical friction between the pin and extensor tendons in cases in which the inserted pin is located within the septal structure. We measured the narrowest width of each septum using in vivo MR images, which was different from the location of the measurements conducted by Iwamoto et al. [11](Fig. 1). Based on the current measurements, we found two septal shape patterns: oval and triangular. The oval 2e3 and 1 R septa had relatively larger, safe pin insertion sites from distal to proximal
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
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P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx
areas (30 mm proximal to the wrist joint). The triangular septa, observed in the 1e2, 3e4, and 4e5 intercompartmental areas, and only the distal aspect (up to 10 mm proximal to the wrist joint) were safe sites for pin insertion. Fig. 3 shows the patterns and mapping of extensor retinacular septa that could guide surgeons to choose an appropriate pin size for specific septa, depending on the fracture pattern and their favoured instruments. We suggest four surgical tips for non-bridging external fixation surgery. (1) A dorsal-to-volar pin (3 mm diameter) can be inserted into the 2-3 septum (30 mm proximal to the wrist joint) to fix distal fracture fragments. (2) Pin insertion at the 1e2, 3e4, and 4-5 septa should be limited to within 10 mm proximal to the wrist joint. (3) A 3-mm pin can be inserted into the 1-2 septum so long as the pin is located within 10 mm proximal to the wrist joint. (4) The 1 R septum may prove to be a new pin insertion site for external fixation of a distal radius fracture that is located just radial to the first compartment and 2e32 mm proximal to the wrist joint. This site may have the advantage of reducing the risk of superficial radial nerve irritation because it is located on an internervous plane between the radial and median nerves. Several devices are available for non-bridging external fixation, and each device has specific recommendations for clinical use [5,8,14e20]. Wolfe used two pins for distal fragment fixation and noted that the first pin was placed between the wrist extensor tendons (extensor carpi radialis longus and extensor carpi radialis brevis) and a second between the fourth and fifth extensor compartments [8]. Based on the current results, we suggest that the first pin can be placed in the 1 R septum, and the second pin can be inserted from the 2-3 septum to reduce tendon friction [9,10] and nerve irritation [21,22]. Gradl et al. and Jupiter used four pins with an AO multiplanar nonbridging external fixator [5,16,19]. Two pins were used for a radial styloid fragment, one pin for a dorsoulnar fragment, and one pin perpendicular to the articular surface with 1.8- to 2.0-mm K wires. We suggest that, for four-pin insertion, one pin is inserted via the 1 R septum, one pin via the 1-2 septum, and the other two pins via the 2e3 and 4-5 septa. Because the 2-3 septum is wide enough for insertion of large pins (3e5 mm), our recommendation may provide more stable fracture fixation and less tendon irritation (Fig. 3). There are several limitations of this study. First, a retrospective MRI review may include different thicknesses of imaging data.
Fig. 3. There are 5 septa for pinning we suggest for distal pin for non-bridging external fixator for each 2 pins (1 R and 2e3), 3 pins (1 R, 2e3, and 1e2), and 4 pins (1 R, 2e3, 1e2 and 4e5).
Furthermore, most of the patients were Japanese woman, and the general size of their bodies may be smaller than that of other populations. 5. Conclusion Morphologically there were two categories of safe pin insertion sites for non-bridging external fixation. We suggest that intraseptal pin insertion is indispensable to reduce the risk of tendon irritation during surgery for distal radius fracture repair. Conflict of interest statement The authors declare that there is no conflict of interest regarding the publication of this manuscript. References [1] Nellans KW, Kowalski E, Chung KC. The epidemiology of distal radius fractures. Hand Clin 2012 May;28(2):113e25. [2] Williksen JH, Husby T, Hellund JC, Kvernmo HD, Rosales C, Frihagen F. External fixation and adjuvant pins versus volar locking plate fixation in unstable distal radius fractures: a randomized, controlled study with a 5-year follow-up. J Hand Surg Am 2015 Jul;40(7):1333e40. [3] Roh YH, Lee BK, Beak JR, Noh JH, Gong HS, Baek GH. A randomized comparison of volar plate and external fixation for intra-articular distal radius fractures. J Hand Surg Am 2015 Jan;40(1):34e41. [4] Shukla R, Jain RK, Sharma NK, Kumar R. External fixation versus volar locking plate for displaced intra-articular distal radius fractures: a prospective randomized comparative study of the functional outcomes. J Orthop Traumatol 2014 Dec;15(4):265e70. [5] Gradl G, Gradl G, Wendt M, Mittlmeier T, Kundt G, Jupiter JB. Non-bridging external fixation employing multiplanar K- wires versus volar locked plating for dorsally displaced fracture of distal radius. Arch Orthop Trauma Surg 2013 May;133(5):595e602. [6] Wilcke MKT, Abbaszadegan H, Adolphson PY. Wrist function recovers more rapidly after volar locked plating than after external fixation but the outcomes are similar after 1 year. Acta Orthop 2011 Feb;82(1):76e81. [7] Eichenbaum MD, Shin EK. Nonbridging external fixation of distal radius fractures. Hand Clin 2010 Aug;26(3):381e90. [8] Wolfe SW. Distal radius fractures. In: Wolfe SW, editor. Green‘s operative Hand surgery. 7th ed. Churchill Livingstone, Philadelphia: PA Elsevier; 2016. p. 531e87. [9] Sharma P, Maffulli N. Tendon injury and tendinopathy: healing and repair. J Bone Joint Surg Am 2005 Jan;87(1):187e202. [10] Lavagnino M, Wall ME, Little D, Banes AJ, Guilak F, Arnoczky SP. Tendon mechanobiology: current knowledge and future research opportunities. J Orthop Res 2015 Jun;33(6):813e22. [11] Iwamoto A, Morris RP, Andersen C, Patterson RM, Viegas SF. An anatomic and biomechanic study of the wrist extensor retinaculum septa and tendon compartments. J Hand Surg Am 2006 Jul-Aug;31(6):896e903. [12] Ljungquist KL, Agnew SP, Huang JI. Predicting a safe screw length for volar plate fixation of distal radius fractures: lunate depth as a marker for distal radius depth. J Hand Surg Am 2015 May;40(5):940e4. [13] Taleisnik J, Gelberman RH, Miller BW, Szabo RH. The extensor retinaculum of the wrist. J Hand Surg Am 1984 Jul;9(4):495e501. [14] Krishnan J, Wigg AE, Walker RW, Slavotinek J. Intra-articular fractures of the distal radius: a prospective randomized controlled trial comparing static bridging and dynamic non-bridging external fixation. J Hand Surg 2003 Oct;28(5):417e21. [15] Hayes AJ, Duffy PJ, McQueen MM. Bridging and non-bridging external fixation in the treatment of unstable fractures of the distal radius: a retrospective study of 588 patients. Acta Orthop 2008 Aug;79(4):540e7. [16] Krukhaug Y, Ugland S, Lie SA, Hove LM. External fixation of fractures of the distal radius: a randomized comparison of the Hoffman compact II nonbridging fixator and the Dynawrist fixator in 75 patients followed for 1 year. Acta Orthop 2009 Feb;80(1):104e8. [17] Yamako G, Ishii Y, Matsuda Y, Noguchi H, Hara T. Biomechanical characteristics of nonbridging external fixators for distal radius fractures. J Hand Surg Am 2008 Mar;33(3):322e6. [18] Mirza A, Jupiter JB, Reinhart MK, Meyer P. Fractures of the distal radius treated with cross-pin fixation and a nonbridging external fixator, the CPX system: a Preliminary Report. J Hand Surg Am 2009 Apr;34(4):603e16. [19] Gradl G, Jupiter JB, Gierer P, Mittlmeier T. Fracture of the distal radius treated with a nonbridging external fixation technique using multiplanar k-wires. J Hand Surg Am 2005 Sep;30(5):960e8. [20] Windolf M, Schwieger K, Ockert B, Jupiter JB, Gradl G. A novel non-bridging external fixator construct versus volar angular stable plating for the fixation
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005
P. Suwanno et al. / Journal of Orthopaedic Science xxx (xxxx) xxx of intra-articular fractures of the distal radius–a biomechanical study. Injury 2010 Feb;41(2):204e9. [21] Hochwald NL, Levine R, Tornetta 3rd P. The risks of Kirschner wire placement in the distal radius: a comparison of techniques. J Hand Surg Am 1997 Jul;22(4):580e4.
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[22] Chen Y, Zheng X, Wang J, Zhu Y, Zhan C. Reliable techniques to avoid damaging the superficial radial nerve due to percutaneous Kirschner wire fixation of the distal radius fracture through the radial styloid process. Surg Radiol Anat 2010 Oct;32(8):711e7.
Please cite this article as: Suwanno P et al., Safe zone of pin insertion for nonbridging external fixators in distal radial fractures: MRI analysis, Journal of Orthopaedic Science, https://doi.org/10.1016/j.jos.2019.12.005