Three-Dimensional Analysis of Polyaxial Volar Locking Plate Position for Distal Radius Fracture

Abstract

Background To avoid screw penetration into the joint when using the polyaxial volar locking plate (VLP) for osteosynthesis of distal radius fractures, it is important to note that the optimal screw insertion angles depending on the plate positions.

Purpose The purpose of this study was 2-fold: first, to evaluate the differences of the most distal plate position where the screw does not penetrate into the joint in the three-dimensional (3D) radius models; second, to evaluate the relationship between the plate position and the transverse diameter of the distal radius.

Patients and Methods Thirty plain X-rays and computed tomography (CT) scans of healthy wrists were evaluated. The transverse diameter was measured on plain X-rays. 3D radius models were reconstructed from CT data. A 3D image of polyaxial VLP was used to investigate the most distal plate position at three different screw insertion angles. The linear distance between the volar articular edge and the plate edge was measured and compared among different screw insertion angles. The correlations between the plate positions and the transverse diameter were also evaluated. In addition, the relationship between the most distal screw place and articular surface was confirmed with one case of distal radius fracture.

Results The optimal positions relative to the neutral were 2.7 mm proximal in the distal swing and 1.9 mm distal in the proximal swing. The linear distance was significantly correlated with the transverse diameter in each group. It was confirmed that the relationship between the most distal screw place and articular surface was applicable in the actual case.

Conclusion The results showed that the most distal position of the polyaxial VLP differed depending on the screw insertion angle and became more proximal as the transverse diameter increased. These results may be useful as a reference for preoperative planning.

Levels of Evidence III.

Keywords

distal radius fracture - volar locking plate - three dimension - computed tomography - computer-assisted

The volar locking plate (VLP) is widely used for the osteosynthesis of distal radius fractures. The VLP has the advantage of providing rigid fixation for comminuted fractures and osteoporotic bone fractures due to the screw and plate locking fixation mechanism. When applying the VLP, the plate and screws must be placed accurately and safely for the subchondral support. The monoaxial VLP was initially popularized as the VLP. Since the screw insertion angle is fixed in the monoaxial VLP, there are some difficulties in avoiding flexor tendon interference and optimally positioning to support subchondral bone. Furthermore, the morphology of the distal radius limits plate positions. It is also challenging to insert a screw into an arbitrary bone fragment in intra-articular fractures. On the other hand, the polyaxial VLP has the advantage of being able to capture specific bone fragments by adjusting the insertion angles of the screws.[1] [2] In a cadaveric study, Rausch et al demonstrated that the polyaxial VLP had similar biomechanical stability and superior properties under cyclic loading to the monoaxial VLP for the management of intra-articular fractures of the distal radius.[2] In addition, it has been reported that the rate of plate-related complications was lower with the polyaxial VLP than with the monoaxial VLP and that the polyaxial VLP was more flexible for plate positioning.[3]

When using the VLP for intra-articular distal radius fractures, screws need to be inserted just below the articular surface and screw penetration into the joint is one of the most common complications.[4] On the other hand, the morphology of the distal radius has significant individual anatomical variations.[5] In a previous study, it has been suggested that there are significant differences in the transverse diameter of the distal radius between males and females.[6] [7] Moreover, significant differences were observed in the volar cortical angle (VCA) between males and females.[6] [7] [8] [9] Therefore, individual differences in the morphology of the distal radius, such as the transverse diameter, may affect optimal plate positions.

A detailed understanding of differences in the most distal plate position where the screw does not penetrate into the joint due to different screw insertion angles is important. In this study, we evaluated the most distal plate position on the radius at different screw insertion angles of the polyaxial VLP from a three-dimensional (3D) perspective. Thus, the purpose of the present study was 2-fold; first, to evaluate differences of the most distal plate position where the screw does not penetrate into the joint with different screw insertion angles of polyaxial VLP in the 3D radius models, second, to evaluate the relationship between the most distal plate position of the polyaxial VLP and the transverse diameter of the distal radius. In addition, we verified the applicability of the principle to actual osteosynthesis using an image dataset of one distal radius fracture case. The hypotheses of this study are that the most distal plate position where the screw does not penetrate into the joint may depend on the distal screw angles, and the plate position can be defined by the transverse diameter of the distal radius.

Patients and Methods

The study protocol was approved by the Institutional Review Board (Approval Code: T2019-0178). We opted out to use the previously obtained data and gave the opportunity to object for using the previous patient's data. This was a retrospective case control study (level of evidence III). The radiographic database was accessed to identify cases with X-rays and computed tomography (CT) scans of normal wrists. Using the image database, we evaluated unaffected wrist X-ray and CT images taken for comparison with the affected side wrist. The absence of a previous history and complaints in the unaffected wrists was confirmed by an interview and medical records.

Plate Position Analysis in Three Dimension

We evaluated the imaging data of 30 patients acquired at one university hospital between January 2016 and March 2022 (12 females, 18 males, mean age 56.3 years, age range: 18–81). CT images were taken with a tube setting of 120 kV and 100 mAs, a section thickness of 1 to 1.5 mm, and a pixel size of 0.3 × 0.3 mm (Sensation Cardiac, Siemens, Berlin, German). CT images were taken from the metacarpal bone level to approximately 13 cm proximal to the radius joint surface. Anteroposterior X-rays were taken from the dorsal side with the cassette placed on the palmar surface of the wrist in the neutral position of the wrist joint. The transverse diameter (W) was measured at the ulnar margin level of the distal radius articular surface drawn orthogonally to the radial bone axis on X-ray images. These measurements were performed using SYNAPSE Vincent (Fujifilm Co., Tokyo, Japan).

The 3D analysis used in the present study included the creation of a 3D model, the construction of a coordinate system for the model, and an analysis of the model using reference points and plate positions. Computer analysis software (Zed-Trauma distal radius stage, LEXI Co., Ltd., Tokyo, Japan, and BoneSimulater, Orthree, Osaka, Japan) were used to analyze the 3D bone model of the distal radius as previously described.[10] [11] [12] The DICOM dataset of CT scans was used for data analysis. The radius bone was segmented according to CT values after image data were imported into the software. A 3D surface model was constructed using a surface construction algorithm. For the further analyses, standard triangulated data of the 3D bone model were used. As described in a previous study, we used the data measurement mode in BoneSimulator to define the coordinate system based on 3D data of the distal radius.[13] The long axis of the radius was automatically calculated as follows. The software found the central curve of the radius shaft from the proximal to the distal end by analyzing cross-sections at different levels. It then calculated the central point at each level from surface data of the radial diaphysis. The long axis of the radius was subsequently defined as a straight line based on each center point. In the 3D coordinate system, the long axis of the radius was defined as the y-axis (positive: the proximal direction; negative: the distal direction). The z-axis (positive: the radial direction; negative: the ulnar direction) was parallel to the orthogonal projection of the line originating at the base on the sigmoid notch of the distal radius and continuing to the radial styloid process on the plane perpendicular to the y-axis. The x-axis (positive: the palmar direction; negative: the dorsal direction) was defined as perpendicular to the yz plane. The coronal, sagittal, and axial planes were defined as the yz, xy, and xz planes, respectively. The origin of the coordinate axes was defined as the intersection of the articular surface and the long axis ([Fig. 1]).

Fig. 1 Schemas of the long axis of the radius and coordinate axes (x, y, and z).

Computer-aided design data on the standard size EVOS wrist plate system (Smith & Nephew, Watford, UK) were used in the analysis. EVOS wrist plate system is a polyaxial VLP for the osteosynthesis of distal radius fractures. 3D data of the plate were placed on the volar surface of the radius along the long axis and moved distally along the long axis. The most distal position at which the distal screw did not penetrate the articular surface was identified. The 3D coordinates of the distal end of the plate center and the volar articular edge along the long axis were measured at that position ([Fig. 2]). The coordinates of the following three different screw insertion angles were measured: 0 degrees (group N), 15 degrees of the distal swing (group D), and 15 degrees of the proximal swing (group P) ([Fig. 3]). The linear distance (distance on the long axis of the radius, Da) between the volar articular edge and the distal end of the plate was measured and compared among different screw insertion angles ([Fig. 4]).

Fig. 2 The plate was placed on the long axis of the radius and at the most distal position at which the distal screw did not penetrate the articular surface, and the 3D coordinates of the distal end of the plate and the volar articular edge were measured at that position.

Fig. 3 The coordinates of three different plates with screw insertion angles of 0 degrees (Group N), 15 degrees of the distal swing (Group D), and 15 degrees of the proximal swing (Group P) were measured.

Fig. 4 The linear distance (distance on the radial axis, Da) between the volar articular edge and the distal end of the plate was measured.

Statistical Analysis

Results are expressed as the mean ± standard deviation. A one-way analysis of variance was used for comparisons among different screw insertion angles. p-Values < 0.05 were considered to be significant. The relationship between Da and W was evaluated by the Pearson's correlation analysis (Excel, Microsoft 365 software, Redmond, WA).

Results

The transverse radial diameter (W) was 29.4 ± 2.3 mm. Linear distances (distance on the bone axis, Da) were 2.3 ± 0.8, 4.9 ± 1.0, and 0.4 ± 0.7 mm in groups N, D, and P, respectively. Group D positions were 2.7 ± 0.6 mm proximal to group N. Group P positions were 1.9 ± 0.6 mm distal to group N. Significant differences were observed among the three groups (p < 0.05).

Da significantly correlated with W in the three groups, with correlation coefficients of 0.474, 0.653, and 0.435 in groups N, D, and P, respectively. Regression equations were Da = 0.17W − 2.6, Da = 0.27W − 3.1, and Da = 0.14W − 3.7 in groups N, D, and P, respectively ([Fig. 5]).

Fig. 5 Scatter plots and regression equations for the relationship between the transverse radial diameter (W) and the linear distance (Da). ⬤ = Group D, ⬛ = Group N, ▲ = Group P.

Case Presentation

A 69-year-old female. She fell in the bathroom at home and sustained a distal radius fracture. She was referred to our hospital 2 days after the initial injury. We tried manual reduction but were unable to achieve an acceptable reduction. Therefore, we decided to conduct surgery. The fracture type was AO–A3. The fracture line existed distally, especially on the ulnar side ([Fig. 6A]).

Fig. 6 3D analysis was performed on one distal radius fracture case. (A) Preoperative 3D image of CT scan. The fracture type was AO–A3. The fracture line existed distally, especially on the ulnar side. (B), (C) The distance between distal end of the plate center and the volar articular edge along the long axis was 4.1 mm (A). (D) The distance between the most distal screw and articular surface was 1.8 mm (B).

We conducted surgery under general anesthesia using a trans-flexor carpi radialis approach. We used the EVOS wrist plate system (Smith & Nephew) for internal fixation. To place the distal screws just below the articular surface to achieve proper stability, we placed the plate distally, right above the watershed line. With reference to intraoperative fluoroscopic images, we inserted distal screws in a neutral position. There was no need to swing the screws proximally at this plate positioning. We confirmed bone union 3 months after surgery. At 1 year's postoperative follow-up, there were no differences in the wrist range of motion and grip strength compared with the contralateral side. Quick-DASH score was 0 for disability and symptoms.

In this case, the same analysis was performed for the plate position where the screw did not penetrate into the joint. The distance between distal end of the plate center and the volar articular edge along the long axis was 4.1 mm ([Fig. 6B, C]). The distance between the most distal screw and articular surface was 1.8 mm according to the CT analysis ([Fig. 6D]). If the plate and screws positioned just at the level of articular surface, the distance between distal end of the plate center and the volar articular edge along the long axis would be 2.3 mm. In the results of 3D analysis of normal radius, the average linear distances was 2.3 ± 0.8 mm in the group N. It was very close to the measurement in this case. Therefore, the relationship between the most distal screw place and articular surface was applicable in the actual case.

Discussion

When the polyaxial VLP is used for the osteosynthesis of distal radius fractures, screw penetration into the joint is one of the most common complications.[14] Nishiwaki et al reported that in the osteosynthesis of unstable intra-articular fractures of the distal radius, screw penetration into the joint occurred in 0 out of 54 cases with the monoaxial VLP and in 4 out of 55 cases with the polyaxial VLP. Therefore, osteosynthesis using the polyaxial VLP was considered to be more prone to technical errors.[15] When using monoaxial VLP, if the plate is placed in the optimal position, the screw is unlikely to penetrate into the joint, but if the plate is placed incorrectly, the screw may penetrate into the joint. On the other hand, polyaxial VLP can be used for various fracture types by changing the screw insertion angle according to the fracture type. However, care must be taken to ensure a proper screw insertion angle that does not penetrate into the joint. Factors contributing to screw penetration into the joint include a mismatch in the shape of the distal radius and plate design, the misperception of the shape of the lunate fossa, and inadequate reduction.[16] The use of intraoperative techniques to confirm screw penetration into the joint, such as imaging by slightly elevating the forearm in the anteroposterior and lateral views to depict the joint plane on fluoroscopy and the use of 3D reconstructed images, are recommended.[16] Soong et al reported that radiographic images from multiple directions are needed to accurately evaluate the placement of all screws in VLP fixation of the distal radius.[4] The majority of studies on VLP placement examined risk factors for flexor pollicis longus tendon rupture based on the relationship between the watershed line and plate placement.[17] [18] The relationship between plate positions and intra-articular screw penetration remains unknown.

Gehweiler et al demonstrated that a computerized anatomical evaluation was a useful assessment method that is noninvasive, nondestructive, and repeatable and allows for a detailed anatomical examination.[19] A computer simulation was suggested to optimize not only implant selection and placement, but also screw lengths. A previous study reported that screw length errors between the manual placement of the plate on the 3D printed model and the placement of the plate on the 3D model on the computer was less than 1 mm and highly reproducible.[19] Yoshii et al reported that the 3D preoperative planning of distal radius fractures using a computer simulation resulted in the significant reproducibility of the reduction shape and the high reproducibility of implant selection.[10]

In the present study, we used 3D preoperative planning software to analyze the most distal position of the plate at different screw insertion angles in the polyaxial VLP. The results obtained showed that the most distal placement positions to avoid intra-articular screw penetration were 2.7 mm proximal at 15 degrees of the distal swing and 1.9 mm distal at 15 degrees of the proximal swing for a neutral screw angle. It was clearly shown that the most distal plate positions where the screw does not penetrate into the joint differed depending on the distal screw insertion angle in the polyaxial VLP. Furthermore, the results suggests that the neutral screw angle (which can be considered as the monoaxial VLP) should be placed more than 2.3 mm proximal to the volar articular edge. If the plate is placed less than 2.3 mm from the volar articular edge, there is a possibility of screw penetration into the joint with neutral screw angle. In such case, the screw should be swung proximally. The results of this study may be useful as a reference for the positioning of the plate when recognizing distances from anatomical landmarks or when using the intraoperative referencing system.[20]

There are several reports of sex differences in VCA in radiographic studies, which showing significantly greater VCA in males.[5] [8] Cho et al also obtained similar findings in their study using 3D models.[6] Yoneda et al found a correlation between bone width and VCA in their analysis of a 3D surface model and showed that VCA increased as bone became wider.[9] This finding suggests that VCA increases as bone becomes wider. When placing a plate on steep bone with a large VCA, the plate needs to be lifted off the bone and placed at a greater angle to the bone shaft than on bone with a smaller VCA. The greater the angle of the plate to the bone shaft, the more distally the distal screw will be inserted and the more proximally the plate must be placed ([Fig. 7]). In the present study, the larger the transverse diameter of the distal radius, the more proximal the plate needed to be placed. This result suggests that the most distal plate position where the screw does not penetrate into the joint is more proximal for larger transverse diameters of bone with a greater VCA.

Fig. 7 The plate needs to be placed at a greater angle to the bone shaft with a high VCA than with a low VCA. As a result, the angle between the plate and shaft is also greater with a high VCA. VCA, volar cortical angle.

There are several limitations in this study. First, this study was performed in a single designed plate. The results obtained may have differed depending on the plate geometry. Second, the position of plate placement may have varied depending on the distal radius morphology and fracture type, particularly the inclination of the ulnar side of the distal radius, which may limit plate placement positions. In addition, it was not clear whether this method can apply to the comminuted distal radius fractures. Since this analysis based on the distance between the articular surface and the distal end of the plate, it may not be applicable in some comminuted distal radius fracture cases. Finally, since this analysis used a 3D model of healthy wrists, the placement position may have differed in cases of insufficient reduction.

In conclusion, the most distal plate position changed with distal screw insertion angles in the polyaxial VLP. The plate placement was more proximal with a larger transverse diameter of the radius. The neutral screw angle should be placed more than 2.3 mm proximal to the volar articular edge. The most distal plate positions where the screw does not penetrate into the joint was 2.7 mm proximal at 15 degrees of the distal swing and 1.9 mm distal at 15 degrees of the proximal swing to the 0 degrees insertion angle. When using the polyaxial VLP for the osteosynthesis of distal radius fractures, these differences need to be considered. The regression equation identified from this study may be useful in knowing the most distal plate positions where the screw does not penetrate into the joint in relation to the transverse diameter of radius.

Conflict of Interest

None declared.

Acknowledgments

None.

Consent for Publication

Written informed consent was obtained from the patients to participate in this study.

Availability of Data and Material

The datasets generated during and analyzed during the current study are available from the corresponding author on reasonable request.

Note

This study was performed at Department of Orthopaedic Surgery, Tokyo Medical University Ibaraki Medical Center, Tsukuba, Ibaraki, Japan.

• References

• 1 Hoffmeier KL, Hofmann GO, Mückley T. The strength of polyaxial locking interfaces of distal radius plates. Clin Biomech (Bristol, Avon) 2009; 24 (08) 637-641
• 2 Rausch S, Klos K, Stephan H. et al. Evaluation of a polyaxial angle-stable volar plate in a distal radius C-fracture model–a biomechanical study. Injury 2011; 42 (11) 1248-1252
• 3 Mehrzad R, Kim DC. Complication rate comparing variable angle distal locking plate to fixed angle plate fixation of distal radius fractures. Ann Plast Surg 2016; 77 (06) 623-625
• 4 Soong M, Got C, Katarincic J, Akelman E. Fluoroscopic evaluation of intra-articular screw placement during locked volar plating of the distal radius: a cadaveric study. J Hand Surg Am 2008; 33 (10) 1720-1723
• 5 Yoneda H, Iwatsuki K, Hara T, Kurimoto S, Yamamoto M, Hirata H. Interindividual anatomical variations affect the plate-to-bone fit during osteosynthesis of distal radius fractures. J Orthop Res 2016; 34 (06) 953-960
• 6 Cho HJ, Kim S, Kwak DS. Morphological study of the anterior surface of the distal radius. BioMed Res Int 2017; 2017: 8963768
• 7 Oppermann J, Bredow J, Beyer F. et al. Distal radius: anatomical morphometric gender characteristics. Do anatomical pre-shaped plates pay attention on it?. Arch Orthop Trauma Surg 2015; 135 (01) 133-139
• 8 Gandhi RA, Hesketh PJ, Bannister ER, Sebro R, Mehta S. Age-related variations in volar cortical angle of the distal radius. Hand (N Y) 2020; 15 (04) 573-577
• 9 Yoneda H, Iwatsuki K, Saeki M, Yamamoto M, Tatebe M. Do anatomical differences of the volar rim of the distal radius affect implant design? A three-dimensional analysis of its anatomy and need for personalized medicine. Anatomia 2022; 1 (02) 177-185
• 10 Yoshii Y, Kusakabe T, Akita K, Tung WL, Ishii T. Reproducibility of three dimensional digital preoperative planning for the osteosynthesis of distal radius fractures. J Orthop Res 2017; 35 (12) 2646-2651
• 11 Yoshii Y, Totoki Y, Shigi A. et al. Computer-aided assessment of displacement and reduction of distal radius fractures. Diagnostics (Basel) 2021; 11 (04) 719
• 12 Yoshii Y, Ogawa T, Shigi A, Oka K, Murase T, Ishii T. Three-dimensional evaluations of preoperative planning reproducibility for the osteosynthesis of distal radius fractures. J Orthop Surg Res 2021; 16 (01) 131
• 13 Ikumi A, Yoshii Y, Eda Y, Ishii T. Computer-aided assessment of three-dimensional standard bone morphology of the distal radius. Diagnostics (Basel) 2022; 12 (12) 3212
• 14 Seuthe R, Seekamp A, Kurz B. et al. Comparison of a ceiling-mounted 3D flat panel detector vs. conventional intraoperative 2D fluoroscopy in plate osteosynthesis of distal radius fractures with volar locking plate systems. BMC Musculoskelet Disord 2021; 22 (01) 924
• 15 Nishiwaki M, Terasaka Y, Kiyota Y, Inaba N, Koyanagi T, Horiuchi Y. A prospective randomized comparison of variable-angle and fixed-angle volar locking plating for intra-articular distal radius fractures. J Hand Surg Am 2021; 46 (07) 584-593
• 16 Aldemir C, Duygun F. Is it possible to avoid intra-articular screw penetration with minimal use of fluoroscopy in the application of distal radius volar plate?. Eklem Hastalik Cerrahisi 2017; 28 (01) 2-6
• 17 Tanaka Y, Aoki M, Izumi T, Fujimiya M, Yamashita T, Imai T. Effect of distal radius volar plate position on contact pressure between the flexor pollicis longus tendon and the distal plate edge. J Hand Surg Am 2011; 36 (11) 1790-1797
• 18 Tokutake K, Iwatsuki K, Tatebe M, Okui N, Mizuno M, Hirata H. Usefulness of CT-based measurement of volar prominence for evaluation of risk of flexor tendon injury following fixation of a distal radius fracture. J Orthop Sci 2019; 24 (02) 263-268
• 19 Gehweiler D, Teunis T, Varjas V. et al. Computerized anatomy of the distal radius and its relevance to volar plating, research, and teaching. Clin Anat 2019; 32 (03) 361-368
• 20 Yoshii Y, Totoki Y, Sashida S, Sakai S, Ishii T. Utility of an image fusion system for 3D preoperative planning and fluoroscopy in the osteosynthesis of distal radius fractures. J Orthop Surg Res 2019; 14 (01) 342

Publication History

Article published online:
08 March 2024