Radiographic Analysis in Reduction Loss After Distal Radius Fracture Fixation with Variable Angle Volar Locking Plate

Background Reduction loss is commonly seen even in the newly designed locking plate xation for distal radius fractures. Our study purpose is to investigate the ecacy of the variable angle volar locking plate (VAVLP) in maintenance of fracture xation. Methods A total of 37 patients of unilateral distal radius fractures receiving VAVLP xation were enrolled. Forearm radiographs immediately after surgery and those at 3 months were retrospectively reviewed by orthopedist, radiologist and medical students for analysis of radiographic parameter including radial height (RH), ulnar variance (UV), radial inclination (RI), volar tilt (VT), tear drop angle (TDA), distal dorsal cortical distance (DDD) and Soong classication (SC). Results By comparing the 3-month measurement and normal data, the difference of RH / UV / TDA was signicant (p-value of 0.000) while the difference of RI / VT was insignicant. However, there was no signicant difference regarding those ve parameters between postoperative and 3-month measurement. Linear regression on DDD exhibited positive dependence with p-value of 0.002 between postoperative and 3-month changes; predictability after modication was 21.3%. Postoperative SC was grade 0 in 13 patients, grade 1 in 21, and grade 2, in 3. There were 7 of Gr 0 and 2 of Gr 1 became one grade up. Conclusion VAVLP xation in distal radius fracture can maintain radiographic alignment without signicant reduction loss for at least 3 months. Realignment within normal range was in RI and VT, but not in RH / UV / TDA.


Background
Distal radial fracture is a very common injury, which has shown a bimodal distribution of age-speci c incidence with an increasing prevalence in adults and aging people [1][2][3]. Non-surgical treatment is generally adopted for non-or minimally displaced fractures. For displaced distal radial fractures, operative management with internal xation using volar locking plate (VLP) is preferred over percutaneous xation in recent years [4].
VLP can be divided into two types, one is of locking screws and pegs in xed angles; the other is of variable angle locking design. While a xed-angle VLP xation can improve the stability by providing a rigid construct with screws inserted and locked in a predetermined direction [5,6], the variable-angle volar locking plate (VAVLP) allows a greater adaptability for screw angle insertion to support the dorsal subchondral bone for weak and comminuted fractures [7]. However, signi cantly decreased ultimate failure moment noted at 15 -inclined screw insertion indicated potential reduction loss and recommend titanium VAVLP be used with precaution [8]. Given that reduction loss remains a critical issue after treatment of distal radius fractures [9] even in using newly designed locking plates [10], radiographic parameters anecdotally used in fracture evaluation and functional correlation [11,12] have been currently adapted for assessment of secondary collapse after fracture xation [13]. This study aims to evaluate the e cacy of VAVLP xation in the maintenance of realignment through a retrospective review and comparison of postoperative radiographs in distal radius fractures.

Methods
To evaluate the stability of VAVLP xation of radial fractures, posteroanterior (PA) and lateral views of forearm x-ray of immediately and 3 months after operation were evaluated [14,15]. The inclusion criteria were: (1) distal radial fracture diagnosed by forearm radiographs (including 5 Smith's type, 18 Colle's type, and 19 Barton's type), and (2) patients with VAVLP xation (Synthes, 2.4 mm Variable Angle LCP). A total of 43 cases which underwent surgical management for distal radial fractures between October 2011 and October 2019 in our hospital were being reviewed. The exclusion criteria were: (1) patient with incomplete medical records and follow-up (5 patients), and poor quality of radiographs (1 patient). Finally, 37 patients were included in this study. Postoperative x-ray images were taken at a mean of 1 day after operation; radiographs of 3 months following the operation were taken at a mean of 84 days after operation. All and the diagnostic imaging studies were assessed by a radiologist, an orthopedist and two medical students in internship training.

Radiographic parameters and analysis
To standardize our measurement, radiological parameters were measured on standard x-rays of the wrist according to the methods introduced by Kreder et al [16]. For both PA view and lateral view, the center of radius was measured at 3 and 5 cm below the mid-region of the proximal lunate articular surface in order to form the central axis of the radius. Radial height (RH), ulnar variance (UV) and radial inclination (RI) were measured on PA view taken with both shoulder abduction and elbow exion in 90°, forearm pronation and supination in 0° [17]. Volar tilt (VT), tear drop angle (TDA) [18], distal dorsal cortical distance (DDD) [19] and Soong classi cation (SC) [20] were measured on lateral view x-rays taken with shoulder abduction, elbow exion and forearm supination, all in 90°. RH represents the distance between the two parallel lines perpendicular to the long axis of the radius where one line passing through the distal articular surface and the other one intersects the distal articular surface of the ulnar head. UV refers to the distance between the levels of radial and ulnar articular surfaces, one line passing through the distal ulnar articular surface parallel to the other one passing through the medial radial articular surface perpendicular to the central axis of the radius. RI on AP projection represents the angle between a line connecting the radial styloid tip and ulnar aspect of the distal radial articular surface and a line perpendicular to the central axis of the radius. VT refers to the angle between a line perpendicular to the central axis of the radius and a line along the distal radial articular surface at the joint margin. TDA is the angle between a line passing through the central axis of the teardrop and a line perpendicular to the central axis. DDD refers to the distance between the tip of the most distal screw and the dorsal rim of distal radius. SC represents a tangential line drawn to the volar rim, which is parallel to the diaphyseal bone of the radial shaft in order to determine the plate prominence. Plates that do not extend the line were graded as Grade 0; Plates that extend volar to the line but remain proximal to the rim were graded as Grade 1; Plates that are distal or directly on the volar rim were graded as Grade 2. The above parameters were measured on the digital images with accuracies up to 0.01 mm and 0.1° (Fig. 1).
According to the central limit theorem, when the sample number is greater than 30 (N = 37), it tends to be normal distribution. Thus, a 2-sample paired T-test was used for comparing the postoperative radiographs with those of 3 months following operation. A 1-sample T-test was used for comparing the parameters of radiographs of 3 months following operation with the normal values quoted in past studies, in order to determine if the normal anatomy was restored. Level of signi cance was set at less than 0.05. Linear regression was applied for comparing the DDD immediately after operation with the change in value of 3 months following operations. Maximum likelihood ratio Chi-square test was used for comparing SC immediately after operation with those of 3 months following operation. With reference to different literatures, the average value of parameters were as follows: RH 11.6 mm; UV 1.5 mm (negative ulnar variance), RI 22.5°; VT 11.2; TDA 68°; value of DDD immediately after the operation is in correlation with the variance of DDD over the 3 months after the surgery [20]. All statistical analyses were performed with SPSS v21 (IBM Corporation, Armonk, NY).

Comparison with normal values
The result of comparison between radiographic parameters of 3 months following the operation with normal values, revealed signi cant differences in RH, UV, TDA when compared to their own normal values, with p = 0.000, p = 0.000 and p = 0.000 respectively. However, there is no signi cant difference for RI and VT compared to the normal values, with p = 0.184 and p = 0.127 respectively (Table 1).

Comparison with values of immediately after operation
The result of comparison between radiographic parameters of immediately after operation with 3 months following the operation, showed no statistical difference was noted when comparing the above values to the values of 3 months following the surgery, with p = 0.207, p = 0.267, p = 0.049, p = 0.368 and p = 0.276 respectively ( Table 2). Comparing the DDD immediately after operation with the change in value of 3 months following operations By comparing the DDD right after the operation with the change in values of DDD of 3 months following the operation DDD by linear regression, results showed signi cant dependence with p = 0.002, and predictability after modi cation is 21.3% (Fig. 2).
Comparing the grading of SC immediately after the operation with SC of 3 months following the operation Regarding SC, 13 cases were graded as Grade 0 after operation; 6 cases remained as Grade 0 (46.2%) and the other 7 cases (53.8%) were progressed to Grade 1 in radiographs of 3-month postoperatively. The remaining 21 cases were graded as Grade 1 after operation; 19 (90.5%) of them remained as Grade 1, and the other 2 (9.5%) cases were progressed to Grade 2 in radiographs of 3 months following the operation.
Three cases were recorded as Grade 2 after operation, and all 3 cases remained as Grade 2 (100%) in radiographs of 3 months following the operation.
To compare the grading of SC immediately after operation and 3 months following operation, maximum likelihood ratio Chi square was used and revealed signi cant dependence with p = 0.000 (Table 3).

Discussion
This study revealed that when using VAVLP for xation in distal radius fractures, RH, UV, TDA could not be restored to its normal values, while RI and VT were successfully restored to their normal values. The above results were noted in cases using xed angle VLP as well [14,15]. The potential causes behind might be due to the heterogeneity in individuals, fracture patterns and the length of treatment [21]. Another study by Pienaar et al in 2013 also stated that no matter which kind of reduction and xation was used, TDA cannot be restored to its normal value [22].
By comparing the values of parameters immediately after operation with those of 3 months following operation, results showed that RH, UV, RI, VT, TDA were able to sustain at least a 3-month period in radioulnar variance.
In analyzing the DDD change in our cases, linear regression showed a positive dependence between the values of postoperative and 3-month radiographs. Optimization of screw/plate position by measuring DDD was rst proposed in 2015 and recommended a limitation of 6 mm in maximum during surgery to avoid subsequent displacement [19]. It was even more critically concerned for elderly patients with osteoporotic bone with suggestion of DDD within 4.6 mm according to another publication in 2018 [23]. In our cases, positive dependence of postoperative DDD was noted on the DDD change at 3 months and the mean of postoperative DDD was 5.23+/-1.70. Maintenance of realignment up to 3 months was achieved in most cases with intraoperative DDD within 6 mm. The design of variable-angled locking holes in VAVLP allows screw insertion in greater adaptability to reach subchondral bone and minimize DDD for providing superior maintenance of fracture xation.
The SC was originally proposed to evaluate volar locking implant prominence and risks in exion tendon rupture. A recent clinical report analyzed 400 cases receiving two different kinds of locking plates and stated that the group using variable angle LCP had a greater SC grading [23]. In analyzing the 37 patients of our study, we found there was a trend that patients with postoperative SC grade 1 and 2 showed less subsequent displacement than those with grade 0; the difference was statistically signi cant (p = 0.000).
There are several limitations in our study. This is a radiographic analysis based on retrospective case review without control group. The sample size is small with heterogeneity in fracture pattern. Only radiographs immediately and 3 months after surgery were evaluated. In addition, no clinical correlation is documented. Institutional review board approval (IRB no. 202000939B0) was obtained to perform a review of patient records and radiographs.