The Effect of Radial Shaft Dorsal Screw Prominence in Volar Locking Plate Fixation of Distal Radius Fractures

Introduction

Over the past 15 years, volar locked plating has become the predominant method of fixation of distal radius fractures. ¹⁰ In addition to being biomechanically stable, they carry less concerns of tendon irritation when compared with dorsal plates. ¹² However, reports of extensor tendon complications with volar locked plates have been reported.^1,2,4,5

Extensor tendon complications in patients with distal radius fractures treated with volar locked plating are likely due to a variety of factors. First, extensor pollicis longus (EPL) tendon ruptures may occur as a result of the injury itself and have been reported even in minimally displaced fractures treated without surgery. ⁶ Second, iatrogenic injury to extensor tendons may be attributable to predrilling past the dorsal cortex or with prominent screw placement. ¹

Research on iatrogenic injuries to extensor tendons has been largely focused on the metaphyseal and epiphyseal regions of the dorsal distal radius. Here, the extensor tendons are in close proximity to the cortical surface as they lie in their extensor compartments and are subject to iatrogenic injury from distal locking screws. However, little attention has been given to the effects of prominent screws in the radial shaft. The purpose of this study was to examine whether there was an association between prominent proximal screw fixation and extensor tendon irritation, tendon rupture, or hardware removal in patients undergoing volar locked plating for distal radius fractures.

Materials and Methods

After institutional review board approval, a retrospective review was conducted to identify patients who had undergone volar locked plating of a distal radius fracture between April 2002 and March 2016 at our institution. The choice of surgical fixation and indication for volar locked plating was determined by the operative surgeon. All patients with radiographic follow-up in our electronic medical record image display application were included in the study. Patients were excluded from the study if they were younger than 18 years of age, pregnant, incarcerated, did not have at least one postoperative lateral radiograph, or were followed for less than 6 months postoperatively.

Each patient’s most immediate lateral postoperative radiograph was reviewed on a digital DICOM image viewer and magnified to 400%. The most prominent cortical screw was identified. A line along the length of the screw was made and measured from the outer dorsal cortex of the radial shaft to the tip of the screw (Figure 1). A single observer (NP) measured all radiographs in the study.

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Figure 1.

Measurement of the most prominent cortical screw on a lateral radiograph. The distance from the tip of the screw to dorsal cortex of the radius is measured along a line bisecting the screw.

During the defined study period, 261 distal radius fractures in 255 patients were identified that met inclusion and exclusion criteria. In all, 198 women and 57 men were treated, with a mean age of 54.6 years (range: 18-93 years). Patients were followed for an average of 17.4 months (range: 6-107 months) after surgical fixation (Table 1). Clinical data were reviewed including demographic variables, extensor tendon irritation, extensor tendon rupture, and hardware removal.

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Table 1.

Demographic Characteristics of the 255 Patients in the Study Population.

Age, years (SD)	54.6 (16.3)
Sex, n (%)
Male	57 (22.4)
Female	198 (77.6)
Body mass index, mean (SD)	27.7 (6.68)
Smoker, n (%)	20 (7.67)
Last follow-up, months (SD)	17.4 (15.9)

A paired Student t test was used to compare continuous preoperative and postoperative variables. A chi-square test was used to compare categorical variables between groups. All analyses were carried out using the JMP statistical software package (Version 8; SAS Institute Inc, Cary, North Carolina). A P value of <.05 was considered significant.

Results

Of the 261 distal radius fractures managed with volar plate fixation, 39 (14.9%) underwent subsequent hardware removal. The mean time from surgical fixation to hardware removal was 15.8 ± 18.6 months. Nine patients (3.5%) were found to have clinically significant extensor tendon irritation including one patient (0.33%) with an extensor tendon rupture.

The most prominent radial shaft screw was a mean 1.48 mm proud of the outer dorsal radial cortex (range: 0-3.8 mm) (Figure 2a). Sixteen (6.2%) fractures were fixed with no screws proud of the dorsal cortex (ie, 0 mm). Twenty-three percent of treated distal radius fractures were found to have a shaft screw greater than 2 mm proud of the outer dorsal radial cortex (Figure 2b).

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Figure 2.

Lateral radiographs with prominent shaft screws measuring 2 mm (a) and 3.5 mm (b).

Comparing patients who underwent hardware removal with those who did not, there was no statistically significant difference in the mean radial shaft screw prominence beyond the outer dorsal radial cortex (1.50 mm vs 1.48 mm, P = .87). Similarly, the proportion of patients with prominent (>2 mm proud of the outer dorsal radial cortex) radial shaft screws was not significant (23.1% vs 22.5%, P = .93). There were 3 hardware removals (18.8%) in the group with no shaft screws proud of the dorsal cortex. There was no statistically significant difference between shaft screw prominence and extensor tendon irritation (P = .45). In the single patient with an EPL tendon rupture, the most prominent shaft screw was 0.4 mm proud of the dorsal cortex. Last, comparing patients with prominent and nonprominent screws, there was no statistically significant difference in hardware removal rates (15.3% vs 14.85%, P = .93) (Table 2, Figure 3).

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Table 2.

Association Between Complications and Prominent Screw Length.

n	Complications
	Hardware removal			Extensor tendon irritation
	Yes	No	P value	Yes	No	P value
	39	222		9	252
Screw length, mm (SD)	1.50 (0.8)	1.48 (0.8)	.87	1.76 (0.8)	1.47 (0.8)	.28
Screw > 2 mm, n (%)	50 (23)	9 (23)	.93	3 (33)	56 (22)	.45

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Figure 3.

Histogram of screw prominence and hardware removal.

A post hoc power analysis demonstrated 80% power to detect a 13% difference in hardware removal rates between patients with screws greater than 2 mm proud and those without.

Discussion

Tendinopathy or tendon irritation is a common complication following plate fixation of distal radius fractures, which may present with prodromal symptoms of pain or difficulty with finger or thumb extension. ² Although more common with dorsal plate fixation, extensor tendon irritation may be seen with volar locked plates as well, with rupture rates as high as 8.6%. ¹ The rate of extensor tendon irritation in our study was 3.5%. This is slightly higher than the 2% reported rate of extensor tenosynovitis in a recent systematic review, which also found a 0.85% rate of extensor tendon rupture with volar plate fixation. ² One patient in our study suffered an extensor tendon rupture.

Much of the research addressing iatrogenic causes of extensor tendon rupture has focused on the distal fixation. ¹³ Cadaveric models have provided relative lengths of distal screws to avoid dorsal cortex penetration.^3,8 Wall et al demonstrated that unicortical locking screws of at least 75% of the length of bicortical screws provided similar biomechanical stiffness. ¹⁵ White et al described a classification system for dorsal screw prominence according to the distance of the screw tip beyond the dorsal cortex (less than or greater than 2 mm) and demonstrated a positive correlation between screw prominence and tendinopathy or rupture. ¹⁶ Finally, special fluoroscopic views have been advocated for intraoperative confirmation of safe screw lengths.^7,11 The purpose of our study, however, was to assess the effect of dorsal screw prominence in proximal radial shaft screws through a volar locking plate.

Often the first radial shaft screw is placed in an oblong hole to lag the plate to bone and allow for adjustments in plate position. ¹ In an effort to gain adequate screw purchase, this first screw may be intentionally longer than necessary. After the plate is reduced to bone and further proximal fixation is achieved, the decision to replace the first screw with a more appropriate length screw is surgeon dependent. Potentially, during final fluoroscopic imaging, other radial shaft screws may appear prominent posing a therapeutic dilemma for the surgeon.

Although no evidence exists to guide decision-making for the surgeon faced with a prominent radial shaft screw, there are a few biomechanical factors to consider. First, most systems use self-tapping radial shaft screws. Because these screws have flutes at their tips, full circumferential thread-bone interface is not possible for the entire length of the screw. ⁹ Second, self-tapping screws create bony threads by either cutting or deforming cortical bone. Thus, multiple attempts at screw fixation lead to less fixation strength. Last, many fixation systems provide shaft screws in 2 mm increments, and so the decision to downsize a screw must take into account the potential fixation of a 2 mm shorter screw.

Our study suggests that the effect of dorsal screw prominence of radial shaft screws does not significantly increase the rate of hardware removal within a range of 2 mm, a common screw length interval. Similarly, we did not find a statistically significant difference between radial shaft screw prominence and tendon irritation. Therefore, when assessing a lateral radiograph after volar plate fixation of a distal radius fracture, we do not recommend routinely revising radial shaft screw less than 2 mm proud of the outer dorsal radial cortex.

Our cutoff of 2 mm was used because of its relevance to fixation systems, but accurately measuring the length of screw prominence on intraoperative fluoroscopic imaging is less precise. Although not published by implant companies, the pitch of the cortical screws used in volar locked plates are usually about 1 mm. Thus, the surgeon can count the number of threads beyond the outer dorsal cortex to estimate the absolute length of the screw.

There are several limitations inherent to this retrospective study. Although fluoroscopic imaging may be more clinically relevant as it is what is used to assess screw lengths intraoperatively, we used postoperative radiographs as they are more readily and reliably available on our DICOM system allowing for proper screw length measurements. Similarly, we did not control for distal screw prominence, as the specialized images required to assess this variable were not routinely obtained postoperatively in our practice. To collect the largest sample size, we did not control for other variables that may have affected our results including mechanism of injury, associated injuries, surgeon experience, surgical approach, and type of implant used.

A minimum follow-up of 6 months may not identify all extensor tendon complications. Thorninger et al reported a median time to extensor tendon rupture of 7.1 months in their study of patients with distal radius fractures followed for a minimum of 2 years. However, their hardware removal rate of 7.1% with 1.7% of patients complaining of tendon irritation was less than that found in our series with shorter follow-up. ¹⁴

Last, we were powered to detect a 13% difference in hardware removal rates between the prominent and nonprominent screw group. This may put us at risk of type II error. Tendon ruptures were rare in our study population, and we were not able to specifically attribute tendon irritation and tendon ruptures to radial shaft screw prominence versus other etiologies. However, we feel that by including all cases of hardware removal, tendon irritation and tendon ruptures, despite the myriad of potential causes, increased the sensitivity of our findings.

Dorsally prominent radial shaft screws present an operative dilemma for the surgeon. Measuring screw lengths in the radial shaft with a depth gauge is clinically appropriate and educational for trainees. However, dorsal screw prominence may be unavoidable in initial lag screw fixation. This study does not support the routine downsizing of prominent screws 2 mm or less.