The Impact of Sigmoid Notch Involvement on the Outcomes of Distal Radius Fractures: Radiological and Clinical Assessments after a Minimum of 5 Years of Follow-up

Abstract

Background

Posttraumatic osteoarthritis (OA) is one of the complications of distal radius fractures (DRFs). Involvement of the sigmoid notch (SN) is a risk factor, but there are few studies that support this. In this study, we hypothesized that SN involvement can affect the radiological and clinical outcomes of surgically treated DRFs and that there would be differences based on the degree of SN involvement.

Methods

The authors reviewed patients who underwent surgical treatment for DRF at our institution and were followed up for over 5 years. The patients were divided into 2 groups based on SN involvement. All patients underwent postoperative plain radiographs at the last follow-up to evaluate posttraumatic OA at the distal radioulnar joint (DRUJ). On computed tomography (CT) scans of the SN involvement group, articular step-off and gap distance were measured. Posttraumatic OA was graded using the Knirk and Jupiter radiographic criteria. For clinical evaluation, grip strength, wrist range of motion, pain visual analog scale score, Disabilities of the Arm, Shoulder, and Hand questionnaires, and Modified Mayo Wrist Score were assessed.

Results

Radiologically, the DRUJ OA grades were significantly higher in the SN involvement group. The step-off and gap distance measured on CT scans revealed no significant correlation with the grades. Clinical outcomes were not significantly different between the 2 groups.

Conclusions

SN involvement did not affect clinical outcomes in DRF patients with a minimum of 5 years of follow-up. However, radiologically, the OA grades were significantly higher in the SN involvement group. Therefore, in cases of DRF with SN involvement, there is no significant difference in clinical outcome, but it is necessary to explain to patients that posttraumatic DRUJ arthritis may occur in the future.

Distal radius fracture (DRF) is the second most common fracture in adults.¹⁾ Surgery is often required for irreducible fractures or uncontrolled fracture reduction. The latest development of volar locking plate (VLP) fixation has remarkably changed DRF treatment.²⁾ However, complications can occur in approximately 30% of affected patients, which include posttraumatic osteoarthritis (OA).³,⁴,⁵⁾ Knirk and Jupiter’s landmark study revealed a correlation between articular step-off and early posttraumatic OA at the distal radiocarpal joint.⁶⁾ Some studies claim that arthroscopic-assisted reduction is necessary for intra-articular fractures.⁷⁾

It is unclear whether DRFs that extend to the sigmoid notch (SN) of the distal radius can produce articular surface disruption and change joint kinematics, leading to post-traumatic arthritis and adversely affecting the clinical outcome of surgically treated DRFs.⁸⁾ The dependence of DRF clinical outcomes on distal radioulnar joint (DRUJ) involvement is controversial. The DRUJ has a complex structure and there are a few parts where the bony structure including SN contributes to stability. For this reason, there is considerable controversy in the literature regarding the outcome of surgical treatment of DRFs according to the presence or absence of SN involvement. Therefore, this study aimed to evaluate whether SN involvement affects the radiological and clinical outcomes of surgically treated DRFs. If there was an effect, the authors evaluated whether there was a difference based on the degree of SN involvement.

METHODS

The Institutional Review Board of the Chonnam National University Hospital (IRB No. CNUH 2021-054) approved this retrospective study and waived the need for informed consent from the anonymized patients.

Patients

The author retrospectively reviewed patients surgically treated using VLP with or without a Kirschner wire (K-wire) for DRFs between January 2005 and January 2016 at our institution. Inclusion criteria were patients aged over 20 years with DRFs diagnosed using plain radiography and computed tomography (CT) scans. At our institution, preoperative CT scans were performed on all patients with wrist fractures. Patients with open fractures, associated bone fractures, and DRUJ dislocation were excluded from this study. Additionally, if the ulnar fovea sign was positive, we considered that there was triangular fibrocartilage complex damage, and the case was excluded because there was accompanying damage in addition to the bone lesion. Patients with a follow-up of < 5 years, cases with malunion of the DRF, and cases with radiocarpal OA at the last follow-up were also excluded. There was no patient who already had DRUJ OA at the time of fracture. Finally, the included patients were divided into 2 groups. The authors defined SN involvement based on whether the fracture line was present in the SN in any plane on axial and coronal views on preoperative CT scans; all other patients were included in the SN-intact group. In the SN involvement group, the authors checked the degree of step-off and gap distance of the articular surface of the SN on preoperative CT scans. Articular step-off was measured in the axial and coronal planes (Fig. 1). The measurement was performed within the articular surface of the DRUJ image, which demonstrated the maximal step-off of the fracture fragments of the articular surface. Similarly, gap distance was measured in the axial and coronal planes and on the image demonstrating the maximal gap of the articular surface (Fig. 2). Measurements were performed for each patient by 2 authors (YSK and JYH) using our institution’s proprietary electronic radiology viewing and measurement software (INFINITT PACS M6). The measurements demonstrated good reliability with an intraclass correlation coefficient > 0.8.

Fig. 1. Flowchart depicting the selection process and number of wrists among patients with distal radius fracture. TFCC: triangular fibrocartilage complex, DRUJ: distal radioulnar joint, DRF: distal radius fracture.

Fig. 2. Points A and B are marked at subchondral fracture margins of the sigmoid notch. The first line was drawn between the dorsal corner or inferior corner of the sigmoid notch and point B. The second line drawn through point A was perpendicular to the first line. The intersection of both lines is point C. Step-off of the sigmoid notch was measured as the distance between points A and C. Gap distance was measured as the distance between points B and C on axial (A) and coronal (B) planes of computed tomography images of the distal radius.

Surgical Technique

All the patients underwent open reduction and VLP fixation under interscalene brachial plexus block or general anesthesia. The VLP was applied through an incision over the volar side of the wrist, and no other combined dorsal approach was used. The surgeons determined the surgical procedure, plate type, and screw number and configuration. Some surgeons used a splint/cast after the procedure; however, the fixed angle stability provided by the VLP was usually sufficient to allow early controlled range of motion (ROM) exercises.

Rehabilitation and Follow-up

The finger, elbow, and shoulder movement exercises resumed the day after surgery. Patients were followed up in 2 weeks, 4 weeks, and then every 4 weeks until fractures healed completely. The surgeons provided wrist exercise advice based on the fracture healing status, a standard postoperative rehabilitation protocol for the wrist that includes exercises to achieve movement in all directions.

Radiological Assessment

All the patients underwent follow-up plain radiography of the operated wrist. These films were then independently assessed for the degree of DRUJ posttraumatic OA. Posttraumatic arthritis on plain radiography was graded using the Knirk and Jupiter radiographic criteria, and the grades were recorded along with the length of time from injury to the final follow-up. The classification according to the Knirk and Jupiter criteria for DRFs were as follows: grade 0, no signs of posttraumatic arthritis; grade 1, slight narrowing of the joint space; grade 2, marked joint space narrowing with marginal osteophyte formation; and grade 3, bone-on-bone posttraumatic arthritis with marginal osteophytes and subchondral cysts (Fig. 3).⁶⁾

Fig. 3. Posteroanterior radiographs of a patient with Knirk and Jupiter grade 0 (A) at 7 years postoperatively and another patient with Knirk and Jupiter grade 2 (B) at 8 years postoperatively. G0: grade 0, G2: grade 2.

Clinical Assessment

Clinical evaluation was performed at the last follow-up. The ROM of the bilateral wrist was measured using a goniometer, and pronation and supination motions were measured based on a neutral position. The piano key and grind tests were performed. Crepitus and pain were assessed during rotation, and the pain was estimated using a pain visual analog scale (VAS), with 0 representing no pain and 10 representing extreme pain. Wrist function was assessed using the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire to evaluate upper extremity dysfunction. The DASH score is a globally established upper extremity disability instrument used to evaluate various disorders of the upper extremity with scores of 0–100 (with 0 representing no disability and 100 representing maximum disability),⁹⁾ and the Modified Mayo Wrist Score (MMWS) was checked. The MMWS comprises a total of 100 points, divided among the evaluator’s assessments of pain (25 points), active flexion/extension arc as a percentage of that of the opposite side (25 points), grip strength as a percentage of that of the opposite side (25 points), and the ability to return to regular employment or daily activities (25 points). The pain was rated as no pain (25 points), mild (20 points), moderate (10 points), or severe (0 points) by the author (YSK and JHL) based on the patient’s subjective description. The total score ranged from 0 to 100 points, with higher scores indicating better results.¹⁰⁾

Statistical Analysis

The independent t-test was performed to assess significant differences between groups for mean VAS scores, MMWSs, and DASH scores. Pearson’s chi-square test was used to compare the frequency distributions between both groups for findings in physical examinations, such as the piano key test, grind test, and crepitus at rotation. The Mann-Whitney U-test was performed to compare the Knirk and Jupiter grades of posttraumatic OA between both groups. Spearman’s rho correlation coefficient compared the association of each score and Knirk and Jupiter grades with the degree of articular step-off of the DRUJ’s cartilage surface (mm) in the axial and coronal planes and gap distance (mm) in the axial and coronal planes. Statistical analyses were performed using the IBM SPSS Statistics for Windows version 18.0 (IBM Corp.).

RESULTS

Demographics

A total of 33 cases in 32 patients were included. Nineteen cases featured a disrupted SN and 14 cases an intact SN. The age of patients in the involved and intact groups was 55.8 years (± 9.7) and 54.2 years (± 13.9), respectively; the mean follow-up durations of the involved and intact groups were 81.0 months (± 24.3) and 99.3 months (± 32.9), respectively (Table 1). No significant differences were observed between both groups with respect to sex (p = 0.797), age (p = 0.695), and dominant hand (p = 0.284).

Table 1. Demographic Variables.

Variable		DRUJ involvement group (n = 19)	DRUJ intact group (n = 14)	p-value*
Age at surgery (yr)		55.8 ± 9.7	54.2 ± 13.9	0.695
Sex				0.797
	Female	9 (47.4)	6 (42.9)
	Male	10 (52.6)	8 (57.1)
Dominant hand affected		13 (68.4)	7 (50.0)	0.284
Time to surgery (hr)		138.9 ± 111.0	174.9 ± 159.0	0.450
Mean follow-up duration (mo)		81.0 ± 24.3	99.3 ± 32.9	0.077
Plate removal		10 (52.6)	5 (35.7)	0.265

Values are presented as mean ± standard deviation or number (%).

DRUJ: distal radioulnar joint.

^*The independent t-test was used to compare the means between the 2 groups, Pearson’s chi-square test was used to compare frequency distributions between the 2 groups, and the Mann-Whitney U-test was used to compare differences in classification deterioration between the 2 groups.

Radiological Outcomes

In radiological assessment, the Knirk and Jupiter grades were significantly higher in the SN involvement group (p = 0.043) (Table 2). However, the degree of step-off and gap distance measured in the axial and coronal planes on preoperative CT revealed no significant correlation with postoperative Knirk and Jupiter grades (Table 3).

Table 2. Radiological and Clinical Outcomes.

Variable		Sigmoid notch involvement group (n = 19)	Sigmoid notch intact group (n = 14)	p-value*
Knirk and Jupiter grade		1.1 ± 0.6	0.6 ± 0.7	0.043†
ROM (°)
	Flexion	74.1 ± 12.2	68.6 ± 16.8	0.301
	Extension	82.3 ± 11.4	83.9 ± 9.1	0.671
	Ulnar deviation	29.1 ± 6.8	31.5 ± 9.4	0.421
	Radial deviation	19.1 ± 7.2	19.3 ± 6.5	0.742
	Pronation	74.9 ± 12.8	77.0 ± 10.1	0.607
	Supination	88.3 ± 4.8	87.9 ± 5.5	0.860
Grip strength compared to intact side (%)		86.6 ± 22.5	80.6 ± 25.9	0.496
	Dominant hand	88.3 ± 25.7 (n = 13)	89.9 ± 25.2 (n = 7)	0.383
	Non-dominant hand	82.5 ± 13.0 (n = 6)	81.3 ± 24.9 (n = 7)	0.894
Physical examination
	Piano key test	0	0	1.000
	Grind test	0	0	1.000
	Crepitus on rotation	4 (21.1)	0	0.052
Clinical score
	VAS	1.15 ± 0.9	0.79 ± 0.6	0.201
	DASH	7.14 ± 9.9	7.04 ± 11.4	0.981
	MMWS	79.12 ± 9.2	82.78 ± 8.7	0.250

Values are presented as mean ± standard deviation or number (%).

ROM: range of motion, VAS: visual analog scale, DASH: Disabilities of the Arm, Shoulder and Hand, MMWS: Modified Mayo Wrist Score.

^*The Mann-Whitney U-test was used to compare differences in osteoarthritis grade deterioration between the 2 groups. The independent t-test was used to compare means between the 2 groups, and the Pearson’s chi-square test was used to compare frequency distributions between the 2 groups.

^†p-value < 0.05.

Table 3. Correlation between Degree of DRUJ Disruption and Posttraumatic Osteoarthritis.

	Fracture step-off		Fracture gap distance
	Axial plane	Coronal plane	Axial plane	Coronal plane
Knirk and Jupiter grade	0.328 (0.199)	0.347 (0.172)	0.239 (0.356)	0.389 (0.123)

Values are presented as Spearman’s rho (p-value).

DRUJ: distal radioulnar joint.

Spearman’s rho correlation coefficient was used to analyze the relationship between step-off and gap distance with Knirk and Jupiter grades.

Clinical Outcomes

At the final follow-up, grip strength (p = 0.496) did not significantly differ between both groups, regardless of whether it was the dominant or non-dominant hand. Furthermore, no significant difference was observed in wrist ROM (p = 0.301–0.860). Similarly, findings in physical examinations such as the piano key test (p = 1.000), grind test (p = 1.000), and crepitus during rotation (p = 0.052) were not significantly different (Table 2).

DISCUSSION

Posttraumatic OA is a common complication of DRFs, with SN involvement identified as a risk factor. This study reviewed patients who underwent surgical treatment for DRF and were followed up for over 5 years. Patients were categorized based on SN involvement, the SN involvement group showed significantly higher Knirk and Jupiter grades radiologically, although step-off and gap distance did not correlate with these grades. Clinically, there were no significant differences between groups.

The DRUJ allows forearm rotation to place the hand in the desired position to perform tasks without interfering with the hand-gripping function. The ulna is the stable part of the forearm in which the radius rotates; the DRUJ stability is provided by the interaction between bones, muscles, and ligaments. Therefore, the authors thought that patients with SN involvement would experience an adverse effect on DRUJ function, and the incidence of functional complications would be higher than that of patients with intact SN. There have been studies on the differences in outcomes according to SN involvement in DRFs. Kong et al.¹¹⁾ reported short-term follow-up results of intensified pain, especially with forearm rotation. However, no difference was observed in the midterm follow-up results of this study. This short-term result may be because the degree of fracture in the DRUJ involvement group was more severe. Vitale et al.¹²⁾ reported that fractures involving the SN did not appear to have a greater prevalence of DRUJ posttraumatic arthritis in operatively treated patients at greater than 6 years of follow-up. Postoperative SN step-off, diastasis, or DRUJ subluxation had a minimal effect on upper extremity function, but fractures with a coronal step-off of > 1.0 mm exhibited higher levels of upper extremity dysfunction. Although the radiological results were contrary to the results of this study, the clinical results were similar in some ways. In this study, the K-L grade was higher in patients with a step off of 1 mm or more, but it was not statistically significant due to the small number of samples. Meanwhile, Liu et al.¹³⁾ stated that DRUJ involvement did not affect clinical outcomes. In this study, no significant clinical difference was observed between both groups, as reported by Liu et al.¹³⁾

According to Giannoudis et al.,¹⁴⁾ different joints, and even different areas of the same joint, exhibit varying tolerances for posttraumatic articular step-offs. For DRUJ, the tolerance cutoff is 1 mm.¹²⁾ The DRUJ is stabilized through a complex arrangement involving both bony congruence and soft-tissue constraints.¹⁵⁾ However, as demonstrated in the cadaveric study by Cole et al.,¹⁶⁾ the bony architecture of the SN does not play a crucial role in the stabilization of the DRUJ in the absence of associated soft-tissue injuries. In this study, there were only 5 cases in which the step-off was more than 1 mm, and since it was measured preoperatively, it is estimated that the step-off in most cases was less than 1 mm after surgery. Additionally, as patients showing DRUJ instability on physical examination were excluded, SN involvement is assumed to have little impact on clinical outcomes in this study.

However, radiologically, the Knirk and Jupiter grades were significantly higher in the SN involvement group. This means that although there were no clinical symptoms, DRUJ damage caused DRUJ arthritis progression after trauma. Conversely, when the step-off and gap distance pre- and postoperatively were markers of the degree of DRUJ damage, no significant effect on the deterioration of Knirk and Jupiter grades was observed. This could mean that DRUJ damages are significant. However, if the injury is properly treated with surgical treatment, the severity of the injury does not have a significant effect on posttraumatic arthritis. It is advisable to explain to patients that there will be no significant difference in clinical outcome, when surgical treatment achieves an acceptable reduction. However, patients with SN involvement should be informed that they may develop posttraumatic DRUJ arthritis in the future and may need subsequent treatment and careful follow-up. DRUJ arthritis can cause pain and limit wrist ROM. The general management of symptomatic DRUJ arthritis is nonsurgical, such as immobilization, lifestyle modification, gentle physical therapy, and administration of non-steroidal anti-inflammatory drugs. However, surgical treatment is required for patients with refractory pain. In patients with uncontrolled pain, surgical treatment is necessary. Resection arthroplasty can be performed for pain management, and it should be performed with great caution due to the significant functional loss that occurs postoperatively.

This study has limitations. First, the authors did not use immediate postoperative CT scans to assess the step-off and gap distance of the SN. The degree of DRUJ disruption on preoperative CT scans does not represent the immediate postoperative step-off or gap as a factor that influences the clinical and radiological outcomes at the last follow-up because the DRUJ disruption degree (step-off or gap distance) would change after VLP use through reduction or surgical procedures. In addition, the proportion of follow-up among all DRF patients was low; therefore, this study’s data might not represent all DRF patients. Studies with a higher level of evidence, such as prospective randomized controlled trials, may be needed.

The Knirk and Jupiter grades were significantly higher in the SN involvement group. However, the step-off and gap distance measured on CT scans revealed no significant correlation with the grades. Clinically, they did not significantly differ after a minimum of 5 years of follow-up. Therefore, in cases of DRFs where preoperative CT reveals involvement of the SN, it is recommended to reassure the patient that if surgical treatment achieves an acceptable degree of reduction, there should be no significant difference in clinical outcomes; however, explaining to the patient that posttraumatic DRUJ arthritis may occur in the future is necessary.