MRI‐Related Risk Factors for Distal Radioulnar Joint Instability

Abstract

Objective

Instability of the dorsal radioulnar ligament (DRUL) is caused by multiple factors from bony and soft tissue structures. Studies of DRUJ instability based on MRI have rarely been reported. This study aims to investigate related instability factors in the distal radioulnar joint (DRUJ) after trauma based on MRI imaging.

Methods

The MRI imaging was performed on 121 post‐traumatic patients with or without DRUJ instability from April 2021 to April 2022. All patients demonstrated pain or attenuated wrist ligamentous tissue quality with physical examination. The interesting variables, including age, sex, the distal radioulnar transverse shape, the triangular fibrocartilage complex (TFCC), DRUL, the volar radioulnar ligament (VRUL), distal interosseus membrane (DIOM), the extensor carpi ulnaris (ECU), and pronator quadratus (PQ), were analyzed using univariable and multivariable logistic regression model. The different variables were compared in radar plots and bar chart.

Results

An average age of 121 patients was 42.16 ± 16.07 years. The 50.4% DRUJ instability existed in all patients and the distal oblique bundle (DOB) presented in 20.7% of patients. The TFCC (p = 0.03), present DIOM (p = 0.001), and PQ (p = 0.006) were identified to be significant in final multivariable logistic model. The percentage of patients with ligament injuries were general higher in DRUJ instability group. The patients with absent DIOM had a higher rate in DRUJ instability, TFCC, and ECU injury. There was higher stability in shape of C‐type, intact TFCC, and present DIOM.

Conclusion

DRUJ instability is closely associated with TFCC, DIOM, and PQ. It could provide a potential for early detection of potential instability risk and taking necessary preventive measures.

Flowchart of patient's identification and selection

Introduction

The distal radioulnar joint (DRUJ) facilitates pronation and supination of the wrist, with only about 10% of articular surface contact at extremes. ¹ The shape of the sigmoid notch is important for wrist instability and is divided into four types, ² with the flat type being more prone to instability. While bony structure only accounts for 20% of the DRUJ's stability, ³ surrounding soft tissues like the triangular fibrocartilage complex (TFCC), dorsal and volar radioulnar ligaments (DRUL and VRUL), and interosseus membrane (IOM) play a crucial role. ⁴ , ⁵ , ⁶ The TFCC is crucial for stabilizing the joint and dampening loads transferred through the ulnocarpal joint, and is a ligament‐cartilage complex consisting of multiple structures.

The DRUL and VRUL attached to the TFCC are other major stabilizers of DRUJ. ⁷ While the radius is pronated around the ulna to limit DRUJ over a range of activity, the dorsal superficial fibers tighten as the deep palmar fibers do. Conversely, the palmar superficial fibers and the deep dorsal fibers tighten in supination of the forearm. ⁸ , ⁹ , ¹⁰ , ¹¹ , ¹² The importance of the ligaments could hold the rotational extent of DRUJ. The pronator quadratus ⁹ , ¹⁰ , ¹¹ , ¹² , ¹³ is an important secondary stabilizer. It could generate tension in the distal radioulnar joint during pronation and prevent interposition of the capsule and joint diastasis. The IOM, as the fibrous connective tissue connecting the radius and ulna, also functions as a longitudinal and a transverse stabilizer of the forearm. ¹⁴ , ¹⁵ , ¹⁶ , ¹⁷ Other secondary stabilizers including the ECU tendon sheath, meniscal homolog, the ulnolunate and ulnotriquetral ligaments, and part of the joint capsule have been less well‐studied. ¹⁸

The importance of studying the risk factors for DRUJ instability lies in several aspects. Firstly, it allows for patient risk assessment to identify potential instability risks and take preventative measures. Secondly, early intervention before the onset of symptoms can reduce their occurrence and development, lower incidence rates, and reduce the economic burden on society and individuals. For diagnosed patients, it can help doctors develop more accurate treatment plans, improve treatment success rates, and guide rehabilitation training.

Instability of DRUJ resulted from multiple factors regading bony and soft tissue structures, and the diagnosis of the instability is mainly based on medical history, physical examination, and imaging examination. The X‐ray, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonography (US) methods ¹⁹ , ²⁰ , ²¹ , ²² play important roles in the diagnosis of DRUJ instability. Actually, because of bone overlap in X‐ray, the radiation exposure associated with CT and lower reproducibility using US. MRI is a non‐invasive imaging technique that offers high‐resolution images of joint soft tissues, enabling the detection of soft tissue abnormalities and pathologies in the ulnar/radial joint. It also allows for quantitative assessment of joint structure and function, making it possible to detect subtle changes in joint stability and accurately evaluate joint pathology and instability degree. MRI provides objective diagnostic evidence, reducing diagnostic errors and missed diagnoses, and is valuable in guiding clinical treatment and rehabilitation. Its use in studying risk factors for ulnar/radial joint instability is a reliable and effective method that provides accurate diagnostic and therapeutic guidance for clinical practitioners. At present, the factors affecting the stability of DRUJ based on MRI imaging analysis are rarely reported in the previous literature. The purpose of the study is (i) explore the potential MRI parameters and evaluate the different risk factors in examining the DRUJ instability; and (ii) explain the meaningful outcome indicators.

Methods

Patient Enrollment and Outcome Definition

From 1 April 2021 to 1 April 2022 we recruited the patients who underwent wrist MRI examinations from our database of radiography. Flowchart of patients’ identification and selection is shown in Figure 1. Inclusion criteria included: (i) patients with wrist joint injury caused by trauma; (ii) instability of the DRUJ which is more significant than the contralateral side were initially diagnosed through physical examination and medical history; (iii) complete clinical data and imaging data with enough scanning range. Exclusion criteria included: (i) insufficient coverage of MRI scan; (ii) history of systemic autoimmune diseases, infection, or tumor; (ii) fracture; (iv) children and adolescents with unclosed epiphyseal plates.

Fig. 1.

Flowchart of patient identification and selection

The primary variables of interest included age, sex, and the following imaging indicators: the distal radioulnar transverse shape, TFCC, DRUL, VRUL, IOM, ECU, PQ. The study was approved by the Ethics Committee of Tianjin Hospital (No. 2020‐02), and informed consent was signed for the participation of patients.

MRI Protocol and Measurement

MRI is effective in identifying and determining the extent of the lesion within the DRUJ and adjacent soft tissue, as shown in Figure 2. (i) Inspection and measurement equipment: the equipment used 3.0T high field intensity MRI (Ingenia CX, Philips Healthcare, Best, the Netherlands) with a 24‐channel limb coil. Image data were measured on an image and information management software (Philips IntelliSpacePortal‐9.0). (ii) Examination position: the patient adopts prone position, the wrist of the affected limb is straight, the palm is fixed downward, the head is padded with sponge pad, and the head is in a comfortable position as far as possible. Forearm pad height and shoulder level, tied external fixation, reduce motion artifacts: align the center of the coil with the distal radioulnar joint (DRUJ). The wrist must be fixed within the coil without movement. Move to the opposite side and bring the distal forearm as close to the center of the magnetic field as possible. (iii) Scanning range: the interosseous membrane of the distal forearm originates from distal 1/6 of the ulna to the lowest margin of the radial sigmoid notch. An early cadaveric study recorded that the average proximal edge of the interosseous membrane of the distal forearm was 59 mm (range, 53–63 mm). Consequently, we chose to cover the forearm from the wrist to the proximal end of the ulnar bone by at least 60 mm. MRI scan range of wrist joint was performed according to conventional scan rules. During MRI, we considered the DOB present when the DIOM thickness was more than 1.0 mm. ²³ Positive results showed that the continuity and homogeneity of the original ligament was interrupted and replaced by curled, high‐intensity edema signal on T2‐weighted imaging. The damage result of TFC was decided according to the classic Palmer classification.

Fig. 2.

MRI scans of the distal radioulnar joint. (A) The normal IOM in the distal radioulnar joint (arrow). (B) MRI scan confirms the distal radioulnar joint instability. (C) the edema of pronation quadratus muscle (arrows). (D) The intact interosseous membrane was interrupted and the surrounding soft tissue was edema (arrow). MRI, magnetic resonance imaging

MRI sequence parameters of distal radioulnar joint was identified on: (1) T2‐weighted imaging (T2WI): TR:4597 ms, TE:65 ms, bandwidth: 235 kHz, field of vision: 140 mm × 109 mm, layer thickness: 2.0 mm, layer spacing: 1 mm, matrix: 173 × 145, excitation times: two, scanning time: 76 msec; (2) 3D‐NeverView: TR: 1800 ms, TE: 120 ms, bandwidth: 290 kHz, field of vision: 200 mm × 120 mm, layer thickness: 1.2 mm, layer spacing: −0.6 mm, matrix: 200 × 119, excitation times: five, scanning time: 227 msec; (3) Cross‐fat suppression proton density weighted imaging (PDWI): Time of Repetition (TR): 2000 ms, Time of Echo (TE): 20 ms, bandwidth: 255 khz, field of vision: 180 mm × 100 mm, layer thickness: 2.5 mm, layer spacing: 0.25 mm, matrix: 256 × 144, excitation times: 1.5, scanning time: 56 s.

Statistical Analysis

Instability of DRUJ was taken as the outcome variable. Independent variables included demographic variables, such as existent of DIOM, injury of the TFCC, DRUL, VRUL, ECU, and PQ. Through a univariate logistic regression analysis, the factors influencing instability of DRUJ were extracted from numerous demographic or categorical variables and included age, sex, lateralization, anatomic shape of DRUJ, ulnolunate ligament, and ulnotriquetral ligament.

Data were analyzed using SPSS 22.0 statistical software (SPSS Inc., Chicago, IL, USA). Continuous variables were showed as mean ± standard deviation or median [interquartile range (IQR)]. To compare data with a normal distribution, independent samples‐ or paired sample‐T tests were utilized, whereas non‐parametric tests were used to analyze data with a non‐normal distribution. To compare the category variables, Pearson's chi‐square tests were used. Where the sample size was abnormal distribution, the data was assumed to be nonparametric and a Mann–Whitney U‐test was used. Univariable and multivariable logistic regression models were applied to detect any the factors affecting DRUJ instability. Variables which presented with a p value of <0.15 in univariate analysis were included in the multivariate analysis with a method of backward stepwise selection process. Results of the univariate and multivariate analyses were shown with OR plus the 95% confidence interval (95% CI), and results were presented in a forest plot. A p value <0.05 was considered statistically significant. A p value <0.1 was referenced, otherwise no valid values (NS) were used.

Results

General Analysis

A total of 121 patients with complete data of MRI examination were included in the final analysis. The average age of the participants was 42.16 ± 16.07 years, ranging from 16 to 85 years. About 50.4% of the participants had instability of the distal radioulnar joint (DRUJ). Patient characteristics for each of the matched cohorts are summarized in Table 1.

TABLE 1.

Baseline characteristics of the study population

Characteristics	Mean or Sample	Percentage
Age (year)	42.16 ± 16.07
<36 years	51	42.1
≥36 years	70	57.9
Sex
Male	61	50.4
Female	60	49.6
Lateralization
Left side	55	45.5
Right side	66	54.5
DRUJ: transverse shape
I: Flat	43	35.5
II: Ski slope	33	27.3
III: C‐type	27	22.3
IV: S‐type	18	14.9
Stability of the DRUJ
Yes	60	49.6
No	61	50.4
TFCC
Intact	54	44.6
IA	8	6.6
IB	35	28.9
IA + IB	18	14.9
II	6	5
IOM
Existent	25	20.7
Deficient	96	79.3
DRUL
Normal	103	85.1
Abnormal	18	14.9
VRUL
Normal	68	56.2
Abnormal	53	43.8
ECU
Normal	85	70.2
Abnormal	36	29.8
PQ
Normal	83	68.6
Abnormal	38	31.4
UL
Normal	106	87.6
Abnormal	15	12.4
UT
Normal	106	87.6
Abnormal	15	12.4
Total	121	100

Note: Distribution of baseline characteristics

Abbreviations: DRUJ, distal radioulnar joint; DRUL, the dorsal radioulnar ligament; ECU, the extensor carpi ulnaris; IOM, interosseus membrane; PQ, pronator quadratus; TFCC, the triangular fibrocartilage complex; UL, ulnolunate ligament; UT, ulnotriquetral ligament; VRUL, the volar radioulnar ligament.

Logistic Regression Analysis

In the multivariate logistic regression analysis, the result demonstrated that the values of DIOM (odds ratio [OR]: 0.107, 95% confidence interval [CI]: 0.028–0.409, p = 0.001), IA + B of TFCC (OR: 4.640, 95% CI: 1.159–18.580, p = 0.030), and PQ (OR: 4.759, 95% CI: 1.563–14.492, p = 0.006) were independent risk factors associated with DRUJ instability. Figure 3 showed statistical outcomes of the univariate and multivariate logistic regression analysis through Forest plot.

Fig. 3.

Forest plot presenting the results of univariable and multivariable logistic regression analyses. Present DIOM (p = 0.005), IB and IA + B type in TFC (p = 0.006, 0.009), DRUL (p = 0.017), VRUL (p = 0.003), PQ (p = 0.003), and ECU (p = 0.022) were demonstrated to be of significant difference in univariate analysis. While in multivariable analysis, present DIOM (p = 0.001), IA + B type in TFC (p = 0.03), PQ (p = 0.006) were identified as significant risk factors for the instability of the distal radioulnar joint. The IB type in TFC (OR = 2.74, CI 95% 1.00–7.56, p = 0.051) and VRUL (OR = 2.42, CI 95% 0.98–5.98, p = 0.054) were shown to be marginally significant. Abbreviations and full names of the ligaments are listed in Table 1

Distribution of Important Indicators

Radar plots for patients with and without DRUJ instability and DIOM existence presented incidence rates of the 10 outcomes. The characteristics related to DRUJ instability groups are summarized in Figure 4. In 61 (50.41%) patients in the DRUJ instability group, there were 68.85% with TFCC injury, 57.37% with VRUL injury, and 44.26% with PQ injury. The percentage of concerning injured ligaments were generally heightened compared to the DRUJ stability group. Compared to the present DIOM groups, the percentage of patients with DRUJ instability in the absent DIOM group was increased to 57.29% from 24%, and TFCC and ECU injury were higher at 58.33% and 34.38%, respectively.

Fig. 4.

Radar plots for comparing two groups of observational indicators: the 10 outcomes were analyzed in group of patients with and without DRUJ instability, the same in other group of patients with and without present IOM. Abbreviations and full names of the grafts are listed in Table 1

Distribution of patients with DIOM and subgroups according to TFCC injury or shape of DRUJ in the instability and stability samples is shown in Figure 5. Compared with the group (blue) of instability DRUJ, more cases (orange) obviously were distributed in shape of C‐type, intact TFCC, and present DIOM in stable DRUJ. Whereas, shape of ski‐type, flat‐type, TFCC‐IB, and IA + B had more distribution in DRUJ instability group.

Fig. 5.

The bar chart gives information about distributions of stability (orange) and instability (blue) of DRUJ in three compared groups. It shows the number of patients distributed in different groups of present DIOM, TFC injury, and shape of DRUJ

Discussion

Instability of DRUJ is common. Patients with simple ligament damage are increasing, but the diagnosis of such patients with wrist pain or even no pain are often in a dilemma. MRI is the most sensitive method for assessing soft tissue changes. It is essential that during wrist evaluation, appropriate sequences are chosen. Independent variables in the multivariate logistic regression analysis included the triangular fibrocartilage complex (TFCC), interosseus membrane (IOM), and pronator quadratus (PQ) tears. We concluded that the three indicators play a crucial role in DRUJ stability.

The Factor of Triangular Fibrocartilage Complex (TFCC)

The TFCC is composed of the ligament complex, the central articular disc, meniscus homolog, and extensor carpi ulnarissub sheath. TFCC injuries may lead to ulnar‐sided wrist pain, DRUJ instability, deterioration of the wrist joint, and functional disability. Palmer classified traumatic TFCC tears into four subtypes based on tear location, aiding diagnosis and management. ²⁴ Schachinger et al. reported with MRI‐based data that instability signs were more obvious in patients with TFCC tears (central and peripheral), as the forearm is extremely in pronation or supination. ²⁵ This conclusion is very similar with our study, patients were recursively split into four subgroups with different TFCC tears location. IA and IB type were classified according to Palmer classification, and IB type was the most of the 35 cases in all TFCC tears, but we found independent variables of DRUJ instability were IA plus IB type simultaneously. Another study by Zhan ²⁶ stated that the largest proportion of TFCC tears was also IB type and found that more detailed injury patterns including capsular injuries, the horizontal tear of the articular disk, and the bucket‐handle tear could not been included in the classic Palmer classification. IB type are peripheral TFCC tears in the vascular zone of the TFCC with/or without ulna styloid fracture. These tears may involve purely ligamentous avulsions from the ulnar attachments of the TFCC through the base of the ulnar styloid process and are often accompanied by DRUJ instability.

Although the Palmer classification is useful, it is important to reemphasize that not all TFCC ligament injuries are neatly accounted for by this system. Although the VRUL and DRUL as variables did not have statistical significance, the biomechanical role of the VRUL and DRUL among the TFCC ligaments was very important. Af Ekenstam et al. ¹ investigated the anatomical structures of the distal radio ulnar joint in fresh‐frozen amputated and cadaveric arm specimens. DRUL was notably tightened to prevent dorsal subluxation of the ulnar head in forearm supination, whereas the deep volar fibers remain loose. In 1991, Schuind et al. ⁷ proposed a completely contradicting mechanism for forearm stability by using a stereophotogrammetric method with phosphorescent markers and computer analysis. The authors considered that the VRUL was taut in supination, while the ulna turns volarly. Subsequently, other study certified this viewpoint and found that the DRUL was more important than the PRUL in forearm pronation, whereas the VRUL was more important in preventing volar subluxation of the distal ulna in supination. The two opposite conclusions were likely reconciled by Hagert, ²⁷ who deemed the volar superficial fibers and the deep dorsal fibers would both be tightened in supination. Conversely, in pronation the dorsal superficial fibers tighten to constrain DRUJ motion, as the deep volar fibers do simultaneously. Our variable of VRUL (p = 0.054) was found to be marginally significant for analyzing DRUJ instability in the multivariate logistic regression analysis. This result could be related to ligament injuries that usually occur from a fall on a pronated forearm and lead to hypertension of deep volar fibers.

The Factor of Distal Interosseus Membrane (DIOM)

The distal oblique bundle (DOB) is a component that links the radius to the ulna, whose fibers run obliquely along the distal 1/6 of the ulna and extend to the inferior rim of the radial sigmoid notch. As a portion structure of interosseus membrane, the MRI scan ranges from the wrist to the proximal end of the ulnar bone by at least 60 mm. Our study showed that a thickness of DOB at least 1.0 cm represented a positive result. Kim et al. ²³ considered that the average thickness of the distal interosseous membrane was 1.4 mm. DOB was present in about 29%–40% of the specimens in cadaveric studies. ²⁸ , ²⁹ Our MRI outcome identified the distal oblique bundle (DOB) in 25 of 121 specimens (20.7%). In statistical analysis, the present DOB is a significant protective factor for DRUJ stability (p = 0.001) and this conclusion is similar to that of most other reports. Kihara et al. ¹⁸ performed a biomechanical cadaver study that DOB acted as a sub‐prime stabilizer in the DRUJ while the triangular fibrocartilage complex (TFCC) was injured. Omokawa et al. ³⁰ found that there exited a certain translation distance between the ulna and the radius from the 3 mm dorsally and 4 mm palmarly by the rotation of the forearm in the intact wrists. He found that the ulnar head translated 10 mm dorsally following complete TFCC dissection, but the same result did not happen in the palmar direction. Additional cuted off the DIOM, in the meanwhile, the significant relative displacement from 23 mm dorsally to 17 mm palmarly was observed. Watanabe et al. ¹⁵ also emphasized that DIOM played an important role in constraining dorsal dislocation of the radius at the DRUJ. Kitamura et al. ²⁹ considered that DRUJ with the presence DOB was more stable than patients without a DOB in the neutral forearm position.

The Factor of Pronator Quadratus (PQ)

The pronator quadratus attaches to the radius and ulna and is another important secondary dynamic stabilizer by passively holding the ulnar head in the ulnar notch on the radius due to its viscoelastic properties. The significant statistical outcome was displayed in the latest multivariate analysis for stabilizing DRUJ (p = 0.006). Several cadaveric studies ⁴ , ¹² have certified that the PQ consists of a superficial and a deep head, which span the distal volar surface of the radius and ulna, just proximal to the DRUJ. The superficial head starts from the ulna and inserts transversely to the radius and the fibers of deep head oriented obliquely to distal radius. From functional view, the deep head is a primary dynamic structure of the DRUJ during pronating actively or supinating passively.

Limitations and Strengths

This study has some limitations. First, the reliability of the MRI interpretation is a limitation. Tears of ventral, dorsal, or central segments of TFCC ligaments were not considered separately. Although we strictly defined the positive or negative abnormal MRI findings of the DRUJ instability, repeated interpretations by observers are needed to increase the inter‐ and intra‐observer reliability. Second, the ligaments of the ECU tendon, DRUL, and VRUL play an important role in DRUJ stability in biomechanical studies, but the statistical significance of the abnormal MRI findings of them is not exhibited. The result may be related to the fact that our study was a cross‐sectional study. Third, we did not collect intact baseline information concerning clinical instability evidence in our following patient charts. Thus, we could not further confirm the relationship between risk factors and the degree of instability.

The strength of this study is the imaging results combined with clinical experience, which leads to important recommendations. The MRI approach to predict patient factors of DRUJ instability provides reference information to clinicians.

Conclusions

Nowadays, higher accuracy can be achieved in detecting the DRUJ instability under high‐ or medium‐field strength MR systems. This study is extremely helpful in identifying the different independent variables, including bony structure and ligaments, which have an impact on instability of DRUJ through MRI imaging. Future studies should examine how to rapidly evaluate DRUJ instability using advanced MRI methods for providing clinicians with specific clues towards the final diagnosis.

Author Contributions

HX, GL participated in the design of the study. Chen F, Li J, Zhang XG, Dong XM, and Zhang HZ collected and measured the data. HX and GL were responsible for the statistical analysis of the study. All authors read and approved the final manuscript.

Funding Information

This study was in part supported by a research fund (Grant No. ZC20018) from Science and Technology Foundation of Tianjin Health Commission.

Conflict of Interest

The authors declare that they have no conflicts of interest.

Ethics Statement

The study was approved by the Institutional Review board of Tianjin Hospital.

Data Availability Statement

All relevant data are included in this manuscript. Additional data may be requested by contacting the corresponding author.