Instability of the Distal Radioulnar Joint

Background: Instability of the distal radioulnar joint (DRUJ) is an often unrecognized complication of distal radius fractures and soft-tissue injuries that can impair function. Its incidence and prevalence in Germany in 2023 were 23.55 and 30.55 per 100 000 inhabitants, respectively.

Methods: This narrative review is based on publications retrieved by a selective search in PubMed and the Cochrane Library (4 of 10 studies were included in the analysis). Current guidelines and expert recommendations were considered as well, and a query on the topic of this review was submitted to the Central Institute for Statutory Health Insurance and to the German Federal Statistical Office.

Results: After clinical examination and specific test procedures (press test, ulna-fovea sign, dorsopalmar stress test and ballottement test), plain films of the wrist are obtained in two strictly orthogonal projections (lateral and dorsopalmar). Thin-slice computed tomography (CT) (radioulnar quotient method) may be performed as well. Magnetic resonance (MR) arthrography displays DRUJ lesions sensitively (100%) and with increasing specificity (80–100%). Arthroscopy is considered the reference standard for the objective demonstration of triangular fibrocartilage complex lesions with regard to DRUJ instability. Depending on the type of injury, anatomical reconstruction of the injured structures may be recommended, e.g., with refixation techniques, ligament replacement grafts, or osteotomies. Fractures of the styloid process of the ulna (PSU) often accompany distal radius fractures and do not always need to be treated by refixation.

Conclusion: Instability of the DRUJ should be recognized and treated specifically to prevent pain and functional impairment. Further studies are needed to provide better scientific evidence for surgical or conservative treatment.

Cite this as: Harbrecht A, Unglaub F, Langer MF, Müller LP, Hug U, Spies CK: Instability of the distal radioulnar joint. Dtsch Arztebl Int 2025; 122: 321–7. DOI: 10.3238/arztebl.m2025.0054

The hand is our most important tool. Certain structural injuries can result in instability of the wrist and, in particular, of the distal radioulnar joint (DRUJ), with serious consequences. Patients who have sustained such injuries usually present with load-dependent ulnocarpal pain on motion and at rest. When examining the patient, it is important to distinguish harmless sprains from manifest injuries to the DRUJ in order to treat the latter as early, as precisely, and as specifically as possible. The aim of the present article is to provide colleagues – including those not specializing in hand surgery – with an overview of specific diagnostic examinations for DRUJ instability to allow appropriate decisions to be made for effective treatment.

Basic anatomy

Both the distal and proximal radioulnar joints are essential components to allow rotation of the forearm (1, 2). Ligaments of the DRUJ lend the joint its primary stability. An intact triangular fibrocartilage complex (TFCC), as one of the most important structures of the DRUJ, allows correct functioning of the joint (3, 4, 5). Together with the interosseous membrane, the TFCC is the major stabilizer of the DRUJ (4, 5, 6, 7, 8). The radioulnar ligaments originate from the ulnar notch on the dorsal and palmar aspects of the distal radius. Their deep fibers insert on the ulnar fovea and the superficial fibers on the ulnar styloid process [USP]) (Figure 1) (4, 9).

Figure 1

Structural appearance of the triangular fibrocartilage complex

Lesions of the DRUJ can restrict movement of the entire upper extremity. Injury to this joint can potentially result in instability and represents a serious complication after common distal radius fractures in particular (10 to 33% of distal radius fractures) (10, 11, 12, 13). Since pure ligamentous lesions can also lead to instability, pathomorphology may vary considerably (Figure 2). The extent of translation between radius and ulna is clinically the most useful parameter for assessing instability (Video 1) (14). Translation of bones in relation to each other describes the linear displacement or sliding movement of one bone relative to another without rotational movement taking place.

Figure 2

Presentation of the ulnocarpal compartment

Clinical tests and radiological procedures for diagnosing instability of the DRUJ vary considerably in their quality (14, 15, 16, 17, 18, 19). The specific and standardized use of clinical tests and technical methods of examination is necessary, however, to reliably diagnose instability early and treat accordingly.

Methods

The present article is a narrative review, based on publications retrieved by a selective search in the PubMed and Cochrane Library databases and on current guidelines and expert recommendations. The work is focused on presenting an expedient diagnostic algorithm. Clinical tests will be characterized with respect to their validity. In addition, inquiries were also submitted to the Central Institute for Statutory Health Insurance Physicians in Germany and to the German Federal Statistical Office.

The eMethods section provides details of the literature search.

Epidemiology

According to the German Federal Statistical Office, 4160 patients were treated as inpatients in 2022 with a primary diagnosis of DRUJ instability. The age peak was between 55 and 60 years. Incidence and prevalence of this type of injury have increased steadily over the past eight years. The Central Institute for Statutory Health Insurance Physicians registered an incidence of 13.05 and a prevalence of 16.26 per 100 000 population in 2014. These figures almost doubled in 2023 with an incidence of 23.55 and a prevalence of 30.55 per 100 000 population. This is evidence of a growing awareness with respect to identification and treatment of significant instability involving the DRUJ.

Etiology

The prevalence of concomitant instability of the DRUJ after a distal radius fracture varies between 10 and 33% (1, 2, 10, 11, 12, 13, 20). A fracture of the ulnar styloid process (USP) may or may not be present. The closer a fracture is to the base of the USP, the more likely will DRUJ instability develop (1, 10). Furthermore, the likelihood of instability also increases with the degree of displacement of the USP fracture (1, 10). Simultaneous fracture of the USP is present in around 60% of distal radius fractures as an associated injury. It is important, therefore, that this type of injury is recognized as coexisting and potentially serious damage with subsequent instability and included in the treatment regime. On the other hand, pure ligament injuries can also produce DRUJ instability. The mechanism of injury for this type of lesion is often twisting of the wrist, for example, secondary to a power-drill knockback injury (3, 14, 15).

On the whole, isolated acute instability of the DRUJ is rare, and there are as yet no scientifically substantiated figures available with regard to frequency.

Diagnostic investigations

A reliable clinical assessment of the DRUJ after fracture of the forearm is not usually possible in the acute situation. If internal fixation of the forearm is indicated, then stability of the DRUJ can be assessed during the procedure. On the other hand, if a fracture is immobilized to achieve bony union, then stability of the DRUJ should be assessed at the latest on termination of immobilization once primary fracture stability has been achieved – usually after six weeks. Patients with a pure ligamentous injury often present with ongoing symptoms after a delay of weeks to months.

Symptoms

Patients usually complain of ulnocarpal pain on loading the wrist or on forearm rotation.

Severity of the symptoms will vary according to the degree of instability. Examination of the contralateral side is always required to distinguish laxity from manifest instability (7).

Key elements of diagnosis (21)

• direction of instability
• pain site
• extent of the lesion
• ligamentous or bony
• ligamentous: complete tear or isolated tear of the superficial or deep anchoring fibers
• TFCC quality: reparable or irreparable
• ulnar variance (positive or negative, in comparison with the contralateral uninjured side)

History

Ideally, the sustained injury should be analyzed by precisely recording the circumstances of the accident. The following factors should also be ascertained:

• pain site
• pain quality (at rest versus on loading)
• functional impairment
• any previous injuries and surgery to the wrist
• patient’s expectations
• hand dominance.

Since the treatment strategy proposed in the present article is identical for both acute and chronic cases of instability, we do not make a distinction between acute (up to six months after trauma) and chronic (more than six months after trauma) instability of the DRUJ, unlike Nakamura (22).

Clinical examination

There is often swelling around the ulnocarpal region, frequently associated with dorsal subluxation of the ulnar head. The carpus presents in external rotation relative to the forearm (23, 24).

Ulnocarpal pain can usually be evoked by rotational movements of the forearm (23, 24, 25). Furthermore, a snapping or jumping of the extensor carpi ulnaris tendon (ECU) may occur on rotating the forearm (25).

In general, clinical examination should always be performed in comparison with the contralateral healthy arm.

Dorsopalmar stress test

The test is conducted with the forearm in neutral position. While the examiner firmly holds the radius with one hand, alternating palmar and dorsal force is applied to the ulnar head with the other hand (Video 2). Translation is divided into four grades, depending on the degree of translational movement:

• Grade 0 represents physiological articulation
• Grade 1 corresponds to ligamentous laxity with no functional impairment and a firm endpoint
• Grade 2 characterizes dynamic instability with loss of function and no firm endpoint
• Grade 3 is defined as spontaneous subluxation and reduction during active forearm rotation (6, 7).

Ballottement test

As a variation of the dorsopalmar stress test, the ballottement test, in contrast to the former, examines translational movement between ulna and radius in different positions of forearm rotation (26). The ballottement test may be performed intraoperatively after fixation of a forearm fracture to assess the DRUJ for instability (27) (eFigure 1). A biomechanical assessment on cadaver specimens showed a significant increase in translation when performing this test after transection of the TFCC (28).

eFigure 1

Intraoperative assessment for DRUJ stability using the ballottement test after palmar plate fixation of the distal radius

Press test

From a seated position, the patient lifts their body weight out of the chair using the armrests while pushing down with both hands. The test is positive if the patient complains of ulnocarpal pain (Video 3) (29).

The authors conclude a sensitivity of 100% from their study which combined a positive test with arthroscopy to confirm the diagnosis (29).

Ulnar fovea sign

The ulnar fovea sign is tenderness in the soft spot between the flexor carpi ulnaris tendon, ulnar styloid process, the pisiform, and palmar surface of the ulnar head (Video 4). This indicates a lesion of the TFCC (4). This test was compared with the reference standard of wrist arthroscopy in 272 patients. Sensitivity of 96.2% and specificity of 85.8% were recorded (4).

Plain X-ray diagnostics

Further diagnostic assessment is based on dorso-palmar and lateral plain radiographs of the affected wrist. Interpretation of the X-rays to detect DRUJ instability is not so easy, so it is most important to obtain correctly centered projections. This is the only way to minimize artefacts and enable the best yield of information – also for the physician providing initial treatment. A computed tomography scan may also be required if X-ray findings are equivocal (8).

True lateral view of the wrist

The following features will confirm a correctly angled lateral X-ray image (Figure 3):

Figure 3

Plain lateral X-ray imaging of the wrist

• projection of the ulnar styloid process usually centered over the ulna (5, 9, 16)
• projection of the palmar cortex of the pisiform midway between the palmar cortex of the distal pole of the scaphoid and the capitate (30, 31)
• complete overlapping of the proximal pole of the scaphoid with the lunate and triquetrum (8, 32)
• central projection of the radial styloid process over the proximal carpal bones.

A high-quality X-ray will also show overlapping of the distal dorsal cortex of the ulna and radius if the DRUJ is normal (Figure 3) (33). If these preconditions are met, then the distances between the distal dorsal cortices of ulna and radius can be precisely assessed. Distances of six millimeters or more between the ulnar and radial dorsal cortices are a clear indication of instability. Distances of three millimeters or less are regarded as normal (34). However, if the lateral projection is tilted by as little as 10°, then reliable statements about subluxation or dislocation of the DRUG are no longer possible (32).

Dorsoplamar view of the wrist

The following features will ensure a correctly angled dorso-palmar X-ray:

• full profile of the radial and ulnar styloid processes. Their bony components will appear farthest apart on this radiograph (5, 16).
• the lunate almost completely contained within the lunate fossa (5).

Radiographic signs of DRUJ instability may include:

• flake avulsions of the ulnar head
• avulsion fracture near the base of the ulna styloid
• distance between the articulate components of the DRUJ much wider in comparison with the contralateral side
• angulations of the distal fragments of radius fractures in the sagittal plane of more than 20° or
• radial shortening of more than five millimeters (14, 35).

Diagnostic computed tomography

Sectional imaging is able to depict the DRUJ in various degrees of forearm rotation, unobscured by overlying structures. This provides optimal conditions for diagnosing DRUJ instability (36, 37). A number of assessment methods for thin-layer computed tomographic sectional imaging have been published (8, 21, 32, 36, 38, 39, 40).

We refer to the literature and eFigure 2 for an evaluation of the radioulnar ratio method (7, 39).

eFigure 2

Radioulnar ratio method

Diagnostic magnetic resonance imaging

Sensitivity of magnetic resonance imaging (MRI) for detecting peripheral TFCC lesion is still low, especially with respect to ulnar avulsions (e1, e2, e3, e4). Under optimal conditions, direct magnetic resonance arthrography has the potential of equaling wrist arthroscopy as the reference standard with regard to sensitivity and specificity (33, e5, e6, e7). Prospective studies have measured a sensitivity of 94% and a specificity of 89% for MRI, as compared with a sensitivity and specificity of 100% for arthroscopy (e8, e9). A further comparative study of partial lesions identified a sensitivity of 68.1% and a specificity of 98% for MRI. Both parameters were 100% for arthroscopy (e10).

Wrist arthroscopy

So, the final step in the diagnostic algorithm is wrist arthroscopy. It is the reference standard for an exact identification of TFCC lesions (e11). It should be carried out either as a therapy in itself or, in the case of unclear findings, has the option of proceeding to treatment. Radiocarpal portals, however, can only allow direct visualization of injuries to superficial TFCC structures or of complete tears. If a positive hook test or a positive push off test is discovered, suggesting an isolated tear of the deep layer, then arthroscopy of the DRUJ via an additional portal should be performed (22, e12). Recognized classifications of TFCC injuries include those of Palmer (e13) (eTable 1) and Atzei (e14) (eTable 2), as well as the more recent CUP (central/ulnar/peripheral) classification system (e15).

Table

Systematic reviews, RCTs, and meta-analysis of the therapy of DRUG instability (USP fracture) after distal radius fractures and of the comparison between open and arthroscopic repair of the TFCC

eTable 1

Palmer Classification of TFCC Abnormalities (e13)

eTable 2

Atzei Classification of Ulnar TFCC Lesions (e14)

Treatment

Given that instabilities of the DRUJ commonly occur after distal radius fractures, these injuries should be treated according to patient-specific indications. The treatment of DRUJ instabilities after distal radius fractures is dealt with more extensively in the Treatment part of the eMethods section. The Table also provides an overview of high-quality studies.

The literature review presents studies with various levels of evidence. A meta-analysis of randomized controlled trials (RCTs) and a further RCT are available dealing with the question of whether USP fractures sustained together with distal radius fractures also need to underdo fixation (e8, e9).

Data suggest that successful surgical fixation of a distal radius fracture with residual persistent instability of the DRUJ produces poorer one-year outcomes when treated by immobilization than the simultaneous management of the instability during the index operation ([1, e8, e16]; meta-analysis of two RCTs and three observational studies).

The general recommendation to perform routine arthroscopy to assess the TFCC after a distal radius fracture cannot be supported on the basis of currently available data. This remains so, even though individual studies have discovered injury to the TFCC in 43 to 84 % of cases of distal radius fracture, yet without providing a more exact quantification of the extent of injury (e17, e18). The potential benefit of simultaneous arthroscopy during surgical management of distal radius fractures to evaluate the TFCC has not been fully confirmed.

According to the literature and based on our experience of the treatment of TFCC lesions associated with clinically obvious instability, the procedures presented in Figure 4 have indeed proven themselves (e19, e20, e21, e22). A literature search retrieved two systematic reviews which address the question of whether fixation of the TFCC should be performed arthroscopically or as an open procedure ([e23, e24] Table, Systematic review of two RCTs and case studies). However, no procedure was able to provide clear evidence of superiority.

Figure 4

Treatment algorithm for DRUJ instability

Summary

Instability of the DRUJ is most variable in its manifestation and severity and should be evaluated using targeted examinations. The diagnosis of DRUJ instability is based on a judicious selection of clinical and technical examination modalities (7, 27). The clinical diagnostic workup should be performed in comparison with the contralateral side. We believe that the tests are becoming all the more reliable as the clinical experience of those using them increases. Plain X-ray diagnostics must fulfill the quality criteria of properly aligned projection to allow correct interpretation. Cross-sectional computed tomographic imaging should be used in equivocal cases to allow visualization of the joint unobscured by overlying structures in comparison with the contralateral side and in appropriate positions of rotation. Furthermore, an MRI scan can also be of help when diagnosing TFCC lesions, although its poor sensitivity for peripheral lesions should be borne in mind. Arthroscopy is still the reference standard for objectifying lesions involving the most important stabilizers of the DRUJ (7, 21, 27, 36, e25, e28). Conclusions for clinical practice are summarized in the Box.

Box

Conclusions for clinical practice

Conflict of interest statement

CKS and FU received research support (third-party funding) from the Richard and Annemarie Wolf Foundation.

UH holds shares in the Medartis company and has consultant contracts with Medartis and

KLS Martin. He received lecture fees from KLS Martin.

MFL received reimbursement of congress fees from KLS Martin.

LPM und AH confirm that there are no conflicts of interest.

Manuscript received on 19 September 2024, revised version accepted on 20 March 2025.

Translated from the original German by Dr. Grahame Larkin.

Corresponding author:
PD Dr. Christian Karl Spies

• Video 1 (mp4)
• Video 2 (mp4)
• Video 3 (mp4)
• Video 4 (mp4)

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