Introduction

The triangular fibrocartilage complex (TFCC) consists of the articular disc, the meniscus homologue, the dorsal and palmar radioulnar ligaments, the ulnolunate and ulnotriquetral ligaments and the extensor carpi ulnaris (ECU) tendon sheath. From the ulnar styloid, the ulnolunate and ulnotriquetral ligaments insert into the carpal bones. The articular disc is surrounded by superficial and deep radioulnar fibers; the deep fibers of the triangular fibrocartilage (TFC) are also called the “ligamentum subcruentum” and insert onto the fovea ulnaris and at the basis of the styloid process whereas the superficial fibers insert onto the ulna styloid [1, 2]. The radioulnar ligaments act as stabilizer of the distal radioulnar joint (DRUJ) [3]. Furthermore, the dorsal capsule is tightened by the ECU tendon sheath. The “ligamentum subcruentum” and the wrist ligaments are depicted in Fig. 1.

Fig. 1
figure 1

Axial histological slide (H&E stain, 2× magnification). Arrow insertion site of the deep fibers of the radioulnar ligaments (lig. subcruentum)

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As a center of forearm rotation, the TFCC plays a key role in stabilization, rotation, translation, loading transmission to the wrist and acts as an essential pivot point [4, 5]. Due to its anatomical location as well as its involvement in the key functions of rotation and load bearing, it is highly prone to injuries and attritional wear [4]. Objective of this article is to review and summarize the recent clinical and experimental research on TFCC regarding histology and pathology, classification, examination and diagnostics.

Histology and pathology

It is generally agreed that the TFCC consists of an articular disc, surrounded by fibrous structures [6–12]. Fibrocartilage cells are typical for the articular disc, particularly at the radial side and its enthesis at the dorsal and palmar regions. The articular disc is a fibrocartilaginous extension of the superficial zone of hyaline articular cartilage, arising from the radius [13]. The articular disc has two laminae, the upper lamina leads towards the styloid process and the head of the ulna, whereas the lower lamina extends beyond the ulna and blends with the ECU tendon sheath and the ulnar collateral ligament (UCL) [14]. The components of the TFCC are further illustrated in Fig. 2.

Fig. 2
figure 2

Coronal histological slide (Masson’s trichrome stain, 2× magnification): U ulna, R radius, D disc, asterisk styloid insertion of the superficial part, hash symbol foveal insertion of the deep part of the TFCC

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The anterior and posterior interosseus arteries supply the TFCC with blood. The peripheral 10–40 % of the TFC is vascularized, compared to the inner portion which is avascular [15–18].

Ulnar negative variances are seen with fewer degenerative wear of the articular disc, on the contrary, ulnar positive variance seems to facilitate the degeneration of the TFC [6, 19]. Unglaub et al. [20, 21] correlate ulna positive variance with a greater occurrence of apoptotic cells in degenerative disc lesions compared to articular discs of patients with ulna neutral variance. Tatebe et al. [22] state that a reduction of ulnar loading achieved through ulnar shortening can trigger repair mechanisms and that 50 % of the studied wrists showed a regeneration of cartilage. Reduction of the ulna length may have benefits on the amount of proliferating cells in the articular disc [23]. Nevertheless, the proliferation potential of the cartilage cells of the TFC is unclear, because it has been shown that cell viability is reduced in palmer 1A lesions [24]. Mikić [7] states that this loss of tissue viability, elastic and collagen fibers, is a central feature of articular disc degeneration. The degeneration of the TFC tissue begins in the third decade. In 38 % of the examined specimens in the third decade, Mikić [7] found erosions, ulcerations and perforations. Still, few studies could detect proliferating cell nuclear antigen (PCNA) in several disc lesions, which indicates that there is a possible regeneration, because PCNA acts as an indicator for mitotic processes and regeneration [20, 23, 25].

Classification

Lesions of the TFCC may be of degenerative or traumatic nature. The commonly used Palmer classification categorizes these lesions based on the nature of their formation and their location in the TFCC [26].

Traumatic tears are usually caused by rotational injuries or accidents while the patient is falling upon a pronated or hyperextended wrist [27]. Those lesions are classified as Class 1 and further divided as type A, B, C or D. Class 1A lesion describes a central tear through the horizontal portion of the TFCC (Fig. 3). Traumatic avulsions of the TFCC from its insertion at the distal ulna are referred to as class 1B lesions. These injuries are related to lesions of the ulnar styloid and instabilities regarding the distal radioulnar joint [3]. Palmer classified distal avulsions of the TFCC as class 1C lesions, for instance ruptured ulnolunate or ulnotriquetral ligaments, which lead to ulnar carpal instability. Finally, class 1D lesions represent radial avulsion of the TFCC with or without sigmoid notch fracture (Fig. 4) [26].

Fig. 3
figure 3

Arthroscopic view of the disc with a traumatic lesion. Typical longitudinal tear, the probe is inserted into the lesion (Palmer 1A)

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Fig. 4
figure 4

Arthroscopic view of the disc in a Palmer 1D lesion. The probe is inserted into the lesion. Hash symbol radial aspect of the radius with hyaline cartilage at the sigmoid notch. Asterisk disc with fibrocartilage tissue

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In contrast to that, class 2 lesions describe degenerative wear and perforation of the TFCC, that may be associated with chronic loading of the ulnocarpal joint, which is also associated with the ulnar impaction syndrome [6]. Those more common degenerative class 2 lesions are subclassified as type A, B, C, D or E. Class 2A stands for wear of the horizontal portion of the TFCC without perforation, the lesion may be located distally, proximally or both. Class 2B lesions resemble 2A with additional chondromalacia of the lunate or ulnar head or both. Progression of the degenerative wear results in perforation of the TFCC, which then is classified as class 2C lesions. Those lesions usually occur in the avascular portion of the TFCC and tend to have an ovoid morphology (Fig. 5). Class 2D lesions describe further advances of the degenerative process with rupture of the lunotriquetral ligament (LTL) and cartilage abnormalities of the ulnar head and the lunate. Deterioration of class 2D lesions coupled with ulnocarpal arthritis represent class 2E lesions [26].

Fig. 5
figure 5

Arthroscopic view of a degenerative disc lesion (Palmer 2C) with a typical round perforation. The tissue is thinned out. The probe is inserted into the lesion. The ulnar head is visible through the perforation of the disc

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However, the Palmer classification does not cover all cases of peripheral TFCC tears [28]. Estrella et al. [29] observed several dorsal tears of the TFCC, which could not be categorized with the Palmer classification. Besides, Henry states that class 1B injuries are broadly applied to lesions irrespective of their origin and association with DRUJ instability [30].

Atzei published a new treatment-oriented classification of TFCC peripheral tears, in which he illustrates 5 classes (Fig. 6) [31]. Atzei describes the ulnar-sided TFCC as 3 structures: the proximal triangular ligament which represents the ligamentum subcruentum, the distal hammock structure, and the UCL, which both make up the distal component of the TFCC [31, 32]. Class 1 lesions depict repairable distal tears with intact proximal TFCC component, which he recommends to treat by traditional arthroscopic suture. If there is a complete tear through the distal and proximal component of the TFCC, with DRUJ instability, the lesion is considered as a class 2 injury and requires foveal reattachment of the TFCC. Whereas, a proximal tear with intact distal TFCC component is considered as a class 3 lesion, but also requires foveal reattachment. Class 4 injuries are characterized, similar to class 2 lesions, by a complete tear through the distal and proximal components of the TFCC, but not repairable and associated with a severe DRUJ instability. As a consequence, class 4 needs reconstruction using a tendon craft. Adams described a technique, which treats posttraumatic DRUJ instability with a reconstruction of the distal radioulnar ligaments using a tendon graft [33, 34]. Furthermore, stabilization of the DRUJ can be performed by the dorsal capsular imbrication [35]. Finally, class 5 lesions stand for an arthritic DRUJ, which should be treated by arthroplasty or joint replacement [31].

Fig. 6
figure 6

Atzei classification of Palmer 1B lesions [31] (with the friendly permission of Springer Science and Business Media)

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Innervation

Gupta et al. [36] dissected ten cadaveric specimens and used the nitric acid maceration technique in nine of those to evaluate the nerves contributing to the innervation of the TFCC. A as result of that, the authors state that the palmar portion of the TFCC is innervated by branches of the ulnar nerve in 100 % of specimens and the dorsal sensory branch of the ulnar nerve in 33 %, whereas the ulnar aspect was innervated by branches of the ulnar nerve in 22 % and the dorsal sensory branch of the ulnar nerve in 33 %. In addition to that, they examined sections of the central and radial parts of the TFCC, which were stained with hematoxylin and eosin, and could not show any nerve fascicles.

Laporte et al. [37] evaluated 11 cadaveric specimens and demonstrated that in the majority the TFCC is innervated by the dorsal sensory branch of the ulnar nerve in 100 % of specimens, the medial antebrachial cutaneous nerve in 91 %, and the palmar branch of the ulnar nerve in 73 %. The TFCC was innervated by the anterior interosseus nerve in 27 % of specimens, the posterior interosseus nerve in 18 %, and the palmar branch of the median nerve in 9 %. Furthermore, the authors pointed out that additionally randomized trials are necessary to evaluate selective TFCC denervation compared to arthroscopic debridement for type 1A injuries.

Published data lack evidence of innervation of the healthy articular disc [36, 38]. To evaluate the hypothesis that traumatic and degenerative lesions may lead to an ingrowth of nerve fibers, which cause ulnar-sided wrist pain, Unglaub et al. [39] investigated the biopsies of 32 patients with Palmer 1A lesions and 17 patients with Palmer 2C lesions and searched for signs of nerve fibers. The biopsies were stained with the primary antibody protein gene product (PGP) 9.5 and none of the specimens showed ingrowth of nerve fibers.

Clinical examination

The patient’s history gives information about a degenerative or traumatic pathoetiology of ulnar-sided wrist pain. TFCC lesions often come along with pain during powerful rotatory hand movement, like squeezing a cloth or pushing down a door knob. Ulnar-sided pain with lifting heavy objects might be a hint for a TFCC lesion and/or DRUJ instability [40].

The wrist should be carefully inspected for a prominence of the ulnar head or swelling along the prestyloid recess or the ECU tendon sheath. Points of tenderness are assessed by palpation: A foveal disruption of the TFCC, but also an inflammatory synovitis of the prestyloid recess or a pathology of the meniscus homologue might cause pain in the “ulnar snuff box”, which is located ulnopalmar to the ECU tendon, between the triquetrum and ulna head. Such a positive “ulnar fovea sign” was proven to have a sensitivity of 95.2 % in detecting foveal TFCC disruption and/or ulnotriquetral ligament injuries and a specificity of 86.5 % [41]. Palpation might provoke tenderness at the proximal ulnar corner of the lunate, the distal surface of the ulnar head and/or the proximal tip of the hamate in case of an ulnocarpal abutment syndrome indicating a chondromalacia [41, 42].

In functional testing, patients with degenerative TFCC lesions and ulnocarpal abutment syndrome experience ulnar-sided pain during passive maximum ulnar deviation and active forearm rotation against resistance (“screwdriver test”) [40]. In addition, a powerful grip might be more painful in supination than in pronation; using the Jamar dynamometer, a difference in grip strength might be assessed (“GRIT test”: ratio grip strength in supination versus grip strength in pronation >1.3) [43].

For the “ulno-carpal stress test” (“TFC grind test”), the forearm is brought in a vertical position and the wrist in a maximum ulnar deviation. Applying axial load, the forearm is rotated from full supination to pronation. Ulnar-sided wrist pain occurring during forearm rotation in the mentioned position (but not in neutral or radial deviation), constitutes a positive test, a painless click is considered a negative test. Nakamura et al. found this test positive in patients with ulnocarpal abutment syndrome, traumatic TFCC tear, LTL tear, and wrist arthritis [44].

For the “TFC shear test” (“pisiform boost test”, “ulno-menisco-triquetral dorsal glide test”), the pisiform is pushed dorsally with the thumb while the index and middle finger translate the ulna head palmarly. If this maneuver provokes pain, the test is considered positive, which was proven to be the case in two-third of the patients with a pathology of the meniscus homologue and the TFC. LaStayo [45] assessed a specificity of 64 %, a positive predictive value (PPV) of 58 %, and a negative predictive value (NPV) of 69 % for this test.

The “press test”, introduced by Lester et al. [46], provokes ulnocarpal pain when a seated patient lifts the body weight up off the chair using the affected wrist.

The “ulnocarpal meniscoid-test” (“waiter’s test”) creates a local stress to the meniscus homologue by bringing the wrist passively from extension to ulnar deviation and from there to flexion while applying an axial load to the ulnar carpus [42]. Repeating this test in supination, neutral, and pronation, a TFCC lesion causes more pain in supination than in pronation. Ruston et al. [47] compared the waiter’s test to arthroscopic findings and assessed a sensitivity of 40 %, a specificity of 92.7 %, a PPV of 76.9 %, a NPV of 71.7 %, and an accuracy of 72.7 % in detecting a TFCC lesion.

A foveal disruption of the TFCC could cause an instability of the DRUJ [48]. The clinical assessment of DRUJ instability is to some degree influenced by the compliance of the patient and the experience of the examiner [3]. The “piano key sign” is tested with the hand lying flat on the table. If there is a subluxation of the DRUJ, a prominent ulna head can be reduced palmarly by the examiner pushing the ulna down, which re-dislocates passively to the initial position without this maneuver. In some cases, the dorsopalmar translation of the ulna head can be observed if the patient presses the hand actively on the table surface [49].

The “bilateral test for potential subluxation of the DRUJ” investigates the relative movement between radius and ulna at the DRUJ, which is palpated by the index and middle fingers, comparing both sides simultaneously during forearm rotation. The test was proven to be 100 % sensitive compared to the computed tomography (CT) [50].

For the “ballottement-test of the distal ulna” the radius is manipulated in a dorsopalmar direction, while the distal ulna is stabilized. The degree of translation is tested in several positions of forearm rotation and should decrease at the end positions in a stable joint [42].

Imaging diagnostics

X-ray

In case of preceding acute trauma, X-ray may be the first imaging modality. Nevertheless, X-ray is useless in assessing the quality of the articular disc. Still X-ray is useful to determine a patient’s ratio between ulna and radius. The neutral position while taking the radiograph is essential, because a pronation of the hand leads to ulna plus variance [51, 52]. To obtain valid radiographic criteria for the wrist, roentgenograms have to be taken with the elbow 90° flexed; using a vertical beam, the upper arm needs to be 90° abducted in the shoulder for the posteroanterior view [53]. Furthermore, radiographs may show signs of fracture and help to distinguish between palmer 1B and 1D lesions (Fig. 7) [26].

Fig. 7
figure 7

X-ray, posterior-anterior view, with a distal radius fracture and an avulsion fracture of the superficial and deep part of the ulnar aspect of the TFCC with instability of the DRUJ

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Arthrography

Arthrography of the wrist is an invasive imaging modality, which rarely leads to complications [54]. Triple-injection arthrography has been favored for evaluation of TFCC lesions [55]. Nevertheless, arthrography of the wrist has a quite high rate of false-negative findings and is less accurate than arthroscopy, especially in diagnosing injured ligaments [56, 57]. Furthermore, Schers et al. [58] state that arthrography detects only 50 % of the TFCC lesions that arthroscopy identified. If arthrography is combined with magnetic resonance imaging (MRI), a sensitivity of 97 % and specificity of 96 % and an accuracy of 97 % can be achieved, compared with arthroscopy [59].

MRI and MR arthrography

Damages of the TFCC can be assessed by several imaging diagnostics. MRI is important and useful for non-invasive evaluation of wrist pain. MRI is accurate in visualizing partial tears and central or radial TFCC lesions, but lacks sensitivity in diagnosing peripheral TFCC lesions at the ulnar insertion [60, 61]. This observation is in accordance with Oneson et al. [62], who reported a sensitivity of 91 % for detecting central degenerative perforations, a sensitivity of 86–100 % for detecting radial tears and a sensitivity of 25–50 % for detecting ulnar-sided avulsions compared with arthroscopy. These results correlate with the findings of Haims et al. [63], who stated a sensitivity of 17 % for detecting peripheral TFCC tears. A study by Iordache et al. demonstrated that MRI scans of asymptomatic patients showed lesions of the TFCC in nearly half of the wrists. Hence, it is essential to view the imaging results in the context of the clinical history. In addition to that the authors described a positive correlation of TFCC degeneration and an increase in age [64].

Since the structures of the wrist are rather small compared to large joints, commonly used 0.2–1.5 T MRI is accompanied by technical limitations of spatial resolution and signal-to-noise ratio. However, 3 T MRI becomes more available in clinical use and recent studies state that 3 T MRI has advantages over 1.5 T MRI, due to an improvement of the contrast-to-noise ratio between bone and cartilage in 3 T MRI [65–67]. Anderson et al. [67] correlated 1.5 and 3 T wrist MRI with wrist arthroscopy findings in patients with ulnar-sided wrist pain and state that 1.5 T wrist MRI had a sensitivity of 85 % and a specificity of 75 % compared with the arthroscopy, whereas 3 T wrist MRI had a sensitivity of 94 % and a specificity of 88 %. On the contrary, the diagnostic improvement of 3 T MRI is still limited and using a dedicated microscopy wrist coil is mostly sufficient enough [49, 68]. However, in clinical reality MRI is often conducted without wrist coils [69].

Nevertheless, 7 T wrist MRI provides excellent images of the wrist and the future of imaging modalities looks promising as seen in Fig. 8. Still at this point, these MRIs are only used for research.

Fig. 8
figure 8

Seven Tesla MRI of the ulnocarpal region in a healthy wrist (U ulna, R radius, L lunate, T triquetrum). The superficial and deep part of the TFCC is visible. The lig. subcruentum inserts onto the fovea of the ulna head and the basis of the styloid (arrow head). The superficial part inserts onto the styloid process (arrow)

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Magnetic resonance arthrography (MRA) of the wrist seems to be superior compared to conventional MRI [70–72]. Schmitt et al. [73] corroborated the advantages of direct MRA and recommended it particularly if the examiner suspects lesions of the scapholunate ligament (SLL) and the TFCC. Nevertheless, Schweitzer et al. [63] stated that indirect MRA improves only the sensitivity in the evaluation of the SLL, but is not superior in evaluating the articular disc of the TFCC. Braun et al. [74] stated that direct MRA is a promising imaging modality and is of equal value compared to diagnostic arthroscopy in detecting complete defects of the intrinsic ligaments and the TFCC. Lee et al. described sensitivity, specificity and accuracy for MRI of 66, 86 and 90 %, and for MRA of 100, 100 and 100 % [72]. Furthermore, Meier et al. stated that the sensitivity of direct MRA approaches that of arthroscopy and, therefore, may avoid invasive diagnostics like arthroscopy in the future, but cannot replace it at the moment [73, 75]. Hahn et al. stated that in clinical routine sensitivities and specificities are rather lower because MRI of the wrist is often performed before a hand surgeon is consulted. Therefore, a detailed clinical examination which is necessary for an appropriate indication for MRI, is missing [69].

CT Arthrography

Sometimes MRI is not available and CT is used to evaluate unclear carpal trauma or wrist pathologies. The CT exam is generally performed using slices with a thickness of 2 mm and a high resolution algorithm. Native CT is used for detection of fractures, which are difficult to define on plain films. To evaluate the articular cartilage and ligaments injection of contrast agents in the distal radioulnar, radiocarpal and mediocarpal compartments is mandatory. Bille et al. [76] showed that computed tomography arthrography (CTA) is a highly accurate imaging modality at evaluating tears of the SLL, LTL and central TFCC tears, but not peripheral tears. De Filippo et al. [77] stated that multidetector computed tomography (MDCT) shows sensitivity, specificity and accuracy ranging between 92 and 94 % for TFCC lesions. In addition to that Lee et al. assessed a sensitivity, specificity and accuracy for CTA of 100, 100 and 100 % [72].

Ultrasound

Despite the fact that ultrasound has several advantages like noninvasiveness, mobility, lack of ionizing radiation and low costs, its use in diagnosing TFCC lesions is rather uncommon because of its inability to provide enough information on the internal structure of the TFCC to allow a diagnosis [78]. Linear transducers of high frequency of 7.5 and 10 MHz are required to obtain sufficient spatial resolution.

Nevertheless, ultrasound is a valuable imaging modality to diagnose ligament injuries and recent studies demonstrated that its usefulness to detect tears of intrinsic ligaments and the TFCC may be underestimated [79, 80].

Arthroscopy and arthroscopic examination

Wrist arthroscopy is the “gold standard” in diagnosis of TFCC injuries [81–86]. It allows an accurate assessment of the TFCC; lesions can be described precisely and it can be distinguished whether a lesion is traumatic or degenerative. Degenerative lesions are often round perforations with frayed borders, which show a yellowish coloring of the articular disc (Fig. 5) [87]. Traumatic lesions would rather show plain longitudinal tears, which keep the white color of the disc. Furthermore, the assessment of accompanying chondral lesions of the ulnar half of the lunate and the proximal pole of the hamate or tears of the LTL are a hint for an ulnar impaction syndrome.

Löw et al. [88–90] stated that the reproducibility of diagnoses based on photo documents in wrist arthroscopies is limited and intra- and interobserver reliability should be improved by labeling structures in photo documents.

There are several techniques to evaluate the TFCC during wrist arthroscopy. Usually, the TFCC is inspected through the 3–4 portal. By a probe, inserted through the 4–5 or 6-R portal, scanning the TFCC surface for tears. The trampoline test evaluates the tautness of the horizontal part by applying a compressive load across it using a small probe (Fig. 9) [91]. If this structure is wavy and soft, it can indicate a peripheral tear. Furthermore, the hook test may be performed to assess the integrity of the deep fibers of the TFCC [31]. The hook test is accomplished by inserting a probe through the 4–5 or 6-R portal and applying traction to the ulnar-most border of the horizontal part of the TFCC. If the tissue can be pulled distally and radially toward the center of the radiocarpal joint, it is positive.

Fig. 9
figure 9

Arthroscopic view of the trampoline test. The tautness of the horizontal part of the TFCC is evaluated by applying a compressive load using a probe

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In addition to that the push-off needle test allows to evaluate if the deep fibers of the radioulnar ligaments are torn [92]. The technique is performed by placing an arthroscope in the 3–4 portal and inserting an 18-gauge Tuohy needle midway between the DRUJ and the ulnar styloid process. The needle can then be advanced distal to the ulna articular surface and radial to the ECU tendon. The tip of the needle faces the distal ulna articular surface during insertion in order to prevent iatrogenic injury to the TFCC. Then the needle is withdrawn out of the ulnocarpal compartment and can be inserted underneath the TFC. If especially the deep fibers of the radioulnar ligaments are torn, the horizontal part of the TFCC can be pushed off the ulna by manipulating the needle up and down against the proximal surface of this structure (Fig. 10).

Fig. 10
figure 10

The needle is inserted underneath the TFC. The horizontal part of the TFCC can be lifted up easily from the foveal insertion, indicating a lig. subcruentum lesion

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Progress in the understanding of TFCC biomechanics and anatomy reveal the importance of the proximal part of the TFCC [93, 94] (see “Introduction”) facing the ulna head and gave rise to new classification systems [12]. Especially the ligamentum subcruentum and its attachment onto the ulnar fovea are at the center of interest. Both can be visualized via portals to the DRUJ that give insight into the space between TFCC and the ulna head (Fig. 11). The arthroscopy of the DRUJ is still estimated as technical demanding and therefore routineously rarely applied. There are only few larger series reported in the literature [95–98]. Attempts to gain access to the DRUJ can be disappointing [99]. The lack of space within the joint makes interventions more difficult and the insertion of the scope into a stable DRUJ is scarcely possible. This is also reflected by earlier series, where the proximal surface of the TFCC was visualized in 100 %, but the foveal insertion of the lig. subcruentum only in 57 % of the cases [96]. Some improvement is promised by the introduction of new palmar portals [100] and smaller (1,9 mm diameter) scopes [101]. Nakamura et al. reported a success rate for the visualization of the foveal attachment of 86 % (170 in 196 cases) [101].

Fig. 11
figure 11

DRUJ arthroscopy with a probe under the lifted articular disc. The lig. subcruentum (asterisk) is visible and tested for stability, hash symbol ulna head

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Despite all technical difficulties, these aspects of the DRUJ arthroscopy will attract rising attention for an improved diagnosis and classification of TFCC lesions [102].