Over-the-Top Foveal Triangular Fibrocartilage Complex Repairs with Distal Radioulnar Joint Instability: A Biomechanical Study

Abstract

Purpose:

The triangular fibrocartilage complex (TFCC) is the primary stabilizer of the distal radioulnar joint (DRUJ). Injury to the TFCC’s foveal insertion can cause ulnar-sided wrist pain and DRUJ instability. The aim of this study was to assess DRUJ stability, as measured by volar-dorsal translation, after TFCC foveal repair using an arthroscopic “over-the-top” technique.

Methods:

After obtaining institutional biospecimens approval, eight fresh frozen cadavers were procured. DRUJ instability was defined as an increase in sagittal translation of the distal ulna relative to the radius. A custom biomechanical testing protocol was implemented, which involved applying a linear translation to the radius and measuring both the applied force and bone displacement in the dorsal-volar direction. The stability of the DRUJ was tested with an intact foveal insertion and ulnar styloid insertion, after release of the entire TFCC foveal insertion and transection of the superficial TFCC attachment to the ulnar styloid, and then after the “over-the-top” technique repair with three different suture configurations. DRUJ stability was assessed in three wrist positions: neutral, 60° pronation, and 60° supination using both translation and stability improvement as outcomes.

Results:

DRUJ translation increased between the intact and injured conditions in neutral, pronation, and supination. Suture repair improved DRUJ translation compared to the injured state. Percent stability improvement, calculated relative to the injured condition, was higher across all repair groups. A single suture repair restored approximately half the stability relative to the injured condition, , whereas the three-suture repair demonstrated the greatest improvement in DRUJ stability.

Conclusions:

“Over-the-top” TFCC foveal repairs can enhance postoperative DRUJ stability.

Clinical Relevance:

“Over-the-top” TFCC foveal repair using three sutures provides the greatest improvement in DRUJ stability in a cadaveric model. These findings may help guide surgical decision-making regarding the optimal number of sutures needed to restore DRUJ stability following foveal TFCC injuries.

Introduction

The triangular fibrocartilage complex (TFCC) plays a crucial role in stabilizing the distal radioulnar joint (DRUJ) and functions as a shock absorber between the ulnar head proximally and the lunate and triquetrum distally ¹. The TFCC is comprised of the articular disc, meniscal homologue, ulnolunate and ulnotriquetral ligaments, extensor carpi ulnaris (ECU) subsheath, and dorsal and volar radioulnar ligaments (RULs). The RULs are the primary soft tissue stabilizer of the DRUJ, consisting of a distal part that inserts onto the ulnar styloid and a deep or proximal part that inserts into the ulnar fovea. Injury to the foveal attachment can cause ulnar-sided wrist pain, DRUJ instability, and subsequent post-traumatic arthritis, often necessitating surgical management ^2-6.

Currently, there are several open and arthroscopic techniques used to address DRUJ instability. ^7-9 Arthroscopy offers advantages including being minimally invasive and potentially providing faster recovery with less joint stiffness. Furthermore, DRUJ arthroscopy allows direct visualization of the foveal insertion. In arthroscopic foveal repair, various techniques have been developed, all of which have shown satisfactory results in the literature ^10-14.

Kakar et al. reported a modification of the arthroscopic inside-out transosseous or “over-the-top” TFCC foveal repair technique to stabilize the DRUJ ^15,16. This procedure offers several advantages: it permits direct repair of the TFCC to the fovea, decreases the risk of ulnar tunnel fracture, obviates the need for fluoroscopy and facilitates easier suture passage.

The purpose of this study was to evaluate the biomechanical stability of the over-the-top TFCC foveal repair procedure with different numbers of sutures. We aimed to determine the optimal number of sutures needed to achieve DRUJ stability. We hypothesized that the over-the-top foveal repair could restore DRUJ stability and that three sutures would most closely match the stability of the intact TFCC.

Materials and Methods

Specimen preparation

Eight fresh-frozen cadaveric arms, amputated at the humerus midshaft, were used in this study. Specimens were obtained from the anatomical bequest program following institutional biospecimen committee approval. Wrists with a history of trauma, inflammatory joint disease, or previous surgery were excluded. Radiographic evaluation was performed to screen cases with evidence of fracture, moderate-to-severe degenerative change, or ulnar positive variance, all of which were excluded. A 1.9 mm arthroscope (NanoScope system, Arthrex, Inc., Naples, Florida) was used to confirm the integrity of the foveal attachment using the hook test ¹⁷ from the radiocarpal portal, and to assess the associated findings using dry arthroscopy. The DRUJ portal was not created in this study.

TFCC injury model

A 3 cm ulnar longitudinal incision was made volar to the ECU tendon, proximal to the hamate body ¹⁵. The extensor retinaculum was incised from palmar to dorsal, leaving the ECU within its subsheath. After testing the intact specimens, the foveal insertion of the TFCC was divided with a surgical blade via a mini-open transverse incision just proximal to the ulnar attachment of the TFCC but distal to the ulnar styloid. The superficial part of the TFCC was completely divided through the same incision, with the adequacy of the transections confirmed arthroscopically by a positive hook test ¹⁷ and DRUJ ballottement test ¹⁸ following the creation of instability. Specimen preparation was performed by the same fellowship-trained hand surgeon.

Over-the-top TFCC foveal repair

The technique has been previously described in detail ^15,16. Briefly, the wrist was suspended in an arthroscopic tower. The 3-4 and 6R radiocarpal portals were established, followed by insertion of a working cannula through the 3-4 portal, with the 6R portal serving as the viewing portal. The first suture (Figure 1, Suture A) was placed at the center of the foveal insertion, which was identified via the ulnar incision used to divide the ligament and confirmed intraarticularly via arthroscopy. The center of the foveal insertion is typically located just dorsal and radial to the pre-styloid recess. This process was repeated for the second and third sutures: the second suture was passed volarly (Figure 1, Suture B) and the third suture dorsally to the first (Figure 1, Suture C). A Straight Micro SutureLasso (Arthrex Inc., Naples, FL, USA) was introduced through the cannula. The TFCC was identified, and the suture position was selected at the radial-most soft tissue portion of the isometric point of the foveal insertion ¹⁹. A nitinol loop-ended flexible guide wire was drilled through the distal part of the TFCC, targeting the deep foveal insertion, and then passed through the distal ulnar cortex. A 2-0 FiberWire suture was passed through the proximal loop of the guide wire and pulled completely through the distal ulnar bone, leaving one end of the suture within the working portal. The SutureLasso was then reinserted through the superficial TFCC, ulnar to the first target, forming a horizontal mattress stitch.

Figure 1:

Radiocarpal joint arthroscopic view visualizing the sequence and location of suture repairs. The first suture (A) was in the center of the ulnar fovea, the second suture (B) was positioned most volarly, and the third suture (C) was located most dorsally.

The aim of this study was to evaluate the effectiveness of 1, 2, or 3 sutures in restoring DRUJ stability. Stability was assessed under five conditions: (1) with the TFCC intact, (2) with the TFCC divided, (3A) with only suture A tied (one suture group), (3B) with sutures A and B tied (two sutures group), and (3C) with sutures A, B, and C tied (three sutures group). In the 1-suture condition, only the central suture was tied; in the 2-sutures condition, both the central and volar sutures were tied; and in the 3-sutures condition, all three sutures—volar, dorsal, and central—were tied. This repair site location was selected to replicate our operative sequence in real patients. The order of conditions 3A–3C was randomized.

All three sutures were inserted following detachment of the TFCC from its foveal and ulnar styloid insertions. Sutures were selectively tied or left untied depending on the testing condition and then tested. Sutures were untied and retied as needed between trials to minimize any laxity introduced by the testing loads.

Biomechanical testing

The biomechanical testing protocol was modified from Kitamura et al.²⁰. The humerus was secured to the base of the testing device, which allowed for testing with the forearm in the neutral position, 60° pronation, and 60° supination. The ulnar shaft was secured using an external fixator. The hand was immobilized by the pin-and-rod-system external fixator (Figure 2). Forearm rotation was measured with a goniometer.

Figure 2:

The upper extremity was affixed to the custom testing equipment, which allowed for distal radial ulnar joint pronation and supination. The loading pin and displacement sensor were controlled by a motor. The pin was inserted into the distal radius at the level of Lister's tubercle.

The volar translation of the radius relative to the ulna, which was considered experimentally equivalent to dorsal translation of the ulna relative to the radius, within the sagittal plane was measured. It was assessed by applying linear displacement to the radius using an instrumented linear actuator powered by a stepper motor driven by a microcontroller (DMX-UMD-23, Arcus Technology, The Colony, TX, USA). A threaded rod was used to affix a probe onto the radius via a mini-open volar Henry approach²³ and a dorsal incision over Lister’s tubercle, positioned perpendicular to the coronal plane. The rod was secured distally to the radius by drilling a transosseous hole just proximal to Lister’s tubercle, inserting the rod, and using nuts and washers affixed on both the dorsal and volar sides. Proximally, the rod was threaded into a force transducer (MLP25, Transducer Techniques, Temecula, CA) attached to the linear actuator. Translation of the actuator was measured with a linear potentiometer (TR50; Novotechnik, Ostfildern, Germany).

From a neutral, unloaded position, radius volar displacement resulting in a resistance load of 20 N was identified and used to set the displacement amplitude for the test. This load level was determined to be appropriate from pilot testing, which confirmed that it would not damage the repairs and was comparable to the load reported in a previous study ^20,24.

Three cycles of loading were applied, moving the actuator under displacement control at a rate of 20 mm/min from the neutral position to the test displacement amplitude and back. Force and displacement data were recorded at a sample rate of 100 Hz. The primary outcome, DRUJ displacement, was defined as the distance moved by the ulna from neutral to 20 N of applied load. Force-displacement curves were plotted to illustrate differences in the maximum DRUJ displacement and stiffness between each condition.

Stability improvement index

In addition to comparing DRUJ translation, we aimed to quantify the change in DRUJ translation relative to the intact state for each condition. The concept of normalizing an outcome to a relevant comparison—such as a control condition or the uninjured state—is well-established in biomechanical literature ^21,22.

DRUJ stability improvement was defined as the ratio of the difference in DRUJ displacement between the injured and repaired conditions to the difference between the injured and intact conditions. The denominator represents the expected range of volar-dorsal DRUJ translation, where the intact and injured states correspond to the minimum and maximum translation, respectively. The numerator quantifies the improvement in stability by measuring the reduction in displacement from the injured state following each specific repair. (Equation 1).

$$StabilityImprovement(\%)=\frac{X_{injury}-X_{repair}}{X_{injury}-X_{intact}}\times 100\%$$ Equation 1:

Statistical methods

A power analysis was conducted based on prior joint stability data ²⁵. A sample size of eight provided 80% power to detect a difference in DRUJ translation of 3 mm, which was assumed to be clinically significant²⁶, with a standard deviation of 2.5 mm, using a two-sided paired t-test with an α of 0.05. Nominal and ordinal data were expressed as percentages, while continuous variables were expressed as means (standard deviations). A multifactor repeated measures analysis of variance (ANOVA) was used to assess overall differences in DRUJ translation across wrist positions and the various suture repair conditions. Post hoc pairwise comparisons were performed using Bonferroni correction. The significance threshold was adjusted by dividing α = 0.05 by the number of comparisons (n = 7), resulting in an adjusted significance level of α = 0.007.

Results

The mean age of the eight cadavers was 66.9 years (range: 53-79 years), with an equal distribution of sexes and left and right sides. All specimens had a negative hook test before ligament sectioning. Three had associated TFCC injuries: two (25.0%) had central tears and one (12.5%) a radial tear according to the Palmer classification ²⁷.

Differences in DRUJ translation (mean ± SD) were observed between the intact and cut TFCC groups: 7.6 ± 2.1 mm versus 14.0 ± 3.5 mm (Δ = 6.4 ± 3.1 mm) in the neutral position, 5.9 ± 1.8 mm versus 11.1 ± 4.0 mm (Δ = 5.2 ± 3.8 mm) in 60° pronation, and 6.8 ± 1.4 mm versus 13.2 ± 3.9 mm (Δ = 6.4 ± 3.1) in 60° supination. These changes represent substantial increases in DRUJ translation following TFCC detachment, consistent with clinically relevant instability.^26,28. The observed differences demonstrate that DRUJ instability was successfully created prior to repair. This was also noted in the force displacement curves (Figure 3).

Figure 3:

The force-displacement curves from three cyclical load tests performed on a cadaver under all conditions and in three wrist positions are presented. The x axis depicts DRUJ displacement in millimeters (mm), and the y axis shows the applied force in Newtons (N). The slope of each curve in its linear region corresponds to the stiffness in each condition.

DRUJ stability improvement was assessed to evaluate the effectiveness of the repair. The 1-suture group showed improvement of 42.3% in neutral, 50.3% in pronation, and 54.7% in supination. The 2-sutures group demonstrated further improvement to 85.3% in neutral, 81.4% in pronation, and 82.8% in supination. The 3-sutures group showed the greatest improvements: 98.4% in neutral, 102.6% in pronation, and 95.6% in supination. These findings suggest that two or three sutures improve DRUJ stability more effectively than one suture, with the three-suture repair achieving near-complete restoration across all wrist positions. (Figure 4)

Figure 4:

Distal radioulnar joint (DRUJ) stability improvement in three repair groups, defined by the number of sutures, in wrist neutral, 60° pronation, and 60° supination. Error bars indicate the standard deviation.

Comparisons of DRUJ stability improvement across different suture repair configurations (one suture vs. two sutures, one suture vs. three sutures, and two sutures vs. three sutures) in the neutral wrist position demonstrated a progressive trend: 43.0% improvement with two sutures and 56.1% with three sutures, relative to the one suture group. While the difference between two and three sutures was modest at 13.1%, the 3-suture configuration consistently showed the greatest improvement. Similar trends were observed in pronation and supination. These observations suggest that increasing the number of sutures may enhance DRUJ stability, with three sutures providing the most complete restoration, although the difference from 2-suture repair may be minimal. (Figure 4)

The effectiveness of 1, 2, or 3 sutures in the over-the-top TFCC repair on DRUJ translation was also assessed. Adding one suture reduced DRUJ translation (mean ± SD) compared to the injured state, from 14.0 ± 3.6 mm to 11.3 ± 3.6 mm in the neutral position (Δ = 2.6 ± 2.5 mm), from 11.1 ± 4.0 mm to 8.6 ± 2.9 mm in pronation (Δ = 2.5 ± 3.0 mm), and from 13.2 ± 3.9 mm to 10.0 ± 3.2 mm in supination (Δ = 3.2 ± 2.6 mm,). With two sutures, mean DRUJ translation decreased to 9.0 ± 2.9 mm in the neutral position (Δ = 5.0 ± 2.7 mm), 7.3 ± 2.6 mm in pronation (Δ = 3.8 ± 3.1 mm), and 8.8 ± 2.8 mm in supination (Δ = 4.4 ± 2.5 mm). With three sutures, mean DRUJ translation further decreased to 8.3 ± 2.6 mm in the neutral position (Δ = 5.7 ± 2.8 mm), 6.6 ± 2.7 mm in pronation (Δ = 4.5 ± 3.2 mm), and 7.9 ± 2.6 mm in supination (Δ = 5.2 ± 2.8 mm). DRUJ translation decreased progressively as the number of sutures increased. The consistent reduction in DRUJ translation supports the biomechanical effectiveness of using multiple sutures (Figure 5).

Figure 5:

Mean distal radioulnar joint (DRUJ) translation under different suture repair conditions in neutral, 60° pronation, and 60° supination. Error bars represent the standard deviation.

Force-displacement curves demonstrated the differences in DRUJ displacement and stiffness between the intact and injured TFCC conditions. Stiffness was reduced in the injured compared to the intact TFCC. Stiffness increased after repairs but not to the level of the intact condition. This pattern was consistent across all cadavers in neutral, pronation, and supination.(Figure 3)

Discussion

This study demonstrated that the over-the-top foveal repair technique effectively enhanced DRUJ stability compared to the injured state. A single suture repair at the center of the foveal insertion restored approximately half (42.3%, 50.3%, and 54.7% in neutral, pronation, and supination, respectively) of the stability compared to the injured condition. The 3-sutures repair construct provided the greatest stability restoration.

Various arthroscopic techniques for treating TFCC injuries with DRUJ instability have been described. Nakamura et al. demonstrated that an arthroscopic outside-in transosseous foveal repair provided excellent outcomes for most patients ⁹. However, recurrent instability occurred in 29% of cases. Fujio used the arthroscopic transosseous inside-out foveal repair technique and reported that 96% of patients experienced complete pain relief, improved grip strength, and were able to return to their normal activities ¹¹. Atzei et al. utilized a suture anchor through a mini-open approach at the 6U and direct fovea portals ¹². This yielded good results in a case series of 18 patients. Kim et al. further substantiated these findings, observing that the technique can enhance DRUJ stability and functional outcomes, even in patients with chronic foveal injuries ²⁹. Ma et al. conducted a biomechanical study comparing open TFCC repair using a suture anchor to arthroscopic transosseous repair of TFCC foveal tears and found that the arthroscopic transosseous suture technique provided superior stability compared to the open anchor suture repair ³⁰. Johnson et al. demonstrated that the arthroscopic transosseous technique effectively restores DRUJ stability to a level similar to that of an intact TFCC when compared to capsular repair ³¹. Additionally, a recent systematic review of biomechanical studies on TFCC foveal repairs supported that the transosseous repair technique provides superior DRUJ stability compared to other techniques ³².

Our study supported the efficacy of the arthroscopic inside-out transosseous over-the-top technique.¹⁶ and provided additional insights for surgeons. This study examined the appropriate number of sutures required to achieve DRUJ stability. As previously described ¹⁶, this technique does not create a large bone tunnel in the distal ulna, potentially reducing the risk of ulnar tunnel fracture.

This study has several limitations. Given the small sample size, future studies with a larger sample size are warranted to enable more robust statistical analyses. This ex vivo study used fresh-frozen cadavers, and the mechanical properties and simulated motion patterns may differ from in vivo outcomes. The age distribution of the specimens was likely older than that of the typical clinical population with TFCC injuries. As this was a cadaveric study, we could not assess clinical outcomes such as pain, patient-reported outcomes, functional scores, postoperative range of motion or recurrent instability. Plain radiographs were used to screen for degenerative changes; however, in some cases, degenerative central TFCC tears or wear were still observed arthroscopically, particularly in the older specimens.

For the 1- and 2-suture testing conditions, the same suture configurations were used. As a result, single sutures in the volar or dorsal positions were not tested, nor were paired sutures in the volar and dorsal positions or the central and dorsal positions. Since the volar and dorsal configuration may best represent the native RUL anatomy, future studies should consider testing different suture pairings.

Despite these limitations, we observed a consistent reduction in DRUJ translation with an increasing number of sutures, supporting the mechanical effectiveness of the over-the-top TFCC repair technique. These findings suggest that increasing the number of sutures may enhance biomechanical restoration.