Abstract
Background Measurement of in vivo distal radioulnar joint (DRUJ) pathomechanics during simple activities can represent the disability experienced by patients and may be useful in diagnostics of DRUJ instability. A first step is to describe the physiological normal limits for DRUJ kinematics in a reproducible and precise test setup, which was the aim of this study.
Methods DRUJ kinematics were evaluated in 33 participants with dynamic radiostereometry (RSA) while performing a standardized press test examination. AutoRSA software was used for image analyses. Computed tomography (CT) forearm bone models were generated, and standardized anatomical axes were applied to estimate kinematic outcomes including, DRUJ translation, DRUJ position ratio, and changes in ulnar variance. Repeatability of dynamic RSA press test double examinations was evaluated to estimate the precision and intraclass correlation coefficient (ICC) test–retest agreement.
Results The maximum force during the press test was 6.0 kg (95% confidence interval [CI]: 5.1–6.9), which resulted in 4.7 mm (95% CI: 4.2–5.1) DRUJ translation, DRUJ position ratio of 0.40 (95% CI: 0.33–0.44), and increase in ulnar variance of 1.1 mm (95% CI: 1.0–1.2). The mean maximum DRUJ translation leveled off after a 5 kg force application. The DRUJ translation ICC coefficient was 0.93 within a prediction interval of ± 0.53mm.
Conclusions This clinical study demonstrates the normal values of DRUJ kinematics and reports excellent agreement and high precision of the press tests examination using an automated noninvasive dynamic RSA imaging method based on patient-specific CT bone models. The next step is the application of the method in patients with arthroscopic verified triangular fibrocartilage complex injuries.
Level of Evidence This is a Level IV, case series study.
Keywords: radioulnar ligaments, distal radioulnar joint, normal values, radiostereometry, joint kinematics
Clinical examination of distal radioulnar joint (DRUJ) instability is subjective, relies on passive testing of increased radioulnar translation, and remains challenged by poor reproducibility. 1 2 3 The diagnosis is often missed both in patients with low-grade DRUJ instability and in patients with high-grade DRUJ instability due to pain or strong muscular joint stabilizers. 4
Methods based on computed tomography (CT) have been suggested for the evaluation of DRUJ instability, but their reliability is limited. 3 5 6 The CT-based methods investigate DRUJ subluxation on axial reconstructions of the forearm in passive supinated and pronated positions. 7 However, static imaging may not reveal the full range of DRUJ instability, which patients can provoke during loaded hand activities and active movement.
Evaluation of DRUJ instability based on ultrasonography (US) was introduced by Hess et al and has shown promising results. 8 Transverse US relies on the timing of snapshots of the ulnar head prominence relative to the distal radius during active patient-induced ulnar head translation.
Previously, we introduced static radiostereometry (RSA) in an experimental setting for the examination of DRUJ translation before and after triangular fibrocartilage complex (TFCC) injury. 9 Radiostereometry may also be applied dynamically (dRSA) as a stereo-image of active joint motions and loaded exercises and is a precise noninvasive calibrated radiographic method that allows for the registration of CT-based bone models and evaluation of joint kinematics. 10 Previously, dRSA has not been applied for the evaluation of DRUJ kinematics in vivo.
The purpose of this study was to determine physiological normal values and variations of DRUJ translation, the position of the ulnar head with respect to the sigmoid notch (SN), and changes in ulnar variance in individuals with asymptomatic uninjured forearms, using dRSA imaging of a participant-applied press test exercise. Furthermore, we evaluated DRUJ translation by US and estimated the reliability of both methods.
Patients and Methods
Study Design and Participants
Thirty-three consecutive participants, 14 men and 19 women were recruited between February 2017 and February 2020 for a prospective cohort study on normative DRUJ kinematics using dRSA imaging.
Study criteria were an age between 18 and 50 years, no ulnar-sided wrist pain, and no previous surgery or sequelae after upper limb injuries. Only one healthy forearm from each participant was included. Informed consent was obtained from the participants. The study was approved by the Danish Data Protection Agency (Journal no.2012–58–006; issued May 2016) and the Central Denmark Region Committees on Health Research Ethics (Journal no.1–10–72–146–16; issued August 2016).
Patient Demographics and Clinical Examination
Patient characteristics included sex, age, hand dominance, and side of the investigated forearm. Clinical examination was performed by the first author. Grip strength was measured using the DHD-1 digital Jamar Hand Dynamometer (SAEHAN Corporation, Gyeongsangnam-do, South Korea) and reported as an average of three measures. The wrist and forearm motion was measured as an angle using a goniometer. Stability of the DRUJ was evaluated clinically with the ballottement test, and the DRUJ instability grade was categorized as less than 5 mm, between 5 and 10 mm, or above 10 mm, as proposed by Atzei et al. 11
Bone Models and Bone-Specific Coordinate Systems
Patients eligible for study participation were referred for a dRSA examination during a standardized press test. Bone models for analysis of dRSA images were obtained from CT image series of the whole forearm on all patients (Philips Brilliance 64, Philips Medical Systems, Best, the Netherlands). All scans were acquired with 120 kV, and 100 mAs settings and images were reconstructed with 0.9 mm slice thickness, 0.45 mm slice increment, and 0.27 mm in-plane pixel size. Individualized three-dimensional (3D) bone volume and surface models of the radius and ulna were created from the CT images by automated graph cut segmentation ( Fig. 1A–D ).
Fig. 1.
Computer tomography (CT)-generated bone models, kinematic landmarks, and bone axes. ( A ) Grayscale information was extracted from CT scans. ( B ) Graph cut segmentation was used to generate ( C ) three-dimensional bone volume models and ( D ) simplified 3D bone surface models of ∼10,000 triangles. Custom-implemented software based on the Insight Segmentation Toolkit and the Visualization Toolkit (Kitware, NY) was used for all image processing as described by Hansen et al. 15 ( E – F ) Bony landmarks were used to define bone axes (x, y, z). The radius landmarks were the proximal rotation center of the radial head (C prox ), the radial styloid tip, and the center of the distal radioulnar joint (RUJ) surface. The ulnar landmarks were the ulnar head center (C dist ), the distal ulnar styloid tip, and the greater sigmoid notch (SN) center. The best-fitted sphere of three points picked on the center of the articulating surfaces of the radial and ulnar heads was used to compute the center points. ( G ) The RUJ axis was the axis of forearm rotation extending through the radial head center to the ulnar head center. ( H ) The SN line connects the midpoint of the volar (landmark A) and dorsal (landmark B) radius SN rims. The position of the ulnar head rotational center on the SN line (DRUJ position) was estimated by projection of the RUJ axis orthogonally on the SN line and measured in millimeters from the volar SN rim. Considering the individual differences in bone sizes and SN line lengths, the DRUJ position ratio was calculated (DRUJ position ratio = DRUJ position/SN line length). Translation in the DRUJ was calculated as the change of DRUJ position in millimeters. The change in ulnar variance was calculated as the change of (Cdist) along the RUJ axis with respect to the SN line midpoint.
Bone-specific orthogonal axes (x, y, z) for each individual 3D CT bone surface model were defined from three anatomical landmarks ( Fig. 1E–F ). 9 12 The anatomical landmarks were also used to define the radioulnar joint (RUJ) axis ( Fig. 1G ) and to estimate kinematic outcomes ( Fig. 1H ).
Kinematic Outcomes
The RUJ axis of forearm rotation was defined as extending through the radial head center to the ulnar head center ( Fig. 1G ). 13 The SN line was defined by connecting the midpoint of the volar and dorsal radius SN rims. This SN length was measured ( Fig. 1H ). The RUJ axis and the SN line were used to estimate the kinematic outcomes. 9
The primary outcome was DRUJ translation at the maximum force applied during the dRSA-evaluated press test motion cycle. Secondary outcomes were US-examined DRUJ translation and maximum force, DRUJ position ratio, and change in ulnar variance within the RSA-evaluated press test motion cycle ( Fig. 1H ).
Press Test Setup
The participants were positioned in a standardized setting to perform a press test examination on a custom-made unidirectional weight platform with a radiolucent plate mounted for force application. Instructions were to apply force by the hypothenar region gradually to their maximum and release the force gradually until no force was applied (one press test motion cycle). Thus, a visually confirmed volar translation of the ulnar head was induced and recorded during the press test by dRSA ( Fig. 2 ). Double examinations were conducted for reliability.
Fig. 2.
Dynamic radiostereometry (dRSA) setup during press test examination on a weight platform. The participants were positioned with ∼60 degrees shoulder flexion, with adducted upper arm, the elbow flexed, and the pronated forearm positioned in the horizontal plane resting with the hand flat on a weight-platform that logged the applied force (measured in kg). The instructions were to gradually apply maximum force through the hypothenar region of the palm resulting in a visually confirmed volar translation of the ulnar head before the force was gradually released. The dRSA test setup consisted of two ceiling-mounted X-ray tubes with a 20 to 20 degrees tube position on the vertical plane and two digital image detectors (Canon CXDI-50RF) slotted beneath a uniplanar carbon box (Carbon box 24, Medis Specials, Leiden, the Netherlands). The source-to-skin distance was 100 cm and the source-to-images distance was 150 cm. The image frequency of the dRSA recordings was 10 Hz.
A custom-made software was designed for a small single-board computer (Raspberry Pi) to timestamp and relate the force (measured in kg) applied on the weight platform and the simultaneously recorded dRSA images.
Dynamic RSA Setup and Recordings
The digital Adora RSA system (NRT X-Ray, Hasselager, Denmark) was used to record the dRSA images at a frequency of 10 images per second (10 Hz) during the press test application ( Fig. 3A ). The dRSA exposures used were 60 kV and 630 mA settings and a 2.0 milliseconds exposure time for acquiring a resolution of 2208 × 2688 pixels resolution (0.16 mm × 0.16 mm image area per pixel). Images were exported as multiframe DICOM files.
Fig. 3.
Analysis of dynamic radiostereometry (dRSA) recordings. ( A ) The participants performed the press test on a weight platform during dRSA with images recorded at 10 Hz. ( B ) Digital reconstructed radiographs (DRR) were generated from computed tomography-based bone surface and volume models. ( C ) Primary manual orientation and positioning of the bone models were required to initialize the DRR image to approximately fit the initial dRSA image. ( D ) The subsequent dRSA images and DRRs were analyzed automatically using AutoRSA software, as the software sets initialization of the next DRR image by extrapolation from the previous movement.
Image calibration was performed on an averaged image of all image frames in the dRSA image series. This reduced image noise from the moving arm and ensured a clear view of fiducial and controls markers from the calibration box.
Analysis of Dynamic RSA
Model-based RSA software (MBRSA 4.11, RSAcore, Leiden, the Netherlands) was used for calibration of the averaged calibration image. 14
An automated custom software system (AutoRSA, Orthopedic Research Unit, Aarhus, Denmark) was used for analysis of the dRSA image series. AutoRSA utilizes digital reconstructed radiographs (DRRs) for 3D to 2D image registration. A DRR is a projection of the 3D CT bone models ( Fig. 3B ) on an 2D image plane, thus a virtual radiograph.
Prior to the automated image registration process, a manual initialization was performed for the first dRSA image. This process included first a manual positioning of the bone models until the 2D DRR projection-overlay approximately fit the first dRSA image ( Fig. 3C ). Second, mathematical optimization algorithms were used to obtain the best match between DRR and the actual dRSA image—defining the 3D position and orientation (i.e., pose) of the ulna and radius bone in the calibration box coordinate system ( Fig. 3D ). Prior to each image registration, extrapolation of the previous poses initialized the approximately pose of the bone models. 10 15 16 The final pose of the bones in the calibration box coordinate system was transformed to the standardized bone-specific coordinate systems ( Fig. 1E–F ).
Data Management
The data logging of the force (kg) applied to the weight-platform was merged with the outcome measures from the analyzed dRSA examinations. The participants' individual delay in applying force on the weight platform was handled using a customized software application to automatically identify the start and end points of the first and second motion cycles. The motion cycle with the highest force application was chosen for data analysis ( Fig. 4 ). The maximum force applied in each cycle was defined as the 50% mark of the motion cycle and was used to normalize the motion cycle in a downstroke and release phase via linear interpolation of the force and the kinematic outcomes.
Fig. 4.
Definition of the motion cycle generated from press test force data and synchronized dynamic radiostereometry outcomes. The first ( A ) and second ( B ) press test motion cycle were determined from the participant-applied force on the weight platform (kg). The cycle start point was defined as the point just before the press data exceeded a threshold value of 0.1 kg relative to the press value corresponding to the course start point, and vice versa the end point was defined in the same manner by tracking from the end of press data (green and red cycles). The cycle with the highest maximum force (P max 2 > P max 1 ) was used for data management (red cycle) of the corresponding outcome (orange) throughout the selected cycle. The maximum force (P max ) was used to define the corresponding maximum force outcome value (PO) (i.e., the distal radioulnar joint [DRUJ] position).
The maximum force (P max ) and corresponding kinematic outcome values (PO) from the two motion cycles were used for the examination of reliability ( Fig. 4 ).
Ultrasonography Examinations
A US-based DRUJ stability examination was performed as described by Hess et al. 8 The participants were placed in a standardized position to measure DRUJ translation (T = X 1 - X 2 ) and calculate the DRUJ translation quotient (Q = [X 1 –X 2 ] / X 1 ) ( Fig. 5 ). The US examination was repeated after ∼4 weeks (range: 3–6) enabling evaluation of test–retest reliability.
Fig. 5.
Examinations of distal radioulnar joint (DRUJ) stability by ultrasonography. The participant was placed on a chair with their arm on a positioner abducting the upper arm 60 degrees from the vertical plane and ensuring standardized measures with ∼30 degrees forearm pronation. Measures were made by placing the transducer dorsal over the DRUJ, perpendicular to the ulna longitudinal axis, displaying the dorsal surface of the distal radius (DR) and the center of the ulnar head (UH) at the level of the Lister's tubercle (LT). The most dorsal bromination of the ulnar head was displayed and chosen for static measurement of the perpendicular distance to an extended line from the floor of the 4 th extensor compartment at the DR at rest (X 1 ), and after maximum force of the palm and the hypothenar region was applied to a leveled box, inducing a palmar shift of the ulnar head, the perpendicular distance was measured again (X 2 ). The DRUJ translation quotient (Q = [ X 1 - X 2 ] / X 1 ) and the DRUJ translation (T = X 1 - X 2 ) were calculated. EDC, extensor digitorum communis; EPL, extensor pollicis longus.
Statistical Analysis
Descriptive analyses of patient demographics were performed. Continuous data estimated from clinical examination, dRSA analysis, and US evaluations were checked for normality by evaluation of frequency and probability plots. Parametric data were reported as means with 95% confidence intervals (95% CI). The Student's independent t -test (equal variance) was used to compare kinematic RSA outcomes, for men and women at the beginning of the cycle (at 0% of the motion cycle) and at maximum force (at 50% of the motion cycle). Categorical data were reported as numbers and were compared between groups using the chi-squared test.
Repeatability of force and kinematic outcomes from the dRSA press test were evaluated to approximate the precision. The systematic bias was reported as the absolute mean difference with standard deviations (SD) and prediction intervals (SD × 1.96). Interrater agreement of dRSA press test and US double examination outcomes was calculated as intraclass correlation coefficients (ICC) based on an assumption of a single rater, absolute-agreement, two-way mixed effects model (ICC [2,1])). The rater consistency was reported with 95% CIs.
The level of significance was set at p < 0.05. All analyses were computed using Stata 16.0 software (StataCorp LP, TX).
Results
Patient Demographics
The included participants had a mean age of 31 years (range: 19–50). Demographic data including sex, side of the investigated forearm, and hand dominance are described in Table 1 .
Table 1. Demographics of the participants investigated.
| Characteristics | Asymptomatic forearms |
|---|---|
| Sex (men/women) | 14/19 |
| Mean age at time of inclusion (range) | 31 (19–50) |
| Investigated healthy hand (dominant hands %) | 58 |
| Dominant hand (right %) | 94 |
Clinical Examination
The forearms were mainly the participant's dominant side (19 out of 33), and all DRUJs were evaluated as stabile using the ballottement test in neutral, supinated, and pronated forearm positions ( Table 2 ). The grip strength was 32.8 kg (95% CI: 30.1–35.5) for women and 53.4 kg (95% CI: 48.7–58.1) for men. Wrist motion and forearm rotation are reported in Table 2 .
Table 2. Clinical results in participants with asymptomatic forearms.
| Examination | Asymptomatic arms |
|---|---|
| Number of participants | 33 |
| Grip strength total (kg) Women ( n = 19) Men ( n = 14) |
41.5 (37.2–45.9) 32.8 (30.1–35.5) 53.4 (48.7–58.1) |
| Wrist motion (degrees) Flexion Extension Radial deviation Ulnar deviation |
79 (75–82) 74 (71–77) 23 (20–25) 36 (34–38) |
| Forearm rotation (degrees) Supination Pronation |
84 (82–87) 81 (78–84) |
| Clinical evaluation of DRUJ stability: Ballottement test ( n ) Neutral forearm rotation Pronated forearm rotation Supinated forearm rotation |
33/0/0
a
33/0/0 a 33/0/0 a |
Abbreviation: DRUJ, distal radioulnar joint.
Note: Numbers are reported as means with 95% confidence intervals and standard deviation (SD).
Definition of Ballottement test stability evaluation: Stable or slight instability ( < 5 mm)/mild instability (5–10mm)/severe instability (>10 mm). Displayed as number of patients ( n ).
DRUJ Kinematics
The dynamic outcomes of normal DRUJ kinematics during the press test examination, including 95% CIs and prediction intervals (1.96 × SD) are shown in Fig. 6 , with the downstroke phase displayed as 0 to 50% of the motion cycle and the release phase as 51 to 100% of the motion cycle.
Fig. 6.
Kinematic outcomes during the press test motion cycle (0–100%) recorded by dynamic radiostereometry (dRSA). Graphs of the means with 95% confidence intervals (CIs; blue area) and prediction interval (gray area; 1.96 × standard deviation). ( A ) Force applied during the press test, ( B ) the corresponding distal radioulnar joint (DRUJ) position ratio, ( C ) the resulting DRUJ translation, and ( D ) ulnar variance.
At the maximum force (50% of the motion cycle), a mean of 6.0 kg (95% CI: 5.1–6.9) was applied onto the weight platform, which induced a DRUJ translation of mean 4.7 mm (95% CI: 4.2–5.5) ( Table 3 ).
Table 3. dRSA outcome measures of the DRUJ in asymptomatic forearms.
| Outcome in asymptomatic forearms | Total | Men | Women | p- Value a |
|---|---|---|---|---|
| Number of forearms | 33 | 14 | 19 | |
| Sigmoid notch length (mm) | 13.4 (13.0–13.8) SD: 1.2 |
14.1 (13.3–14.8) SD: 1.3 |
12.9 (12.4–13.4) SD: 0.9 |
0.005 |
| At 0% of the motion cycle | ||||
| Forearm pronation (degrees) | 62 (58–66) SD: 11 |
57 (53–61) SD: 7 |
65 (59–71) SD: 12 |
0.03 |
| DRUJ position ratio | 0.75 (0.71–0.78) SD: 0.10 |
0.72 (0.65–0.79) SD: 0.12 |
0.77 (0.73–0.81) SD: 0.08 |
0.23 |
| At 50% of the motion cycle | ||||
| Maximum force (kg) | 6.0 (5.1–6.9) SD: 2.4 |
6.3 (4.7–7.9) SD: 2.8 |
5.8 (4.8–6.8) SD: 2.1 |
0.55 |
| Forearm pronation (degrees) | 53 (48–57) SD: 13 |
48 (42–54) SD: 10 |
56 (50–63) SD: 13 |
0.08 |
| DRUJ translation (mm) | 4.7 (4.2–5.1) SD: 1.3 |
4.3 (3.5–5.0) SD: 1.3 |
4.9 (4.4–5.5) SD: 1.2 |
0.15 |
| DRUJ position ratio | 0.40 (0.33–0.44) SD: 0.11 |
0.42 (0.37–0.47) SD: 0.09 |
0.38 (0.33–0.44) SD: 0.11 |
0.32 |
| Increase in ulnar variance along the RUJ axis (mm) | 1.1 (1.0–1.2) SD: 0.4 |
1.1 (0.8–1.3) SD: 0.5 |
1.1 (0.9–1.3) SD: 0.4 |
0.94 |
Abbreviations: dRSA, dynamic radiostereometry; DRUJ, distal radioulnar joint; RUJ, radioulnar joint.
Independent t -test comparing men and women. Numbers are reported as means with 95% confidence intervals and standard deviation (SD).
The SN length was significantly different in men and women ( p = 0.005) ( Table 3 ). Taking the SN length into account, the calculated DRUJ position ratio was not significantly different between genders before force application ( p = 0.23). The press test moved the center of the ulnar head below the SN center at the maximum force in both men and women to a common mean DRUJ position ratio of 0.40 (95% CI: 0.33–0.44) ( Table 3 ).
Twenty-four of the 33 patients pressed 5 kg or more ( Table 3 ), and a clear flooring effect of the press test-induced DRUJ position ratio was seen after 5 kg of force application ( Fig. 7 ).
Fig. 7.
Relationship between press test force (kg) and the distal radioulnar joint (DRUJ) position ratio recorded by dynamic radiostereometry (dRSA) . The mean DRUJ position ratio with 95% confidence intervals displays a floor effect with increased force during the press test.
The ulnar variance increased mean 1.1 mm (95% CI: 1.0–1.2) during the press test ( Table 3 ).
Reliability of the Press Test
There was no systematic bias of the applied maximum force in the first and second tests. The absolute mean difference of the maximum force was 0.80 kg, and the biological variation of the group resulted in a prediction interval of the applied force of ± 1.35 kg. This maximum force difference generated a mean difference of 0.39 mm absolute DRUJ translation, a mean difference of 0.02 in the DRUJ position ratio, and a mean difference of 0.10 mm in ulnar variance ( Table 4 ).
Table 4. Repeatability of the press test and synchronized kinematic outcomes recorded by dRSA double examinations.
| Value | Maximum force (kg) | DRUJ translation at max force (mm) | DRUJ position ratio at max force | Ulnar variance (mm) |
|---|---|---|---|---|
| Double examinations | 33 | 33 | 33 | 33 |
| Mean difference (SD) | 0.80 (0.69) | 0.39 (0.27) | 0.02 (0.02) | 0.10 (0.09) |
| Prediction interval (SD × 1.96) | 1.35 | 0.53 | 0.04 | 0.18 |
| ICC (95% CI) | 0.87 (0.76–0.94) |
0.93 (0.86–0.96) |
0.95 (0.91–0.98) |
0.996 (0.99–1.00) |
Abbreviations: CI, confidence interval; dRSA, dynamic radiostereometry; DRUJ, distal radioulnar joint, ICC, intraclass coefficient; SD, standard deviation.
Notes: The systematic biases are reported as absolute mean differences with standard deviations (SD) and prediction intervals (SD × 1.96).
ICC (2,1) calculated as two-way mixed effects, absolute agreement to evaluate rater consistency between first and second examinations.
ICC rater consistency of the test–retest maximum force, DRUJ translation, DRUJ position ratio, and ulnar variance at maximum force was excellent ( r > 0.90), with a lower limit 95% CI indicating good or excellent consistency ( r > 0.80).
Sonography Test Retest Reliability
Specificity of US measurements was 82%, since 6 of the 33 asymptomatic forearms in the first US examination were above the DRUJ translation quotient cutoff value (Q = 0.80) proposed by Hess et al. 8 The US-measured DRUJ translation quotient (Q) had a mean of 0.59 (95% CI: 0.44–0.74) and 0.56 (95% CI: 0.45–0.68) ( p = 0.59), and the DRUJ translation (T) had a mean of 2.3 mm (95% CI: 1.7–2.8) and 2.4 mm (95% CI: 1.8–2.9) at the first and second examinations, respectively ( p = 0.58). The ICC (2,1) rater consistency of the test–retest sonography-examined DRUJ translation indicated moderate reliability ( r = 0.74, 95% CI: 0.53–0.87).
Discussion
DRUJ Translation and DRUJ Position Ratio
In the present study, the patient-induced DRUJ translation during the dRSA press test had a mean of 4.7 mm (SD: 1.3) in asymptomatic stable joints; the DRUJ position ratio with pronated unloaded forearm had a mean of 0.75, (SD: 0.10), and at maximum force a mean of 0.40 (SD: 0.11). In a previous static radiostereometry study evaluating ex vivo DRUJ kinematics during a passive piano key test in uninjured cadaver forearms, a limited DRUJ translation of 1.36 mm was detected. 9 This translation measure was unidirectional, and ex vivo examination of DRUJ kinematics may not directly resemble in vivo measures.
In the US-based study by Hess et al, a DRUJ translation of mean 2.5 mm (SD: 1.03) was reported when the applied force exceeded 5 kg. 8 This was similar to our reported US DRUJ translation of 2.3 mm (SD: 1.5) using the same press test. Thus, the unidirectional DRUJ translation of 4.7 mm (SD: 1.3) detected during our dRSA press test was higher compared with US-based measures, whereas the variation was similar. The correlation between the US measured translation and the RSA measured DRUJ translation at maximum force was poor ( r = 0.137; 95% CI: -0.228 to 0.469). This may be an effect of the dynamic detection, which ensures registration of the full range of DRUJ translation, whereas US-based still pictures may not be taken exactly at minimum and maximum force applications. Furthermore, in the present study, the forearm pronation had a mean of 53 degrees (95% CI: 48–57) when the maximum force was applied, whereas US-based method was performed with the forearm in a standardized position at ∼30 degrees pronation.
The DRUJ is not a constricted joint due to the different radiuses of the articular surfaces of the ulnar head and the SN. This allows for a sliding contact point during forearm rotation, which is most pronounced in an interval from 0 to 60 degrees pronation where the ulnar head glides dorsally in the SN. 17 Thus, unidirectional examinations of DRUJ translations that initiate from a more pronated forearm position may contribute to the higher translation measures. In contrast, the radioulnar ligaments are known to yield a stabilizing effect of the ulnar head in the SN as they tighten increasingly with pronation, 18 and from 60 to 90 degrees pronation, the dorsal sliding of the ulnar head is limited. 17
Gender differences in DRUJ translation were seen, but the mean values detected in women (5.11 mm) were not significantly higher than in men (4.42 mm). The SN length has been estimated as a mean of 15 mm in cadaver specimens. 19 We report a similar SN length of 13.4 mm, but also significant anatomical variation between men and women, with a larger SN length in men. Thus, estimates of DRUJ translation should preferably be normalized by considering the individual anatomical variation of the SN length.
Ulnar Variance
Ulnar variance plays a role in the dynamic process of ulnocarpal abutment, but TFCC pathology with DRUJ instability has also been related to increased ulnar variance. In asymptomatic forearms, static tests with a strong grip or heavy axial load the ulnar variance increased up to 1.95 mm (SD: 0.74). 20 21 22 This change in ulnar variance may not be directly comparable with the increase in ulnar variance of mean 1.1 mm (SD: 0.4) during the dynamic press test, as this was induced by a volar-directed force application by the hand despite the forearm supinated slightly during the press test. Nevertheless, these types of loading increased the ulnar variance.
Test Reliability
The applied force peaked (50% of the motion cycle) at a mean of 6.0 kg, whereas the DRUJ translation and the DRUJ position ratio flattened out at 40 to 60% of the motion cycle ( Fig. 6 ).
This floor effect of the measured DRUJ position started at forces lower than the maximum force and may explain the high precision and excellent ICC agreement ( r >0.93) of the press test kinematic outcomes.
Likewise, the press test sonography study by Hess et al concluded that maximum DRUJ translation was present at 5 kg force, as higher forces (measured from 0 to 10 kg at 2.5 kg intervals) did not further increase DRUJ translation. 8 This was supported by the current study, as we detected a flooring effect of the DRUJ position ratio when a force of 5 kg or more was applied. A clear force threshold creates the option of a simpler static RSA test setup comparing DRUJ kinematics between an unloaded and a minimum 5 kg-loaded press test setup. Such a setup can be created in any radiology department with a mobile X-ray tube in addition to the standard tube.
The US-based method benefits from device availability and easy application in clinical practice, but measures and reliability are highly subjective. In the present study, the ICC rater consistency of the test–retest US-examined DRUJ translation had moderate reliability for one hand surgeon with moderate US experience ( r = 0.75 [ 95% CI: 0.54–0.87]). In comparison, Hess et al reported high interobserver agreement of sonographic measurements (Pearson correlation r = 0.83). Despite the fact that the participants forearms being pain free, uninjured, and evaluated as completely stable by clinical examination using the ballottement test, the US specificity was 82%, similar to the specificity reported by Hess et al. 8 Thus, to reduce the false positive rate, this emphasizes the importance of comparison with the patients uninjured DRUJ.
Limitations
DRUJ translation in normal joints with an intact TFCC can be seen with broad variability ranging from hypermobility to highly stable joints and an inability to relax the DRUJ-supporting muscular stabilizers during testing. Likewise, force application varies and especially women did not exceed a 5 kg force application during the press test. Thus, this may affect the normal values and variations reported in the study.
Conclusions
In conclusion, this study demonstrates excellent agreement between repeated press test examinations using an observer-independent noninvasive dRSA imaging method based on patient-individual CT-based bone models and AutoRSA in clinical practice.
The DRUJ position ratio in asymptomatic participants leveled off at 5 kg force; hence, the complicated dRSA setup may be replaced by a simplified unloaded and loaded static RSA test setup, which should be applicable in any institution.
Press test examination and AutoRSA analysis in patients with confirmed TFCC injuries have not yet been evaluated, but is likely applicable, and previous cadaver studies have shown promising results concerning detection of differences in DRUJ translations using RSA. 9 23 Evaluation of kinematic differences between uninjured and injured forearms remains to be examined in vivo.
Acknowledgments
The authors thank radiographer Lars Lindgren from the Department of Radiology, Aarhus University Hospital, and Michael Frosted Mathiasen, from the Department of Radiology, Hospital Unit Vest, for their valuable help with the radiostereometric recordings.
Funding Statement
Funding This research has received grants from Health Research Fund of Central Denmark Region, Aarhus University, The Danish Rheumatism Association and Innovation Fund Denmark (Grant 69-2013-1). All funding sources did not play a role in the study investigation.
Conflict of Interest None declared.
Note
The institutions at Which the work was performed were Department of Orthopaedics, University Clinic for Hand, Hip and Knee Surgery, Hospital Unit West, Lægaardvej 12, 7500 Holstebro, Denmark and Department of Orthopaedic Surgery, Aarhus University, Palle Juul-Jensens Boulevard 165, 8200 Aarhus N, Denmark
Ethical Approval
The Danish Data Protection Agency (Journal no.2012–58–006; issued May 2016) and The Central Denmark Region Committees on Health Research Ethics (Journal no.1–10–72–146–16; issued August 2016) approved the study. Informed consent was obtained from the participating subjects.
References
- 1.Nagata H, Hosny S, Giddins G E. In-vivo measurement of distal radio-ulnar joint translation. Hand Surg. 2013;18(01):15–20. doi: 10.1142/S0218810413500032. [DOI] [PubMed] [Google Scholar]
- 2.Pickering G T, Nagata H, Giddins G EB. In-vivo three-dimensional measurement of distal radioulnar joint translation in normal and clinically unstable populations. J Hand Surg Eur Vol. 2016;41(05):521–526. doi: 10.1177/1753193415618110. [DOI] [PubMed] [Google Scholar]
- 3.Wijffels M, Stomp W, Krijnen P, Reijnierse M, Schipper I. Computed tomography for the detection of distal radioulnar joint instability: normal variation and reliability of four CT scoring systems in 46 patients. Skeletal Radiol. 2016;45(11):1487–1493. doi: 10.1007/s00256-016-2455-y. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Schnetzke M, Porschke F, Hoppe K, Studier-Fischer S, Gruetzner P A, Guehring T. Outcome of early and late diagnosed Essex-Lopresti Injury. J Bone Joint Surg Am. 2017;99(12):1043–1050. doi: 10.2106/JBJS.16.01203. [DOI] [PubMed] [Google Scholar]
- 5.Park M J, Kim J P. Reliability and normal values of various computed tomography methods for quantifying distal radioulnar joint translation. J Bone Joint Surg Am. 2008;90(01):145–153. doi: 10.2106/JBJS.F.01603. [DOI] [PubMed] [Google Scholar]
- 6.Lo I K, MacDermid J C, Bennett J D, Bogoch E, King G J. The radioulnar ratio: a new method of quantifying distal radioulnar joint subluxation. J Hand Surg Am. 2001;26(02):236–243. doi: 10.1053/jhsu.2001.22908. [DOI] [PubMed] [Google Scholar]
- 7.King G J, McMurtry R Y, Rubenstein J D, Gertzbein S D. Kinematics of the distal radioulnar joint. J Hand Surg Am. 1986;11(06):798–804. doi: 10.1016/s0363-5023(86)80225-8. [DOI] [PubMed] [Google Scholar]
- 8.Hess F, Farshad M, Sutter R, Nagy L, Schweizer A. A novel technique for detecting instability of the distal radioulnar joint in complete triangular fibrocartilage complex lesions. J Wrist Surg. 2012;1(02):153–158. doi: 10.1055/s-0032-1312046. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Thillemann J K, De Raedt S, Jørgensen P B, Rømer L, Hansen T B, Stilling M. Distal radioulnar joint stability measured with radiostereometry during the piano key test. J Hand Surg Eur Vol. 2020;45(09):923–930. doi: 10.1177/1753193420934689. [DOI] [PubMed] [Google Scholar]
- 10.Christensen R, Petersen E T, Jürgens-Lahnstein J. Assessment of knee kinematics with dynamic radiostereometry: validation of an automated model-based method of analysis using bone models. J Orthop Res. 2021;39(03):597–608. doi: 10.1002/jor.24875. [DOI] [PubMed] [Google Scholar]
- 11.Atzei A, Rizzo A, Luchetti R, Fairplay T. Arthroscopic foveal repair of triangular fibrocartilage complex peripheral lesion with distal radioulnar joint instability. Tech Hand Up Extrem Surg. 2008;12(04):226–235. doi: 10.1097/BTH.0b013e3181901b1. [DOI] [PubMed] [Google Scholar]
- 12.McDonald C P, Moutzouros V, Bey M J. Measuring dynamic in-vivo elbow kinematics: description of technique and estimation of accuracy. J Biomech Eng. 2012;134(12):124502. doi: 10.1115/1.4007951. [DOI] [PubMed] [Google Scholar]
- 13.Hagert C G. The distal radioulnar joint in relation to the whole forearm. Clin Orthop Relat Res. 1992;(275):56–64. [PubMed] [Google Scholar]
- 14.Kaptein B L, Valstar E R, Stoel B C, Rozing P M, Reiber J HC.Evaluation of three pose estimation algorithms for model-based roentgen stereophotogrammetric analysis Proc Inst Mech Eng H 2004218(4, H4):231–238. [DOI] [PubMed] [Google Scholar]
- 15.Hansen L, De Raedt S, Jørgensen P B, Mygind-Klavsen B, Kaptein B, Stilling M. Marker free model-based radiostereometric analysis for evaluation of hip joint kinematics: A validation study. Bone Joint Res. 2018;7(06):379–387. doi: 10.1302/2046-3758.76.BJR-2017-0268.R1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Hemmingsen C K, Thillemann T M, Elmengaard B. Elbow biomechanics, radiocapitellar joint pressure, and interosseous membrane strain before and after radial head arthroplasty. J Orthop Res. 2020;38(03):510–522. doi: 10.1002/jor.24488. [DOI] [PubMed] [Google Scholar]
- 17.Chen Y R, Tang J B. In vivo gliding and contact characteristics of the sigmoid notch and the ulna in forearm rotation. J Hand Surg Am. 2013;38(08):1513–1519. doi: 10.1016/j.jhsa.2013.04.023. [DOI] [PubMed] [Google Scholar]
- 18.Xu J, Tang J B. In vivo changes in lengths of the ligaments stabilizing the distal radioulnar joint. J Hand Surg Am. 2009;34(01):40–45. doi: 10.1016/j.jhsa.2008.08.006. [DOI] [PubMed] [Google Scholar]
- 19.af Ekenstam F, Hagert C G. Anatomical studies on the geometry and stability of the distal radio ulnar joint. Scand J Plast Reconstr Surg. 1985;19(01):17–25. doi: 10.3109/02844318509052861. [DOI] [PubMed] [Google Scholar]
- 20.Hojo J, Omokawa S, Iida A, Ono H, Moritomo H, Tanaka Y.Three-dimensional kinematic analysis of the distal radioulnar joint in the axial-loaded extended wrist position J Hand Surg Am 201944043360–3.36E8., e336 [DOI] [PubMed] [Google Scholar]
- 21.Ozer K, Zhu A F, Siljander B, Lawton J N, Waljee J F. The Effect of Axial Loading on Ulnar Variance. J Wrist Surg. 2018;7(03):247–252. doi: 10.1055/s-0038-1627458. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Friedman S L, Palmer A K, Short W H, Levinsohn E M, Halperin L S. The change in ulnar variance with grip. J Hand Surg Am. 1993;18(04):713–716. doi: 10.1016/0363-5023(93)90325-w. [DOI] [PubMed] [Google Scholar]
- 23.Thillemann J K, De Raedt S, Hansen T B, Munk B, Stilling M. Distal radioulnar joint stabilization with open foveal reinsertion versus tendon graft reconstruction: an experimental study using radiostereometry. J Exp Orthop. 2021;8(01):10. doi: 10.1186/s40634-021-00329-y. [DOI] [PMC free article] [PubMed] [Google Scholar]