Abstract
Background Previous studies on computed tomography (CT) in patients with a suspected triangular fibrocartilage complex (TFCC) injury have not been successful in assessing distal radioulnar joint (DRUJ) laxity. The aim of this study was to develop a novel servomotor-driven device for the assessment of DRUJ by applying increasing torque to the DRUJ in pronation and supination.
Methods A custom-built device was designed to function during four-dimensional (4D) CT of the wrist. A torque meter, positioned between the incoming hand holder, and a direct current (DC) servomotor were used for angular positioning and for applying rotational force to the patient's arm. A total of 110 healthy participants were recruited to gather reference values for the range of motion (ROM), maximum torque in neutral and supinated/pronated position, and the ability to withstand an increasing, device-generated torque in these positions. The device was also used during 4D DRUJ CT in five patients with suspected TFCC injuries.
Results A gender- and age-relevant reference chart for ROM and torque was created. Men showed a tendency (ns) toward having a larger ROM and increasing strength with increasing age, whereas women showed the opposite. Also, the dominant hand showed a tendency toward having a larger ROM and being stronger than the nondominant hand (ns). A smaller cohort of patients ( n = 5) with suspected TFCC injuries showed a significantly decreased ability to withstand increasing torque in both supination (2.1 ± 0.3 vs. 3.1 ± 0.2 s; p < 0.005) and pronation (2.3 ± 0.5 vs. 3.1 ± 0.4 s; p < 0.0005) and also showed a clear laxity on real-time 4D CT image sequences. Decreased strength at all positions was also found (average 74% decrease compared to noninjured side).
Conclusion Reference values for torque strength and ability to withstand increasing torque can be used clinically in the assessment of patients with symptoms that could represent ligamentous injuries to the TFCC. The ability to use the device during CT enables radiographic evaluation of instability during increasing torque.
Level of Evidence This is a Level II study.
Keywords: DRUJ Instability, TFCC injury, 4D CT, torque
Injuries to the triangular fibrocartilage complex (TFCC) occur both as isolated ligamentous injuries after traumatic impaction of the wrist and forced pro/supination movements, such as after the use of power tools or, in the elderly, after spontaneous ligamentous degeneration. They are also common after dorsally displaced distal radius fractures (DRFs). Varying numbers have been presented, but some studies suggest that as much as 60% of patients with DRF have an associated TFCC injury. 1 Although not all of these patients heal with conservative treatment, a majority will remain, to the more part, asymptomatic. Many factors may be involved in the explanation of this. The most common hypothesis is that the forearm muscles have the ability to compensate for some of the laxity by functioning as external stabilizers of the joint. However, in situations where the wrist is under sudden changes in load or stress, the laxity of the TFCC becomes evident and clinically presents as ulnar-sided wrist pain and subjective instability of the distal radioulnar joint (DRUJ). 1 2
Although the radioulnar stress test has been shown to be reliable in diagnosing clinical significant laxity, it can only detect gross laxity and is less useful when the laxity is subtle. It is also highly dependent on the examiner's experience and subjective assessment. 3
Previous efforts of using computed tomography (CT) to look for DRUJ instability have been based on its excellent ability to visualize the relative positions of radius and ulna with high spatial resolution. Several imaging-based methods to assess DRUJ subluxation have been developed. Lo et al have described a quantifying method called the radioulnar ratio (RUR). This method has been compared and validated against other CT-based techniques including the epicenter method, congruency method, and Mino criteria. 4 In short, all these techniques use anatomical landmarks, such as the borders of the sigmoid notch and the relation of the concentric circles of the notch and ulnar head, to assess incongruences that may indirectly be a sign of instability.
However, these have never become widespread because of difficulties in identifying standardized criteria for abnormal subluxation. One of the reasons for this is that there is a large individual variability in physiological translation that is most likely explained by differences in the soft tissue stabilizing structures around the wrist. Another major limitation of CT in diagnosing ligamentous injury is that it only indirectly assesses laxity in varying unprovoked, static conditions. Patients with TFCC injuries are, however, not troubled by instability in static positions but rather during dynamic loading. This is probably why CT-based methods correlate moderately with clinical examinations such as the radioulnar stress test. 5 6 In this study, we propose a method of visualizing the DRUJ under stress, which overcomes the aforementioned problems and that possibly could be more usable in clinical practice.
The purpose of this study was therefore to validate a novel device for evaluation of DRUJ stability. Patient-generated torque was measured, and the joint was stressed by applying increasing torque to the wrist in pronation and supination while the external muscular stabilizers of the forearm are immobilized. Reference values from a large cohort of healthy individuals of both sexes and different age intervals were established for future use of the technique as a diagnostic tool, and day-to-day reproducibility of the measured values was assessed. Also, the applicability and functionality of using the device during four-dimensional (4D) CT scanning was evaluated in five patients with suspected TFCC injuries.
Test Participants, Patients, and Methods
Test Participants
A total of 110 test participants were included in the study after they had given their informed and written consent. Exclusion criteria were prior injuries to the DRUJ, distal radius, or the proximal radioulnar joint (PRUJ). Any injuries to the interosseous membrane or the PRUJ must be addressed prior to use of the device.
Five participants had to be excluded completely because of transient technical problems with the torque meter (three men and two women), which leaves 105 participants whose measurements were analyzed. Demographics of the study group are presented in Table 1 .
Table 1. Test protocol divided into eight separate tests performed both in the dominant and nondominant hands.
| Test no. | Description of test |
|---|---|
| 1 | Maximum supination (degrees): ROM supination |
| 2 | Maximum pronation (degrees): ROM pronation |
| 3 | Rotated supination strength (Nm) in maximum supinated position minus 10 degrees |
| 4 | Rotated pronation strength (Nm) in maximum pronated position minus 10 degrees |
| 5 | Neutral supination strength (Nm) |
| 6 | Neutral pronation strength (Nm) |
| 7 | Maximum resistance to inward rotation (supination) force in maximum supinated position (s): resisting torque supination |
| 8 | Maximum resistance to inward rotation (pronation) force in maximum pronated position (s): resisting torque pronation |
Abbreviation: ROM, range of motion.
To evaluate the possible effects of age, sex, weight, and height, we recorded these parameters for our statistical testing. All test participants were divided into two defined age groups to allow for age-differentiated evaluation of the data (18–35 and 35–65 years).
Ethical approval for the study was obtained from the Regional Ethics Review Board at Linköping University (2016/12-31).
Torque Meter
The custom-built torque meter is made in two separate parts ( Fig. 1A , B ). The first part is the hand orthosis, where the test participant's hand is positioned in neutral rotation, with the fingers extended. This position of the hand minimizes the effect of muscle contraction on stabilizing the wrist, such as in grip position (external stabilizers). It also allows for reproducible forearm positioning between test participants. Four different orthoses were used, one smaller for each hand (right and left) and one larger for each hand (right and left). As the hand is placed in the orthosis, two straps are used to firmly stabilize that hand within the orthosis and to minimize inter- and radiocarpal movement during the tests. As there is no metal covering the DRUJ, it is possible to perform tests with the torque meter in a CT scanner.
Fig. 1.
Schematic illustration of the device and setup. (A,B) The tested hand is mounted on an orthosis that holds the fingers and thumb to prevent activation of external muscular stabilizers. The axis of rotation is designed to go through the distal radioulnar joint (DRUJ). The device consists of three parts: (1) a torque meter with a sensitivity of 0 to 25 Nm, (2) a direct current (DC) engine with an encoder that generates angles and torque, and (3) a microprocessor that runs the algorithm and provides real time data through a custom-made PC program. (C) During testing, the participant stands upright with the elbow flexed at 90 degrees. The opposite hand supports the elbow of the tested arm firmly to the body. The whole setup is mounted on a table that can be moved up and down to correct for different body heights. (D,E) Patients undergo four-dimensional computed tomography of the DRUJ in “superman” position. Due to the short scan duration and a low-dose image acquisition protocol, the scattered radiation dose to the torso and head is negligible.
The second part of the device is connected to the orthosis by a metallic shaft that is positioned such that it aligns with the center point of the DRUJ, and consists of a passive strain gauge torque meter (MTRS25NM, AEP Transducers, Modena, Italy) ( Fig. 1A , B ) positioned between the incoming shaft and a Maxon direct current (DC) servomotor (474014 motor RE40, Maxon Motor AG, Sachseln, Switzerland). The motor is used for angular positioning of the shaft as well as applying rotational force by which the strength of the patient can be measured. The system hardware is controlled by an Ardino microcontroller (MEGA2560, Torino, Italy), which, in turn, communicates with a Java application on a laptop computer (Microsoft Surface, Microsoft, Redmond, WA). The microcontroller is programmed to run the test protocol and provides the real-time measurement data to the custom-built software.
The device was calibrated by comparing the data output with a known applied torque. A torque wrench (10-242, Biltema Sweden AB, Helsingborg, Sweden), with a measurement range of 4 to 20 Nm and a maximum deviation of 3%, was used for this test. Fifty repetitive tests were performed using three different settings on the torque wrench (10, 12, and 14 Nm), all within the middle of the wrench's range to minimize measurement error. By comparing the applied force to the data output in all 50 tests a mean value of all ratios was calculated, which was used to calibrate the device.
Test Protocol
The participants were instructed to only use their forearm strength while the test leader made sure they were standing in the preferred position ( Fig. 1 ), with shoulders at the same height and the elbow at approximately 90 degrees. The test participants were instructed to hold their tested upper arm with their opposite hand in order to keep their elbow close to their side throughout the tests ( Fig. 1C ).
The test protocol was divided into eight different tests ( Table 1 ). First, the range of motion (ROM) was assessed (degrees, supination and rotation, tests 1 and 2), after which torque strength generated was measured with the forearm at maximum rotation minus 10 degrees, as well as in neutral position (Nm, tests 3–6). In the last tests (7 and 8), the participants resisted against a linearly increasing inward rotational torque load (1.5 Nm/s) generated by the torque meter in their maximum supinated and pronated positions minus 10 degrees, respectively. These tests dynamically provoke the DRUJ by simulating increasing load of the wrist, which is important in diagnosis and can be visualized using CT imaging. The time (s) from the start of the increasing torque load until the test person cannot longer steadily withhold the wrist in maximum pronated and supinated position is recorded.
Reproducibility
To test the day-to-day reproducibility of the measurement protocol, duplicate measurements were performed in 10 participants (five women and five men) on a separate day (all were right-handed). These measurements were always performed at scheduled appointments after lunch, 3 days after the initial measurement.
Patient Data
Patients with typical clinical subjective symptoms of TFCC insufficiency were recruited. The cohort consisted of five men and two women. The mean age was 41 years. None of the patients had any history of neuromuscular or degenerative joint diseases. All the patients in the study were secondary referrals to our department, with injuries occurring more than 6 months before examination. All patients had a history of significant unilateral wrist trauma. All but one had a history of DRF.
First, the same test protocol as in the normal population data was used. Then, a 4D CT scan of the wrist was performed. Patients were asked to lay supine on the CT table with their arms in a superman position ( Fig. 1D ) and with the device mounted on the head support mount. First, the uninjured arm and then the injured arm were tested ( Fig. 2 ). To limit the measurement time and radiation dose, only the ability to withstand increasing torque in supination and pronation was evaluated. All five patients subsequently underwent a diagnostic arthroscopy (radio- and intercarpal portals only, no portals in the DRUJ), which in all cases revealed a Palmer 1b lesion. This corresponds to suspected foveal tears in all, no superficial tears. This was followed by open repair of the ligament insertion through bone channels through the distal ulna.
Fig. 2.
Representative image slices from a four-dimensional CT sequence with (A) injured side and (B) uninjured side. Arrow represents the rotational force placed on the hand from the device. The patient tries to resist the increasing force but instinctively loses torque as instability occurs. This is seen as a rapid translational movement of the ulnar head (*) in the opposite direction of the force put on the hand. The time this takes is referred to as the ability to withstand increasing torque. As the torque is lost, there is a second rapid translational movement in the opposite direction, when the ulnar head moves back to its foveal position (**).
Data Analysis
The Wilcoxon matched pair test and Kruskal–Wallis test were performed on data on ROM, whereas all other data were analyzed with parametric tests, that is, paired and unpaired t -tests and one-way analysis of variance.
Correlations between torque meter measurements, and the test participants' weight, length, and body mass index (BMI) were analyzed using Pearson's correlation for all data except ROM, which was analyzed using Spearman's correlation. The interclass correlation (ICC) was calculated to assess day-to-day reproducibility. All data are presented as mean ± standard deviation except ROM, which is presented as median ± range.
All statistical analyses were performed using GraphPad Prism (version 7.0, GraphPad Software, San Diego, CA). Values of p < 0.05 were considered statistically significant.
Results
Descriptive data for the study cohort are summarized in Table 2 , strength tests are summarized in Table 3 , and the ability to withstand increasing torque loads and reproducibility tests in Tables 4 and 5 , respectively.
Table 2. Descriptive data.
| n | Weight (kg) | Height (cm) | BMI (kg/m 2 ) | |
|---|---|---|---|---|
| Female, 18–35 y | 37 | 65 ± 10 | 170 ± 8 | 23 ± 3 |
| Female, 35–65 y | 20 | 67 ± 8 | 165 ± 9 | 25 ± 3 |
| Male, 18–35 y | 27 | 79 ± 10 | 183 ± 6 | 24 ± 3 |
| Male, 35–65 y | 21 | 82 ± 6 | 183 ± 6 | 25 ± 2 |
Note: Of the 105 test participants, 8 were left-handed and the other 97 were right-handed (mean ± standard deviation).
Table 3. Rotated supination strength and rotated pronation strength (performed in maximum supination/pronation minus 10 degrees position taken from the study person's ROM from tests 1 and 2), and neutral supination strength and neutral pronation strength (performed in neutral position) presented in Nm ± SD.
| Dominant | Nondominant | Dominant | Nondominant | Dominant | Nondominant | Dominant | Nondominant | ||
|---|---|---|---|---|---|---|---|---|---|
| n | Rotated supination strength (Nm) | Rotated pronation strength (Nm) |
Neutral supination strength (Nm) | Neutral pronation strength (Nm) | |||||
| Female, 18–35 y | 37 | 1.9 ± 0.7 | 2 ± 0.6 | 2 ± 0.5 b | 1.6 ± 0.5 | 4.1 ± 1.4 b | 3.9 ± 1.4 | 3.8 ± 0.9 b | 3.4 ± 1.2 |
| Female 35–65 y | 20 | 1.9 ± 0.5 | 1.9 ± 0.4 | 1.9 ± 0.2 b | 1.7 ± 0.5 | 3.8 ± 0.8 b | 3.8 ± 0.8 | 3.7 ± 0.8 b | 3.5 ± 0.8 |
| Male 18–35 y | 27 | 2.4 ± 1.2 a | 2.3 ± 0.6 a | 2.4 ± 0.9 a b | 2.1 ± 1.1 a | 6.1 ± 2.4 a b | 5.6 ± 2.4 a | 5.7 ± 1.8 a b | 5.3 ± 2.2 a |
| Male 35–65 y | 21 | 3.1 ± 1.5 a | 2.9 ± 1.2 a | 3.1 ± 1.1 a b | 2.6 ± 1.7 a c | 8.4 ± 2.4 a c | 7.1 ± 1.5 a | 7 ± 1.4 a – c | 7.4 ± 1.8 a c |
Abbreviations: ROM, range of motion; SD, standard deviation.
Indicates significant difference in strength in age-matched men vs. women.
Indicates significant difference in strength in age-matched dominant vs. nondominant arms.
Indicates significant difference in strength in older vs. younger test participants.
Table 4. The ability to resist increasing torque forces in supination and pronation.
| Dominant | Nondominant | Dominant | Nondominant | ||
|---|---|---|---|---|---|
| n | Resisting torque supination (s) | Resisting torque pronation (s) | |||
| Female, 18–35 y | 37 | 3.3 ± 0.7 | 3.3 ± 0.7 | 3.3 ± 0.5 | 3.2 ± 0.6 |
| Female, 35–65 y | 15 | 2.8 ± 0.4 | 3.3 ± 0.6 | 3 ± 0.4 | 3.1 ± 0.5 |
| Male, 18–35 y | 27 | 3.5 ± 0.9 | 3.3 ± 0.6 | 3.6 ± 1.3 | 3.7 ± 1 |
| Male, 35–65 y | 21 | 3.6 ± 0.9 | 3.9 ± 0.9 | 3.8 ± 0.9 | 4 ± 0.8 |
Note: Data are presented in mean seconds ± standard deviation. No statistical differences were found between age- and gender-matched groups.
Table 5. The ICC with repeated measurements in 10 participants for all tests (1–8, see Table 1 ) .
| Test No. | ICC | 95% CI of ICC | Mean difference (day 1 and 2) | Day 1 mean ± SD | Day 2 mean ± SD |
|---|---|---|---|---|---|
| 1: ROM supination | 0.87 | 0.56–0.97 | –0.8 degrees | 80.5 ± 6.6 degrees | 79.7 ± 7.4 degrees |
| 2: ROM pronation | 0.90 | 0.67–0.98 | –0.4 degrees | 77.5 ± 13 degrees | 77.1 ± 11.7 degrees |
| 3: rotated supination strength | 0.90 | 0.67–0.98 | 0.2 Nm | 1.7 ± 0.6 Nm | 1.9 ± 0.7 Nm |
| 4: rotated pronation strength | 0.96 | 0.85–0.99 | –0.2 Nm | 1.9 ± 0.9 Nm | 2.1 ± 1.1 Nm |
| 5: neutral supination strength | 0.97 | 0.88–0.99 | 0.2 Nm | 4.6 ± 2.1 Nm | 4.4 ± 2.1 Nm |
| 6: neutral pronation strength | 0.88 | 0.58–0.97 | 0.1 Nm | 4.7 ± 1.6 Nm | 4.6 ± 1.4 Nm |
| 7: resisting torque supination | 0.50 | –0.15 to 0.85 | –0.18 s | 3.3 ± 0.4 s | 3.5 ± 0.2 s |
| 8: resisting torque pronation | 0.47 | –0.19 to 0.84 | 0.01 s | 3.5 ± 0.3 s | 3.5 ± 0.2 s |
Abbreviation: ICC, interclass correlation.
Note: Data are presented as ICC, 95% confidence interval, mean difference, and mean ± standard deviation for days 1 and 2.
Range of Motion Tests (tests 1 and 2)
The device is unable to measure ROM greater than 90 degrees in both supination and pronation. Dominant hand maximum supination was >90 degrees in 31 of 105 participants, and for these participants, the ROM measurement was set to 90 degrees. Because of this, median ROM values were calculated and ROM measurements were thereafter analyzed using nonparametric tests. Median (range) ROM was 83 (12) and 84 (11) for dominant supination and pronation, respectively. ROM was 80 (12) and 83 (12) for nondominant supination and pronation, respectively. Men showed a tendency (ns) toward having a larger ROM with increasing age, whereas females showed the opposite. Also, the dominant hand showed a tendency toward having a larger ROM the nondominant hand; however, this difference was not significant.
Strength Tests (Tests 3–6)
A complete data set is presented in Table 3 .
Men were found to be stronger than age-matched women in all groups ( p < 0.005). Men in the age group of 35 to 65 years showed a tendency toward being stronger than men in the age group of 18 to 35 years. This difference was significant in nondominant rotated pronation strength (RP; p < 0.05), dominant neutral supination strength (NS; p < 0.05), dominant neutral pronation strength (NP; p < 0.05), and nondominant neutral pronation strength (NP; p < 0.05). This difference was not seen in women, for whom instead a tendency was observed toward younger participants being stronger. This difference was, however, not statistically significant.
The dominant hand was found to be significantly stronger than the nondominant hand in all age groups, for RP ( p = 0.03), NS ( p < 0.005) and NP ( p = 0.04), but not in rotated supination strength (RS, p = 0.21). Both NS and NP (tests 5 and 6) were significantly stronger compared to RS and RP (tests 3 and 4) in both age groups and both genders ( p < 0.05).
Resisting Increasing Torque (Tests 7 and 8)
Data are presented in Table 3 . No statistical differences were found between age- and gender-matched groups. There was no difference between dominant and nondominant hands in the ability to resist increasing torque in supination ( p = 0.62), whereas the dominant hand tended to better resist torque in pronation ( p = 0.08).
Day-to-Day Reproducibility
The day-to-day reproducibility was very good for ROM for both supination and pronation measurements as well as for the strength measurements, with ICC values between 0.87 and 0.97. Measurement of resisting increasing torque was fairly reproducible, with ICC values of 0.50 for supination and 0.47 for pronation.
Correlation Analysis
All correlation analyses of weight, length, and BMI with strength (tests 3–6) and resistance to increasing torque (tests 7 and 8) were performed regardless of age and gender and only for the dominant hand. The strongest correlation was of length to NS ( r = 0.6; p < 0.0001) and NP ( r = 0.7; p < 0.0001) respectively. Similarly, RS ( r = 0.4; p < 0.005) and RP ( r = 0.5; p < 0.005) correlated to length, and NS ( r = 0.2; p < 0.05) and NP ( r = 0.3; p < 0.05) to weight. NS ( r = 0.2; p < 0.05) and NP ( r = 0.2, p < 0.05) correlated to BMI.
Patients
Results from tests 3 to 8 in injured and noninjured arms are presented in Table 6 . Representative image slices from a 4D CT sequence are depicted in Fig. 2 .
Table 6. The mean (SD) torque forces (Nm) generated by patients with suspected TFCC injuries in tests 3 and 4, as well as the mean (SD) time the patients could withstand increasing torque forces in tests 5 and 6.
| Test no. | Injured side, mean (SD) | Noninjured side, mean (SD) | Difference, mean (% change) |
|---|---|---|---|
| 3: Rotated supination strength | 1.32 Nm (0.13) | 1.92 Nm (0.22) a | –0.6 Nm (69) |
| 4: Rotated pronation strength | 1.34 Nm (0.11) | 1.80 Nm (0.16) a | –0.5 Nm (75) |
| 5: Neutral supination strength | 3.8 Nm (0.9) | 4.9 Nm (1) a | –1.2 Nm (76) |
| 6: Neutral pronation strength | 3.7 Nm (0.8) | 4.8 Nm (1) a | –1.1 Nm (78) |
| 7: Resisting torque supination | 2.1 s (0.3) | 3.1 s (0.2) a | –1 s (48) |
| 8: Resisting torque pronation | 2.3 s (0.5) | 3.1 s (0.4) a | –0.8 s (35) |
Abbreviations: SD, standard deviation; TFCC, triangular fibrocartilage complex.
Note: Injured and noninjured arms, as well as mean difference and the percentage difference, are presented. In all tests, the injured arms generated significantly less torque and could resist significantly less machine generated torque when compared to the noninjured arms ( p < 0.005).
Discussion
This is the first example of a technique where increasing torque loads to the forearm are applied using a custom-built device, with the aim to objectively evaluate the function of the DRUJ. The gathered data provide a reference standard chart for the future assessment of relevant patient groups using this device. Also, this study shows the ability of the device to be used in a 4D CT setting to visualize laxity within the DRUJ during externally applied increasing torque. This allows for better visualization of joint subluxation compared with other methods used today.
The results in our small patient cohort indicate that the technique not only has the ability to visualize the joint instability but also gives an indirect measure of the decreased ability to withstand an increasing torque. Despite the small sample size, the results suggest that decreased ability to withstand torque is indicative for a TFCC injury, as proven by the arthroscopic findings.
The question whether decreased forearm rotation strength is associated with DRUJ laxity has been explored using a few different types of devices. Lindau et al studied patients 2 years after DRF and found that DRUJ laxity was indeed associated with impaired hand function; however, they found no loss of strength in forearm rotation. 2 Contrary to these results, Andersson et al showed in a more recent study that patients who had arthroscopic signs of TFCC also had a concomitant loss in strength in forearm rotation. 7 The difference between these two studies lies in the difference in duration from onset of symptoms until the torque strength test was done. It may be speculated that the long duration of 2 years from injury to test in Landau's patient group enabled compensatory muscle groups to get strong enough to create stability in the test situation. Also, as all tests in these studies are performed in neutral position, with the patient firmly gripping the test device handle, it is reasonable to believe that the grip handle design may create a bias by activation of secondary muscle-dependent stabilizers of the forearm, such as the extensor carpi ulnaris tendon, the pronator quadratus (PQ) muscle, and finger flexors and extensors. 8 9 Furthermore, clinically it is well known that instability is mostly apparent during sudden movements or when some kind of provocation to the hand is applied. It is likely that this happens when these secondary muscle-dependent stabilizers are not activated. For these reasons, we decided to design our device in such a manner that external stabilizers (i.e., forearm flexors and extensors) are immobilized as much as possible. This is accomplished by placing the hand in a tight cast with fingers and wrist in a straight position ( Fig. 1 ), not allowing muscles over the wrist to actively stabilize the DRUJ by gross muscular contraction and tendon excursion across the wrist joint. A smaller remaining effect on stability of the wrist by the external stabilizers may, however, be anticipated as an effect of isometric muscle forces. This effect is, however, believed to be minor. The tight cast was designed to limit laxity within the carpus as much as possible; however, small movements therein cannot be excluded and may therefore affect the results of the ROM measurements.
Previous studies of pronation and supination torque report measurements similar to ours. The general conclusions are that rotational torque varies with forearm position, gender of the test participants, and type of hand fixation. Gordon et al reported rotational torque values much lower than others, including ours, which could be attributed to their method of fixating the hand with a wrist clamp. 10 Huh et al also reported peak torque values comparable to our findings, although they used isokinetic testing instead of isometric. 11 Matsuoka et al and McConkey et al reported a somewhat higher mean peak torque values than ours, but their standard deviations intermingle with ours in several tests. 12 13 A fist grip handle position was used in their studies to fixate the hand, which seems to generate higher torque values because it allows finger and wrist flexors and extensors to contribute to the rotation.
As a proof of concept, we gathered data from a smaller cohort of patients with subjective instability of the DRUJ, where an injury to the TFCC was suspected and later confirmed during surgery. Measurements from both the torque meter and 4D CT scans of the joint were performed while stressing it by applying increasing torque to the joint. This initial trial cohort has proven that the torque meter can be used while the patient is scanned and that the technique functions as intended. The 4D image sequences of the patients DRUJ shows a clear translation of ulna when provoked by increasing torque. This method of visualizing TFCC injury thus shows very promising results for future studies and translation into clinical practice. Previous studies have evaluated traditional 3D CT methods (RUR, epicenter method, congruency method, and Mino criteria) to assess instability of the DRUJ; however, these studies are hampered by the fact that they are performed in unprovoked, static conditions. Therefore, these methods only show a moderate correlation to clinical examinations. 5 6
The study setup has some shortcomings. First, we discuss pro/supination as a DRUJ specific movement; however, the concept of the forearm as a triarticulate joint for forearm rotation is well established. ROM in the forearm in this paper is, however, translated to being a function of DRUJ rotation, as the ulna is considered fixed and the elbow is consistently kept in a flexed position and held tight to the side.
Second, it is sometimes difficult to avoid that the test participants apply their body weight during the test and thereby produce higher torques than expected.
Third, the device is unable to measure ROM greater than 90 degrees. This shortcoming does not, however, affect the applicability of the device as ROM was primarily used to define what angle should be used in tests 7 and 8. The technique could be improved by allowing measurements at fixed angles, in addition to measurements in the neutral position. With the setup used in this paper, there is a risk that test participants who have a greater ROM will be regarded weaker in maximum force pronation and supination, as they will perform these tests at greater starting angle (maximum pronation/supination minus 10 degrees). Measuring rotational torque in fixed angles would solve this problem quite easily and likely improve accuracy in comparison between test participants.
Fourth, although more than 100 participants were included in the study, a larger study population would have allowed stratification into smaller age groups, where differences related to age would have been clearer. For, example the fact that older men seemed to be stronger than men from the younger cohort may be affected by the large age span of the two groups.
Possible future directions include not only further tests on patients with suspected TFCC but also in-depth analysis of the external stabilizers impact on DRUJ instability. For example, electromyographical (EMG) analysis of muscle activation patterns upon DRUJ loading and increased knowledge on the necessity of the deep head of PQ as a primary stabilizer for the DRUJ. 13 14 Despite this, it still remains unclear whether or not repairing of the PQ after volar plating of DRFs has any positive effect on clinical outcome. 11 14 15 This is a functionally important question that we hope to be able to address with the torque meter eventually. Also, effects of isometric and isotonic muscular activation on stability can be addressed to further strengthen the current proposed test design.
Footnotes
Conflict of Interest None.
References
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