Contact area inside the distal radioulnar joint: effect of axial loading and position of the forearm

The optimal tension for the reconstruction of the distal radioulnar ligaments

PURPOSE

This study aimed to investigate the optimal tension for the reconstruction of the distal radioulnar ligaments (DRULs) in the treatment of the distal radioulnar joint (DRUJ) instability.

METHODS

A total of eight human cadaver upper extremities were used. First, the Tekscan sensor film system was used to measure the contact characteristics of the intact DRUJ. Following this, the DRULs were resected, and the measurement was repeated. The DRULs were then reconstructed according to Adams' procedure, and the contact forces under different initial tension were compared with that of the intact group to obtain the optimal tension. At that point, the contact force of the DRUJ was close to normal. The reliability of the obtained tension was verified by translational testing, which reflected the stability of the DRUJ.

RESULTS

In the neutral position, the contact force, area, and pressure inside DRUJ were 0.51 ± 0.10 N, 64.08 ± 11.58 mm², and 8.33 ± 2.42 kPa, respectively. After the DRULs were resected, they were 0.19 ± 0.02 N, 41.75 ± 5.01 mm², and 4.86 ± 1.06 kPa, respectively. The relationship between the tension and contact force was linear regression (Y = 0.0496x + 0.229, R² = 0.9575, P < 0.0001). According to the equation, when the tension was 3.64-7.68 N, the contact force was close to normal. There was no statistical difference in the stability of the reconstructed DRUJ under this tension compared with the intact group (P = 0.08).

CONCLUSION

By comparing the contact forces under different reconstruction tensions with the normal value, we obtained the optimal tension, which can provide the theoretical basis for the clinical treatment of chronic DRUJ instability.

Biomechanical evaluation of interference screw fixation techniques for distal radioulnar ligament reconstruction: a cadaveric experimental study

INTRODUCTION

In the reconstruction of distal radioulnar ligaments (DRULs), interference screws can be used for antegrade or retrograde fixation of grafts to the ulna. However, the biomechanics of interference screw fixation are currently unknown. This study aimed to determine the biomechanical effects of these two fixations on the distal radioulnar joint (DRUJ) in a cadaveric model and to investigate the appropriate initial tension.

MATERIALS AND METHODS

A total of 30 human cadaver upper extremities were used, and the DRULs were reconstructed according to Adams' procedure. First, eight specimens were randomly divided into two groups: antegrade and retrograde, followed by translational testing and load testing. Then, the other eight specimens were divided into the two groups above, and the contact mechanics, including forces, areas, and pressures, were measured. Finally, to investigate the appropriate initial tension, the remaining 14 specimens were fixed with interference screws under different tensions in an antegrade way, and the translational testing was repeated as before.

RESULTS

In the neutral position, antegrade fixation exhibited less translation than retrograde fixation (7.21 ± 0.17 mm versus 10.77 ± 1.68 mm, respectively). The maximum failure load was 70.45 ± 6.20 N in antegrade fixation, while that in retrograde fixation was 35.17 ± 2.95 N (P < 0.0001). Antegrade fixation exhibited a larger increase in contact force than retrograde fixation (99.72% ± 23.88% versus 28.18% ± 10.43%) (P = 0.001). The relationship between tension and displacement was nonlinear (Y = - 1.877 ln(x) + 7.94, R² = 0.868, P < 0.0001).

CONCLUSIONS

Compared with retrograde fixation, the antegrade fixation of interference screws may be a more reliable surgical technique, as it shows a higher failure load and stability. In addition, to avoid the risk of potential arthritis caused by anterograde fixation, we propose an equation to determine the appropriate initial tension in DRUL reconstruction.

Force transmission through the wrist during performance of push-ups on a hyperextended and a neutral wrist

STUDY DESIGN

Cross-sectional cohort.

INTRODUCTION

Push-ups are used ubiquitously to evaluate and strengthen the upper body. They are usually performed in 1 of 2 main ways: with the wrist in hyperextension and with the wrist in a neutral position.

PURPOSE OF THE STUDY

The purpose of our study was to compare the dynamic forces in the wrist during the 2 push-up styles.

METHODS

Fourteen volunteers performed push-ups in 2 different patterns: on a hyperextended wrist and a neutral wrist (NW). Two force plates and a motion capture system were used to measure the ground reaction forces (GRFs) and the kinematics of the upper extremity during push-ups. Kinematic and kinetic analyses were performed using Matlab software (Mathworks, Natick, MA).

RESULTS

The GRF vector was distributed differently during the different types of push-ups. For both methods, the total GRF carried by the upper dominant extremity was larger than those of the nondominant extremity. In the NW configuration, the GRF vector was more uniform throughout the push-up in the vertical direction. The horizontal distance between the capitate bone location and the GRF origin was smaller in hyperextension. The forces traveled more dorsally over a wider area and more ulnarly in the hyperextended wrist.

DISCUSSION

Forces are transmitted differently through the wrist in the 2 methods. Push-ups on an NW are likely safer because ligaments may be preferentially loaded in hyperextension. Further study may delineate the differences in the anatomic location of force transmission and the long-term clinical effect on the wrist.

CONCLUSIONS

This study supports the performance of push-ups on a wrist in neutral flexion extension; both to enable patients after surgery or injury to strengthen the upper body and prevent injury and long-term wear in the wrist. The knowledge gained from this study may assist in outlining guidelines for push-up performance.

LEVEL OF EVIDENCE

Diagnostic level 2a.

[Anatomy and biomechanics of the distal radioulnar joint]

BACKGROUND

The functionality of the upper extremity is decisively based on rotation of the forearm. The rotation depends on the extent of motion of the distal radioulnar joint. Rotation enables complete and focused usability of the hand in order to cope with daily activities. The configuration of the distal radioulnar joint has developed over millions of years of evolution.

ANATOMIC CONDITIONS

The triangular fibrocartilage complex is the crucial stabiliser of the latter joint since osseous structures are limited. The palmar and dorsal radioulnar ligaments belong to this complex. The superficial and deep parts of the latter ligaments insert both centrically in accordance to the axis of rotation and eccentrically. This arrangement guarantees stability of the joint throughout pronosupination. The interosseous membrane is a further relevant stabiliser that guarantees sufficient load transmission from radius to ulna. The distal oblique bundle of the interosseous membrane is outstanding in this context. The pronator quadratus muscle is the relevant dynamic stabiliser of the distal radioulnar joint. Contraction of the muscle prevents diastasis of the joint. The deep head of the muscle is always activated during pronosupination.

Morphological characteristics of the sigmoid notch of the distal radius affect the stress distribution patterns in the distal radioulnar joint

The aim of this study was to clarify the effects of morphological patterns of the sigmoid notch on the stress distribution across the articular surface of the distal radioulnar joint using a computed tomography osteoabsorptiometry method. Fourteen wrists from 13 patients were classified into two groups according to the type of sigmoid notch, namely the 'C' type and ski-slope sigmoids, and the percentages of high-density areas on the articular surface were quantitatively analysed. The percentage of the high-density area of the dorsal region in the ski-slope sigmoid group was significantly greater than that of the 'C' type sigmoid group (16% vs 4.1%) and of the volar region of the ski-slope sigmoid group (16% vs 2.4%). The results indicate that bony morphological differences in the radial sigmoid notch affect the stress distribution pattern through the distal radioulnar joint.

The Effect of Dorsal Angulation on Distal Radioulnar Joint Arthrokinematics Measured Using Intercartilage Distance

Background  The effects of dorsal angulation deformity on in vitro distal radioulnar joint (DRUJ) contact patterns are not well understood. Purpose  The purpose of this study was to utilize intercartilage distance to examine the effects of forearm rotation angle, distal radius deformity, and triangular fibrocartilage complex (TFCC) sectioning on DRUJ contact area and centroid position. Methods  An adjustable implant permitted the creation of simulated intact state and dorsal angulation deformities of 10, 20, and 30 degrees. Three-dimensional cartilage models of the distal radius and ulna were created using computed tomography data. Using optically tracked motion data, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics. Results  DRUJ contact area was highest between 10 and 30 degrees of supination. TFCC sectioning caused a significant decrease in contact area with a mean reduction of 11 ± 7 mm ² between the TFCC intact and sectioned conditions across all variables. The position of the contact centroid moved volarly and proximally with supination for all variables. Deformity had a significant effect on the location of the contact centroid along the volar-dorsal plane. Conclusion  Contact area in the DRUJ was maximal between 10 and 30 degrees of supination during the conditions tested. There was a significant effect of simulated TFCC rupture on contact area in the DRUJ, with a mean contact reduction of 11 ± 7 mm ² after sectioning. Increasing dorsal angulation caused the contact centroid to move progressively more volar in the sigmoid notch.

Arthrokinematics of the Distal Radioulnar Joint Measured Using Intercartilage Distance in an In Vitro Model

PURPOSE

Current techniques used to measure joint contact rely on invasive procedures and are limited to statically loaded positions. We sought to examine native distal radioulnar joint (DRUJ) contact mechanics using nondestructive imaging methods during simulated active and passive forearm rotation.

METHODS

Testing was performed using 8 fresh-frozen cadaveric specimens that were surgically prepared by isolating muscles involved in forearm rotation. A wrist simulator allowed for the evaluation of differences between active and passive forearm rotation. Three-dimensional cartilage surface reconstructions were created using volumetric data acquired from computed tomography. Using optically tracked motion data, the relative position of the cartilage models was rendered and used to measure DRUJ cartilage contact mechanics. The effects of forearm movement method and rotation angle on centroid coordinate data and DRUJ contact area were examined.

RESULTS

The DRUJ contact area was maximal at 10° supination. There was more contact area in supination than pronation for both active and passive forearm rotation. The contact centroid moved volarly with supination, with magnitudes of 10.5 ± 2.6 mm volar for simulated active motion and 8.5 ± 2.6 mm volar for passive motion. Along the proximal-distal axis, the contact centroid moved 5.7 ± 2.4 mm proximal during simulated active motion. These findings were statistically significant. The contact centroid moved 0.2 ± 3.1 mm distal during passive motion (not significant).

CONCLUSIONS

It is possible to examine cartilage contact mechanics of the DRUJ nondestructively while undergoing simulated, continuous active and passive forearm rotation. The contact centroid moved volarly and proximally with supination. There were higher contact area values in supination compared with pronation, with a peak value at 10° supination.

CLINICAL RELEVANCE

This study documented normal DRUJ arthrokinematics using a nondestructive in vitro approach. It further reinforced the established biomechanical and clinical literature on contact patterns at the native DRUJ during forearm rotation.

Anatomic Relationships of the Distal and Proximal Radioulnar Joints Articulating Surface Areas and of the Radius and Ulna Bone Volumes - Implications for Biomechanical Studies of the Distal and Proximal Radioulnar Joints and Forearm Bones

Background

Previous work from this laboratory has evidenced the biomechanical role of forearm osseoligamentous structures in load transfer of applied forces. It has shown that forces transmitted across the distal radioulnar joint (DRUJ) and proximal radioulnar joint (PRUJ) are similar, though not identical, under axial loading conditions. The purpose of the study was to assess the articulating surface areas of the radioulnar joints and the volumes of the forearm bones addressing the hypothesis that there may be anatomic adaptations that reflect the biomechanical function of the integrated forearm unit.

Methods

The articulating surface areas of PRUJ and DRUJ were assessed using a laser scanner in 24 cadaver forearms. The articulating joint surfaces were additionally delineated from standardized photographs assessed by three observers. The surface areas of matched pairs of joints were compared on the null hypothesis that these were the same within a given forearm specimen. An additional 44 pairs of matched forearm bone volumes were measured using water displacement technique and again compared through statistical analysis (paired sample t-test and Bland–Altman analysis).

Results

The findings of this study are that the articulating surface areas of the DRUJ and PRUJ as well as the bone volumes are significantly different and, yet, strongly correlated. The paired sample t-test showed a significant difference between the surface areas of the DRUJ and PRUJ (p < 0.05). The PRUJ articulating surface area was marginally larger than the DRUJ with a PRUJ:DRUJ ratio of 1.02. Paired sample t-test showed a significant difference between the two bone volumes (p < 0.01) with a radius to ulna bone volume ratio of 0.81. When the olecranon was disregarded, radius volume was on average of 4% greater than ulna volume.

Conclusion

This study demonstrates and defines the anatomical relationships between the two forearm bones and their articulating joints when matched for specimen. The data obtained are consistent with the theory of integrated forearm function generated from published biomechanical studies.

The Effect of Elbow Extension on the Biomechanics of the Osseoligamentous Structures of the Forearm

PURPOSE

To investigate the hypothesis that elbow extension alters the biomechanics of forearm rotation including force transmission in the distal and proximal radioulnar joints (DRUJ and PRUJ) and the interosseous ligament (IOL).

METHODS

A cadaver model with a custom-designed jig was used to measure forearm pronosupination ranges, transmitted forces and contact areas across the PRUJ and DRUJ, and tension in the 3 main components of the IOL's central band. Testing with applied loads was undertaken throughout pronosupination with the elbow fully flexed (n = 15) and fully extended (n = 11).

RESULTS

Elbow extension-flexion affected the range of forearm pronosupination, shifting the arc of rotation such that the forearm supinated maximally with the elbow flexed and pronated maximally with the elbow extended. Elbow extension also increased transmitted forces across the DRUJ and PRUJ while also increasing contact areas within the DRUJ and PRUJ. Elbow extension significantly increased tension in the central band of the IOL when the forearm was maximally pronated.

CONCLUSIONS

Maximum supination occurred with the elbow flexed. Maximum pronation occurred with it extended. Elbow position altered forearm biomechanics, including force transmission across the PRUJ and DRUJ and transmitted tension in the IOL.

CLINICAL RELEVANCE

The interplay of osseoligamentous forearm structures is such that we would anticipate surgical alteration of any one of them to have effects upon function of the others.

The biomechanical and functional relationships of the proximal radioulnar joint, distal radioulnar joint, and interosseous ligament

This biomechanical study assessed integrated function of the proximal radioulnar joint (PRUJ), interosseous ligament (IOL), and distal radioulnar joint (DRUJ). Tekscan™ pressure sensors were inserted into the DRUJ and PRUJ of 15 cadaveric specimens. MicroStrain(®) sensors were mounted onto the IOL on nine of these specimens. A customized biomechanical jig was used to apply axial loads and take measurements through pronosupination. The PRUJ, IOL, and DRUJ were shown to function as an integrated osseoligamentous system distributing applied load. The PRUJ has transmitted pressure profiles similar to those of the DRUJ. Different IOL components support loading at different stages of pronosupination. The IOL is lax during pronation. Mid-IOL tension peaks in the midrange of forearm rotation; distal-IOL tension peaks in supination. Axial loading consistently increases IOL strain in a non-linear fashion. There are clinical implications of this work: disease or surgical modification of any of these structures may compromise normal biomechanics and function.

The push-off test: development of a simple, reliable test of upper extremity weight-bearing capability

STUDY DESIGN

Longitudinal clinical measurement study.

INTRODUCTION

The push-off test (POT) is a novel and simple measure of upper extremity weight-bearing that can be measured with a grip dynamometer. There are no published studies on the validity and reliability of the POT. The relationship between upper extremity self-report activity/participation and impairment measures remain an unexplored realm.

PURPOSE

The primary purpose of this study is to estimate the intra and inter-rater reliability and construct validity of the POT. The secondary purpose is to estimate the relationship between upper extremity self-report activity/participation questionnaires and impairment measures.

METHODS

A convenience sample of 22 patients with wrist or elbow injuries were tested for POT, wrist/elbow range of motion (ROM), isometric wrist extension strength (WES) and grip strength; and completed two self-report activity/participation questionnaires: Disability of the Arm, Shoulder and the Hand (DASH) and Work Limitations Questionnaire (WLQ-26). POT's inter and intra-rater reliability and construct validity was tested. Pearson's correlations were run between the impairment measures and self-report questionnaires to look into the relationship amongst them.

RESULTS

The POT demonstrated high inter-rater reliability (ICC affected = 0.97; 95% C.I. 0.93-0.99; ICC unaffected = 0.85; 95% C.I. 0.68-0.94) and intra-rater reliability (ICC affected = 0.96; 95% C.I. 0.92-0.97; ICC unaffected = 0.92; 95% C.I. 0.85-0.97). The POT was correlated moderately with the DASH (r = -0.47; p = 0.03). While examining the relationship between upper extremity self-reported activity/participation questionnaires and impairment measures the strongest correlation was between the DASH and the POT (r = -0.47; p = 0.03) and none of the correlations with the other physical impairment measures reached significance. At-work disability demonstrated insignificant correlations with physical impairments.

CONCLUSION

The POT test provides a reliable and easily administered quantitative measure of ability to bear the load through an injured arm. Preliminary evidence supports a moderate relationship between loading bearing measured by the POT and upper extremity function measured by the DASH.

LEVEL OF EVIDENCE

1b.

Instability of the distal radioulnar joint

The distal radioulnar joint is a complex structure necessary for forearm motion and force transmission across the wrist. Anatomic and biomechanical advances have revealed broad contributions to distal radioulnar joint stability and refined our understanding of the forces acting across it. Instability often co-occurs with other modes of pathology, such as arthrosis or malunion; and appropriate diagnosis and treatment require a comprehensive understanding of all contributing factors. Distal radioulnar joint instability can be broadly categorized as primary, post-traumatic or post-surgical. Treatment strategies include percutaneous, arthroscopic, soft-tissue, osteotomy and arthroplasty techniques. The purpose of this article is to review distal radioulnar joint instability and its management.

Functional anatomy of the distal radioulnar joint in health and disease

The distal radioulnar joint (DRUJ) is critical to the function of the forearm as a mechanical unit. This paper is concerned with the concepts and observations that have changed understanding of the function of the DRUJ, notably with respect to the biomechanics of this joint. The DRUJ has been shown to be important in acting to distribute load and removal of the ulna head leads to the biomechanical equivalent of a one-bone forearm. The soft tissues with topographical relations to the distal forearm and DRUJ have also been investigated in our experimental series with findings including the description of a clinical disorder termed subluxation-related ulna neuropathy syndrome.

The effect of distal radius locking plates on articular contact pressures

PURPOSE

Fractures of the distal radius are among the most common injuries treated in hand surgery practice, and distal radius locking plates have become an increasingly popular method of fixation. Despite widespread use of this technology, it is unknown whether the subchondral placement of locking screws affects the loading profile of the distal radius. Our study was designed to determine whether subchondral locking screws change the articular contact pressures in the distal radius.

METHODS

Twelve cadaveric forearms underwent a previously described axial loading protocol in a materials testing machine. We used an intra-articular, real-time computerized force sensor to measure peak contact pressure, total pressure, and contact area in the distal radius. Internal validation of sensor placement and reproducibility was conducted. Each specimen was tested before fixation (control), after application of a palmar distal radius locking plate, and after simulation of a metaphyseal fracture.

RESULTS

We identified no statistically significant differences in maximum pressure, total pressure, and contact area among control, plated, and plated and fractured specimens. However, the contact footprint-represented by squared differences in force across the sensor-were significantly different between the control group and both plated groups.

CONCLUSIONS

The technique for measuring contact pressures produces highly repeatable values. Distal radius locking plates with subchondral hardware placement do not seem to significantly change articular contact pressures.

The functional anatomy of forearm rotation

The elbow, forearm and wrist act as a unified structure to provide a stable, strong and highly mobile strut for positioning the hand in space and for conducting load-bearing tasks. An understanding of the relevant anatomy and biomechanics is important for the surgeon assessing and treating disorders of forearm function. This paper is concerned with illuminating the principles and concepts governing forearm rotation and load-bearing functions.