In-vivo measurement of distal radio-ulnar joint translation

Normal Values of Distal Radioulnar Joint Kinematics during a Dynamic Press Test

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.

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.

The reliability of clinical assessment of distal radioulnar joint instability

Accurate assessment of distal radioulnar joint (DRUJ) stability is increasingly recognized as an important part of clinical examination of the wrist. The ability of 30 specialist UK hand surgeons to clinically determine the stability of four volunteers' wrists was assessed. Volunteers' wrist stability had previously been confirmed with a validated measurement rig. Use of the wrist ballottement test as the primary examination technique yielded a positive predictive value of 81%, a negative predictive value of 55%, a specificity of 94% and a sensitivity of only 24%, for the detection of DRUJ instability. No correlation between background speciality (orthopaedic versus plastic surgery), nor years of clinical experience was found. Clinical assessment of DRUJ instability among experienced clinicians appears unreliable and instability is typically under recognized. Previous research to date using this clinical assessment method as a parameter of success is therefore brought into question.Level of evidence: IV.

In vivo measurement of distal radioulnar translation following distal radius fracture

The incidence of distal radioulnar joint instability following a distal radius fracture is estimated around one in three based upon clinical examination. Using a validated rig, we objectively measured distal radioulnar joint translation in vivo following distal radius fracture. Dorsopalmar translation of the distal radioulnar joint was measured in 50 adults with previous distal radius fractures. Measurements were compared with the uninjured wrist and against a database of previous measurements within healthy and clinically lax populations. Translation at the distal radioulnar joint was greater in injured wrists at 12.2 mm (range 10-15, SD 1.2) than the uninjured wrists at 6.4 (range 4-9, SD 0.8) (p < 0.001) and was always outside the established normal range. There was no statistically significant link between translation and the severity of the injury. Instability appears almost inevitable following a distal radius (wrist) fracture, albeit subclinical in the vast majority.

Finite element analysis of different locking plate fixation methods for the treatment of ulnar head fracture

Background

Ulnar head fractures are increasingly higher with the growing proportion of the elderly people. Failure to achieve a stable anatomic reduction of ulna head fracture may lead to a distal radioulnar joint (DRUJ) dysfunction and nonunion of the distal radius. Due to the lack of the postoperative reporting outcomes and the biomechanical studies, it has not been well established about the optimal management of the comminuted distal ulna head fracture. Hence, the purpose of this study is to use finite element analysis to explain the advantages and disadvantages of ulnar-side locking plate fixation compared with dorsal-side locking plate fixation and its screw arrangement in the treatment of ulnar head fractures.

Methods

FE models of the ulnar head fracture and the models of ulnar-side locking plate and dorsal-side plate with two or three distal screws was constructed. In order to simulate forces acting on the ulnar and the osteosynthesis material during daily-life activity in subjects who underwent reconstructive surgery, we applied three loading conditions to each model, viz. 20 N axial compression, 50 N axial compression, 1 N∙m torsion moment, 1 N∙m lateral bending moments, and 1 N∙m extension bending moments. Under these conditions, values of the von Mises stress (VMS) distribution of the implant, peak VMS, the relative displacement of the head and shaft fragments between the fracture ends and the displacement and its direction of the models were investigated.

Results

The stress values of ulnar-side plates were lower than those of dorsal-side plates. And the ulnar-plate fixation system also has smaller maximum displacement and relative displacement. When adding a screw in the middle hole of the ulnar head, the values of model displacement and the peak stress in fixation system are lower, but it may evidently concentrate the stress on the middle screw.

Conclusions

In conclusion, our study indicated that ulnar-side locking plates resulted in a lower stress distribution in the plate and better stability than dorsal-side locking plates for ulnar head fracture fixation. Adding an additional screw to the ulnar head could increase the stability of the fixation system and provide an anti-torsion function. This study requires clinical confirmation of its practicality in the treatment of ulnar head fractures. This study requires clinical confirmation as to its practicality in the treatment of ulnar head fracture.

A Novel Technique to Assess Distal Radioulnar Joint Stability Using Increasing Torque

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.

Rehabilitation of distal radioulnar joint instability

Distal radioulnar joint (DRUJ) instabilities are common and often combined with other injuries of the interosseous membrane and/or the proximal radioulnar joint. Once they are diagnosed and the treatment is chosen, physiotherapists have limited choices due to the lack of validated protocols. The benefits of proprioception and neuromuscular rehabilitation have been brought to light for the shoulder, knee and ankle joints, among others. However, no program has been described for the DRUJ. The purpose of this article is to study the muscular elements responsible for active DRUJ stability, and to propose a proprioceptive rehabilitation program suited to this condition.

In-vivo three-dimensional measurement of distal radioulnar joint translation in normal and clinically unstable populations

Assessment of distal radioulnar joint instability is clinically difficult and subjective. The distal radioulnar joint is postulated to 'tighten' in ulnar/radial deviation and pronation/supination. Using a rig, we measured mean distal radioulnar joint translation in neutral forearm rotation and neutral wrist radial and ulnar deviation, as well as extremes of wrist radial and ulnar deviation and forearm rotation. We tested the rig on ten cadaver forearms to validate the measurements we made. We tested 50 normal adults and 50 patients with clinical distal radioulnar joint instability. Distal radioulnar joint stability in men and women and on contralateral sides were comparable. Distal radioulnar joint translation decreased significantly with wrist radial and ulnar deviation and forearm pronation and supination, matching clinical practice and further validating the rig. The data in normal patients is comparable with previous computed tomography-based studies. Translation in all positions was statistically increased within the clinical instability group and did not cross-over with the normal ranges. Distal radioulnar joint translation is a physically measurable phenomenon. Our device appears to be a valid test of distal radioulnar joint translation, establishing normal data in vivo.

LEVEL OF EVIDENCE

III.

Supination and Pronation Strength Deficits Persist at 2-4 Years after Treatment of Distal Radius Fractures

Forearm rotation is a key function in the upper extremity. Following distal radius fracture, residual disability may occur in tasks requiring forearm rotation. The objectives of this study are to define pronation and supination strength profiles tested through the range of forearm rotation in normal individuals, and to evaluate the rotational strength profiles and rotational strength deficits across the testing range in a cohort of patients treated for distal radius fracture associated with an ulnar styloid base fracture. In a normative cohort of 29 subjects the supination strength profile showed an increasing linear relationship from supination to pronation. Twelve subjects were evaluated 2-4 years after anatomical open reduction and volar plate fixation of a distal radius fracture. The injured wrist was consistently weaker (corrected for hand dominance) in both supination and pronation strength in all testing positions, with the greatest loss in 60 degrees supination. Mean supination strength loss across all testing positions was significantly correlated with worse PRWE scores, highlighting the importance of supination in wrist function.

Traumatic disorders of forearm rotation: anatomy, biomechanics and treatment

The forearm is a complex structure which produces a wide range of movement. Forearm injuries are very common, but many injuries are missed or poorly treated. This article examines the anatomy and biomechanics of the forearm, and describes the important injuries to be recognized.