Force distribution across wrist joint: application of pressure-sensitive conductive rubber

Structural Design and DLP 3D Printing Preparation of High Strain Stable Flexible Pressure Sensors

Flexible pressure sensors are crucial force-sensitive devices in wearable electronics, robotics, and other fields due to their stretchability, high sensitivity, and easy integration. However, a limitation of existing pressure sensors is their reduced sensing accuracy when subjected to stretching. This study addresses this issue by adopting finite element simulation optimization, using digital light processing (DLP) 3D printing technology to design and fabricate the force-sensitive structure of flexible pressure sensors. This is the first systematic study of how force-sensitive structures enhance tensile strain stability of flexible resistive pressure sensors. 18 types of force-sensitive structures have been investigated by finite element design, simultaneously, the modulus of the force-sensitive structure is also a critical consideration as it exerts a significant influence on the overall tensile stability of the sensor. Based on simulation results, a well-designed and highly stretch-stable flexible resistive pressure sensor has been fabricated which exhibits a resistance change rate of 0.76% and pressure sensitivity change rate of 0.22% when subjected to strains ranging from no tensile strain to 20% tensile strain, demonstrating extremely low stretching response characteristics. This study presents innovative solutions for designing and fabricating flexible resistive pressure sensors that maintain stable sensing performance even under stretch conditions.

Current rehabilitation recommendations following primary triangular fibrocartilage complex foveal repair surgery: A survey of Australian hand therapists

BACKGROUND

Following injury to the Triangular Fibrocartilage Complex (TFCC), foveal repair surgery may be indicated to restore joint stability and function. Protection of the repaired ligament is a clinical consideration during post-surgical rehabilitation, although no "gold standard" rehabilitation protocol currently exists.

PURPOSE

To describe the professional opinions of Accredited Hand Therapists (AHT) regarding post-operative rehabilitation recommendations following TFCC foveal repair surgery.

STUDY DESIGN

Cross-sectional descriptive study.

METHODS

All Australian AHTs were invited to complete a quantitative, online, 10-item survey between December 2019 and March 2020. The survey included questions regarding clinical recommendations for wrist and forearm immobilization, range of motion and exercise methods, and timeframes. AHT characteristics and experience of patients sustaining a TFCC re-rupture were also collected. Categorical and nominal survey responses were reported descriptively and effects of AHT characteristics on survey responses were assessed using Pearson Chi2, with significance set to <0.05.

RESULTS

Survey responses were received from 135 AHTs or approximately 37% of the available population at the time of completion (March 2020). Recommendations for post-surgery immobilization ranged from "not required" to 8 weeks, 6 weeks representing the most common answer. Wrist and forearm range of motion commencement time ranged from "immediately" to "later than 8 weeks," with 6 weeks also the most common answer. When asked whether post-surgery rupture had been experienced in their respective patient groups, 15 therapists (11%) indicated "Yes." The most recommended thermoplastic orthosis was a Sugartong orthosis (41%) followed by a Muenster orthosis (30%), both of which immobilizes the wrist and forearm.

CONCLUSIONS

Rehabilitation varied widely between AHTs. Further prospective research is recommended to explore whether patient-related or rehabilitation factors influence outcomes following TFCC repair.

Casting Position for Distal Radius Fractures Changes Radiocarpal Joint Forces: A Cadaveric Study

PURPOSE

Nonsurgical distal radius fracture treatment requires immobilization and classical teaching suggests varying cast positions. We investigated the effect of cast position on the force and pressure experienced by the articular cartilage in the scaphoid and lunate fossae.

METHODS

Ten fresh-frozen cadaveric specimens were used. A standardized extra-articular distal radius fracture was made. Force sensors were affixed to the articular cartilage of the scaphoid and lunate fossae. Baseline data were obtained. Specimens were then placed into a short arm cast with the wrist either neutrally aligned or flexed and ulnarly deviated (FUD). Specimens had a standard load applied, and a force profile was obtained. The cast was removed and the other cast type was placed and measurements were repeated. Overall force and pressure values were compared between baseline data and the 2 cast types. Additionally, differences in volar and dorsal scaphoid and lunate fossa forces and pressures were compared pairwise within the 2 cast types. The relative force and pressure values across cast types were also compared.

RESULTS

Both cast types significantly reduced the median force and pressure experienced by the radiocarpal joint compared with no cast. In the FUD cast, the volar and dorsal lunate fossa experienced significantly greater force, and the dorsal lunate fossa experienced significantly greater pressure compared with the dorsal scaphoid fossa. There were no differences for any fossae in the neutral cast. When comparing between casts, the volar lunate fossa experienced a significantly greater relative force in the FUD cast compared with the neutral cast.

CONCLUSIONS

Casting a distal radius fracture decreases the forces and pressures in the radiocarpal joint. Placing the wrist in a FUD position results in greater forces and pressures on the lunate fossa compared with the scaphoid fossa.

CLINICAL RELEVANCE

When immobilization is needed, we advocate for the placement of patients in a relatively neutral short-arm cast with minimal FUD to avoid this increased pressure.

Association of the Interfacet Angle and the Lunate Facet Inclination Angle With Kienböck Disease

PURPOSE

The etiology of Kienböck disease remains unclear, although mechanical, vascular, and metabolic risk factors have been suggested. We aimed to investigate the association of the angle between the curvatures of the distal radius and the development of Kienböck disease.

METHODS

The lunate facet inclination (LFI), scaphoid facet inclination, and interfacet angle (IFA) values were measured using posteroanterior plain radiographs of 82 patients diagnosed with Kienböck disease. The results were compared with normative angular reference values published based on an analysis of 400 wrists of Caucasian patients aged between 20 and 45 years. The posteroanterior radiographs were divided into 3 categories: negative, neutral, and positive based on ulnar variance, and the relationship between ulnar variance and facet angles was evaluated.

RESULTS

The IFA value was significantly higher than the normative angular reference value in the patients with Kienböck disease. Conversely, the LFI values were significantly lower in the Kienböck patient group. There were no statistically significant differences in the IFA and LFI values among the ulnar variance groups.

CONCLUSIONS

Measuring IFA and LFI allows the evaluation of the bifacet curvature of the distal radius articular surface in the coronal plane. Steep IFA and shallow LFI are associated with Kienböck disease. Increased IFA may lead to abnormal load transmission to the intermediate column, which might eventually lead to increased stress on the lunate.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

Wrist and forearm range of motion commencement time following primary triangular fibrocartilage complex foveal repair surgery: A scoping review

STUDY DESIGN

Scoping review.

BACKGROUND

Rehabilitation guidelines following triangular fibrocartilage complex (TFCC) foveal repair surgery have been inconsistently reported in the published literature, with no consensus regarding wrist or forearm range of motion (ROM) commencement time.

PURPOSE OF THE STUDY

To scope the available literature to identify the extent and strength of the evidence supporting the clinical guidelines for wrist and forearm ROM commencement time following primary TFCC foveal repair surgery.

METHODS

A systematic search produced 26 studies (3 retrospective cohort studies, 1 prospective cohort study, 1 retrospective comparative study, and 21 retrospective case series) that described specific rehabilitation protocols following TFCC foveal repair surgery.

RESULTS

No supporting evidence was identified regarding rehabilitation protocol recommendations across all the included studies. Postsurgery wrist ROM commencement ranged from 2 to 8 weeks; forearm ROM commencement ranged from 2 to 12 weeks. ROM commencement times did not appear to systematically influence the rate of adverse events, although adverse events were poorly reported.

CONCLUSIONS

TFCC rehabilitation protocols were poorly reported and varied widely between the included studies. Additional research is recommended to comprehensively evaluate the association between wrist and/or forearm ROM and the rate of adverse events for this complex and multifaceted condition.

Osteoarthritis of the Wrist: Pathology, Radiology, and Treatment

Osteoarthritis (OA) is a degenerative disease that can manifest in any synovial joint under certain conditions. It leads to destruction of articular cartilage and adjacent bone, as well as formation of osteophytes at the edges of afflicted joint surfaces. Regarding the wrist, typical degenerative arthritis affects particular joints at a specific patient age, due to asymmetric load distribution and repetitive microtrauma. However, in the presence of instability or systemic diseases, early-onset degeneration can also impair the range of motion and grip strength in younger patients. Although advanced stages of OA display characteristic signs in radiography, the detection of early manifestations frequently requires computed tomography or magnetic resonance imaging (in some cases with additional arthrography). If a wrist becomes unstable, timely diagnosis and precise treatment are essential to prevent rapid disease progression. Therefore, close collaboration between radiologists and hand surgeons is obligatory to preserve the carpal function of patients.

Carpal Instability: I. Pathoanatomy

The pathoanatomy of carpal instability is multifactorial and usually complex. A thorough medical history and clinical examination are essential, as well as profound knowledge of the specific instability patterns. The stability of the wrist is ensured by the carpal joint surfaces, by intact intra-articular (particularly the scapholunate interosseous ligament) and intracapsular ligaments, and by crossing extensor and flexor tendons, the latter making the proximal carpal row an "intercalated segment." An important classification feature is the distinction between dissociative and nondissociative forms of carpal instability. Among others, scapholunate dissociation, lunotriquetral dissociation, midcarpal instability, and ulnar translocation are the most common entities. Early forms of instability are considered dynamic. In the natural course, static instability of the wrist and osteoarthritis will develop. This review focuses on the pathoanatomical fundamentals of the various forms of carpal instability.

Strategies for Specific Reduction in High-Energy Distal Radius Fractures

High-energy distal radius fractures frequently result in comminution with intra-articular fragmentation. Knowledge of predictable patterns of injury allows the surgeon to develop a preoperative plan for anatomic reduction and stable fixation of individual fragments that are too small or too distal to be fixed with standard volar locked plating. We review the column model, which organizes the distal radius into an intermediate column, radial column, and pedestal as the basis of a reconstructive algorithm and emphasize the importance of the volar ulnar fragment. Specific reduction and fixation techniques are described to assist the surgeon in treating these injuries.

Mechanical performance comparison of two surgical constructs for wrist four-corner arthrodesis via dorsal and radial approaches

BACKGROUND

Four-corner arthrodesis, which involves fusing four carpal bones while removing the scaphoid bone, is a standard surgery for the treatment of advanced stages of wrist arthritis. Nowadays, it can be performed using a dorsal approach by fixing a plate to the bones and a new radial approach is in development. To date, there is no consensus on the biomechanically optimal and most reliable surgical construct for four-corner arthrodesis.

METHODS

To evaluate them biomechanically and thus assist the surgeon in choosing the best implant orientation, radial or dorsal, the two different four-corner arthrodesis surgical constructs were virtually simulated on a 3D finite element model representing all major structures of the wrist. Two different realistic load sets were applied to the model, representing common tasks for the elderly.

FINDINGS

Results consistency was assessed by comparing with the literature the force magnitude computed on the carpal bones. The Von Mises stress distribution in the radial and dorsal plates were calculated. Stress concentration was located at the plate-screw interface for both surgical constructs, with a maximum stress value of 413 MPa for the dorsal plate compared to 326 MPa for the radial plate, meaning that the stress levels are more unfavourable in the dorsal approach.

INTERPRETATION

Although some bending stress was found in one load case, the radial plate was mechanically more robust in the other load case. Despite some limitations, this study provides, for the first time, quantified evidence that the newly developed radial surgical construct is mechanically as efficient as the dorsal surgical construct.

Ulnar-Side Wrist Pain Management Guidelines: All That Hurts is Not the TFCC!

BACKGROUND

Ulnar-sided wrist pain is a common clinical problem, most often misdiagnosed as triangular fibrocartilage complex (TFCC) injury. It may be frustrating to the patient, as one may end up wearing a wrist splint for an unusually long period, disrupting their routine.

PURPOSE

Because of the dilemmas in the diagnosing the cause of ulnar-sided wrist pain, various algorithms have been suggested but it is an individual's choice to do a systematic assessment and follow in their routine clinical practice. We propose the 'storey concept' for examining the ulnar side of the wrist, with ulnar styloid as the reference point. The lower storey identifies the pathologies of the DRUJ, the intermediate storey identifies the pathologies of the radiocarpal joint and the upper storey identifies the pathologies of midcarpal and carpometacarpal joint.

CONCLUSION

Also, it is important to ramify the cause of pain into stable or unstable wrist, with or without arthritis, as this will guide us in managing the pain arising from distal radioulnar joint. In addition to methodical clinical examination, ideal radiographs and high-resolution MRI are critical to diagnose wrist pathologies. The role of wrist arthroscopy has consistently increased, and complements in both diagnosis and treatment of wrist pain especially in ambiguous situations.

Determination of the Optimal Location for Bone Graft Harvest in the Distal Radius

Background: The distal radius is commonly used as a bone graft donor site for surgery in the hand and wrist. The aim of this study was to evaluate the volume and relative density of cancellous bone in the distal radius. Methods: Thirty-four consecutive computed tomographic scans of the wrist in 33 patients without distal radius pathology were included. For each subject, 6 spherical regions of interest (ROIs) were identified within the distal radius. In each ROI, volumetric measurements and mean Hounsfield unit (HFU) values were recorded by 2 observers using a 3-dimensional imaging reconstruction software. Results: Compared with proximal bone, distal bone had larger volume (0.82 vs 0.27 cm³) and greater relative density (178 vs 152 HFU) on average. Among the 6 ROIs, the distal-central region had the largest average volume (1.20 cm³) and the distal-ulnar ROI had the greatest average relative density (193 HFU). Conclusion: Based on these results, we recommend performing cancellous autograft harvest relatively distal and ulnar within the distal radius.

Lunate loads following different osteotomies used to treat Kienböck's disease: A 3D finite element analysis

BACKGROUND

One of most accepted principles for treating Kienböck's disease before wrist degeneration settles in is to decompress the lunate by an osteotomy. Several osteotomies have been proposed since 1935. However, they are based on biomechanical hypotheses that are sometimes conflicting: This study compares the decompression effect of radius transverse shortening, radius lateral closing and medial closing wedge osteotomies, capitate shortening - with and without hamate shortening - and a Camembert-type radius wedge osteotomy with and without ulnar head shortening according to Sennwald.

METHODS

We built a 3D wrist model using finite elements that included the metacarpal, carpal and forearm bones. All wrist ligaments and Triangular Fibrocartilage Complex were incorporated in the simulation. Load was applied on the metacarpals with the forearm bones fixed. We then applied the different osteotomies to the model.

FINDINGS

When load was applied to the wrist, the osteotomies that best unloaded the lunate were the capitate shortening osteotomy combined with hamate shortening and the Camembert osteotomy combined with ulna shortening; the latter was the only osteotomy that completely unloaded the lunate.

INTERPRETATION

We think the association of the radius Camembert osteotomy and ulna Sennwald's shortening osteotomy is the most effective procedure to propose in Kienböck's disease.

Assessment of Articular Cartilage Disorders After Distal Radius Fracture Using Biochemical and Morphological Nonenhanced Magnetic Resonance Imaging

PURPOSE

To assess radiocarpal articular cartilage after distal radius fracture, with and without intra-articular extension, compared with healthy controls using multiparametric, nonenhanced magnetic resonance imaging (MRI).

METHODS

In this prospective study, multiparametric MRI of the radiocarpal articular cartilage was performed in 26 participants (16 males and 10 females; mean age, 39.5 ± 14.7 years; range, 20-70 years) using 3T MRI. The cohort consisted of 14 patients with a distal radius fracture and 12 healthy volunteers. The radiocarpal articular cartilage was assessed using morphological (Double Echo Steady-State [DESS] and True Fast Imaging With Steady-State Precession [TrueFISP]) and biochemical (T2∗) MRI sequences without an intravenous contrast agent. The modified Outerbridge classification system for morphological analyses and region-of-interest biochemical analysis were applied to assess the degree of articular cartilage damage in each patient.

RESULTS

Morphological articular cartilage assessment showed no difference between the DESS sequence and the reference standard, TrueFISP. In the morphological (DESS and TrueFISP) and biochemical (T2∗) assessments, patients with intra-articular fractures did not show articular cartilage damage different from those with extra-articular fractures. Greater articular cartilage degradation was observed after distal radius fracture compared with controls.

CONCLUSIONS

Posttraumatic radiocarpal articular cartilage damage did not differ between fractures with intra-articular and extra-articular extension, but patients with fractures had notably higher articular cartilage degradation compared with healthy controls. Magnetic resonance imaging using advanced multiparametric sequences may facilitate accurate, noninvasive assessment of articular cartilage changes after distal radius fracture without the need for a contrast agent.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic IV.

Functional Outcomes After Salvage Procedures for Wrist Trauma and Arthritis (Four-Corner Fusion, Proximal Row Carpectomy, Total Wrist Arthroplasty, Total Wrist Fusion, Wrist Denervation): A Review of Literature

Background:

Several salvage procedures for the arthritically destroyed wrist exist. Each of these has advantages as well as disadvantages.

Aims:

The aim of this article is to give practical insights for the clinician on: (1) biomechanical and clinical fundamentals of normal and impaired wrist motion; (2) difficulties in assessment of postoperative outcome between measured motion by the surgeon and self-reported outcome by the patient; (3) indications for each procedure; and (4) differences in functional outcome between partial and complete motion-preserving as well as complete motion-restricting salvage procedures.

Methods:

In trend, Proximal Row Carpectomy (PRC) is slightly superior over four-corner fusion (4CF) in terms of functional outcome, but the methodology-related postoperative motion is decreased for both procedures. Furthermore, PRC is easier to perform, needs lower costs, and has fewer complications than 4CF. Total Wrist Arthroplasty (TWA) has the advantage compared to PRC and 4CF that the preoperative motion values are preserved, but it is limited by decreased load-bearing capacity for the wrist. Total Wrist Fusion (TWF) is associated with a higher load-bearing capacity for the wrist than TWA, but it is limited for carrying out essential activities of daily living. Both PRC and 4CF can be combined primarily by wrist denervation. Wrist denervation alone does not impair the movement of the wrist.

Results and Conclusion:

Salvage procedures for the arthritically destroyed wrist should be detected regarding patients age- and gender-related claims in work and leisure. Not all of them can be successfully re-employed in their original occupations associated with high load-bearing conditions.

Size and stabilization of the dorsoulnar fragment in AO C3-type distal radius fractures

INTRODUCTION

Volar locking plate (VLP) fixation has become the gold-standard treatment for distal radius fractures (DRFs). Especially, internal fixation of the volar lunate facet fragment is essential for the treatment of AO C3-type DRFs. On the other hand, the necessity of the fixation of the dorsal lunate facet fragment (dorsoulnar fragment) remains unclear. The purpose of the present study was to measure three-dimensionally the size of the dorsoulnar fragments in AO C3-type DRFs using computed tomography (CT) images in detail, and to reveal relationships of the size and stabilization of the dorsoulnar fragment with postoperative fracture displacement after VLP fixation.

MATERIALS AND METHODS

We retrospectively reviewed the 101 consecutive Japanese patients who underwent surgical treatment for AO C3-type distal radius fractures. If patient had dorsoulnar fragment, the three-dimensional size of this fragment and the occupying ratio to the radiocarpal joint (RCJ) and the distal radioulnar joint (DRUJ) were anatomically evaluated using the preoperative CT images. In addition, we investigated the relationship of the size and stabilization of the dorsoulnar fragment with fracture displacement after VLP fixation. We statistically compared the size parameters and occupying ratio of the dorsoulnar fragment between the displaced group and the stable groups using a two-tailed t-test. We also statistically compared the numbers of screws inserted into the dorsoulnar fragments between the displaced and stable groups using a chi-square test.

RESULTS

The mean dorsoulnar fragment size was 9.4 mm × 7.9 mm × 11.0 mm and the occupying ratio to the DRUJ and RCJ was 50% and 10%, respectively. The number of patients treated with volar locking plate fixation was 77, of which 12 patients had postoperative displacements. Although the size of the dorsoulnar fragment was not associated with postoperative displacement, stabilization following screw insertion into the dorsoulnar fragment was significantly associated with displacement.

CONCLUSION

Stabilization of the dorsoulnar fragment with at least one screw of the volar locking plate was necessary to prevent postoperative fracture displacement regardless of dorsoulnar fragment size in AO C3-type distal radius fractures.

SPRING PLATES IN DISTAL RADIO FRACTURES: "IN VITRO" MECHANICAL PROPERTIES

Background:

Distal radius fractures are one of the most common orthopedic injuries and appear in various patterns. Volar plate fixation is not always considered the gold standard treatment.

Objective:

To measure the resistance of a fragment-specific fixation assembly model obtained by plate fixation associated with different K-wire sizes.

Method:

In this original experimental study, novel II, axial compression of bone materials was tested.

Results:

In both groups, the maximum force supported by the fixation method in our study was ten times greater than the physiological load to which the wrist was subjected under physiological conditions.

Discussion:

In this study, we obtained encouraging results when compared to results reported in the literature. Our study showed that our bone fixating system was mechanically adequate for articular fractures of the intermediate column of the radius (Melone classification). The results were similar or superior to the results of pressure resistance and stiffness when data from the literature was used as reference.

Conclusion:

The proposed fixation method demonstrated adequate resistance for fixation of the intermediate column of the distal radius. Increasing K wire size caused augmented resistance of the fixation. Level of Evidence II, Prospective comparative study.

Differences of radiocarpal cartilage alterations in arthritis and osteoarthritis using morphological and biochemical magnetic resonance imaging without gadolinium-based contrast agent administration

OBJECTIVES

To identify differences of radiocarpal cartilage alterations in osteoarthritis and arthritis using multiparametrical magnetic resonance imaging (MRI) comprising morphological and biochemical sequences without gadolinium-based contrast agent administration.

METHODS

In this prospective study, multiparametrical MRI of the radiocarpal cartilage was performed in 47 participants (mean age, 46.6 ± 17.6 years; min., 20 years; max., 79 years) on a 3 Tesla MRI. The cohort consisted of 11 patients suffering from arthritis, 10 patients with osteoarthritis, 14 patients after distal radius fracture, and 12 healthy volunteers. The radiocarpal cartilage was assessed using morphological (DESS, TrueFISP) and biochemical (T2*) MRI sequences without the application of intravenous contrast agent. The modified Outerbridge classification system for morphological and region-of-interest analyses for biochemical analysis was applied to assess the degree of cartilage damage in each patient before data were statistically tested for significant difference between the groups using a post hoc Tukey test.

RESULTS

In morphological imaging, cartilage damage was significantly more frequent in arthritis and osteoarthritis than in healthy volunteers (DESS: p = 0.01, p = 0.0004; TrueFISP: p = 0.02, p = 0.0001). In T2* imaging, patients with osteoarthritis showed higher cartilage damage compared to patients with arthritis (p = 0.01).

CONCLUSION

With multiparametrical MRI, it is possible to identify differences of radiocarpal cartilage alterations of patients with arthritis and osteoarthritis using the combination of morphological and biochemical MR imaging of the radiocarpal cartilage without the application of contrast agent. Multiparametrical MRI without the usage of contrast agent may be a potential tool helping to distinguish both entities.

KEY POINTS

• Multiparametrical MRI with morphological and biochemical sequences allows the differentiation of patients with arthritis and osteoarthritis. • High-resolution MRI of radiocarpal cartilage is possible without administration of contrast agent.

Radiographic analysis of anatomic risk factors for scaphoid fractures; A case-control study

AIM

The purpose of this study was to investigate the role of anatomic variations in distal radius radiographic indices in patients with or without scaphoid fractures.

MATERIALS AND METHODS

Radial inclination (RI), volar tilt (VT), radial height (RH) and ulnar variance (UV) were measured on wrist radiographs of 320 patients with (Group I, n = 167) or without (Group II, n = 153) scaphoid fracture, fall on outstretched hand (FOOSH). Receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic performance for each variable. Sensitivity (Sn), specificity (Sp), cutoff value, and area under the ROC curve were analyzed. Odds ratio was calculated for defined cutoff values.

RESULTS

The mean age of the groups was similar (29.3 ± 10.2 vs 31.1 ± 9.9 years, p = 0.060). RI (30.0 ± 2.9 vs 26.8 ± 2.3°) VT (11.4 ± 2.4 vs 10.5 ± 2.2°), RH (14.8 ± 2.1 vs 13.2 ± 1.9 mm), UV (-0.46 ± 1.7 vs 0.00 ± 1.5 mm) were higher in scaphoid fracture group (Gr I vs Gr II, p = 0.000, p = 0.000, p = 0.001, p = 0.012 respectively). Ulna minus variant was more prevalent in fracture group (p = 0.001). Optimal cutoff points for RI, VT, RH and UV in differentiating fractured and intact scaphoid were 28.6° (Sn = 81.0%, Sp = 26.3%), 12.2° (Sn = 80.4%, Sp = 67.1%), 14.85 mm (Sn = 80.4%, Sp = 52.1%) and 0 mm (Sn = 88.6%, Sp = 75.8%), respectively. Odds ratios for defined cutoff points for RI, VT, RH and UV were 10.4 (95% CI, 6.2-17.4), 1.8 (95% CI, 1.1-3.0), 3.7 (95% CI, 2.3-6.2) and 2.2 (95% CI, 1.3-3.7) respectively.

CONCLUSION

Increased RI, VT, RH and negative UV were found to be predisposing anatomical risk factors for scaphoid fracture when FOOSH.

Prolonged high force high repetition pulling induces osteocyte apoptosis and trabecular bone loss in distal radius, while low force high repetition pulling induces bone anabolism

We have an operant rat model of upper extremity reaching and grasping in which we examined the impact of performing a high force high repetition (High-ForceHR) versus a low force low repetition (Low-ForceHR) task for 18weeks on the radius and ulna, compared to age-matched controls. High-ForceHR rats performed at 4 reaches/min and 50% of their maximum voluntary pulling force for 2h/day, 3days/week. Low-ForceHR rats performed at 6% maximum voluntary pulling force. High-ForceHR rats showed decreased trabecular bone volume in the distal metaphyseal radius, decreased anabolic indices in this same bone region (e.g., decreased osteoblasts and bone formation rate), and increased catabolic indices (e.g., microcracks, increased osteocyte apoptosis, secreted sclerostin, RANKL, and osteoclast numbers), compared to controls. Distal metaphyseal trabeculae in the ulna of High-ForceHR rats showed a non-significant decrease in bone volume, some catabolic indices (e.g., decreased trabecular numbers) yet also some anabolic indices (e.g., increased osteoblasts and trabecular thickness). In contrast, the mid-diaphyseal region of High-ForceHR rats' radial and ulnar bones showed few to no microarchitecture differences and no changes in apoptosis, sclerostin or RANKL levels, compared to controls. In further contrast, Low-ForceHR rats showed increased trabecular bone volume in the radius in the distal metaphysis and increased cortical bone area its mid-diaphysis. These changes were accompanied by increased anabolic indices, no microcracks or osteocyte apoptosis, and decreased RANKL in each region, compared to controls. Ulnar bones of Low-ForceHR rats also showed increased anabolic indices, although fewer than in the adjacent radius. Thus, prolonged performance of an upper extremity reaching and grasping task is loading-, region-, and bone-dependent, with high force loads at high repetition rates inducing region-specific increases in bone degradative changes that were most prominent in distal radial trabeculae, while low force task loads at high repetition rates induced adaptive bone responses.

Effect of Push-Up Position on Wrist Joint Pressures in the Intact Wrist and Following Scapholunate Interosseous Ligament Sectioning

PURPOSE

To determine the contact pressures between the scaphoid and lunate and the distal radius during 2 wrist push-up positions before and following scapholunate interosseous ligament (SLIL) sectioning.

METHODS

Eight fresh cadaveric wrists were tested in a neutral flexion-extension (knuckle) push-up position and in an extended push-up position. Pressure measurements were acquired as each wrist was loaded with the wrist in extension and with the wrist in a neutral position. Data were acquired with the SLIL intact and following sectioning of its dorsal, volar, and proximal components. The wrist was disarticulated and a map drawn on each sensor to identify each joint fossa.

RESULTS

A push-up performed with the wrist in extension caused a significantly greater peak pressure in the radioscaphoid fossa but not in the radiolunate fossa. Moving the wrist into extension caused a significant dorsal movement of the pressure centroid an average of 2.9 mm in the radiolunate fossa and an average of 5.7 mm in the radioscaphoid fossa. Sectioning the SLIL caused the centroid of pressure in the radioscaphoid fossa to significantly move an average 1.4 mm radially.

CONCLUSIONS

A push-up with the wrist in extension causes a significant increase in the pressure in the radioscaphoid fossa but not in the radiolunate. This finding may help explain why degenerative arthritis first develops in the radioscaphoid fossa before involving the radiolunate fossa. As expected, gapping that occurs with SLIL injury was observed here as a radial translation of the scaphoid and not as a movement of the lunate. The new location of scaphoid contact may be an additional reason for the development of radioscaphoid arthritis occurring before radiolunate arthritis.

CLINICAL RELEVANCE

This study provides a possible explanation as to why degenerative arthritis may first occur in the radioscaphoid fossa.

Wearable Stretch Sensors for Motion Measurement of the Wrist Joint Based on Dielectric Elastomers

Motion capture of the human body potentially holds great significance for exoskeleton robots, human-computer interaction, sports analysis, rehabilitation research, and many other areas. Dielectric elastomer sensors (DESs) are excellent candidates for wearable human motion capture systems because of their intrinsic characteristics of softness, light weight, and compliance. In this paper, DESs were applied to measure all component motions of the wrist joints. Five sensors were mounted to different positions on the wrist, and each one is for one component motion. To find the best position to mount the sensors, the distribution of the muscles is analyzed. Even so, the component motions and the deformation of the sensors are coupled; therefore, a decoupling method was developed. By the decoupling algorithm, all component motions can be measured with a precision of 5°, which meets the requirements of general motion capture systems.

Kinematics of the anthropoid os centrale and the functional consequences of scaphoid-centrale fusion in African apes and hominins

In most primates, the os centrale is interposed between the scaphoid, trapezoid, trapezium, and head of the capitate, thus constituting a component of the wrist's midcarpal complex. Scaphoid-centrale fusion is among the clearest morphological synapomorphies of African apes and hominins. Although it might facilitate knuckle-walking by increasing the rigidity and stability of the radial side of the wrist, the exact functional significance of scaphoid-centrale fusion is unclear. If fusion acts to produce a more rigid radial wrist that stabilizes the hand and limits shearing stresses, then in taxa with a free centrale, it should anchor ligaments that check extension and radial deviation, but exhibit motion independent of the scaphoid. Moreover, because the centrale sits between the scaphoid and capitate (a major stabilizing articulation), scaphoid-centrale mobility should correlate with scaphocapitate mobility in extension and radial deviation. To test these hypotheses, the centrale's ligamentous binding was investigated via dissection in Pongo and Papio, and the kinematics of the centrale were quantified in a cadaveric sample of anthropoids (Pongo sp., Ateles geoffroyi, Colobus guereza, Macaca mulatta, and Papio anubis) using a computed-tomography-based method to track wrist-bone motion. Results indicate that the centrale rotates freely relative to the scaphoid in all taxa. However, centrale mobility is only correlated with scaphocapitate mobility during extension in Pongo-possibly due to differences in overall wrist configuration between apes and monkeys. If an extant ape-like wrist characterized early ancestors of African apes and hominins, then scaphoid-centrale fusion would have increased midcarpal rigidity in extension relative to the primitive condition. Although biomechanically consistent with a knuckle-walking hominin ancestor, this assumes that the trait evolved specifically for that biological role, which must be squared with contradictory interpretations of extant and fossil hominoid morphology. Regardless of its original adaptive significance, scaphoid-centrale fusion likely presented a constraint on early hominin midcarpal mobility.

Arthroscopic Management of Ulnocarpal Impaction Syndrome and Ulnar Styloid Impaction Syndrome

Both ulnocarpal impaction syndrome and ulnar styloid impaction syndrome can produce ulnar wrist pain. The definition and clinical differentiation are explained. The relevant anatomy, biomechanics, causes, diagnosis, and arthroscopic treatments, as well as the surgical indications, techniques, and outcomes of these syndromes are discussed in detail.

[Biomechanics of distal radius fractures : Basics principles and GPS treatment strategy for locking plate osteosynthesis]

Fractures of the distal radius are most commonly caused by hyperextension injuries of the wrist. Tensile forces and force vectors, strength of impact, bone strength and soft tissue tension create individually different fracture patterns. Metaphyseal comminution, loss of cortical support, ligament avulsion and shear fragments are defining parameters for fracture instability. The dislocation of the articular fragment follows the force vectors of the extrinsic forearm muscles bridging the joint. The goal-plan-standardized (GPS) treatment strategy has proven to be helpful in choosing the ideal individual treatment. It is based on individual patient demands on wrist function and an analysis of fracture instability in computed tomography (CT) scans. The "goal" is a realistic expectation assessed by patient and surgeon. The "plan" includes a benefit-risk analysis and selection of an appropriate treatment modality. The "standardized treatment" of surgical and follow-up treatment is based on biomechanical knowledge. Locking plate osteosynthesis aims to neutralize dislocating force vectors and to allow early active mobility. Unidirectional instability can be indirectly neutralized by palmar locking plate systems. A multidirectional instability can be addressed by multiple plating following the column theory. Distal shear and avulsion fractures may require a fragment-specific osteosynthesis approach.

In vitro experimental investigation of the forces and torque acting on the scaphoid during light grasp

The aim of this study was to measure the magnitude and direction of forces and torque within osteotomized scaphoids within cadaveric wrists during grasping movement of the hand. The mechanical contributions of clinically relevant individual wrist-crossing tendon groups were investigated. Wrists of eight forearms were immobilized in the sagittal, transverse, and coronal plane on a fixation device with unhindered axial gliding. The scaphoid was osteotomized and the fragments stabilized using an interlocking nail. The nail served as a sensor for measurement of inter-fragmentary forces orthogonal and torque around the sensor axis. Thus, torque and cantilever forces were measured which originated between the fragments through co-contraction through the activity of wrist-crossing tendons. Grasping movement of the hand induced a mean maximum torque of 0.038 ± 0.051 Nm and a force of 4.01 ± 1.71 N on the scaphoid. The isolated activation of thumb tendons resulted in a torque of 9.9 E^-3 ± 7.7 E^-3 Nm and a force of 1.42 ± 0.49 N. Despite immobilization of the wrist, grasping movement of the hand caused substantial forces and torque within the osteotomized scaphoid bone in varying directions and severity among different specimens. These factors may contribute to the development of nonunions and malunions in unstable scaphoid fractures through interfragmentary micromotion. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1734-1742, 2016.

A biomechanical model of the wrist joint for patient-specific model guided surgical therapy: Part 2

An enhanced musculoskeletal biomechanical model of the wrist joint is presented in this article. The computational model is based on the multi-body simulation software AnyBody. Multi body dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to wrist joint degeneration and restoration. In this study, the simulation model of the wrist joint was used for investigating deeper the biomechanical function of the wrist joint. In representative physiological scenarios, the joint behavior and muscle forces were computed. Furthermore, the load transmission of the proximal wrist joint was investigated. The model was able to calculate the parameters of interest that are not easily obtainable experimentally, such as muscle forces and proximal wrist joint forces. In the case of muscle force investigation, the computational model was able to accurately predict the computational outcome for flexion and extension motion. In the case of force distribution of the proximal wrist joint, the model was able to predict accurately the computational outcome for an axial load of 140 N. The presented model and approach of using a multi-body simulation model are anticipated to have value as a predictive clinical tool including effect of injuries or anatomical variations and initial outcome of surgical procedures for patient-specific planning and custom implant design. Therefore, patient-specific multi-body simulation models are potentially valuable tools for surgeons in pre- and intraoperative planning of implant placement and orientation.

Can the use of variable-angle volar locking plates compensate for suboptimal plate positioning in unstable distal radius fractures? A biomechanical study

OBJECTIVE

To compare the biomechanical stability under load-to-failure conditions of optimally placed fixed-angle volar locking plates versus suboptimally placed variable-angle volar locking plates in unstable, intraarticular distal radius fractures.

METHODS

A Melone type 1 (AO 23-C3) fracture was created in 25 sawbone radii and plated with either a fixed-angle or variable-angle Synthes plate with identical profile. Four plate positions were tested: distal ulnar (DU, positioned distally to obtain subchondral support and ulnar to hold the lunate facet fragments), distal radial (DR, 3 mm radial to DU), proximal ulnar (PU, 3 mm proximal to DU), and proximal radial (PR, 3 mm proximal and 3 mm radial to DU). The specimens were loaded until failure as defined by a 2-mm displacement of any fracture fragment. The fixed-angle plates were tested in the DU position, whereas the variable-angle plates were tested in all 4 positions.

RESULTS

The dorsal lunate fragment was the first to fail in every group followed by the radial styloid and volar lunate fragments, respectively. Load-to-failure, from greatest to least, occurred at the DR (278 ± 56 N), PR (277 ± 68 N), DU fixed-angle (277 ± 68 N), DU variable-angle (236 ± 31 N), and PU (202 ± 75 N) positions, respectively. Rigidity was calculated using the slope of the dorsal lunate force-displacement curve before failure (at loads 100-150 N). Rigidity was greatest at the PU position (126 ± 60 N/mm) followed by PR (125 ± 30 N/mm), DU fixed-angle (125 ± 25 N/mm), DR (122 ± 66 N/mm), and DU variable-angle (101 ± 35) positions, respectively. Univariate analysis of rigidity and load-to-failure was not significantly different between groups.

CONCLUSIONS

In this experimental model, variable-angle screws provided a leeway of 3 mm in both the sagittal and coronal directions without sacrificing construct strength, which may considerably facilitate fixation of these difficult fractures.

Computationally efficient magnetic resonance imaging based surface contact modeling as a tool to evaluate joint injuries and outcomes of surgical interventions compared to finite element modeling

Joint injuries and the resulting posttraumatic osteoarthritis (OA) are a significant problem. There is still a need for tools to evaluate joint injuries, their effect on joint mechanics, and the relationship between altered mechanics and OA. Better understanding of injuries and their relationship to OA may aid in the development or refinement of treatment methods. This may be partially achieved by monitoring changes in joint mechanics that are a direct consequence of injury. Techniques such as image-based finite element modeling can provide in vivo joint mechanics data but can also be laborious and computationally expensive. Alternate modeling techniques that can provide similar results in a computationally efficient manner are an attractive prospect. It is likely possible to estimate risk of OA due to injury from surface contact mechanics data alone. The objective of this study was to compare joint contact mechanics from image-based surface contact modeling (SCM) and finite element modeling (FEM) in normal, injured (scapholunate ligament tear), and surgically repaired radiocarpal joints. Since FEM is accepted as the gold standard to evaluate joint contact stresses, our assumption was that results obtained using this method would accurately represent the true value. Magnetic resonance images (MRI) of the normal, injured, and postoperative wrists of three subjects were acquired when relaxed and during functional grasp. Surface and volumetric models of the radiolunate and radioscaphoid articulations were constructed from the relaxed images for SCM and FEM analyses, respectively. Kinematic boundary conditions were acquired from image registration between the relaxed and grasp images. For the SCM technique, a linear contact relationship was used to estimate contact outcomes based on interactions of the rigid articular surfaces in contact. For FEM, a pressure-overclosure relationship was used to estimate outcomes based on deformable body contact interactions. The SCM technique was able to evaluate variations in contact outcomes arising from scapholunate ligament injury and also the effects of surgical repair, with similar accuracy to the FEM gold standard. At least 80% of contact forces, peak contact pressures, mean contact pressures and contact areas from SCM were within 10 N, 0.5 MPa, 0.2 MPa, and 15 mm2, respectively, of the results from FEM, regardless of the state of the wrist. Depending on the application, the MRI-based SCM technique has the potential to provide clinically relevant subject-specific results in a computationally efficient manner compared to FEM.

Scaphoid interfragmentary motions due to simulated transverse fracture and volar wedge osteotomy

BACKGROUND

Our goal was to determine 3-dimensional interfragmentary motions due to simulated transverse fracture and volar wedge osteotomy of the scaphoid during physiologic flexion-extension of a cadaveric wrist model.

METHODS

The model consisted of a cadaveric wrist (n = 8) from the metacarpals through the distal radius and ulna with load applied through the major flexor-extensor tendons. Flexibility tests in flexion-extension were performed in the following 3 test conditions: intact and following transverse fracture and wedge osteotomy of the scaphoid. Scaphoid interfragmentary motions were measured using optoelectronic motion tracking markers. Average peak scaphoid interfragmentary motions due to transverse fracture and wedge osteotomy were statistically compared (P<0.05) to intact.

FINDINGS

The accuracy of our computed interfragmentary motions was ± 0.24 mm for translation and ± 0.54° for rotation. Average peak interfragmentary motions due to fracture ranged between 0.9 mm to 1.9 mm for translation and 5.3° to 10.8° for rotation. Significant increases in interfragmentary motions were observed in volar/dorsal translations and flexion/extension due to transverse fracture and in separation and rotations in all 3 motion planes due to wedge osteotomy.

INTERPRETATION

Comparison of our results with data from previous in vitro and in vivo biomechanical studies indicates a wide range of peak interfragmentary rotations due to scaphoid fracture, from 4.6° up to 30°, with peak interfragmentary translations on the order of several millimeters. Significant interfragmentary motions, indicating clinical instability, likely occur due to physiologic flexion-extension of the wrist in those with transverse scaphoid fracture with or without volar bone loss.

Scapholunate ligament injury adversely alters in vivo wrist joint mechanics: an MRI-based modeling study

We investigated the effects of scapholunate ligament injury on in vivo radiocarpal joint mechanics using image-based surface contact modeling. Magnetic resonance images of 10 injured and contralateral normal wrists were acquired at high resolution (hand relaxed) and during functional grasp. Three-dimensional surface models of the radioscaphoid and radiolunate articulations were constructed from the relaxed images, and image registration between the relaxed and grasp images provided kinematics. The displacement driven models were implemented in contact modeling software. Contact parameters were determined from interpenetration of interacting bodies and a linear contact rule. Peak and mean contact pressures, contact forces and contact areas were compared between the normal and injured wrists. Also measured were effective (direct) contact areas and intercentroid distances from the grasp images. Means of the model contact areas were within 10 mm(2) of the direct contact areas for both articulations. With injury, all contact parameters significantly increased in the radioscaphoid articulation, while only peak contact pressure and contact force significantly increased in the radiolunate articulation. Intercentroid distances also increased significantly with injury. This study provides novel in vivo contact mechanics data from scapholunate ligament injury and confirms detrimental alterations as a result of injury.

Volar versus dorsal latest-generation variable-angle locking plates for the fixation of AO type 23C 2.1 distal radius fractures: a biomechanical study in cadavers

INTRODUCTION

Anatomicaly preformed variable-angle locking plates are technologically mature and appear to be optimal for the fixation of distal radius fractures. However, there is still much argument about whether volar plating is equivalent to dorsal (buttressing) plating, especially in the management of intra-articular extension fractures. This biomechanical study was performed to determine, in a simple intra-articular fracture model, whether dorsal or volar plate constructs would be more stable.

MATERIALS AND METHODS

Six pairs of fresh frozen radii were examined with dual-energy absorptiometry (DXA) to determine their bone mineral density (BMD). An AO type 23 C2.1 fracture was created. Volar fixation was with a 2.4mm Variable-Angle LCP Two-Column Volar Distal Radius Plate; dorsal fixation was with two orthogonal 2.4 mm Variable-Angle LCP Dorsal Distal Radius Plates (both devices: Synthes, Oberdorf, Switzerland). Biomechanical testing used a proven protocol involving static tests of stiffness, and a cyclic test to obtain range of motion (ROM), maximum deformation, and subsidence data.

RESULTS

None of the constructs failed during biomechanical testing. The two groups (volar and dorsal plating, respectively) did not differ significantly in terms of initial (pre-cyclic-testing) and final (post-cyclic-testing) stiffness. Equally, there was no significant difference between the subsidence values in the two groups. The post-cyclic-testing ROM was significantly greater in the dorsal-plate group as compared with the volar-plate group. The volar constructs showed a significant decrease in the ROM between pre- and post-cyclic testing.

CONCLUSION

Biomechanically, volar plating with a modern variable-angle locking plate is equivalent to dorsal plating with two modern variable-angle locking plates.

In vivo kinematics of the scaphoid, lunate, capitate, and third metacarpal in extreme wrist flexion and extension

PURPOSE

Insights into the complexity of active in vivo carpal motion have recently been gained using 3-dimensional imaging; however, kinematics during extremes of motion has not been elucidated. The purpose of this study was to determine motion of the carpus during extremes of wrist flexion and extension.

METHODS

We obtained computed tomography scans of 12 healthy wrists in neutral grip, extreme loaded flexion, and extreme loaded extension. We obtained 3-dimensional bone surfaces and 6-degree-of-freedom kinematics for the radius and carpals. The flexion and extension rotation from neutral grip to extreme flexion and extreme extension of the scaphoid and lunate was expressed as a percentage of capitate flexion and extension and then compared with previous studies of active wrist flexion and extension. We also tested the hypothesis that the capitate and third metacarpal function as a single rigid body. Finally, we used joint space metrics at the radiocarpal and midcarpal joints to describe arthrokinematics.

RESULTS

In extreme flexion, the scaphoid and lunate flexed 70% and 46% of the amount the capitate flexed, respectively. In extreme extension, the scaphoid extended 74% and the lunate extended 42% of the amount the capitates extended, respectively. The third metacarpal extended 4° farther than the capitate in extreme extension. The joint contact area decreased at the radiocarpal joint during extreme flexion. The radioscaphoid joint contact center moved onto the radial styloid and volar ridge of the radius in extreme flexion from a more proximal and ulnar location in neutral.

CONCLUSIONS

The contributions of the scaphoid and lunate to capitate rotation were approximately 25% less in extreme extension compared with wrist motion through an active range of motion. More than half the motion of the carpus when the wrist was loaded in extension occurred at the midcarpal joint.

CLINICAL RELEVANCE

These findings highlight the difference in kinematics of the carpus at the extremes of wrist motion, which occur during activities and injuries, and give insight into the possible etiologies of the scaphoid fractures, interosseous ligament injuries, and carpometacarpal bossing.

[Anatomy and biomechanics of distal radius fractures: a literature review]

Distal radius fractures remain the most frequent fractures in the adult. Associated osteoporosis increases morbidity risk (secondary displacement is the most frequent) and mortality risk (in women older than 60). Severity of the fracture and functional results are related to the bone mineral density. Anatomy has been recently revisited with better description of palmar and dorsal aspects in order to avoid material-related complications. Standard postero-anterior, lateral and oblique radiographs of the wrist show the fracture and the displacement. CT scan is warranted if conventional X-rays are insufficient to show the articular surface. The involvement of the metaphysis (comminution), the epiphysis (articular fracture) and the ulna is different in each case and each fracture is an association of these three components. The MEU classification describes the fracture with sufficient inter-observer reliability and intra-observer reproducibility to be a useful tool for treatment and prognosis. The PAF system is used to propose the most appropriate treatment for each patient. Anatomical reduction and stable fixation are associated with good functional results but in high demanding patients.

Surgical technique of a radial wedge "camembert" osteotomy in Kienböck disease

The main accepted principle to treat Kienböck disease is to decompress the lunate. Radius shortening is the most used technique. Three transverse osteotomies of the radius are described: neutral shortening osteotomy, lateral closing wedge osteotomy, and medial closing wedge osteotomy. Shortening the radius decompress the lunate and more or less the scaphoid. This deviates axial constraints toward ulna and triangular fibrocartilage complex. But the ulnar wrist is not able to support important axial constraints. The authors propose a solution to decompress only the lunate and not the scaphoid. This solution deviates axial constraints toward the scaphoid, which is naturally the most capable bone to support it. The authors describe a new radial nontransverse decompression wedge osteotomy. It allows to shorten the radius in front of the lunate. The fixation is done with a dorsal staple. To complete lunate decompression, authors propose to associate a metaphysal ulnar oblique shortening, essentially if ulnar variance is neutral or positive. The preliminar results on 10 cases are presented.

Another light in the dark: review of a new method for the arthroscopic repair of triangular fibrocartilage complex

The triangular fibrocartilage complex (TFCC) is an anatomically and biomechanically important structure. Repair of radial-sided TFCC tear has previously been challenging. We designed a new method of radial-sided TFCC tear repair and found that it was also applicable for ulnar-sided TFCC tear repair. From October 2006 to December 2010, 10 patients underwent this operation and were reviewed: 9 men and 1 woman, with a mean age of 33.9 years. Average postoperative follow-up was 8 months. We graded results according to the Mayo modified wrist score. We rated 2 of the 10 patients (20%) as "excellent," 3 (30%) as "good," and 5 (50%) as "fair." The 5 patients who were rated as "fair" returned to regular jobs or had restricted employment. Based on this small sample, we recommend that this technique be considered an alternative method for TFCC repair.

Validation of radiocarpal joint contact models based on images from a clinical MRI scanner

This study was undertaken to assess magnetic resonance imaging (MRI)-based radiocarpal surface contact models of functional loading in a clinical MRI scanner for future in vivo studies, by comparison with experimental measures from three cadaver forearm specimens. Experimental data were acquired using a Tekscan sensor during simulated light grasp. Magnetic resonance (MR) images were used to obtain model geometry and kinematics (image registration). Peak contact pressures (PPs) and average contact pressures (APs), contact forces and contact areas were determined in the radiolunate and radioscaphoid joints. Contact area was also measured directly from MR images acquired with load and compared with model data. Based on the validation criteria (within 25% of experimental data), out of the six articulations (three specimens with two articulations each), two met the criterion for AP (0%, 14%); one for peak pressure (20%); one for contact force (5%); four for contact area with respect to experiment (8%, 13%, 19% and 23%), and three contact areas met the criterion with respect to direct measurements (14%, 21% and 21%). Absolute differences between model and experimental PPs were reasonably low (within 2.5 MPa). Overall, the results indicate that MRI-based models generated from 3T clinical MR scanner appear sufficient to obtain clinically relevant data.

MRI-based modeling for radiocarpal joint mechanics: validation criteria and results for four specimen-specific models

The objective of this study was to validate the MRI-based joint contact modeling methodology in the radiocarpal joints by comparison of model results with invasive specimen-specific radiocarpal contact measurements from four cadaver experiments. We used a single validation criterion for multiple outcome measures to characterize the utility and overall validity of the modeling approach. For each experiment, a Pressurex film and a Tekscan sensor were sequentially placed into the radiocarpal joints during simulated grasp. Computer models were constructed based on MRI visualization of the cadaver specimens without load. Images were also acquired during the loaded configuration used with the direct experimental measurements. Geometric surface models of the radius, scaphoid and lunate (including cartilage) were constructed from the images acquired without the load. The carpal bone motions from the unloaded state to the loaded state were determined using a series of 3D image registrations. Cartilage thickness was assumed uniform at 1.0 mm with an effective compressive modulus of 4 MPa. Validation was based on experimental versus model contact area, contact force, average contact pressure and peak contact pressure for the radioscaphoid and radiolunate articulations. Contact area was also measured directly from images acquired under load and compared to the experimental and model data. Qualitatively, there was good correspondence between the MRI-based model data and experimental data, with consistent relative size, shape and location of radioscaphoid and radiolunate contact regions. Quantitative data from the model generally compared well with the experimental data for all specimens. Contact area from the MRI-based model was very similar to the contact area measured directly from the images. For all outcome measures except average and peak pressures, at least two specimen models met the validation criteria with respect to experimental measurements for both articulations. Only the model for one specimen met the validation criteria for average and peak pressure of both articulations; however the experimental measures for peak pressure also exhibited high variability. MRI-based modeling can reliably be used for evaluating the contact area and contact force with similar confidence as in currently available experimental techniques. Average contact pressure, and peak contact pressure were more variable from all measurement techniques, and these measures from MRI-based modeling should be used with some caution.

Evaluation of a polyaxial angle-stable volar plate in a distal radius C-fracture model--a biomechanical study

INTRODUCTION

Polyaxial angle-stable plating is thought to be particularly beneficial in the management of complex intra-articular fractures of the distal radius. The purpose of the present study was to investigate whether the technique provides stability to match that of conventional (fixed-angle) angle-stable constructs.

MATERIAL AND METHODS

In seven pairs of human cadaver radii, an Arbeitsgemeinschaft für Osteosynthese (AO) 23 C2.1 intra-articular fracture was created. One radius of each pair received a juxta-articular 2.4-mm locking compression plate (LCP) Volar Distal Radius Plate, whilst the contralateral one received a 2.4-mm Variable Angle Locking Compression Plate (LCP) Two-Column Volar Distal Radius Plate (both plates: Synthes, Oberdorf, Switzerland). Parameters tested were construct stiffness (static axial loading with 150 N), range of motion and secondary loss of reduction (dynamic 150 N axial loading over 5000 cycles). Stiffness and range of motion were measured both pre- and post-cycling.

RESULTS

The polyaxial constructs were significantly stiffer, both before and after cyclic testing. However, the two-column plates showed a significant loss of stiffness during cyclic testing. The range of motion was significantly greater, both initially and at the end of cyclic testing, in the fixed-angle constructs. The conventional constructs had significantly greater secondary loss of reduction.

CONCLUSION

The polyaxial two-column plate tested in this study provides a biomechanically sound construct for the management of intra-articular fractures of the distal radius.

Biomechanical comparison of locking versus nonlocking volar and dorsal T-plates for fixation of dorsally comminuted distal radius fractures

OBJECTIVES

The purpose of this study was to gain insight into the effect of plate location and screw type for fixation of extra-articular distal radius fractures with dorsal comminution (Orthopaedic Trauma Association Type 23-A3.2).

METHODS

Sixteen pairs of cadaver radii were randomized to four plating configurations: dorsal locking, dorsal nonlocking, volar locking, and volar nonlocking. A standard 1-cm dorsal wedge osteotomy was used. Cyclic axial loads were applied for 5000 cycles. Stiffness and fragment displacement were recorded at 500 cycle-intervals. Pre- and postcyclic loading radiographs were analyzed. An axial load to failure test followed and construct stiffness and failure strength recorded. Biomechanical data were analyzed using a two-way analysis of variance (P < 0.05). Failure modes were descriptively interpreted.

RESULTS

Cyclic testing data revealed no difference between constructs at any interval. Within all construct groups, displacement that occurred did so within the first 500 cycles of testing. Pre- and postcyclic loading radiographic analysis showed no differences in construct deformation. Load to failure testing revealed no differences between groups, whereas volar constructs approached significance (P = 0.08) for increased failure strength. Dorsal constructs failed primarily by fragment subsidence and fragmentation, whereas volar constructs failed by plate bending.

CONCLUSIONS

No difference in all measured biomechanical parameters supports equivalence between constructs and surgeon discretion in determining operative method. Minimal fragment displacement and construct deformation during physiological testing support previous data that early postoperative motion can be recommended. Fragment displacement that occurs does so in the early periods of motion.

Efficacy of radial styloid targeting screws in volar plate fixation of intra-articular distal radial fractures: a biomechanical study in a cadaver fracture model

Background

The locking screws target the radial styloid, theoretically provide greater stability against radial styloid fragment. However, it is unknown whether the radial styloid locking screws increased the stability of the volar plating system fixation along the entire distal radius or not. In this study, we evaluated the stability of the volar plating system fixation with or without the radial styloid screws using a biomechanical study in a cadaver fracture model.

Methods

Six matched pairs of fresh-frozen human cadaver wrists complete from the proximal forearm to the metacarpal bones were prepared to simulate standardized 3-part intra-articular and severe comminuted fractures. Specimens were fixed using the volar plating system with or without 2 radial styloid screws. Each specimen was loaded at a constant rate of 20 mm/min to failure. Load data was recorded and, ultimate strength and change in gap between distal and proximal fragments were measured. Data for ultimate strength and screw failure after failure loading were compared between the 2 groups.

Results

The average ultimate strength at failure of the volar plate fixation with radial styloid screws (913.5 ± 157.1 N) was significantly higher than that without them (682.2 ± 118.6 N). After failure loading, the average change in gap between the ulnar and proximal fragment was greater than that between the radial and proximal fragment. The number of bent or broken screws in ulnar fragment was higher than that in radial fragment. The number of specimens with bent or broken screws in cases with radial styloid screws was fewer than that in the fixation without radial styloid screws group.

Conclusion

The ulnar fragment is more intensively stressed than the radial fragment under axial loading of distal radius at full wrist extension. The radial styloid screws were effective in stable volar plate fixation of distal radial fractures.

Ulnar variance and scaphoid fracture

Between 1997 and 2006, radiographs of 66 scaphoid fractures were retrospectively reviewed to evaluate ulnar variance. Twenty-one (31.8%) patients had an 'ulna neutral' wrist, six (9.1%) had an 'ulna plus' and 39 (59.1%) had an 'ulna minus' wrist. The mean ulnar variance was -1.3 (SD 1.8) mm (range -5.5, 2.5). We observed a significant difference in the distribution of ulnar variance (P < 0.00001) and in the proportion of cases with ulna minus (OR = 5.0; 95% CI: 2.7, 9.3) compared to previous publications.

A novel non-bridging external fixator construct versus volar angular stable plating for the fixation of intra-articular fractures of the distal radius--a biomechanical study

Non-bridging external fixation has recently been introduced as an alternative to volar angular stable plating for the fixation of unstable intra-articular distal radial fractures. The purpose of this study was to biomechanically compare a new non-bridging external fixator construct to volar angular stable plate fixation in a dorsally comminuted intra-articular fracture model of the distal radius.

MATERIALS AND METHODS

Five pairs of fresh frozen human cadaveric radii were randomly supplied with either a non-bridging external fixator or a stainless steel volar locking plate. A three-fragmental AO 23-C2.1 fracture was created by removing a 15 degrees dorsal wedge with remaining volar cortical contact and by an intra-articular osteotomy lateral to the lister-tubercle. Physiological load transfer via the wrist was simulated by means of a custom-made seesaw. For biomechanical testing, the bones were loaded in cyclic axial compression. Starting at 100N, the load was monotonically increased at 0.025 degrees N per cycle until failure of the construct. Motion of the lunate and scaphoid fragments with respect to the radial diaphysis was acquired by optical three-dimensional (3D) motion tracking. Plastic wedge deformation was determined after 2000, 4000 and 6000 cycles.

RESULTS

The amplitude of wedge motion at the beginning of the test as a measure for construct stiffness was significantly lower for the fixator group (P=0.003, power=0.99). Plastic wedge deformation after 2000, 4000 and 6000 cycles was found significantly lower for the external fixator (repeated measures analysis of variance (ANOVA), P=0.009, power=0.86). Displacement of the intra-articular gap was found below 0.6mm (mean) for both groups (P>0.05).

CONCLUSION

The study revealed superior biomechanical properties of the proposed non-bridging external fixation compared to volar locked plating in an unstable intra-articular fracture model with volar cortical support. However, both fixation techniques seem to apply sufficient stabilisation to restore and retain anatomy after fracture of the most distal part of the radius and should be individually chosen according to distinct criteria.

Conformational changes in the carpus during finger trap distraction

PURPOSE

Wrist distraction is a common treatment maneuver used clinically for the reduction of distal radial fractures and midcarpal dislocations. Wrist distraction is also required during wrist arthroscopy to access the radiocarpal joint and has been used as a test for scapholunate ligament injury. However, the effect of a distraction load on the normal wrist has not been well studied. The purpose of this study was to measure the three-dimensional conformational changes of the carpal bones in the normal wrist as a result of a static distractive load.

METHODS

Using computed tomography, the dominant wrists of 14 healthy volunteers were scanned at rest and during application of 98 N of distraction. Load was applied using finger traps, and volunteers were encouraged to relax their forearm muscles and to allow distraction of the wrist. The motions of the bones in the wrist were tracked between the unloaded and loaded trial using markerless bone registration. The average displacement vector of each bone relative to the radius was calculated, as were the interbone distances for 20 bone-bone interactions. Joint separation was estimated at the radiocarpal, midcarpal, and carpometacarpal joints in the direction of loading using the radius, lunate, capitate, and third metacarpal.

RESULTS

With loading, the distance between the radius and third metacarpal increased an average of 3.3 mm +/- 3.1 in the direction of loading. This separation was primarily in the axial direction at the radiocarpal (1.0 mm +/- 1.0) and midcarpal (2.0 mm +/- 1.7) joints. There were minimal changes in the transverse direction within the distal row, although the proximal row narrowed by 0.98 mm +/- 0.7. Distraction between the radius and scaphoid (2.5 mm +/- 2.2) was 2.4 times greater than that between the radius and lunate (1.0 mm +/- 1.0).

CONCLUSIONS

Carpal distraction has a significant (p < .01) effect on the conformation of the carpus, especially at the radiocarpal and midcarpal joints. In the normal wrist, external traction causes twice as much distraction at the lunocapitate joint than at the radiolunate joint.

A pilot feasibility study for ultrasound evaluation of living human wrist cartilage: site-specific differences in acoustic properties

PURPOSE

The field of cartilage repair has changed dramatically in the past decade but has not answered the question of how to treat an articular cartilage lesion in the wrist. Indeed, the characteristics of wrist articular cartilage, such as cartilage thickness, hardness, and smoothness, have not been clarified. The purpose of this study was to evaluate and quantify the acoustic properties of wrist articular cartilage quantitatively using a new acoustic probe under arthroscopic observation.

METHODS

We evaluated 10 consecutive patients (9 men, 1 woman) who were examined or treated arthroscopically. The mean age at evaluation was 27 years. In total, 468 points of wrist articular cartilage were investigated using the ultrasonic probe, and the data were transformed into a wavelet map by wavelet transformation. Two parameters, maximum magnitude and echo duration, which are indices of articular cartilage stiffness and macroscopic surface roughness, respectively, were used to evaluate the acoustic properties of wrist cartilage.

RESULTS

The distribution pattern of the acoustic properties was similar to that of previous results for the ankle joint. The mean maximum magnitude and echo duration were 3.41 +/- 1.50 (range, 0.89-7.53) and 1.33 mus +/- 0.30 (range, 0.51-2.17 mus), respectively. For the scaphoid fossa, the maximum magnitude of the radial side was significantly lower than that of the ulnar side, and the echo duration of the radial side was significantly longer than that of the ulnar side.

CONCLUSIONS

A new measurement system using an acoustic probe made it possible to perform a quantitative analysis of wrist articular cartilage, similar to the case for knee and ankle articular cartilage. In addition, site-specific differences in the acoustic properties of the distal radial cartilage were detected in living human wrist cartilage.