Automatic identification of radius and ulna bone landmarks on 3D virtual models.

BACKGROUND: For bone morphology and biomechanics analysis, landmarks are essential to define position, orientation, and shape. These landmarks define bone and joint coordinate systems and are widely used in these research fields. Currently, no method is known for automatically identifying landmarks on virtual 3D bone models of the radius and ulna. This paper proposes a knowledge-based method for locating landmarks and calculating a coordinate system for the radius, ulna, and combined forearm bones, which is essential for measuring forearm function. This method does not rely on pre-labeled data. VALIDATION: The algorithm is validated by comparing the landmarks placed by the algorithm with the mean position of landmarks placed by a group of experts on cadaveric specimens regarding distance and orientation. RESULTS: The median Euclidean distance differences between all the automated and reference landmarks range from 0.4 to 1.8 millimeters. The median angular differences of the coordinate system of the radius and ulna range from -1.4 to 0.6 degrees. The forearm coordinate system's median errors range from -0.2 to 2.0 degrees. The median error in calculating the rotational position of the radius relative to the ulna is 1.8 degrees. CONCLUSION: The automatic method's applicability depends on the use context and desired accuracy. However, the current method is a validated first step in the automatic analysis of the three-dimensional forearm anatomy.

Stability of the distal radioulnar joint with and without activation of forearm muscles.

The purpose of this study was to quantify the effect of the flexor carpi ulnaris and the extensor carpi ulnaris muscles on distal radioulnar joint stability. The anteroposterior ulnar head translation in relation to the radius was measured sonographically when the forearm was in a neutral resting position and when the hand was actively pressed on to a surface, with and without intentional flexor carpi ulnaris and extensor carpi ulnaris activation, while also being monitored by an electromyogram. Data on 40 healthy participants indicated a mean anteroposterior translation in the distal radioulnar joint of 4.1 mm (SD 1.08) without and 1.2 mm (SD 0.54) with muscle activation. Our results indicate that intentional ulnar forearm muscle activation results in 70% less anteroposterior ulnar head translation and greater distal radioulnar joint stability. Therefore, the flexor carpi ulnaris and extensor carpi ulnaris muscles serve as dynamic stabilizers of the distal radioulnar joint. This finding may be clinically significant since ulnar forearm muscles strengthening may increase distal radioulnar joint stability.

Skeletal Effects of Sleeve Gastrectomy in Adolescents and Young Adults: A 2-Year Longitudinal Study.

CONTEXT: Vertical sleeve gastrectomy (VSG) is an increasingly common tool to achieve weight loss and improve metabolic health in adolescents and young adults with obesity, although it may adversely affect bone health. OBJECTIVE: This work aimed to evaluate the effect of VSG on bone health in youth. METHODS: An observational 2-year study was conducted at a tertiary care center of 66 patients aged 13 to 24 years with moderate-to-severe obesity meeting criteria for VSG. The patients underwent VSG (n = 30) or nonsurgical (n = 36) management per the decision of patient and clinical team. Main outcome measures included dual-energy x-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HRpQCT) measures of bone mineral density (BMD), geometry, and microarchitecture. RESULTS: VSG patients achieved 25.3 ± 2.0% weight loss at 2 years (P < .001) while control subjects gained 4.0 ± 2.0% (P = .026). Total hip BMD declined 8.5 ± 1.0% following VSG compared with 0.1 ± 1.0% gain in controls (P < .001), with similar results at the femoral neck (P < .001). Total volumetric BMD (vBMD) decreased both at the distal radius and tibia following VSG (P < .001) driven primarily by trabecular vBMD loss (P < .001). Two-year changes in cortical vBMD did not differ between groups, though cortical porosity decreased following VSG both at the radius and tibia (P = .048 and P < .001). Cortical thickness increased in controls but not in VSG (P = .022 and P = .002 for between-group comparisons at the radius and tibia, respectively). Following VSG, estimated failure load decreased at the radius and did not demonstrate the physiologic increases at the tibia observed in controls. CONCLUSION: VSG leads to progressive changes in bone health over 2 years, and may lead to increased skeletal fragility in adolescents and young adults.

Role of Dynamic Stabilizers of the Elbow in Radiocapitellar Joint Alignment: A Prospective In Vivo Study.

PURPOSE: To investigate the effect of dynamic stabilizers of the elbow on radiocapitellar joint alignment, before and after the administration of regional anesthesia. METHODS: At a single institution, 14 patients were prospectively enrolled in a study using a within-subjects control design. Before performing a supraclavicular regional block, 10 fluoroscopic images (1 anteroposterior and 9 lateral views) of the elbow were obtained for each patient. The lateral images were obtained with the forearm in maximal supination, neutral rotation, and maximal pronation, and these forearm positions were repeated for 3 elbow positions: (1) full extension; (2) flexion to 90°, with 0° of shoulder internal rotation; and (3) flexion to 90°, with 90° of shoulder internal rotation. After obtaining the 10 initial images, a block was performed to achieve less than 3/5 motor strength of the imaged extremity, followed by obtaining the same 10 images in each patient. Radiocapitellar ratio, defined as the minimal distance between the right bisector of the radial head and the center of the capitellum divided by the diameter of the capitellum, was measured in each image. RESULTS: The 14 patients had a mean age of 47.8 ± 15.7 years, and 10 (71.4%) patients were women. A difference between radiocapitellar ratios measured before and after the regional block administration was observed for all lateral images (-1.0% ± 7.2% to -2.2% ± 8.0%), although this difference was less than the minimum clinically important difference. CONCLUSIONS: Paralysis of the dynamic stabilizers of the elbow produces a difference in the radiocapitellar joint alignment, but this did not reach the minimum clinically important difference. CLINICAL RELEVANCE: Paralysis of the dynamic stabilizers of the elbow via a supraclavicular nerve block produces no clinically relevant effect on the radiocapitellar alignment of uninjured elbows.

Plasma Growth and Differentiation Factor 15 Predict Longitudinal Changes in Bone Parameters in Women, but Not in Men.

Bone fragility can progress with aging, but biomarkers to detect emerging osteopenia have not been fully elucidated. Growth/differentiation factor 15 (GDF-15) has pleiotropic roles in a broad range of age-related conditions, but its association with osteopenia is unknown. We examined the relationship between plasma GDF-15 levels and rate of change in bone parameters over 9 years of follow-up in 596 adults in the InCHIANTI study (baseline age, 65-94 years; women, 52.4%; mean follow-up, 7.0 ± 3.0 years). Plasma GDF-15 concentrations were measured using the 1.3k HTS SOMAscan assay. Eight bone parameters were measured in the right tibia by peripheral quantitative computed tomography; total bone density, trabecular bone density, medullary plus trabecular bone density, cortical bone density, total bone area, cortical bone area, medullary bone area, and minimum moment of inertia (mMOI). We ran sex-specific linear mixed-effect models with random intercepts and slopes adjusted for age, age-squared, education, body mass index, the rate of change in weight, smoking, sedentary behavior, cross-sectional areas of calf muscles and fat, 25-hydroxyvitamin D, parathyroid hormone, calcium, diabetes mellitus, and follow-up time. We found a significant association of "baseline GDF-15 × time" in models predicting cortical bone density and the mMOI in women, suggesting that the rates of decline in these bone parameters increased with higher GDF-15 (false discovery rate <0.05). Higher plasma levels GDF-15 predicted an accelerated decline in bone parameters in women, but was less associated in men. Furthermore studies are needed to understand the mechanisms underlying these sex differences.

Alteration of Bone Density, Microarchitecture, and Strength in Patients with Camurati-Engelmann Disease: Assessed by HR-pQCT.

Camurati-Engelmann disease (CED) is a rare autosomal-dominant skeletal dysplasia caused by mutations in the transforming growth factor-ß1 (TGFB1) gene. In this study, a retrospective review of patients with CED evaluated at Peking Union Medical College Hospital in Beijing, China, between November 30, 2000 and November 30, 2020 was conducted. Data including demographic data, manifestations, and examination results were characterized. Furthermore, bone geometry, density, and microarchitecture were assessed and bone strength was estimated by HR-pQCT. Results showed the median age at onset was 2.5 years. Common manifestations included pain in the lower limbs (94%, 17/18), abnormal gait (89%, 16/18), genu valgum (89%, 16/18), reduced subcutaneous fat (78%, 14/18), delayed puberty (73%, 8/11), muscle weakness (67%, 12/18), hearing loss (39%, 7/18), hepatosplenomegaly (39%, 7/18), exophthalmos or impaired vision or visual field defect (33%, 6/18), and anemia (33%, 7/18). Twenty-five percent (4/16) of patients had short stature. Serum level of alkaline phosphatase was elevated in 41% (7/17) of patients whereas beta-C-terminal telopeptide was elevated in 91% of patients (10/11). Among 12 patients, the Z-scores of two patients were greater than 2.5 at the femur neck and the Z-scores of five patients were lower than -2.5 at the femur neck and/or lumbar spine. HR-pQCT results showed lower volumetric BMD (vBMD), altered bone microstructure and lower estimated bone strength at the distal radius and tibia in patients with CED compared with controls. In addition, total volume bone mineral density and cortical volumetric bone mineral density at the radius were negatively correlated with age in patients with CED, but positively correlated with age in controls. In conclusion, the largest case series of CED with characterized clinical features in a Chinese population was reported here. In addition, HR-pQCT was used to investigate bone microstructure at the distal radius and tibia in nine patients with CED, and the alteration of bone density, microstructure, and strength was shown for the first time. © 2021 American Society for Bone and Mineral Research (ASBMR).

The effect of the interosseous ligament and selected antebrachiocarpal ligaments on rotation of the radius during extension of the carpus.

OBJECTIVE: To evaluate the effect of the interosseous ligament and selected antebrachiocarpal ligaments on the internal rotation of the radius relative to the ulna, during carpal extension. STUDY DESIGN: Cadaveric study. SAMPLE POPULATION: Twenty-four cadaveric canine forelimbs. METHODS: Twenty-four forelimbs were disarticulated at the elbow joint and the antebrachia were prepared for testing. The forelimbs were divided to 6 groups, defined by the order in which ligaments were transected. All specimens were tested intact and after transecting each of the ligaments with the order defined by the group. Rotation of the radius relative to the ulna, caused by extension of the carpus, was measured using a sensor connected to the radius. RESULTS: The mean(±sd) maximum internal rotation of the radius (5.94° ± (1.23°)) with all the ligaments intact was significantly greater (p < 0.012) than the mean(±sd) maximum internal rotation of the radius (3.13° (± 1.13°)) after transecting the interosseus ligament. Transecting the interosseous ligament subsequent to one of the other ligaments caused a decrease in internal radial rotation (p = 0.629), while, transecting the short radial collateral ligament caused an increase in radial rotation (p = 0.629). Transecting the palmar radiocarpal and ulnocarpal ligaments had no effect on radial rotation. CONCLUSION: The interosseous ligament was stretched with internal rotation of the radius due to carpal extension. Carpal flexion resulted in external rotation of the radius. This effect was lost when the interosseus ligament was transected. CLINICAL SIGNIFICANCE: Rotation of the radius is associated with carpal extension, and is likely an intrinsic part of forelimb biomechanics.

Force Distribution in the Canine Proximal Radio-Ulnar Joint on Extension of the Carpal Joint: A Cadaveric Study.

OBJECTIVE: The aim of this study was to measure the load on the lateral and medial aspects of the proximal radio-ulnar joint during extension of the carpus. STUDY DESIGN: This was an ex vivo biomechanical study. SAMPLE POPULATION: Twenty-two cadaveric Greyhound thoracic limbs were used. METHODS: Twenty-two paired thoracic limbs were used. The olecranon was attached to a custom jig with the foot resting on a stationary anvil. Load sensors were inserted into the proximal radio-ulnar joint, between the radial head and the lateral coronoid process, and between the radial head and the medial coronoid process. Specimens were tested under compression with measurements taken at 0, 4, 9 and 13.5 mm of axial displacement. Data collected at each point included forces on the specimen and medial and lateral coronoid processes as well as the angle of carpal joint extension. RESULTS: A linear mixed effects model relating load on the specimen and carpal joint extension angle had an R-squared value of 0.66, and load at the level of the medial coronoid process and angle of carpal extension had an R-squared value of 0.61. There was a significant difference in the loads measured on the lateral and medial coronoid processes at all angles (p < 0.0001). CONCLUSION: Extension of the carpus results in asymmetric loading of the proximal radio-ulnar joint. CLINICAL SIGNIFICANCE: The findings of this study show that loading of the medial coronoid process may be more complex than originally thought and supports the future investigation of novel management and therapeutic options for affected patients.

Evolution of the Ring Concept for the Forearm and Its Implication on Treatment: From Galeazzi, Monteggia, Essex-Lopresti, and Darrach to the Current Era.

Geometrically, rings distribute their stress along their arc instead of concentrating at any one point. The forearm ring is composed of the radius, ulna, proximal radioulnar joint, and distal radioulnar joint. The annular ligament, interosseous membrane, and triangular fibrocartilage complex link and stabilize the ring. Injuries to the forearm occur along a continuum with recognized patterns of ring disruption, including Galeazzi, Monteggia, and Essex-Lopresti injuries. The Darrach procedure causes a disruption to the forearm ring and can lead to painful convergence between the radius and distal ulnar stump. Injuries to the forearm ring are unstable. Management of forearm injuries is centered on the restoration of the anatomy and stability of the forearm ring. Forearm ring injuries and their treatment are discussed in this article.

Differences in the Rotation Axes of the Scapholunate Joint During Flexion-Extension and Radial-Ulnar Deviation Motions.

PURPOSE: To determine the location of the rotation axis between the scaphoid and the lunate (SL-axis) during wrist flexion-extension (FE) and radial-ulnar deviation (RUD). METHODS: An established and publicly available digital database of wrist bone anatomy and carpal kinematics of 30 healthy volunteers (15 males and 15 females) in up to 8 different positions was used to study the SL-axis. Using the combinations of positions from wrist FE and RUD, the helical axis of motion of the scaphoid relative to the lunate was calculated for each trial in an anatomical coordinate system embedded in the lunate. The differences in location and orientation between each individual axis and the average axis were used to quantify variation in axis orientation. Variation in the axis location was computed as the distance from the closest point on the rotation axis to the centroid of the lunate. RESULTS: The variation in axis orientation of the rotation axis for wrist FE and RUD were 84.3° and 83.5°, respectively. The mean distances of each rotation axis from the centroid of the lunate for FE and RUD were 5.7 ± 3.2 mm, and 5.0 ± 3.6 mm, respectively. CONCLUSIONS: Based on the evaluation of this dataset, we demonstrated that the rotation axis of the scaphoid relative to the lunate is highly variable across subjects and positions during both FE and RUD motions. The range of locations and variation in axis orientations in this data set of 30 wrists shows that there is very likely no single location for the SL-axis. CLINICAL RELEVANCE: Scapholunate interosseous ligament reconstruction methods focused on re-creating a standard SL-axis may not restore what is more likely to be a variable anatomical axis and normal kinematics of the scaphoid and lunate.

Quantitative assessment of distal radioulnar joint stability with pressure-monitor ultrasonography.

BACKGROUND: Diagnosing distal radioulnar joint (DRUJ) instability remains a challenge as it relies on physical examination. To quantitatively assess DRUJ stability, a pressure-monitor ultrasound system was developed. The objective of this study was to evaluate the force-displacement relationship of DRUJ in normal subjects. METHODS: Nine wrists of 9 asymptomatic volunteers were evaluated. The pressure-monitor ultrasound system was developed to apply pressure to the tissue with a pre-determined cycle and displacement of the transducer. Each subject was imaged sitting with the elbow flexed and forearm pronated. The dorsal surface of the distal radius and the center of the ulnar head were displayed at DRUJ level. The pressure toward palmar direction was applied to the distal ulna with different levels of transducer displacements, i.e., 1 mm, 2 mm, and 3 mm. The distance between the dorsal surface of the ulnar head and the dorsal surface of the distal radius was measured. The first measurement was performed at the initial position, and the second measurement was performed when the transducer pressed down the ulna to the degree that the ulnar head had shifted to the most palmar position. At the same time, the pressure to the transducer was measured. The changes of radioulnar distance (=the measurement at the most palmar position-the measurement at the initial position) and pressure, and pressure/distance ratio were compared among the different transducer displacements. RESULTS: The pressure was significantly increased as the transducer displacement became larger (P < 0.01). The changes of radioulnar distance were smaller in the 1 mm displacement condition compared to the 2 and 3 mm displacement conditions (P < 0.05). The pressure/distance ratio was larger in the 1 mm displacement condition compared to the 2 and 3 mm displacement conditions (P < 0.05). CONCLUSIONS: A method to assess DRUJ stability by measuring changes in radioulnar distance and force application was developed. It was found that the application of 2 mm displacement and 200 g force was the critical stress for the capsuloligamentous structures to start stabilizing DRUJ. This methodology and the indices may be clinically useful to investigate the mechanical properties of patients with DRUJ instability.

Comparison of cross-sectional geometrical properties and bone density of the proximal radius between Saint Bernard and other giant breed dogs.

OBJECTIVE: To compare the geometrical properties and bone mineral density (BMD) of the proximal radius between Saint Bernard and other giant breed dogs. STUDY DESIGN: Observational, cross-sectional, descriptive study. ANIMALS: Thirteen client-owned Saint Bernard dogs and 13 other client-owned giant breed dogs. METHODS: Computed tomography (CT) studies of Saint Bernard and other giant breed dogs were reviewed. Multiplanar reconstruction of the CT images was used to determine cross-sectional variables at the proximal half of the radius, including mean cortical thickness (mCT) and moment of inertia (MOI). Cortical BMD was estimated from Hounsfield unit measurements at each cross-section and averaged per bone. One-way analysis of variance was used to detect differences between groups. RESULTS: Proximal radii of Saint Bernard dogs had a lower cortical/medullary ratio (1.75 vs 2.2, P < .001), mCT (1.96 vs 2.64 mm, P < .001), and MOI in all planes (mediolateral [ML]: 2086.09 vs 2757.69 mm4 , P < .001; craniocaudal [CrCd]: 3736.36 vs 4370.28 mm4 , P = .025; and polar: 5852.45 vs 7127.97 mm4 , P = .002) compared with bones of other breeds. Cross-sectional BMD did not differ between groups of dogs, but the mean BMD of all cross-sections was lower in Saint Bernard dogs (1214.27 vs 1289.80 mg/mm3 , P = .029). CONCLUSION: The proximal radii of Saint Bernard dogs had thinner cortices and lower CrCd, ML, and polar MOI compared with corresponding bones in giant breed dogs. CLINICAL SIGNIFICANCE: The structural properties of the proximal radius of the Saint Bernard differ from those in other giant breeds and could reduce the ability of this region to sustain biomechanical loads. These properties could predispose Saint Bernard dogs to complications after surgical limb-sparing procedures.

Indirect 3D printing technology for the fabrication of customised ß-TCP/chitosan scaffold with the shape of rabbit radial head-an in vitro study.

BACKGROUND: With the development of indirect three-dimensional (3D) printing technology, it is possible to customise individual scaffolds to be used in bone transplantation and regeneration. In addition, materials previously limited to the 3D printing (3DP) process due to their own characteristics can also be used well in indirect 3DP. In this study, customised ß-TCP/chitosan scaffolds with the shape of rabbit radial head were produced by indirect 3D printing technology. METHODS: Swelling ability, porosity, mechanical characterisation, and degradation rate analysis were performed, and in vitro studies were also implemented to evaluate the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) on the scaffolds. CCK8 cell proliferation assay kit and alkaline phosphatase (ALP) staining solution were used to study cell proliferation and early ALP content at the scaffold surface. Moreover, the osteogenic differentiation of MSCs on scaffolds was also evaluated through the scanning electron microscopy analysis. RESULTS: ß-TCP/chitosan scaffold has good performance and degradation rate, and in vitro cell experiments also confirm that the scaffold has adequate cytocompatibility and bioactivity. CONCLUSION: This study provides a promising new strategy for the design of customised scaffolds for the repair of complex damaged tissues.

Study of human radius construction systematics: evaluation by DXA in dry bone.

This study has been undertaken in order to describe the bone mass distribution of the dry human radius via dual x-ray absorptiometry (DXA) with a Norland XR-800 densitometer machine. A sample of 39 dry radius bones was used. Two projections were made: antero-posterior and lateral, and five regions of interest were selected. The bone densities and the bone mineral contents of the various regions of the radius in the two projections were compared using Student's t tests for paired samples, with statistically significant differences being found in all of the values, except in the proximal extremity (P Ext). The area of greatest bone mineral content (BMC) was the medial diaphysis (M Diaph), followed by the distal extremity (D Ext), with the lowest value being found in the proximal extremity (P Ext). As for bone mineral density (BMD), a great symmetry is observed if we take the mean point of the longitudinal axis as a reference, with it being distributed from highest to lowest from the central part to the extremities. A correlation study of the BMD and BMC values between the segments themselves and with the total, in both positions, provides us with a high correlation (p ≤ 0.01), with the highest correlation value being found for the proximal diaphysis (P Diaph) region, indicating the heterogeneous nature of the distribution of the radius bone mass. Bone densitometry via DXA is useful in order to establish an overview of the structural construction of the human radius.

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.

Bone mineral density changes after parathyroidectomy are dependent on biochemical profile.

BACKGROUND: Bone mineral density (BMD) has been found to improve after parathyroidectomy (PTX) in patients with primary hyperparathyroidism. There are few data on the effect of PTX on BMD in normocalcemic and normohormonal primary hyperparathyroidism. METHODS: A retrospective analysis of 92 primary hyperparathyroidism patients who underwent PTX between 2004 and 2012 with pre- and post-PTX dual-energy x-ray absorptiometry was performed. Within-person changes in BMD pre- and post-PTX were analyzed using log linear mixed models, stratified by biochemical status. RESULTS: Bone mineral density increased post-PTX in the whole cohort at the lumbar spine (+2.5%), femoral neck (+2.1%), and total hip (+1.9%) and decreased at the one-third radius (-0.9%). On comparison of BMD changes by profile, BMD increased in those with the typical profile at the lumbar spine (3.2%), femoral neck (2.9%), and total hip (2.9%) but declined at the one-third radius (-1.5%). In contrast, BMD improved only at the femoral neck (4.3%) in the normohormonal group and did not change at any site in the normocalcemic group. The typical group had a greater increase in BMD over time at the femoral neck and total hip compared with normocalcemic patients. CONCLUSION: Our results indicate that the skeletal benefit of PTX was attenuated in normocalcemic and normohormonal patients, suggesting that skeletal changes after PTX may depend on biochemical profile.

Moderate to vigorous physical activity and impact loading independently predict variance in bone strength at the tibia but not at the radius in children.

The objectives of this study were (i) to assess whether daily minutes of moderate to vigorous physical activity (MVPA) or vigorous physical activity (VPA) and impact counts (acceleration peaks ≥3.9g) independently predict variance in bone strength in children and youth and (ii) to estimate bone strength gain associated with increases in daily MVPA, VPA, or impact counts. We recorded 7-day activity of 49 participants (mean age 11.0 years, SD 1.7) using accelerometers and estimated radius and tibia bone strength using peripheral quantitative computed tomography. We used linear regression models adjusted for sex, body mass, and muscle area to address our objectives. Daily MVPA (mean 50 min, SD 23) and VPA (mean 17 min, SD 11) or impacts (mean 71 counts, SD 59) did not predict variance in radius strength. Daily VPA (ß = 0.24) predicted variance in tibia strength at the distal and shaft sites, and shaft strength was also predicted by MVPA (ß = 0.20) and impact counts (ß = 0.21). Our models estimated a 3%-6%, 4%, or 4%-11% gain in tibia strength after increasing daily MVPA by 10-20 min, VPA by 5 min, or impacts by 30-100 counts, respectively. In conclusion, daily minutes of MVPA or VPA and impact counts are independent predictors of tibia but not radius strength. Objective recording of activities associated with forearm bone strength and trials testing the efficacy of increasing daily MVPA, VPA, and related impacts on bone strength development in children and youth are warranted.

Association Between Cortical Bone Microstructure and Statin Use in Older Women.

Context: Treatment with statins has been associated with increased bone mineral density, but whether this association depends on differences in cortical or trabecular volumetric bone microstructure is unknown. Objective: The aim of this study was to investigate if treatment with statins is associated with bone microstructure and geometry in older women. Design Setting and Participants: Older women were included in a population-based study of 3028 women (mean age ± SD, 77.8 ± 1.6 years) from the greater Gothenburg area in Sweden. Information regarding medical history, medication, and lifestyle factors was obtained from validated questionnaires. Main Outcome: Bone geometry and microstructure were measured at the ultradistal and distal (14%) site of radius and tibia using high-resolution peripheral quantitative computed tomography. Results: The 803 women in the cohort who used statins had higher body weight, worse physical function, and more frequent cardiovascular disease and diabetes than nonusers (P < 0.05). Statin users had lower cortical porosity (radius, 2.2 ± 1.9 vs 2.5 ± 2.0%; tibia, 5.2 ± 2.4 vs 5.4 ± 2.5; P = 0.01), higher cortical bone density (radius, 1008 ± 39.1 vs 1001 ± 38.4 mg/cm3; tibia, 919 ± 42.6 vs 914 ± 41.5; P < 0.01), and greater cortical area (radius, 60.5 ± 9.6 vs 58.6 ± 9.7 mm2; tibia, 150.0 ± 23.6 vs 146.7 ± 23.8; P < 0.01) than nonusers after adjustment for a large number of confounders, including age, weight, smoking, other medications, and prevalent diseases. Conclusions: Use of statins was associated with better cortical bone characteristics in older women.

Forces in the Distal Radius During a Pushup or Active Wrist Motions.

PURPOSE: To determine the 6 degrees of freedom forces and moments in the distal radius that occur during a pushup or other active wrist motions. METHODS: Eight fresh-frozen cadaveric wrists were moved through 6 physiological motions and held at 1 static pushup position while the force through the distal radius was measured with a 6 degrees of freedom load cell. Three levels of compressive force were applied at the pushup position. RESULTS: Active wrist motions caused axial forces up to 283 N and moments up to 0.7 N-m. Those motions with a smaller range had significantly smaller axial forces than the larger flexion-extension or dart-thrower's motions. With an 89-N pushup force applied, the average maximum axial force was 69 N, the radially directed force was 12 N, and the moment about the radioulnar axis was 2.3 N-m. Linear extrapolation of the forces to 100% body weight indicate that the axial force going through the distal radius would be 663 N, the radial force would be 147 N, and the moment about the radioulnar axis would be 18.6 N-m. CONCLUSIONS: Large distal radius forces and moments can occur during pushup and active wrist motions. There are not only large axial compressive forces but also nontrivial radially directed forces. CLINICAL RELEVANCE: This study may help surgeons and therapists better treat complicated distal radius fractures as well as provide for better comparisons of existing or new distal radius plates and constructs that are designed to treat these complicated loading patterns.

The Parallelogram Effect: The Association Between Central Band and Positive Ulnar Variance.

PURPOSE: Ulnar impaction syndrome is a poorly understood degenerative wrist condition characterized by symptoms of pain thought to be caused by increased loads between the ulnar head and the carpals. Radiographic evaluation often reveals an ulnar-positive wrist. We hypothesize that progressive elongation of the central band of the forearm interosseous ligaments changes the longitudinal radial-ulnar relationships, resulting in an ulnar-positive wrist. The objective of the study was to identify a relationship between the loss of integrity of the forearm interosseous ligaments and increased ulnar variance. METHODS: Six cadaveric human forearms were used to measure displacement of the radius relative to the ulna during axial loading of the lunate fossa of the radius. Radial heights were measured in supination and pronation under a 5-lbF (22-N) preload. Gradual axial loads were applied up to 50 lbF (222N); the resultant axial displacement was measured in supination and pronation. All measurements were evaluated with the interosseous ligament intact and repeated with the central band cut. RESULTS: With an applied 5-lbF preload, cutting the central band increased ulnar variance by 3.02 ± 0.80 mm in supination and by 2.15 ± 0.79 mm in pronation. In supination, when the loads were increased from the 5-lbF preload to 50 lbF, the radius displaced 2.1 times further after the central band was cut (3.00 mm) compared with the group with the intact forearm construct (1.41 mm). In pronation, when the loads were increased from the 5-lbF preload to 50 lbF, the radius displaced 1.8 times further when the central band was cut (2.84 mm) than with the intact forearm construct (1.57 mm). CONCLUSIONS: Because of a parallelogram effect, the radius shifted proximally under a 5-lbF preload, creating an ulnar-positive wrist relationship. Dynamic loading of the forearm after ligament excision resulted in significant additional radial displacement relative to the intact forearm. CLINICAL RELEVANCE: Deficiency in the ligamentous restraints of the central band leads to positive ulnar variance, which could be a factor (among others) that contributes to idiopathic ulnar impaction syndrome.