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.

Biomechanical Analysis of Capsular Repair Versus Arthrex TFCC Ulnar Tunnel Repair for Triangular Fibrocartilage Complex Tears.

Background: This study compares the effectiveness of a peripheral capsular repair with a knotless arthroscopic transosseous ulnar tunnel repair (TR) in restoring distal radioulnar joint (DRUJ) stability and stiffness in the setting of a massive triangular fibrocartilage complex (TFCC) tear. Methods: Eight matched pairs of fresh-frozen cadaveric forearms were tested. Each forearm was tested in supination and pronation using 3-dimensional (3D) optical tracking devices prior to any intervention. Each specimen then underwent a diagnostic wrist arthroscopy and sectioning of the TFCC's deep and superficial fibers. All specimens were then retested to assess instability secondary to the tear. The TFCC was repaired with either a peripheral capsular repair (CR) using three 2-0 polydioxanone sutures or a transosseous ulnar TR using a 2-0 FiberWire, and then retested (statistical significance; P < .05). Results: After TFCC arthroscopic sectioning, all specimens were unstable with a significant increase in translation and a significant decrease in stiffness. TFCC repair with TR resulted in displacement and stiffness similar to the native tissue. CR specimens were found to have significantly greater displacement and significantly decreased stiffness compared with the intact state. Conclusions: Arthroscopic sectioning of the TFCC resulted in DRUJ instability, as measured by stiffness and ulnar translation. TR effectively restored DRUJ stability and demonstrated no significant difference in postoperative stiffness or maximal displacement when compared with the intact specimen in pronation and supination. This study provides biomechanical evidence that an arthroscopic ulnar tunnel technique can restore stability to the DRUJ after a massive TFCC tear.

During forearm rotation the three-dimensional ulnolunate distance is affected more by translation of the ulnar head than change in ulnar variance.

Ulnolunate abutment has been thought to be aggravated by pronation because of an increase in ulnar variance. We hypothesized that the ulnolunate distance might be greater in pronation because the ulnar head is dorsally translated. Twenty-one three-dimensional reconstructions of computed tomographic scans of wrists taken in supination and pronation were investigated. The ulnolunate distance was measured in each position, and the change in ulnolunate distance from supination to pronation was calculated. The changes in ulnar variance from supination to pronation and the amount of translation of the ulnar head were measured directly by superimposing three-dimensional reconstructions. The mean ulnolunate distance in pronation was significantly greater than in supination. There was no significant correlation between the changes in ulnolunate distance and in the ulnar variance. The change in ulnolunate distance had a significant positive linear relationship with the amount of translation of the ulnar head. The change in ulnolunate distance during forearm rotation is determined by the amount of translation of the ulnar head rather than by change in ulnar variance. Level of evidence: IV.

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.

Reduction in ulnar pressure distribution when walking with forearm crutches with a novel cuff design: Cross-sectional intervention study on the biomechanical efficacy of an ulnar recess.

Walking with crutches is an effective way of reducing the load on the lower extremity and is often indicated after injury or surgery. However, walking with forearm crutches with conventional cuffs can trigger symptoms including tenosynovitis in the biceps tendon, ulnar neuropraxia at the wrist, pain, or skin hematoma. The purpose of this study was to test the hypothesis that a crutch cuff design with an ulnar recess reduces ulnar pressure during walking with forearm crutches. The pressure distribution between the forearm and crutch cuff was measured in 15 healthy participants for crutch walking with conventional and novel cuffs, respectively. Relative peak pressure in the proximal medial region compared to the overall peak pressure was reduced by 8.6% when walking with crutches with the novel cuff design compared to conventional cuffs (p < 0.001). Relative peak pressure in the distal intermediate and lateral regions were increased by 3.3% and 3.7% for the novel compared with conventional cuffs, respectively (p < 0.001 for both). Hence, the novel crutch cuffs shifted regions of high pressure away from the proximal ulnar region towards more distal regions that are covered by more soft tissue.

Effect of distal ulnar ostectomy on carpal joint stability during weight bearing in the dog.

OBJECTIVE: To assess the influence of a 50% distal ulnectomy on mediolateral carpal stability in the dog. STUDY DESIGN: Canine cadaveric study. SAMPLE POPULATION: Seven canine thoracic limbs METHODS: Thoracic limbs were placed in a jig to mimic weight bearing with a load representing 30% of body weight. Carpal extension angle was standardized at 190° ± 5°. Frontal plane carpal angles were measured with the limb loaded on craniocaudal radiographs before and after ulnectomy. Valgus and varus stress radiographs with the limb loaded were acquired before and after ulnectomy. The limbs were palpated and were subjectively graded for valgus or varus instability by 2 investigators before and after ulnectomy. RESULTS: Mean (±SD) valgus angulation increased after ulnectomy (2.1° ± 1.7°; P = .017; CI95 = 0.5°-3.7°) when the limb was loaded without valgus or varus stress applied. Mean valgus angulation increased after ulnectomy (2.7° ± 2.8°; P = .032; CI95 = -0.2°-5.5°) when valgus stress was applied to the loaded limb. Varus angulation was unchanged after ulnectomy (0.6° ± 4.6°; P = .383; CI95 = -4.2°-5.3°) when varus stress was applied to the loaded limb. Palpation detected increased valgus score after ulnectomy. CONCLUSION: Distal ulnectomy with excision of the lateral styloid process induces a slight increase in valgus in canine cadaver carpi. The clinical consequences of that valgus on carpal function and health should be assessed in clinical patients.

Segmental composite porous scaffolds with either osteogenesis or anti-bone resorption properties tested in a rabbit ulna defect model.

A functional biomaterial with a therapeutic effect is desirable as an adjuvant therapy to enhance bone formation and prevent local recurrence of bone tumours, especially when the resection margins are not identifiable. In this study, novel composite materials were developed with dual properties of osteopromotion and bone resorption to mimic the tumour inhibition effect, including water-soluble phosphorylated chitosan (P-chitosan) for increasing osteoblasts activity and disodium (1 → 4)-2-deoxy-2-sulphoamino-ß-d-glucopyranuronan (S-chitosan) for inhibiting bone resorption activity. First, P-chitosan and S-chitosan were respectively incorporated into two kinds of PLGA/TCP-based scaffold, i.e. PLGA-TCP-P-chitosan (P/T/P-chitosan) and PLGA-TCP-S-chitosan (P/T/S-chitosan) scaffolds. We subsequently tested combined scaffolds of PLGA-TCP-P-S-P-chitosan (P/T/PSP-chitosan) made of P/T/P-chitosan and P/T/S-chitosan to assess their integral effect, on enhancement of bone formation with P/T/P-chitosan and inhibition of tissue regeneration with P/T/S-chitosan, in an established rabbit ulnar bone defect model to imitate bone resection post-bone tumour. To compare bone healing in the defects, the P/T/P-chitosan group was regarded as a bone formation enhancement group, while the P/T group served as a control. Bone mineral density (BMD) in the P/T/P-chitosan and P/T/PSP-chitosan groups were found to be significantly higher than those in the P/T group, while that in the P/T/P-chitosan group was greater than that in the P/T/PSP-chitosan group (p < 0.05). These findings demonstrated that P/T/PSP-chitosan scaffolds possessed more osteogenic potential than the P/T scaffold but less osteogenic effect than the P/T/P-chitosan scaffold, as the S-chitosan component inhibited the activities of osteoblasts for bone formation. These findings implied a dual function of the designed P/T/PSP-chitosan for further preclinical validation and potential applications in the prevention of local recurrence and for enhancing bone repair after bone tumour resection. Copyright © 2013 John Wiley & Sons, Ltd.

Development and verification of a mathematical model to quantify the joint spaces of the elbow.

The purpose of the study was a development and verification of a model to quantify elbow joint spaces focusing on posterolateral rotatory instability. The model was tested for feasibility and applied to open and arthroscopic surgeries. A mathematical kinematic model was created, consisting of two segments representing the humerus and radius and ulna. Model calculations of the joint opening were compared with direct measurements on a mechanical model with attached marker arrays, and compared with values determined by a digital sliding caliper in order to evaluate the mathematical kinematic rigid body model of the elbow joint. Joint angles predicted by the mathematical model were compared with values determined by a two axis goniometer. The evaluation showed significant accordance (intercorrelation coefficient ≥0.8). The highest difference was 1.54° (root mean square: 0.46°) for all movement conditions. Ligament transaction at the open surgery situation affected an increase in joint opening (maximum joint opening: 10.9 mm±0.3). Distances in the ulnohumeral joint space (ligaments intact) under arthroscopic surgery situation varied between 4.0 and 6.8 mm (mean: 5.2 mm±1.0). Thus a possibility is created to achieve an objective assessment of joint space opening to provide a more complete description of the elbow kinematics using this approach.

In vivo three-dimensional elbow biomechanics during forearm rotation.

BACKGROUND: It is unclear how elbow kinematics changes during forearm rotation. This study investigated in vivo 3-dimensional elbow kinematics during forearm rotation. METHODS: We studied 12 normal elbows using in vivo 3-dimensional computed tomography data in maximum forearm supination, neutral, and maximum pronation with the elbows in extension. We measured the motion of the radius and ulna relative to the humerus using a markerless bone registration technique and the contact area of the radiocapitellar joint, proximal radioulnar joint, and ulnohumeral joint using a proximity mapping method. RESULTS: When the forearm rotated from the supinated position to the pronated position, the radius showed significant varus rotation, internal rotation, and extension relative to the humerus. The center of the radial head significantly translated anteriorly, proximally, and laterally. The ulna significantly rotated in valgus, and the deepest point on the sagittal ridge of the trochlear notch translated medially with forearm pronation. The contact area of the radiocapitellar joint was largest in pronation. The contact area of the proximal radioulnar joint was largest in supination. The contact area of the ulnohumeral joint showed no significant change during forearm rotation. CONCLUSIONS: In pronation, because of the proximal migration of the radial head, the radiocapitellar joint was most congruent compared with other positions. The proximal radioulnar joint was most congruent in supination. The ulnohumeral joint congruency was not affected by forearm rotation. This study provides useful information for understanding 3-dimensional elbow motion and joint osseous stability related to forearm rotation.

Contact mechanics of reverse engineered distal humeral hemiarthroplasty implants.

Erosion of articular cartilage is a concern following distal humeral hemiarthroplasty, because native cartilage surfaces are placed in contact with stiff metallic implant components, which causes decreases in contact area and increases in contact stresses. Recently, reverse engineered implants have been proposed which are intended to promote more natural contact mechanics by reproducing the native bone or cartilage shape. In this study, finite element modeling is used in order to calculate changes in cartilage contact areas and stresses following distal humeral hemiarthroplasty with commercially available and reverse engineered implant designs. At the ulna, decreases in contact area were -34±3% (p=0.002), -27±1% (p<0.001) and -14±2% (p=0.008) using commercially available, bone reverse engineered and cartilage reverse engineered designs, respectively. Peak contact stresses increased by 461±57% (p=0.008), 387±127% (p=0.229) and 165±16% (p=0.003). At the radius, decreases in contact area were -21±3% (p=0.013), -13±2% (p<0.006) and -6±1% (p=0.020), and peak contact stresses increased by 75±52% (p>0.999), 241±32% (p=0.010) and 61±10% (p=0.021). Between the three different implant designs, the cartilage reverse engineered design yielded the largest contact areas and lowest contact stresses, but was still unable to reproduce the contact mechanics of the native joint. These findings align with a growing body of evidence indicating that although reverse engineered hemiarthroplasty implants can provide small improvements in contact mechanics when compared with commercially available designs, further optimization of shape and material properties is required in order reproduce native joint contact mechanics.

Correlation between dorsovolar translation and rotation of the radius on the distal radioulnar joint during supination and pronation of forearm.

This study aimed to describe the patterns of movements about radius and ulna in individual degrees of forearm rotation. And, we also determined the effect of forearm rotation on translation and rotation of the radius with reference to the ulna, and to measure the relationship between forearm rotation, translation and rotation of the radius. Computed tomography of multiple, individual forearm positions, from 90° pronation to 90° supination, was conducted in 26 healthy volunteers (mean age, 43.9 years) to measure dorsovolar translation and rotation of the radius in the DRUJ in each forearm position. The mean dorsovolar translations were within 1.99 mm at 90° pronation to -2.03 mm at 90° supination. The rotations of the radius were 71.20° at 90° pronation and -46.63° at 90° supination. There were strong correlations between degrees of forearm rotation and dorsovolar translation (r=0.861, p<0.001) and rotation of the radius (r=0.960, p<0.001), suggesting that the DRUJ, carpal joints, and rotatory laxity of the carpal ligament, especially in supination, contribute to forearm supination and pronation. These findings provide an understanding of wrist kinematics, are may be useful in reconstructive wrist surgery to achieve normal range of motion, and are may be helpful for the design of DRUJ reconstruction using prostheses.

Force variations in the distal radius and ulna: effect of ulnar variance and forearm motion.

PURPOSE: To better define normal wrist joint forces during wrist motion and forearm motion at specific wrist and forearm positions and to see if there is a relationship between these forces and the amount of ulnar variance. A secondary purpose was to determine the relationship between the thickness of the articular disk of the triangular fibrocartilage complex and the amount of force transmitted through the distal ulna. METHODS: Multi-axis load cells were attached to the distal radius and ulna of 9 fresh cadaver forearms. The axial radial and ulnar compressive forces were recorded while each wrist was moved through wrist and forearm motions using a modified wrist joint simulator. During each motion, the tendon forces required to cause each motion were recorded. The ulnar variance and triangular fibrocartilage complex articular disc thickness were measured. RESULTS: The axial force through the distal ulna and the wrist extensor forces were greatest with the forearm in pronation. No relationship was found between the amount of force through the distal ulna and the amount of ulnar variance. A strong inverse relationship was found between the triangular fibrocartilage complex thickness and the ulnar variance. CONCLUSIONS: Wrists with positive ulnar variance have generally been thought to transmit greater loads across the distal ulna, which has been felt to predispose these wrists to the development of ulnar impaction. The results of this study appear to show that all wrists have similar loading across the distal ulna regardless of ulnar variance. By comparison, pronation relatively increases loading across the distal ulna. CLINICAL RELEVANCE: Because these results suggest that within reasonable ranges of ulnar variance loading across the distal ulna is independent of ulnar variance, the clinically observed incidence of ulnar impaction is more likely the result of increased wear on a thinner and less durable triangular fibrocartilage complex than due to increased distal ulna loading in ulnar positive variant wrists.

Effect of elbow flexion angles on stress distribution of the proximal ulnar and radius bones under a vertical load: measurement using resistance strain gauges.

OBJECTIVES: This study aimed to explore the surface stress at the proximal ends of the ulna and radius at different elbow flexion angles using the resistance strain method. METHODS: Eight fresh adult cadaveric elbows were tested. The forearms were fixed in a neutral position. Axial load increment experiments were conducted at four different elbow flexion angles (0°, 15°, 30°, and 45°). Surface stain was measured at six sites (tip, middle, and base of the coronoid process; back ulnar notch; olecranon; and anterolateral margin of the radial head). RESULTS: With the exception of the ulnar olecranon, the load-stress curves at each measurement site showed an approximately linear relationship under the four working conditions studied. At a vertical load of 500 N, the greatest stress occurred at the middle of the coronoid process when the elbow flexion angles were 0° and 15°. When the flexion angles were 30° and 45°, the greatest stress occurred at the base of the coronoid process. The stress on the radial head was higher than those at the measurement sites of the proximal end of the ulna. CONCLUSION: The resistance strain method for measuring elbow joint surface stress benefits biomechanics research on the elbow joint. Elbow joint surface stress distributions vary according to different elbow flexion angles.

The proximal and distal position of the radius relative to the ulna through a full range of elbow flexion and forearm rotation.

The purpose of this study was to measure the position of the radius relative to the ulna through a complete range of elbow flexion and forearm rotation. Twenty cadaveric upper extremities were mounted on a testing jig that allowed simultaneous control of elbow flexion and forearm rotation. The longitudinal position of the radius relative to the ulna was measured using a three-dimensional digitizer at full pronation, mid-pronation (45°), neutral (0°), mid-supination (45°) and full supination at 10°, 30°, 60°, 90° and 120° of elbow flexion. Our results showed that the radius is located distally when in supination and is located more proximally as it is rotated into pronation. The longitudinal position of the radius changes over 9 mm when moving through a complete arc of forearm rotation. The angle of elbow flexion had a secondary effect on the longitudinal position of the radius, causing changes of less than 0.8 mm.

A comparison of 3-D computed tomography versus 2-D radiography measurements of ulnar variance and ulnolunate distance during forearm rotation.

Positive ulnar variance is associated with ulnar impaction syndrome and ulnar variance is reported to increase with pronation. However, radiographic measurement can be affected markedly by the incident angle of the X-ray beam. We performed three-dimensional (3-D) computed tomography measurements of ulnar variance and ulnolunate distance during forearm rotation and compared these with plain radiographic measurements in 15 healthy wrists. From supination to pronation, ulnar variance increased in all cases on the radiographs; mean ulnar variance increased significantly and mean ulnolunate distance decreased significantly. However on 3-D imaging, ulna variance decreased in 12 cases on moving into pronation and increased in three cases; neither the mean ulnar variance nor mean ulnolunate distance changed significantly. Our results suggest that the forearm position in which ulnar variance increased varies among individuals. This may explain why some patients with ulnar impaction syndrome complain of wrist pain exacerbated by forearm supination. It also suggests that standard radiographic assessments of ulnar variance are unreliable.