Bilateral Ulnar Deviation Supination Stress Test to Assess Dynamic Scapholunate Instability.

PURPOSE: We describe a new radiologic test to assess the integrity of the scapholunate ligament in dynamic scapholunate dysfunction. METHODS: A bilateral forearm-holding device was designed to perform a comparative radiographic assessment of the scapholunate joint gap during resisted isometric contraction of the extensor carpi ulnaris muscle with full supination of the forearm. The concept is based on the known scaphoid pronation effect of this muscle. Clinical data from 12 patients were collected retrospectively and used to analyze the patients' symptomatic and asymptomatic (contralateral) wrists with a newly developed test called the Bilateral Ulnar Deviation Supination (BUDS) test. A wrist arthroscopy was performed in all cases as a reference standard for the radiologic test. RESULTS: The test was positive in 7 patients, with a mean scapholunate joint gap of 4.8 mm. The mean differences in the scapholunate joint gaps between both wrists were 2.6 mm in BUDS-positive patients and 0.2 mm in BUDS-negative patients. A Geissler stage III or IV scapholunate ligament rupture was confirmed in all BUDS-positive patients; by contrast, BUDS-negative patients exhibited either no lesion or a Geissler stage I injury. CONCLUSIONS: The BUDS test is a new radiologic test based on proven biomechanical effects that is able to accurately assess dynamic scapholunate dysfunctions. The analysis carried out found a correlation between radiographic and arthroscopic findings. Further research is needed to confirm the validity and reliability of the test. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic III.

The effect of orthoses on the kinematics of the trapeziometacarpal, scaphotrapeziotrapezoidal, and radioscaphoid joints.

The in vivo effect of four different types of thumb and thumb-wrist orthoses on the three-dimensional kinematics of the trapeziometacarpal (TMC), scaphotrapeziotrapezoidal (STT) and radioscaphoid joints was quantified using computed tomography (CT). Eighteen healthy female volunteers were recruited. The dominant hand of each subject was scanned in four thumb and wrist positions, each in three conditions: without orthosis, with a thumb orthosis (Push Ortho and immediate fitting, IMF) and with a thumb-wrist orthosis (Ligaflex Manu and IMF). CT images were analyzed and rotations relative to the more proximal bone were expressed in a joint-specific coordinate system. Without orthosis, the largest STT rotations were observed during radioulnar deviation of the wrist and the STT range of motion (ROM) was significantly lower during wrist flexion-extension. All tested orthoses caused a significant reduction of the ROM at each joint compared to free motion. Significant differences in movement reduction were observed between prefabricated and IMF orthoses.The IMF thumb-wrist outperformed the Ligaflex Manu in terms of immobilization of the radioscaphoid joint. In addition, the IMF thumb orthosis immobilized the TMC joint significantly better during thumb abduction and adduction than the Push Ortho. We found that different types of thumb and thumb-wrist orthotics are effective in reducing joint mobility. While this reduction tends to be higher using IMF compared to prefabricated orthoses, this effect is only significant for the radioscaphoid and TMC joint. The finding that thumb movements do not induce large STT rotations suggests that the thumb does not need to be immobilized in case of isolated STT osteoarthritis.

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.

The Use of Contact Biomechanics to Study the Intact, Proximal Row Carpectomy and Scaphoid Excision, Four Bone Fusion Wrist.

The study of contact biomechanics of the wrist is a challenge. This is partly due to the relatively small size of the joint as well as the lack of space in the radiocarpal joint which makes the delivery of investigative materials such as pressure sensitive film without causing artifact, difficult. Fortunately, a number of authors have studied the intact wrist, the scapholunate ligament injured wrist, the proximal row carpectomy and the scaphoid excision, four bone fusion. Despite some contrasting findings, there are some general concepts that we understand about wrist mechanics.

The Effect of Lunate Morphology in Carpal Disorders: Review of the Literature.

Variation in lunate morphology can exist based on the absence (Type I) or presence (Type II) of medial facet on the distal articular surface of the lunate that contacts the proximal pole of the hamate. This additional lunatohamate articulation can affect load transmission across the radiocarpal joint and exert an influence on carpal kinematics. A Type II lunate is protective against carpal instability patterns associated with scaphoid nonunions and scapholunate dissociations. It may also play a role in the progression of carpal collapse that occurs in Kienböck disease. This review summarizes the effect of lunate morphology in the outcomes of non-operative and operative treatment of carpal disorders.

Computer Modelling of Wrist Biomechanics: Translation into Specific Tasks and Injuries.

BACKGROUND: The carpus is a complicated and functionally challenged mechanical system, advancements in the understanding of which have been compromised by the recognition that there is no standard carpal mechanical system and no typical wrist. This paper covers components of a larger project that seeks to develop a kinetic model of wrist mechanics to allow reverse analysis of the specific biomechanical controls or rules of a specific patient's carpus. Those rules, unique to each patient, could be used to create a forward synthesis mathematical model to reproduce the individual's anatomical motion in a virtual environment. OBJECTIVE AND METHODS: Based on the previous observations, the carpus essentially moves with only two degrees of freedom-pitch (flexion/extension) and yaw (radial deviation/ulnar deviation)-while largely preventing roll (pronation/supination). The objective of this paper is, therefore, to present the background and justification to support the rules-based motion (RBM) concept, which states that the motion of a mechanical system, such as the wrist, is the net interplay of four rules: morphology, constraint, interaction, and load. The stable central column theory (SCCT) of wrist mechanics applies the concept of RBM to the carpus, and by using a reverse engineering computational analysis model, a consistent pattern of isometric constraints was identified, creating a "two-gear four-bar" linkage. This study assessed the motion of the carpus using a 3D (three-dimensional) dynamic visualization model. The hypothesis was that the pattern and direction of motion of the proximal row and the distal row with respect to the immediately cephalad carpal bones or radius would be similar in all directions of wrist motion. To identify the unique motion segments, 3D models were created from five normal wrists that underwent CT scanning in multiple positions of radial and ulnar deviation as well as flexion and extension. Each carpal row (proximal and distal) was animated in a virtual environment with the cephalad carpal bones or radius held immobile. The rotational axis and position of each bone and each row were then compared in sagittal (flexion-extension) and coronal (radial and ulnar deviation) motion. RESULTS: The carpus appeared to have only two degrees of freedom, and yet was stable in those arcs with the loads applied proximally in the forearm. The proximal row moved in a singular arc, but with a varying extent during sagittal and coronal motion. The isometric constraints were consistent in both directions. The distal row moved on an axis formed by a pivot joint laterally (between the trapezium and scaphoid) and a saddle joint medially (between hamate and triquetrum). The sagittal and coronal alignment of this axis changed as the proximal row moved. This created a distinct pattern of row motion to achieve the various required positions of wrist function. On wrist radial deviation, the scaphoid (with the proximal row) was flexed and the distal row was extended, whereas, in wrist flexion, the scaphoid flexed (with the proximal row) and so did the distal row. The pattern was reversed in the opposite wrist movements. While the general direction of motion of each row was consistent, the extent was quite variable. CONCLUSION: This review supports the SCCT of carpal mechanics and the carpus acting as a twogear four-bar linkage, as well as the concept of RBM as a means to understand the biomechanics of the wrist, and how this is translated into specific functional tasks. More sophisticated 3D modelling will be required to further understand the specifics of carpal motion; however, reverse engineering of the specific rules that define each individual wrist can also be applied to a mathematical model to provide a "what if" test of particular surgical interventions for a variety of wrist injuries. The use of quantitative 3D Computed Tomography Scan (CT) analysis, surgical planning and virtual surgical intervention allows potential surgical solutions to be applied to a computer model of an injured wrist to test the possible outcomes and prognosis of a proposed treatment.

Real-time three-dimensional MRI for the assessment of dynamic carpal instability.

BACKGROUND: Carpal instability is defined as a condition where wrist motion and/or loading creates mechanical dysfunction, resulting in weakness, pain and decreased function. When conventional methods do not identify the instability patterns, yet clinical signs of instability exist, the diagnosis of dynamic instability is often suggested to describe carpal derangement manifested only during the wrist's active motion or stress. We addressed the question: can advanced MRI techniques provide quantitative means to evaluate dynamic carpal instability and supplement standard static MRI acquisition? Our objectives were to (i) develop a real-time, three-dimensional MRI method to image the carpal joints during their active, uninterrupted motion; and (ii) demonstrate feasibility of the method for assessing metrics relevant to dynamic carpal instability, thus overcoming limitations of standard MRI. METHODS: Twenty wrists (bilateral wrists of ten healthy participants) were scanned during radial-ulnar deviation and clenched-fist maneuvers. Images resulting from two real-time MRI pulse sequences, four sparse data-acquisition schemes, and three constrained image reconstruction techniques were compared. Image quality was assessed via blinded scoring by three radiologists and quantitative imaging metrics. RESULTS: Real-time MRI data-acquisition employing sparse radial sampling with a gradient-recalled-echo acquisition and constrained iterative reconstruction appeared to provide a practical tradeoff between imaging speed (temporal resolution up to 135 ms per slice) and image quality. The method effectively reduced streaking artifacts arising from data undersampling and enabled the derivation of quantitative measures pertinent to evaluating dynamic carpal instability. CONCLUSION: This study demonstrates that real-time, three-dimensional MRI of the moving wrist is feasible and may be useful for the evaluation of dynamic carpal instability.

Computational Simulation of Synovial Fluid Kinematics of the Scapholunate Joint.

Background: The interaction between wrist kinematics and synovial fluid pressure has yet to be studied. To our knowledge, this is the first study to determine the effect of scapholunate joint kinematics on synovial fluid pressure change using finite volume method. Methods: The carpal bones of a cadaveric hand were obtained from Computed Tomography (CT) scans. CT images of the carpal bones were segmented and reconstructed into 3D model. The 3D synovial fluid model between the scaphoid and lunate was constructed and then used for computational simulations. The kinematics data of scapholunate joint obtained from radioulnar deviation of the wrist was investigated. Results: It was found that the pressure in synovial fluid varied from -1.68 to 2.64 Pa with maximum pressure located at the scaphoid-fluid interface during the radial deviation. For ulnar deviation, the pressure increased gradually from the scaphoid-fluid interface towards the lunate-fluid interface (-1.37 to 0.37 Pa). Conclusions: This new computational model provides a basis for the study of pathomechanics of ligament injury with the inclusion of synovial fluid.

A four-dimensional-CT study of in vivo scapholunate rotation axes: possible implications for scapholunate ligament reconstruction.

Additional fixation of the palmar scapholunate interosseous ligament has been advocated to improve the long-term results of dorsal scapholunate interosseous ligament reconstruction. To investigate the validity of this approach, we determined normal scapholunate motion patterns and calculated the location of the scapholunate rotation axis. We hypothesized that the optimal location of the scapholunate interosseous ligament insertion could be determined from the scapholunate rotation axis. Four-dimensional computerized tomography was used to study the wrist motion in 21 healthy participants. During flexion-extension motions, the scaphoid rotates 38° (SD 0.6°) relative to the lunate; the rotation axis intersects the dorsal ridge of the proximal pole of the scaphoid and the dorsal ridge of the lunate. Minimal scapholunate motion is present during radioulnar deviation. Since the scapholunate rotation axis runs through the dorsal proximal pole of the scaphoid, this is probably the optimal location for attaching the scapholunate ligament during reconstructive surgery.

The Effect of Radioscapholunate Fusion With and Without Distal Scaphoid and Triquetrum Excision on Capitolunate Contact Pressures.

PURPOSE: To determine the effects of motion-increasing modifications to radioscapholunate (RSL) arthrodesis on capitolunate contact pressure in cadaveric wrist specimens. METHODS: Ten fresh-frozen cadaveric wrists were dissected of all superficial soft tissue, potted in polymethyl-methacrylate, and the carpus exposed via a ligament-sparing capsulotomy. An RSL arthrodesis was simulated using 2 2.4-mm distal radius plates with locking screws. The distal scaphoid pole and triquetrum were removed with an osteotome and rongeur, respectively. Contact area, pressure, and force were measured in the capitolunate joint during the application of a 35-N uniaxial load using pressure-sensitive film. Measurements were obtained before and after simulated RSL fusion, following distal scaphoidectomy and after triquetrectomy. RESULTS: The combination of RSL fusion with distal scaphoid excision (DSE) increased contact forces in the capitolunate joint by 50% over controls. An RSL fusion, and RSL fusion with DSE and triquetrum excision (TE), exhibited intermediate levels of contact force between controls and RSL fusion with DSE. Capitolunate contact pressures were similar between all experimental groups. Contact area in the capitolunate joint increased by 43% after RSL fusion with DSE over intact specimen controls. Lastly, contact area in wrists with RSL fusion, and RSL fusion with DSE and TE, were elevated, but not significantly different from intact controls. CONCLUSIONS: A DSE performed at the time of RSL fusion results in increased midcarpal joint contact force and area, with resultant contact pressures unchanged. Triquetrectomy, which has been previously shown to improve range of motion, did not increase contact forces in the capitolunate joint. CLINICAL RELEVANCE: If a surgeon is contemplating performing an RSL arthrodesis with DSE, we recommend adding a triquetrectomy to improve motion because this does not add to the potentially deleterious effects of increased midcarpal contact force.

A composite 3D printed model of the midcarpal joint.

Three-dimensional (3D) printing has recently been developed as a resource for teaching human anatomy through the accurate reproduction of anatomical specimens. Using a composite 3D printed model with the incorporation of metal and magnets, we were able to demonstrate and analyse movements at the midcarpal joint during the 'dart thrower's motion', which is an important motion in daily activities involving the use of the hand. The hand component with the distal row of carpal bones was subjected to flexion and extension at the midcarpal joint and observed for simultaneous abduction/adduction. Notable adduction was observed in the flexed position as compared to the extended position. Moreover, while the primary movements at the midcarpal joint were taking place in the medial part of the joint, the lateral part of the joint (which is ellipsoid) served to accommodate the arc of movement. We suggest that such composite 3D printed models are useful teaching tools for enhancing the understanding of complex joint movements.

The Effect of Dorsally Angulated Distal Radius Deformities on Carpal Kinematics: An In Vitro Biomechanical Study.

PURPOSE: The purpose was to quantify the effect of distal radius dorsal angulation (DA) on carpal kinematics and the relative roles of the radiocarpal and midcarpal joints during wrist motion. METHODS: Six cadaveric specimens (69 ± 17 y) were mounted at 90° elbow flexion in a custom wrist motion simulator. The wrist was guided through planar passive flexion and extension motion trials (∼ 5°/s). A custom modular distal radius implant was used to simulate native alignment and 3 distal radius DA deformities (10°, 20°, 30°). An optical tracking system captured carpal bone motion, from which radiocarpal and midcarpal joint motion was determined. RESULTS: The radiocarpal joint made a greater contribution to wrist motion than the midcarpal joint in flexion, and the midcarpal joint made a greater contribution to motion than the radiocarpal joint in wrist extension. Increasing DA caused the radiocarpal joint contribution to increase throughout the motion arc, with the effect being more pronounced in wrist flexion. Conversely, as DA increased, the midcarpal joint contributed less rotation to the total wrist motion and its overall motion arc decreased; the magnitude of effect was greater in wrist extension. Dorsal angulation resulted in increased lunate flexion with respect to the distal radius. CONCLUSIONS: Our findings agree with current literature that suggests that, in an uninjured wrist, the radiocarpal joint predominates flexion, and the midcarpal joint predominates extension. In addition, the radiocarpal joint has an amplified contribution in wrist flexion with greater DA malunion. CLINICAL RELEVANCE: The altered contributions of the radiocarpal and midcarpal joints may contribute to pain, stiffness, and the development of arthritis, which is commonly seen at the radiocarpal joint after malunion of the distal radius.

Reduction of the A-Frame Angle of Incline does not Change the Maximum Carpal Joint Extension Angle in Agility Dogs Entering the A-Frame.

OBJECTIVE: This article aims to investigate the effect of a decrease in the A-frame angle of incline on the highest carpal extension angle in agility dogs. METHODS: Kinematic gait analysis (two-dimensional) measuring carpal extension was performed on 40 dogs entering the A-frame at 3 angles of incline: 40° (standard), 35° and 30°. The highest carpal extension angle from three trials at each incline was examined for a significant effect of A-frame angle with height, body weight and velocity included as covariates. RESULTS: There was no significant effect of A-frame angle on the highest carpal joint extension angle for the first or second limb. The adjusted mean carpal extension angle for the first limb at 40° was 64° [95% confidence interval (CI), 60-68), at 35° was 61° (95% CI, 57-65) and at 30° was 62° (95% CI, 59-65). The raw mean carpal extension angle for all dogs across all A-frame angles for the first limb was 62° (95% CI, 60-64) and the second limb was 61° (95% CI, 59-63). CLINICAL SIGNIFICANCE: Decreasing the A-frame angle of incline from 40° to 30° did not result in reduced carpal extension angles. The failure to find a difference and the narrow CI of the carpal angles may indicate that the physiologic limits of carpal extension were reached at all A-frame angles.

Dynamic CT Scan of the Normal Scapholunate Joint in a Clenched Fist and Radial and Ulnar Deviation.

BACKGROUND: Injuries to the scapholunate can have severe long-term effects on the wrist. Early detection of these injuries can help identify pathology. The purpose of this study was to evaluate the motions of the scapholunate joint in normal wrists in a clenched fist and through radial and ulnar deviation using novel dynamic computed tomography (CT) imaging. METHODS: Fifteen participants below 40 years of age consented to have their wrist scanned. Eight participants were randomized to have the right wrist scanned and 7 the left wrist. Volunteers were positioned at the back of the gantry with the wrist placed on the table, palmar side down. Participants began with the hand in a relaxed fist position and then proceeded through an established range of motion protocol. Dynamic CT imaging was captured throughout the range of motion. RESULTS: The movement in the healthy scapholunate joint through a clenched fist and radial and ulnar deviation is minimal. The averages were 1.19, 1.01, and 0.95 mm, representing the middle, dorsal, and volar measurements, respectively. CONCLUSIONS: This novel dynamic CT scan of the wrist is a user-friendly way of measuring of the scapholunate distance, which is minimal in the normal wrist below 40 years of age.

Kinematic analysis of the thoracic limb of healthy dogs during descending stair and ramp exercises.

OBJECTIVE To compare the kinematics of the thoracic limb of healthy dogs during descent of stairs and a ramp with those during a trot across a flat surface (control). ANIMALS 8 privately owned dogs. PROCEDURES For each dog, the left thoracic limb was instrumented with 5 anatomic markers to facilitate collection of 2-D kinematic data during each of 3 exercises (descending stairs, descending a ramp, and trotting over a flat surface). The stair exercise consisted of 4 steps with a 35° slope. For the ramp exercise, a solid plank was placed over the steps to create a ramp with a 35° slope. For the flat exercise, dogs were trotted across a flat surface for 2 m. Mean peak extension, peak flexion, and range of movement (ROM) of the shoulder, elbow, and carpal joints were compared among the 3 exercises. RESULTS Mean ROM for the shoulder and elbow joints during the stair exercise were significantly greater than during the flat exercise. Mean peak extension of the elbow joint during the flat exercise was significantly greater than that during both the stair and ramp exercises. Mean peak flexion of the elbow joint during the stair exercise was significantly greater than that during the flat exercise. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that descending stairs may be beneficial for increasing the ROM of the shoulder and elbow joints of dogs. Descending stair exercises may increase elbow joint flexion, whereas flat exercises may be better for targeting elbow joint extension.

Length Changes in Scapholunate Interosseous Ligament With Resisted Wrist Radial and Ulnar Inclination.

PURPOSE: To investigate the changes in length of the scapholunate interosseous ligament (SLIL) when the wrist is resisting horizontal lateral load and the forearm is in full pronation in vivo. METHODS: We obtained computed tomography scans of the wrists of 6 volunteers in 3 situations: 0° position (0° extension and 0° ulnar inclination) and full forearm pronation without force, and in the same position but with resisted ulnar and radial deviation. Nine zones of 3 subregions of the SLIL were measured and analyzed with computer modeling. RESULTS: Changes in length of the palmar SLIL with resisted ulnar deviation were significantly greater than those without an applied lateral load. In contrast, the changes in length of the dorsal SLIL with resisted radial deviation were statistically greater than those in the 0° position without loading. However, no significant differences in the changes in length of the proximal SLIL were found in any of 3 situations, except the dorsal zone with resisted radial deviation. CONCLUSIONS: Application of lateral load has an effect on the separation of the palmar and dorsal insertions of the SLIL. The palmar subregion of the SLIL was more highly strained with wrist-resisted ulnar deviation. Conversely, the dorsal subregion of the SLIL was under greater tension with wrist-resisted radial deviation. CLINICAL RELEVANCE: For patients undergoing nonsurgical treatment of SLIL tears, a sudden contraction of ulnar or radial deviation agonist muscles may be harmful and contribute to SL instability.

Relative Contributions of the Midcarpal and Radiocarpal Joints to Dart-Thrower's Motion at the Wrist.

PURPOSE: To identify the relative contributions of the radiocarpal (RC) and midcarpal (MC) joints to dart-thrower's motion (DTM) of the wrist. METHODS: Six cadaveric upper extremities were fixed to a custom-designed loading jig allowing for pure moment-rotation analysis in 24 different directions of wrist motion. Each specimen was tested in 3 states: intact, simulated radiocarpal fusion (sRCF) and simulated pancarpal fusion (sPCF). Moments of ± 1.5 Nm were applied at each of 24 directions for each state and the resulting wrist rotation recorded. Data from each specimen were reduced to compute the range of motion (ROM) envelopes and the orientation of the ROM for the 3 different states. RESULTS: The ROM was significantly decreased in the sRCF and sPCF groups compared with the intact group in the directions of the pure extension, radial extension, ulnar flexion, and ulnar deviation. No significant difference in ROM was detected between the sRCF and sPCF groups in any direction. The ROM envelopes for the intact, sRCF, and sPCF groups were all oriented obliquely to the axis of pure wrist flexion-extension near a path of ulnar flexion-radial extension, consistent with prior reports on DTM. CONCLUSIONS: Although both simulated fusion types decreased ROM compared with the intact wrist, the principal direction of wrist motion along the path of DTM was not significantly altered by simulated RCF or PCF. CLINICAL RELEVANCE: These findings suggest that the RC and MC joints can each contribute to a similar mechanical axis of motion located along the path of DTM when the other joint has been eliminated via fusion. Surgical options such as partial wrist fusions may maintain the native wrist's mechanical axis if either the RC or the MC joint is preserved, despite significant reduction in overall ROM.

Decoupling the Wrist: A Cadaveric Experiment Examining Wrist Kinematics Following Midcarpal Fusion and Scaphoid Excision.

At the wrist, kinematic coupling (the relationship between flexion-extension and radial-ulnar deviation) facilitates function. Although the midcarpal joint is critical for kinematic coupling, many surgeries, such as 4-corner fusion (4CF) and scaphoidexcision 4-corner fusion (SE4CF), modify the midcarpal joint. This study examines how 4CF and SE4CF influence kinematic coupling by quantifying wrist axes of rotation. Wrist axes of rotation were quantified in 8 cadaveric specimens using an optimization algorithm, which fit a 2-revolute joint model to experimental data. In each specimen, data measuring the motion of the third metacarpal relative to the radius was collected for 3 conditions (nonimpaired, 4CF, SE4CF). The calculated axes of rotation were compared using spherical statistics. The angle between the axes of rotation was used to assess coupling, as the nonimpaired wrist has skew axes (ie, angle between axes approximately 60°). Following 4CF and SE4CF, the axes are closer to orthogonal than those of the nonimpaired wrist. The mean angle (±95% confidence interval) between the axes was 92.6° ± 25.2° and 99.8° ± 22.0° for 4CF and SE4CF, respectively. The axes of rotation defined in this study can be used to define joint models, which will facilitate more accurate computational and experimental studies of these procedures.

Carpal Kinematics and Kinetics.

The complex interaction of the carpal bones, their intrinsic and extrinsic ligaments, and the forces in the normal wrist continue to be studied. Factors that influence kinematics, such as carpal bone morphology and clinical laxity, continue to be identified. As imaging technology improves, so does our ability to better understand and identify these factors. In this review, we describe advances in our understanding of carpal kinematics and kinetics. We use scapholunate ligament tears as an example of the disconnect that exists between our knowledge of carpal instability and limitations in current reconstruction techniques.

Effect of Regional Intravenous Limb Perfusate Volume on Synovial Fluid Concentration of Amikacin and Local Venous Blood Pressure in the Horse.

OBJECTIVE: To determine the effect of volume of amikacin perfusate for intravenous regional limb perfusion (IVRLP) via the cephalic vein in standing, sedated horses on (1) amikacin concentrations in the synovial fluid of the radiocarpal joint (RCJ) and distal interphalangeal joint (DIPJ) and, (2) amikacin concentration in the systemic circulation, and (3) regional intravenous pressure. STUDY DESIGN: Randomized cross-over design. ANIMALS: Six adult horses. METHODS: Each horse received IVRLP using 4 perfusate volumes (10, 30, 60 & 120 ml) in random order, after a minimum of 1 week washout. After application of a pneumatic tourniquet, IVRLP with 1 g of amikacin in 0.9% NaCl was performed. Synovial fluid from the RCJ and DIPJ, and systemic and regional venous blood were sampled, and regional blood pressure was measured, immediately before perfusion (time 0), and 15 and 30 minutes after perfusion but before tourniquet release. RESULTS: No difference was observed in the mean amikacin concentration of synovial fluid for the 4 perfusate volumes (P>.09). For all volumes, mean amikacin concentration for DIPJ synovial fluid was higher than for RCJ (P<.0001). The mean amikacin concentration in DIPJ synovial fluid was therapeutic for resistant pathogens using the 10, 60, and 120 mL volumes but the mean amikacin concentration for RCJ synovial fluid was not therapeutic for resistant pathogens with any perfusate volume. All volumes resulted in an immediate increase in mean regional intravascular pressure after perfusion (P<.0001) but was not different across the 4 perfusate volumes. CONCLUSION: Cephalic IVRLP of 1 g of amikacin diluted to a volume of 10-120 mL with 0.9% NaCl will achieve amikacin concentrations therapeutic for resistant pathogens in the synovial fluid from the DIPJ. Concentrations below therapeutic levels for resistant pathogens are reached in the synovial fluid from the RCJ.