Load relaxation and forces with activity in Hoffman external fixators.
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Biomechanical Phenomena↗
Biomedical subjects
S W Wolfe
Publications and source records attributed to S W Wolfe.
Load-displacement behavior in a distal radial fracture model. The effect of simulated healing on motion.
External fixation of fractures of the distal end of the radius neutralizes external forces and maintains axial alignment during healing. As far as we know, there have been no biomechanical studies of the effects of early removal of the fixator in a partially healed fracture model. The purpose of the present study was to observe the load-displacement behavior of a distal radial fracture model in which we had simulated partial healing by injection of butyl-rubber caulk and augmented this simulated healing with Kirschner-wire fixation. Sixteen fresh-frozen hand-wrist-forearm specimens from cadavera were mounted in mid-rotation in resin pots, and a load was applied. An osteotomy was used to simulate the fracture. Relative motion at the site of the osteotomy was compared, with use of a three-dimensional Optotrak kinematic device, during physiological loading of six constructs with Kirschner-wire transfixion or outrigger fixation. In the experimental group, partial healing was simulated by injection of butyl-rubber caulk into the site of the osteotomy and testing with simulated muscle-loading was performed through a full range of motion of the wrist. No difference could be detected between the relative motion at the osteotomy sites that had been treated with standard fully augmented external fixation and that in the experimental group (p > 0.05). T test analysis revealed that motion was equivalent regardless of whether Kirschner-wire transfixion or outrigger fixation had been used (p = 0.62) and that all of the augmented constructs had significantly less relative motion than all of the nonaugmented constructs (p < 0.001).
Bone Wires↗
Recurrent compartment syndrome of the hand: a case report.
A young man presented with severe symptoms and markedly elevated hand compartment pressures 5 weeks after undergoing successful decompressive fasciotomies for acute compartment syndrome. The patient's initial postoperative course was complicated by reflex sympathetic dystrophy (RSD). It is hypothesized that the vasomotor instability and the periodic vasospastic episodes associated with RSD prompted postischemic swelling and edema and led to the development of this unusual complication.
Adult↗
Augmented external fixation of distal radius fractures: a biomechanical analysis.
An in vitro model of an unstable extra-articular distal radius fracture was created in 8 fresh-frozen cadaveric specimens and stabilized with an external fixator. Rotation and translation kinematics of the distal radial fracture fragment were measured in relation to the proximal radius during physiologic loading, using infrared light-emitting diodes and a 3-dimensional motion-sensing device. The effect of supplemental single and combination Kirschner wire (K-wire) fixation on fracture fragment stability was assessed. Fixation of supplemental K-wires to the fixator frame via a custom-developed outrigger assembly was also analyzed. Significant reductions in sagittal plane (flexion/extension) rotation and neutral zone were recorded when the fracture fragment was stabilized with a single styloid or dorsal transfixion K-wire. Equivalent stability was afforded by attachment of a nontransfixion K-wire to the fixator frame via the outrigger assembly. The dorsal constructs compared favorably to the styloid constructs in reduction of the sagittal plane neutral zone and coronal (radioulnar) rotation. These data lend biomechanical support to the concept of augmentation of distal radius external fixation and provide a physiologic model to test fixation methods for other fracture patterns.
Bone Wires↗
Wide excision of the distal ulna: a multicenter case study.
Excision of the distal ulna to treat degenerative disease or instability has fallen into disfavor following reports of radioulnar impingement, carpal instability, and distal ulnar instability. Alternative procedures for reconstruction of the painful distal ulna have been developed to address these problems; the results have been generally favorable. When faced with distal ulnar reconstruction that has failed after multiple surgical procedures, or a distal ulnar neoplasm, the surgeon is left with few treatment options. Creation of a one-bone forearm, free fibular transfer, and allograft replacement have been attempted, with mixed outcomes. We report the results of 5 men and 7 women who underwent wide excision of the distal ulna, defined as surgical excision of 25% to 50% of the ulnar length. The diagnosis was failed distal radioulnar reconstruction or excision in 8 patients, osteomyelitis in 1, congenital pseudoarthrosis of the radius in 1, and neoplasm in 2. No soft tissue reconstruction was performed. Patients were examined at an average of 22 months after surgery for radiocarpal and radioulnar instability, functional outcome, pain relief, grip strength, and range of motion. Nine of the 12 procedures resulted in good or excellent results; 1 patient had a fair result after resection for osteosarcoma, and the procedure in 2 patients failed, requiring conversion to a one-bone forearm. Grip strength was restored to 75% of the normal side and range of motion was restored to 86% of the normal side. Wide excision of the distal ulna without soft tissue reconstruction is a simple and durable treatment of neoplasms of the distal ulna or salvage of the failed reconstruction of the distal radioulnar joint. We do not recommend its use in patients with incompetency or disruption of the interosseous membrane.
Adult↗
MRI of multiple glomus tumors of the finger.
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Adult↗
A non-invasive method for studying in vivo carpal kinematics.
Seven uninjured and three injured patients were studied using midsagittal computed tomographic (CT) images at 10 degrees increments from full extension to full flexion. Each injured patient had a confirmed scapholunate ligament tear and normal radiographs. CT bony contours were digitized, and incremental motion determined using a specifically designed automated contour-matching algorithm. We expressed wrist motion as a ratio of lunocapitate (midcarpal) motion, and radiolunate (radiocarpal) motion. In normal wrists, motion occurred equally at the midcarpal and radiocarpal joints. In wrists with scapholunate ligament disruption, lunocapitate motion increased significantly throughout the arc of motion.
Adult↗
The effects of exercise on ligamentous stiffness in the wrist.
The purpose of this study was to determine if exercise alters wrist joint laxity, as measured by the mechanical behavior of the scaphoid bone. The load-displacement behavior of the scaphoid was studied in the palmar-dorsal direction in both wrists of 7 healthy volunteers (n = 14) before and after 2 exercise protocols (grip and push-up). When compared to the rested values, both exercise protocols significantly increased the displacement at 40 N by 47% (grip) and by 34% (push-up). Accordingly, the stiffness decreased significantly by 36% (grip) and by 32% (push-up). Partial recovery was documented after 1 hour of rest and there were no differences between any of the groups after 24 hours of rest. The increase in laxity documented during these exercise protocols reduces the ligament loads at comparable wrist positions and may thereby reduce the likelihood of traumatic ligamentous injury during participation in strenuous activity or sports.
Adult↗
Kinematics of the scaphoid shift test.
Twenty-five uninjured subjects (50 wrists) were examined clinically and fluoroscopically during performance of the scaphoid shift test. Wrists were placed into 3 groups on the basis of the degree of palpable carpal motion that occurred during the clinical examination. Kinematic parameters of rotation and displacement were calculated from digitized images of the carpals at rest and at maximum displacement. On clinical exam, 36% of normal individuals had positive findings on scaphoid shift test. Dorsal displacement of the scaphoid was not significantly associated with positive scaphoid shift test results in these subjects, while total displacement of the scaphoid (the sum of axial and dorsal displacement) was significantly associated with positive test results. The principle confounding factor appeared to be a high degree of displacement that occurred at the capitolunate joint in some individuals, termed a "midcarpal shift." The data demonstrate that despite a high prevalence of positive scaphoid shifts among uninjured individuals, the ability to accurately detect dorsal displacement of the scaphoid using the scaphoid shift test is limited. On the basis of their findings, the authors recommend that positive test results be confirmed fluoroscopically.
Adult↗
Detection of nerve rootlet avulsion on CT myelography in patients with birth palsy and brachial plexus injury after trauma.
OBJECTIVE: Recent advances in neurosurgical treatment of traumatic and birth-related brachial plexus injuries require differentiation of preganglionic nerve rootlet avulsion from postganglionic lesions. The purpose of this study was to evaluate the efficacy of thin-section high-resolution CT myelography for revealing cervicothoracic nerve rootlet avulsion in patients with brachial plexus injuries before surgery. MATERIALS AND METHODS: We evaluated eight patients with posttraumatic or birth-related brachial plexus injury on cervical plain film myelography and high-resolution CT myelography before surgical exploration and repair. CT myelograms were retrospectively evaluated for nerve rootlet avulsion, traumatic pseudomeningocele, and deformity of the subarachnoid space. Results were correlated with surgical exploration and intraoperative somatosensory evoked potentials. RESULTS: Seventy-two (95%) of 76 imaged cervicothoracic levels were adequately shown on CT myelography. Nerve rootlet avulsion, or preganglionic disruption, was shown at 21 levels. Associated pseudomeningocele, or deformity of the subarachnoid space, was seen at 12 (57%) of the 21 avulsion levels. Surgical exploration and intraoperative somatosensory evoked potentials showed complete preganglionic nerve rootlet avulsion at 22 levels. One of the complete avulsions revealed by surgery was not included on the patient's CT myelogram. Of the 21 imaged levels, 20 were correctly revealed on CT myelography (95% sensitivity, 98% specificity). At surgery, partial nerve rootlet avulsion was found at three other levels. None of the partial avulsions was correctly identified on the CT myelograms. CONCLUSIONS: High-resolution CT myelography with thin contiguous axial section is sensitive for revealing complete nerve rootlet avulsion in patients with brachial plexus birth palsies and brachial plexus injuries after trauma. Preoperative CT myelography in these patients allows a more complete injury evaluation for accurate prognosis and surgical planning.
Adolescent↗
Radiographic progression to dorsal intercalated segment instability.
We present a case of an acute hyper-extension wrist injury that progressed from normal carpal alignment to dorsal intercalated segment instability over a short period of time. Disruption of the scapholunate interosseous and radioscapholunate ligaments was proven arthroscopically, while the intercapsular ligaments were demonstrated to be intact. We have shown that lunate malalignment can occur over time, as secondary lunate ligamentous supports attenuate under abnormal carpal kinetics.
Accidental Falls↗
Two-dimensional rigid-body kinematics using image contour registration.
A method for calculating two-dimensional rigid-body kinematic parameters using shape features is presented. Proposed applications include the noninvasive quantification of planar joint motion in vivo. By using digitized images (computed tomographs, radiographs, etc.) of a bone contour at two positions, the contour curvatures can be 'best-fit' to obtain a one-to-one mapping or registration of the bone images. This produces a dense field of displacement vectors from which planar rigid-body kinematic parameters can be estimated. Accuracy was studied using radiographic images of cadaveric femoral bone. The two motions of pure rotation with a fixed center of rotation and of pure translation were simulated. For pure rotation, error in rotation was independent of the rotation magnitude, with an average (n = 10) error of 0.3 +/- 0.8 degrees. The translation error averaged 0.9 +/- 0.5 mm. For pure translation, the error in rotation was -0.01 +/- 0.69 degrees and the error in translation was -0.62 +/- 0.98 mm (n = 10). This novel method has broad applications in the field of planar kinematics, especially in cases for which marker fixation is neither possible nor practical.
Algorithms↗
Arthroscopic-assisted reduction of distal radius fractures.
The outcomes of seven patients with severe comminuted intraarticular fractures of the distal radius treated by arthroscopic reduction and percutaneous external fixation (ARPEF) were retrospectively reviewed. All of the fractures were classified as C3 types using the AO classification scheme. Outcomes were evaluated using the Gartland and Werley functional criteria, an objective wrist examination, a radiographic analysis, and a self-assessment outcome form at an average follow-up of 27 months (range, 12 to 45 months). All patients were free of pain and had returned to their prior occupations. No patient had articular incongruency of greater than 1 mm, and there was no evidence of radiocarpal degenerative change. Active range of motion and maximal grip strength averaged 92% and 98%, respectively, of the uninjured wrist. The technique of arthroscope-assisted reduction and percutaneous external fixation yielded excellent results in a small group of patients, with minimal complications.
Adult↗
Safety and efficacy of percutaneous trigger finger release.
Twenty-five A1 pulleys in 5 fresh cadaveric hands and 13 trigger fingers in 11 patients were released percutaneously with a 19 gauge needle, as described by Eastwood et al., to determine the efficacy and safety of the technique. Over 90% of the length of each individual finger and thumb A1 pulley were successfully released in the cadaveric digits with no injuries to the A2 pulley, nerves, or vessels. Superficial abrasions were noted in four superficialis tendons. In our surgical series, complete clinical release (eradication of triggering) was achieved in each digit. In 8 of 13 digits, the A1 pulley was found to be completely divided on open exploration. In five digits, while triggering was eliminated, some of the A1 pulley remained intact. There were no complications. Because of the proximity of digital nerves, we do not perform percutaneous release in the index finger or thumb.
Adult↗
Intra-articular impaction fractures of the phalanges.
Six patients with acute impacted fractures of the base of the proximal or middle phalanges were treated with open reduction and internal fixation. Two of three patients who presented with chronic injuries also underwent surgical reconstruction. Contiguous 1.5-mm sagittal computed tomographic imaging was performed on each proximal interphalangeal joint fracture; the imaging documented an average impaction of 30% of the articular surface area. Metaphyseal bone grafting was necessary to support the articular surface in three acute and both late patients. Rigid internal fixation, most frequently employing a composite wire tension band technique, allowed immediate postoperative range of motion exercises. At an average follow-up period of 21 months, all six acute patients had restoration of an excellent painless range of motion. There was no loss of articular congruency on final x-ray films. Late or conservative treatment of these injuries was uniformly less successful.
Accidental Falls↗
Optimal marker placement for calculating the instantaneous center of rotation.
A computer simulation with error propagation was performed to determine the optimal placement of marker points for calculating the instantaneous center of rotation (CRi). The authors assume that planar rigid body motion occurs between two positions, each defined by marker points. Noisy marker points were generated by perturbing their coordinates with random values from a normal population of errors. The effects of these errors on the range of errors in calculating CRi location were investigated. Parametric analysis determined that marker point placement had important effects on CRi error. Marker placement was optimal when the estimated CRi was located at the midpoint between the marker points. While increasing the distance between marker points increased accuracy, there is a critical distance above which no additional increase in accuracy was noted when using this placement. The farther the marker midpoint was from the CRi, the greater was the error. At these placements, increasing the distance between the marker points continually decreased CRi error. The methodologies presented here help to improve the accuracy with which the location of the CRi can be calculated. However, it is emphasized that the CRi remains sensitive to noise and investigations should apply this kinematic parameter knowingly.
Biomechanical Phenomena↗
Mechanical evaluation of the scaphoid shift test.
Manipulative examination of the carpal bones is an important facet of the examination of the wrist. Abnormal translation of portions of the carpus in response to applied force is a commonly used clinical indicator of ligament injury. Unilateral scaphoid hypermobility during the so-called scaphoid shift test is felt to represent traumatic instability, especially in the context of wrist injury. The test, however, is subjective, and requires considerable experience to correlate the degree of scaphoid mobility with pathologic significance. We used an instrument that quantifies the load-displacement behavior of the scaphoid and its supporting ligaments during application of a dorsally directed load at the scaphoid tubercle. We evaluated 18 uninjured (normal) wrists with clinical ligament examination and with mechanical testing. Subjects who exhibited a positive scaphoid shift had significantly increased displacement and significantly decreased stiffness when compared with subjects who did not have a shift.
Adult↗
Septic arthritis in a normal interphalangeal joint following a dental procedure.
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Adult↗