Ernest W. April
Columbia University
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Featured researches published by Ernest W. April.
Arthroscopy | 1990
Louis U. Bigliani; Robert M. Dalsey; Peter D. McCann; Ernest W. April
The course of the suprascapular nerve and its distance from fixed scapular landmarks were measured in 90 cadaveric shoulders. In an additional 15 cadavers, three pins were passed at various angles in a general anterior-posterior direction through the middle of the glenoid neck just inferior and lateral to the base of the coracoid process. The distance between the exit site on the posterior glenoid neck and the suprascapular nerve at the base of the scapular spine was recorded for each pin. Inferiorly directed pins were the furthest from the suprascapular nerve and averaged 16 mm. On the basis of these data, a relative safe zone is described in the posterior glenoid neck. Knowledge of the anatomic course of the suprascapular nerve may aid the physician in the diagnosis and treatment of suprascapular neuropathies. Appreciation of the safe zone may help the shoulder surgeon avoid iatrogenic injury to the suprascapular nerve during arthroscopic Bankart procedures and other open surgical procedures requiring dissection of the posterior glenoid neck.
Spine | 2009
Brian W. Su; Paul Kim; Thomas D. Cha; Joseph H. Lee; Ernest W. April; Mark Weidenbaum; Alexander R. Vaccaro
Study Design. An anatomic study that describes the relationship of the pedicle center to the mid-lateral pars (MLP) in the lower lumbar spine as a guide to pedicle screw placement. Objective. Describe morphometric data of the lower lumbar pedicles, the unique coronal pedicle footprints of L4 and L5, and their impact on the relationship of the pedicle center to the MLP. Summary of Background Data. Traditional medial-lateral starting points for lumbar pedicle screws use the facet as an anatomic reference for all lumbar levels. The facet is often a difficult landmark to use secondary to degenerative changes and the desire to minimize damage to the facet capsule in the most cephalad level. These techniques can also result in pedicle violation particularly in the lower lumbar spine. Use of the nonarthritic MLP is proposed in this study as an alternative anatomic reference point for the pedicle center. Methods. Seventy-two pedicles (L3–S1) from embalmed cadaveric spines were used. Linear and angular dimensions of the pedicle were measured, including the degree of coronal pedicle tilt of L4 and L5. The center of the pedicle relative to the MLP and relative to the midline of the base of the transverse process was measured. The axial superior facet angle and angle of pedicle screw insertion were also measured. Results. The minimum pedicle width was 10.9 and 12.4 mm and the coronal pedicle tilt was 36° and 55° for L4 and L5, respectively. A classification of 2 types of L5 pedicles relevant to pedicle center location was developed. In the medial-lateral direction, the pedicle center is 2.9 mm lateral to the MLP at L3 and L4. At L5, it is 1.5 and 4.5 mm lateral to the MLP for a type I and type II pedicle, respectively. In the superior-inferior direction, the pedicle center is 1 mm superior to the midline of the transverse process base for all lower lumbar levels. Significant differences between a type I and II L5 pedicle were a larger pedicle width and distance of the pedicle center to the MLP for a type II pedicle. The difference between the axial pedicle screw insertion angle and anatomic superior facet angles was 8° from L4–S1. Conclusion. The MLP is a reliable anatomic reference point for the center of the pedicle in the lower lumbarspine. Consideration needs to be taken when inserting pedicle screws at L4 and L5 because of the degree of their coronal tilts and unique pedicle footprints. It is important to distinguish a type I from type II L5 pedicle as a type II pedicle is wider, has a more lateral pedicle center relative to the MLP, and has the potential for lateral screw placement while still remaining within the pedicle.
Pflügers Archiv: European Journal of Physiology | 1986
Ernest W. April; David W. Maughan
Filament spacing is shown to have a pronounced effect on active force in skinned striated muscle fibers of crayfish. At constant filament overlap and constant ionic strength, the separation between the myofilaments (measured by low-angle X-ray diffraction) was adjusted by application of osmotic pressure. Force was induced by a calcium-containing activating solution. In the absence of compression, calcium-activated force in skinned fibers was approximately 80% of that in normal intact fibers. In fibers compressed somewhat beyond the dimension of intact fibers, force was maximal. With further compression, force was reduced and then abolished. The filament spacing-force relation reported here suggests that, at any instant, the distance between the myosin filaments and actin filaments affects either (a) the axial force per cross bridge or, more likely, (b) the number of cross bridges in the force-generating state.
Spine | 2009
Brian W. Su; Thomas D. Cha; Paul Kim; Joseph H. Lee; Ernest W. April; Mark Weidenbaum; Todd J. Albert; Alexander R. Vaccaro
Study Design. An anatomic study of lumbar facet anatomy for transfacet fixation. Objective. Describe the ideal starting point and trajectory for percutaneous transfacet fixation. Summary of Background Data. Percutaneous transfacet fixation is gaining popularity for posterior stabilization after anterior lumbar interbody fusion. Despite biomechanical and clinical studies, there are no anatomic guidelines for safe placement of percuatenous transfacet screws. Methods. Eighty L3-S1 facet joints from embalmed cadaveric spines were analyzed. Linear and angular measurements of the facets were recorded. Under direct visualization, the segments were pinned with an ipsilateral transfacet technique. The degrees of angulation in the sagittal and axial plane were recorded. The distances of the starting point relative to landmarks of the superior body were measured. Under fluoroscopy, radiographic parameters for ideal visualization of the pin and pin ending points were determined. Results. Inferior and superior facet heights ranged from 15.7 to 17.5 mm at all levels. The percentage of inferior facet extending below the L3 and L4 end plates was 84% and 86% respectively and decreased at L5 to 72%. The percentage of superior facet extending above the end plate ranged from 36% to 44% at all levels. The transverse facet angle progressively increased from L3 to S1. The L2-L3 segments could not be instrumented from the ipsilateral side due to the vertical facet orientation. For L3-S1 segments, the starting point in the coronal plane is based on the superior body of the instrumented segment and should be in line with the medial border of the pedicle in the medial-lateral direction and in line with the inferior end plate in the cranial-caudal direction. The screw should be laterally angulated approximately 15° in the axial plane approximately 30° caudally in the sagittal plane. The screw should end in the inferolateral quadrant of the pedicle on the AP radiograph and at the pedicle-vertebral body junction on the lateral radiograph. 35° of axial rotation is the optimal fluoroscopic view for confirming screw placement. Conclusion. Ipsilateral transfacet fixation can be successfully performed in the L3-S1 segments by using the inferior end plate and medial pedicle wall of the superiorly instrumented level as anatomic landmarks in conjunction with axial and sagittal angles of insertion.
Molecular Crystals and Liquid Crystals | 1981
Raymond J. Hawkins; Ernest W. April
Abstract Low-angle X-ray diffraction measurements of the distance between myosin filaments comprising the smectic B1 liquid crystal found in skinned crayfish striated muscle were made. The interfilament distanceas a function of applied compressive osmotic pressure wasdetermined and the bulk modulus of this myofilament liquid crystal ascertained. Under compression the behavior of this myosin filament lattice is shown to be predicted well by the Murnaghan equation of state. The isothermal bulk modulus, B o, of this myosin filament liquid crystal is 1.51 × 105 dynes/cm2 at 2°C and at 46% actin overlap.
Journal of the Neurological Sciences | 1979
Dallas L. Pulliam; Ernest W. April
The ultrastructure at the neuromuscular junction (NMJ) of red, white, and intermediate skeletal muscle fibers undergoes specific changes following either unilateral severance of the phrenic nerve or unilateral topical treatment of the phrenic nerve with colchicine. Both procedures were performed in the cervical region and produce similar rates of muscle fiber degeneration. The severity of degeneration appears to be related to muscle fiber type with white fibers being most severely affected and red fibers least affected. Degeneration rates of the axon terminal also correlate with fiber type in the orderwhite, intermediate, red. However, the rates of degeneration of the specific axon terminals are more rapid with surgical severance than with colchicine treatment. Statistical analysis of morphometric data indicates that hemidiaphragms denervated surgically exhibited significant axon terminal degeneration before significant muscle degeneration. Conversely, diaphragmatic muscle fibers of colchicine-treated phrenic nerves exhibit significant degeneration before loss of the axon terminal. Despite reversal of the temporal sequences for loss of axonal and muscular components between the two preparations, degenerative characteristics of muscle fiber structure are similar. This suggests that the presence of fiber-specific neurotrophic substances transmitted from the neuronal cell body to the axon terminal and released at the NMJ may be an important factor in the maintenance of normal muscle fiber morphology.
Molecular Crystals and Liquid Crystals | 1983
Raymond J. Hawkins; Ernest W. April
Abstract The osmotically produced planar deformation behavior of skinned striated muscle fibers (smectic B, lattice microstructure) is investigated using light microscopy and compared with analogous results determined using x-ray diffraction. The nonlinear pressure-volume relationship measured using light microscopy is shown to be essentially the same as that resultant of similar experiments using x-ray diffraction. The application of a continuum analysis based on the Murnaghan equation of state to this deformation behavior is examined. The Murnaghan equation is shown to approximate well the nonlinear planar deformation behavior of these muscle fibers.
Archive | 1986
Ernest W. April; Robert A. Aldoroty
Electrochemical potentials (measured with microelec-trodes) in the liquid-crystalline lattices of striated muscle result from Donnan equilibriums established by the fixed charge associated with the myosin rods and actin filaments in the ionic cytosol. From these electrochemical potentials and the unit-cell volumes (measured by x-ray diffraction) together with Donnan theory, the effective linear charge densities are derived for the respective myosin rods and actin filaments. Electrochemical potentials also were measured under conditions that varied the parameters of the Donnan equation. Modeling predicted Donnan potentials for the same conditons. The predicted Donnan potentials correlate well with the measured electrochemical potentials for both the A-band and I-band liquid-crystalline lattices.
Journal of Cell Biology | 1972
Ernest W. April; Philip W. Brandt; Gerald F. Elliott
Nature | 1968
Ernest W. April; Philip W. Brandt; John P. Reuben; Harry Grundfest