Alejandro A. Espinoza Orías

Anterior Cruciate Ligament Reconstruction: Can Anatomic Femoral Placement Be Achieved With a Transtibial Technique?

Background: Recent reports have suggested that a traditional transtibial technique cannot practically accomplish an anatomic anterior cruciate ligament (ACL) reconstruction. Hypothesis: The degree to which a transtibial technique can anatomically position both tibial and femoral tunnels is highly dependent on tibial tunnel starting position. Study Design: Descriptive laboratory study. Methods: Eight fresh-frozen adult knee specimens were fixed at 90° of flexion and then dissected to expose the femoral and tibial ACL footprints. After the central third patellar tendon length was measured for each specimen, computer-assisted navigation was used to identify 2 idealized tibial tunnel starting points, optimizing alignment with the native ligament in the coronal plane but distal enough on the tibia to provide manageable bone-tendon-bone autograft–tibial tunnel mismatch (point A = 10-mm mismatch; point B = 0-mm mismatch). Tibial tunnels were then reamed to the center of the tibial insertion using point A in half of the knees and point B in the other half. Guide pin positioning on the femoral side was then assessed before and after tibial tunnel reaming, after beveling the posterolateral tibial tunnel rim, and after performing a standard notchplasty. After the femoral tunnel was reamed, the digitized contours of the native insertions were compared with those of both tibial and femoral tunnels to calculate percentage overlap. Results: Starting points A and B occurred 15.9 ± 4.5 mm and 33.0 ± 3.3 mm distal to the joint line, respectively, and 9.8 ± 2.4 mm and 8.3 ± 4.0 mm from the medial edge of the tibial tubercle, respectively. The anterior and posterior aspects of both tibial tunnels’ intra-articular exits were within a few millimeters of the native insertion’s respective boundaries. After the tibial tunnel was reamed from the more proximal point A, a transtibial guide pin was positioned within 2.1 ± 1.6 mm of the femoral insertion’s center (vs 9.3 ± 1.9 mm for point B; P = .02). After beveling a mean 2.6 mm from the back of the point A tibial tunnels, positioning improved to within 0.3 ± 0.7 mm from the center of the femoral insertion (vs 4.2 ± 1.1 mm for the point B tibial tunnels; P = .008). Compared with the more distal starting point, use of point A provided significantly greater insertional overlap (tibial: 97.9% ± 1.4% vs 71.1% ± 15.1%, P = .03; femoral: 87.9% ± 9.2% overlap vs 59.6% ± 8.5%, P = .008). No significant posterior femoral or tibial plateau breakthrough occurred in any specimen. Conclusion: Tibial and femoral tunnels can be positioned in a highly anatomic manner using a transtibial technique but require careful choice of a proximal tibial starting position and a resulting tibial tunnel that is at the limits of practical. Traditional tibial tunnel starting points will likely result in less anatomic femoral tunnels. Clinical Relevance: A transtibial single-bundle technique can accomplish a highly anatomic reconstruction but does require meticulous positioning of the tibial tunnel with little margin for error and some degree of graft-tunnel mismatch.

Biomechanics of Intervertebral Disk Degeneration

Degenerative changes in the material properties of nucleus pulposus and anulus fibrosus promote changes in viscoelastic properties of the whole disc. Volume, pressure and hydration loss in the nucleus pulposus, disk height decreases and fissures in the anulus fibrosus, are some of the signs of the degenerative cascade that advances with age and affect, among others, spinal function and its stability. Much remains to be learned about how these changes affect the function of the motion segment and relate to symptoms such as low back pain and altered spinal biomechanics.

Comparison of Animal Discs Used in Disc Research to Human Lumbar Disc Torsion Mechanics and Collagen Content

Study Design. Experimental measurement and normalization of in vitro disc torsion mechanics and collagen content for several animal species used in intervertebral disc research and comparing these with the human disc. Objective. To aid in the selection of appropriate animal models for disc research by measuring torsional mechanical properties and collagen content. Summary of Background Data. There is lack of data and variability in testing protocols for comparing animal and human disc torsion mechanics and collagen content. Methods. Intervertebral disc torsion mechanics were measured and normalized by disc height and polar moment of inertia for 11 disc types in 8 mammalian species: the calf, pig, baboon, goat, sheep, rabbit, rat, and mouse lumbar discs, and cow, rat, and mouse caudal discs. Collagen content was measured and normalized by dry weight for the same discs except the rat and the mouse. Collagen fiber stretch in torsion was calculated using an analytical model. Results. Measured torsion parameters varied by several orders of magnitude across the different species. After geometric normalization, only the sheep and pig discs were statistically different from human discs. Fiber stretch was found to be highly dependent on the assumed initial fiber angle. The collagen content of the discs was similar, especially in the outer annulus where only the calf and goat discs were statistically different from human. Disc collagen content did not correlate with torsion mechanics. Conclusion. Disc torsion mechanics are comparable with human lumbar discs in 9 of 11 disc types after normalization by geometry. The normalized torsion mechanics and collagen content of the multiple animal discs presented are useful for selecting and interpreting results for animal disc models. Structural organization of the fiber angle may explain the differences that were noted between species after geometric normalization.

In vivo topographic analysis of lumbar facet joint space width distribution in healthy and symptomatic subjects.

Study Design. In vivo 3-dimensional facet joint space width measurement. Objective. To determine lumbar facet joint space width within clinically relevant topographical zones in vivo and its correlations with age, level, and presence of lower back pain symptoms. Summary of Background Data. Facet joint gap narrowing, articular cartilage thinning, and subarticular cortical bone hypertrophy are frequently observed age-related changes. Facet joint space width is a well-defined parameter to evaluate osteoarthritis. To the best of our knowledge, there is no other study that quantifies 3-dimensional facet joint space width distribution in vivo. Methods. Three-dimensional measurement to quantify facet joint space width distribution based on 5 clinically relevant topographic zones in a cohort of healthy and symptomatic volunteers with low back pain, using subject-based 3-dimensional computed tomographic models with respect to spinal level, subject age, sex, and presence/absence of lower back pain. Results. Facet joint space width (mean ± SD) was 1.93 ± 0.51 mm for the central zone, 1.75 ± 0.48 mm for the superior zone, 1.63 ± 0.49 mm for the inferior zone, 1.48 ± 0.44 mm for the medial zone, and 1.65 ± 0.48 mm for the lateral zone, respectively. There were no significant differences between right and left facet joints. Male patients showed larger space width than female patients. Overall, space width of symptomatic subjects was significantly narrower than that of the asymptomatic group. Facet joints in the peripheral zones were narrower than in the central zone. Age-group comparisons showed that local narrowing occurring as early as in the third decade at the inferior zone of L5–S1, with all the remaining zones implicated after the fourth decade. Conclusion. This in vivo study shows variations in facet joint space width narrowing with spinal level and region within the facet joint and in vivo evidence of localized, age-influenced facet cartilage thinning. Techniques developed in this study may be applied in the detection of early osteoarthritis-related changes in the facet joints.

In Vivo Measurement of Lumbar Facet Joint Area in Asymptomatic and Chronic Low Back Pain Subjects

Study Design. In vivo measurement of lumbar facet joint surface area. Objective. To investigate lumbar facet joint surface area in relation to age and the presence of chronic low back pain. Summary of Background Data. Facet joint surface area is an important parameter for understanding facet joint function and pathology, but information on the lumbar facet joint is limited, especially in relation with age and low back pain symptoms. Methods. In vivo measurements of the lumbar facet joints (L3/L4-L5/S1) were performed on 90 volunteers (57 asymptomatic subjects and 33 chronic low back pain subjects) using subject-based 3-dimensional facet joint surface computed tomography models. Results. The facet joint surface area increased significantly at each successive inferior level. In the low back pain subjects aged >40 years, both superior and inferior facet surface areas increased except superior facets at L5/S1 compared with younger subjects. In the asymptomatic subjects aged >40 years, only the superior facets showed an increase in the L3/4 facet surface area compared with younger subjects. Conclusion. The lumbar facet areas measured in vivo in this study were similar to previous cadaveric studies. The lumbar facet area was significantly greater at the inferior lumbar levels and also increased with age. This age-related increase in the facet joint surface was observed more in the low back pain subjects compared with asymptomatic subjects. The increase in the area of the facet joint surface is probably secondary to increased load-bearing in the lower lumbar segments and facet joint osteoarthritis.

Biomechanical comparison of three different types of C7 fixation techniques: Lateral mass screw, transpedicular screw, and intralaminar screw

Study Design. In vitro biomechanical comparison of 3 C7 posterior fixation methods. Objective. To investigate the posterior cervical construct stability afforded by this novel C7 intralaminar screw with lateral mass and transpedicular screw. Summary of Background Data. The intralaminar screw method is recently introduced and used in C7 fixation. However, no biomechanical comparisons of the C7 intralaminar screw with lateral mass screw or transpedicular screw technique have been performed. Methods. Ten fresh frozen human cadaveric C6-C7 motion segments were tested before and after 3 different types of C7 screw fixation (lateral mass screw, intralaminar screw and pedicle screw). After the kinematic study was completed, the pull out strength test for each type of C7 screw was performed. Results. To compare 3 C7 fixation techniques, normalized range of motion (ROM) of each type of screw was analyzed relative to the intact state. There were no significant differences between 3 types of C7 screws in terms of mean ROM in flexion/extension. The mean lateral bending ROM of C7 intralaminar screw construct (30.5% ± 9.2%) was significantly larger than C7 pedicle screw construct (19.2% ± 6.9%, P < 0.05). The mean axial rotation of C7 lateral mass construct (52.0% ± 27.1 %) was significantly larger than C7 pedicle screw construct (38.7% ± 23.8%, P < 0.05). The pull-out strength of lateral mass screw was significantly weaker than other 2 types of C7 screw (intralaminar and pedicle screw). However, there was no significant pull-out strength difference between the C7 intralaminar and C7 pedicle screw techniques. Conclusion. This study demonstrates that the pedicle screw fixation is the strongest instrumentation method for C7 fixation. However, if C7 pedicle fixation is unfavorable, in case that vertebral artery course through the C7 transverse foramen or C7 pedicle is not large enough to insert screw, the C7 laminar screw can be an alternative fixation point with similar limitation of motion except in lateral bending.

Overexpression of DMP1 accelerates mineralization and alters cortical bone biomechanical properties in vivo.

Dentin matrix protein-1 (DMP1) is a key regulator of biomineralization. Here, we examine changes in structural, geometric, and material properties of cortical bone in a transgenic mouse model overexpressing DMP1. Micro-computed tomography and three-point bending were performed on 90 femora of wild type and transgenic mice at 1, 2, 4, and 6 months. Fourier transform infrared imaging was performed at 2 months. We found that the transgenic femurs were longer (p<0.01), more robust in cross-section (p<0.05), stronger (p<0.05), but had less post-yield strain and displacement (p<0.01), and higher tissue mineral density (p<0.01) than the wild type femurs at 1 and 2 months. At 2 months, the transgenic femurs also had a higher mineral-to-matrix ratio (p<0.05) and lower carbonate substitution (p<0.05) compared to wild type femurs. These findings indicate that increased mineralization caused by overexpressing DMP1 led to increased structural cortical bone properties associated with decreased ductility during the early post-natal period.

Emerging ideas: Novel 3-D quantification and classification of cam lesions in patients with femoroacetabular impingement.

BackgroundFemoroacetabular impingement (FAI) can lead to labral injury, osseous changes, and even osteoarthritis. The literature contains inconsistent definitions of the alpha angle and other nonthree-dimensional (3-D) radiographic measures. We present a novel approach to quantifying cam lesions in 3-D terms. Our method also can be used to develop a classification system that describes the exact location and size of cam lesions.Questions/HypothesesWe asked whether automated quantification of CAM lesions based on CT data is a reasonable way to detect CAM lesions and whether they may be classified based on location.Method of StudyWe developed a method to quantify femoral head cam lesions using 3-D modeling of CT scans. By segmenting raw DICOM data, we can determine the distance from the cam lesion’s surface points to the centroid of the femoral head to quantify the mean bump height, volume, and location. The resulting 3-D femoral and acetabular models will be analyzed with custom software. We then will quantify the cam lesion with 3-D parameters using a modified zoning method. The mean bump height, volume, and location on the clock face, and relative zoning will be calculated. Zonal differences will be statistically analyzed. To assess the ability of this method to predict arthroscopic findings, we will obtain preoperative CT scans for 25 patients who undergo hip arthroscopy for FAI. We will compare measurements with the method with our measurements from arthroscopy. The clinical implications of our method’s measurements then will be reviewed and refined for future prospective studies.SignificanceWe present a novel approach that can quantify a cam lesion’s location and size. This method will be used to provide guidelines for the exact amount of bony resection needed from a specific location of the proximal femur. There is also potential to develop software for ease of use so this method can be more widely applied.

In Vivo Three-Dimensional Morphometric Analysis of the Lumbar Pedicle Isthmus

Study Design. In vivo noninvasive study. Objective. To properly quantify pedicle anatomic parameters, using subject-based CT three-dimensional models and compare the data from 2-dimensional transverse-CT images. Summary of Background Data. Accurate measurement of morphometric parameters of pedicle isthmus is important for transpedicular procedures. Anatomically, the lumbar pedicle is known to be elliptical cross-sectionally and slightly inclined in the vertical plane in the lower lumbar levels. Therefore, measurement of the pedicle isthmus may be overestimated when transverse images are used. More accurate measurement of the 3-dimensional geometry of the pedicle is therefore needed. To the best of our knowledge, 3-dimensional geometry of the pedicle has not been reported as the literature values are based on 2-dimensional image data. Methods. In vivo measurements of the lumbar pedicle isthmus were performed on the 3-dimensional subject-based CT models, using custom-developed software in 89 volunteers. Results. The least axis of pedicle, the longest axis of pedicle and the transverse plane width were largest at L5 in both genders. The isthmus angle declined in the lower levels. The ratio of the transverse plane width to the least axis of pedicle was largest at L5. Conclusion. Our results showed that the least axis of pedicle, the longest axis of pedicle and the transverse plane width peaked at L5, and the transverse plane width became approximately twice as long in the lower levels compared to the upper levels. The ratio of the transverse plane width to the least axis of pedicle increased by about 40% at L5. These findings highlight the fact that measuring the isthmus width from CT transverse images leads to overestimation, especially in the lower lumbar spine. Therefore, a 3-dimensional inclination of the least axis of the pedicle should be taken into account for the determination of the pedicle diameter in the lower lumbar vertebrae.

Spinal kinematics and facet load transmission after total disc replacement.

Study Design. In vitro human cadaveric biomechanical study. Objective. The objectives were to determine the effect of total disc replacement (TDR) on kinematics, especially range of motion (ROM), helical axis of motion (HAM), and facet joint contact force. Summary of Background Data. Ball-and-socket type artificial discs are designed to mimic normal motion, but the biomechanical effect on kinematics has not been thoroughly clarified. Methods. Fourteen human cadaveric L4–L5 units were tested before and after TDR. In 7 specimens, facet contact forces were directly measured with thin-film piezoresistive load transducers inserted in the facet joints. In the other 7 specimens, the facet joint capsules were kept intact. Moments (±7.5 Nm) were applied in flexion/extension, lateral bending, and axial rotation motion, with and without an axial compressive preload of 400 N. Three-dimensional motion was recorded, and each angular ROM and HAM were calculated. Results. Without axial compressive preload, the TDR did not produce significant differences in ROMs in all cases. However, under compressive preload, the TDR produced significantly larger ROMs for flexion (4.0° and 8.7°) and lateral bending (2.4° and 5.6°) (intact state and TDR, respectively). The TDR did not alter the HAM significantly except the location in lateral bending without compressive preload and the orientation in flexion/extension against horizontal plane. The location of HAM was slightly shifted caudally by the compressive preload in intact and TDR states. Despite the increased ROMs, the facet contact forces were not significantly altered by the TDR either with or without compressive preload (26 N and 27 N in extension, 41 N and 41 N in lateral bending, 117 N and 126 N in axial rotation). Conclusion. TDR using a ball-and-socket type artificial disc significantly increased ROM under axial load and maintained the HAM with similar facet contact forces to the intact state.