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Pomerantz M.L.,University of California at San Diego | Glaser D.,Aurora Spine | Doan J.,Orthopedic Biomechanics Research Center | Kumar S.,University of California at San Diego | Edmonds E.W.,University of California at San Diego
Skeletal Radiology

Objective: To validate femoral version measurements made from biplanar radiography (BR), three-dimensional (3D) reconstructions (EOS imaging, France) were made in differing rotational positions against the gold standard of computed tomography (CT).Materials and methods: Two cadaveric femurs were scanned with CT and BR in five different femoral versions creating ten total phantoms. The native version was modified by rotating through a mid-diaphyseal hinge twice into increasing anteversion and twice into increased retroversion. For each biplanar scan, the phantom itself was rotated −10, −5, 0, +5 and +10°. Three-dimensional CT reconstructions were designated the true value for femoral version. Two independent observers measured the femoral version on CT axial slices and BR 3D reconstructions twice. The mean error (upper bound of the 95 % confidence interval), inter- and intraobserver reliability, and the error compared to the true version were determined for both imaging techniques.Results: Interobserver intraclass correlation for CT axial images ranged from 0.981 to 0.991, and the intraobserver intraclass correlation ranged from 0.994 to 0.996. For the BR 3D reconstructions these values ranged from 0.983 to 0.998 and 0.982 to 0.998, respectively. For the CT measurements the upper bound of error from the true value was 5.4–7.5°, whereas for BR 3D reconstructions it was 4.0–10.1°. There was no statistical difference in the mean error from the true values for any of the measurements done with axial CT or BR 3D reconstructions.Conclusion: BR 3D reconstructions accurately and reliably provide clinical data on femoral version compared to CT even with rotation of the patient of up to 10° from neutral. © 2014 ISS Source

Liu R.W.,Case Western Reserve University | Yaszay B.,Rady Childrens Hospital and Health Center | Glaser D.,Rady Childrens Hospital and Health Center | Glaser D.,Orthopedic Biomechanics Research Center | And 2 more authors.

STUDY DESIGN.: Bench-top and retrospective radiographical analyses to determine apical vertebral rotation based on differential rod curvature on the postoperative lateral radiograph. OBJECTIVE.: To develop a clinically relevant methodology for measuring apical vertebral rotation on postoperative lateral radiographs in patients with adolescent idiopathic scoliosis, based on the distance between the spinal rods. SUMMARY OF BACKGROUND DATA.: Traditional methods of analyzing vertebral rotation on plain radiographs are limited in the postoperative spine with segmental instrumentation. A previous methodology based on pedicle screw tip to rod distances on the posteroanterior radiograph is effective but limited by surgical technique and patient positioning relative to the x-ray beam. METHODS.: The trigonometric relationship between the inter-rod distances on lateral radiographs was defined and validated on a biomechanical model, with apical rotation varying from 0° to 20°. The ability to correct for malposition on the lateral radiograph was tested on 11 postoperative radiographs and correlated against corresponding postoperative computed tomographic scans. RESULTS.: The bench-top model had a strong correlation between actual apical rotation and calculated rotation for the full range of image rotations (intraclass correlation coefficient, 0.99). For the 11 clinical cases, comparisons of apical rotation measured on computed tomographic scans were highly correlated to the proposed lateral radiograph calculations (r = 0.84). CONCLUSION.: A technique for measuring apical vertebral rotation based on the inter-rod distance on the lateral and posteroanterior radiographs was developed and validated. This technique is resilient to rotation of the patient within the x-ray machine and can complement measurement of rotation on postoperative posteroanterior radiographs. Copyright © 2012 Lippincott Williams & Wilkins. Source

Lee Y.-P.,University of California at San Diego | Robertson C.,Orthopedic Biomechanics Research Center | Mahar A.,University of California at San Diego | Kuper M.,University of California at San Diego | And 3 more authors.
Journal of Spinal Disorders and Techniques

STUDY DESIGN: Cadaveric biomechanical investigation. OBJECTIVES: To test the feasibility of transfacet screws as a minimally invasive posterior fixation device for the cervical spine by comparing the biomechanical stability of transfacet screws to lateral mass screws and rods in a multilevel cervical corpectomy model. SUMMARY OF BACKGROUND DATA: Minimally invasive surgery (MIS) of the spine has gained increasing acceptance and popularity. However, a minimally invasive means of instrumenting the posterior cervical spine has yet to be discovered. Posterior transfacet screws have been described as a means of posterior fixation. In addition, they have the potential of being placed percutaneously through stab incisions. However, validation of transfacet screws in an unstable cervical model in which posterior instrumentation may be necessary has not been carried out till date. METHODS: Sixteen cadaveric cervical spines were randomized to transfacet or lateral mass instrumentation groups. The spines were tested in the following conditions: (a) intact, (b) after multilevel corpectomies with strut graft placement with stand-alone posterior fixation, and (c) with an additional anterior plate over the strut graft. Corpectomy site loading was measured with a custom-designed strut graft. Data were collected for spinal stiffness, range of motion, and strut graft loading, and was analyzed using 2-way analysis of variance (P<0.05). RESULTS: Stand-alone transfacet screw fixation was found to provide inferior spinal stability and resulted in increased spinal motion and graft loading compared with the other constructs (P<0.05 for all). CONCLUSIONS: It is unclear what kind of mechanical stiffness is necessary to stabilize the cervical spine and obtain solid fusion. However, decreased stability and increased graft loading suggest that transfacet screws may not be the ideal method of posterior fixation to supplement multilevel anterior cervical corpectomies and fusions despite their potential as a minimally invasive method for posterior cervical instrumentation. Copyright © 2011 by Lippincott Williams &Wilkins. Source

Leek B.T.,University of California at San Diego | Robertson C.,Orthopedic Biomechanics Research Center | Robertson C.,University of California at Irvine | Mahar A.,Orthopedic Biomechanics Research Center | Pedowitz R.A.,University of California at Los Angeles
Arthroscopy - Journal of Arthroscopic and Related Surgery

Purpose: Our purpose was to investigate the importance of medial-row knot tying to mechanical stability in a double-row rotator cuff repair by comparing a knotless construct with transtendon anchor passage versus a similar construct implementing medial knots. Methods: A standard defect was created in the infraspinatus tendons of 14 bovine humeri. All defects were repaired with 2 medial and 2 lateral anchors (SutureCross System; KFx Medical, Carlsbad, CA). The medial anchors were either placed by transtendon passage in a knotless construct or placed directly into bone with needle passage of suture to create bursal-sided knots medially. Constructs were subjected to a cyclic loading protocol and then loaded to failure. Results: The medially knotted constructs had a statistically higher stiffness at both the initial and final cycles (P < .001 and P < .001, respectively) and a lower displacement during cyclic loading (P < .02). There were strong trends toward decreased gauge displacement (P = .12) and decreased cycles to 3 mm of displacement (P = .07) in the medially knotted group. Maximal yield strength was greater in the medially knotted group (350 ± 270 N v 650 ± 530 N), although this was not found to be statistically significant (P = .5). Conclusions: Our data suggest that creation of medial knots increases construct stiffness and stability in arthroscopic double-row cuff repair. This is likely because of increased load transfer to the lateral anchor and suture-tendon interface in the knotless construct. Clinical Relevance: Medial knots create increased mechanical stability that theoretically may improve rotator cuff healing. This mechanical advantage must be weighed against surgical efficiency, with consideration given to factors such as tissue quality. © 2010 Arthroscopy Association of North America. Source

Schmitz M.R.,San Antonio Military Medical Center | Farnsworth C.L.,Rady Childrens Hospital | Doan J.D.,Orthopedic Biomechanics Research Center | Glaser D.A.,Orthopedic Biomechanics Research Center | And 3 more authors.
Journal of Pediatric Orthopaedics

Background: In a prior biomechanical study, 2-screw fixation of anatomically reduced slipped capital femoral epiphysis (SCFE) demonstrated marginally greater stability than single-screw fixation. However, the authors judged the benefits of a second screw to be minimal compared with the additional complication risk. A similar evaluation of fixation stability in unstable moderately displaced SCFE is performed. Methods: SCFE model: Transverse periosteal incision and epiphyseal separation from the metaphysis by leveraging in 25-monthold porcine femurs. Four groups were evaluated: pinned (3.5mm cortex screws; Synthes, Monument, CO) with no displacement (1 screw=group N1; 2 screws=group N2) or with moderate posterior-inferior displacement of 50% of the epiphyseal diameter (1 screw=group D1; 2 screws=group D2). Biomechanical testing: Cyclical shear forces (40 to 200 N, 1Hz) were applied along the physeal plane. Maximum load increased by 100N every 500 cycles until failure (epiphyseal translation greater than one third the epiphyseal diameter). Force cycles (the sum of the maximum cycle loads) and number of cycles to failure were reported. Results: A sample from each D1 and D2 had fixation problems (D1, D2: n=4; N1, N2: n=5). One D1 failed through the femoral neck; all others failed through the epiphysis. The data showed nonsignificant trends of greater force cycles for nondisplaced over displaced (P=0.13) and for 2 screws over 1 (P=0.19). Number of cycles to failure showed similar trends, with no significant differences between nondisplaced and displaced (P=0.10) and screw number (P=0.13). Force cycles were significantly greater in the N2 group than in the D1 group. Conclusions: A trend toward higher force cycles to failure in nondisplaced and 2-screw groups was observed. Higher force cycles correspond to greater physeal stability and thus decreased risk for subsequent displacement. Within displacement groups, adding a second screw did not significantly increase stability. Reduction of displaced SCFE also did not significantly increase stability. Only the D1 and N2 groups were significantly different. Clinical Relevance: Nondisplaced SCFE does not require 2 screws. In situ fixation of displaced SCFE might be optimized with 2 screws. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. Source

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