Diana Glaser

Comparison of 3-dimensional spinal reconstruction accuracy: biplanar radiographs with EOS versus computed tomography.

Study Design: Experimental study for systematic evaluation of 3-dimensional (3D) reconstructions from low-dose digital stereoradiography. Objective. To assess the accuracy of EOS (EOS Imaging, Paris, France) 3-dimensional (3D) reconstructions compared with 3D computed tomography (CT) and the effect spine positioning within the EOS unit has on reconstruction accuracy. Summary of Background Data. Scoliosis is a 3D deformity, but 3D morphological analyses are still rare. A new low-dose radiation digital stereoradiography system (EOS) was previously evaluated for intra/interobserver variability, but data are limited for 3D reconstruction accuracy. Methods. Three synthetic scoliotic phantoms (T1-pelvis) were scanned in upright position at 0°, ±5°, and ±10° of axial rotation within EOS and in supine position using CT. Three-dimensional EOS reconstructions were superimposed on corresponding 3D computed tomographic reconstructions. Shape, position, and orientation accuracy were assessed for each vertebra and the entire spine. Additional routine planer clinical deformity measurements were compared: Cobb angle, kyphosis, lordosis, and pelvic incidence. Results. Mean EOS vertebral body shape accuracy was 1.1 ± 0.2 mm (maximum 4.7 mm), with 95% confidence interval of 1.7 mm. Different anatomical vertebral regions were modeled well with root-mean-square (RMS) values from 1.2 to 1.6 mm. Position and orientation accuracy of each vertebra were high: RMS offset was 1.2 mm (maximum 3.7 mm) and RMS axial rotation was 1.9° (maximum 5.8°). There was no significant difference in each of the analyzed parameters (P > 0.05) associated with varying the rotational position of the phantoms in EOS machine. Planer measurements accuracy was less than 1° mean difference for pelvic incidence, Cobb angle (mean 1.6°/maximum 3.9°), and sagittal kyphosis (mean less than 1°, maximum 4.9°). Conclusion. The EOS image acquisition and reconstruction software provides accurate 3D spinal representations of scoliotic spinal deformities. The results of this study provide spinal deformity surgeons evidence pertaining to this new upright 3D imaging technology that may aid in the clinical diagnosis and decision making for patients with scoliosis.

Postoperative changes in spinal rod contour in adolescent idiopathic scoliosis: an in vivo deformation study.

Study Design. Prospective case series. Objective. To evaluate the change in spinal rod contour from before implantation to after surgical correction of thoracic curves in patients with adolescent idiopathic scoliosis. Summary of Background Data. With segmental pedicle screw spinal instrumentation and vertebral derotation, many authors have reported a loss of thoracic kyphosis postoperatively. Although surgeons anticipate some flattening of the preimplantation rod contour in the sagittal plane, the magnitude of this change in shape has not been documented. Methods. The concave and convex rod shapes of 5.5-mm ultrahigh-strength steel spinal rods (200 KSI) from patients with thoracic adolescent idiopathic scoliosis (n = 27), which were contoured with benders by the surgeon, were traced prior to insertion. Postoperative (average, 5 weeks) sagittal rod shape was determined from lateral 2-dimensional radiographs. Maximal rod deflection and angle of the tangents to rod end points (Cobb) were measured. Repeated measures analysis of variance assessed differences between pre- and postoperation. Results. The scoliosis of 55° ±14° was corrected 72% to 15° ± 5°. The preinsertion rod shapes were more kyphotic for the concave (45.6°) than for the convex (31.4°) rods. Following correction, the concave rods flattened, with decrease in deflection of 13 mm and reduction in angle of 21° (both P < 0.001). The convex rods increased 1.5 mm in deflection and 2° in angle (P < 0.01, P = 0.18). The sagittal profile was maintained postoperatively as measured from T5–T12: 19° ±14° versus 22° ± 6° (pre vs. post, P > 0.1). Conclusion. We found a significant difference between pre- and postoperative rod contour, particularly for concave rods. Rod overcontouring (by ∼20° for concave rod) resulted in high degrees of correction without loss of sagittal alignment. The resulting deformations are likely associated with substantial in vivo deforming forces.

Biomechanical Analysis of Pin Placement for Pediatric Supracondylar Humerus Fractures: Does Starting Point, Pin Size, and Number Matter?

Background: Several studies have examined the biomechanical stability of smooth wire fixation constructs used to stabilize pediatric supracondylar humerus fractures. An analysis of varying pin size, number, and lateral starting points has not been performed previously. Methods: Twenty synthetic humeri were sectioned in the midolecranon fossa to simulate a supracondylar humerus fracture. Specimens were all anatomically reduced and pinned with a lateral-entry configuration. There were 2 main groups based on specific lateral-entry starting point (direct lateral vs. capitellar). Within these groups pin size (1.6 vs. 2.0 mm) and number of pins (2 vs. 3) were varied and the specimens biomechanically tested. Each construct was tested in extension, varus, valgus, internal, and external rotation. Data for fragment stiffness (N/mm or N mm/degree) were analyzed with a multivariate analysis of variance and Bonferroni post hoc analysis (P<0.05). Results: The capitellar starting point provided for increased stiffness in internal and external rotation compared with a direct lateral starting point (P<0.05). Two 2.0-mm pins were statistically superior to two 1.6-mm pins in internal and external rotation. There was no significant difference found comparing two versus three 1.6-mm pins. Conclusions: The best torsional resistances were found in the capitellar starting group along with increased pin diameter. The capitellar starting point enables the surgeon to engage sufficient bone of the distal fragment and maximizes pin separation at the fracture site. In our anatomically reduced fracture model, the addition of a third pin provided no biomechanical advantage. Clinical Relevance: Consider a capitellar starting point for the more distally placed pin in supracondylar humerus fractures, and if the patient’s size allows, a larger pin construct will provide improved stiffness with regard to rotational stresses.

Adolescent Patella Instability Extensor Mechanics: Insall Extensor Realignment Versus Medial Patellofemoral Ligament Reconstruction.

Background: A plethora of surgical procedures have been promoted in the literature regarding the treatment of patella instability in the adolescent population; yet, none have compared the joint reaction forces of knee extensor mechanics after extensor mechanism realignment (Insall) or medial patellofemoral ligament reconstruction (MPFLR). The purpose of this study was to determine if there was a difference in knee extensor mechanics between these techniques. Methods: Three cohorts of 10 age-matched adolescents (normal control, Insall, and MPFLR) were compared using preoperative magnetic resonance imaging and postoperative x-ray in the 2 surgical groups. Patella and patella tendon length were measured and the actual moment arm calculated. Compression angles were estimated and the effective moment arms determined. Patellofemoral and quadriceps joint reaction forces were calculated. Comparisons within and between the 3 groups were determined and the dependent variables analyzed for statistical differences. Results: Mean ages (15.6±2.2 y), preoperative measures and dependent variables were not different between the groups (P>0.05). Postoperatively, there was a significant difference for the patellofemoral joint reaction force with respect to the quadriceps force (Fr/Fq), being larger within the Insall group (1.08±0.08) than the MPFLR group (0.92±0.09) (P<0.001). The postoperative MPFLR group variables were not significantly different to the control group. In contrast, the postoperative Insall group yielded larger joint reaction forces compared with control (1.08±0.08 vs. 0.83±0.11, P<0.001), as well as different effective moment arms, Insall versus control (51.23±8.8 vs. 41.9±5.9, P<0.001). Conclusions: Not all surgical interventions for recurrent patella instability affect knee mechanics similarly. Although an extensor realignment procedure may still have indications in children, the treating surgeon should be aware that it does not appear to restore normal joint mechanics. Clinical Relevance: The Insall-type procedure may increase the patellofemoral joint reaction forces beyond normal without fully restoring the effective moment arms; whereas, MPFL reconstruction appears to restore the effective moment arm without excessive joint reaction forces.

Isocentric reattachment of ligamentum teres: a porcine study.

Background: Recent reports reveal interest in the mechanical importance of ligamentum teres (LT) in hip dislocation. In the previously established procedure of anteroinferior acetabular LT reattachment in developmental dysplasia of the hip, the LT functions as a check-rein, showing promising results. However, this position of reattachment could potentially limit motion. The purpose of this study was to evaluate the feasibility of an isocentric point for reattachment of the LT and to study its impact on hip function using a young porcine model. Methods: Pelvic specimens with intact anatomy were obtained from 6 skeletally immature pigs (12 hips). Through a careful anteromedial capsulotomy, the LT was detached from its acetabular insertion then reattached to 1 of 2 positions: (1) anteroinferior lip of the acetabulum; (2) proposed isocentric position. Intra-articular stress distribution was measured through a complete range of motion with a prescale Fuji pressure film. Tension was then applied to the LT and the stresses were recorded again. In addition, radioopaque solution was injected into the substance of the LT, then floroscopy tracked the LT location initially and after the 2 reattachment positions through a full hip range of motion. Results: Reattachment of the LT at an isocentric point is feasible in a pig model. With careful physiologic tensioning of this reattachment, hip can maintain full motion with no excessive pressure areas created within the joint. On the contrary, the initial technique of anteroinferior extra-articular attachment limits external rotation and extremes of abduction. We found this LT tracking technique (with radioopaque dye injection) to be reliable and reproducible. Conclusions: The isocentric reattachment of the LT is feasible in this pig model and serves as a natural check-rein to dislocation without limiting joint motion or causing abnormal cartilage pressures. Clinical Relevance: Isocentric LT reattachment may provide a method for improving stability of open reductions when treating children with such conditions.

Loop Securities of Arthroscopic Sliding-Knot Techniques When the Suture Loop Is Not Evenly Tensioned

PURPOSE The purpose of this study was to evaluate the loop security of arthroscopic sliding knots when tension is only applied to the post strand and not the loop strand. METHODS Six different locking sliding knots (Weston, Nicky, Roeder, SMC, San Diego, and Dines) were included. Loop securities were evaluated in 2 ways: with a conventional method (equal tension applied to the suture loop) and with a worst-case scenario (WCS) method (only the post strand of the suture loop was tensioned). Differences between test methods were evaluated for significance. To help assess the applicability of each test method, loop-security testing in a cadaveric shoulder was performed with 1 type of knot (SMC). RESULTS Loop securities with the conventional method versus the WCS method were as follows: 10.74 ± 4.20 N versus 6.90 ± 3.90 N for Weston, 21.25 ± 14.74 N versus 8.73 ± 3.35 N for Nicky, 26.14 ± 15.57 N versus 7.95 ± 4.23 N for Roeder, 42.67 ± 22.96 N versus 8.67 ± 4.33 N for SMC, 52.99 ± 21.36 N versus 18.25 ± 10.58 N for San Diego, and 89.27 ± 27.96 N versus 12.48 ± 3.40 N for Dines (P < .05 for each knot). All knots failed at significantly lower loads when the suture loop was not evenly tensioned. Cadaveric testing (SMC) resulted in a loop security of 5.53 ± 6.06 N, which was similar to the WCS setting. CONCLUSIONS The locking mechanism of the sliding knots is maintained when the suture loop is evenly tensioned at both post and non-post strands. When tension is not applied to the non-post strand side, the knots slide more easily and fail at lower loads than previously reported. CLINICAL RELEVANCE When surgeons tie locking sliding knots in single-row rotator cuff repair, they should be aware that the knots could fail at much lower loads than previously reported.

A method for assessing axial vertebral rotation based on differential rod curvature on the lateral radiograph.

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.

Biomechanical Testing of Unstable Slipped Capital Femoral Epiphysis Screw Fixation: Worth the Risk of a Second Screw?

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-month-old porcine femurs. Four groups were evaluated: pinned (3.5 mm 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, 1 Hz) were applied along the physeal plane. Maximum load increased by 100 N 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.

3D Visualization of Vertebral Growth Plates and Disc: The Effects of Growth Modulation.

After tethered growth or sham surgery, spinal motion segments underwent microtomography to determine physeal and disc 3-dimensional (3D) morphology. Instrumented and contralateral sides of tether and sham surgical groups were compared. OBJECTIVES To determine the 3D morphological effects of growth modulation via anterolateral tethering on vertebral physeal and intervertebral disc morphology in a rapidly growing bovine model. SUMMARY OF BACKGROUND DATA Growth modulation acts through physeal loading. Providing a promising alternative to arthrodesis for scoliosis correction, tethering vertebral growth maintains further growth (open/functioning physes) and motion (disc integrity). Standard physeal and disc evaluation using histology reduces 3D geometries to single planar samples. METHODS Five-week-old calves received anterolateral flexible spinal tethers (n = 6) or sham surgeries (n = 6) followed by 6 months of growth. Individual motion segments were imaged by microtomograph (36 μm). Physeal space and disc space thickness maps were generated from surface reconstructions. Normalized thickness differences were compared between instrumented and contralateral sides of tether and sham groups (analysis of variance, p < .05). Physeal closure was estimated and regions of bony bridging were marked closed. RESULTS Tethering caused significant physeal thickness reduction on the instrumented side compared with the contralateral side (7.6% ± 2.0%; p = .0002). This reduction was greater (p = .003) in tethered physes than in the sham, which demonstrated no reduction (0.8% ± 3.7%; p = .6). Small regions of physeal closure were observed in sham and tether groups (medians of 1.4% and 0.1% and maximums of 6.8% and 2.7%, respectively). Tethered discs were 29% thinner than sham, but demonstrated no contralateral to instrumented-side thickness difference (5.2% difference; p = .3). CONCLUSIONS Tethering resulted in thinner physes on the tethered side without notable physeal closure. With no side differences in the sham group, tethering apparently applied instrument-sided compressive forces. Tethering also resulted in thinner discs, although they were apparently. Producing consistent histological samples is difficult; misaligned slices may lead to inaccurate conclusions. Evaluating entire physes or discs produces more robust results.