Biomechanical Evaluation of Plate Versus Lag Screw Only Fixation of Distal Fibula Fractures.

Traditional fixation of unstable Orthopaedic Trauma Association type B/C ankle fractures consists of a lag screw and a lateral or posterolateral neutralization plate. Several studies have demonstrated the clinical success of lag screw only fixation; however, to date no biomechanical comparison of the different constructs has been performed. The purpose of the present study was to evaluate the biomechanical strength of these different constructs. Osteotomies were created in 40 Sawbones(®) distal fibulas and reduced using 1 bicortical 3.5-mm stainless steel lag screw, 2 bicortical 3.5-mm lag screws, 3 bicortical 3.5-mm lag screws, or a single 3.5-mm lag screw coupled with a stainless steel neutralization plate with 3 proximal cortical and 3 distal cancellous screws. The constructs were tested to determine the stiffness in lateral bending and rotation and failure torque. No significant differences in lateral bending or rotational stiffness were detected between the osteotomies fixed with 3 lag screws and a plate. Constructs fixed with 1 lag screw were weaker for both lateral bending and rotational stiffness. Osteotomies fixed with 2 lag screws were weaker in lateral bending only. No significant differences were found in the failure torque. Compared with lag screw only fixation, plate fixation requires larger incisions and increased costs and is more likely to require follow-up surgery. Despite the published clinical success of treating simple Orthopaedic Trauma Association B/C fractures with lag screw only fixation, many surgeons still have concerns about stability. For noncomminuted, long oblique distal fibula fractures, lag screw only fixation techniques offer construct stiffness similar to that of traditional plate and lag screw fixation.

Generation of a Patient-Specific Model of Normal Sagittal Alignment of the Spine.

STUDY DESIGN: Mathematical modeling of normal sagittal spinal alignment. OBJECTIVE: To create a patient specific 3-dimensional (3D) model of normal adolescent spinal shape and alignment. SUMMARY OF BACKGROUND DATA: Recreating normal sagittal balance is a key goal in spinal deformity surgery. Because of the variation in normal sagittal alignment based on inherent pelvic parameters, it is difficult to know what is normal for a given patient who presents with spinal deformity. METHODS: Simultaneous biplanar 2-dimensional digital radiographs were taken for pediatric patients with no known spinal disease using the EOS system. Three-dimensional reconstructions were produced using sterEOS and imported into custom MATLAB software. The researchers defined relationships to approximate orientations and positions of the vertebral bodies from patients' pelvic incidence (PI). The predicted spinal contour was then calculated to optimize congruence to patients' sagittal T1-sacrum offset, sagittal curve inflection point location, and predicted vertebral body orientations and positions. RESULTS: A total of 75 patients (26 male and 49 female) were included, mean age 14.5 ± 2.6 years. Baseline measurements were PI 46.7° ± 10.2°, sacral lope 40.2° ± 8.9°, T1-T12 kyphosis 39.8° ± 8.8°, and L1-L5 lordosis -37.1° ± 11.2°. Average difference in vertebral position in the anteroposterior direction between actual spines and their predicted models was 1.2 ± 1.2 mm and varied from an absolute minimum of 0.2 mm (T3) to an absolute maximum of 3.7 mm (L2). CONCLUSIONS: This model uses an adolescent patient's PI to predict the normal sagittal alignment that best matches that patient's native sagittal curve. The model was validated on patients with no spinal deformity; average difference between actual sagittal positions of each vertebra and those predicted by the model was less than 5 mm at each vertebral level. This model may be useful in adolescent scoliotic patients with altered sagittal alignment to determine the magnitude of 3D deformity (compared with predicted normal values) and the completeness of 3D correction.

Three-dimensional biplanar radiography as a new means of accessing femoral version: a comparitive study of EOS three-dimensional radiography versus computed tomography.

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.

Sex Differences in Cartilage Topography and Orientation of the Developing Acetabulum: Implications for Hip Preservation Surgery.

BACKGROUND: Increased attention is being placed on hip preservation surgery in the early adolescent. An understanding of three-dimensional (3-D) acetabular development as children approach maturity is essential. Changes in acetabular orientation and cartilage topography have not previously been quantified as the adolescent acetabulum completes development. QUESTIONS/PURPOSES: We used a novel 3-D CT analysis of acetabular development in children and adolescents to determine (1) if there were sex-specific differences in the growth rate or surface area of the acetabular articular cartilage; (2) if there were sex-specific differences in acetabular version or tilt; and (3) whether the amount of version and tilt present correlated with acetabular coverage. METHODS: We assessed acetabular morphology in 157 patients (314 hips); 71 patients were male and 86 were female. Patient ages ranged from 8 years to 17 years. A 3-D surface reconstruction of each pelvis was created from CT data using MIMICs software. Custom MATLAB software was used to obtain data from the 3-D reconstructions. We calculated articular surface area, acetabular version, and acetabular tilt as well as novel measurements of acetabular morphology, which we termed "coverage angles." These were measured in a radial fashion in all regions of the acetabulum. Data were organized into three age groups: 8 to 10 years old, 10 to 13 years old, and 13 to 17 years old. RESULTS: Male patients had less acetabular anteversion in all three age groups, including at maturity (7° versus 13°, p<0.001; 10° versus 17°, p<0.001; 14° versus 20°, p<0.001). Males had less acetabular tilt in all three age groups (32° versus 34°, p=0.03; 34° versus 38°, p<0.001; 39° versus 41°, p=0.023). Increases in anteversion correlated with increased posterior coverage angles (r=0.805; p<0.001). Increases in tilt were correlated with increases in superior coverage angles (r=0.797; p<0.001). The posterosuperior regions of the acetabulum were the last to develop and this process occurred earlier in females compared with males. Articular surface area increased from 18 (8-10 years) to 24 cm(2) (13-17 years) in males and from 17 (8-10 years) to 21 cm(2) (13-17 years) in females. [corrected]. Articular surface area was higher in males beginning in the 10- to 13-year-old age group (p=0.001). CONCLUSIONS: Using a novel technique to analyze acetabular morphology, we found that acetabular development occurs earlier in females than males. The posterosuperior region of the acetabulum is the final region to develop. The articular cartilage surface area and articular cartilage coverage of the femoral head are increasing in addition to total coverage of the femoral head during the final stages of acetabular development. LEVEL OF EVIDENCE: Level III, prognostic study.

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.

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.

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.