Growth modulation response in vertebral body tethering depends primarily on magnitude of concave vertebral body growth.

PURPOSE: There is variability in clinical outcomes with vertebral body tethering (VBT) partly due to a limited understanding of the growth modulation (GM) response. We used the largest sample of patients with 3D spine reconstructions to characterize the vertebra and disc morphologic changes that accompany growth modulation during the first two years following VBT. METHODS: A multicenter registry was used to identify idiopathic scoliosis patients who underwent VBT with 2 years of follow-up. Calibrated biplanar X-rays obtained at longitudinal timepoints underwent 3D reconstruction to obtain precision morphological measurements. GM was defined as change in instrumented coronal angulation from post-op to 2-years. RESULTS: Fifty patients (mean age: 12.5 ± 1.3yrs) were analyzed over a mean of 27.7 months. GM was positively correlated with concave vertebra height growth (r = 0.57, p < 0.001), 3D spine length growth (r = 0.36, p = 0.008), and decreased convex disc height (r = - 0.42, p = 0.002). High modulators (patients experiencing GM > 10°) experienced an additional 1.6 mm (229% increase) of mean concave vertebra growth during study period compared to the Poor Modulators (GM < - 10°) group, (2.3 vs. 0.7 mm, p = 0.039), while convex vertebra height growth was similar (1.3 vs. 1.4 mm, p = 0.91). CONCLUSION: When successful, VBT enables asymmetric vertebra body growth, leading to continued postoperative coronal angulation correction (GM). A strong GM response is correlated with concave vertebral body height growth and overall instrumented spine growth. A poor GM response is associated with an increase in convex disc height (suspected tether rupture). Future studies will investigate the patient and technique-specific factors that influence increased growth remodeling.

The Anterior Modified San Diego Acetabuloplasty Does Not Increase Superior-Anterior Coverage in Patient-Specific 3D-Printed Models.

BACKGROUND: Patients with developmental dysplasia of the hip may require pelvic osteotomies to improve acetabular coverage. The purpose of this study was to compare the changes in acetabular version, tilt, and regional coverage angles following the San Diego acetabuloplasty (SDA), the modified San Diego acetabuloplasty (mSDA), and the Pemberton acetabuloplasty (PA). METHODS: Fourteen patients with developmental dysplasia of the hip and computed tomography (CT) imaging were identified. From CT images, 2 identical pelvises were 3-dimensional-printed for each patient. Bone was printed with rigid material, and cartilage with flexible material. For each model pair, the SDA was performed on one and the PA was performed on the other. CT scans were obtained before and after acetabuloplasties. Next, the bone graft in the SDA model was moved anteriorly, representing the mSDA, and the model was rescanned. Acetabular version, tilt, and coverage angles (posterior, superior-posterior, superior, superior-anterior, and anterior) were calculated. Preoperative to postoperative differences were compared (repeated measures analysis of variance or Wilcoxon signed rank test). The significance was set to P <0.05. RESULTS: The mean age at CT was 5.8±1.2 years (range: 3.9 to 7.5 y). All 3 procedures (SDA, mSDA, and PA) significantly increased acetabular tilt; P <0.045), with a similar change observed for all 3 ( P =0.868). PA was the only procedure to significantly decrease relative acetabular version (6.5±6.5 degrees, preoperative: 12.9±5.3 degrees; P =0.004). Both the SDA and mSDA procedures significantly increased coverage in the superior-posterior octant (SDA: 92.6±9.3 degrees, mSDA: 92.3±9.8 degrees, preoperative: 81.9±9.5 degrees; P <0.02), with a similar percent change among the 2 ( P =1.0). All 3 procedures significantly increased superior coverage ( P <0.04); the increase was similar among the 3 ( P =0.205). The PA was the only procedure to produce a significant increase in coverage in the superior-anterior octant (91.0±16.7 degrees, preoperative: 74.0±12.1 degrees; P =0.005) or the anterior octant (50.7±11.7 degrees, preoperative: 45.8±8.9 degrees; P =0.012). CONCLUSIONS: The SDA and mSDA procedures produced similar postoperative changes, primarily in the superior and superior-posterior acetabular octants. Placing the graft more anteriorly did not increase anterior coverage in the mSDA, and only the PA increased coverage in the superior and superior-anterior acetabular octants.

A comparison of cone beam computed tomography, standard computed tomography and plain radiographs in the evaluation of medial epicondyle humerus fractures.

The ideal technique to measure medial epicondyle humerus fracture displacement minimizes radiation exposure while maximizing measurement accuracy and reliability. This study compares the radiation exposure and accuracy of displacement measurements of the four-view X-ray examination (XR), computed tomography (CT) and in-clinic cone-beam CT (CBCT). A cadaveric humerus underwent medial epicondyle osteotomy. The fragment was fixed to the humerus at clinically relevant displacements (6 to 18 mm). Dosimeters were placed around the distal humerus and simulating thyroid location. XR, CT and CBCT were performed at each displacement. Four pediatric orthopedists measured the maximum linear displacement on each XR and 3D reconstruction of the CT and CBCT images. Focal (elbow location) and thyroid radiation exposure was compared between modalities. Intra- and interclass correlation coefficients (ICC) for displacement measurements were determined. Mean focal radiation exposures for XR, CT and CBCT were 0.008, 2.061 and 0.478 rad, respectively (P = 0.001). Exposures 10 inches from the elbow for XR, CT and CBCT were 0.001, 0.066 and 0.010 rad, respectively (P = 0.006). At 12 inches, there was no significant difference in exposure between XR and CBCT ( P = 0.114). Intra- and interobserver reliabilities were excellent for all measures, except lateral x-ray. CBCT and CT had significantly less deviation from the actual displacement compared to XR ( P < 0.05). In-office CBCT of the elbow exposes patients to significantly less radiation than conventional CT. All X-ray images (except lateral), CT and CBCT had equal reliability in evaluating medial epicondyle fractures, which contrasts with previous evidence.

3-D acetabular morphology of the neuromuscular hip: implications for preoperative planning.

The importance of precisely understanding the pathoanatomy of acetabular dysplasia prior to surgical treatment has long been recognized. Acetabuloplasties for neuromuscular hip dysplasia have typically aimed to improve the acetabulum by increasing posterior-superior coverage, as previous three-dimensional (3-D) computed tomography (CT) studies have shown that acetabular dysplasia in neuromuscular hips is primarily in the direction of posterior-superior subluxation or dislocation. The purpose of this study was to identify differences in 3-D morphology between normal hips and dysplastic neuromuscular hips, specifically to identify areas of acetabular deficiency to guide preoperative decision-making. Patients treated for neuromuscular hip dysplasia at a single institution between 2009 and 2017 with a preoperative high-resolution pelvic CT scan (28 hips) were evaluated with custom software to measure acetabular morphology. Acetabuli were divided into equal octants; coverage angles were measured for each octant of interest. Variables were compared with age- and sex-matched normal controls (56 hips). We found a wide range of hip pathology in our study cohort. Five hips had no sectors with abnormal coverage. One hip (4%) was overcovered anteriorly. The remaining pathology was undercoverage located anteriorly [n = 7 (25%)], superiorly [n = 6 (21%)], posteriorly [n = 4 (14%)] or globally [n = 5 (18%)]. Our findings indicate that individual patients with neuromuscular acetabular dysplasia have unique deformities that do not uniformly conform to a specific area of acetabular deficiency. It is imperative to define the specific 3-D acetabular deficiency location and magnitude for accurate preoperative planning. Level of evidence: Level III.

Distal tibial osteotomy to address internal tibial torsion: Should the fibula be cut?

Background Rotational tibial osteotomy seeks to address pathologic tibial torsion. Inclusion of fibular osteotomy during this procedure remains controversial. This study aimed to determine how external rotation through a tibial osteotomy, with or without a fibular osteotomy, would influence tibiofibular joint congruity. Methods Eight cadaveric legs underwent distal tibial osteotomies. Pins were placed to designate neutral, 10°, 20°, 30° of external rotation. Computed tomography (CT) imaging was performed at each rotation without, then with a fibular osteotomy. Magnetic Resonance Imaging was performed prior to fibular osteotomy to confirm that ligaments remained intact. Custom software calculated tibial torsion using CT scan 3D reconstructions. Proximal tibiofibular joint rotation, distal tibiofibular gapping and ankle mortise were measured on each CT exam. Groups without and with fibular osteotomy were compared. Findings There was no difference between tibial osteotomy rotation magnitude with or without the fibular osteotomy (P = 0.2). The group without the fibular osteotomy had greater proximal fibular rotation at the tibiofibular joint at 20°, 30° (P < 0.05), greater posterior distal tibiofibular gap at 10°, 20°, 30° (P < 0.05) and less anterior distal tibiofibular gap at 20°, 30° (P < 0.05). The medial tibiotalar space was narrowed without the fibular osteotomy at 20°, 30° (P < 0.05) compared to pre-rotation. Interpretation Deformity at the proximal tibiofibular and ankle joints become most pronounced at >20° of tibial rotation without a fibular osteotomy. The first joint to be affected is the distal tibiofibular joint. To limit ankle and proximal tibiofibular articular deformation during tibia rotational osteotomy, a fibular osteotomy is recommended when correcting over 20° of rotation.

The influence of 3D curve severity on paraspinal muscle fatty infiltration in patients with adolescent idiopathic scoliosis.

PURPOSE: In a sex-inclusive cohort of patients with adolescent idiopathic scoliosis (AIS): (1) assess the relationship between 3D curve severity, curve flexibility, and paraspinal muscle fatty infiltration, and (2) describe three-dimensional (3D) fatty infiltration of the paraspinal muscles. METHODS: Fat signal fraction of the paravertebral muscles was measured in pre-operative magnetic resonance images (MRIs) of males and females with AIS at the apex, ± 1, and ± 2 levels from the apex of the curve (n = 62). In a subset of patients with biplanar erect radiographic imaging (n = 35), 3D measures of deformity (axial rotation of the apical vertebrae, thoracic kyphosis, and coronal Cobb angle) were measured. RESULTS: Contrary to previous studies, no relationship between coronal Cobb angle and fatty infiltration was found. However, axial apical rotation and sagittal Cobb angle were found to be significant predictors of paravertebral fatty infiltration (R2 = 0.196-0.222). Curve concavity, female sex, and proximity to the curve apex were found to be the strongest predictors of fatty infiltration. Greater fatty infiltration of the paravertebral muscles was found on the concave side of the curve (15-24% vs. 11-13%), with increasing fatty infiltration toward the apex of the curve. Fatty infiltration was protected on the convex side of the curve, with no differences in the amount of fatty infiltration across levels. CONCLUSION: These findings highlight that coronal curve severity and flexibility are not the primary influencing factors for the degree of paraspinal fatty infiltration in patients with AIS. This may have implications for nonsurgical rehabilitation strategies such as bracing and physical therapy. LEVEL OF EVIDENCE: II.

Defining a new three-dimensional method for determining femoral torsional pathology in children.

The purpose of this study was to compare 2D femoral torsional values to measurements made from 3D reconstructions, in pediatric patients with torsional pathology. Seventeen patients were included in this study. Femoral torsion was measured in 2D and 3D and compared using interclass correlation and Bland-Altman plots. The 2D and 3D measurements had excellent correlation (r > 0.79, P < 0.001). However, we found a fixed bias of -5.1 ± 11.3°, with 3D being consistently lower than 2D. This bias persisted when looking at only subjects with normal neck shaft angles. A proportional bias of 1.2 ± 7.8° was found when comparing 2D and 3D MRI measurements indicating that as the magnitude of the torsion changed, the difference between the two measurement techniques also changed. Given the proven accuracy of 3D reconstructions in the measurement of femoral torsion, clinicians should consider this method in pediatric patients with torsional pathology. Although 2D and 3D computed tomography (CT)/MRI torsional measurements correlate well, the presence of fixed and proportional biases indicates that the two methods cannot be used interchangeably. We submit that 3D reconstructed CT/MRI imaging, aligned along the mechanical axis, should be considered to assess femoral torsion in pediatric patients. Level of evidence: III Diagnostic Study.

3D cone-beam tomosynthesis provides axial imaging of the spine with lower radiation compared to computed tomography.

STUDY DESIGN: Three imaging techniques were compared using porcine spines. OBJECTIVES: To compare image acquisition time, radiation exposure, pedicle width measurement, assessment of screw breach, and image artifact between cone-beam tomosynthesis (CBT) single mode, CBT dual mode (stereotactic CBT), and computed tomography (CT) imaging with and without spinal implants. CT is the standard for axial imaging of orthopedic procedures. CBT technology is being developed, allowing real-time intraoperative imaging and 3D surgical guidance. CBT may deliver useful axial imaging quicker with less radiation than current technologies. METHODS: Six porcine spines were instrumented with bilateral pedicle screws at six levels connected with 5.5 mm rods. Dosimeters were attached to four surfaces of spines. CT, CBT single and CBT dual images were acquired pre-implant and post-implant. Image acquisition and 3D reconstruction times were recorded. Pedicle widths were measured before and after instrumentation. Screw medial breaches were graded (0: no breach, 1: < 2 mm, 2: 2-4 mm, 3: > 4 mm). Artifact and/or distortion of each image was ranked (0 = none, 1 = mild, 2 = moderate, 3 = large). Image acquisition and reconstruction times, radiation dose, pedicle width, screw breach and artifact were compared between techniques. RESULTS: Total image acquisition and reconstruction times of CBT was significantly less (single: 9.9 ± 0.2 s, p < 0.001; dual: 60.0 ± 8.7 s, p < 0.001) than CT (250.3 ± 36.7 s). CBT had significantly less radiation exposure than CT (CT: 0.7 ± 0.1 rad, single: 0.03 ± 0.02 rad, dual: 0.07 ± 0.03 rad; p < 0.001). No difference in pedicle width change pre-implant to post-implant was found (CT: p = 0.449, single: p = 0.430, dual: p = 0.528). Pedicle width (pre-implant: p > 0.5, post-implant: p > 0.9) and pedicle width change (p > 0.4) was similar amongst all techniques. Breach assessment was not different between groups (p = 0.257). CBT images had consistently lower artifact grades than CT. CONCLUSIONS: Although CBT axial image quality appeared subjectively inferior to CT, it enabled consistent assessment of pedicle width and screw breach, at half time and 10× lower radiation exposure. With continued refinements, CBT technology may allow for adequate intra-operative axial imaging using low radiation exposure.

Three-dimensional Analysis of Acetabular Morphology and Orientation in Patients With Slipped Capital Femoral Epiphysis.

BACKGROUND: Previous studies analyzing the acetabuli in patients with slipped capital femoral epiphysis (SCFE) have not definitively addressed the relationship between SCFE and acetabular shape. Femoral head overcoverage and acetabular version are thought to contribute to SCFE. The purpose of this study was to determine the acetabular morphology and orientation in hips with SCFE and compare them with normally developing children. METHODS: Pelvic computed tomography (CT) images of patients with SCFE were compared with pelvic CTs of patients without orthopedic abnormalities (normal controls). Three-dimensional (3-D) reconstructions were created from each CT examination. Custom software uniformly aligned the pelvis then determined acetabular measures from the reconstructions including acetabular version, acetabular tilt, articular surface area, and acetabular coverage angle measured in a radial manner dividing the acetabulum into octants. RESULTS: Two-hundred forty-four hips were included (53 SCFE, 31 unaffected contralateral hips in patients with SCFE, and 160 controls). The acetabular version was similar among SCFE hips, unaffected contralateral hips, and normal controls (P=0.48). Control hips had higher acetabular tilt than SCFE-affected hips (P=0.01) and unaffected contralateral hips (P=0.04). The acetabular surface area was higher in SCFE-affected hips compared with controls (P<0.05). SCFE-affected hips and the unaffected contralateral hips in patients with SCFE had increased acetabular coverage compared with controls in all 5 acetabular octants. CONCLUSIONS: Contrary to some previous studies, the authors did not find the acetabulum to be retroverted in patients with SCFE compared with controls. Both affected and unaffected hips of patients with SCFE have decreased acetabular tilt. Acetabular surface area is higher in hips with SCFE compared with normal controls, and both the SCFE-affected hips and unaffected hips had increased acetabular coverage compared with controls in all 5 octants of the acetabulum. The shared morphology of affected and unaffected hips in patients with SCFE suggests that their acetabular anatomy may predispose them to slip. LEVEL OF EVIDENCE: Level III.

Reliability of Low-dose Biplanar Radiography in Assessing Pediatric Torsional Pathology.

BACKGROUND: Low-dose biplanar radiographs (LDBRs) significantly reduce ionizing radiation exposure and may be of use in evaluating lower extremity torsion in children. In this study, we evaluated how well femoral and tibial torsional profiles obtained by LDBR correspond with 3-dimensional (3D) computed tomography (CT) and magnetic resonance axial imaging (MRI) in pediatric patients with suspected rotational abnormalities. METHODS: Patients who had both LDBR and CT/MRI studies performed for suspected lower extremity rotational deformities were included. Unlike previous publications, this study focused on patients with lower extremity torsional pathology, and bilateral lower extremities of 17 patients were included. CT/MRI torsion was measured using the Reikerås method, after conversion to 3D reconstructions. The LDBRs were deidentified and sent to the software division of EOS imaging, who created 3D reconstructions and evaluated each reconstruction for the torsional quantification of the femurs and tibiae. These imaging modalities were compared using correlation statistics and Bland-Altman analyses. RESULTS: The mean age of the cohort was 12.1±1.7 years old. Torsional values of the femur were significantly lower in LDBRs versus 3D CT/MRIs at 17.7±15.1 and 23.3±17.3, respectively (P=0.001). Torsional values of the tibia were similar in LDBRs versus 3D CT/MRIs at 23.6±10.6 and 25.3±11.2, respectively (P=0.503). There was a good intermodality agreement between LDBR and 3D CT/MRI torsional values in the femur (intraclass correlation coefficient=0.807) and tibia (intraclass correlation coefficient=0.768). Bland-Altman analyses showed a fixed bias with a mean difference of -5.6±8.8 degrees between femoral torsion measurements in LDBRs versus 3D CT/MRIs (P=0.001); 15% (5/34) of femurs had a clinically significant measurement discrepancy. Fixed bias for LDBR measurements compared with 3D CT/MRIs for the tibia was not observed (P=0.193), however, 12% (4/34) of tibias had a clinically significant measurement discrepancy. CONCLUSION: Although we found strong correlations between torsional values of the femur and tibia measured from LDBRs and 3D CT/MRIs, torsional values of the femur produced from LDBRs were significantly lower than values obtained from 3D CT/MRIs with some notable outliers. LEVEL OF EVIDENCE: Level III.

Assessment of three-dimensional acetabular coverage angles.

The purpose of this article is to report the inter- and intra-observer reliability of a computerized objective technique to quantify patient-specific acetabular morphology. We describe the use of and provide the software code for a technique to better define the location and magnitude of acetabular pathology. We have developed software code that allows the end user to obtain detailed measurements of the acetabulum using traditional computed tomography data. We provide the code and detailed instructions on how to use it in this article. The methodology was validated by having an unbiased observer (that was not involved in this project but has been trained in this software measurement methodology) to perform the entire acquisition, reconstruction and analysis procedure and compare their measurements to the measurements of one of the authors. The author then repeated the procedure 2 months later to determine intra-observer reliability. Inter- and intra-observer reliability for version, tilt, surface area and total acetabular coverage angles ranged from an intra-class correlation coefficient of 0.805 to 0.997. The method provided in this manuscript gives a reproducible objective assessment of three-dimensional (3D) acetabular morphology that can be used to assist in the diagnosis of hip pathology and to compare the morphological parameters of subjects with and without hip pathology. It allows a surgeon to understand the 3D shape of each individual's acetabulum, share these findings with patients and their parents to demonstrate the magnitude and location of the clinical abnormality and perform patient-specific surgical corrections to optimize the shape and coverage of the hip.

Medial Epicondyle Fractures: Biomechanical Evaluation and Clinical Comparison of 3 Fixation Methods Used in Pediatric Patients.

BACKGROUND: Screw fixation is the most commonly employed fixation strategy for displaced medial epicondyle fractures, but in younger patients with minimal ossification, the fracture fragment may not accommodate a screw. In these situations, Kirschner-wires (K-wire) or suture anchors may be utilized as alternatives. The purposes of this study were to examine the biomechanical properties of medial epicondyle fractures fixed with a screw, K-wires, or suture anchors, to evaluate clinical outcomes and complications of patients 10 years of age or younger treated with these approaches, and to perform a cost-analysis. METHODS: Biomechanical assessment: Immature pig forelimbs underwent an osteotomy through the medial epicondyle apophysis, simulating a fracture. These were then fixed with a screw, K-wires or suture anchors. Cyclic elongation (mm), displacement (mm), load to failure (N), and stiffness (N/mm) were assessed. Clinical assessment: a retrospective review was performed of patients 10 years of age or younger with a medial epicondyle fracture fixed with these strategies. Radiographic outcomes, postoperative data and complications were compared. These data were used to perform a cost-analysis of each treatment approach. RESULTS: Biomechanically, screws were stronger (P=0.047) and stiffer (P=0.01) than the other constructs. Clinically, 51 patients met inclusion criteria (screw=27, wires=11, anchor=13). Patients treated with K-wires were younger (P<0.05) and patients treated with screw fixation had a shorter casting duration (P=0.008). Irrespective of treatment strategy, all fractures healed (100%) and only 1 patient in the screw group lost reduction. Clinical outcomes and complications were similar between groups, but the suture anchor group was less likely to require a second surgery for implant removal (P<0.05). This lower reoperation rate led to a cost-saving of 10%. CONCLUSIONS: Biomechanically, all 3 approaches provided initial fixation exceeding the forces observed across the elbow joint with routine motion. The screw construct was the strongest and stiffest. Clinically, all 3 strategies were acceptable, with screw fixation offering a shorter casting duration, but greater implant removal need with higher associated costs.

Increased Hip Intracapsular Pressure Decreases Perfusion of the Capital Femoral Epiphysis in a Skeletally Immature Porcine Model.

BACKGROUND: Increased intracapsular hip pressure is thought to be one of the possible etiologies of femoral head avascular necrosis after intra-articular proximal femoral fractures or acute slipped capital femoral epiphysis. The purpose of this study was to evaluate the relationship between intra-articular hip pressure (IAP) and epiphyseal perfusion pressure (EPP), and its dependency on skeletal maturity using a porcine model. METHODS: Seven female Yorkshire-hybrid pigs were used to study the direct relationship between IAP and EPP. A needle inserted into the capsule provided both IAP monitoring and saline infiltration until IAP was above mean arterial pressure (MAP). Video simultaneously documented IAP, EPP, MAP. Parameters for all trials in each hip were averaged and compared between the 2 age groups. Significance was P<0.05. RESULTS: Four young hips (in pigs 10.3±1.0 wk, 27.4±2.0 kg) and 5 older hips (21.1±0.1 wk, 89.4±7.1 kg) were studied. There was no significant difference in the MAP (50.0±11.8 and 55.5±7.0 mm Hg respectively, P=0.411) between the 2 age groups. In the older hips, biphasic EPP persisted despite increasing IAP to an average of 177 mm Hg over MAP. In the young pigs, the biphasic EPP waveform ceased with increased IAP to an average of 28 mm Hg over MAP. Biphasic waveforms returned once IAP fell to an average of 5 mm Hg over MAP. CONCLUSIONS: Increased IAP resulted in tamponade of epiphyseal perfusion in the young, but not in the older hips. An intact physis may preclude intraosseous metaphyseal vessels from penetrating the epiphysis, leaving it vulnerable to retinacular artery tamponade. CLINICAL RELEVANCE: The IAP and EPP relationship has direct clinical practice implications. Hip capsulotomy and decompression in young patients with intra-articular proximal femoral fractures and increased intracapsular pressure may decrease avascular necrosis risk.

Femoral derotational osteotomy level does not effect resulting torsion.

PURPOSE: The purpose of this study was to assess the effect on femoral torsion by rotational osteotomies at three different levels as measured in 3D using both the mechanical and the anatomic axes. METHODS: Ten cadaveric lower extremities underwent femoral osteotomies perpendicular to the anatomic axis (AA) at three levels: subtrochanteric, mid-diaphyseal and supracondylar. Parallel pins were placed, one in each femur segment. Computed tomography (CT) was acquired in post-osteotomies neutral position, then post-external rotation of the femur at each osteotomy level. Femurs were returned to neutral rotation between imaging exams. Using 3D CT reconstructions, custom software calculated femoral torsion (angle between the femoral neck axis and the posterior condylar axis in the transverse plane) and pin angle between segments, reoriented to both the mechanical axis (MA) and the AA. Pin angle and torsion change were compared for the three osteotomy locations (regression analysis and ANOVA performed). RESULTS: Two specimens were omitted (inadequate imaging); the remaining eight donors were 55-90 years old (mean: 64 ± 15 years), CT confirmed no bony defects. All three levels of osteotomy demonstrated significant correlations between the amount of rotation at the osteotomy (pin angle change) and the resulting change in femoral torsion (R square range 0.658-0.847). No significant differences were found between osteotomy level in torsion (MA:p = 0.285, AA:p = 0.156) or in pin angle (MA:p = 0.756, AA:p = 0.753). CONCLUSIONS: Performing a corrective rotational osteotomy orthogonal to the AA achieves the desired effect on MA regardless of location. This suggests that a surgeon's osteotomy level choice may be based on other risks/benefits of the various techniques.

Spinal rod gripping capacity: how do 5.5/6.0-mm dual-diameter screws compare?

STUDY DESIGN: Biomechanical comparative study. OBJECTIVE: To evaluate pedicle screw gripping capacity from five suppliers, comparing single-diameter (S-D) systems using 5.5-mm-diameter rods to dual-diameter (D-D) systems accepting 5.5- and 6.0-mm-diameter rods with both cobalt chromium (CoCr) and titanium alloy (Ti) rods. D-D systems have become increasingly prevalent; however, these systems theoretically may compromise spinal rod gripping, particularly when a smaller-diameter rod is used within a D-D pedicle screw. METHODS: D-D pedicle screw systems from three suppliers (accepting 5.5- and 6.0-mm-diameter, Ti and CoCr rods), and S-D systems from two suppliers (accepting 5.5-mm-diameter, Ti and CoCr rods) were tested on an MTS MiniBionix machine. Axial load was applied in line with the rod to measure axial gripping capacity (AGC), and torsional load was applied to measure torsional gripping capacity (TGC) for each rod material and diameter. AGC and TGC were compared between D-D and S-D constructs, suppliers, rod diameters, and materials with subsequent classification and regression tree (CART) analysis. RESULTS: 5.5-mm rods within D-D screws were no weaker than 5.5-mm rods in S-D systems for AGC (dual > single, p = 0.043) and TGC (p = 0.066). As a whole, D-D systems had greater AGC than S-D systems (p = 0.01). AGC differed between suppliers (p < 0.001). No rod diameter (p = 0.227) or material (p = 0.131) effect emerged. With CART analysis, Supplier was the most significant predictor for greater AGC. As a whole, D-D systems had greater TGC than S-D systems (p = 0.008). TGC differed between suppliers (p < 0.001). Rod diameter was a significant predictor of higher TGC (6.0 > 5.5 mm, p = 0.002). CoCr rods had greater TGC than Ti (p < 0.001). CART analysis revealed that Supplier and CoCr material were significant predictors for increased TGC. CONCLUSIONS: Despite 30%-70% variability in gripping capacity due to rod supplier and material, overall D-D pedicle screw systems had similar AGC and TGC as S-D systems. LEVEL OF EVIDENCE: N/A.

Periosteal incarceration versus interposition adipose tissue grafting in physeal fractures: pilot study in immature rabbits.

PURPOSE: The purpose of this study is to evaluate bar formation following physeal fracture with incarcerated periosteum or adipose tissue graft using radiographic and histological methods in an immature rabbit model. METHODS: Ten-week-old rabbits underwent induced proximal tibia physeal fractures with a contralateral sham. Fractures had periosteum (n = 5) or adipose tissue (n = 5) interposed. Radiographs were compared over time by tibial medial-lateral side difference (TMLSD)(mm), femoral-tibial angle and tibia plateau angle, and physeal bars evidence. MicroCT was performed, growth plates reconstructed, and physeal area calculated and normalized to same animal contralateral physes. Physeal disruption and chondrocyte organization were evaluated histologically. RESULTS: Radiographic: After 6 weeks, physeal bars formed in both periosteum (4 of 4) and fat groups (3 of 5). The periosteum group showed a significant increase in the TMLSD between immediate post-op and 10 days later (p = 0.028); but, after 6 weeks, TMLSD change was not significantly different between the three groups (p = 0.161). MicroCT: The normalized physeal area of every physis in the fat group was more than 0.9 (0.99 ± 0.06). Only half of the periosteum group was over 0.9 (0.81 ± 0.24). HISTOLOGY: Physeal disruption was seen by microscopic evaluation in none of the sham group, all 4 in the periosteum group and 4 of 5 in the fat group. CONCLUSIONS: Fat interposition may prevent, or at least delay, the onset of bars across a fractured physis compared to periosteum, but it is not completely protective.

Under Pressure: The Utility of Spacers in Univalved Fiberglass Casts.

BACKGROUND: Univalving fiberglass casts after fracture manipulation or extremity surgery reduces the risk of developing compartment syndrome (CS). Previous experiments have demonstrated that univalving decreases intracompartmental pressures (ICPs), but increases the risk for loss of fracture reduction due to altering the mechanical properties of the cast. The purpose of this study was to correlate cast valve width within a univalved cast model to decreasing ICP. METHODS: Saline bags (1 L) were covered with stockinette, Webril, and fiberglass tape then connected to an arterial pressure line monitor. Resting pressure was recorded. A water column was added to simulate 2 groups (n=5 each) of clinical CS: low pressure CS (LPCS range, 28 to 31 mm Hg) and high pressure CS (HPCS, range, 64 to 68 mm Hg). After the designated pressure was reached, the fiberglass was cut (stockinette and Webril remained intact). Cast spacers were inserted into each univalve and secured with varying widths: position #1 (3 mm wide), #2 (6 mm), #3 (9 mm), and #4 (12 mm). Pressure was recorded after cutting the fiberglass and following each spacer placement. RESULTS: In LPCS and HPCS groups, after univalve and placement of spacer position #1, pressure dropped by a mean of 52% and 58%, respectively. Spacer #2, decreased the pressure by a mean of 78% and 80%, respectively. Both spacer sizes significantly decreased the underlying pressure in both groups. Spacer #3 and #4 progressively reduced pressure within the cast, but not statistically significantly more than the previous spacer widths. CONCLUSIONS: This experimental model replicates the iatrogenic elevation in interstitial compartment pressure due to rigid cast application, not necessarily a self-sustained true CS. Increasing the univalved cast spread by ≥9 mm of the initial cast diameter will reduce pressure to a pre-CS level; however, a spread of only 6 mm can effectively reduce the pressure to <30 mm Hg depending on the initial elevated ICP. Cutting the Webril and stockinette in our model yielded a pressure decrease of 91% and 94% from the starting experimental pressure in the LPCS and the HPCS groups, respectively. CLINICAL RELEVANCE: Although the utility of splitting fiberglass casts has been previously demonstrated, we present evidence highlighting the benefit of spacing the split by at least 6 to 9 mm.

Comparison of 3 Pediatric Pelvic Osteotomies for Acetabular Dysplasia Using Patient-specific 3D-printed Models.

BACKGROUND: Children with developmental dysplasia of the hip may require a pelvic osteotomy to treat acetabular dysplasia. Three osteotomies are commonly performed in these patients (Pemberton, Dega, and San Diego), though comparative studies of each are limited. The purpose of this study was to compare changes in acetabular morphology (acetabular version, volume, and octant coverage angles) created by these 3 osteotomies using matched patient-specific 3D-printed pelvic models. METHODS: Fourteen patients with developmental dysplasia of the hip and preoperative computed tomography (CT) imaging were retrospectively included. For each patient CT, bone and cartilage tissues were independently segmented, and 3 identical pelvises were 3D-printed using a dual material printer. Bone was printed with rigid material and cartilage with flexible material to simulate the flexibility of the triradiate cartilage and pubic symphysis. Pemberton, Dega, and San Diego acetabular osteotomies were performed on the triplicate set of 3D prints. Acetabular version, volume, and octant coverage angles (posterior, superior-posterior, superior, superior-anterior, and anterior) were determined before and after each mock surgery by morphologic assessment using preoperative and postoperative CT images. RESULTS: San Diego osteotomy yielded a small increase (+3.34±1.71 degrees) in version, compared with decreases with Pemberton (-5.47±1.54 degrees) and Dega (-8.57±1.21 degrees, P<0.05). Acetabular volume decreased similarly for Pemberton (-13.36%±2.88%), Dega (-19.21%±2.73%), and San Diego (-19.29%±2.44%; P=0.215) osteotomies. San Diego osteotomy tended to have a larger postoperative increase in the posterior regions, and the Dega and Pemberton osteotomies tended to have larger postoperative increases in the anterior coverage regions. CONCLUSIONS: Quantifiable differences were identified in acetabular octant coverage angles and version between the 3 pelvic osteotomies. San Diego osteotomy increased acetabular coverage posteriorly resulting in acetabular anteversion, whereas Pemberton and Dega had greater superior-anterior coverage resulting in relative acetabular retroversion. This study is the first known to utilize 3D-printed models for comparison of surgical approaches in pediatric pelvic osteotomies.

Bioabsorbable plating in the treatment of pediatric clavicle fractures: A biomechanical and clinical analysis.

BACKGROUND: Classic implants for operative intervention of mid-shaft clavicle fractures in adolescents can become symptomatic, requiring removal. This study compares 1) biomechanical properties and 2) clinical outcomes in adolescents of mid-shaft clavicle fracture fixation with bioabsorbable versus metal implants. METHODS: Six synthetic clavicles with mid-shaft fractures underwent bioabsorbable plating. A testing frame applied 10 non-destructive torsion and 10 axial compression cycles, followed by cantilever bending to failure. Stiffness was calculated; maximum failure load and failure mode were recorded. Results were compared to previous data for locked metal constructs. Retrospective review of surgically treated clavicle fractures over three years included functional and radiographic outcomes. FINDINGS: Bioabsorbable plates had lower torsional stiffness (P < 0.001) and maximum cantilever load (P < 0.0001) than locked metal plates. There was no significant difference in compression stiffness (P = 0.2) or cantilever bending stiffness (P = 0.4). Primary failure of metal plates was screw pull-out compared to plate bending in bioabsorbable constructs. Seven patients with bioabsorbable implants were included. All patients with bioabsorbable constructs achieved radiographic union, but 71% lost reduction. Despite fracture angulation, all achieved normal shoulder function after one year determined by QuickDASH evaluation. None required a second surgery. INTERPRETATION: Bioabsorbable implants had lower torsional stiffness and cantilever failure load, but comparable compression stiffness to metal implants. Bioabsorbable implants failed via gradual bending versus the catastrophic failure seen in metal implants. The clinical review allows understanding of the sequelae of this lower failure load of bioabsorbable plates where their use allowed in fracture displacement, yet achievement of ultimate radiographic union and acceptable functional outcomes.