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.

3D Knee Trochlear Morphology Assessment by Magnetic Resonance Imaging in Patients With Normal and Dysplastic Trochleae.

BACKGROUND: Trochlear dysplasia is recognized as a significant risk factor for patellar instability, but current imaging modalities fail to allow full visualization and classification of the complex 3-dimensional (3D) anatomy of the trochlea. The purpose of this study was to elucidate primary differences in trochlear morphology between patients with and without patellar instability by utilizing 3D magnetic resonance imaging (MRI) reconstructions of the trochlea. METHODS: An institutional review board-approved retrospective review included 24 patients with a diagnosis of patellar instability and an age-matched and sex-matched control population of 12 patients. 3D models of the femoral trochlea were created from MRI images and measurements were performed. 3D measurements were trochlear groove volume and surface area that were normalized to the femoral width. 2D measurements were performed throughout the length of the trochlea including the bony and cartilaginous sulcus angles as well as the bony and cartilaginous trochlear depths. Differences were also assessed between sex, skeletal maturity, and trochlear dysplasia severity. RESULTS: Surface topography of the trochlea varied significantly based on location with the trochlea becoming progressively more flat proximally away from the notch (P<0.05). Patients with patella instability had reduced trochlear volumes and trochlear depths compared with control patients (P<0.05). These differences were more pronounced with the cartilaginous measurements as well as more proximally within the trochlea. Patients with high-grade dysplasia had greater reductions in trochlear volumes and depth especially proximally in the trochlea (P<0.05). Once femoral size was standardized, minimal differences were observed based on sex or skeletal maturity (P>0.05). CONCLUSIONS: Novel 3D MRI reconstructions demonstrated that measurements of trochlear morphology varied significantly between patients with and without patellar instability. When trochlear dysplasia is present, it appears to affect the majority of the trochlear surface, but preferentially the proximal extent. Future trochlear dysplasia classification systems may benefit from assessment of articular cartilage surface measures rather than primarily osseous structure measurements. LEVEL OF EVIDENCE: Level III-case-control prognostic study.

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.

The 3D Sagittal Profile of Thoracic Versus Lumbar Major Curves in Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective. OBJECTIVE: To compare the 3D sagittal profile of patients with main thoracic or thoracolumbar/lumbar adolescent idiopathic scoliosis (AIS) to a normal cohort. SUMMARY OF BACKGROUND INFORMATION: Thoracic AIS is often associated with a loss of kyphosis. Classically, this measure has been made in 2D, which may underestimate the true sagittal deformity. METHODS: Biplanar upright radiographs were obtained on 152 primary thoracic (TH: Lenke 1-4), 50 primary thoracolumbar/lumbar (TL/L: Lenke 5-6) curves, and 89 normal controls (NC). 3D spinal reconstructions were created using sterEOS software. MATLAB code was used to create segmental measurements of kyphosis/lordosis for each vertebral and disc segment from T1 to S1 in the local coordinate system of each motion segment. Comparisons were made between groups for the 3D summed segmental measures (T1-T5, T5-T12, T12-S1), pelvic incidence, sacral slope, and pelvic tilt. RESULTS: Mean 2D Cobb was 57°±12° (range 40°-115°) for TH curves and 52°±9° (range 37°-75°) for TL/L curves. Significant differences in 3D sagittal measures were found between the 3 groups. Post hoc tests revealed significant differences at T1-T5, TH

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.

Predicting 3D Thoracic Kyphosis Using Traditional 2D Radiographic Measurements in Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective. OBJECTIVE: To develop and validate a prediction formula to estimate three-dimensional (3D) T5-T12 kyphosis in adolescent idiopathic scoliosis (AIS) from standard two-dimensional (2D) radiographic measurements. SUMMARY OF BACKGROUND DATA: 2D measurements of thoracic kyphosis in AIS patients overestimate 3D kyphosis; however, there is a lack of widespread availability of 3D imaging technology. METHODS: Retrospective review was performed for AIS patients with right thoracic curves evaluated with EOS Imaging from January 2010 to June 2014. Standard 2D posteroanterior and lateral radiographic measurements, pelvic incidence, Nash-Moe grade, Perdriolle rotation, and "3D T5-T12" sagittal measures (reconstructed with sterEOS, analyzed with custom MatLab code) were input into a multivariate logistic analysis to create a prediction model for 3D T5-T12 sagittal alignment. An initial cohort of 66 patients (curves 14°-85°) was used to create a predictive model, and a separate cohort of 129 patients (curves 16°-84°) was used to validate the formula. RESULTS: 2D thoracic coronal Cobb and 2D T5-T12 kyphosis were the only significant predictors in the model. The prediction formula for estimating 3D T5-T12 sagittal measurement from standard 2D measurements, in degrees, was 18.1 + (0.81*2D T5-T12 sagittal Cobb) - (0.54*2D coronal Cobb), r2 = 0.84. The average model error between predicted and measured 3D T5-T12 kyphosis was ±7°. The predicted 3D T5-T12 kyphosis (8.6° ± 12.1°) and measured 3D T5-T12 kyphosis (8.5° ± 13.0°) were not significantly different (p = .8). 3D kyphosis was less than standard measures of 2D kyphosis (8.5° ± 13.0° vs. 20.2° ± 12.6°, p < .001). CONCLUSION: This simple validated formula to predict 3D T5-T12 sagittal alignment using routine 2D thoracic Cobb and T5-T12 kyphosis for thoracic AIS patients has great potential value in assessing historical data collected prior to the development of 3D imaging methods as well as understanding/planning surgical hypokyphosis correction in patients without access to 3D imaging.

Paper #10: 3D Assessment of Spine Growth in Early Onset Scoliosis during Growing Rod Lengthening.

Measuring the true spine growth during growing rod (GR) lengthening is limited with 2D radiographs. With 3D imaging, this study demonstrates that during GR lengthening the spine lengthens and vertebra increase in size suggesting spinal growth that matches the relative increase in rod length during the distraction period.

Risk of Implant Loosening After Cyclic Loading of Fusionless Growth Modulation Techniques: Nitinol Staples Versus Flexible Tether.

STUDY DESIGN: Biomechanical evaluation using porcine spines. OBJECTIVE: Compare the fixation strength of two currently used fusionless adolescent idiopathic scoliosis correction techniques following cyclic loading using porcine spines. SUMMARY OF BACKGROUND DATA: The ability of fusionless implants to control or correct scoliosis in a growing patient requires such implants to maintain spinal fixation. Because they cross the disc, motion may weaken fixation over time. METHODS: Eight pig spines were divided into cycled segments (T10-T13) and uncycled segments (T7-T8, L2-L3). Initial range of motion (ROM) was determined in torsion, flexion-extension, and lateral bending (0.5°/s to 1.75 N·m).Staple group (n = 4): 6 mm parallel staples were inserted on the right anterolateral spine across each intervertebral disc. Cycled segments received six staples (three adjacent discs) and uncycled segments received four staples (two separate discs).Tether group (n = 4): 5.35 × 35 mm right anterolateral vertebral body screws were placed into each vertebra. Cycled segments received four screws and uncycled segments received four screws. Screws in cycled segments were connected with a flexible tether tensioned to straight alignment.ROM of instrumented cycled segments was measured, and then segments were loaded to the measured ROM in flexion-extension (2000 cycles), lateral bending (1000 cycles), and axial rotation (2000 cycles). Implants were axially loaded to failure. Parametric tests compared pre- to postimplant ROM; nonparametric tests compared staple to screw pullout strength; P < 0.05 was significant. RESULTS: There were no differences in ROM before instrumentation between groups. ROM was not changed except tethers decreased left lateral bending (-6.2°). Although staple pullout was less than screw pullout for cycled and uncycled segments (P < 0.05 and P = 0.057, respectively), there was no difference in pullout strength with and without cyclic loading for either group (P = 0.4). CONCLUSION: Tethers decreased lateral bending away from the tether. Screws had almost five times greater load to failure than staples. Five thousand cycles did not result in loosening of either staple or tether screws. LEVEL OF EVIDENCE: N/A.

Medial Patellofemoral Ligament Reconstruction: Fixation Technique Biomechanics.

Introduction The medial patellofemoral ligament (MPFL) is the primary soft-tissue stabilizer of the patella and it is often reconstructed in patients with recurrent patella instability. This biomechanical analysis evaluates the integrity of four methods of MPFL reconstruction subjected to cyclic loading using a porcine model. Methods Four techniques of MPFL reconstruction were analyzed using a 4 mm flexor tendon graft, all with two points of patellar fixation to best recreate the native MPFL anatomy. The four techniques were: (1) interference screw technique, (2) suture anchor technique, (3) converging tunnel technique, and (4) two bone tunnel technique. Maximum load, yield load, and stiffness of the graft fixation/bone complex were analyzed, and statistics were performed with SPSS and significance set at a p-value of < 0.05. Results The converging tunnel technique demonstrated the highest maximum load and yield load, significantly higher than the interference screw or suture anchor groups (p = 0.007). In addition, the converging tunnel technique demonstrated the greatest stiffness with significantly greater stiffness than the two bone tunnel techniques (p = 0.016). Conclusion The combination of strength and stiffness, the avoidance of patella implants, and the creation of a single transosseous tunnel make the converging tunnel technique a desirable technique for MPFL reconstructions.

Defining the "Three-Dimensional Sagittal Plane" in Thoracic Adolescent Idiopathic Scoliosis.

BACKGROUND: Obtaining accurate measurements of scoliosis from two-dimensional (2-D) radiographs can be challenging because of the three-dimensional (3-D) nature of the deformity. Previous studies have shown that the sagittal plane, in particular, is misrepresented on 2-D radiographs because of the influence of axial plane rotation. The purpose of the current study was to define a methodology for measuring the 3-D segmental sagittal alignment of the spine in patients with adolescent idiopathic scoliosis (AIS) and to assess the effect of axial plane rotation on differences between 3-D and 2-D measures of deformity. METHODS: Preoperative and postoperative EOS images of 120 consecutive patients with AIS (primary thoracic curves) treated with segmental thoracic pedicle-screw instrumentation were analyzed in the "3-D sagittal plane." The technique measured 3-D kyphosis or lordosis in the specific plane of sagittal motion for each spinal motion segment. The kyphosis (+) and lordosis (-) values of the segments from T5 to T12 were summed to give the 3-D measurement of T5-T12 kyphosis. These values were compared with the standard 2-D measurements of T5-T12 kyphosis on lateral radiographs, and a correlation analysis with regard to axial plane rotation of the apex was performed. RESULTS: The average age (and standard deviation) of the patients was 14 ± 2 years. The mean preoperative Cobb angle on the standard 2-D view was 55° ± 10° and on the 3-D view was 52° ± 9° (p ≤ 0.001). On the 3-D view, the mean preoperative T5-T12 kyphosis was 6° ± 14°, and the kyphosis significantly increased to 26° ± 6° postoperatively (p < 0.001). The T5-T12 kyphosis on the standard 2-D view measured 18° ± 13° preoperatively and 27° ± 6° postoperatively (p < 0.001). The difference between the 2-D and 3-D measurements of T5-T12 kyphosis strongly correlated with apical vertebral rotation (r = 0.85; p < 0.01). CONCLUSIONS: Routine 2-D measurements of thoracic kyphosis erroneously underestimate the preoperative loss of kyphosis in AIS because of errors associated with axial plane rotation, an inherent component of thoracic scoliosis.

Extrusion of the Hamate: A Case Report with Proposed Classification Amendment.

CASE: A thirteen-year-old right-hand-dominant girl sustained a right hamate fracture-extrusion with associated pisiform dislocation and volar degloving injury with open fractures of the scaphoid, capitate, lunate, and trapezoid following an all-terrain-vehicle rollover. She was noted to have paresthesias in the median nerve distribution. Treatment involved irrigation and debridement of the right wrist and internal fixation of the hamate, capitate, and scaphoid. At fifteen months of follow-up, she had returned to competitive softball as a pitcher. Radiographs demonstrated fully healed fractures. CONCLUSION: Complete extrusion of the hamate through an open wound can be treated with good functional outcomes.

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.

The modulation of spinal growth with nitinol intervertebral stapling in an established swine model.

PURPOSE: Anterior spinal stapling for the treatment of adolescent idiopathic scoliosis has been shown to slow progression in small curves; however, its role in larger curves remains unclear. The purpose of this study was to evaluate the effectiveness of nitinol staples to modulate spinal growth by evaluating the two-dimensional and three-dimensional morphological and histological effects of this method in a well-established porcine model. METHODS: Three immature Yucatan miniature pigs underwent intervertebral stapling. Two staples spanned each of three consecutive mid-thoracic discs and epiphyses. Monthly radiographs were obtained. Computed tomography (CT) was conducted at harvest after 6 months of growth. Measurements of wedging and height for each disc and vertebral body were conducted. Micro CT was used to compare physeal closure between stapled and non-stapled levels. Histology of the growth plate also compared the hypertrophic zone thickness for control and stapled vertebrae. RESULTS: After 6 months of stapled growth, the average coronal Cobb angle of the stapled segments increased by 7.7 ± 2.0° and kyphosis increased by 3.3 ± 0.6° compared to preoperative curves. Increased vertebral wedging and decreased disc height (p < 0.001) were noted in stapled regions. Overall, 26 ± 23 % of each growth plate was closed in the stapled segments, with 6 ± 8 % closure in the unstapled levels. No difference was observed regarding the hypertrophic zone height when comparing instrumented to uninstrumented levels, nor was a difference recognized when comparing right versus left regions within stapled levels alone. CONCLUSIONS: Six months of nitinol intervertebral stapling created a mild coronal and sagittal deformity associated with reduced vertebral and disc height, and increased coronal vertebral and sagittal disc wedging.