MRI-based 3D retinal shape determination

ObjectiveTo establish a good method to determine the retinal shape from MRI using three-dimensional (3D) ellipsoids as well as evaluate its reproducibility.Methods and analysisThe left eyes of 31 volunteers were imaged using high-resolution ocular MRI. The 3D MR-images were segmented and ellipsoids were fitted to the resulting contours. The dependency of the resulting ellipsoid parameters on the evaluated fraction of the retinal contour was assessed by fitting ellipsoids to 41 different fractions. Furthermore, the reproducibility of the complete procedure was evaluated in four subjects. Finally, a comparison with conventional two-dimensional (2D) methods was made.ResultsThe mean distance between the fitted ellipsoids and the segmented retinal contour was 0.03±0.01 mm (mean±SD) for the central retina and 0.13±0.03 mm for the peripheral retina. For the central retina, the resulting ellipsoid radii were 12.9±0.9, 13.7±1.5 and 12.2±1.2 mm along the horizontal, vertical and central axes. For the peripheral retina, these radii decreased to 11.9±0.6, 11.6±0.4 and 10.4±0.7 mm, which was accompanied by a mean 1.8 mm posterior shift of the ellipsoid centre. The reproducibility of the ellipsoid fitting was 0.3±1.2 mm for the central retina and 0.0±0.1 mm for the peripheral retina. When 2D methods were used to fit the peripheral retina, the fitted radii differed a mean 0.1±0.1 mm from the 3D method.ConclusionAn accurate and reproducible determination of the 3D retinal shape based on MRI is provided together with 2D alternatives, enabling wider use of this method in the field of ophthalmology.

Understanding sagittal compensation in adult spinal deformity patients: relationship between pelvic tilt and lower-extremity position

OBJECTIVE In adult spinal deformity (ASD), quantifying preoperative lower-extremity (LE) compensation is important in formulating an operative plan to achieve optimal global sagittal alignment. Whole-body radiographs are not always available. This study evaluated the possibility of estimating LE compensation without whole-body radiographs. METHODS In total, 200 consecutive ASD patients with full-body radiographic assessment were categorized into the following three groups according to their cranio-hip balance (distance from the cranial sagittal vertical axis to the hip axis [CrSVA-H]): group 1, anterior-shift (A-shift) group (CrSVA-H > 40 mm); group 2, balanced group, −40 mm < CrSVA-H < 40 mm; and group 3, posterior-shift (P-shift) group, CrSVA-H < −40 mm. After analyzing the correlation between CrSVA-H, pelvic tilt (PT), and LE parameters, the cutoff PT and PT/pelvic incidence (PI) values that correlated with the presence of LE compensation were determined. Previously published data from asymptomatic volunteers were used as a baseline threshold (sacrofemoral angle [SFA] > 217.0° and knee flexion angle [KA] > 11.0°). RESULTS Among the hip, knee, and ankle, only KA showed a significant increase in the A-shift group compared to the other two groups (p < 0.01). With a wide threshold (SFA > 208.0° and KA > 5.0°), 84.9% of the A-shift group showed LE compensation (hip or knee or both), which was a significantly greater percentage than those in the balanced and P-shift groups (48.4% and 51.9%, p < 0.01). With a narrow threshold (SFA > 217.0° and KA > 11.0°), 62.2% of the A-shift group showed any LE compensation, which was also a higher percentage than the other two groups. The CrSVA-H was moderately correlated with KA (r = 0.502), but had no correlation with PT, SFA, and ankle dorsiflexion angle (AA). PT showed a moderate/strong correlation with SFA, KA, and AA (r = 0.846, 0.624, and 0.622, respectively). With receiver operating characteristic curves, the authors determined that a 23.0° PT with PT/PI > 0.46 predicts the presence of any type of LE compensation with use of the wide threshold. CONCLUSIONS ASD patients with increased CrSVA-H, which represents cranio-hip anterior imbalance, demonstrated a higher prevalence of LE compensation, especially knee flexion, compared to those with neutral and posterior shift of CrSVA. PT represents the extent of LE compensation in patients with spinal sagittal malalignment. Using the cutoff value of PT determined in this study, surgeons can preoperatively estimate the extent of LE compensation without obtaining a full-body radiograph.

Dynamics of the meniscus underweight-loading conditions: an investigation using upright magnetic resonance imaging

Objectives: Meniscal morphology underweight-loading conditions remains unknown, because weight loading is rarely performed during magnetic resonance imaging (MRI). We focused on the weight-loading condition and developed an upright MRI. This study aimed to investigate the shift of the medial and lateral meniscus in healthy adults under both fully weight loaded and unloaded conditions, using both supine and upright MRI. Methods: Eighteen volunteers (13 men and 5 women) without previous knee complaints underwent an MRI of the right knee. The mean age of the subjects was 21.8±3.1 years. The examination was performed in three positions: supine, double-leg upright (DLU), and single-leg upright (SLU). The knees were fully extended in each position. For both the supine and upright examinations, we used a special MRI apparatus (Gravity MRI, Hitachi, Japan) that is capable of imaging in any position with a static magnetic field strength of 0.4 T (Figure). T1-weighted images were obtained in both coronal and sagittal planes with a slice thickness of 2 mm. The medial or lateral, anterior and posterior shifts of both the medial and lateral meniscus were measured, against the tibial wedge. The medial and lateral meniscal shift rates were measured as assessment items under each condition. The shift rate was defined as the proportion of the measured meniscal shift compared to the overall width of the medial and lateral meniscus. The MRI reference section on the sagittal plane was the midpoint of the medial or lateral femoral condyle. On the coronal plane, the reference point was the midpoint of the medial and lateral tibial condyle. The measurement items were compared in all three imaging positions using analysis of variance and multiple comparison tests, with statistical significance set at P < 0.05. Results: We show the results from the analysis of the dynamics of the medial and lateral meniscus in Table. The difference among the three conditions for the medial shift rate of the medial meniscus was significant. The medial shift rate was significantly greater in the DLU and SLU positions than in the supine position (supine: 7.3±5.8% vs. DLU: 20.0±8.8 % (P<0.01), supine vs. SLU: 21.5±7.6% (P<0.01), DLU vs. SLU (P=0.7)). No significant differences were observed for the anterior and posterior shift rates of the medial meniscus (anterior: P=0.6, posterior: P=0.4). In the lateral meniscus, the lateral shift rate was significantly greater in the SLU position than in the supine position, but no significant difference was observed in the DLU position (supine: -1.2±11.8% vs. DLU: 2.7±11.1 % (P=0.2), supine vs. SLU: 4.5±10.8% (P=0.04), DLU vs. SLU: P=0.7). Both anterior and posterior shift rates in the lateral meniscus were significantly greater in DLU and SLU positions than in the supine position (anterior/ supine: -20.6±14.3% vs. DLU: -14.7±12.2% (P<0.01), supine vs. SLU: -8.9±14.9% (P<0.01), DLU vs. SLU: P=0.3, posterior/ supine: -78.0±19.6% vs. DLU: -63.7±18.7 % (P<0.01), supine vs. SLU: -57.8±19.2% (P<0.01), DLU vs. SLU: P=0.4). Conclusions: Under upright weight-loading conditions, the medial meniscus showed only medial shift, whilst the lateral meniscus was seen to shift in lateral, anterior, and posterior directions. No significant difference was observed between the DLU and SLU shift rates in both the medial and lateral meniscus in healthy adults. We believe that this result will be useful when considering loading and rehabilitation following meniscal repair. [Table: see text]

The Role of the Posterolateral Tibial Slope in the Rotational Instability of the Knee in Patients Affected by a Complete Isolated Anterior Cruciate Ligament Injury: Its Value in the Decision-Making Process during the Anterolateral Ligament Reconstruction

Purpose The aim of this retrospective, multicenter study was to investigate the correlation between a high degree of rotatory instability, posterolateral tibial slope (PLTS), and anterolateral ligament (ALL) injury. Methods The study population consisted of 76 adults with isolated, complete noncontact anterior cruciate ligament (ACL) tear. The sample was divided into two groups according to the preoperative degree of rotator instability (group A: pivot-shift test grades 2 and 3; group B: pivot-shift test grade 1). Preoperative magnetic resonance imaging (MRI) assessment included angle of PLTS, posterior shift of the lateral femoral condyle (16 mm) on the tibial plateau, and the presence/absence of ALL injury. The two groups were compared for differences. Results There was a statistically significant association between pivot-shift test grades 2 and 3 (group A), PLTS slope angle > 9 degrees, and ALL injury (p < 0.05). Group A also demonstrated a greater posterior shift of lateral femoral condyle (>11 mm), which was, however, not statistically significant when evaluated as an isolated variable. Conclusion Our study indicates that an increased PLTS is associated with an increased incidence of ALL injury and an increased grade of pivot shift in patients with ACL tear. Assessment of posterolateral tibial slope on MRI can therefore play a key adjunct role in the surgical planning of ALL reconstruction, especially in cases when ALL damage is radiologically difficult to detect or doubtful. Level of Evidence This is a retrospective comparative level III study.

Cdx2 Animal Models Reveal Developmental Origins of Cancers

The Cdx2 homeobox gene is important in assigning positional identity during the finely orchestrated process of embryogenesis. In adults, regenerative responses to tissues damage can require a replay of these same developmental pathways. Errors in reassigning positional identity during regeneration can cause metaplasias—normal tissue arising in an abnormal location—and this in turn, is a well-recognized cancer risk factor. In animal models, a gain of Cdx2 function can elicit a posterior shift in tissue identity, modeling intestinal-type metaplasias of the esophagus (Barrett’s esophagus) and stomach. Conversely, loss of Cdx2 function can elicit an anterior shift in tissue identity, inducing serrated-type lesions expressing gastric markers in the colon. These metaplasias are major risk factors for the later development of esophageal, stomach and colon cancer. Leukemia, another cancer in which Cdx2 is ectopically expressed, may have mechanistic parallels with epithelial cancers in terms of stress-induced reprogramming. This review will address how animal models have refined our understanding of the role of Cdx2 in these common human cancers.

Investigation of Lateral Column Lengthening Osteotomy on the Movement of the Calcaneus: A Cadaveric Study

Category: Hindfoot Introduction/Purpose: Lateral column lengthening calcaneus osteotomy has been used widely in treating Stage IIB flexible flatfoot deformity in order to shift the anterior segment of the calcaneus forwards, which improves the coverage of the talonavicular joint by forefoot adduction. The premise of this investigation is that in addition to shifting the forefoot anteriorly around the axis of the talar head, there is also a posterior translation of the tuberosity of the calcaneus which is detrimental in that the angle of Gissane then impinges upon the posterior facet of the subtalar joint causing pain. Our hypothesis is that in addition to anterior translation of the calcaneus, posterior shift of the calcaneal tuberosity occurs with lengthening osteotomy of the calcaneus. Methods: An acute cadaveric flatfoot model was created on 5 fresh frozen cadaver feet with no previous foot and ankle deformity. In order to simulate the surgical scenario, the study was performed with no external load on the limb. A vertical osteotomy was performed 1 cm posterior of the calcaneocuboid joint. Commercially available precut wedges of 6 mm, 8 mm, 10 mm, and 12 mm were used for lateral column lengthening. After the insertion of the bone grafts, positional changes in sagittal plane of both the anterior and posterior calcaneus segments were monitored on lateral views under both fluoroscopy and a 3D digital high-resolution motion capture system. Results were calculated in percentage change from the base line horizontal distance between the talar and both anterior and posterior calcaneus markers before insertion of the wedges. Results: According to fluoroscopic measurements, the anterior translation of the anterior calcaneus segment was 7.27%+/-0.06 for 6 mm wedge, 16.11%+/-0.06 for 8 mm wedge, 20.81%+/- 0.08 for 10 mm wedge and 18.16%+/-0.07 for 12 mm wedge. The posterior translation of the posterior calcaneus segment was 9.85%+/-0.09 for 6 mm wedge, 13.15%+/-0.09 for 8 mm wedge, 12.04+/-0.09 for 10 mm wedge, and 14.06%+/-0.10 for 12 mm wedge. Statistical analysis showed that: 6 mm wedges did not cause significant changes in the translation of both anterior and posterior calcaneus segments with respect to the talus. 8 mm, 10 mm and 12 mm wedges caused significant translations both anteriorly and posteriorly. There was no statistically significant difference in the amount of either anterior or posterior translation caused by 8 mm, 10 mm or 12 mm wedges. These results were corroborated by 3D measurements. Conclusion: Of interest is that a 6 mm graft did not cause any significant anterior or posterior shift of the calcaneus. Lateral column lengthening with the 8,10, and 12 mm grafts however caused forward shifting of the anterior calcaneus, but also statistically significant posterior translation of the tuberosity, causing impingement of the posterior facet which was visible in each cadaver tested. There was no statistical difference between the sizes of the wedge above 6 mm and the translations they caused either anteriorly or posteriorly. Surgeons should be aware of the potential for painful impingement with the lateral column lengthening osteotomy.

Cranial ontogeny of Thamnophis radix (Serpentes: Colubroidea) with a re-evaluation of current paradigms of snake skull evolution

Accurate knowledge of skeletal ontogeny in extant organisms is crucial in understanding important morpho-functional systems and in enabling inferences of the ontogenetic stage of fossil specimens. However, detailed knowledge of skeletal ontogeny is lacking for most squamates, including snakes. Very few studies have discussed postnatal development in snakes, with none incorporating data from all three major ontogenetic stages—embryonic, juvenile and adult. Here, we provide the first analysis encompassing these three ontogenetic stages for any squamate, using the first complete micro-computed tomography (micro-CT)-based segmentations of any non-adult snake, based on fresh specimens of Thamnophis radix . The most significant ontogenetic changes involve the feeding apparatus, with major elongation of the tooth-bearing elements and jaw suspensorium causing a posterior shift in the jaw articulation. This shift enables macrostomy (large-gaped feeding in snakes) and occurs in T. radix via a different developmental trajectory than in most other macrostomatans, indicating that the evolution of macrostomy is more complex than previously thought. The braincase of T. radix is also evolutionarily unique among derived snakes in lacking a crista circumfenestralis, a phenomenon considered herein to represent paedomorphic retention of the embryonic condition. We thus present numerous important challenges to current paradigms regarding snake cranial evolution.