Accurate placement of the glenoid component in total shoulder arthroplasty (TSA) is critical to optimize implant longevity. Commercially available patient-specific instrumentation systems can improve implant placement, but may involve considerable expense and production delays of up to six weeks. The purpose of this study was to develop a novel technique for in-house production of 3D-printed, patient-specific glenoid guides, and compare the accuracy of glenoid guidepin placement between the patient-specific guide and a standard guide using a cadaveric model. Twenty cadaveric shoulder specimens were randomized to receive glenoid guidepin placement via standard TSA guide (Wright Medical, Memphis, TN) or patient-specific guide. Three-dimensional scapular models were reconstructed from CT scans with Mimics 20.0 imaging software (Materialise NV, Leuven, Belgium). A pre-surgical plan was created for all specimens for the central glenoid guidepin of 0º version and inclination angles. Central pin entry and exit points were also calculated. Patient-specific guides were constructed to achieve the planned pin trajectory in Rhino3D software (Robert McNeel & Associates, Seattle, WA). Guides were 3D-printed on a Form2 printer with Formlabs Dental SG Resin (Formlabs, Somerville, MA). Glenoid labrum and cartilage were removed with preservation of other soft tissues in all specimens to mimic intraoperative TSA conditions. A fellowship-trained, board-eligible orthopaedic surgeon placed a 2.5 mm diameter titanium guidepin into each glenoid using the assigned guide for each specimen. After pin placement, repeat CT scans were performed, and a blinded measurer used superimposed 3D scapular reconstructions to calculate deviation from the pre-surgical plan in version and inclination angles, dot product angle, and guide pin entry and exit points. Student's t tests were performed to detect differences between pin placements for the two groups.Background
Methods
Kinematics analyses of the spine have been recognized as an effective method for functional analysis of the spine. CT is suitable for obtaining bony geometry of the vertebrae but radiation is a clinical concern. MRI is noninvasive but it is difficult to detect bone edges especially at endplates and processes where soft tissues attach. Kinematics analyses require tracking of solid bodies; therefore, bony geometry is not always necessary for kinematics analysis of the spine. This study aimed to develop a reliable and robust method for kinematics analysis of the spine using an innovative MRI-based 3D bone-marrow model. This IRB-approved study recruited 17 patients undergoing lumbar decompression surgery to treat a single-level symptomatic herniation as part of a clinical trial for a new dynamic stabilization device. T1 & T2 sagittal MRI scans were acquired as part of the pre-operative evaluation in three positions: supine and with the shoulders rotated 45° to the left and right to induce torsion of the lumbar spine. 3D bone-marrow models of L5 and S1 at the neutral and rotated positions were created by selecting a threshold level of the bone-marrow intensity at bone-marrow/bone interface. Validated 3D-3D registration techniques were used to track movements of L5 and S1. Segmental movements at L5/S1 during torsion were calculated.Introduction
Materials and Methods
As a consequence from cervical arthroplasty, spine structural stiffness, loading and kinematics are changed, resulting in issues like adjacent segment degeneration and altered range of motion. However, complex anatomical structures and lack of adequate precision to study the facet joint (FJ) segmental motion in 3D have prevented proper quantitative analyses. In the current study, we investigate the innovative use of a local coordinate system on the surface of the superior articular process of the caudal vertebral body in order to analyze FJ segmental motion using CT-based 3D vertebral models in flexion/extension. CT images were obtained from six patients (2F/4M, mean age: 53 y.o.) with cervical degenerative disc disease in neutral, flexion and extension positions. CT data was used to create subject-specific surface mesh models of each vertebral body. From these, mean normal vectors were calculated for all FJ surfaces and posterior walls from C3/4 down to C6/7 (Fig. 1). The global coordinate system (x, y, z) corresponds to the CT scanner. Within this system, a new local coordinate system (u, v, w) was set on the centroid of each FJ surface (Fig. 1), where the u-, v-, and w- axes correspond to the INTRODUCTION:
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