Total shoulder arthroplasty does not correct the orientation of the eroded glenoid.

BACKGROUND AND PURPOSE: Alignment of the glenoid component with the scapula during total shoulder arthroplasty (TSA) is challenging due to glenoid erosion and lack of both bone stock and guiding landmarks. We determined the extent to which the implant position is governed by the preoperative erosion of the glenoid. Also, we investigated whether excessive erosion of the glenoid is associated with perforation of the glenoid vault. METHODS: We used preoperative and postoperative CT scans of 29 TSAs to assess version, inclination, rotation, and offset of the glenoid relative to the scapula plane. The position of the implant keel within the glenoid vault was classified into three types: centrally positioned, component touching vault cortex, and perforation of the cortex. RESULTS: Preoperative glenoid erosion was statistically significantly linked to the postoperative placement of the implant regarding all position parameters. Retroversion of the eroded glenoid was on average 10° (SD10) and retroversion of the implant after surgery was 7° (SD11). The implant keel was centered within the vault in 7 of 29 patients and the glenoid vault was perforated in 5 patients. Anterior cortex perforation was most frequent and was associated with severe preoperative posterior erosion, causing implant retroversion. INTERPRETATION: The position of the glenoid component reflected the preoperative erosion and "correction" was not a characteristic of the reconstructive surgery. Severe erosion appears to be linked to vault perforation. If malalignment and perforation are associated with loosening, our results suggest reorientation of the implant relative to the eroded surface.

Measurement of femoral head penetration in polyethylene using a 3-dimensional CT-scan technique.

BACKGROUND: Current techniques for measuring in vivo polyethylene wear suffer from a range of problems, resulting in an unacceptable lack of repeatability and/or insufficient accuracy when they are used to measure the low wear rates associated with new, highly crosslinked polyethylene. We describe an improved CT method for measurement of 3D femoral head penetration in PE acetabular cups that has sufficient accuracy and repeatability to allow assessment of the wear potential of modern implants. METHOD: The accuracy and repeatability of the CT-scan method was determined by blindly repeating measurements on a precisely calibrated 28-mm prosthetic head and by comparing them with direct metrological measurements on 10 acetabular specimens with in vitro wear from machining, and on 8 explanted acetabular specimens with in vivo wear. RESULTS: The intra- and interobserver errors in femoral head diameter were 0.036 mm (SD 0.044) and 0.050 mm (SD 0.022), respectively. CT estimated femoral head penetration in both all-poly and metal-backed acetabular components with accuracy ranging from 0.009 to 0.245 mm (mean 0.080; SD 0.067). INTERPRETATION: We found that the CT method is rapid, is accurate, and has repeatability and ease of availability. Using a slice thickness of 0.0625 mm, this method can detect wear­and also the threshold for the wear rate that causes osteolysis­much earlier than previous methods.

Glenoid loosening after total shoulder arthroplasty: an in vitro CT-scan study.

Glenoid fixation failure has only been grossly characterized. This lack of information hinders attempts to improve fixation because of a lack of methodologies for detecting and monitoring fixation failure. Our goal was twofold: to collect detailed data of glenoid fixation fracture, and to investigate computed tomography (CT)-scanning as a tool for investigations of fixation failure. Six cadaver scapulas and six bone-substitute specimens were cyclically loaded and CT-scanned at clinical settings after 0, 1,000, 5,000, 10,000, 30,000, 50,000 and 70,000 load cycles. The fixation status was evaluated by inspection of the scans. After 70,000 cycles, the specimens were sectioned, and the fixation inspected by microscopy. The results of the microscopy analysis were compared to the CT-scan analysis. Fracture of the glenoid fixation initiated at the edge of the glenoid rim and propagated towards and around the keel of the implant. The entire process from initiation to complete fracture took place at the polyethylene implant-cement interface, while the cement, the adjacent bone, and the cement-bone interface remained intact. Thus, strengthening the polyethylene-cement interface should improve glenoid fixation. Microscopy results validated the CT methodology, suggesting that the CT technique is reliable.

The asymmetric profile of the acetabulum.

Despite the curvaceous profile of the acetabulum, orthopaedic surgeons have continued to implant hemispheric cups since the introduction of total hip arthroplasty. The geometric discrepancies between the natural acetabulum and implant can result in painful iliopsoas impingement attributable to prosthetic overlap at the anterior acetabular ridge over which the iliopsoas tendon extends to leave the pelvis. We expanded on previous in vitro observations of acetabular morphology using a large in vivo sample and quantified the dimensions of the psoas valley. We studied computed tomographic scans of 200 healthy hips from 50 men and 50 women. The acetabular ridges were digitized on three-dimensional bone reconstructions and their coordinates were manipulated in spreadsheets to deduce acetabular diameter, anteversion, and inclination and to plot the rim profile. Our results confirm the acetabular rim is an asymmetric succession of three peaks and three troughs. The psoas valley has the following shape distribution: 79% curved, 11% angular, 10% irregular, and 0% straight. The mean depth of the psoas valley is 5 mm and the latitude of its trough is on average 6 mm below the acetabular equator. The use of side-specific cups that replicate the curvaceous acetabular profile could prevent prosthetic overlap and reduce the incidence of iliopsoas impingement.

Placental perfusion and permeability: simultaneous assessment with dual-echo contrast-enhanced MR imaging in mice.

PURPOSE: To assess placental perfusion and permeability in mice with magnetic resonance (MR) imaging. MATERIALS AND METHODS: This study was conducted according to French law and National Institutes of Health recommendations for animal care. Twenty-two pregnant BALB/c mice were examined at 1.5 T with a single-section dual-echo fast spoiled gradient-echo sequence. Two injection protocols were used: monophasic injection (double the clinical dose of contrast agent) and biphasic injection (quadruple the clinical dose). Signal intensities (SIs) were measured in the maternal left ventricle, placenta, and fetus (n = 16). At these high gadolinium doses, a T2* effect correction was used. SIs were converted to gadolinium concentrations and were analyzed by using a three-compartment model. Quantitative microcirculation parameters were calculated. Results with the monophasic and biphasic protocols were compared, and final arterial concentrations determined with MR imaging were compared with those determined with atomic emission spectrophotometry by using the unpaired Student t test. RESULTS: Perfusion and permeability parameters for monophasic and biphasic injections were similar: Mean placental blood flow was 180 mL/min/100 g, mean permeability surface coefficient from maternal placental to fetal placental compartment was 10.3 x 10(-4) sec(-1) +/- 6.81 (standard deviation), mean permeability surface coefficient from fetal placental to maternal placental compartment was 4.65 x 10(-4) sec(-1) +/- 4.37, and mean fractional volume of the maternal vascular placental compartment was 36.5% +/- 0.9. Placental (146 vs 105 micromol/L, P < .004) and fetal (33.3 vs 19.1 micromol/L, P < .001) gadolinium concentrations were higher with the biphasic than with the monophasic protocol. Arterial gadolinium concentrations at MR imaging did not differ significantly from those at spectrophotometry for the monophasic (P = .254) or biphasic (P = .776) injection protocol. CONCLUSION: Placental perfusion and permeability can be measured in vivo by using high gadolinium doses and a dual-echo MR imaging sequence.