Subchondral involvement in osteonecrosis of the femoral head: insight on local composition, microstructure and vascularization

OBJECTIVE

To determine changes of subchondral bone composition, micro-structure, bone marrow adiposity and micro-vascular perfusion in end-stage osteonecrosis of the femoral head (ONFH) compared to osteoarthritis (OA) using a combined in vivo and ex vivo approach.

DESIGN

Male patients up to 70 years old referred for total hip replacement surgery for end-stage ONFH were included (n = 14). Fifteen patients with OA were controls. Pre-operative MRI was used to assess bone perfusion (dynamic contrast-enhanced (DCE) sequences) and marrow fat content (chemical shift imaging). Three distinct zones of femoral head subchondral bone - necrotic, sclerotic, distant - were compared between groups. After surgery, plugs were sampled in these zones and Raman spectroscopy was applied to characterize bone mineral and organic components (old and newly-formed), and contrast-enhanced micro-computed tomography (CE-μCT) to determine bone micro-structural parameters and volume of bone marrow adipocytes, using conventional 2D histology as a reference.

RESULTS

In the necrotic zone of ONFH patients compared to OA patients: 1) the subchondral plate did not exhibit significant changes in composition nor structure; 2) the volume fraction of subchondral trabecular bone was significantly lower; 3) type-B carbonate substitution was less pronounced, 4) collagen maturity was more pronounced; and 5) bone marrow adipocytes were significantly depleted. The sclerotic zone from the ONFH group showed greater trabecular thickness, and higher DCE-MRI AUC and K_trans. Volume fraction of subchondral bone, trabecular number, and K_ep were significantly lower in the distant zone of the ONFH group.

CONCLUSIONS

This study demonstrated alterations of subchondral bone microstructure, composition, perfusion and/or adipose content in all zones of the femoral head.

Dual-energy computed tomography in calcium pyrophosphate deposition: initial clinical experience

OBJECTIVE

To determine the dual-energy computed tomography (DECT) attenuation properties of meniscal calcifications in calcium pyrophosphate deposition (CPPD) in vivo, and assess whether DECT was able to discriminate meniscal CPP deposits from calcium hydroxyapatite (HA) in subchondral and trabecular bone.

METHOD

Patients with clinical suspicion of crystal-related arthropathy (gout and/or CPPD) and knee DECT scans were retrospectively assigned to CPPD (n = 19) or control (n = 21) groups depending on the presence/absence of chondrocalcinosis on DECT. Two observers drew standardized regions of interest (ROI) in meniscal calcifications, non-calcified menisci, as well as subchondral and trabecular bone. Five DECT parameters were obtained: CT numbers (HU) at 80 and 140 kV, dual-energy index (DEI), electron density (ρ_e), and effective atomic number (Z_eff). The four different knee structures were compared within/between patients and controls using linear mixed models, adjusting for confounders.

RESULTS

Meniscal calcifications (n = 89) in CPPD patients had mean ± SD CT numbers at 80 and 140 kV of 257 ± 64 and 201 ± 48 HU, respectively; with a DEI of 0.023 ± 0.007, and ρ_e and Z_eff of 140 ± 35 and 8.8 ± 0.3, respectively. Meniscal CPP deposits were readily distinguished from calcium HA in subchondral and trabecular bone (p ≤ 0.001), except at 80 kV separately (p = 0.74). Z_eff and ρ_e both significantly differed between CPP deposits and calcium HA in subchondral and trabecular bone (p < 0.0001).

CONCLUSION

This proof-of-concept study shows that DECT has the potential to discriminate meniscal CPP deposits from calcium HA in subchondral and trabecular bone in vivo, paving the way for the non-invasive biochemical signature assessment of intra- and juxta-articular calcium crystal deposits.

Preoperative assessment of idiopathic scoliosis in adolescent and young adult with three-dimensional T2-weighted spin-echo MRI

PURPOSE

To compare tridimensional (3D) T2-weighted spin-echo MRI and CT for minimal pedicle width measurements in the preoperative assessment of adolescent idiopathic scoliosis (AIS) in adolescent and young patients.

MATERIALS AND METHODS

A total of 22 adolescents/young patients suffering from AIS were retrospectively included. There were 18 females and 4 males with a mean age of 15.3±2.3 (SD) years (range: 11-21years). Preoperative lumbar spine MRI and CT examinations of the 22 patients were reviewed by two independent readers who measured the minimal width of 259 pedicles. Inter-reader agreement for CT and MRI was assessed using intra-class correlation coefficient (ICC). Intra-reader agreement and relative differences in measurements between MRI and CT were also assessed for each reader.

RESULTS

Inter-reader agreement was excellent (ICC≥0.8) for both CT and MRI. Relative differences in measurements between CT and MRI was 10.3% for reader 1 and 9.4% for reader 2.

CONCLUSION

3D T2-weighted spin-echo MRI underestimates minimal pedicle width by only 9.4 - 10.3% compared to CT. 3D T2-weighted MRI appears as a valuable alternative to CT for preoperative measurements of vertebral pedicles in AIS.

Comparison between enhanced susceptibility-weighted angiography and time of flight sequences in the detection of arterial occlusion in acute ischemic stroke

PURPOSE

Optimizing the MRI protocol in acute ischemic stroke remains a challenging issue. In this field, susceptibility-weighted sequences have proved their superiority over T2*. Besides the strengthened susceptibility effect, enhanced susceptibility-weighted angiography (eSWAN) sequence provides also a time-of-flight (TOF) effect, allowing the exploration of the intracranial arterial circulation. The objective of our study was to compare eSWAN and 3D TOF, considered as the reference, in the detection of arterial occlusion in acute stroke.

METHODS

Patients who underwent MRI between March and July 2014 for suspected acute stroke with an acute ischemic lesion on diffusion-weighted imaging (DWI) were prospectively included in this study. eSWAN and TOF images were analyzed under double-blind conditions by a junior radiologist and a senior neuroradiologist for the detection of arterial occlusion. eSWAN images were assessed in order to estimate the inter-observer agreement. After a consensus, eSWAN and TOF data were compared to calculate inter-modality agreement.

RESULTS

Thirty-four patients were included. Inter-observer agreement was excellent (kappa: 0.96) for eSWAN detection of occlusion. After consensus, comparison between TOF and eSWAN showed substantial agreement (kappa: 0.71). eSWAN provided better detection of distal occlusions, but poorer performance for detection of siphon occlusions.

CONCLUSIONS

Shortest echoes eSWAN images enabled detection of arterial occlusion with substantial agreement with TOF images. The susceptibility vessel sign associated with the TOF effect improved the identification of distal occlusions. In acute stroke protocol, eSWAN may represent a valuable alternative to T2* and TOF sequences.

Geometrical analysis results of 42 resurfacing shoulder prostheses: A CT scan study

BACKGROUND

Shoulder resurfacing arthroplasty was introduced in Scandinavia in the early 1980s then developed by SA Copeland.

HYPOTHESIS

Resurfacing prostheses restore the normal anatomy of the proximal humerus. Here, our objective was to evaluate humeral resurfacing prosthesis position on radiographs and computed tomography (CT) images.

MATERIALS AND METHODS

We retrospectively reviewed 42 consecutive cases seen at a single centre between 2004 and 2009. Mean patient age was 65 years. CT was performed routinely before prosthesis implantation and at re-evaluation. The Copeland Mark III(®) (Biomet France SARL, 26903 Valence, France) implant was used in 32 cases and the Aequalis Resurfacing Head(®) (Tornier France, 38334 Saint-Ismier, France) in 10 cases. The post-implantation CT images were used to measure the angle of inclination, medial humeral offset, lateral glenohumeral offset, and version of the implant.

RESULTS

Mean follow-up was 18 months. Compared to baseline, no significant changes were found at re-evaluation for the angle of inclination or lateral glenohumeral offset. In contrast, medial humeral offset increased by 3.47mm, and excessive anteversion of 4.23° compared to the bicondylar line was noted.

DISCUSSION

Humeral head resurfacing prostheses restore the overall anatomy of the proximal humeral head. Our CT scan evaluation protocol seems reproducible and enables an evaluation of implant geometry. In our experience, resurfacing arthroplasty restored the native humeral offset. Inadequate retroversion was noted and was probably related to insufficient exposure during surgery.

LEVEL OF EVIDENCE

Level IV, retrospective study.

In vivo MR tractography of thigh muscles using diffusion imaging: initial results

The aims of this preliminary study were (1) to demonstrate the feasibility of providing in vivo 3D architecture of human thigh muscles using tractography on a 1.5T magnet, and (2) to assess the value of tractography images to obtain averaged microstructural parameters, i.e., the fractional anisotropy (FA) and the mean apparent diffusion coefficient (ADC), over the whole thigh. Five healthy volunteers were included in this study. Their right thighs were imaged using diffusion tensor imaging and gradient-echo T2* sequences. Muscular tractography was performed on each muscle. MR tractography provided a good approach of the muscle shape and of the orientation of the muscle fibers. There was no aberration in the color-encoding scheme nor in the luminosity assigned to each fiber. In contrast, tendons were not drawn in any of the muscles studied. FA values ranged from 0.27 to 0.38. Mean ADC values ranged from 0.76 to 0.96 x 10(-3) mm2/s. Our study demonstrated the feasibility of providing in vivo 3D architecture of human thigh muscles using tractography on a 1.5T magnet, and of determining muscular microstructural parameters (FA and ADC). Musculoskeletal radiologists should be aware of these new developments that may provide complementary information on muscles to the usual sequences.