Background Existing ultrashort echo time magnetic resonance imaging (UTE MRI) methods require prohibitively long acquisition times (~ 20–40 min) to quantitatively assess the clinically relevant fast decay T2* component in ligaments and tendons. The purpose of this study was to evaluate the feasibility and clinical translatability of a novel abbreviated quantitative UTE MRI paradigm for monitoring graft remodeling after anterior cruciate ligament (ACL) reconstruction. Methods Eight patients who had Graftlink™ hamstring autograft reconstruction were recruited for this prospective study. A 3D double-echo UTE sequence at 3.0 Tesla was performed at 3- and 6-months post-surgery. An abbreviated UTE MRI paradigm was established based on numerical simulations and in vivo validation from healthy knees. This proposed approach was used to assess the T2* for fast decay component ($$ {T}_{2s}^{\ast } $$ T 2 s ∗ ) and bound water signal fraction (fbw) of ACL graft in regions of interest drawn by a radiologist. Results Compared to the conventional bi-exponential model, the abbreviated UTE MRI paradigm achieved low relative estimation bias for $$ {T}_{2s}^{\ast } $$ T 2 s ∗ and fbw over a range of clinically relevant values for ACL grafts. A decrease in $$ {T}_{2s}^{\ast } $$ T 2 s ∗ of the intra-articular graft was observed in 7 of the 8 ACL reconstruction patients from 3- to 6-months (− 0.11 ± 0.16 ms, P = 0.10). Increases in $$ {T}_{2s}^{\ast } $$ T 2 s ∗ and fbw from 3- to 6-months were observed in the tibial intra-bone graft ($$ {\varDelta T}_{2s}^{\ast } $$ ΔT 2 s ∗ : 0.19 ± 0.18 ms, P < 0.05; Δfbw: 4% ± 4%, P < 0.05). Lower $$ {T}_{2s}^{\ast } $$ T 2 s ∗ (− 0.09 ± 0.11 ms, P < 0.05) was observed at 3-months when comparing the intra-bone graft to the graft/bone interface in the femoral tunnel. The same comparisons at the 6-months also yielded relatively lower $$ {T}_{2s}^{\ast } $$ T 2 s ∗ (− 0.09 ± 0.12 ms, P < 0.05). Conclusion The proposed abbreviated 3D UTE MRI paradigm is capable of assessing the ACL graft remodeling process in a clinically translatable acquisition time. Longitudinal changes in $$ {T}_{2s}^{\ast } $$ T 2 s ∗ and fbw of the ACL graft were observed.
Purpose: To use serial PET/MRI imaging to radiographically evaluate the metabolic activity of the ACL graft over the first post-operative year. Methods: Six patients undergoing primary ACL reconstruction were recruited in this prospective study in an inpatient university hospital. All patients underwent femoral and tibial suspensory cortical fixation with quadrupled semitendinosus autograft hamstring ACL reconstruction by an orthopaedic surgeon. Simultaneous 18 F-FDG PET and MRI of both the operative and non-operative knee was performed at three, six, and 12 months post-operatively. Quantification of the mean standardized uptake value (SUV) within the whole-knee, as well as tibial tunnel, femoral tunnel, and intra-articular graft regions of interest (ROIs). Results: PET whole-knee activity was increased at all time-points post-operatively compared to the control, nonoperative knee. Activity decreased over time, yet considerable generalized activity remained 1 year post-operatively, with relative intensity 34% percent higher than control. When the operative knee was divided into three wholeregions, there was greater activity in the tibia at three than 12 months, the femur at six than 12 months, and in the tibia compared to the intra-articular region at 3 months. When they were separated into sub-regions, results demonstrated greater activity closer to the joint surface. Conclusions: PET/MRI evaluation of ACL graft reconstructions demonstrates evolving biologic activity within the graft and both tunnels. Focal areas of increased activity within the tunnels may indicate of ligamento-osseous morphologic changes. These data suggest that graft incorporation continues well beyond 1 year post-operatively. Level of evidence: Level IV.
An important anatomical structure commonly encountered during major head and neck surgery is the recurrent inferior laryngeal nerve. Nonrecurrent inferior laryngeal nerve variants are rarely encountered. Although much less common, these variants represent a significant risk for intraoperative nerve injury and patient morbidity. We present a case of a right nonrecurrent inferior laryngeal nerve variant along with a retrospective analysis and systematic review investigating the overall incidence of these variants.
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