The variability of CT scan protocols for total hip arthroplasty: a call for harmonisation

CT is the principal imaging modality used for the pre-operative 3D planning and assessment of total hip arthroplasty (THA). The image quality offered by CT has a radiation penalty to the patient. Higher than necessary radiation exposure is of particular concern when imaging young patients and women of childbearing age, due to the greater risk of radiation-induced cancer in this group. A harmonised low-dose CT protocol is needed, evidenced by the huge variability in the 17 protocols reviewed. The majority of the protocols were incomplete, leading to uncertainty among radiographers when performing the scans. Only three protocols (20%) were optimised for both 'field of view' and image acquisition parameters. 10 protocols (60%) were optimised for 'field of view' only. These protocols included imaging of the relevant landmarks in the bony pelvis in addition to the knees - the reference for femoral anteversion. CT parameters, including the scanner kilovoltage (kV), milliamperage-time product (mAs) and slice thickness, must be optimised with a 'field of view' that includes the relevant bony landmarks. The recommended kV and mAs values were very wide ranging from 100 to 150 and from 100 to 250, respectively. The large variability that exists amongst the CT protocols illustrates the need for a more consistent low-dose CT protocol for the planning of THA. This must provide an optimal balance between image quality and radiation dose to the patient. Current CT scanners do not allow for measurements of functional pelvic orientation and additional upright imaging modalities are needed to augment them

SPECT/CT in patients with painful knee arthroplasty—what is the evidence?

SPECT/CT is increasingly recognized as a promising imaging modality for the investigation of patients with a painful knee after knee arthroplasty. In this review article, we give an overview of the clinical value and current and future applications of SPECT/CT for patients with knee pain following joint arthroplasty. A detailed evidence-based literature review is performed and presente

Gender similarities and differences in skeletal muscle and body composition: an MRI study of recreational cyclists

OBJECTIVES: This study aims to quantitatively evaluate whether there are muscle mass differences between male and female recreational cyclists and compare muscle quality and body composition in the pelvis region between two well-matched groups of fit and healthy male and female adults. METHODS: This cross-sectional study involved 45 female and 42 male recreational cyclists. The inclusion criteria for both groups were to have cycled more than 7000 km in the last year, have an absence of injuries and other health problems, have no contraindication to MRI, and be 30-65 years old. Our main outcome measures were fat fraction, as a measure of intramuscular fat (IMF) content, and volume of the gluteal muscles measured using Dixon MRI. The gluteal subcutaneous adipose tissue (SAT) volume was evaluated as a secondary measure. RESULTS: We found that there were no gender differences in the IMF content of gluteus maximus (GMAX, p=0.42), gluteus medius (GMED, p=0.69) and gluteus minimus (GMIN, p=0.06) muscles, despite women having more gluteal SAT (p<0.01). Men had larger gluteal muscles than women (p<0.01), but no differences were found when muscle volume was normalised by body weight (GMAX, p=0.54; GMED, p=0.14; GMIN, p=0.19). CONCLUSIONS: Our study shows that despite the recognised hormonal differences between men and women, there is gender equivalence in the muscle mass and quality of the gluteal muscles when matched for exercise and body weight. This new MRI study provides key information to better understand gender similarities and differences in skeletal muscle and body composition

The analysis of defects in custom 3D‐printed acetabular cups: A comparative study of commercially available implants from six manufacturers

Three-dimensional (3D) printing is used to manufacture custom acetabular cups to treat patients with massive acetabular defects. There is a risk of defects occurring in these, often in the form of structural voids. Our aim was to investigate the presence of voids in commercially available cups. We examined 12, final-production titanium custom acetabular cups, that had been 3D-printed by six manufacturers. We measured their mass, then performed micro-computed tomography (micro-CT) imaging to determine their volume and density. The micro-CT data were examined for the presence of voids. In cups that had voids, we computed (1) the number of voids, (2) their volume and the cup volume fraction, (3) their sphericity, (4) size, and (5) their location. The cups had median mass, volume, and density of 208.5 g, 46,471 mm3, and 4.42 g/cm3, respectively. Five cups were found to contain a median (range) of 90 (58–101) structural voids. The median void volume and cup volume fractions of cups with voids were 5.17 (1.05–17.33) mm3 and 99.983 (99.972–99.998)%, respectively. The median void sphericity and size were 0.47 (0.19–0.65) and 0.64 (0.27–8.82) mm, respectively. Voids were predominantly located adjacent to screw holes, within flanges, and at the transition between design features; these were between 0.17 and 4.66 mm from the cup surfaces. This is the first study to examine defects within final-production 3D-printed custom cups, providing data for regulators, surgeons, and manufacturers about the variability in final print quality. The size, shape, and location of these voids are such that there may be an increased risk of crack initiation from them

Statistical Shape Modelling of the Large Acetabular Defect in Hip Revision Surgery

The assessment of three-dimensional (3D) bony defects is important to inform the surgical planning of hip reconstruction. Mirroring of the contralateral side has been previously used to measure the hip centre of rotation (CoR). However, the contralateral side may not be useful when diseased or replaced. Statistical Shape Models (SSMs) can aid reconstruction of patient anatomy. Previous studies have been limited to computational models only or small patient cohorts. We used SSM as a tool to help derive landmarks that are often absent in hip joints of patients with large acetabular defects. Our aim was to compare the reconstructed pelvis with patients who have previously undergone hip revision. This retrospective cohort study involved 38 patients with Paprosky type IIIB defects. An SSM was built on 50 healthy pelvises and used to virtually reconstruct the native pelvic morphology for all cases. The outcome measures were the difference in CoR for 1) SSM vs diseased hip, 2) SSM vs plan and 3) SSM vs contralateral healthy hip. The median differences in CoR were 31.17 mm (IQ: 43.80 - 19.87 mm), 8.53 mm (IQ: 12.76 - 5.74 mm) and 7.84 mm (IQ: 10.13 - 5.13 mm), respectively. No statistical difference (p > 0.05) was found between the SSM vs plan and the SSM vs contralateral CoRs. Our findings show that the SSM model can be used to reconstruct the absent bony landmarks of patients with significant lysis regardless of the defect severity, hence aiding the surgical planning of hip reconstruction and implant design. This article is protected by copyright. All rights reserved

Rod Fracture in Magnetically Controlled Growing Spine Rods

Background: The mechanisms of fracture in magnetically controlled growing rods (MCGRs) and the risk factors associated with this are poorly understood. This retrospective analysis of explanted MCGRs aimed to add understanding to this subject. / Methods: From our cohort of over 120 retrieved MCGRs, we identified 7 rods that had fractured; all were single-rod constructs, retrieved from 6 patients. These were examined and compared with 15 intact single-rod constructs. Retrieval and fractographic analyses were used to determine the failure mode at the fracture site and the implant's functionality. Cobb angle, degree of rod contouring, and the distance between anchoring points were computed on anteroposterior and lateral radiographs. / Results: 5/7 versus 3/15 rods had been inserted after the removal of a previously inserted rod, in the fractured versus control groups. All fractured rods failed due to bending fatigue. Fractured rods had greater rod contouring angles in the frontal plane (P = 0.0407) and lateral plane (P = 0.0306), and greater distances between anchoring points in both anteroposterior and lateral planes (P = 0.0061 and P = 0.0074, respectively). / Conclusions: We found all failed due to a fatigue fracture and were virtually all single rod configurations. Fracture initiation points corresponded with mechanical indentation marks induced by the intraoperative rod contouring tool. Fractured rods had undergone greater rod contouring and had greater distances between anchoring points, suggesting that it is preferable to implant double rod constructs in patients with sufficient spinal maturity to avoid this complication

Morphometric analysis of patient-specific 3D-printed acetabular cups: a comparative study of commercially available implants from 6 manufacturers

Background 3D printed patient-specific titanium acetabular cups are used to treat patients with massive acetabular defects. These have highly porous surfaces, with the design intent of enhancing bony fixation. Our aim was to characterise these porous structures in commercially available designs. Methods We obtained 12 final-production, patient-specific 3D printed acetabular cups that had been produced by 6 manufacturers. High resolution micro-CT imaging was used to characterise morphometric features of their porous structures: (1) strut thickness, 2) the depth of the porous layer, (3) pore size and (4) the level of porosity. Additionally, we computed the surface area of each component to quantify how much titanium may be in contact with patient tissue. Statistical comparisons were made between the designs. Results We found a variability between designs in relation to the thickness of the struts (0.28 to 0.65 mm), how deep the porous layers are (0.57 to 11.51 mm), the pore size (0.74 to 1.87 mm) and the level of porosity (34 to 85%). One manufacturer printed structures with different porosities between the body and flange; another manufacturer had two differing porous regions within the body of the cups. The cups had a median (range) surface area of 756.5 mm2 (348 – 1724). Conclusions There is a wide variability between manufacturers in the porous titanium structures they 3D print. We do not currently know whether there is an optimal porosity and how this variability will impact clinically on the integrity of bony fixation; this will become clearer as post market surveillance data is generated

Magnetic Resonance Imaging of the Hips of Runners Before and After their First Marathon Run: Does it Lead to Acute Changes?

BACKGROUND: No studies have focused on magnetic resonance imaging (MRI) of the hips of marathoners, despite the popularity and injury risks of marathon running. PURPOSE: To understand the effect of preparing for and completing a marathon run (42 km) on runners’ hip joints by comparing MRI findings before and after their first marathon. Study Design: Case-control study; Level of evidence, 3. METHODS: A total of 28 healthy adults (14 males, 14 females; mean age, 32.4 years) were recruited after registering for their first marathon. They underwent 3-T MRI of both hips at 16 weeks before (time point 1) and 2 weeks after the marathon (time point 2). After the first MRI, 21 runners completed the standardized, 4 month--long training program and the marathon; 7 runners did not complete the training or the marathon. Specialist musculoskeletal radiologists reported and graded the hip joint structures using validated scoring systems. Participants completed the Hip disability and Osteoarthritis Outcome Score (HOOS) at both imaging time points. RESULTS: At time point 1, MRI abnormalities of the hip joint were seen in 90% of participants and were located in at least 1 of these areas: labrum (29%), articular cartilage (7%), subchondral bone marrow (14%), tendons (17%), ligaments (14%), and muscles (31% had moderate muscle atrophy). At time point 2, only 2 of the 42 hips showed new findings: a small area of mild bone marrow edema appearance (nonweightbearing area of the hip and not attributable to running). There was no significant difference in HOOS between the 2 time points. Only 1 participant did not finish the training because of hip symptoms and thus did not run the marathon; however, symptoms resolved before the MRI at time point 2. Six other participants discontinued their training because of non–hip related issues: a knee injury, skin disease, a family bereavement, Achilles tendon injury, illness unrelated to training, and a foot injury unrelated to training. CONCLUSION: Runners who completed a 4-month beginner training program before their first marathon run, plus the race itself, showed no hip damage on 3-T MRI scans

The Performance of MAGEC X Spine Rods: A Comparative Retrieval Study

Study Design: Multicentre comparative analysis of explanted Spine Magnetically Controlled Growing Rods (MCGRs). Objectives: MAGEC X, the latest commercially available generation, was recalled in 2020 due to the risk of post-implantation separation of an actuator end-cap component. Currently, the supply of all MAGEC rods was temporarily suspended in the UK and the EU. Objective of this study is to compare the performance of the MAGEC X MCGR to the earlier MAGEC 1.3 design iteration, by means of retrieval analysis. Methods: Fifteen of both MAGEC X and MAGEC 1.3 rods were consecutively collected from five different hospitals following removal surgery and matched by time to removal. Clinical and implant data was collected for all MCGRs. Analysis comprised visual assessments of external damage, plain radiograph evaluations, force and elongation testing, MAGEC X end-cap torque testing and disassembly. Mann-Whitney U tests were used to statistically compare groups. Results: Rod distraction reached in vivo was significantly higher in the MAGEC 1.3 (P =.002). There was no statistically significant difference in the total external damage score (P =.870), maximum force produced (P =.695) or distraction reached during force test (P =.880). No pin fracture was detected. Elongation of stroke was mildly higher (P =.051) for the MAGEC X implants. One MAGEC X had evident end cap component loosening. Internal damage scores were mildly lower in the MAGEC X group. Conclusion: MAGEC X showed similar performance results than the previous design iteration MAGEC 1.3. End-cap component loosening was observed, with no major consequences on the internal mechanism

The variability of CT scan protocols for total hip arthroplasty: a call for harmonisation

CT is the principal imaging modality used for the pre-operative 3D planning and assessment of total hip arthroplasty (THA). The image quality offered by CT has a radiation penalty to the patient. Higher than necessary radiation exposure is of particular concern when imaging young patients and women of childbearing age, due to the greater risk of radiation-induced cancer in this group. A harmonised low-dose CT protocol is needed, evidenced by the huge variability in the 17 protocols reviewed. The majority of the protocols were incomplete, leading to uncertainty among radiographers when performing the scans. Only three protocols (20%) were optimised for both ‘field of view’ and image acquisition parameters. 10 protocols (60%) were optimised for ‘field of view’ only. These protocols included imaging of the relevant landmarks in the bony pelvis in addition to the knees – the reference for femoral anteversion. CT parameters, including the scanner kilovoltage (kV), milliamperage–time product (mAs) and slice thickness, must be optimised with a ‘field of view’ that includes the relevant bony landmarks. The recommended kV and mAs values were very wide ranging from 100 to 150 and from 100 to 250, respectively. The large variability that exists amongst the CT protocols illustrates the need for a more consistent low-dose CT protocol for the planning of THA. This must provide an optimal balance between image quality and radiation dose to the patient. Current CT scanners do not allow for measurements of functional pelvic orientation and additional upright imaging modalities are needed to augment them