Prevalence of metal hypersensitivity in patients with shoulder pathologies.

BACKGROUND: To date, medical history and dedicated questionnaires are the fastest and easiest way to assess risks of joint metal hypersensitivity. No published studies determined the overall prevalence of hypersensitivity to metals in patients with shoulder pathologies. The purpose of this study was therefore to estimate the prevalence of metal hypersensitivity reported by patients with shoulder pathologies, and to identify patients at risk of joint metal hypersensitivity based on a dedicated questionnaire. METHODS: The authors prospectively asked all adult patients consulting for shoulder pathologies between September 2018 and February 2019 at 10 centers to fill in a form. The main outcome was "reported hypersensitivity to metals," comprising belt buckles, coins, earrings, fancy jewelry, keys, leather, metallic buttons, piercings, spectacles, watch bracelets, or zips. RESULTS: A total of 3217 patients agreed to fill in the survey, aged 55 ± 16 (range, 18-101) with equal proportions of men (51%) and women (49%), and a majority of patients consulting for cuff pathology (55%). A total of 891 (28%) patients had professions considered at risk for metal hypersensitivity. The most frequently reported metal hypersensitivities were fancy jewelry (15%), earrings (13%), and watch bracelets (9%). A total of 629 (20%) patients, of which the vast majority were women, reported hypersensitivity to 1 or more metals. CONCLUSIONS: This survey of 3217 patients identified 20% who reported metal hypersensitivities, though only 2.2% had done patch tests. Matching profiles of those with positive patch tests to those with no patch tests revealed that 9.4% of the total cohort had similar sex and self-reported metal hypersensitivities. Factors associated with a positive patch test were female sex, self-reported cutaneous allergy, and self-reported metal hypersensitivity. The clinical applicability of these estimates remains uncertain as there is insufficient evidence that allergy to metal implants can be predicted by questionnaires or patch tests.

Mechanical characterization and optoelectronic measurement of parietal bone thickness before and after monocortical bone graft harvest: design and validation of a test protocol.

Parietal bone grafts are commonly used in craniomaxillofacial surgery. However, bone removal may weaken the parietal bone and lead to deleterious complications. The aim of our study was to design a test protocol for characterization of the impact resistance of parietal bone before and after monocortical bone graft harvest and to validate an optoelectronic measurement of parietal bone thickness. Twelve fresh human cadaver heads were used for the validation study. To evaluate impact resistance, we developed a pendulum Charpy impact testing machine. The impact force was gradually increased until failure (fracture) of the defined parietal bone area. According to the protocol, we measured the maximum absorbable energy or impact force to failure. With our test setup, measurement of the impact resistance of parietal bone was accurate to within 0.025 J. We defined a range of values and particularly a threshold value. The initial maximal impact must not to exceed 4 J. For more accuracy, we compared 5 nondestructive measurement methods using a surgical navigation system with optoelectronic tracking. We achieved an algorithm based on 2 methods that ensured a measurement resolution of 0.1 mm. Validation of this protocol will allow us to evaluate the loss of strength resulting from bone removal and the correlation between strength and thickness of the parietal bone.

Effect of RSA glenoid baseplate central fixation on micromotion and bone stress.

BACKGROUND: In reverse shoulder arthroplasties (RSA), osseous in-growth is promoted if glenoid micromotion does not exceed 150 µm. The purpose of this study was to determine whether the configuration of central fixation for RSA glenoid baseplates reduces implant micromotion or changes scapula bone stresses. METHODS: Using finite element analysis, glenoid baseplate fixation was tested in a cohort of 3 male and 2 female patients who were to undergo RSA. Computer models were created for 3 different RSA glenoid baseplate and 84 glenosphere designs, a central threaded peg (1 variant, D-TP), a central unthreaded peg (2 variants, I- 85 P(15) and I-P(25)), and a central peg with a screw (2 variants, A-PS and I-PS). A compressive and shear force of 756 N was distributed across the glenosphere with the scapula anchored. RESULTS: Displacement was within 20-130 µm at the glenosphere baseplate-bone interface for all baseplates. The glenospheres with unthreaded pegs had intermediate displacement values (I-P(15): median, 89 µm; range, 32-112 µm; and I-P(25): median, 93 µm; range, 31-109 µm). The von Mises stresses were 1.8-7.0 MPa within cortical bone and 0.6-1.6 MPa within trabecular bone. Cortical bone stresses were similar with unthreaded pegs (I-P(15): median, 4.2 MPa; range, 1.8-6.0 MPa; and I-P(25): median, 4.2 MPa; range, 1.8-6.1 MPa), whereas mean trabecular stresses were similar for all configurations. CONCLUSIONS: All configurations yielded adequate stability, with micromotions being below 150 µm. The unthreaded pegged designs provided a valid alternative to the stable threaded pegged convex baseplates in terms of micromotions and bone stresses.

Comparison of revision rates and radiographic observations of long and short, uncoated and coated humeral stem designs in total shoulder arthroplasty.

There is no consensus on outcomes of long versus short and uncoated versus coated uncemented stems in total shoulder arthroplasty (TSA).We reviewed the literature to compare revision rates and adverse radiographic observations at ⩾ 2 years of various uncemented humeral stem designs.We performed an electronic PubMed search for studies on uncemented primary TSA that reported one or more of the following observations at ⩾ 2 years for distinct stem designs: stem revision; subsidence; stress shielding; radiolucent lines; and humeral loosening.The search returned 258 records, from which 20 articles (22 cohorts) met the inclusion criteria.The most frequently reported designs were short uncoated stems (7/13 cohorts) at < 3 years and long uncoated stems (8/9 cohorts) at > 3 years.The incidences of revisions and adverse radiographic observations were lower for short coated designs, compared with short and long uncoated designs, but these findings should be confirmed by prospective studies with a longer follow-up. Cite this article: EFORT Open Rev 2019;4:70-76. DOI: 10.1302/2058-5241.4.180046.

Influence of uncemented humeral stem proximal geometry on stress distributions and torsional stability following total shoulder arthroplasty.

BACKGROUND: While surgeons tend to implant larger stems to improve torsional stability, numerous studies demonstrated that increasing humeral stem diameter could exacerbate stress-shielding and lead to bone resorption. We aimed to determine the influence of humeral stem proximal geometry on stress distributions and torsional stability following total shoulder arthroplasty. METHODS: Preoperative computed tomography scans were acquired from 5 patients and processed to form 3-dimensional models of the proximal humerus. Computer models of 3 generic implants were created based on three designs: predominantly oval, semi-angular, and predominantly angular. All stems shared identical head geometry and differed only in the proximal metaphyseal area. Finite element analyses were performed, with the humerus rigidly constrained distally, and loaded to simulate the joint reaction force. Implant torsional stability and proximal bone stress distributions were assessed for the three different stem designs with three sizes: oversized (stem making contact with the cortical diaphysis), normosized (one increment smaller) and undersized (two increments smaller). RESULTS: Considering the normosized stems, the angular design increased the physiologic bone stresses at the proximal section by 39-42%, while the oval and semi-angular designs reduced them by 5-9% and 8-13%, respectively. The oval design exhibited a median rotation of 2.1°, while the semi-angular and angular designs exhibited median rotations of 1.8°. CONCLUSION: The semi-angular stem granted an adequate compromise between physiologic stress distributed by the oval stem and torsional stability of the angular stem. Surgeons should be aware of the various benefits and drawbacks of the different humeral stem designs to ensure adequate torsional stability and physiologic loading.

Is global humeral head offset related to intramedullary canal width? A computer tomography morphometric study.

BACKGROUND: While most anatomic TSA stems allow some intra-operative adjustments, the default configuration assumes that head offset is directly proportional to stem diameter. Some authors reported that humeral head diameter is proportional to intra-medullary canal width and humeral head offset, but none investigated the direct relationship between head offset and endosteal measurements. The purpose of the study was to determine whether global humeral head offset is proportional to intramedullary canal width at the distal metaphysis and proximal diaphysis. METHODS: We analyzed 100 Computed Tomography shoulder scans of patients aged 59.1 ± 20.5 with no signs of gleno-humeral arthritis nor humeral dysplasia. The width of the intramedullary diaphyseal canal was determined at four transverse sections 65, 70, 100 and 105 mm below the head center. The inter-observer agreement was excellent for intramedullary canal width (ICC = 0.96), head diameter (ICC = 0.97) and global head offset (ICC = 0.85). Correlations were analysed using Pearson's coefficients and multivariable regressions were performed to determine associations between head offset and five independent variables (gender, age, intramedullary canal width, head diameter). RESULTS: Global head offset was negatively correlated with head diameter (r = - 0.31, p = 0.002), but not correlated with intramedullary canal width (r = - 0.11, p = 0.282). Multivariable regression confirmed that global head offset was independently associated with head diameter (beta = - 0.15, p = 0.005), but not with intramedullary canal width (beta = 0.06, p = 0.431). CONCLUSIONS: The present study revealed that humeral offset is not correlated with intramedullary canal width. Implant manufacturers and shoulder surgeons should be aware of the subtle morphologic features, to enhance humeral stem design and restore native anatomy.

Evaluation of skull strength following parietal bone graft harvest.

BACKGROUND: Parietal bone grafts are commonly used in craniomaxillofacial surgery. The primary aim of this study was to quantify the loss of strength following monocortical parietal bone graft harvest. The secondary aim was to establish a correlation between strength and thickness of calvaria. METHODS: Thirty fresh human cadaver heads (nonfrozen, unembalmed heads) were used for this study. Loss of strength was determined by comparing the maximum impact resistance of bone on the donor side versus the intact side, using a precalibrated pendulum Charpy impact testing machine. Thickness was measured using a surgical navigation system with optoelectronic tracking. RESULTS: Loss of strength at the donor site was 36 percent (p=0.0000000001) for a 40 percent loss of thickness. Although correlation between these two parameters is rather moderate (r=0.46), it is highly significant (p<0.0001). CONCLUSIONS: Although loss of strength is quite significant, serious complications at the donor site are rare. As shown in this study, these risks are nonnegligible. However, because of strong legal pressure, surgeons must carefully weigh the risks incurred by the patient against the expected benefits, whether immediate or deferred. Therefore, the patient should receive well-documented information before such monocortical parietal bone graft harvest is performed.