Horror of three synergistic factors in THA: high mechanical stress, dissimilar metals, low elasticity stem: a case report

Background A large-diameter femoral head is effective in preventing dislocation after total hip arthroplasty. However, although rare, catastrophic stem tribocorrosion may occur at the head-stem junction. Case presentation A 70-year-old woman underwent revision surgery 7.5 years after total hip arthroplasty because of catastrophic stem corrosion with dissociation of the metal head (cobalt/chromium) and stem (TiMo12Zr6Fe2). Abnormal levels of cobalt were found in the intra-articular fluid, capsule, hip muscle, and blood. Revision surgery was performed via the direct anterior approach. The well-fixed femoral stem was explanted, and a cemented stainless stem with stainless head was implanted. Three months after the revision surgery, the cobalt concentration in the blood had decreased to normal. Conclusions Stem dissociation in the present case might have been caused by synergistic combination of a 36-mm-diameter femoral head and long neck length offset with high frictional torque, a cobalt-chromium head with a high risk of galvanic corrosion, and a TMZF (TiMo12Zr6Fe2) alloy stem with a low Young’s modulus of elasticity. The combination of these factors must be avoided.

Does the use of the largest possible metal head increase the wear of vitamin E-doped cross-linked polyethylene? Two-year results from a randomized controlled trial

Aims We aimed to investigate if the use of the largest possible cobalt-chromium head articulating with polyethylene acetabular inserts would increase the in vivo wear rate in total hip arthroplasty. Methods In a single-blinded randomized controlled trial, 96 patients (43 females), at a median age of 63 years (interquartile range (IQR) 57 to 69), were allocated to receive either the largest possible modular femoral head (36 mm to 44 mm) in the thinnest possible insert or a standard 32 mm head. All patients received a vitamin E-doped cross-linked polyethylene insert and a cobalt-chromium head. The primary outcome was proximal head penetration measured with radiostereometric analysis (RSA) at two years. Secondary outcomes were volumetric wear, periacetabular radiolucencies, and patient-reported outcomes. Results At two years, 44 patients in each group were available for RSA assessment. The median total two-year proximal head penetration was -0.02 mm (IQR -0.09 to 0.07; p = 0.548) for the largest possible head and -0.01 mm (IQR -0.07 to 0.10; p = 0.525) for 32 mm heads. Their difference was not statistically significant (p = 0.323). Neither group demonstrated a bedding-in period. The median steady-state volumetric wear rates were 6.1 mm3/year (IQR -59 to 57) and 3.5 mm3/year (-21 to 34) respectively, and did not differ between the groups (p = 0.848). There were no statistically significant differences in periacetabular radiolucencies or patient-reported outcomes. Conclusion The use of the largest possible metal head did not increase vitamin E-doped cross-linked polyethylene wear compared with 32 mm heads at two years. Linear wear was negligible and volumetric wear rates were very low in both head size groups. There was a tendency towards higher values of volumetric wear in large heads that warrants longer-term evaluation before any definite conclusions about the association between head size and wear can be drawn. Cite this article: Bone Joint J 2021;103-B(7):1206–1214.

No difference in whole-blood metal ions between 32-mm and 36- to 44-mm femoral heads in metal-on-polyethylene total hip arthroplasty: a 2-year report from a randomised control trial

Aim: To investigate the effect of femoral head size on blood metal-ion levels caused by taper corrosion in metal-on-polyethylene total hip arthroplasty, comparing 36- to 44-mm heads with 32-mm heads. Methods: In a randomised, controlled, single-blinded trial, 96 patients were allocated to receive either a 32-mm metal head or the largest possible metal head (36–44 mm) that could be accommodated in the thinnest available vitamin E, cross-linked polyethylene insert. Blood metal ion levels were collected at 1- and 2-year follow-ups. Results: At 1-year, metal-ion levels did not differ between the groups. The median (interquartile range) blood-ion levels for the 32-mm versus the 36- to 44-mm group were 0.11 µg/L (0.08–0.15) versus 0.12 µg/L (0.08–0.22), p = 0.546, for cobalt, 0.50 µg/L (0.50–0.59) versus 0.50 µg/L (0.50–1.20), p = 0.059, for chromium and 1.58 µg/L (1.38–2.05) versus 1.48 µg/L (1.14–1.87), p = 0.385, for titanium. At 2 years, there was no difference either and the corresponding values were 0.15 µg/L (0.12–0.24) versus 0.18 µg/L (0.12–0.28), p = 0.682 for cobalt, 0.50 µg/L (0.50–0.50) versus 0.50 µg/L (0.50–0.57), p = 0.554, for chromium and 1.54 µg/L (1.16–1.87) versus 1.42 µg/L (1.01–1.72), p = 0.207 for titanium. Conclusions: The use of the largest possible metal head (36–44 mm) compared to a 32-mm head in metal–on-polyethylene bearings does not appear to elevate blood metal-ion levels up to 2 years postoperatively. As taper corrosion is probably time-dependent, longer-term reports are needed to evaluate the association between large metal heads and blood metal ion levels. Trial registration: ClinicalTrials.gov (reg. ID NCT0231 6704)

Spontaneous Early Intraprosthetic Dislocation of 22 mm Skirted Femoral Head in Dual Mobility Hip Prosthesis: A Case Report

Introduction: There is a trend for increasing use of dual mobility hip designs for both primary and revision hip arthroplasty settings. It provides dual articular surfaces along with increased jump distance to increase the stability of construct. However, this design has some unique complications of its own which surgeons should be aware of especially intraprosthetic dislocation (IPD). Case Report: A 76-year-old lady presented to clinic with painful hip hemiarthroplasty after fracture neck of femur. She underwent revision surgery with dual mobility uncemented acetabular cup and femoral stem was retained as it was well fixed. She was mobilizing well and around 5 weeks post her surgery, developed pain in hip region and difficulty in weight-bearing. Radiographs showed eccentric position of femoral neck in the socket. A diagnosis of IPD was established and revision surgery was planned. Intraoperatively, metal head had dislocated from the polyethylene head and both components were resting in the acetabular socket. No macroscopic erosion of acetabulum was noticed. The polyethylene component and femoral head were retrieved. With previous failed dual mobility, decision was made to achieve stability with larger head size and lipped liner posteriorly. Conclusion: IPD is a rare occurrence and unique complication to dual mobility implants. This report highlights that patients can have IPD without fall or trauma. Keywords: Intraprosthetic dislocation, dual mobility cup, dislocation, total hip replacement.

Early Post-operative Rises in Serum Metal Ion Levels in Total Hip Arthroplasty

Background: Serum Cobalt (Co) and Chromium (Cr) forms part of the diagnostic process for metallosis following Total Hip Arthroplasty (THA). While knowledge exists on longer term metal ion levels, expected early post-operative rises in serum Co and Cr in Metal-on-Polyethylene (MoP) THAs are currently unknown. This study aims to describe early rises in serum Co and Cr at 6 months post-operatively. Methods: A prospective cohort study of 100 consecutive patients with an uncemented titanium stem from a single THA manufacturer was performed. Patients had either a metal (n=50) or ceramic (n=50) head articulating with a highly cross-linked polyethylene. Serum Co and Cr levels were measured 6 months post-operatively. Analysis compared mean values between groups and to determined baseline levels. Subgroup analysis investigated the effect of femoral head size and offset on metal ion levels. Results: A mean difference of 2.259 nmol/L (95% CI 0.449-4.069; p=0.015) was found when comparing 6-month serum Co in the metal head group compared to baseline. No significant differences were found in serum Cr (p=0.943). Mean serum Co levels were higher in the MoP group compared to the CoP (Ceramic-on-Polyethylene) comparator group (p=0.012). There were no differences in serum Cr (p=0.976). Variations in femoral head size and offset did not impact metal ion levels. Conclusion: At six months, a higher magnitude of serum Co exists in metal heads when compared to baseline (p=0.015) and to ceramic heads (p=0.012). Further study is required to determine whether serum concentrations of metal ions will continue to increase over time.

15-year follow-up of MoM 36-mm THA: clinical, laboratory, and radiological (CT and MRI) prospective assessment

Introduction: There is limited knowledge of the long-term results of metal-on-metal total hip arthroplasty (MoM THA), particularly concerning adverse local tissue reaction (ALTR), Co/Cr ions level and revision rate. Even if MoM bearing surfaces are no longer used, long-term data could help in defining the course and best management for these patients. The purpose of this study is to investigate the clinical outcomes, describe radiological findings including CT metal artefact reduction algorithm for orthopaedic implants (O-MAR) and MRI multi acquisition variable resonance image combination (MAVRIC) in 36-mm MoM THA. Methods: In this long-term prospective study, 46 consecutive patients with primary MoM THA (mono- or bilateral) were enrolled between 2004 and 2005. Pinnacle acetabular cup, Summit cementless stem with 36-mm metal head and Ultamet CoCr alloy liner (Depuy Inc.) were implanted, in the same centre by the same senior surgeon. Patients were reviewed at 5-, 10- and 15-years, including Co/Cr levels and standard radiographs at every follow-up, whilst the 15-year follow-up included hip sonography, MRI MAVRIC and CT O-MAR. Results: At 15 years, the overall survival rate of the implants (both stems and cups) was 83% (30/36). Revisions were performed in 9% (4/46) because of ALTR, 2% (1/46) septic loosening and 2% periprosthetic fracture. Both Cr and Co concentration increased over time, even though remaining at low level risk at 15 years: Co from 0.11 (+/– 0.18) to 4.29 (+/– 3.26) and Cr from 0.38 (+/– 0.32) to 1.37 (+/– 1.15). Functional scores in non-revised patients showed good to excellent results in more than 90%. Engh-score correlated with time from surgery ( p = 0.017) and with sonographic, CT and RM findings ( p < 0.05). Concordance has been found between CT and MRI findings (sign-rank test, p = 0.241; Intraclass Correlation Coefficients 0.987); however, no specific MRI or CT lesion patterns could be recognised among symptomatic and non-symptomatic patients. Discussion: The long-term rate of ALTR after 36-mm MoM THA was comparable with previous studies; a regular follow-up for those implants is mandatory. During follow-up Co-Cr levels increased over time and radiography was a suitable screening technique; the Engh score in particular, proved to be a reliable assessment tool. CT O-MAR and MRI with MAVRIC protocols may add valuable data in clinical practice, although MRI is significantly more efficient than CT in the identification of ALTR lesions, peri-articular effusion and in the evaluation of soft tissues.

Hip Spacers with a Metal-on-Cement Articulation Did Not Show Significant Surface Alterations of the Metal Femoral Head in Two-Stage Revision for Periprosthetic Joint Infection

Two-stage revision is considered the gold standard treatment for chronic periprosthetic joint infection (PJI). During the interim period, between explantation of the infected hip endoprosthesis and revision arthroplasty, individually formed articulating hip spacers made of polymethylmethacrylate (PMMA) bone cement can be used to provide better soft tissue preservation, local antibiotic release, and improved postoperative mobilization. If effective prevention from luxation is achieved, hip function and hence overall patient satisfaction is improved. Zirconium oxide particles inside conventional PMMA bone cement, however, are known to enhance third-body wear, which may cause alterations of the metal head in the articulating spacer and hence become a serious risk for the patient. Therefore, the aim of our study was to analyze whether the articular surface of cobalt-chrome (CoCr) femoral heads is significantly altered in the setting of a metal-on-cement articulation during the interim period of two-stage revision for PJI. We analyzed a consecutive series of 23 spacer cases and compared them with femoral heads from two series of conventional hip arthroplasty revisions with metal-on-polyethylene articulations and different time intervals in situ. To investigate metallic wear, the femoral heads were thoroughly examined, and their surface roughness was measured and analyzed. We found no significant differences between the two conventional hip arthroplasty groups, despite their very different times in situ. Furthermore, the individually different times in situ within the spacer group had no significant impact on surface roughness, either. Compared with the spacer group, the surface roughness of the metal femoral heads from both conventional hip arthroplasty groups were even higher. Within the spacer group, roughness parameters did not show significant differences regarding the five predefined locations on the metal head. We conclude that metal-on-cement articulations do not cause enhanced surface alterations of the metal femoral head and hence do not limit the application in articulating hip spacers in the setting of two-stage revision for PJI.

Study of Contact Pressures in Total Hip Replacement

Total hip arthroplasty is a complex procedure. The achievements of implantology enabled the development of a faithful representation of hip joint physiology as well as the production of materials that can successfully replace damaged natural tissues. A very important issue is the correct selection of the geometry of the endoprosthesis adequate to the load of the joint. Materials used for endoprosthesis are a metal head and a polymer cup (e.g. PE-UHMW). The main interactions in the endoprosthesis are friction and surface pressure, which must be limited, exceeding them causes the destruction of the biomechanical system - plastic deformation of the polymer and the formation of too large and unacceptable radial clearances. Based on the author's developed calculation method of hip joint endoprosthesis contact parameters, the impact on maximum contact pressure and the angle of contact of the joint load was estimated depending on the diameter of the endoprosthesis and radial clearance. The correctness of changing the values of maximum contact pressure from the mentioned parameters was determined. Correspondingly: an increase in joint load causes a linear increase in the maximum contact pressure; increasing the diameter of the endoprosthesis head - their non-linear decrease, and increasing radial clearance - their increase

Improving the Aluminium Rolling Ingot Recovery using Tqm Technique

To improve productivity and profitability in Aluminium continuous casting industry the main action is to reduce losses due to defects resulting into revenue losses. Improving Rolling Ingot Recovery is possible by reducing the rejections & using the resources effectively (resources MAN, MACHINE, MATERIAL & CAPITAL) by applying TQM technique. This study presents a case about minimizing defects in aluminium continuous casting using Total Quality Management (TQM) techniques in which why-why analysis, Standard Operating Procedures (SOPs),and Cause and Effect analysis is used. It can be concluded from study that rejections, shell zone & inclusion can be reduced by, Continuous monitoring the health of the moulds, quality & quantity of water, the metal casting temperature, metal head in mould, water impingement angle, use of Ceramic foam filter plates, awareness & the adherence towards the guidelines