Pseudotumour formation due to tribocorrosion at the taper interface of large diameter metal on polymer modular total hip replacements.

We present an in-depth failure analysis of two large diameter bearing metal-on-polymer (MoP) modular total hip replacements, which have required revision surgery due to pseudotumour formation. The failure analysis showed a discrete pattern of material loss from the distal end of the head taper/stem trunnion interface. We postulate that the use of a proximal contacting taper design had provided insufficient mechanical locking between the head and the stem, enabling the head to toggle on the trunnion. In addition, the difference in angle between the taper and the trunnion formed a crevice between the two components. Through a combination of crevice environment, mechanically assisted corrosion, mechanical wear and erosion; debris and metal-ions have been released resulting in the adverse local tissue reactions (ALTR).

A data-driven crop model for maize yield prediction.

Accurate estimation of crop yield predictions is of great importance for food security under the impact of climate change. We propose a data-driven crop model that combines the knowledge advantage of process-based modeling and the computational advantage of data-driven modeling. The proposed model tracks the daily biomass accumulation process during the maize growing season and uses daily produced biomass to estimate the final grain yield. Computational studies using crop yield, field location, genotype and corresponding environmental data were conducted in the US Corn Belt region from 1981 to 2020. The results suggest that the proposed model can achieve an accurate prediction performance with a 7.16% relative root-mean-square-error of average yield in 2020 and provide scientifically explainable results. The model also demonstrates its ability to detect and separate interactions between genotypic parameters and environmental variables. Additionally, this study demonstrates the potential value of the proposed model in helping farmers achieve higher yields by optimizing seed selection.

Dislocation of large diameter metal-on-metal bearings an indicator of metal reaction?

We report 3 patients who underwent total hip arthroplasty (THA) using large diameter metal-on-metal bearing. These patients initially presented with pain but went on to develop dislocation of the THA while awaiting investigations. Any pain following metal-on-metal bearing THA should be taken seriously and should trigger investigations to identify a metal reaction. If left untreated, these reactions can cause progressive soft tissue necrosis leading to instability. These patients should be considered for early revision of the bearing surface to prevent further soft tissue damage.

Femoral revision in hip resurfacing compared with large-bearing metal-on-metal hip arthroplasty.

It has been suggested that revision of the femoral component of hip resurfacing after femoral failure would be straightforward and have an outcome comparable to primary total hip arthroplasty (THA). We have compared the outcome of femoral side-only revision resurfacings to the results of primary modular large-bearing metal-on-metal THA. Fourteen consecutive patients underwent revision surgery of the failed femoral component, to a cemented tapered stem (CPT, Zimmer, Warsaw, Indiana) with a large modular metal head (Smith and Nephew Orthopaedics Ltd, Memphis, Tennessee, or Adept, Finsbury Orthopaedics, Surrey, England). The acetabular component was found to be well fixed, well orientated, and was left in situ. The 14 matched patients in the primary THA group received the same components. At a mean follow-up of 49 months (range, 30-60 months), clinical outcome measured using the Oxford and Harris Hip Scores showed no significant difference (P = .11, P = .45, respectively). Operative time and blood loss were comparable for both groups. We conclude that revision of the failed femoral resurfacing component gives excellent results.

Prevalence of Anterior Femoral Neck Osteophyte in a Total Hip Arthroplasty Population: Analysis of Preoperative Surgical Plans.

Despite strongly positive results of total hip arthroplasty (THA), patients remain at risk for complications including dislocation. Spinopelvic motion and the hip-spine relationship have been recognized as important factors in surgical planning and implant positioning in THA. Periarticular osteophytes are one of the hallmark pathoanatomic features of osteoarthritis and may influence implant positioning and joint stability; residual osteophytes at the anterior femoral neck may cause anterior impingement and posterior instability. No studies have been identified which establish the prevalence of anterior femoral neck osteophyte for incorporation into THA planning. 413 consecutive patients scheduled for THA underwent preoperative planning taking into account spinopelvic motion to establish optimal component position. Each surgical plan was reviewed retrospectively by four independent raters who were blinded to other imaging and intraoperative findings. Anterior femoral neck osteophytes were rated as being absent, minor, or extensive for each case. A single outlying rater was excluded. Inter-rater reliability was calculated manually. The patient group comprised 197 male and 216 female hips, with a mean age of 63 years (range 32-91). The presence of anterior femoral neck osteophytes was identified in a mean of 82% of cases (range 78-86%). A significant number of patients were found to have large or extensive osteophytes present in this location (mean 27%; range 23-31%). Inter-rater reliability was 70%. A large majority of our THA patients were found to have anterior femoral neck osteophytes. These must be considered during preoperative planning with respect to the spinopelvic relationship. Failure to identify and address osteophytes intraoperatively may increase the risk of impingement in flexion and/or internal rotation, leading to decreased range of motion, joint instability, and possibly dislocation. Planned future directions include incorporation of an impingement and instability model into preoperative planning for THA.

Damage mechanisms at the cement-implant interface of polished cemented femoral stems.

The occurrence of damage on polished femoral stems has been widely reported in the literature, and bone cement has been implicated in a tribocorrosive failure process. However, the mechanisms of cement-mediated damage and the impact of cement formulation on this process are not well understood. In this study, 13 Zimmer CPT polished femoral stems, and the corresponding cement specimens were retrieved at revision surgery and analyzed using high-resolution imaging techniques. Surface damage attributed to tribocorrosion was observed on all stems. Corrosion product, in the form of black flaky surface debris, was observed on the surface of cement specimens; both energy-dispersive X-ray spectroscopy and inductively coupled plasma mass spectrometry(ICP-MS) confirmed the presence of cobalt and chromium, with the ICP-MS showing much higher levels of Cr compared to Co when compared to the original stem material. Agglomerates of ZrO2 radiopacifier were also identified on the cement surface and, in some cases, showed evidence of abrasive wear; the size of these particles correlated well with elliptical pitting evident on the surfaces of the corresponding stems. This evidence supports the hypothesis that agglomerates of hard radiopacifier particles within the cement may induce a wear-dominated tribocorrosive interaction at the stem-cement interface that damages the surface of polished CoCr femoral stems. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2027-2033, 2017.

Bone and metal: an orthopaedic perspective on osseointegration of metals.

The area of implant osseointegration is of major importance, given the predicted significant rise in the number of orthopaedic procedures and an increasingly ageing population. Osseointegration is a complex process involving a number of distinct mechanisms affected by the implant bulk properties and surface characteristics. Our understanding and ability to modify these mechanisms through alterations in implant design is continuously expanding. The following review considers the main aspects of material and surface alterations in metal implants, and the extent of their subsequent influence on osseointegration. Clinically, osseointegration results in asymptomatic stable durable fixation of orthopaedic implants. The complexity of achieving this outcome through incorporation and balance of contributory factors is highlighted through a clinical case report.

Taking tissue-engineering principles into theater: augmentation of impacted allograft with human bone marrow stromal cells.

Human bone marrow contains bone progenitor cells that arise from multipotent mesenchymal stem cells. Seeding bone progenitor cells onto a scaffold can produce a 3D living composite with significant mechanical and biological potential. This article details laboratory and clinical findings from two clinical cases, where different proximal femoral conditions were treated using impacted allograft augmented with marrow-derived autogenous progenitor cells. Autologous bone marrow was seeded onto highly washed morselized allograft and impacted. Samples of the impacted graft were also taken for ex vivo analysis. Both patients made an uncomplicated clinical recovery. Imaging confirmed defect filling with encouraging initial graft incorporation. Histochemical and alkaline phosphatase staining demonstrated that a live composite graft with osteogenic activity had been introduced into the defects. These studies demonstrate that marrow-derived cells can adhere to highly washed morselized allograft, survive the impaction process and proliferate with an osteoblastic phenotype, thus creating a living composite.