The Exeter Contemporary flanged cemented acetabular component in primary total hip arthroplasty

Aims: We report on the outcome of the Exeter Contemporary flanged cemented all-polyethylene acetabular component with a mean follow-up of 12 years (10 to 13.9). This study reviewed 203 hips in 194 patients. 129 hips in 122 patients are still in situ; 66 hips in 64 patients were in patients who died before ten years, and eight hips (eight patients) were revised. Clinical outcome scores were available for 108 hips (104 patients) and radiographs for 103 hips (100 patients). Patients and Methods: A retrospective review was undertaken of a consecutive series of 203 routine primary cemented total hip arthroplasties (THA) in 194 patients. Results: There were no acetabular component revisions for aseptic loosening. Acetabular revision was undertaken in eight hips. In four hips revision was necessitated by periprosthetic femoral fractures, in two hips by recurrent dislocation, in one hip for infection and in one hip for unexplained ongoing pain. Oxford and Harris hip scores demonstrated significant clinical improvement (all p < 0.001). Radiolucent lines were present in 37 (36%) of the 103 acetabular components available for radiological evaluation. In 27 of these, the line was confined to zone 1. No component had migrated. Conclusion: Kaplan–Meier survivorship, with revision for aseptic loosening as the endpoint, was 100% at 12.5 years and for all causes was 97.8% (95% confidence interval 95.6 to 100) when 40 components remained at risk. The Exeter Contemporary flanged cemented acetabular component demonstrates excellent survivorship at 12.5 years. Take home message: The Exeter Contemporary flanged cemented acetabular component has excellent clinical outcomes and survivorship when used with the Exeter stem in total hip arthroplasty.

Morbid obesity in total hip arthroplasty: Redefining outcomes for operative time, length of stay, and readmission

Background The incidence of obesity amongst patients presenting for elective Total Hip Arthroplasty (THA) has increased in the last decade and the relationship between obesity and the need for joint replacement has been demonstrated. This study evaluates the effects of morbid obesity on outcomes following primary THA by comparing short-term outcomes in THA between a morbidly obese (BMI ≥40) and a normal weight (BMI 18.5 - <25) cohort at our institution between January 2003 and December 2010. Methods Thirty-nine patients included in the morbidly obese group were compared with 186 in the normal weight group. Operative time, length of stay, complications, readmission and length of readmission were compared. Results Operative time was increased in the morbidly obese group at 122 minutes compared with 100 minutes (p=0.002). Post-operatively there was an increased 30-day readmission rate related to surgery of 12.8% associated with BMI ≥40 compared with 2.7% (p= 0.005) as well as a 5.1 fold increase in surgery related readmitted bed days - 0.32 bed days per patient for normal weight compared with 1.64 per patient for the morbidly obese (p=0.026). Conclusion Morbidly obese patients present a technical challenge and likely this and the resultant complications are underestimated. More work needs to be performed in order to enable suitable allocation of resources.

Ductile deformation of single inclusions in simple shear with a finite-strain hyperelastoviscoplastic rheology

We examine the 2D plane-­strain deformation of initially round, matrix-­bonded, deformable single inclusions in isothermal simple shear using a recently introduced hyperelastoviscoplastic rheology. The broad parameter space spanned by the wide range of effective viscosities, yield stresses, relaxation times, and strain rates encountered in the ductile lithosphere is explored systematically for weak and strong inclusions, the effective viscosity of which varies with respect to the matrix. Most inclusion studies to date focused on elastic or purely viscous rheologies. Comparing our results with linear-­viscous inclusions in a linear-­viscous matrix, we observe significantly different shape evolution of weak and strong inclusions over most of the relevant parameter space. The evolution of inclusion inclination relative to the shear plane is more strongly affected by elastic and plastic contributions to rheology in the case of strong inclusions. In addition, we found that strong inclusions deform in the transient viscoelastic stress regime at high Weissenberg numbers (≥0.01) up to bulk shear strains larger than 3. Studies using the shapes of deformed objects for finite-­strain analysis or viscosity-­ratio estimation should establish carefully which rheology and loading conditions reflect material and deformation properties. We suggest that relatively strong, deformable clasts in shear zones retain stored energy up to fairly high shear strains. Hence, purely viscous models of clast deformation may overlook an important contribution to the energy budget, which may drive dissipation processes within and around natural inclusions.