Introduction

Studies of metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) have reported high complication and failure rates due to elevated metal ion levels. These rates were shown to be especially high for the Articular Surface Replacement (ASR) HRA, possibly due to its unique design. Associations between metal ion concentrations and various biological and mechanical factors have been reported. Component positioning as measured by acetabular inclination has been shown to be of especially strong consequence in metal ion production in ASR HRA patients, but few studies have evaluated acetabular anteversion as an independent variable.

The primary objective of this study was to evaluate the associations between component orientation, quantified by acetabular inclination and anteversion, and blood metal ions. Secondly, we sought to report whether conventional safe zones apply to MoM HRA implants or if these implants require their own positioning standards.

Introduction

Total Hip Arthroplasty (THA) is currently one of the most widely performed surgical procedures in clinical orthopaedic practice. Despite the recorded number of uncemented implants has steadily increased in recent years, cemented fixation still remains the benchmark in THA, accounting for most of the procedures performed nowadays. The Friendly Short is a novel cemented short-stem that grants a less invasive and more bone conservative approach due to its shortened height and innovative cementing technique. It is indicated to treat elderly patients with the aim of preserving bone diaphysis while decreasing postoperative recovery times. Its instrument set allows to optimize the cement mantle thickness via an improved pressurization and stem centralization system.

Introduction

Although total knee arthroplasty (TKA) has become a successful routine procedure in clinical orthopaedics, up to 20% of patients are not satisfied with the outcome of their surgery. Dissatisfaction in high-demand patients has been associated with the functional limitations of conventional TKA implants, as they do not recreate the natural biomechanics of the knee.

A novel knee prosthesis has been designed to replicate the natural rolling & gliding mechanism of the knee joint, aiming to restore a physiological movement whilst improving implant stability and pain-free function.

This TKR system includes 3 versions (CR, PS, KR); the KR (Kinematic Retaining) preserves the posterior cruciate ligament (PCL); the femoral component incorporates a thin anterior flange and a deep, broad trochlear groove to reduce anterior knee pain and to reproduce physiological patellar tracking without constraining the patella. The sagittal plane multiple radii of the femoral condyles (J-curve) allows the carefully designed femur to physiologically tension the collateral ligaments during the entire flexion/extension cycle. Tibial liners are also asymmetrical, presenting a concave medial shape with a saddle-like lateral shape. These asymmetric articulating surfaces have been designed to reproduce a more natural physiological roll-back and rotation of the femur over the tibia, thus reducing the sliding friction in the early phases of knee flexion. Furthermore, the roll-back motion relieves the stress from the patella and restores the physiological function of the quadriceps.

The use of a cemented implant instead of a spacer has been proposed due to the improved function in comparison with a spacer. Unfortunately the removal of a conventional cemented stem can be challenging. The use of a short cemented stem can overcome this problem.

Between July 2011 and May 2013, 10 infected hips were treated with a short cemented stem as a spacer. The infected implants were cemented in 6 cases and cementless in 4 cases. Mean time from index operation was 3 years (range 0 to 8 years). It was the first treatment for infection in all cases. Antibiotic loaded cement and an all-poly cup was used in all cases. The bugs were staph aureus and staph epidermidis in most cases. A Friendly short cemented stem with specific cement restrictor and standard cementing tecnique was used in all cases. This stem has been successfully tested in over 200 patients and approved by TUV to be released on the marked.

In all cases, the infection was successfully cured with antibiotics for a period ranging from 3 to 5 months. 2 patients were revised after the infection was cured for recurrent dislocation. No recurrent infection was found at the latest follow up.

One stage revision is gaining in popularity for the decreased morbidity and better quality of life of the patients. Weak points of one-stage revision are slightly inferior results in terms of eradication of the infection and the fact that it can be done only with cemented implants. Cemented implants show inferior durability than cementless implants and are difficult to remove if revision is needed. The use of a short cemented stem can couple the advantages of one stage revision and the fact that it is easily removed if this is needed for various reasons (aseptic loosening, recurrent dislocation and periprosthetic fracture). Contraindications to this technique are severe bone loss in the acetabulum or in the proximal femur.