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.

The idea of resurfacing the femoral head instead of removing it has been attractive for a long time.

Unfortunately the results have been invariably poor if compared with contemporary available conventional hip prosthesis. In the last decade metal on metal technology with very accurate manufacturing made hip resurfacing a viable option. The main complication of this operation is early failure due to femoral neck fracture. This event is still incompletely understood and probably multi-factorial. Accurate placement of the femoral component to avoid notching the femoral neck, cementing technique to avoid over-penetration of the cement, small implantation forces and careful soft tissue handling to minimize the damage to the bone vascularity are thought to be the main issues. The ideal candidates for this operation are young and active patients because they have good bone quality and will take advantage of the improved performances that hip resurfacing can offer.

Unfortunately young men are also the group of patients at higher risk for the formation of heterotopic ossifications.). To prevent this complication radiotherapy was administered in a single dose of 6 Gy with two opposite fields of 18 MV generally the first post operative day. When we started to perform hip resurfacing we did not consider changing our protocol. Between March 2004 and May 2005, 55 hip resurfacings were performed using the ASR implant (DePuy) by a single surgeon (LM). Most males under the age of 60 received radiotherapy. There were 4 femoral neck fractures in the 23 male patients who received radiotherapy (17.3 %) and 1 fracture in the 32 patients who did not receive radiotherapy (3.1 %, Chi-square test: p= 0.07). All the fractures occurred between the 90th and the 120th postoperative day. No fractures were reported in the 12 women included in this study. What arouse our attention was the unacceptably high number of femoral neck fractures. The learning curve alone could not explain what was happening. At first the radiotherapy was not considered at all as factor but errors in the surgical technique were looked for. The clue came from the observation that there were no women in the fracture group in spite of the fact that the surgical technique was the same and also in spite of the fact that women should be at higher risk due to poorer bone quality as shown in the literature. This led us to check the incidence of fractures in the radiotherapy and in the non radiotherapy group. At this stage things became quite clear. Subsequently the histology of the specimen was re-examined with regard to this factor. Bone necrosis of the femoral head in the patients who underwent radiotherapy was much more pronounced then in other failures which show different degrees of necrosis. In conclusion there are strong indications that radiotherapy of the femoral head should not be performed in combination with hip resurfacing.