Impaction forces might contribute to trunnion corrosion
Large off-axis forces can affect the modular component fixation during impaction of the femoral head on the stem. At this year’s AAOS Meeting Noble et al. presented the results of their experiment in which fifteen surgeons replicated their surgical technique on a surrogate lower limb and impacted a 32mm metal head with an instrumented hammer on an instrumented femoral stem. Magnitude, direction and temporal variation of the impaction force of each hammer blow were recorded. The force components at work along the axis of the neck and in the AP and ML directions were continuously sampled using accelerometers.
The peak impaction force varied between 2.4 and 6.3kN and the direction from 14 to 43 degrees between individual surgeons. This variability was not associated with the level of training or experience. According to the authors, the results show that large off-axis forces are exerted during impaction, with a large variation in magnitude and direction. They concluded that this variability in intraoperative assembly might contribute to the severity and incidence of mechanically assisted corrosion in total hip replacement.
A recently published book edited by Prof. Veit Krenn, MD, and Giorgio Perino, MD gives a concise overview on the “Histological Diagnosis of Implant-Associated Pathologies”. The authors deal, among others, with the analysis of the synovial-like interface membrane (SLIM), adverse local tissue reactions (ALTR) associated with metallic implant wear and classification of PE debris. They offer a particle algorithm as a guide for the identification of particulate material in the periprosthetic tissue.
The book points out that a histological analysis of the synovial-like interface membrane (SLIM) according to the expanded international consensus classification and wear particle characterization allows for improved diagnosis of implant failure and can also provide guidance in the determination of a suitable postoperative treatment, follow-up and optimization of the therapeutic regime.
The particle algorithm provides an easy and reliable guide for the identification of particulate material in the periprosthetic tissue. It is useful for identifying mechanisms of failure of the prostheses in the context of clinical, allergological, microbiological, histological, radiological, and biomechanical findings. The expanded international consensus classification of SLIM is also useful in the diagnosis of all inflammatory-toxic and hypersensitive-allergic reactions. It provides detailed information that can be relevant for clinical management.
ALTR associated with metallic implant wear include immunologically mediated reaction to particle toxicity as well as hypersensitivity or allergy to metallic particles and ions. The analysis of PE debris is important because it is still a main cause of osteolysis, a major cause for the failure of joint implants. It should be associated with the examination and technical description of the implant, including in the pathological final report.
The basic subdivision of the PE debris into micro-, macro-, and supramacro-particulate is proposed to be correlated with the biomechanical analysis of the implant and the oxidative state of the material. The occurrence of supra-macroparticles in PE degradation should be reported as a major failure of the insert. The cause of its occurrence should be determined for each implant with detailed biomechanical analysis to differentiate among material oxidative degradation and mechanical failures such as misalignment, impingement, dislocation, rim fractures, and third-body wear.
CoC with excellent results
In a retrospective study evaluating 347 THA in patients under 50 with a mean follow-up of 7.8 years, Kim et al. found excellent medium-term results with BIOLOX®delta ceramic-on-ceramic bearings. The Kaplan-Meier survival rate was >99%. There was no osteolysis and no ceramic fracture. Osteonecrosis and osteoarthritis following developmental dysplasia had been the most common indications for primary surgery performed by a single surgeon using 36mm (283 hips) and 32mm BIOLOX®delta ceramic-on-ceramic bearings.
Lowest ion levels with ceramic
Cobalt and chromium ion levels in the serum were mostly below the detection limit in THA patients with CoC bearings. Barlow et al. reached this finding in a comparison of four groups with different types of bearings. Patients with metal heads had significantly higher serum levels of Co ions than those with ceramic heads. Nevertheless, the absolute levels within the study period were low, appearing to have little clinical significance, as there was no difference in PROMs between the groups.
Ceramic heads on the rise
The German Society for Orthopaedics and Orthopaedic Surgery (DGOOC) calls for papers for its Heinz Mittelmeier Research Award 2017 to be submitted by July 31. The 5,000 € prize is donated by CeramTec and awarded to clinicians, engineers or scientists not older than 40 years for outstanding contributions to research and development in the field of bioceramics, clinical results from ceramic implants and problems associated with wear in arthroplasty.