Importance of surgical assembly technique on the engagement of 12/14 modular tapers.

Fretting-corrosion at the modular taper junction in total hip replacements (THR), leading to implant failure, has been identified as a clinical concern and has received increased interest in recent years. There are many parameters thought to affect the performance of the taper junction, with the assembly process being one of the few consistently identified to have a direct impact. Despite this, the assembly process used by surgeons during THR surgery differs from a suggested 'ideal' process. For example, taper junctions of cutting tools should be pushed together rather than impacted, while ensuring as much concentricity as possible between the male and female taper and loading axis. This study devised six simple assembly methodologies to investigate how surgical variations affect the success of the compressive fit achieved at the taper interface compared to a controlled assembly method, designed to represent a more 'ideal' scenario. Key findings from this study suggest that a more successful and repeatable engagement can be achieved by quasi-statically loading the male and female taper concentrically with the loading axis. This was shown by a greater disassembly to assembly force ratio of 0.626 ± 0.07 when assembled using the more 'ideal' process, compared to 0.480 ± 0.05 when using a method closer to that used by a surgeon intraoperatively. Findings from this study can be used to help inform new surgical instrumentation and an improved surgical assembly method.

Disassociation of a Cold-Welded Bimodular Titanium Femoral Stem by Intraoperative Ice Cooling.

Modularity in total hip arthroplasty allows a surgeon to have intraoperative versatility, allowing for fine adjustments of the femoral offset, leg length, and version. However, modularity can be a source of multiple complications. This case report describes a novel intraoperative solution for the problem of cold welding of a neck-stem junction using sterile ice to cryogenically disengage the modular components.

Flexural Rigidity, Taper Angle, and Contact Length Affect Fretting of the Femoral Stem Trunnion in Total Hip Arthroplasty.

BACKGROUND: Modularity at the head-neck junction in total hip arthroplasty allows for intraoperative adjustments but may be a source of metallic debris. We determined how flexural rigidity, taper angle, contact length, and lever arm affect fretting and corrosion at this junction. METHODS: A total of 77 metal-on-polyethylene total hip arthroplasties retrieved over a 10-year period at a single institution were obtained. Head tapers and stem trunnions were graded for fretting and corrosion. RESULTS: Stem fretting was inversely related to rigidity and taper angle, while positively correlated to contact length. Head fretting and head and stem corrosion were not associated with any of these parameters. CONCLUSION: Design and assembly factors at the modular head-neck connection affected stem fretting among the retrieved components, suggesting that these parameters are important to consider when choosing a modular system.

Corrosion and Fretting of a Modular Hip System: A Retrieval Analysis of 60 Rejuvenate Stems.

Femoral stems with dual-taper modularity were introduced to allow independent control of length, offset, and version. Corrosion and fretting related to micromotion at the neck-stem junction are thought to stimulate an adverse local tissue reaction (ALTR). Analysis of 60 consecutively retrieved modular-neck stem implants (Rejuvenate, Stryker) revised primarily for ALTR was done to determine the variables influencing corrosion and fretting patterns at the neck-stem interface. Taper damage evaluation was performed with stereomicrocopic analysis with two observers. Evidence of fretting and corrosion was seen at the neck-stem taper in all implants, including three implants revised for periprosthetic fractures within four weeks of the index surgery indicating that this process starts early. Femoral stems paired with the long overall neck lengths had significantly higher corrosion scores. Correlation of the corrosion severity at particular locations with the length of implantation suggests that the neck-stem junction experiences cyclic cantilever bending in vivo. The positive correlation between the length of implantation and fretting/corrosion scores bodes poorly for patients who still have this implant. Scanning electron microscopy on a subset of specimens was also performed to evaluate the black corrosion material. We strongly urge frequent follow-up exams for every patient with this particular modular hip stem.

Correlation of corrosion and biomechanics in the retrieval of a single modular neck total hip arthroplasty design: modular neck total hip arthroplasty system.

Increased modularity of total hip arthroplasty components has occurred, with theoretical advantages and disadvantages. Recent literature indicates the potential for elevated revision rates of modular neck systems and the potential for local pseudotumor and metallosis formation at the modular neck/stem site. Retrieval analysis of one modular neck implant design including SEM (SCANNING ELECTRON MICROSCOPY) assessment was done and correlated with FEA (finite element analysis) as well as clinical features of patient demographics, implant and laboratory analysis. Correlation of the consistent corrosion locations to FEA indicates that the material and design features of this system may result in a biomechanical reason for failure. The stem aspect of the modular neck/stem junction may be at particular risk.

Spontaneous Dissociation of Anatomic Medullary Locking A Plus (AML A Plus) Femoral Component at the Head-Neck Interface.

INTRODUCTION: Innovations in the design of total hip arthroplasty components have been developed to address certain limitations with the use of standard monoblock prosthesis. With increasing use and long-term follow up, certain complications particularly related to fretting, corrosion and fatigue have been recognized. CASE REPORT: A 31 year old active male patient presented with spontaneous dissociation of the Anatomic Medullary Locking A Plus (AML A Plus) Femoral Component at head and neck interface 10 years after surgery. At revision surgery, wear of the acetabular liner and head and neck taper was noted. Definitive treatment required complete revision of the femoral component and change of acetabular liner. CONCLUSION: While modularity allows change of worn out components, this case highlights the importance of various factors in avoiding this complication and the need for surgeon to be prepared to use 'taper sleeves' or revise the components if taper exchange fails particularly in cases with dissociation of head-neck interface which is usually associated with taper damage.

Usefulness of a Modular Hip System for Combined Anteversion in Cementless Total Hip Arthroplasty / 대한고관절학회지

PURPOSE: The purpose of this study is to evaluate the usefulness of a modular total hip system for combined anteversion in cementless modular total hip arthroplasty. MATERIALS AND METHODS: We performed twenty cementless modular total hip arthroplasty procedures. The patients lay in lateral position and 15degreesinternal rotation of the thigh. The surgeon inserted an acetabular cup component first, followed by a femoral component. He selected an appropriate modular neck component using an intra-operative manual combined anteversion test. All patients underwent post-operative computed tomography. RESULTS: The average measurement of anteversion of the acetabular cup was 15.9+/-2.9degrees and anteversion of the femoral stem was 15.2+/-11.9degrees. Then, the combined anteversion was calculated to 24.0+/-8.2degrees. Significant difference was observed between combined anteversion and theoretical combined anteversion. CONCLUSION: The method using an intra-operative manual combined anteversion test cannot realize the theoretical combined anteversion in cementless modular hip arthroplasty.