Ahmad Faizan

Development and verification of a cementless novel tapered wedge stem for total hip arthroplasty.

Most current tapered wedge hip stems were designed based upon the original Mueller straight stem design introduced in 1977. These stems were designed to have a single medial curvature and grew laterally to accommodate different sizes. In this preclinical study, the design and verification of a tapered wedge stem using computed tomography scans of 556 patients are presented. The computer simulation demonstrated that the novel stem, designed for proximal engagement, allowed for reduced distal fixation, particularly in the 40-60 year male population. Moreover, the physical micromotion testing and finite element analysis demonstrated that the novel stem allowed for reduced micromotion. In summary, preclinical data suggest that the computed tomography based stem design described here may offer enhanced implant fit and reduced micromotion.

Evaluation of surgical impaction technique and how it affects locking strength of the head–stem taper junction

Cases of fretting and corrosion at the taper junction have been reported in large metal-on-metal bearing combinations, and more recently, this concern has included metal-on-polyethylene bearing combinations. Many of these patients have been revised due to adverse local tissue reaction secondary to taper corrosion. This taper corrosion–related adverse local tissue reaction seems to be a multifactorial issue and difficult to assess. The aim of this study was to look at one potential variable, the impaction behavior (impaction force, number of blows, etc.) of orthopedic surgeons, and understand how this can affect the locking strength of tapers. A group of experienced orthopedic surgeons were asked to use their typical surgical approach to impact a femoral head onto a hip femoral stem using an Operating Room (OR)-simulated test setup. Impaction parameters such as impaction force, velocity, and energy, as well as the number of impacts, were characterized and applied in a bench-top study used to evaluate the effect of these parameters on the initial stability of the taper junction. High variation was found in the surgical impaction parameters, but overall it was determined that increased impaction force correlated to superior stability of the taper junction.

Comparison of Head Center Position and Screw Fixation Options Between a Jumbo Cup and an Offset Center of Rotation Cup in Revision Total Hip Arthroplasty: A Computer Simulation Study.

Jumbo acetabular cups are commonly used in revision total hip arthroplasty (THA). A straightforward reaming technique is used which is similar to primary THA. However, jumbo cups may also be associated with hip center elevation, limited screw fixation options, and anterior soft tissue impingement. A partially truncated hemispherical shell was designed with an offset center of rotation, thick superior rim, and beveled anterior and superior rims as an alternative to a conventional jumbo cup. A three dimensional computer simulation was used to assess head center position and safe screw trajectories. Results of this in vitro study indicate that a modified hemispherical implant geometry can reduce head center elevation while permitting favorable screw fixation trajectories into the pelvis in comparison to a conventional jumbo cup.

Anthropometric Computed Tomography Reconstruction Identifies Risk Factors for Cortical Perforation in Revision Total Hip Arthroplasty

BACKGROUND The incidence of revision hip arthroplasty is increasing with nearly 100,000 annual procedures expected in the near future. Many surgeons use straight modular tapered stems in revisions; however, complications of periprosthetic fracture and cortical perforation occur, resulting in poor outcomes. Our objective was to identify patient demographics and femoral characteristics that predispose patients to cortical perforation when using the straight modular stems. METHODS We used a computed tomography database and modeling software to identify patient demographics and morphologic femoral characteristics that predispose patients to cortical perforation during revision hip arthroplasty. Overall, 561 femurs from patients of various backgrounds were used, and statistical analysis was performed via the 2-sample t test. RESULTS Decreased patient height (mean 163.0 vs 168.8 cm), radius of curvature (818 vs 939 mm), anterior-posterior (8.5 vs 13.8 mm) and medial-lateral (7.9 vs 11.3 mm) width of the isthmus, and distance of the isthmus from the greater trochanter (179 vs 186 mm) were all statistically significant risk factors for cortical perforation (P < .05). CONCLUSION This study identifies several patient-specific risk factors for cortical perforation during revision hip arthroplasty using straight modular tapered stems and highlights the importance of preoperative planning especially in patients with shorter stature, proximal location of the femoral isthmus, narrow femoral canal, and smaller radius of curvature. Also, when using a mid-length modular tapered stem without an extended trochanteric osteotomy, consideration should be given to using a kinked stem to avoid anterior cortical perforation.

Changes in Femoral Version During Implantation of Anatomic Stems: Implications on Stem Design

BACKGROUND Component positioning in total hip arthroplasty (THA) is among the primary indicators for longevity and success. Acetabular component positioning has been discussed in literature at length; however, femoral component positioning is also important as it contributes to combined anteversion. METHODS In this study, we examined the changes in femoral anteversion after the implantation of anatomic stem ABG II. A cadaveric study, a computed tomography-based computer modeling study, and a clinical study using a navigation system were conducted to document these changes. RESULTS These studies demonstrated that the anatomic stem ABG II increased the postimplantation femoral version by approximately 7°. The postimplantation versions followed a bimodal distribution. The computed tomography and navigation data also highlighted that the patient population may roughly be divided into 2 groups: the first group that needs anteverted stem and the second group that needs little or no anteversion in the stem to recreate the desired version and offset. CONCLUSION Based upon our data, we propose a new anatomic stem design that is offered in 2 version angles of 0° and 7° to help create the desired version and offset.

Friction in modern total hip arthroplasty bearings: Effect of material, design, and test methodology:

The purpose of this study was to characterize the effect of a group of variables on frictional torque generated by acetabular components as well as to understand the influence of test model. Three separate test models, which had been previously used in the literature, were used to understand the effect of polyethylene material, bearing design, head size, and material combinations. Each test model differed by the way it simulated rotation of the head, the type of frictional torque value it reported (static vs. dynamic), and the type of motion simulated (oscillating motion vs. continuous motion). It was determined that not only test model may impact product ranking of fictional torque generated but also static frictional torque may be significantly larger than a dynamic frictional torque. In addition to test model differences, it was discovered that the frictional torque values for conventional and highly cross-linked polyethylenes were not statistically significantly different in the more physiologically relevant test models. With respect to bearing design, the frictional torque values for mobile bearing designs were similar to the 28-mm diameter inner bearing rather than the large diameter outer liner. Testing with a more physiologically relevant rotation showed that frictional torque increased with bearing diameter for the metal on polyethylene and ceramic on polyethylene bearings but remained constant for ceramic on ceramic bearings. Finally, ceramic on ceramic bearings produced smaller frictional torque values when compared to metal on polyethylene and ceramic on polyethylene groups.

Effect of the support systems’ compliance on total hip modular taper seating stability

Assembly of a femoral head onto the stem remains non-standardized. The literature shows altering mechanical conditions during seating affects taper strength and lower assembly load may increase fretting corrosion during cyclic tests. This suggests overall performance may be affected by head assembly method. The purpose of this test was to perform bench-top studies to determine influence of peak force magnitude, load rate, and compliance of the systems support structure on initial stability of the taper. Custom manufactured CoCrMo femoral heads and Ti-6Al-4V taper analog samples were assembled with varying peak force magnitudes (2–10.1 kN), load rates (quasi-static vs impaction), and system compliance (rigid vs compliant). A clinically-relevant system compliance design was based off of force data collected during a cadaver impaction study. Tensile loads were then applied to disassemble the taper and quantify initial taper stability. Results indicated that taper stability (assessed by disassembly forces) increased linearly with assembly force and load rate did not have a significant effect on taper stability. When considering system compliance, a 42%–50% larger input energy, dependent on assembly force, was required in the compliant group to achieve a comparable impaction force to the rigid group. Even when this impaction force was achieved, the correlation between the coefficient, defined as distraction force divided by assembly load, was significantly reduced for the compliant test group. The compliant setup was intended to simulate a surgical scenario where patient and surgical factors may influence the resulting compliance. Based on results, surgical procedure and patient variables may have a significant effect on initial taper stability.

Simultaneous Hip Head-Stem Taper Junction Measurements of Electrochemical Corrosion and Micromotion: A Comparison of Taper Geometry and Stem Material

Disclosures: L. Scholl: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics. V. Swaminathan: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics. R. Lee: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics. L.K. Raja: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics. A. Faizan: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics. M. Thakore: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics. K. TenHuisen: 3A; Stryker Orthopaedics. 4; Stryker Orthopaedics.