Christos S. Georgiou

Large Diameter Femoral Heads Impose Significant Alterations on the Strains Developed on Femoral Component and Bone: A Finite Element Analysis

Total Hip Arthroplasty aims at fully recreating a functional hip joint. Over the past years modular implant systems have become common practice and are widely used, due to the surgical options they provide. In addition Big Femoral Heads have also been implemented in the process, providing more flexibility for the surgeon. The current study aims at investigating the effects that femoral heads of bigger diameter may impose on the mechanical behavior of the bone-implant assembly. Using data acquired by Computed Tomographies and a Coordinate Measurement Machine, a cadaveric femur and a Profemur-E modular stem were fully digitized, leading to a three dimensional finite element model in ANSYS Workbench. Strains and stresses were then calculated, focusing on areas of clinical interest, based on Gruen zones: the calcar and the corresponding below the greater trochanter area in the proximal femur, the stem tip region and a profile line along linea aspera. The performed finite elements analysis revealed that the use of large diameter heads produces significant changes in strain development within the bone volume, especially in the lateral side. The application of Frost’s law in bone remodeling, validated the hypothesis that for all diameters normal bone growth occurs. However, in the calcar area lower strain values were recorded, when comparing with the reference model featuring a 28mm femoral head. Along line aspera and for the stem tip area, higher values were recorded. Finally, stresses calculated on the modular neck revealed increased values, but without reaching the yield strength of the titanium alloy used.

Dual-fibular reconstruction of a massive tibial defect after Ewing's sarcoma resection in a pediatric patient with a vascular variation.

Background In the management of malignancies of the extremities, limb salvage procedures have recently taken on greater significance. For those patients under intense adjuvant chemotherapy and with massive bone loss, free vascularized fibular grafting is currently advocated as a reliable reconstructive option, maybe because of the controversial results of bone transport in similar situations. However, when there is a vascular abnormality of either the recipient or donor extremity, microsurgical procedures are not feasible, further limiting potential reconstructive alternatives. Methods We present the case of a 13-year-old female patient with Ewings sarcoma of the right tibia. Preoperative angiography showed that vascularity of the affected side depended totally on a single peroneal artery. The patient was treated initially with multiagent chemotherapy, followed by an excision of 23 cm. The defect was bridged by a gradual medial transportation of the ipsilateral fibula with the Ilizarov technique and strengthened by nonvascularized transfer of the contralateral fibula. Results Total external fixation time was 162 days. After the removal of the Ilizarov frame a walking cast was applied for another month. At 5 years postoperatively there was no recurrence of the malignancy. The patient had full weight-bearing ability on the affected limb, with preservation of the ankle and knee joints motion and without any limb length discrepancy or axial deformity. The functional outcome that was visible was graded excellent. Conclusions Transverse distraction osteogenesis of the ipsilateral fibula performed well under chemotherapy, showing unproblematic callus formation. Supplemented with nonvascularized transfer of the contralateral fibula, provided a reconstructive option with biological affinity, sufficient biomechanical strength and durability, and with a decreased complication rate. This case report presents a viable option, especially in cases in which vascular abnormalities of either the donor or the recipient limb, combined with multiagent chemotherapy, restrict potential reconstructive alternatives. It also highlights why vascularized bone graft should not be regarded as a panacea for all situations in which a fibular graft is required. Level of Evidence Level IV, case report.

Does Choice of Head Size and Neck Geometry Affect Stem Migration in Modular Large-Diameter Metal-on-Metal Total Hip Arthroplasty? A Preliminary Analysis.

Due to their theoretical advantages, hip systems combining modular necks and large diameter femoral heads have gradually gained popularity. However, among others, concerns regarding changes in the load transfer patterns were raised. Recent stress analyses have indeed shown that the use of modular necks and big femoral heads causes significant changes in the strain distribution along the femur. Our original hypothesis was that these changes may affect early distal migration of a modular stem. We examined the effect of head diameter and neck geometry on migration at two years of follow-up in a case series of 116 patients (125 hips), who have undergone primary Metal-on-Metal total hip arthroplasty with the modular grit-blasted Profemur®E stem combined with large-diameter heads (>36 mm). We found that choice of neck geometry and head diameter has no effect on stem migration. A multivariate regression analysis including the potential confounding variables of the body mass index, bone quality, canal fill and stem positioning revealed only a negative correlation between subsidence and canal fill in midstem area. Statistical analysis, despite its limitations, did not confirm our hypothesis that choice of neck geometry and/or head diameter affects early distal migration of a modular stem. However, the importance of correct stem sizing was revealed.

Local and Distant Reaction to Metallic Wear Debris

Total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) have become some of the most successful elective surgical procedures in modern medicine that it has been described as “the operation of the twentieth century”. Worldwide, it is estimated that approximately one million are implanted every year. About 270,000 hip arthroplasties are done in the United States, and this is projected to increase by 174 % between 2005 and 2030. The National Joint Registry of England and Wales reported 68,907 primary operations in 2010. The number of younger patients receiving a THA is continuously increasing. In England and Wales, 12 % of patients are younger than 55 years. In Canada, the number of patients aged less than 45 years having hip replacements during 2002 rose by 11.0 % compared with 1994.

Cementless Tapered Fluted Implant-Bone Interface in Revision Total Joint Arthroplasty

Surgical revision of the failed total hip arthroplasty (THA) due to implant failure and osteolysis is becoming an increasingly more common surgical procedure. Even with the improvement of prosthetic designs, the number of necessary revisions will increase due to increased life expectancy as well as younger average age of initial implantation. In general, revision arthroplasty has a higher complication rate than primary surgery in all types of complications. After loosening of a femoral component in THA, a proximal femoral defect is usually left in the proximal femur. In this poor bone environment, it is difficult to fixate a cemented or a cementless prosthesis. The proximal femoral bone loss thus continues to challenge adequate fixation and osseointegration with proximally fixed components.

Can the Increased Loosening Rate of the Modular-Neck Hip Systems Be Attributed to Geometric Design Parameters? An Alternative Approach Using Finite Element Analysis

Modular necks are a relatively new innovation in total hip arthroplasty (THA). They offer the surgeon the potential to effectively restore hip biomechanics with the ability to independently adjust offset, version, and limb length during operation. These should theoretically improve implant stability, decrease the dislocation and impingement rate, and assist in equalization of leg length (Grupp et al. 2010). Initially they were reserved for the severe torsional deformities of the developmental hip dysplasia (Umeda et al. 2003). However, due to their compelling rationale, the intraoperative flexibility and the fast learning curve, indications quickly expanded up to the younger and more active patients. To further serve the demands of these patients, several manufacturers currently combine modular necks with hard bearings, either metal on metal (MoM) or ceramic on ceramic (CoC) (Grupp et al. 2010). However, whether the advantages conferred by the neck modularity outweigh the additional complexity remains a question. Since the introduction of the modular-neck systems in the clinical practice, vulnerabilities of their application are being continuously revealed. Concerns for fretting corrosion and concomitant metal ion release from the additional MoM junction have been widely expressed (Gill et al. 2012; Jacobs and Hallab 2006; Grupp et al. 2010). Furthermore, corrosion, possibly influenced by the neck adapter material, may lead to fatigue component fracture at the modular site (Grupp et al. 2010). Dissociation at the stem–neck interface, even without trauma, has been also described (Kouzelis et al. 2011). The long-term success of adding a second modular junction has, therefore, yet to be established.