Stress Shielding in Cemented Hip Implants Assessed from Computed Tomography
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2019, Vol 18, Issue 3
Abstract
Background: Aseptic loosening is the major cause of revisions for hip replacement. This mode of failure is often caused by stress shielding. Stress shielding in the femur occurs when some of the loads are taken by the prosthesis and shielded from going to the bone. There is little information regarding the stress shielding among cemented hip implants. Purpose: The purpose of this study is to investigate the effect of stress shielding on the proximal femur with a femoral prosthesis. Methods: A patient had undergone open reduction and internal fixation (ORIF) due to a comminuted reversed oblique fracture of the right intertrochanteric hip. ORIF had failed and was converted to bipolar hemiarthroplasty. CT scans were performed on both the right and left hips. Housefield units were determined by using the probe tool. By using equations formulated by Carter and Hays, Linde et al., various parameters such as apparent density, Young’s’ modulus and ultimate strength were calculated. The results were compared to that a native hip. Results: The hip with the cemented implant had a significant increase in the apparent density, Young’s modulus and ultimate strength, when compared to the left hip. In addition, it was found that the right hip had a higher strain energy density than that of the left. Interpretation: It has been concluded the most stress shielding occurred in the calcar region of the femur. The instances of stress shielding have been extensively reported for non-cemented or direct bone to implant constructs, this paper reports stress shielding in cemented implants supported by imaging data and biomechanical calculations carried out at the bone-cement-metal interface.Total hip arthroplasty (THA) is often the gold standard for treatment in patients who have arthritic hip joints. There are approximately 231,000 THA which have been performed in the United States, and the incidence has been increasing yearly [1]. The success of these devices is dependent upon bone quality, weight, and activity level [2]. However, THA does have some complications including aseptic loosening, stress shielding, and peri-prosthetic fracture. Bone resorption that occurs as a result of aseptic loosening can often arise from mismatch in material properties between the implant and native femoral bone [3]. Hip implants are generally made of titanium-based alloys, cobalt-chromium alloys, and 316L stainless steel which have greater stiffness values than that of bone. When a metal implant is implanted into the femur, the physiological loading is often transferred to the implant from the surrounding bone. Therefore, the implanted femur is experiencing decreased loads when compared to when it is in its natural state. Bone remodeling occurs in which bone gets resorbed and loses mass, which is known as stress shielding [4]. The reduced bone stock can lead to serious complications including peri-prosthetic fracture, and clinically can present with thigh pain [5]. In addition, stress shielding can also reduce the quality of the remaining bone stock which lead to an increased risk for fracture and aseptic loosening. There has been an increased incidence of revision THAs due to patients who are undergoing THA at a younger age, and increased life expectancy. Another important complication of artificial hip implants is bone failure, which is often due to increased stress at the contact point between bone and implant. The implant can act as an indentor through a mechanism of interfacial motion of the implant. Therefore, the bone displaces from the implant which causes microcracks in the bone [6,7]. Over the course of several million cycles, those microcracks accumulates and result in failure of bone. In a recent study shows that the failure of bone occurs at the femoral neck, which is the weakest part of the bone [8]. In this study, there was a linear relationship between maximum stress and the number of cycles, that concluded that Maximum stresses decreases as the number of cycles increases.
Authors and Affiliations
Bharadwaj Cheruvu, Indresh Venkatarayappa, Tarun Goswami DSC
Keywords
Related Articles
- EP ID EP620671
- DOI 10.26717/BJSTR.2019.18.003163
- Views 173
- Downloads 0
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