Gait disorders contribute to the risk of falls and successive injuries, especially to elderly populations. The risk of falls becomes higher for hip osteoarthritis (OA) and hip arthroplasties patients due to poor balancing and gait impairment. Bone adaptation and bone loss are fundamental issues in considering the changes of bone behavior and gait pattern. In this study, computational analysis of the lower limbs was conducted to estimate the bone adaptation after hip arthroplasties procedure. 3D inhomogeneous model of lower limb was developed from computed topography (CT- based) data of 79 years old patient with hip osteoarthritis problem in left limb. Two types of arthroplaties were constructed in the left limb, namely total hip arthroplasty and resurfacing hip arthroplasty using commercial biomedical software, Mechanical Finder v6.1. Prosthesis stem and acetabular cup of THA were modelled as titanium alloy material (E = 114 GPa, v = 0.34), femoral ball and bearing insert as alumina properties (E = 370 GPa, v = 0.22). Meanwhile, RHA implant was assigned as Co-Cr-Mo material (E = 230 GPa, v = 0.30). Contact between both implants and bone were considered to be perfectly bonded at the interface. A load case of quiet standing position was conducted in this analysis with 60 kg of the patients’ body weight. The load was applied at the cross sectional lumbar vertebra and fixed at the distal of femoral shafts. Results show different patterns of stress distribution in right and left (operated) limbs for hip OA, THA and RHA models. An indication of stress alteration on both limbs after arthroplasties suggested that the bone adaptation occurred. The higher percentage of change in the left limb projected that the adaptation was more critical in operated limb.
Total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA) are two approaches that commonly used for hip osteoarthritis (OA) treatment. Advantage and disadvantage of each procedure were still discussed till nowadays, especially in promoting long term stability. In general, RHA approaches only requires a small amount of femoral head removal or resurfacing techniques while THA demand for total replacement. Continuous improvement of surgical techniques and design of implant [
Computational analysis had extensively used to predict the stability and performance of hip arthroplasties. Most studies were focused on the affected (osteoarthritis) and operated (arthroplasties) limb where the prosthesis implanted. Unfortunately, the hip OA disease presence had altered the performance of both affected and non- affected limbs [
The objective of this paper was to investigate the effects of different hip arthroplasties on bone adaptation in lower limb, namely total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA). Finite element analysis on both operated and non-operated limbs was conducted to promote primary understanding of gait stability.
Finite element (FE) model of the lower limb employed in this analysis was constructed based on computed tomography (CT) image data of a 79-year old female patient with hip osteoarthritis (OA), collected from Kyushu University Hospital, Japan. Different gray scales extracted from the CT image presenting the variety of bone density and consequently creating the inhomogeneous 3D model. The procedure was conducted using commercial biomedical software, Mechanical Finder v7.0 while estimation of young modulus distribution was generated based on Keyak et al. [
Two types of arthroplasties were considered in this study, namely total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA). Both were modeled based on commercial products and implanted into the left limb which was suffering from hip osteoarthritis (OA). The hip cartilage model was defined as homogeneous in the lower limb model with elastic modulus of 0.004 GPa and Poisson ratio of 0.4. In THA model, ceramic-on-ce- ramic (CoC) type of implant was used which presenting Alumina ceramic as femoral ball and acetabular liner. The prosthesis stem and acetabular cup were assigned as biocompatibility material, namely titanium alloy. Meanwhile, cobalt chrome material was determined in the RHA model for both acetabular cup and prosthesis pin. Illustration of lower limbs with THA and RHA was shown in
Density Range | Young Modulus (MPa) | Density Range | Yield Strength (MPa) |
---|---|---|---|
ρ = 0 | E = 0.001 | ||
0 < ρ ≤ 0.27 | E = 33900ρ2.20 | ρ ≤ 0.2 | σyield = 1.0 × 1020 |
0.27 < ρ < 0.6 | E = 5307ρ + 469 | 0.2 < ρ < 0.317 | σyield = 137ρ1.88 |
0.6 ≤ ρ | E = 10200ρ2.01 | 0.317 ≤ ρ | σyield = 114ρ1.72 |
ρ = 0 | E = 0.001 |
Model | Material | Elastic Modulus, E (GPa) | Poisson Ratio, v | |
---|---|---|---|---|
THA | Acetabular cup | Titanium Alloy | 114 | 0.34 |
Bearing liner | Alumina | 370 | 0.23 | |
Femoral ball | Alumina | 370 | 0.23 | |
Prosthesis stem | Titanium Alloy | 114 | 0.34 | |
RHA | Acetabular cup | Cobalt Chrome | 230 | 0.30 |
Prosthesis pin | Cobalt Chrome | 230 | 0.30 |
The posture of quite standing with foot side-by-side position contributes to functional and structural equivalent in the lower limbs [
Biomechanical behavior and prediction of bone adaptation in the analysis was presented in corresponding to equivalent stress (Drucker-Prager) distribution and changes of maximum principal stress after implantation. The observation of the stress alteration was conducted on both operated and non-operated limbs which further estimated the contribution to gait adaptation.
Stress shielding phenomenon is a common issue that related to hip arthroplasties. It occurred when there was a mismatch in the elastic modulus of two materials. The presence of stiffer materials of arthroplasties will dominate the bodyweight loading and consequently unloaded the surrounding bones. Bones with reduced load were expected to experience bone resorption and become weak [
In THA lower limb model as shown in
after the implantation. The right limb also experienced similar findings, but in smaller scale. However, the pattern of stress almost similar to that observed in hip OA model. The results were significant as the implant in RHA only required for minimal bone removal and the implant was designed as cobalt chrome material with a higher modulus of elasticity.
Three different regions in femoral shaft were assigned to observed stress behavior which were proximal, middle and distal region. The peak value of maximum principal stress of the respective region was selected to calculate the prediction of stress and bone adaptation after arthroplasties.
Performance of non-operated limb was normally neglected in analysis as most researchers more interested and concentrated in operating limb. However, research of rehabilitation studies had observed that the gait adaptation was also occurring in non-operated limb of arthroplasties’ patient [
The factor of stiffer material of implant might be the reason of great differences (reduced magnitude) in RHA model. However, the pattern of stress distribution in the model was observed to be almost similar to that predicted in hip OA model. Instead of smaller changes, proper stress distribution along the limb was also important as it will promote bone growth and long term stability [
itation study, which reported the characteristic of surface hip arthroplasty allowed the gait to return to most normative pattern compared with THA [
A number of limitations in the present study were identified. Variability of different physiological loading and consideration of muscle reaction was not conducted. Body-mass index (BMI) and muscle strength factors were contributed to gait balancing and stability [
The results of the present study discovered basic understanding of load distribution in the lower limb and prediction of bone adaptation after arthroplasty on the resulting stress distribution. Changes of stress variation in both limbs suggested both operated and non-operated limb were potential to experience bone adaptation. Lower limbs with resurfacing hip arthroplasty indicated a similar pattern of stress distribution to that predicted in hip osteoarthritis model. Stress alteration was more critical in RHA limb compared with THA limb model.
The authors would like to acknowledge with gratitude Prof. Yukihide Iwamoto and Assoc. Prof Yasuharu Nakashima from Kyushu University Hospital for their assistance in providing CT scan data from the hospital. This research was supported, in part, by Ministry of Education Malaysia.
Abdul Halim Abdullah,Mitsugu Mitsugu Todo, (2015) Effects of Hip Arthroplasties on Bone Adaptation in Lower Limbs: A Computational Study. Journal of Biosciences and Medicines,03,1-7. doi: 10.4236/jbm.2015.34001