Predictions on preserving bone mass in knee arthroplasty with bisphosphonates

Effect of bisphosphonates on selected markers of bone turnover in patients after total knee arthroplasty

PURPOSE

Osteoporosis is a problem for many patients after total knee arthroplasty (TKA). The aseptic loosening of the prosthesis is also a significant problem. Therefore, in these patients, bisphosphonates (BPs) are used that, by influencing the level of bone turnover markers, reduce the risk of osteoporotic fractures and aseptic revisions in TKA. The purpose of the study was to assess whether the Pamifos® present in bone cement has any effect on the level of selected bone turnover markers and cytokines in patients after total knee arthroplasty.

METHODS

The study group consisted of 30 women with degenerative changes of the knee joint, whose total knee prosthesis was stabilized with cement enriched with Pamifos®. The control group consisted of 30 women treated for degenerative changes of the knee joint without the use of bisphosphonate-enriched cement for prosthetic stabilization.

RESULTS

In the study group, we found a decrease in tumour necrosis factor (TNF-α) levels 12 weeks after surgery, whereas the control group experienced an almost twofold increase in TNF-α level. The concentration of OPG, a natural RANKL antagonist, was highest in patients of the study group six weeks after surgery and was four times higher compared to the control group. Statistically significant differences were found in the RANKL level (P < 0.05). In the control group, there was a continuous increase in RANKL concentration from the first to the 12th week after surgery. The highest level of RANKL in patients of the study group was found six weeks after the surgery, and 12 weeks after knee arthroplasty, it was significantly lower. It was found that the concentration of osteocalcin (OC) in the study group was the lowest three weeks after the surgery, then it increased and remained at a similar level after 12 weeks. The concentrations of selected cytokines (IL-1β, IL-2, IL-6, IL-10, IL-17AF) also showed statistically significant differences.

CONCLUSIONS

The BP-stimulated increase in the level of OPG and the decrease in the level of RANKL, as well as the impact on the level of the analyzed interleukins in the bone microenvironment, may be an important element of the mechanisms limiting bone resorption. Therefore, the use of BP-enriched cement implants appears to be justified.

Effect of one-year post-operative alendronate treatment on periprosthetic bone after total knee arthroplasty

Total knee arthroplasty (TKA) is known to lead to a reduction in periprosthetic bone mineral density (BMD). In theory, this may lead to migration, instability and aseptic loosening of the prosthetic components. Bisphosphonates inhibit bone resorption and may reduce this loss in BMD. We hypothesised that treatment with bisphosphonates and calcium would lead to improved BMD and clinical outcomes compared with treatment with calcium supplementation alone following TKA. A total of 26 patients, (nine male and 17 female, mean age 67 years) were prospectively randomised into two study groups: alendronate and calcium (bisphosphonate group, n = 14) or calcium only (control group, n = 12). Dual energy X-ray absorptiometry (DEXA) measurements were performed post-operatively, and at three months, six months, one, two, four, and seven years post-operatively.

Mean femoral metaphyseal BMD was significantly higher in the bisphosphonate group compared with controls, up to four years following surgery in some areas of the femur (p = 0.045). BMD was observed to increase in the lateral tibial metaphysis in the bisphosphonate group until seven years (p = 0.002), and was significantly higher than that observed in the control group throughout (p = 0.024). There were no significant differences between the groups in the central femoral metaphyseal, tibial medial metaphyseal or diaphyseal regions of interest (ROI) of either the femur or tibia.

Bisphosphonate treatment after TKA may be of benefit for patients with poor bone quality. However, further studies with a larger number of patients are necessary to assess whether this is clinically beneficial.

Cite this article: Bone Joint J 2015;97-B:337–45.

Simulation on the internal structure of three-dimensional proximal tibia under different mechanical environments

Background

Bone can adjust its morphological structure to adapt to the changes of mechanical environment, i.e. the bone structure change is related to mechanical loading. This implies that osteoarthritis may be closely associated with knee joint deformity. The purposes of this paper were to simulate the internal bone mineral density (BMD) change in three-dimensional (3D) proximal tibia under different mechanical environments, as well as to explore the relationship between mechanical environment and bone morphological abnormity.

Methods

The right proximal tibia was scanned with CT to reconstruct a 3D proximal tibia model in MIMICS, then it was imported to finite element software ANSYS to establish 3D finite element model. The internal structure of 3D proximal tibia of young normal people was simulated using quantitative bone remodeling theory in combination with finite element method, then based on the changing pattern of joint contact force on the tibial plateau in valgus knees, the mechanical loading was changed, and the simulated normal tibia structure was used as initial structure to simulate the internal structure of 3D proximal tibia for old people with 6° valgus deformity. Four regions of interest (ROIs) were selected in the proximal tibia to quantitatively analyze BMD and compare with the clinical measurements.

Results

The simulation results showed that the BMD distribution in 3D proximal tibia was consistent with clinical measurements in normal knees and that in valgus knees was consistent with the measurement of patients with osteoarthritis in clinics.

Conclusions

It is shown that the change of mechanical environment is the main cause for the change of subchondral bone structure, and being under abnormal mechanical environment for a long time may lead to osteoarthritis. Besides, the simulation method adopted in this paper can more accurately simulate the internal structure of 3D proximal tibia under different mechanical environments. It helps to better understand the mechanism of osteoarthritis and provides theoretical basis and computational method for the prevention and treatment of osteoarthritis. It can also serve as basis for further study on periprosthetic BMD changes after total knee arthroplasty, and provide a theoretical basis for optimization design of prosthesis.

Theoretical analysis of alendronate and risedronate effects on canine vertebral remodeling and microdamage

Bisphosphonates suppress bone remodeling activity, increase bone volume, and significantly reduce fracture risk in individuals with osteoporosis and other metabolic bone diseases. The objectives of the current study were to develop a mathematical model that simulates control and 1 year experimental results following bisphosphonate treatment (alendronate or risedronate) in the canine fourth lumbar vertebral body, validate the model by comparing simulation predictions to 3 year experimental results, and then use the model to predict potential long term effects of bisphosphonates on remodeling and microdamage accumulation. To investigate the effects of bisphosphonates on bone volume and microdamage, a mechanistic biological model was modified from previous versions to simulate remodeling in a representative volume of vertebral trabecular bone in dogs treated with various doses of alendronate or risedronate, including doses equivalent to those used for treatment of post-menopausal osteoporosis in humans. Bisphosphonates were assumed to affect remodeling by suppressing basic multicellular unit activation and reducing resorption area. Model simulation results for trabecular bone volume fraction, microdamage, and activation frequency following 1 year of bisphosphonate treatment are consistent with experimental measurements. The model predicts that trabecular bone volume initially increases rapidly with 1 year of bisphosphonate treatment, and continues to slowly rise between 1 and 3 years of treatment. The model also predicts that microdamage initially increases rapidly, 0.5-1.5-fold for alendronate or risedronate during the first year of treatment, and reaches its maximum value by 2.5 years before trending downward for all dosages. The model developed in this study suggests that increasing bone volume fraction with long term bisphosphonate treatment may sufficiently reduce strain and damage formation rate so that microdamage does not accumulate above that which is initiated in the first two years of treatment.

Biological options to enhance periprosthetic bone mass

There is a potential for the use of pharmacological agents to enhance the quality of bone around a total hip or knee prosthesis, reducing the risk of implant failure or periprosthetic fracture. Bisphosphonates are currently used for the management of postmenopausal osteoporosis and recent investigations also suggest a potential role for the management of postoperative periprosthetic bone loss. Current evidence suggests that the short-term gains may not be sustained in the long term. Teriparatide and parathyroid hormone 1-84 have been licensed to treat postmenopausal osteoporosis and may also be investigated for the potential to enhance periprosthetic bone mass. In addition, other agents such as calcitonin and strontium ranelate, non-anabolic agents such as doxycycline, and recombinant OPG adeno-associated virus (rAAV) gene therapy, may in the future provide solutions for enhancing periprosthetic bone mass.