Osteoarthritic bone structural changes may result from physiologic bone adaptation
Citation for published version (APA):
Cox, L. G. E., Donkelaar, van, C. C., Rietbergen, van, B., & Ito, K. (2011). Osteoarthritic bone structural changes may result from physiologic bone adaptation. Poster session presented at Mate Poster Award 2011 : 16th Annual Poster Contest.
Document status and date: Published: 01/01/2011 Document Version:
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Results
Altered microarchitecture
Predicted changes in microarchitecture in response to both high joint loading and low bone matrix mineralization were similar to those observed in OA (Table 2).
Table 2: Increases (+) and decreases (-) in bone structure parameters.
.
Replacement of cartilage with bone tissue
Bone adaptation simulations resulted in the successful replacement of cartilage with bone tissue (Fig. 2).
Fig. 3: The bone adaptation process may result in cartilage thinning.
Cyst development
Simulations of bone adaptation in response to fluid pressure resulted in the development of cavities with a typical cyst-like appearance (Fig. 3).
Fig. 4: Left: Simulation of the growth of a rounded fluid-filled cavity with
a sclerotic rim. Right: Subchondral bone cyst in the femoral head.
Discussion
Currently OA therapies are being developed that inhibit bone cellular activity. However, our simulations indicate that bone cells may not be affected in OA. Instead, bone changes may result from physiologic adaptation in response to altered circumstances in OA joints. As bone adaptation serves to remove microdamage and optimize local bone tissue load, inhibiting bone cellular activity could have an adverse effect and compromise bone strength.
References
[1] Huiskes et al., Nature, 2000.
Introduction
No cure is available for osteoarthritis (OA), the most com-mon joint disease. Therapies focus on the degenerating cartilage, but bone plays an important role in the disease process as well. Bone microarchitecture changes, cartilage is replaced with bone, and cysts develop (Fig. 1). Each of these changes may contribute to OA progression or aggra-vate symptoms. The question is whether the bone changes result from a pathologic process or from physiologic adap-tation in response to altered circumstances in OA joints.
Fig. 1: During OA progression both cartilage and bone tissue change.
Methods
We tried to answer this question using an established com-putational bone adaptation model1 (Fig. 2). In the model, osteoblasts form bone in response to mechanical load sensed by osteocytes, and osteoclasts resorb bone near randomly occuring microcracks. With finite element analysis we calculated strain energy density (SED) values.
Fig. 2: Left: Bone adaptation of a single trabecula. Right: Schematic
representation of the mathematical model.
Based on experimental and clinical data from the literature, we investigated the effect of bone adaptation in reponse to various factors that may play a role in OA joints (Table 1).
Table 1: OA bone structural changes and altered joint circumstances
that may initiate an adaptation response causing these changes.
Orthopaedic Biomechanics
/ Department of Biomedical Engineering
Osteoarthritic bone structural changes may
result from physiologic bone adaptation
Lieke Cox, René van Donkelaar, Bert van Rietbergen, Keita Ito
Bone structural change Altered joint circumstance
1. altered microarchitecture - high joint loading
- low bone matrix mineralization 2. replacement of cartilage with
bone tissue
osteoclast delivery as a result of vasculari-zation of the mineralized cartilage
3. cyst development entrance of joint fluid into the bone tissue
Parameter OA high load low mineralization
bone volume fraction + + +
trabecular thickness + + + trabecular number - - - trabecular separation - - - Resorption Formation cartilage bone marrow
Normal knee Osteoarthritic knee
cartilage
subchondral bone joint capsule
cartilage degeneration cyst formation
altered bone micro- architecture
replacement of cartilage with bone tissue
