Age-Dependent Recovery of Bone During Reloading Following a Period of Hindlimb Unloading in Rats

Our work, Age-Dependent Bone Loss and Recovery During Hindlimb Unloading and Subsequent Reloading in Rats, has been accepted for publication in BMC Musculoskeletal Disorders! Congratulations to Hailey and all those involved!

Background: Bone structure and strength are rapidly lost during conditions of decreased mechanical loading, and aged bones have a diminished ability to adapt to increased mechanical loading. This is a concern for older patients that experience periods of limited mobility or bed rest, but the acute effects of disuse on the bones of aged patients have not been thoroughly described. Previous animal studies have primarily examined the effect of mechanical unloading on young animals. Those that have studied aged animals have exclusively focused on bone loss during unloading and not bone recovery during subsequent reloading. In this study, we investigated the effect of decreased mechanical loading and subsequent reloading on bone using a hindlimb unloading model in Adult (9 month old) and Aged (28 month old) male rats.

Methods: Animals from both age groups were subjected to 14 days of hindlimb unloading followed by up to 7 days of reloading. Additional Aged rats were subjected to 7 days of forced treadmill exercise during reloading or a total of 28 days of reloading. Trabecular and cortical bone structure of the femur were quantified using ex vivo micro-computed tomography (μCT), and mechanical properties were quantified with mechanical testing.

Results: We found that Adult rats had substantially decreased trabecular bone volume fraction (BV/TV) following unloading (-27%) while Aged animals did not exhibit significant bone loss following unloading. However, Aged animals had lower trabecular BV/TV after 3 days of reloading (-20% compared to baseline), while trabecular BV/TV of Adult rats was not different from baseline values after 3 days of reloading. Trabecular BV/TV of Aged animals remained lower than control animals even with exercise during 7 days of reloading and after 28 days of reloading.

Conclusions: These data suggest that aged bone is less responsive to both increased and decreased mechanical loading, and that acute periods of disuse may leave older subjects with a long-term deficit in trabecular bone mass. These finding indicate the need for therapeutic strategies to improve the skeletal health of elderly patients during periods of disuse.

Be sure to check out the open-access paper in BMC Musculoskeletal Disorders: https://bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/s12891-018-2156-x

Successful BMEGG Student Research Symposium!

The Christiansen Lab was well-represented at this year’s UC Davis Biomedical Engineering Graduate Group Research Symposium.

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Armaun moderated all of the oral sessions.
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Hailey presented her work on systemic bone loss after fracture.
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Allison presented her research on osteophytes and fracture calluses.

We also came home with an award! Congratulations to Allison for winning the People’s Choice Award for her oral presentation.

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Thank you to the BME Student Association for putting on such a great event and giving us the opportunity to share our work with our peers!

Comparison of Knee Injury Threshold During Tibial Compression Based on Limb Orientation in Mice

Our new short communication, Comparison of Knee Injury Threshold During Tibial Compression Based on Limb Orientation in Mice, has been accepted for publication by the Journal of Biomechanics!

In this study, we perform murine tibial compression with mice in either prone or supine positions. Our results indicate that differences in mouse positioning can significantly impact the rate of ACL injury with tibial compression.

Be sure to check out our study in the Journal of Biomechanics! (https://www.sciencedirect.com/science/article/pii/S0021929018302872)

Comparison of Knee Injury Threshold During Tibial Compression Based on Limb Orientation in Mice. Hsia AW, Tarke FD, Shelton TJ, Tjandra PM, and Christiansen BA. J Biomechanics 2018.

 

Osteophytes and Fracture Calluses Share Developmental Milestones and are Diminished by Unloading

Osteophytes and fracture calluses are both examples of new bone formation in the body. Osteophytes are a hallmark radiographic finding of osteoarthritis (OA), while fracture calluses are formed during fracture healing. Our new study explores the similarities and differences of these two structures, adding insight into the factors that may influence osteophyte formation. Check out our work in the Mechanobiology Special Issue of the Journal of Orthopaedic Research.

 

 

Osteophytes and fracture calluses share developmental milestones and are diminished by unloading. Hsia AW, Emami AJ, Tarke FD, Cunningham HC, Tjandra PM, Wong A, Christiansen BA, Collette NM. Journal of Orthopaedic Research.