Exposing the Skeletons in the Closet of SCI Rehab
W. Brent Edwards, PhD.
•SCI associated with marked bone loss
•2x more likely to experience a fx due to minor trauma with small amounts of force
•Most valuable window is acute phase SCI rehab.
•No intervention yet has demonstrated complete or sustained recovery of SCI bone loss
Form Follows Function
•Bone is a dynamic tissue and constantly remodeling in response to it’s mechanical environment.
•Adapts to resist the load of habitual activity
•Mechanical Stimuli = Bone Strain. Called “Functional Adaptation” or “Wolf’s Law”.
(Bone remodels according to demands, grows and/or decreases in size and strength)
Three Rules for Bone Adaptation
1. Driven by dynamic, rather than static, loading
2. Only a SHORT duration of loading is necessary; extended loading durations have diminishing adaptive returns ( i.e. long distance running).
3. Bone cells get accommodated to customary loading (and thus less responsive)
Two Process of Adaptation
•Modeling: the independent actions of Osteoblasts (OB) & Osteoclasts (OC) change the size and shape of bone
•Remodeling: the sequential actions of OB & OC to remove old bone and replace with new bone
•OB- bone forming
•OC- bone absorbing
•Bone metabolism is out of balance: Osteoclast activity (they eat bone) outweighs the Osteoblast (which form bone).
•Bone loss is rapid and profound
•In two years: 25% in hip, 50% in knee
•Increased in areas below injury
•LE bone loss similar among para and quads
•UE unaffected in para, variably affected in quads
•Age, weight and gender not important determinants of bone loss
Fractures Source of Morbidity
•Only a small amount of force is required
•Common causes: falls & transfers from W/C & rolling over in bed
•Common location: proximal tibia, distal femur
•Fracture healing delayed
•Pressure ulcers (secondary complication)
•7x longer hospital duration
•High rate of D/C to SNF
How Do We Prevent This From Happening?
•Tailor programs secondary to preventing increased bone loss
•Rehabilitation: Weight- bearing exercise, Functional Electrical Stimulation (FES) and Vibration Stimulation
•Pharmacological: antiresorptive agents & anabolic agents
•In Acute SCI: most effective weight-bearing should be more dynamic and longer duration (i.e. litegait).
•In chronic SCI: static weight bearing (tilt table/standing frame) less effective.
•Vibration shows potential (while standing) 30 min 3-5x a week 1.5 years and with disabled children (CP, MD)
•FES shows most potential: with response limited to bone spanned by stimulated muscle (stimulated muscular forces carry more load to bone than gravity)
•Benefits not sustained after training
•Antiresorptive Agents (Bisphosphonates): Inhibit OC activity and evidence of efficacy in acute SCI and in chronic SCI no significant diff.
•Anabolic Agents (Parathyroid Hormone) effect number and activity of OC’s. Not been studied in SCI but in rats saw complete reversal of bone loss and has a synergistic anabolic effect on bone formation when combined with mechanical loading.
Summary of Interventions
•In Acute SCI rehab: Bone maintenance with sufficient mechanical stimuli or use of bisphosphonate therapy.
- In Chronic SCI rehab: Rehab & bisphosphonate therapy not effective and concurrent rehab with anabolic pharmacology may be required
•2x more likely to experience a fx
•Small amount of force can create a fx (rolling over in bed)
•Most valuable window for intervention is in acute phase of SCI
•No intervention has illustrated complete or sustained recovery of SCI bone loss