In Vivo strain measurements in rat femur

The purpose of the present study was to evaluate strain in the femora of rats during walking. Uni-directional strain gauge units were implanted. Peak strain at the anterior and medial aspects of the rat femur was compressive, while peak strain at the posterior aspect was tensile during walking. Median strain values at the anterior mid-diaphyseal aspect varied between 297x10-6 and 434x10-6. There were no statistical differences between recordings at different times after implantation as evaluated by daily measurements for one week. Neither was there any statistically significant difference in strain values between the walking speeds of 6.0, 10.2, and 14.7 m/min, or between values for right and left femur. In vitro measurements on replaced gauges corresponded within 5 per cent with results from bones where gauges had been implanted for one week. Waterproofing the strain gauge unit with a resin did not significantly affect the measurements. The method, therefore, enables studies of strain behavior of bone from small species in vivo under physiological and pathophysiological conditions

Cutpoints for mild, moderate and severe pain in patients with osteoarthritis of the hip or knee ready for joint replacement surgery

<p>Abstract</p> <p>Background</p> <p>Cutpoints (CPs) for mild, moderate and severe pain are established and used primarily in cancer pain. In this study, we wanted to determine the optimal CPs for mild, moderate, and severe pain in joint replacement surgery candidates with osteoarthritis (OA) of the hip or knee, and to validate the different CPs.</p> <p>Methods</p> <p>Patients (n = 353) completed the Brief Pain Inventory (BPI), the WOMAC Arthritis Index, and the SF-36 health status measure. Optimal CPs for categorizing average pain with three severity levels were derived using multivariate analysis of variance, using different CP sets for average pain as the independent variable and seven interference items from the BPI as the dependent variable. To validate the CPs, we assessed if patients in the three pain severity groups differed in pain as assessed with WOMAC and SF-36, and if BPI average pain with the optimal CPs resulted in higher correlation with pain dimensions of the WOMAC and SF-36 than other CPs.</p> <p>Results</p> <p>The optimal CPs on the 0–10 point BPI scale were CP (4,6) among hip patients and CP (4,7) among knee patients. The resulting pain severity groups differed in pain, as assessed with other scales than those used to derive the CPs. The optimal CPs had the highest association of average pain with WOMAC pain scores.</p> <p>Conclusion</p> <p>CPs for pain severity differed somewhat for patients with OA of the hip and knee. The association of BPI average pain scores categorized according to the optimal CPs with WOMAC pain scores supports the validity of the derived optimal CPs.</p