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On Sunday, after my morning 30 mile bike ride-in just under two hours (no hills but lightening and thunder))-, I watched the last stage of the Tour De France. Later in the day, my wife gave me an article she had cut out of the July 11, 2011, Chicago Tribune, “Pitcher with artificial joint wants shot at the majors” by Bob Young.  It calls to mind the ongoing lack of consensus concerning restrictions after an artificial joint and why I am so interested in the rejuvenative potential of Platelet Rich Plasma and Mesenchymal Stem Cells.


While there is an abundance of research on the throwing arm of a pitcher, there is little data on the forces across the hip during the pitching cycle. Young described in the Tribune article, the drive behind 25-year-old Isaac Hess and his quest to pitch in the majors even though at 20, he had undergone a total hip replacement for an arthritic condition. I was reminded of Bo Jackson, whose major league career ended about six months after a total hip replacement and the multiple revision surgeries that followed. Because of my personal interest in cycling, I do know something about forces across the knee.  The following summarizes research in which I have been very involved.





Cycling is a recommended activity after total knee arthroplasty (TKA) and it has been shown that up to 50 % of the TKA patients ride a bike and 25 % think that cycling has an important place in their life. Our studies investigated the contact pressures in TKA components for common recreational activities (cycling, power walking, downhill walking, jogging and concluded that cycling produces relatively low contact forces and

therefore is a safe activity for TKA patients.


In order to investigate the kinetic conditions under which the knee was functioning, three-dimensional pedal forces were recorded. The force measurement system was integrated into the crankshafts and was based on strain gage technology. Forces were calculated in a global coordinate system and the impulse introduced to each leg was determined. Motion analysis was performed using a technique called “point cluster technique” Twenty-one reflective markers were placed on the thigh and shank creating two cluster groups. Marker motion was observed with a four-camera optoelectronic system. Subjects were instructed to cycle at a self-selected speed at a preset resistance. Based on the determined eigen values the rigid body motion of thigh and shank was calculated and the relative joint motion was computed.


RESULTS:  Resultant pedal forces and generated impulse showed no significant differences between TKA patients and Normals. No significant differences for force and impulse values were found comparing left/right, dominant/non-dominant and operated/nonoperated knee. Patients with contra-lateral osteoarthritis (OA), as defined by the clinical examination and the knee society score, showed higher forces and impulses at the operated leg.


DISCUSSION: Interestingly, in this study, force and impulse of TKA patients with contemporary prostheses were comparable to healthy subjects indicating functional restoration of the joint. Contra lateral osteoarthritis may cause higher forces at the operated leg and thus, relatively higher stresses at the artificial articulation.

As expected, the generated forces at the bike pedal were low (20 – 25% body-weight) calling for little muscle activity and low compressive joint forces.


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