Friday, March 2, 2001
A THR was performed on six cadavers using two designs of femoral prosthesis with the same heel (shaft angle 132 degrees): One implant (A) had a 12 mm diameter neck with 48 mm head offset while the second component (B) had a 14 mm diameter neck with 41mm head offset.
Each specimen was instrumented with cables simulating the action of seven muscles controlling the hip joint during rising from a low chair, and then mounted in an MTS machine. The hip was placed in 15, 20, 25, 30, 35, and 40 degrees of adduction and flexed from 80 degrees until frank dislocation. The position of the hip at impingement and dislocation were monitored electronically. The test procedure was performed with modular heads of 38 mm and 28 mm diameter.
In changing the head size from 28 to 38 mm, hip flexion at impingement increased by an average of 6.0 degrees with implant A (94.6 degrees vs. 100.6 degrees ; p < 0.0001), and 6.4 degrees with implant B (97.7 degrees vs. 104.1 degrees ; p < 0.0001). At dislocation, the 38 mm head increased hip flexion of component A by an average of 6.8 degrees (105.2 degrees to 112.0 degrees ; p < 0.0001). However, flexion of the prosthesis with the 14 mm neck only increased by 2.3° (108.4 degrees to 110.7 degrees; p = 0.048).
With both neck designs, 38 mm heads increased the incidence of bony impingement prior to dislocation, say the researchers Philip C. Noble, PhD; Vibor Paravic, BS; and Sabir Isnaily, BS, all of Houston, Texas.
|2001 Academy News March 2 Index C|
Last modified 15/February/2001 by IS