Distal Fit Research Articles

The Anatomic Basis of Femoral Component Design

The shape of the femoral canal is variable, much more variable, in fact, than most contemporary designs of femoral components would suggest or can accommodate. In the face of this variability, line-to-line or surface-to-surface contact is not expected between cementless implants and much of the endosteal surface. It also is apparent that changes in implant design are still needed if the normal biomechanics of the hip joint are to be restored in each patient and if component fixation is to be optimized. Most cementless components aim to achieve proximal load transfer to the femoral canal. However, increasing clinical evidence suggests that distal filling of the femur also is necessary to minimize the incidence of postoperative symptoms, particularly in revision procedures. If this is indeed the case, more accommodating designs of femoral components are needed that will enable proximal and distal fitting at the femoral canal so that stable fixation may be achieved regardless of variations in bone geometry.

The Effects of the Collar on Total Hip Femoral Component Subsidence

Twenty-four preserved autopsy femurs were used to evaluate the effect of the collar and tight distal fit on noncemented femoral component subsidence, micromotion, and load to failure. Ten collared implants (five with tight and five with loose distal fit) and 14 collarless implants (seven with tight and seven with loose distal fit) were inserted with press-fit technique. They were compressively loaded in an Instron machine (Instron, Canton, Massachusetts) at 25-kg increments with 20 cycles applied at each load level. Subsidence was significantly decreased, and load to failure increased by the collar. None of the parameters was significantly affected by tight fit of the cylindrical distal stem. Tightening of the collarless implant by subsidence could not be relied upon to achieve fixation, and may not be reliable in a clinical situation. Improved rigidity of fixation and increased strength achieved by seating on the collar are distinctive advantages for pain control and biologic fixation of noncemented femoral components.

Prediction of Semirigid Penile Prosthesis Diameter From Saline Erection

A total of 14 impotent men without Peyronie’s disease underwent implantation of paired, semirigid penile prostheses after determination of the subcoronal dorsal diameters of the saline erections. The subcoronal saline erection diameter was divided by the diameter of the semirigid penile prosthesis, and the best lateral and distal fitting occurred when the quotient was 3 or greater. Dividing the subcoronal saline erection dorsal diameter by 3 allows selection of the appropriate semirigid penile prosthesis diameter.