GEOMETRIC ANALYSIS OF THE PROXIMAL MEDULLARY CAVITY OF THE FEMUR IN THE GERMAN-SHEPHERD DOG

Forty-one cadaver femora of German Shepherd dogs were prepared for imp lantation of a cementless total hip prosthesis by reaming of the proxi mal medullary cavity with standard orthopaedic instruments. Silicone p aste imprints of the cavity were taken and measured with a 3 D laser r eflection system. Data were processed statistically according to a geo metric model with these parameters: distal diameter O-dist, medio-fron tal radius r. laterofrontal angle alpha, medio-frontal angle beta, hel ix angle gamma and increment eccentricity delta(e). Correlations betwe en body mass and O-dist, body mass and r, body mass and beta were mode rately significant (p < 0.05, p < 0.06, p < 0.05 resp.). Other correla tions between body mass and parameters were not significant. Simple we ighing of a German Shepherd is not a useful predictor of the internal dimensions of the proximal femur. The distribution of the most importa nt parameter O-dist was compared with the range of O-dist sizes of the iso-elastic veterinary hip prosthesis (IVHP). This comparison showed that the test sample of 41 bents could be fitted with four IVHP sizes. However, 25 femora out of 41 do not fit into the available r values o f the IVHP assortment. Less than adequate proximal canal fill will be the result if an IVHP is implanted, unless substantial reaming is done proximomedially. It was shown that measurements on radiographs of int act dog cadaver femora do not yield equivalent results to the imprints . Moreover. comparison of the internal dimensions of the medullary cav ity of the human femur showed that a press-fit human prosthesis cannot be geometrically proportional to the IVHP.