The application of advanced CT imaging and computer graphics methods to reconstructive surgery of the hip.

Advanced computed tomographic and computer graphic techniques enhance diagnostic accuracy and offer the means by which three-dimensional operative planning can be achieved. These techniques have been used to diagnose hip pathology, rehearse and evaluate surgical plans, assess postoperative results, and design individualized prostheses.

Improving the fit of press-fit hip stems.

The implant-bone fit is critical to the longevity of press-fit total hips. Maximum contact on the internal cortical bone surface, especially proximally, produces more normal strain values and reduces micromotion and sinkage. Stem design computer software was developed to design both individualized hip stems that maximize implant-bone contact for a unique anatomy, and average anatomic hip stems in which the mean error of fit is minimized for many patients. Cadaver femurs were used to test the following two hypotheses: (1) Average anatomic stems, designed using the optimal-fit software for an average femoral geometry, improve implant-bone fit when compared with standard stems; and (2) Individualized optimal-fit stems provide an even better fit than average anatomic stems. Results showed that the average anatomical stems fit better than the standard stems. However, the individualized hip stems, designed from individual three-dimensional geometry data, fit the best.

Design of custom hip stem prostheses using three-dimensional CT modeling.

Long life expectancy, demand for high activity levels, and bone loss at the time of revision motivate the search for reliable and successful noncemented hip stem designs. It is hypothesized that improved implant fit may increase the longevity of noncemented total joints. Quantitative X-ray CT has enabled the use of a computerized stem design program, which designs an optimal-fit hip stem for individual femurs. Computed tomography and interactive image processing methods are used to generate the individual three-dimensional femoral models, which are used by the stem design program. Optimal-fit design provides maximum stem-bone contact while satisfying the requirement of being surgically insertable. Previous methods of custom implant design, including those that use three-dimensional CT modeling, have not provided optimal stem-bone fit. Quantitative results of this new process are presented.