The effect of stem length on femoral component positioning in canine total hip arthroplasty.

OBJECTIVE

To determine the effects of femoral prosthesis stem length on positioning of the femoral component within the canine femur.

STUDY DESIGN

An in vitro experimental study.

SAMPLE POPULATION

Eleven adult, mixed breed, canine cadaver femurs.

METHODS

Polymethylmethacrylate centralized Biomedtrix size 5, 6, and 7 standard and 1cm shortened implants were placed in specimens, manipulated to achieve maximal displacements of the implant tip in each plane, and radiographed. Measurements of the implant angle, tip offset, and minimal tip to endosteal surface distance were obtained with image processing software. The effects of implant length and size on implant positioning were evaluated with the use of Student's t, chi(2) exact, and 2-way ANOVA testing.

RESULTS

Statistically significant increases were noted in tip to caudal cortex distance in the sagittal plane, and available angle variability and tip offset variability in the transverse plane for shortened size 6 and 7 stems relative to the standard stems. No significant differences were noted in size 5 stems. Statistically significant increases in tip to caudal cortex distance and transverse plane available angle variability for standard 6 compared to standard 7 stems were noted.

CONCLUSIONS

Shortened stems result in statistical improvement of several variables of femoral component positioning. However, the improvement appears to be clinically negligible.

CLINICAL RELEVANCE

Alteration of current stem lengths is not recommended. The use of undersized standard implants may improve femoral component positioning in total hip arthroplasty.