Abstract:

BACKGROUND: The template method used in cementless total hip arthroplasty is influenced by many factors, so the accuracy is poor. Studies demonstrated that femoral isthmus plays an important role in total hip arthroplasty, which affect femoral prosthesis.

OBJECTIVE: To discuss the effects of femoral isthmus on cementless total hip arthroplasty.

METHODS: The images of 4 cadaver femoral isthmus were obtained by computer tomography. The relations between femoral component and cortical bone contact were observed on coronal slices by sawing manully. The longest and the smallest medullary canal dimensions and the cortical thickness of femoral isthmus were measured by CT films from 50 patients (55 hips) prepared for primary total hip arthroplasty. The size of prosthesis was predicted based on the smallest medullary canal dimension of isthmus. And the conventional preoperative template was served as control.

RESULTS AND CONCLUSION: There were a press fit and good contact between the femoral component and cortical bone of isthmus in 3 cadaver femoral bones. In 50 patients, the longest medullary canal dimensions of femoral isthmus were 8.2-22.4 mm (mean 14.2±3.1 mm). The smallest medullary canal dimensions of femoral isthmus were 6.1-17.9 mm [mean (10.2±2.9) mm], and the cortical thickness of femoral isthmus were 2.7-12.7 mm [mean (7.5±1.8) mm]. The results of CT-isthmus measurement method predicted sizes were excellence in the 50.9% cases. There was statistically significant difference of predicted sizes between the excellence rate of CT-isthmus measurement method and the rate of control (P < 0.05). Particularly, the excellence rate of CT-isthmus measurement method was 63.9% in the group aged below or equal to 65 years. When the ratio of the longest medullary canal dimensions and the smallest medullary canal dimensions of femoral isthmus was large than or equal to 1.4, the excellence rate of CT-isthmus measurement method was 70%. The press fit and good contact between the femoral component and femoral isthmus plays a very important role in stabilizing of femoral prosthesis in total hip arthroplasty. The predicted sizes of femoral prosthesis depending on the medullary canal dimensions of femoral isthmus measured by CT film has better accuracy than the conventional preoperative template.