Patients with a Dorr type C femoral bone require attention for using a Summit cementless stem: Results of total hip arthroplasty after a minimum follow-up period of 5 years after insertion of a Summit cementless stem.

BACKGROUND: The Summit cementless stem has been used as a device to occupy the proximal medullary canal space in total hip arthroplasty (THA). The purpose of this study was to evaluate the mid-term clinical and radiographic results of the Summit stem and the differences in the results as a function of medullary cavity shape.

METHODS: This study analyzed the 90 consecutive patients who underwent THA by using the Summit cementless stem. The minimum clinical and radiographic follow-up period for the patients was 5 years (mean, 5.5 years; range, 5.0-7.1 years). The radiographic and Harris hip scores (HHS) were evaluated across the three Dorr type classifications of femoral bone.

RESULTS: The postoperative HHSs were significantly higher than the preoperative HHS scores (p < 0.05). No significant differences in preoperative and postoperative HHSs were found among the three Dorr types. Stress shielding was observed in 58 hips. Spot welds and cortical hypertrophy were observed in various zones in 53 and 11 hips, respectively. No significant difference in the number of occurrences of cortical hypertrophy was found among the three Dorr types. However, the number of occurrences of severe stress shielding in Dorr type C was higher than that in Dorr type B. The number of occurrences of spot welds in Dorr type C was lower than that in both Dorr types A and B.

CONCLUSIONS: Mid-term clinical results were good regardless of the medullary cavity shape. However, severe stress shielding in Dorr type C was more frequently than that in Dorr type B. Therefore, attention should be paid to the types of medullary cavity shapes for Summit stem use.