Clinical and radiologic effects of diaphyseal stem extension in noncemented total knee replacement.

OBJECTIVE

To determine the clinical and radiologic effects of the addition of a diaphyseal stem extension to the tibial component in noncemented total knee replacement.

DESIGN

A cohort study.

SETTING

A university-affiliated institution specializing in elective orthopedic surgery.

PARTICIPANTS

One hundred and twenty-one patients with arthritis of the knee underwent noncemented total knee arthroplasty with a diaphyseal stem extension. All agreed preoperatively to prolong postoperative follow-up. Forty-six of the patients had a 100-mm stem extension, 56 had a 50-mm stem extension and 19, who had good bone with no intraoperative micromotion, had no stem extension. One patient died 6 weeks after operation and was excluded, leaving 120 knees available for study. Follow-up was 6 months to 3 years.

INTERVENTION

Noncemented total knee replacement with the Tricon II prosthesis.

MAIN OUTCOME MEASURES

Clinical effects of the diaphyseal stem extension as determined by the Hospital for Special Surgery rating system and radiologic effects as determined by the Cameron classification.

RESULTS

Clinically there was little difference between the three groups, with more than 90% in all groups scoring good or excellent. Radiologically, after elimination of single-zone lucency, both stem-extension groups showed a profound decrease in stem lucency. In patients who had a 100-mm stem extension, 90.9% had type IA lucency and 9.1% had type IB; no type II or type III lucency was seen. There was no correlation between radiologic and clinical results.

CONCLUSION

The addition of a diaphyseal stem extension to the Tricon II prosthesis reduces the amount of radiolucency in the tibial component in noncemented total knee replacement.