The ratio of patient body mass index to age: a cost-effective implant selection guideline for total knee arthroplasty

Background We sought to develop an objective implant selection guideline based on the ratio of patient body mass index (BMI) to age in order to select implants preoperatively and reduce cost while maintaining quality. The BMI-to-age ratio can be used to distinguish patient demand and select those patients who may benefit from newer technology and higher cost implants and those who would do well with standard-demand implants. Methods A retrospective analysis investigated the types of implants received by patients undergoing total knee arthroplasty from January 2012 to August 2014. Patients with a BMI-to-age ratio >0.60 were categorized as high demand and were eligible for either a high-demand implant or a standard-demand implant. Patients with a BMI-to-age ratio ≤0.60 were recognized as standard demand and would be eligible for only standard-demand implants. The actual implant received was identified and compared with the implant as predicted by the BMI-to-age ratio and potential cost savings were identified. Results A total of 1507 operative knees were identified. The high-demand implant carries a 31% greater cost than that of a standard-demand implant. Thirty-eight of 1084 high-demand implants were placed in standard-demand knees. An additional 1.1% cost was realized with 38 standard-demand knees receiving high-demand implants and 28.6% if high-demand knees had been used in all standard-demand patients. Conclusions Limiting the use of high-demand implants to high-functional-demand patients based on the BMI-to-age ratio may guide the surgeon's choice in optimizing implant selection while providing value-based purchasing criteria to the selection of total knee arthroplasty implants.