MFS medical expenses

My wife's medical expenses were high enough this year (and her income low enough) that it's to our advantage to file as Married Filing Separately, so we can deduct the part of her medical costs that exceed 7.5% of her income. We'd lose the deduction if we had to meet a threshold of 7.5% of our joint income. However, we paid these medical bills out of our joint credit card and checking accounts. Some of the IRS material I've seen suggests the medical expenses must be deducted by the spouse who paid them (I guess 50% for each of us since we used a joint account), rather than the spouse who actually incurred them (which would be 100% for my wife). Am I interpreting this correctly? By the way, we do NOT live in a community property state. Thanks.