Suketu Upadhyay
Executive Vice President and Chief Financial Officer at Zimmer Biomet
Thanks, and good morning, everyone. We had a good quarter, driven by faster-than-expected recovery of elective procedures, giving us the confidence to raise our full year revenue and earnings per share outlook.
Let's turn to our Q1 results and how that translates into our updated full year financial guidance. Unless otherwise noted, my statements will be about the first quarter 2022 and how it compares to the same period in '21. And my commentary will be on a constant currency and adjusted continuing operations basis. Please note, we have changed our geographic revenue reporting to U.S. and international, and we released a Form 8-K last week to provide unaudited recasted financial information related to our ZimVie spinoff, as well as a change in non-GAAP reporting of in-process R&D-related expenses.
Moving to first quarter performance. Net sales in the first quarter were $1.663 billion, up 3.9% on a reported and 6.8% on a constant-currency basis. As previously guided, selling days contributed about 130 basis points of tailwind in the quarter. Revenue was driven by continued execution along with stronger and faster than expected COVID recovery across most markets, with the largest uplift in the U.S. After significantly pressured January, recovery ramped through the quarter with improvement in February and a strong rebound in March.
On a consolidated basis, March grew versus pre-pandemic levels, and that recovery has continued into April. U.S. sales grew 5.8%, driven by strong recovery as COVID cases subsided and elective procedures returned. By the end of the quarter, U.S. cancellation rates have returned to pre-pandemic levels and procedure volumes were above 2019. International sales grew 8.1%, driven by strong growth across Europe, and we saw continued recovery despite COVID surges in certain European markets in China.
Turning to our business category performance in the first quarter. As a reminder, China VBP is expected to be about neutral to overall revenue growth for the full year. And so far, the 2022 impact is broadly in line with our original expectations. While we don't expect a material impact from VBP on full year 2022 growth, we do expect there to be fluctuation by quarter. In the first quarter, we saw about 200 basis points to 300 basis points of pressure across our global knee, hip and S.E.T. segments, which we expect to be broadly offset through the next three quarters, with the majority coming in the fourth quarter.
Global knees grew 11%, with U.S. knees up 11.7% and international knees up 10.1%, driven by solid commercial execution, continued traction for Persona Revision, Robotics pull-through and strong knee procedure recovery across most markets.
Global hips grew 4.5%, with U.S. hips up 3.3% and international hips up 5.6%, driven by recovery in both primary and revision hip procedures, and we're seeing positive early traction on ROSA Hip. The sports and extremities and trauma category increased 1.8%, driven by strong performance in CMFT, sports medicine and upper extremities. And finally, our other category grew 11.5%.
Moving to the P&L. For the quarter, on a continuing operations basis, we reported GAAP diluted earnings per share of $0.35 compared to GAAP diluted earnings per share of $0.92 in the first quarter of 2021. This decrease was driven primarily by an unrealized investment loss due to a decline in the value of our investment in ZimVie and higher litigation related and restructuring charges. On an adjusted basis, diluted earnings per share from continuing operations of $1.61 represents an increase from $1.55 in the first quarter of 2021. The increase was largely driven by higher sales and lower interest expense.
Adjusted gross margin was 70.6%, lower than the prior year as expected due to VBP and higher input and manufacturing costs, which were partially offset by higher volumes and better mix. Our adjusted operating expenses were about $735 million, up from the prior year, driven by higher investments in R&D. Our adjusted operating margin for the quarter was 26.4%, down versus the prior year, but ahead of expectations and driven by higher revenue. The adjusted tax rate was 16.1% in the quarter, in line with our expectations.
Now, turning to cash and liquidity. Operating cash flows from continuing operations were $360 million and free cash flow totaled $223 million for the quarter. We reduced our debt by about $650 million, excluding the effects of foreign currency and ended the first quarter with cash and cash equivalents of about $435 million. Our improving financial performance in tandem with our ongoing debt reduction continue to strengthen our balance sheet.
Moving to our updated financial outlook for 2022. While we continue to manage through macro headwinds related to foreign currency, Russia, inflation and supply chain challenges, a faster and stronger COVID recovery in tandem with a positive first quarter to give us the confidence to raise and tighten our financial guidance.
Against this backdrop, our current expectations for the full year are as follows: on a constant currency basis, we now expect to grow 2% to 4% versus 2021, with an expected foreign currency headwind of approximately 350 basis points. This translates into a reported revenue growth projection in the range of negative 1.5% to positive 0.5% versus 2021. Note that the selling day tailwind that we saw in the first quarter will be fully reversed in the fourth quarter, with no material full year selling day impact.
Adjusted operating profit margins continue to be in the range of 26.5% to 27.5%. This assumes inflationary pressure of about 150 basis points versus our original estimate of about 50 basis points. Of the incremental 100 basis points of pressure, a half will hit 2022, but be offset by expected higher revenue and roughly half will be capitalized and impact 2023.
Adjusted tax rate expectations remain in the range of 16% to 16.5%. Adjusted diluted earnings per share is now expected to be higher at $6.65 to $6.85, and we are increasing free cash flow to $750 million to $850 million. Inside of that guidance, we have a tougher comp in the second quarter due to COVID recovery we experienced in 2021. But we do expect revenue to grow in the low single digits over the second quarter of '21, and to exceed pre-pandemic levels for the full quarter.
In summary, we expect that the environment will remain dynamic, but we believe the pace of recovery, our continued execution and the strength of ZB's underlying business fundamentals position us well to improve our financial outlook.
With that, I'll turn the call back over to Keri.