If there's a single word that encapsulates what most investors want from their stocks, it's growth, growth, and even more growth. And even amid a market downturn, inflation, and issues with the global supply chain, the good news is that there are plenty of places to find monster growth, as long as you're willing to accept some risk.

On that note, there are a pair of medical device companies that are expanding ravenously despite underperforming the market over the last 12 months. What's more, there's little to stop them from continuing to gobble up their markets over the next decade and perhaps even beyond. Neither stock is cheap, but there's not much reason to expect a discount anytime soon, so let's take a look at both to see why they're worth buying and holding for as long as you can stomach.

1. STAAR Surgical

When it comes to businesses that have the potential to profitably penetrate massive international markets in the coming decades, STAAR Surgical (STAA -0.19%) should be one of the first that springs to mind. Its Implantable Collamer Lens (ICL) technology can be thought of as a semi-permanent solution to nearsightedness, putting the lenses in direct competition with eyeglasses and contact lenses. As they're implantable, people don't need to worry about dry eyes, smudged lenses, or accidentally losing a contact with ICLs. And, with the number of people needing vision correction predicted by the company's management to grow to reach a stunning sum of nearly half of the global human population by 2050, it's safe to say that its market is nowhere close to drying up or getting too crowded.

From 2017 to 2021, its revenue rose with a compound annual growth rate (CAGR) of 26%, and it's expected to grow by 28% this year. Right now, STAAR is working overtime to penetrate the massive and expanding market for ICLs in China, where it held a 20% market share as of 2020. Per its second-quarter update, that's going fantastically, as it shipped 42% more lenses to the country than a year prior, contributing to its total revenue of $81.1 million in the quarter.

In the last three months alone, its share price rose by above 91.7%, with most of the gains concentrated in mid-August after it reported better-than-expected earnings. There isn't much that could trip up the business from proceeding with its plans, and its global market share will likely continue to improve over time. While its shares are likely to face headwinds owing to the market's dislike of growth stocks at the moment, STAAR is going to keep shipping lenses until the cows come home, and eventually, the sentiment will improve. So, if you're eager for a monster growth stock, it's a great choice that doesn't require taking on a lot of risk to hold. 

2. Align Technology

Align Technology's (ALGN 1.54%) products are perhaps just as evergreen as STAAR Surgical's. Rather than correcting patients' vision, however, Align makes Invisalign tooth straighteners that correct their teeth, much like braces. Beyond that, it also develops imaging devices and software targeted at dental health providers so that they can fit patients for its straighteners and address their issues more effectively. And its business has been booming for more than two decades now, as its straighteners are allegedly more comfortable and less visually intrusive in comparison to braces.

Align's top line grew with a CAGR of 30% from 2016 to 2021, which is quite fast -- but what's even more impressive is that it grew with a CAGR of 23% from 2001 to 2015. Therefore, its annual growth rate is accelerating, even after an incredibly long run of moderate- to fast-paced performance. Furthermore, it's profitable despite the significant inroads it's making in its markets. Toward the end of 2021, it held a market share of around 10% globally in terms of the number of product-associated orthodontic treatment initiations. 

2022 is an especially good time to start a position in Align's stock because of the recent difficulties it's been having. Its total revenue of $969.6 million in Q2 faced headwinds from coronavirus-related issues in China and macroeconomic issues elsewhere, leading it to shrink by 4.1% year over year. But demand for tooth straightening isn't going anywhere, and eventually, the present headwinds will ebb. And when they do, Align's stock will likely return to an upward march alongside its rising earnings, rewarding investors in the process.