CHICAGO (Reuters) - Investors in U.S. medical device companies will soon learn to what extent patients are delaying back surgeries and knee replacements.

Stocks in the sector once considered an economic safe haven have stumbled along with the broader market in this recession as investors reasoned that Americans who are paying an ever-increasing portion of their medical bills out of pocket would delay or avoid treatment, and struggling hospitals would be forced to slash budgets for upgrading equipment.

With unemployment on the rise and hospitals seeing more uninsured patients, analysts expect the strain to be reflected in quarterly results for the medical technology sector in the next few weeks.

"Historically, orthopedic and cardiac companies have been resistant to economic downturns. This really will be the first quarter that will take the full brunt of the economic slowdown," said Edward Jones analyst Aaron Vaughn.

The fears are baked into medical technology stocks. The Standard and Poor's health care equipment index .GSPMED is down 5.4 percent since the year began, while the S&P 500 has fallen 8.7 percent for the year to date.

"We think there is an elective surgery slowdown, we know there are capital equipment spending freezes, and we would anticipate pricing pressure from hospitals whose volumes are declining, but we don't know how severe it is," said Tim Nelson, healthcare analyst at asset management firm FAF Advisors. "I think we'll see missed numbers. Certainly we have that potential."

While some device makers offered cautious 2009 forecasts as the year began, the recession's impact on orders has yet to be quantified.

"In the fourth quarter it became apparent hospitals were curtailing their spending. The big question is, how much?" said Raj Denhoy, analyst with Thomas Weisel Partners.

"Clearly these stocks are reflecting a tougher outlook for the back half of the year, and these results will show if the expectations are too great or too little," he said of the numbers to come.

Analysts stress that the diverse range of products and equipment under the umbrella of medical technology make it hard to generalize about how well the sector is holding up. A patient with an emergency heart condition, for example, is less likely to forgo a procedure than someone who is considering laser eye surgery or breast implants.

A handful of smaller medical equipment makers have warned of weaker results this quarter, each citing curtailed capital spending by hospitals. They include Zoll Medical Corp (ZOLL.O), a maker of automated external defibrillators, which last week said North American hospital revenue fell by more than 30 percent in the fiscal second quarter compared with a year ago.

Natus Medical Inc (BABY.O), whose monitoring systems are used in hospitals, warned of a 9 percent to 12 percent drop in overall revenue in the first quarter versus last year.

SonoSite Inc (SONO.O), which makes portable ultrasound machines, said the slowdown in U.S. hospital capital spending drove a mid-teen percentage decline in its U.S. hospital revenue for the first quarter, while overall revenue was down by 1 percent to 2 percent. Its shares have been edging higher since it reported the preliminary results on Monday.

Orthopedic device makers have been a focal point of anxiety centered around how long patients with deteriorating knees, hips and backs will put up with the misery.

"You are in pain, and the question is, how long will people tolerate that?" said Leerink Swann analyst Rick Wise. "The worry is that there are people who don't have jobs or insurance, or are frightened to leave their desks to take the time to do these procedures."

Late on Tuesday, privately held Biomet Inc said worldwide hip sales rose 5 percent and knee sales increased 3 percent in the fiscal third-quarter, buoying shares of competitors Zimmer Holdings Inc (ZMH.N), Stryker Corp (SYK.N), Wright Medical Group Inc (WMGI.O) and Smith & Nephew (SN.L).

"What should matter more to the group come (first-quarter) earnings season, though, will be gaining additional visibility, beyond anecdotal reports, into the forward surgical calendar," J.P. Morgan analyst Michael Weinstein said in a note to clients on Wednesday.

In a report last week, Weinstein identified robotic surgical equipment maker Intuitive Surgical Inc (ISRG.O), mammography systems maker Hologic Inc (HOLX.O), wound care device maker Kinetic Concepts Inc (KCI.N), radiation therapy companies Varian Inc (VARI.O), Accuray Inc (ARAY.O), TomoTherapy Inc (TOMO.O), and Steris Corp (STE.N), which makes infection prevention products, as among those most vulnerable to capital spending cuts.

Analysts said results from bellwether Johnson & Johnson (JNJ.N), whose medical products range from orthopedic devices, contact lenses and blood glucose meters for diabetics to stents that treat clogged heart arteries, will be a key barometer for the overall health of the sector.

(Editing by Bernard Orr)