2008 XC-90 non-turbo with 89858 miles.
Rotated my tire today and noted a minor abnormal wear pattern starting to develop. Tires are Nokian WRG3-SUV 235/65 R17 All Weather tires. Tires are 108H rated XL (speed rating 130 mph, 2200 lb. load). Tire pressure has been maintained at 36 psi. Tires have been on the vehicle for 13113 miles. They were rotated at 81369 (4624 miles after installation and again today (8489 miles since last rotation). Rotation is standard Volvo pattern of front to rear and rear to front, keeping left tires on left and right tires on right.
Now to the abnormal pattern: All tires looked good and showed no evidence of damage. The two tires removed from the front showed an abnormal wear pattern on the inside. Both had a sort of a cupping starting. Every eighth rib had more wear than the seven ribs between two worn ribs. The wear was minor and some of the cuttings in the rib were still evident and present. Otherwise the war pattern appears normal and even. The "6" and "4" cut into the center rib is still totally visible on all tires.
My question; because I am experiencing the same indication on each side I am ruling out alignment and wondering if I am starting to see the indications of weak struts or other front suspension issues.
Any thoughts or comments are appreciated.

Well, everything is pointing to it might be time for struts and shocks. My XC90 is a C4 chassis with the nivomat self leveling shocks and struts. I am have a time finding a source for the parts. Dealer quotes the shocks at about $650 each and the struts at $300 each. I believe OEM is a Sachs product. I think the Sachs P/N for the shocks is 30683451. Would like to confirm that. Did find some shocks out there for just under $400 but again, would like to confirm P/N. Currently don't have a P/N for the struts. I can and will work with swapping the springs on the struts but prefer coming up with strut assembles so I can just do a swap out. Can anyone confirm part numbers for me and identify any sources? Thanks.

On FCP site, it says to look at product plate for the correct number (26):

https://www.fcpeuro.com/products/volvo-shock-absorber-rear-xc90-30683451#desc

$400 each? Did you check the Nivomats for wear? They last a very long time, much longer than the front struts. All you need to do is measure the empty car rear bumper height, put in about 200 lbs in the rear, measure again (lower), drive around the block. Then measure one more time and see if the ride height is the same as the first measurement.

You are correct about the front struts, they are Sachs. I would be a bit leery about getting a cheap no-brand set of pre-loaded struts, the springs and bushings may not be up to snuff...
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Keeping it running is better than buying new

I strongly agree with Klaus about the ride height test.

Not long after we got our '96 855R with Nimovats, I noticed different space between the rear tires and the fenders if the car sat for a few days.

If I took it for a ride, the clearances evened up.

I drove that car for 11 years and never had problems with the shocks.

The most severe test was when I picked up a B16 engine and transmission - the car dropped at least 3 inches when loaded.

My buddy looked at me - I told him to wait a mile or so - we stopped at a gas station and the car was back up.

It is possible that alignment or other issues can be different at different tread depths.

a tiny problem can be hidden by flex in deep tire tread, then show up when the tread gets shorter.

This happened to me on our '96 855R.

At about half the tread depth, rear alignment problems showed up severely on the 17 inch Volans with Yokohama Prada Spec 2s. Great performance tires with a high load rating.

Our 15 inch snow tires wore evenly for the 11 years we had the car.

Get the wheels off the ground and check that there's no slop with the suspension.
Check for sloppy ball joints, worn/sloppy strut mounts, busted motor mounts,
loose sway bar end links, slop in the rack.
Don't rule out realignment, plus don't go to some chain store, find a garage
that specializes in front end work.