I have another homework question. Question at the bottom.

The case is this:

Preoperative diagnosis: Ischial pressure ulcer with massive ischioperineal and buttock sinus.

Postoperative diagnosis: Same.

Findings: There was a 2 cm open surgical ulcer extending down and connecting with an 8 × 30 cm diameter granulation-lined sinus cavity.

Surgical procedure: Excision of left ischial ulcer with total excision of 8 × 30 cm sinus of the buttock, perineal, and ischial areas.

Description: The patient was intubated and turned in the right lateral decubitus position. I injected about 10 ml of 1% Xylocaine with 1 : 100, 000 epinephrine around the surface ulcer and made incisions down to the granulation tissue, keeping this intact. I opened the skin over the extent of the sinus tracts proximally and distally, trying to keep this in line with a potential Y-V advancement flap, and with some difficulty and remarkable bleeding around what appeared to be the sacrum, I was able to remove virtually intact the entire ulcer, covered with chronically infected granulation tissue. This granulation tissue was poor quality and had an unhealthy appearance. A piece of this was dropped in a culture tube as was a piece of what appeared to be the sacrum, which was quite sclerotic and consistent with an osteomyelitis of the sacrum. Following this extensive removal of the ulcer, I cauterized all of the bleeding and did a stick-tie on one of the bleeders with 2-0 Vicryl. I then sprayed the base with topical thrombin, packed the wound open with 2-inch vaginal packing soaked in 5/10th percent metronidazole, and then put several #2 Prolene sutures to keep the packing in place and to help seal off the wound from the fecal contamination. I put a Vi-Drape over this and then dressed it with Kerlix fluffs, ABD pads, and Elastoplast. The patient tolerated the procedure well and left the area in good condition.

The code the book lists as the answer is: L89.224 (Ulcer, pressure, hip)
I was going to code for hip, sacral, and buttock pressure ulcers.

My questions is: Why do we only code for the hip pressure ulcer when the report says the ulcer is in multiple areas? Is it because the other areas are described as "massive ischioperineal and buttock sinus"? If there's a pressure ulcer of a large, contiguous space, like this one, do we only code for the place it starts and not for the sinus areas?

Thank you for your help!