Link to UCSC gtexGene track description page for selected gene symbol
You never want to include the hgsid parameter in your url because that is the link to your current browsing session and all its specific contents. So if you send that link to someone else and then they start browsing around that link may not work correctly again in the future if you or the person you sent the link to modify your browsing session.

As to how to create links to hgc pages, the usually follow a somewhat general format:
http://genome-euro.ucsc.edu/cgi-bin/hgc?db=hg19&amp;c=chr2&amp;o=242498135&amp;t=242513546&amp;g=gtexGene&amp;i=BOK

You need the db and g parameters to specify the assembly build and track, and then you need to provide the position in the form of the c,o and t parameters. The last thing you want is the i paramter to specify the item name. The reason the i parameter alone is not enough is because we do not require uniqueness on item names (there may be many copies of an item across the genome for instance).

You can obtain the c, o, t and i parameters by selecting the chrom, chromStart, chromEnd and name fields from the gtexGene table:

$ mysql --user=genome --host=genome-mysql.soe.ucsc.edu -A -P 3306 -e "select chrom, chromStart, chromEnd, name from gtexGene limit 1" hg38
+-------+------------+----------+---------+
| chrom | chromStart | chromEnd | name    |
+-------+------------+----------+---------+
| chr1  |      11868 |    13052 | DDX11L1 |
+-------+------------+----------+---------+