# define the array
$a = @("a.sprint-100","a.sprint-99","a.sprint-49","a.sprint-98")

# escape hard defined string in regex
$escapedString = [regex]::escape(".sprint-")

# create regex which matches <AnyCharacter>.sprint-<SprintNumber>
[regex]$regex = "(.+)$escapedString([0-9]{2,3})"

# process the regex on all strings and print out the sprint number
$a | %{[System.Text.RegularExpressions.Regex]::Match($_, $regex)} | %{$_.Groups[2].value}

# output: 100 99 49 98

# but my sort logic doesn't work
 $a | %{[System.Text.RegularExpressions.Regex]::Match($_, $regex)} | Sort-Object -Property {$_.Groups[2].value} -Descending | %{$_.Groups[2].value}

# output: 99 98 49 100