Back Button Problem

I have sorting enabled in my gridview.

I sort through the gridview and press my button:

<asp:Button ID="btnback" runat="server" Text="Go Back to Counts" />

This code does this for me in pageload:

 If Page.IsPostBack = False Then            ViewState.Add("NbrPostbacks", "1")
        Else            ViewState.Item("NbrPostbacks") += 1        End If
        btnback.PostBackUrl = String.Format("javascript:history.go(-{0});", ViewState.Item("NbrPostbacks")

When I added the radiobuttonlist

 <asp:RadioButtonList ID="Pending" runat="server" AutoPostBack="True" 
                     OnSelectedIndexChanged="Populategrid" Height="16px" 
                     RepeatDirection="Horizontal" Width="755px">
                     <asp:ListItem Value="250" >Pending Over 250</asp:ListItem>
                     <asp:ListItem Value="300">Pending Over 300</asp:ListItem>
                     <asp:ListItem Value="350">Pending Over 350</asp:ListItem>
                     <asp:ListItem Value="400" Selected="True">Pending Over 400</asp:ListItem>
                 </asp:RadioButtonList>

I have to go through all of the sorting I have done on the page before I get back to the orginal page:

Do I need to put this in the btnback_client event and if I do, do I change the code?

 Protected Sub btnback_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnback.Click
        If Page.IsPostBack = False Then
            ViewState.Add("NbrPostbacks", "1")        Else
            ViewState.Item("NbrPostbacks") += 1        End If
        btnback.PostBackUrl = String.Format("javascript:history.go(-{0});", ViewState.Item("NbrPostbacks"))
    End Sub