Open TFS WorkItem within a running Visual Studio instance

gistfile1.cs

private static DocumentService _workItemDocumentService;

private static void OpenWorkItem(TeamFoundationServer tfsServer, int workItemId)
  {
    if(_workItemDocumentService == null)
      _workItemDocumentService = (DocumentService)DTE2.DTE.GetObject("Microsoft.VisualStudio.TeamFoundation.WorkItemTracking.DocumentService");
      // you can also use _workItemDocumentService = (DocumentService)Package.GetGlobalService(typeof(DocumentService));  

    IWorkItemDocument workItemDocument = workItemDocumentService.GetWorkItem(activeTFS, workItemId, this);
    
    try
    {
      if (!workItemDocument.IsLoaded)
        workItemDocument.Load();

      workItemDocumentService.ShowWorkItem(workItemDocument);
    }
    finally
    {
      workItemDocument.Release(this);
    }
}