Is it possible to remove horizontal borders from xtable?

I have a bit of code from a shinyapp that determines what will be exported to a pdf document:

  special_ortho_table <- reactive({
    if(input$ortho == "yes"){
      sp_ortho_table <- drugsUI %>%
        filter(Ortho == "yes", Special_ortho == TRUE) %>% 
       select(Name, Recommendations)
     }else{
       sp_ortho_table <- drugsUI[0,]
       names(sp_ortho_table) <- c("", "", "", "")
       }

    return(sp_ortho_table)
  })

 output$ortho_table <- renderTable({
    xtable(special_ortho_table())
  })

The corresponding code in rmd is:

xtable(special_ortho_table())

You can see that I tried to remove the column names but the pdf still produces a blank table with horizontal borders. Is there any way that I can remove the borders, if not, can anyone suggest a work around that would allow me to leave something that is blank when input$ortho == "no"?