This invention relates generally to spine surgery and, in particular, to methods and apparatus for treating spinal stenosis. Pressure and temperature telemetry data received from the satellite can be analyzed using a maximum likelihood estimation approach that reconstructs a predicted tank pressure signal using the temperature data and determines a pressurant volume necessary to make the reconstructed pressure signal match the received pressure signal. We show that many more 21- and 22-nt expressed RNAs, termed microRNAs,, exist in invertebrates and vertebrates, and that some of these novel RNAs, similar to let-7 stRAN, are also highly conserved.