Likewise in ps.-Zonaras. The headword is (neuter) plural, with a singular gloss. It refers here -- other applications are attested -- to the four rails which form the frame of a bedstead (LSJ s.v.).
Though it can be used substantively, the headword is actually an adjective (meaning driven-in) which, in an instance like this, presupposes a noun such as 'timbers'. The phrase e)nh/lata cu/la occurs in one of the extensive papyrus fragments (314.316 Radt) of Sophocles' satyr-play Trackers; cf. Pollux 10.34.