The thing is that most any tricep extension exercise will offer the more potential for elbow joint injury (unless your a 500-600lb+ PL'er). Be it French presses, skullcrushers, lying extensions, etc. And while using either a straight bar, EZ bar or DB. Even with a complete warm-up/stretch, elbow thermo wrap's or a heat rubbing compound used before and during a tricep workout, the odds may be greater when doing extensions.. While an exercise like close grip, elbows in throughout, BP's (or dips) may lessen the full stress on the elbows themselves.
Those press downs , that Pumpster suggest, can be well worth the effort.. I've watched gymnist do them, but on horizontal bars. Wide or medium grip, not so much narrow, for them. Where I train at, we have a dipping setup that allows the knuckles to face forward, giving a different angle to tricep development. Personal view (for what's it's worth) is that extensions should never be the only form of a tricep exercise in a workout, but should follow a compound triceps exercise. Another observation (again, for what it's worth) is that a Hammer grip seems to lessen the overall stress on the elbows/wrist and affects the triceps in a more positive way. Good Luck.
Side Bar: I've seen a couple of guy's, over the years, do Skullcrushers with 300+ (Skullcrushers are partial movements) with excellent results and not any sign of elbow trouble (so far). At another time, I was standing next to a experienced BB'er who was doing French press with only a 105lb BB and snapped a tendon in his left elbow (SS'ing bicep/triceps). The outter head of the tricep just wadded up and formed a big muscle and blood knot near the joint. Nasty stuff.