In-Plane vs Out-of-Plane: Knowing Where the Needle Tip Is

Written by Dr. Glenn Barnes

Updated September 2026 ·8 min read

Two ways exist to bring a needle to a target under ultrasound, and the choice determines whether you can see the needle tip. Since almost every avoidable complication in guided injection comes from not knowing where the tip is, the decision matters more than it first appears.

This follows the teaching of Dr. Glenn Barnes, a diagnostic and interventional ultrasound specialist.

In-plane and out-of-plane

The terms describe the needle's trajectory relative to the long axis of the probe.

In-plane means the needle travels parallel to the long axis, within the ultrasound beam, entering from the end of the probe. Because the beam is a thin slice and the needle lies inside that slice, the whole needle is visible.

Out-of-plane means the needle is inserted perpendicular to the long axis, crossing the beam. It passes through the slice rather than lying in it.

Why in-plane is the default

Barnes's recommendation is unambiguous: “Most injections and interventions should be done with the in-plane technique… When possible, this is the technique I would strongly advise that you use.”

The reason is complete visualisation. In-plane, you see “the entire needle during the entire procedure” — both the shaft and, critically, the tip, which he notes is identified by the bevel. That, as he puts it, “maximises safety and accurate placement of your intervention.”

Seeing the shaft tells you the angle. Seeing the bevel tells you exactly where the business end is. Seeing both continuously means a vessel or nerve in the path is visible before the needle reaches it, not after.

Out-of-plane, and the trap inside it

Out-of-plane has a real weakness, and Barnes describes it precisely enough that the failure mode is obvious once stated.

Because the needle crosses the beam rather than lying in it, “the shaft of the needle will not be visualised.” What appears instead, once the needle enters the plane, is a bright white dot.

Here is the part that matters: “when the bright white dot first appears on the screen is your best assessment of where the needle tip is. If you continue to advance the needle tip beyond the initial appearance of the bright white dot” — you no longer know where the tip is.

The dot does not move with the tip. It marks wherever the needle currently crosses the imaging plane. Advance further and you are seeing a cross-section of the shaft while the tip travels on, unseen and unmeasured, into tissue you cannot assess.

That is the single most important safety concept in ultrasound-guided injection, and it explains why in-plane is the default rather than a preference.

When out-of-plane is nonetheless right

It has legitimate uses, and Barnes names one specifically.

For the first metatarsophalangeal joint, he prefers out-of-plane. The joint is tiny, the approach is along the dorsal aspect of the toe with a small-footprint high-frequency linear probe in long axis, and there simply is not room to bring a needle in parallel.

The general principle: out-of-plane suits very superficial, very small targets where the in-plane path is not available and the distance travelled beyond the dot is negligible. Where a structure is deep, or vessels and nerves are nearby, the calculus changes entirely.

What you must see before the needle

Guidance does not replace knowing the anatomy, and Barnes's teaching consistently identifies what must be recognised before an injection begins.

At the lateral hip, for a greater trochanteric bursa injection, the muscles that insert on the greater trochanter are the gluteus medius and gluteus minimus. He is equally explicit about what does not: “the gluteus maximus does not insert into the greater trochanter. Instead, it inserts into the posterior aspect of the iliotibial band.”

Mistaking one for another under the probe means injecting the wrong structure with perfect technique.

For intra-articular hip injection he gives a confirmation you can watch for in real time: the injectate should be seen spreading and staying underneath the joint capsule. Ultrasound shows not only where the needle is but where the drug goes, which landmark technique cannot.

The hand that holds the probe

Needle visualisation depends on a stable image, and the image depends on the scanning hand.

Ultrasound gel is slippery. Barnes's requirement is at least two fingers of the probe hand resting on the patient, because otherwise the probe “will slip and slide all over the place, making diagnosis and needle visualisation impossible.” Anchoring converts gross hand movement into small purposeful adjustment.

A needle that keeps disappearing from view is usually a probe-hand problem rather than a needle problem.

Getting the technique reliable

1. Scan first, then decide. Identify the target and everything between skin and target before any needle is opened.
2. Plan the in-plane path and check what lies along it.
3. Anchor the probe hand with two fingers down before advancing.
4. Watch the bevel, not the shaft. The tip is what causes harm.
5. If you lose the tip, stop. Reacquire before advancing further, every time.
6. Watch the spread. Injectate going somewhere unexpected is the earliest sign the tip is not where you believe it is.

Barnes's honest framing of the whole skill is that the learning curve — not the equipment cost — is the main obstacle to adoption, and that it is best overcome with practice outside the clinic and slow integration rather than a hard switch.