Superficial and Deep Dry Needling- a little perspective using the Trapezius of female research participants as a point of reference
When dry needling TPs a distinction is made between superficial (SDN) and deep dry needling (DDN). SDN is thought to achieve its effect indirectly, inhibiting C fiber pain impulses, where as DDN stimulates affected muscle directly, causing rapid depolarization of affected fibers in the area of the MFTrP nidus. DDN appears to affect clinical outcomes more strongly, but also gives rise to post-needle soreness; a side effect stemming from the repeated insertions, required to abolish local twitch responses (LTR).
A few years ago a couple of colleagues and I conducted an experimental study, during which the issue of needle depth came up. We determined needle depth using the following method:
Deep dry needling
DDN of symptomatic participants was based on the appearance and exhaustion of the twitch response phenomenon. The twitch response is a reliable criterion for the presence of trigger points when fibers in the immediate vicinity of the MFTrP nidus are stimulated. The purpose of needling in this sub-group therefore was to elicit and exhaust twitch responses with repeated fanning needling insertion. An experimental pilot protocol was developed on five non-participants (with appropriate anthropometric characteristics), in order to develop an idea of the needle penetration that might be expected as well as the time that would be required. We observed that, in order to repeatedly elicit twitch responses, no less than 10mm of the needle had to penetrate the epidermis over a period of 90 seconds. As no twitch response would exist for asymptomatic subjects, none could be induced. Therefore, the needles were marked at 10mm pre-intervention, so that the insertion depth would be similar to participants receiving deep needle insertion.
Superficial dry needling
We standardised this procedure, by tapping (using the index finger) the needle into the epidermis until it remained erect and could support its own weight. Again we piloted this protocol on 5 non-participants to determine what depth of penetration this resulted in. The needle penetration depth was determined to be 5mm. Current guidelines for superficial needling concurred with our findings, suggesting an insertion depth of between 5-10mm. No twitch response was expected for symptomatic or asymptomatic subjects, therefore intervention time was standardised to 90 seconds.
Overall the comparative needle insertion depth was 6,0mm (SD 1.2) for SDN and 12,3mm (SD 2.2) for DDN (p<0.001).
So whats the point?
Well, its interesting and important to note that although there exists a significant difference in the needle insertion depths, when one considers the actual value (12.3mm) its actually not very deep.
TPs are more likely to be located in the outer (superficial) layers of skeletal muscle- closer to the fascia (hence the term myofascial TPs). Therefore, it makes more clinical sense to start needling superficially and then proceed deeper (beyond 15mm in this instance) if the required clinical effect is not achieved.
Note: I have limited this discussion to muscles that can be needled directly, however, the principle may very well apply to muscles situated deeper e.g. Quadratus Lumborum.
Myburgh C, Hartvigsen J, Aagaard P, Holsgaard-Larsen A. Skeletal muscle contractility, self-reported pain and tissue sensitivity in females with neck/shoulder pain and upper Trapezius myofascial trigger points- a randomized intervention study. Chiropractic & Manual Therapies 2012, 20:36.