Sir, fifty million cartridges of local anaesthetic are delivered annually by dentists and surgeons in the UK.1 Fortunately, needle breakage is uncommon and is typically a complication of inferior alveolar nerve blocks.2,3,4 Only one needle breakage during an infiltration has been found in the literature.5

We wish to share a rare encounter during an infiltration using a single use system (Fig. 1). When a 27-gauge needle was used under general anaesthetic, the plastic hub failed to retain the metal needle. Upon withdrawal, the needle separated from the plastic hub and remained in the patient's tissue. Due to careful observation by the surgeon this was spotted immediately and recovered uneventfully with a fine mosquito clip. Within one month, two further identical needle breakages occurred, experienced by a total of three different clinicians. All three needles were retrieved without complication.

Figure 1
figure 1

The retained needle in the patient's mouth and the needle separated from the plastic hub

Full size image

We theorised that the disposable plastic syringe used was not compatible with the needle tip as both of these parts are manufactured by different companies. Screwing this particular needle into that particular syringe may have led to over-working of the threads within the plastic hub of the needle resulting in a loosened grip between plastic and metal.

Given this rare and potentially dangerous occurrence repeating itself within a short space of time where the correct anaesthetic technique had been employed and where patient movement could not be attributed to the breakage, we flagged our concern to the manufacturer. Interestingly, this type of mechanical failure of the needle had never before been reported to the manufacturer. When an investigation was launched, it became apparent that all the broken needles belonged to the same batch, highlighting the importance of recording batch number.

The retained broken needle and a total of 206 unused needles belonging to that batch were retrieved from outpatients, A&E, operating theatres and equipment stores and returned to the manufacturer as per their request. Each was visually inspected and underwent rigorous testing of the glue point. The broken needle and one other unused needle showed a low quantity of glue between the plastic hub and the metal needle. All the tested needles passed a resistance test (dynamometer test) to observe the behaviour of the cannula on the hub. The formal analysis report concluded that the repeated needle breakage was due to an insufficient quantity of glue secondary to deficiencies during glue distribution. The manufacturer's actions included replenishing all the collected needles, re-briefing their staff on the importance of visual controls and implementing a new production process to commence in 2017.

A major learning point from this is for clinicians to always diligently watch the needle during administration as well as on withdrawal until it is safely out of the patient's mouth. Needle fractures in tissues can be devastating and stressful for both clinician and patient therefore to prevent the risk posed to patient safety by faulty equipment we highly recommend liaising with the manufacturer if problems arise. We also advise not discarding any faulty equipment but retaining it for testing.