A low-cost and high-fidelity animal model for nonpalpable implant removal: A pilot study

Abstract

The subdermal contraceptive etonogestrel implant Nexplanon (Organon, New Jersey, USA) is widely used all around the world. Despite a new applicator design to facilitate the correct insertion (compared to the first version of Implanon) and the new site insertion recommendations, deeper insertion continue to occur in 1/1000 women.¹ The manufacturer recommends an optimal placement between the dermis and the subcutaneous tissue, ensuring that the implant is immediately palpable: there is no recommended normal depth of implant insertion. A deeply inserted implant is defined as nonpalpable.² Removal might be difficult even in centers of experience (i.e., specialized centers in which experts have experience in removing nonpalpable implants). Training programs for deeper removals of the implant should be very useful with the need to first localize deeper implants by ultrasonography (US) followed by surgical removal. Because visualization by US is impossible on plastic or rubber model arms (due to the foam layer simulating the soft tissue beneath the thin vinyl skin),³ we developed a low-cost, high-fidelity animal model where anatomical structures are similar to the human arm. In this pilot study, we aimed to evaluate the feasibility of nonpalpable implant US detection and removal.

Placebo implants were deeply inserted into chicken legs. The primary outcome measure was to evaluate the localization of deep implants by US. The secondary outcome measure was to confirm whether surgical removal was possible using a visual analogue scale (VAS): the operator rated technical difficulties of implant removal using a 10-cm VAS ranging from 0 (very difficult) to 10 (easy). This study did not need to be approved by the university hospital's ethics committee as it did not involve any living vertebrate animal.⁴ Fresh chicken legs were obtained from a local supermarket.

Two placebo implants were deeply inserted into three different chicken legs (one implant at each end of the chicken leg) by a single operator (GC). All of them (six implants) were deeply inserted and intramuscular: the depth of the implant was 5.3 mm (3.7–9.3). In all cases, US detection was always possible. Implant removal was performed by a single operator (GC). In terms of the estimated technical difficulty with the 10-cm VAS, the operator considered it easy to use (10 points on the VAS) in all cases.

For the imaging localization technique, we used the same ultrasound modality as previously described in women with deeper implants.⁵ A high-frequency linear probe was needed; we used a 12-MHz linear array transducer (GE Healthcare, Limonest, France). The transducer was first placed transversely to find the small hyperechogenic dot of the implant and the acoustic shadow under the implant (Figure 1). The probe was then turned 90° to have a longitudinal view of the implant as a hyperechogenic line measuring 4 cm.

The depth of the implant could be easily evaluated by measuring the distance between the skin and the small hyperechogenic dot of the implant in the transversal view and/or the distance between the skin and the echogenic line in the longitudinal axis.

After mapping the implant location on the chicken skin (a 4-cm line) under ultrasound guidance, a 10-mm longitudinal skin incision with the scalpel was made followed by blunt dissection. Removal could be performed with small mosquito forceps (Figure S1).

Deeper implant removal is a difficult skill, and it is estimated that more than 50% of women who are referred for difficult or nonpalpable implant removals have had at least one attempt at removal prior to referral.¹

Simulation-based medical education has been developed and is strongly recommended in obstetrics and gynecology to mimic a clinical setting in to develop the technical skills and competency required for health care.^{3, 6} One of the limitations is to have a relevant training model/simulator.⁷ The dry model (the plastic or rubber model arm) might fit for insertion and removal of a correctly inserted implant but is not suitable for a deeper implant.³ A cadaveric model is likely one of the best training models, but this model is difficult to access. Based on the frequent use of porcine and chicken high-fidelity models in laparoscopic and robotic simulation exercises,⁸ we developed the idea to use chicken leg models for training and skill assessment in deep implant removal. The chicken leg model is low cost and closer to human skin and muscle. Localization was always possible using a high-frequency probe in our pilot study, and surgical removal was easy. One of the goals of the centers of experience is to reinforce the knowledge of the healthcare professionals already trained through continuous training by creating modules on specific themes around insertion, location, and difficult/deep removals of implants.^{1, 5} Our model could be relevant and useful for clinicians involved in the care of women with deep implants. To confirm these preliminary results, we have planned a study in which French centers of experience experts to evaluate the chicken leg model.

An easy-to-use, low-cost, and high-fidelity animal model could be useful for a training program for healthcare professionals involved in deep implant removal. Other studies are needed to confirm these preliminary results.

Design, planning, conduct, data analysis, manuscript writing: Gautier CHENE. Conduct, data analysis, manuscript writing: Emanuele CERRUTO. Conduct, data analysis, manuscript writing: Erdogan NOHUZ.

G. Chene^a,b has served as a consultant and member of advisory boards for Organon. The other authors (E. Cerruto^a, E. Nohuz^a) declare no conflict of interest to disclose.