The process of choosing an implant has been constrained to patient desires, external anatomy, and in vitro implant characteristics. This has made the process of implant selection more of an art than science. This study attempts to gain a better understanding of the implant dimensions in vivo and the influence of the soft tissue, muscle thickness, gravity, and the viscoelastic properties of soft tissue. Using a sitting, open MRI, we were able to gain measurements of breast implants in-vivo.
Methods/Technique: 23 patients with 46 silicone implants were scanned with a standing MRI. There were also 6 patients with saline implant but were not included in the statistical analysis due to the small sample size. All of the breast augmentations were performed by the senior author. The MRI was performed with the patient in a sitting position using a lightweight (compressive force of light sweater) breast coil. The MRI’s were obtained after a minimum of 6 months post-operatively. Eight different measurements were taken by a single radiologist for each implant: maximum width of the implant, maximum height of the implant, projection of the implant at 2cm relative to the superior edge of the implant, projection of the implant 4 cm relative to the inferior edge of the implant, maximum projection of the implant, location of the maximum projection of the implant relative to the inferior edge of the implant, the position of the pectoralis muscle inferior edge relative to the superior edge of the implant, and the thickness of the pectoralis muscle at the superior pole of the implant (2cm from the superior edge of the implant), These measurements were compared to the measurements given to us by the manufacturer, to the expected value, or the implant size.
Results/Complications:
The average age of the patient was 29.4 years. There were no complications. The average time between surgery and MRI was 11.8 months. The results show that there is a significant difference in the implant characteristics from those provided by the implant manufacturer when the implant is in-vivo and sitting up. The quantitative difference varies with the size of the implant. The following factors significantly influenced the dimensions of the implant: there is a linear correlation between the size of the implant and the projection of the upper pole (average difference of 1.56cm), pectoralis muscle thickness correlates linearly with theprojection of the upper pole of the implant, the measured width was significantly lower than the manufacturer labeled width, superior pinch thickness did notsignificantly affect any implant characteristics, the skin stretch significantly affect the implant projection, the position of maximal projection was significantly affected by the size of the implant, the N-IMF distance did not significantly affect the position of the maximal projection, and the implant base has the characteristics of an ellipse more than a circle.
Conclusion:
Historically, we have used the limited dimensions of an implant given to us by the manufacturer to choose the correct implant for a patient. Though we know this to be inaccurate, there was no other option. This study aims to help define the implant dimensions in vivo and in the upright position. Also, with the use of the standing, open MRI, we were able to obtain several other measurements that may be critical in implant selection. The results show us that there are significant differences between the implant dimensions provided by the manufacturer and those that were measured with a MRI. Clearly, we will need to study the different profiles of the implants and the full range of implants sizes to get a better understanding of the actual implant measurements.