Breast augmentation is one of the most common cosmetic plastic surgery procedures performed worldwide, with more than 290,000 surgeries performed during 2005 in the United States alone [1]. Over the years, evolutions in operative technique (incision selection, different planes of dissection) and improvements in implant variables (volume, shape, surface texture, and filler type) have led to excellent results with minimal complications.

Despite the increasing popularity of breast augmentation, some patients experience sensory changes after the procedure, with the incidence estimated to be as high as 41% [2]. Alterations in breast sensibility seem to be the second most common patient complaint after breast augmentation, after capsular contracture [3].

Earlier studies performed to evaluate postoperative sensory changes used imprecise measurements such as light finger touch or pinprick [4]. The sensibility level could not be precisely quantified using these crude methods. Recent studies evaluating sensibility changes use the Semmes-Weinstein monofilament test to assess the pressure threshold [5,6]. Other methods, such as measuring static and moving two-point discrimination, have proved to be unreliable and inconsistent [7]. Although some newer studies use a pressure-specified sensory device [8,9], the clinical relevance of such methods is still unclear [10].

The use of the Semmes-Weinstein monofilaments remains a simple, clinically applicable, and objective method [10,11]. The perception of monofilaments involves an expression of touch, pressure, and pain [10], which makes the monofilaments suitable for our purpose.

The anatomy of the female breast innervation has been well described. The breast receives sensory fibers from the second to the sixth intercostal nerves, with the upper breast skin innervated by supraclavicular nerves from the third and fourth branches of the cervical plexus. Each intercostal nerve divides itself into an anterior cutaneous branch (supplying the medial aspect of the breast) and a lateral cutaneous branch (innervating the lateral aspect of the breast). Most authors agree that the sensory innervation of the nipple–areola complex (NAC) is provided primarily by the fourth intercostal nerve, but that the third and fifth intercostal nerves participate as well [10,11], and even the second [10] in some cases. These various nerve branches converge into the NAC, providing breast skin sensation.

The implants all were placed through the following incisional approachs: the periareolar approach, the inframammary approach, and the transareolar (or Pitanguy incision) approach.

This study aimed to investigate the factors that affect the sensation of breast skin after subglandular implant placement. The analyzed variables included the relative volume of the implant, the surgical approach (inframammary, periareolar, or transareolar incision), the previous lactation, the role of minor complications, and the patients’ subjective perception of sensibility alterations.

Patients and Methods

A prospective study investigated patients who underwent aesthetic breast augmentation between June 2004 and October 2005 at the 38th Ward of the Santa Casa General Hospital of Rio de Janeiro (the Ivo Pitanguy Institute). Breast sensibility was tested before and after surgery using Semmes-Weinstein monofilaments. Breast sizers 10 was used to compare the pre- and postoperative breast volumes. No financial or other compensation was provided for the patients enrolled in the study.

The exclusion criteria specified medical conditions that could affect sensory functions (neurologic, endocrine, nutritional, metabolic, or hematologic abnormalities; collagen or autoimmune diseases), previous breast surgery (including biopsy), and altered mammography or breast sonography images. Patients scheduled to receive submuscular implants also were excluded from this protocol.

Sensory Testing

Skin sensation was tested preoperatively using Semmes-Weinstein monofilaments, which consist of nylon filaments applied perpendicularly to the breast skin. With the patient seated comfortably in a room temperature environment, each monofilament was tested over nine points on each breast while the patient kept her eyes closed. The locations of these nine points were established as in previous sensibility studies [5,6]: one on the nipple, one on each of the four areola quadrants, and one on each of the four breast skin quadrants. The tactile thresholds were defined as the minimal bending force of the thinnest filament sensed by the patient. After three attempts, one single affirmative response determined a positive result for each of the nine points.

The kit of six monofilaments was labeled from 1.69 to 5.47. These values represent the logarithm of 10 in the base of the force in milligrams required to bend the nylon monofilament. The same test performed preoperatively was repeated 6 months postoperatively. As shown in previous sensibility studies [5,9], sensory losses tend to stabilize after this period and normally show no significant improvement after 6 months.

Breast Volume Assessment

Breast volume was measured preoperatively and 6 months after surgery using a set of seven breast sizers [17] (transparent plastic molds used under the bra to simulate the breast size after breast augmentation, intended to help in planning of the implant size). These breast sizers have volumes measuring from 120 to 660 ml. Each sizer is held by the patient so as to fit exactly the breast surface.

The sizers were applied over the breast with the patient seated in an upright position (Fig. 1). The patient chose the one mold that best simulated the final breast volume she desired.

Fig. 1.
figure 1

Preoperative volumes of breasts measured using sizers, which consists of transparent plastic casts designed to fit exactly the breast volume.

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Other Examined Factors

In a postoperative patient questionnaire, symptoms such as pain, tenderness, and paresthesis were recorded for each breast. Patients were asked about their subjective perception of sensibility changes. Local complications (seroma, hematoma, or partial wound dehiscence) also were registered for each breast.

Statistical Analysis

The results of the sensory testing were classified in a qualitative fashion in two groups: group 1 (patients with unaltered postoperative sensibility) and group 2 (patients with altered postoperative sensibility). To verify the association among the variables of interest, statistical analysis was performed using a chi-square test at a significance level (α) of 0.05. The analyzed variables included the relative volume of the implant (i.e., an index defined by the quotient resulting from the implant volume divided by the preoperative breast size), the incision approach (transareolar, periareolar, or inframammary), the presence of minor complications, the breast-feeding history, and the subjective perception of sensibility alterations.

Results

A total of 37 healthy women scheduled for elective aesthetic breast augmentation agreed to participate in this study. All the patients were examined before surgery and scheduled to be reexamined 6 months after the operation. Eight patients did not return for medical consultation in the 6th month after surgery. Our final sample therefore consisted of 29 patients (58 breasts) with mean age of 33 years. Two of these patients had undergone previous unilateral biopsies, thus excluding 2 breasts from our study, for a final sample of 56 breasts. The features of our population sample are summarized in Table 1. Of the 56 breasts, 40 (71%) had previously been submitted to breast-feeding.

Table 1. Features of the sample (n = 56)
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All the breasts received silicone gel-filled implants. The periareolar approach was used for 31 breasts (55.3%), the inframammary approach for 17 breasts (30.3%), and the transareolar approach for 8 breasts (14.3%). Nine breasts (16%) presented minor complications: partial wound dehiscence in 6 breasts, seromas in 5 breasts, dehiscence with seroma drainage in 1 breasts, and hematoma in 1 breast. None of the breasts showed capsular contracture by the time of reexamination.

Subjective Perception

Subjective complaints were reported for 21 breasts (37.5%). Among these, the main complaint was paresthesia (14 breasts, 66.6%), followed by allodynia (3 breasts, 14.2%). For the remaining four breasts (19%), the patients complained of sensory alterations but could not specify their symptoms based on our questionnaire. No patient reported spontaneous pain after 6 months of follow-up evaluation.

Objective Alterations

Objective alterations were observed for 18 breasts (32.1%), with sensibility loss demonstrated by higher postoperative tactile thresholds in examination with the Semmes-Weinstein monofilaments. In this subset of breasts, the most affected region was the NAC. Objective alterations in the inferior region of the areola were observed with all 18 breasts (100%). Among the four regions of the breast skin, the lower (i.e., the “6 o’clock” point) also was the most affected (Table 2).

Table 2. Affected regions in breasts with altered postoperative thresholds (n = 18)
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Variables Associated with Sensibility Alterations

With regard to the different surgical approaches, no difference could be found between the periareolar and the inframammary incisions. The number of breasts with a transareolar incision (n = 8) was too small to allow a valid statistical comparison.

The relative volume of the implant was found to have a positive association with sensibility alterations. Higher values of this index (i.e., larger implants or smaller breasts) were associated with higher postoperative sensibility thresholds (p < 0.05). No association between the presence of minor complications and sensibility alterations was found. The patient breast-feeding history showed no statistical relation with sensory changes. Patients who claimed to have subjective alterations were not associated with a higher incidence of objective alterations than patients who had no subjective complaints (Table 3).

Table 3. Statistical analysis
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Discussion

After augmentation mammaplasty, many factors are involved in sensory alterations. Endogenous conditions such as previous breast-feeding cannot be altered by the surgeon, but our findings suggest that this plays a minor role in sensory changes. Complications may appear, as with any other surgical procedure, but such events (seroma, partial wound dehiscence, or hematomas) are not likely to interfere with sensory outcomes, as the results of this study demonstrate.

The information gathered in our study suggests that subjective perception of sensibility changes is not associated with objective alterations, although the former is more frequent. The patient’s subjective perception is undoubtedly an important factor to be considered, but this evaluation is beyond the scope of this study. After all, for the majority of patients, the satisfaction with improvement in body contour and self-image greatly outweighs the experienced sensory alterations [2,3,18].

In practical terms, the surgeon must limit the possible factors for sensory alteration to the technical aspects of the surgical procedure: incision selection, choice of plane for implant placement, and size of the implant to be used. These are the variables that can be modified by the surgeon in accordance with the desires, expectations, and possibilities of the patient.

Distinct surgical approaches to avoid sensory loss are advocated by different authors. On the basis of anatomic studies, Farina et al. [15] state that the fourth intercostal nerve reaches the left mammary gland at the 4 o’clock position and the right gland at the 8 o’clock position, thus supporting a medialized periareolar incision. This approach also was defended by Spear [19].

On the other hand, Schlenz et al. [14] report that medialized periareolar incisions increase the risk of nerve damage. After extensive anatomic dissections, Schlenz concluded that the main source of innervation for the NAC, the nerve fibers of the anterior cutaneous branch, presents a more superficial course within the subcutaneous tissue to reach the medial areolar edge. Accordingly, these nerves are best protected if incisions on the medial border of the areola are avoided.

Pitanguy [20] advocates the transareolar incision. Because the innervation shows a constant centripetal pattern, this approach would lower the risk of nerve lesions. Jaspars et al. [16], describing the lack of a consistent anatomic nerve distribution, suggest that a vertical approach (from a cranial or caudal direction) to the NAC would minimize the chance of nerve injury. More recently, Okwueze et al. [8] concluded that the periareolar incision produces less sensory loss than the inframammary incision.

Our study compared the periareolar approach with the inframammary approach and found no difference in terms of objective sensibility alterations. These findings agree with those presented by the pioneer work of Courtiss and Goldwyn [4], and more recently with those published in the study of Mofid et al. [9], which showed no difference in sensory outcomes among different incision approaches. This valuable information can help plastic surgeons and their patients in deciding whether a periareolar or inframammary approach would be more suitable.

As for the plane choice, submuscular placement is thought to minimize nerve damage [18,19], although some authors claim that there is no reason to presume that implant position, either subglandular or submuscular, should affect sensory innervation [9,18]. Notwithstanding this controversy, all the patients included in our study had their implants placed in a subglandular plane. Dissection was performed under direct vision (with the use of fiberoptic-assisted illumination) using both scalpel and blunt dissection. The pocket of undermining was large enough to accommodate the implants well without risk of creating creases and contour irregularities.

Based on the information provided in our study, implant size seems to play an important role in determining sensory changes. This was first pointed out by the studies mentioned earlier [4,9]. Because the implant volume determines the size of the pocket to be undermined, the risk of nerve lesion is greater with more extensive dissections, especially those in the lower quadrants of the breast [5]. The same size pocket undermined in a medium-sized breast with no final sensory alteration can presumably produce a permanent sensory impairment in a small-sized breast, caused by nerve section (neurotmesis) during the undermining.

In addition, sensory alterations may be caused by neurapraxis of the nerve fibers, due to excessive tension, if the implant is placed under a relatively small breast [9]. Other factors, such as the alleged higher innervation density of small breasts [6], may contribute to more noticeable sensory alterations in patients with smaller breasts.

In the view of the cited authors, the relative volume (implant volume divided by preoperative breast size) adequately corrects this analytical distortion. Higher values of this index are associated with an increased postoperative sensibility threshold, suggesting greater sensibility loss. For statistical inference purposes, however, our sample was not large enough to establish a maximum security limit for such an index (i.e., a value above which the procedure would be associated with prohibitive rates of sensory losses).

The concept of relative volume should not be regarded merely as a mathematical finding. Rather, it emphasizes the implications of choosing larger implants, especially for small-breasted women. The possible sensory complications that may arise from this choice should always be explained to the patient and discussed before surgery. The information provided in our study suggests that larger implants or smaller breasts show an increased association with postoperative sensory alterations, and plastic surgeons and their patients should be aware of this possibility.