A modified minimally invasive osteotomy for hallux valgus enables reduction of malpositioned sesamoid bones

The current minimally invasive distal metatarsal osteotomy for hallux valgus (HV) is V-shaped, which prevents the correction of the rotational metatarsal head deformity and reduction of the sesamoid bones. We sought to determine the optimal method for sesamoid bone reduction during HV surgery. We reviewed the medical records of 53 patients who underwent HV surgery between 2017 and 2019 using one of three techniques: open chevron osteotomy (n = 19), minimally invasive V-shaped osteotomy (n = 18), and a modified straight minimally invasive osteotomy (n = 16). The sesamoid position was graded using the Hardy and Clapham method on weight-bearing radiographs. When compared to open chevron and V-shaped osteotomies, the modified osteotomy resulted in significantly lower postoperative sesamoid position scores (3.74 ± 1.48, 4.61 ± 1.09, and 1.44 ± 0.81, respectively, P < 0.001). Furthermore, the mean change in postoperative sesamoid position score was greater (P < 0.001). The modified minimally invasive osteotomy was superior to the other two techniques in correcting HV deformity in all planes, including sesamoid reduction.


Introduction
Hallux valgus (HV) surgery, also known as bunion surgery, is a commonly performed procedure by foot and ankle surgeons [1,2]. Patients present with a painful medial bump, a medial deviation of the first ray, and lateral deviation and pronation of the big toe [3]. Over the years, more than 150 open surgical techniques for correcting this deformity have been described [2,4]. Over the last decade, there has been a paradigm shift in bunion surgery [5], with minimally invasive approaches becoming increasingly popular [1,[6][7][8][9][10][11][12]. The main advantages of these new techniques are lower morbidity and shorter recovery times [13]. However, the reported outcomes have varied [1,[14][15][16][17]. The minimally invasive chevron and akin (MICA) procedure, described primarily by Vernois and Redfern [17], has become widely used. The main advantage of this procedure is that it is extra-articular, which reduces the likelihood of postoperative complications.
The success rate of HV surgeries has been correlated with the preoperative severity of the deformity. HV angles (HVA) greater than 37 or 40° have been reported as a risk factor for recurrence [18,19]. However, the HVA represents only one aspect of a three-dimensional deformity [20]. As the first metatarsal bone (MT1) shifts medially, the tendon and ligament insertions change their orientation. As a result, the generated muscle forces abduct and pronate the hallux and internally rotate the MT1. The MT1 head shifts further medially with respect to the hallux flexors, where the sesamoid bones are embedded. Consequently, the sesamoid 1 3 bones are repositioned laterally and drift dorsally. Up to 88% of HV cases present with an internally malrotated hallux on clinical examination [21]. The laterally displaced sesamoid bones can be clearly visualized on a dorsoplantar X-ray radiograph. Incomplete reduction of the laterally displaced sesamoid bones has been associated with recurrence [21]. Furthermore, unreduced sesamoid bones have been associated with joint arthritis and pain while walking [22,23]. Therefore, proper reduction of the sesamoid bones is essential in HV surgery.
As described by Vernois and Redfern, the minimally invasive distal metatarsal osteotomy is V-shaped. This configuration, as stated in previous publications, may limit the ability to correct the rotational deformity of the MT1 head [21,[24][25][26][27][28]. Consequently, the sesamoid bones have often been found to stay unreduced despite an open or close chevron osteotomy [28,29], which have been found to be associated with inferior clinical outcomes [17,18,22,23,28]. We recently developed a modification of the procedure in which a straight osteotomy, perpendicular to the MT1 shaft, is made instead of the V-shaped incision (Fig. 1). This allows the MT1 head to be de-rotated, thereby reducing the sesamoid bones to their normal position beneath the MT1 head. In this study, we compared the postoperative positions of the sesamoid bones following three surgical techniques: open chevron osteotomy, minimally invasive V-shaped osteotomy, and the modified straight minimally invasive osteotomy. We sought to determine the optimal method for sesamoid bone reduction in HV surgery.

Methods
Following the approval of the hospital ethical committee we reviewed the medical records of 53 patients who underwent HV surgery by a single surgeon between 2017 and 2019. The patients underwent surgery using one of three surgical techniques. In 2017, an open chevron osteotomy was performed on 170 patients with mild to moderate HV, according to the Nyska classification [30]. "Group C" consisted of the last 19 patients who underwent surgery using this method in 2017. In 2018, 18 HV patients were treated with a minimally invasive V-shaped osteotomy (MICA), forming "Group V." We included 16 HV patients in "Group M" who had surgery using the modified straight minimally invasive osteotomy in late 2018 and throughout 2019. (Figs. 1 and 2).
We included both male and female patients over the age of 15 years who had a mature bone structure (closed physis on preoperative X-ray radiographs). They all had preoperative weight-bearing orthogonal foot radiography available. Study exclusion criteria were immature bones, a history of multiple foot surgeries, Charcot foot or other structural foot abnormalities in addition to HV, metatarsus adductus associated with HV, and recent foot trauma. There is some debate on the precise cut-offs that should be used to define HV, with normal intermetatarsal angle (IMA) cut-off ranging from 8 to 12 [31][32][33][34][35][36]. Based on a few highly cited and popular publications we defined HV as an IMA greater than 8 degrees [31,[33][34][35][36]. The indication for surgery was pain resulting from a diagnosed HV that was not alleviated by non-surgical measures.
Preoperative and postoperative standing X-ray radiographs were evaluated for each patient. We used radiographs that were obtained at a mean of 12 ± 3 weeks postoperatively. Pre-and postoperative HVA and IMA were measured by a single surgeon (EP) using PACS software (Carestream Vue PACS, Fujifilm Corporation, Japan) [30]. We used the Hardy and Clapham method [35] to assess the position of the medial sesamoid bone on an anteroposterior radiograph of the foot. The position of the medial sesamoid on the dorsoplantar plane was determined relative to the centerline of the first metatarsal. Position I was considered normal. Position IV was defined when the first metatarsal midline crossed the medial sesamoid midline, and a displacement (positions V-VII) was graded based on the medial distance of the sesamoid location (Fig. 3).
The original V shaped percutaneous chevron osteotomy was previously described [6,9,14,17,37,38]. When conducting this procedure we adhered to the published technique guidelines, utilizing a dorsal comparably vertical limb and a plantar limb that was directed proximally to construct a v shape [38]. In the modification presented herein, the osteotomy was performed in a straight line, perpendicular to the metatarsal axis on the sagittal view, as shown in Fig. 2. Before fragment fixation, we supinated the big toe, pulling the MT1 head along with it, until fluoroscopy revealed that the sesamoids had returned to their normal position beneath the metatarsal head (Fig. 4). K-wires were then inserted into the metatarsal head, followed by cannulated screw fixation (Figs. 4 and 5). When needed, an Akin osteotomy was also performed [7]. Soft tissue procedures have been performed following osteotomies [27,29]-open chevron osteotomies were always followed by a medial capsular imbrication. In minimally invasive surgery this procedure was added when the first metatarso-phalangeal joint stayed incongruent after the completion of the osteotomy and fixation. The postoperative regimen included immediate weight-bearing with a flat DARCO shoe (MedSurg™, Huntington, WV). During the first follow-up visit, at two weeks, dressings were changed, and weight-bearing X-rays were taken. At 6 weeks, the K-wires were removed if necessary, and weight-bearing X-rays were taken again at 12 weeks.  The Fisher's exact test and the Student's t-test were used to compare categorical and continuous variables, respectively. An ANOVA test was used to compare the pre-and postoperative IMA, HVA, and sesamoid bone positions of patients who underwent the three procedures, followed by a post-hoc pairwise analysis when necessary. The IMA, HVA, and sesamoid bone positions of patients who underwent the three procedures were compared using a paired samples t-test before and after surgery. A P value of less than 0.05 was considered significant.

Results
Age, sex, and radiographic measurements of the study population are presented in Table 1. There were no statistically significant differences in the demographic variables or IMA between the three study groups (P > 0.05). HVA was the narrowest (i.e., a smaller deformity) in group C (open chevron osteotomy) (P < 0.01).
Overall, the mean preoperative sesamoid bone position score was 5.04 ± 1.26 and it did not differ significantly between the three groups (P = 0.16). Postoperatively, this score was significantly lower in Group M (1.44 ± 0.81, P < 0.001) compared to groups C (3.74 ± 1.48) and V (4.61 ± 1.09). While the sesamoid bone position score improved by 4 ± 1.37 points in Group M, the mean decreases (improvement) were only 0.89 ± 0.99 and 0.5 ± 0.71 points in groups C and V, respectively (P < 0.001) (Fig. 6). Group  M had the greatest mean decreases (improvement) in IMA and HVA (P < 0.01, Table 1).

Discussion
Our study showed that a modified straight osteotomy performed using a minimally invasive approach corrected the IMA and HVA in patients with HV while also reducing the laterally displaced sesamoid bones into their normal position. The modified osteotomy allowed us to address the three-dimensional configuration of the deformity and correct its rotational aspect. That resulted in more effective sesamoid reduction when compared to the open chevron osteotomy and the original V-shaped MICA ( Table 2). The significance of MT1 rotation during HV surgery has increased in recent years [25]. Residual postoperative lateral displacement of the sesamoid bones is associated with HV recurrence [18,19,21,25], walking pain, and arthritis [23]. Accordingly, several attempts have been made to correct the rotational component of the HV deformity and reduce the sesamoid bones into their natural position. Nyska et al. [39]. investigated various Ludloff osteotomy angles in an attempt to identify the optimal incision for correcting the pronation. Wagner et al. [25]. proposed an osteotomy technique to address the three-dimensional complexity of the HV deformity using a proximal rotational metatarsal osteotomy (PROMO). Okuda presented a proximal supination osteotomy that would simultaneously correct both the varus and the pronation of the MT1 [40]. Although effective, these are open surgical techniques, thus lacking the benefits of the minimally invasive approach.
The minimally invasive technique introduced by Vernois and Redfern [17] is composed of three basic elements: a percutaneous V-shaped distal osteotomy, lateral displacement of the head, and fixation of the new fragment configuration. These procedures, which can be combined with a bunion osteo-resection and an akin osteotomy, are performed through skin incisions of several millimeters in length. The benefits of a minimally invasive technique include reduced morbidity, shorter recovery time, less pain, and improved range of motion of the metatarsophalangeal joint [13]. In addition, the minimal skin incisions result in fewer skin complications and smaller scars [41]. Although the V-shaped osteotomy [17] enables the correction of both mild and severe deformities, it limits the surgeon to a single plane of correction. The de-rotation of the MT1 head and consequent correction of sesamoid position is not possible when the metatarsophalangeal center of rotation shift is insufficient for sesamoid reorientation. The modification described here eliminates the restriction imposed by the V-shaped osteotomy and enables the correction of the sesamoid bone position by de-rotating the MT1 head. In the current series of fifty-three patients, the straight osteotomy was the only technique that resulted in a successful sesamoid reduction. This method made it possible to combine the benefits of a minimally invasive procedure with the ability to correct the three-dimensional HV configuration. Disadvantages of the technique include the plantar or dorsiflexion displacement of the metatarsal head during the translation, as there is no V shape to prevent the displacement. Particular attention should be paid during the fixation, which should be performed under true lateral fluoroscopy. The V-shaped osteotomy offers two main advantages. First, when compared to a straight cut, the V shape creates a larger contact surface between the two bone fragments. Secondly, the V-Y configuration is thought to be more stable than two flat-shaped bones that could slide over each other. Nevertheless, we feel that these advantages are outweighed by the ability to manipulate the MT1 head in all planes, resulting in optimal correction. The shearing and rotational movements between the two bone fragments are eliminated with the eventual fixation using two cannulated screws.
This study had several limitations. Its retrospective nature prevented prospective patient randomization to the three procedure groups. The use of standing X-ray radiographs for sesamoid evaluation was also mandated by the study design, as this is the imaging modality most used for patients with HV at our medical center. However, standing CT scans could have better demonstrated the precise sesamoid position [25]. Moreover, a three dimensional imaging modality would have allowed us to calculate the correlation between the rotation correction extent and the sesamoid reduction. Since this modality was not available, this calculation was beyond the scope of this study. We could not state the exact rate of patients who underwent a medial imbrication as part of their MIS bony procedure. We did not present our patients' clinical outcomes or union rates since this was solely a radiographic study. Clinical follow-up, on the other hand, is of great interest, so we are planning a future study in which these data will be presented in detail.
In conclusion, although the straight osteotomy modification of the MICA procedure has the possible drawback of being a less stable construct, it enabled us to reduce the HV deformity in all planes and was the only method by which we were able to reduce the sesamoid bones into their normal position.
Author contributions EP: study design, surgery, and preparation of the first draft of the manuscript. NO: critical review of the manuscript and interpretation. DS: statistical analysis, manuscript preparation, critical review. AT: statistical analysis. RA: manuscript critical review. YB , VF: data collection and review of the manuscript. NM: study design.
Funding This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Conflict of interest
There are no competing interests to declare.
Ethical approval All protocols were conducted per relevant guidelines and regulations, a statement confirming all the methods were approved by the Institutional Ethical Committee (Meir Medical Center Institutional Review Board). The study was approved by the Meir Medical Center Institutional Review Board.