Background
Percutaneous forefoot surgery to correct hallux valgus (HV) is reported to have advantages over open surgery, such as fewer cutaneous/infectious complications, shorter procedural time, and quicker post-operative recovery [
1‐
3].
Distal first metatarsal osteotomies (DFMO) are normally indicated for treating moderate hallux valgus, with intermetatarsal angle between 12 and 20 degrees [
4]. Numerous percutaneous DFMO have been described using different shapes of osteotomy and with or without osteosynthesis [
4‐
6]. Although most authors performing percutaneous DFMO prefer to combine the osteotomy with a cannulated screw [
7], some techniques have been described using minimal fixation (Kirschner wire) or no fixation whatsoever [
3,
6,
8]. There have been few studies comparing DFMO techniques, as most publications report the results of one specific operative technique [
2,
4,
11,
12]. The few comparative studies, published to date, usually compare an open procedure with a percutaneous one [
9,
10].
On the other hand, most studies focus only on the anteroposterior (AP) X-ray view; stability in the sagittal plane is seldomly included. This could be due to the difficulty in taking any measurement on the lateral X-ray, as bony profiles might be hard to distinguish. However, as an alteration on the sagittal position of bony fragments can potentially affect the load distribution of the forefoot, it would be desirable to assess sagittal displacement. Recently, weight-bearing computer tomography has facilitated the assessment of the sagittal plane, but many professionals do not have it readily available yet and still rely on plain weight-bearing X-rays.
In the present study, set in an anatomy laboratory, we compared two common percutaneous distal first metatarsal osteotomies. The first is a technique described by Bösch in 1990 [
11]. It consists of a linear osteotomy at the metatarsal neck level using a Kirschner wire as a lever to lateralize the metatarsal head. The K-wire does not traverse the metatarsal head, but goes through the capsule of the metatarsophalangeal joint. The second procedure was a percutaneous chevron osteotomy, a V-shaped osteotomy at the metatarsal neck level without hardware stabilization. For both techniques, the authors allowed immediate ambulation using post-operative shoes that transfer weight-bearing to the hindfoot [
3]. Even with this shoe, the axial forces acting on the forefoot during full weight-bearing ambulation are still remarkable [
13] and could potentially affect non-fixated osteotomies.
The first objective of our study was to develop a systematic and reproducible way of measuring displacement on a lateral foot X-ray. The second objective was to assess the behavior of these two surgical techniques under a controlled axial load.
Discussion
Hallux valgus is a frequent deformity of the first digit of the foot, with progressive abduction and pronation of the first phalanx. There is adduction, elevation, and pronation of the first metatarsal (metatarsal primus varus) concurrent with lateral capsule retraction of the metatarsophalangeal (MTP) joint [
8]. In addition to its esthetic effect, hallux valgus changes the foot dynamics, leading to what Viladot defined as a first ray insufficiency [
15]. Inflammation of the bursa overlying the medial eminence of the metatarsal head causes pain and discomfort, and irritation of the dorsal medial cutaneous nerve of the hallux [
6,
17]. First radius insufficiency can also lead to second and third metatarsal head overload [
18,
19]. Therefore, when surgery is indicated, it is essential to correct the metatarsus primus varus as well as the hallux valgus [
20]. For moderate hallux valgus (intermetatarsal –IMTT- angle < 20 degrees), this can be achieved with a DFMO [
3]. For greater deformities, other techniques such as proximal osteotomy of the first metatarsus can be indicated [
21].
Many open surgery procedures have been described for osteotomy of the distal first metatarsal, but not until the 1980s did minimally invasive and percutaneous procedures start to appear [
22]. The authors believed that the benefits from percutaneous hallux valgus surgery (esthetic improvement, soft tissue conservation, shorter surgical time, shorter recovery time, and better post-operative pain control) outweigh the potential risk of neurovascular or tendon injury, which is minimal [
23]. The first widely disseminated percutaneous procedure, published by Bauer et al. [
8], was a variation of Reverdin osteotomy (medial closing wedge osteotomy at the metatarsal distal third) together with an Akin osteotomy, adductor tenotomy and bunionectomy [
6]. None of the osteotomies was fixated with hardware. This procedure corrects both the Hallux Valgus angle (HVA) and MDA but does not improve the IMTT angle, and it is not recommended for cases with IMTT angle greater than 12–13 degrees [
5,
24].
To achieve greater IMTT angle correction, Bösch et al. [
11] designed a new DFMO, not taking a wedge but using a Kirschner wire as a lever to help move the metatarsal head laterally. This procedure was later popularized by Giannini et al. [
3] as Simple, Effective, Rapid and Inexpensive technique (SERI). Giannini et al. [
3] published some very good radiological and functional results, although they described dorsal displacement of the metatarsal head in a very few patients (1%). To avoid this, they recommended a thick K-wire (2.0 mm). However, as the K-wire does not traverse the metatarsal head, its thickness is not necessarily key to the stability of the osteotomy, and SERI should be considered a non-fixated technique. Other authors performing SERI have found much greater metatarsal head dorsal displacements (12–20%) [
25,
26], even up to 60% [
4]. This displacement could lead to shortening of the first metatarsal, which could produce secondary transference metatarsal pain.
Percutaneous chevron osteotomy was first described by Vernois and Redfern [
7,
27]. It is a V-shaped osteotomy in which the first part is dorsal, short, and vertical and the second part is plantar, longer, and almost horizontal [
17]. It allows the HVA, MDA and IMTT angles to be corrected. Vernois and Redfern described percutaneous chevron osteotomy with a screw fixation between the bony fragments, but we used no hardware fixation. Austin [
28], who first described the chevron osteotomy during the 1960s, considered the V-shaped osteotomy inherently stable, and open surgery studies show that the chevron osteotomy confers no advantage in fragment fixation [
29,
30]. For this reason, and in order to compare the stability of the osteotomy shape between Bösch and chevron osteotomies under similar conditions, we decided to perform the percutaneous chevron osteotomy without fixation.
Radwan et al. [
10] compared the SERI technique with an open chevron, both fixated only with a K-wire. However, to our knowledge, no comparisons between Bösch and percutaneous chevron osteotomies have been published. Most of the studies we reviewed only focused on the AP X-ray view, measuring HVA, DMA and IMTT angle, and did not assess stability in the sagittal plane. Some authors [
3,
4,
9,
31] report dorsal malunion but do not specify how they measured it. Only Faour-Martin et al. [
25] specify that they measured the percentage of the transverse diameter of the osteotomy line on lateral X-ray, finding 29% of dorsiflexion on average, but this only assessed the bony displacement and did not consider angulation. We have described a method that allowed us to measure both the fragment distance and the angulation systematically on lateral X-ray. To our knowledge, this is the first study to take into account changes in MDA in the sagittal plane.
With the Bösch technique, we observed a plantar displacement of 4.3 mm and a plantar angulation of 0.8 degrees with no load. As the load on the foot increased progressively, the plantar displacement decreased (2.2 mm at 60 kg axial load), but the plantar angulation of the metatarsal head continued to increase up to 6.8 degrees at 60 kg load. This variability during the stress test shows that Bösch osteotomy is highly unstable in the sagittal plane.
With chevron osteotomy there was less fragment displacement. With no load, there was a dorsal displacement of 0.5 mm, which remained quite stable, and at 60 kg load, the displacement was a 0.1 mm. Chevron displacement was significantly less than Bösch technique when the load was less than 30 kg. However, from 30 kg, as the plantar displacement of Bösch technique decreased, this statistical difference disappeared. The 0.1 mm displacement at 60 kg load in chevron osteotomy was lower than the 2.2 mm in Bösch technique, but the difference was not significant.
On the other hand, chevron osteotomy gave 7.3 degrees plantar angulation, which remained quite constant, reaching 7.8 degrees at 60 kg load (mean 6.9 degrees over all loads). Therefore, although there was less displacement of the bony fragments, chevron osteotomy failed to control the metatarsal head angulation, even though this angulation change remained stable during the loading test.
Studies investigating both Bösch and chevron techniques typically report dorsal metatarsal head displacement [
3,
22,
31]. However, we observed plantar displacement in all cases. This could be explained as follows: since the plantar displacement decreased as the load on the foot increased, allowing patients to weight-bear post-operatively probably helps to displace the osteotomy upward.
Being a study based on lateral foot X-rays, the measurements might not be as reliable as those achieved with a weight-bearing computed tomography, especially as there might be a variability in the C-arm or foot placement, and also because the assessment of a lateral X-ray might be confusing due to the overlapping with the minor metatarsal bones. Further research into the measurement of MDA and fragment displacement in the sagittal plane, in which inter-observer variability is measured, is now necessary.
Although our study could have revealed greater differences between these two surgical procedures if more subjects had been examined, the fragment angulation in the sagittal plane shows unacceptable instability in both techniques. A 5–6 degree change in metatarsal head angulation could disturb the metatarsal formula and lead to iatrogenic metatarsalgia, or potentially to limitation of the flexion–extension of the metatarsophalangeal joint. We believe both techniques could benefit from sturdier fixation such as screw fixation.
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