1.                   Introduction

A normal intermetatarsal angle between the I^st and II^nd metatarsal (IM-angle) is defined to be below 10 ^̊ and a normal hallux angle is a valgus of 15 ̊ or less. Moderate to severe hallux valgus is indicated by an IM-angle of 16 - 20^° and a hallux valgus angle of 31^° - 50^°. [1-7]. There are more than 130 methods described for correction of hallux valgus. Only few of them use osteotomies in the shaft. The severe or extreme deformities can also be corrected with proximal ostetomies or arthrodesis of the TMT-I joint [8]. The criteria for an optimum operation are: Correction the pathological I^st intermetatarsal angle and the hallux valgus angle. A pathological pronation rotation should be normalized and a pathological DMAA has to be be corrected to an amount of less than 15 ̊ valgus. [1-7]. A metatarsus primus elevatus should be corrected by plantarization of the distal fragment. The length of the first metatarsal has to be preserved. A slight shortening can be achieved in cases of a diminished ROM in the I^st MPJ. Shortenings could cause transfer metatarsalgia.

Furthermore, facilitate immediate mobilization and immediate loading of the operated foot rapid bone healing and avoid joint stiffness, swelling and M. Sudeck. The use of K-wires should be avoided because transfixion of the MPJ I and protrusion out of the toe for weeks may cause stiffness, infection and patient discomfort. Patients should be mobilized without crutches, cast or forefoot unloading shoes, but with elastic shoes with full loading. Patients should exercise their I^st MPJ to increase the ROM.

The most popular methods for the correction of moderate to severe hallux valgus are the Scarf osteotomy, the closing-wedge osteotomy, the opening wedge osteotomy, the crescentic ostetomy and the proximal chevron osteotomy. Each of the most popular operations show potential problems due to their physical characteristics: The Scarf osteotomy was described by Burutaran 1976 [9]. It is a z-shaped shaft osteotomy for IM angles up to 16° [10]. The DMAA can also be improved. The problems of this method are shortening and troughing. The potential of correction of the IM angle is limited and there is almost no potential of correction of a pronation rotation. The procedure is technically difficult and has a complication rate of 19% with reoperations needed up to 11% [11]. Coetzee wrote 2003: “Scarf osteotomy has multiple potential pitfalls”, he reported complications in 47% [12]. The closing wedge osteotomy is also technically demanding and entails the risk of shortening in average 5 mm (from 1mm to 26 mm!), dorsal malalignment, and transfer metatarsalgia. The most important disadvantage is the need of unloading or a cast for 6 weeks as reported by Trnka et.al 1999 [13].

Wanivenhaus et. al reported transfer metatarsalgia in 27% [14]. The opening wedge osteotomy leads to a significant increase of the DMAA which is equal to the closing wedge osteotomy. The osteosynthesis with a low-profile plate has to be unloaded with a special shoe for 6 weeks as reported [15,16]. The so called proximal crescentic osteotomy is a curved osteotomy and surgeons use a curved saw blade as described by Mann in 1992 [17,18]. The osteotomy is stabilized by a screw or plate and needs an unloaded mobilization for 6 weeks. The further disadvantages are the danger of dorsal malunion, Mann reported 28% of dorsiflexion malunion [17] and a worthening of the DMAA due to physical circumstances [19-21]. The proximal chevron osteotomy, popularized by Sammarco 1998 [22] is frequently stabilized by a special designed plate to facilitate early mobilization with partial weight bearing. There was observed no dorsiflexion malunion [23]. The results were reported to be equal to the results of the Ludloff ostetomies [24]. Disadvantages are the low correction potential in terms of DMAA, pronation rotation and plantarization.

There is not one operation described in literature, which meets all the desired criteria without significant disadvantages [25]. The disadvantages of greatest importance are for the authors the necessity of unloaded or partial unloaded mobilization for 6 weeks in all types of base osteotomies, the danger of dorsiflexion malunion, the worthening of the DMAA and the quite high percentage of possible transfer metatarsalgia. To quote Xiaojun Duan 2011 [26]: “The rate of complications in hallux valgus surgery ranges from 10% to 55%. No single procedure can be recommended given the complexity of the deformity.” The rates of reoperations range from 5% to 9% [27].

2.                   Materials and Methods

In the year 2007 and 2008 we tried to develop or modify an operation method to come as close as possible to an optimal correction of all criteria which lead to the moderate to severe hallux valgus [28]. The goal was to avoid the use of K-wires and to shorten the I^st metatatarsal as few as possible. Patients should load their feet immediately after the operation with full weight bearing in an elastic comfort shoe.

We applied our successful concept in the treatment of the mild to moderate hallux valgus [25] with a simple transverse osteotomy fixed with an intramedullary angle stable locking plate to the base osteotomy. To reach these criteria without any accompanying disadvantages, we had to adapt the fixation devices and increased length and thickness of the plates in order to increase stability. We developed a set of 36 mm long intramedullary located and angle stable from cortex to cortex transfixed titanium plates. These plates are fixed intramedullary with 2 or 3 screws with a diameter of 3.5 mm and the osteotomized distal metatarsal fragment is mounted in an angle stable manner on the head of the plate with additional 2 screws of the same diameter. The distal fragment can be placed in stepless fashion in optimum position in terms of lateralization, plantarization, derotation, improvement of DMAA regardless the quality of contact between the bone partners. There are plates with different offsets available, which permit the metatarsal to be shifted 2 mm, 4 mm or 6 mm (Figure 1).

Surgical Technique: Skin incision of about 5 to 6 cm, or as a minimally invasive approach with an incision of less than 2 cm, with additional stab incisions for the lateral release, the transfixing locking screws and the optional Akin osteotomy. Then longitudinal incision of the capsule. The pseudoexostosis is removed by a chisel or power saw and a bone cut is performed approximately 2.5 cm distal to the TMT-I-joint as a transverse osteotomy with a lazy-L at the plantar third of the I^st metatarsal (Figure 2).

A generous soft tissue release is performed. The distal metatarsal fragment is now brought to the optimum position. The plate is pushed into the intramedullary space. For this maneuver we use an inserter, which is also a target device for drilling and screwing. The drilling takes place from medial through the medial cortex, through the plate (drilling through holes in the plate) and through the lateral cortex (Figure 3 and Figure 4). There are three threaded holes in the proximal part of each plate. The drill diameter is 2.5 mm and the screw diameter is 3.5 mm.

The screws fix the plate angle-stable, due to the corresponding threads in the plates. Screw lengths are usually 12 mm, 16 mm and 18 mm. In some cases, we used only 2 proximal screws. The distal fragment is then aligned and all parameters are corrected. The plate has a straight head with threaded holes for two 3.5 mm screw heads. After the distal fragment is drilled with a 2.5 mm drill, the first metatarsal is now screwed in an angle stable manner to the plate head. The screw length here is usually 16 mm (Figure 5). Given the extremely rigid fixation only a point contact or even no contact is adequate. As a result, a shift of 100% of even more is possible. To demonstrate the extreme potential of the technique, we show a situation which is a result of a too vigorous displacement. The distal fragment was placed beside the proximal fragment with a gap of about 2-3 mm. The patient was mobilized with full load despite a bilateral operation and despite the special situation of a non-contact in the osteotomy site of the left foot. The gap healed within 6 month and after that time the patient started running marathon. (Figures 6-9). In cases of interphalangeal hallux valgus an Akin osteotomy is performed [29]. The osteosynthesis can be fully loaded immediately after surgery and patients can resume their usual activities immediately using postoperative flexible and elastic so-called “medic ballerinas” (Figure 10).

3.                   Results

We included 48 patients with 55 operated feet into this retrospective study. The patients were operated between January 2011 and December 2012. There were 42 females and 6 males.

81.25% (39 patients) underwent simultaneously other forefoot surgeries like Akins, FDL-Transfers and PIP arthrodesis for hammertoes, metatarsal shortening osteotomies for the lesser metatarsals or repair of tailor’s bunions. Ages ranged from 28 to 86 years (mean age 56 years). The follow up was performed after 72 months in average, from 61 to 84 months. (Figures 11- 30).

We documented pre- and postoperatively and in the follow up evaluation for this study the following parameters: AOFAS Score, the IM angle, the HV angle, the DMAA angle, the angle of pronation rotation of the big toe, the circumference of the foot in the area of the metatarsal heads, the plantarization of the first metatarsal and the amount of shortening of the first metatarsal. X-rays were performed preoperatively, 1st day postoperatively, 6 weeks post operation and at the follow up. The patients were asked about their satisfaction with the operation. As analysis method we used the t-test. The AOFAS Score improved from 48.15 (between 26 and 75) to 98.36 (between 76 and 100) which is highly significant (t = 39.55, p < 0.001) (Table 1). (Figures 31, 32). The IM angle improved from mean 17.15 ̊ (from 12 ̊ to 20 ̊) to 4.60 ̊ (from 0 ̊ to 8 ̊) which is a difference of mean 12.55^° and highly significant (t = 74.76, p < 0.001) (Table 2). (Figure 33, Figure 34). The Hallux valgus angle (HV) improved also highly significantly (t = 38.52, p < 0.001) from 33.15 ̊ preoperative (from 22 ̊ to 50 ̊) to 9.13 ̊ (from 0 ̊ to 19 ̊) which is a difference of mean 24.02 ̊ (Table 3). (Figures 35, 36). The pronation malrotation decreased from 21.67 ̊ (0 ̊ - 54 ̊) to 1.47 ̊ (0 ̊ - 5 ̊) which is also highly significant (t = 11.04, p < 0.001). (Table 4). (Figures 37, 38).

The DMAA angle decreased from mean 21.65 ̊ (0 ̊ - 40 ̊) to 4.09^° (0 ̊ - 6 ̊) statistically high significant (t = 12.24, p < 0.001). (Table 5). (Figures 39, 40). The sesamoid position was improved from mean 5.07 (3-7) to mean 1.13 (1 - 2). This is also statistically high significant (t = 17.28, p < 0.001). (Table 6). (Figures 41, 42) The circumference of the forefoot measured in the area of the metatarsal heads was preoperative 27.01 cm (24.0 cm to 28.0 cm) and postoperative 25.62 cm (22.1 cm to 27.4 cm) which is a difference of 1.39 cm and statistically significant (t = 20.02, p < 0.001). (Table 7). (Figures 43, 44). The I^st metatarsal head was plantarized mean 2.4 mm (0 mm - 3.7 mm). The shortening of the first metatarsal was 0.8 mm (between 0 mm and 2 mm). 93.75% of the patients (45 patients) were very satisfied or satisfied with the operation. 6.25% rated the operation as fair (3 patients) and no patient was unsatisfied. Except of the removal of osteosynthesis material in 4.16% (2 patients) no reoperations were necessary.

Complications: We recorded no cases of transfer metatarsalgia or recurrent hallux valgus. Other complications were swellings in almost 100%, delayed wound healing in 2 cases (4.16%) with help of antibiotics. There were no cases of malunion, no deep infection. We had to remove the osteosynthesis material (one screw or all screws and the plate) in 2 cases (4.16%) due patient psychological discomfort with foreign material in the bone.

4.                   Discussion

The shaft/base osteotomy fixed with a very stable intramedullary angel-stable locked plate is able to correct all parameters which lead to a moderate to severe hallux valgus. Our goal was only to achieve a good reposition of all particular deformities despite of good bone contact between the osteotomy partners. We did not try to achieve bone compression to avoid shortening. Bone healing occurred in all cases, we did not observe any nonunion of , the osteotomies, even in cases of poor contact of the osteotomized bone partners and even if a gap of some Millimeters resulted. The intramedullary plates are very rigid titanium implants and we could mobilize all patients the same day after the operation. Even the bilaterally operated patients loaded their feet with full weightbearing in a so-called medic ballerina elastic comfort shoe. Bone healing occurred usually within eight weeks. There was no changing of angles or hardware position between the postoperative and the follow up x-rays. As the study demonstrates all desired parameters of a moderate to severe hallux valgus could be normalized or improved statistically significant. These parameters are: IM angle, HV angle, DMAA, Sesamoid position, pronation malrotation, circumference of the foot, elevation of the I^st metatarsal. We noticed a minimum shortening of the I^st MPJ. 93.75% of the patients were very satisfied or satisfied with the result of the operation.

Ethical Clearance: The authors declare no conflict of interests. The informed consent was obtained from all patients before the operation.

Table 1: AOFAS before and after OP.

Table 2: IM angles before and after OP.

Table 3: HV angle - difference before and after OP.

Table 4: Pronation angles before and after OP.

Table 5: DMAA before and after OP.

Table 6: Sesamoid-Positions before and after OP.

Table 7: Circumferences before and after OP.

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