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Biplanar Chevron Osteotomy Caio Nery, Rui Barroco and Cibele Réssio Foot Ankle Int 2002 23: 792 DOI: 10.1177/107110070202300903 The online version of this article can be found at: http://fai.sagepub.com/content/23/9/792

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FOOT & ANKLE INTERNATIONAL Copyright © 2002 by the American Orthopaedic Foot & Ankle Society, Inc.

Biplanar Chevron Osteotomy Caio Nery, MD.; Rui Barraco, MD.; Cibele Ressio, M.D. Sao Paulo, Brazil

patients are disabled.v-'" The use of internal fixation by means of K-wires, absorbable pins, or screws is highlighted as the most significant improvement to the tech nique. 4,12.13,16.17,25.30,38.44,46.50,52

ABSTRACT Results of biplanar chevron osteotomy performed on patients with mild-to-moderate hallux valgus deformity with an increased distal metatarsal articular angle (DMAA) are shown. The study included clinical data of 32 patients (54 feet) who had completed a 2-year follow-up, and radiological data of these 32 and other 29 patients (50 feet) for a total of 61 patients (104 feet, 53 right and 51 left). There were 59 females and two males with ages varying from 11 to 66 years. According to the AOFAS' Hallux Rating, the preoperative average score (50) improved to 90 (average score after the surgery). The hallux valgus angle was improved from an average of 25° to 14°, the first intermetatarsal angle from 12° to 8° and the DMAA from 15° to 5°. At the end of treatment, 94% of patients were classified as having grade 0 or I sesamoid lateral sub-luxation. Given improvement in angles and 90% of patients satisfied with an average AOFAS postoperative score of 90, the technique seems indicated for treatment of symptomatic hallux valgus deformity with increased DMAA.

Since Pigott's observations on the evolution of juvenile hallux valgus, the importance the relationship of the articular surface of the proximal phalanx to the articular surface of the first metatarsal head has been demonstrated, as well as the vector of acting forces in this region to the onset of lateral deviation of the metatarsal head." A lateral deviation of the first metatarsal distal articular surface would be expected, in response to varus of this bone in association with valgus of the hallux. This "minor" deformity would be responsible for the poor results in a large number of patients submitted to other surgical procedures rather than to those focusing on correction of the distal metatarsal articular angle. 9- 11,18,26,27 We added the excision of a dorsal, medially based wedge to the chevron osteotomy proposed by Kenneth Johnson,'3.19.20 transforming it into a biplanar chevron osteotomy."

INTRODUCTION

MATERIALS AND METHODS

Hallux valgus deformity can be treated through various techniques for distal and proximal osteotomies. 5,6.14.22.24,28, 29.31.32,36,40,43.48.51 Chevron osteotomy has been widely used all over the world in the past two decades to correct mild-to-moderate hallux valgus detorrnlties.'> It has also been modified to improve its intrinsic stability, decrease complications. and decrease the time

Sixty-one patients (104 feet) two male (3.3%) and 59 female (96.7%), participated in the study. The average age was 35.4 years (range, 11 to 66 years). They all presented mild-to-moderate hallux valgus and were submitted to the same biplanar chevron osteotomy at dates between 1996 and 2000. Besides the usual characteristics of hallux valgus deformity, the criterion to include patients in this study was a OMAA >8°, a level considered to be above normal. 35 Pre- and postoperative radiographic examinations were performed following the classical AP and lateral weightbearing views. The hallux valgus angle (HVA), the first intermetatarsal angle (IMA), the distal metatarsal articular angle (OMAA), the sesamoid deviation (SO), and the relative length of the 1- and II radii of the foot (1-2RL) were measured, in both the pre- and postoperative radiographs. 33-37,41,47

Foot and Ankle Clinic, Federal University of Sao Paulo - Escola Paulista de Medicina Corresponding Author: Caio Nery, M.D. Rua Afonso Bras, 817 04511-011 Sao Pauio, SP, Brazil Phone: 55 11 3842.8333 Fax: 55 11 3842.8573 E-mail: [email protected]

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Foot & Ank/e /nternationa/No/. 23, No. 9/September 2002

B/PLANAR CHEVRON OSTEOTOMY

The DMAA was obtained by measuring the angle between the perpendicular to the medial diaphyseal axis of the first metatarsal and the line determined by the extreme ends (medial and lateral) of the distal articular surface of this bone.

1. A 5 em-long medial incision is made to expose the first MTP joint. 2. Subcutaneous dissection is performed to isolate and protect the neural cutaneous branches. Dorsal and lateral dissections are made very carefully to prevent injuries to the lateral vascular supply to the metatarsal head. 3. A V-shaped capsulotomy is made, keeping a "V" capsular flap attached to the base of the proximal phalanx of the hallux (Fig. 1). 4. The medial prominence of the metatarsal head is exposed and removed with a saw used for small

bones, dorso-plantarward in line with the medial edge of the foot. 5. The geometric center of the head is marked in the region of the exostectomy and from this point the segments of the osteotomy will be drawn. The lower segment is cut parallel to the inferior surface of the foot (Fig. 2) while the upper segment is almost perpendicular to the plantar plane of the foot (Fig. 3). This procedure makes the lower segment more horizontal than in the original technique, while the upper segment is more vertical (the angle between them is 80°), providing a larger surface of inferior contact where the interfragmentary screw will be fixed. 6. According to preoperative measurements of the DMAA, a small wedge of medial base is removed from the capital fragment so that this fragment can be rotated (Fig. 4). To determine the correct size of the medial wedge to be removed to correct the DMAA, one can use the trigonometric formula:

Fig. 1: A V-shaped capsulotomy is made, keeping a "V" capsular flap attached to the base of the proximal phalanx of the hallux.

Fig. 2: The lower segment of the Chevron osteotomy is cut parallel to the inferior foot surface.

Fig. 3: The upper segment of the osteotomy is almost perpendicular to the foot plantar plane.

Fig. 4: A small wedge of medial base is removed from the capital fragment so that this fragment can be rotated.

Operative Technique


793

794

NERY, BARRaCO AND RESSIO

Wedge Width :::: tan DMAA x Metatarsal Head Width;45 draw the wedge corresponding to the measured DMAA over the AP radiographic image of the first metatarsal head, measuring its base in the medial border of the metatarsal head or, by direct vision during the operation, make the distal cut parallel to the distal metatarsal articular surface and the proximal cut perpendicular to the long axis of the first metatarsal" (Fig. 5). Width of wedge ranged from 2 to 6 mm in our study. 7. According to preoperative measurements of the IMA, the distal fragment is displaced laterally (Fig. 6).33 8. Following the traditional technique for interfragmentary synthesis described by AO, a hole is made for a minifragment screw (2.7 mm). This hole is made keeping the distal inclination at 10° and the lateral at 15° to increase impaction of the fragments and to protect the articular area from the end of the

Foot & Ankle InternationalNol. 23, No. 9/September 2002

screw (Fig. 7). Hebert's screws can be used in this part of the surgery, since they have the advantage of being kept inside the bone-fragments. 9. The metaphyseal triangle on the medial aspect of the osteotomy is removed clearing bony fragments of the first metatarsal. 10. The superficial planes of tissue are sutured as usual. After removing the tourniquet, a compression dressing is made to keep the hallux in alignment and to achieve correction by means of a interdigital spacer. The patient is allowed to bear weight as tolerated in a postoperative shoe. Only 32 patients (54 feet) completed the 2-year minimum follow-up (average two years and 11 months; maximum four years and two months) and were submitted to clinical evaluation according to the Hallux Metatarsophalangeal Interphalangeal Scale of the American Orthopaedic Foot and Ankle Society." Data on

Fig. 6: According to preoperative IMA measurements. the distal fragment is displaced laterally at the same time that it is internally rotated.

Fig. 5: The distal cut of the wedge is made parallel to the distal metatarsal articular surface and the proximal cut is made perpendicular to the long axis of the first metatarsal.

Fig. 7: Placement of the screw following the interfragmentary technique.


Foot & Ank/e /nternationa/lVo/. 23, No. 9/September 2002

B/PLANAR CHEVRON OSTEOTOMY

Table 1

Grade Grade Grade Grade Total

0 I II III

Pre-op n 2 41 48 13 104

Pre-op % 1.9 39.4 46.2 12.5 100.0

Post-op n 57 41 6 0 104

Post-op % 54.8 39.4 5.8 0.0 100.0

the other 28 patients (51 feet) (average follow-up of 1.1 year) were used only for numeric calculation (statistical analysis). The results were analyzed using non-parametric tests taking into consideration the nature of distributions or the variety of measurements. Student's "t" test was used, the null hypothesis being at 0.05 or 5%. RESULTS

Clinical Results

Of the 32 patients who completed two years followup, three (9.4%, three feet) were dissatisfied with the procedure (patient #2, right foot; patient #14, left foot; patient #22, left foot) due to the undercorrection obtained. All of them required re-operation to correct the deformity. The main reason these patients required reoperation was the variation between their own two feet. Patients #2 and #14 who had bilateral surgery were satisfied with the correction obtained in one of their two feet; patient #22 has a normal right foot. It was the comparison between their feet, rather than pain or functional impairment, that had these patients to ask for a new intervention. Another three patients (9.4%, four feet), (patient #9, both feet; patient #24, right foot; patient #29, right foot) complained of pain in the dorsal aspect of the distal metaphysis of the first metatarsal, where a prominent head of a screw could be found. These patients required removal of the screws to feel free of pain, but they were not considered to have bad results. At the end of the average follow-up period of two years and 11 months (minimum of two years and maximum of four years and two months), we found no case of transfer metatarsalgia among these 32 patients reviewed. They complained of stiffness of the first MTF joint and pain under the first metatarsal head at the early beginning of their recovery but, with time and along with the progress of the rehabilitative program, such complaints became rare, disappearing at last. The intensity and persistence of these symptoms were considered to be compatible with those in other large series of patients submitted to the classic chevron osteotomy.33,3437 On the basis on the AOFAS Clinical Rating System, the preoperative average

No Changes n 2 11 2 0

No Changes % 1.9 10.6 1.9 0.0

795

score was 50 (range, 44 to 62) and the postoperative average score was 90.5 (range, 47 to 100). Except for the three patients with bad results (9.4%), due to undercorrection the remaining 29 (90.6%) said they would undergo the same procedure again.

Radiographic Results

To improve observation of the surgical technique, all 61 patients (104 feet) were included in the part of the study. Both pre- and postoperative radiographs were available for all feet, and final measurements were made after complete healing of the osteotomy site (eight weeks after surgery).9-11,33-37A1 The timing of final individual evaluation for this analysis, however, varied from 11 weeks (patient #60) to 23 months (patient #33) with an average of 13 months. The preoperative average hallux valgus angle (HVA) was 25° while the postoperative was 14°. Preoperative average first intermetatarsal angle (IMA) was 12° and the postoperative average was 8°. The preoperative average angle of the DMAA was 15° while the postoperative average DMAA was 5°. The average correction was 11 ° for the HVA, 4° for the first IMA, and 10° for the DMAA. The preoperative average of the relative length of 1st and 2nd metatarsals was zero, while the postoperative average was -2 mm. This little amount of shortening of the first metatarsal could be expected considering the geometry of the osteotomy and the relationship of the of bony surfaces at the osteotomy site. As the lateral border of the first metatarsal did not experience shortening, removal of the medially-based wedge will promote internal rotation of the distal fragment instead of shortening of the metatarsal. The comparison of preand postoperative values using Student's t-test was statistically significant and showed p