The effect of screw type on the biomechanical properties of SCARF and crescentic osteotomies of the first metatarsal

Comparison of contact surface areas of metatarsal diaphyseal osteotomies for correction of hallux valgus: Experimental study

OBJECTIVE

This study aimed to determine, pre-correction, the potential change in the osteotomy-site bony contact surface area that would occur during standard metatarsal diaphyseal procedures with the Baran-Unal modification of Mau osteotomy and then to compare it, post-correction, with the actual osteotomy-site bony contact surface area changes for a standard degree of deformity correction.

METHODS

A total of 30 standard, same sized, biomechanically equivalent, left first metatarsal sawbones were included in this experimental study. They were divided equally into five groups for each of the planned osteotomy techniques: Myerson's modification of Ludloff, Mau, scarf, Offset V, and Baran-Unal modification of Mau osteotomy. The normal osteotomy for each sample was considered as the control, while the corrective osteotomy was the test. Computerized tomography scans and three-dimensional (3D) reconstruction imaging were performed for objective and accurate measurements. The techniques of the osteotomy and post-corrective osteotomy bony contact surface areas were investigated by the two independent research assistants.

RESULTS

There was a statistically significant difference between the contact surface area changes of all pre- and post-corrective osteotomy groups (P<0.05). When the pre- and post-correction contact surface areas of any one group were compared with the other groups, the differences were or were not statistically significant. Mean differences between pre-correction and post-correction areas for Ludloff, Mau, scarf, Offset V, and Baran-Unal osteotomies were 180.7, 122.3, 226.2, 191.9, and 68.9 mm2, and the percentages of area loss were 22.9%, 15.5%, 28.6%, 24.3%, and 8.7%, respectively. The most bony contact area was found in the scarf osteotomy group (mean pre-correction area: 490.5 mm2 and mean post-correction area: 264.3 mm2), but the Baran-Unal modification group has significantly the highest post-correction bony contact area among the all other groups (mean pre-correction area: 413.3 mm2 and mean post-correction area: 344.4 mm2).

CONCLUSION

Metatarsal diaphyseal osteotomies for hallux valgus deformity have the potential not only for deformity correction, but also for contact surface area preservation. This study reaffirms the considerable potential of this new Baran-Unal modification to confer outstanding contact surface area values, even with the operative correction of hallux valgus deformity.

Comparison of Three-Dimensional Displacement Among Different Metatarsal Osteotomies

Hallux valgus is a slowly progressing complex 3-dimensional biomechanical process. Therefore, precise understanding of 3-dimensional deformity is essential for satisfactory clinical result. Uniplanar correction on anteroposterior view of foot would be insufficient, and rotation on frontal plane as well as sagittal alignment should also be well corrected. This article will review the 3-dimensional components of bony displacement in different surgical methods for hallux valgus correction.

Correction of moderate to severe hallux valgus with isometric first metatarsal double osteotomy

BACKGROUND

The operative treatment for the moderate to severe bunion continues to present challenges. The indications for a single, double, or triple first ray osteotomy remain controversial. In addition, it is not clear whether an opening wedge osteotomy leads to clinically relevant arthritis at the first metatarsophalangeal joint. However, it is this theoretical concern that has led the authors to develop an isometric correction of the first ray.

METHODS

Thirty-two patients underwent operative correction of hallux valgus with a double osteotomy of the first metatarsal using an opening wedge proximally and a closing wedge distally. The mean follow-up period was 59.3 months with a range of 55 to 65 months.

RESULTS

The 1-2 intermetatarsal angle preoperatively was a mean of 18.9 degrees (range 17-23), correcting postoperatively to a mean angle of 8.6 degrees (range 5-12), for an average correction of 10.4 degrees (range 6-16). The postoperative AOFAS scores were 39.4 out of 40 points for pain, 42.4 out of 45 points for function, and 15 points for alignment. The total score was excellent with 94.2 out of 100 possible points. Radiographic union occurred in all cases. There was one case of painful edema of the foot and two cases of early avascular necrosis (AVN) diagnosed by residual pain at the hallux metatarsophalangeal joint and transient osteopenia of the metatarsal head on radiographs. No late sequelae associated with AVN such as arthritis or metatarsal head collapse were noted with long-term follow-up. These healed within months without specific treatment.

CONCLUSION

A double osteotomy of the first metatarsal with a nonlocking, low-profile plate was an effective procedure for correcting severe hallux valgus that carried a low complication rate and high patient satisfaction. It has clear advantages over isolated opening wedge procedures, including potentially better correction especially in those bunions associated with an increased distal metatarsal articular angle.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Quantitative analysis of the long- and short-arm crescentic shelf bunionectomy osteotomies in fresh cadaveric matched pair specimens

Two variations of crescentic shelf osteotomies have been described for the treatment of moderate to severe hallux abductovalgus: a short arm and a long arm. This study tested the hypothesis that the short-arm osteotomy will have a greater moment to failure and angular stiffness than the long arm. Eighteen first metatarsal specimens were dissected from 9 matched pairs of fresh frozen cadaveric specimens. One metatarsal from each pair received a short-arm osteotomy, whereas the other received a long-arm osteotomy. Each osteotomy was fixed with 2 screws. The short arm was fixed with 1 oblique screw and 1 dorsal-to-plantar screw. The long arm was fixed with 2 dorsal-to-plantar screws: 1 at the proximal aspect and 1 at the distal aspect of the shelf. Each specimen was loaded in a materials testing machine to measure moment to failure and angular stiffness. The base of the first metatarsal was potted and load applied to the plantar aspect of the metatarsal head at a constant rate until failure of the osteotomy. The mean maximum moment to failure of the short arm was significantly greater than the long arm (2.04 ± 0.96 Newton meter [Nm] vs. 1.48 ± 0.67 Nm, P = .03). The mean angular stiffness was significantly greater for short arm versus long arm (23.8 ± 19.11 Nm/radian vs. 0.98 ± 9.08 Nm/radian, P = .01). We report statistically significant data supporting the short-arm crescentic shelf osteotomy to have a greater moment to failure and angular stiffness compared with the long-arm crescentic shelf osteotomy.

Biomechanical consequences of first metatarsal osteotomy in treating hallux valgus

BACKGROUND

Among the numerous osteotomies for correction of hallux valgus, the modified chevron is known for its good intrinsic stability and the scarf for its large corrective potential. An intermediate design, the reversed-L osteotomy, has been developed to combine these competing biomechanical objectives. The purpose of this in vitro study was to compare the structural and local biomechanical performance of these three designs.

METHODS

Stiffness, cortical bone strains (a factor relevant to bone remodeling), strength and failure mode of the scarf, modified chevron and reversed-L osteotomies were measured on human specimens in two different loading configurations.

FINDINGS

The scarf osteotomy caused significant changes in stiffness and cortical bone strains with the proximal apex being at the origin of bone failure. The chevron and reversed-L had a generally comparable response to the intact bone. The chevron specimens failed by pivoting of the distal fragment, and the reversed-L by pivoting or fracture.

INTERPRETATION

This is the first study to investigate the cortical bone strain changes induced by these invasive osteotomies. Alterations from the intact bone response could be directly related to the design of the osteotomy. Notably, the critical weakening proximal apex of the scarf is avoided in the reversed-L, leading to results comparable to the chevron. This study provides support in favor of the intermediate design of the reversed-L as an effective compromise between the competing biomechanical objectives of corrective potential and mechanical stability.

Biomechanical properties of new mini compression screws

BACKGROUND

The aim of the current study was to compare the compression forces achieved by the new commercial mini compression screws in cortical and cancellous bone.

MATERIALS AND METHODS

The following screws were tested: AO partially threaded 4-mm cancellous screw, AO 3.5- and 2.7-mm cortical screws (Synthes - USA) , self-tapping cannulated 3-mm VisAntares (EOS - France), 3- and 2.3-mm Omnitech (Biotech - France), 3-mm Barouk (DePuy - France), and 3-mm Bold screws (Newdeal - France). The compression forces of screws in bone were tested using a load cell between pieces of longitudinally-split sheep tibias as a cortical and cancellous bone model.

RESULTS

The AO 3.5-mm, 2.7-mm cortical and 4.0-mm partially threaded cancellous headed screws provided significantly (p < = 0.05) better compression forces than all the tested headless screws, both in cortical and cancellous bone. A loss of compression was noted when the headless screws were totally countersunk.

CONCLUSION

The cortical and cancellous screws with heads provided superior compression than headless screws.

CLINICAL RELEVANCE

Headed screws may be preferable to headless differential pitch screws in situations where compression is important ie, arthrodeses or fracture fixation. Care should be taken not to countersink the headless screws during insertion into cortical bone.

Screw versus plate fixation of proximal first metatarsal crescentic osteotomy

BACKGROUND

Hallux valgus associated with metatarus primus varus is a deformity that disrupts normal foot function. Standard treatment has often included distal or proximal metatarsal osteotomy with or without a distal soft tissue procedure. The intrinsically unstable proximal crescentic osteotomy relies on operative fixation for stability. This study examined the strength of fixation of a single screw versus a plate for stabilization of proximal first metatarsal crescentic osteotomies for correction of hallux valgus.

MATERIALS AND METHODS

A crescentic osteotomy was performed on nine pairs of fresh/frozen cadaveric feet. The distal fragment was rotated laterally and the osteotomy was temporarily stabilized with a Kirschner wire. The osteotomized metatarsal fragments were fixed with a cancellous screw on one side and single plate on the contralateral side. Each specimen was loaded in a mechanical testing machine, and its response was measured by monitoring the opening of the osteotomy and change in alignment of the fragments. Position and alignment of the proximal and distal fragments were calculated.

RESULTS

All of the measures of fixation strength were statistically greater in specimens treated with a plate rather than with screw fixation. Plate fixation provided approximately twice the resistance to disruption of the osteotomy under cyclic loading conditions.

CONCLUSION

The dorsal plate is biomechanically more stable than a single cancellous screw when applied to proximal crescentic osteotomies.

CLINICAL RELEVANCE

The greater stability of the plate construct may be helpful in selecting the fixation device for these osteotomies.

Evaluation of surgical experience and the use of an osteotomy guide on the apical angle of an Austin osteotomy

BACKGROUND

Distal osteotomies of the first metatarsal are commonly used to correct hallux valgus deformities. Of the distal osteotomies, the Austin osteotomy is popular among foot surgeons on an international level. The precision of the osteotomy is important to achieve a congruous osteotomy.

OBJECTIVES

The purpose of this study was to examine the effects of experience and technique on creating a precise Austin osteotomy.

METHOD

Three individuals with varying levels of experience (student, resident and podiatric physician) created Austin osteotomies in metatarsal sawbones, using three different techniques (freehand, guide wire and osteotomy guide). The medial and lateral apical angles were measured, and the mean, standard deviation, and range of the angles were calculated. The differences between medial and lateral angles were also calculated.

RESULTS

The results indicated that the mean and range of the angles varied considerably with the freehand and guide wire techniques at all experience levels. The angles were accurate and consistent for all experience levels; however, when an osteotomy guide was used. The use of an osteotomy guide also noticeably reduced the number of divergent and convergent osteotomies.

CONCLUSIONS

The use of an osteotomy guide consistently resulted in a more precise Austin osteotomy for all experience levels.

Minifragment screw fixation of the Scarf osteotomy

BACKGROUND

Various techniques have been used for internal fixation of Scarf osteotomies. Stability of fixation plays an important role in determining the outcome. We prospectively studied 23 consecutive cases of hallux valgus treated with a scarf osteotomy, which were internally fixed with AO mini fragment screws. The aim of our study was to evaluate the clinical efficacy of the AO mini fragment screw used as fixation device in Scarf osteotomy.

MATERIALS AND METHODS

Twenty-three feet (1 male, 16 female) were evaluated. Bilateral procedures were performed on six patients. Mean age was 46 years. The mean followup was 18 months. One surgeon performed all the procedures.

RESULTS

43.5% of the patients were very satisfied, 52.2% were satisfied and 4.34% were not satisfied. All osteotomies united without any hardware complications. The mean global AOFAS score improved significantly from a preoperative score of 55 points to 91.95 (p < 0.001). The intermetatarsal, hallux valgus angle, and DMMA improved from the mean preoperative values of 15.9 degrees, 31.2 degrees, and 14.1 degrees to 9.1 degrees, 15.2 degrees, and 8.4 degrees, respectively (p < 0.001 for all). One patient developed a superficial wound infection, which responded to antibiotics and one patient developed a painful spur at first MTPJ.

CONCLUSION

We conclude that this is a safe and simple technique of fixing a Scarf osteotomy. It is cost effective, provides stable fixation and maintains correction until the osteotomy unites.

Scarf osteotomy - Is it the procedure of choice in hallux valgus surgery? A preliminary report

Many procedures are described in the literature for the surgical management of hallux valgus. There are over 130 surgical procedures described but the surgeon usually limits these to a few which he is comfortable with and which gives the best aesthetic and functional result to the patient. There is ever rising enthusiasm among orthopaedic surgeons regarding diaphyseal osteotomy ever since Burutaran described the procedure in 1973. Weil in United States and Barouk in Europe popularized the technique. Scarf is a double chevron diaphyseal osteotomy which is inherently more stable than other osteotomies on the first metatarsal and allows early return to work. The author reports his early experience with SCARF osteotomy, which is a comparatively new technique for hallux valgus correction which was done in Ibri Regional Hospital in the Sultanate of Oman. All patients who presented with symptomatic hallux valgus were taken up and there were three patients who required surgical intervention for hallux valgus. The purpose of this study was to find its effectiveness in terms of stability of the osteotomy and early return to work. Proximal phalangeal osteotomy was not found necessary in none of the three cases operated by us. Scarf osteotomy is safe and found to give better aesthetic and functional result and early return to work. All our three patients had good functional recovery and early return to work.

Midshaft first-ray osteotomies for hallux valgus

In this article, the authors describe the indications, contraindications, surgical technique and its fixation considerations, postoperative care, results, and potential complications of the offset V and the traditional Z osteotomies. Because of its versatility, inherent stability, minimal first metatarsal shortening, good intermetatarsal reduction, and ease of rigid internal fixation, shaft osteotomies are gaining popularity as procedures for the correction of hallux valgus. Strong and stable internal fixation allows for earlier functional recovery and primary bone healing. Shaft osteotomies can provide predictable and rewarding results for the patient and surgeon for the correction of hallux valgus.

Stability of a cannulated screw versus a Kirschner wire for the proximal crescentic osteotomy of the first metatarsal: a biomechanical study

The purpose of this study was to compare the stability of a Kirschner wire (K-wire) versus a single cannulated screw for fixation of the proximal crescentic first metatarsal osteotomy. Seven matched pairs of fresh-frozen human cadaver first metatarsal specimens were dissected out en bloc at the first metatarsal-medial cuneiform complex; right and left specimens were randomized as to fixation. In screw specimens, a cannulated screw was mounted from the proximal medial side of the metatarsal, traversing osteotomy and engaging the lateral diaphyseal cortical bone. In the corresponding specimen, a K-wire was placed from the distal medial metatarsal cortex oriented as close to the longitudinal metatarsal axis as possible. Using a materials testing machine, a continuous load was applied to the plantar aspect of the metatarsal head at a rate of 5 mm/min until a displacement of 10 mm was reached. The following parameters were measured: initial stiffness of the entire specimen, stiffness of the osteotomy, the force required to create a 1-mm displacement, the force required to create a 0.15-mm gap across the osteotomy, and the ultimate force to create the 10-mm displacement. Both specimen and osteotomy stiffness were found to be significantly higher for screw fixation versus the K-wire (P <.05). Although there was also a difference in the force-to-failure load in favor of screw fixation, this result was found not found to be statistically significant.