Chamfered Uniform Diameter Multizone Single-Screw Fixation in Minimally Invasive Bunion Surgery: A Case Report of Radiographic Stability and Osseous Integration

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AUTHORS

Keith A. Crenshaw, DPM, MS, AACFAS^1*
Jeffrey E. McAlister, DPM, FACFAS^2†

ABSTRACT

Minimally invasive bunion surgery continues to evolve, with implant design intended to improve fixation stability and reduce hardware prominence. This case report uses a chamfered uniform diameter multizone single-screw construct for hallux valgus correction, designed to achieve rotational stability through cortical and cancellous purchase in MIBS. A 57-year-old female with symptomatic right hallux valgus deformity underwent transverse first metatarsal osteotomy and Akin osteotomy after failed conservative treatment. Fixation was achieved with a 4.0-mm chamfered uniform diameter multizone screw placed under fluoroscopic guidance using a guidewire trajectory intended to maximize cortical purchase. Serial postoperative radiographs showed maintained correction without hardware loosening, subsidence, or failure. The intermetatarsal angle improved from 14.9° preoperatively to 4.6° at 6 months, with progressive osseous healing on serial postoperative radiographs. The uniform diameter multizone single-screw construct in this case report was associated with radiographic stability and osseous regeneration following minimally invasive bunion surgery.

INTRODUCTION

Minimally invasive bunion surgery (MIBS) continues to evolve, but fixation strategy remains an important consideration in stability and complication risk. Prior studies have identified both implant configuration and surgical technique as important contributors to adverse outcomes, including complications associated with two-screw constructs^1-3. Recent implant refinements have shifted toward single-screw designs intended to increase cortical engagement, improve rotational stability, and reduce hardware prominence through a multizone design and beveled head that seats more flush with cortical bone⁴.

Within this context, multizone screws represent a newer fixation concept that aims to combine cancellous and cortical purchase while limiting excessive compression across the osteotomy. However, their performance in MIBS remains incompletely defined. This case report describes the use of a uniform diameter multizone single-screw construct for MIBS and presents fluoroscopic follow-up demonstrating fixation stability and osseous integration.

CASE REPORT

A healthy 57-year-old woman with right hallux valgus deformity, body mass index of 30, and nonsmoking status presented with shoe-related pain rated 5/10 on the visual analog scale (VAS), affecting ambulation and activity. Upon physical examination, the patient was reducible with no crepitus at the first metatarsophalangeal joint or at the interphalangeal joint. There was pain on palpation of the medial first metatarsal head with soft-tissue edema. Radiographic evaluation of the patient's hallux valgus deformity found an intermetatarsal angle (IMA) of 14.9° and a 5 tibial sesamoid position (TSP) (Figure 1). After exhausting conservative treatment, she underwent right MIBS with transverse first metatarsal osteotomy and medial-based wedge osteotomy of the proximal phalanx.

SURGICAL TECHNIQUE

The patient was placed supine on the operating table. The operative extremity was prepared and draped in standard sterile fashion. The operating room setup was optimized with a mini C-arm fluoroscopy positioned on the patient’s right side, the back table on the left, and the surgeon at the foot of the operative table. No tourniquet was used, and all Shannon burr operation was accompanied by normal saline irrigation.

A marking pen was used to identify the incision sites using anatomic landmarks and fluoroscopic guidance. A medial incision was made at the surgical neck of the first metatarsal, proximal to the medial protrusion of the metatarsal head. A second incision was made over the first tarsometatarsal joint, dorsal to the medial plantar vein and proximal to its junction with the medial marginal vein (Figure 2).

Through the distal incision, blunt dissection was carried to the bone, and the periosteum was elevated dorsally and plantarly with a mosquito clamp. A Shannon burr was then used to create a transverse osteotomy under fluoroscopic guidance. The mosquito clamp was inserted into the osteotomy site to release the lateral periosteum, allowing improved mobilization of the metatarsal head. A K-wire was then placed into the dorsal-medial first metatarsal head to be utilized as a joystick for rotational correction. A hemostat was inserted into the metatarsal intramedullary canal and levered laterally, translating the head until the medial cortex aligned with the lateral cortex of the metatarsal shaft. The hallux and first metatarsal head were then held in the corrected position with dorsal pressure plantar to the metatarsal head, rotational correction using the joystick, and lateral translation with the hemostat.

A K-wire for the 4.0 mm chamfered uniform diameter multizone chamfered screw (MiniLock MIS chamfered screws, Fusion Orthopedics, Mesa, AZ) was inserted through the proximal incision at the first metatarsal base, midline on lateral view, and aiming for the center of the metatarsal head. The wire was advanced under fluoroscopy toward the lateral cortex with tactile feedback to avoid penetrating the cortex until verified fluoroscopically. Its angulation was confirmed to engage the lateral cortex at approximately 50% of the metatarsal shaft, to improve stability by increasing the size of the cortical purchase zone (CPZ). This technique is deemed the 50% rule for wire placement⁵. Before cortical purchase, a lateral fluoroscopic view was obtained to confirm sagittal alignment of the guidewire and first metatarsal head position and to avoid dorsal or plantar translation or angulation. The wire was then advanced distally into the metatarsal head.

A second guidewire was placed parallel to the first, just distal to it, to improve rotational stability during screw placement. The initial wire was then used for drill guidance and screw insertion. Fixation was performed under fluoroscopic guidance to confirm that no distraction or displacement occurred during insertion. Once the screw was seated with the chamfered head flush to the medial cortex of the first metatarsal base, the temporary fixation K-wires were removed.

The hallux valgus angle was then reassessed, and an Akin osteotomy was performed to aid in deformity correction. Under fluoroscopy, a medial incision was made, and an oblique medial-based wedge osteotomy was completed.
A K-wire for a 3.0 mm compression screw was placed perpendicular to the osteotomy.

Once satisfied with deformity correction and achieving anatomic alignment, all incisions were irrigated and closed with 3-0 nylon suture. The standard postoperative protocol was used: immediate weight-bearing as tolerated in a controlled ankle motion boot for 2 weeks, followed by 3 weeks in a postoperative shoe, and return to stable shoe gear by week 5. Once the sutures were removed at the first postoperative visit (12 days), the patient was advised to perform range-of-motion exercises to the first metatarsophalangeal joint.

Preoperative weight-bearing anteroposterior and lateral radiographs showed an IMA of 14.9° (Figure 1). At the first postoperative visit (12 days), weight-bearing radiographs confirmed stable fixation without hardware loosening, subsidence, or failure. Serial radiographs were then obtained at 5 weeks, 3 months, and 6 months (Figure 3), showing progressive osseous regeneration with maintenance of IMA from 4.4° at 12 days to 4.6° at 6 months.

DISCUSSION

This case report evaluated the surgical technique and radiographic outcome after hallux valgus correction using an innovative uniform diameter multizone single-screw construct for MIBS. Several aspects of the procedure warrant emphasis. A single-screw construct may preserve more medial eminence from the metatarsal shaft for resection, as described by Blitz et al, who introduced the term “Medial Ledge Resection Triangle” (MLRT) and reported that it is larger with a single-screw construct than with a two-screw construct⁴. Although fixation is reduced, two-screw constructs have been associated with a higher risk of metatarsal fracture, possibly due to decreased CPZ real estate³. A single-screw construct may increase the length of the CPZ, whereas two screws can create two cortical penetrations that may function as stress risers and increase fracture risk⁶. In the surgical technique described here, we applied the 50% rule for guidewire placement in the CPZ, targeting approximately 50% of the metatarsal shaft under fluoroscopic guidance. If the wire does not reach at least 50% of the metatarsal, early cortical contact is likely, and the trajectory should be adjusted to remain within the safe zone to maximize CPZ⁵.

The single-screw construct may also provide more space in the metatarsal head for positioning and lateral callus formation. This pattern has been described as first metatarsal regeneration with lateral bone deposition⁷. Radiographs showed lateral callus formation by 3 months and complete osseous bridging by the
6-month follow-up. Schnepp et al reported that radiographic union of more than 2 cortices was present in 90% of patients at 6 months, with a mean union time of 13 weeks, and that union was not associated with the degree of first metatarsal head translation, which is consistent with the present findings⁸.

The stability was appreciated as the patient was instructed to perform immediate weight-bearing as tolerated in a CAM boot, then transitioned from boot to postoperative shoe at the first postoperative visit. Then the patient is transitioned to a stiff-soled shoe by 5 weeks. The intermetatarsal angle improved from 14.9° to 4.6°, which is consistent with published MIBS outcomes⁹. Correction was maintained throughout the postoperative period without recurrence or hardware complications.

Recent reports have noted that single-screw constructs may carry risks of instability and nonunion compared with two-screw constructs, and these concerns should be considered when selecting a fixation strategy. Many reported complications in the MIBS literature have been attributed to surgical technique, which is important given the recognized learning curve of approximately 35.5 cases to plateau. The learning curve underscores the importance of technical precision and patient selection^1,10.

This case report has limitations inherent to a single-subject, single-surgeon, single-institution report. Therefore, the findings should be interpreted as hypothesis-generating rather than definitive. The main contribution of this report is the demonstration of stable fixation without deviation, loosening, or fracture using an innovative uniform diameter multizone screw in MIBS. The construct was associated with stability and osseous regeneration in this case.

This case suggests that a single-screw construct with a uniform diameter multizone cortical and cancellous purchase can support osseous regeneration through stable fixation in MIBS. The screw design provides uniform advancement with a uniform diameter multizone dual-thread profile intended to enhance rotational stability while limiting compression across the construct.

CLOSING REMARKS

As MIBS technology and technique continue to evolve, future studies will help clarify whether single-screw or two-screw constructs are preferable and which patients are best suited for each approach. Future studies should consider the comparison of single compression, non-compression, and uniform diameter multizone screw fixation on MIBS outcomes, and better understand the role of the uniform diameter multizone screw. Further work is also needed to define whether age, bone density, or comorbidity thresholds can help optimize outcomes. Additional studies should examine postoperative protocols and their relationship to function and recovery.

Technical pearls emphasized by this case include:

FIGURES

Figure 3. Post-operative AP radiographs at 12 days (IMA 4.4°) (a), 5 weeks (stable fixation) (b), 3 months (lateral bone callus development) (c), and 6 months (complete osseous bridging) (IMA 4.6°) (d) of the right foot following single uniform diameter multizone screw fixation for MIBS, callus formation developing at 3 months, and complete osseous union achieved at 6 months.

References