IOFix™ with plate construct is similar to locking plate construct for Lapidus bunionectomy procedure outcomes

Abstract

Background

The Lapidus bunionectomy has evolved with advanced fixation constructs since its first description. These new techniques have aimed to reduce complications such as non-union or hardware related symptoms. The IOFix™ system, an intramedullary device that has been designed to enhance stability and compression, may offer outcomes that are comparable to traditional medial locking plate with lag screw constructs.

Purpose

To compare outcomes of the Lapidus bunionectomy using the IOFix™ and plate construct versus a traditional medial locking plate with a plantar lag screw.

Methods

This IRB-approved retrospective case-control study reviewed 46 patients (23 per cohort) treated by a single surgeon between 2014 and 2022, with minimum 24-month follow-up. Patients underwent Lapidus bunionectomy using either an IOFix™ and dorsal plate (intervention) or a locking plate with plantar lag screw (control). Outcome measures included incidence of non-union, hardware removal, loss of correction (1st IMA >8° or HAA >20°), and AOFAS Hallux scores. Statistical analysis used two-tailed t-tests and Fisher’s exact test with significance set at P < 0.05.

Results

All cases in both IOFix™ and locking plate groups achieved a union rate of 100 %. There were no reported infections, non-unions, or revision surgeries in either cohort. Hardware removal rates were not significantly different between IOFix™ (26 %) and control (13 %) groups (P = 0.46), and only the dorsal plates were removed. There were no reported cases of removal of the IOFix™ device. AOFAS scores improved significantly in both groups post-operatively (P < 0.0001), with no significant difference between groups pre- or post-operatively. There were no significant differences in demographic data, loss of correction, or complication rates between groups.

Conclusion

The IOFix™ and dorsal plate construct offers comparable outcomes to traditional locking plate with lag screw fixation in the Lapidus bunionectomy, with similar union rates, clinical outcomes, and hardware-related complications. These findings suggest that IOFix™ is an effective alternative fixation method. Further studies with larger sample sizes and long-term follow-up are warranted.

1 Introduction

The Lapidus bunionectomy procedure has become increasingly popular in the past two decades. This procedure was originally described by Paul Lapidus in 1934 as a bunionectomy and reduction of the first intermetatarsal angle via fusion of the first metatarsal base with the 1st cuneiform. With the advent of osteosynthesis, fixation methods improved outcomes. Non-union, loss of correction and other forms of complications of the procedure appear to have decreased particularly with locking plate fixation as compared to the traditional one, two or as many as three screw fixation constructs across the first metatarsocuneiform joint.

The evolution of Lapidus fixation has paralleled shifts in biomechanical understanding. Li et al. described how modifications to implant design, positioning and early weight bearing have influenced modern fixation strategies . In addition to choice of implant, surgical technique plays a critical role in outcome. Mani et al. reported a non-union rate of only 2.7 % using a modified Lapidus technique with shear-strain-relieved bone graft and compression aimed to enhance osseous contact of the first metatarsocuneiform joint .

Locking plate fixation with a plantar lag screw has been shown to allow for earlier weightbearing and similar complication rates when compared to crossed lag screws, supporting its use as a traditional construct in Lapidus procedures . Despite these improvements, incidence of non-union persists; most long-term studies reveal it is 2.5–15 % . Symptomatic hardware removal rates are typically an issue. Recent biomechanical studies have demonstrated the advantages of plantar plating, which positions fixation along the tension side of the construct. This method has been shown to improve compression across the arthrodesis site, increase stability, and reduce rates of symptomatic hardware removal when compared to dorsomedial constructs ^, . These insights have influenced the development of newer fixation systems, including the IOFix™, which is designed to optimize load distribution and minimize complications by offering an alternative to traditional plate-and-screw constructs.

The IOFix™ construct is essentially a screw within a screw. This design has been shown to increase compression forces across the joint, which may theoretically enhance fusion rates. In a study by Weigert comparing IOFix™ to a headless compression screw construct for ankle arthrodesis, the IOFix™ group demonstrated a more even distribution of compression forces, resulting in a larger contact area at the arthrodesis site . Similarly, a cadaveric study by Parker et al. found that the IOFix™ construct produced significantly greater average compression force (3.95 kg vs. 2.4 kg) and contact area compared to a conventional lag screw .

The IOFix™ construct has also demonstrated promising results in other foot and ankle procedures. In a study evaluating its use in triple arthrodesis, Loomans et al. reported a union rate of 90 % . This is notably higher than union rates reported with conventional fixation techniques, where nonunion has been cited in 29.9–41 % of cases ^, . Similarly, in an isolated talonavicular joint arthrodesis utilizing IOFix, the nonunion rate was 9 %, markedly lower than the 20.4 % nonunion rate reported in the literature with traditional fixation methods ^, .

The purpose of this case-control study is to evaluate traditional locking plate and plantar lag screw construct (control) for the Lapidus bunionectomy procedure compared to the IOFix™ and plate construct (intervention). We hypothesized that the IOFix™ with plate construct would demonstrate comparable union rates, radiographic correction, and clinical outcomes to traditional locking plate with plantar screw fixation in the Lapidus bunionectomy.

2 Methods

Patients from one surgeon’s practice were reviewed from 2014 to 2022 (minimum follow-up of 24 months from the index procedure) that underwent the Lapidus procedure as a non-inferiority IRB approved study. Patients were divided into two cohorts based on the fixation construct used at the time of surgery, as documented in the operative report and implant logs. The first 23 consecutive cases utilized the traditional medial locking plate with plantar lag screw (control group), and the subsequent 23 consecutive cases used the IOFix™ with plate construct (intervention group). All procedures were performed by the same surgeon following identical postoperative protocols. Outcome measures were the incidence of non-union, loss of correction (1st Intermetatarsal angle >8° or Hallux Abductus angle > 20°), hardware removal and AOFAS Hallux score. Patients who had this data recorded were included and those where this information was missing were excluded. Also excluded were those patients who only had isolated IOFix construct without a plate in the intervention group and those with only plate fixation in the control group.

Post-operative care for both groups was the same: all were kept non-weightbearing for four weeks in a below-knee cast or boot and then weight bearing another four weeks in a below-knee cast boot. Formal physical therapy was then initiated pending x-ray signs of bony healing between eight and twelve weeks.

The Lapidus bunionectomy procedure is performed by an incision extending from the 1st MPJ dorso-medially, proximally to the medial aspect of the 1st cuneiform. The medial eminence of the 1st metatarsal head is exposed, resected at the appropriate level and then a lateral release/tenotomy of the adductor hallucis, extensor hallucis brevis and lateral sesamoid complex is performed. Next deep dissection is carried down to the 1st tarso-metatarsal joint, which is then disarticulated. The articular surfaces are exposed, cartilage resected, and the joint surfaces fenestrated or drilled with a 2.0 mm drill bit or 0.062” K-wire. The 1st metatarsal is then repositioned to reduce the 1st intermetatarsal angle and hallux valgus via pronation and manipulation. The reduced deformity is temporarily stabilized with 0.062” K-wires. Autogenous bone is maintained for supplemental bone graft if needed.

If using a medial locking plate, a plantar lag 3.5 mm screw is placed first, oriented from plantar medial at the base of the 1st metatarsal directed into the first and even 2nd cuneiform when multi-joint fusion is necessary. Then a four-hole trapezoidal locking plate is placed dorso-medially fixated typically with three 2.7 locking screws, two proximal and one distal in the dorsal hole ( Fig. 1 ).

When using the “IOFix™ 2.0” construct, a 4.5 mm “post” is first place in the 1st metatarsal base at least one cm proximal to the joint angle slightly dorsal distal. A clearing tool is used to create a groove in the 1st metatarsal so a cannulated screw can be placed through the post into the 1st cuneiform ( Fig. 2 ).

Next a two or four-hole straight plate is place dorso-medially and one 2.7 mm locking screw proximally is placed into the 1st cuneiform and a non-locking 2.7 mm screw is used to secure the 1st metatarsal distal to the IOFix™ construct ( Fig. 3 ).

With both techniques, closure is done in layers. Repair of the Tibialis insertion is performed if needed as well as the 1st MPJ capsule. Standard bunion dressing is applied. Post-operative care is as listed above. Statistical analysis was performed using Excel ™ and STAT SAK™, with two-tailed T-test and Fisher’s exact test where appropriate, with significance set at 95 % Confidence Interval and P < 0.05.