Positive Results Using Variable Fixation in Medial Opening Wedge High Tibial Osteotomies in Patients with Unilateral Knee Osteoarthritis: An Observational Clinical Investigation

Abstract

Background: Medial opening wedge high tibial osteotomy (HTO) treats medial knee osteoarthritis by realigning the knee joint, though it still carries quite a high risk of complications. A new Variable Fixation Locking Screw technology, designed to gradually reduce construct stiffness and promote bone healing, aims to address these issues. This observational study evaluates the safety and effectiveness of this innovative approach in improving clinical outcomes. Methods: Data were prospectively collected on a cohort of the first ten consecutive patients (over 18 years of age) who underwent corrective medial opening wedge high tibial osteotomy using Variable Fixation Locking Screws (VFLSs). The procedure followed the standard surgical technique, with osteotomies stabilized using a Tomofix plate and a combination of standard locking screws and VFLSs. This study aimed to evaluate outcomes such as fracture healing, patient safety, and procedural success at 6 and 12 weeks and at 6 months. Results: No complications, side effects, or need for implant removal were observed. By six months, 70% of patients showed radiographic and clinical healing, and 100% of patients achieved full functional recovery without any issues like length discrepancy, instability, pain, or joint stiffness. Conclusions: This first clinical observation study indicates that Variable Fixation Locking Screws are safe and effective for medial opening wedge high tibial osteotomies, showing promising results in reducing the risk of delayed closure or non-closure of the wedge. Further studies with a larger patient population are needed to confirm their effectiveness.

Keywords: HTO; VFLS; Variable Fixation Locking Screw; dynamization; fracture healing; high tibial osteotomy; knee; osteoarthritis.

Figure 1

A conceptual schematic showing how the support provided to the cis cortex by the Variable Fixation Locking Screw evolves over time, along with its impact on interfragmentary movements (top graph) and strain (bottom graph). Initially, a stable and well-centered resorbable sleeve (yellow circle) minimizes both interfragmentary movement and strain. As the sleeve gradually degrades, the support from the VFLS progressively decreases, resulting in a controlled increase in interfragmentary displacement and strain (yellow arrow). This gradual change is limited by design, allowing the newly formed bone to complete its calcification and remodeling processes [14,18,19,20].

Figure 2

The figure shows 3 exemplary cases of HTOs that were treated with VFLS. The first image in the series shows the pre-operative planning in each case, followed by the X-ray checks post-operatively, after 12 weeks and 6 months. (A) 4 mm opening wedge, (B) 6 mm opening wedge, (C) 9 mm opening wedge.

Figure 3

This image illustrates the expected strain distribution within the osteotomy gap. Green areas indicate where the strain is expected to support new bone formation, while light-blue areas show strain levels that are likely too low to promote bone apposition (white). (A) Initial strain conditions at the start of treatment using both standard locking screws (LSs) and Variable Fixation Locking Screws (VFLSs). Strain levels with LS fixation decrease over time, potentially leaving parts of the gap unfilled for extended periods. (B,C) As the degradable sleeve of the VFLS resorbs, gap strain conditions evolve, progressively increasing the likelihood of reaching strain levels conducive to bone formation throughout the entire gap.