The Effect of Anterior Closing Wedge Slope-Reducing Osteotomy on Coronal Alignment-Effect of Osteotomy Technique, Starting Point, and Degree of Correction.

BACKGROUND

Techniques for anterior closing wedge slope-reducing osteotomy (ACW-SRO) remain variable regarding management of the tibial tubercle and osteotomy starting point. Moreover, the potential unintended effect on coronal alignment has not yet been determined.

PURPOSE

To determine the effect of the ACW-SRO technique and starting point on coronal alignment in knees with an elevated posterior tibial slope (PTS).

STUDY DESIGN

Descriptive laboratory study.

METHODS

Full-length lower extremity computed tomography scans were retrospectively reviewed in patients presenting to our level 1 trauma center to identify patients with an elevated PTS of ≥12° without secondary trauma to the lower extremity. Materialise software was used to generate 3-dimensional models and simulate supratubercle, transtubercle, and infratubercle ACW-SROs. Six osteotomies per tibia were simulated, with 3 using an anterior start point centered at the tibial tubercle, and 3 using a start point at the perfect anterior-posterior mid-axis point of the tibia (-AP). The PTS was corrected to 6° universally. Coronal alignment was measured using the medial proximal tibial angle (MPTA) before and after osteotomy.

RESULTS

Eleven tibias were included, with a mean native PTS of 14.5° (range 12°-18°). Transtubercle-AP and infratubercle-AP osteotomies had the largest mean ΔMPTA of 1.72° of varus (range, 0°-3°; = .03) and 1.82° of varus (range 0°-3.5°; = .03), respectively. There was a strong positive correlation between the degree of PTS correction and ΔMPTA. Supratubercle-AP, transtubercle-AP, and infratubercle-AP had the strongest correlations (0.77, = .005; 0.66, = .03; 0.68, = .02, respectively). The mean ΔMPTA increased varus in all 6 osteotomies in tibias with PTS corrections of ≥9°.

CONCLUSION

Isolated ACW-SRO can affect coronal alignment of the knee by introducing additional varus, particularly in transtubercle and infratubercle osteotomies utilizing the AP starting point. This is especially apparent in tibias requiring larger PTS correction. The tibial tubercle-referenced starting point may minimize coronal changes.

CLINICAL RELEVANCE

This simulated study showed that coronal alignment is affected by the ACW-SRO technique and starting point in patients with elevated PTS. All osteotomies created additional varus, which must be considered when planning PTS correction.