Influence of Joint Line Level on Clinical Outcomes and Range of Motion in Total Ankle Arthroplasty

Abstract

Category: Ankle Arthritis; Ankle Introduction/Purpose: Restoring the native joint line correlates with better clinical outcomes in total knee arthroplasty. Yet, the effect of joint line elevation on clinical outcomes after total ankle arthroplasty (TAA) remains unclear. A previous study reported that pre- and post-TAA joint line heights, as measured by the joint line height ratio (JLHR), were elevated compared to non- arthritic ankles. However, the clinical impact of this has yet to be determined. Therefore, this study assessed the relationship between the TAA joint line level with post-TAA range of motion (ROM) and PROMIS scores. We hypothesized that an elevated joint line would be associated with restricted post-TAA dorsiflexion and worse postoperative PROMIS scores. Methods: This is a single-center review of 150 patients who underwent primary TAA. Patients with (1)fibular or medial malleolar osteotomy, (2) component subsidence, and (3) incomplete radiographs or outcome scores were excluded. Demographic data, surgical protocol, pre- and postoperative radiographs, and 1-year postoperative PROMIS scores were reviewed. Radiographic measurements included JLHR, pre- and post-TAA tibiotalar dorsiflexion and plantarflexion, and tibial component sagittal alignment. Two graders measured post-TAA JLHRs, and the average of the two graders was used for the analysis. Rater agreement was assessed using intraclass correlation coefficients (two-way random effects model). Relationships between JLHR, post-TAA tibiotalar ROM, and PROMIS scores were investigated using Pearson correlation. Multiple linear regression models were used to investigate the association of JLHR with post-TAA tibiotalar total ROM, dorsiflexion, and plantarflexion, after adjusting for pre- TAA ROM, tibial component sagittal alignment, gastrocnemius release (GR), Tendo-Achilles lengthening (TAL), and polyethylene size. Results: The interobserver reliability of the JLHR was excellent (r=0.98). Mean JLHR decreased from 1.66 pre-TAA to 1.55 post- TAA (P < 0.001), indicating the joint line was significantly lowered postoperatively. Greater elevation of the post-TAA JLHR was associated with significantly decreased post-TAA dorsiflexion (r=-0.26, P< 0.001) and worse 1-year PROMIS physical function (r=- 0.22, P=0.046), pain intensity (r=0.22,P=0.042), and pain interference scores (r=0.29,P=0.007). There was no correlation between JLHR and post-TAA plantarflexion (P=0.76). Regression analysis identified a 5º reduction in post-TAA dorsiflexion with each 1.0 unit increase in JLHR (Coef=-5.13, P=0.005). Post-TAA total ROM (Coef=-3.6,P=0.21) and plantarflexion (Coef=0.91, P=0.67) were not associated with JLHR. Additionally, there was no association between post-TAA total ROM and tibial component sagittal alignment, GR, TAL, or polyethylene size. Conclusion: In this study, the joint line of the ankle was lowered after TAA, and the JLHR was a reliable and clinically applicable method for assessing it. An elevated joint line significantly correlated with restricted post-TAA dorsiflexion, but this may only be clinically relevant for patients with significant (>1.0 unit) changes in the joint line level. In addition, a higher joint line was correlated with worse 1-year PROMIS scores. These results suggest that surgeons should consider the joint line level during TAA preoperative planning to obtain improved clinical outcomes and ankle dorsiflexion.