The Effect of Tibiotalar Joint Line Level Alterations on Tibiotalar Range of Motion Following Total Ankle Arthroplasty

Abstract

Category: Ankle; Ankle Arthritis Introduction/ Purpose: With the increased utilization of total ankle arthroplasty (TAA) for the treatment of end-stage ankle arthritis, the effect of joint line level on patient outcomes remains unclear. It has previously been demonstrated that patients with end-stage ankle arthritis have an elevated joint line level compared with nonarthritic ankles, and the joint line post-TAA remains elevated compared with nonarthritic ankles. The objectives of this study were to (1) Propose a reliable radiographic method to measure the ankle joint line level that can be applied both pre- and postoperatively following TAA and (2) Determine the effect of joint line level alterations in relation to tibiotalar range of motion (ROM) following TAA. Methods: A retrospective review was performed on patients who underwent a TAA at a single institution between January 2018 to April 2021. Inclusion criteria required patients to have a minimum of one-year postoperative follow-up with preoperative weight-bearing anteroposterior (AP) radiographs and postoperative weight-bearing AP and lateral flexion-extension ROM radiographs. Patients with concomitant procedures affecting ROM were excluded. Radiographic joint line and ROM measurements were performed by two observers. The proposed joint line measuring technique computes four joint line measurements for each AP radiograph- high, low, center of the talus, and center of the axis (Figure 1). Paired T-tests, Student T-tests, Chi-Square tests, univariable and multivariable regression models, and Spearman Correlation Coefficients were computed. The ankles were divided into two cohorts for subanalyses- lowered versus elevated joint line. Intra-class correlation coefficients (ICC) were calculated to assess inter-observer reliability. A probability of 0.05 or less was considered significant for all analyses. Results: A total of 33 patients were included with 17(51.5%) valgus-aligned ankles and 16(48.5%) varus ankles. The average postoperative tibiotalar ROM was 6.7°(±7.1°) dorsiflexion to 21.7°(±8.3°) plantarflexion. 22 patients had a lowered joint line compared to 11 patients with an elevated joint line (2.2±1.25mm lowered versus 1.9±1.2mm elevated; p< 0.0001). Of the four joint line measurements, three(high, center, axis) demonstrated a significant positive correlation between lowering the joint line and improved tibiotalar dorsiflexion and total ROM (all p< 0.05). Plantarflexion was not significantly affected by joint line alterations. Compared to patients with an elevated joint, patients with a lowered joint line had improved tibiotalar dorsiflexion (8.8° versus 2.5°; p=0.0015) and total ROM (31.0° versus 22.9°; p=0.0191), respectively. The inter-rater reliability was nearly perfect, ranging from ICC=0.96-0.99. Conclusion: Lowering the tibiotalar joint line level may more closely reestablish the native tibiotalar joint line and results in improved tibiotalar dorsiflexion and total ROM following TAA. This evidence may refute the concern that “overstuffing” the joint decreases postoperative ROM.