Increased Union Rates in Subtalar Joint Arthrodesis with Hybrid Nitinol Dynamic Compression Device

Abstract

Category: Hindfoot Introduction/Purpose: Subtalar joint arthrodesis (STJA) is a well-established and widely accepted surgical procedure utilized for the treatment of numerous hindfoot conditions. Several fixation constructs in STJA have been described in the literature. With the current advancements in orthopedic technology, new devices utilizing nitinol elements have been developed in an effort to maintain sustained compression in the event of bony resorption which may occur during arthrodesis healing. The primary aim of our study is to introduce a hybrid nitinol dynamic compression (HNDC) device for STJA which provides dynamic compression without proximal locking fixation and compare union rates with a previous nitinol dynamic compression nail (NDCN) as well as a standard two-compression screw fixation construct. The secondary aim was to compare hardware removal rates amongst the three cohorts. Methods: From May 2019 through February 2022, 26 consecutive patients treated with a novel HNDC for STJA were compared to 15 patients treated with NDCN for STJA and 41 patients undergoing STJA using a two-compression screw fixation method. Patients were included in our study if they were greater than 18 years of age, underwent STJA with the use of one of the internal fixation constructs under investigation, and had a minimum 1-year follow-up with radiographs; there were no other exclusion criteria. Arthrodesis sites were augmented with autologous bone graft with or without bone graft substitute in all patients. Standard postoperative protocols were used amongst all three cohorts. Primary outcomes included subtalar joint union rates determined by radiographic and clinical assessment. The incidence of hardware removal was recorded and compared between groups. Patient-specific risk factors were studied to assess any potential negative effects on STJA union rates. Results: Union rates between the HNDC device and the NDCN group did not demonstrate a statistically significant difference at final follow-up. There was a statistically significant difference in union rates between subjects who underwent STJA with the HNDC device versus those who underwent STJA with a two-compression screw construct. Furthermore, there was a statistically significant increase in union rates in subjects who received nitinol dynamic compression fixation devices, HNDC or NDCN, versus standard compression screws. There was not a statistically significant difference in hardware removal rates among the 3 cohorts. No significant relationship was seen between smoking, diabetes, or alcohol consumption and union rates. Conclusion: Our data supports the HNDC device to have superior union rates to the two-screw fixation group. In addition, the HNDC device provides improved union rates, though not statistically significant, when compared to the NDCN. Furthermore, the HNDC device was found to have lower rates of hardware removal when compared to the two-screw fixation and the NDCN groups though this was not statistically significant. The early results of this HNDC device for STJA are encouraging and appear to offer a further improved alternative fixation construct with excellent union rates and minimal complications.