Isolated repair shows higher postoperative patellar height according to the Insall-Salvati index compared to biological augmentation in acute patellar tendon ruptures.

Background and objective: Patellar tendon ruptures (PTR) are rare but highly disabling injuries. Surgical treatment is the standard approach. Postoperative patellar height (PH) is used to determine the success of the intervention, with various indices described in the literature. The objective of the study was to determine if there are differences in PH according to the Insall-Salvati index in the immediate postoperative period and at 4 months, between two groups of patients operated on for acute PTR: The first group underwent isolated repair techniques (IR) and the second group had biological augmentation with autograft or allograft added to the repair (BAR). Our hypothesis was that the BAR group would have lower PH in the immediate postoperative period and at 4 months.

Materials and methods: All patients with acute PTR treated at our center between 2016 and 2022 were reviewed retrospectively. Patients with re-rupture of the operated tendon and those with non-biological augmentation were excluded. PH according to the Insall-Salvati index was measured in radiographs taken the day after surgery and at 4 months postoperatively by three orthopedic surgeons with a subspecialty in knee surgery, independently. A fourth blind evaluator analyzed the measurement results, determining the average PH and the intraclass correlation coefficient for absolute agreement among the three evaluators. The primary outcome was the difference in PH between both groups the day after surgery and at 4 months. The secondary outcome was the difference in PH between the immediate postoperative measurement and at 4 months in both groups.

Results: This was a retrospective observational study. Thirty-one operated knees were included. IR was performed on 15 knees (48.38%), and biological augmentation was added in 16. The intraclass correlation coefficient between observer 1 and 2 was 0.88; between 2 and 3 it was 0.89; and between observers 1 and 3 it was 0.92, showing at least substantial agreement among observers. The average Insall-Salvati index the day after surgery and at 4 months was 1.15 and 1.21 for the IR group, and 0.97 and 1.07 for the BAR group, respectively. A statistically significant difference in the Insall-Salvati index was found between the two groups, both in the measurement taken the day after surgery (p<0.0001) and at 4 months (p=0.0002). Additionally, significant differences were observed indicating an increase in average PH when comparing the immediate postoperative measurement and at 4 months in each study group (for IR p=0.0016 and for BAR p<0.0001).

Conclusions: The Insall-Salvati index was significantly lower in BAR cases both the day after surgery and at 4 months postoperatively. Additionally, a significant increase in PH was observed at 4 months, regardless of the surgical technique used. Substantial inter-observer agreement was achieved for PH measurement in this cohort.