Ideal length of accessory rod for the prevention of rod fracture after pedicle subtraction osteotomy in adult spinal deformity: short or long?

Objective: Pedicle subtraction osteotomy (PSO) is an effective surgical procedure for adult spinal deformity (ASD). However, the complexity of the procedure and its associated complications including rod fracture (RF) remain challenging issues. Among several RF reduction methods, the accessory rod (AR) is an important surgical technique. To date, knowledge about the ideal length and configuration of the AR is limited. This study aimed to assess the influence of the connection levels and configuration of the AR on RF occurrence in patients with ASD who underwent long level constructs and PSO.

Methods: The authors retrospectively selected 57 consecutive patients (mean age 70.6 years) who underwent deformity correction including PSO and the AR technique with a minimum 2-year follow-up. The patients were classified into a non-RF group (n = 49) and an RF group (n = 8). Along with analysis of patient and radiological factors in the 2 groups, comparative studies were performed including configuration of the AR (D shaped vs linear shaped) and the connection levels of AR (long AR [the lower end below S1-2] vs short AR [above L5-S1]).

Results: The overall rate of RF incidence was 14% (8/57 cases) at an average of 42.5 months (2 patients with unilateral RF and 6 with bilateral RF). RF occurred most commonly at the L4-5 level, below the lower end of the AR: 6 below the lower end of the AR and 2 at the PSO site. There were no significant differences in patient and radiological factors between the groups. Comparisons between the 2 groups indicated that more RFs occurred when the configuration of the AR was a linear shape (p = 0.016) and when the distal end of the AR was above L5-S1 (p = 0.025).

Conclusions: In this study the authors found that the D-shaped configuration of the AR and lower end of the AR below S1-2 (i.e., long AR) could be preventive methods for reducing RF after deformity correction performed using PSO and the AR technique for ASD. Here, the authors have provided the first comprehensive outline for the AR technique. These findings could establish effective guidelines for spine surgeons.