Introduction:

In 2019, Moufid and Gille published a study in which they proposed certain radiological parameters that may justify the mismatch between the lordosis of the lumbar segment and the lordosis of the rod bar using polyaxial screws. The aim of this study is to reproduce the measurements performed by Moufid and Gille and try to validate their findings.

Material and methods:

A retrospective study was performed including patients submitted to L3-L5 posterior fusion with or without interbody devices using polyaxial screws and titanium rods, for degenerative disease. Radiological parameters were analysed:the distance between the posterior wall and the rod for each vertebra(the standard deviation of the three distances was called Alpha); the angle between the screw and the rod for each screw(mean of the three was called Theta); the angle between screws and superior endplate for each instrumented vertebra(mean of the three was called Lambda). The difference between post-operative segmental lordosis and the lordosis of the rod was called DiffL.

Results:

A total of 58 cases were included. The most frequent fusion surgery was posterolateral fusion(77.6%). The mean value of lumbar lordosis, fused segmental lordosis, pelvic incidence, Alpha, Theta, Lambda and DiffL were 48.7 ± 12.7°, 28.4 ± 9.2°, 60.7 ± 11.9°, 3.4 ± 1.6 mm, 90.5 ± 1.8°, 3.9 ± 1.8° e 9.9 ± 9.5° respectively. The mean value of rod lordosis was 20.5 ± 8.1°. DiffL varied between 0.1° (practically no mismatch) and 30.5° of mismatch. DiffL didn’t correlate with gender, fusion type, age, PI and Alpha, Theta or Lambda. There was a significant positive correlation between lumbar lordosis and DiffL(ρ = 0.28; p = 0.03). No correlation was found between the radiological parameters for the cut-off point proposed by Moufid and Gille(Alpha 4.7 mm, Theta 86°, Lambda 2.8°) and the DiffL value.

Conclusion:

No significant factors were identified in this study to aid in achieving an ideal match between rod and segmental spine lordosis, therefore not validating the study by Moufid and Gille.