gms | German Medical Science

Objective: In cases of adjacent level degeneration extension of spondylodesis is indicated. When the primary instrumentation has been performed elsewhere, often years before and by using former systems, it is crucial to identify the system implanted to extend the instrumentation in a compatible manner. Operation reports might be missing, not available or incorrect. Seeking for a non-invasive, rapid and reliable identification of spondylodesis systems we compiled radiological characteristics of the most common systems.

Method: Plain Xray of 34 different pedicle screw systems of 15 companies were reviewed. Manufactures of pedicle screw systems where contacted to provide radiological picture or samples of their products. The latter were used to perform plain biplanar Xrays. As validation cohort plain Xrays of 10 patients treated with seven different systems were evaluated by an independent surgeon, whether the system has been correctly assigned by the characteristics.

Results: 28/34 (82%) spondylodesis systems could reliably be distinguished by five characteristics. Special radiological features could be assigned to the remaining six systems, providing clear assignment of all systems. The 5 characteristics are the screw tip (1): 15 are threaded and conical, seven are threaded and cylindrical and 12 are rocket-shaped. Out of the 15 threaded and conical screws nine are cannulated (2) and six not cannulated. Out of these nine threaded, conical and cannulated screws, five have rounded tulip-shaped screw heads (3), two angled tulip-shaped screw heads, one has an extra element and one has a connecter with a flap-lock mechanism. Blocking mechanism (4) and thread (5) are the remaining characteristics of systems following an decision tree. 9/10 systems of the validation cohort could be identified correctly.

Conclusions: All common pedicle screw systems could be identified with biplanar Xray using the decision tree and subsequent special features. This decision tree will be implemented in a smart phone app for rapid and precise clinical demands planning extension or revision of pedicle screws.