Osseodensification drilling vs conventional manual instrumentation technique for posterior lumbar fixation: Ex‐vivo mechanical and histomorphological analysis in an ovine model

Abstract

Lumbar fusion is a procedure associated with several indications, but screw failure remains a major complication, with an incidence ranging 10% to 50%. Several solutions have been proposed, ranging from more efficient screw geometry to enhance bone quality, conversely, drilling instrumentation have not been thoroughly explored. The conventional instrumentation (regular [R]) techniques render the bony spicules excavated impractical, while additive techniques (osseodensification [OD]) compact them against the osteotomy walls and predispose them as nucleating surfaces/sites for new bone. This work presents a case‐controlled split model for in vivo/ex vivo comparison of R vs OD osteotomy instrumentation in posterior lumbar fixation in an ovine model to determine feasibility and potential advantages of the OD drilling technique in terms of mechanical and histomorphology outcomes. Eight pedicle screws measuring 4.5 mm × 45 mm were installed in each lumbar spine of eight adult sheep (four per side). The left side underwent R instrumentation, while the right underwent OD drilling. The animals were killed at 6‐ and 12‐week and the vertebrae removed. Pullout strength and non‐decalcified histologic analysis were performed. Significant mechanical stability differences were observed between OD and R groups at 6‐ (387 N vs 292 N) and 12‐week (312 N vs 212 N) time points. Morphometric analysis did not detect significant differences in bone area fraction occupancy between R and OD groups, while it is to note that OD showed increased presence of bone spiculae. Mechanical pullout testing demonstrated that OD drilling provided higher degrees of implant anchoring as a function of time, whereas a significant reduction was observed for the R group.

Evaluation of instrumentation and pedicle screw design for posterior lumbar fixation: A pre‐clinical in vivo/ex vivo ovine model

“…In terms of mechanical pull‐out testing, our results showed increased values in the rotary group compared with the hand instrumentation at 24 weeks (~1100 N) but not at the earlier healing time of 6 weeks. The superiority of mechanical stability for the rotary group concurs with observations from our previous study 29 . However, it must be noted that our previous investigation presented lower values relative to the present study due to mechanical testing method variation, where pull‐out strength to interfacial failure was used 29 unlike full pullout as in the present study.…”

“…This study compared hand (conventional) versus rotary ("additive") instrumentation, to confirm and validate the observations of our previous study 29 Indications for lumbar spinal fusion surgery have experienced a growth toward instability and deformity conditions, mainly among the elderly population (65+ years old) and patients affected by co-morbidities, particularly osteoporosis. 1,2 Taking into consideration the projection of the current demographic trend, which indicates that by 2050 the population of elderly patients will outnumber adolescents and youth (15-24 years old), 34 suitable protocols and materials/ devices that will deliver positive outcomes in a reproducible manner along with limited complications are highly desirable.…”

“…As seen with BIC, the BAFO presented significantly higher values in the rotary instrumentation group, suggesting that rotary instrumentation promotes stronger initial bone formation, possibly due to the autografted bone particles acting as nucleating surfaces for new bone formation as we have previously described. 13,14,29,48 The rotary instrumentation effect on osseointegration is further observed on analysis of histology. Densification around the implants is visualized in the samples placed into osteotomies prepared with rotary instrumentation, as this group presented greater volume of woven bone as well as bone-implant contact relative to samples instrumented with the hand instrumentation, especially at the 6-week time point.…”

“…Despite substantial research and development, pedicle screw loosening and instability of the constructs has remained an issue particularly in the elderly population and osteoporotic patients 41,42 . Despite the plethora of osteosynthesis implants currently available, until recently minimal consideration has been given to the preparation of the osteotomy required for placement of the devices, a paramount factor for biomechanical stability and osseointegration 12–14,18,24–27,29,43 . This work aimed to build on our group's earlier studies 14,29,44,45 where we explored the novel rotary instrumentation sequence for endosteal implants used in oral and maxillofacial and orthopedics, for placing spinal lumbar fusion multiaxial pedicle screws.…”

“…The time dependent change in applied load during instrumentation or post healing has also been linked to increased levels of bone formation by Duncan and Turner. 28 In our group's previous study 29 the objective focused on the instrumentation, comparing conventional (hand) instrumentation and "additive" osseodensification rotary drilling protocol used to prepare the osteotomy sites for pedicle-screws. The results revealed increased primary stability in osteotomies prepared using the rotary instrumentation relative to the conventional hand instrumentation.…”