Revisiting Anterior Stand-Alone Fixation (ASAF) Devices for the Treatment of Single Level Lumbosacral Degenerative Disease

locking screw technology, which significantly augments the overall construct strength and rigidity. The goal of the anterior stabilized stand-alone device is to negate the need for posterior fixation by promoting stability of the implant via the locking screws. The benefit of creating an anterior stand-alone fixation device is that the spine surgeon can achieve adequate stabilization to ensure fusion while avoiding the increased morbidity associated with the posterior approach. Schleicher et al published one of the early biomechanical studies using a human cadaver model comparing the Anterior stabilized stand-alone device implants to an established stand-alone interbody implant. The study showed greater stiffness in lateral bending for the anterior stabilized stand-alone device compared to the established implant. Additionally, the study showed that for the anterior stabilized stand-alone device, the anterior cage takes most of the load during flexion, whereas the screws and the screwplate junction assume most of the load during extension, and it’s this augmentation of stability in extension moments that is especially important to the success of stand-alone interbody fusion. In practice, the cage provides the stability lost by resection of the anterior longitudinal ligament in extension, which is the main biomechanical limitation of anterior lumbar interbody fusion (ALIF) procedures. The net effect of the implant design is that the compressive loads are evenly distributed across the implant, whereas the anterior stabilization plate and divergent locking screws serve to neutralize the tensile forces. Examining the effects of these new ASAF devices in practice, Strube et al performed a prospective cohort study comparing patients undergoing anteroposterior fusion (ALIF with transpedicular fixation: APLF) to patients undergoing anterior lumbar interbody fusion (ALIF) alone using the anterior stabilized standalone device. They found that the blood loss and duration of surgery were significantly lower in the ALIF group, and that while the Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) scores improved in both groups, they were significantly better in the ALIF group. Additionally, rates of fusion were not statistically significant between groups at long term (41 month) follow up and only a 5% complication Low back pain (LBP) affects 50-80% of the population at some point in their lifetime and is a frequent cause of decreased mobility and unemployment. Fusion of lumbar motion segments continues to be the foundation of treatment of intractable LBP secondary to degenerative disc disease (DDD), and can be achieved via anterior-only, posterior-only and anteroposterior approaches. Historically, the majority of fusions are performed via posterior surgical approaches. However, fusions performed via posterior surgical approaches, whether with or without instrumentation or with or without additional interbody fusion, have suffered from complications such as graft site morbidity, screw loosening, pseudoarthrosis, sagittal imbalance, high rates of adjacent level pathologies, and considerable complication and reoperation rates. Additionally, the posterior approach has been shown to result in muscle atrophy which in itself becomes a new LBP generator. As an attempt to mitigate these negative side effects, posterior percutaneous techniques gained some popularity as a less invasive, more muscle sparing alternative; however, minimally invasive techniques resulted in higher x-ray exposure and significantly increased rates of adjacent level facet joint violations. In order to avoid the aforementioned complications, anterior stand-alone fusion (ASAF) devices have been introduced as an alternative method to avoid damage to the paravertebral muscles, to prevent screw displacement-related neurological and vascular complications and to reduce the rate of adjacent segment degeneration. ASAF devices provide a potential advantage by avoiding posterior muscle trauma, avoiding violation of the cranial facet joints and permitting improved sagittal balance reconstruction. Despite reduced invasiveness and previously reported reduced infection rates, historical data exists that reports contradictory results regarding significant rates of nonunion associated with ASAF devices. This can be partially attributed to implants previously utilized to perform anterior interbody fusions, which were not stable enough to reliably achieve fusion, and thus resulted in high rates of pseudoarthroses. However, new implants have been designed which are anterior stabilized, e.g. with plates and Blair Ashley MD Vincent Arlet MD