Outcome of anterior lumbar interbody fusion : a retrospective study of clinical and radiologic parameters

Objective. This study aims to critically evaluate the long-term results of stand-alone anterior lumbar interbody fusion (ALIF), without use of rhBMP-2, as a therapeutic option for symptomatic patients with degenerative disc disease (DDD). Furthermore this study intends to identify predictive parameters for anterior lumbar interbody fusion outcome. Methods. A retrospective cohort study with additional telephone interview to obtain missing data was performed. All patients who underwent a L4-L5 and/or L5-S1 ALIF-procedure in the period between 2006 and 2011 were identified. The medical files of 123 patients with 154 fusion levels were reviewed. All patients were contacted by phone to gather supplementary and missing information. Pain and functionality scores (Visual Analogue Scale [VAS] and Oswestry Disability Index [ODI]), radiological (intervertebral disc height, Modic and Pfirrmann classifications) and different clinical parameters were gathered. Results. The mean age at surgery of the population was 46.2 years. Overall, 59 female and 64 male patients were included in the study. The mean visual analogue scales (VAS) for back and leg pain improved significantly (P<0.001) with 5 and 4.4 points respectively at 3 years follow-up. Modic-type I changes are associated with a better improvement in VAS-score for back pain (P=0.026), Pfirrmann-grades IV and V and an intervertebral disc height of less than 5 mm are associated with a better improvement in leg pain (respective P-values: 0.045 and 0.033). Overall, 89% of patients would reconsider the surgical intervention. Conclusions. The ALIF-technique is a durable treatment option for patients with DDD. This study suggests different predictive parameters for treatment outcome

Design optimisation for optically tracked pointers

The use of mechanical pointers in optical tracking systems is needed to aid registration processes of unlocated rigid bodies. Error on the target point of a pointer can cause wrong positioning of vital objects and as such these errors have to be avoided. In this paper, the different errors that originate during this process are described, after which this error analysis is used for the optimisation of an improved pointer design. The final design contains six coplanar fiducials, favored by its robustness and low error. This configuration of fiducials is then analysed theoretically as well as practically to understand how it is performing. The error on tracking the target point of the pointer is found with simulation to be around 0.7 times the error of measuring one fiducial in space. However, practically this error is about equal to the fiducial tracking error, due to the non-normally distributed errors on each separate fiducial