Screw-Lock: A Novel Technique to Secure Burr Hole Base Ring in DBS Surgery

Need

Deep brain stimulation (DBS) therapy is now accepted as a standard of care for movement disorders. To obtain the optimal and sustained effect of DBS therapy, accurate placement of the lead at the target site and permanent stable anchoring of the lead are critical. Hardware-related complications requiring revision surgery are reported in 4.5% of patients. ¹ In these patients, an additional surgery with revision, exchange, or removal of system components is frequently required.^2,3 Importantly, postoperative lead migration or displacement has been reported in over 10% of DBS leads in a large cohort, with failure of lead fixation at the burr hole site identified as a key contributing risk factor. ⁴ The most common reason for failed lead fixation is base ring and burr hole size mismatch. ⁵ Currently available systems to hold the assembly in place are Stim-Loc (Medtronic, Minneapolis, MN, USA) which comes at an additional cost to the patient and burr hole ring base and cap that comes with the lead and does not add to the cost (Figure 1). ⁶ In India, DBS equipment comes with burr hole ring base and cap at no additional cost and hence most often used for lead fixation. In addition, using 14 mm perforators for all the burr holes is not possible due to cost of the perforators and drills. Hand held Hudson brace or match-stick drill is most often used to make a burr hole. This can often result in base ring and burr hole size mismatch. It places a DBS lead at risk of misplacement even after proper micro-electrode (MER) mapping of the target nucleus. No cost-effective alternative currently exists to address this gap; the authors therefore wish to share a novel and cost-effective screw-lock technique to secure the burr hole base ring to the skull (Figures 1 and 2).OPEN IN VIEWER

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Figure 2.

Intraoperative photograph showing fixation of the burr hole base ring to the skull using two titanium self-tapping screws passed through the holding holes

Technical Solution

Once the burr hole is done, before we open the dura widely to accommodate multiple MER tracts, stability of base ring needs to be assessed. Usually, the base ring is held using a small artery forceps using the two holes provided at the open ends of the ring and placed in the burr hole (Figure 1). If the size of the burr hole is larger than the base ring diameter then the ring does not get stably anchored in the burr hole (Figure 3A). This can lead to rotatory movements as well as displacement of the base and the DBS lead (Figure 3A). To address this, we placed the base ring in the oversized burr hole. Then used the two holes provided for holding the base and placed 6 mm self-tapping titanium screws (Figure 2). This made the base ring stable (Figure 3B).OPEN IN VIEWER

Proof of Concept

We have shown that securing the ring with two screws prevents rotatory instability and dislodgment from the burr hole (Figures 2 and 3B). Even in the expensive, commercially available burr hole fixation systems like Stim-Loc (Medtronic, Minneapolis, MN, USA), there are only two screws providing fixation. So, two-point fixation is adequate for a stable base ring on the burr hole. ⁷

Next Steps

It is advisable to place these screws in all cases where a dedicated holding assembly is not available. They can be included in commercial kits. Expandable base rings can also be manufactured to fit all burr hole sizes.

Conclusion

This technique is particularly valuable in resource-limited countries where commercially available fixation systems are beyond the financial reach of most patients. The advantages of this technical innovation are

1. It secures the base ring and the DBS lead effectively.