Deep brain stimulation (DBS) and other related procedures involving implantation of electrical stimulation leads within the brain of a patient are increasingly used to treat disorders, such as Parkinson's disease, dystonia, essential tremor, seizure disorders, obesity, depression, restoration of motor control, and other debilitating diseases via electrical stimulation via stimulation of one or more target sites, including the ventrolateral thalamus, internal segment of globus pallidus, substantia nigra pars reticulate, subthalamic nucleus (STN), or external segment of globus pallidus. DBS has become a prominent treatment option for many disorders, because it is a safe, reversible alternative to lesioning. For example, DBS is the most frequently performed surgical disorder for the treatment of advanced Parkinson's Disease. There have been approximately 30,000 patients world-wide that have undergone DBS surgery. Consequently, there is a large population of patients who will benefit from advances in DBS treatment options.
During DBS procedures, at least one burr hole is meticulously cut through the patient's cranium as not to damage the brain tissue below, a large stereotactic targeting apparatus is mounted to the patient's cranium, and a cannula is scrupulously positioned towards the target site in the brain. A stimulation lead is then introduced through the cannula, through the burr hole, and into the parenchyma of the brain, such that one or more electrodes located on the lead are strategically placed at a target site in the brain of the patient. Typically, an imaging device, such as a magnetic resonant imager (MRI), will be used to visualize the lead relative to the target site. Once the lead is properly positioned, the portion of the lead exiting the burr hole is subcutaneously routed underneath the patient's scalp to an implantable pulse generator (IPG) implanted in the patient at a site remote from the burr hole (e.g., the patient's shoulder or chest region). Further details discussing the treatment of diseases using DBS are disclosed in U.S. Pat. Nos. 6,845,267, 6,845,267, and 6,950,707, which is expressly incorporated herein by reference.
Significantly, it is crucial that proper location and maintenance of the lead position be accomplished in order to continuously achieve efficacious therapy. This is especially so with DBS applications, in which cases, the target site (or sites) that is intended for electrical stimulation is about the size of a pea and is located deep within the patient's brain. Thus, lead displacements of less than a millimeter may have a deleterious effect on the patient's therapy. Therefore, it is important that the electrode(s) of the lead be accurately located at the target site and that such electrode(s) be securely maintained at the target site during and after implantation of the lead.
To address these issues, a cranial burr hole plug is installed within the burr hole during the implantation procedure to hold the stimulation lead in place, as well as to seal the burr hole. Typically, the burr hole plug is composed of a multitude of components, including a ring-shaped base and a retainer that are integrated together to form the burr hole plug. Optionally, a cap may be further integrated with the base and retainer.
In particular, before the stimulation lead is introduced through the burr hole, the ring-shaped plug base is centered about the burr hole using a special centering tool that is disposed through the plug base into the burr hole, and is then permanently mounted to the patient's cranium using conventional means, such as bone screws. The stimulation lead is then introduced through the plug base and into the parenchyma of the brain. Notably, any displacement of the portion of the lead exiting the burr hole will result in the translation of the electrodes positioned in the brain relative to the target site, thereby requiring the lead to be repositioned—a time consuming process.
Thus, once the lead is properly located at the tissue site, the retainer is installed within the plug base (typically in an interference arrangement, such as a snap-fit arrangement) to secure the lead, thereby preventing migration of the lead relative to the target site during subsequent manipulation of the lead and installation of the optional cap. In one exemplary embodiment, the retainer comprises a disk having a slot for receiving the lead and a clamping mechanism that can be rotated within the slot towards a mating surface on the disk to frictionally clamp the received lead therebetween. The clamping mechanism may have one or more locking mechanisms that can engage or disengage complementary locking mechanisms on the disk to prevent rotation of the clamping mechanism. The portion of the stimulation lead exiting the retainer can then be bent downward towards the plane of the disk into a recess formed in the plug base, and the optional cap can be installed onto the plug base over the retainer to permanently secure the lead within the recess, as well as to seal the burr hole. Alternatively, instead of a cap, a biocompatible glue or other suitable adhesive can be used to seal the burr hole.
It can thus be appreciated from the foregoing that the burr hole plug serves as the platform for the entire DBS system, and therefore, it is important for this component to be robust, well-designed, and easy to use. Importantly, the burr hole plug should be designed, such that lead migration is minimized during installation of the burr hole plug. While prior art burr hole plugs have proven to be useful in the DBS context, there are still improvements that can be made.
For example, due mostly to their flexible nature and ability to lock in only one position, the clamping mechanisms of prior art burr hole plugs are not designed to firmly retain stimulation leads. As such, the stimulation lead may still inadvertently move even when it is supposedly secured by the clamping mechanism. Also, because these clamping mechanisms have only one set position when clamping down on a stimulation lead, prior art burr hole plugs are designed to be used with stimulation leads having one size. That is, the dimension between the retaining surface of the clamping device and the mating surface of the disk when the clamping device is in the locked position is designed to be slightly less than the diameter of the lead. If the diameter of the actual lead used with the burr hole plug is smaller than this intended diameter, the retention force applied to the lead by the clamping mechanism will not be sufficient. In contrast, if the diameter of the actual lead used with the burr hole plug is greater than this intended diameter, too much force will need to be applied to the lead in order to place the clamping mechanism within the locking position, thereby potentially damaging the retainer.
As another example of a problem suffered from prior art burr hole plugs, the retainer may rotate within the plug base, potentially resulting in the inadvertent movement of the stimulation lead from the target site. Such rotation of the retainer may typically occur in response to the manipulation of the clamping mechanism, and in particular, a downward force applied to the clamping mechanism that causes partial disengagement between the retaining disk to which the clamping mechanism is mounted and the plug base, and a lateral force applied to the clamping mechanism that causes the disengaged disk to rotate within the plug base.
As yet another example, once the plug base is mounted to the patient's cranium via bone screws, it is difficult to adjust the position of the plug base when desired. Also, due to the relatively large size of the stereotactic targeting apparatus, there is often little working space available between the targeting apparatus and the burr hole to secure the stimulation and to anchor the plug base to the cranium of the patient.
There, thus, remains a need for a burr hole plug that includes an improved means for securing a stimulation lead, for affixing the retainer to the plug base of the burr hole plug, and to anchor the burr hole plug within the burr hole formed in the cranium of a patient.