This invention relates to an articulated arm for holding a tool and more specifically for holding a medical instrument during a surgical procedure.
In the modern practice of medicine, surgeons and other medical personnel often use endoscopic scopes, tissue retractors, and other medical instruments that must be kept steady for extended periods of time during their use on a patient. Traditionally, it may be the job of a nurse or surgical assistant to hold the instrument. However, it can be quite difficult for a person to hold the instrument steady for extended periods of time due to fatigue. Also, many of these instruments, such as tissue retractors, require great amount of force to be applied, which can rapidly lead to extreme fatigue as well as make it very difficult to keep the instrument adequately steady.
For this reason, a number of mechanical support devices have been devised to accomplish these otherwise manual tasks. One such device, as disclosed in U.S. Pat. No. 3,858,578 to Milo, consists of an arm-like structure that is made up of a series of ball and socket members held together by a cable. One end of the arm is rigidly attached to a support structure, such as an operating table rail. The opposite end supports a surgical tissue retractor. Initially, the arm is flexible and can be positioned as necessary. When the interconnecting cable is tightened by applying a fluid pressure to a piston attached at one end, the arm becomes rigid until the cable is manually released by discharging the fluid.
There are, however, many drawbacks to this and other similar prior art devices. Generally, the locking force applied to these devices is minimal, making them suitable only for very lightweight medical applications. Those devices which are capable of withstanding greater forces are generally bulky, complex and cumbersome to operate. For example, see U.S. Pat. No. 4,863,133 to Bonnell and U.S. Pat. No. 5,184,601 to Putman.
Another disadvantage that applies specifically to prior art fluid operated devices is reliability. These devices are prone to leakage, which even in a small amount can cause the locking mechanism to give out over an extended period of use. This leakage is often caused by flexible tubing which has failed due to repeated flexing. Further, if fluid pressure is lost completely during a medical procedure, the device may disengage completely, without warning, potentially causing injury to the patient. To solve this problem, some such devices have been designed to lock by default and require positive fluid pressure to unlock. While this approach provides fail-safe locking and eliminates the problem of slow leakage altogether, if fluid pressure is lost completely, a surgeon may not be able to unlock the device when needed which may also lead to the injury of the patient.
Another problem with prior art devices is their method of actuation. Most of the prior art fluid powered devices have a foot-switch which allows for hands-free operation. However, a typical modern operating room will already have several foot switches associated with various pieces of equipment. Thus, it may be exceedingly difficult for a surgeon to quickly locate the correct switch and may lead to the inadvertent release of the device. However, many hand-operated or other types of switches used in the prior art tend to be impractical, since the surgeon generally requires one or more free hands to manipulate the device and to perform other tasks.
The present invention provides an articulated arm for holding surgical instruments which comprises a plurality of elongated arm members and a plurality of rotational joints connecting said arm members end to end. The members are pivotable about the joints and at least one of the joints is selectively lockable by positive fluid pressure. A plurality of tubes communicate fluid pressure between two adjacent joints. When two adjacent members are pivoted relative to one another, the plurality of tubes located on each of the members that connect two joints remains substantially stationary with respect to the arm member connecting the pair of joints, such that it is possible for the plurality of tubes to be constructed from a rigid material.
As another aspect of the present invention, the articulated arm is provided with a fluid pressure operated friction brake for locking at least one of the joints. The friction brake includes a substantially frustoconically shaped engaging surface.
As a further aspect of the present invention, the arm is provided with a check valve that prevents inadvertent unlocking of the joints in the event that a source of fluid pressure is interrupted.
As an even further aspect of the present invention, a plurality of isolated fluid paths is provided to each joint and each of the fluid paths within each joint is isolated from the others within the joint. These fluid paths allow fluid pressure to be communicated through the joint without the need for flexible tubing.
As a still further aspect of the present invention, the articulated arm is provided with a fluid switch located near a distal end of the arm for selectively controlling the fluid pressure within at least one of the joints, thereby unlocking the joint or joints. All of the plurality of joints may be unlocked by operating the single fluid switch.
As a yet further aspect of the present invention, wherein an arm member is pivotable with respect to at least one of the joints by greater than 360 degrees.
As a yet further still aspect of the present invention, a motion-limiting mechanism is provided to at least one of the joints to prevent the inadvertent collapse of the arm.