Motorised Shaver System

Besides hand held manual instruments, surgeons also use motorised systems that resect the damaged soft tissue using powered instrumentation. This powered instrumentation that is used for soft tissue resection is called as Shaver System. Shaver system shaves off the unwanted, defective soft tissue. The shaver system comprises of a control unit, a motor drive unit and a foot switch. The actual shaving devise, blades, attach to the motor drive unit and are controlled using the foot switch. The blades perform this function of shaving by rotating in high RPM and cutting the soft tissue with their sharp edges. This rotation of blades is in three directions, clockwise, anti-clockwise and oscillatory. The control unit provides attachment for motor drive unit and the foot switch. It also, generally, displays the speed and direction of rotation of the attached blades. Foot switch provides buttons for controlling the direction of rotation of blades. The motor drive unit is the main part of the shaver system and it is this part which contains the main motor that drives the blades. Motor drive unit also provides for suction of the recessed tissue. Shaver system is used for Synovectomy and resection of other damaged soft tissue in the joint. It is also useful in abrading bones.

Modern day shaver systems also act as powered instruments for drilling and sawing hard tissues like bones. Arthroscopy surgeons need to drill or saw bones during ACL/PCL reconstruction surgeries. Besides the ordinary motor drive unit for blades, they also provide for attachment of drill and saw drives. This addition of function necessitates another motor drive unit. Thus, two different motor drive units are used and each is activated when required.

Another very important part of any shaver system is the blade that does the actual cutting/shaving. The construction of a blade is similar to that of a scope by virtue of being a cylinder enclosed inside a cylinder. The similarity ends here. Blade is made up of two hollow, concentric cylinders. Each cylinder has a window-like opening at its distal end. The edges of this window vary with the type of blade. The edge can be either toothed or entire but equally sharp. The outer cylinder is fixed while the inner one rotates at high RPM generated by the motor drive unit. The cutting mechanism is achieved by trapping the soft tissue between the edges of two cylinders and slicing across it. It is possible to cut fine edges in the soft tissue without pulling it because of the high speed of blades. Besides blades, burrs also attach to the motor drive unit. Burrs are used for abrading bones. They are different from blades in that instead of having a window at the distal end, they end up in a bulb-like structure which has ridges running down its entire periphery. The material is very hard and ridges very sharp. This combination abrades hard tissue like bone in seconds. At the proximal end of blades/burrs, hubs are provided that engage with the receptacles built inside the motor drive unit. The attachment of blades to the motor drive unit is possible because of these hubs. These hubs are different for different makes making it impossible to use blades of one make with shaver of another.

Blades are available in two varieties, reusable and disposable. In any medical equipment business, patient safety is of paramount importance. Disposable blades are in line with this maxim. Anything that enters the body of patient has to be void of all infection. This necessitates the complete sterility of the instrument. Even if reusable blades are autoclaved, they are not 100% infection free. All instruments are minimally infected only untill they are in their sterile packs. Hence, it is advisable to use only those instruments that are opened inside the OT during the surgery. They tend to pose minimum risk to the patient.

All the commercially available shaver blades rotate at around 5000 RPM. To achieve this kind of speed without seizing due to heat and at the same time cutting effectively and efficiently, the blades need to have the following features:

1. Sharpness
2. Speed
3. Strength
4. Surface Finish
5. Tolerance
6. Friction Reduction

To attain speed and strength, all the companies use stainless steel (medical grade). But the limitation with stainless steel is that it seizes at high speeds. To retain the above properties and yet work on high speeds, blades manufacturing process needs to be altered to get high performance. The manufacturing process has to incorporate procedures that would reduce the friction between the two cylinders when operated.