The present invention relates generally to continuous passive motion devices used in the rehabilitation of body limbs that have been disabled in some way. More particularly, the present invention provides improvements to a knee continuous passive motion (CPM) machine. Existing CPM devices have been used for sometime to assist doctors and patients in recovering all or part of the use of a body member such as a hand, wrist, knee, ankle, etc. that has been disabled in someway. Patients hurt in accidents or patients having limbs affected by disease have benefitted greatly from the mechanical assistance provided by a CPM device to assist the patient in reacquiring use of a damaged limb.
Existing CPM machines have been found by the present inventor to have at least three deficiencies which are addressed by the present invention. First, in existing machines there is no adequate way of securing the lower limb (below the knee) to maintain alignment of the lower limb throughout a machine cycle. This may be due to the second problem which is that there is no convenient means afforded the patient for locking (entering) and unlocking (exiting) the lower limb from existing machines. Third, the existing devices do not offer controlled resistance with respect to limb extension.
With respect to the first problem of locking the limb in place, the present inventor has discovered that a patient's limb must be secured adequately in the machine or otherwise the full benefits of the CPM device will not be realized. By more rigidly securing the limb in place in the machine it reduces the upward motion of the lower limb while the machine moves the limb into flexion.
With respect to affording the patient a convenient means for entering and exiting the machine, most patients find it difficult and uncomfortable to bend forward to a position where they could actuate any mechanism of the machine at or near their ankle position. Some patients may find it impossible due to obesity, pain, or overall weakness to reach this far.
The last of the three above mentioned problems is the lack of means for generating controlled resistance for patients having extension contractures. Existing CPM devices do not provide calibrated, reproducible, and controlled means for generating resistance and extension. Extension and flexion are not treated similarly by the CPM device. When flexion is set it is limited to within a patient's tolerance. The same should be considered with respect to extension. The machine should be designed to insure that extension is indeed taking place. Existing CPM devices provide extension motion but do not ensure that extension is actually being experienced by the patient.
The present invention provides answers to the above referenced problems. In the present invention the lower extremity is secured into place in the machine. The location of the securing structure of the present invention is preferably between the tibial length adjustment knob and the foot cradle on existing knee CPM machines. In the present invention an ankle lock is built into the frame of the carriage. Motion is restricted to the longitudinal axis of the frame. Within this range of motion, compensating for any forward and backward movement of the leg during a motion cycle, compression and expansion of controlled springs will tend to restore the distal member to a center position. A lock, latch or hinge of various types may be provided to allow opening and closing of the ankle lock for entering and exiting from the ankle cradle. When the lock is closed the lower extremity is completely surrounded and made immobile for motions perpendicular to the frame's longitudinal axis. This arrangement keeps the motion of the distal extremity parallel to the frame's longitudinal axis throughout a flexion and extension cycle. This accomplishes a calibrated and reproducible range of motion. Angular measurements made on the machine members therefore accurately represent the flexions experienced between the distal and proximal members of the patient. Having a calibrated and reproducible range of motion allows doctors' recommendations, regarding flexion settings and patients' tolerance, to be strictly followed.
Also in the present invention handle means attached to the machine may be provided for securing and releasing the distal member from the ankle lock. Therefore, even a patient in a prone position can operate the ankle lock device. A long handle may be specially equipped so that a rotary motion of the handle will be translated into locking or unlocking of the mechanism.
To solve the third problem, the present invention may be equipped with an extension piece. Clamping the proximal member affords a means for controlling the extension resistance to be generated. Similar to the ankle lock, the extension piece is preferably secured to the frame in an area above the normal knee position. Adjustment of the extension piece position along the frame may be provided to accommodate different proximal member lengths. An adjustable clamping arrangement is one preferred extension piece for fastening the proximal member to the machine. In one embodiment of the present invention a one time set-up adjustment of the extension piece may be made to fit a particular patient enabling quick release and locking to be accomplished during subsequent use. This added capability gives the clinician an accurate way to gauge and control the amount of resistance being applied to extension thus providing a reproducible method of treating extension contractures with the CPM device.
Further features of the present invention may include the placement of cushioned material or padding on all areas of the device that bear against the patient's skin and inflatable bladders which may form part of the inner portion of the ankle lock and/or extension piece to softly but firmly secure a limb in place. With the above listed improvements of the present invention there will be increased accuracy in the measurement and setting of the range of motion of the device relative to the actual range of motion experienced by the patient. The present invention further provides easier entering and exiting and will offer slight, constant, and controlled resistance to the upper leg which improves the device's capability of controlling resistance in extension.
The foregoing and other objects and advantages of the present invention will become more apparent when viewed in light of the accompanying drawings and following detailed description.