Ambulatory traction

Abstract

A device and method for applying intermittent passive traction (IPT) that includes an initial phase followed by a sustained traction phase and finally a relaxation phase. During the first phase of IPT, the spinal elements are placed under gentle traction. This period of time reduces the normal forces across the vertebral bodies, facet joints, paraspinal musculature, etc. The second phase holds the spine in sustained traction, further reducing the forces across the spinal elements, encouraging natural healing to occur and allowing the muscles a period of relaxation. The third phase includes the gradual reduction of traction. During this final phase, the normal forces across the spine are reestablished as the IPT device slowly releases traction. The method resolves many of the most limiting problems associated with traction, CPM, and passive treatment modalities.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 11/284,250 filed Nov. 21, 2005, which is a continuation of U.S. Ser. No. 11/094,862 filed Mar. 31, 2005, which is a continuation-in-part of U.S. Ser. No. 11/035,485 filed Jan. 15, 2005, now abandoned, which claims priority to U.S. Ser. No. 60/640,479 filed Sep. 30, 2004, each of which are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to medical treatment modalities, and more particularly relates to a device and method for implementing intermittent passive traction (IPT) therapy.

2. Description of the Prior Art

Continuous passive motion (herein after referred to as CPM) is a well known and established technique used by the medical community to benefit a patient's recovery. The modality relies on passive movement of a joint through a predetermined range of motion to reestablish the kinematics of the joint and surrounding soft tissues. This is typically achieved by a device in which the joint and associated soft tissues are secured and gently moved through a predetermined motion cycle. CPM devices typically allow the range of motion, rate of motion, and other parameters to be adjusted per patient comfort and therapeutic parameters outlined by their health care provider. Most patients tolerate the device administering the passive range of motion and see it as an adjunct in their care and rehabilitation program. The benefits of CPM have been well established in therapeutic centers and have been extensively documented in the medical literature.

Traction is another treatment modality frequently used by the medical/therapeutic community to relieve pain, muscle spasms, and general discomfort to joints and surrounding soft tissues involved. The application of traction across a body region has been achieved in many different ways. Chiropractors often use a number of techniques and positional maneuvers to place a region of the spine in traction. Other health care providers use traction devices; these typically require patients to lie down on a specialized traction table in which traction across the spine is applied. Most health care providers require patients to visit clinics or therapy centers to have access to these devices. The benefits of traction are well established in the medical/chiropractic communities and well documented in the medical literature.

The benefits of traction and CPM are substantial. A significant draw back with these modalities however, lies in the cost of the devices and/or the time required to frequent health care professionals administering the technique(s). The purchase price of CPM machines and traction tables can be thousands of dollars. Most patients cannot afford to purchase these devices for self-directed care. Because of this, patients frequent treatment centers in order to gain access to these devices/techniques. Treatment regimens are typically set up by health care professionals in which the CPM and/or traction devices are used. Patients spend time, and often substantial amounts of money to be treated.

In view of the foregoing background, it would be extremely beneficial and advantageous to provide an intermittent passive traction (IPT) device that will combine the effects of traction and continual passive motion. These devices would be reasonably priced so patients who respond to these treatment techniques can purchase the device outright and use it when they deem necessary. Patients would take control of their own care without requiring inconvenient and expensive clinic treatment regimens devised by others. Many of the most limiting problems associated with traction, CPM and passive treatment modalities could then be resolved.

SUMMARY OF THE INVENTION

The present invention is directed to an intermittent passive traction (IPT) device that combines the effects of traction and continual passive motion therapy. These devices are reasonably priced so patients who respond to these treatment techniques can purchase the device outright and use it when they deem necessary. Patients will be able to take control of their own care without requiring inconvenient and expensive clinic treatment regimens devised by others. Many of the most limiting problems associated with traction, CPM and passive treatment modalities would then be resolved.

The IPT therapy device in one embodiment consists of two principal elements: 1) a soft vest combined with 2) an electromechanical traction unit. The soft vest is provided with features necessary to isolate one or more desired regions of the spine requiring treatment. These regions can include cervical, thoracic and/or lumbar. Each vest in contoured in such a fashion that it will accommodate a variety of body habitues. The electromechanical traction unit (ETU) is incorporated within the vest and functions in principal similar to a CPM device.

The motion across the patient's spine is directed along the longitudinal axis of the spine to effectively apply traction across the spine. The traction is most preferably applied in an intermittent fashion as typically implemented via CPM devices. Parameters such as rate of motion, length of distraction, force of distraction, and the like will be controllable. The IPT device applies traction in such a manner as to create longitudinal forces and also flexion/extension or lateral bending forces depending upon the specific needs of the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features and advantages of the present invention will be readily appreciated as the invention becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing figures wherein:

FIGS. 1A-1B illustrate a lumbar IPT vest according to one embodiment of the present invention;

FIGS. 2A-2B illustrate a lumbar/thoracic IPT vest according to one embodiment of the present invention;

FIGS. 3A-3B illustrate a lumbar/thoracic/cervical IPT vest according to one embodiment of the present invention;

FIGS. 4A-4B illustrate a thoracic/cervical IPT vest according to one embodiment of the present invention;

FIGS. 5A-1 and 5A-2 illustrate one IPT vest that is being operated to implement CPM front-to-back flexation on a patient using varying IPT cycles;

FIGS. 5B-1 and 5B-2 illustrate one IPT vest that is being operated to implement CPM lateral flexation on a patient using varying IPT cycles;

FIGS. 6A and 6B illustrate one IPT vest that is being operated to implement intermittent traction on a patient using varying IPT cycles;

FIG. 7 illustrates one IPT vest that is being operated to implement orbital CPM on a patient using random IPT cycles;

FIG. 8 illustrates an IPT vest suitable for implementing CPM and traction according to one embodiment of the invention;

FIG. 9 illustrates a patient wearing an IPT vest for implementing CPM and traction according to one embodiment of the invention;

FIG. 10 illustrates an IPT vest suitable for implementing CPM and traction according to one embodiment of the invention;

FIG. 11 illustrates an IPT vest controller for controlling a fluidic lifter device according to one embodiment of the invention;

FIG. 12 illustrates an IPT vest controller for controlling an electromechanical lifter device according to one embodiment of the invention;

FIG. 13 illustrates an IPT vest applied to a patient in a hydrotherapy environment;

FIG. 14 illustrates an IPT device lifter that operates solely in response to a spring latching mechanism; and

FIG. 15 illustrates an IPT device suitable for spinal treatment in a patient's cervical region.

While the above-identified drawing figures set forth particular embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Looking now at FIGS. 1A and 1B, an IPT vest is shown according to one embodiment of the present invention. The IPT vest includes a lumbar region belt 12 and a thoracic region belt 14 that are joined in the patient front side via a pair of anterior CPM lifter/stabilizer units 16, 18, and joined in the patient's back side via a single posterior CPM lifter/stabilizer unit 20. CPM lifter/stabilizer units 16, 18 and 20 can be of the type described in U.S. patent application Ser. No. 11/094,862 (‘862’ application) that is incorporated by reference in its entirety herein, and may be, for example, fluidic, electromechanical, or various combinations of fluidic and electromechanical units. A patient operated controller 22 is provided that may be battery operated or optionally may be operated via AC power under predetermined operating conditions. The CPM lifter/stabilizer units can be attached to the upper thoracic belt 14 and the lower lumbar belt 12 via any suitable mechanical means such as the use of rivets 24 as shown. Using the controller 22, the patient can then program the IPT vest such that lifter/stabilizer units 16, 18 and 20 extend and retract as desired to implement the intermittent passive traction treatment necessary to the patient's recovery.

FIGS. 2A and 2B illustrate a lumbar/thoracic IPT vest according to one embodiment of the present invention. The IPT vest is similar to the IPT vest shown in FIG. 1, except the thoracic belt 14 is located much higher into the patient's arm pit area. The IPT vest depicted in FIGS. 1A and 1B, for example, may be employed to treat lumbar region L1-L5 while the IPT vest depicted in FIGS. 2A and 2B may be employed to treat a lumbar-thoracic region including the complete lumbar region up to, for example, the T6 thoracic region. This embodiment is preferable in circumstances where a patient may have a disc problem in the upper/thoracic are which is too close to the patient's heart region such that a surgical operation is a disadvantageously dangerous solution.

FIGS. 3A and 3B illustrate a lumbar/thoracic/cervical IPT vest according to one embodiment of the present invention. This embodiment is useful for treatment of a patient's entire (lumbar, thoracic and cervical) spinal region. This IPT vest can be seen to include a cervical collar 42 attached to a lower/lumbar belt 12 via a single posterior lifter 20; and is particularly useful to simulate a hydrotherapy modality for the patient. The cervical collar 42 importantly should be customized to prevent any damage to a patient's mandible region of the body.

FIGS. 4A and 4B illustrate a thoracic/cervical IPT vest according to one embodiment of the present invention. In this embodiment, a thoracic belt 14 is supported and secured to the patient's upper/thoracic region via a pair of shoulder straps 52, 54. Adjustment of the straps 52, 54 and a frontal fastener 56 allows the patient to position the thoracic belt 14 in a selected area of the patient's thoracic region. In this regard, this IPT vest is versatile to provide IPT in more than one area of the thoracic region as desired or necessary. Controller 22 can be implemented as a preprogrammed unit or may optionally be implemented as a unit that is programmable on-the-go by the patient. Such controller units are well known in the art, and so structural details of the controller 22 will not be discussed herein to preserve brevity and enhance clarity. The controller 22 may utilize stored algorithmic software or algorithmic software stored on external programmable media to control operation of the IPT vest. Operation of an IPT vest to implement intermittent passive traction on a patient is discussed in further detail below.

FIGS. 5A-1 and 5A-2 illustrate one IPT vest 60 that is being operated to implement CPM front-to-back flexation on a patient using varying IPT cycles. Extension of the posterior lifter/stabilizer unit with simultaneous retraction of the anterior lifter/stabilizer unit as illustrated in FIG. 5A-1 causes the patient to bend over in a forward motion; while extension of the anterior lifter/stabilizer unit with simultaneous retraction of the posterior lifter/stabilizer unit as illustrated in FIG. 5A-2 causes the patient to bend or flex his/her body in a rearward motion. This continuous passive motion (CPM) has been found useful in reducing spinal stiffness following spinal surgery.

FIGS. 5B-1 and 5B-2 illustrate one IPT vest 70 that is being operated to implement CPM lateral flexation on a patient using varying IPT cycles. It should be apparent that a single IPT vest may accommodate appropriate lifter/stabilizer units to provide both the front-to-back flexation and the side-to-side flexation depicted in FIGS. 5A-1, 5A-2, 5B-1 and 5B-2 respectively.

FIGS. 6A and 6B illustrate use of an IPT vest to implement intermittent traction on a patient using varying IPT cycles. More particularly, FIG. 6A shows an IPT vest 80 having two lifter-stabilizer units 82, 84 being retracted into a spinal compression mode; while FIG. 6B shows the units 82, 84 being extended to put the patient's spine into a traction mode.

FIG. 7 illustrates an IPT vest that is being operated to implement orbital CPM on a patient using random IPT cycles in accordance with a programmed algorithmic software controlling extension and retraction of a plurality of lifter-stabilizer units. The lifter-stabilizer units can thus be operated to cause the patient to rotate the upper portion of the patient's body about an axial point-similar to the motion used when operating a hoola-hoop.

FIG. 8 illustrates an IPT vest 100 suitable for implementing CPM and traction according to one embodiment of the invention. Some patients may require substantial vest customization in order to achieve the desired results from IPT. IPT vest 100 thus includes an adjustable scissor-jack apparatus 102 that may be operated to apply a desired force against that arch portion of the patient's back. Scissor-jack apparatus 102 may be extended and retracted, for example, by a threaded rod and driven worm gear assembly 104. IPT vest 100 also includes a thoracic belt 14 and a lumbar belt 12 connected via a lifter-stabilizer that also employs a screw thread 106 and a motor driven worm gear assembly 108. An upper receiver portion 109 of the lifter-stabilizer unit is adapted to receive the screw thread 106. Rotation of screw thread 106 raises and lowers the lifter-stabilizer unit. Several lifter-stabilizer units suitable for use with IPT vest 100 are discussed in detail in the ‘862’ application discussed herein before and incorporated by reference in its entirety herein.

FIG. 9 illustrates a patient wearing an IPT vest 200 for implementing CPM and traction (IPT) according to one embodiment of the invention. IPT vest 200 includes a shoulder orthosis 202 (similar in fashion to a football shoulder pad), and can be seen to include at least one anterior swivel plate 204 and at least one posterior swivel plate 206. Screw threads 208, 210 are attached at one end to the shoulder orthosis 202 via a motor driven worm gear assembly 212, 214 respectively. The other end of the anterior screw thread 208 is attached to swivel plate 204 via a swivel hinge 218. The other end of the posterior screw thread 210 is attached to swivel plate 206 via a swivel hinge 222. Rotation of anterior screw thread 208 via the motor driven worm gear assembly 212 selectively raises and lowers swivel plate 204; while rotation of posterior screw thread 210 via the motor driven worm gear assembly 214 selectively raises and lowers swivel plate 206. A lower anterior screw thread 224 is attached at its upper end to the lower portion of the upper anterior screw thread 208. Similarly, a lower posterior screw thread 226 is attached at its upper end to the lower portion of the upper posterior screw thread 210. Rotation of lower anterior screw thread 224 and lower posterior screw thread 226 is provided via motor driven worm gear assemblies 230 and 232 respectively. Rotation of the lower screw threads 224, 226 operates to apply or remove a desired force from the anterior and posterior regions of the patient as shown in the figure. In this manner, selective operation of the lifter-stabilizer units 240, 242 in combination with selective operation of the motor driven worm gear assemblies 212, 214, 230, 232 causes the patient to receive a desired prescription of intermittent passive traction (IPT) to speed-up the patient's recovery.

FIG. 10 illustrates an IPT vest 300 suitable for implementing CPM and traction (IPT) according to one embodiment of the invention. IPT vest 300 includes several features that have been found by the present inventors to aid a patient's recovery from a spinal injury. IPT vest 300 can be seen to include an upper (thoracic) belt 302, a lower (lumbar) belt 304. The upper and lower belts 302, 304 are coupled to one another via a plurality of lifter-stabilizer units 306, 308, 310 that may be of one or more types, e.g. fluidic, electro-mechanical, such as discussed herein before. IPT vest 300 can also be seen to include a lumbar pillow portion 320 that may employ hot and/or cold compresses integrated therein. Electrodes 330 are strategically positioned throughout various portions of the IPT vest 300, and may be used to provide electrical stimulation to numerous nerves and muscles in association with the IPT. A power unit 340 is integrated into the lumbar belt 304 to supply power to the various lifter-stabilizer units 306, 308, 310 and also to the electrodes 330. A programmable controller 350 is also integrated into the lumbar belt 304, and is used to control the parameters of the patient's intermittent passive traction, among other treatment parameters.

FIG. 11 illustrates an IPT vest controller for controlling a fluidic lifter-stabilizer device 400 according to one embodiment of the invention. Fluidic lifter-stabilizer device 400 includes a fluidic cylinder 402 that receives a fluid from a pressure source 404. A pressure transducer 406 responds to a fluidic pressure supplied via the fluidic cylinder 402 to feed back a signal to a controller unit 408. The controller unit 408 employs the feedback signal from the transducer 406 to modify the fluid pumped from the pressure source 404. When the fluidic cylinder 402 is devoid of fluid, no pressure is exerted on the pressure transducer 406; and the fluidic lifter-stabilizer device 400 is in its natural unbiased state in which a residual cushioning/stabilizing force is provided by a spring 410. The present invention is not so limited however, and any number of residual cushioning mechanisms can be employed to provide a desired level of residual cushioning and/or stabilization. A residual cushioning device 412 is also shown at the bottom portion of the IPT vest. This cushioning device 412 could be provided, for example, by use of any number of cushioning materials such as a gel material, rubber, cork, spring(s), etc.

FIG. 12 illustrates an IPT vest controller for controlling an electromechanical lifter device 450 according to one embodiment of the invention. The electro-mechanical lifter device 450 operates in similar fashion as the fluidic device described herein before with reference to FIG. 11. Electro-mechanical lifter device 450 however, employs a screw thread 502 that is driven via an electric motor assembly 504 with an internal worm gear for turning the screw thread 502. A strain gage 506 is used to supply the requisite feedback signal to the controller unit 408. The controller unit 408 can be implemented with a CPU, a micro-controller, a micro-computer, or any other programmable device that can be made to be portable and that is capable of controlling the IPT vest in a manner consistent with the principles described herein.

Keeping the above principles in mind, a method of providing intermittent passive traction according to one embodiment of the invention is now described below. Subsequent to selecting an IPT vest such as one of those described herein before, the IPT vest is placed on a patient and adjusted according to the patient's physical characteristics and also according to a selected treatment regimen. The CPM motion across the patient's spine will be directed along the longitudinal axis of the spine as stated herein before. This in effect will apply traction across the spine. The traction will be applied in an intermittent fashion as typically seen in CPM devices. Parameters such as rate of motion, length of distraction, force of distraction, and the like will be controllable. The application of traction may be applied in such a manner as to create longitudinal forces and also flexion/extension or lateral bending forces, depending upon the specific needs of the patient.

In view of the above, the initial phase of operation will involve a gradual application of traction across the spinal elements. The term gradual as used herein means increasing or decreasing by fine or slight or often imperceptible degrees. The initial phase will be followed by a sustained traction phase and finally a relaxation phase. During the first phase of IPT, the spinal elements will be placed under gentle traction. This period of time will reduce the normal forces across the vertebral bodies, facet joints, paraspinal musculature, etc. The second phase will hold the spine in sustained traction, further reducing the forces across the spinal elements, encouraging natural healing to occur and allowing the muscles a period of relaxation. The third phase will be the gradual reduction of traction. During this final phase, the normal forces across the spine will reestablish as the IPT device slowly releases traction.

The IPT vests discussed above are most preferably contoured in such a fashion that they will accommodate a variety of body habitues, as stated herein before. The foregoing IPT modalities and devices may also be employed by the patient in a variety of selected therapy environments such as, but not limited to, the hydrotherapy setting as illustrated in FIG. 13 that depicts a patient wearing an IPT device 500 that is controlled via a controller unit 512 in accordance with the principles described herein above.

A portion of one simple IPT vest 600 that may be suitable for IPT hydrotherapy is shown in FIG. 14, and can be seen to include a manually controlled spring-latch mechanism 602. Since the patient will already be in a buoyant hydrotherapy environment, one IPT modality may only require the cyclic setting and release of the mechanical spring-latch mechanism 602.

FIG. 15 illustrates one embodiment of an IPT device 700 that is suitable for treatment of the cervical portion of a patient's spine. IPT device 700 includes an upper (mandible) jaw collar 702 and a lower (shoulder) support collar 704 coupled together via a pair of anterior lifter-stabilizer devices 706, 708 and a single posterior lifter-stabilizer device 710. Lifter-stabilizer devices 706, 708, 710 are adjusted in response to a controller unit 712 having embedded algorithmic software to establish the IPT therapy regimen. The controller unit 712 may also be a programmable unit that may include a patient programmable keyboard and/or keypad for manual entry of program parameters, or may include integrated storage devices such as flash memory, EEPROMS, and the like, that may be programmed upon receipt of algorithmic program instructions stored on external storage media. A pair of mechanical stops 714, 716 are included and may be adjustable to limit the range of vertical movement allowed for a particular patient.

In summary explanation, IPT modalities are provided to benefit the spinal elements, similar to the benefits provided by CPM and traction in other areas of the body. The IPT units, such as described herein above with reference to the figures, will be dynamic in nature, allowing the patient freedom of movement, i.e. an ambulatory traction device. Desired therapeutic effects than can be achieved by combining the traction effect, CPM, and ambulation.

The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this specification are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims

1-26. (canceled)

27. An ambulatory cervical spinal unloading apparatus configured to provide a desired amount of traction force to a spine of a patient and to absorb an intermittent and/or unexpected shock and/or vibration, with the traction force provided via a plurality of lifter assemblies, comprising:

an upper jaw collar;

a lower support collar;

a residual cushioning device; and

the plurality of lifter assemblies;

wherein the plurality of lifter assemblies each independently expands or retracts to control distance between the orthotic belts to provide the traction force to a cervical portion of a spine of a patient, and each of the lifter assemblies further comprises a residual cushioning device that independently provides a desired residual cushioning effect by compression of a spring and/or damper to thereby absorb an intermittent and/or unexpected shock and/or vibration, wherein the spring and/or damper is effective to provide the residual cushioning for the lifting assembly in a deactivated state.

28. The apparatus of claim 27 with the lifter assemblies each comprising a worm gear tuning a threaded rod or a piston actuated fluidic lifting device.

29. The apparatus of claim 28, with at least one of the lifter assemblies comprising a piston actuated fluidic lifting device.

30. The apparatus of claim 29 wherein the piston actuated fluidic lifting device comprises a pneumatically operated piston.

31. The apparatus of claim 29 wherein the piston actuated fluidic lifting device comprises a pair of pistons connected by a piston rod, and with each piston fitting a pneumatic cylinder.

32. The apparatus of claim 31 her comprising a gel-filled chamber that provides the residual cushioning.

33. The spinal unloading apparatus according to claim 27, wherein at least one orthotic belt comprises integrated electrodes selectively positioned to provide a desired level of muscle or nerve stimulation in response to a desired electrical bias.

34. The apparatus of claim 27 further comprising a plurality of contact electrodes to deliver transcutaneous electrical nerve stimulation.

35. The apparatus of claim 27 wherein the upper orthotic belt and/or the lower orthotic belt comprises a plurality of contact electrodes to deliver transcutaneous electrical nerve stimulation.

36. The spinal unloading apparatus according to claim 27, wherein the residual cushioning device comprises a gel-filled chamber.

37. The spinal unloading apparatus according to claim 27, wherein the residual cushioning device comprises the spring.

38. The spinal unloading apparatus according to claim 27, wherein the residual cushioning device comprises the damper.

39. The spinal unloading apparatus according to claim 27, wherein each of the plurality of lifter assemblies comprises no more than one fluidic chamber.

40. The spinal unloading apparatus according to claim 27, wherein the plurality of lifter assemblies each comprise at least one electric motor configured in combination with a mechanical extension shaft assembly to selectively control the distance.

41. The spinal unloading apparatus according to claim 40, wherein the mechanical extension shaft assembly comprises at least one element selected from the group consisting of belts, pulleys, cables, threaded shafts, and gears.

42. The spinal unloading apparatus according to claim 41, further comprising a hot pack.

43. The spinal unloading apparatus according to claim 27, further comprising a recording apparatus operational to selectively record desired information associated with at least one parameter selected from the list consisting of traction, spinal unloading, stimulation, and/or therapeutic parameters.

44. A method of spinal unloading comprising:

providing an ambulatory spinal unloading apparatus that comprises a first collar, a second support collar, and a plurality of lifter assemblies configured to selectively vary a distance between the collars comprising a residual cushioning device that provides a desired residual cushioning effect achieved by compression of a spring and/or damper to thereby absorb an intermittent and/or unexpected shock and/or vibration for at least one of the lifter assemblies in a deactivated state.

45. The method of claim 44 further comprising providing transcutaneous electrical nerve stimulation through a plurality of contact electrodes.

46. The method of claim 44 further comprising providing transcutaneous electrical nerve stimulation through a plurality of contact electrodes located on the upper collar or the support collar.

47. The method of claim 46 further comprising providing a heat source in combination with the transcutaneous electrical nerve stimulation.

48. The method of claim 46, with at least one of the lifter assemblies comprising a piston actuated fluidic lifting device that comprises a pneumatically operated piston.

49. The method of claim 46 wherein the piston actuated fluidic lifting device comprises a pair of pistons connected by a piston rod, with each piston fitting a pneumatic cylinder, and further comprising supplying a gas to one of the cylinders for moving the piston rod.