Automatic ankle clamp

An automatic ankle clamp for use with an extramedullary alignment device includes a cradle having a triggering device movably mounted thereon. A pair of clamp arms are resiliently mounted for movement on the triggering device between an open position and a closed position. A latch device interconnects the clamp arms and the cradle for retaining the clamp arms in the open position and for simultaneously releasing the clamp arms to the closed position in response to movement of the triggering device relative to the cradle. The clamp is attachable to an extramedullary alignment device such that urging the cradle and triggering device into engagement with a patient's ankle, automatically and simultaneously releases the clamp arms to grip the patient's ankle. A base is mounted on the cradle for calibrated medial/lateral adjustment of the clamp relative to the extramedullary alignment device.

BACKGROUND
 The disclosures herein relate generally to total knee replacement and more
 particularly to an automatic clamp for an alignment guide used in
 resecting the tibial plateau.
 During total knee surgery, the proximal portion of the tibia is cut away in
 preparation for a tibia implant. A cutting block or guide is typically
 used to aid the surgeon in locating and making the cut. Placement of the
 tibia cutting block is critical to establishing the plane of the tibial
 plateau for providing the proper alignment of the implant. One device
 commonly used for achieving property alignment is an extramedullary
 alignment assembly including an elongated rod. The distal end of the rod
 is connected to an ankle clamp used to stabilize the rod in order to
 assist in establishing the correct angle of cut for the tibial plateau.
 Several known devices are used for this purpose. One such device includes a
 cradle that provides a "V" shaped notch for receiving the ankle. In this
 device the surgeon or an assistant must hold the ankle cradle in place
 during alignment.
 In another known device, a "V" shaped cradle is held in place by a strap or
 a tension spring which wraps around the ankle and fastens to the cradle.
 This device securely holds the clamp in place after alignment is
 established. However, two hands are required to position the device during
 alignment.
 U.S. Pat. No. 5,628,750 discloses a tibial resection guide alignment device
 including an extramedullary mount having a separate extramedullary member
 which may be removably mounted to a base member. A bottom assembly is
 connected to the extramedullary member by which the device may be
 connected around a patient's lower leg or ankle. A "V" shaped cradle
 includes two spring loaded arms that close around the ankle for stability
 and require the use of two hands for operation.
 In U.S. Pat. No. 5,197,944, an ankle clamp apparatus for use in tibial
 cutting instruments has a frame with pivoting arms attached for gripping a
 patient's ankle during use. The arms can be held open with latches prior
 to placement and quickly released to grip the patient's leg by depressing
 the latches. A "V" shaped cradle includes spring loaded arms. The arms may
 be locked in an open position and released to a closed position in
 response to depressing an individual button for each arm. Although this
 device purports to be for single handed operation, it requires each button
 to be separately depressed for releasing a respective arm. Therefore, in
 order to release both arms simultaneously, both buttons must be depressed
 simultaneously, which requires two handed operation.
 Single handed use is very desirable during surgery. A probable limitation
 with the individual buttons for releasing the arms is the inability to
 simultaneously reach both buttons with the same hand that is positioning
 the clamp, therefore negating the single handed use. Another problem might
 be the accidental misalignment of the clamp. When only one arm closes from
 one side, the cradle may shift to the opposite side that is not yet being
 held. Again, this may require the use of a second hand to maintain
 alignment during clamping.
 Therefore, what is needed is a clamping device which attaches to the
 alignment rod and which automatically clamps onto the patient's ankle when
 engaged therewith such that the surgeon's hands remain free to stabilize
 the extramedullary alignment assembly and cutting block.
 SUMMARY
 One embodiment, accordingly, provides a clamp that may be locked in an open
 or cocked position which holds spring loaded arms ready to automatically
 and simultaneously release and clamp onto the ankle after alignment is
 accomplished. To this end, an automatic clamp includes a cradle having a
 first part and a second part movable relative to the first part. A pair of
 clamp arms are resiliently mounted for movement on the cradle between an
 open position and a closed position. A latch device interconnects the
 clamp arms and the cradle for releasing the clamp arms for movement from
 the open position to the closed position in response to the second part
 moving relative to the first part.
 A principal advantage of this embodiment is that the clamp arms may be set
 in an open position. Using one hand the surgeon may align the clamp. Once
 alignment is made, merely pushing the "V" cradle including a triggering
 device against the distal tibia will release both arms to lock the
 instrument in place. Both arms will close simultaneously, not allowing the
 cradle to shift in either direction. No shifting of the hand or reaching
 with fingers to push buttons is required, thus allowing a true, one handed
 operation.

DETAILED DESCRIPTION
 An automatic clamp device is generally designated 10 in FIG. 1, and is
 provided for use with an extramedullary alignment device for one-handed
 operation in securing the device onto a patient's ankle. Clamp device 10
 includes a cradle 12 including a first side 12a and a second side 12b,
 each joined at a main portion 12c. A triggering device 14 is provided to
 be movably mounted on cradle 12 and includes a first side 14a and a second
 side 14b, also joined at a main portion 14c. A first clamp arm 16a is
 provided for pivotal movement on first side 12a of cradle 12 and is
 engaged with an end of first side 14a of triggering device 14. Similarly,
 a second clamp arm 16b is provided for pivotal movement on second side 12b
 of cradle 12 and is engaged with an end of second side 14b of triggering
 device 14. A base 18 is mounted on cradle 12 for calibrated adjustment
 therewith. An extension 20 is provided on base 18 for adjustably attaching
 the cradle 12 to an extramedullary alignment device (to be discussed
 below).
 A respective mandrel 22 is used to mount each clamp arm 16a, 16b on cradle
 12. This is accomplished by mounting the arms 16a, 16b on a respective
 side 12a, 12b of cradle 12, so that an opening 24 of each clamp arm 16a,
 16b is aligned with an opening 26 of each respective side 12a, 12b of
 cradle 12. Also, a respective torsion spring 28 has a first end 28a
 engaged in an opening 30 in each clamp arm 16a, 16b, and a second end 28b
 engaged in an opening 32 in each mandrel 22. Each mandrel 22 is seated in
 an opening 34 in a respective one of the torsion springs 28 such that an
 end 36 of each mandrel 22 extends into opening 24 in a respective one of
 the clamp arms 16a, 16b. A respective fastener 38 extends through each
 opening 26 of sides 12a, 12b to engage the end 36 of each mandrel 22.
 Triggering device 14 is mounted for reciprocal movement on cradle 12 by
 means of a pair of fasteners 40, each of which extend through a respective
 slot 42 formed in triggering device 14, and are received in a respective
 threaded opening 44 formed in cradle 12. A portion of a spring 46 is
 compressed in a slot 48 formed in cradle 12 and another portion of the
 spring is also compressed in a similar slot 48a formed in triggering
 device 14. Slots 48 and 48a are of the same size but are slightly offset
 so as to normally position triggering device 14 offset from cradle 12
 toward clamp arms 16a, 16b. A plurality of seep holes 50 are provided in
 triggering device 14 in communication with slot 48a for providing access
 to clean any debris accumulated around the spring 46. Movement of
 triggering device 14 relative to cradle 12 is guided by a pair of guide
 tabs 52, only one of which is visible in FIG. 1. One of the guide tabs 52
 is mounted in a slot 54 in side 12a of cradle 12 and another tab is
 mounted in a slot in side 12b (not visible in FIG. 1). Tabs 52 also seat
 in a pair of similar slots 56 formed in sides 14a and 14b of triggering
 device 14 and aligned with slots 54.
 Cradle 12 includes a key 58 which is movably mounted in the keyway 60
 formed in base 18. A threaded fastener 62 extends through an elongated
 slot 64 formed in keyway 60. Fastener 62 is received and retained in a
 movable friction connection with base 18 by means of a threaded receiver
 65 and a spring washer 66, so that medial/lateral adjustment of cradle 12
 may be made relative to base 18. The adjustment is calibrated by varying
 alignment between a scale 68 on cradle 12 and a reference 70 on base 18.
 In operation, clamp arms 16a, 16b, FIG. 2 each include a notch 72 on a
 distal end thereof. A mating tab 74 extends from a distal end of sides
 14a, 14b for engagement with notches 72. The torsion springs 28 which
 resiliently mount clamp arms 16a, 16b on cradle 12, described above,
 permit clamp arms 16a, 16b to be cocked into a first or open position C
 wherein notches 72 engage with tabs 74, FIG. 2a. Also, triggering device
 14 is urged into an offset position O, relative to cradle 12 such that a
 movable trigger edge 76 of triggering device 14 overhangs a stationary
 edge 78 of cradle 12 due to a force imposed by compressed spring 46,
 discussed above, which also urges tabs 74 into notches 72.
 Forced engagement of trigger edge 76 with a patient's lower leg or ankle
 region 80, moves triggering device 14 relative to cradle 12 to a released
 position R, FIG. 3, such that movable trigger edge 76 of triggering device
 14 is substantially aligned with stationary edge 78 of cradle 12. This
 movement is sufficient to move tabs 74 out of engagement with notches 72,
 which permits forces imposed by torsion springs 28 to rotate clamp arms
 16a, 16b to a second or clamped position L, see also FIGS. 3a and FIG. 4.
 The force imposed by compressed spring 46 maintains tabs 74 engaged with
 an articulating surface 82 of clamp arms 16a, 16b, see FIG. 3a. As a
 result, when clamp arms 16a, 16b are returned to the cocked open position
 C, FIG. 2, tabs 74 are urged into notches 72.
 Extension 20 of base 18 is inserted into a slot 84 of an extramedullary
 alignment device 86, FIG. 5. A first end 88 of extramedullary device 86 is
 appropriately attached to a patient's knee, not shown, in a manner which
 is well known. An alignment rod 90 extends to a second end 92 of
 extramedullary device 86. Clamp 10 is attached to second end 92 by
 insertion of extension 20 into slot 84. An adjustment member 94 at second
 end 92 permits anterior/posterior adjustment of clamp 10 via extension 20
 within slot 84, in the directions indicated by directional arrow A/P.
 Threaded receiver 65 may be manipulated to permit medial/lateral
 adjustment of clamp 10 via movement of key 58 in keyway 60 for calibrated
 adjustments measured by scale 68 and reference 70, in the directions
 indicated by directional arrow M/L.
 As a result, one embodiment provides an automatic clamp including a cradle
 having a first part and a second part movable relative to the first part.
 A pair of clamp arms are resiliently mounted for movement on the cradle
 between an open position and a closed position. A latch device
 interconnects the clamp arms and the cradle for releasing the clamp arms
 for movement from the open position to the closed position in response to
 the second part moving relative to the first part.
 Another embodiment provides an automatic clamp including a cradle and a
 triggering device movably mounted on the cradle. A pair of clamp arms are
 resiliently mounted for movement on the triggering device between an open
 position and a closed position. A latch device interconnects the clamp
 arms and the cradle for releasing the clamp arms for movement from the
 open position to the closed position in response to movement of the
 triggering device relative to the cradle.
 Another embodiment provides an automatic ankle clamp for use with an
 extramedullary alignment device including a cradle having a first part and
 a second part. A cradle includes a trigger movably mounted thereon. A pair
 of clamp arms are resiliently mounted for movement on the cradle between
 an open position and a closed position. A latch device interconnects the
 clamp arms and the trigger for simultaneously releasing the clamp arms for
 movement from the open position to the closed position in response to the
 trigger being moved relative to the cradle. An extension is provided for
 adjustably attaching the cradle to the alignment device.
 Another embodiment provides an automatic gripping clamp including a cradle
 and a trigger movably mounted thereon. A pair of clamp arms are
 resiliently mounted for movement on the cradle between an open position
 and a closed position. A latch device interconnects the clamp arms and the
 trigger for retaining the clamp arms in the open position and for
 simultaneously releasing the clamp arms to the closed position in response
 to movement of the trigger relative to the cradle. A base is mounted on
 the cradle for calibrated adjustment of the cradle.
 A further embodiment provides a method of securing an alignment device on a
 patient's ankle. A triggering device is movably mounted on a cradle. A
 pair of clamp arms are resiliently mounted on the triggering device for
 movement between an open position and a closed position. The clamp arms
 and the cradle are interconnected with a latch device for retaining the
 clamp arms in the open position and for releasing the clamp arms to the
 closed position. The cradle is attached to an extramedullary alignment
 device. The latch device is engaged for resiliently loading the clamp arms
 in the open position. The cradle and triggering device are urged into
 engagement with the patient's ankle for automatically and simultaneously
 releasing the clamp arms to grip to patient's ankle.
 As it can be seen, the principal advantages of these embodiments are that
 the clamp may be locked open or cocked by an assistant or by the surgeon
 at the time of use. Cocking the clamp holds the two spring loaded arms in
 the open position. Using one hand the surgeon may align the clamp. Once
 alignment is made, merely pushing the "V" shaped cradle including the
 triggering device against the distal tibia adjacent the ankle will release
 both arms to lock the instrument in place. Both arms will close
 simultaneously, not allowing the cradle to shift in either direction. No
 shifting of the hand or reaching with fingers to push buttons is required,
 thus allowing a true, one handed operation.
 Additionally, the surgeon may shift the distal tip of the extramedullary
 rod in either the medial or lateral direction by sliding the
 medial/lateral adjustment on the ankle clamp. The slide is held in place
 by spring tension or may be securely locked in place with a finger knob.
 To further aid the surgeons ability to obtain the proper slope for the
 bone resection, the distal tip of the extramedullary rod may also be
 shifted in the anterior or posterior direction. Adjustment is accomplished
 by sliding the extramedullary rod to the desired position on the ankle
 clamp.
 Although illustrative embodiments have been shown and described, a wide
 range of modifications, change and substitution is contemplated in the
 foregoing disclosure and in some instances, some features of the
 embodiments may be employed without a corresponding use of other features.
 Accordingly, it is appropriate that the appended claims be construed
 broadly and in a manner consistent with the scope of the embodiments
 disclosed herein.