Arm angle indicator

An angle measurement device is provided for determining the version angle for the prosthetic humeral head during shoulder replacement surgery. The device has a first collar for contacting the forearm and has a first coupling element in the form of a rod aligned with the ulna. The device has a second collar for contacting the upper arm when the elbow is flexed to 90°. The second collar has a second coupling element coupled thereto extending in a direction generally perpendicular to the humerus. The second coupling element is pivotally coupled to the first coupling element for rotation about a pivot point axis. An angle indicator having angle indicia is located at said pivot point and fixed to one of said first or second arm contacting collars for indicating the angle between the ulna and the humerus during external rotation of the forearm.

BACKGROUND OF THE INVENTION

This invention relates to an extramedullary angle indicator, i.e. goniometer for measuring the version angle of the humeral head. The version angle is then used to orient a humeral prosthesis in the canal of the humerus.

One of the most critical steps in successful shoulder replacement is determining and maintaining the version of the humeral head. Most surgical techniques for total shoulder replacement advise the surgeon that the humeral component should be set at approximately 30-40° of retroversion. This will restore the shoulder's range of motion and the overall stability of the joint. Although the recommendations for humeral head retroversion are similar in most shoulder surgeries, the method in which this version is measured varies.

A prior art technique developed by Stryker Corp. for their Solar™ total shoulder, as shown inFIG. 1, instructs the surgeon to flex the patient's elbow 90° and externally rotate the forearm 30-40°.

In this system, as shown inFIG. 1, the surgeon uses the patient's sagittal plane (90° arrow) as a zero reference while rotating the forearm 30-40° away from the body. At this point, the surgeon visually sets the forearm at 30-40° and thereafter makes the humeral head resection in a known manner (not shown). The humeral head resection cut is made at right angles to the plane of the humeral shaft and head, thereby achieving 30-40° of retroversion.

As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. The sagittal plane is a vertical plane running from head to toe and dividing the body into right and left sections. The frontal or coronal plane is a vertical plane dividing the body into front and back sections.

SUMMARY OF THE INVENTION

It is one aspect of the invention to provide an instrument capable of measuring the version angle of the head of the humerus in a patient's shoulder joint.

It is yet another aspect of the invention to provide a instrument which connects to the forearm and to the upper arm via a pivotal connection which includes an angle measuring portion such as a distal face with angle markings and a locking portion so that the surgeon can dial in a selected version angle.

These and other aspects of the invention are provided by an arm angle measurement and indication device for determining the version angle of the humeral head during shoulder replacement surgery. The angle measurement device includes a first element in the form of a collar for contacting the forearm with the elbow flexed to 90°, and a second element also in the form of a collar for contacting the upper arm. The first element has a coupling element such as an L-shaped rod having a first link extending in a direction perpendicular to the forearm and a second link extending in a direction generally parallel to the axis of the forearm, thus forming the L-shaped configuration. The second element includes a coupling element, for example, in the form of a short rod which extends generally perpendicular to the axis of the upper arm, i.e. the humerus. The links of the first and second element are pivotally connected at a pivot point with a pivot axis extending, when the elbow is at 90°, in an inferior-superior direction along a plane parallel to both the sagittal plane and the frontal plane. An angle indicator having angle indicia located thereon centered at the pivot point is fixed to one of the first or second elements for indicating the angle between the first and second coupling elements for various external rotational position of the forearm with respect to the upper arm.

The angle indicator has a dial face with angle indicia from ±40° preferably at 5° increments centered about the pivot point. The 0° point is the position where the axis of the forearm or ulna and the humerus are in a plane parallel to the sagittal plane. V-shaped detents are provided on the edge of the dial.

The angle indicator is preferably mounted on the second element, i.e. the element for connecting to the upper arm. A spring loaded locking element is slidably mounted on the L-shaped arm connected to the first element, i.e. the element connected to the forearm and is biased into engagement with the detents on the angle indicator. The detents may be recesses in the dial face which recesses are preferably located at 5° increments ±40° on either side of the 0 point.

The first and second elements are preferably in the form of semi-circular collars having posterior open ends which fit over the forearm and upper arm in the bicep area. Straps may be included on the collars for positively coupling them to the arms.

DETAILED DESCRIPTION

Referring toFIG. 1, there is shown a prior method of setting the version angle with a patient viewed from above, having his forearm placed in a first position A where the forearm is parallel to the sagittal plane B and rotated to a second position C where the forearm position causes the humerus to be retroverted between 30 and 40° with respect to the shoulder glenoid. Referring toFIG. 2, there is shown the angle indicator of the present invention generally denoted as10having a first collar element12for coupling to the forearm and a second element14for coupling to the upper arm in the bicep area. In the preferred embodiment, each collar12,14is generally semi-circular and includes ends16and18which include slots20and22for receiving straps not shown. The straps are designed to couple to ends16and18through slots20and22and wrap around either the forearm or the upper arm. The straps may be held in position by Velcro fastening systems coupled to each end of a separate strap. Thus, with the elbow at 90°, when the pair of straps coupled to collar12are wrapped around the forearm and the pair of straps coupled to collar14are wrapped around the upper arm, the angle indicator is snuggly mounted externally of the arm.

Collar element14includes a post24rigidly coupled thereto preferably at the center of the strap between ends16and18. Likewise, collar element12includes a post26coupled to collar12intermediate ends16and18thereof. In the preferred embodiment, post24is rigid and straight whereas post26is L-shaped having a 90° bend and has a locking element28mounted thereon. Referring toFIGS. 7 and 8, it can be seen that post26includes an extension portion32which extends within angle indicator27and is pivotally coupled to pivot pin29. Preferably, pin29extends through indicator27in a direction perpendicular to the axis of the ulna when the elbow is at 90°.

Referring toFIGS. 3-7, it can be seen that angle indicator27has numbered angle indications of ±40° in 10° increments along curved portion30of angle indicator27with 5° marking lines intermediate the 9 numbers. Curved surface30has its center at pivot pin29. An annular angle locking element28is moveable along a first link32of angled rod26and is spring biased into engagement with surface30of angle indicator27. As can be seen inFIGS. 7 and 8, end portion32of rod26can be formed as a separate piece fixably attached to rod26. End portion32has a flange34at the end thereof adjacent rod26ands supports locking element28which is slidably mounted on the outer surface of portion32. Slidable locking element28is spring biased into engagement with outer curved surface30of angle indicator27by spring36. Spring36surrounds the outer surface of portion32and has a first end engaging flange34and a second end engaging an annular inner surface on locking element28. Since flange34is integral with portion32, locking element28is spring biased into engagement with surface30of indicator27.

In the preferred embodiments, surface30includes a plurality of generally V-shaped indented portions38which can be best seen inFIG. 6. In the preferred embodiment, each indented portion38corresponds to a 5° increment in either direction about the 0 point, i.e. the point where the forearm is parallel to the sagittal plane through the body. In the preferred embodiment, locking element28includes a V-shaped nose portion40which engages a corresponding V-shaped indentation38to lock extension32and rod26in a desired angular position.

As shown in the figures, extension32and rod26are pivotally coupled within angle indicator27at pivot point29by a preferably cylindrical pivot pin42shown best inFIG. 7. In the preferred embodiment, rod26is fixedly coupled to collar12in any convenient manner such as a rivet44shown inFIG. 5or by having a screw threaded through the wall of collar12into a threaded hole in lower portion46of rod26. In the preferred embodiment, a similar coupling system is used to couple collar14to rod24.

As best seen inFIGS. 2,7and8, the preferred angle indicator27has two spaced apart upper and lower walls50and52. In the preferred embodiment, these walls are spaced a distance equal to or slightly greater than the outer diameter of extension32of rod26. As can be seen inFIG. 8, angle indicator27has outer walls54and56which have V-shaped inner surfaces58and60which act as stops or limits for the angular rotation of extension32of rod26within angle indicator27. As shown inFIG. 8, rod24is coupled to end62of angle indicator27in any convenient manner such as by being threaded into a threaded bore in end62or in a permanent manner such as by welding rod24to end62. It would also be possible to eliminate rod24and attach the angle indicator directly to collar14.

Referring toFIGS. 9 and 10, there is shown the arm angle indicator mounted on a patient's upper right arm (bicep area) and forearm. As shown, collar12engages the forearm and collar14engages the upper arm. InFIG. 9, the angle indicator is shown in the 0 position with the forearm position parallel to the sagittal plane. InFIG. 10, the forearm is externally rotated to between 30 and 40° to properly measure the version angle required for a prosthetic humeral implant with regard to the patient's right shoulder. The arm angle indicator10allows the surgeon to “dial in” the version of the humeral head. The same arm angle indicator can be used with the left arm with the 0° to 40° on the opposite side of 0° being used during external rotation of the left arm. Thus, the placement of the angle indications of between 5 and 40° on both sides of the 0° reference allows the arm angle indicator10to be used on the both left and right shoulder since, in all cases, the forearm is externally located as shown inFIG. 1. Incorporating the arm angle indicator10into the surgical procedure allows the surgeons to accurately and consistently set the version of the humeral components. Specifically, after the shoulder incision is made, the rotator interval and the anterior capsule are exposed. The capsulotomy is completed and the humeral head delivered for visualization and the articular surface defined using the arm angle indicator. The following instructional steps make up the goniometer or arm angle indicator. Attach collar14to bicep and collar12to forearm using supplied straps as shown inFIG. 9. Pull release knob28and externally rotate the forearm as specified in the prosthetic shoulder surgical protocol to the position for example ofFIG. 10. Using the goniometer scale30dials the rotation of the forearm and releases the locking knob to lock the forearm in position. Once the rotation is set, continue to follow the prosthetic shoulder surgical protocol. Once the margin of the articular surface is determined, a humeral resection guide, (not shown), is placed on the humeral shaft and the rest of the surgical protocol is completed in the standard manner.