Goniometer

1. A goniometer comprising:

a first arm having a first part extending along one longitudinal axis and a second part extending along a different longitudinal axis;

a second arm;

a connecting portion pivotally connecting the first arm to the second arm about a pivot axis that is parallel to the longitudinal axis of the second part of the first arm, wherein the connecting portion comprises:

(a) an outer ring extending around the pivot axis; and

(b) an inner ring defining an aperture, the inner ring being (i) disposed within the outer ring, (ii) centered about the pivot axis and (iii) coupled to the outer ring by a third arm that extends from the outer ring, the aperture being aligned with the pivot axis between the first and second arms and arranged to allow an anatomical feature to be observed through the aperture along the pivot axis; and

a tubular sleeve coupled to the second part of the first arm, the tubular sleeve being configured for coupling to a surgical instrument, the tubular sleeve having a bore having a longitudinal bore axis that intersects the pivot axis and is parallel to the longitudinal axis of the first part of the first arm;

wherein the first part of the first arm is coupled to the second part of the first arm in a manner that allows for relative translational movement between the first part and the second part so that the distance between the tubular sleeve and the longitudinal axis of the first part of the first arm is adjustable; and

wherein the relative translational movement between the first part and second part of the first arm is in a direction transverse to the longitudinal axis of the first part of the first arm.

2. The goniometer of claim 1 , further comprising a rod having a central portion received within the aperture and first and second enlarged end portions, the central portion being slidable through the aperture and aligned with the pivot axis, the first and second enlarged end portions being sized to prevent either the first or second enlarged end portions from passing through the aperture.

3. The goniometer of claim 1 , wherein the second arm is extendable.

4. The goniometer of claim 1 , wherein the inner ring defines a tubular aperture, and further comprising a rod having a central portion, the central portion received within the tubular aperture.

5. The goniometer of claim 4 , wherein the outer ring comprises a first ring portion and a second ring portion coupled together and rotatable with respect to one another about the pivot axis, the first arm being fixedly coupled to the first ring portion and the second arm being fixedly coupled to the second ring portion such that the angle between the first arm and the second arm varies when the first ring portion and the second ring portion are rotated relative to one another.

6. The goniometer of claim 5 , further comprising a locking mechanism for locking the second arm to the first ring portion to fix the angle between the first arm and the second arm.

7. The goniometer of claim 6 , wherein the locking mechanism comprises a barrel disposed around either the first arm or the second arm such that the barrel is rotatable between a first unlocked position and a second locked position, wherein the barrel bears against the outer ring preventing the first ring portion and the second ring portion from rotating relative to one another.

8. The goniometer of claim 5 , wherein the first ring portion further comprises a rack extending around at least a portion of the periphery of the connecting portion, and one of the first arm and the second arm further comprising a sprung pawl attached thereto to selectively engage the rack.

9. The goniometer of claim 1 , wherein the outer ring further comprises a gauge arranged to indicate the angle between the first arm and the second arm.

10. The goniometer of claim 1 , wherein the outer ring has a first side and a second side, and wherein the third arm comprises a first portion and a second portion, the first portion extends from the first side of the outer ring and the second portion extends from the second side of the outer ring.

11. The goniometer of claim 10 , wherein the inner ring extends from the first portion to the second portion to define the aperture.

12. The goniometer of claim 1 , wherein the third arm extends from the outer ring along an axis that is perpendicular to the pivot axis.

13. The goniometer of claim 1 , wherein the outer ring has an outer perimeter and an inner perimeter, the inner perimeter defining an opening, and the inner ring is disposed within the opening.