Tissue spreader with force measurement, force indication or force limitation

A retractor assembly, comprising:

• a first blade;
• a second blade that can move relative to said first blade;
• movement means for moving said second blade relative to said first blade;
• and, torque measuring means for measuring a torque applied to said movement means.

A retractor assembly, comprising:

• a first blade;
• a second blade;
• a gear assembly coupled to said first and second blades;
• and, a force measuring device coupled to said gear assembly.

A retractor assembly, comprising:

• a first blade;
• a second blade that can move relative to said first blade;
• movement means for moving said second blade relative to said first blade;
• and, force measuring device for measuring a force applied by said second blade.

A retractor assembly, comprising:

• a first blade;
• a second blade;
• a gear assembly coupled to said first and second blades;
• and, a slip clutch coupled to said gear assembly.

A retractor assembly, comprising:

• a first blade;
• a second blade that can move relative to said first blade;
• movement means for moving said second blade relative to the first blade, said movement means including a rack and pinion gear;
• and,
• clutch means for limiting the movement of said second blade.