I solved it using b2WeldJoint:
var jointDef = new b2WeldJointDef();
jointDef.referenceAngle = 0.0;
jointDef.collideConnected = false;
jointDef.bodyA = body;
jointDef.bodyB = lastBody;
jointDef.localAnchorA = body.tileOffset;
jointDef.localAnchorB = lastBody.tileOffset;
var joint = this.world.CreateJoint(jointDef);