Abnormal bone wound healing and FIX replacement to maintain health of bones following hemarthrosis in normal and in FIX^−/−mice. (A) Preservation of articulating surface of joint following hemarthrosis (microCT images). Three-dimensional rendering of the injured knee joint from microCT imaging obtained at 2 weeks after a single induced hemarthrosis followed by a single dose of placebo or FIX therapy at 20 minutes after wounding. WT: Hemostatically normal mouse, sham treated with IV NS. FIX^−/−: Hemophilia B mouse sham treated with IV NS. FIX^−/− + rFIX: Hemophilia B mouse treated with rFIX (Benefix) 250 IU/kg IV. FIX^−/− + N9-GP: Hemophilia B mouse treated with glycoPEGylated rFIX (N9-GP) 250 IU/kg IV. (B) Quantification of loss of integrity of articulating surface of the joint following hemarthrosis (“ratio of smoothness”). To quantify the observed loss of surface integrity, a mathematical model was derived from the imaged joints that calculated the shape of a theoretically perfectly smooth joint surface, which was assigned a value of 1.0. Any imaged depressions or elevations resulted in deviations from absolute smoothness, resulting in values of <1.0, giving a measurement of “ratio of smoothness” that is less than the ideal. At 2 weeks after the induced hemarthrosis, joints from animals treated with N9-GP demonstrated preservation of articular surface smoothness that was not statistically significantly different from that seen in hemostatically normal WT mice (ratio = 0.901 and 0.906, respectively). rFIX was less effective at preserving the integrity of the surface of the articulating bones. Points that are significantly different from “WT” are indicated by “*.” Points that are significantly different from “NS” are indicated by “#.” Markers of significance are used as follows: **P < .01, ****P < .0001, ^###P < .001, ^####P < .0001.