Influence of Heterotopic Ossification on Range of Motion aft
The incidence of heterotopic ossification (HO) after total knee arthroplasty (TKA) varies. This study aimed to identify the incidence of HO in patients undergoing revision TKA for either stiffness or aseptic loosening/instability and determine if the presence of HO is associated with inferior absolute range of motion (ROM) and ROM gains.

To assess ROM after revision TKA, 87 patients were prospectively enrolled and divided into two cohorts. Patients in Group 1 (N=40) were evaluated for stiffness, while those in Group 2 (N=47) were evaluated for either aseptic loosening or instability. Preoperatively, as well as at 6-weeks, 6-months, and 1-year postoperatively, goniometer-measured ROM values were collected. A Fisher's exact test was used in the statistical analysis to see whether there was a connection between preoperative HO and final ROM 1 year after revision TKA.

--HO was identified on preoperative radiographs in 17 patients (20%).
--There was a significantly higher rate of preoperative HO in patients revised for stiffness compared to patients revised for instability or loosening (30% vs 11%).
--5 cases of HO qualitatively identified as most clinically severe were associated with lower ROM at each timepoint compared to the remainder of HO cases in this study cohort.

Finally, in patients undergoing revision TKA for stiffness, the presence of HO is higher. Furthermore, the magnitude of HO tends to have a significant impact on the preoperative and postoperative ROM trajectory. This knowledge should assist patients in setting realistic standards, and it emphasizes the need for a robust, structured HO classification system.