Contact Stress Elevations Following Acetabular Fracture Fixation are Associated With Radiographic Osteoarthritis At Minimum Two-Year Follow-Up.

Background: Despite improvements in fixation strategies over the past few decades, post-traumatic osteoarthritis (PTOA) rates following acetabular fracture have remained relatively constant. Chronic exposure to elevated contact stresses has been shown to result in both radiographic evidence of osteoarthritis and articular cartilage degeneration, but no association between contact mechanics and PTOA risk in reduced acetabular fractures has been established. The objective of this study was to determine if elevated contact stresses after acetabular fracture fixation are associated with future radiographically apparent PTOA. Methods: Sixteen adult patients treated for acetabular fractures with operative fixation between January 1, 2004 and December 31, 2016 who had (1) minimum two-year radiographic follow-up or conversion to hip arthroplasty and (2) an immediate post-operative pelvis CT scan for contact stress assessment met inclusion criteria for this study. Follow-up radiographs were graded using the modified Tonnis scale, and PTOA was considered present for grades >2 or if converted to hip arthroplasty. Discrete element analysis (DEA) was used to compute patient-specific contact mechanics for hips with acetabular fractures and intact contralateral hips. Results: Eleven of sixteen patients developed PTOA by Tonnis grading at a mean follow-up of 43.3 months. There were no differences in demographics or lengths of follow-up between patients who developed PTOA and those who did not. Acetabular fractures that developed PTOA had significantly different (p<0.024) contact mechanics than contralateral intact hips, while no significant differences (p>0.438) in contact mechanics metrics were found between intact and fractured sides in patients that did not develop PTOA. Only peak contact stress was significantly (p=0.027) higher in acetabular fractures that developed PTOA than those that did not. All contact stress metrics demonstrated significant, yet moderate, correlations with Tonnis grade across all hips. Conclusion: Development of radiographically apparent PTOA after acetabular fracture fixation is associated with persistently elevated contact stresses. Further, returning contact mechanics after surgical treatment of these fractures to levels similar enough to native intact hips may successfully help prevent PTOA. Clinical Relevance: These findings confirm the importance of anatomical articular fracture reduction during fixation of acetabular fractures to reduce elevated contact stresses and prevent future joint failure.