Knee Extension Does Not Reliably Reduce Acute Type II Tibial Spine Fractures: MRI Evaluation of Displacement During Extension Versus Resting Flexion

BACKGROUND: Type II tibial spine avulsion (TSA) fractures have traditionally been managed by first attempting to achieve closed reduction with extension and immobilization, with surgical indications reserved for those who fail to reduce within 3 mm. However, the frequency with which appropriate reduction can be achieved is largely unknown. PURPOSE: To evaluate changes in displacement of type II TSA fractures by comparing magnetic resonance imaging (MRI) scans obtained with the knee in flexion and in extension. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Ten patients with type II TSA fractures were identified. Fracture displacement was measured using 3 images for each patient: (1) initial lateral view radiography, (2) sagittal-plane MRI of the knee in resting flexion, and (3) sagittal-plane MRI of the knee in passive extension. Maximum displacement of the bony fragment was measured in the 2 MRI studies for all patients, and the corresponding change in displacement was calculated. Displacement in flexion was compared with displacement in extension using a paired-sample t test. Statistical significance was set at P < .05. RESULTS: The displacement distance of the bony fragment was reduced by a mean of 0.97 mm on MRI when the knee was in extension compared with flexion in patients with type II TSA fractures (P = .02). Mean displacement with extension was 6.14 mm, with no fractures reduced below 4 mm. The largest reduction observed was 2.80 mm. The displacement distance increased in 2 knees with extension. The intermeniscal ligament (IML) was entrapped in 4 of 10 patients; however, the amount of reduction achieved did not differ based on the presence of IML entrapment (P = .85). CONCLUSION: While the amount of tibial spine displacement warranting surgical treatment can be debated, the study findings suggest that knee extension is not reliable in obtaining adequate closed reduction for type II TSA fractures. Management decisions may need to be based on the initial displacement distance of the fracture, with a lower threshold for operative treatment than previously recognized.