Dynamic fluoroscopic examination of the affected hip under anesthesia is considered the best method of predicting hip stability. Fragment size, which can be calculated using the Keith, Moed, or Calkins method, can be used to predict hip stability radiographically, however they are not as accurate. In general it is thought that posterior wall fractures involving less than 20% of the posterior wall are stable, whereas those involving greater than 40%-50% are unstable. Unfortunately, this leaves an indeterminent zone (20-40%) which does not provide guidance in treatment.
Moed et al retrospectively reviewed 33 patients with posterior wall fractures who underwent dynamic fluoroscopic stress testing and compared the results of this testing to the Moed, Calkins, and Keith method of hip stability prediction. They found that the Moed method is the only reliable technique that is predictive of hip stability for small fracture fragments while also being predictive of instability for large fracture fragments. However, they also stated that there remain a substantial number of fractures involving 20% or more of the posterior wall that are both stable and unstable by examination under anesthesia. Therefore, they recommend dynamic fluoroscopic examination for assessment of hip stability in the presence of a posterior wall fracture.
Tornetta et al conducted a study in which dynamic fluoroscopic stress views were taken of 41 acetabular fractures that met the criteria for non-operative management to determine subtle signs of instability. Of the 41 fractures, 38 were found to be stable and 91% of these had good or excellent outcomes at 2.7 years. They concluded that dynamic stress views can identify subtle instability in patients who would normally be considered for non-operative treatment.
1-> Keith Method - Depth of the fracture segment in injured hip is compared to the contralateral intact posterior wall depth at the level of the fovea
2-> Moed - Depth of the fracture segment in the injured hip is compared to contralateral posterior wall depth at the level of the greatest amount of fracture involvement
3-> Calkins - Length of posterior acetabular arc from each hip is compared at the level of the greatest amount of fracture involvement.
Moed BR, Ajibade DA, Israel H. Computed tomography as a predictor of hip stability status in posterior wall fractures of the acetabulum. J Orthop Trauma. 2009 Jan;23(1):7-15.
PMID:19104298 (Link to Abstract)
Tornetta P 3rd. Non-operative management of acetabular fractures. The use of dynamic stress views. J Bone Joint Surg Br. 1999 Jan;81(1):67-70.
PMID:10068006 (Link to Abstract)
Routt MLC Jr. Surgical treatment of acetabular fractures. In: Browner BD, Jupiter JB, Levine AM, Trafton PG, Krettek C, eds. Skeletal Trauma: Basic Science, Management, and Reconstruction. 4th ed. Philadelphia, PA: Saunders Elsevier; 2009:1171-1218