Background: Poly (methyl methacrylate) (PMMA) bone cement is widely used to anchor total joint replacements to the contiguous bone. Among the clinically-relevant properties of this material is its intrusion depth (ID) because it indicates the potential for interdigitation of the curing cement into the interstices of the cancellous bone. ID is determined using procedures stipulated in ISO 5833. There is only one study in which ISO 5833 was examined critically, but only one exogenous variable was considered.
Purpose: In the present work, we carried out an extensive critical analysis of the ISO 5833 Standard.
Materials and Methods: 7 approved PMMA bone cement brands were used in two series of tests. In the first, the influence of time at which ID was determined (relative to achievement of cement doughing time (DT)) was delineated. In the second series, the influence of three clinically-relevant variables on ID on each of these brands was determined and, then, response surface methodology was used to analyze the results.
Results: ID results are given for both series of tests. Over the range of the variables used, the optimum IDs for a low-, a medium-, and a high-viscosity brand were computed to be 5.7 mm, 3.1 mm, and 2.4 mm, respectively.
Conclusion: The findings allowed us to recommend the following revisions to stipulations in ISO 5833: prior to running ID test, store the cement unit at 1 ° 60 minutes after removing the cement unit from the storage medium, mix the cement powder and liquid at 120 rpm; and determine ID 3 minutes after DT is achieved.