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: We carried out an extensive critical analysis of the ISO 5833 Standard with a view to making
recommendations for revising it.
Materials and Methods: 7 approved PMMA bone cement brands (covering low-, medium-, and
high-viscosity brands) were used in two series of tests. In the first series, 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 for 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-, medium-, and 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 that the following revisions be made to stipulations
in ISO 5833 for determining ID: prior to running the ID test, store the cement unit at 1°C; 60
minutes after removing the cement unit from the storage medium, mix the cement powder and liquid,
in a vacuum chamber, at 120 rpm; and determine ID 3 minutes after DT is achieved.