The effect of isotonic saline on the strength of bone cement during the polymerisation period

Release characteristics of enoxaparin sodium-loaded polymethylmethacrylate bone cement

BACKGROUND

This study aimed to prepare the polymethylmethacrylate (PMMA) bone cement release system with different concentrations of enoxaparin sodium (ES) and to investigate the release characteristics of ES after loading into the PMMA bone cement.

METHODS

In the experimental group, 40 g Palacos®R PMMA bone cement was loaded with various amount of ES 4000, 8000, 12,000, 16,000, 20,000, and 24,000 AXaIU, respectively. The control group was not loaded with ES. Scanning electron microscopy (SEM) was used to observe the surface microstructure of the bone cement in the two groups. In the experiment group, the mold was extracted continuously with pH7.4 Tris-HCL buffer for 10 days. The extract solution was collected every day and the anti-FXa potency was measured. The experiment design and statistical analysis were conducted using a quantitative response parallel line method.

RESULTS

Under the SEM, it was observed that ES was filled in the pores of PMMA bone cement polymer structure and released from the pores after extraction. There was a burst effect of the release. The release amount of ES on the first day was 0.415, 0.858, 1.110, 1.564, 1.952, and 2.513, respectively, from the six groups with various ES loading amount of 4000, 8000, 12,000, 16,000, 20,000, and 24,000 AXaIU, all reaching the peak of release on the first day. The release decreased rapidly on the next day and entered the plateau phase on the fourth day.

CONCLUSION

The prepared ES-PMMA bone cement has high application potential in orthopedic surgery. ES-PMMA bone cement shows good drug release characteristics. The released enoxaparin sodium has a local anti-coagulant effect within 24 h after application, but it will not be released for a long time, which is complementary to postoperative anti-coagulation therapy.

Bone temperature during cementation with a heatsink: a bovine model pilot study

Background

Bone cement is an effective means of supporting implants, but reaches high temperatures while undergoing polymerisation. Bone has been shown to be sensitive to thermal injury with osteonecrosis reported after one minute at 47°C. Necrosis during cementing may lead to loosening of the prosthesis. Some surgeons fill the joint cavity with cool irrigation fluid to provide a heatsink during cementing, but this has not been supported by research. This paper assesses a simple technique to investigate the efficacy of this method.

Findings

We used a model acetabulum in a bovine humerus to allow measurement of bone temperatures in cementing. Models were prepared with a 50 mm diameter acetabulum and three temperature probe holes; two as close as possible to the acetabular margin at half the depth of the acetabulum and at the full depth of the acetabulum, and one 10 mm from the acetabular rim. Four warmed models were cemented with Palacos RG using a standard mixing system and a 10 mm polyethylene disc to represent an acetabular component. Two of the acetabular models were filled with room temperature water to provide a heatsink. An electronic probe measured temperature at 5 second intervals from the moment of cementing.

In the models with no heatsink, peak temperature was 40.3°C. The mean temperature rise was 10.9°C. In the models with a heatsink, there was an average fall in the bone temperature during cementing of 4.4°C.

Conclusions

These results suggest that using a heatsink while cementing prostheses may reduce the peak bone temperature. This study demonstrates a simple, repeatable technique which may be useful for larger trials.