Vibration, drainage can give denser graft compaction for impaction bone grafting

Femurs in study group showed less hoop strain than those undergoing standard grafting.

Issue: Issue 6 2007

England flag

Using a vibration and drainage technique during femoral impaction bone grafting may decrease the risk of femoral fracture while increasing graft compaction and prosthetic stability, according to British investigators.

In an in vitro study of femurs modified to represent those undergoing revision hip replacements, researchers compared a control group that underwent standard impaction bone grafting with femurs that had impaction bone grafting using vibration and drainage.

They discovered that the vibration and drainage group demonstrated significantly less mean peak load transferred to the femur during proximal impaction (P=.005) than the control group. The study also revealed significantly less mean mid-shaft hoop strain (P=.006) and peak proximal hoop strain (P=.09) in the experimental group.

Benjamin J. Bolland

Likewise, three-dimensional micro CT-imaging showed a higher percentage of graft and lower volumes of air, water and cement in the middle femoral regions of the experimental group, illustrating more dense graft compaction. Loading to 50,000 cycles also revealed significantly lower axial subsidence in the vibration group, but showed no significant differences between the groups regarding rotational subsidence.

“The use of vibration/drainage to impact bone graft resulted in reduced peak loads and hoop strains being transmitted to the femur and, therefore, reduced the risk of possible fracture,” Benjamin J. Bolland said during his presentation at the Trainees Prize Session at the British Orthopaedic Association Annual Congress. “It resulted in denser graft compaction, which in turn conferred to better prosthetic stability as marked by less subsidence on cyclical loading.”

Study design

The investigators studied femoral impaction bone grafting using a vibration hammer affixed with a perforated tamp/phantom in the experimental group and standard impaction bone grafting using Stryker’s X-change instruments in the control group. They repeated bone grafting using washed, morsellized allografts and inserted a cemented Exeter [Stryker] stem when they reached the endpoint of impaction.

“In the control group, this corresponded to there being no further movement to the phantom after 10 consecutive blows with the slap hammer,” Bolland said.

Investigators determined the endpoint in the experimental group when they found no further movement of the tamp despite being hit with a pneumatic hammer, according to the study. They discovered that significantly less graft was used in the control group compared to the vibration group, Bolland said.

A safer technique

Measuring of the mean peak load transferred to the femur
Bolland and his colleagues measured the mean peak load transferred to the femur and also studied the mid-shaft hoop strain and peak proximal hoop strain.

Graft compaction

The investigators also performed mechanical testing of the femurs to test prosthetic subsidence and stability. They used spacers to measure axial and rotational subsidence and three-dimensional micro CT-imaging to assess the portions of air, water, cement and bone graft in distal, middle and proximal regions of the femur.

While imaging revealed more dense graft compaction in the middle region of femurs in the vibration group compared to the controls, investigators found no significant differences between the groups regarding graft, air, water or cement volume in the distal region.

An analysis of the proximal region also showed a greater percentage of graft and lower ratios of water and air in the vibration group compared to the controls. However, investigators found no significant differences between the groups regarding cement volume in this region.

Good vibrations

Bolland said the use of vibration and drainage could also help surgeons identify the line between over- and underimpaction.

“More importantly, it gave a specific endpoint to the surgeon to know and, despite when the bone graft is fully impacted ongoing use of the instrumentation, it didn’t lead to any further increase in load or strain being transmitted through to the femur as well as providing a great safety net against over impaction and possible fracture,” he said. “Therefore, I think that this is a very safe and reliable — but more reproducible — technique to impact bone graft which will hopefully lead to more widespread use of impaction bone grafting in the future.”

Washed morsellized allograft

Cemented Exeter [Styker] stem

The investigators used washed morsellized allograft during the impaction process and inserted a cemented Exeter [Styker] stem.

Images: Bolland BJ

For more information:
Benjamin J. Bolland is a research specialist registrar in the School of Medicine at the University of Southampton, England. He can be reached at University Road, Southampton SO17 1BJ, England; +44-(0)23-8059-5000; bbolland@btopenworld.com. This research project was sponsored by the Engineering and Physical Sciences Research Council, Biotechnology and Biological Sciences Research Council and Stryker U.K.
Reference:
Bolland BJ, New AMR, Oreffo ROC, Dunlop DG. The role of vibration in femoral impaction bone grafting. Presented at the British Orthopaedic Association Annual Congress. Sept. 25-28, 2007. Manchester.