Rinsing

Rinsing grafts has been shown to improve the shear strength of impacted allografts.^{42, 44B}  The mechanisms for this are two fold. First, the removal of fat and marrow fluid reduces the lubrication of particles and thereby increasing frictional resistance. Secondly, removal of fat before impaction increases the compactability of the graft, allowing greater interdigitation between particles. These advantages have been borne out in a whole construct model of femoral impaction grafting

in bovine femora and during in vivo human studies.⁴³ The authors reported a statistically significant reduction in subsidence using rinsed graft compared to using non-rinsed graft. Similar improvements in cup stability have also been demonstrated in an acetabular model.^{41 + 41B}

Despite a clear effect on mechanical implant stability,  the biological effects of rinsing are not as clear. On the one hand, freshly milled graft may contain growth factors and cytokines that stimulate the incorporation of the morselized graft bed by encouraging ingrowth and new bone formation. On the other hand, immunogenic factors present in the freshly frozen allograft bone may reduce bone ingrowth. Recently, a goat model was used to study the effect of rinsing on bone ingrowth into

morselized impacted autograft and allograft bone.⁴⁴ Without rinsing, the autograft bone showed more bone ingrowth than did the allograft bone. Rinsing prior to impaction reduced ingrowth into the autograft bone but increased ingrowth into the allograft bone. Similar results have been found with solvent defatted allograft in non-impacted bone chamber models in rabbits.⁴⁵ It is not clear whether this increased ingrowth is secondary to the more porous nature of rinsed bone or whether there is some form of biological inhibition from the marrow. Allograft produces an immunogenic response to the graft and most antigenic cells are

found in the marrow. Rinsing the graft removes most of the marrow, resulting in a reduction in the immunological load to the patient. Furthermore, the risk of disease transmission is reduced with removal of blood, marrow, cells and bacteria. Rinsing the bone bed also reduces thromboembolic extravasation of bone marrow during cement application. Sherman et al.⁴⁶ compared hemodynamic and blood gas changes during THA in a dog model and suggested that thorough bone lavage before cementing had a highly effective prophylactic effect on cardiovascular complications. Similarly, Byrick et al.⁴⁷ found a significant reduction of fat emboli using high-volume pulsed lavage in comparison to low-volume lavage and no lavage during cemented arthroplasty in a dog model. The most effective method of rinsing grafts has not yet been determined.