The etiology and pathophysiology of Bone Cement Implantation Syndrome are complex and not fully understood. Early theories proposed that circulating methyl methacrylate (MMA) monomers caused vasodilation, leading to cardiovascular and pulmonary effects. However, subsequent research demonstrated that the concentration of MMA in plasma after cemented hip arthroplasty is significantly lower than the level required to produce these effects. This led researchers to focus more on an embolic-mediated model, which has gained more support in explaining BCIS. This theory suggests that embolization of particles such as fat, bone marrow, cement, and air, which occurs during the cementation process, is a primary contributor to the syndrome.
Monomer-Mediated Model
The monomer-mediated model was one of the first explanations for BCIS, theorizing that circulating MMA monomers cause vasodilation and cardiovascular symptoms. While this was demonstrated in vitro, in vivo studies found that the plasma concentration of MMA after arthroplasty is insufficient to cause the observed cardiovascular effects. As a result, researchers shifted their attention to the embolic model as a more plausible explanation for BCIS.
Embolus-Mediated Model
The embolic model suggests that during cementation and prosthesis insertion, high intramedullary pressures develop, causing embolization of particles into the circulatory system. These emboli, which contain fat, marrow, air, and cement particles, travel to the right atrium, right ventricle, and pulmonary vasculature. Once lodged in the pulmonary vessels, they lead to increased PVR and the clinical manifestations of BCIS. The emboli may cause both mechanical obstruction and trigger the release of vasoactive or pro-inflammatory mediators that exacerbate the condition. Although widely accepted, the embolic model has its limitations, as the degree of embolization often does not correlate with the severity of hemodynamic changes.
Mechanical Effects
The mechanical effects of emboli are a significant factor in Bone Cement Implantation Syndrome . During prosthesis insertion, high intramedullary pressures force embolic particles into the circulation. These emboli can cause physical obstruction in the pulmonary vessels, leading to increased PVR, right ventricular failure, and decreased cardiac output. Although modifications in cementing techniques, such as using a suction catheter during prosthesis insertion, have been shown to reduce embolization, the exact relationship between the embolic load and cardiovascular compromise in BCIS remains unclear.
Mediator Effects
In addition to the mechanical obstruction caused by emboli, there are mediator effects that further increase PVR. Emboli may damage the endothelium, releasing endothelin-1, which causes vasoconstriction. They can also trigger the release of vasoactive and pro-inflammatory mediators, such as thrombin and tissue thromboplastin, which directly or indirectly increase PVR. These mediators may also contribute to ventilation-perfusion mismatch and hypoxemia, further worsening the patient’s condition.
Histamine Release and Hypersensitivity
Some studies suggest that histamine release may play a role in Bone Cement Implantation Syndrome . Patients undergoing cemented hip arthroplasty who experience hypotension have been found to have elevated plasma histamine levels. However, the cause of histamine release, whether direct or IgE-mediated, remains unclear. While histamine receptor blockers have shown some protective effects, these findings have not been consistently replicated, leaving this theory inconclusive.
Complement Activation
The complement system, specifically the peptides C3a and C5a, has also been implicated in BCIS. These peptides are potent vasoconstrictors and bronchoconstrictors, and their increased levels in response to either a direct action of MMA or hypersensitivity can lead to pulmonary vasoconstriction and systemic hypotension. Despite initial studies supporting this theory, later research has failed to confirm complement activation as a definitive mechanism in BCIS.
| Proposed mechanism | How it would produce BCIS | Standing in the evidence |
|---|---|---|
| Monomer mediated | Circulating methyl methacrylate monomer causes vasodilation with cardiovascular and pulmonary effects | Shown in vitro, but plasma MMA after cemented arthroplasty is far below the concentration needed, so attention shifted to the embolic model |
| Embolus mediated | High intramedullary pressures during cementation and prosthesis insertion drive fat, marrow, air and cement particles to the right heart and pulmonary vasculature, raising pulmonary vascular resistance | Widely accepted, though the degree of embolization often does not correlate with the severity of hemodynamic change |
| Mechanical obstruction | Embolic particles physically obstruct pulmonary vessels, raising PVR and causing right ventricular failure and reduced cardiac output | Cementing changes such as a suction catheter during insertion reduce embolization, but the link between embolic load and cardiovascular compromise is still unclear |
| Mediator effects | Emboli damage endothelium and release endothelin-1, thrombin and tissue thromboplastin, which raise PVR and worsen ventilation–perfusion mismatch and hypoxemia | Offered as an addition to mechanical obstruction |
| Histamine release and hypersensitivity | Elevated plasma histamine accompanies hypotension after cemented hip arthroplasty | Inconclusive; whether release is direct or IgE mediated is unknown and the protective effect of histamine blockers has not been consistently replicated |
| Complement activation | C3a and C5a act as potent vasoconstrictors and bronchoconstrictors, producing pulmonary vasoconstriction and systemic hypotension | Supported by early studies, but later research failed to confirm it as a definitive mechanism |
