Background and Aim 

Chronic periprosthetic Joint Infection (PJI) is a serious complication following total joint arthroplasty (TJA). During two-stage revision surgery, antibiotics can be delivered locally using an antibiotic-loaded cement spacer (ALCS). Yet, it is unclear whether sufficient local target tissue concentrations are reached. We quantified intramedullary bone concentrations following vancomycin-loaded spacer implantation and compared these to the individual Minimal Inhibitory Concentration (MIC).

Methods

Stage One - Spacer Implantation

1 gram (group A) or 2 gram vancomycin (group B) was manually added to one batch (40g) PALACOS® R+G bone cement.

Custom-made articulating spacers were fabricated for hip patients (Link® Lubinus Classic Plus Stem and Link® IP 46 mm Acetabular Cup). Spacer molds were used in knee patients (COPAL® molds).

Stage Two - Spacer Removal & Sample collection

Timing of spacer removal and therefore sample collection followed routine clinical practice.

Bone samples were collected after spacer removal from the intramedullary bone stock, primarily from the acetabulum (hip) and distal femur (knee).

Analytical Methods 

Samples were analyzed using validated ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) assay.
Bone concentrations were crushed and compared to the individual minimum inhibitory concentration (MIC) by applying a bone density of 1.9 kg/L.[1]
If the individual MIC was unavailable, the epidemiological cutoff (ECOFF) for the respective microorganism was used as an alternative reference.[2]

Results 

In total (A+B): 71.4% of the knee patients and 57,1% of the hip patients exceeded the individual MIC at a mean of 65 days after spacer implantation (range 25-114 days)

Increasing the vancomycin from 1g to 2g did not seem to result in more patients achieving their individual MIC

Knee: 72.7% vs. 66.7%. Hip: 54.5% vs. 66.7%

Thicker knee spacers yielded higher mean vancomycin concentrations compared to medium and thin spacers. 

Conclusions

Antibiotic-loaded spacers can achieve adequate bone concentrations up to 16 weeks after spacer implantation. Doubling the vancomycin dosage to 2g did not increase bone concentrations.