Introduction: The medial unicompartmental knee prosthesis (UKA) is less invasive than total knee arthroplasty (TKA) and preserves undamaged structures of the joint. The range of movement and recovery are better in UKA, while postoperative pain reduction is at least equal to TKA. UKA have a higher revision rate than TKA (15% vs 10% after 10 years). One main reason for revision is mechanical loosening1. There is a paucity of information regarding cement fixation of UKA. We compared jet lavage to conventional lavage with focus on cement pressures, interface temperatures and cement penetration.
Materials and Methods: UKA was performed in 10 paired entire human cadaver legs (Oxford Phase III, Biomet, Dordrecht, NL). Customized tibial implants and a pressure probe insert were used to measure the cement pressure anterior, posterior and near the implant fin during implantation and polymerisation. A drilling and fixation jig was used for standardized positioning of the three temperature probes. The polymerization heat was measured 5 mm below the bone surface at the medial and lateral plateau as well as under the fin. The same cementing technique was performed for all knees using Refobacin® Bone Cement R. One side of the paired knees was cleaned using jet lavage, contra lateral cleaning was done with conventional lavage. The lavage volume was equal for both
Methods: AP radiographs were taken and digitalized to quantify the cement penetration areas and depths, using a pixel-analysis-software. Group comparisons were done with the Wilcoxon-Test using SPSS (SPSS Inc., Chicago, Illinois).
Results: Average cement pressure under the tibial implant is significantly higher for conventional lavage (avg cement pressure 25.69 ± 17.85 kPa, p= 0.005) than for jet lavage (avg cement pressure 13.28 ± 12.82 kPa). Mean temperature increase measured 5 mm below the bone surface medial and lateral, as well as under the implant fin, were statistically significant higher for the cementing technique with jet lavage (lat. 14.10 ± 5.72°C, p= 0.018/med. 8.49 ± 4.20°C, p= 0.176/fin 5.95 ± 1.92°C, p= 0.063) than for the conventional lavage (lat. 9.42 ± 5.17°C/med. 6.42 ± 2.21°C/fin 3.96 ± 2.03°C). On AP radiographs, cement penetration areas under the tibial implant were significantly higher for jet lavage (penetration area: 122.15 ± 33.94 sq mm, p= 0.046) than for conventional lavage (penetration area: 89.82 ± 23.92 sq mm).
Discussion: The use of jet lavage showed clear advantages in our cadaver studies. Jet lavage resulted in higher cement penetration despite of lower cement pressures under the tibial implant. The higher cement penetration lead to higher interface temperatures but exposure to high temperatures over 50 °C with a risk for bone necrosis could not be measured.
