Medium-term osteolysis with the Wallaby I® deep-dished total knee prosthesis

Area of Science:

• Orthopedic surgery
• Biomaterials science
• Medical device engineering

Background:

• Highly congruent total knee prostheses aim to reduce polyethylene wear and osteolysis.
• Conventional gamma-irradiated polyethylene inserts have shown high rates of aseptic loosening.
• The Wallaby I® prosthesis utilizes a deep-dished tibial insert made of conventional polyethylene.

Purpose of the Study:

• To assess the medium-term outcomes of the Wallaby I® total knee prosthesis.
• To compare the rates of aseptic loosening and osteolysis with posterior-stabilised prostheses.
• To evaluate the hypothesis that the Wallaby I® prosthesis has similar or lower rates of aseptic loosening and osteolysis.

Main Methods:

• Retrospective analysis of 121 consecutive total knee arthroplasty (TKA) patients between 2001-2005.
• Complete follow-up data over 4 years for 89 patients, with a mean follow-up of 96 months.
• Clinical and radiographic IKS scores were analyzed.

Main Results:

• 10 knees required revision TKA due to osteolysis and aseptic loosening after a mean of 81 months.
• Mean 9-year prosthesis survival was 88±17%.
• Insert delamination, fracture of the tibial baseplate, and insert mobility were observed in several cases.

Conclusions:

• Medium-term outcomes were inferior compared to posterior-stabilised components.
• Potential causes include polyethylene quality variations and increased shear stresses from the deep-dish design leading to backside wear.
• The Wallaby I® prosthesis is not recommended for use; CT follow-up is advised for patients with this implant.