Crosslinked polyethylene stopped wearing after five years in uncemented knees

Design

Double-blinded randomised controlled trial with radiostereometric analysis

Population

96 uncemented cruciate-retaining total knee replacements

Primary outcome

Insert wear and component migration at 10 years

Effect

Medial wear 0.13 mm (crosslinked) vs 0.46 mm (conventional) at 10 years; tibial migration 0.99 vs 1.05 mm

This double-blinded randomised trial allocated 96 uncemented cruciate-retaining total knee replacements to a sequentially annealed highly crosslinked polyethylene insert or a conventional insert, and measured wear and component migration with radiostereometric analysis for ten years.

Medial wear in the crosslinked group did not progress after five years (0.15 mm at five years, 0.13 mm at ten), while wear in the conventional group continued to rise (0.22 mm to 0.46 mm). Tibial and femoral component migration was about 1 mm in both groups at ten years and stable after the initial settling. Patient-reported outcomes did not differ.

Radiostereometric wear is a surrogate: lower wear at ten years should mean less osteolysis and fewer revisions later, but the trial was not designed to show that. Concerns that crosslinked polyethylene might be brittle or loosen in uncemented knees were not borne out over this period.

• Consider highly crosslinked polyethylene inserts in younger, active knee replacement patients expected to load the implant for decades.
• Expect early migration of about 1 mm in uncemented components, settling after the first period.
• Do not expect a difference in patient-reported outcomes at ten years.
• Keep long-term radiographic follow-up for osteolysis whichever insert is used.

Why it matters

It eases a worry that crosslinked polyethylene might perform worse in the knee than it does in the hip.

Don't overread it

Wear and migration are surrogate measures in 96 knees; the trial does not show fewer revisions.

The statistics, in plain English

Radiostereometric analysis measures implant movement to fractions of a millimetre. The migration confidence intervals for the two groups overlap almost completely, so fixation was similar. The wear difference is clear but its effect on revision rates is not yet known.

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