Seventy-six patients who had eighty-seven unicompartmental knee
replacements were followed for an average of fifty-three months (range, two
to twelve years). The operation was on the medial side in eighty-two knees
and on the lateral side in five. Fifty replacements were unconstrained and
thirty-seven were constrained. Of the fifty knees that had an unconstrained
replacement, forty-nine (98 per cent) had a good or excellent result,
compared with only twenty-six (70 per cent) of the knees that had a
constrained replacement; the difference is significant (p = 0.0007). No
knee that had an unconstrained replacement had a poor result, compared with
nine (24 per cent) of the knees that had a constrained replacement (p =
0.0009). Four (8 per cent) of the fifty knees that had an unconstrained
replacement later had a revision total knee arthroplasty, compared with ten
(27 per cent) of the thirty-seven knees that had a constrained replacement;
the difference is significant (p = 0.04). Noteworthy degenerative changes
in the opposite compartment occurred in only one of the eighty-seven knees
(a knee in which an unconstrained prosthesis had been inserted).