Difficulties with bearing dislocation and breakage using a movable bearing total knee replacement system.

ABSTRACT

In 1980, the low contact stress, or New Jersey, system was introduced with movable high-density polyethylene bearings between the metallic femoral and tibial components. This system was developed to deal with two principal concerns of conventional knee replacement systems loosening and wear. A federal Drug Administration review was required, and the study was performed in two phases. From 1981 until 1984, components were cemented in 40 knees, which then were evaluated for an average of seven years after surgery. From 1984 until 1986, 16 knees were selected for cementless fixation and were followed for an average of five years. The cemented group had a failure rate of 10% (four knees), two from tibial component loosening, one from bearing dislocation, and one from infection. Failure was determined by the necessity for revision. The uncemented group had a failure rate of 31% (four knees from bearing fracture and one from knee pain of uncertain source). Bearing failure was attributable to the entrapment of the subluxed lateral bearing. Sacrifice of the anterior cruciate ligament predisposes the system to bearing subluxation and failure.