DIFFICULTIES WITH BEARING DISLOCATION AND BREAKAGE USING A MOVABLE BEARING TOTAL KNEE REPLACEMENT SYSTEM

In 1980, the low contact stress, or New Jersey, system was introduced with movable high-density polyethylene bearings between the metallic f emoral and tibial components. This system was developed to deal with t wo principal concerns of conventional knee replacement systems: loosen ing and wear. A federal Drug Administration review was required, and t he study was performed in two phases. From 1981 until 1984, components were cemented in 40 knees, which then were evaluated for an average o f seven years after surgery. From 1984 until 1986, 16 knees were selec ted for cementless fixation and were followed for an average of five y ears. The cemented group had a failure rate of 10% (four knees), two f rom 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 bearin g fracture and one from knee pain of uncertain source). Bearing failur e was attributable to the entrapment of the subluxed lateral bearing. Sacrifice of the anterior cruciate ligament predisposes the system to bearing subluxation and failure.