Patella resurfacing in total knee replacement: functional evaluation and complications

Three different knee replacements, with three trochlear designs, were prosp ectively evaluated clinically and radiographically for patellar function an d presence of patellar complications. They included the Insall-Burstein (IB ) I and the IB-II (posterior cruciate ligament substituting) and the Menisc al Bearing Knee (MBK; posterior cruciate ligament recession). The trochlea of the IB-I was short and shallow with an anterior sharp edge of the interc ondylar box (later modified to a smoother edge) and the femoral component h ad a prominent "shoulder." In the IF-II the trochlea was deeper to allow fo r soft tissue clearance. In the MBK the trochlea was more prolonged, with R and L components and the "shoulder" was less prominent. In all the cases t he patella was resurfaced with an all polyethylene dome prosthesis. Knees w ith tibiofemoral problems were excluded. From the data of the present study the following conclusions can be drawn: (a) The most frequent problem was impingement (clunks) with the early version of the IB-I. Smoothening of the anterior edge significantly reduced the incidence of dunks to 5% in the mo dified IB I. (b) With the IB-II deepening the trochlea for soft tissue clea rance improved the degree, not the incidence of dunks (4.5%), compared to t he modified IB I. (c) With the MBK dunks were very rare and patellar functi on improved. (d) Throughout the three series patellar stress fractures and instability were rare and loosening or wear not evident. (e) Normal functio n (including stairs ascending and descending) can be expected in over 80% o f category A patients. (f) Of the various radiological parameters only pate lla baja was correlated with symptoms in the IB prostheses. (g) We still pr efer the dome design because is more tolerant and with cold flow may better conform to the trochlea increasing contact area.