The menisci are integral to normal knee function. The purpose of this study was to measure the contact pressures transmitted to the medial tibial plateau under physiological loads as a function of the percentage of the meniscus involved by the radial tear or repair. Our hypotheses were that (1) there is a threshold size of radial tears above which contact mechanics are adversely affected, and (2) partial meniscectomy results in increased contact pressure compared with that found after meniscal repair. A knee simulator was used to apply physiological multidirectional dynamic gait loads across human cadaver knees. A sensor inserted below the medial meniscus recorded contact pressures in association with (1) an intact meniscus, (2) a radial tear involving 30% of the meniscal rim width, (3) a radial tear involving 60% of the width, (4) a radial tear involving 90% of the width, (5) an inside-out repair with horizontal mattress sutures, and (6) a partial meniscectomy. The effects of these different types of meniscal manipulation on the magnitude and location of the peak contact pressure were assessed at 14% and 45% of the gait cycle. The peak tibial contact pressure in the intact knees was 6 +/- 0.5 MPa and 7.4 +/- 0.6 MPa at 14% and 45% of the gait cycle, respectively. The magnitude and location of the peak contact pressure were not affected by radial tears involving up to 60% of the meniscal rim width. Radial tears involving 90% resulted in a posterocentral shift in peak-pressure location manifested by an increase in pressure in that quadrant of 1.3 +/- 0.5 MPa at 14% of the gait cycle relative to the intact condition. Inside-out mattress suture repair of a 90% tear did not restore the location of the pressure peak to that of the intact knee. Partial meniscectomy led to a further increase in contact pressure in the posterocentral quadrant of 1.4 +/- 0.7 MPa at 14% of the gait cycle. Large radial tears of the medial meniscus are not functionally equivalent to meniscectomies; the residual meniscus continues to provide some load transmission and distribution functions across the joint.