This study demonstrates that clinical MRI can provide accurate measurements of cartilage topography, thickness, contact areas and surface curvatures of the knee.

This study characterizes the donor and recipient sites involved in osteochondral autograft surgery of the knee with respect to articular cartilage contact pressure, articular surface curvature, and cartilage thickness. Five cadaveric knees were tested in an open chain activity simulation and kinematic data were obtained at incremental knee flexion angles from 0 degrees to 110 degrees. Surface curvature, cartilage thickness, and contact pressure were determined using a stereophotogrammetry method. In all knees, the medial trochlea, intercondylar notch, and lateral trochlea demonstrated nonloadbearing regions. Donor sites from the distal-medial trochlea were totally nonloadbeadng. For the intercondylar notch, lateral trochlea, and proximal-medial trochlea, however, the nonloadbearing areas were small, and typical donor sites in these areas partially encroached into adjacent loadbearing areas. The lateral trochlea (77.1 m(-1)) was more highly curved than the typical recipient sites of the central trochlea (23.3 m(-1)), medial femoral condyle (46.8 m(-1)), and lateral femoral condyles (42.9 m(-1)) (P < 0.05). Overall, the donor sites had similar cartilage thickness (average, 2.1 mm) when compared with the typical recipient sites (average, 2.5 mm). The lateral trochlea and medial trochlea curvatures were found to better match the recipient sites on the femoral condyles, while the intercondylar notch better matched the recipient sites of the central trochlea. The distal-medial trochlea was found to have the advantage of being nonloadbearing. Preoperative planning using the data presented will assist in more conforming, congruent grafts, thereby maximizing biomechanical function.

Double-bundle reconstructions achieve more physiologic knee function.

Rehabilitation of the symptomatic patellofemoral joint aims to strengthen the quadriceps muscles while limiting stresses on the articular cartilage. Some investigators have advocated closed kinetic chain exercises, such as squats, because open kinetic chain exercises, such as leg extensions, have been suspected of placing supraphysiologic stresses on patellofemoral cartilage. We performed computer simulations on geometric data from five cadaveric knees to compare three types of open kinetic chain leg extension exercises (no external load on the ankle, 25-N ankle load, and 100-N ankle load) with closed kinetic chain knee-bend exercises in the range of 20 degrees to 90 degrees of flexion. The exercises were compared in terms of the quadriceps muscle forces, patellofemoral joint contact forces and stresses, and "benefit indices" (the ratio of the quadriceps muscle force to the contact stress). The study revealed that, throughout the entire flexion range, the open kinetic chain stresses were not supraphysiologic nor significantly higher than the closed kinetic chain exercise stresses. These findings are important for patients who have undergone an operation and may feel too unstable on their feet to do closed chain kinetic chain exercises. Open kinetic chain exercises at low flexion angles are also recommended for patients whose proximal patellar lesions preclude loading the patellofemoral joint in deeper flexion.

This technique can be useful for in vivo clinical evaluation of cartilage thinning in the osteoarthritic patellofemoral joint.