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Since its introduction in the 1970s, unicompartmental knee arthroplasty (UKA) has become a standardized routine technique. Increasing experience in determining the indication for UKA and improvements in design and materials of the prosthesis have led to better results. The AMC UKA has an unconstrained mobile bearing with congruent area contact from 0 degrees to 30 degrees of flexion. The principle is that a polyethylene mobile bearing, concavely spherical above and flat below, can maintain perfect congruity between the spherical metal femoral condyle and the flat metal tibial plateau. This ensures complete freedom to rotate and slide upon one other with physiologic kinematic and low intrinsic stability. The low contact stress results in reduced polyethylene wear. The 361 AMC UKA replacements of the current study showed safe anchorage of the prosthesis and good durability of the mobile bearings. The clinical results of the investigated patients demonstrate that the AMC UKA is a successful concept. The comparison of 30 minimally invasive UKA with 30 conventional UKA and 30 total knee replacements shows an advantage of the minimally invasive technique with regard to reduced rehabilitation time. The accuracy of implantation was comparable between the conventional and the minimally invasive techniques.

The introduction explains the general problems of knee joint replacement by artificial hinge-type prostheses, due to the reduction of the physiological "degrees of freedom" to only rotational movements around a horizontal axis. These problems are compared with the advantages of this type of prosthesis. Subsequently a description of some significant constructional characteristics of the hinge-type prosthesis, 13 given as there are placement of the joint, size of the contact surface, safety of the rotational device, design of the hinge-mechanism, the patella shield and the prosthetic stems as well as the breaking of dynamic forces, which all are subsequently compared in their values. Finally a hinge-type prosthesis is described with characteristics judged optimal according to our present scientific knowledge. We statistically evaluated our material of hinge-type prostheses with regard to final results and frequency of serious complications.

Over the past two decades, orthopaedics has gone through major changes, principally in the surgical treatment options for articular defects of the knee. This paper explores the advantages and shortcomings of the current surgical treatment modalities for cartilaginous defects in the knee. Emphasis is placed on current techniques in knee arthroplasty, including a view on the future of orthopaedic knee surgery.