The success of total knee replacement depends on several factors, however, surgical technique is particularly important. In fact mistakes in alignment of prosthtic components are common causes of aseptic loosening.

Serious improper alignment (more than 3°) was found out, according to several papers, in about 10% of the implants; this appears not correlated with surgeon’s experience when they use mechanical alignment devices either extra medullary or intra medullary. The development of computer-based systems to achieve correct prosthetic components alignement has the purpose to solve the problems of traditional mechanical alignement systems. At present computer-assisted navigation systems, either they areimage-free or imege-based, are widely empolied while robotic systems are not so commonly used. The Authors describe in this paper the features of the computer-assisted navigation system they at present employ. They moreover emphasize its precision and the reproducibility of the results they can achive. The features of this system (it is based on an image-free navigation method; it allows quantification of the kinematics of the knee; it allows the use of either specially designed cutting bolcks or standar instruments), are an intresting evolution of computer-assisted navigation systems for knee replacement.

The degenerative processes of the glenohumeral joint can be derived from primitive glenohumeral arethrosis, post traumatic arthrosis, neurogenic arthropaty and rotator-cuff arthropaty with inveterate cuff tears. These conditions have shared characteristics but the arthropaty from an inveterate tear of the rotator cuff estabilishes a characteristic connected to the distinctive lesions that culminate in the well-known radiologic imaging of ace-tabularization.

Our experience of prothesization of the shoulder referring to this final result, with wich we previously tented toward using a bipolar endoprothesis, often with comforting but at time also decidedly disappointing results. Overall, our dissatifaction was attributed to the insufficient mobility regained with modest remaining muscle-tendons available, and to the anterior instability of the implant if not contained in a valid coracoacromiale arch. For this reason we are tending toward ageo-metric inverse prothesis with the supposition of intrinsic stability and a lever arm favorable to the contraction of slight muscolar recruitment. The inverse Delta prothesis provide an innovative therapeutic option for many patients with serious glenohumerale arthrosis associated with massive tear of the rotator cuff with the rising up of the humeral head. Our work intends to show which are the advantages and the limits, including surgical ones, of using the result of the prothesization of eight specially selected patients treated with the Delta prothesis. Without doubt the innovative architecture and the recent modification ofthe prothesis become clear; it becomes possible to do certain manouvers very easily which in the past were more complicated; also highlighted is the immediate symptomatic benefit that the patient obtain from the joint-substitution operation with this type of prothesis. On the other hand, it is therefore fundamental to select the patients in a very precise way who can undergo this operation, to have a notable improvement in their lifestyle. The modest but significant esperience derived from these first cases treated with the geometri inverse prothesis have introduced us to a relative simple prosthetic system, but just a bit more invasive than the endoprosthetic surgery; it is stable and well-tolerated, able to adequately satisfy the modest functional request permitted by the residual anatomic substratum. The autors, based on this limited but significant experience, intented tomention same technological problems inherent to the various od the implantation including the dif-ficulties occasionally met and resolved.