CEMENTLESS MODULAR COMPONENTS FOR HIP REVISION IN COMPLEMOBILIZATIONS OF STEM AND CUP.

Abstract

Great diffusion of hip prosthetic surgery, in relatively-young patients too, generates as consequence an increase in prosthesis failures associated with limited or massive bone losses, making revision surgery mandatory, even in most advanced degrees of osteolysis.

In best surgery strategy planning are essential: - evaluation of osteolysis degree with standard x-Rays; - evaluation of periprosthetic bone turn-over with scintigraphy (both a specific as they give merely qualitative evaluations of bone remodeling); – quantitative evaluation of periprosthetic bone mineral density with periprosthetic mineralometry (D.E.X.A.). Data obtained with these methods allow more accurate decisions, during the pre-operative phase, regarding the most indicated implant for revision surgery: mid or long-stem, with or without omoplastic transplants, with or without materials promoting bone rehabitation. In any case, the surgeon must have all possible solutions in order to eventually change the operative plan during surgical act.

Following qualitative and quantitative periprosthetic bone evaluations, we use to classify stem and cup mobilizations with Italian Group for Revision (GIR) classification. According to GIR classification, our actual trends in the choice of revision prostheses, in the most advanced degrees of complex mobilizations of stem and cup, are the following: - GIR 3 (Enlargement of the femoral shaft with thinning of cortical bone and loosing of 2 or more walls; loosening and acetabular deformation with losing of one ore more columns and the bottom). In this degree we prefer a long-stem concept straight prosthesis; this prosthesis allows an immediately more stable implant, due to optimized length, in opposition to rotation forces and assuring force transfer in both proximal and distal direction. When osteolysis is wider, it was necessary a strategy change, searching a more distal locking of the implant, according to Wagner’s criteria. The SL Wagner’s prosthesis restores cohesion with the reabsorbed bone surface, generating a relative stability in the immediate post-op period; in the following 2 months, an intense bone apposition, which brings to a progressive filling of bone losses, takes place. For this purpose, it is not indicated, apart from surgical way used, cutting the muscle insertions around the thinned wall. This revision prosthesis is fixed without the use of cement due to the distal blocking, guaranteed by his conical shape; the stem is straight and it is not fit to the natural front-bending of femoral shaft. For this last explained reason, we follow these guidelines, improving our results, using a cementless anatomic modular stem: with this kind of implant design, that preserves cortical bone of femoral shaft from stress shielding, and the extremely wide (XX combination) choice of head and neck components, we are now able to regain as well as possible, the correct offset and center of rotation. For the acetabular loosening, we use to implant oval cups, that naturally fit the acetabular lesion, with or without bone grafts impaction in bone loss areas.- GIR 4 (Massive proximal bone loss all around the shaft; massive peri-acetabular loss). In the past we implanted wide-resection cemented (Muller) or non cemented (Kotz) prosthesis, originally designed for onchologic patients, to treat complete femoral osteolysis. The wide resection uncemented prosthesis, after follow up, supports the Wagner’s theory of distal support, because in spite of an almost complete bone sacrifice, there is an attempt of periprosthetic corticalization by the femoral bone. Since some years we implant even in this cases a modular distally-anatomic revision prosthesis, this type of prosthesis, thanks to his proximal component, provides a relative primary metaphyseal support, that improves global stability of implant. In massive peri-acetabular loss we prefer the use of oval components with peripheral supports and obturatory hook, with bone graft impaction. Only as “extrema ratio” we choose for the implant a McMinn stemmed cup.

From these guidelines, integrated with clinical observation at mid range follow-up, appears clerarly that cementless prosthesis in hip revision surgery, even in most advanced degrees of osteolysis, are really able to guarantee good results for the patient. These patients, previously implanted with hip prosthesis, have intrinsic limitations of hip joint ROM, sometimes associated with muscular impairments; therefore it’s rarely possible to bring back the hip to an optimal degree of function, especially if compared with a normal joint. The goodness of long-term results must be therefore evaluated in relation to patient’s conditions before the operation itself, especially according to bone conditions regarding osteointegration of prosthesis. If follow up of patient is constant, allowing to program with good timing the revision surgery, if necessary, the use of cementless prostheses is a very powerful (nevertheless conservative) instrument for good functional recovery of these patients.