Aims: the aim of the job is the evaluation of the pressure values between bone cement and the stem of hip prosthesis in post-operating medium-term conditions.

Methods: the experimental activity was developed in two phases. During the first one the hygroscopic behaviour of some cements in various application conditions was characterized. In particular some cylindrical specimens were realized using two types of cements: the Surgical Simplex P by HowmedicaA8 and the CMW 1 Radiopaque by DePuyA8. The specimens were obtained both with vacuum techniques and manual techniques. The specimens was instrumented with resistive strain gages and placed in a 37A1C water thermostatic bath. In the second part of the activity models of stems realized with aluminium tubular elements (diameter 10 mm) were instrumented with strain gages in order to measure the circumferential strains from which is possible to evaluate the pressure acting on the stems. The models was then inserted in cylindrical cavities representing the femoral cavities (diameter 15 mm) in which the same cements used in the first test were injected with the same operative conditions. Such specimens were inserted in the thermostatic bath to estimate the effects of the hygroscopic phenomena acting on the stems. Cements temperatures during the polymerization was also evaluated by means of special sensors applied on the stems. For all the phases the strains were acquired for an 8 weeks period.

Result: The activity permitted to analyze the hygroscopic expansion coefficients of the considered bone cements and to estimate the pressure values on the prosthetic stems. The pressure values evaluation have shown that, after an initial phase, during which we assist at a depression due to the volumetric shrinkage due to the polymerization of the resin, it follows a compression action on the stem due to absorption of humidity coming from the biological fluid by cements.

Purpose: Severe open fractures of the forearm, particularly with bone loss, are particularly difficult to treat. Internal fixation is dangerous and cannot achieve restituitio ad inte-grum. The purpose of our clinical study was to present the method we use that has provided satisfactory results.

Material and method. Over an 18-year period starting in 1981, we have used external fixation of forearm fractures for only five cases, all men, aged 23–65 years. Three were work accident victims, one was a traffic accident victim and the last was an explosion victim. During this same period a total of 181 forearm fractures treated surgically in our unit with the AO method. The five men were treated in an emergency setting within three hours after the accident. The procedure included: 1) debridement to remove damaged soft tissue and minute bone fragments; 2) reduction with a 1.8 endomedullary Kirschner pin (bridging the bone loss); 3) application of a three-ring external fixation plus a 5/8 ring at the elbow to allow complete elbow fixation; 4) proximal osteotomy of the ulna and distal osteotomy of the radius for internal lengthening (0.5 mm per day) designed to achieve bone regeneration known to be slow in the forearm.

Results: In four out of five cases, we obtained bone reconstruction and bone healing within a delay of 176 to 248 days. In one patient, after 125 days, and after filling the bone loss, we converted to internal fixation with a plate and bone grafts to achieve cure 159 days later.

Discussion: Our experience is limited but does include very severe cases where septic complications were avoided and bone loss of 5 to 8 cm was resolved. Internal fixation with intermediary bone grafts would be imprudent in our opinion due to the risk of complication. The shorter limb on which we apply the Ilizarov device favours cure of the soft tissue damage.

Conclusion: The severe open fractures of the forearm, especially in cases with bone loos, can be resolved with external fixation using the Ilizarov method, avoiding the serious complications of necrosis and infection often encountered in these cases.