Metal either solid or a mesh type restrictor, would have had the problem of its extraction at revision. In contact with the stem would invite fretting.

Cement restrictors would demand a range of sizes, instrumentation inventory and all the problems associated with it. Flexible cement restrictors were experimented with. Composition of the cement was altered to give a relatively flexible shuttlecock-type restrictor. The idea was reasonable but it’s execution met with difficulties. The formulation of a suitable cement mix proved difficult; the end product’s properties were temperature dependent. It worked well when warm but became brittle when cold. At surgery it showed its visco-elastic properties rather dramatically: a slight tap on the introducer would shatter the restrictor.

UHMWPE was the obvious choice, but not without possible long-term problems. A solid restrictor would have to carry with it instrumentation for measuring the medullary canal before the appropriate size could be chosen and placed at a correct level. The chosen size would only fit at a certain level – which may not be under the surgeon’s control. A shuttlecock-type design was obvious, its manufacture less so. Insertion down the medullary canal would invite abrasion of UHMWPE against cancellous bone and shedding of plastic particles. (This fact became obvious when there were opportunities to revise some loose stems when this design had been used: “petals” of the plastic could be found anywhere from the level of the greater trochanter down to the distal cement). Removal of such a device was not easy: designed to close on insertion it would tend to open on extraction! If failures were to present in the future, and if tissue reaction to UHMWPE wear particles did prove to be the cause of the problem, then clearly UHMWPE was best avoided; cavitation at the tip of the stem would demand by-passing the defect with a longer stem.