Abstract
Small canals are usually in small people, but occasionally some normal-sized people have huge cortical thickness with a corresponding small canal.
To give adequate strength to the cement mantle, either pure cement or cement/cancellous bone, it must be at least 2mm thick. If the medullary canal is 9mm or less, then the thickest stem, which can be used with cement will be 5mm. This stem is so small that under load, it may deform repetitively, i.e. cycle. If it does cycle, it will break up the cement mantle. In order to get in a stem large enough to prevent cycling, hard reaming will be required, thus, removing most of the cancellous bone so the cement interlock is poor.
Small stems are also usually fairly short stems. With a follow-up of more than 15 years, inevitably, some lucency between the cement and bone occurs in zones one and seven. If the stem is long enough, that is of no significance. If the stem is short, i.e. 120mm or less, then the area of distal fixation becomes precariously small.
For these reasons, if the canal is small, it is preferable to use a non-cemented stem. The reaming technique for a non-cemented stem is to reach endosteal cortical contact either circumferentially with a canal-filling stem or at the point of wedge for a wedge-shape stem. The metaphyseal bone may be poor quality in the elderly, but it is going to be removed anyway to load the endosteal cortex.
This means that a large stem can be used, which is, therefore, stronger and less likely to undergo mechanical failure and fixation failure.
