## 4 Discussion
### Selection of the Appropriate Techniques According to Measurement Purposes  
It is important to choose the right technique for measurement according to our needs and the purpose of measuring. In general, clinicians or researchers may measure the residual lower limb volume changes from macroscopic and microscopic aspects, and different techniques of measuring may be applied according to the specific post-operative period. The American Academy of Orthotists and Prosthetists (AAOP) State of the Science Conference on Post-Operative Management of the Lower Extremity Amputee stated that there are five main stages in the post-operative recovery period: (1) the pre-operative stage; (2) the acute hospital post-operative phase (5-14 days post amputation); (3) the immediate post-acute hospital stage (4-8 weeks post amputation); (4) the intermediate recovery stage (4-6 months post amputation); and (5) the transition to a stable stage (12-18 months post amputation). At the early stage post amputation (phase 2), the residual limb normally experiences oedema, and this condition reduces over time. During this phase, it is important to monitor the shape and volume of the residual limb as a preparation for the first prosthetic fitting. The most suitable technique that may be applied to measure the residual limb volume during this phase is the anthropometric measurement technique since this technique is the simplest, fastest, and easiest way to measure the change in the residual limb. Inclinical practice, clinicians or prosthetists can easily record, keep, and compare the residual limb circumference measurement to determine whether the residual limbs are ready for the first prosthetic fitting. Then, during the first prosthesis usage (phases 3 and 4), the anthropometric measurement technique is no longer suitable for measuring the changes in the residual limb volume because the changes are less compared to the early post-amputation phase because of a decrease in oedema over time during phase 2. More accurate and precise residual limb volume measurement techniques are thus needed, since some publications found that the circumference measurement is not so related to the residual limb volume measurement. Water displacement, contact probes, ultrasound, MRI, and optical or laser scanning were seen to yield good outcomes to determine the changes in the volume during this phase. In phases 3 and 4, there are still changes in the residual limb volume that cause the residual limb to be unable to reach a stable state. Thus, correct volume measurement techniques help to determine whether the residual limb has already reached its stable state. When the residual limb has reached its stable state, only very small changes in the residual limb volume can be detected. Therefore, more sensitive measuring techniques such as bioimpedance and SXCT are required to study the changes in the residual limb volume. At the same time, these techniques are also able to measure the residual limb volume without worrying about the post-dofing effect. Although the SXCT technique seems to have benefits in this phase, the technique is not so suitable in all cases of measurement since it is only limited to the stationary position of the subjects. Only the bioimpedance technique can measure the volume changes in the residual limb while the subjects are standing and walking. Bioimpedance seems to have benefits in measuring the residual limb volume fluctuation in real time as researchers may directly analyse the effects of the suspension system, socket design, and activity level. Hence, researchers can not only concentrate on the residual limb, but can also pinpoint the precise location of volume gain or loss within a particular region.