## 4 Discussion
### Selection of the Appropriate Techniques According to Measurement Purposes
Clinicians or researchers also need to understand the aim of measuring the fluctuation in the residual lower limb volume because the residual lower limb volume can be measured in two ways: (1) by measuring the residual limb volume as a whole and (2) by only measuring the change in the residual limb volume (i.e., neglecting the actual residual limb volume). Seven techniques can be used to measure the residual lower limb volume, and only the bioimpedance and SXCT techniques can be used to measure the change alone, i.e., the fluctuation in the residual limb volume. There are pros and cons while measuring the residual limb as a whole volume as opposed to just measuring the changes in the residual limb volume. When the residual limb measurement is conducted as the whole volume, clinicians can record and compare the volume measurement from time to time (from phase 2 to phase 5 post operation). It is a good practice in the clinical field when clinicians can track any changes in the residual limb volume as they can plan further for the amputee's improvement programme, especially in terms of prosthetic usage. At some point after the amputee has reached a stable state of their residual limb (phase 5 post operation), the clinicians can prescribe a better prosthesis component for the improvement of the amputee's quality of life. On the other hand, by just measuring the changes in the residual limb volume, there are a few advantages such as its speed in determining the residual limb volume fluctuation since it may directly give the final reading of fluctuation. Also, it is prone to have a sensitive measurement since it is not influenced by the post-dofing effects. Finally, another advantage is that it is a real-time volume measurement that is taken while the subject is walking or standing. In terms of the disadvantages of measuring the residual limb as a whole volume, researchers and clinicians are facing some difficulties in obtaining accurate results of the residual limb volume fluctuation. In most of the previous works, the researchers compared the residual limb volume before and after to obtain the amount of residual limb volume fluctuation. This means that the residual limb volume was not measured in real time. Some factors such as the post-dofing effect and the activity level of the amputee while performing the experiment possibly contributed to the wrong interpretations of the residual limb volume fluctuation. Even though the bioimpedancetechnique could give good results of the volume fluctuation, this measurement technique is not so user-friendly compared to other techniques. The bioimpedance technique is difficult to use in clinical fields since it has some complicated setups that need to be run by skiful researchers. In addition, due to some limitations in the bioimpedance technique, there are only publications on transtibial amputation levels. On the other hand, the laser scanning technique appears to be more user-friendly for both clinicians and prosthetic users as this technique can immediately be used at the clinic. The procedure of this laser scanning is simple to learn, and the scanning of the residual limb can be performed in a short time. Due to these reasons, this technique has potential for use in the clinical field. However, some instrumentation errors need to be resolved, and perhaps more importantly, the results must be proven to be accurate. Other than these, the interaction of the laser with soft tissue and numerous other issues vary by product. Thus, these variations and issues need to be resolved and improved. Additionally, the laser scanning technique also has some limitations because the residual limb volume may be impacted by the post-doffing effect since the prosthetic socket must be doffed before scanning can be completed, and slow scanning times will change the residual limb volume. As previously discussed, the authors concluded that choosing the appropriate technique is crucial for evaluating the residual limb volume.