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Research from Hong Kong on Prosthetic Alignment
Ironically, the latest issue of the Journal of Rehabilitation Research and Development contains an article on transtibial prosthetic alignment that is a good illustration of the value of scientific investigation for clinical practice. The investigators, from the Chinese University of Hong Kong and the Hong Kong Polytechnic University, recruited a convenience sample of unilateral transtibial amputees, and had them all fitted with a new prosthesis by the same prosthetist using the same components.
They then systematically altered the sagittal plane alignment from a pre-defined "neutral" position in carefully measured increments, and recorded the subjective evaluations of the patient and the prosthetist based on typical iterative visual gait analysis. After many, many trials, they were able to map the maximum acceptable range of alignment for each individual amputee. In my view, this explains the common observation that no two prostheses are aligned identically: the range of acceptable alignment is fairly broad.
The researchers then repeated the gait trials, but this time on uneven surfaces such as stairs and ramps. The results showed that, when walking on such irregular surfaces, the amputees accepted a much smaller range of alignments. The patients also commented that ramp walking was more sensitive to alignment changes than any other conditions. This suggests that it would be useful to finalize dynamic alignment in the sagittal plane by asking our patients to walk on a ramped surface, as this will result in less variation than level walking.
Finally, they compared the alignments that were acceptable to all the subjects under all the tested conditions, and found that these data defined a very small range the researchers termed the "critical alignment zone". In other words, all tested patients would have accepted alignment within the "critical zone" as being satisfactory. Figure three from the paper is reproduced below to illustrate these results.
Like all good research, this work raises at least as many questions as it answers. For example, the researchers note that it would be valuable to measure key biomechanical data to see how they would correspond to the range of alignment the amputees and prosthetists judged subjectively as "acceptable". In principle, it might be possible to identify "best alignment" by minimizing undesirable biomechanical forces on the residual limb, involved leg, or contralateral side.
But, this small study certainly supports the clinical notion that there are boundaries to alignment and that it is unacceptable to the amputee to exceed those limits. The finding that "ramp-optimized alignment" always falls near the average of the acceptable range determined during level walking is intriguing, and may prove to be a practical method for the prosthetist to zero in on a good long-term alignment with more confidence. If this result is corroborated in subsequent studies with larger numbers of amputees, it could become one of the EBCP tenets for sagittal plane alignment of transtibial prostheses in the future.
The full text of this article is posted at http://www.vard.org/jour/01/38/1/sin381.htm; the citation is Sin SW, Chow DHK, Cheng JCY "Significance of non-level walking on transtibial prosthesis fitting with particular reference to the effects of anterior-posterior alignment", JRRD 38:1, 1-6. January-February 2001.
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EBCP
Dear Mr.Michael,
I thank you for 'eyeopener' coments on this subject. Your discussion has led us to grasp this subject at the earliest. May I inform you that your given website of Univ. college Dublin's on-line Hand Book with a 'CAT' revie... read more
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EBCP
Hi John
This reminds me of ISO 9000 standards it has lots of paperwork but no meat. Otto Bock, I have notice since they implemented these standards they have had a few things that has broken on us. (Tube adaptors) I see that their focus ha... read more
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