Abstract-The purpose of this research was to pursue quality standards for computer-manufacturing of prosthetic sockets for people with transtibial limb loss. Thirty-three duplicates of study participants' normally used sockets were fabricated using central fabrication facilities. Socket-manufacturing errors were compared with clinical assessments of socket fit. Of the 33 sockets tested, 23 were deemed clinically to need modification. All 13 sockets with mean radial error (MRE) greater than 0.25 mm were clinically unacceptable, and 11 of those were deemed in need of sizing reduction. Of the remaining 20 sockets, 5 sockets with interquartile range (IQR) greater than 0.40 mm were deemed globally or regionally oversized and in need of modification. Of the remaining 15 sockets, 5 sockets with closed contours of elevated surface normal angle error (SNAE) were deemed clinically to need shape modification at those closed contour locations. The remaining 10 sockets were deemed clinically acceptable and not in need modification. MRE, IQR, and SNAE may serve as effective metrics to characterize quality of computer-manufactured prosthetic sockets, helping facilitate the development of quality standards for the socket manufacturing industry.

In this research we investigated the degree of error during the carving phase of central fabrication of prosthetic sockets for people with limb amputation. Three different model shapes were ordered from each of ten central fabrication companies. Using an accurate custom mechanical digitizer and alignment algorithm, we digitized the models and then compared the model shapes with the electronic file shapes. Results showed that 24 of the 30 models had volumes larger than the electronic file shapes while 24 had volumes that were smaller. 29 of the 30 models were oversized at the proximal aspect of the tibial tuberosity and undersized at the patellar tendon and popliteal areas. This error would result in a socket that had less tibial tubercle relief than intended in addition to a larger anterior-posterior dimension than desired. Comparison of the model shapes with socket shapes assessed for nine of the companies in a previous study showed that for five of the companies the sockets were relatively undersized over the tibial crest and fibular head. The results indicate that the socket the prosthetist receives will not always fit as planned, and that errors in the carving process are a source of the discrepancies.

Abstract-This article presents an assessment technique for testing the quality of prosthetic socket fabrication processes at computer-aided manufacturing facilities. The assessment technique is potentially useful to both facilities making sockets and companies marketing manufacturing equipment seeking to assess and improve product quality. To execute the assessment technique, an evaluator fabricates a collection of test models and sockets using the manufacturing suite under evaluation, then measures their shapes using scanning equipment. Overall socket quality is assessed by comparing socket shapes with electronic file (e-file) shapes. To characterize carving performance, model shapes are compared with e-file shapes. To characterize forming performance, socket shapes are compared with model shapes. The mean radial error (MRE), which is the average difference in radii between the two compared shapes, provides insight into sizing quality. Interquartile range (IQR), the range of radial error for the best-matched half of the points on the compared socket surfaces, provides insight into regional shape quality. The source(s) of socket shape error may be pinpointed by separately determining MRE and IQR for carving and forming. The developed assessment technique may provide a useful tool to the prosthetics community and industry to help identify problems and limitations in computer-aided manufacturing and give insight into appropriate modifications to overcome them.

The purpose of this research was to determine if prior activity affected the shape of a plaster cast taken of a trans-tibial residual limb. Plaster casts were taken twice within a day on 24 participants with trans-tibial limb loss, with 5 s between doffing and casting in one trial (PDI-5s), and 20 min in the other trial (PDI-20m). The ordering of the trials was randomized. The mean radial difference between PDI-20m and PDI-5s was 0.34mm (s.d. 0.21) when PDI-5s was conducted first and −0.02mm (s.d. 02.0) when PDI-20m was conducted first. Ordering of the trials had a statistically significant influence on the mean radial difference between the two shapes (p=0.008). The result shows that prior activity influenced the residual limb cast shape. Practitioners should be mindful of prior activity and doffing history when casting an individual’s limb for socket design and prosthetic fitting.