The study employed a prospective design, conducted at the Faculty of Medicine Ramathibodi Hospital, a tertiary care hospital in Thailand, from April 2021 to September 2022; and approved by the Hospital's Committee on Human Rights Related to Research Involving Human Subjects (COA. MURA2021/292). Written informed consents were obtained from individual patients and their legal guardians. The study was divided into three phases: measurement of transmitted impact force, fabrication of knee supports, and randomized cross-over trial of natural rubber and sponge knee supports.

Phase I: Transmitted impact forces were measured using an impact tester (Model DC Power Supply GW Instek GPS-30300 and Multi-Meter Fluke DT-9208a). Three types of knee support samples, size 30 x 30 x 1 cm (W x L x H), were prepared: with no barrier, with natural rubber cushion, and with sponge cushion and tested. The test was performed using the same force in the ballistic pendulum test (1 kg momentum ball with a radius of 50 cm). The test was repeated three times, and the average results were recorded as force (Newton) and time (sec) after the sphere hit the receptive sensor. Natural rubber used in this study was made from natural rubber and polymer (Patent ID 74814).

Phase II: Knee supports were designed and fabricated in various sizes. Three measurements, knee circumferences, patella sizes, and knee heights, were taken from 20 Thai children aged between 9 months and 10 years and having body weights within the 50th to 75th percentile. The knee support comprised two parts, the support body and the protective cushion. The width of the support body was derived from half of the knee circumference, and the length was taken from 80% of the knee height, measured from knee to medial malleolus. From those measurements, final knee supports were categorized into four sizes, S, M, L and XL according to widths and lengths, as follows: size S, 8x17 cm; size M, 10x19 cm; size L, 12x24 cm; and size XL, 14x28 cm. The support body was made of stretchable natural cotton fabrics, which were comfortable, breathable, washable, less irritant and flexible.22 Similarly, the protective cushion was classified into four sizes: S, M, L and XL with diameters (based on the patellar diameters) of 5, 6, 7 and 8 cm, respectively. Cushions were made from either natural rubber or sponge and inserted at the front of the support body (to cover the patellar). As a result, natural rubber and sponge knee supports were fabricated, and they both had similar external appearance.

Phase III: A randomized cross-over trial using natural rubber and sponge knee supports was conducted among patients with bleeding disorders. The patients were divided into two groups, A and B, by computer-generated randomization sequence using a box of ten. A total of 44 patients were enrolled with 21 in Group A and the other 23 in Group B. Later, two patients in Group A were excluded due to loss of follow-ups. Therefore, the final number of patients in the study was 42 with 19 in Group A and 23 in Group B. Group A was first assigned to Treatment I of natural rubber knee support followed by Treatment II of sponge knee support, while Group B was first assigned to Treatment II followed by Treatment I. Patients were advised to use the supports during physical activities; for example, walking and crawling among toddlers and playing sports among school-aged children. Each treatment covered a period of eight weeks, with four weeks of wash-out period of cross-over from the first treatment to the second. Survey data on demographics, number of bleeds, types of bleeding (extraarticular or intraarticular), and user's satisfaction were collected. User's compliance and bleeding data, including severity and activity when injury occurred, were collected weekly using freeware application, online electronic form, or direct telephone contact. Satisfaction survey was conducted following the Client Satisfaction with Device module of Orthotics and Prosthetic User' Survey (CSD-OPUS)24 with Thai translation. The survey consisted of nine aspects: fitting well, weight, comfort, ease to use, attractiveness, durability, irritation, pain, and overall satisfaction. Patients aged \>7 years and all parents were included in the survey, sent to them in electronic format, twice; i.e., at the end of the two treatments. Scores were graded in absolutely agree, agree, disagree, and absolutely disagree. At the end of the second treatment, parents of both groups were asked to choose either the knee support of Treatment I or Treatment II as a preference.

Patients The inclusion criteria were bleeding disorder patients, aged 9 months to 12 years old, with written consents The enrolled patients had no coexisting diseases affecting their activities, or bleeding episodes two weeks before the study. Children or parents who were not able to continue the study until the end were excluded.