Knee brace

Figure 2.12 Orientation of the strain gage sensor on the anteromedial aspect of the anterior cruciate ligament. (From B D Beynnon, M H Pope, C M Werthheimer, R J Johnson, B F Fleming, C E Nichols and J G Howe, The effect of functional knee-braces on strain on the anterior cruciate ligament in vivo, 1992 The Journal of Bone and Joint Surgery 74 A, no 9, 1298-1312.)... 

Beynnon B D, Pope M H, Werthheimer C M, Johnson R J, Fleming B F, Nichols C E and Howe J G 1992 The effect of functional knee-braces on strain on the anterior cruciate ligament in vivo J. Bone Joint Surg. A 74 1298-312 Doebelin E O 1990 Measurement Systems Application and Design 4th edn (New York McGraw-Hill)... 

Yeaple, F. 1989. Composite knee brace returns stability to joint. Design News, 46,116. 

This research focuses mainly on one of the least exploited properties of spacer fabrics the elastic properties. Considering that the best attribute of spacer fabrics is their thermophysiological properties, a combination of these with the elastic properties gave birth to a very important medical application compression ther y. This research has focused on pressure garments, namely knee braces and pressure garments for third degree bums. 

The main objective of this project was to characterise and develop novel three-dimensional knitted stmetures with improved thermophysiological properties to be used in knee braces and bum garments. It was the intention to develop a mathematical model of these structures which relates the tensile properties of each of the different stmetures with its elastic properties as a way to predict Ihe level of compression on the patient s limb. 

Two pq)ers have been previously published which discussed the development of novel three-dimoisional spacer fabrics for knee braces. In these publicadons a thorough analysis of the tensile and thermophysiological properties of each of the structures developed was also presented and critically compared with commercially available fabrics for the same end-use [3,4]. 

This p per deals with the empirical modelling of the elastic properties of the novel three-dimensional fabrics developed during this research for knee braces. 

During this research commercially available fabrics have been ftiUy analysed and characterised for their properties for both knee braces and bum garments. 

Commercially available knee braces and third degree bum garments are currently made from a wide range of materials. A selection of commercial products and fabrics has been folly tested and analysed for their dimensional, ftiermophysiological, taosile and elastic properties in order to bench mark the optimum properties for such applications. Most of these results have been discussed in previous p >ers [3,4]. 

Commercially available knee braces are currently manufactured om neoprene, knitted fabrics, foams or a combination of these. When tested, these have proven to be very uncomfortable this means that wearers are not able to withstand them for as long as they should, especially when performing physical activity [9,10]. It has also been found that many of these products do not offer the correct compression levels required for knee braces. 

A niunber of knitted spacer fabrics have been developed, tested and analysed during this research with view to study their suitability for using as a knee brace material. Of these, two spacers have been identified as having the desirable properties sought after for such supports. These two novel fabrics have been produced by two different methods, weft knitting and warp knitting. 

Table 1 shows e values of the tensile properties for the novel q iacers developed for knee braces warp knitted fabric, 5870, and weft knitted bric, quality 3S00C. It can be seen from this table that the results for both knee brace fiihrics are quite similar in the cross direction and 45 degrees however, significant differences exist in the machine direction. This is due mainly to the two entirely different manu cturing techniques used in the construction of these two fabrics, as one is warp knitted and the other is weft knitted. 

A knee brace in its basic form is a tubular structure around the patient s joint therefore, the authors have considered that the cross direction of the fatdc is the most important one to be analysed. The cross direction represents the circumference of the knee. Taking this into consideration it can be seen from Table 1 that these two fabrics possess identical tensile properties in the cross-direction, CD. 

Table 2 shows the results of the elastic properties of the novel knitted spacer fabrics developed for knee braces according to the British test method BS7505. 

Using the statistical software package SPSS, it was possible to establish a relationship between the tensile and elastic properties of the materials studied in this work. This has been carried out for the cross-direction of the material only as this is considered to be the relevant direction for compression in a knee brace. It was established that there is a good correlation between the tension ratio (tr), working extension (we) and differential extension factor (def) with both specific modulus (m) and breaking extension (be). A multi-linear regression equation for the dependent variables tr, we and def with the independent variables be and m was established for each material and the equations are shown in Table 3. 

Using Laplace Equation based on circumference (Equation 1), theoretical pressures in mmHg were calculated for each load values for the determined circumference values (Table S). Using Table S, a grqth was created to illustrate the inversely proportional relationship between pressure and circumference which is shown in Fig.l. For knee braces the maximum circumference of the largest part of the knee would be around SOcm. 

For a knee brace the optimum pressure has been determined as 15.S nunHg. The tensions (N) were calculated for this optimum pressure for different circumferences (cm) and are presented in Table 6[a]. 

From Table 6[c] it is possible to plot a graph (Fig.3) which illustrates the relationship between limb circumference and percentage reduction of material s width dimensions required when manufacturing a knee brace. From this graph a best lit third order polynomial regression equation and its correlation coefticient were determined (see Fig. 

The same set of calculations was performed for the weft knitted spacer 3S00C as it is to be used for the same application, knee braces, and therefore the same amount of pressure is required, 15.5 mniHg. The results are shown in Table 7. The percentage reduction in circumference required for optimum pressure is plotted for different limb circumferences in Fig. 5. 

Of all the novel products developed during this research, two knitted three-dimensional fabrics have been found to possess die desirable diramoidiysiological, mechanical and elastic properties soug after in materials for knee braces these were the warp knitted spacer 5870 and the weft knitted spacer 3S00C. 

It has been established that knee braces are required to offer a siqiport of around IS.SmmHg to the patient s limb and for testing purposes these have been conqiaied to a type 2 bandage according to BS750S. A knee brace in its basic form has a tubular shape and therefore the cross-direction of the material has been considered for analytical purposes in this paper. 

S Pereira, S C Anand, S Rajendran and C Wood, Novel 3D knits for knee braces . Knitting International, November 2006 32-35. 

After graft fixation, the tensions of the grafted tendons should be checked arthroscopically, and then, the synovium is sutured over the graft-remnant composite to create a closed tube of the reconstructed ACL extending between the tibial and the femoral anatomical foot prints (Eig. 28.7). After skin closure, the knee is fixed with a soft knee brace. After surgery, the tunnel positions should be assessed using 3D CT. (Fig. 28.8). 

Immobilization with a cast or knee brace may be safest after surgery. The period of immobilization depends on the stability of the fragment during the surgery. A knee brace is applied for 2-4 weeks. The range of motion exercise is allowed 2-3 weeks... 

Brackets— This type of support may be welded to structural members or certain pieces of equipment. It may have a cantilever design or knee bracing for supporting heavy loads. Lines may be U-bolted, guided, or hung by rod hangers from the bracket or may rest on shoes. 

On very wide platforms or those that support heavy iping loads, knee bracing is required in addition to he usual plsnform steel, as illustrated in Exhibit 10-49-rhe potential obstruction immediately under die knee irace roust be kept in mind during platform design. 

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