The stabilizing effect of TSM knee supports

In early 1998, BASiS Institut Munich (Institute for Biomechanics), TÜV Product Service, Munich carried out comparative measurements of various TSM knee supports with stabilizing elements on a newly developed knee simulator.The knee supports were tested for their stabilizing properties on isolated knee movements, specifically:“Protective function against anterior drawer” and

“Determination of varus/valgus stability”.

Testing arrangement “Protective function against anterior drawer”

Flexion angle:	30°
Translation distance (y-axis):	30 mm
Translation rate:	10 mm/s
Muscle simulation:	off
Overall tone of the soft tissue:	hard

Testing arrangement “Determination of varus/valgus stability”

Flexion angle (° flex):	15°
Rate of angular flexion:	10°/s
Valgus angle:	+/- 10°
Muscle simulation:	off
Basic tone of thesoft tissue:	hard

Result of comparative measurements

The following comments generally apply:

The greater the forces absorbed, the greater the stabilizing effect of the support-/orthosis on the particular action.

1. Anterior drawer

The varied stabilizing effect of TSM supports is based on a modular system of various knee hinge stays with and without limitation of flexion and extension, with and without locking and with the additional action of a patellar ligament strap (PSB).
In this way, it is possible to provide proper care for various different types of instability. Under the conditions investigated here (30° flexion limit, translation distance 30 mm (yaxis), translation rate 10 mm/s), the maximum of the range of forces (Mx [Nm]) to be absorbed in order to limit anterior drawer reaches the capacity of conventional frame orthoses, for example of item no. 3173-6 “FEV” (see table). Moreover, subject to correct fitting, slippage of TSM supports is almost completely prevented by the slip-resistant lining fabric.

2. Varus/valgus stability

The valgus stabilizing effect is of primordial importance. As with “anterior drawer”, force absorption (My [Nm]) may be varied as a function of the hinge stays used. By virtue of its design, item no. 3173-6 “FEV”, for example, does not quite achieve the values of commercial frame orthoses, but does cover a wide range of indications.

Support order		"Anterior drawer"		Vargus/valgus stability
		Mx (Nm)	Fy (N)	vargus My (Nm)	valgus My (Nm)
3171	double-hinge steel stays	34,0	83,0	4,0	5,5
3471	double-hinge steel stay „FE“ ^*	31,0	75,6	2,7	4,5
3571	double-hinge steel stay „FEV“	54,0	132,0	4,0	6,0
3264	double-hinge, light metal stay + patellar tendon strap	49,0	119,5
3364	double-hinge steel stay "FEV" + patellar tendon strap	49,5	120,7	3,3	5,2
3173-3	double-hinge steel stay	42,4	103,4	3,0	6,1
3173-6	double-hinge steel stay "FEV"	55,0	134,0
3173-3	double-hinge steel stay + patellar tendon strap	59,7	145,6
3173-6	double-hinge steel stay "FEV" + patellar tendon strap	66,5	162,0
	Neoprene support with lateral stays ^*	53,0	129,3	23	3,0
	frame orthoses ^**	70,0	170,7	7,3	8,3

* model not yet available
** commercial product

Measurement “Anterior drawer”
Means of at least 6 repetitions per item F_y is equal to the force resulting from the moment M_x at the height of the knee gap.

Measurement Varus/valgus stability
Means of at least 6 repetitions per item.

Results: “Anterior drawer stability at 30° flexion angle”

TSM knee supports, 37 cm long, order no. 3171, 3471, 3264, 3364

blue: order no. 3264
red: order no. 3471
green: order no. 3171
light blue: order no. 3364

TSM knee supports, order no. 47 cm long, 3173-3 without PLS, 3173-3 with PLS*, 3173-6 without PLS, 3173-6 with PLS

blue: order no. 3173-6 without PSB
red: order no. 3173-6 with PSB
green: order no. 3173-3 without PSB
light blue: order no. 3173-3 with PSB

Results : “Varus/valgus stability at 15° flexion angle”

TSM knee supports, 37 cm long, order no. 3171, 3471, 3571, 3364

blue: order no. 3364
red: order no. 3471
green: order no. 3171
light blue: order no. 3571

TSM knee supports, 47 cm long, order no. 3173-6, 3173-6 *
Comparison: commercial frame orthosis

red: frame orthosis
green: order no. 3173-6 (standard)
blue: order no. 3173-6 *

* AET double-hinged “FE” test stay: without locking, straight