How can one platelet injection after tendon injury lead to a stronger tendon after 4 weeks?: Interplay between early regeneration and mechanical stimulation

Figures & data

Figure 1. Activity cage.

Figure 2. A. Normal rat Achilles tendon. B. Achilles tendon transection. C. Callus 14 days after transection.

Table 1.  No effect of platelets (PC) after 14 days in rats with calf muscles paralyzed with Botox

	PC		Control
	Mean	SD	Mean	SD
Force (N)	16	6.3	15	2.5
Stiffness (N/mm)	3.7	1.2	3.0	0.6
Energy (Nmm)	22	11	25	12
Area (mm2)	4.3	0.8	4.0	0.8
Stress (MPa)	3.9	1.8	4.1	1.3

Table 2.  Effect of activity with or without platelets*

Experiment no.	Cage and treatment	n	Force (N)		Stiffness (N/mm)		Energy (Nmm)		Area (mm^2)		Stress (MPa)
			Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
1	Activity	8	55	5.8	17	1.7	123	25	9.1	2.5	6.5	2.1
1	Normal	10	45	10	13	3.9	96	25	8.5	3.0	5.7	1.6
2	Activity control	9	48	6.5	12	2.2	136	13	11	1.8	4.6	0.9
2	Activity platelets	9	50	8.2	14	3.8	119	29	9.0	1.5	5.6	1.3
2	Normal control	10	47	9.1	13	1.8	126	37	7.7	2.5	6.4	1.5
2	Normal platelets	9	55	8.4	15	3.1	155	27	6.8	1.1	8.2	1.3

*Significant p-values as follows. Experiment 1: force 0.02; stiffness 0.03; energy 0.04. Experiment 2: Effect of activity: area < 0.001; stress < 0.001. Effect of platelets: stiffness 0.02; area 0.05; stress 0.005.

Table 3.  Combined data from activity cages, excluding Botox-treated groups

			Biomechanical data		Percent increase by activity
	Cage	n	Mean	SD	Mean	95% CI	P-value
Force (N)	Activity	18	51	6.8	12	0.8–23	0.04
	Normal	20	46	9.4
Stiffness (N/mm)	Activity	18	14	3.2	8.4	−6.5–23	0.3
	Normal	20	13	2.9
Energy (Nmm)	Activity	18	131	20	18	2.0–34	0.04
	Normal	20	111	34
Area (mm^2)	Activity	18	10	1.8	24	4.6–43	0.02
	Normal	20	8.0	1.5
Stress (MPa)	Activity	18	5.5	1.8	−9.5	−29–8.1	0.3
	Normal	20	6.0	1.5

Table 4.  Effects of platelet gel in rats killed on days 3 and 5

				Biomechanical data		Percent increase by platelets
	Days	Treatment	n	Mean	SD	Mean	95% CI	P-value
Force (N)	5	Platelet gel	10	5.7	1.4	37	11–63	0.01
	5	Control	10	4.1	1.0
Stiffness (N/mm)	5	Platelet gel	10	2.9	0.9	52	15–87	0.01
	5	Control	10	1.9	0.7
Area (mm^2)	3	Platelet gel	10	5.0	1.1	53	28–76	< 0.001
	3	Control	10	3.3	0.6
	5	Platelet gel	10	2.1	1.4	64	−25–154	0.009
	5	Control	10	1.3	1.1