Table 2 Screw properties and measured values (mean value ± one standard deviation) including screw characteristics: outer diameter, flank overlap area, contact surface, compacting, displaced diameter, insertion torque, \(D_{o} \cdot V_{c}\) and \(D_{o} \cdot T_{i}\).

From: Influence of thread design on anchorage of pedicle screws in cancellous bone: an experimental and analytical analysis

Screw properties	Screw type 1^a		Screw type 2^a		Screw type 3^a		Screw type 4		Screw type 5		Screw type 6
Screw properties	ST1_6	ST1_7	ST2_6	ST2_7	ST3_6.2	ST3_7	ST4_6.5	ST4_7.5	ST5_6.5	ST5_7.5	ST6_6.5	ST6_7.5
Outer diameter \(D_{o}\) in mm	6	7	6	7	6.2	7	6.5	7.5	6.5	7.5	6.5	7.5
Mean core diameter \(D_{c}\) in mm	3.65	4.04	3.86	3.94	4.36	5.03	4.15	4.78	4.25	4.99	4.45	5.10
Screw pitch \(p\) in mm	3.00	3.00	3.00	3.00	2.00	2.00	4.00	4.00	2.75	2.75	2.80	2.80
Flank overlap area \(FOA\) in mm²	148	214	138	219	191	232	123	164	173	224	157	212
Contact surface \(A_{c}\) in mm²	429	532	430	519	548	599	464	564	591	716	500	605
Compacting \(V_{c}\)	0.32	0.35	0.31	0.28	0.41	0.45	0.34	0.34	0.41	0.45	0.37	0.41
Displaced diameter \(d_{d}\) in mm	1.69	2.07	1.67	1.86	1.99	2.35	1.89	2.12	2.07	2.52	1.99	2.40
\(D_{o} \cdot V_{c}\) in mm	1.90	2.45	1.86	1.98	2.56	3.15	2.19	2.55	2.63	3.37	2.43	3.06
Measured values
PCF 15 (237.2 ± 0.3) kg/m³
Insertion torque \(T_{i}\) in Nm	1.36 ± 0.07	1.88 ± 0.07	1.31 ± 0.07	1.83 ± 0.03	1.82 ± 0.01	2.50 ± 0.03	1.32 ± 0.08	1.72 ± 0.11	1.72 ± 0.06	2.59 ± 0.02	1.20 ± 0.05	1.67 ± 0.03
Mean value difference	p = 0.002		p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001
Pull-out strength \(F_{exp}\) in N	870 ± 10	931 ± 12	855 ± 12	923 ± 12	965 ± 20	1074 ± 16	902 ± 10	975 ± 18	966 ± 18	1072 ± 12	858 ± 19	798 ± 24
Mean value difference	p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001		p = 0.001
\(D_{o} \cdot T_{i}\) in Nm·mm	8.29	13.23	8.00	12.83	11.27	17.57	8.58	13.03	11.31	19.41	7.71	12.55
PCF 10 (158.0 ± 0.5) kg/m³
Insertion torque \(T_{i}\) in Nm	0.60 ± 0.02	0.93 ± 0.03	0.60 ± 0.07	0.90 ± 0.04	0.95 ± 0.03	1.26 ± 0.05	0.63 ± 0.02	0.87 ± 0.01	0.90 ± 0.03	1.31 ± 0.05	0.57 ± 0.02	0.80 ± 0.04
Mean value difference	p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001
Pull-out strength \(F_{exp}\) in N	446 ± 4	476 ± 5	441 ± 13	479 ± 15	510 ± 13	555 ± 10	445 ± 12	491 ± 9	485 ± 13	534 ± 13	426 ± 6	435 ± 17
Mean value difference	p < 0.001		p = 0.001		p < 0.001		p < 0.001		p < 0.001		p = 0.25
\(D_{o} \cdot T_{i}\) in Nm·mm	3.65	6.48	3.45	6.31	5.91	8.93	4.07	6.55	5.87	9.94	3.74	5.94
PCF 5 (85.8 ± 0.2) kg/m³
Insertion torque \(T_{i}\) in Nm	0.22 ± 0.01	0.35 ± 0.02	0.18 ± 0.01	0.31 ± 0.01	0.38 ± 0.01	0.51 ± 0.01	0.27 ± 0.01	0.35 ± 0.01	0.33 ± 0.01	0.51 ± 0.01	0.21 ± 0.01	0.30 ± 0.01
Mean value difference	p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001
Pull-out strength \(F_{exp}\) in N	187 ± 1	209 ± 1	173 ± 2	201 ± 2	218 ± 3	248 ± 2	178 ± 2	196 ± 3	196 ± 1	221 ± 2	181 ± 2	190 ± 3
Mean value difference	p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001		p < 0.001
\(D_{o} \cdot T_{i}\) in Nm·mm	1.35	2.38	1.08	2.16	2.39	3.54	1.74	2.64	2.13	3.83	1.37	2.28

^aThese screws have a double thread, therefore the thread pitch here corresponds to the distance between two thread flanks.

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Table 2 Screw properties and measured values (mean value ± one standard deviation) including screw characteristics: outer diameter, flank overlap area, contact surface, compacting, displaced diameter, insertion torque, \(D_{o} \cdot V_{c}\) and \(D_{o} \cdot T_{i}\).

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