All the assessments were performed in all the retrieved rods with obtained results summarised in Table 1.
Case
|
Rod
|
Rod type
|
Lot number
|
Plain radiographs
|
Visual inspection (wear marks)
|
Map 1
|
Map 2
|
Wear depth (μm)
|
Wear area (mm2)
|
Normalised wear area (mm2/mm)
|
1
|
1
|
1.2
|
A130313-03
|
intact
|
circumferential
|
unmatched
|
matched
|
41.2
|
0.428
|
0.071
|
2
|
1.2
|
A130523-01
|
intact
|
circumferential
|
unmatched
|
unmatched
|
1.9
|
0.008
|
0.001
|
2
|
3
|
1.2
|
A130130-02
|
intact
|
circumferential
|
matched
|
matched
|
95.8
|
2.757
|
0.084
|
3
|
4
|
1.2
|
120314-002
|
unclear
|
circumferential
|
unmatched
|
unmatched
|
5.8
|
0.002
|
0.001
|
4
|
5
|
1.2
|
A140702-09
|
intact
|
circumferential
|
matched
|
matched
|
62.2
|
0.588
|
0.098
|
6
|
1.2
|
A140605-01
|
dislocated thread
|
longitudinal
|
matched
|
matched
|
131.0
|
0.567
|
0.142
|
5
|
7
|
1.2
|
A141014-17
|
intact
|
circumferential
|
matched
|
matched
|
26.9
|
0.063
|
0.016
|
8
|
1.2
|
A150220-08
|
intact
|
no
|
unmatched
|
unmatched
|
2.3
|
0.005
|
0.002
|
6
|
9
|
1.1
|
110112-010-017
|
intact
|
circumferential
|
matched
|
matched
|
38.2
|
1.169
|
0.032
|
7
|
10
|
1.2
|
A130614-04
|
fractured pin
|
combined
|
matched
|
matched
|
103.0
|
2.918
|
0.224
|
11
|
1.2
|
A130306-03
|
dislocated thread
|
combined
|
matched
|
matched
|
85.4
|
3.946
|
0.219
|
8
|
12
|
1.2
|
A130604-10
|
fractured pin
|
combined
|
unmatched
|
matched
|
129.0
|
12.873
|
0.348
|
9
|
13
|
1.2
|
A140127-09
|
intact
|
circumferential
|
unmatched
|
unmatched
|
12.2
|
0.060
|
0.002
|
14
|
1.2
|
A130919-13
|
intact
|
circumferential
|
matched
|
matched
|
28.7
|
0.747
|
0.026
|
10
|
15
|
1.3
|
A150403-08
|
intact
|
circumferential
|
matched
|
matched
|
15.8
|
0.087
|
0.005
|
16
|
1.3
|
A150717-14
|
intact
|
circumferential
|
matched
|
matched
|
60.7
|
2.574
|
0.135
|
11
|
17
|
1.3
|
A150728-01
|
intact
|
circumferential
|
matched
|
matched
|
25.6
|
0.077
|
0.013
|
18
|
1.2
|
A140702-09
|
intact
|
circumferential
|
matched
|
matched
|
26.9
|
0.518
|
0.020
|
12
|
19
|
2.0
|
A150519-14-00
|
fractured pin
|
longitudinal
|
unmatched
|
matched
|
92.4
|
3.424
|
0.245
|
20
|
2.0
|
A150519-12-00
|
fractured pin
|
longitudinal
|
unmatched
|
unmatched
|
48.9
|
1.252
|
0.125
|
13
|
21
|
1.2
|
A140604-05
|
intact
|
circumferential
|
matched
|
unmatched
|
89.0
|
4.675
|
0.195
|
22
|
1.2
|
A140220-03
|
intact
|
circumferential
|
matched
|
matched
|
44.0
|
0.161
|
0.032
|
14
|
23
|
1.2
|
A131111-06
|
unclear
|
circumferential
|
unmatched
|
unmatched
|
10.2
|
0.004
|
0.002
|
24
|
1.2
|
A140414-06
|
intact
|
circumferential
|
matched
|
matched
|
27.2
|
0.051
|
0.026
|
15
|
25
|
1.2
|
A140425-12
|
intact
|
circumferential
|
matched
|
matched
|
65.2
|
1.147
|
0.048
|
26
|
1.2
|
A140127-09
|
intact
|
circumferential
|
unmatched
|
matched
|
31.4
|
0.168
|
0.013
|
16
|
27
|
1.2
|
A140301-05
|
intact
|
circumferential
|
matched
|
matched
|
52.7
|
1.423
|
0.119
|
28
|
1.2
|
A140813-02
|
intact
|
circumferential
|
matched
|
matched
|
88.5
|
1.187
|
0.148
|
17
|
29
|
1.2
|
A140604-05
|
intact
|
circumferential
|
matched
|
matched
|
65.4
|
1.728
|
0.052
|
30
|
1.2
|
A131111-06
|
intact
|
circumferential
|
matched
|
matched
|
15.8
|
0.367
|
0.015
|
18
|
31
|
1.2
|
A140127-09
|
fractured pin
|
longitudinal
|
matched
|
matched
|
16.7
|
0.099
|
0.008
|
19
|
32
|
1.2
|
A141222-01
|
fractured pin
|
circumferential
|
matched
|
matched
|
9.9
|
0.036
|
0.009
|
20
|
33
|
1.2
|
A140308-03
|
fractured pin
|
combined
|
matched
|
matched
|
168.0
|
10.356
|
0.414
|
34
|
1.2
|
A140127-08
|
fractured pin
|
combined
|
matched
|
matched
|
99.4
|
4.043
|
0.225
|
Table 1 Results of plain radiographs, visual inspection, surface mapping and material loss assessment
Plain radiographs
An intact internal mechanism was observed in 22 rods (65%), while 10 rods (29%) showed evidence of a damaged internal mechanism (Fig. 5). Fractures of locking pins were detected in 8 rods (24%), while the internal thread mechanism of telescopic bars was dislocated in 2 rods (6%). The status of internal mechanism was unclear in 2 rods (6%).
Visual inspection
33 rods (97%) showed evidence of wear marks on one side of the telescopic bars (Fig. 6). Circumferential wear marks were seen in 24 rods (71%), while longitudinal wear marks were noticed in 9 rods (27%), of which 5 rods were combined with circumferential wear marks. 2 rods (rod-19 and -20) showed modified design in the telescopic bars (Fig. 6e).
Surface mapping
The median (INQ) of the measuring length (mm) was 13 (5.8-25), while the median (INQ) number of traces was 12.5 (9-16.5). The resulting contour maps of 24 rods (71%) corresponded to the visible wear marks in the telescopic bars, while surface mapping in 10 rods (29%) failed to reflect the actual profile of surface wear (Fig. 7).
Quantitative assessment of material loss
For surface mapping in the most worn region, the median (INQ) number of traces was 60 (42.3-60). The obtained contour maps of 27 rods (79%) corresponded to the visible wear marks (Fig. 7). As for the quantification of material loss, the medians (INQ) of wear depth (μm), wear area (mm²) and normalised wear area (mm2/mm) were 42.6 (16.5-88.6), 0.577 (0.074-2.619) and 0.040 (0.012-0.143), respectively.
Mann-Whitney test found a significant difference in the three material loss values between rods with intact and damaged internal mechanism (p<0.05) (Fig. 8). For the damaged group, the medians (INQ) of these three values were 95.9 (40.9-129.5), 3.171 (0.450-5.621) and 0.222 (0.096-0.270), higher than that of the intact group, i.e. 34.8 (23.2-63.0), 0.473 (0.074-1.246) and 0.029 (0.013-0.087). No significant difference was found in these three values between rods with different types of damages in the internal mechanism (p>0.05).
Spearman correlation test found a significant and positive correlation between time to explantation and wear area (r=0.433, p<0.05), while a stronger correlation (r=0.692, p<0.05) was found between time to explantation and the summed wear area of dual constructs. No significant correlation was found in the wear depth and normalised wear area between the two variables (p>0.05).
Kruskal-Wallis test showed a significant difference in the wear area between different pre-operative diagnosis groups (p<0.05), although no significant difference was found in wear depth and normalised wear area between these groups (p>0.05). By comparing material loss between any two diagnosis groups, the idiopathic scoliosis group was found to have significantly higher medians (INQ) of the three material loss values (p<0.05) (Fig. 9), i.e. 50.8 (26.6-71.2), 1.167 (0.166-1.939) and 0.050 (0.014-0.139), compared with 13.5 (9.9-24.6), 0.043 (0.012-0.087) and 0.009 (0.004-0.021 for the syndromic scoliosis group.
Rods from planned revision were found to have a significantly higher wear area (mm2), i.e. 1.576 (1.173-2.878), compared with 0.246 (0.005-0.583) for rods from unplanned revision (p<0.05) (Fig. 10), although no significant difference was found in wear depth and normalised wear area between the two groups (p>0.05). No significant difference was found in material loss between different revision reason groups (p>0.05). No significant relationship was found between the three material loss values and the gender and age at implantation of patients (p>0.05).
Repeatability and reproducibility
No significant difference was found in the three material loss values between two intra-observer repeats of Talyrond scanning and TalyMap calculations as well as the two inter-observer repeats of TalyMap calculations (p>0.05).