1 Introduction
Total knee arthroplasty was standard surgery for end-stage degenerative and rheumatoid knee disease. With high incidence of osteoarthritis in China, the amount of TKA has been rapidly increasing over the past decade.[1–4] [1] [2,3] [1,2,5–7]
Tibial morphology has significant impact on biomechanical stability and motion function of knee joint in patients who underwent TKA. Postoperative complications of TKA such as prosthetic loosening and subsidence mainly occurred in tibial side.[2,6,7]
Measurement of TKA resected surface was of great importance in the design of platform shape. In order to achieve accurate coverage, it is necessary to keep tML/tAP ratio identical between tibial resected surface and prostheses.[1–3,5,6] [8,9] [10–19] [1,3] [4,13,14]
The objective of this study was to measure size of tibia plateau and TKA resected surface, medial PTS (MPTS) as well as lateral PTS (LPTS) of 164 northeast Chinese participants to provide reference for platform design of tibial prosthesis in TKA. Gender difference of tibial morphology within northeast Chinese population was also evaluated in this study. Comparison with that of Caucasian will also be discussed in this study.
2 Methods
This study was performed on 164 tibias from 86 male and 78 female participants. All participants were recruited from northeast China, aged from 21 to 27 (Average 24.2 ± 2.0 years old). Complete lower limbs CT-scan (Scope from superior margin of acetabulum to inferior margin of ankle joint) was conducted for each volunteer. Average height of male and female participants was 171.8 ± 8.4 cm and 163.8 ± 3.7 cm respectively. Ethic approval was obtained from Medical Research Ethics Committee of our hospital before execution. Inform consent was obtained from each participant who had been recruited. It was promised that all information of participants would be kept secret. One knee of each participant was chosen for measurement by random (either left or right). The inclusion criteria were healthy knee without symptoms of knee joint pain, joint stiffness and limited range of motion. The exclusion criteria were morbid knee with radiology evidence of osteoarthritis, rheumatoid arthritis, fracture, and bone tumor of knee joint.
2.1 CT acquisition and data management
CT image was obtained with 256-rows CT scanner (Philips Healthcare. Japan). The parameter of CT scan was drawn lessons from relative study[20] vol : 20.8 mGy, DLP: 705.3 mGy∗cm, Collimation: 64 × 0.625, Pitch: 0.579, Matrix: 512 × 512. After image acquisition, CT image was preserved as DICOM (Digital imaging and communications in medicine) format which was exported into Mimics Software (Materilase Corporation. Belgium). Afterward, 3D-reconstruction of CT image was performed with Mimics Software. Meanwhile, tibia was separated from acquired 3D-model.
2.2 Measurement methods
2.2.1 Measurement method of tibia plateau
Draw on the experience of previous studies, medial and lateral tibia plateau were measured by creating best-fitted ellipses which matched precisely with the boundary of tibia plateau.[1,20,21] Fig. 1 ). Average value of tMAP and tLAP was defined as tAP length. tML/tAP ratio of tibia plateau was calculated and compared between Northeast Chinese male and female.
Figure 1: Brief procedure of measurement method of tibia plateau. (A): Origin CT image (B): Operation of 3D reconstruction (C) Measurement method of tibia plateau.
2.2.2 Measurement method of posterior tibial slope
Posterior tibial slope (PTS) was gauged in Magics Software (Materialise Corporation. Belgium). Three-dimensional reference was automatically established in this Software. In order to guarantee measurement accuracy, orientation of tibial mechanical shaft should be posed cautiously. Draw on the experience of Ho et al's study, tibial mechanical shaft was defined as the line which passed through center points of tibia plateau and distal tibia.[17] Fig. 2 C, D). Center of sphere was considered as center point of distal tibia (Fig. 2 B). Subsequently, boundaries of medial and lateral tibia plateau were drawn respectively in Mimics software (Materialize Corporation. Belgium). Afterwards, geometrical centers of these two regions were generated automatically. Mid-point of geometrical centers of medial and lateral tibial plateau was defined as center of tibia plateau (Fig. 2 A). For convenience and accuracy of measurement, tibial mechanical shaft was kept vertical with horizontal plane and paralleled with z axis in 3D reference. Then planes which fitted precisely with the boundary of tibia plateau were generated to measure medial and lateral PTS respectively (Fig. 2 C, D). The intersectional angle between tibial mechanical shaft and the plane of medial and lateral tibia plateau and were defined as MPTS and LPTS.
Figure 2: Flow chart of measurement of posterior tibia slope. Boundary of medial and lateral tibia plateau were drawn, while geometric center (yellow points) were automatically generated. Red circle represented the center of tibia plateau (A) and distal tibia (B). Lateral (C) and anteroposterior (D) view of measurement procedure of PTS. A best-fitted sphere was created to match distal tibia. Column which passed through center of tibia plateau and distal tibia was tibial mechanical shaft (C and D).
2.2.3 Measurement method of tibial resected surface
Typical TKA resection was performed for each tibia with 3° posterior tilt and 0° varus/valgus rotation. Following Clary et al's recommendation, cartilage on tibia plateau with thickness of one millimeter should be take into consideration. Seeing that, cartilage on tibia plateau could not be reconstructed in 3D model, tibial resected surface was located at 8 mm below joint surface of lateral tibia plateau (Fig. 3 A, B).[6] epicondylar axis of femur in coronal view.[2] epicondylar axis of femur. According to Cheng et al 's suggestion, surgical transepicondylar axis of femur was drawn as the connecting line which passed through the lateral epicondylar prominence and medial sulcus of the medial epicondyle[3] Fig. 3 C). tMAP and tLAP of tibial resected surface were defined as lines which passed through the posterior-most points of tibial condyles and perpendicular with tML line. Similar as the measurement method of tibia plateau, average value of tMAP and tLAP was defined as tAP length. tML/tAP ratio was calculated to represent morphology character of tibial resected surface. tMAP/tLAP ratio of tibial resected surface was calculated to represent degree of asymmetry.
Figure 3: Schematic representation of measurement methods of tibial resected surface. and (B): Bone cutting of proximal tibia was conducted 8 mm below lateral tibia plateau with 3° posterior tilt. (C): tML line of tibial resected surface was paralleled with transepicondylar axis of femur. tMAP and tLAP lines passed through most posterior point of medial and lateral tibial condyles and perpendicular with tML line.
2.3 Statistical analysis
All parameters were expressed as mean ± SD. SPSS Statistics for Windows version 21.0 (Released 2012, IBM Corp, Armonk, NY) was applied to carry out statistical analysis. First, Kolmogorov–Smirnov test was used to test normality. Subsequently independent sample t test was used to test statistical significance (with a level of significance α = .05).
3 Result
After measurement of 164 cases of 3D tibial models, it was realized that northeast Chinese male has generally larger size tibia plateau than female. Both tML, tMAP and tLAP length of tibia plateau have statistical significance between male and female (P < .001) (Fig. 4 A, B). Nevertheless, female has larger tML/tAP ratio of tibia plateau than male. The ratio of female was 1.77 ± 0.09 (Range: 1.52∼1.98) and male 1.71 ± 0.07 (Range: 1.52∼1.87) (P < .001) (Table 1 ).
Figure 4: Relation between tML and tAP length. Relation between tML and tAP length of tibia plateau and TKA resected surface of male (A) and female (B). (C): Relation between tML/tAP ratio of TKA resected surface and tAP length.
Table 1: Measurement result of tibia plateau and TKA resected surface.
Medial and lateral posterior tibial slope of northeast Chinese male were 8.81 ± 2.87° and 8.44 ± 2.76°. MPTS and LPTS of northeast Chinese female were 9.56 ± 2.96° and 8.57 ± 3.19° (Fig. 5 and Table 2 ). Though female has larger PTS than male, no significant gender difference between male and female was found both in MPTS (P = .10) and LPTS (P = .54) (Table 3 ). Meanwhile, no statistical difference between MPTS and LPTS was found in male (P = .13). But MPTS of northeast Chinese female was significantly higher than their LPTS (P = .01).
Figure 5: Statistical chart of MPTS, LPTS, and average PTS.
Table 2: Comparison of PTS between this study and previous published works.
Table 3: Measurement result of PTS.
As for measurement result of TKA resected surface, northeast Chinese male had larger tML, tMAP and tLAP length than female (P < .001). No significant difference of tML/tAP ratio of TKA resected surface was investigated between male (1.60 ± 0.05) and female (1.61 ± 0.06) (P = .10) (Table 1 ). tMAP/tLAP ratio of TKA resected surface represented degree of asymmetry, and this ratio of male and female were 1.31 ± 1.03 and 1.11 ± 0.05 respectively. Asymmetry degree of tibial resected surface of male was statistically larger than female (P < .001).
4 Discussion
In total knee arthroplasty , accurate coverage of tibial resected surface and appropriate posterior angle of tibial osteotomy was of great importance to good clinical outcomes.[2–6,16,18] [16] [1–4,14]
Previous studies mainly focused on tibial measurement through X-Ray, 2D, and 3D CT, MRI as well as cadaveric study.[1–12,16] [1] [1] [5] [1–3,6,7]
Commercial available tibial prostheses have been reported relative poor coverage rate in Asian population.[1–5] [18] [1–6,16,18] [8] [2,4,7,9] [5] [3] [1]
In addition, negative correlation existed between tML/tAP ratio (1.48∼1.71) and tAP length (45.1∼55.0 mm) in this study (Fig. 4 C). Similar conclusion was also obtained in studies of Kwak et al and Cheng et al.[3,5] P < .05). Therefore gender-specific prostheses were recommended. This suggestion is similar with the opinion of Dai et al and Cheng et al's study.[1–3,7] [7]
Posterior tibial slope (PTS) was another essential characteristic in prostheses design and posterior angle of tibial osteotomy in TKA.[15,21–27] [2,3,14] [10,15,17,23]
It was widely accepted that Asian population has higher PTS than Caucasian. For instance, 100 normal Chinese knees were measured by Ho et al, in which MPTS and LPTS was 10.8 ° and 10.0°, respectively.[17] [1] [10]
Currently most commercially available tibial prostheses designed for Caucasian population have PTS of 3° to 7°, which means some of them are not suitable for Chinese patients. Shen et al applied 3D finite element to analyze contact stresses between polyethylene and femoral prostheses.[14] [9] [1,2]
Several limitations still existed in this study. First, 3° to 7° posterior tilt of tibial osteotomy was recommended in TKA surgery. But only resected surface of 3° was assessed in this study. Various resected surface with different tilt would be measured in further studies. The ignorance of coronal tibial slope was another limitation. Coronal tibial slope was defined as intersection angle between tML line of tibia plateau and tibial mechanical shaft which might interfere measurement result of PTS.[10,17]
5 Conclusion
In conclusion, gender difference within northeast Chinese population was found in this study. Northeast Chinese male has larger knee size and smaller PTS than female. As for measurement of TKA resected surface, northeast Chinese male has higher degree of asymmetry than female. According to the measurement results of tibia plateau and TKA resected surface, it could be concluded that northeast Chinese knee was generally smaller than Caucasian knee. In contrast to Caucasian knee, higher PTS and larger tML/tAP ratio were found in northeast Chinese knee. In consideration of morphological difference of proximal tibia, Chinese-specific and gender-specific tibial protheses were strongly recommended to be designed. Further clinical study would be warranted to verify these conclusions.
Acknowledgments
All authors appreciated Radiology Department of the Second Hospital of Jilin University for resource of computed tomography image. In addition, all authors sincerely appreciated Pengju Zhang for his hard working in image processing.
Author contributions
Conceptualization: Kesong Zhang, Qing Han, Bingpeng Chen, Shiruo Zhang, Jincheng Wang, Haichen Chu.
Data curation: Kesong Zhang, Qing Han, Bingpeng Chen, Yong Zhang, Jincheng Wang.
Formal analysis: Kesong Zhang, Hecheng Wang, Yong Zhang, Jincheng Wang.
Funding acquisition: Qing Han, Bingpeng Chen, Jincheng Wang.
Investigation: Qing Han, Hecheng Wang, Bingpeng Chen, Jincheng Wang, Haichen Chu.
Methodology: Kesong Zhang, Hecheng Wang, Kerong Yang, Bingpeng Chen, Yong Zhang, Shiruo Zhang, Jincheng Wang.
Resources: Kesong Zhang, Kerong Yang, Bingpeng Chen, Jincheng Wang.
Software: Kesong Zhang, Hecheng Wang, Kerong Yang, Yong Zhang, Jincheng Wang, Haichen Chu.
Supervision: Kesong Zhang, Kerong Yang, Jincheng Wang, Haichen Chu.
Validation: Hecheng Wang, Jincheng Wang.
Visualization: Jincheng Wang.
Writing – original draft: Kesong Zhang.
Writing – review & editing: Kesong Zhang.
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