Abstract
Purpose
The primary aim in fixation of the tibial plateau fractures is the restoration of normal anatomy. Evaluation of the widening of the tibial plateau, which has been linked with adverse long term outcomes, still needs precise markers for quantification. The purpose of this study is to analyze the normal limits of tibial plateau widening in the Indian population in relation to the distal femur in a standardized manner to provide important radiological parameters for the same.
Methods
We retrospectively analyzed electronically archived true AP radiographs of uninjured normal knee joints during one year between 2018 and 2019. We measured the mediolateral width of the articular surface and extraarticular extent of the tibial plateau and compared them with the distal femoral articular and extra-articular extents. The measurements were compared between the male and female groups.
Results
Tibial plateau articular width was found to be 4% wider in relation to the distal femoral articular surface. The medial articular rim of distal femur matches closely to the medial articular rim of the tibial plateau. The lateral articular rim of distal femur lies medial to the lateral articular rim of tibial plateau with a mean distance of 3.49 mm.
Conclusions
Owing to individual variations in bony extents around the knee, the differential extent of tibial plateau relative to distal femur would be a more reliable parameter than absolute measurements. Medially the articular extent of distal femur matches closely with the articular extent of tibial plateau while the lateral extra-articular extent of distal femur matches closely with the lateral tibial articular extent. Gender-based differences do not significantly affect these two parameters.
Keywords: Tibial plateau, Tibial plateau width, Tibial plateau widening, Tibial plateau fractures, Pathological widening
1. Introduction
Fractures around proximal tibia should ideally be reduced anatomically to prevent short and long term complications, especially post traumatic arthritis.1 Various parameters have been studied including the uniform joint space, surrounding condylar height in case of depression, metaphyseal buttressing and mechanical axis restoration, which help in proper alignment as well as anatomical reduction of tibial plateau fractures.2, 3, 4, 5, 6, 7, 8, 9, 10 The issue related to the widening of tibial plateau could result from inefficient buttressing of condyles, deformation of the condyle during manipulation and due to gap at the articular zone of fracture. This pathological widening has adverse effects on long term functional outcomes and has been implicated in the early development of posttraumatic arthritis.2, 3, 4, 5, 6, 7, 8, 9, 10 The widening of more than 5 mm is usually considered to have worse functional outcomes. This could possibly result from nonuniform weight distribution at the tibial articular surface or due to change in the biomechanics of menisci and collateral ligaments, the alignment of which will automatically change with the outward shift of tibial plateau.4 Although arthroscopic techniques for assessment of articular reduction have been emerging, the intraoperative fluoroscopy is still the most commonly used medium for assessment of the quality of reduction.10 The widening seen in fluoroscopic images is generally qualitatively assessed based on surgeons observation which is purely subjective. The precise quantification markers for measurement of widening of tibial plateau have not been adequately studied in the literature. To the best of authors’ knowledge, there has been only two such studies which had analyzed widening of the tibial plateau and those were based on the American population. There is a need for more such studies considering the large evidence of morphometric variations around knee joint among different ethnic groups.11 The purpose of our study is to present a software-based analysis of the normal variations in width of tibial plateau, to compare the relative extent of tibial plateau to that of distal femur, to analyse the gender-based variations of tibial plateau width and to check the validity of findings presented in previous studies in an Indian scenario.
2. Materials and methods
This retrospective study was conducted in a tertiary care center. The study was purely based on radiological data stored in an electronic archiving system and did not involve any human subjects. Data from consecutive AP radiographs of uninjured knee joints within the age group between 18 years and 65 years, performed during a one year period between 2018 and 2019, was retrieved. Only True AP radiographs with Patella in centre of intercondylar notch were included. We excluded the cases with signs of degenerative or inflammatory arthritis, deformities, skeletal dysplasias, tumors, hypoplastic bones and signs of old fracture or surgery. The analysis was done using Stratus ® PACS software for precise measurements. The measurements were made on true AP radiographs with an intention to keep the methodology more standardized and to make it replicable for intraoperative assessment of widening of tibial plateau on AP fluoroscopic images. Following parameters were measured:
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1.
Articular width of tibial plateau (TA) - It was measured as the distance between the medial and lateral articular rims of the tibial plateau in a direction parallel to its articular surface (Fig. 1).
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2.
Extra-articular width of tibial plateau (TE) - It was measured as the maximal mediolateral extent of tibial plateau outside the limits of articular surface in a direction parallel to the tibial articular surface (Fig. 1).
-
3.
Articular width of distal femur (FA) - It was measured as the distance between the medial and lateral articular inflection points of the distal femur in a direction parallel to the articular surface of tibial plateau (Fig. 1).
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4.
Extra-articular width of distal femur (FE) - this was measured as the maximal mediolateral extent of distal femur outside the limits of the articular surface in a direction parallel to the articular surface of the tibial plateau (Fig. 1).
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5.
Articular Ratio TA/FA - the proportion of articular width of the tibial plateau over articular width of the distal femur.
-
6.
Extra-articular ratio TE/FE - the proportion of extra-articular width of tibial plateau over extra-articular width of the distal femur.
-
7.
Medial articular mismatch (mTaFa) - measured as the medial gap between medial tibial articular rim and the medial femoral articular inflection point in a direction parallel to the articular surface of the tibial plateau. Negative values indicate that medial articular rim of the tibial plateau is lying lateral to the articular rim of the medial femoral condyle (Fig. 2).
-
8.
Lateral articular mismatch (lTaFa) - the lateral gap between lateral tibial articular rim and the lateral femoral articular inflection point in a direction parallel to the articular surface of the tibial plateau. Negative values indicate that lateral articular rim of the tibial plateau is lying medial to the articular rim of the lateral femoral condyle (Fig. 2).
-
9.
Medial tibial articular - femoral condylar mismatch (mTaFe) - measured as the medial gap between medial tibial articular rim and medial most extent of the distal femur in a direction parallel to the articular surface of the tibial plateau. Negative values indicate that medial articular rim of the tibial plateau is lying lateral to the medial extent of the medial femoral condyle (Fig. 2).
-
10.
Lateral tibial articular - femoral condylar mismatch (lTaFe) - measured as the lateral gap between lateral tibial articular rim and lateral most extent of the distal femur in a direction parallel to the articular surface of the tibial plateau. Negative values indicate that lateral articular rim of the tibial plateau is lying medial to the lateral extent of the lateral femoral condyle (Figs. 2 and 3).
-
11.
Lateral tibial articular - extraarticular mismatch (lTaTe)- This was measured as the difference between the lateral articular rim of the tibial plateau and lateral most extraarticular extent of the tibial plateau in a direction parallel to its articular surface. Negative values indicate that lateral articular rim of the tibial plateau is lying medial to its extraarticular extent on the lateral aspect (Fig. 2).
Fig. 1.
A representational anteroposterior radiographs of right knee joint showing the measurements of articular and extraarticular extents of tibial plateau and distal femur in line with tibial plateau articular surface. Articular extent of tibial plateau (TA), Extraarticular extent of tibial plateau (TE), Articular extent of distal femur (FA), Extraarticular extent of distal femur (FE) are being measured.
Fig. 2.
Measurements of articular and extraarticular differences of tibial plateau in relation to distal femur have been shown. Medial articular mismatch (mTaFa), Medial tibial articular - femoral condylar mismatch (mTaFe), Lateral articular mismatch (lTaFa), Lateral tibial articular - femoral condylar mismatch (lTaFe), Lateral tibial articular - extraarticular mismatch (lTaTe) are being measured. lTaFe is found to be ‘zero’ here as lateral condylar extent of femur matches the lateral articular extent of tibial plateau.
Fig. 3.
A radiograph showing non-zero measurement of lTaFe when lateral condylar extent of distal femur falls out of the line corresponding lateral tibial articular extent.
The means of above measurements were calculated and statistically analyzed using IBM ® SPSS 22 software. A p value of less than 0.05 was considered to be significant. Findings between male and female cases were compared.
3. Results
A total of 101 true AP radiographs were analysed as per inclusion criteria. There were 49 male cases and 52 female ones. Mean age was 40.27 years (male = 37.34years, female = 42.48). Tibial articular surface was found to be wider in relation to the distal femoral articular surface by a mean difference of 4%. Contrarily, the extraarticular extent of the tibial plateau which includes its lateral flare was found to be smaller in relation to the condylar extent of the distal femur with a mean difference of 4%. The medial articular rim of tibial plateau matched closely to the medial articular inflection point of the distal femur, while the lateral articular rim of tibial plateau matched closely to the lateral femoral condylar extent (Table 1). Overall bony extents of the distal femur and proximal tibia were found to be smaller in females. However, interestingly, the ratio related parameters (TA/FA and TE/FE), medial articular mismatch (mTaFa), lateral articular mismatch (lTaFa) and lateral tibial articular - femoral condylar mismatch (mTaFe) in females were found to be comparable to male group. Table 2 presents a detailed analysis of gender-based differences concerning tibial plateau width.
Table 1.
Various parameters related to assessment of tibial plateau width in relation to distal femur.
| Parameter | Observed value | Remarks |
|---|---|---|
| Age (years) | Mean = 40.27 | - |
| Range = 18-64 | ||
| SD = 11.53 | ||
| Male:female ratio | 49:52 | Comparable numbers |
| Articular extent of tibial plateau, TA (in mm) | Mean = 78.37 | Wide range and variability |
| Range = 68 to 97 | ||
| SD = 6.17 | ||
| Extraarticular extent of tibial plateau, TE (in mm) | Mean = 80.65 | Wide range and variability |
| Range = 69 to 102.1 | ||
| SD = 6.60 | ||
| Articular extent of distal femur, FA (in mm) | Mean = 75.09 | Wide range and variability |
| Range = 63 to 96 | ||
| SD = 6.21 | ||
| Extraarticular extent of distal femur, FE (in mm) | Mean = 84.36 | Wide range and variability |
| Range = 70.2 to 102 | ||
| SD = 6.77 | ||
| Articular Ratio of TA/FA | Mean = 1.04 | Tibial articular width is slightly (mean = 4%) wider than femoral articular surface |
| Range = 0.95–1.13 | ||
| SD = 0.03 | ||
| Extra articular Ratio of TE/FE | Mean = 0.96 | Tibial condylar width is slightly (mean = 4%) narrower than femoral condylar width |
| Range = 0.87 to 1.04 | ||
| SD = 0.03 | ||
| Medial articular mismatch (mTaFa) (in mm) | Mean = −0.01 | Medial articular extents of distal femur and proximal tibia have minimal overlap with low variation |
| Range = −3.4 to 3.5 | ||
| SD = 1.62 | ||
| Medial tibial articular - femoral condylar mismatch (mTaFe) (in mm) | Mean = −5.06 | Medial femoral condylar extent lies more medial to the medial articular extent of tibial plateau |
| Range = −10.1 to −1 | ||
| SD = 1.87 | ||
| Lateral articular mismatch (lTaFa) (in mm) | Mean = 3.49 | Articular surface of tibial plateau extends more lateral than the femoral articular surface on lateral aspect in majority of the cases |
| Range = −3 to 7.2 | ||
| SD = 2.09 | ||
| Lateral tibial articular - femoral condylar mismatch (lTaFe) (in mm) | Mean = −0.82 | Lateral extra articular extent of distal femur and lateral articular extent of proximal tibia have minimal overlap and also the least varying quantifiable parameter between two bones. However, it was of limited use as it did not belong to distal femur. |
| Range = −5.2 to 4.2 | ||
| SD = 1.47 | ||
| Lateral tibial articular - extraarticular mismatch (lTaTe) (in mm) | Mean = −2.44 | Extra articular flare of lateral tibial plateau lies lateral to its lateral articular extent. However it is of limited value as it doesn't belong to distal femur. |
| Range = −5.3-0 | ||
| SD = 1.33 |
SD = standard deviation.
Table 2.
Comparison of parameters related to tibial plateau width among male and female groups.
| Parameter | Male | Female | Remarks |
|---|---|---|---|
| Age (in years) | Mean = 37.34 | Mean = 42.48 | p = 0.025 |
| SD = 11.41 | SD = 11.18 | Significant difference with p < 0.05 | |
| Articular extent of tibial plateau, TA (in mm) | Mean = 82.48 | Mean = 74.34 | p < 0.05 |
| SD = 5.51 | SD = 3.64 | Articular width of tibial plateau is significantly smaller in females | |
| Extraarticular extent of tibial plateau, TE (in mm) | Mean = 85.41 | Mean = 76.39 | p < 0.05 |
| SD = 5.80 | SD = 3.69 | Extra articular width of tibial plateau is significantly smaller in females | |
| Articular extent of distal femur, FA (in mm) | Mean = 79.14 | Mean = 71.13 | p < 0.05 |
| SD = 5.35 | SD = 4.10 | Articular width of distal femur is significantly smaller in females | |
| Extraarticular extent of tibial plateau, TE (in mm) | Mean = 88.72 | Mean = 80.25 | P < 0.05 |
| SD = 6.32 | SD = 4.07 | Extra articular width of distal femur is significantly smaller in females | |
| Articular Ratio of TA/FA | Mean = 1.04 | Mean = 1.04 | p = 0.585 |
| SD = 0.03 | SD = 0.03 | Non significant difference | |
| Extra articular Ratio of TE/FE | Mean = 0.96 | Mean = 0.95 | p = 0.066 |
| SD = 0.027 | SD = 0.03 | Non significant difference | |
| Medial articular mismatch (mTaFa) (in mm) | Mean = −0.29 | Mean = 0.32 | p = 0.056 |
| SD = 1.52 | SD = 1.65 | Non significant difference | |
| Medial tibial articular - femoral condylar mismatch (mTaFe) (in mm) | Mean = −5.5 | Mean = −4.6 | p = 0.012 |
| SD = 1.70 | SD = 1.92 | Significant difference p < 0.05 | |
| Lateral articular mismatch (lTaFa) (in mm) | Mean = 3.77 | Mean = 3.16 | p = 0.145 |
| SD = 1.94 | SD = 2.18 | Non significant difference | |
| Lateral tibial articular - femoral condylar mismatch (lTaFe) (in mm) | Mean = −0.65 | Mean = −1.00 | p = 0.234 |
| SD = 1.46 | SD = 1.47 | Non significant difference | |
| Lateral tibial articular - extraarticular mismatch (lTaTe) (in mm) | Mean = −2.92 | Mean = −2.05 | P = 0.001 |
| SD = 1.39 | SD = 1.12 | Difference can be considered significant at p < 0.05. |
SD = standard deviation.
4. Discussion
Tibial plateau width forms an important component for restoration of normal anatomy of tibial plateau.2,3 While the pathological widening of the tibial plateau should be avoided due to the risk of long term complications,4 lack of knowledge regarding the normal variation of tibial plateau width can lead to over-compression of the tibial plateau. This could put undue stress on surrounding ligaments and capsule which could affect the knee function.
This study is an attempt to screen various relations between the tibial plateau and distal femur and to quantify and analyze them in order to bring out the least varying parameters which can be measured by surgeons intraoperatively on fluoroscopic images in a standardized manner. True anteroposterior radiographs with the patella in center of the intercondylar notch were used for analysis to make the measurements techniques more standardized for intraoperative use.
A widening of more than 5 mm is suggested to have poor functional outcomes not only because of associated ligamentous and meniscal injuries but also because of altered biomechanics due to altered tibial plateau width.4, 5, 6 However, the criteria of this widening, whether it accounts for widening additional to normal widening or is inclusive of it, has not been established.2,3,7
This could possibly account for noncorrelation between soft tissues injuries with the existence of widening of the tibial plateau as observed by Wang et al..8
Our results suggested that the individual variations in tibial plateau width are high with a wide range. Moreover, males have larger tibial plateau width compared to females. The shortcoming of individual variations of tibial width can be overcome to some extent by the application of ratios, which assess the size of tibial plateau relative to distal femur (both articular as well as extraarticular extents), which had very low variation as well as insignificant differences between male and female groups in our results. However, these ratios will not explain the normal medialization or lateralization of tibial condyles, especially when addressing bicondylar tibial plateau fractures. This issue can be addressed by measurement of tibial condylar overlap in relation to the femoral condyles. The mTaFa (medial overlap of tibial articular surface relative to femoral articular surface) and lTaFe (lateral overlap of tibial articular surface relative to lateral femoral condylar extent), are the two parameters which have very low individual variation in both male and female groups and thus can be considered for assessment of medial and lateral position of tibial plateau. Based on the wide range of individual variations in the width of the tibial plateau, we feel that ratios of tibial plateau width in relation to distal femur would be more helpful to quantify the widening. Thus, 4% of extra width relative to femoral articular surface can be considered normal for the tibial plateau. When interpolated to mean distal femoral articular widths this results in a normal widening of 3.1 mm in males and 2.8 mm in females. When using the extra-articular extents of the distal femur and proximal tibia for evaluating widening, the tibial extent will remain slightly smaller than femoral condylar extents by a mean difference of 4% relative to the distal femur. The lateral tibial articular - extraarticular mismatch (lTaTe) which was found to have low variations among individuals. However, it of limited use as it did not belonged to distal femur which was used for analysing relations with distal tibia.
Comparing with the results in the previous two studies, the Indian patients have smaller distal femoral and tibial plateau widths with difference close to 10 mm in both these measurements.2,3 However, the ratios of femoral and tibial articular extents are similar to our observations. The articular overlap between the tibial plateau and distal femur on medial and lateral aspects has been analyzed in only one study and is similar to our results.2 The normal widening is suggested to be 2.1 mm. However, this widening considers the relative extra-articular extent of a tibial plateau over femoral extra-articular extents. The measure of widening of the tibial articular surface in relation to the femoral articular surface had not been suggested.
Our study is the first study which has analyzed the tibial plateau width in Indian population and compared the results from the previous two studies on the American population. Moreover, important markers for assessment of tibial plateau width which do not vary much with individual and gender-based differences have been highlighted. The methodology used has been standardized to true AP view of the knee with the patella in center and articular surface of tibial plateau serves as a template for making measurements parallel to it. This would help in more practical assessment than intraoperative eyeballing for assessment. There have been a few limitations considering the retrospective nature, radiographic measurements rather than a CT based analysis and sole mediolateral dimension being analyzed. However, considering the limited evidence in the literature regarding tibial plateau widening, this study will help in forming the basis for more advanced research and in the thought building process.
To conclude, this study attempts to define normal widening of the tibial plateau in Indian population using various parameters in relation to the distal femur. The tibial plateau in males is generally wider when compared to females. Owing to individual variations in bony extents around knee, differential extent of tibial plateau relative to distal femur would be a more reliable parameter than an absolute measurement. The articular surface of tibial plateau is wider than the distal femoral articular surface. Articular and extra-articular ratios, medial articular mismatch and Lateral tibial articular-femoral condylar mismatch are among the least varying parameters on an individual basis as well as among male and female groups.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Conflicts of interest
None of the authors have any conflicts to declare.
Acknowledgement
We would like to thank Prof. Shishir Rastogi for his kind support and guidance in conducting this study.
Contributor Information
Arvind Kumar, Email: arvindmamc@gmail.com.
Jigyasa Passey, Email: jigyasapassey@gmail.com.
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