|Year : 2022 | Volume
| Issue : 2 | Page : 146-150
Can the tibial length predict the size of tibial component of total knee arthroplasty?
Olasode Israel Akinmokun1, Eyitayo Oluwasakin Alabi1, George Okwudilichukwu Enweluzo1, Akindele Rafiu Balogun2, Ismail Abidemi Oyebiyi2
1 Department of Surgery, College of Medicine, University of Lagos, Lagos, Nigeria
2 Department of Orthopaedics, Lagos University Teaching Hospital, Idi-Araba, Lagos, Nigeria
|Date of Submission||20-Oct-2021|
|Date of Decision||26-Nov-2021|
|Date of Acceptance||03-Jan-2022|
|Date of Web Publication||23-Apr-2022|
Olasode Israel Akinmokun
Department of Surgery, College of Medicine, University of Lagos, Idi-Araba, Lagos
Source of Support: None, Conflict of Interest: None
Background: Total knee arthroplasty (TKA) is performed worldwide. TKA is performed to relief pain, correct deformities and improve mobility in patients with debilitating diseases of their knee joints. Templating is done as pre-operative planning for TKA. Certain parameters, such as shoe size, had been studied as predictor (s) for implant size. This study aimed to determine if the tibial length (TL) can also be as a predictor of a tibial component of TKA. Materials and Methods: TL and tibial plateau width (TPW) measurements were done on dry adult tibiae. Proximal tibiae were traced on tracing paper, to obtain anterior–posterior and lateral tracings. Length of tracings confirmed with measurement on dry bones. A TKA template, converted to 100% scale was used to estimate the tibial baseplate by two orthopaedic surgeons. Results: A total of 51 matured, non-sexed, non-paired tibiae were studied. There was a statistically significant positive relationship between the TL and the TPW (P = 0.0001). Furthermore, a statistically significant positive relationship was also observed between the TL and the tibial implant baseplate (P = 0.0001). The study showed that a particular range of tibia length will accommodate certain sizes of the tibial implant baseplate. Conclusion: The tibia length can be used as a predictor of the size of tibial baseplate of TKA.
Keywords: Africans, anthropometry, knee prosthesis, knee, Nigerians, planning, pre-operative, proximal tibia, replacement, total
|How to cite this article:|
Akinmokun OI, Alabi EO, Enweluzo GO, Balogun AR, Oyebiyi IA. Can the tibial length predict the size of tibial component of total knee arthroplasty?. Niger Postgrad Med J 2022;29:146-50
|How to cite this URL:|
Akinmokun OI, Alabi EO, Enweluzo GO, Balogun AR, Oyebiyi IA. Can the tibial length predict the size of tibial component of total knee arthroplasty?. Niger Postgrad Med J [serial online] 2022 [cited 2022 May 22];29:146-50. Available from: https://www.npmj.org/text.asp?2022/29/2/146/343736
| Introduction|| |
Total knee arthroplasty (TKA), a procedure that involves the replacement of worn-out knee joint with prosthesis, is performed worldwide. This procedure helps to relief pain, correct deformities and improves mobility in patients with debilitating disease involving their knee joints. During the pre-operative planning of TKA, templating is usually done. Templating is the procedure through which the implant size that would be used during the TKA is estimated. It is an important step that helps in the great efficiency of the surgical process and time during the procedure. Documentation on the accuracy of templating reported that the size obtained during templating is usually within one size difference of the implants used at surgery,, Templating can be done either with the use of acetate template on printed radiographs or the use of digital templating. Specht et al. documented both acetate and digital templating accurately predicted the size of the implanted component to within one size in 91% and 93%, respectively.
However, Arora et al. documented poor inter-observer and intra-observer mismatches during the templating process itself. They observed inter-observer mismatches in 46.8% of the readings and intra-observer mismatches in 43.6% of the readings. They opined that templating is a highly subjective and observer-dependent technique. Trickett et al. using digital templating in their study, however, reported otherwise in their study.
Studies were conducted to find other determinants that would correlate and predict implant size. Sershon et al., in their study using the demographic details (height, weight and gender) of the patients, documented that both femoral and tibial sizes were accurately predicted within 1 size of the final implants in 71%–92% and 81%–97% using the demographics alone but combining both templating and demographics increase the accuracy to 85%–99% in femoral components and 90%–99% for tibia components. Blevins et al. also used demographic variables such as patient's age, sex, height, weight and body mass index. They concluded that implant size was correlated with demographic variables, such as height, weight and body mass index.
A study in which Shoe size was used as a determinant to predict the implant size for TKA was also done. van Egmond et al. documented the correlation coefficient for both femoral and tibial components with shoe size to be 0.751 and 0.759, respectively. Furthermore, shoe size showed a 94% agreement and 86% agreement scores for both femoral and tibial component, respectively when a deviation of ± 1 component size was allowed. They, therefore, concluded that both femoral and tibial component size have a good correlation with shoe size and thus suggested that the shoe size may be used as a predictor in pre-operative implant size planning for primary TKA. Rehman et al. also documented a positive correlation between the shoe and total knee replacement (TKR) component sizes. Trainor et al. not only posited that shoe size was a predictor of TKA component dimensions but also that it was better than the body height.
Based on these previous studies that showed correlations between the patient's demographics, especially the height, and shoe size with the TKA implants, and even more, that the shoe size can be used as a predictor of TKA components, this study was, therefore, conducted to document the correlation between the length of the tibia and tibial baseplate implant component and to determine if the tibial length (TL) can also be as a predictor of a tibial component of TKA.
| Materials and Methods|| |
This was a prospective descriptive study conducted at the College of Medicine, University of Lagos. It was a study conducted on dry tibiae specimens. Ethical approval was obtained from the Lagos University Teaching Hospital's Health Research Ethics Committee (LUTH HREC) located at room 107, 1st floor, LUTH Administration block, before the commencement of the study. LUTH HREC registration number is NHREC: 19/12/2008a. The approval dated from 13th March 2020 to 13th March, 2021. The health research committee assigned number was ADM/DCST/HREC/APP/3466. The tibiae used in the study were from the Department of Anatomy, College of Medicine, University of Lagos. The measurements were done within the gross laboratory of the Department of Anatomy. The data collection was done between 31st August 2020 and 30th October, 2020. A total of 51 matured, non-sexed, non-paired tibiae were used in this study. Mensuration of certain parts of the tibial bones was done using digital Vernier calipers and osteometric board. The measurements done included:
- Maximum tibia length (TL)-the maximum distance from the highest point of the upper part of the tibia (tip of intercondylar eminence) to the lowest point of the tibia (tip of medial malleolus) using osteometric board
- Tibial plateau breadth (TPB)– the widest diameter between the anterior and posterior margins of the tibia plateau
- Tibial plateau width (TPW)– the widest diameter between the medial and lateral margins of the tibia plateau
- Anterior–Posterior distance of lateral condyle (APDLC)-the maximum anterior–posterior diameter of the lateral condyle of tibia
- Anterior–Posterior diameter of medial condyle-the maximum anterior–posterior diameter of the medial condyle of tibia.
Each measurement was done two times by two authors independently. Measurements with large discrepancies (>5 mm) were resolved by re-measuring the affected part (s) together. The average of each measured value was calculated and documented.
The proximal part of each tibia was thereafter, traced on tracing paper, with the tibia bone lying in anatomic position. The anterior–posterior and lateral projections of each tibial bone were made. The measured and already documented values of TBW and APDLC of each tibia were used to confirm the accuracy of the tracing of that particular proximal tibia.
The template to be used for the estimation of the tibial baseplate size was prepared. The original template had a scale of 110% and has to be converted to 100% for this study. The template used for this study was that of PFC sigma® knee system template (X-ray overlay Cat No. 9068-76-000, DEPUY Lot No. PI1 004 026 from DEPUY, a Johnson and Johnson company) The conversion was achieved by initially photocopying the template into 100% scale, i.e., by reducing the size by 10% during the photocopying process. The scale on the produced copy was cross-checked and confirmed to be 100% using a measure ruler. The copied templates were thereafter printed on transparencies. The scale was again cross-checked and confirmed using the measuring ruler to ensure that the scale on produced templates was 100% and accurate.
The prepared templates with confirmed 100% scale were then overlaid over the traced proximal part of the tibia to estimate and obtain the size of the tibial baseplate that would likely fit that particular proximal tibia. This was done by two arthroplasty surgeons, experienced in total knee replacement, separately and documented [Figure 1]. The results were compared after the individual measurements to resolve discrepancies and record the final size accepted by both surgeons. The dimensions (both mediolateral [ML] and anterior–posterior [AP]) of the tibial baseplate implants from multiple implants manufacturers were retrieved from their product monograms.
|Figure 1: Template overlaid on the traced proximal tibia drawing to estimate the size of the tibial implant baseplate|
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Analyses were performd with Microsoft excel 2010 (Microsoft Corporation, Redmond, Washington, United States) and STATA version 13 (StataCorp, Texas. USA). Mean and standard deviation were documented. Pearson's correlation coefficient, inter-observer agreement analysis, Chi-square and regression analysis were performed for associations. Statistical significance was set at P ≤ 0.05.
| Results|| |
The TL measured ranged from 33.2 cm to 44.1 cm with an average of 40.3 ± 2.2 cm. The TPW ranged from 62.1 cm to 80.4 cm with an average measured value of 73.0 ± 3.9 cm, while the TPB measured ranged from 42.1 cm to 54.8 cm with an average of 48.4 ± 3.1 cm. The regression analysis between the TL and the TPW was statistically significant (P = 0.0001) and generated the equation:
- TL = 18.5 + 0.3 × TPW
- TPW = 34.4 + 0.9 × TL (± 9 mm).
The scatter diagram of TL and TPW showed a positive gradient trend line, indicating that an increase in TL will correspond to an increase in TPW, though not in direct proportion [Figure 2].
|Figure 2: Scatter plot showing the relationship between the tibial plateau widths and tibial lengths|
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Size 3 tibial baseplate was estimated most frequently at 51% and 49%, respectively, for both raters. Size 2 tibial baseplate had the least frequencies at 1.96% and 5.88%, respectively. The frequencies of other sizes, as estimated, are shown in the [Table 1]. Cohen's kappa for the two raters was 0.1756, indicating only slight agreement. The inter-observer agreement was 43.14% against the expected agreement value of 31.03%, but was statistically significant (P = 0.0173). However, Pearson's correlation of the estimated sizes of tibial baseplate by the two raters was strong (r = 0.7182). None of the differences in the estimated sizes by both raters was more than a size difference.
|Table 1: Frequencies of the estimated tibial implant baseplates by the two raters|
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Regression analysis of the TL and the tibial baseplate size was statistically significant (P = 0.0001). The scatter diagram between TL and the size of the tibia baseplate showed a trend line with a positive gradient, indicating that the size of the tibial baseplate estimated increased as the length of the tibia increased, though not directly proportional [Figure 3]. It also showed that within a particular TL range, certain size predominate. Size 2.5 was mostly estimated for TL range from 33.0 cm to 37.9 cm at 62.5%, followed by size 3 baseplate at 25% and size 2 at 12.5%. In the tibiae with lengths that ranged from 38 cm to 39.9 cm, size 2.5 constituted 50%, while size 3 was 40% and size 2 was 10%. Other distribution is shown in [Figure 4].
|Figure 3: Relationship between the tibial length and the tibial baseplate size|
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|Figure 4: Distribution of the tibial baseplate within a range of tibial length|
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| Discussion|| |
This study showed a statistically significant positive correlation between the length of the tibia and the tibial baseplate size. It also showed that tibial baseplate implant size can be estimated from the length of the tibia. It was deduced from the study that certain sizes of the tibial baseplate will fit a particular range of lengths of the tibia. The size of the tibial baseplate that would likely be utilized for TL from 33.0 cm to 37.9 cm are sizes 2, 2.5 and 3 (baseplate dimension, ML × AP: 64 mm × 43 mm; 67 mm × 45 mm and 71 mm × 47 mm) while TL from 38.0 cm to 39.9 cm would likely accept sizes 2.5 and 3 (baseplate dimension, ML × AP; 67 mm × 45 mm and 71 mm × 47 mm). Length from 40 cm to 42.9 cm would likely accommodate sizes 2.5, 3 and 4 (baseplate dimension, ML × AP; 67 mm × 45 mm, 71 mm × 47 mm and 76 mm × 51 mm) TL from 43 cm to 44 cm would likely use sizes 3 and 4.(baseplate dimension, ML × AP; 71 mm × 47 mm and 76 mm × 51 mm). This finding can be useful in the pre-operative planning. The length of the tibia of the patient that is being prepared for TKA can be measured and the length can be used to predict roughly, the implant size. The tibia length is measured clinically, from the uppermost part of the tibia at the knee joint, to the lowermost tip of the medial malleolus. These bony edges can be palpated clinically and marked. A standard tape rule can then use to measure the distances between these two bony edges. The ML dimensions of the PFC Sigma® baseplate were inputted for easy referencing and comparison to other baseplate from other manufacturers. Different manufacturers used different dimensions and different size nomenclature. The tibial baseplate size nomenclature for PFC sigma® knee system was sizes 1.5, 2, 2.5, 3, 4, 5 and 6 but NEXGEN® (from Zimmer) and GENESIS II® (from Smith and Nephew) sizes were from 1 to 6 and 1–8 respectively. The dimensions for PFC Sigma® Size 1.5 is 61 mm by 41 mm, while the dimensions for size 1 baseplate for GENESIS II® is 60 mm by 42 mm and the dimensions for size 2 baseplate for NEXGEN®, is 62 mm by 41 mm. It, therefore, means that a size 1.5 baseplate for PFC Sigma® correspond to size 1 baseplate of GENESIS II® but size 2 baseplate of NEXGEN® implant. This non-standardisation of dimension of the tibial baseplate implant is one of the downsides of this study. The tibial baseplate dimensions of three manufacturers are compared in [Table 2].
It must be stated that the aim of templating is far more than the size estimation alone. The seating of the implant, offset and likely alignment is other parameters that are studied during templating. It is important that such parameters are studied with the acetate or digital template. This study has only demonstrated that the length of the tibia can be used as a predictor of the size of tibial baseplate to be used in a TKA and can be used in conjunction with the templates. The TL will predict the range of tibial baseplate likely to be used for the surgery. The use of TL will help to know quickly the implant size on the template where acetate or digital templating can be started from. It will also save time while templating as the size to start from is known already.
The low inter-observer agreement with the use of template was noted in this study too. This was also documented by Arora et al. in their study. The use of acetate template, which is quite common in this part of the world, could be fraught with inter-observer mismatches as it highly subjective. We believe that using the length of the tibia to estimate the baseplate size can provide an adjunct to be used in conjunction with templating. We, therefore, believe that measuring the tibia length can be helpful in developing and underdeveloped countries can help improve the accuracy of templating in places where digital templating is not available.
The anatomic variations had been documented in different ethnic groups in different geographical locations around the world. The findings from this study are only relevant and suitable for our geographical location. Similar study in other geographical locations is needed. The non-standardisation of the sizes of the tibial baseplate implant is a major limitation of this study.
Finally, the major strength of the present study was the derivation of an equation that can be used to estimate the length of the tibia from intact proximal tibia, in which the TPW can be measured. This is important in forensic medicine. The equation is given as: TL = 18.5 + 0.3 × TPW. The height of the individual can therefore be computed from the estimated TL.
| Conclusion|| |
The tibia length can be used as a predictor of the size of the tibial baseplate of TKA. This can be used in conjunction with templating during pre-operative planning to improve the accuracy and reliability of the pre-operative planning period. The equation 'TL = 18.5 + 0.3 × TPW' can be used in forensic medicine to estimate the TL.
- The TL can be used as part of the pre-operative determination of the tibial baseplate of TKR in Nigerians
- Similar study that involved the TL and tibial implant baseplate should be conducted among other racial groups and in other geographical locations.
We are grateful to Messrs. Oladele Wale and Izegbu Michael for the assistance rendered during the collection of the dry tibiae bones used for this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]