Femoral Component Sizing in Oxford Unicompartmental Knee Replacement: Existing Guidelines Do Not Work for Indian Patients

Preoperative Templating for Total Hip Arthroplasty: A Method for Calibrating Digital Radiographs Using Patient Demographics and Anthropometric Measurements

Background Preoperative templating aids the surgeon in estimating implant size and placement. Calibration markers are used to set the correct magnification of digital images before templating. Improper marker placement or complete absence can lead to inaccuracy or an inability to calibrate images altogether. Aims This study describes a method for calibrating images using a patient's femoral head size (FHS) predicted using demographics and anthropometric data. Materials and methods A formula predicting the FHS was derived from a cohort of 507 patients who underwent hemiarthroplasty for an intracapsular fractured neck of the femur through multivariate regression analysis. A separate validation cohort (n=50) who had undergone total hip arthroplasty (THA) had postoperative radiographs calibrated using the predicted FHS and the native contralateral hip as a surrogate calibration marker. The THA femoral head implant size was subsequently measured and compared with the actual implant size selected intraoperatively. Measurements were performed by two independent assessors to determine intra- and interobserver reliability. Results Multivariate regression analyses showed four variables significantly correlated with the size of the femoral head: gender (p < 0.001), height (p < 0.001), weight (p < 0.001), and race (Asian) (p = 0.01). Using these, a regression model to predict the FHS was obtained with an R2 value of 0.65 and a standard error of 2.18 mm. The validation cohort showed that THA head implant size could be accurately measured with an average root-mean-squared error (RMSE) of 1.41 mm (SD = 0.97 mm; %RMSE = 4.7%). The implant head size was measured to be within 5%, 10%, and 15% RMSE in 57.5%, 93.0%, and 100.0% of cases, respectively. There was excellent intraobserver (R2 = 0.94 and 0.95) and interobserver (R2 = 0.94) reliability. Conclusions The novel method proposed and validated in this study, using a predicted FHS to calibrate digital images, provides an alternative means of templating THA for fractured neck of the femur patients, in whom external calibration markers are often absent.

Using MRI Measurement to Improve Accuracy of Femoral Component Sizing in Oxford Unicompartmental Knee Arthroplasty

Unicompartmental knee arthroplasty (UKA) can achieve better kinematics and faster recovery than total knee arthroplasty. The Phase III Oxford UKA system has five sizes of femoral components to approximate the normal knee geometry. However, these different sizes may also induce problems, such as the misselection of component size. Different criteria have been proposed to predict the ideal size preoperatively. However, no single method can be applied universally. Therefore, this study aimed to develop a preoperative measurement using knee magnetic resonance imaging (MRI) to predict femoral component size. A total of 68 patients who underwent UKA were investigated from June 2019 to April 2020. 16 knees using a different MRI protocol were excluded. We developed an MRI measurement method to determine femoral size instead of gender- and height-based methods. The accuracy of different methods was compared using postoperative true lateral view radiographs. Three different kinds of gender- and height-based criteria, preoperative templating and intraoperative spoon measurement were compared. The accuracy of MRI measurement was 90.3%. Therefore, a significant difference was found between MRI measurements and all other methods, such as templating or gender- and height-based methods. In conclusion, the MRI measurement method can be concluded to accurately predict femoral component size in UKA. This method could be used regardless of different ethnic groups, individual knee geometry, or soft tissue tension.

CT Morphometric Analysis of Medial Tibial Condyles: Are the Currently Available Designs of Unicompartmental Knee Arthroplasty Suitable for Indian Knees?

BACKGROUND

The main purpose of this study is to assess the compatibility of medial tibial condyle (MTC) morphometry of Indian population with that of six contemporary UKA prostheses tibial components. We hypothesized that from the currently available UKA designs at least one would fit the MTC morphometry optimally as per the manufacturer's recommendation.

METHODS

We used CT morphometric data of 100 (66 males and 34 females) consecutive nonarthritic adult knees with reference to the MTC to assess the compatibility of currently available (in India) UKA prostheses. Each MTC was measured in the anteroposterior dimension, mediolateral at pre-defined points and the MTC aspect ratio calculated. Proportion of knees which could be optimally fitted with the existing UKA tibial components was calculated.

RESULTS

The mean age was 39.6 (SD 15.9) years. Anteroposterior and mediolateral dimensions in males were higher as compared to females (p < 0.001). As the anteroposterior dimension increased, the MTC aspect ratio decreased. There was asymmetry of anteroposterior halves with maximum mediolateral width being posterior to the central mediolateral width by 5.5 (SD 2.8) mm. Optimal anteroposterior fit ranged from 66 to 93%. However, optimal mediolateral fit as well, ranged from 5 to 37% with underhang present in 17-61% and > 2 mm medial overhang present in 0-35% cases. In 23% of cases, not a single implant could be fitted optimally.

CONCLUSION

Currently available UKA implants do not provide optimal tibial fit in nearly 25% of Indian patients. A surgeon needs to be aware of these limitations of existing implants when considering UKA.

Prosthesis size distribution in Oxford phase III unicompartmental knee arthroplasty - Based on more than 1900 Chinese patients

Introduction

It is difficult to determine the optimal size of unicompartmental knee arthroplasty (UKA) prosthesis both pre-operatively and intra-operatively. Inappropriate femoral and tibial components are still the leading cause of failure. Several guidelines based on the Western population may not apply to the Chinese patients. We consequently try to investigate distributions of Oxford-UKA prosthesis in Chinese patients in order to provide a good reference for surgeons preoperatively.

Methods

From January 2010 to December 2019, 1909 patients (2307 knees) with primary anteromedial osteoarthritis accepted Oxford phase III UKA. Statistical analyses were performed on the distributions of the femoral, tibial, and matching of the femoral-tibial prosthesis. The possible factors affecting the sizes of femoral components, including gender, height based on gender were investigated.

Results

1. The distributions of femoral size components include extra-large (XL) 0, large (L) 1.08%, medium (M) 26.09%, small (S) 59.64%, extra-small (XS) 13.18%; the tibial sizes components were F 0, E 0.69%, D 7.80%, C 19.59%, B 24.79%, A 34.16%, AA 12.96%. 2. The matching of femur-tibia components were L-E 0.52%,L-D 0.52%,M-E 0.17%, M-D 7.28%,M - C 16.60%,M - B 1.95%,M-A 0.13%, M-AA 0.04%, S-C 2.99%, S-B 22.67%, S-A 31.12%, S-AA 2.82%, XS-B 0.17%, XS-A 2.90% and XS-AA 10.10%. The optimal matches between femoral and tibial components were: XL with F; L with E; M with C and D; S with A and B. 3. The patient's gender and height based on gender are necessary considerations for selection of femoral components (P＜0.01).

Conclusion

In Chinese patients, the size of femoral components is mainly small (S) for women, medium (M) for men. The tibial components of female patients are mainly A and B, whereas C is predominant for male patients. The more commonly used matching forms are S-A and S-B.

Improved sizing with image-based robotic-assisted system compared to image-free and conventional techniques in medial unicompartmental knee arthroplasty

AIMS

Ideal component sizing may be difficult to achieve in unicompartmental knee arthroplasty (UKA). Anatomical variants, incremental implant size, and a reduced surgical exposure may lead to over- or under-sizing of the components. The purpose of this study was to compare the accuracy of UKA sizing with robotic-assisted techniques versus a conventional surgical technique.

METHODS

Three groups of 93 medial UKAs were assessed. The first group was performed by a conventional technique, the second group with an image-free robotic-assisted system (Image-Free group), and the last group with an image-based robotic arm-assisted system, using a preoperative CT scan (Image-Based group). There were no demographic differences between groups. We compared six parameters on postoperative radiographs to assess UKA sizing. Incorrect sizing was defined by an over- or under-sizing greater than 3 mm.

RESULTS

There was a higher rate of tibial under-sizing posteriorly in the conventional group compared to robotic-assisted groups (47.3% (n = 44) in conventional group, 29% (n = 27) in Image-Free group, 6.5% (n = 6) in Image-Based group; p < 0.001), as well as a higher rate of femoral under-sizing posteriorly (30.1% (n = 28) in conventional group, 7.5% (n = 7) in Image-Free group, 12.9% (n = 12) in Image-Based group; p < 0.001). The posterior femoral offset was more often increased in the conventional group, especially in comparison to the Image-Based group (43% (n = 40) in conventional group, 30.1% (n = 28) in Image-Free group, 8.6% (n = 8) in Image-Based group; p < 0.001). There was no significant overhang of the femoral or tibial implant in any groups.

CONCLUSION

Robotic-assisted surgical techniques for medial UKA decrease the risk of tibial and femoral under-sizing, particularly with an image-based system using a preoperative CT scan. Cite this article: Bone Joint J 2021;103-B(4):610-618.

Does new instrument for Oxford unicompartmental knee arthroplasty improve short-term clinical outcome and component alignment? A meta-analysis

Background

The Microplasty (MP) instrumentation designed for the Phase III Oxford mobile-bearing unicompartmental knee arthroplasty (UKA) system is considered a better option to achieve more accurate component positioning and alignment. In the present study, we focused on short-term clinical and radiological outcomes to determine whether the MP instrumentation can reduce the short-term revision rate and occurrence of outliers of metallic components.

Methods

The literature in PubMed, Embase, the Cochrane Library, and Web of Science was searched up to May 2020. Studies were scrutinized by two independent authors, and the revision rate, complication spectrum, and radiological assessment with outlier rates were specifically analyzed. RevMan 5.3 was used for the statistical analysis.

Results

Seven studies were included in the meta-analysis. Four studies reported both clinical and radiological outcomes, two reported only radiological outcomes, and one reported only clinical outcomes. The pooled analysis showed that the revision rate in the MP instrumentation group was 0.866 per 100 component years, while that in the control group was 1.124 (odds ratio, 0.77; p < 0.05). The subgroup analysis of the bearing dislocation rate showed a significantly greater reduction in the Korean population than in the populations of other countries (p < 0.05). The radiological assessment showed that the alignment of the femoral component was significantly improved (p < 0.05), while that of the tibial component was not (p > 0.05).

Conclusion

The newly developed MP instrumentation for Oxford UKA significantly reduced the revision rate of this treatment. The positioning of the femoral component was also proven to be better by radiological assessments.