Bristol index of patellar width to thickness (BIPWiT): a reproducible measure of patellar thickness from adult MRI

Evaluation of patellar dimension and Bristol Index in Asian population: An MRI study

Background

Restoration of patellar thickness is pivotal during a total knee arthroplasty (TKA). Several studies showed there are differences in the knee measurements between Asian and Western population.

Purpose

This study aims to evaluate the patellar dimension and Bristol Index of patellar width to thickness (BIPWiT) using magnetic resonance imaging (MRI) in Asian population.

Study design

This is a descriptive epidemiology study.

Methods

101 MRI scans of young adult patients with normal patellofemoral joint (PFJ) age 17-40 were evaluated from January 2019 to December 2020. Exclusion criteria included patella-femoral pathology and degenerative joint disease. Data of gender, body height and weight were obtained from physical examination, while patella height, width and thickness were obtained using MRI measurement. Descriptive analysis was used to get the mean and standard deviation of patella dimension, whereas correlation between patella thickness with patella width and length were analyzed using Pearson correlation and BIPWiT ratio was obtained by dividing the patellar width and patellar thickness.

Results

Mean patellar length was 30.06 ± 2.94 (29.48-30.64); patellar width was 44.13 ± 4.44 (43.26-45.01); and patellar thickness was 23.89 ± 2.33 (23.43-24.35). Patellar dimension in male were significantly larger compared to female (P < 0.001). However, there was no difference in cartilage thickness between male and female (P = 0.305). There was strong correlation between patellar width and patellar thickness (r = 0.66; P < 0.001) with BIPWiT ratio of 1.85 ± 0.15.

Conclusion

BIPWiT of 1.8:1 between patellar width and patellar thickness was recommended as a guide for patellar thickness restoration during TKA. There is no difference of patellar dimension between Asian and Western population in a healthy knee.

Clinical relevance

The result of BIPWiT ratio found in this study may aid upon pre-operative planning prior TKA for surgeons in order to achieve optimal patellar thickness and avoid patellofemoral problem.

What is known about the subject

Currently there are raising concerns about the different sizes of knee measurements between Asian and Western population which will affect techniques during TKA to achieve optimum result.

What this study adds to the existing knowledge

This study not only prove that there is no difference between patellar dimension of Asian and Caucasian but also found a similar BIPWiT ratio for patellar resection during TKA with previous literature.

Level of evidence

Level III.

Conforming patellar button design improves outcome of total knee arthroplasty

BACKGROUND

Patellar resurfacing is commonly performed during total knee arthroplasty (TKA), and the patellar button design can vary within a TKA implant. Implant design is known to affect patella kinematics, contact mechanics, and ultimately the outcome of TKA. The aim of this study was to compare the patient-reported outcomes of TKA with either a conforming (CP) or medialized dome (MD) patellar component.

METHODS

The study was a prospective cohort study of 100 TKAs performed between December 2015 and August 2017. We compared a consecutive series of 50 TKA subjects with a CP, with the previous 50 TKA subjects with an MD patella. The primary outcome measure was difference in Knee Injury and Osteoarthritis Score (KOOS) at 12 months. Other patient-reported outcome measures included EQ5D as a general health measure, and patient satisfaction.

RESULTS

There was no significant difference in baseline characteristics, KOOS, or EQ5D between the two groups. At 12 months, the CP Group had a higher mean KOOS function score (87 vs. 80, P = 0.04), and greater patient satisfaction (98% vs. 82% satisfied, P = 0.009) compared with the MD group. The CP Group had significantly lower frequency of pain with level walking, less difficulty with stairs, and lower mean EQ5D mobility at 12 months compared with the MD group.

CONCLUSIONS

TKA performed using a conforming patella has superior results over a medialized dome patellar component for KOOS function, patient satisfaction, walking pain, stair performance, and mobility at 12 months postoperatively. The differences observed with the change in patellar design may be unique to this prosthesis.

Anthropometric measurements of patella and its clinical implications

INTRODUCTION

Early patellar failures in tricompartmental total knee arthroplasty (TKA) have been related to universal designing of implants. Establishing the appropriate patellar bone-prosthesis composite thickness is one of the important steps in ensuring functional success in arthroplasty. Since there is a paucity of data concerning the anthropometric measurements of Indian patella, the objective of this study was to obtain anatomic information of the patella of the northern Indian population and to analyze how it differs from western patellae that will improve patellar component design and implantation in TKA.

MATERIALS AND METHODS

A total of 266 consecutive knee radiographs were evaluated. All data were collected by a single doctor using X-ray console, where height (mm) and breadth (mm) were taken in anteroposterior views and thickness (mm) in lateral view.

RESULTS

The mean, standard deviation, 95% confidence interval and P value of the measurements were calculated. It was found that Indians had thinner and smaller patella as compared to westerners and also males had significantly (P < .001) larger patella as compared to females.

CONCLUSION

Anthropometric patellar dimensions can influence implant design and surgical outcomes and can be used as a guideline for future designing of more regional and gender-specific patellar component and patellar plate.

Comprehensive assessment of patellar morphology using computed tomography-based three-dimensional computer models

BACKGROUND

The objectives of this study were to assess patellar morphology using computed tomography-based three-dimensional computer models and to determine the utility of the subchondral method for patellar resection in total knee arthroplasty (TKA).

METHODS

Overall, 120 subjects (60 males, 60 females) from 20 to 50 years old were included. Computer tomography images were used to construct 3D computer models of 240 knees. An anthropometric analysis of variance was used with the models to detect differences between the sides, age groups, and genders.

RESULTS

Based on the available numbers, there were significant gender differences in the patellar length, width, and thickness even with strict control for the height and weight of the patients. The average patellar width/thickness ratio was 1.95, regardless of gender, and there was a good correlation between the patellar width and thickness (male: r=0.68, p<0.01; female: r=0.75, p<0.01). After using the subchondral method to virtually resect the patellae, the mean thickness for males and female was 14.0mm and 12.3mm, respectively. The proportion of the residual bony thickness that was less than 12 mm was 5.83% (seven cases) in the male group and up to 42.5% (51 cases) in the female group. There was excellent intra-observer reliability and inter-observer reliability regarding the dimensional measurements in this study.

CONCLUSIONS

A robust method of measuring and virtually resecting the patella was established. The anthropometric dimensions of this study could provide basic data for guiding surgical management of the patella in TKA and are useful in designing patellar implants.

CLINICAL RELEVANCE

The anthropometric patellar information is essential for surgeons to perform patellar resurfacing in TKA.