Review Article for Uni Knee

Mismatched Unicompartmental knee arthroplasty in Indian population using prosthesis designed for Caucasian Population: An attempt to address the unmet clinical need

Abstract

The functional success of the unicompartmental knee arthroplasty (UKA) is significantly influenced by the selection of the proper knee prosthesis sizing. Comparative studies of various populations have revealed significant variations in the anthropometric measurements of knees in different ethnic groups, thus making it   impractical to use a single-sized implant system across multiple ethnic groups and gender. The majority of UKA implants are designed using anthropometric data from the Caucasian population. As compared to Western population, Indians and Asians have shorter stature, smaller knee dimensions with high bending, deep flexion and extensions, squatting and demanding daily activities. Also the tibial implants present currently in the market do not meet the 25% on Indian patient’s need and today there is a need for developing UKA prosthesis based on specific Asian population, morphometry which would lessen the complications led by current generation Western influenced implants. This article is an attempt towards focusing on these gaps and hypothesizing the need for designing the UKA implants specifically addressing the unmet clinical needs of Indian and Asian patients.

Keywords: Asian population, Caucasian population, Mismatched implants, Proximal morphometry, Implant sizes, Unicompartmental knee implants, Unicompartmental Knee arthroplasty.

Introduction

Unicompartmental knee arthroplasty (UKA), also known as partial knee replacement, is a surgical procedure that involves replacing only one part of the knee joint affected due to Osteoarthritis (OA) or other degenerative conditions (1). It is an alternative to total knee arthroplasty (TKA) for patients with isolated damage to one compartment of the knee, usually the medial (inner) or lateral (outer) compartment (2). During a UKA, the damaged portion of the knee joint, typically the articular surface of the femur and tibia, is replaced with artificial implants made of metal and plastic. The remaining healthy portions of the knee, including ligaments and other structures, are preserved (3). The advantages of UKA compared to TKA include preservation of healthy bone and tissues, smaller incision and faster recovery (4).

The morphology of the knee joint varies significantly among different ethnic groups, genders, and morphotypes of patients. Having data specific to a particular population subset is essential for designing knee joint prostheses that provide the best fit and size for individuals (5). However, it is worth noting that most implants have been designed based on anthropometric parameters in the Caucasian population, which may not align with the morphological parameters in Indian patients. Previous studies on anthropometry among different races have demonstrated significant differences in these parameters between Caucasian, African, Asian, and Indian patients (6). Suboptimal sizing and placement can lead to issues such as patellar maltracking, persistent pain, early loosening, loss of bone stock, and an increased risk of periprosthetic fractures (7). Therefore, achieving optimum coverage of resected bone surfaces is important to ensure proper flexion and extension gaps, adequate quadriceps strength, and optimal knee function. Mediolateral (ML) sizing also plays a crucial role in promoting even stress distribution between the articulating surfaces and ensuring proper tracking of the patella in the trochlear groove (8).

Although, manufacturers have tried to design the implants that are specific to racial groupings, particularly for Asian patients, however, due to the dearth of patient specific designs, most surgeons employ implants made for Caucasian patients on Indian population instead of those developed to fit the anthropometric characteristics, affecting the successful outcomes of UKA (9). Several studies have measured the femoral and tibial articular surfaces’ such as ML and anteroposterior (AP) dimensions in Indian patients using a three-dimensional (3D) computerized tomography (CT) scan as shown in Figure 1 and compared the results with those from other ethnic groups and widely used commercial knee implants in India (Table 1 and 2 ) (9-12).

Anthropometric data on Indian Knee

Several studies have recorded the dimensions and sizes of the human knees using plain radiography, cadaveric dissections, intraoperative measurements, CT scans, and/or magnetic resonance imaging (MRI) to studythe variations in ethnicities, races, genders and commercially available implants (13). The majority of research conducted on the Indian and Asian population concur that there is a distinct disparity between morphologic measurements and the commercially available knee implants, and they have urged for the development of gender-specific prostheses to better fit the geometry of the male and female knee joints (14-21).

In Indian population, men have significantly larger knees than females (22). A study conducted by Ranjan M, et al., revealed that all the femoral parameters including AP and ML lengths and aspect ratio were significantly higher in men than in women (13). The average femoral AP (fAP) and ML (fML) dimensions for the Indian population in terms of the distal morphology were reported to be 58.0 ± 4.2 mm and 74.5 ± 5.8 mm respectively.According to the study, the mean measurement values of medial condyle AP length (fMAP) and lateral condyle AP length (fLAP) dimensions of the Indian population were 54.6 ± 4.3 mm and 57.8 ± 4.2 mm, respectively. Males had significantly larger values of fML, fAP, fMAP, and fLAP dimensions when compared with females (p<0.0001). Also, males were found to have a statistically significantly larger femoral aspect ratio (fR) than females (p=0.0006). The same study reported that, the proximal tibial morphology, the average ML (tML) and AP (tAP) dimensions for the Indian population was 69.1 ± 5.5 mm and 43.8 ± 3.6 mm, respectively, and the average medial AP length (tMAP) and lateral AP length (tLAP) dimensions were 46.0 ± 4.2 mm and 42.9 ± 4.0 mm, respectively. When compared with females, males reported variations for tML, tAP, tMAP, and tLAP dimensions (p < 0.0997) (13). Ethnicity variations was shown to have significant differences in measured anthropometric parameters of knee parts as reported by Mohan H et al., 2020. The study reported,tAP and tML lengths to be significantly smaller in women, while no difference was seen in terms of tibial aspect ratio. The average Insall-Salvati Ratio (ISR) for the entire study group was 1.14 ± 0.17 and there was no significant difference in the ISR between male and female knees (p=0.545) (11). The Indian distal femur had a significantly smaller AP length than the Caucasian knees (p<0.001) (11) (Table 1). Mohan H et al., 2020 showed that though the ML length of Indian knees were smaller than Caucasian knees, the difference was not statistically significant (p=0.2). According to this report, Indian knees had a significantly higher aspect ratio than Caucasians (p<0.01) and resembled the Chinese knees with similar AP, ML lengths and aspect ratio (p>0.05) (11). Indian knees were significantly smaller than Hispanic knees with smaller AP and ML lengths and a smaller aspect ratio. While the proximal tibia of Indian knees had a significantly smaller ML length than Caucasian knees (p < 0.001), the AP length was significantly smaller only in women (11) (Table 2). Though the Chinese proximal tibia had a larger ML length than Indian knees (p=0.01), their AP lengths were similar (11). The Indian proximal tibia was smaller than Hispanic knees in terms of both AP and ML lengths (p<0.001) (11).

Kantanavar R et al., 2021 conducted a study to evaluate the compatibility of medial tibial condyle (MTC) morphometry in the Indian population with six contemporary UKA prostheses (Stryker Triathlon, Depuy sigma high-performance partial knee system, Smith and Nephew Journey, Zimmer Biomet Oxford,Link Sled prosthesis—all poly and Link Sled prosthesis—metal backed) (22). They utilized CT morphometric data from 100 nonarthritic adult knees (66 males and 34 females) to assess the suitability of currently available UKA prostheses in India. They took the measurements for the AP and ML dimensions of the MTC at predefined points, and calculated the MTC aspect ratio. The proportion of knees that could be optimally fitted with existing UKA tibial components was determined. The study revealed that approximately 25% of Indian patients did not have optimal tibial fit with the available UKA implants. Surgeons should be aware of these limitations when considering UKA procedures specially for Asian populations as the success of UKA depends on surgical technique, post-operative physiotherapy, and prosthesis design (23-24). It is crucial to achieve a proper match between the resected surface of the tibia and the tibial component. Inadequate support from a smaller-sized tibial component can lead to implant subsidence and loosening, while an oversized component can cause soft tissue irritation and pain (25). Limited literature is available on the fit of different tibial component designs for UKA based on MTC morphometry in the Indian population. Similar studies conducted in non-Caucasian populations, such as Chinese, Korean, and Turkish, have shown tendencies towards oversizing, ML overhang, and significant differences in anthropometric measurements compared to Western populations. These findings highlight the importance of considering population-specific anatomical variations when designing UKA components (26-29).

Anthropometric data on Caucasian Population

Several studies have reported that knee dimensions of Caucasian population is comparatively larger than other ethnicities for example Indians, Chinese and Hispanics (11). They have reported a fML of 74.6 ± 3.9 mm in males and 65.4 ± 1.4mm in females; fAP of 59.6 ± 3.2 mm in males and 55.4 ± 2.8 mm in females. In tibial morphology, Caucasian population have reported tML of 79.4 ± 4.3mm in males and 70.2 ± 2.7 mm in females; tAP of 49.5 ± 2.9mm in males and 45.2 ± 2.3mm in females. A comparative data of distal femoral knee, proximal tibial morphology of different ethnicities including Caucasian, Chinese and Hispanic population are given in Table 1 and 2. While the gender specific knee morphological changes across different ethnicities are given in Table 3 and 4.

Review of Differences

Several studies have reported a mismatch between the dimensions of the distal femur morphology of Indian Knees and the available implants which are manufactured as per anthropometric data on Caucasian knee populationare PFC Sigma (Depuy, Warsaw, IN, USA), Attune (Depuy), Triathlon (Stryker, Kalamazoo, IN, USA), Nexgen (Zimmer, Warsaw, IN, USA), and Vanguard (Biomet, Warsaw, IN, USA). These implants may have drawbacks when implanted in Indian patients (6,11,30,31). Vaidya et al., in a study evaluated the anthropometric CT scans to design the femoral components for patients undergoing knee arthroplasties. The authors observed that in 86 knees of 47 Indians patients with OA (21 men, 26 women) were randomized in 3 groups based on AP diameter (<55 mm, 55–59 mm, >59 mm). It was reported that around 88.8% of Indian men could have satisfactory outcomes as available femoral component matched with the anthropometric measurements,whereas, significant number of women (60.4%, p<0.001) in the study had smaller measurements in comparison to the smallest available femoral components (55 mm). Differences in ML dimension (> 10 mm) in available AP sizes were noted in all 3 groups (6).

In similar lines, Mohan H et al., reported that a significant difference exist between the knees of different races. The Indian knees resembled the Chinese knees with smaller AP and ML lengths than the Caucasian and Hispanic knees but had larger aspect ratios. This racial difference explains the implant size mismatch seen in their study. It was noted that female knees measurements were significantly smaller than the male knees (p<0.05). There was a mismatch between the distal femur morphology and the diameters of all implants. For a measured knee AP and ML lengths, all implant dimensions were found to be smaller for femur morphology, however in their study, the tibial components of each implant studied (Attune, PFC Sigma, Vanguard, and Nexgen) well fitted with the measured tibial morphology (11).This resulted in insufficient coverage when choosing an implant size to match the fAP length and led to overhang of the implant when attempting to match the fML lengths. Table 5 shows the femoral and tibial component dimensions of the commercially available UKA prosthesis.

Multiple studies have compared the knee morphology of Asian patients with the dimensions of available prostheses, and it has been suggested that the currently available prostheses are not well-suited for Indian or Asian patients due to the differences in knee shape between Caucasians and the Asian population. A prosthesis as per the knee morphology of Indian ethnicity is needed for an effective treatment of knee replacement surgeries (11,22,30,32,33). In a study conducted by Cheng et al., 2010 the knee dimensions of Chinese patients were compared to five contemporary knee prostheses available in China. The findings revealed that all available sizes of the prosthesis resulted in overhanging of the fML dimensions, indicating a mismatch (10). Similarly, Ha CW et al., 2012 conducted a study in Korean femurs and observed a mismatch between the femur dimensions and the available knee prostheses. They found that Korean femurs tended to be wider compared to small femoral components and narrower compared to larger ones, resulting in ML under-coverage for smaller femoral dimensions and ML overhang for larger femoral dimensions with the current knee prosthesis (34).

In addition to femoral component sizing, the accurate sizing of tibial components is also crucial in knee arthroplasty to achieve proper coverage of the resected proximal tibial surface (35, 36). A study in the Chinese population observed mismatches between available tibial components and the patients’ tibial dimensions. They found overhanging of tML dimensions with larger-sized prostheses and under-sizing of tML dimensions with smaller-sized prostheses (10). Similar findings were reported by Surendran et al., in the Korean population, where the average tML dimension was smaller compared to symmetric commercially available knee implants (26). In the Indian population, Ranjan et al., 2022 reported mean tML and tAP dimensions of the proximal tibia, along with gender differences (13). They found that Indian knees were smaller than Caucasian knees and concluded that currently available knee prostheses might not be suitable for Indian patients due to the mismatch in knee anatomy (13). Bansal et al., 2018 also highlighted the differences in size and shape of Indian knees compared to other ethnicities, emphasizing the need to consider Indian knee morphometry in knee prosthesis design (37).

In a study conducted by Hema N et al., showed the tibial medial and lateral condylar dimensions along with intercondylar area of the Indian population. It was found that the mean AP dimension of the medial condyle on the left and right was 38.98 ± 4.46 38.81 ± 5.05 mm, respectively. The measurements of the lateral condyle on the left and right was 32.99 ± 4.01 mm and 32.42 ± 4.88 mm, respectively. The intercondylar area dimension at AP plane on the left and right knee was 44.78 ± 3.87 mm and 44.19 ± 4.51mm, respectively. The study concluded that data from their study will help in designing the optimal tibial prosthesis implants for the Indian population. Their study was in line with aforementioned observations that the dimensions of the tibial plateau vary between populations, and the present available implants are designed based on the measurements of the Caucasian populations (38).

The aforementioned studies observed a progressive decrease in the aspect ratio with an increase in AP dimensions for both the tibia and femur, in contrast to the constant aspect ratio exhibited by conventional prostheses. This discrepancy leads to mismatches between these implants and the Asian population (10,26).

The solution to this is to have implants designed to suit the different populations. With improved anatomical conformity, these implants will provide better fit and coverage. This can restore the normal biomechanics of knees, leading to better gait patterns and favorable long-term outcomes.

Conclusion

In this review, we examine the differences in knee dimensions between Indians and other ethnic groups. We discovered that commercially available UKA implants, which are predominantly designed with measurements from Caucasian populations in mind, can result in significant mismatches between the implant and the resected bone surfaces in Indian patients. This mismatch may have a negative effect on functional outcomes, resulting in suboptimal outcomes. To address this issue, it is imperative that a UniKnee system designed specifically for the Indian population and taking into consideration their unique anatomical characteristics be developed. Designs of ethnic group- and gender-specific Uniknee implants can aid in achieving better alignment and fit, thereby enhancing the overall functionality and performance of knee replacement surgeries in Indian patients and have the potential to enhance functionality, mobility, and patient satisfaction.

Table 1:Distal femoral morphology for Indian and Asian-Pacific population (11).

Femur	Indian	Caucasian		Chinese		Hispanic
	Mean±SD	Mean±SD	p-value	Mean±SD	p-value	Mean±SD	p-value
Mediolateral
Male	73.74±4.07	74.6±3.9	0.204	72.7±3.8	0.146	77.2±4.1	<0.001
Female	64.75±3.37	65.4±1.4	0.129	64.4±2.6	0.588	66.3±3.0	0.004
Anteroposterior
Male	57.52±3.12	59.6±3.2	<0.01	56.5±2.5	0.048	49.9±3.8	<0.001
Female	52.8±3.13	55.4±2.8	<0.001	52.8±2.6	1.00	45.6±3.2	<0.001
Aspect Ratio
Male	1.28±0.07	1.25±0.05	0.004	1.29±0.04	0.334	1.55±0.11	<0.001
Female	1.23±0.07	1.18±0.05	<0.001	1.22±0.05	0.442	1.46±0.09	<0.001

Table 2:Proximal tibial morphology for Indian and Asian-Pacific population (11).

Tibia	Indian	Caucasian		Chinese		Hispanic
	Mean±SD	Mean±SD	p-value	Mean±SD	p-value	Mean±SD	p-value
Mediolateral
Male	75.66±4.29	79.4±4.3	<0.001	77.4±3.3	0.013	80.3±4.0	<0.001
Female	65.52±3.21	70.2±2.7	<0.001	69.1±2.8	<0.001	69.8±3.1	<0.001
Anteroposterior
Male	49.12±3.85	49.5±2.9	0.505	49.6±2.4	0.409	54.7±3.3	<0.001
Female	43.29±2.7	45.2±2.3	<0.001	44.2±2.3	0.095	47.1±2.6	<0.001

Table 3:Anthropometric data on male knees from different ethnicities (11).

Study	Study group	Nature of knee	Method of study	fML	fAP	fAR	tML	tAP	tAR
Mohan et al., 2020 (11)	Indian	Healthy	MRI	73.74±4.07	57.52±3.12	1.28±0.07	75.66±4.29	49.12±3.85	1.55±0.1
Li et al., 2014 (39)	Caucasian	Healthy	MRI	74.6±3.9	59.6±3.2	1.25±0.05	79.4±4.3	49.5±2.9	1.61±0.08
Li et al., 2014(39)	Chinese	Healthy	CT	72.7±3.8	56.5±2.5	1.29±0.04	77.4±3.3	49.6±2.4	1.56±0.07
McNamara et al., 2018 (40)	Hispanic	Healthy	MRI	77.2±4.1	49.9±3.8	1.55±0.11	80.3±4.0	54.7±3.3	–
Yue et al., 2011 (41)	Caucasian	Healthy	MRI	86.0±5.6	67.5±3.6	1.28±0.07	78.7±5.4	45.0±2.8	1.75±0.11
Yue et al., 2011 (18)	Chinese	Healthy	CT	82.6±3.6	65.0±2.8	1.27±0.03	75.2±3.6	41.5±2.1	1.82±0.07
Chaichankul et al., 2011 (41)	Thai	Healthy	MRI	70.15±3.87	48.55±3.73	1.45±0.11	74.44±3.44	50.15±3.09	–
Shah et al., 2013 (30)	Indian	Arthritic	CT	83.6±2.6	67.2±2.9	1.25±0.05	80.9±2.6	58.5±2.5	1.51±0.05
fML: femoral mediolateral; fAP: femoral anteroposterior; fAR: femoral aspect ratio; tML: tibial mediolateral; tAP: tibial anteroposterior; tAR: tibial aspect ratio; MRI: Magnetic resonance image; CT: computed tomography

Table 4: Anthropometric data on female knees from different ethnicities (11).

Study	Study group	Nature of knee	Method of study	fML	fAP	fAR	tML	tAP	tAR
Mohan et al., 2020 (11)	Indian	Healthy	MRI	64.75±3.37	52.8±3.13	1.23±0.07	65.52±3.21	43.29±2.7	1.52±0.07
Li et al., 2014 (39)	Caucasian	Healthy	MRI	65.4±1.4	55.4±2.8	1.18±0.05	70.2±2.7	45.2±2.3	1.54±0.07
Li et al., 2014 (39)	Chinese	Healthy	CT	64.4±2.6	52.8±2.6	1.22±0.05	69.1±2.8	44.2±2.3	1.56±0.07
McNamara et al., 2018 (40)	Hispanic	Healthy	MRI	66.3±3.0	45.6±3.2	1.46±0.09	69.8±3.1	47.1±2.6	–
Yue et al., 2011 (18)	Caucasian	Healthy	MRI	76.4±4.0	59.7±2.6	1.28±0.06	69.0±4.2	39.3±2.6	1.76±0.08
Yue et al., 2011 (18)	Chinese	Healthy	CT	72.8±2.6	58.8±2.5	1.24±0.04	66.2±2.1	37.3±2.8	1.78±0.10
Chaichankul et al., 2011 (41)	Thai	Healthy	MRI	59.91±3.75	43.32±3.69	1.39±0.12	64.95±3.45	43.23±2.57	–
Shah et al., 2013 (30)	Indian	Arthritic	CT	76.3±3.8	62.1±4.9	1.23±0.06	72.2±3.6	52.2± 4.2	1.51±0.08
fML: femoral mediolateral; fAP: femoral anteroposterior; fAR: femoral aspect ratio; tML: tibial mediolateral; tAP: tibial anteroposterior; tAR: tibial aspect ratio; MRI: Magnetic resonance image; CT: computed tomography

Table 5: Table on UKA femoral and tibial component (22).

UKA tibial components		Size 1	Size 2	Size 3	Size 4	Size 5	Size 6
		AP–ML (ratio%)	AP–ML (ratio%)	AP–ML (ratio%)	AP–ML (ratio%)	AP–ML (ratio%)	AP–ML (ratio%)
Stryker Triathlon		4.1–2.3	4.4–2.5	4.7–2.7	5.0–2.9	5.3–3.1	5.6–3.3
Depuy sigma high-performance partial knee system		4.2–2.4	4.5–2.6	4.8–2.8	5.1–3.0	5.4–3.2	5.7–3.4
Smith and Nephew Journey		3.8–2.4	4.2–2.5	4.6–2.7	4.9–2.9	5.2–3.0	5.5–3.2
Zimmer Biomet Oxford		3.8–2.6	4.1- 2.6	4.4- 2.8	4.7– 3.0	5–3.2	5.3–3.4
Link Sled prosthesis—all	All-poly	4.5–2.2	5.0–2.7	0.5–2.9	5.8–3.1	–	–
	Metal-backed	4.5–2.25	5.0–2.5	5.5–2.75
UKA femoral and tibial components Size
Oxford’M Meniscal UKA system (Femoral component)		22.0 mm	23.8 mm	25.7 mm	27.5 mm
Oxford’M Meniscal UKA System(Tibial component)		38 x 26	41 x 26	44x 28	47 x 30	50 x 32	53 x 24

Figure

Figure1:Representative MRI illustrations of axial and sagittal plane of femoral and tibial parameters. (A) Distal femoral cut, (B) Proximal tibial cut, (C) Sagittal section of the knee for measurement of the patellar length and patellar tendon length.

fAP: femoral anteroposterior, tAP: tibial anteroposterior, fML: femoral mediolateral, tML: tibial mediolateral, PL: patellar length, TL: tendon length.

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