Comparison of joint awareness after total knee arthroplasty, medial unicompartmental knee arthroplasty, and high tibial osteotomy: a retrospective study

doi:10.21203/rs.3.rs-2848574/v1

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Research Article

Comparison of joint awareness after total knee arthroplasty, medial unicompartmental knee arthroplasty, and high tibial osteotomy: a retrospective study

https://doi.org/10.21203/rs.3.rs-2848574/v1

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Introduction: This study aimed to compare the Forgotten Joint Score-12(FJS) outcomes after high tibial osteotomy (HTO), unicompartmental knee arthroplasty (UKA), and total knee arthroplasty (TKA) with short-term follow-up (at least 2 years). We hypothesized that there would be differences in subjective outcomes between the three procedures as measured by FJS.

Methods: Patients who underwent HTO, UKA, and TKA from January 2016 to December 2020 and were followed up for a minimum of 2 years were included in the study. Patient were asked to complete the FJS and Knee Injury and Osteoarthritis Outcome Scores (KOOS) questionnaires. The preoperative and postoperative clinical outcomes were compared and evaluated the patient-related factor. The FJS scores were predicted using multiple linear regression analysis. In addition, we used Patient’s Joint Perception (PJP) questions as anchors to determine whether achieve the forgotten joint and FJS thresholds were calculated using the receiver operating characteristic curve.

Results:391 patients were included in the final study, and there were 111 patients in HTO groups,128patients in UKA groups, and 150 patients in TKA groups. The mean follow-up was 47.0 months. There was a significant difference in the total FJS between the HTO, UKA, and TKA groups (p <0.001).In multiple linear regression, younger age, and higher Function Score (FS) were significant predictors of better FJS.we found the thresholds of the FJS of HTO, UKA, and TKA were 63.54, 69.79, and 61.45, respectively.

Conclusion: Medial UKA was associated with superior patient awareness compared to HTO and TKA as measured by FJS.

Forgotten Joint Score-12(FJS)

high tibial osteotomy (HTO)

unicompartmental knee arthroplasty (UKA)

total knee arthroplasty (TKA)

The incidence of Knee Osteoarthritis (KOA) is on the rise among the aging population, especially in women, and the lifetime risk of symptomatic knee OA is 50%[1].KOA manifests several symptoms, such as pain, stiffness, dysfunction, and even deformity, which Reduces the quality of life[2]. Medial KOA affects up to 50% of OA patients and exhibits lesser changes compared to the lateral and patellofemoral compartments [3].

At present, the mainstream surgical approach for the treatment of medial OA includes total knee arthroplasty(TKA), unicompartmental knee arthroplasty (UKA), and high tibial osteotomy(HTO)[4]. UKA and HTO generally have better postoperative functional outcomes than TKA[5–8]. Although the survival rate in TKA has improved, a relevant number of patients remain unsatisfied with the outcome, and range from 20–30%, regardless of specific TKA design features[9, 10]. For medial OA patients, medial compartment UKA is a viable alternative to HTO or TKA[4, 11, 12]. However, HTO appears to be a better choice for younger patients with high functional activity needs[13].

There has always been debate among surgeons regarding procedures choice between the TKA and UKA and HTO since the three procedures share some similar indications. However, the predominance of the three procedures is inconclusive. Maybe the outcome measures used in previous studies are inadequate to distinguish three procedures. In fact, one possible reason for the phenomenon is that TKA, UKA, and HTO differ greatly in terms of concept. This relatively large variance may occur because the joint surface is resected in TKA and UKA while it is preserved in HTO and the knee alignment is greatly changed in HTO and TKA, while the change after UKA is minimal[14, 15]. Different procedures may lead to differences in patient awareness after surgery, which could be detected by the Forgotten Joint Score-12 (FJS)[15]. Generally, Healthy joints have no joint awareness, while unhealthy joints have pain, instability, and other functional limitations[16].FJS is composed of 12 items to detect patients’ awareness of their knees in daily life[17].

To compare FJS outcomes between TKA, UKA, and HTO patients, and determine if UKA has superior FJS outcomes and lower joint awareness. To our knowledge, this is the first study assessment to compare the FJS outcomes and define thresholds of the FJS for a forgotten joint in a population of patients undergoing HTO, UKA, and TKA.

Patients and Data Collection

This retrospective, single-center study collected medical records anonymously and retrospectively from January 2016 to December 2020. Ethical approval for data collection was granted by the Ethics Committee and complied with the Declaration of Helsinki (Research Ethics Approval Code: IIT2022-27). Informed consent was obtained from all participants. The collected baseline and clinical data included age, sex, body mass index (BMI), preoperative Kellgren-Lawrence (KL) grade, American Society of Anesthesiology (ASA), and range of motion. The study recruited 411 patients with KOA scheduled to undergo TKA, UKA, and HTO from January 2016 to December 2020. The three groups were matched based on BMI and sex, and were followed for at least two years.

Both UKA and HTO were selectively performed in patients diagnosed with an isolated medial compartment lesion with preserved status in other compartments, and intact anterior and posterior cruciate ligaments[8]. Exclusion criteria[18, 19] were applied, including patients with either lateral or patellofemoral compartmental OA (K-L grade ≥ III), those with knee flexion under 120°, flexion contracture over 20°, or combined ligamental instability, and those with inflammatory arthropathy. Patients who underwent bilateral HTO were also excluded to eliminate confounding factors. Moreover, the operating surgeon intraoperatively assessed the status of the lateral compartment and decided to perform either UKA or TKA. TKA was performed on all patients who did not qualify for UKA and HTO, and on those with apparent lateral and patellofemoral arthritis on preoperative X-rays and grades II-IV on the Kellgren-Lawrence scale [20].

Patient-Reported Outcome Measurements

Patient-reported outcome measures (PROMs) were electronically evaluated using touch-screen devices or mobile phones, beginning in January 2020. These measures included the Function Joint Score (FJS), Knee Injury and Osteoarthritis Outcome Scores (KOOS), Knee Society Knee Score (KS), and Function Score (FS). The FJS is a 12-item questionnaire where patients rate their knee function on a 5-point Likert scale: "Never," "Almost never," "Seldom," "Sometimes," or "Mostly"[21]. The KOOS is composed of five subscales: (1) Pain (9 items), (2) Symptoms (7 items), (3) Function in Daily Living (16 items), (4) Function in Sport and Recreation (5 items), and (5) Knee-related Quality of Life (4 items)[22]. The Knee Society Knee Score (KS) and Function Score (FS) assess the range of motion, stability, and pain of the knee after surgery[23]. Both scores range from 0 to 100, with higher scores indicating better outcomes.

Anchor Questions for the Forgotten Joint

In this study, the Patient's Joint Perception (PJP) question served as the anchor question for measuring patients' perceptions of their joint. [24]. The PJP question asked patients to rate their joint perception on a scale of 1 to 5, with 1 being "like a native or natural joint" and 5 being "like a nonfunctional joint." This rating system was found to be reliable and valid in identifying the forgotten joint phenomenon [25]. Patients who responded with a rating of "like a native or natural joint" were considered to have a forgotten joint.[26].

Procedures

TKA procedures in this group were performed using prostheses from LINK (Hamburg, Germany). The senior surgeon performed the UKA procedures in this group using the mobile Oxford medial UKA device (Biomet, Bridgend, UK). In the HTO group, we corrected varus malalignment of the lower limb according to Fujisawa's technique, setting the target alignment so that the mechanical axis deviation was 62.5%. The medial end of the tibial plateau was defined as 0%, while the lateral end was defined as 100%.[27]. Unless a patient who underwent HTO surgery specifically requests to have the plate removed, our physicians typically do not remove it.

Statistical analysis

The sample size was estimated using G*Power software (version 3.1.9.7, Düsseldorf, Germany) with ANOVA: fixed effects, omnibus, one-way measures (F test). A power of 0.8 was calculated with an alpha level of 0.05. To detect differences between the three groups, a sample size of 53 patients in each group was required. Categorical variables were expressed as frequencies or percentages, while continuous data were presented as mean ± standard deviation (SD). The significance of continuous variables was determined using the One-way ANOVA test or Kruskal-Wallis H test, and chi-square tests were used for categorical variables. We conducted a post hoc test using the Mann-Whitney U test with Bonferroni correction. We tested the reliability of FJS-12 using Cronbach’s alpha and analyzed correlations between FJS-12 and other PROMs using Spearman’s correlation coefficients. To predict FJS scores, we used multiple linear regression based on age, BMI, sex, ASA, KL, KS, FS, and surgery (HTO, UKA, and TKA). We added a dummy variable for TKA to use it as a control for HTO and UKA. A P-value of < 0.05 was considered statistically significant.

We utilized receiver operating characteristic (ROC) curves to evaluate each PROM's ability to differentiate between patients with and without a forgotten joint. We calculated the area under the curve (AUC) for each ROC. Youden's method was used to determine the forgotten joint thresholds for each PROM, with the cutoff point being the maximum Youden index (sensitivity + specificity-1). We conducted all statistical analyses using SPSS v26 (IBM Corporation, Armonk, NY).

Initially, 467 patients underwent a thorough review of their medical records. An additional 38 patients were excluded for not meeting the inclusion criteria, and 40 patients were lost to follow-up. Therefore, the final analysis included 389 patients (Fig. 1).

Table 1 presents the demographic data of the 391 patients. Patients in the TKA group were significantly older than those in the HTO and UKA groups. Furthermore, significant differences were found between TKA and HTO/UKA groups in terms of mean preoperative ROM, KS, and FS (p < 0.05). Additionally, FS had distinct differences between UKA and TKA groups (p = 0.048). However, no significant differences were found in other baseline clinical characteristics among the three groups.

Table 1

Demographics of participants
	Mean ± SD
	HTO(n = 111)	UKA(n = 128)	TKA(n = 150)	P Value
Age(years)	61.7 ± 5.7	63.25 ± 3.7	67.9 ± 5.9	< 0.001^a
BMI (kg/m2)	25.4 ± 3.3	26.3 ± 3.4	25.6 ± 3.8	0.075
Sex (%)				0.773
Male	20 (18.0)	19(14.8)	23(15.3)
Female	91 (82.0)	109(85.2)	127(84.7)
Side (%)				0.930
Left	51(45.9)	59(46.1)	72(48.0)
Right	60(54.1)	69(53.9)	78(52.0)
KL (%)				< 0.001
1	16(14.4)	0(0)	0(0)
2	59(53.2)	0(0)	0(0)
3	34(30.6)	88(68.8)	90(0.60)
4	2(1.8)	40(31.3)	60(0.40)
ASA (%)				0.342
Ⅰ	18(16.2)	11(8.6)	24(16.0)
Ⅱ	80(72.1)	104(81.3)	110(73.3)
Ⅲ	13(11.7)	13(10.2)	16(16.2)
Follow up(months)	46.1 ± 12.9	48.7 ± 12.6	46.1 ± 7.6	0.076
Preoperative
ROM
Flexion(°)	114.5 ± 14.8	114.3 ± 13.7	106.7 ± 66.5	< 0.001^b
KS	55.0 ± 3.50	55.5 ± 6.6	51.0 ± 4.5	< 0.001^c
FS	63.6 ± 4.3	63.6 ± 4.4	62.5 ± 4.3	0.027^d
SD, standard deviation; BMI, body mass index; KL, Kellgren–Lawrence; ASA, American Society of Anesthesiology; ROM, range of motion; KS, Knee Score; FS, Function Score
^a HTO vs UKA:P = 0.304. Other pairwise comparisons: P < 0.001
^b HTO vs UKA:P = 1.000. Other pairwise comparisons: P < 0.001
^c HTO vs UKA:P = 0.694. Other pairwise comparisons: P < 0.001
^d HTO vs UKA:P = 1.000. HTO vs TKA: P = 0.101. UKA vs TKA: p = 0.048

Table 2 presents a comparison of postoperative clinical outcomes between the HTO, UKA, and TKA groups. Significant differences were found between the TKA group and the other groups in terms of PROM. Regarding the HTO and UKA groups, significant differences were observed in KS, activities of daily living (ADL), and sport and recreation (KS: 82.9 ± 7.5 and 84.2 ± 9.9, p = 0.025; ADL: 84.3 ± 6.2 and 82.1 ± 6.5, p = 0.001; sport and recreation: 68.3 ± 9.5 and 57.1 ± 7.7, p < 0.001, respectively). However, no significant differences were observed between the HTO and UKA groups in other outcomes.

Table 2

Postoperative clinical outcomes among groups HTO, UKA, and TKA.
	Mean ± SD			P Value
	HTO(n = 111)	UKA(n = 128)	TKA(n = 150)	Overall	HTO vs UKA	HTO vs TKA	UKA vs TKA
KS	82.9 ± 7.5	84.2 ± 9.9	80.1 ± 8.2	< 0.001	0.025	0.008	< 0.001
FS	83.79 ± 8.8	85.9 ± 8.2	79.2 ± 8.5	< 0.001	0.061	< 0.001	< 0.001
KOOS
Symptoms	75.7 ± 5.9	75.9 ± 6.1	70.3 ± 6.8	< 0.001	1.000	< 0.001	< 0.001
Pain	80.0 ± 7.5	79.2 ± 9.7	74.4 ± 7.2	< 0.001	0.581	< 0.001	< 0.001
ADL	84.3 ± 6.2	82.1 ± 6.5	80.1 ± 5.0	< 0.001	0.001	< 0.001	< 0.001
Sports and rec	68.3 ± 9.5	57.1 ± 7.7	50.1 ± 7.9	< 0.001	< 0.001	< 0.001	< 0.001
QOL	66.2 ± 8.5	67.1 ± 7.8	59.0 ± 9.4	< 0.001	0.871	< 0.001	< 0.001
SD, standard deviation; KS, Knee Score; FS, Function Score; KOOS, Knee injury and Osteoarthritis Outcome Score; ADL, activities of daily living, Rec, recreation, QOL, quality of life.

Table 3 compares the HTO, UKA, and TKA groups using FJS in a single variable analysis. A significant difference was found in the total FJS between the HTO, UKA, and TKA groups (59.38 ± 7.25, 66.69 ± 7.44, and 56.90 ± 6.85, respectively; p < 0.001). Similarly, a significant difference was found between TKA, UKA, and HTO groups in each of the 12 items of postoperative FJS. However, no significant differences were found in HTO and UKA groups in Q1, Q2, Q3, and Q6. In the HTO and TKA groups, no significant differences were found in Q2, Q4, Q8, Q9, and Q10. Additionally, in the UKA and TKA groups, no significant differences were found in Q1, Q7, and Q12. The internal consistency of FJS in terms of Cronbach’s alpha was 0.806.

Table 3

Comparison between HTO, UKA and TKA groups using FJS in a single variable analysis
	Mean ± SD			P Value
	HTO(n = 111)	UKA(n = 128)	TKA(n = 150)	Overall	HTO vs UKA	HTO vs TKA	UKA vs TKA
Total FJS	59.38 ± 7.25	66.69 ± 7.44	56.90 ± 6.85	< 0.001	< 0.001	0.020	< 0.001
Q1	0.28 ± 0.54	0.39 ± 0.52	0.53 ± 0.60	0.001	0.159	< 0.001	0.192
Q2	0.97 ± 0.29	0.91 ± 0.44	1.03 ± 0.49	0.029	0.285	1.000	0.026
Q3	1.26 ± 0.51	1.28 ± 0.60	1.87 ± 0.62	< 0.001	1.000	< 0.001	< 0.001
Q4	1.16 ± 0.39	0.99 ± 0.32	1.14 ± 0.39	0.001	0.002	1.000	0.003
Q5	1.14 ± 0.35	0.95 ± 0.39	1.31 ± 0.49	< 0.001	0.005	0.007	< 0.001
Q6	2.18 ± 0.58	2.33 ± 0.75	2.62 ± 0.66	< 0.001	0.226	< 0.001	0.001
Q7	1.67 ± 0.55	1.24 ± 0.45	1.87 ± 0.61	< 0.001	< 0.001	< 0.001	0.056
Q8	2.11 ± 0.64	1.35 ± 0.54	2.11 ± 0.61	< 0.001	< 0.001	1.000	< 0.001
Q9	2.57 ± 0.64	2.05 ± 0.77	2.59 ± 0.67	< 0.001	< 0.001	1.000	< 0.001
Q10	1.61 ± 0.56	1.15 ± 0.38	1.51 ± 0.55	< 0.001	< 0.001	0.416	< 0.001
Q11	2.64 ± 0.62	1.80 ± 0.58	2.01 ± 0.49	< 0.001	< 0.001	< 0.001	0.015
Q12	2.08 ± 0.54	1.57 ± 0.57	2.09 ± 0.54	< 0.001	< 0.001	< 0.001	1.000
Total FJS is equal to 100 − [(total score for each question)/12 (if there is no response, divided by the number of questions answered) × 25], where the score of each question ‘Are you aware of your artificial joint…,’ from 0 to 4 points (never, 0 points; almost never, 1 point; seldom, 2 points; sometimes, 3 points; mostly, 4 points) SD, standard deviation, FJS, forgotten joint score-12

Table 4 presents the results of a multiple linear regression analysis predicting the Forgotten Joint Score (FJS) based on age, body mass index (BMI), sex, Kellgren-Lawrence (KL) grade, American Society of Anesthesiologists (ASA) grade, preoperative flexion, Knee Society (KS) score, Functional Score (FS), and type of surgery HTO, UKA, or TKA. The standardized residuals for the model demonstrated a standard normal distribution. The regression analysis resulted in an F value of 18.365 (P < 0.001) and an R² value of 0.309, indicating that the model is valid. The predicted FJS can be calculated as 76.644 − 0.327 (age) − 0.116 (BMI) − 1.703 (sex) + 0.203 (KL grade) + 0.516 (ASA grade) + 0.848 (if the surgery was HTO) or 8.623 (if the surgery was UKA) − 0.01 (preoperative flexion) − 0.093 (KS score) + 0.203 (FS). Age is measured in years, BMI in kg/m2, and flexion as an angle. Sex is coded as 1 for male and 2 for female, while KL grade is divided into 1, 2, 3, and 4, and ASA grade is divided into 1, 2, and 3. KS and FS scores are calculated on a hundred-point scale.

Table 4

A multiple linear regression calculated to predict FJS based on their age, BMI, sex, KL, ASA, preoperative flexion, KS, FS and received surgery (HTO, UKA and HTO).
	Parameter estimate	Standard error	t value	p-value
Intercept	76.644	9.336	8.210	< 0.001
Age (years old)	-0.327	0.073	-4.488	< 0.001
BMI (kg/m²)	-0.116	0.101	-1.145	0.253
Sex (male = 1, female = 2)	-1.703	0.971	-1.753	0.080
KL	0.203	0.667	0.304	0.761
ASA	0.516	0.739	0.698	0.486
HTO	0.848	1.263	0.671	0.502
UKA	8.623	1.019	8.460	< 0.001
TKA	0	0	0	0
Preoperative factors
Flexion(°)	-0.010	0.008	-1.261	0.208
KS	-0.093	0.097	-0.958	0.339
FS	0.203	0.082	2.491	0.013
Participant’s predicted FJS is equal to 76.644 − 0.327 (age)-0.116 (BMI) -1.703(sex) + 0.203 (KL grade) + 0.516(ASA grade) + 0.848 (If is HTO) or 8.623(If is UKA) -0.01(Flexion)-0.093(KS) + 0.203(FS).

Table 5 presents the correlations between the FJS and Knee Injury and Osteoarthritis Outcome Score (KOOS), KS, and FS subscales in three groups. The results showed moderate-to-strong positive correlations between the FJS and KOOS subscales, except for symptoms (r = 0.549–0.888).

Table 5

Spearman’s Coefficients Between clinical outcomes and Forgotten Joint Score-12 KS, Knee Score; FS, Function Score; *KOOS*, Knee injury and Osteoarthritis Outcome Score; *ADL*, activities of daily living, *Rec*, recreation, *QOL*, quality of life.
	HTO		UKA		TKA
	correlation	p-value	correlation	p-value	correlation	p-value
KOOS
Symptoms	-0.016	0.867	0.181	0.041	0.129	0.117
Pain	0.788	< 0.001	0.810	< 0.001	0.806	< 0.001
ADL	0.731	< 0.001	0.881	< 0.001	0.882	< 0.001
Sports and rec	0.549	< 0.001	0.850	< 0.001	0.627	< 0.001
QOL	0.677	< 0.001	0.800	< 0.001	0.823	< 0.001
KS	0.870	< 0.001	0.693	< 0.001	0.888	< 0.001
FS	0.867	< 0.001	0.856	< 0.001	0.828	< 0.001

Table 6 displays Spearman’s coefficients between clinical outcomes and the anchor (Patient’s Joint Perception [PJP]) questions in three groups. The FJS, KOOS, and anchor (PJP) were strongly correlated (P < 0.001), as depicted in Fig. 2. Overall, 20 of the 111 patients (18.0%) in the HTO group, 24 of the 128 patients (18.8%) in the UKA group, and 25 of the 150 patients (16.7%) in the TKA group reported that their joints felt “like a native or natural joint” and were considered to have a forgotten joint. In the HTO group, the AUC for the FJS was 0.9385, and AUC for the KOOS was 0.6687(Fig. 3). In the UKA group, the AUC for the FJS was 0.9547, and AUC for the KOOS was 0.8810. In the TKA group, the AUC for the FJS was 0.9683, and AUC for the KOOS was 0.9137. The threshold of the FJS-12 that maximized the sensitivity and specificity for detecting a forgotten joint was 63.54 (sensitivity:0.90, specificity:0.75) in the HTO group, 69.79 (sensitivity:0.958, specificity:0.775) in UKA group and 61.45 (sensitivity:0.92, specificity:0.832) in TKA group. This threshold for the KOOS score was 77.08 (sensitivity: 1, specificity:0.297) in the HTO group, 78.27 (sensitivity:0.917, specificity:0.754) in the UKA group, and 74.11 (sensitivity:0.92, specificity:0.664) in TKA group. Internal consistency in terms of Cronbach’s alpha was 0.806 for FJS.

Table 6

Spearman’s Coefficients Between clinical outcomes and Anchor (PJP) Questions.
	HTO		UKA		TKA
	correlation	p-value	correlation	p-value	correlation	p-value
KOOS	-0.621	< 0.001	-0.729	< 0.001	-0.758	< 0.001
FJS	-0.826	< 0.001	-0.842	< 0.001	-0.756	< 0.001
PJP, Patient’s Joint Perception; KOOS, Knee injury and Osteoarthritis Outcome Score; FJS, forgotten joint score-12.

Among the patients who underwent HTO, UKA, and TKA procedures, 18.0%, 18.8%, and 16.7%, respectively, reported that their joints felt like a natural joint, thus qualifying as having a forgotten joint. The HTO group had an AUC of 0.9385 for the FJS and 0.6687 for the KOOS, as depicted in Fig. 3. The UKA group had an AUC of 0.9547 for the FJS and 0.8810 for the KOOS. The TKA group had an AUC of 0.9683 for the FJS and 0.9137 for the KOOS. The FJS-12 threshold that yielded the highest sensitivity and specificity for identifying a forgotten joint was 63.54 (sensitivity:0.90, specificity:0.75) in the HTO group, 69.79 (sensitivity:0.958, specificity:0.775) in the UKA group, and 61.45 (sensitivity:0.92, specificity:0.832) in the TKA group. The optimal threshold for the KOOS was 77.08 (sensitivity: 1, specificity: 0.297) in the HTO group, 78.27 (sensitivity: 0.917, specificity: 0.754) in the UKA group, and 74.11 (sensitivity: 0.92, specificity: 0.664) in the TKA group. The internal consistency of the FJS, as measured by Cronbach's alpha, was 0.806.

In the present study, we observed a significant difference in the mean FJS among patients who underwent HTO, UKA, and TKA. Our results showed that medial UKA was superior to HTO and TKA in terms of patient awareness. Currently, there is no consensus or studies regarding the outcomes of HTO, UKA, and TKA. Some studies have reported significant differences in FJS between UKA and TKA after an average of one year following surgery, with score values of 73.9 ± 22.8 and 59.3 ± 29.5 for UKA and TKA, respectively (p = 0.002)[29]. However, Thienpont et al. found no significant difference in FJS between the UKA and TKA groups after two years following (UKA:76.4 ± 19; TKA: 73.2 ± 22, p = 0.436, respectively)[30]. Thus, our finding is similar to the result found by some studies[30–32].

Although several studies have reported FJS following UKA and TKA[20, 29, 31, 33], there is a paucity of research on FJS after HTO. However, Itoh et al.[16] have demonstrated the reliability and validity of FJS in evaluating patients who have undergone HTO. The FJS-12 questionnaire showed high internal consistency in our study (Cronbach's alpha = 0.806), indicating that it is a reliable tool for evaluating patients who have undergone HTO, UKA, or TKA. A Cronbach's alpha value greater than 0.7 is considered acceptable[34]. Our study revealed a significant difference in FJS between the HTO and UKA groups (Table 3), in contrast to the findings of Watanabe et al.[8] and Jin et al.[35]. These differences could be attributed to plate irritation of the skin and subcutaneous tissue of the proximal medial lower leg, which may reduce postoperative subjective satisfaction, particularly in younger patients with high functional activity requirements. Another possible explanation is that the plate used in the HTO patients in the studies by Watanabe et al.[8] and Jin[35] was removed during the last follow-up. Some reports have shown that HTO is superior to UKA in ROM[36, 37], and no certainty has been reached. In our results, UKA was inferior postoperative ROM compared to those of HTO (Table 2), which is consistent with the above study. In our study, we found that a female at, younger age leads to lower FJS (Table 4). This is aligned with the results of Li et al[38], who reported that females, younger age, and higher BMI have lower FJS in patients before TKA. Our results confirm that preoperative FS would predict better FJS.

The FJS thresholds for HTO, UKA, and TKA were 63.54, 69.79, and 61.45, respectively. As there are no prior studies reporting FJS thresholds for these procedures, comparisons cannot be made. However, Wang et al [17] measured FJS thresholds for a forgotten joint in UKA patients and found that an FJS of > 84.38 corresponds to a forgotten joint when using the same anchor question. The reasons for the discrepancy are unclear, and further investigation is necessary. These thresholds may be useful for surgeons to interpret FJS scores in daily practice. Scores above the threshold suggest that the patient has achieved a forgotten joint status, which is defined by the anchor question as feeling like they have a natural joint. The anchor question used in this study reflects the patients’ joint perception, with the best answer being “like a native or natural joint,” which is consistent with the concept of a forgotten joint [17]. Our study found that 18.0% of HTO, 18.75% of UKA, and 16.67% of TKA patients achieved a forgotten joint. Furthermore, older patients undergoing TKA surgery achieved a forgotten joint more frequently than those undergoing HTO and UKA surgery, with TKA thresholds being lower than those in the other two groups. This finding may be explained by the fact that younger patients, particularly those undergoing HTO and UKA, have higher activity levels and expectations than older patients and may be more sensitive to joint perception during daily activities [26]. We also found that the KOOS performs worse than the FJS in detecting a forgotten joint. This result can be attributed to the FJS focusing solely on joint perception while the KOOS does not evaluate joint awareness. However, the benefit of KOOS is that it can evaluate clinical outcomes for each characteristic subscale, which FJS lacks. Combining FJS and KOOS can provide a comprehensive evaluation of patient outcomes.

However, there are several limitations to this study. Firstly, the indications for HTO, UKA, and TKA are different, and discrepancies in patient gender, age, and BMI were adjusted using linear multivariate regression. However, we could not control the difference in the number of compartments affected by arthritis because the indications of these surgeries are inherently different[31]. Secondly, typical dichotomous anchor questions[40] were not used in our study. However, the cutoff was clear and reliable [26]. For the forgotten joint, only the answer "like a native or natural joint" was selected because the second answer "like an artificial joint with no restriction" shows that the patient has an artificial joint. Finally, all of our study subjects were Chinese, and ethnic and cultural differences in this population may affect the FJS threshold. Additionally, this was a predominantly female cohort, which may limit the generalizability of the findings. In the future, more prospective randomized controlled trials (RCTs) with strict criteria are necessary to confirm our results in other patient populations.

Our study suggests that medial UKA yields better patients’ awareness than HTO and TKA. Additionally, younger age and higher FS were identified as significant predictors of better FJS through multiple linear regression analysis. The FJS thresholds for HTO, UKA, and TKA were found to be 63.54, 69.79, and 61.45, respectively. These thresholds can assist surgeons in interpreting FJS scores during clinical follow-up and provide practical reference values for clinical operation options.

Ethical Approval

Applicable for both human studies. This study was approved by The First Affiliated Hospital of Guangzhou University of Chinese Medicine Ethical Review Board (Research Ethics Approval Code: IIT2022-27) and it complied with the Declaration of Helsink. Informed consent was obtained from all participants.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

Yirong Zeng and Haitao Zhang designed the clinical experimental steps, while Yiwei Huang wrote the main manuscript text. Hao Ge and Bo Peng collected the clinical data. Wenjun Feng reviewed and revised the English language to ensure its clarity and readability.

Funding

The work was supported by High-Level Hospital Construction Project of the First Affiliated Hospital of Guangzhou University of Chinese Medicine (211010010722) ，National Natural Science Foundation of China (82104882) and Guangzhou Science and Technology Plan Project(202201020585).

Availability of data and materials

The authors declare that all the data supporting the fndings of this study are available within the article.

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No competing interests reported.

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Comparison of joint awareness after total knee arthroplasty, medial unicompartmental knee arthroplasty, and high tibial osteotomy: a retrospective study

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Patient-Reported Outcome Measurements

Anchor Questions for the Forgotten Joint

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