Factors Affecting Squatting Ability in Total Knee Arthroplasty Using High Flexion Prosthesis

doi:10.21203/rs.3.rs-734850/v1

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Factors Affecting Squatting Ability in Total Knee Arthroplasty Using High Flexion Prosthesis

https://doi.org/10.21203/rs.3.rs-734850/v1

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Background: Total knee arthroplasty (TKA) is widely used as a treatment for knee osteoarthritis. Few studies have analyzed the factors affecting squatting ability of patients after TKA. The purpose of this study is to comprehensively analyze the factors affecting squatting ability after TKA and to determine which important factors should be paid attention to.

Methods: Three hundred primary TKA cases with a minimum 3-year follow-up were retrospectively analyzed. All patients received a conventional posterior-stabilized TKA implant and underwent a standard perioperative care pathway. The patients were divided into two groups according to the knee flexion angle (Group I -squatting group, Group II - inability squatting group). Demographic, operative, and clinical data were collected. Radiographic assessment included joint line joint line elevation, patella position, posterior condylar offset (PCO) , etc. Statistical analysis of effect of all the above factors on squatting ability was done.

Results: The univariate analysis showed age, prosthesis size, preoperative ROM and joint line position were correlated with squatting ability (p-values ≤0.10). In the final multivariate analysis, joint line position and preoperative ROM were independent influencing factors that affecting squatting ability after TKA (p-values < 0.01).

Conclusion: Preoperative ROM and joint line position were independent influencing factors affecting squatting ability after TKA. Patients should be counseled accordingly and made to understand these factors. In order to ensure patients can squat postoperatively, we should improve surgical techniques to control joint line elevation.

Orthopedic Surgery

Squatting ability

Joint line elevation

Preoperative ROM

Total knee arthroplasty

Total knee arthroplasty (TKA) is an effective surgical intervention for patients with end-stage knee joint degeneration(1). The primary goals of TKA are to relieve pain and improve knee function, thereby improving the patient's quality of life. Satisfaction after total knee arthroplasty ranges from 75 to 90%(2). Squatting, which covers a wider range of knee flexion than gait, is one of the most unsatisfactory motions after total knee arthroplasty(3). In the Asian population, squatting is an important part of daily activities(4). Many daily activities require knee flexion greater than 90°, while squats require knee flexion of 110° to 130°(5, 6).

At present, many studies have focused on factors affecting the range of motion (ROM) of patients after TKA, while few studies on the influence of patients' postoperative squatting ability. ROM after TKA depends on the individual patient, joint line (JL), patella baja, implant, and many other factors(7–9). Individual patient’s factors included BMI, age and Pre-operative ROM, etc. The study on the effect of joint line on postoperative mobility is the most reported at present. Whether these factors also affect squatting ability in patients after TKA requires our study. Although some previous literatures have analyzed the influence of individual factor on the range of motion of patients after TKA, no comprehensive analysis of multiple factors has been conducted. In our study, we will perform a comprehensive analysis after screening these factors.

To the authors' knowledge, there has been no direct studies in the literature on factors that affecting squatting after TKA in Asians. The aim of the present study is to analyze the influence of multiple factors on the squatting ability of patients after TKA, and to determine which factor is the significant factor affecting squatting ability.

We retrospectively reviewed case series of 300 knees that underwent primary TKA by a senior surgeon from 2009 to 2018. The patients included in our study satisfied the following criteria: (1) Their preoperative diagnosis was osteoarthritis, (2) The high flexion prosthesis was used for TKAs. The patients excluded based on the following criteria: (1) with joint replacement other than knee replacement; (2) follow-up < 3 years; and (3) incomplete data.

Radiological data included a weightbearing full length lower extremity antero-posterior radiograph performed with centered patella showing the entire lower limb, a medio-lateral view performed strictly perpendicularly to the superior face of tibial condyles, and an anterio-posterior view performed with strictly centered patella. Sex, age, weight, height of each subjects were noted. Other operative data on the use of the prosthesis size, and the thickness of the polyethylene insert used were collected from the patients’ electronic records. The most recent follow-up data were used. The patients were placed under general or spinal‑epidural combined anesthesia and an air tourniquet was applied in all cases. In all knees the same surgical technique was followed, using standard intramedullary alignment blocks, standard ligament-balancing techniques, an anterior femoral referencing system, and a constant tibial articular slope of 3°.

We divided the patients into two groups according to the knee flexion angle in the weight-bearing position (Group I -squatting group, Group II - inability squatting group). The flexion angle of squatting knee joint was greater than 110 °, and the flexion angle of inability squatting knee joint was less than 110 °. Each patient received routine preoperative and postoperative clinical care. Evaluations included serial radiographs, squatting ability, and all components of the Knee Society Score (KSS) system, Western Ontario and McMaster Universities (WOMAC).

Radiographic assessment

Preoperative radiographs served as a baseline, to which all postoperative radiographs were compared. According to Hofmann’s method(10), The JL was evaluated on preoperative and postoperative knee radiographs compared to a line drawn from the adductor tubercle of the femur. The Insall Salvati ratio (ISR) on lateral radiographs taken at 30° of flexion were used to evaluate the patellar position and diagnosis of the patella baja and pseudo-patella baja. ISR < 0.8 was defined as patella baja (normal ISR is 1 ± 0.2)(11) while ISR ≥ 0.8 was defined as pseudo-patella baja(12) .

Lateral X-rays of the knee were used to measure posterior condylar offset (PCO). The preoperative PCO was measured on the true lateral radiograph, as the tangential distance between the posterior cortex of the femoral diaphysis and the apex of the posterior femoral condyle. The postoperative PCO was measured as the tangential distance between the posterior cortex of the femoral diaphysis and the apex of the posterior femoral component post-operatively. Then compared the preoperative and postoperative measurements. Radiograph of knee anteroposterior view was used to assess the ratio of the transverse diameter of the patient's femoral prosthesis and the width of the distal femur. The distal femoral width (FW), described as the line joining the medial and lateral epicondyles at their most prominent points. All radiographs were evaluated by the same senior surgeon and the results were recorded.

Statistical analysis

All patients were divided into two groups: squatting group (Group I) and inability squatting group (Group II). Baseline characteristics and squatting ability were compared between the two groups. Descriptive statistics are reported as the mean and standard deviation, as the mean and range, or as the number and percentage. Univariate and multivariate logistic regression analyses were performed to estimate the odds ratio for the correlation between baseline characteristics and ORR. A p-value of < 0.05 was considered statistically significant. Analysis was performed using SPSS Version 25.0 software (IBM, Armonk, NY, USA).

The baseline information including demographical and clinical data, prosthesis were clearly listed in Table 1, and radiological data were summarized in Table 2. The KSS scores and WOMAC scores of squatting group (Group I) were improved compared with that of the inability squatting group (Group II), but the improvement in scores was not significant.

Table 1

Demographic, prosthetic and clinical data of two groups
Variable	Group I	Group II
Age (year)	64.9 ± 7.7	61.7 ± 6.6
Gender (M/F)	9/91	28/173
BMI (kg/m2)	27.3 ± 4.2	27 ± 3.2
Preoperative ROM	82.9 ± 12.6	107 ± 9.6
Model of prosthesis
Femoral	2.73 ± 0.8	2.97 ± 0.8
Tibia	2.58 ± 0.62	2.77 ± 0.67
Liner Thickness	11.12 ± 1.55	10.85 ± 1.43
Patella resurfacing	66 (66%)	94 (47%)
KSS
Post-operation	82.5 ± 7.4	90 ± 5.7
WOMAC
Post-operation	18 ± 6.5	12 ± 5.8
BMI, Body Mass Index; WOMAC, Western Ontario and McMaster Universities; KSS, American knee society knee score

Table 2

Radiographic results
Variable	Group I	Group II
patella baja after TKA (ISR < 0.8)	10(10%)	13(6.5%)
joint line elevation Post-TKA	3.24 ± 1.07	1.83 ± 0.89
Changes in PCO
Post- TKA	0.61 ± 1.38	0.47 ± 1.10
FC/FM	0.88 ± 0.09	0.87 ± 0.06
ISR, Insall-Salvati ratio; PCO, posterior condylar offset; FW, the femoral width, described as the line joining the medial and lateral epicondyles at their most prominent points; FC, Femoral Side Component Width

Univariate logistic regression analysis of baseline factors affecting ORR was performed for the following factors: Age, gender, BMI, prosthesis size, patella resurfacing, patella baja, joint line position, Preoperative ROM, FC/FM, and changes in PCO. Age, prosthesis size, pre-operative ROM and joint line position showed p-values ≤ 0.10 in the univariate analysis. Variables having p-value of p < 0.1 in univariate analyses were tested with multivariate analysis. Multivariate analysis identified joint line position and preoperative ROM as independent predictors of ORR (p < 0.01) (Table 3). Joint line position and preoperative ROM were independent influencing factors that affecting squatting ability after TKA.

Table 3

Univariate and multivariate logistic regression analysis for factors affecting ORR.
	Odds Ratio (95% CI) p	Odds Ratio (95% CI) p
Gender (M/F)	0.98 (0.42-2.26) ＞0.1	——
BMI (kg/m2)	0.98 (0.91-1.05) ＞0.1	——
Patella resurfacing	1.46 (0.80-2.66) ＞0.1	——
patella baja	0.66 (0.28-1.59) ＞0.1	——
Changes in PCO	0.91 (0.73-1.14) ＞0.1	——
FC/FM	0.10 (0.00-4.08) ＞0.1	——
Age (year)	0.94 (0.90-0.98) ＜0.1	0.97 (0.88-1.07) ＞0.05
joint line elevation	0.22 (0.15-0.34）＜0.1	0.09 (0.32-0.25）＜0.01
Prosthesis size Femoral Tibia Liner Thickness	1.57 (1.07-2.30) ＜0.1 1.56 (0.99-2.44) ＜0.1 0.83 (0.71-0.98) ＜0.1	1.04 (0.20-5.54）＞0.05 2.98 (0.43-20.76）＞0.05 0.95 (0.66-1.37）＞0.05
Preoperative ROM	1.23 (1.16-1.30) ＜0.1	1.34 (1.20-1.49) ＜0.01
BMI, Body Mass Index; ISR, Insall-Salvati ratio; PCO, posterior condylar offset; FW, the femoral width, described as the line joining the medial and lateral epicondyles at their most prominent points; FC, Femoral Side Component Width, ROM Range of motion

The factors affecting squatting ability after TKA had not been reported in the literature. The main finding of this study was that joint line was the only significant factor that affecting squatting ability in patients after TKA.

Majority of literatures had reported the factors affecting range of motion after TKA. However, no previous studies had reported the factors affected the patient's squatting ability after TKA. In Asian populations, activities such as cross-legged sitting, kneeling, and squatting are an important part of daily activities(4). Therefore, it’s necessary and important to clarify the influencing factors of squatting.

Some literatures reported that sex had no correlation in affecting the knee ROM postoperatively after total knee arthroplasty(13–15). Bellemans J et al(16).found the use of standard implants could lead to mediolateral overhang in women, causing irritation and pain of the soft tissue capsular envelope of the knee because of female knees were narrower than male knees. However, the results of this study show that the relationship between gender and clinical outcomes remains uncertain. In our study, gender was not a factor that influenced patients' squats. But the women in our study were the majority, which may have influenced our final results.

Sancheti KH et al(17). found that age and patella replacement didn’t affect the postoperative joint ROM, whereas BMI had a negative influence on postoperative joint. In our study, age was related to postoperative squatting in univariate analysis, but after multivariate analysis, age, BMI and patella replacement proved not to be the influencing factors of postoperative squatting. The study of Razzaki T et al(18). was specifically about the relationship between BMI and clinical outcome in patients following TKA. In this study, Razzaki T et found the mean 2-year Knee Society Knee Score was significantly higher in the patients who gained weight while the patients who lost weight had the highest mean 2-year Oxford Knee Score and the lowest mean 2-year Knee Society Function Score, and weight change following TKA does not affect clinical outcomes, which remain good across all BMI groups.

Physiological patellofemoral joint motion was important for knee flexion function. ISR < 0.8 was defined as patella baja (PB). PB was known to affect patellofemoral joint motion; a shortening of more than 10% of the tendon has been hypothesized to significantly reduce knee flexion due to shortening of the extensor mechanism length(9, 19, 20). There were also many reports in the literature that patella baja can restrict the ROM of the knee(21–23). However, recent studies had shown that patella baja doesn’t affect the patient's postoperative range of motion(24, 25). In our study, patella baja(P༞0.1) was also not the influencing factors of whether squatting. Bellemans et al.(26) defined a parameter termed “posterior condylar offset(PCO amount of posterior projection of the femoral implant to the tangent of the posterior femoral cortex).” Bellemans et al. found PCO was associated with a postoperative change in flexion angle in CR knees, whereas this correlation was not observed in PS knees. Yang et al.(27) found PCO didn’t seem to have a significant influence on the postoperative knee flexion after PS TKA. The prostheses of the patients in our study were all PS knees, which also explained why PCO had no effect on the postoperative squatting ability in our findings.

Oversizing the implant could theoretically increase tension and capsule/ligament friction on the implant, thus affecting clinical outcomes(28). Bonnin MP et al.(28) found oversizing of the lateral side of the prosthesis was a factor that may predicted poor TKA results, and surgeons avoided selecting oversized prostheses. Therefore, we included the prosthesis size and FC/FM to determine whether these would affect the patient's squatting ability in our study. The results showed that neither the model of the prosthesis nor FC/FM can affect squatting ability after TKA. We consider that the reason for this result is that this surgeon has a superb surgical technique and can accurately select the appropriate prosthesis model for different patients, because it can be seen from our data that the FC/FM(0.88 ± 0.09vs0.87 ± 0.06) of the group I and the group II are similar, so we cannot be sure the model of the prosthesis and FC/FM didn’t affect the squatting ability.

Gatha NM et al.(29) assessed whether specific preoperative and postoperative variables were associated with postoperative ROM in 135 patients who underwent TKA. Their results showed that preoperative ROM was the only significant predictor of postoperative ROM. Ritter et al. (30) retrospectively reviewed more than 4,700 total knee arthroplasty procedures and used regression tree analysis to describe the combination of variables affecting postoperative ROM. The primary predictor of postoperative ROM in this study was preoperative ROM. In a recent study, Konrads C et al.(31) demonstrated preoperative ROM is a good predictor of postoperative ROM after primary TKA. The results of these studies were similar to those of our study, in which preoperative ROM was also a contributing factor affecting postoperative squatting ability of patients.

Mean joint line elevation 1.1–5.6 mm after primary TKA(32). Some studies had reported a correlation between elevated joint lines and patients' postoperative range of motion(24, 33, 34), while others had found no such correlation(35). There were currently many explanations for why elevated joint lines lead to reduced range of motion after TKA. One view was that elevation of the joint line could lead to mid-flexion instability which reduced the range of motion after TKA(36).Matziolis et al.(37) also found Joint line position was associated with mid-flexion instability, which could lead to reduced range of motion after TKA. The term “mid-flexion instability” was a definition to describe instability during flexion–extension movement, which had not been proven as a unique type of instability in clinical practice(38).But another view is that joint line elevation causing patella baja can result in reduced the force of the extensor mechanism, patellar impingement on the insert caused anterior knee pain, and tightening of collateral ligaments and diminished femoral rollback resulted in limited knee motion(39). In our study, we performed univariate analysis with both patella baja and joint line elevation as influencing factors, and the results showed that patella baja was not a factor affecting ROM after TKA. Therefore, in view of our results, joint line elevation led to mid-flexion instability, which was the reason affected squatting ability of patients after TKA.

There were also limitations in this study. First, our study included limited generalizability as our cohort belongs to a single surgeon and a single institution, and women made up the majority. Second, we only preliminarily defined squatting according to the flexion angle of the knee joint in the weight-bearing position, because there is no formal definition of squatting in patients after TKA.

This study demonstrated that joint line elevation and preoperative ROM were independent influencing factors affecting the squatting ability after TKA. Patients with poor preoperative ROM should be counseled that they may not achieve satisfactory squatting ability postoperatively. In addition, in order to ensure that patients can squat after TKA, we should focus on controlling the joint line elevation. The joint line elevation was determined by the surgical technique of the surgeon, and whether the patient can squat after TKA is a test of the surgeon's skill.

TKA: Total knee arthroplasty; BMI: Body Mass Index; WOMAC: Western Ontario and McMaster Universities; KSS: American knee society knee score; ISR: Insall-Salvati ratio; PCO: posterior condylar offset; FW: the femoral width, described as the line joining the medial and lateral epicondyles at their most prominent points; FC: Femoral Side Component Width; ROM: Range of motion;

Ethics approval and consent to participate

This retrospective review study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The study was approved by the medical ethics committee of our hospital. Informed consent Informed consent was obtained from all individual participants included in the study

Consent for publication

Not applicable.

Availability of data and material

All data generated or analyzed during this study are included in this published article.

Competing interests

The authors declare that they have no competing interests.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author’s contributions

T-JL analyzed the data and drafted the manuscript. J-YS and Z-SG assessed the radiographs and collected the data. Y-QD assessed the radiographs, and analyzed the data. H-YM followed up the patients, collected the data, and analyzed the data. Y-GZ participated in the design of the study, performed the surgery, and revised the manuscript. All authors read and approved the final manuscript.

Acknowledgements

The authors would like to thank all staff from the participating departments and clinics.

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Factors Affecting Squatting Ability in Total Knee Arthroplasty Using High Flexion Prosthesis

Status:

Journal Publication

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Abstract

Introduction

Materials And Methods

Radiographic assessment

Statistical analysis

Results

Discussion

Conclusion

Abbreviations

Declarations

References

Status:

Journal Publication

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