The influence of post-operative knee coronal alignment parameters on long-term patient-reported outcomes after closed-wedge high tibial osteotomy

Abstract

Background

Both intra-articular and extra-articular knee alignment pathologies can affect clinical outcomes after high tibial osteotomy. The purpose of this study was to investigate post-operative knee coronal alignment parameters that affect long-term patient-reported outcomes after closed-wedge high tibial osteotomy (CW-HTO).

Methods

This study included 105 osteoarthritic knees that underwent CW-HTO. Long-term patient-reported outcomes were defined by the 2011 Knee Society Score (KSS) and were collected at an average follow-up of 10.2 years. Post-operative knee coronal alignment parameters, consisting of the femoral tibial angle (FTA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), tibial plateau inclination (TPI), and joint line convergence angle (JLCA), were measured using standing radiographs of the knee at an average follow-up of 11.0 months. The correlations between these parameters and KSS were then assessed by Spearman's correlation analysis. Comparisons of groups classified by MPTA and TPI cutoff values were performed by the Wilcoxon rank-sum test.

Results

Post-operative JLCA showed a significant negative correlation with two KSS sub-scores: satisfaction (R = −0.2232, P = 0.022) and total function (R = −0.2059, P = 0.035). There was no significant difference in any KSS sub-score between the “low” groups (MPTA and TPI less than 95 and 5°, respectively) and the “high” groups (MPTA and TPI greater than 98 and 7°, respectively).

Conclusions

Among knee coronal alignment parameters, a large post-operative residual JLCA, which is an intra-articular varus deformity, was independently associated with worsened long-term clinical outcomes after CW-HTO.

Level of evidence

Level Ⅳ, Retrospective cohort study.

1. Introduction

Knee osteoarthritis (OA) is the most prevalent joint disorder, leading to significant disability and impaired quality of life.¹ A reliable surgical option for varus OA patients who wish to preserve their joints is high tibial osteotomy (HTO), which re-aligns the mechanical axis to a slightly valgus align. Previous studies have reported acceptable long-term survival rates without arthroplasty conversion up to 10 years after HTO, although the survival rate of the knee decreases with time over 10–15 years.2, 3, 4, 5

Post-operative knee coronal malalignment has been reported as one of the factors that most strongly contributes to poor clinical outcomes, including conversion to arthroplasty, in the long-term after HTO.^3,6,7 Knee coronal alignment expressed as the femoro-tibial angle (FTA) is defined based on two extra-articular bony parameters, namely the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA), and an intra-articular parameter, the joint line convergence angle (JLCA). Recently, a large post-operative JLCA after HTO was reported to constitute a residual intra-articular varus deformity,^8,9 and was correlated with lower clinical scores at a mean follow-up of 2 years.¹⁰ On the other hand, increased joint-line obliquity on the proximal tibia, defined by a MPTA greater than 95°, led to eccentric valgus shear stress on articular cartilage¹¹ and influenced clinical functional outcomes at 2 years after open-wedge HTO (OW-HTO).¹²

Both intra-articular and extra-articular knee alignment pathologies can affect clinical outcomes after HTO, but no prior studies have investigated the influence of post-operative alignment parameters, including JLCA and MPTA, on long-term patient-reported outcomes after closed-wedge HTO (CW-HTO). The purpose of this study was therefore to assess the relationship between post-operative knee alignment parameters and long-term patient-reported outcomes. It was hypothesized that the post-operative values of both JLCA and MPTA would affect patient-reported outcomes, even in the long-term after CW-HTO.

2. Materials and methods

2.1. Patient recruitment

The data of patients who underwent CW-HTO for knee OA with varus alignment at Kyushu University Hospital or Japan Community Health Care Organization Kyushu Hospital were retrospectively extracted. A total of 105 knees in 88 patients who had been examined with anteroposterior weight-bearing knee radiographs after surgery were included in this study. The patients were mailed the 2011 Knee Society Score (KSS) survey, a self-reported outcome measure that asked patients to grade their symptoms, satisfaction, expectations, and functional activities.¹³ Patient data, including sex, age at the time of surgery, body mass index, and post-operative follow-up period, were collected from their medical records.

This study was approved by the institutional review board of both participating institutions, and all patients provided written informed consent.

2.2. Surgical procedures

Lateral interlocking closed-wedge osteotomy,¹⁴ a type of CW-HTO, was performed in all knees. A proximal cut of the wedge was performed parallel to the joint line, leaving the posterior cortex intact. Next, a distal cut of the wedge was made based on pre-operative planning, leaving the anterior cortex intact. The bone wedge was then removed and the empty wedge was closed with an internal rotation of the distal tibia. Finally, fixation was carried out with staples or a locking plate. Full weight-bearing was allowed after 6–8 weeks of gradually increasing partial weight-bearing.

2.3. Radiological assessment

On standing anteroposterior knee radiographs obtained at an average of 11.0 months after CW-HTO, five parameters related to knee alignment were measured: FTA, LDFA, MPTA, tibial plateau inclination (TPI) to the ground, and JLCA (Fig. 1). If the apex of the JLCA was medial, it was recorded as positive (+). If the TPI to the ground was laterally inclined, it was recorded as positive (+).

Fig. 1.

Radiographic parameters for the evaluation of knee coronal alignment.

FTA, femoral tibial angle; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle; TPI, tibial plateau inclination; JLCA, joint line convergence angle.

2.4. Statistical analysis

Patient demographic data and radiographic measurements were expressed as mean ± standard deviation (range). Correlations between radiographic measurements and KSS sub-scores were assessed using Spearman's rank correlation coefficient analysis. For further analysis, the subjects were divided into four groups: based on MPTA, a group with a low MPTA ≤95°, and a group with a high MPTA ≥98°; and based on TPI, a group with a low TPI ≤5°, and a group with a high TPI ≥7°. Between-group comparisons were performed using Student's t-test and the Wilcoxon rank-sum test. All statistical analyses were performed using JMP Pro (Ver. 13.0.0; SAS, North Carolina, USA). P < 0.05 was considered statistically significant.

3. Results

Patient characteristics, including gender, age, body mass index, follow-up period, and post-operative radiographic measurements, are shown in Table 1. The patients’ mean age at the time of surgery was 61.0 ± 7.4 years. The mean follow-up period was 10.2 ± 3.1 years.

Table 1.

Patient characteristics.

Variable	value
Gender (female/male)	21/84
Age (years)	61.0 ± 7.4 (47–82)
Body mass index (kg/m2)	25.5 ± 3.6 (19.1–36.5)
Post-operative follow-up period (years)	10.2 ± 3.1 (5–19.7)
Postoperative radiographic measurements
FTA	169.1 ± 3.7 (157.4–177.5)
LDFA	82.5 ± 2.8 (71.4–89.8)
MPTA	96.6 ± 4.1 (80.2–105.8)
TPI	4.6 ± 3.6 (−5.8 - 16.1)
JLCA	3.1 ± 2.0 (−0.6 - 8.9)

The values are given as mean ± standard deviation (range).

FTA: femoral tibial angle; LDFA: lateral distal femoral angle; MPTA: medial proximal tibial angle; TPI: tibial plateau inclination; JLCA: joint line convergence angle.

Results of the correlation coefficients between post-operative radiographic measurements and KSS sub-scores are shown in Table 2. There was a significant negative correlation between JLCA and two KSS sub-scores: satisfaction (R = −0.2232, P = 0.022) and function (R = −0.2059, P = 0.035).

Table 2.

Correlation coefficients between each alignment parameter and KSS sub-scores.

	FTA	LDFA	MPTA	TPI	JLCA
Symptom	−0.0151	0.0308	−0.0711	0.0002	−0.1815
Satisfaction	−0.0560	0.0138	−0.0495	0.0012	−0.2232 *
Expectation	−0.0163	0.1299	0.0314	0.1044	−0.0721
Total function score	−0.1683	−0.0437	0.022	−0.0831	−0.2059 *

* Statistically significant correlation (p ˂ 0.05).

FTA: femoral tibial angle; LDFA: lateral distal femoral angle; MPTA: medial proximal tibial angle; TPI: tibial plateau inclination; JLCA: joint line convergence angle.

On the other hand, FTA, LDFA, MPTA, and TPI were not correlated with KSS sub-scores (Table 2). In addition, as shown in Table 3, there were no significant differences in KSS sub-scores between the groups with MPTA ≤95° and MPTA ≥98°, or between the groups with TPI ≤5° and TPI ≥7° (Table 3).

Table 3.

Results of group comparisons divided by MPTA or TPI values.

	low MPTA group (≤95°)	high MPTA group (≥98°)	p value	low TPI group (≤5°)	TPI higher group (≥7°)	p value
Follow up period (years)	10.2 ± 3.4	10.0 ± 2.9	n.s	10.2 ± 3.5	10.5 ± 2.8	n.s
Age	62.0 ± 7.4	60.5 ± 8.0	n.s	61.7 ± 7.0	60.9 ± 8.0	n.s
Body mass index	25.9 ± 3.6	26.4 ± 4.2	n.s	25.8 ± 3.4	26.8 ± 4.4	n.s
KSS sub-score
Symptom	17.1 ± 6.2	14.8 ± 7.0	n.s	13.9 ± 7.2	13.7 ± 7.8	n.s
Satisfaction	21.2 ± 6.9	19.6 ± 6.5	n.s	18.8 ± 8.6	18.4 ± 7.7	n.s
Expectation	8.6 ± 2.9	8.8 ± 2.5	n.s	7.9 ± 3.4	8.4 ± 2.6	n.s
Total function	62.7 ± 25.9	61.9 ± 21.7	n.s	57.7 ± 25.0	54.4 ± 22.8	n.s

Values are expressed as mean ± standard deviation.

MPTA: medial proximal tibial angle; TPI: tibial plateau inclination; KSS: knee society score.

4. Discussion

The main finding of this study is that larger JLCA after surgery was significantly correlated with worse patient-reported outcomes, specifically the satisfaction and function scores of the KSS, in the long-term after CW-HTO with an average follow-up of 10.2 years. Contrary to our hypothesis, post-operative MPTA did not show any significant impact on KSS in the long-term period after CW-HTO.

When its medial apex is defined as positive, JLCA generally decreases after HTO following the transition of the mechanical axis to the lateral side,^15,16 as this restores good congruency between the femoral condyle and tibial plateau. However, there are varus cases with a separated and subluxated lateral compartment, resulting in a large JLCA, even when the mechanical axis is successfully translated to the lateral side by HTO.⁹ In such cases, the reallocation of stress distribution by HTO cannot be achieved, and therefore Ji et al. proposed that a large JLCA after HTO is a “residual intra-articular varus deformity” that may affect the post-operative clinical outcome.⁸ Indeed, a recent study reported that post-operative JLCA values after OW-HTO were a significant factor associated with poor clinical scores at a mean follow-up of 2 years.¹⁰ In our study, a large JLCA after CW-HTO negatively affected patient satisfaction and function even at a long-term average follow-up of 10.2 years. Collectively, a large post-operative residual JLCA should be considered to have an adverse effect on short-to long-term clinical outcomes after HTO.

The degree to which post-operative non-anatomical joint line obliquity (JLO) influences clinical outcomes after HTO remains a considerable concern.^11,12,17, 18, 19, 20 Coventry first reported a relationship between excessively negative JLO exceeding 10° and poor outcomes of closing-wedge “varus osteotomy” of the proximal tibia for valgus deformity at an average follow-up of 9.4 years.²⁰ In regard to “valgus osteotomy,” several researchers also considered that non-anatomical JLO after HTO may adversely affect clinical outcomes due to problems such as increased shear force at the knee joint surface.^11,12,17, 18, 19 Using a three-dimensional finite element model, Nakayama et al. demonstrated excessive shear stress on the articular cartilage caused by JLO of more than 5° after OW-HTO.¹¹ In a recent clinical study, Akamatsu et al. reported that a post-operative MPTA >95° with high JLO correlated with a lower sports and recreational function sub-score of the Knee injury and Osteoarthritis Outcome Score (KOOS) at 2 years after OW-HTO.¹² In contrast, Polat et al. reported that CW-HTO with the greatest valgization effect on MPTA showed no significant differences in patient functional outcomes compared to OW-HTO at the mean follow-up of 12.4 years.²¹ Similarly, in our study, neither MPTA nor TPI were correlated with long-term KSS sub-scores at an average of 10.2 years after CW-HTO, suggesting that articular inclination of the knee due to high MPTA was not a decisive factor that directly affected long-term patient outcomes. This discrepancy between reports might be due to the difference in either the follow-up period or the type of osteotomy, namely OW-HTO vs. CW-HTO; for example, a large amount correction may affect patellofemoral joint in OW-HTO rather than CW-HTO.²² Further studies in other cohorts should be performed to determine the influence of post-operative non-anatomical JLO on the long-term clinical outcomes of HTO.

There are several limitations of this study that require consideration. First, all HTO procedures were performed using the closed-wedge procedure, and therefore our results cannot be applied to other types of HTO. Second, because of insufficient availability of whole-leg standing radiographs, we used only knee radiographs to assess alignment parameters around the knee joint. Finally, our results did not define ideal JLCA cut-off values for achieving better long-term outcomes after HTO.

5. Conclusions

Among various intra-articular and extra-articular pathologies of knee alignment, a large post-operative residual JLCA, an intra-articular varus deformity, was found to be an independent factor that adversely impacted long-term clinical outcomes after CW-HTO.

Funding

No financial support was provided to this study.

Declaration of competing interest

The authors state that there are no conflicts of interest, which might have influenced the preparation of this manuscript.