Postoperative radiologic outcome comparison between conventional and computer-assisted navigation total knee arthroplasty in extra-articular tibia vara

Abstract

Purpose:

Total knee arthroplasty (TKA) is the definite treatment for osteoarthritis. Meanwhile, significant inherent extra-articular varus angulation is associated with abnormal postoperative hip–knee–ankle (HKA) angle. Computer-assisted navigation TKA (CAS-TKA) used in patients who have severe varus deformity. The purpose of this study was to compare postoperative radiologic outcome between CAS-TKA and conventional TKA for extra-articular tibia vara.

Methods:

A retrospective review of postoperative HKA on standing lower extremity views was conducted in patients who underwent TKA by a single surgeon from 2010 to 2018, including knee with conventional TKA (n = 83) and CAS-TKA (n = 246). Extra-articular tibia vara was assessed by measuring the metaphyseal–diaphyseal angle (MDA) of the tibia in preoperative standing lower extremity view. Postoperative alignment was assessed by measuring the HKA in postoperative standing lower extremity view.

Results:

There was no significant difference in age (p = 0.063), gender (p = 0.628), body mass index (p = 0.426), preoperative range of motion (p = 0.524), preoperative HKA (p = 0.306), preoperative MDA (p = 0.523), or postoperative HKA (p = 0.416) between the two groups (conventional TKA and CAS-TKA). There was no significant difference in postoperative alignment for cases with MDA ≤4° (p = 0.351) or MDA >4° (p = 0.866) in each group. There was a positive correlation between preoperative HKA and postoperative HKA in the CAS-TKA group (p < 0.001, r = 0.243). However, there was no significant correlation between preoperative HKA and postoperative HKA in the conventional TKA group (p = 0.732).

Conclusions:

There was no significant difference in postoperative alignment between conventional TKA and CAS-TKA in extra-articular tibial vara even for cases with MDA >4°.

Keywords

arthroplasty computer-assisted knee replacement surgery

Introduction

Total knee arthroplasty (TKA) is the definite treatment for osteoarthritis. One goal of using surgical technique in TKA is to create symmetric balanced flexion and extension gaps.¹ To achieve this goal, gap balancing technique and measured resection technique have been used to determine component position.² Failure to correct malalignment of the mechanical axis of the lower extremity will shorten the longevity of TKA.³

Extra-articular angulation of the proximal tibia may lead to difficulties in correct implant alignment due to distorted anatomic alignment and landmarks.^4,5 Saibaba et al. have reported that significant extra-articular varus angulation of metaphyseal–diaphyseal angle (MDA) greater than 4° is associated with abnormal postoperative hip–knee–ankle (HKA) angle.⁶

In recent years, computer-assisted navigation TKA (CAS-TKA) has become more popular because it could lead to better accuracy in implanting the prosthesis and realigning lower extremities.⁷ Literature data have shown that CAS-TKA can increase the accuracy of proximal tibial cut with the capability to track independent lengthening and shortening collateral ligaments to facilitate sizing of a femoral component that can properly tense these ligaments through a full range of motion (ROM).^8,9 CAS-TKA is effective in assisting surgeons to obtain more accurate alignment in cases with extra-articular tibia vara.¹⁰ However, some authors have reported that CAS-TKA cannot improve alignment in extra-articular tibia vara.^11,12 The purpose of this study was to compare postoperative radiologic outcome between CAS-TKA and conventional TKA for cases with extra-articular tibia vara.

Materials and methods

Patients

Data of patients who underwent primary TKA were reviewed retrospectively. Inclusion criteria were a primary cemented TKA using Columbus® (B. Braun, Melsungen, Germany) implant performed between 2010 and 2018 in our institute by a single surgeon. If a patient underwent TKA on both knees, then both sides of the knee were analyzed. Total 699 knees were enrolled. Exclusion criteria were previous knee surgery, inflammatory arthritis, and missing preoperative or postoperative standing lower extremity view. This series included 235 patients and 329 knees. Of these 235 patients, 215 were females and 20 were males. Their mean age was 72.87 years (95% confidence interval = 72.14–73.60 years; range 53–94 years). The preoperative mean ROM was 107°. If the navigation system was available, the CAS-TKA was performed using navigation system. When the navigation system was being used by another surgeon or system failure, the conventional TKA was performed. A total of 246 (75%) TKAs were performed using computer-assisted navigation system OrthoPilot® (B. Braun). The number of conventional TKA was 83 (25%). This research has been approved by the Institutional Review Board of the authors’ affiliated institution (protocol number: KBSMC 2018-06-020).

Surgeon factors and surgical techniques

The surgeon (H-JJ) was in a high-volume center and he performed more than 3000 cases of TKA in over 30 years including CAS-TKA. Paramedial incision and subvastus arthrotomy were performed using air tourniquet at 300 mmHg under general or spinal anesthesia. After bone resection according to navigation or conventional system, all implants were fixed with cement.

Navigation system technique

Kinematic and the required anatomical selected points were registered. Then, the lower extremity alignment by navigation in knee extension (0°) and knee flexion (90°) position was recorded. The osteophytes, anterior, posterior cruciate ligaments, and medial meniscus were removed. A tibial cut was made perpendicular to the long axis of tibia using a cutting block positioned under navigation guidance. After the distal and posterior condyles of femur had been recorded, an optimization of anterior points on the femur with the pointer. The joint gap in extension and flexion was measured with the distractor. Based on the recorded information, the resection plan was established with the help of the computer system. The distal femur resection block was positioned as planned under navigation system, and distal femur was resected. After reassessing the distal resection, the four-in-one cutting guide was positioned as planned rotation alignment using navigation system. Anterior, posterior, and chamfer cut were performed in sequence.

Conventional system technique

The osteophytes, anterior, posterior cruciate ligaments, and medial meniscus were removed same as above. Using femur first measured resection technique, femoral intramedullary guide, which was set valgus 6° to femur anatomical axis, was inserted and we fixed cutting block. Then, the distal femur was resected with saw under cutting block. Extramedullary tibial guide, which was set perpendicular to tibia anatomical axis, was inserted toward second toe and fixed with hammer. After removing tibial guide, tibial cutting block was inserted and resected tibia under cutting block. After resection of the tibia plateau, the ligamentary tension was checked to confirm rectangular gap. If the gap was not rectangular, then the additional ligament balancing procedure was performed. Trial was inserted with bearing and we examined flexion and extension gap. Final prosthesis was implanted with bone cement.

Measurements

Height and body weight of all patients were reviewed to calculate body mass index (BMI). Preoperative ROM was measured with a goniometer. Surgical time was reviewed on anesthesia record. The extra-articular tibia vara was assessed by measuring the MDA (Figure 1) of the tibia in preoperative standing lower extremity view. MDA was defined as the angle created between the ankle joint line and the line perpendicular to midmedullary of the tibia. We divided each group into two subgroups based on the preoperative tibial MDA by 4°. Because Saibaba et al. have reported that MDA above 4° was associated with abnormal postoperative HKA.⁶ Preoperative and postoperative alignment were assessed by measuring HKA in preoperative and postoperative standing lower extremity view, respectively. HKA was defined as the angle created between the mechanical axis of the femur and the mechanical axis of the tibia (Figure 2). All angles were measured with the cobb angle tool in a picture archiving and communication system (PI View STAR, version 5025; Infinitt, Seoul, South Korea). A single orthopedic surgeon, not the one who operated, measured all MDA and HKA without noticing for which group they belonged to.

Figure 1.

MDA is defined as an angle formed between perpendicular line of the tibial diaphysis line and parallel line of ankle joint line. MDA: metaphyseal–diaphyseal angle.

Figure 2.

(a) Preoperative HKA angle and (b) postoperative HKA angle. Note that the postoperative HKA was reduced to normal alignment of the lower extremity. HKA: hip–knee–ankle.

Statistical analysis

SPSS Statistics for Windows, version 24.0. (IBM, New York, USA), was used for all statistical analyses. Intergroup comparisons were made using independent t-test. In the comparison for gender difference, χ ² test was performed. The number of cases with MDA ≤4° and >4° was compared using a χ ² test. The relationship between variables was analyzed using Pearson’s correlation coefficient in overall cases and in each group. A p value of less than 0.05 was considered statistically significant. All data are expressed as mean ± standard deviation.

Results

There was no statistically significant difference in age, gender, BMI, preoperative ROM, preoperative HKA, or preoperative MDA (p value: 0.063, 0.628, 0.426, 0.524, 0.306, and 0.523, respectively) between CAS-TKA group and conventional TKA group. But surgical time of CAS-TKA group was statistically significant longer than surgical time of the conventional TKA group (p = 0.011). The number of cases with MDA ≤4° and >4° in CAS-TKA group was 162 and 84. In conventional TKA group, the number of cases with MDA ≤4° and >4° were 61 and 22. There was no difference in number of cases with MDA ≤4° and >4° (p = 0.198; Table 1).

Table 1.

Demographic data.^a

	CAS group	Conventional group	p Value
Age	72.47 ± 6.65	74.06 ± 6.94	0.063
BMI	26.69 ± 3.81	28.40 ± 19.39	0.426
Preoperative ROM	107 ± 4.6	105 ± 3.3	0.524
Surgical time (min)	123 ± 0.02	113 ± 0.02	0.011
Preoperative HKA angle	9.56 ± 5.91	10.35 ± 6.51	0.306
Preoperative tibial MDA	3.37 ± 2.44	3.16 ± 3.02	0.523
MDA ≤ 4°cases	162	61	0.198
MDA > 4°cases	84	22
Total	246	83	329

CAS: computer-assisted navigation; BMI: body mass index; ROM: range of motion; HKA: hip–knee–ankle; MDA: metaphyseal–diaphyseal angle.

^a Data are shown as mean ± standard deviation.

No statistically significant difference was found in postoperative HKA (p = 0.416) between the two groups. There was no statistically significant difference in postoperative alignment for cases with MDA ≤4° (p = 0.351) or MDA >4° (p = 0.866) in each group (Table 2).

Table 2.

Postoperative radiological results.^a

	CAS group	Conventional group	p Value
Postoperative HKA angle	2.74 ± 2.36	2.50 ± 2.19	0.416
Postoperative HKA angle in case MDA ≤ 4°	2.86 ± 2.34	2.53 ± 2.39	0.351
Postoperative HKA angle in case of MDA > 4°	2.50 ± 2.38	2.41 ± 1.56	0.866

CAS: computer-assisted navigation; HKA: hip–knee–ankle; MDA: metaphyseal–diaphyseal angle.

^a Data are shown as mean ± standard deviation.

There were positive correlations between preoperative HKA and postoperative HKA in overall cases (p = 0.001, r = 0.187; Table 3). However, in the conventional group, there were no significant correlations between preoperative HKA and postoperative HKA (p = 0.732), although there were positive correlations in the navigation TKA group (p < 0.001, r = 0.243; Table 4).

Table 3.

Correlations between variables in overall cases.^a

	Postoperative HKA angle	Preoperative HKA angle	Preoperative tibial MDA
Postoperative HKA angle
Pearson correlation		0.187	0.015
p Value		0.001	0.781
Preoperative HKA angle
Pearson correlation	0.187		0.021
p Value	0.001		0.699
Preoperative tibial MDA
Pearson correlation	0.015	0.021
p Value	0.781	0.699

HKA: hip–knee–ankle; MDA: metaphyseal–diaphyseal angle.

^a Correlation is significant at 0.01 level (two-tailed).

Table 4.

Correlations between variables in each group.^a

	Postoperative HKA angle	Preoperative HKA angle	Preoperative tibial MDA
Conventional group
Postoperative HKA angle
Pearson correlation		0.038	0.027
p Value		0.732	0.806
Preoperative HKA angle
Pearson correlation	0.038		-0.135
p Value	0.732		0.222
Preoperative tibia MDA
Pearson correlation	0.027	-0.135
p Value	0.806	0.222
CAS group
Postoperative HKA angle
Pearson correlation		0.243	0.009
p Value		<0.001	0.891
Preoperative HKA angle
Pearson correlation	0.243		0.096
p Value	<0.001		0.133
Preoperative tibia MDA
Pearson correlation	0.009	0.096
p Value	0.891	0.133

CAS: computer-assisted navigation; HKA: hip–knee–ankle; MDA: metaphyseal–diaphyseal angle.

^a Correlation is significant at 0.01 level (two-tailed).

Discussion

Numerous studies have compared radiologic outcome between conventional TKA to CAS-TKA. According to these studies,^13

–17 CAS-TKA shows better postoperative alignment compared to conventional TKA and CAS-TKA was reported to be superior to conventional TKA in the majority of published reports. It was believed that the use of computer navigation in TKA could make an inexperienced TKA surgeon more like an expert TKA surgeon.¹² However, Burnett and Barrack¹⁸ and Gharaibeh et al.¹⁹ have reported that there is no significant difference between conventional and CAS-TKA.

Extra-articular tibia vara is typically seen in Asian patients with varus osteoarthritis.²⁰ This has made it difficult to attain proper coronal alignment and correct implant positioning in TKA because the tibial anatomical axis does not align with the tibial mechanical axis.²¹ Extra-articular tibia vara is often mild and amenable to correction during TKA by bone cutting or releasing ligament intra-articularly. Ritter and Faris²² suggested that any deformity could be corrected intra-articularly with careful attention to ligamentous instability. But in severe extra-articular tibia vara, correction by intra-articular bone cutting requires extensive resection on the lateral side, which may induce laxity.²³

A postoperative HKA that deviates more than 3° from neutral correlates with worse functional outcome and prosthesis survival.²⁴ Saibaba et al.⁶ have reported that extra-articular tibia vara measured by MDA is associated with abnormal postoperative HKA (beyond 180° ± 3°) when MDA is above 4° with a sensitivity of 78.1%, specificity of 62.5%, and p value of 0.03. This was why our study divided MDA by 4°.

We used MDA to measure tibia extra-articular vara, but there were other ways to measure that. Ko et al.²⁵ used the angle between the tibial anatomical axis and mechanical axis. Yau et al.²⁶ proposed the angle formed between the midmedullary lines of the proximal and distal thirds of the tibial diaphysis. Chiu et al.²⁷ used the angle between the midmedullary lines of the proximal and distal halves of the tibial diaphysis. But Saibaba et al. reported that MDA showed the most positive correlation with expected tibial varus angulation (HKA − (femoral varus + joint line convergence angle)).

The conclusion of this study is that postoperative HKA is not significantly different between CAS-TKA and conventional TKA in extra-articular tibia vara even if MDA is above 4°. Although CAS-TKA can help the operator to correct postoperative HKA, correction of the HKA is completed intra-articularly by measured resection and ligament balancing. Mullaji et al.¹¹ found no significant difference in the postoperative HKA with varus exceeding 20° between conventional TKA group and CAS-TKA group.

The interesting point was that CAS-TKA showed significantly positive correlation between preoperative and postoperative HKA although there was no significant correlation in the conventional TKA. In the conventional TKA, without considering the preoperative HKA, the distal femur was resected valgus 6° to femur anatomical axis and proximal tibia was resected 90° to tibia anatomical axis. But in CAS-TKA, cutting was based on preoperative HKA which is registered on the computer, so it is assumed that correlation occurred in this process.

This study has some limitations. First, the evaluation of cases was retrospective. Since the type of surgical method was determined by surgeon’s choice, the subjective preference of the surgeon was involved inevitably. Thus, there was unavoidable selection bias. Second, only radiologic outcomes in a single coronal plane were evaluated. Subsequent studies that deal with clinical outcomes and measurements in a sagittal plane are needed. Third, according to patients’ posture and flexion contracture, measurement error of radiological parameter of simple X-ray might have occurred. Therefore, high-quality randomized controlled trial studies are needed in the future to overcome these limitations.

Conclusions

There is no statistical difference in postoperative alignment between conventional TKA and CAS-TKA for extra-articular tibial vara even in cases with MDA >4°.

Footnotes

Declaration of conflicting interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Jai Hyung Park

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