Orthopedics

Feature Article 

Navigation-Assisted Total Knee Arthroplasty for a Valgus Knee Improves Limb and Femoral Component Alignment

Sung-Sahn Lee, MD; Kyeu-Back Kwon, MD; Yong-In Lee, MD; Young-Wan Moon, MD, PhD

Abstract

The purpose of this study was to evaluate the influence of navigation-assisted surgery on radiographic and clinical outcomes after total knee arthroplasty (TKA) for a valgus knee. The authors identified all patients who underwent TKA for a valgus knee between January 2005 and December 2015. Among 83 conventional TKA cases and 55 navigation-assisted TKA cases, propensity score matching was performed for age, sex, body mass index, and preoperative lower limb mechanical axis. Fifty knees were matched to 50 knees. Each case was evaluated regarding lower limb mechanical axis, mechanical lateral distal femoral angle, medial proximal tibial angle, patellar tilt angle, Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society score, and range of motion. Lower outliers of lower limb mechanical axis (30% vs 8%, P=.008) and mechanical lateral distal femoral angle (24% vs 10%, P=.046) were found in navigation-assisted TKA. However, outliers of medial proximal tibial angle, Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society score, and range of motion were similar between the 2 different surgical techniques. Navigation-assisted surgery is correlated with fewer outliers of postoperative lower limb alignment and femoral component position but not tibial component position in TKA for preoperative valgus knee. Clinical outcomes for navigation-assisted TKA were not superior to those for conventional TKA. [Orthopedics. 2019; 42(2):e253–e259.]

Abstract

The purpose of this study was to evaluate the influence of navigation-assisted surgery on radiographic and clinical outcomes after total knee arthroplasty (TKA) for a valgus knee. The authors identified all patients who underwent TKA for a valgus knee between January 2005 and December 2015. Among 83 conventional TKA cases and 55 navigation-assisted TKA cases, propensity score matching was performed for age, sex, body mass index, and preoperative lower limb mechanical axis. Fifty knees were matched to 50 knees. Each case was evaluated regarding lower limb mechanical axis, mechanical lateral distal femoral angle, medial proximal tibial angle, patellar tilt angle, Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society score, and range of motion. Lower outliers of lower limb mechanical axis (30% vs 8%, P=.008) and mechanical lateral distal femoral angle (24% vs 10%, P=.046) were found in navigation-assisted TKA. However, outliers of medial proximal tibial angle, Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society score, and range of motion were similar between the 2 different surgical techniques. Navigation-assisted surgery is correlated with fewer outliers of postoperative lower limb alignment and femoral component position but not tibial component position in TKA for preoperative valgus knee. Clinical outcomes for navigation-assisted TKA were not superior to those for conventional TKA. [Orthopedics. 2019; 42(2):e253–e259.]

The influence of coronal alignment on implant survivorship and patient satisfaction after total knee arthroplasty (TKA) are of great interest to orthopedic surgeons. Several studies have shown that placing implant components within 3° of the mechanical axis is correlated with a lower rate of component loosening and early implant failure.1–4 Navigation-assisted TKA has been introduced for accurate surgery and reportedly reduces lower limb mechanical axis (MA) and implant positioning outlier rates for the femoral and tibial components.5–8 However, whether clinical outcomes are improved compared with those of conventional jig-based TKA remains unclear.9–12

Total knee arthroplasty for a valgus knee is a challenge because of different bony and soft tissue abnormalities.13,14 When achieving neutral alignment, the distortion of the distal femur anatomy and bony canal leads to improper limb and femoral component alignment, and early studies reported full restoration of the anatomical axis in 70% to 78% of valgus knees.15,16 On careful review of the literature, however, few clinical studies have compared navigation-assisted surgery with the conventional technique for a valgus knee.

Therefore, the purpose of the current study was to compare postoperative limb alignment, component position, and clinical outcomes between the conventional jig-based technique and the navigation-assisted technique for TKA for a valgus knee. The authors hypothesized that navigation-assisted TKA would result in fewer outliers of postoperative limb alignment and femoral component positioning.

Materials and Methods

This study was a retrospective review of prospectively collected data; the authors reduced the variability of the preoperative demographics and lower limb MA using propensity score matching. Data collected from 2587 consecutive TKAs performed between January 2005 and December 2015 were reviewed. All patients who had preoperative valgus deformity with lateral compartment arthritis were included in the study, resulting in 210 TKAs. From these, patients were excluded if (1) preoperative radiographs or clinical scores were unavailable or inadequate, (2) the follow-up period was shorter than 24 months, (3) they had received a constraint-type implant, or (4) they had received concurrent corrective osteotomy because of an extra-articular deformity. After applying the exclusion criteria, 83 knees (72 patients) remained for conventional jig-based TKA and 55 knees (50 patients) remained for navigation-assisted TKA (Figure 1). Propensity score matching was performed using matched variables of age, sex, body mass index, and lower limb MA. After propensity score matching, 50 knees were enrolled in each group, and all variables were successfully matched (Table 1). The preoperative Western Ontario and McMaster Universities Osteoarthritis Index,17 Knee Society score,18 and range of motion (ROM) were not significantly different between the conventional and navigation-assisted groups. Mean follow-up was 60.5 months and 59.0 months in the conventional and navigated groups, respectively. Five knees were diagnosed with rheumatoid arthritis in each group, and 90 knees were diagnosed with osteoarthritis. This study received institutional review board approval.

Flow chart describing patient enrollment in the study. Abbreviation: TKA, total knee arthroplasty.

Figure 1:

Flow chart describing patient enrollment in the study. Abbreviation: TKA, total knee arthroplasty.

Patient Characteristics Before and After Propensity Score Matching

Table 1:

Patient Characteristics Before and After Propensity Score Matching

Surgical Techniques

All surgical procedures were performed by 1 experienced surgeon (Y.W.M.) using posterior cruciate ligament–sacrificing implants. Three types of prostheses were used: Scorpio NRG (Stryker, Mahwah, New Jersey; 41 knees from the conventional group), LPS (Zimmer-Biomet, Warsaw, Indiana; 9 knees from the conventional group), and Columbus (B. Braun Aesculap, Tuttlingen, Germany; 50 knees from the navigation group). The patients chose the surgical method after complete explanation of the advantages and disadvantages of the 2 techniques. The cost of using navigation was not reimbursed due to the national health insurance program.

The operations were performed with the use of a tourniquet following a single dose of antibiotics. Use of a median skin incision, medial parapatellar arthrotomy, and omission of patellar resurfacing were the same in the 2 groups. To obtain a rectangular gap, soft tissue release was performed after proximal tibial and distal femoral resection in some instances, as described in previous studies.19,20 First, the iliotibial band was released; the posterolateral corner was also released, if necessary. The popliteus tendon was preserved as far as possible. In the conventional jig-based TKA procedure, the anterior and posterior cruciate ligaments were removed; then, a distal femoral resection was performed using an intramedullary cutting guide. The intramedullary rod for the distal femoral cut was inserted at an angle of 3° to 6° of valgus based on the preoperative radiograph.19,21 Proximal tibial cutting using an extramedullary guide followed. The initial registration process was completed in the navigation-assisted TKA procedure using an image-free device (OrthoPilot; B. Braun Aesculap). Both anterior and posterior cruciate ligaments were then removed, and proximal tibial and distal femoral cutting were performed in a plane perpendicular to the MA of the tibia and femur. Femoral component rotation was determined using a navigation system, and anterior and posterior femoral bone cutting were then performed. The femoral and tibial components were cemented.

To avoid peroneal neuropraxia, knees were placed in a position of 30° of flexion until ROM exercises commenced. All patients began active and passive ROM exercises on the second day postoperatively.

Radiographic and Clinical Assessment

The preoperative and final follow-up whole-leg radiographs with the patella oriented in a forward-facing position were analyzed and measured. Pre- and postoperative lower limb MA measured mechanical axis deviation between the femur and the tibia using a whole-leg radiograph (Figure 2). The mechanical femoral axis was defined as the line connecting the center of the hip with the midpoint of the widest dimension of the distal femur. After TKA, the midpoint of the femoral component replaced the midpoint of the widest dimension of the distal femur. The mechanical tibial axis was defined as the line connecting the center of the tibial spines to the center of the talus. After TKA, the mechanical tibial axis was determined using the line connecting the center of the polyethylene insert to the center of the talus.22–24 A positive value indicated a valgus deformity. To investigate implant position in the coronal plane, the mechanical lateral distal femoral angle (mLDFA) and the mechanical medial proximal tibial angle (mMPTA) were measured (Figure 3). The mLDFA was the lateral angle between a line parallel to the femoral component condyles and the MA of the femur. The mMPTA was the medial angle between a line parallel to the tibial component and the anatomical axis of the tibia. The outlier of lower limb MA was defined as more than 3° or less than −3°. The outlier of component position (mLDFA, mMPTA) was defined as more than 93° or less than 87°, as defined in a previous study.25 The patellar tilt angle was defined as the angle between the line from one corner of the patella to the other and the line connecting the anterior limits of the femoral condyles or femoral component.26 A positive value indicated opening toward the medial side of the patella. The above variables were measured using a picture archiving and communication system (Centricity; General Electric, Chicago, Illinois). The radiographs were evaluated by 2 independent orthopedic surgeons (K.B.K., Y.I.L.) for interobserver reliability. Two observers performed the measurements twice at intervals of 6 weeks to ensure intraobserver reliability.

Measurement of lower limb mechanical axis preoperatively (A) and postoperatively (B).

Figure 2:

Measurement of lower limb mechanical axis preoperatively (A) and postoperatively (B).

Measurement of mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA).

Figure 3:

Measurement of mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA).

Clinical assessments including Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society score, and ROM were evaluated preoperatively and at final follow-up. Postoperative lower limb MA, mLDFA, mMPTA, patellar tilt angle, clinical outcomes, and ROM were compared for the 2 different surgical techniques.

Statistical Analysis

The authors performed a power calculation to detect a difference of alignment of 1°, with a standard deviation of 2.8° as in previous studies.25,27 This study had a power of 97.1%, with a 2-sided alpha set at 0.05 by using post hoc analysis. The interobserver and intraobserver reliabilities for alignment measurement were evaluated with intraclass correlation coefficients. The paired t test was used to compare alignment parameters, clinical outcomes, and ROM. The chi-square test was used to compare outliers of alignment parameters. Statistical analyses were performed using SPSS version 22 software (SPSS, Chicago, Illinois). Statistical significance was set at P<.05.

Results

All interobserver and intraobserver intraclass correlation coefficients showed good agreement for lower limb MA, mLDFA, and mMPTA reliability (Table 2). Mean postoperative lower limb MA, mLDFA, mMPTA, and patellar tilt angle were not different between conventional and navigated TKA techniques. However, not only were lower limb MA outliers greater in conventional TKA (15 knees, 30%) than in navigation-assisted TKA (4 knees, 8%; P=.008), but outliers of mLDFA were also higher in conventional TKA (12 knees, 24%, vs 5 knees, 10%; P=.046). There were only 2 mMPTA outliers in conventional TKA and 3 in navigation-assisted TKA. Clinical outcomes including Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society knee score, Knee Society function score, and postoperative ROM were similar between the 2 different surgical techniques (Table 3). No knees were revised or considered for revision during follow-up.

Interobserver and Intraobserver Intraclass Correlation Coefficients

Table 2:

Interobserver and Intraobserver Intraclass Correlation Coefficients

Postoperative Radiographic and Clinical Outcomes for the 2 Surgical Techniques

Table 3:

Postoperative Radiographic and Clinical Outcomes for the 2 Surgical Techniques

Discussion

The most important finding of the current study was that navigation-assisted TKA for a valgus knee leads to fewer lower limb MA and femoral component position outliers. However, tibial component position outliers and clinical outcomes were similar to those in conventional jig-based TKA.

Total knee arthroplasty is not always successful. The factors associated with implant failure include inaccurate correction of lower limb MA and poor implant positioning.1,8,28 It has been proven that navigation-assisted TKA improves alignment in TKA.5–8,29 To the authors' knowledge, only 1 institution, in Taiwan, has compared navigation-assisted and conventional techniques using TKA for a valgus knee.21,27,30 In the study27 that enrolled the most patients (conventional, 36 knees; navigated, 34 knees), the navigation-assisted technique was reportedly not superior regarding limb and component alignment. This is in contrast to the current study (lower limb outliers, conventional vs navigated, 30% vs 8%; P=.008). During TKA for a valgus knee, special consideration is needed because of bony deformities such as lateral femoral condylar hypoplasia and metaphysealdiaphyseal valgus.19,20 Some studies have suggested distal femur cutting in cases with less valgus to the anatomical axis, as opposed to the typical 5° to 7° of valgus, to prevent undercorrection of the characteristic deformity. Recent studies have suggested that a pre-set intramedullary femoral guide should be determined based on severity of deformity rather than using a fixed setting of 3° of valgus.19,21,31 According to a previous suggestion, the authors performed distal femoral cutting in conventional TKA with 3° to 6° of valgus to the anatomical axis; however, navigation-assisted distal femoral cutting led to less error than the conventional technique in the current study (mLDFA outlier, conventional vs navigated TKA, 24% vs 10%). This finding suggests that the navigation-assisted technique is more accurate than individual setting of a femoral intramedullary guide. Regarding tibial component position, few outliers were found (conventional, 4%; navigated, 6%), and significance was not found between the 2 different techniques. This was similar to a previous meta-analysis that showed relatively fewer tibial component position outliers using the conventional technique compared with femoral component or limb alignment outliers using the navigation-assisted technique (outlier rate, navigated vs conventional technique, limb alignment 13.4% vs 28.5%, femoral component 4.6% vs 15.7%, and tibial component 4.2% vs 9%).6 A tibial plateau with less deformity than the femur in a valgus knee is also a possible explanation for the results.32

Theoretically, a navigation system has the advantage of accurate soft tissue balancing and component positioning, thereby enhancing patient satisfaction.33 However, many publications have reported that although navigation-assisted TKA showed better alignment, clinical outcomes were not significantly different,7,34,35 accounting for the results in the current study. Navigation-assisted TKA also is more costly and time consuming; therefore, surgeons are hesitant to perform it.36 However, this must be offset by the potential cost savings incurred by reduced revisions if improved alignment is proven to increase survivorship.1 Novak et al37 reported that cost savings might be obtained if additional cost is $629 or less per navigated operation. In the current study, navigation-assisted TKA produced better alignment outcomes for valgus knees. Navigation-assisted TKA for a valgus knee might have the potential advantages of lower revision rate and cost-effectiveness.

This study had several limitations. First, 3 different TKA implants were used, and the distribution ratio of these prostheses was different in the 2 groups. The heterogeneity of the TKA implants in the 2 groups might have reduced the validity of the comparative results of clinical outcomes. However, all surgeries were performed by a single surgeon (Y.W.M.), and there were no significant differences in clinical outcomes between the various implants.38,39 Moreover, the main focus of the current study was limb alignment and component position. Second, this was a retrospective study, which has inherent limitations and biases. However, the authors minimized the differences in preoperative characteristics and alignment by using propensity score matching. Third, this study did not have long-term follow-up, and the longevity of TKA could not be assessed. A long-term study is needed to determine the clinical relevance of postoperative limb malalignment and its effects on implant survival in TKA for a valgus deformity. Fourth, only plain radiographs were evaluated before surgery. Computed tomography can assist in preoperative planning, especially in conventional jig-based femoral cutting.40,41 However, because computed tomography generates more radiation and cost, image-free navigation might be sufficient for well-aligned TKA in a valgus knee. To the authors' knowledge, despite several limitations, this was the largest cohort study to compare conventional and navigation-assisted TKA for a valgus knee.

Conclusion

The navigation-assisted technique is associated with fewer postoperative lower limb alignment and femoral component position outliers in TKA for a valgus knee. This finding suggests that navigation-assisted surgery can be recommended for preoperative valgus deformity to enhance alignment of limb and femoral components. However, tibial component outliers and clinical outcome were not different using the conventional jig-based technique.

References

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Patient Characteristics Before and After Propensity Score Matching

CharacteristicConventional TKANavigated TKAP
Before propensity score matching
  Knees, No.8355
  Age, mean±SD, y69.7±9.566.4±5.8.052
  Body mass index, mean±SD, kg/m225.3±3.726.8±3.8.053
  Sex, M:F, No.15:6810:45.839
  MA of lower limb, mean±SD7.6°±7.0°6.0°±4.1°.192
After propensity score matching
  Knees, No.5050
  Age, mean±SD, y66.6±6.966.4±5.8.906
  Body mass index, mean±SD, kg/m226.4±3.926.8±3.8.878
  Sex, M:F, No.9:419:411.000
  MA of lower limb, mean±SD6.6°±5.3°6.6°±4.2°.993
  Patellar tilt angle, mean±SD7.0°±5.4°6.0°±3.4°.366
  WOMAC Index57.7±12.457.8±13.4.910
  Knee Society score, mean±SD102.1±15.6103.1±15.7.816
  Range of motion, mean±SD119.0°±24.7°121.4°±19.2°.677
  Follow-up, mean±SD, mo60.5±24.859.0±23.5.819

Interobserver and Intraobserver Intraclass Correlation Coefficients

ReliabilityIntraclass Correlation Coefficient

Limb AlignmentFemoral ComponentTibial Component
Interobserver
  First measurement0.8910.8160.843
  Second measurement0.8230.8190.905
Intraobserver
  Surgeon 10.9560.8870.936
  Surgeon 20.9330.9370.917

Postoperative Radiographic and Clinical Outcomes for the 2 Surgical Techniques

OutcomeConventional TKA (n=50)Navigated TKA (n=50)P
Mechanical axis of lower limb, mean±SD2.2°±3.4°1.1°±2.1°.101
Outlier of mechanical axis, No.15 (30%)4 (8%).008
mLDFA, mean±SD89.9°±2.9°90.3°±1.8°.476
Outlier of mLDFA, No.12 (24%)5 (10%).046
mMPTA, mean±SD90.2°±1.8°89.6°±1.8°.108
Outlier of mMPTA, No.2 (4%)3 (6%)1.000
Patellar tilt angle, mean±SD7.4°±4.0°7.8°±3.2°.682
WOMAC Index, mean±SD9.5±8.410.2±6.4.689
Knee Society knee score, mean±SD90.4±9.791.4±6.7.540
Knee Society functional score, mean±SD69.2±15.573.5±13.9.165
Range of motion, mean±SD134.9°±13.9°132.5°±12.9°.432
Authors

The authors are from the Department of Orthopedic Surgery (SSL), Ilsan Paik Hospital, Inje University School of Medicine, Goyangsi, and the Department of Orthopedic Surgery (KBK, YIL, YWM), Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Young-Wan Moon, MD, PhD, Department of Orthopedic Surgery, Samsung Medical Center, Sung-kyunkwan University School of Medicine, 81 Ilwon St, Gangnam-Gu, Seoul, South Korea 06351 ( ywmoon@skku.edu).

Received: March 21, 2018
Accepted: September 10, 2018
Posted Online: February 14, 2019

10.3928/01477447-20190211-02

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