International Orthopaedics (SICOT) DOI 10.1007/s00264-017-3509-z

ORIGINAL PAPER

Clinical, radiological and survivorship results after ten years comparing navigated and conventional total knee arthroplasty: a matched-pair analysis Clemens Baier 1 & Jochen Wolfsteiner 1 & Franziska Otto 1 & Florian Zeman 2 & Tobias Renkawitz 1 & Hans-Robert Springorum 1 & Günther Maderbacher 1 & Joachim Grifka 1

Received: 12 November 2016 / Accepted: 7 May 2017 # SICOT aisbl 2017

Abstract Purpose Our aim was to compare the long-term outcome between navigated and conventional total knee arthroplasty (TKA), which is currently not known. Methods Long-term survivorship, clinical scores and radiographic results of a matched-pair group of 350 patients (350 knees) treated with navigated (n = 157) or conventional (n = 188) TKA for osteoarthritis over a period of 11 years were reviewed retrospectively. Results The mean clinical follow-up was ten years. There were no clinically relevant differences with respect to any clinical outcome, patient satisfaction or pain between the two groups. Coronal leg alignment was closer (1.7-3.1°) to the neutral mechanical axis in the navigated group compared with the conventional group (2.6-4.7°). A total of 12 knees (6.4%) in the conventional group and three (1.9%) in the navigated group underwent revision surgery (p = 0.04), resulting in an absolute risk reduction of 4.5% for revision surgery by using navigation. Using any revision as an end point, the tenyear Kaplan-Meier survivorship was 98.1% in the navigated and 92.5% in the conventional group. Conclusions Navigated TKA improves implant survivorship compared with conventional TKA.

* Clemens Baier [email protected]

1

Orthopaedic Department, University Hospital Regensburg, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany

2

Centre for Clinical Studies, University Hospital Regensburg, Regensburg, Germany

Keywords Long-term results . Navigated total knee arthroplasty

Introduction Primary total knee arthroplasty (TKA) is one of the most commonly performed and high-cost procedures in orthopaedic surgery [1]. Current studies have demonstrated implant survival rates of 90% at 15 years and 82% at 22 years after TKA [2, 3]. At the same time, the number of revision surgeries after TKA is rising worldwide [4, 5]. The longevity of implants depends on many factors: surgical ones [6] which imply exact implant alignment [7] and restoration of a neutral mechanical axis [8, 9]. Various authors have emphasised the correlation between malalignment and early implant failure in TKA [6, 10–12]. Others have found no association between component alignment and outcomes [13]. The use of imageless navigation systems has been shown to increase the accuracy of component alignment [8, 14], provides for lower blood loss [15], and some studies have also reported about improved clinical outcomes [16] and fewer total adverse events within the first years after surgery [17]. To date, there is no evidence of an advantage of navigation technique concerning knee function, patient satisfaction and revision surgery compared with conventional technique. First published long-term results comparing both methods show heterogeneous data concerning clinical outcome and revision rates [2, 16–19]. We undertook a blinded and prospective, single-centre matched-pair study to assess whether the use of navigated TKA would lead to improved clinical outcomes, precise component alignment and increased implant survivorship compared with results obtained with conventional TKA.

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Materials and methods Sample size The study design, procedures and consent were approved by our local medical ethics committee (12–101-0147). Analysis of the hospital’s database showed that a total of 2,197 patient received TKA between 2000 and 2005 by seven experienced orthopaedic surgeons. In 1,234 patients, surgery was performed with the conventional jig-based technique (CON) and in 963 patients with the help of an imageless navigation system [computer-aided surgery (CAS)]. All patients with osteoarthritis of the knee that received primary TKA with the same condylar, cruciate-retaining prosthesis during that timeframe were included in our analysis. We excluded patients who were not eligible for follow-up. Thus, 188 remained in the CON group and 157 in the CAS group. To get a sufficient power for the analyses, we aimed to include 75 patients per group for clinical and radiological follow-up. Patients were matched by age and sex. Data of revision surgery was ascertained of all primarily included patients, 188 of the conventional and 157 of the CAS group. Surgical treatment All patients received a standard, cemented condylar prosthesis, cruciate-retaining with fixed platform (PFC Sigma; DePuy, Warsaw, USA). All procedures were performed by seven experienced surgeons (>500 TKAs) being familiar with the two imageless navigation systems used (Vector Vision and Ci Knee, Version 1.0; BrainLab, Feldkirchen, Germany/Depuy Orthopaedic, Johnson and Johnson, Warsaw, IN, USA). Both systems were based on the same software and algorithms for calculating the mechanical leg axis and leg alignment. All TKA surgeries were started through a standard midline incision with a medial parapatellar arthrotomy. In the navigated group, after exposing the knee, two passive optical reference arrays were attached on the medial distal femur and the medial proximal tibia. An optical tracking unit with an infrared camera detected these arrays. After approval of the required anatomical landmarks the software calculated the mechanical axes of femur and tibia in coronal and sagittal planes [10]. The surgical technique was based on a tibia-first approach according to the navigation target (postoperative leg axis) in a gapbalancing technique. In the CON group, the surgical technique was based on a femur-first approach with measured resection technique. Intramedullary alignment guides for the femoral cuts and extramedullary instrumentation for the tibial alignment were used. Following the hospital’s standard guidline, all surgeons aimed to restore a neutral mechanical axis of the leg. In both

groups, no patella prostheses were used. A patelloplasty— removing osteophytes and sclerosis—was performed in all knees. All patients received the same post-operative treatment and rehabilitation with full weight-bearing. Clinical measurement tools For the post-operative clinical examination, the validated Knee Society Score [29], the WOMAC score [30] were used. Possible knee pain was measured with a visual analogue scale (0 = no pain; 10 = greatest possible pain). Complications or revision surgery were registered and the specific procedure of knee revision intervention was verified by checking the documentation from surgery. All follow-up examinations were performed by a blinded observer. Radiographic evaluation of component and patellar alignment At latest follow-up, standard radiographs (long-leg weightbearing radiography of the lower extremity with the patient in standing position, knee in sagittal plane with flexed knee of 60° and anteroposterior as well as the sunrise view in knee flexion of 45° [20]) were performed. The following parameters were assessed: In long-leg radiographs the mechanical axis (α) and the coronal femoral (β)/tibial component alignment (γ) were measured according to the Knee Society Radiological Score [6, 21] (Fig. 1a and b). The deviation from the ideal value as well as the type of deformity (varus/valgus) was quoted. In the sagittal plane the sagittal femoral component angle (δ) and the tibial slope (ε) were evaluated (Fig. 1c). The patella tilt (π) and shift were analysed on the sunrise view (Fig. 2a and b). Radiographs were examined for osteolysis or radiolucent lines and evaluated in terms of location. All measurements were made by an independent observer and determined by a medical planning software program MediCAD® (Hectec, Altfrauenhofen, Germany). Five patients of the CAS group had to be excluded from the radiological measurements due to extra-articular deformities. Statistical analysis Calculation of the study results and statistical evaluation were performed at the Centre for Clinical Studies at the corresponding university. Data were presented as mean and standard deviation (SD) or as a median, together with the interquartile range (IQR) for continuous variables or as numbers and percentages for qualitative variables. Our primary endpoint was implant survivorship. Secondary endpoints were clinical outcomes and component alignment. Differences of the clinical and radiographic results between the CON and CAS group

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Fig. 1 a Radiological mechanical axis. The mechanical axis (α) is the connecting line between the centre of the femoral head, notch of femoral component and ankle centre; ideal value α = 180°; angle <180° indicates valgus, >180° indicates varus. b Coronal femoral and tibial alignment. The coronal femoral component alignment (β) is measured as the angle between the line from the femoral head centre to the centre of the distal femur and a line parallel to the femoral condyles; ideal value = 90°. The coronal tibial component alignment (γ) is measured as the angle between the line from the centre of the ankle to the centre of the proximal

tibia and a line along the tibial component’s plateau; ideal value = 90°. c Sagittal femoral and tibial alignment. The sagittal femoral component angle (δ) is measured as the angle between the frontal femoral cortex and the inner frontal part of the femoral component [22]. In addition, 5° was subtracted as a correction parameter for the prosthesis having an aperture angle of 95°. This angle expresses the degree of femoral component flexion; ideal value = 0°. The sagittal tibial slope (ε) is measured as the angle between the posterior tibial cortex and the plateau of the tibial component; ideal value = 90°

were analysed using the Mann-Whitney U test. The subgroup of patients with both operation techniques was analysed using the Wilcoxon signed-rank test. Differences in time to revision surgery were analysed using a log-rank test. Differences of p < 0.05 were considered statistically significant. Box plots were used to visually summarise the differences of the WOMAC score and the Knee Society score between both groups. The box height is the interquartile range which represents 50% of all values. Twenty-five percent of the measured values are above and 25% of values are below the box. The median is represented by a horizontal line across each box. The minimum and maximum values are shown as vertical lines. Evidence-based medicine measures of therapeutic effects in terms of relative and absolute risk reductions were

calculated for implant survivorship. The number needed to treat (NNT) as a measure of risk and benefit in considering the consequences of navigated or conventional TKA was also calculated. All analyses were performed using R, version 3.2.1 (The R Foundation for Statistical Computing).

Results The mean age of patients in the computer-assisted group was 75.6 years and 75.0 years in the conventional group. Twothirds of the patients in each group were female. Mean follow-up was ten years (9.2–10.8 years).

International Orthopaedics (SICOT) Fig. 2 a Patella tilt. The patella tilt (π) is the angle between the transverse axis of the patella and the anterior intercondylar line. The patellar transverse axis is defined as the line between the medial and lateral patellar corners; ideal value = 0° [23]. b Patella shift. The patella shift is the distance between deepest point of the trochlear groove and the lowest point of the articular ridge of the patella; ideal value = 0 mm [24, 25]

Clinical results Ten years after surgery, we found comparable score results between the CAS and CON groups. Table 1 presents a detailed overview of the results from the clinical data ten years after surgery. No statistical significant differences were detected between both groups concerning the Knee Society Score (see Fig. 3) besides the range of motion (ROM) of the Knee Score. Concerning the WOMAC score significant differences relating to stiffness could be detected between both groups (see Table 1). Pain, Activity and total WOMAC score did not show any significant differences between CAS and CON (see Fig. 4). Radiographic results The mean deviation from the neutral mechanical axis was 1.7° ± 1.4° in the CAS group and 2.6° ± 2.1° in

Table 1

the conventional group. With a p = 0.006 these results showed significant lower deviation from the mechanical axis in the CAS group. Regarding femoral frontal component alignment the mean deviation value for the computer-assisted patients was 1.9° ± 1.5° and 2.3° ± 1.6 for the CON group. There was a significant difference between both groups (p = 0.049). Concerning tibial frontal component alignment the mean deviation value for the CAS group was 1.5° ± 1.2 and 1.8° ± 1.4 for the conventional group. The difference was not significant (p = 0.229). The femoral sagittal component alignment in the CAS group was 3.8° ± 2.6° and 4.6° ± 3.3° in the CON group (p = 0.115). The tibial sagittal component alignment in the CAS group was 2.7° ± 2.3° and 2.9° ± 2.1° in the CON group (p = 0.395). The rotation of the femoral component in the CAS group was 4.2° ± 3.3° externally and 3.2° ± 0.7° externally in the CON group (p = 0.030).

Comparison between the CAS (computer-aided surgery) and CON (conventional) group regarding Knee Society Score and WOMAC score Knee Society Score

CAS CON p value

WOMAC

Pain

ROM

Stability

Total

43.07 (10.37) 42.67 (10.57) 0.695

22.76 (2.08) 21.93 (2.18) 0.021

20.29 (5.41) 19.84 (4.70) 0.382

85.97 (12.88) 85.07 (13.37) 0.633

Data shown are mean (SD) ROM range of motion

Functional score 73.93 (21.46) 74.87 (22.48) 0.576

Pain

Stiffness

Activity

Total

5.17 (7.48) 3.69 (4.25) 0.755

1.88 (3.58) 0.38 (1.71) 0.039

23.6 (26.93) 20.12 (23.99) 0.414

30.66 (35.61) 24.56 (27.49) 0.372

International Orthopaedics (SICOT) Fig. 3 Knee Society Score of the CAS (computer-aided surgery) and CON (conventional) groups

Average patella tilt value was 4.4° ± 4.2° in the CAS group and 4.5° ± 4.3° in the CON group (p = 0.920). The mean patella shift was 7.9 mm ± 4.4 mm in the CAS group and 8.2 mm ± 4.1 mm in the CON group (p = 0.619). Implant survivorship There were 15 (4.4%) revision surgeries, three (1.9%) in the navigated TKA group and 12 (6.4%) in the conventional TKA Fig. 4 WOMAC score of the CAS (computer-aided surgery) and CON (conventional) groups

group. Considering these event rates in both goups, we calculated a relative risk reduction of 70.3% and an absolute risk reduction of 4.5% for revision surgery by using navigation. These numbers result in a number needed to treat (NNT) of 22, which means that 22 patients need to be treated by navigated TKA to prevent one patient from having revision surgery over an average of 10 years. The reasons for revision surgery within the navigated TKA group were aseptic loosening (two patients, 1.3%) and postoperative late infection (one patient, 0.6%). One of these

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patients was treated by complete prosthesis replacement surgery, another patient was treated with replacement surgery only of the tibial component and the third was treated with explantation, temporary spacer implantation and after ruling out infection reimplantation of a constrained implant. All three patients showed a neutral leg alignment after the initial procedure. The reasons for revision surgery within the conventional TKA group were aseptic loosening (five patients, 2.7%), late infection (two patients, 1.0%), instability (three patients, 1.6%) and anterior knee pain (two patients, 1.0%). Seven of these patients were treated by complete prosthesis replacement surgery, two patients underwent patelloplasties based on patellar malalignment or anterior knee pain and in three cases the PE insert had to be replaced due to instability. Two of the patients that were revised due to aseptic loosening and one of the patients that were revised due to instability showed a deviation from the neutral mechanical axis. A further analysis of the mechanical failures (instability, three patients; anterior knee pain, two patients) revealed the following results: The first patient was a 71-year-old lady who was diagnosed with medial instability and malrotation of the tibial component. After ruling out infection with punctuation, the tibial component was removed and a higher-grade polyethylene replacement inserted. All measured radiological parameters were within the normal range. The second patient was a 66-year-old man who was diagnosed with both medial and lateral instability. After ruling out infection with punctuation, a higher-grade polyethylene replacement component was inserted. All measured radiological parameters were within the normal range. The third patient was a 71-year-old lady who was diagnosed with lateral instability and a slight deviation from the neutral mechanical axis (4.8° varus). After ruling out infection with punctuation, a higher-grade polyethylene replacement component was inserted. Due to the small axis deviation, we spared a complete prosthesis replacement. The fourth patient was a 67-year-old man who was diagnosed with anterior knee pain due to a slight extension deficit. After ruling out infection with punctuation, we performed a patelloplasty and a dorsal capsular release. All measured radiological parameters were within the normal range. The fifth patient was a 70-year-old man who was diagnosed with anterior knee pain due to a high patella shift (10.2 mm). After ruling out infection with punctuation, we performed a patelloplasty with a medial capsular augmentation. Besides patella shift, all other measured radiological parameters were within the normal range.

The revision rate in the CAS group was significantly lower than in the CON group (p = 0.04). The ten-year survival rate according to Kaplan-Meier was 98.1% in the CAS group and 92.5% in the CON group (see Fig. 5).

Discussion The results of this trial indicate that the revision rate was significantly lower within the navigated TKA group. There was a statistically significant but clinically insignificant improvement for ‘clinical’ ROM testing in flexion in the navigated group. We were unable to identify any differences in the clinical outcomes between the two groups. During the last decade, computer navigation in TKA has been proved to enhance the accuracy of mechanical axis’ restoration and placement of components by many authors [8, 14]. At the same time, several studies were unable to find any significant advantage for the use of navigation systems during TKA at short and mid-term follow-up [23, 24]. At the same time, disadvantages of computer-assisted surgery, such as longer operation times and high acquisition costs, as well as the rare risk of fractures and infections around the navigation pins, are mentioned in many major studies. In a recent meta-analysis, Xie et al. [25] detected an extended surgical time of 14 minutes for navigation–based TKA. So far very few long-term data about the clinical and radiological impact of navigated surgery exist in literature. To our best knowledge, this ten-year follow-up is the first study to publish long-term implant survival, clinical and radiological results. Concerning radiological parameters, our results could demonstrate significantly better alignment and component positioning in the CAS group, verifying the results of many short- and mid-term studies [8, 14]. Our radiological results did not reveal significant differences of patellar shift and tilt between the two groups. This, however, is only a non-scaled radiological analysis of non-weight-bearing radiographs in just one more or less fixed position of the knee (joint flexion of 45°). Generally, TKA is a very successful surgical procedure. In this study, highly experienced surgeons used a successful condylar implant in the setting of a high-volume centre for total joint arthroplasty. Future studies could use a multicentre approach with different levels of experience and different implants. This might better discriminate any influence on clinical outcome of computer-assisted navigation in TKA. These results are supported by DeSteiger et al. [19] and Schnurr et al. [17]. DeSteiger et al. analysed the Australian

International Orthopaedics (SICOT) Fig. 5 Kaplan-Meier survivorship curve of CAS and CON groups

implant registry and found out that computer navigation reduced the overall rate of revision in patients less than 65 years of age. They included data of approximately 310,000 patients after TKA; among them, approximately 45,000 with navigated TKA [19]. Schnurr et al. [17] showed lower revision rates after navigated TKA in a mid-term follow-up of two to four years in a retrospectively analysed cohort of 1,054 patients. A reason for the lower revision rate in the CAS group might be the restoration of limb axis [10], resulting in less abnormal wear and thus not inducing aseptic loosening. Furthermore we believe that this reduces peak loads, especially on the patella, resulting in less anterior knee pain. As a matter of fact, we had no revision in the CAS group due to anterior knee pain and patellar problems, whereas in the CON group two patients had to be revised due to this pathology. Schnurr et al. [17] highlight this with a significant lower revision rate for navigated TKA compared with conventional TKA, mainly due to a significantly reduced rate of aseptic implant loosening after 2.4 years of follow-up. Recent developments as hand-held or pinless navigation [26, 27] can help to facilitate computer-aided surgery and could enhance distribution of navigated TKA. Still, manual

cutting guides can introduce a systematic error resulting in malaligned components [28]. An inherent limitation of our study was that this was not a prospective, randomised, controlled comparison between navigated and conventional TKA. In addition, some relevant variables, such as preoperative ROM and body mass index were not collected consistently and, therefore, could not be included in this matching exercise; thus, we cannot exclude the possibility that there was an imbalance between the two groups for certain prognostic factors. Second, seven surgeons performed the procedures. Although all of them were very experienced with TKA and familiar with the navigation technique, this might result in some bias. Third, we cannot exclude an inaccuracy of the radiological measurements, although our results highlight established data with improved leg alignment after navigated TKA [8]. In conclusion, navigated TKA increases implant survivorship 10 years after surgery. Radiological frontal and coronal component alignment was closer to a neutral mechanical axis. However, concerning clinical function, we were not able to show significant differences between CAS and CON TKA.

International Orthopaedics (SICOT) Acknowledgements The above-mentioned data are part of the dissertation of Mrs. Franziska Otto.

14.

Compliance with ethical standards All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.

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Conflict of interest All authors declare that they have no conflict of interest. On behalf of all authors, the corresponding author states that there is no conflict of interest.

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