Accuracy of the Precision Saw versus the Sagittal

THEKNE-02512; No of Pages 8 The Knee xxx (2017) xxx–xxx

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The Knee

Accuracy of the Precision Saw versus the Sagittal Saw during total knee arthroplasty: A randomised clinical trial Peter Z. Feczko a,⁎, Hugo J.P. Fokkenrood b, Tijmen van Assen c, Patrick Deckers d, Pieter J. Emans a, Jacobus J. Arts a a

Dept. of Orthopedic Surgery, CAPHRI Research School, Maastricht University Medical Centre, Maastricht, The Netherlands Dept. of General Surgery, Rijnstate Hospital, Arnhem, The Netherlands c Dept. of Sports Medicine, Utrecht University Medical Centre, Utrecht, The Netherlands d Dept. of Orthopedic Surgery, Zuyderland Hospital, Heerlen, The Netherlands b

a r t i c l e

i n f o

Article history: Received 22 February 2017 Received in revised form 12 July 2017 Accepted 31 July 2017 Available online xxxx Keywords: Orthopaedic saw Total knee arthroplasty Navigation Accuracy Surgery time

a b s t r a c t Background: The aim of this study was to compare the accuracy of the oscillating tip saw system (Precision Saw = PS) with the more conventional fully oscillating blade system (Sagittal Saw = SS) during computer-assisted total knee arthroplasty (CAS-TKA). Methods: A prospective, randomised, controlled trial included 58 consecutive patients who underwent primary CAS-TKA and were randomly assigned in the PS group or the SS group to compare the accuracy of both blades. The primary outcome was the difference between the intended cutting planes and the actual cutting planes in degrees (°) in two planes of both the femur and the tibia. The secondary outcome was total surgery time. Results: Tibia: In the VV-plane no significant differences were registered for the mean absolute deviation (p = 0.28). The PS was more accurate in the AP-plane (p = 0.03). Femur: The PS showed significantly fewer mean absolute deviations in the VV-plane (p = 0.03); however, the SS revealed better accuracy in the FE-plane (p = 0.04). The difference in the surgery time between the groups was not statistically significant (p = 0.45). Two outliers were measured using the SS, while seven outliers were detected using the PS. Conclusion: The Precision Saw is not proven to be overall more accurate than the Sagittal Saw. Significantly better accuracy was shown with the PS in the two cutting planes, with the exception of one cutting plane that favoured the SS. Greater number of outliers were found using the PS. Level of evidence: II © 2017 Elsevier B.V. All rights reserved.

1. Introduction Accurate postoperative alignment in all planes is an important prognostic factor in determining the durability and clinical performance of total knee arthroplasty (TKA) [1,2]. However, surgical outliers are not uncommon. Around 80% of the reported postoperative alignments were considered to be satisfactory [1,2]. Regardless of the method of implantation, a number of potential causes can lead to implant and lower limb mal-alignment. One of these potential errors is the execution of the bone cuts [3,4], Abbreviations: PS, Precision Saw; SS, Sagittal Saw; CAS-TKA, computer-assisted total knee arthroplasty. ⁎ Corresponding author at: Dept. of Orthopedic Surgery, CAPHRI Research School, Maastricht University Medical Centre, P. Debyelaan 25, 6229 HX Maastricht, The Netherlands. E-mail addresses: [email protected] (P.Z. Feczko), [email protected] (P. Deckers), [email protected] (P.J. Emans), [email protected] (J.J. Arts).

http://dx.doi.org/10.1016/j.knee.2017.07.018 0968-0160/© 2017 Elsevier B.V. All rights reserved.

Please cite this article as: Feczko PZ, et al, Accuracy of the Precision Saw versus the Sagittal Saw during total knee arthroplasty: A randomised clinical trial, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.07.018

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P.Z. Feczko et al. / The Knee xxx (2017) xxx–xxx

which can be dependent on surgical instrumentation such as cutting guides, jigs and saws used to complete the osteotomies [5]. A relatively underexposed research domain is the development and performance of saw blades [5–7]. Bone saws are available in different designs. The design that is widely used currently features a fully oscillating blade shaft (Sagittal Saw (SS thickness: 1.27 mm, length: 90 mm), Figure 1, above). A newer design features an oscillating tip powered through an internal mechanism of a stationary, hollow shaft called a Precision Saw (PS thickness: 1.33 mm, length: 90 mm) (Figure 1, beneath), which has the potential to be more accurate [8,9]. Because only the tip of the saw is oscillating, the distance between the fulcrum and the cutting edge is reduced (Figure 1). Moreover, the increased stiffness, thickness, the design of the cutting teeth (Figure 1) and the increased cutting speed might lead to enhanced control to perform the osteotomy [9]. Although no significant differences between both blades with respect to accuracy were found in a cadaveric model [5], the saw blades have never been compared in daily practice in a randomised clinical trial to investigate the above-mentioned statements. The aim of this study was to evaluate the accuracy of the Precision Saw versus the Sagittal Saw in clinical patients during computer-assisted total knee arthroplasty (CAS-TKA). Computer navigation is an ideal method for measuring the difference between the planned and resected bone cuts given its reported accuracy of one degree [10]. The primary outcome was to measure the accuracy which was defined as the absolute difference in degrees (°) between the intra-operative intended and actual performed bone resections (Figures 2 and 3) in coronal (varus/valgus = VV) and sagittal (antero-posterior = AP of the tibia or flexion/extension = FE of the femur) planes of both the proximal tibial and distal femoral cuts. The secondary outcome was the difference in surgical time using both blades and the differences in accuracy between surgeons. The hypothesis was that PS would be more accurate and would produce fewer outliers than SS. Using the PS was expected to result in less surgery time, due to less necessary corrections of the cutting planes. 2. Methods 2.1. Trial design A prospective, randomised, single-centre, controlled trial was performed that included 58 consecutive patients to compare the Precision Saw with the Sagittal Saw during primary CAS-TKA with a standard parapatellar approach. Patients with end-stage osteoarthritis of the knee were randomised to either the PS or SS group. This study was performed at the Department of Orthopaedic Surgery at Maastricht University Medical Centre (MUMC+) in the Netherlands. 2.2. Ethics Ethical approval was obtained from the local Institutional Review Board (MEC 09-4-027). 2.3. Participant selection and consent Patients were randomised (random permuted blocks of four) into either the PS group or the SS group. Randomisation was performed using sealed envelopes. Only the researchers (TA, HF) had access to the randomisation key. The envelopes were randomised and opened before each TKA procedure. The patients and the surgeon were blinded before this randomisation process. A written informed consent was obtained from all participants. Fifty-eight participants were included for the study. Standard medical care follow-up (six weeks and one year) took place postoperatively. Three experienced senior knee surgeons (PD: n = 25, PE: n = 22, PF: n = 11) performed all the surgeries. Due to the permuted blocks of four, both blades were randomised nearly equally for all surgeons.

Figure 1. Schematic of cutting motions of Sagittal (above) and Precision (beneath) Saw blades with close-up of saw blade teeth configuration.



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Figure 2. Schematic drawing of the cutting planes of the distal femur and the proximal tibia. A: FE-plane of the femur, B: AP-plane of the tibia, C: VV-plane of the femur, D: VV-plane of the tibia.

2.4. Sample size analysis Sample size estimation was performed by a power analysis based on a literature search and an interim analysis. A sample size of 30 subjects per group was calculated, based on a minimally clinical important mean difference of 0.5° and a found sigma of 0.7° with a power number of 80% and level of significance of 0.05.

2.5. Inclusion and exclusion criteria Sixty consecutive patients who had an established diagnosis of knee osteoarthritis requiring primary total knee replacement were included. Patients who were diagnosed with varying bone density due to systemic bone diseases, that is, rheumatoid arthritis (RA), severe osteoporosis and Paget's disease or abnormal bone anatomy that would affect overall outcome of the study, were excluded.

Figure 3. Navigation image of the intended cutting plane. The surgeon determined the intended femoral–tibial alignment based on the data from the navigation system before cutting. The corresponding cutting planes of the distal femur and the proximal tibia were stored in the computer navigation system and defined as the intended cutting planes.


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Figure 4. Overview of Precision and Sagittal Saw blades before (1), and directly after (2) the TKA procedure. Image of the used saw blades after the cleaning procedure (3).

2.6. Interventions (operative procedure) The aim of the operation was to achieve neutral coronal limb alignment ±2° (not more than two degrees of varus or valgus deviation from neutral limb alignment) [1] and a stable knee, defined as having a maximum 0 to three millimetres (three degree opening on the navigation screen) laxity of the collateral ligaments [11]. Patients in both groups received a cemented Scorpio or Scorpio NRG total knee prosthesis (Stryker, Kalamazoo, Michigan, USA). All operations were assisted with an image-free, active, cordless, personal computer (PC)-based computer navigation system (Precision, Stryker, Kalamazoo, Michigan, USA). After performing a medial parapatellar approach, the navigation system trackers were then attached to the surface of the femur and Please cite this article as: Feczko PZ, et al, Accuracy of the Precision Saw versus the Sagittal Saw during total knee arthroplasty: A randomised clinical trial, Knee (2017), http://dx.doi.org/10.1016/j.knee.2017.07.018


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the tibia as described in the instruction manual. The hip joint rotation centre and the centre of the knee and ankle joint were established as reference points for the leg axis. A bony referenced, tibia first technique was intended to be used. Based on the mapping of this system, cutting blocks were attached to the femur and tibia. Three sets of cutting blocks were randomly used throughout the study. The cutting blocks were only used for CAS-TKA related studies (thickness of the slots: 1.40 mm). In both types of prostheses the same distal femoral and proximal tibial cutting blocks were used. The surgeon determined the intended femoral–tibial alignment based on the data from the navigation system before cutting. The corresponding cutting planes of the distal femur and the proximal tibia were stored in the computer navigation system (Figure 2) and defined as the intended cutting planes. The resection planes to be performed were determined with the tracker tool and were additionally stored in the computer navigation system. Correction of the cutting plane took place if the difference was greater than two degrees. 2.7. Outcome measurements 2.7.1. Primary outcome The primary outcome was to determine the accuracy of both saw blades in both the sagittal (FE-plane of the femur and AP-plane of the tibia) and coronal planes (VV-plane) of the proximal tibia and the distal femur (Figures 2 and 3). To evaluate the accuracy, the pre-cut, planned plane was compared to the resected plane after the very first cut. The differences between the pre- and after cut of both the tibia and femur in both the coronal and sagittal planes in degrees were used as the primary outcome measurements. Outliers were registered as more than two degrees of difference between the intended and performed resection planes [1]. Correction of the osteotomy took place when it was necessary. 2.7.2. Secondary outcomes Surgery time was measured in minutes by the electronic anaesthesia patient system. Differences in accuracy between surgeons in all planes were analysed. 2.8. Statistics Demographic data was analysed with a Wilcoxon non-parametric test for numerical data, while a chi-square test was used for categorical data. Normal distribution was defined if skewness and kurtosis values were between −1 and one. A Mann–Whitney U test was utilised to compare primary outcome values in case of non-normal distribution whereas an unpaired students T-test analysed normal distributed variables. To identify potential differences in accuracy due to the use of multiple surgeons, a Friedman two-way analysis of variance test with a Bonferroni correction method was used as a post hoc procedure to correct for multiple comparison testing. Intention-to-treat analysis was not applicable because the clinical patient outcome variables were not obtained after surgery. All statistical tests were based on a significance level of p b 0.05. Statistical data analysis was executed using SPSS Software Version 18.0 for Mac OSX (SPSS Inc., Chicago, Illinois). 3. Results 3.1. Demographics The data of two patients was not stored in the navigation system, leaving 58 knees for the statistical analysis. There was no significant difference between the two surgical groups with respect to number of knees, age, sex, Body Mass Index (BMI) and side of operation (Table 1). 3.2. Primary outcome Mean absolute cutting deviation never exceeded 2.0° in both groups, yet statistically significant differences between saw blades were observed (Table 2). The PS was significantly more accurate in two planes, accurate in one plane. In one plane no statistical significant difference was measured. The PS was more accurate in the AP plane of the tibial cut (0.64 ± 0.59° vs. 1.07 ± 0.81°; p = 0.03), while no differences were found in the tibial VV-plane (0.38 ± 0.42° vs. 0.51 ± 0.55°; p = 0.28). Subsequently the PS

Table 1 Demographic data.

Number of knees Age (years) Sex (male/female) Body mass index (kg/m2) Side (right/left)

Precision Saw

Sagittal Saw

p-Value

28 64 (SD ±10) 13/15 27.3 (SD ±2.7) 17/11

30 67 (SD ±12) 14/16 28.3 (SD ±5.3) 16/14

0.79 0.33 0.99 0.80 0.57


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P.Z. Feczko et al. / The Knee xxx (2017) xxx–xxx Table 2 Mean deviances and standard deviations for positioning angles in the Precision Saw group and in the Sagittal Saw group during tibial and femoral cuts during surgery where the tibia was always cut first. Precision Saw n = 28 Primary outcomes Femur Varus/valgus (SD) Flexion/extension (SD) Tibia Varus/valgus (SD) Anterior/posterior (SD) Secondary outcomes Surgery time (SD)

Sagittal Saw n = 30

p-Value

0.52 (±0.44) 1.39 (±1.19)

0.80 (±0.52) 0.79 (±0.63)

0.03 0.04

0.38 (±0.42) 0.64 (±0.59)

0.51 (±0.55) 1.07 (±0.81)

0.28 0.03

99.1 (±18.8)

102.6 (±17.0)

0.45

showed significantly better accuracy in the femoral VV-plane as well (0.52 ± 0.44° vs. 0.80 ± 0.52°; p = 0.03), while the SS revealed more accuracy in the FE-plane (1.39 ± 1.19° vs. 0.79 ± 0.63°; p = 0.04). Two outliers of 2.5° and 3.5° were measured in the AP plane of the tibia using the SS. Seven outliers were detected in the FE-plane of the femur using the PS. Five of the seven outliers were as large as 2.5°, while 3.5° and 5.5° were measured once. 3.3. Secondary outcomes 3.3.1. Surgery time No significant differences (p = 0.45) were measured in operation time between the PS group (99.1 ± 18.8) and the SS group (102.6 ± 17.0) (Table 2). 3.3.2. Differences in accuracy between the three surgeons No differences in accuracy between the three surgeons (PD: n = 25, PE: n = 22, PF: n = 11) in any of the planes were found (p = 0.32, 0.019, 0.92, 0.82 VV and FE femur, VV and AP tibia respectively) (Table 3). 4. Discussion The hypothesis of this study that PS was more accurate and would produce fewer outliers was not confirmed. The PS was more accurate in two of the four investigated planes, in the VV-plane of the femur and the AP plane of the tibia. In contrast, SS was significantly more accurate in the FE-plane of the femur. The mean absolute cutting deviation never exceeded the limit of two degrees in both groups, however outliers were found. Two outliers were found in the SS group and seven in the PS group. All outliers were detected in the sagittal plane. Longer sawing distance, stiffness of the blades and stability of the cutting blocks can have an influence on the outliers in the sagittal plane. Initial bone cutting error accuracy of the distal femur and proximal tibia during TKA was already investigated. The authors also reported more cutting errors and higher outliers in the sagittal plane. The bending and wobbling of the saw were found to be the main cause of the inaccuracy, causing incomplete cutting posteriorly [12–14]. Otani et al. [15] investigated the relationship between slot and saw blade thickness. Less cutting errors were found using thicker saw blade or thinner slot [15]. However using a thicker oscillating blade in a thinner slot can cause more friction and wear during sawing, in contradiction to the not oscillating Precision Saw. Inadequate fixation of the cutting guide to the bone was also found to be a reason of cutting errors [15,16]. Wetzel et al. [5] could not find a statistically significant difference between the same blades in a cadaveric study; however, only eight cutting planes were analysed. The quality of bone could have influenced his result as well. The PS performed better in this study in both planes of the tibia, although only in the AP-planes was the difference significant. The PS performed much worse creating the femoral cut. Close inspection of the used tip saws after surgery showed that their saw teeth design may present two distinct problems: the teeth are susceptible to wear and bone tissue was found to clog the space between the teeth (Figure 4). Table 3 The Friedman two-way analysis of variance test determined differences between multiple assessments. A Bonferroni method was used as a post hoc procedure for correction of multiple comparison testing. No statistically significant differences between individual surgeons in all four planes were found.

Femur Varus/valgus (SD) Flexion/extension (SD) Tibia Varus/valgus (SD) Anterior/posterior (SD)

PD (n = 25)

PE (n = 22)

PF (n = 11)

p-Value

0.56 (±0.43) 0.83 (±0.67)

0.79 (±0.54) 1.38 (±1.32)

0.70 (±0.54) 1.05 (±0.72)

0.32 0.19

0.44 (±0.50) 0.83 (±0.80)

0.58 (±0.58) 0.83 (±0.71)

0.40 (±0.32) 1.00 (±0.71)

0.92 0.82



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Because the tibia first technique was used in this study, more clogging was present during the femoral cut than the tibial cut since the blade was already used. The exact influence of clogging of saw teeth, bone density, thickness and stiffness of the sawblade, length of the cut on execution and precision of the bone cuts remains unknown. Surgeon factors seem not to play a major role in the precision of bone cuts, as no significant differences were found between the three observers in this study. Wetzel [5] also found the most deviation in the FE plane of the femur, which correlates with our findings. The mean deviation was between 0.38° and 1.39° with the higher deviations in the sagittal plane. Kim et al. [4] also measured the cutting errors during CAS-TKA and found more deviations of the femur in the sagittal plane than the coronal plane. The errors of the tibial cuts were comparable in both planes. Yau [3] also found greater cutting errors and more outliers in the sagittal plane compared to the coronal plane. Biant [17] reported more accurate cutting planes of the tibia compared to the cutting planes of the femur. The results of this study are in line with these findings. The research does not reveal the reason why PS is less accurate during the femoral cutting. Clogging of bone might be a possible explanation. Further research is necessary to show what happens when the blades are cleaned between cuttings or when the femur first technique is used. The reason why PS is more accurate in the other planes also remains unclear, since stiffness, length, cutting speed and the different design of the cutting teeth can play a role. Which one of these factors is the most important is a question that remains unanswered. The role of cutting deviations on the final limb and component alignment was unknown in this study, since all cutting errors were recognized and corrected intra-operatively using computer navigation. The final alignment was also checked at the end of the surgery. However the effect of cutting errors on the final alignment remains a concern during conventional TKA where the difference between the intended and performed cutting planes is more difficult to recognize. Furthermore all cutting deviations were found in the sagittal plane (slope of the distal femoral and proximal tibial cuts) which do not have an effect on the overall limb alignment or the rotational position of the components. Errors in the sagittal plane might effect femoral sizing [18], flexion– extension gap balancing [19] and anterior knee pain [20]. Surgery time was not significantly different between groups. Due to the correction of seven outliers intra-operatively in the PS group versus the correction of two outliers in the SS group, a longer surgery time was expected of the PS group, however surgical time depends on many factors. The authors did not analyse these different factors into detail in this study. 5. Limitations of the study Our clinical study had some limitations. Although no significant difference between surgeons was found, some inter-surgeon variation might have influenced the outcome results. Finally, no assessment of patient reported outcomes was obtained and therefore no statements could be made about patient benefits compared to cutting with a conventional blade. 6. Conclusion Our hypothesis that PS would be more accurate and would produce fewer outliers than SS was not confirmed in this study. Our results suggest that both saws are accurate since the mean cutting deviation was less than two degrees. 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