Saw Cut Accuracy in Knee Arthroplasty

In this article, we’ll try to explain to you Saw Cut Accuracy Arthroplasty.

Since the use of computers in orthopedics (navigated total knee arthroplasty ), awareness of misalignment of implant has increased and alignments have been measured accurately during the operation process. Adil Ajuied at al. focused on the following two hypotheses in their study in 2015. These are;

– “Slotted osteotomies are more accurate than non-slotted” (The “Slotted” mentioned in this article is the gap in the cutting guide where the saw blade moves.)
– ”Second pass of the saw blade improves the accuracy of osteotomies” (Second pass means repeating the same cutting process after the first cutting process is finished.)

Aseptic loosening following primary total knee arthroplasty (TKA) is the most common reason for revision surgery (Lützner J et al., 2011). There are several factors that can cause improper implant alignment. (Adil Ajuied et al., 2015) These are;

– Surgical technique or experience (Macdonald W et al., 2004)
– Deviation of the oscillating saw blade (Minns RJ, 1992)
– Thickness of the saw blade (Bäthis H et al., 2005) ( Otani T et al., 1993)
– Sub-optimal cutting jig stability (Belvedere C et al., 2007) (Yau WP, Chiu KY, 2008)
– Limited accuracy of jig alignment systems (Yau WP, Chiu KY, 2008)
– Uneven cement mantles (Schnurr C et al., 2011)

Current literature has examined many of these factors and in 2002 (Plaskos C et al., 2002) it was found that cutting guide movement caused 10% to 40% of the total cutting error. Therefore, this study by Adil Ajuied et al. shows that discussing only the accuracy of sawing cannot guarantee correct implant position.

Today, most commonly used knee systems have slotted and non-slotted cutting guide options. It is the cutting guide that determines the movement of the saw blade and therefore the accuracy of the surface where the implant will be inserted. For this reason, correct alignment is very important. The saw blade must be orientated in such a way as to avoid bending the saw blade thus levering upon the cutting block. (Adil Ajuied et al., 2015)

Adil Ajuied et al. (2015) made incisions on a human cadaver bone with a single experienced surgeon in their study. They focused on two different variables. The first is slotted and un-slotted cutting guides, the second is to make a second correction pass after the first incision is finished. They measured the accuracy of the cutting area using a navigation software.

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Figures 1 and 2 show the angular errors of tibial cutting processes in the coronal and sagittal planes. Figures 3 and 4 show angular errors in femoral cutting processes. A single saw pass was used for all 4 figures.

As can be seen in Figures 1 and 2, in the tibial results, the cutting operations performed with the slotted cutting guide are concentrated towards the desired area. But it is seen that angular errors are more in the cut made with un-slotted cutting guides.

There is no significant difference in the femoral cutting results (Figures 3 and 4).

When the tibial cutting errors of slotted cutting guide compared with errors of unslotted cutting guide; you can see that the slotted cutting guide is more advantageous.

The saw blade thickness must be proper to the gap thickness of cutting guide. That is to say, the difference between blade thickness and cutting guide gap thickness should be minimal. This will help the saw blade to make a smoother cut. Also, if the difference of thickness is big, deviations caused by the clearance may cause the guide to come loose. If the working length of the blade is reduced to the minimum possible, bending and deflection of the blade at first contact with the bone can be prevented. (Adil Ajuied et al., 2015) 

As can be seen in Figures 5,6,7 and 8, the second pass of cut helps correct angular errors in the first cut.  It is seen in the graphic that the points are more concentrated on the desired cutting angle. Because in the second pass, the blade restarts at the border of the bone at the correct resection level and helps to remove the excess bones remaining from the first pass. (Adil Ajuied et al., 2015) 

As a result, the use of a slotted cutting guide and a second correction cutting helps the implant to be placed on a smoother surface. However, as mentioned above, these practices do not guarantee prevention of aseptic loosening. Because there are other factors that should not be ignored and affect this loosening.

Read the article The Origin of Surgical Blades and Blade Types in Bone Cutting Process


  1. Ajuied A, Smith C, Carlos A, Back D, Earnshaw P, et al. (2015) Saw Cut Accuracy in Knee Arthroplasty – An Experimental Case-Control Study. J Arthritis 4: 144. doi: 10.4172/2167 – 7921.1000144.
    • Lützner J, Hübel U, Kirschner S, Günther KP, Krummenauer F (2011) Longterm results in total knee arthroplasty. A meta-analysis of revision rates and functional outcome. Chirurg 82: 618-624.
    • Plaskos C, Hodgson AJ, Inkpen K, McGraw RW (2002) Bone cutting errors in total knee arthroplasty. J Arthroplasty 17: 698-705.
    • Macdonald W, Styf J, Carlsson LV, Jacobsson CM (2004) Improved tibial cutting accuracy in knee arthroplasty. Med Eng Phys 26: 807-812.
    • Minns RJ (1992) Surgical instrument design for the accurate cutting of bone for implant fixation. Clin Mater 10: 207-212.
    • Bäthis H, Perlick L, Tingart M, Perlick C, Lüring C, et al. (2005) Intraoperative cutting errors in total knee arthroplasty. Arch Orthop Trauma Surg 125: 16-20.
    • Otani T1, Whiteside LA, White SE (1993) Cutting errors in preparation of femoral components in total knee arthroplasty. J Arthroplasty 8: 503-510.
    • Belvedere C, Ensini A, Leardini A, Bianchi L, Catani F, et al. (2007) Alignment of resection planes in total knee replacement obtained with the conventional technique, as assessed by a modern computer-based navigation system. Int J Med Robot 3: 117–124.
    • Yau WP, Chiu KY (2008) Cutting errors in total knee replacement: assessment by computer assisted surgery. Knee Surg Sports Traumatol Arthrosc 16: 670-673.
    • Schnurr C, Eysel P, König DP (2011) Do residents perform TKAs using computer navigation as accurately as consultants? Orthopedics 34: 174.


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