Dear Mr. Aylinde,

your question is quite hard to answer as there a several factors influencing the precision of such surgical guides. Several different surgical guides exist for various joints and procedures. Each guide works different, uses different landmarks, is based on a different 3D imaging technology (MRI or CT) and protocol, different segmentation process, some templates are used as optical others as mechanical guides,......

So, your question could only be answered for one specific type of guide.

Best Regards,

Manuel Krämer

p.s.: We will publish informations regarding the precision of surgical guides for hip arthroplasty very soon.

Доброе время суток. Согласен с Manuel Krämer, вопрос не простой, точнее всё очень индивидуально. Для понимания, необходимо изучить конкретные клинические случаи.

Thank you Manuel Krämer,

Could you please comment on the precision of surgical guides used for hip arthroplasty?

Thank you Alexandr Sletov,

Could you please write in English Language: I could not understand what you wrote? Thank you.

Уважаемый Самэль! Я челюстно-лицевой хирург. В своей работе использую 3D и стереолитографические модели. Могу помочь, присылайте конкретный клинический пример пациента.

Thank you Alexandr Sletov,

Could you please write in English Language: I could not understand what you wrote? Thank you.

Hi,

the precision of the guides jigs and navigation is depending on the system you use. We have validated our navigation system for hip socket placement with a postoperative CT scan and the measured postoperative cup anteversion and abduction were within 2 degrees of the intraoperatively measured,

Friendly regards

Rihard Trebše

Thank you Rihard Trebse

In our experience of more than 200 knees, CT based patient specific blocks made by 3D laser printing have a very good accuracy rates

Based on our experience, for knee arthroplasties, PSI is not as accurate as navigation (either with MRI or scanner planification) especially for the tibal cut (slope++). We have almost 40% of conversion from PSI to conventionnal procedure during surgery.

Thank you Raju Vaishya

Thank you Nicolas Tardy

I find the patient specific cutting guides superb.

You just have to spent a little time positioning them.

The corrections that they give are very accurate.

Much better that the manual jigs I used to use and much superior to using computer navigation.

I fully agree with Nigel

Hello,

I've used Signature guides in 730 cases. It's very accurate easy to use and reduce the operating time. It's the only system that give you the accurate rotation of the femoral component but you have to make preoperative planning yourself every time.

I am a hand Surgeon and I use these to correct malunited fractures - primarily of the distal radius but also have used it for Radius-Ulna fractures. The guides are very accurate, make life extremely easy in the OR and need little practise to handle. However the bone surface needs to be smooth, the preparation takes time and good to be very precise in the cuts. 

Wonderful innovative technique!

This is something I've spent a considerable amount of time investigating. Our team has developed surgical planning software for various procedures and have looked at all of these issues.

- Imaging of the bone model: This is very accurate using CT scanners (and MRI). You can obtain CT scans of a human down to 0.2mm or less voxel spacing (meaning a density sample every 0.2mm in 3D space) on standard medical CT scanners and have error tolerances less then than when compared against actual measurements. The important thing here is to choose a resolution that makes sense for the problem and also minimizing the radiation dosage to the patient. Patient movement and a poor rad technician can also play a role here.

- Preoperative planning with the imaging: there are two main parts to consider here, the software itself and the operator. Most surgical planning software if designed properly will have nearly zero error on top of the error inherent in the data operated upon. This can be validated by comparing measurements on input versus output data from the software. The error in pre-surgical planning comes mainly from the clinical operator of the software. It is important to perform intra- and inter-operator studies to understand the variation among operators due to human variations. This can be very high, several millimeters (or degrees if angles are important), and can also simply be completely wrong due to a major human error. The key here is developing a precise and easy to follow procedure to train and guide operators when using the software. It is also a good idea to perform some sanity check at the end to validate some basic assumptions about the output. For example, if a set of points should have symmetric counter parts, software can be added to automatically evaluate symmetry prior to output -- or a surgical guide could be evaluated to determine if it may interfere with other bone regions.

- Manufacturing of the guides: this is also very accurate. This depends upon the mode used, additive printing or CNC manufacturing for example. CNC is ultimately more accurate I believe, down to 0.001mm or better and some 3D printing technologies are close to that.

- During surgical operation: many factors play a role at this stage. However, the ease of use of the surgical guide can greatly affect error at this stage. The guide itself should be designed such that it only fits in a single position. Consider a guide that sits upon a large flat region versus one that fits into the nooks and crannies of an orbital rim. Bony features are required to constrain the 3D placement of the guide in 3D space, you need to have all three directions locked down by some feature. If you don't the surgeon will have a great deal of trouble aligning the guide. Further, there should be visual cues engraved onto the guide to further eliminate error, such as: patient name, patient ID, manufacture date, LEFT/RIGHT, anatomic directions guiding placement, etc. The surgeon needs to be able to pick the guide up without ever seeing it before and know exactly how it goes into place. There are also issues with how the guide sits upon the surface. For example, there could be cartilage that did not appear in the CT scan that blocks final placement of the guide. The surgeon then needs to scrape this away before placing the guide.

- Other issues: the guide is for drilling or cutting, so what comes after that? Placement of a prosthetic or construction of a mandible? There can be additional significant error sources here as well.

We were involved in some cadaver studies that measured the final placement of  total-knee prosthetics using our surgical guides and we obtained less then 0.5mm and 0.5 degrees of variation for the final prosthetic from our intended plan for several cadavers as measured from a post-operative CT -- this is considered significantly better than the current standard or care.

If it's not clear, the main source of error is human. So, study each step and determine where humans are involved and either minimize or eliminate them from the step or provide clear guidance to create a repeatable and robust process.

We provide some software that can be used to perform 3D measurements based upon landmark points. This software, Checkpoint can load DICOM data, render it in 3D, provides tools for landmark placement and measurement of lengths and angles among a variety of other things. This can be used to quantitate error at the various stages.

https://www.stratovan.com/products/checkpoint?utm_source=rg&utm_medium=ans&utm_campaign=meas2