Towards a standard in assessment of bone cutting for total knee replacement

Accuracy of Computer-Aided Techniques in Orthopaedic Surgery: How Can It Be Defined, Measured Experimentally, and Analyzed from a Clinical Perspective?

Surgical accuracy is multifactorial. Therefore, it is crucial to consider all influencing factors when investigating the accuracy of a surgical procedure, such as the surgeon's experience, the assistive technologies that may be used by the surgeon, and the patient factors associated with the specific anatomical site. For in vitro preclinical investigations, accuracy should be linked to the concepts of trueness (e.g., distance from the surgical target) and precision (e.g., variability in relation to the surgical target) to gather preclinical, quantitative, objective data on the accuracy of completed surgical procedures that have been performed with assistive technologies. The clinical relevance of improvements in accuracy that have been observed experimentally may be evaluated by analyzing the impact on the risk of failure and by taking into account the level of tolerance in relation to the surgical target (e.g., the extent of the safety zone). The International Organization for Standardization (ISO) methodology enables preclinical testing of new assistive technologies to quantify improvements in accuracy and assess the benefits in terms of reducing the risk of failure and achieving surgical targets with tighter tolerances before the testing of clinical outcomes.

Transfer accuracy and precision scoring in planar bone cutting validated with ex vivo data

The use of interactive surgical scenarios for virtual preoperative planning of osteotomies has increased in the last 5 years. As it has been reported by several authors, this technology has been used in tumor resection osteotomies, knee osteotomies, and spine surgery with good results. A digital three-dimensional preoperative plan makes possible to quantitatively evaluate the transfer process from the virtual plan to the anatomy of the patient. We introduce an exact definition of accuracy and precision of this transfer process for planar bone cutting. We present a method to compute these properties from ex vivo data. We also propose a clinical score to assess the goodness of a cut. A computer simulation is used to characterize the definitions and the data generated by the measurement method. The definitions and method are evaluated in 17 ex vivo planar cuts of tumor resection osteotomies. The results show that the proposed method and definitions are highly correlated with a previous definition of accuracy based in ISO 1101. The score is also evaluated by showing that it distinguishes among different transfer techniques based in its distribution location and shape. The introduced definitions produce acceptable results in cases where the ISO-based definition produce counter intuitive results.

Evaluation of a CT-based technique to measure the transfer accuracy of a virtually planned osteotomy

Accurate transfer of a preoperatively planned osteotomy plane to the bone is of significance for corrective surgery, tumor resection, implant positioning and evaluation of new osteotomy techniques. Methods for comparing a preoperatively planned osteotomy plane with a surgical cut exist but the accuracy of these techniques are either limited or unknown. This paper proposes and evaluates a CT-based technique that enables comparing virtual with actual osteotomy planes. The methodological accuracy and reproducibility of the technique is evaluated using CT-derived volume data of a cadaver limb, which serves to plan TKA osteotomies in 3-D space and to simulate perfect osteotomies not hampered by surgical errors. The methodological variability of the technique is further investigated with repeated CT scans after actual osteotomy surgery of the same cadaver specimen. Plane displacement (derr) and angulation errors in the sagittal and coronal plane (βerr, γerr) are measured with high accuracy and reproducibility (derr=-0.11±0.06mm; βerr=0.08±0.04°, γerr=-0.03±0.03°). The proposed method for evaluating an osteotomy plane position and orientation has a high intrinsic accuracy and reproducibility. The method can be of great value for measuring the transfer accuracy of new techniques for positioning and orienting a surgical cut in 3-D space.

Reflections on current methods for evaluating skills during joint replacement surgery

Valid and reliable techniques for assessing performance are essential to surgical education, especially with the emergence of competency-based frameworks. Despite this, there is a paucity of adequate tools for the evaluation of skills required during joint replacement surgery. In this scoping review, we examine current methods for assessing surgeons’ competency in joint replacement procedures in both simulated and clinical environments. The ability of many of the tools currently in use to make valid, reliable and comprehensive assessments of performance is unclear. Furthermore, many simulation-based assessments have been criticised for a lack of transferability to the clinical setting. It is imperative that more effective methods of assessment are developed and implemented in order to improve our ability to evaluate the performance of skills relating to total joint replacement. This will enable educators to provide formative feedback to learners throughout the training process to ensure that they have attained core competencies upon completion of their training. This should help ensure positive patient outcomes as the surgical trainees enter independent practice.

Cite this article: Bone Joint J 2013;95-B:1445–9.

Total knee arthroplasty with a computer-navigated saw: a pilot study

BACKGROUND

Computer-aided surgery aims to improve implant alignment in TKA but has only been adopted by a minority for routine use. A novel approach, navigated freehand bone cutting (NFC), is intended to achieve wider acceptance by eliminating the need for cumbersome, implant-specific mechanical jigs and avoiding the expense of navigation.

QUESTIONS/PURPOSES

We determined cutting time, surface quality, implant fit, and implant alignment after NFC of synthetic femoral specimens and the feasibility and alignment of a complete TKA performed with NFC technology in cadaveric specimens.

METHODS

Seven surgeons prepared six synthetic femoral specimens each, using our custom NFC system. Cutting times, quality of bone cuts, and implant fit and alignment were assessed quantitatively by CT surface scanning and computational measurements. Additionally, a single surgeon performed a complete TKA on two cadaveric specimens using the NFC system, with cutting time and implant alignment analyzed through plain radiographs and CT.

RESULTS

For the synthetic specimens, femoral coronal alignment was within ± 2° of neutral in 94% of the specimens. Sagittal alignment was within 0° to 5° of flexion in all specimens. Rotation was within ± 1° of the epicondylar axis in 97% of the specimens. The mean time to make cuts improved from 13 minutes for the first specimen to 9 minutes for the fourth specimen. TKA was performed in two cadaveric specimens without complications and implants were well aligned.

CONCLUSIONS

TKA is feasible with NFC, which eliminates the need for implant-specific instruments. We observed a fast learning curve.

CLINICAL RELEVANCE

NFC has the potential to improve TKA alignment, reduce operative time, and reduce the number of instruments in surgery. Fewer instruments and less sterilization could reduce costs associated with TKA.

Sequential versus automated cutting guides in computer-assisted total knee arthroplasty

The accuracy and efficiency of automated cutting guides in CAS systems have not been previously compared with conventional CAS techniques. Therefore, it is not yet clear if these more advanced technologies are warranted. We hypothesized that a novel automated cutting guide with CAS for total knee arthroplasty would be more efficient and more accurate than conventional navigation with sequential cutting blocks. Twelve cadaver legs were used in total. Each leg was randomly assigned to either an automated guide positioning or a conventional freehand computer-navigated guide positioning. The guide positions postosseous fixation and the final bone-cut surfaces were digitized and compared to the targeted cutting planes. The final location of the impacted trial implant was also digitized and compared to the planned implant location. The time for each step and the total time taken to prepare the femur were measured for both groups. The mean femoral preparation time was shorter with the automated cutting guide than the conventional method (5.5 min versus 13.8 min, p<0.001). The average deviation in the final bone resections from the planned resections was significantly lower for the automated cutting guide in the frontal/rotational plane (0.55° versus 1.1°), sagittal plane (0.75° versus 2.0°), and cut height direction (0.56 mm versus 1.6 mm). Therefore, based on these results, we concluded that automated cutting-guide positioning resulted in more efficient and more accurate femoral cuts in comparison to the conventional navigation method in a cadaveric model.

Computer-assisted and robot-assisted technologies to improve bone-cutting accuracy when integrated with a freehand process using an oscillating saw

BACKGROUND

In orthopaedic surgery, many interventions involve freehand bone cutting with an oscillating saw. Such freehand procedures can produce large cutting errors due to the complex hand-controlled positioning of the surgical tool. This study was performed to investigate the potential improvements in cutting accuracy when computer-assisted and robot-assisted technologies are applied to a freehand bone-cutting process when no jigs are available.

METHODS

We designed an experiment based on a geometrical model of the cutting process with use of a simulated bone of rectangular geometry. The target planes were defined by three variables: a cut height (t) and two orientation angles (beta and gamma). A series of 156 cuts were performed by six operators employing three technologically different procedures: freehand, navigated freehand, and robot-assisted cutting. After cutting, we measured the error in the height t, the absolute error in the angles beta and gamma, the flatness, and the location of the cut plane with respect to the target plane.

RESULTS

The location of the cut plane averaged 2.8 mm after use of the navigated freehand process compared with 5.2 mm after use of the freehand process (p < 0.0001). Further improvements were obtained with use of the robot-assisted process, which provided an average location of 1.7 mm (p < 0.0001).

CONCLUSIONS

Significant improvements in cutting accuracy can be achieved when a navigation system or an industrial robot is integrated into a freehand bone-cutting process when no jigs are available. The procedure for navigated hand-controlled positioning of the oscillating saw appears to be easy to learn and use.

Accuracy in planar cutting of bones: an ISO-based evaluation

BACKGROUND

Computer- and robot-assisted technologies are capable of improving the accuracy of planar cutting in orthopaedic surgery. This study is a first step toward formulating and validating a new evaluation methodology for planar bone cutting, based on the standards from the International Organization for Standardization.

METHODS

Our experimental test bed consisted of a purely geometrical model of the cutting process around a simulated bone. Cuts were performed at three levels of surgical assistance: unassisted, computer-assisted and robot-assisted. We measured three parameters of the standard ISO1101:2004: flatness, parallelism and location of the cut plane.

RESULTS

The location was the most relevant parameter for assessing cutting errors. The three levels of assistance were easily distinguished using the location parameter.

CONCLUSIONS

Our ISO methodology employs the location to obtain all information about translational and rotational cutting errors. Location may be used on any osseous structure to compare the performance of existing assistance technologies.