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Computer-assisted Surgery of Cartilage Defects in the Knee: Comparison of Rigid-body Fixation Techniques in a Human Cadaver Study

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Abstract

This experimental cadaver study assessed computer navigation for the arthroscopic measurement of full-thickness cartilage defects in the knee joint. Cartilage defects were measured during arthroscopy using three cartilage defect-managing modules to compare fixed (invasive) and noninvasive rigid-body fixations. The comparison of all three systems tested revealed a difference between the noninvasive and the fixed rigid-body fixation, with a mean value of 0.07 mm for the width, 0.15 mm for the height, and 0.17 mm for the surface area of the cartilage defect (P > .05). Every point of the cartilage defect was attainable with the pointer tip. The force applied to the instrument during the defect palpation to keep the leg stable during the navigation process was acceptable. In conclusion, the cartilage defect-managing module allows the precise measurement of full-thickness cartilage defects in the knee joint during arthroscopy and that the module can be used with noninvasive rigid-body fixation.

Computer-assisted surgery (CAS) has expanded to the field of orthopedic surgery. Computer-assisted surgery is used prominently in total knee replacement (TKR), spinal instrumentation, total hip replacement (THR), total hip resurfacing, and correction osteotomies.¹ Benefits of this technique include greater precision of implant positioning and reduced surgical complications.^2-5 New tracking technologies, dedicated instruments, and ergonomic software can help to improve the visualization of instruments and implants with regard to patient anatomy.

In the field of human articular cartilage repair, new methods, such as the cultivation and implantation of autologous chondrocytes, have become well established.^6,7 The cells are used either as a cell suspension or in combination with 3-dimensional (3D), bioresorbable scaffolds. However, these tissue-engineered transplants generally need to be inserted in the cartilage defects via arthrotomy. For further development of the technique, especially for arthroscopic applications, navigation could be a useful tool, because valid assessment of cartilage defect size is necessary for success of the procedure.

The objective of this study was to assess computer navigation for the arthroscopic measurement of full-thickness cartilage defects in the knee joint using invasive and noninvasive rigid-body fixation on the femur and tibia.

Materials and Methods

Using a standard arthroscopic approach, 17 full-thickness cartilage defects were made on the lateral and medial condyle of the two human cadaver knees used in this study. For navigation, the OrthoPilot navigation system (B. Braun Aesculap, Tuttlingen, Germany) with special designed software (cartilage defect-managing module [CDM]; B. Braun Aesculap, Tuttlingen, Germany) was used. The defined and prepared cartilage defect was measured with the pointer of the OrthoPilot during arthroscopy.

During the study, the following objectives were evaluated.

General Feasibility of the Study

Initially, the feasibility of acquiring the defect’s general geometric shape with an arthroscopic approach was evaluated, according to the following:

1. Was every point of the cartilage defect attainable with the pointer tip?
2. How much force had to be applied on the instrument (pointer) and for a noninvasive rigid body, which requires stability during the cartilage defect palpation process?
3. Could fixed (invasive) vs noninvasive rigid bodies be compared?

Standard rigid bodies were used for data acquisition. These rigid bodies generally can be mounted invasively (fixed), in which the rigid body is fixed by K wires drilled into the bone; and noninvasively, in which the rigid body is mounted with rubber bands on the leg (Figure 1). Fixation with rubber bands is always susceptible to displacement during the cartilage-defect palpation process, which results in inaccurate data acquisition. For standard arthroscopy of the knee joint with measurement of the size of a cartilage defect, noninvasive rigid-body fixation would be advantageous. This leads to the question of whether there is any statistically significant difference between fixed and noninvasive rigid-body fixation for the precise calculation of the defect size. Therefore, three set-ups were tested in the experiment (Table 1).

1. Fixed rigid body vs noninvasive rigid body on the femur – light version
2. Fixed rigid body vs noninvasive rigid body on the femur – full version
3. Fixed rigid body vs noninvasive rigid body on the femur – standard version

Each defect was measured by the same surgeon, and the maximal height, width, and area of the cartilage defect were recorded and calculated.

A difference of more than 10% between fixed and mobile rigid body on the femur was rated as unacceptable. The system tolerance of the OrthoPilot is ±1 mm. For the statistical analysis, descriptive statistics was used with the calculation of the difference between the measurements of three fixations of the rigid bodies and determination of the mean value, median, and standard deviations. The Kruskal-Wallis-H-test was used to analyze these data. P<.05 was considered statistically significant.

Results

In general, arthroscopic access was adequate for the acquisition of the cartilage defect geometry. The handling, visibility, and leg movements during palpation were suitable for the arthroscopic use of cartilage defect-managing module navigation. Every point of the cartilage defect was attainable with the pointer tip, even if the defect size was large. The force applied to the instrument during the defect palpation was acceptable when the arthroscopic access was suitable. Movements of the leg during the arthroscopic palpation induced by the manipulation of the pointer were minimal. A leg holder was strongly recommended to secure the leg. With the camera positioned on the contralateral side of the leg, the palpation of defects on the medial condyle was easily accomplished. The palpation of defects on the lateral condyle caused some handling issues with regard to the visibility of the rigid body pointer, which can be covered by the arthroscope.

Comparison of all three systems tested revealed a difference between the noninvasive and the fixed rigid-body fixations, with a mean value of 0.07 mm for the width, 0.15 mm for the height, and 0.17 mm for the surface area of the cartilage defect. No significant difference was found for the three values (P>.05). The difference between fixed rigid-body fixation compared with noninvasive rigid-body fixation for all three test systems are shown in Figure 2.

The individual comparison of the three test systems (light, full, and standard) for fixed and noninvasive rigid-body fixation also showed no statistically significant differences. The values determined are shown in Tables 2 through 4. Some determined values were outside the range of all measurements. These values were attributed to pronounced movement of the leg during arthroscopy.

Comparison of the three systems (light, full, and standard) showed some differences. In the light version, assuming that the femur was stable during the palpation process, differences in the measurements between fixed and noninvasive rigid-body fixations on the femur were negligible. Nearly all values outside the tolerance (more than 10% standard deviation [SD]) were based on worst-case circumstances, such as intentionally induced severe femur movements, inadequate rubber band fixation, or general system inaccuracy.

In the full version, the differences between fixed and noninvasive rigid-body fixation were apparent. Because of the repeated intraoperative movement of the rigid body from the tibia to the femur during palpation, it was not possible to keep the femur entirely stable.

In the standard version, the differences between the measurements were acceptable. Although this is a comparison between two stand-alone measurements, the differences are acceptable because most of the values outside the tolerance (more than 10% SD) are based on the selection of the palpation points within the two palpation procedures compared.

Discussion

Navigation systems are well-established tools for orthopedic surgical procedures. Modular systems with implant-adapted or universal software applications are available, depending on the needs of surgeons and patients. Standard applications with optical tracking systems allow routine use in TKR, THR, and spinal surgery.¹ Use of navigation systems was first reported in the literature in spinal navigation with pedicle instrumentation of the lumbar and thoracic spine.^2,8 Many studies have proven the benefit of navigation. Thousands of navigated surgeries have been performed for TKR.^3,5,9-12 Prospective randomized studies have shown that axis alignment is more precise and outliers can be avoided compared with results with manual alignment techniques.⁹ Navigated total hip resurfacing is the latest development in this field.¹³ Approaches may become less invasive, and individualized implant position adjustment could be improved. Additional research on the implementation of navigation is continuing in other areas of joint surgery. Cartilage repair has become an important subject of research, because of the development of biological cartilage resurging technologies.^7,14 The combination of biological cartilage repair and navigation technologies will be an additional step forward and will enable arthroscopy to become part of the surgical technique. Accurate determination of the size of the cartilage defect through the use of computer navigation has been proven in experimental studies.¹⁵ In these settings, fixed rigid-body fixation is used. Fixation of the rigid bodies in the bone leads to high stability and less susceptibility for displacement, which can result in inaccurate data acquisition but increases the invasive characteristic of the arthroscopic procedure. Therefore, noninvasive fixation of the rigid body would be advantageous.

In this experimental study, we compared the difference between the measurements of full-thickness cartilage defects in the knee joint using fixed rigid bodies in the bone and noninvasive rigid bodies, which were secured with rubber bands on the operated leg. Three settings were used with different fixation of the rigid bodies on the femur and tibia. During the experiment, actual arthroscopic conditions were simulated with different movement levels of the leg during the procedure. In general, all measurements showed very small differences between fixed and noninvasive rigid-body fixation. The highest degree of consistency was found only when femoral rigid bodies were used. Nearly all values outside the accepted tolerance were based on severe movements of the femur during the arthroscopic procedure. All points of the defects were attainable with the pointer tip, and the general handling of the pointer was not different from the handling of other arthroscopic instruments.

Conclusion

The cartilage defect-managing module allows for the precise measurement of full-thickness cartilage defects in the knee joint during arthroscopy and can be used with noninvasive rigid-body fixation. Nevertheless, some technical improvements must be made to ensure the consistent, reliable measurement of full-thickness cartilage defects.

References

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Authors

Drs Marlovits, Zimmermann, Vekszler, and Resinger are from the Medical University of Vienna, Department of Traumatology, Vienna, Austria.

Correspondence should be addressed to Dr Stefan Marlovits, MD, Medical University of Vienna, Department of Traumatology, Waehringer Guertel 18–20, A-1090 Vienna, Austria.

This study was supported by B. Braun Aesculap, Tuttlingen, Germany.

Drs Marlovits and Zimmermann have no financial relationships to disclose. Drs Resinger and Vekszler have no financial relationships to disclose.