Non-invasive, non-radiological quantificationof anteroposterior knee joint ligamentous laxity: A study in cadavers

Noninvasive navigated assessment of the lower limb axis prior to knee arthroplasty: a feasibility study

The purpose of the study was to assess accuracy and repeatability of a noninvasive navigated (NIN) measurement of the lower limb axes by comparison with the conventional, invasive navigated (IN) technique. The tested hypothesis was that NIN measure will significantly differ from IN measure when performed on a supine patient under general anesthesia just prior to knee arthroplasty. The accuracy study involved 20 cases. The following measures were performed with both systems: maximal extension angle, coronal mechanical femoro-tibial angle at the previously assessed maximal extension angle, coronal mechanical femoro-tibial angle at 30° of knee flexion. NIN and IN measures were compared with the appropriate statistical tests. The repeatability study involved 14 cases. The same measures were performed with the NIN system twice by two independent observers. The intra- and inter-observer variability was assessed by the calculation of the intra-class correlation coefficient. After correction for the systematic biases, the differences between the two systems were not significant. A good correlation, a good coherence and an excellent agreement between NIN and IN measures of maximal extension angle and coronal femoro-tibial mechanical angle at maximal extension. But measures at 30° of flexion were inconsistent. The NIN system can be considered as an accurate and precise tool for the assessment of the knee extension angle and the coronal deformation at maximal extension prior to knee arthroplasty. But this system is less accurate and less repeatable when measuring coronal femoro-tibial mechanical angle at 30° of flexion and should not be used for this purpose.

Lower limb alignment and laxity measures before, during and after total knee arthroplasty: A prospective cohort study

BACKGROUND

This study compared knee alignment and laxity in patients before, during and after total knee arthroplasty, using methodologically similar procedures, with an aim to help inform pre-operative planning.

METHODS

Eighteen male and 13 female patients were recruited, mean age 66years (51-82) and mean body mass index of 33 (23-43). All were assessed pre- and postoperatively using a non-invasive infrared position capture system and all underwent total knee arthroplasty using a navigation system. Knee kinematic data were collected and comparisons made between preoperative clinical and intraoperative measurements for osteoarthritic knees, and between postoperative clinical and intraoperative measurements for prosthetic knees.

FINDINGS

There was no difference in unstressed coronal mechanical femoral-tibial angles for either osteoarthritic or prosthetic knees. However, for sagittal alignment the knees were in greater extension intraoperatively (osteoarthritic 5.2° p<0.001, prosthetic 7.2° p<0.001). For osteoarthritic knees, both varus and valgus stress manoeuvres had greater angular displacements intraoperatively by a mean value of 1.5° for varus (p=0.002) and 1.6° for valgus (p<0.001). For prosthetic knees, only valgus angular displacement was greater intraoperatively (0.9°, p=0.002).

INTERPRETATION

Surgeons performing total knee arthroplasties should be aware of potential differences in alignment and laxity measured under different conditions to facilitate more accurate operative planning and follow-up.

Current use of navigation system in ACL surgery: a historical review

PURPOSE

The present review aims to analyse the available literature regarding the use of navigation systems in ACL reconstructive surgery underling the evolution during the years.

METHODS

A research of indexed scientific papers was performed on PubMed and Cochrane Library database. The research was performed in December 2015 with no publication year restriction. Only English-written papers and related to the terms ACL, NAVIGATION, CAOS and CAS were considered. Two reviewers independently selected only those manuscripts that presented at least the application of navigation system for ACL reconstructive surgery.

RESULTS

One hundred and forty-six of 394 articles were finally selected. In this analysis, it was possible to review the main uses of navigation system in ACL surgery including tunnel positioning for primary and revision surgery and kinematic assessment of knee laxity before and after different surgical procedures. In the early years, until 2006, navigation system was mainly used to improve tunnel positioning, but since the last decade, this tool has been principally used for kinematics evaluation. Increased accuracy of tunnel placement was observed using navigation surgery, especially, regarding femoral, 42 of 146 articles used navigation to guide tunnel positioning. During the following years, 82 of 146 articles have used navigation system to evaluate intraoperative knee kinematic. In particular, the importance of controlling rotatory laxity to achieve better surgical outcomes has been underlined.

CONLUSIONS

Several applications have been described and despite the contribution of navigation systems, its potential uses and theoretical advantages, there are still controversies about its clinical benefit. The present papers summarize the most relevant studies that have used navigation system in ACL reconstruction. In particular, the analysis identified four main applications of the navigation systems during ACL reconstructive surgery have been identified: (1) technical assistance for tunnel placement; (2) improvement in knowledge of the kinematic behaviour of ACL and other structures; (3) comparison of effectiveness of different surgical techniques in controlling laxities; (4) navigation system performance to improve the outcomes of ACL reconstruction and cost-effectiveness.

LEVEL OF EVIDENCE

IV.

The dynamic nature of alignment and variations in normal knees

The restoration of knee alignment is an important goal during total knee arthroplasty (TKA). In the past surgeons aimed to restore neutral limb alignment during surgery. However, previous studies have demonstrated alignment to be dynamic, varying depending on the position of the limb and the degree of weight-bearing, and between patients. We used a validated computer navigation system to measure the femorotibial mechanical angle (FTMA) in 264 knees in 77 male and 55 female healthy volunteers aged 18 to 35 years (mean 26.2). We found the mean supine alignment to be a varus angle of 1.2° (standard deviation (sd) 4), with few patients having neutral alignment. FTMA differs significantly between males and females (with a mean varus of 1.7° (sd 4) and 0.4° (sd 3.9), respectively; p = 0.008). It changes significantly with posture, the knee hyperextending by a mean of 5.6°, and coronal plane alignment becoming more varus by 2.2° (sd 3.6) on standing compared with supine. Knee alignment is different in different individuals and is dynamic in nature, changing with different postures. This may have implications for the assessment of alignment in TKA, which is achieved in non-weight-bearing conditions and which may not represent the situation observed during weight-bearing.

Collateral ligament laxity in knees: what is normal?

BACKGROUND

Proper alignment and balancing of soft tissues of the knee are important goals for TKA. Despite standardized techniques, there is no consensus regarding the optimum amount of collateral ligament laxity one should leave at the end of the TKA.

QUESTIONS/PURPOSES

I asked (1) what is the collateral laxity in young healthy volunteers, and (2) is there a difference in collateral laxity between males and females.

METHODS

The femorotibial mechanical angle (FTMA) was measured in 314 knees in healthy volunteers aged 19 to 35 years. Subjects with a history of pain, malalignment, dysplasia, or trauma were excluded. Twenty-five knees were excluded because the hip center could not be acquired, and 22 were excluded because of a history of pain and trauma, leaving 267 knees for inclusion in the study. Of these, 155 were from men and 112 were from women. A validated method using a computer navigation system was used to obtain the measurements. A 10-Nm torque was used to stress the knee in varus and valgus at 0° extension and 15° flexion. An independent t-test and ANOVA were applied to the data to calculate any significant difference between groups (p<0.05).

RESULTS

The mean (SD) unstressed supine FTMA was varus of 1.2° (SD, 4°) in 0° extension and varus of 1.2° (SD, 4.4°) in 15° flexion (p=0.88). On varus torque of 10 Nm, the supine FTMA changed by a mean of 3.1° (SD, 2°) (95% CI, 2.4°-3.8°; p<0.001) in 0° extension and 6.9° (SD, 2.6°) (95% CI, 6.2°-7.7°; p<0.001) in 15° flexion. On valgus torque of 10 Nm, the FTMA changed by a mean of 4.6° (SD, 2.2°) (95% CI, 3.9°-5.3°; p<0.001) in 0° extension and 7.9° (SD, 3.4°) (95% CI, 7.1°-8.7°; p<0.001) in 15° flexion. The mean unstressed FTMA in 0° extension was varus of 1.7° (SD, 4°) in men and 0.4° (SD, 3.9°) in women (p=0.01). Differences in collateral ligament laxity were seen between men and women (p<0.001 for valgus torque and 0.035 for varus torque in 15° flexion). With valgus torque at 0° flexion, the supine FTMA change was valgus of 4.2° (SD, 2.0°) for men and 5.0° (SD, 2.4°) for women, while at 15° flexion the FTMA change was valgus 7.6° (SD, 3.6°) for men and 8.3° (SD, 3.2°) for women With varus torque at 0° flexion, additional varus was -3.0° (SD, 1.8°) for men and -3.3° (SD, 2.2°) for women, while at 15° flexion, varus was -7.0° SD, (2.5°) for men and -6.9° (SD, 2.8°) for women.

CONCLUSIONS

The collateral laxity in young healthy volunteers was quantified in this study. The collateral ligament laxity is variable in different persons. In addition, ligaments in women are more lax than in men in valgus stress.

CLINICAL RELEVANCE

This study was conducted on young, healthy knees. Whether the findings are applicable to arthritic knees and replaced knees needs additional evaluation. However the findings provide a baseline from which to work in the evaluation of arthritic knees and in the case of TKA.

Repeatability and accuracy of a non-invasive method of measuring internal and external rotation of the tibia

PURPOSE

The ability to quantify rotational laxity of the knee would increase understanding of functional rotatory instability, identify the best treatment methods for soft tissue injury, and have a role in diagnosis of soft tissue injury. This study aimed to report the reliability, repeatability and precision of a non-invasive adaptation of image-free navigation technology by comparing with a validated invasive system used for computer-assisted surgery.

METHODS

Twelve cadaveric lower limbs were tested with a commercial image-free navigation system using passive trackers secured by bone screws. They were then tested a non-invasive fabric-strap system. Manual application of torque was used consistent with clinical examination to rotate the tibia to the end of internal rotation and external rotation range. Measurements were taken at 10° intervals from full extension to 90° flexion, and protocol was repeated twice using each system. Intraclass correlation coefficient (ICC) was used to reflect reliability of measurements. At each flexion interval, coefficient of repeatability (CR) was calculated for each system, and limits of agreement (LOA) were used to reflect agreement between the systems.

RESULTS

The results for internal and external rotation were combined throughout flexion: ICC invasive; 0.94 (0.86-0.99), non-invasive; 0.92 (0.7-0.99), CR invasive; 2.4° (1.3-4.8°), non-invasive; 3.5° (1.8-6.6), LOA; 8.2° (4.3-13.5).

CONCLUSION

Non-invasive optical tracker fixation gives improved agreement with a validated method of measurement compared with devices measuring tibial rotation by foot position. This system gives the added possibility of dynamic, weight-bearing testing in the clinically important range of 0°-30° knee flexion without the need for any limb restraint.