Knee rotation in healthy individuals related to age and gender

The knee kinematic patterns and associated factors in healthy Thai adults

BACKGROUND

Reference values for normal knee kinematics were limited in Asian population and were influenced by race and other factors. This study was aimed to establish the reference values and identify the factors associated with knee kinematics in healthy Thai adults, aged 18-40 years.

METHODS

A retrospective cohort study was conducted between 2016 and 2020. Healthy Thai adults aged 18-40 years old with body mass index (BMI) between 18.5 and 24.9 kg/m2 were included. All eligible participants were attached with reflective markers. Their walking was captured by 8-digital cameras, and assessed by motion analysis software. The primary outcomes were average knee kinematic data (degrees) in three dimensional planes as valgus-varus, flexion-extension, and internal-external rotation. Paired t-test and multiple linear regression were applied to compare the outcomes and to determine their associated factors.

RESULTS

Ninety-eight participants (60 females and 38 males) were included with mean age 28.5 ± 5.4 years, and BMI 21.1 ± 2.0 kg/m2. Knee kinematics showed slight adduction during the swing phase, flexion during the stance phase, and obvious external rotation throughout the gait cycle, with a peak of 30-31 degrees during mid-swing. Right knee was significantly more adducted, flexed and externally rotated than the left side, particularly at mid-stance (P = 0.047, 0.017, and < 0.001, respectively). Females had more knee abduction, flexion and external rotation than males. Age, sex, and BMI were significantly correlated with knee abduction at terminal stance (correlation coefficient - 0.12, 95% confidence interval (CI) -0.23, -0.01; -1.37, 95%CI -2.54, -0.20; and - 0.32, 95%CI -0.61, -0.39, respectively), and rotation at mid-swing (correlation coefficient - 0.36, 95%CI -0.69, -0.02; -7.37, 95%CI -10.82, -3.92; and 0.89, 95%CI 0.01, 1.78, respectively).

CONCLUSION

Knee kinematics demonstrates external tibial rotation throughout the gait cycle, significant side differences, and are associated with age, sex, and BMI. Reference values from this study will be useful for functional gait assessment in healthy Thais. However, further comprehensive knee kinetic study including spatio-temporal parameter is recommended.

Effects of the abdominal drawing-in maneuver on hamstring rotational activity and pelvic stability in females

BACKGROUND

The medial hamstring (MH) and lateral hamstring (LH) can be selectively trained through tibial internal and external rotation during prone knee flexion. However, no study has identified how a combined tibial rotation and lumbo-pelvic stability strategy influences MH and LH muscle activities.

OBJECTIVE

To investigate the combined effects of tibial rotation and the abdominal drawing-in maneuver (ADIM) on MH and LH muscle activities as well as pelvic rotation during prone knee flexion.

METHODS

Fifteen female volunteers performed prone knee flexion with tibial internal and external rotation, with and without the ADIM. Under each condition, MH and LH muscle activities were measured by surface electromyography (EMG), and the pelvic rotation angle by a smartphone inclinometer application.

RESULTS

The results showed increased MH (without the ADIM: p< 0.001, effect size (d) = 2.05; with the ADIM: p< 0.001, d= 1.71) and LH (without the ADIM: p< 0.001, d= 1.64; with the ADIM: p= 0.001, d= 1.58) muscle activities under internal and external tibial rotation, respectively. However, addition of the ADIM led to increased MH (internal tibial rotation: p= 0.001, d= 0.67; external tibial rotation: p= 0.019, d= 0.45) and LH (internal tibial rotation: p= 0.003, d= 0.79; external tibial rotation: p< 0.001, d= 1.05) muscle activities combined with reduced pelvic rotation (internal tibial rotation: p< 0.001, d= 3.45; external tibial rotation: p< 0.001, d= 3.01) during prone knee flexion.

CONCLUSIONS

These findings suggest that the ADIM could be useful for reducing compensatory pelvic rotation and enhancing selective muscle activation in the MH and LH, according to the direction of tibial rotation, during prone knee flexion.

Lower extremity range of motion and alignment: A reliability and concurrent validity study of goniometric and three-dimensional motion analysis measurement

Background

Knowing correlations between passive goniometric and dynamic three-dimensional motion analysis measurements of lower extremity range of motion and alignment would benefit knee injury risk assessment.

Purpose

To investigate reliability and concurrent validity of lower extremity assessment with goniometry and three-dimensional motion analysis.

Methods

Thirty-eight participants (76 limbs) were examined in standardized positions by two physiotherapists with simultaneous goniometric and three-dimensional motion analysis measurements of passive range of motion and alignment. Intra-class correlation coefficient (ICC) and median differences were calculated.

Results

Hip rotation reliability, ICC 0.74–0.89 and validity 0.74–0.94. Tibial rotation reliability, ICC 0.24–0.75 and validity 0.08–0.61. Knee extension reliability, ICC 0.44–0.73 and validity 0.22–0.60. Knee valgus/varus reliability, ICC 0.36–0.68 and validity 0.25–0.62. Tibial torsion reliability, ICC 0.52–0.77 and validity 0.58–0.81. Ankle dorsiflexion reliability, ICC 0.12–0.73 and validity 0.51–0.83. Median differences in reliability and validity ranged from -2.0° to 3.0° and from -6.6° to 7.5° respectively.

Conclusion

Goniometric and three-dimensional motion analysis methods define the lower body segments differently making some degree of discrepancy in the measurements inevitable. Nevertheless, the variables chosen in this study are all strongly associated with anterior cruciate ligament rupture and some may prove useful to identify individuals at risk of knee injury during sport activities.

Study design

Cross-sectional laboratory study.

Knee injury prevention in alpine skiing. A technological paradigm shift towards a mechatronic ski binding

BACKGROUND

Skiing can be beneficial for the sense of delight and wellbeing. Nonetheless, the risk of injury should not be ignored. The traditional ski binding, working solely on a mechanical principle, performs well with regards to a prevention of mid-shaft tibia fracture. However, with respect to knee injuries, it is not able to provide protection. Future concepts, such as mechatronic binding designs have the potential to decrease knee injuries that traditional bindings cannot prevent. In addition to mechanical loads, this kind of binding design uses additional parameters, e.g. knee kinematics and the skier's muscle state, to control the binding release.

METHODS

This paper provides a review about our knowledge of injury mechanisms in recreational alpine skiing and previous work regarding mechatronic ski binding concepts. Also, our own biomechanical approach towards a mechatronic ski binding is described. Four input variables for an algorithm are discussed with respect to existing sensor solutions and designs of our own. A concept for an algorithm, based on our current knowledge in injury mechanisms is presented.

CONCLUSIONS

Though first designs were described in the 80s, for decades the idea of a mechatronic ski binding was not further pursued by research. Technological improvements in the field of micro-electronics and wearable sensors, as well as decreasing costs of these devices, make a mechatronic concept feasible. Main challenge is still the missing knowledge about injury mechanisms in alpine skiing and hence the quantification of the influence of possible input variables for the mechatronic system on those injuries.

Tibiofemoral kinematics in healthy and osteoarthritic knees during twisting

Purpose

The purpose of this study was to determine the in vivo kinematics of healthy knees and those with osteoarthritis (OA), during twisting using density-based image-matching techniques.

Methods

Five healthy subjects and 26 patients with medial knee OA performed twisting under periodic X-ray imaging.

Results

The tibiofemoral rotation at the ipsilateral/contralateral twist in healthy and OA knees were 11° ± 9.3° externally/9.5° ± 5.6° internally (p < 0.05) and 4.4° ± 7.2° externally/2.7° ± 8° internally (p < 0.05), respectively.

Conclusions

The kinematic analysis of OA knees during twisting revealed significantly smaller tibiofemoral rotation than those of healthy knees.

Comparison of a simplified skin pointer device compared with a skeletal marker for knee rotation laxity: A cadaveric study using a rotation-meter

AIM

To compare the measurements of knee rotation laxity by non-invasive skin pointer with a knee rotation jig in cadaveric knees against a skeletally mounted marker.

METHODS

Six pairs of cadaveric legs were mounted on a knee rotation jig. One Kirscher wire was driven into the tibial tubercle as a bone marker and a skin pointer was attached. Rotational forces of 3, 6 and 9 nm applied at 0°, 30°, 45°, 60° and 90° of knee flexion were analysed using the Pearson correlation coefficient and paired t-test.

RESULTS

Total rotation recorded with the skin pointer significantly correlated with the bone marker at 3 nm at 0° (skin pointer 23.9 ± 26.0° vs bone marker 16.3 ± 17.3°, r = 0.92; P = 0.0), 30° (41.7 ± 15.5° vs 33.1 ± 14.7°, r = 0.63; P = 0.037), 45° (49.0 ± 17.0° vs 40.3 ± 11.2°, r = 0.81; P = 0.002), 60° (45.7 ± 17.5° vs 34.7 ± 9.5°, r = 0.86; P = 0.001) and 90° (29.2 ± 10.9° vs 21.2 ± 6.8°, r = 0.69; P = 0.019) of knee flexion and 6 nm at 0° (51.1 ± 37.7° vs 38.6 ± 30.1°, r = 0.90; P = 0.0), 30° (64.6 ± 21.6° vs 54.3 ± 15.1°, r = 0.73; P = 0.011), 45° (67.7 ± 20.6° vs 55.5 ± 9.5°, r = 0.65; P = 0.029), 60° (62.9 ± 22.4° vs 45.8 ± 13.1°, r = 0.65; P = 0.031) and 90° (43.6 ± 17.6° vs 31.0 ± 6.3°, r = 0.62; P = 0.043) of knee flexion and at 9 nm at 0° (69.7 ± 40.0° vs 55.6 ± 30.6°, r = 0.86; P = 0.001) and 60° (74.5 ± 27.6° vs 57.1 ± 11.5°, r = 0.77; P = 0.006). No statistically significant correlation with 9 nm at 30° (79.2 ± 25.1° vs 66.9 ± 15.4°, r = 0.59; P = 0.055), 45° (80.7 ± 24.7° vs 65.5 ± 11.2°, r = 0.51; P = 0.11) and 90° (54.7 ± 21.1° vs 39.4 ± 8.2°, r = 0.55; P = 0.079). We recognize that 9 nm of torque may be not tolerated in vivo due to pain. Knee rotation was at its maximum at 45° of knee flexion and increased with increasing torque.

CONCLUSION

The skin pointer and knee rotation jig can be a reliable and simple means of quantifying knee rotational laxity with future clinical application.

Does gender make a difference in knee rotation proprioception and range of motion in healthy subjects?

BACKGROUND

Knee proprioception is an integral component of neuromuscular control system that stabilizes the joints, reducing incidence of injury. Knee injuries' incidences differ between genders. Knee rotation is a component of different knee injury mechanisms. Gender differences in knee proprioception in internal (IR) and external (ER) rotations are not sufficiently studied.

OBJECTIVE

To check whether proprioceptive acuity in IR and ER directions of knee rotation is inherently lower in women compared to men. Moreover, to assess gender difference in ranges of knee rotation.

METHODS

Thirty volunteers (15 women and 15 men) participated. Knee proprioception acuity and ranges of knee rotation were assessed using the knee rotatory kinesthetic device (KRKD). Proprioception was tested using absolute judgment task, subject's ability to discriminate different rotation movements (stimuli) randomly presented, then just notable difference (JND) was calculated; least difference accurately discriminated in 75% of trials.

RESULTS

Women had lower proprioception acuity in IR than men (1.70∘± 0.79∘ and 1.12∘± 0.32∘, p= 0.011) respectively. Active IR (women: 41.29∘± 7.46∘, men 32.80∘± 3.64∘, p= 0.000), and passive IR (women: 53.43∘±11.67∘, men: 37.94∘± 5.22∘, p= 0.000) were higher in women compared to men. Active ER (women: 49.71∘± 11.37∘, men: 39.16∘± 5.46∘, p= 0.003), and passive ER (women: 62.29∘± 13.74∘, men: 48.89∘± 7.09∘, p= 0.002) were, also, higher in women.

CONCLUSION

Gender difference in knee proprioception acuity was found in IR, which is the direction of rotation that anterior cruciate ligament (ACL) stabilize. Women's ranges of knee rotation are greater than men in both IR and ER.

Method for Estimating Three-Dimensional Knee Rotations Using Two Inertial Measurement Units: Validation with a Coordinate Measurement Machine

Three-dimensional rotations across the human knee serve as important markers of knee health and performance in multiple contexts including human mobility, worker safety and health, athletic performance, and warfighter performance. While knee rotations can be estimated using optical motion capture, that method is largely limited to the laboratory and small capture volumes. These limitations may be overcome by deploying wearable inertial measurement units (IMUs). The objective of this study is to present a new IMU-based method for estimating 3D knee rotations and to benchmark the accuracy of the results using an instrumented mechanical linkage. The method employs data from shank- and thigh-mounted IMUs and a vector constraint for the medial-lateral axis of the knee during periods when the knee joint functions predominantly as a hinge. The method is carefully validated using data from high precision optical encoders in a mechanism that replicates 3D knee rotations spanning (1) pure flexion/extension, (2) pure internal/external rotation, (3) pure abduction/adduction, and (4) combinations of all three rotations. Regardless of the movement type, the IMU-derived estimates of 3D knee rotations replicate the truth data with high confidence (RMS error < 4 ° and correlation coefficient r ≥ 0.94 ).

Kinematic analysis of stair climbing in rotating platform cruciate-retaining and posterior-stabilized mobile-bearing total knee arthroplasties

INTRODUCTION

The aim of our study was to compare and contrast the effects of two types of mobile-bearing total knee arthroplasties (TKA), namely, the cruciate-retaining (CR) and posterior-stabilized (PS) TKAs, on clinical outcomes and in vivo kinematics during stair climbing.

MATERIALS AND METHODS

The Press-Fit Condylar Sigma rotating platform was used for both CR and PS TKAs. Patient-reported outcomes were assessed using the 2011 Knee Society Score. Quadriceps muscle strength was evaluated by isokinetic dynamometry. In vivo kinematics were evaluated using periodic sagittal plane radiographic images obtained during stair climbing to quantify anteroposterior (AP) tibiofemoral translation, implant flexion and axial rotation angles using image-matching techniques. Outcomes were evaluated in 20 TKAs, which had been undergone with clinical success, including ten knees with CR types and ten knees with PS types.

RESULTS

There were no significant differences between the CR and PS TKA groups (p > 0.05) in isometric extensor torque (1.0 ± 0.2 and 1.1 ± 0.6 N m/kg, respectively) or patient-reported score for stair climbing function (4.0 ± 0.5 and 3.8 ± 0.9, respectively). Both types of TKAs showed stable AP translation in the mid range of knee flexion and paradoxical translation in the low range of flexion, with limited rotation, during stair climbing. There were no significant differences between the CR and PS TKA groups (P > 0.05) in anterior translation from 80° to 40° of knee flexion (4.2 ± 1.2 and 3.5 ± 1.6 mm, respectively), posterior translation from 40° to 10° of knee flexion (2.3 ± 1.9 and 2.0 ± 1.5 mm, respectively), and total external rotation (2.8° ± 4.9° and 0.5° ± 5.0°, respectively).

CONCLUSIONS

Both CR and PS types of rotating platform mobile-bearing TKAs provided reproducible knee joint kinematics during stair climbing and equivalent clinical outcomes.

LEVEL OF EVIDENCE

IV.

Clinical assessment of antero-medial rotational knee laxity: a systematic review

PURPOSE

To inventory the examination methods available to assess antero-medial rotational laxity (AMRL) of the knee following medial collateral ligament injury.

METHODS

Searches were conducted in accordance with the PRISMA guidelines and using four online databases: WEB OF SCIENCE, MEDLINE, EMBASE, and AMED. The Critical Appraisal Skills Programme guidelines for Diagnostic Test Studies were used for the quality assessment of the articles.

RESULTS

A total of 2241 articles were identified from the database searches. From this, four articles were included in the final review. All were case-control studies, considered a combined ACL/MCL injury and had small study populations. Specialised equipment was required in all studies, and one needed additional imaging support before measurements could be taken. Two employed commercially available measuring equipment as part of the assessment process.

CONCLUSION

Clinical assessment of AMRL in relation to a MCL injury remains challenging. Although methods have been developed to support clinical examination, they are limited by a number of factors, including the need for additional time in the clinical environment when setting up equipment, the need for specific equipment to produce and measure rotational movement and imaging support. In addition, there are patient safety concerns from the repeated imaging. A reliable and valid clinical examination remains to be found to truly assess antero-medial rotational laxity of the knee.

LEVEL OF EVIDENCE

IV.

The Restoration of Passive Rotational Tibio-Femoral Laxity after Anterior Cruciate Ligament Reconstruction

While the anterior cruciate ligament (ACL) is considered one of the most important ligaments for providing knee joint stability, its influence on rotational laxity is not fully understood and its role in resisting rotation at different flexion angles in vivo remains unknown. In this prospective study, we investigated the relationship between in vivo passive axial rotational laxity and knee flexion angle, as well as how they were altered with ACL injury and reconstruction. A rotometer device was developed to assess knee joint rotational laxity under controlled passive testing. An axial torque of ±2.5Nm was applied to the knee while synchronised fluoroscopic images of the tibia and femur allowed axial rotation of the bones to be accurately determined. Passive rotational laxity tests were completed in 9 patients with an untreated ACL injury and compared to measurements at 3 and 12 months after anatomical single bundle ACL reconstruction, as well as to the contralateral controls. Significant differences in rotational laxity were found between the injured and the healthy contralateral knees with internal rotation values of 8.7°±4.0° and 3.7°±1.4° (p = 0.003) at 30° of flexion and 9.3°±2.6° and 4.0°±2.0° (p = 0.001) at 90° respectively. After 3 months, the rotational laxity remained similar to the injured condition, and significantly different to the healthy knees. However, after 12 months, a considerable reduction of rotational laxity was observed towards the levels of the contralateral controls. The significantly greater laxity observed at both knee flexion angles after 3 months (but not at 12 months), suggests an initial lack of post-operative rotational stability, possibly due to reduced mechanical properties or fixation stability of the graft tissue. After 12 months, reduced levels of rotational laxity compared with the injured and 3 month conditions, both internally and externally, suggests progressive rotational stability of the reconstruction with time.

Objective measurements of static anterior and rotational knee laxity

Several devices allow to measure anterior and rotational static knee laxity. To date, the use of rotational laxity measurements in the daily clinical practice however remains to be improved. These measurements may be systematically integrated to the follow-up of knee injuries. Physiologic laxity measurements may particularly be of interest for the identification of risk factors in athletes. Furthermore, knee laxity measurements help to improve the diagnosis of knee soft tissue injuries and to follow up reconstructions. Further prospective follow-ups of knee laxity in the injured/reconstructed knees are however required to conclude on the best treatment strategy for knee soft tissue injuries.

Low-Contact-Stress Knee Arthroplasty: Past History or Ahead of Time?

Low-contact-stress mobile-bearing (MB) total knee arthroplasty (TKA) can rely on a long history. Its concept comprises a combination of high condylar congruency and compensatory bearing rotation to promote load sharing. However, other MB designs have become available, and critical points have been raised about the benefit of MB in general. Although there is kinematic and kinetic support for the low-contact-stress concept, there is no tribologic or clinical proof of its superiority over fixed-bearing concepts. Further study should be controlled for differences in polyethylene quality and need to provide a measure of condylar congruency to differentiate authentic low-contact-stress variants form others. [Orthopedics. 2016; 39(3):e402-e412.].

In vivo kinematics of healthy male knees during squat and golf swing using image-matching techniques

PURPOSE

Participation in specific activities requires complex ranges of knee movements and activity-dependent kinematics. The purpose of this study was to investigate dynamic knee kinematics during squat and golf swing using image-matching techniques.

METHODS

Five healthy males performed squats and golf swings under periodic X-ray images at 10 frames per second. We analyzed the in vivo three-dimensional kinematic parameters of subjects' knees, namely the tibiofemoral flexion angle, anteroposterior (AP) translation, and internal-external rotation, using serial X-ray images and computed tomography-derived, digitally reconstructed radiographs.

RESULTS

During squat from 0° to 140° of flexion, the femur moved about 25 mm posteriorly and rotated 19° externally relative to the tibia. Screw-home movement near extension, bicondylar rollback between 20° and 120° of flexion, and medial pivot motion at further flexion were observed. During golf swing, the leading and trailing knees (the left and right knees respectively in the right-handed golfer) showed approximately five millimeters and four millimeters of AP translation with 18° and 26° of axial rotation, respectively. A central pivot motion from set-up to top of the backswing, lateral pivot motion from top to ball impact, and medial pivot motion from impact to the end of follow-through were observed.

CONCLUSIONS

The medial pivot motion was not always recognized during both activities, but a large range of axial rotation with bilateral condylar AP translations occurs during golf swing. This finding has important implications regarding the amount of acceptable AP translation and axial rotation at low flexion in replaced knees.

LEVEL OF EVIDENCE

IV.

Motion analysis of Chinese normal knees during gait based on a novel portable system

Normative tibiofemoral data of Chinese or Asian subjects during gait is rarely reported. This study is aimed at investigating the six-degree-of-freedom (6DOF) knee kinematics of adult Chinese during gait, based on a novel portable system. Twenty-eight healthy Chinese subjects (56 knees) were studied during their treadmill gaits. A set of optical marker clusters were attached to the thighs and shanks of each subject, who was tracked by an optical joint kinematics measurement system. Knee landmarks were initially digitized with respect to the marker cluster sets to determine the local coordinate systems for calculation of 6DOF knee joint kinematics. The range of motion (ROM) in 6DOF and 5 kinematic parameters were calculated and compared between bilateral knees and genders. We discovered that knee rotations, as well as motion in proximodistal and mediolateral translations, showed similar patterns in flexion and extension. However, the anteroposterior translations did not show a clear pattern. The results of ROM in 6DOF obtained in this study are comparable with those reported in existing literature. No statistical difference was found between left and right knees either in the ROMs or in the 5 kinematic parameters. However, the ROM in the mediolateral direction during gait was found to be higher in men than women (P=0.014). In addition, the femurs of female subjects rotated more internally than the femurs of male during the stance phase (P=0.011). We concluded that normal Chinese knees exhibited distinct gait patterns, except for anteroposterior motion. Women and men exhibit different axial rotations and mediolateral translation patterns during their treadmill gait.

Combined anterior and rotational laxity measurements allow characterizing personal knee laxity profiles in healthy individuals

PURPOSE

The aim of this study was to quantify sagittal and rotational knee laxity profiles taking into account individual influencing factors.

METHODS

Linear regression models were used to determine which individual characteristics (age, height, body mass and sex) influenced the outcome in a group of 104 healthy subjects. The standardized residuals were used as individualized (corrected) laxity scores and were combined to determine knee laxity profiles.

RESULTS

Anterior knee laxity was not influenced by individual characteristics. Rotational knee laxity was higher in females and inversely related to body mass. The correlation between anterior laxity and internal rotation scores was weak (r = 0.24, p = 0.02). The proportion of knees concerned by increased laxity scores (scores >1) was similar for anterior displacement, internal and external rotation (15 %). Only 32 % of the tested subjects showed a normal profile (score >-1 and <1) for all three directions, 33 % were concerned by hyperlaxity, 40 % by hypolaxity and 5 % by both.

CONCLUSIONS

The diversity of laxity profiles found here highlights that the interpretation of multidirectional knee laxity is complex and suggests the necessity for individualized care of knee diseases and injuries. These results contribute to the understanding of knee laxity and throw the basis for prevention strategies and improvement of treatment outcomes in injuries and diseases.

LEVEL OF EVIDENCE

Case series with no comparison groups, Level IV.

Mobile-bearing total knee arthroplasty: More rotation is evident during more demanding tasks

BACKGROUND

Some reports showed few but significant more axial femorotibial rotation in favor of mobile-bearing (MB) versus fixed-bearing (FB) total knee arthroplasty (TKA), mostly during knee bend fluoroscopic studies. The goal of the current study was to submit MB and FB groups of TKA patients to a turning activity, in which additional rotation was to be expected.

METHODS

Two consecutive cohorts of patients after TKA (10 FB and 11 MB knees in a total of 18 patients) were assessed using motion analysis five year postoperatively, while performing gait and sit-to-walk (STW) movements with and without turning steps.

RESULTS

Mean range of rotation in the FB group increased from 9.7° during gait, to 11.7° during STW straight, and to 14.3° during STW turning. Mean range of rotation in the MB group increased from 13.4° during gait to 21.0° during STW straight, and stayed at 21.1° during STW turning.

CONCLUSIONS

Too many uncontrolled variables in the current study hinder a meaningful discrimination of MB from FB TKA rotation. However, the study does illustrate how more demanding task loads could be helpful in exploring the geometric constraints of TKA variants.

LEVEL OF EVIDENCE

Level III, therapeutic study.

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.