Knee positioning systems for X-ray environment: a literature review

Ultrasound-based bone tracking using cross-correlation enables dynamic measurements of knee kinematics during clinical assessments

Purpose

Measuring joint kinematics in the clinic is important for diagnosing injuries, tracking healing and guiding treatments; however, current methods are limited by accuracy and/or feasibility of widespread clinical adoption. Therefore, the purpose of this study was to develop and validate an ultrasound (US)-based method for measuring knee kinematics during clinical assessments.

Methods

We mimicked four clinical laxity assessments (i.e., anterior, posterior, varus, valgus) on five human cadaver knees using our robotic testing system. We simultaneously collected B-mode cine loops with an US transducer. We computed the errors in kinematics between those measured using our bone-tracking algorithm, which cross-correlated regions of interest across frames of the cine loops, and those measured using optical motion capture with bone pins. Additionally, we conducted studies to determine the effects of loading rate and transducer placement on kinematics measured using our US-based bone tracking.

Results

Pooling the trials at experimental speeds and those downsampled to replicate clinical laxity assessments, the maximum root-mean-square errors of knee kinematics using our bone-tracking algorithm were 2.2 mm and 1.3° for the anterior-posterior and varus-valgus laxity assessments, respectively. Repeated laxity assessments proved to have good-to-excellent repeatability (intraclass correlation coefficients [ICCs] of 0.81-0.99), but ICCs from repositioning the transducer varied more widely, ranging from poor-to-good reproducibility (0.19-0.89).

Conclusion

Our results demonstrate that US is capable of tracking knee kinematics during dynamic movement. Because US is a safe and commonly used imaging modality, when paired with our bone-tracking algorithm, US has the potential to assess dynamic knee kinematics across a wide variety of applications in the clinic.

Level of Evidence

Not applicable.

Functional Imaging of the Knee-A Comprehensive Review

Knee pain is a common presenting problem in the general population. Radiographs and magnetic resonance imaging (MRI) are the cornerstones of imaging in current clinical practice. With advancements in technology, there has been increasing utilization of other modalities to evaluate knee disorders. Dynamic assessment utilizing computed tomography and portable ultrasounds have demonstrated the capacity to accurately assess and reproducibly quantify kinematics of knee disorders. Cartilage physiology can be evaluated with MRI. Emerging research has even demonstrated novel musculoskeletal applications of positron emission tomography to evaluate anterior cruciate ligament graft metabolic activity following reconstruction. As technology continues to evolve and traditional ways are improved upon, future comparative studies will elucidate the distinct advantages of the various modalities. Although radiology is still primarily an anatomic specialty, there is immense potential for functional imaging to be the standard of care. This review focuses on the most common musculoskeletal applications of functional imaging as well as future utilization.