Measurement of Tibial Tuberosity–Trochlear Groove Offset Distance by Weightbearing Cone-Beam Computed Tomography Scan

Abstract

Background:Computed tomography (CT) scans are useful for objectively measuring bone alignment because they show bone detail particularly well, and these scans have been used extensively to assess patellar orientation. The tibial tubercle–trochlear groove (TT-TG) offset distance has been shown to be influenced by knee flexion and weightbearing, yet conventional CT scans are obtained with the subject relaxed, supine, and with the knee in full extension. A new cone-beam CT scanner has been designed to allow for weightbearing images, potentially providing a more physiologically relevant assessment of patellofemoral alignment.Purpose/Hypothesis:The purpose of this study was to measure the TT-TG offset in healthy individuals without any history of knee complaints when CT scans were obtained while fully weightbearing on a flexed knee. Our hypothesis was that the TT-TG offset measurement in these healthy knees would be reproducible and less than the historically reported normal range.Study Design:Cross-sectional study; Level of evidence, 3.Methods:Twenty healthy volunteers without any history of knee complaint were recruited to undergo a weightbearing cone-beam CT scan of the knee flexed at 30°. The scans were reviewed by a radiologist and an orthopaedic surgeon, and TT-TG offset was measured using the digital tools of a picture archiving and communication system. Paired t tests were used to compare TT-TG offset on 2 separate occasions for both raters. Inter- and intrarater reliability were assessed using a 2-way mixed-effects model intraclass correlation coefficient with corresponding 95% confidence intervals for TT-TG offset.Results:The mean TT-TG offset was 2.7 mm. There were no statistically significant differences in TT-TG offset between raters (P rater1 = .70; P rater2 = .49) and time of read (P time1 = .83; P time2 = .19). Good to moderate interrater reliability was found at the time of both reads, and good intrarater reliability was found for both raters.Conclusion:When measured by CT scan and obtained from a subject while weightbearing on a flexed knee, the TT-TG offset is reproducible and the distance is less than that obtained via a conventional CT scan.

Weight bearing versus conventional CT for the measurement of patellar alignment and stability in patients after surgical treatment for patellar recurrent dislocation

“…Tilt and congruence angles and TT-TG offset were all found significantly smaller under weight-bearing condition compared to conventional CT scan. Later, the same authors investigated the possible TT-TG offset variation between conventional CT and CBCT in a population of normal subjects [ 16 ] and concluded that also in this case CBCT scans result in significantly smaller values.…”

“…A p value of less than 0.05 was considered to be statistically significant; otherwise, the nonsignificance was indicated. The size of the patient sample analyzed in the present study was estimated by considering previous relevant literature [ 16 , 17 ], reporting the same acquisition technique as in the present study, and meets the criteria for achieving differences in measurements with 80% statistical power and a level of 0.05.…”

“…The original raw data-set is three-dimensional (3D), but standard bi-dimensional views in Dicom format are available in a few minutes [ 13 , 14 ]. In a few previous studies, CBCT scanners have been used already to investigate variations of patellofemoral stability and alignment parameters between the standard supine position obtained with conventional CT and the weight-bearing position from CBCT, in healthy subjects [ 15 , 16 ] and in patients diagnosed with lateral patellar instability [ 17 ]. To the best of the authors’ knowledge, no studies have been conducted yet in patients surgically treated via MPFL for recurrent patellar instability.…”

Atlas-based algorithm for automatic anatomical measurements in the knee

“…[1][2][3] Assessment and correction of patellar instability involve measurements of trochlear groove and position of the patella relative to other bones. 1,[4][5][6] Anatomical metrics might also provide risk stratification in anterior cruciate ligament injury. 3,[7][8][9] However, the repeatability and reliability of anatomical measurements are often challenged by factors associated with operator training and measurement techniques, 1,[10][11][12] diminishing their potential as quantitative biomarkers.…”

“…The proposed algorithm is applied to data of 24 subject volunteers acquired with a specialized extremity CBCT scanner. 23 Extremity CBCT systems provide the unique capability for weight-bearing three-dimensional (3-D) imaging of the knee 4,15,24 and foot. 15,24,25 Development of diagnostic applications of this new modality will benefit from improvements in the workflow, repeatability, and reliability of anatomical measurements that are anticipated with the automatic algorithm.…”