Abstract
Objectives:
The choice of graft for anterior cruciate ligament (ACL) reconstruction is dependent on a number of factors. However, in adolescents with closing or closed physes, patellar tendon bone-tendon-bone (BTB) autograft has demonstrated higher rates of return to sport and lower rates of revision, when compared to hamstring tendon autograft. ACL graft size may be one predictor of post-operative success as smaller graft diameter is associated with higher rates of rupture requiring revision. Measuring the intra-articular tendinous graft diameter in a BTB graft with standard intra-operative methods is difficult given that cylindrical sizing tubes must pass over the eccentric bone plugs, which tend to be larger than the central soft tissue region. Previous ultrasound and magnetic resonance imaging (MRI)-based studies have validated methods for measuring patellar tendon thickness, yet variance in patellar tendon graft size, including the influence of age and sex, has not been well studied. Therefore, the purpose of this study was to determine the cross-sectional area of the soft tissue portion of a standard 10mm BTB autograft and, by calculation, determine the “collagen graft size” (i.e. graft diameter), as would typically be reported in ACL reconstruction studies. Secondarily, the study sought to assess variance in BTB graft diameter based on age and sex.
Methods:
A total of 100 patients (10 females and 10 males at each age from 13-17) who underwent a knee MRI at a single academic orthopedic center without documented extensor mechanism pathology were included.
After confirming acceptable interrater reliability, patellar tendon cross-sectional areas were measured using MRI images by two independent, blinded examiners and averaged for all analyses. Using the multiplanar reformation (MPR) mode, on the axial plane image the central 10 mm of the patellar tendon that would be harvested for BTB autograft was measured. The Region of Interest (ROI) Area tool was then used to measure the cross-sectional area of a 10-millimeter BTB graft (
Intraclass correlation coefficient (ICC) values (via 2-way random-effects model for single measure absolute agreement) were calculated for all measured cross-sectional areas. A threshold coefficient greater than 0.70 indicates sufficient inter-rater reliability. Cross-sectional areas were compared between sex and age using independent samples t-tests and ANOVA, respectively, with a two-tailed significance threshold of P ≤ 0.05. Coefficient of variation was calculated as the ratio of the standard deviation to the mean value. SPSS version 22.0 (IBM Corp., Armonk, NY) was used for all statistical analysis.
Results:
A total of 100 adolescent patients were included in this study, 50 male and 50 female. All patients’ MR imaging showed evidence of closing or closed physes. The mean age was 15.5 years. The intraclass correlation coefficient for cross-sectional areas between the two examiners was 0.72, 95% CI: [0.609, 0.802]. The average between the two measurements for each image were subsequently calculated and used in all downstream analyses. The mean cross-sectional area was 32 ± 5.13 mm2 (coefficient of variation = 0.16) (
Conclusions:
Modern imaging-based measurement techniques demonstrate that the true intra-articular tendinous soft tissue portion of 10mm BTB autografts show great variance, but the large majority are under 7mm in diameter and therefore significantly smaller than quad tendon and most hamstring tendon autografts utilized in ACLR surgery today. In light of favorable overall re-tear rates, relative to other graft options, these data suggest the advantages of the BTB construct may stem from graft features other than the actual collagenous intra-articular segment, such as minimal creep, immediate relative rigidity and preservation of the critical dynamic knee flexors/stabilizers. Moreover, future comparative clinical research involving BTB and soft tissue autografts should consider quantifying and utilizing the diameter of the soft tissue component of BTB autografts, which is feasible utilizing MRI-based methods, rather than utilizing the diameter of the associated bone plugs and tunnels.
