Anterior Cruciate Ligament Graft Tunnel Placement and Graft Angle Are Primary Determinants of Internal Knee Mechanics After Reconstructive Surgery

Abstract

Background: Graft placement is a modifiable and often discussed surgical factor in anterior cruciate ligament (ACL) reconstruction (ACLR). However, the sensitivity of functional knee mechanics to variability in graft placement is not well understood. Purpose: To (1) investigate the relationship of ACL graft tunnel location and graft angle with tibiofemoral kinematics in patients with ACLR, (2) compare experimentally measured relationships with those observed with a computational model to assess the predictive capabilities of the model, and (3) use the computational model to determine the effect of varying ACL graft tunnel placement on tibiofemoral joint mechanics during walking. Study Design: Controlled laboratory study. Methods: Eighteen participants who had undergone ACLR were tested. Bilateral ACL footprint location and graft angle were assessed using magnetic resonance imaging (MRI). Bilateral knee laxity was assessed at the completion of rehabilitation. Dynamic MRI was used to measure tibiofemoral kinematics and cartilage contact during active knee flexion-extension. Additionally, a total of 500 virtual ACLR models were created from a nominal computational knee model by varying ACL footprint locations, graft stiffness, and initial tension. Laxity tests, active knee extension, and walking were simulated with each virtual ACLR model. Linear regressions were performed between internal knee mechanics and ACL graft tunnel locations and angles for the patients with ACLR and the virtual ACLR models. Results: Static and dynamic MRI revealed that a more vertical graft in the sagittal plane was significantly related ( P < .05) to a greater laxity compliance index ( R2 = 0.40) and greater anterior tibial translation and internal tibial rotation during active knee extension ( R2 = 0.22 and 0.23, respectively). Similarly, knee extension simulations with the virtual ACLR models revealed that a more vertical graft led to greater laxity compliance index, anterior translation, and internal rotation ( R2 = 0.56, 0.26, and 0.13). These effects extended to simulations of walking, with a more vertical ACL graft inducing greater anterior tibial translation, ACL loading, and posterior migration of contact on the tibial plateaus. Conclusion: This study provides clinical evidence from patients who underwent ACLR and from complementary modeling that functional postoperative knee mechanics are sensitive to graft tunnel locations and graft angle. Of the factors studied, the sagittal angle of the ACL was particularly influential on knee mechanics. Clinical Relevance: Early-onset osteoarthritis from altered cartilage loading after ACLR is common. This study shows that postoperative cartilage loading is sensitive to graft angle. Therefore, variability in graft tunnel placement resulting in small deviations from the anatomic ACL angle might contribute to the elevated risk of osteoarthritis after ACLR.

The effect of modelling parameters in the development and validation of knee joint models on ligament mechanics: A systematic review

“…According to the quality assessment results presented in Table 2 , several articles had limited modelling technique descriptions [ 15 , 16 , 19 , 20 , 27 , 33 ] and validation methods [ 16 , 18 , 25 , 27 , 35 , 37 , 38 ]. In 12 of the selected studies [ 14 – 17 , 20 , 24 – 27 , 31 , 37 , 38 ], the sensitivity of the model outputs on ligament model parameters has not been assessed.…”

“…A range of musculoskeletal modelling software packages has been used across the selected studies ( Fig 2A and Table 3 ). 14 studies [ 15 – 17 , 20 – 25 , 27 , 29 , 32 , 34 , 35 ] used OpenSim [ 39 ], four studies [ 18 , 36 – 38 ] used SIMM [ 40 ], two studies [ 26 , 28 ] used AnyBody Modelling System (AnyBody Technology, Aalborg, Denmark), one study [ 30 ] used ADAMS [ 41 ], one study [ 14 ] used SimWise-4D platform (Design Simulation Technologies, DST, Canton, MI, USA), one study [ 19 ] used KneeSIM (LifeModeler Inc., San Clemente, CA), one study [ 33 ] used Musculoskeletal Joint Modeler [ 42 ], and one study [ 31 ] used Working Model 3D (Working Model 3D, MSC, Software Corp., Santa Ana, CA, USA).…”

“…Out of the 25 studies included, 20 studies were designed to simulate the intact knee joint [ 14 – 17 , 19 – 22 , 24 – 27 , 29 – 34 , 37 , 38 ], two studies modelled both intact and ACL-deficient knee [ 35 , 36 ], one study modelled the intact and PCL-deficient knees [ 28 ], one study modelled the ACL-reconstructed knee [ 18 ], and one study modelled the lateral extra-articular reconstructed knee [ 23 ] ( Fig 2B and Table 3 ). Nine studies modelled one leg [ 19 , 21 , 23 , 24 , 29 – 31 , 33 , 36 ], eight studies developed the whole-body models [ 15 , 16 , 20 , 22 , 26 – 28 , 34 ] and eight studies modelled the lower-body [ 14 , 17 , 18 , 25 , 32 , 35 , 37 , 38 ] ( Fig 2C and Table 3 ).…”

“…These models included geometry from 127 participants/patients’ knees and three cadaveric knees. Intact knee geometries were extracted fully or partially from segmented medical imaging (CT or MRI) of cadaveric specimens [ 25 , 26 , 30 ], participants [ 14 , 21 , 23 , 24 , 29 , 31 , 36 ], patients [ 18 , 22 ], saw bone [ 33 ] or by scaling the generic reference models based on anthropometric data of study participants [ 15 – 17 , 20 , 21 , 27 , 28 , 32 , 34 , 35 , 37 ] ( Fig 2D and Table 3 ). In the rest of the studies, the geometry was taken from available data in the literature [ 19 , 38 ].…”

“…Six studies included the femoral and tibial cartilages [ 14 , 18 , 26 , 28 , 30 , 33 ] and three studies had the femoral cartilage only [ 17 , 25 , 29 ] ( Fig 2E and Table 3 ). The remainder of the studies did not consider cartilage geometry.…”