Biomechanics of patellar tendon autograft for reconstruction of the anterior cruciate ligament in the goat: Three‐year study

While a number of in vitro studies have shown that the tension on an anterior cruciate ligament (ACL) replacement graft at the time of fixation has an affect on joint stability, most in vivo studies have reported little or no long-term difference in outcome. The objectives of this study were to ( 1 ) establish a large animal model in which differences in knee stability are present at time-zero after ACL reconstruction with grafts fixed at a low ( 5 N) and high (35 N) initial tension and to ( 2 ) quantitatively determine if these initial effects remain after six weeks of healing and if the tensile properties of an ACL replacement graft are influenced by initial graft tension. Seventeen skeletally mature female Saanan breed goats were used. Using the roboticlUFS testing system, the knee kinematics and in situ forces in the replacement graft in response to an externally applied 67 N anterior-posterior (A-P) tibial load were evaluated at time-zero and after six weeks of healing. Afterward, the femur-ACL graft-tibia complexes (FGTCs) from the six-week group were tested under uniaxial tension so that the stress relaxation and structural properties of the FGTC were obtained.At time-zero, knees fixed with a high initial graft tension could better reproduce the A-P trailslation of the intact knee in response to the 67 N A-P tibial load. Further, in situ forces in these grafts were also closer to those in the intact ACL under the same external loading condition. After six weeks of healing, the A-P translation of the knee and in situ forces in the replacement grafts became similar for the low and high tension groups, while both were significantly different from controls. Further, the percentage of stress relaxation as well as the stiffness, ultimate load at failure, ultimate elongation at failure, and energy absorbed of the FGTCs for both reconstruction groups were not significantly different from each other, but were significantly different from controls. These results demonstrate that while the high initial graft tension could better replicate the normal knee kinematics at time-zero, these effects may diminish during the early graft healing process.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The effect of initial graft tension on the biomechanical properties of a healing ACL replacement graft: A study in goats

Abramowitch¹,

Papageorgiou²,

Withrow³

et al. 2003

“…The non-vascularized tendon graft subsequently undergoes a process of remodeling after implantation into the intraarticular environment by means of reorganizing its cellularity and extracellular matrix structure [40]. The process of graft tissue remodeling has been extensively studied in the past with respect to revascularization and reinervation, changes in cell morphology and distribu-tion, collagen fiber reorganization, and restoration of extracellular matrix protein distribution [3,4,6,[8][9][10]23,27,28,40]. So far the expression of cytoskeletal proteins as markers of phenotypic modulations of fibroblastic cells has not been investigated during cruciate ligament autograft remodeling.…”

Section: Introductionmentioning

confidence: 99%

α‐Smooth muscle actin is expressed by fibroblastic cells of the ovine anterior cruciate ligament and its free tendon graft during remodeling

Weiler

Unterhauser

Bail

et al. 2002

Contractile fibroblastic cells expressing the a-smooth muscle actin isoform, so-called myofibroblasts, have been identified to play a possible role during the healing of the medial collateral ligament by means of restoring the tissues in situ strain via extracellular matrix contraction. Recently, these cells have also been identified to be a normal part of the human anterior cruciate ligament. It has been hypothesized that myofibroblasts play a role in the wrinkling of the extracellular matrix. The goal of the present study was to identify myofibroblasts in the intact ovine anterior cruciate ligament and a free autologous tendon graft during remodeling after anterior cruciate ligament reconstruction. In 36 mature merino sheep the anterior cruciate ligament was replaced with an ipsilateral Achilles tendon split graft. Midsubstance tissue samples were immunostained for a-smooth muscle actin at 6,9, 12,24, 52, and 104 weeks. Myofibroblasts were identified in the intact ovine anterior cruciate ligament as well as in the Achilles tendon graft prior to implantation. During remodeling the first myofibroblasts were found at six weeks within newly formed fiber bundles. At 24, 52, and 104 weeks myofibroblast distribution and cell density were similar to those of the intact ovine anterior cruciate ligament. These findings indicate that a-smooth muscle actin containing fibroblastic cells are a regular part of the intact as well as the remodeled anterior cruciate ligament. There is evidence that myofibroblasts may be involved in maintaining tissue homeostasis in the mature ligament e.g., by means of crimp formation. The presence of these cells during the early remodeling may further indicate that asmooth muscle actin containing fibroblastic cells are involved in the earliest stages of fiber bundle formation. The role and function of this special cell type for the anterior cruciate ligament needs to be further clarified.

“…AP translations for unilateral ACL reconstructions in goats, dogs, and sheep and this study (at 30 N). The grey band represents the range of reported values (white circles) [7,9,[11][12][13]15,19,27,28]. AP translations ofjoints with ACL cut (black line) [9,15], at zero and six months represent an upper limit of AP translation.…”

mentioning

confidence: 99%

The effects of graft width and graft laxity on the outcome of caprine anterior cruciate ligament reconstruction

Cummings

Grood

Levy

et al. 2002

We studied how initial graft size and initial graft laxity alkcted the biomechanics of anterior cruciate ligament (ACL) reconstruction at six months. Sixteen goats had bilateral reconstructions staged eight weeks apart. Autografts 4 and 7 mm wide were taken from the central patellar tendon (PT). Lax grafts were created by adding 4 mm slack to the graft before fixing. We reconstructed each joint using a combination of width and laxity treatments. Both factors were changed for the contralateral joint and all combinations appeared with equal frequency. At six months we measured the joint extension limit, anterior-posterior (AP) translation, and osteoarthritic changes. The grafts were then tested to failure to determine their mechanical properties. After six months the difference in initial treatments had disappeared: there was no difference in graft cross-section due to the different initial widths and there was no difference in joint AP translation due to the initial graft laxity. We did observe that wide grafts were associated with a block to extension, decreased joint A P translation, and increased articular cartilage damage and osteophyte formation. While AP translation was reduced, it was correlated with decreased extension, possibly indicating an increase in scar tissue formation rather than a more functional graft. Neither graft width nor graft laxity produced differences in any graft mechanical properties. This suggests that the use of larger grafts to prevent increased A P translation has undesirable complications. Ultimately, we conclude that neither of these surgical treatments strongly affects the biomechanical result of caprine ACL reconstruction.