The effect of a nonanatomic repair of the meniscal horn attachment on meniscal tension: a biomechanical study.

PURPOSE: The purpose of this biomechanical study was to investigate the potential effect of a nonanatomic repair of the meniscal horn attachment on the resultant circumferential tension in a large animal model and to show that the circumferential tension of the meniscus affects the local stress of the cartilage. METHODS: All investigations were done in the medial compartment of porcine knees. First, the anterior horn attachment of the meniscus was mechanically separated from the surrounding tibial bone and fitted with a force transducer (n = 8). The femorotibial joint was loaded in compression at different flexion angles, and the resultant tension at the horn attachment was recorded. The measurements were done with the horn attachment at its anatomic position and repeated with the horn attachment being displaced medially or laterally by 3 mm. In the second part the local deformation of the cartilage under a femorotibial compressive load was measured at different levels of meniscal hoop tension (n = 5). RESULTS: A nonanatomic position of the horn attachment had a significant effect on the resultant tension (P < .01). Placing the horn attachment 3 mm medially decreased the tension at the horn attachment by 49% to 73%, depending on flexion angle and femorotibial load. The opposite placement resulted in a relative increase in the tension by 28% to 68%. Lower levels of meniscal hoop tension caused increased deformation of the cartilage (P < .05), indicating increased local stress. CONCLUSIONS: A nonanatomic position of the horn attachment strongly affects conversion of femorotibial loads into circumferential tension. There is a narrow window for a functionally sufficient repair of meniscal root tears. CLINICAL RELEVANCE: Although clinical inferences are limited because the specimens used were from a different species, there seems to be only a narrow window for a mechanically sufficient repair of root tears.

ACL graft migration under cyclic loading.

Elongation and migration of ACL grafts will lead to a deterioration of the initial stability of ACL reconstructions. The graft migration has been sparsely investigated independently from the elongation of the graft-fixation complex. The hypothesis of this investigation was that cyclic tensile loads cause a measurable migration of the grafts. Three graft/fixation combinations were investigated in human femora (n = 7): human bone-patellar tendon grafts fixed with a biointerference screw (BPTG-IS) and free tendon grafts (porcine) fixed with either a Bio-TransFix pin (FTG-TF) or an Endobutton CL (FTG-EB). The grafts were fitted with tantalum markers. Then, the specimens were repetitively loaded (50-250 N, 800 cycles). The marker position was fluoroscopically determined at defined intervals and the migration calculated from the change in position relative to a fiducial marker within the bone. A migration of the grafts occurred in all three groups. The migration in the FTG-EB group was significantly larger than in the two other groups (P < 0.01). After 800 cycles, average migration was 0.3 (+/-0.2) mm in the BPTG-IS group, 0.7 (+/-0.4) mm FTG-TF group, 2.0 (+/-1.3) mm in the FTG-EB group. This migration might contribute to a loss of initial stability. Because the graft migration was dependent on the technique, the presented data might provide additional arguments for making the decision on the most appropriate graft/fixation combination.

Tensile forces at the porcine anterior meniscal horn attachment.

Tibiofemoral compression causes circumferential tension in the knee meniscus, which is transferred to the tibial bone at the anterior and posterior attachments. The objective of the study was to measure the resulting tensile forces at the horn attachment in a porcine model. The anterior horn attachment of the porcine medial meniscus (n = 10) was separated from the surrounding bone with a core reamer. A force transducer was installed such that tensile forces acting upon the now mobile horn attachment could be measured. The tibiofemoral joint was loaded in compression, starting at a preload of 30 N, with three 150-N increments, giving 180, 330, and 480 N load. Flexion angles of 0, 30, and 60 degrees were investigated. The average resultant tension at the horn attachment was 26.3, 40.6, and 55.4 N with full extension, 29.2, 47.8, and 62.2 N at 30 degrees flexion and 30.1, 49.6, and 68.1 N at 60 degrees flexion. The tibiofemoral compression had a significant effect on the tension (p < 0.001), whereas no influence of the flexion angle was found (p = 0.291). The study demonstrates that tibiofemoral compressive loads cause considerable tensile forces at the anterior meniscal horn attachment. The data are of interest for models of the repair or replacement of the knee menisci.

Tensile forces on sutures in the human lateral knee meniscus.

Tensile strength is the most often reported parameter in biomechanical investigations of meniscal repair techniques. However, the magnitude of the tensile forces that actually occur on repaired lesions is not clear. The purpose of this study was to investigate if tensile forces occur on repaired lateral meniscal lesions, which could exceed the failure strength of common repair techniques. In human knees (n = 6), vertical-longitudinal lesions 25 mm in length were created in the posterior horn of the lateral meniscus at a distance of 3 mm from the meniscosynovial junction and the popliteal hiatus. A braided steel wire, resembling a vertical suture, was inserted into the meniscal tissue and fitted with a force transducer. The knees were mounted in an apparatus, which simulated weight bearing and non-weight bearing conditions. Repeated measurements were conducted with both internal and external rotation at flexion angles of 0 degrees , 30 degrees , 60 degrees , 90 degrees and 120 degrees . Weight loading alone caused no tension on the suture. Combined flexion and rotation generated mean forces between 0.5 and 4.1 N. No significant effect of the flexion angle or direction of rotation was found. If a minimum strength of 10 N was assumed for the common meniscal repair techniques, the tensile forces were well below this limit under all circumstances (P < 0.001). These data indicate that, within the range of motion investigated, no significant tensile forces occur on longitudinal lateral lesions. Forces other than tension and biological factors are of greater importance for the healing. Therefore, the assessment of repair techniques should not be based on alone the ability to resist high distraction forces.

Distraction forces on repaired bucket-handle lesions in the medial meniscus.

BACKGROUND: Numerous studies have investigated the biomechanical properties of meniscal repair techniques. One of the most commonly discussed parameters is the failure load in the axis of insertion, although little is known about the distraction forces actually occurring at repaired bucket-handle lesions. HYPOTHESIS: There are clinically relevant distraction forces on repaired meniscus bucket-handle lesions. STUDY DESIGN: Controlled laboratory study. METHODS: Meniscus bucket-handle lesions were created and repaired in human cadaveric knees with a vertical suture made from a braided steel wire. A small-sized load sensor was connected to the wire at the periphery of the meniscus. The distraction forces acting on the lesion were measured at different knee joint angles (0 degrees -120 degrees of flexion) with internal and external rotation and with and without weight loading. Forces in excess of 10 N were considered to have clinical relevance. RESULTS: Mean forces on the meniscus repair ranged from 1.64 to 4.72 N. Irrespective of the modalities (ie, different flexion angles, weight load, direction of rotation), it was found that the forces were well below the cutoff value of 10 N (P < .01). Increasing flexion angles generally did not cause an increase in distraction forces. CONCLUSION: The data suggest that distraction forces are not the primary factor in the mechanical stability of meniscal repair. It must therefore be assumed that other factors such as shear forces are of greater significance. CLINICAL RELEVANCE: The results may help to validate the biomechanical properties of different meniscal repair techniques.