PurposeModern total knee arthroplasty (TKA) systems are designed to reproduce the normal knee kinematics and improve patient outcome. The authors compared two different third‐generation medial pivot TKA implants, having a single‐radius or a J‐curve design in their sagittal plane, hypothesizing no clinical differences. MethodsTwo cohorts of 50 patients who underwent primary TKA were first preoperatively matched by sex, deformity, body mass index (BMI), Oxford Knee Score (OKS), Knee society score (KSS) and range of motion (ROM) and then statistically analyzed at a minimum follow‐up (FU) of 2 years. An identical surgical technique, which aimed to reproduce a slightly tighter medial than lateral compartment, was used in all knees. ResultsAt a minimum follow‐up of 2 years (range 24–34 months) there were no statistically significant differences in OKS and KSS between the two implant groups. The final ROM differed statistically between the two groups: the average maximum active flexion was 123° in the J‐curve femoral design group with an adapted “medially‐congruent” polyethylene insert, and 116° in the single radius femoral design with a medial “ball‐in‐socket” articulation. ConclusionNo clinical and radiological differences were found when the two cohorts of patients were compared. This study showed that the implant design played a minor role in the final outcome as opposed to a precise surgical technique. Level of evidenceRetrospective case‐control study, Level III.
Purpose The present study tested and compared the biomechanical properties of four different triplicate graft tendon techniques. Methods 32 tripled tendons from the common extensor muscle of bovine fingers were tested on a material testing machine, passing the end loop over a metal rod of a clevis connected to the load cell on the upper side, and fixing the lower end to a clamp. The samples were divided into four groups: (A) tripled with a free end sutured only to one of the two fixed bundles (B) tripled with a free end positioned between the two fixed strands and sutured to both (C) tripled with an S-shape and all the three strands sutured together at the upper and lower extremities of the graft (D) partially quadrupled with the free end sutured together with the other three bundles at the upper extremity. Each sample was pretensioned at 50 N for 10 min and then subjected to 1000 load control cycles between 50 and 250 N. Finally, each sample was subjected to a load to failure test. Authors also present some preliminary results on the feasibility of a non-contact and full-field Thermoelastic Stress Analysis technique, based on Infrared Thermography, to evaluate the level of stress on the whole graft, and hence on each strand, during fatigue loading. Results Eighty five percent of the samples failed at the level of the clamp. The cyclical elongation progressively decreased in all the samples and there was a simultaneous increase in stiffness. An increased stiffness was noted between Group 2 vs Group 3 and Group 2 vs Group 4 at the 500th and 1000th cycle. The failure loads were as follows: (a) 569.10 N, (b) 632.28 N, (c) 571.68 N, (d) 616.95 N. None of the parameters showed a statistically significant difference between the four groups. Conclusion This study reported similar biomechanical behavior of four different models of tripled grafts suitable for ACL reconstruction. In addition, the biomechanics of overall tripled tendon grafts seems more affected by the viscoelastic property of the tendon itself rather than the preparation method.
Purpose. This study aimed to compare the biomechanical proprieties of 4 and 5-strandgrafts. Methods. For the present study, fresh-frozen bovine common digital extensor tendons were used. Tendon grafts were prepared and sized to have a length of almost 27 cm and a cylinder 4 strand diameter of 8 mm. In half of all samples (Group A, n=12,), the graft was formed by 2 bundles duplicated around a metallic rod creating a 4-strand-tendon construct. In the other half of samples (Group B, n= 12,) 5-strand-tendon construct was created duplicating a single tendon around the rod, and tripling the other one. The grafts were preconditioned at 50 N for 10 min, followed by 1,000 cyclic loading between 50 and 250 N. Load-to-failure test was then carried out at a rate of 1 mm/s. Results. No statistically significant differences were found between two groups concerning cyclic elongation at the 500 th cycle and at the final cycle. An increased stiffness was observed in the Group B during cyclic loads and at pull-out (p<0.05). Significant differences were noted at the ultimate load-to-failure between Group A (1533 ± 454 N) and Group B (1139 ± 276 N) (p< 0.05). Conclusion. This study showed that both graft construct appears to be biomechanically effective in a bovine tendon model. 5-strand-graft showed an increased stiffness and a decreased ultimate load-to-failure comparing to the 4-strand-graft construct. Biomechanically, no real benefit could be observed in the clinical setting increasing the numbers of strands used for the ACL reconstructive surgery.
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