Significant Differences In Stiffness Research Articles

Three-dimensional Load Displacement Properties of

Pedicular fixation devices for the posterior treatment of segmental spinal instability are thought to offer enhanced stabilization compared with sublaminar wire systems, while avoiding the immobilization of multiple normal motion segments. We compared the performance of three dissimilar stabilization systems: the Hartshill rectangle, the Acromed/Steffee interpedicular screw and plate, and the Synthes/Dick fixateur interne. Human cadaveric lumbosacral specimens were first tested intact, then after a laminectomy and a facetectomy at the L3/L4 level, and finally after the fixation devices were sequentially attached. Constructs spanning two to four vertebral levels were compared for stabilization of the resected lumbar spine segments. When tested in compression, the Acromed/Steffee system with pedicular screws at L2-L5 allowed significantly less intersegmental distraction than the Synthes/Dick construct with screws at L2 and L5 only, and less than the intact and the destabilized uninstrumented spine. When sagittally rotated, the Acromed/Steffee construct with screws at L2-L5, or at L2 and L5, allowed significantly less distraction than the intact or destabilized segments, and the construct with screws at L2 through L5 allowed less distraction than the Synthes/Dick constructs with screws at L3/L4 or L2/L5. With the exception of the Acromed/Steffee system with screws at four levels, there were no significant differences in distraction allowed between the Synthes/Dick and Acromed/Steffee constructs, or between the multisegment and single segment constructs. There were no significant differences in stiffness across levels L3/L4 with the various implants. Results indicate that the use of posterior spine constructs significantly augment the stability of posterior segmental defects. Pedicular fixation immediately cephalad and caudad to the defect provided stable fixation in this application.

Replacing the medial collateral ligament with an allogenic tendon graft. An experimental canine study

In order to determine whether an allogeneic tendon could be used to replace an extra-articular ligament, the right medial collateral ligament from 11 adult dogs was replaced with a fresh-frozen allogeneic patellar tendon. At each of 3, 6, 15, 30 and 52 weeks postoperatively, one dog was killed for micro-angiographical and histological studies; at 52 weeks the remaining six dogs were killed for tensile testing. Micro-angiograms showed that the allogeneic tendon was revascularised with infiltration of the mesenchymal cells from the surrounding tissues and both ends of the graft. Histologically, the alignment of the fibroblasts and collagen bundles became more regular over time, without any immunological rejection. A biomechanical study performed at 52 weeks found no significant difference in stiffness or ultimate load between normal and reconstructed ligaments. Fresh-frozen allogeneic tendons are therefore considered useful for extra-articular ligament reconstruction.

Treatment of the Anterior Cruciate Ligamentabsent Knee with Associated Meniscal Tears Instrumented Testing and Clinical Evaluation of Two Patient Groups

The UCLA instrumented clinical testing apparatus was used to measure postoperative stiffness and laxity for two groups of patients with documented chronic absence of the anterior cruciate ligament (ACL) and associated meniscal tears. Group 1 consisted of 76 patients (average age, 25 years) who had undergone anterior cruciate substitution using the torn meniscus, and a second group of 34 patients (average age, 31 years) who had partial meniscectomy alone without ACL substitution. Subjective and objective evaluations were significantly higher and symptoms of pain and buckling significantly lower in the substitution group. In addition, 29% of Group 1 and only 7% of Group 2 patients were able to return to their preinjury sports without limitations, while 5% of the former and 12% of the latter could not return to any sport. At 90 degrees of flexion, there were no significant differences in stiffness or laxity between the patient groups. At 20 degrees of flexion and neutral foot rotation, the meniscal substitution group had an average of 1.4 mm less side-to-side laxity difference than the partial meniscectomy patients; 51% of the substituted patients still had an injured knee laxity that was at least 2 mm greater than the uninjured knee, as contrasted to 67% of the partial meniscectomy patients who exceeded this upper limit of the normal range. At 20 degrees, anterior stiffness of the injured knees of the substitution patients was 28% greater than the injured knees of the partial meniscectomy group; 42% of the substituted patients had an injured knee stiffness within the normal range, while only 18% of the partial meniscectomy patients fell within normal limits. There were no statistical correlations of stiffness or laxity values with clinical scores or patient symptomatology in either group.