A new, low cost, locking plate for the long-term fixation of a critical size bone defect in the ratfemur: in vivo performance, biomechanical and finite element analysis.

BACKGROUND: The optimum fixation device for the critical size bone defect is not established yet. OBJECTIVE: A reliable, feasible and low-cost fixation device for the long-term maintenance of a critical bone defect. METHODS: A custom-made plate made of poly-methyl-methacrylate was used for the fixation of a critical defect of rats' femurs. The screws were securely fixing both on the plate and the bone. A three point bending test, aimed to resemble the in vivo loading pattern, a Finite Element Analysis and a 24-week in vivo monitoring of the integrity of the plate fixation were utilized. RESULTS: The plate has linear and reproducible behavior. It presents no discontinuities in the stress field of the fixation. Its properties are attributed to the material and the locking principle. It fails beyond the level of magnitude of the normal ambulatory loads. In vivo, 100% of the plates maintained the bone defect intact up to 12 weeks and 85% of them at 24 weeks. CONCLUSION: This novel locking plate shows optimal biomechanical performance and reliability with high long-term in vivo survival rate. It is fully implantable, inexpensive and easily manufactured. It can be qualified for long term critical defect fixation in bone regeneration studies.

The scapholunate interosseous ligament afferent proprioceptive pathway: a human in vivo experimental study.

PURPOSE: To examine the afferent pathways of the scapholunate interosseous ligament (SLIL)-generated stimuli and their contribution to the overall carpal proprioception. METHODS: We examined 5 selected patients with preganglionic global root avulsion, confirmed by previous brachial plexus exploration, during the initial stage of carpal arthrodesis surgery. Despite their anesthetic-flail extremity, both the distal axon and the ganglionic cell were intact and able to transfer afferent stimuli. We placed electrodes subcutaneously over the adjacent areas of the ulnar, median, and radial nerves at the elbow region and performed an intraoperative neurophysiologic study. We studied the homologous sensory action potentials (SAPs) generated at the wrist in relaxation, flexion, extension, radial deviation, and ulnar deviation positions at each nerve and repeated them in 2 stages. The first took place with the SLIL intact and the second with the SLIL lacerated. The noise from the rest of the wrist elements was digitally eliminated. RESULTS: After the SLIL laceration, SAP intensities recorded at the median nerve in every wrist position were reduced. The radial and ulnar nerves showed differences of lesser degrees between the recorded SAP intensities before and after the ligament sectioning in every carpal position, with only the radial nerve following a specific pattern. The SAP intensity recorded at the median nerve in every carpal motion after the SLIL laceration was similar to the SAP intensity at relaxation with the SLIL intact, whereas recordings of various intensities were present for the radial and ulnar nerves. CONCLUSIONS: The SLIL generates proprioceptive stimuli at every wrist position. The main innervation of the whole SLIL derives from the anterior interosseous nerve; a partial contribution of the posterior interosseous nerve focused on the dorsal subregion of the ligament may also be present.