Late Implant Failure in Cervical Disc Arthroplasty (M6-C, Spinal Kinetics) Causing Radiculopathy and Myelopathy

Cervical disc arthroplasty (CDA) is an approved surgical treatment option in selected patients with cervical spinal disc degeneration. Even though CDA is a standard procedure since 20 years, there is a lack of information about long term performance. The published reoperation rates after CDA are low and comparable to anterior cervical fusion. The authors describe a severe failure and dysfunction with a partial core dislocation of a cervical prosthesis into the spinal canal (M6-C, Spinal Kinetics, Sunnyvale, CA, USA). Six years after implantation of a cTDR (cervical Total Disk Replacement) of the M6 type at C4/5 level, a 52 year-old women presented herself with new clinical signs of cervical myelopathy and radicular pain. Complete posterior dislocation of the central core of the implant into the spinal canal was identified as a cause. The failed device was removed completely and an ACCF (anterior cervical corpectomy and fusion) was performed. Intraoperatively, rupture of the posterior portion of the mesh tissue with posterior dislocation of the whole prosthesis core was detected. This is the second described case of a severe implant failure with core dislocation in this type of cTDR device. Even though there are thousands of successful implantations and middle term outcomes, it seems to be necessary to continue with long term radiological follow up to exclude similar failure in this type of prosthesis.

The Transient Motion of a Ramp-Core Supersonic Dislocation

The transient motion of a ramp-core dislocation spreading from −∞<x<∞ and jumping from rest to a supersonic speed in the x direction, is investigated by analysis on the complex transform plane. The new result of this analysis is that, instead of the Mach cone of the Volterra dislocation, there are two lines of discontinuity (of the stress) propagating in the ±z directions, inside of which there are arctan delta sequence (ε≠0) radiated supersonic fields, as well as subsonic fields. The lines of discontinuity arise at the tangent point of the Mach wavefront (ε=0) to the cylinder with radius r=c2t.

Hexagonal Stacking at Order Interfaces Between Lamellae in TiAl

ABSTRACTStacking faults at order interfaces in TiAl have been examined by HREM. In addition to very extensive OCISF formation, C-core dislocation complexes spread over two parallel { 111 } planes have been observed at order interfaces lying predominantly parallel to the original (0002)α, planes. Such C-cores, corresponding to 1/2<211] and 1/2<112] interfacial dislocations, have been observed with localised regions of both extrinsic and hexagonal stacking.