Hybrid revision total hip arthroplasty: a 7-year follow-up study.

The hybrid method for fixation of total hip arthroplasty (THA) has shown excellent results during the first decade in primary operations. To investigate its role in revision surgery, data on 48 revision THAs in 45 patients that met the inclusion criteria were gathered prospectively, using HGP cementless acetabular components and precoated cemented femoral components inserted with so-called second generation femoral cementing technique in each case. For the 48 hips during an average follow-up period of 7.4 years, no acetabular components was loose or had pelvic lysis. One acetabular component was revised for recurrent dislocation; 1 of 48 femoral components was revised for aseptic loosening and 1 for periprosthetic fracture. Three additional femoral stems (6%) were loose. In this small series, the hybrid concept for revision of failed nonseptic THAs has shown excellent results.

The strength of a cement acetabular locking mechanism.

To minimize the morbidity associated with revision of a well-fixed acetabular shell, some surgeons advocate cementing a polyethylene liner into the shell when a liner exchange is not possible. So far the strength of this cement locking mechanism has been measured on only a few specimens. The purpose of this study is to correct that oversight by measuring the push-out and lever-out strengths of an acetabular polyethylene liner cemented into a porous-coated shell. We cemented acetabular liners into porous-coated acetabular shells using first-generation cementing techniques. Each of 30 specimens was tested for its push-out or lever-out strength. The results suggest that the strength of a cemented polyethylene liner locking mechanism is similar to that of an uncemented acetabular shell.

Erroneous aluminum and cobalt tissue concentrations from using formalin.

Because of the liberation of metal particles from orthopedic implants, concerns have been voiced about their long-term safety. To document the presence and measure the amount of metal in periprosthetic tissues, many reports have analyzed tissue specimens obtained from revision surgery. Some report the inclusion of formalin in tissue processing. However, the unavailability of any medical-grade formalin solution with a known metal content raises the suspicion of sample contamination. The purpose of this study was to measure the concentration of the metals in the formalin found in common orthopedic alloys and to assess this chemical's role in removing metal ions from tissue samples. To do this, tissues with known metal concentrations of cobalt and aluminum were mixed with formalin, and the differences in the formalin and tissue concentrations of these elements were evaluated. Tissue and formalin samples were tested prior to and immediately after their mixing and then at three 10-day intervals. At the end of the study additional unmixed samples of formalin and tissue for both metals were tested to ensure there had been no contamination. Both cobalt and aluminum were found in off-the-shelf formalin, with observed decreases in tissue metal concentration and increases in formalin metal concentration.

The interosseous membrane of the forearm: structure and its role in Galeazzi fractures.

A cadaveric study was performed to anatomically describe and mechanically document the interosseous membrane of the forearm using gross, histologic, scanning electron microscopic, and mechanical testing. The membrane was found to be a complex structure composed of nerves and vessels but mainly of collagen fibers that thicken to form bands coursing from radius to ulna. Strain-gauge studies demonstrated that the load transfer occurs from the radius to the ulna via the membrane and changes with supination or pronation. With specimens under a specific test load, sectioning of the membrane allowed the fractured radius to shorten by 6.25 mm and sectioning of the triangular fibrocartilage complex resulted in shortening of 7.7 mm. Total shortening after osteotomy and sectioning of the complex structure and membrane ranged from 15 to 40 mm. In Galeazzi fractures, the interosseous membrane acts as a constraint to radial shortening. Anatomic reduction with internal fixation is indicated for this fracture-dislocation.

Metal ion concentrations in retrieved polyethylene total hip inserts and implications for artifactually high readings in tissue.

Although there are many studies which document high metal ion concentrations in clinically retrieved tissues surrounding total joint replacements, most investigations have remained cautious in their interpretation due to the artifactual influences of metal particulate. The possible contribution of polyethylene wear debris to artifactually high periprosthetic metal ion concentration readings has not been previously considered. This study documents the potential role of polyethylene particulate contamination in causing artifactually high metal concentration readings in tissues. The data showed metal ion contamination in the polyethylene was progressive at each stage of exposure to metal: from bar stock preparation, to manufacturing, to in vivo ambulation. The manufacturing and machining processes showed a statistically significant (P < or = .05) increase in metal ion concentrations in the nonarticulated acetabular inserts over bar stock. The results of this study demonstrate that periprosthetic tissue and synovial fluid metal ion concentration data must be interpreted with caution due to possible artifactual problems associated with metal ion contaminated polyethylene particulate.