The changing paradigm of revision of total hip replacement in the presence of osteolysis.

Osteolysis tends to remain clinically silent and presents a treatment challenge. In the past, the progression of implant wear was used to determine the timing of interventions. Recent reports of lesions associated with metal-on-metal implants and trunnion corrosion with femoral head sizes larger than 32 mm suggest that other mechanisms of wear debris production may be present; observation alone may not provide adequate monitoring. Advanced imaging modalities, such as MRI, should be used along with routine radiography to assess soft-tissue involvement and the size of osteolytic lesions. Intraoperative mechanical stress applied to the acetabular cup helps determine if revision or retention is selected when osteolysis is present. Options for the management of acetabular osteolysis include porous metal cups, oblong cups, antiprotrusio cages, impaction grafting, structural grafts, and, more recently, versatile porous metal cups. Porous metal cups can be used with or without augments or as cup-cage constructs. Porous metal cups have shown excellent results at short-term follow-ups. Modular, uncemented, titanium stems are now more commonly used for femoral revisions. Impaction grafting and allograft-prosthesis composites are occasionally useful in femoral revision surgery. A high incidence of adverse tissue reactions has been reported with metal-on-metal bearings with large heads. Recent focus also has been directed to debris generation by the modular junctions in these bearings. Removal of all sources of debris generation should be attempted during revision of metal-on-metal hip replacements. A thorough débridement of soft-tissue masses and the use of ceramic heads should be considered.

Repeated early failure of a newly designed hinged knee system.

We report a case of acute and recurrent accelerated wear of the polyethylene bushings of the hinge mechanism in the Zimmer Segmental Knee System. This resulted in an unacceptable recurvatum deformity leading to multiple revision knee operations, which was unexpected in a modern design hinged knee system. A custom modification of the original design was used to prevent further recurvatum deformity. The current design of the hinge post mechanism in this system appears to be inadequate, which led to the development of a significant recurvatum deformity in our patient. Surgeons should be aware of this potential complication when considering the use of this revision knee system.

Histological and ultrastructural evaluation of Leeds-Keio ligament 20 years after implant: a case report.

We were capable of undertaking a histological and ultrastructural evaluation of an intact Leeds-Keio ligament implanted 20 years ago to assess the neoligamentization process inside this artificial ligament. The histological evaluation disclosed a collagen fibrils orientation very close to the structure of a normal anterior cruciate ligament (ACL) where the collagen fibres are multidirectional [Strocchi et al. in J Anat 180(3):515-519, 1992]. On the other hand we found an unimodal distribution of collagen fibrils in the reconstructed ACL. This suggests that even at long-term follow-up stress exerts a variable influence. The multidirectional arrangement of collagen fibres resembles a normal ACL, but the unimodal distribution of fibrils is quite different from those seen in normal tendon and ligaments which tend to have a bimodal peak [Decker et al. in J Submicrosc Cytol Pathol 23:9-21, 1991; Strocchi et al. in J Anat 180(3):515-519, 1992]. Studies based on biopsy suffer from the potential weakness that the specimen may not have been representative of the entire prosthesis. Further long-term studies, possibly with the entire prosthesis and not only a biopsy, would highlight the behaviour and remodelling of this artificial ligament in greater detail and could be important for the development of future generations of artificial ligaments or tissue engineering ACL reconstruction.