Distal femoral varus osteotomy for painful genu valgum. A five-to-11-year follow-up study.

From 1978 until 1984, 23 patients (24 knees) were treated with varus producing distal femoral osteotomy for painful, lateral compartment osteoarthrosis. Evaluation at five to 11 years (average, 8.3 years) included orthopedic examination, calculation of the Hospital for Special Surgery (HSS) knee score, and standing knee roentgenograms. Based on the objective knee scores, 71% of the patients had good or excellent results, with no difference in those followed for longer periods. Complications occurred in 63% of the cases, including nonunion (25%) and loss of correction (21%). Both complications were associated exclusively with staple fixation, which was performed during the period of this study and is now known to be inadequate to fix this osteotomy. Despite increasing morbidity rates, these complications did not appear to influence the ultimate result. A statistically significant prognostic factor was the severity of the disease as reflected by the pre- and postoperative knee scores. Further, the degree of correction was a function of the initial deformity. At follow-up evaluation 13% of the knees had been converted to a total knee replacement.

Torsional strength reduction due to cortical defects in bone.

This study correlated torsional strength reduction with circular defect size in cortical bone, to define the "stress riser" and "open-section" effect of the defects. The experimental model was developed and verified. Circular defects from 10 to 60% of bone diameter were then created in paired sheep femora and the bones loaded to failure. Contrary to theory, this experimental study suggests that small defects (10%) of bone diameter cause no significant torsional strength reduction. A 20% defect caused a 34% decrease in strength, representing the "stress riser" dimension. Defects between 20 and 60% of bone diameter decreased strength linearly as a function of defect size, and thus no discrete "open section" dimension was identified. For circular defects, we were unable to demonstrate a discrete "open-section" effect at which dramatic strength reduction is observed. These data may prove to be helpful when planning surgery that involves placing defects in bone such as for infection, biopsy, and prosthesis removal. The accepted guideline to avoid defects of greater than 50% of the bone diameter may be too great. Our data reveal this 62% reduction in torque strength and 88% energy to failure exist with a 50% circular defect.

Total shoulder arthroplasty: complications and revision surgery.

Fortunately, revision surgery after prosthetic shoulder arthroplasty is rarely required. However, various complications or combinations of complications can lead to the need for revision surgery. For many of these, several treatment options are possible. Recognizing all the problems that contributed to failure in an individual patient may be difficult before revision surgery. Understanding the abnormality present at the time of surgery requires considerable experience. For example, glenoid loosening, in addition to being accompanied by scapular bone loss, may be associated with rotator-cuff tearing, instability, or joint contracture. In addition to the component loosening, all of these must also be treated if the revision procedure is to be successful. When addressing glenoid loosening, it seems to be best to revise the component, if possible. If there is extreme bone loss, one may have to bone graft the deficiencies and not replace the glenoid component. Fortunately, clinically significant humeral loosening is rare. When it occurs, revision of the component is justified and almost always possible. In hemiarthroplasties with pain, conversion to a total shoulder arthroplasty by placing a glenoid component is highly effective. In instability after shoulder arthroplasty, soft-tissue repair does not always create stability. Unfortunately, for most patients, component revision is a necessary part of the revision surgery. When rotator-cuff tearing is acute, repair is indicated; for chronic rotator-cuff tearing, repair depends on the severity of the symptoms. When infection develops after shoulder arthroplasty, implant removal is almost always necessary, but occasionally, in low-grade infections, a primary or secondary exchange procedure may be possible.

Structural consequences of transcortical holes in long bones loaded in torsion.

Finite element models were used to predict the structural consequences of transcortical holes through long bones loaded in torsion. Several parameters were investigated including hole size, anelastic behavior of the bone, cortical wall thickness, cortical wall symmetry, curvature along the bone's long axis and the axial length of the defect. Finite element model predictions of percent intact bone strength were compared to experimental data for sheep femora with transcortical drill holes loaded to failure in torsion. Hole size was expressed as hole diameter divided by the outer bone diameter. Linear finite element model predictions were in conservative agreement with the experimental data for large hole sizes. A transcortical hole with a diameter 50% of the outer bone diameter reduced the torsional strength by 60%. However, the linear models predict a 40% drop in strength for small holes whereas in vitro data suggest that small holes have no significant effect on strength. Models which represent non-linear anelastic behavior in bone overpredicted torsional strengths. Asymmetric cortical wall thickness and long bone bowing have minor effects, while the length of an elongated defect strongly influences the torsional strength. Strength reductions are greatest for bones with thin cortical walls.