Ipsilateral shoulder and elbow replacements: on the risk of periprosthetic fracture.

BACKGROUND: Ipsilateral shoulder and elbow replacements may leave only a short segment of bone bridging the two implants in the humerus. The potential for high stress concentrations as a result of this geometry has been a concern with regard to periprosthetic fracture, especially with osteoporotic bone. The study aims to determine the optimum length of the bone-bridge between shoulder and elbow humeral implants, and to assess the effect of filling the canal with cement. METHODS: A three-dimensional finite element model was used to compare the stresses between a humerus with a solitary prosthesis and a humerus with both proximal and distal cemented prostheses. The length of the bone-bridge and the effect of filling the canal with cement were studied under bending and torsion. FINDINGS: Gradual load transfer from prosthesis to bone was observed for all cases, and no stress concentration was evident. The length of the bone-bridge had no deleterious effect on stresses in the humerus, and filling the canal with cement did not appreciably decrease the loads carried by the humerus. INTERPRETATION: The length of the bone-bridge between stem tips has little effect on the resultant stresses in the humerus. Filling the canal with cement adds little benefit to the structural integrity of the humerus. Ipsilateral shoulder and elbow prostheses may be considered independent of one another in terms of risk of periprosthetic fracture.

Fixation of trochanteric slide osteotomies: a biomechanical study.

OBJECTIVE: (1) Determine the effect of a compressive force on the stability of trochanteric slide osteotomies repaired with a cable repair system or a suturing technique. (2) Develop an approach to surgical decision making for trochanteric repair. DESIGN: Muscle forces acting on the greater trochanter were experimentally modeled by the application of shear and compressive loads to osteotomized greater trochanters. A repeated measures design was used to compare suture and cable fixation. BACKGROUND: The use of cables and wires for trochanteric repair has been associated with a high incidence of acetabular loosening and trochanteric bursitis. With trochanteric slide osteotomies, the vastus lateralis remains attached to the trochanter, which results in a compressive force being generated across the osteotomy and relatively small shear forces. The use of less rigid fixation techniques for trochanteric repair, such as sutures, may reduce the complications of cables and wires. METHODS: Seven cadaveric femora with trochanteric osteotomies were tested sequentially after repair with a cable system and with a suturing technique. A cyclic shear load of constant amplitude was applied while a compressive load was decreased in a stepwise fashion. Migration and cyclic motion of the trochanter were measured, and the coefficient of friction was also determined. RESULTS: Cyclic motions of the trochanter in both superior and anterior directions were generally less than 0.5 mm and were not significantly different between the cables and sutures at high compressive loads. At low compressive loads, cyclic motion was significantly lower with the cable system. CONCLUSIONS: Compression across the trochanteric slide osteotomy has a significant effect on stability. Cyclic motion of the trochanter is similar for both suture or cable repair of a trochanteric slide with good preservation of soft tissue attachments. RELEVANCE: Based on theoretical and experimental evidence, repair of trochanteric slide osteotomies with a suture technique may be a viable alternative to the use of cables and wires in selected cases.