The influence of the strength of bone on the deformation of acetabular shells: a laboratory experiment in cadavers.

Concerns have been raised that deformation of acetabular shells may disrupt the assembly process of modular prostheses. In this study we aimed to examine the effect that the strength of bone has on the amount of deformation of the acetabular shell. The hypothesis was that stronger bone would result in greater deformation. A total of 17 acetabular shells were inserted into the acetabula of eight cadavers, and deformation was measured using an optical measuring system. Cores of bone from the femoral head were taken from each cadaver and compressed using a materials testing machine. The highest peak modulus and yield stress for each cadaver were used to represent the strength of the bone and compared with the values for the deformation and the surgeon's subjective assessment of the hardness of the bone. The mean deformation of the shell was 129 µm (3 to 340). No correlation was found between deformation and either the maximum peak modulus (r² = 0.011, t = 0.426, p = 0.676) or the yield stress (r² = 0.024, t = 0.614, p = 0.549) of the bone. Although no correlation was found between the strength of the bone and deformation, the values for the deformation observed could be sufficient to disrupt the assembly process of modular acetabular components.

Early complications following Q-switched neodymium: YAG laser posterior capsulotomy.

A prospective evaluation was conducted of Q-switched neodymium: YAG laser capsulotomy in 53 eyes followed for one postoperative month. The first 31 eyes were seen at two-hour intervals for the first eight hours, and the remaining eyes were checked only at the second postoperative hour during that day. Eighty-nine percent of eyes required a pulse setting of less than 1.7 mJ to successfully penetrate the posterior capsule. Visual acuity was improved in 91% of eyes. A transient immediate postoperative intraocular pressure (IOP) elevation was seen in over 75% of treated eyes, and one-third had an IOP elevation greater than 10 mmHg over the preoperative IOP. This elevation was most common in glaucomatous eyes and occurred in almost one-half of the treated eyes by the second postoperative hour. This IOP change did not correlate with the degree of inflammation, bleeding, anterior chamber debris, or total energy delivered. Minimal iris bleeding occurred in 9% of treated eyes and was associated with iridocapsular adhesions. Eighty-one percent of eyes with posterior chamber implants developed some degree of lens damage.