A Biomechanical Study on the Fixational Strength of the Trans-pedicular Screw: In vitro measurement / 대한정형외과학회잡지

With porcine vertebrae, the static and dynamic holding power of the pedicle screws under various conditions were measured to understand the biomechanical nature of the transpedicular screw fixation in spine. The objectives of the present study were; (1) to find the correlation between the insertion depth of the screw and the resulting holding power, (2) to determine the effect of bone cement augmentation on the screw fixation in a loosened hole, and (3) to assess the load-sharing mechanism between the cortical and the cancellous one surrounding the screw in this fixational system. The geomorphological characteristics of each porcine vertebra was measured directly with a micro-caliper. The bone mineral density of the specimens was also measured. Material with screw was holded in the fixed cross head of material testing system(Autograph E-10T). Testing force was applied and graph was obtained in the chart record. The results of the static pull-out tests in this study showed that there was a statistically-significant positive correlation between the screw diameter and the pull-out resistance(p < 0.05). The strength of the fixation did not actually increase as much as the insertion depth of the screw increased in these tests(r=0.457). In low-cycle fatigue tests, the increased number of cycles was required to clinical failure in the deeper-inserted crews. Considering the mechanical failure, a statistically-significant positive correlation between the failure cycle and the insertion depth was observed in both deep and shallow insertion groups(p < 0.05). Nonpressurized PMMA augmentation appeared to restore the ability of the screws to withstand pullout loading of the original value. On the effect of the cortical and cancellous bone, the most important factor was the cortical bone of the entrance near the screw.

Management of Infected Total Knee Arthroplasty / 대한정형외과학회잡지

A total of 15 revision total knee arthroplasties in infected cases had been followed for an average 31.4 moths(ranging between 1 year 4 months and 10 years) from 1983 to 1992 at Kyung Hee University Hospital. Average age of the patients was 60 years old (ranging between 27 and 80 years). Of the total 15 infected total knee arthroplasties, original diagnosis was osteoarthritis in 11 patients, rheumat,oid arthritis in three patients, and tuberculosis in one patient. In nine of 15 patients, causative orgamisms were not found. But such clinical evidences as increased erythrocyte sedimentation rate, draining sinus, local heating, intraoperative findings, and pathologic findings demonstrated the infection of total knee arthroplasty. In 15 cases, seven cases were early infection and eight were late infection. Two cases of tuberculosis were diagnosed with intraoperative pathology. The majority of prosthetic loosening was found on the tibial side. Several methods of treatment were applied to the infected cases. One-stage or two-stage reimplantation were used in seven cases, knee fusion in six cases, and conservative treatment was used in two cases. Average period from initial total knee arthroplasty to prosthesis removal of fusion is 20. 3 months(ranging between 11 months and 64 months). In cases of two stage reimplantation, antibiotic-mixed bone cement was implanted after removal of prosthesis to increase the local concentration of antibiotics. The average interval from prosthesis removal to revision in 4 cases of two stage reimplantation was 9.9 weeks(ranging between 43 days and 122 days). All patients were evaluated according to the knee rating Scale of Hospital for Special Surgery. Prior to revision operation in 7 reimplantation cases, the average knee score was 50.1 points, and the average range of motion was 70°. After revision, the average knee score was 81. 1 points. The average range of motion was 98°. Complete union was obtained in all cases of knee fusion. Even though at the time of follow up there has been no recurrence of infection after revision or fusion, long term follow up is needed. Interrmittent knee joint swelling and pus drainage were observed in conservatively treated cases.