Patellofemoral crepitus in high flexion rotating platform knee arthroplasty.

INTRODUCTION: Recently, implant manufacturers have made modifications to currently available implants in an attempt to improve postoperative flexion. The Low Contact Stress (LCS) RPS (DePuy Orthopaedics Inc., Warsaw, IN, USA) is one such prosthesis which is a modification of the established LCS RP design. Satisfactory results have been obtained without patella resurfacing in the original LCS RP design. METHODS: We report on a single surgeon series showing an alarmingly high incidence of patellofemoral crepitus when this new prosthesis, LCS RPS, is used without patella resurfacing. In addition, the outcomes for this prosthesis from the Australian National Joint Replacement registry will be reported. These results show a high revision rate with most revisions being patella resurfacing for patellofemoral pain. RESULTS: Affected patients who elected to have a revision procedure underwent either an arthroscopic patellaplasty procedure or revision to resurface the patella. Both of these procedures resulted in satisfactory resolution of symptoms in the majority of patients. DISCUSSION: Potential causes for this complication are discussed. It is the recommendation of the authors that when using this prosthesis the patella is resurfaced.

Quantification of denitrification potential in carbonaceous trickling filters.

Biofilm samples from a carbonaceous trickling filter (TF) were evaluated in bench scale reactors to determine their maximum potential denitrification rates. Intact, undisturbed biofilms were placed into 0.6 L bench-scale reactors filled with sterilized, primary clarifier effluent spiked with nitrate to a final concentration of 16-18 mg/L as N. Dissolved oxygen concentrations were maintained between 2 and 4 mg/L in the bulk aqueous phase. Nitrate loss from the reactors was monitored over a 5h period. Denitrification rates of 3.09-5.55 g-N/m(2)day were observed with no initial lag period. This suggests that the capacity for denitrification is inherent in the biofilm and that denitrification can take place even when oxygen is present in the bulk aqueous phase. There were no significant differences in denitrification rates per unit area of media (g-N/m(2)day) either between (a). experimental runs or (b). sampling locations over the trickling filter. This suggests that denitrification potentials are uniform over the entire volume of the full-scale TF. For wastewater treatment plants with TFs that currently nitrify downstream, this approach may be used to meet less stringent permitted discharge concentrations and may allow some facilities to postpone or eliminate construction of additional unit processes for denitrification.

Effect of alkalinity type and concentration on nitrifying biofilm activity.

The effect of alkalinity on nitrifying biofilm activity was determined by collecting 21-day-old biofilm samples from the top of a full-scale nitrifying trickling filter and evaluating bench-scale nitrate plus nitrite generation rates at (1) various initial carbonate alkalinity concentrations and (2) with four types of available alkalinity: carbonate only, phosphate only, phosphate plus hydroxide, and phosphate plus carbonate. Initial carbonate alkalinity concentrations were varied between 308 and 20 mg/L as calcium carbonate (CaCO3). Ammonia, nitrite, and nitrate concentrations were measured at time zero, 90 minutes, 180 minutes, and 270 minutes. Generation rates in grams of nitrogen per square meter per day were calculated for each time period and normalized against dry-weight biomass. Generation rates were impaired at initial carbonate alkalinity concentrations of 40 mg/L and lower (as CaCO3) and were unaffected at concentrations of 45 mg/L and greater. For reactor runs with different alkalinity types, ammonia, nitrite, and nitrate concentrations were measured at time zero and at 375 minutes. The type of alkalinity, carbonate versus phosphate, affected nitrification rates. When the carbonate alkalinity was less than 45 mg/L, nitrification rates were impaired regardless of the total alkalinity concentration. This effect seems to be independent of pH for the range of 6.92 to 7.99 evaluated here. This suggests that in addition to neutralizing the acid generated by the nitrification process, a minimum level of carbonate alkalinity is necessary to meet the ammonia-oxidizer's inorganic carbon requirement for cellular synthesis and growth.