Lack of initial mechanical stability of cementless prostheses may be responsible for fibrous tissue fixation of prosthetic components to bone. To study the influence of micromovements on bony ingrowth into titanium alloy (Ti) and hydroxyapatite (HA)‐coated implants, a loaded unstable device producing movements of 500 μm during each gait cycle was developed. Mechanically stable implants served as controls. The implants were inserted into the weight‐bearing regions of all four femoral condyles in each of seven mature dogs. Histological analysis after 4 weeks of implantation showed a fibrous tissue membrane surrounding both Ti and HA‐coated implants subjected to micromovements, whereas variable amounts of bony ingrowth were obtained in mechanically stable implants. The pushout test showed that the shear strength of unstable Ti and HA implants was significantly reduced as compared with the corresponding mechanically stable implants (p < 0.01). However, shear strength values of unstable HA‐coated implants were significantly greater than those of unstable Ti implants (p < 0.01) and comparable to those of stable Ti implants. The greatest shear strength was obtained with stable HA‐coated implants, which was threefold stronger as compared with the stable Ti implants (p < 0.001). Quantitative determination of bony ingrowth agreed with the mechanical test except for the stronger anchorage of unstable HA implants as compared with unstable Ti implants, where no difference in bony ingrowth was found. Unstable HA‐coated implants were surrounded by a fibrous membrane containing islands of fibrocartilage with higher collagen concentration, whereas fibrous connective tissue with lower collagen concentration was predominant around unstable Ti implants. In conclusion, micromovements between bone and implant inhibited bony ingrowth and led to the development of a fibrous membrane. The presence of fibrocartilage and a higher collagen concentration in the fibrous membrane may be responsible for the increased shear strength of unstable HA implants. Mechanically stable implants with HA coating had the strongest anchorage and the greatest amount of bony ingrowth.

In previous studies, we have demonstrated a fibrocartilaginous membrane around hydroxyapatite-coated implants subjected to micromovement in contrast to the fibrous connective tissue which predominates around similarly loaded titanium alloy implants. In the present study, in mature dogs, we investigated the effect of immobilising titanium (Ti)- or hydroxyapatite (HA)-coated implants already surrounded by a movement-induced fibrous membrane and compared the results with those of similar implants in which continuous micromovement was allowed to continue. The implants were inserted in the medial femoral condyles of 14 dogs and subjected to 150 microns movements during each gait cycle. After four weeks (when a fibrous membrane had developed), half the implants were immobilised to prevent further micromovement. The dogs were killed at 16 weeks and the results were evaluated by push-out tests and histological analysis. The continuously loaded Ti-coated implants were surrounded by a fibrous membrane, whereas bridges of new bone anchored the HA-coated implants. The immobilised implants were surrounded by bone irrespective of the type of coating. Push-out tests of the continuously loaded implants showed better fixation of those with HA coating (p < 0.001). The immobilised Ti-coated implants had four times stronger fixation than did continuously loaded Ti-coated implants (p < 0.01) but there was no equivalent difference between the two groups of HA-coated implants. The amount of bone ingrowth was greater into immobilised HA-coated implants than into immobilised Ti-coated implants (p < 0.01). Two-thirds of the HA coating had been resorbed after 16 weeks of implantation, but 25% of this resorbed HA had been replaced by bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Background Postoperative pain after total knee arthroplasty (TKA) can be difficult to manage and may delay recovery. Recent studies have suggested that periarticular infiltration with local anesthetics may improve outcome. Methods 80 patients undergoing TKA under spinal anesthesia were randomized to receive continuous femoral nerve block (group F) or peri- and intraarticular infiltration and injection (group I). Group I received a solution of 300 mg ropivacaine, 30 mg ketorolac, and 0.5 mg epinephrine by infiltration of the knee at the end of surgery, and 2 postoperative injections of these substances through an intraarticular catheter. Results More patients in group I than in group F could walk < 3 m on the first postoperative day (29/39 vs. 7/37, p < 0.001). Group I also had significantly lower pain scores during activity and lower consumption of opioids on the first postoperative day. No differences between groups were seen regarding side effects or length of stay. Interpretation Peri- and intraarticular application of analgesics by infiltration and bolus injections can improve early analgesia and mobilization for patients undergoing TKA. Further studies of optimal drugs, dosage, and duration of this treatment are warranted.

Background: Accelerated perioperative rehabilitation protocols following total hip and knee arthroplasties are currently being implemented worldwide, but the cost-effectiveness of these protocols from a societal perspective is not known. We compared the cost-effectiveness of an accelerated perioperative care and rehabilitation protocol with that of a more standard protocol for patients treated with total hip and knee arthroplasty. Methods: A cost-effectiveness study was undertaken as a study piggybacked on a randomized clinical trial comparing early outcomes of an accelerated and intensive postoperative rehabilitation regimen with those of a more standard rehabilitation protocol. We assessed eighty-seven patients (forty-two who received the standard protocol and forty-five who received the accelerated protocol) for a total of twelve months. Costs from the time of the patient's visit immediately before the operation to one year postoperatively were calculated with use of activity-based costing analysis. Postoperative quality-adjusted life-years (QALYs) were calculated from validated patient diaries and questionnaires at fifteen time points. The primary objective was to determine whether one intervention was dominant over the other during a twelve-month period or, if neither was dominant, to determine the incremental cost-effectiveness ratio. Results: The result of the randomized clinical trial showed the accelerated intervention to be effective, with a reduction in the length of the hospital stay and a gain in health-related quality of life at the three-month follow-up time point. The cost-effectiveness study showed the accelerated protocol to be significantly less expensive than the standard protocol (p = 0.036), with an average reduction in cost of 18,880 Danish kroner (95% confidence interval, 1899 to 38,152) (approximately US $4000). Patients treated with the accelerated protocol following hip arthroplasty had an additional average gain of 0.08 QALY (95% confidence interval, 0.02 to 0.15) compared with the patients who received the standard protocol (p = 0.006); this led to a 98% dominance of the accelerated protocol over the standard protocol. No significant or clinically relevant difference in the numbers of QALYs associated with the two protocols was observed for the patients treated with knee arthroplasty. Conclusions: An accelerated perioperative care and rehabilitation protocol can be both cost-saving and clinically more effective after total hip arthroplasty, whereas it can be cost-saving with no observed significant difference in effect, from a societal perspective, after knee arthroplasty. Level of Evidence: Economic and decision analysis Level I. See Instructions to Authors for a complete description of levels of evidence.