Abstract-If musculoskeletal tissues are indeed efficient for their mechanical function, it is most reasonable to assume that this is achieved because the mechanical environment in the tissue influences cell differentiation and expression. Although mechanical stimuli can influence the transport of bio active factors, cell deformation and cytoskeletal strain, the question of whether or not they have the potential to regulate tissue differentiation sequences (for example, during fracture healing or embryogenesis) has not been answered.To assess the feasibility of biophysical stimuli as mediators of tissue differentiation, we analysed intcrfacial tissue formation adjacent to a micromotion device implanted into the condyles of dogs, A biphasic finite element model was used and the mechanical environment in the tissue was characterised in terms of (i) forces opposing implant motion, (ii) relative velocity between constituents, (iii) fluid pressure, (iv) deformation of the tissue and (v) strain in the tissue. It was predicted that, as tissue differentiation progressed, subtle but systematic mechanical changes occur on cells in the interfacial tissue. Specifically, as the forces opposing motion increase, the implant changes from being controlled by the maximum-allowable displacement (motion-control) to being controlled by the maximum-available load (force-control). This causes a decrease in the velocity of the fluid phase relative to the solid phase and a drop in interstitial fluid pressure accompanied by a reduction in peri-prosthetic tissue strains. The variation of biophysical stimuli within the tissue can be plotted as 'mechano-regulatory pathway', which identifies the transition from motion-control to force-control as a branching event in the tissue differentiation sequence. © 1997 Elsevier Science Ltd

Summary: 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 pm 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 'l'i 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 iibrocartilage 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. Key Words: Bone ingrowth-Fibrous membraneHydroxyapatite-Micromotion-Porous ingrowth-Titanium. Porous coated prostheses were designed to obtain permanent fixation by ingrowth of bone into the porous implant surface. However, recent histological analyses of cementless tibia1 components (1 1,16) and total hip replacements (10,12) retrieved 285

BackgroundPostoperative 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 Epidural analgesia gives excellent pain relief but is associated with substantial side effects. We compared wound infiltration combined with intraarticular injection of local anesthetics for pain relief after total hip arthroplasty (THA) with the well-established practice of epidural infusion. Methods 80 patients undergoing elective THA under spinal block were randomly assigned to receive either (1) continuous epidural infusion (group E) or (2) infiltration around the hip joint with a mixture of 100 mL ropivacaine 2 mg/mL, 1 mL ketorolac 30 mg/mL, and 1 mL epinephrine 0.5 mg/mL at the conclusion of surgery combined with one postoperative intraarticular injection of the same substances through an intraarticular catheter (group A). Results Narcotic consumption was significantly reduced in group A compared to group E (p = 0.004). Pain levels at rest and during mobilization were similar in both groups but significantly reduced in group A after cessation of treatment. Length of stay was reduced by 2 days (36%) in group A compared to group E (p < 0.001).Interpretation Wound infiltration combined with 1 intraarticular injection can be recommended for patients undergoing THA. Further studies of dosage (high/low) and duration of intraarticular treatment are warranted.

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.

Objective. To investigate the efficacy of 4 weeks of preoperative and 4 weeks of postoperative progressive resistance training (PRT), compared to 4 weeks of postoperative PRT only on functional performance, muscle strength, and patient-reported outcomes in patients undergoing total knee arthroplasty (TKA). Methods. In total, 59 patients were randomized to 4 weeks of preoperative PRT (intervention group) or to a group who lived as usual (control group). Both groups performed 4 weeks of PRT after TKA. At 6 weeks and 1 week before TKA, and at 1, 6, and 12 weeks after TKA, performance-based measures (30-second chair stand test [30sCST], timedup-and-go [TUG], and walking tests), knee extensor and flexor muscle strength (dynamometry), patient-reported functional performance, health-related quality of life, and pain scores were evaluated. Results. When comparing the changes from baseline to the primary test point 6 weeks after TKA, a significant group difference in favor of the intervention group was found for the 30sCST (2. Conclusion. Supervised preoperative PRT is an efficacious and safe intervention for improving postoperative functional performance and muscle strength, but improvements in patient-reported outcomes were not detected.

Although osteomyelitis (OM) remains a serious problem in orthopedics, progress has been limited by the absence of an in vivo model that can quantify the bacterial load, metabolic activity of the bacteria over time, immunity, and osteolysis. To overcome these obstacles, we developed a murine model of implant-associated OM in which a stainless steel pin is coated with Staphylococcus aureus and implanted transcortically through the tibial metaphysis. X-ray and micro-CT demonstrated concomitant osteolysis and reactive bone formation, which was evident by day 7. Histology confirmed all the hallmarks of implant-associated OM, namely: osteolysis, sequestrum formation, and involucrum of Gram-positive bacteria inside a biofilm within necrotic bone. Serology revealed that mice mount a protective humoral response that commences with an IgM response after 1 week, and converts to a specific IgG2b response against specific S. aureus proteins by day 11 postinfection. Real-time quantitative PCR (RTQ-PCR) for the S. aureus specific nuc gene determined that the peak bacterial load occurs 11 days postinfection. This coincidence of decreasing bacterial load with the generation of specific antibodies is suggestive of protective humoral immunity. Longitudinal in vivo bioluminescent imaging (BLI) of luxA-E transformed S. aureus (Xen29) combined with nuc RTQ-PCR demonstrated the exponential growth phase of the bacteria immediately following infection that peaks on day 4, and is followed by the biofilm growth phase at a significantly lower metabolic rate (p < 0.05). Collectively, these studies demonstrate the first quantitative model of implant-associated OM that defines the kinetics of microbial growth, osteolysis, and humoral immunity following infection. ß

Periacetabular osteotomy can be performed with a good outcome at medium-term follow-up, suggesting that it may be applied by experienced surgeons with satisfactory results. To further improve the outcome, focus should be on the potential negative influence of parameters that are easily assessed, such as the preoperative grade of osteoarthritis, the presence of an os acetabuli, and severe acetabular dysplasia.