Purpose: Unicompartmental replacement for medial compartment arthrosis of the knee has become popular with eligible patients because of the shortened recovery time, decreased tissue damage and easier future revision. Contemporary multimodal anesthesia has added the potential to safely perform this as outpatient surgery reducing inpatient bed burden. We describe our initial pilot experience with this approach.

Method: The first 25 patients who fulfilled the criteria developed underwent same day surgery for unicompart-mental arthroplasty for medial (19) or lateral (3) compartment replacement with either the Oxford knee (20) or the Uniglide (2). All patients were treated with an indwelling femoral nerve catheter supplied by Ropivacaine through a constant release pump (Stryker) which was discontinued at 48 hours. Home care support was made available in first 72 hours by way of RN and physiotherapy visits and mandatory use of walker or crutches for the first 48 hours.

Results: Patients in this cohort were universally very satisfied with the model of postop care as described and particularly pleased to avoid a hospital stay. Eighty percent of those who were offered this model chose it. The use of narcotic oral medication was consistently about 50% less than that observed to similar inpatients treated without catheter, and eight patients had complete opioid sparing experience. There were no complications related to the catheter, in particular serious falls or longer term neurologic sequelae. The clinical results were very good and equal to those who were in patients.

Conclusion: Outpatient unicompartmental replacement can be performed safely recognizing the decreased surgical trauma and pain stimuli associated with UKR and a relatively younger and healthier cohort screened for this alternative. These patients are amongst the most satisfied with their perioperative course and all would do the same again if given the chance. Other models of analgesia could be considered, though the catheter does seem to have a large opioid sparing effect that likely contributed to patient well being and satisfaction.

Increasing numbers of young people receive metal on metal (CoCr on CoCr) total hip replacements. These implants generate nano-particles and ions of Co and Cr. Previous studies have shown that micro-particles, nano-particles and ions of CoCr cause DNA damage and chromosomal abberrations in human fibroblasts in tissue culture, and in lymphocytes and bone marrow cells in patients with implants. Several surgeons have used these implants in women of child-bearing age who have subsequently had children. Significantly elevated levels of cobalt and cromium ions have been measured in cord blood of pregnant women with CoCr hip implants. The MHRA (Medicines and Healthcare products Regulatory Agency) subsequently stated that there is a need to determine whether exposure to cobalt and chromium represents a health risk during pregnancy.

In an attempt to investigate this risk, we used a well established in vitro model of the placental barrier comprised of BeWo cells (3 cells in thickness) derived from the chorion and exposed this barrier to nanometer (29nm) and micron (3.4μm) sized CoCr particles, as well as ions of Co2+ and Cr6+ individually or in combination. We monitored DNA damage in BJ fibroblasts beneath the barrier with the alkaline gel electrophoresis comet assay and with γH2AX staining.

The results showed evidence of DNA damage after all types of exposure. The indirect damage (through the barrier) was equal to the direct damage at the concentrations tested. The integrity of the barriers was checked with measurements of electrical resistance (TEER values) and permeability to sodium fluorescein (376Da) and found to be intact.

In light of these results and with the knowledge that BeWo cells express the transmembrane protein Connexin 43, we tested the theory that a damaging signal was being relayed via gap junctions or hemi channels in the BeWo cells to the underlying fibroblasts. We used the connexin mimetic peptides Gap19 and Gap26 (known to selectively block hemichannels and gap junctions respectively) and 18α-glycyrrhetinic acid (non-selective gap junction blocker). All of these compounds completely obliterated the indirect damaging effect seen in our previous experiments.

We conclude that CoCr particles can cause DNA damage through a seemingly intact barrier, and that this damage occurs via a bystander mechanism. It would be of interest to test whether this is simply a tissue culture effect or could be seen in vivo.

Introduction: Autologous chondrocyte implantation is routinely used for the repair of articular cartilage defects. A similar method may be employed to treat degenerate intervertebral discs or other connective tissues. A system in which cells could not only be delivered, but also retained would offer advantages compared to ACI. Such a vehicle would also allow a homogenous distribution of cells throughout the defect and enhance nutrient penetration to the seeded cells.

Methods: Bovine nucleus cells were isolated via enzyme digestion and expanded in number to passage 3. The cells were resuspended in 0.8% alginate and loaded into poly vinyl alcohol (PVA) cubes. These constructs were placed into a solution of calcium chloride to ‘gel’ the alginate. Constructs were cultured in DMEM+10% FBS within 15ml conical tubes rotated at 37°C for up to 28 days. Cell distribution/morphology and proliferation were assessed on H& E and Ki-67 stained sections, respectively. The re-expression of a disc cell phenotype was assessed using toluidine blue staining and immunohistochemistry (with antibodies to collagen types I, II, IIA, VI and X, and to the glycosaminoglycans, chondroitin-4- and -6-sulphate and keratan sulphate. RT-PCR was performed using oligonucleotide primers to collagen types I, II and X, aggrecan, link protein, and small leucine-rich PGs.

Results: H& E staining of 10μm-thick cryosections revealed an even distribution of loaded cells throughout the scaffold at day 1 being maintained through to day 28. Toluidine blue staining revealed the presence of GAGs, increasing with time. Ki-67 revealed approximately 5% of cells were proliferating at all time points. Immunohistochemistry demonstrated the production of collagen types I, II, IIA, VI and X and the glycosaminoglycans, chondroitin-4-, -6 and keratan sulphate. RT-PCR results showed mRNA expression of fibromodulin throughout the experiment, lumican at days 14, 21 and 28. Types II and X collagen were present at days 21 and 28.

Conclusions: Combining 0.8% alginate with PVA retained 100% of the seeded cells and allowed an even distribution of cells throughout the scaffold. The immunohistochemistry and RT-PCR demonstrated that the system allowed the bovine nucleus cells to express phenotypic markers expressed by disc cells in vivo. These preliminary results indicate that the PVA/alginate system could act as a suitable delivery device for cells during autologous repair of the intervertebral disc or other connective tissues such as meniscus.