Introduction and Aims: Titanium foam implants simulate the trabecular structure of bone to maximise porous space for bone ingrowth. Plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Chemical deposition is an attractive alternative that produces consistent coats on porous surfaces.

Method: Titanium foam cylinders (5mm diameter by 25mm length) were implanted bilaterally in 40 rabbit femurs. Twenty implants were coated with 20 microns of hydroxyapatite (T-HA) by electrochemical deposition while 20 implants had no hydroxyapatite coat (T). Osseointegration was measured at six and 12 weeks by automated computerised histomorphometry of scanning electron microscopy images of sections taken through the implant at two levels: diaphyseal and metaphyseal. Bone ingrowth was quantified in the pores and was also measured up to 1mm beyond the surface of the implant to determine the pattern of bone growth.

Results: For the T-HA surface, bone ingrowth increased from 35.0 ±8.5 % at six weeks to 41.5 ± 7.4 % at 12 weeks (p < 0.05). For the T surface, bone growth was 14.1 ± 8.8% at six weeks and 11.4 ± 4.2 % at 12 weeks. At both time points mean bone ingrowth was significantly different between hydroxyapatite-coated and non-hydroxyapatite-coated implants, (p< 0.01). No significant differences were noted between the diaphyseal and metaphyseal bone response.

Conclusion: For the T-HA surface, bone ingrowth increased from 35.0 ±8.5 % at six weeks to 41.5 ± 7.4 % at 12 weeks (p < 0.05). For the T surface, bone growth was 14.1 ± 8.8% at six weeks and 11.4 ± 4.2 % at 12 weeks. At both time points mean bone ingrowth was significantly different between hydroxyapatite-coated and non-hydroxyapatite-coated implants, (p< 0.01). No significant differences were noted between the diaphyseal and metaphyseal bone response.

Introduction and Aims: A significant proportion of patients currently undergoing total knee arthroplasty have uni-compartmental disease. Unicondylar knee replacement (UKA) offers the benefits of less bone resection and better soft tissue retention. However, knee kinematic changes after UKA have not been established.

Method: A significant proportion of patients currently undergoing total knee arthroplasty have uni-compartmental disease. Unicondylar knee replacement (UKA) offers the benefits of less bone resection and better soft tissue retention. However, knee kinematic changes after UKA have not been established.

Results: In the normal knee, knee flexion was accompanied by femoral rollback and tibial internal rotation. Similar patterns of rollback and rotation were seen after UKA. Surprisingly, resecting the ACL did not affect rollback or tibial rotation. However, tibial rotation was significantly different and was more variable after TKA. This suggests that loss of the ACL may not be the major cause of abnormal kinematics after TKA.

Conclusion: Abnormal kinematics have been previously reported after TKA. However, UKA appeared to maintain normal kinematics. This study reported kinematic advantages to UKA, in addition to less bone resection and better recovery.

Introduction and Aims: Complications after total knee arthroplasty (TKA) have been attributed to soft-tissue imbalance. The current approach to soft-tissue balance is static measurements in extension and 90 degrees flexion. Dynamic balancing during the entire range of flexion may be more valuable.

Method: Complications after total knee arthroplasty (TKA) have been attributed to soft-tissue imbalance. The current approach to soft-tissue balance is static measurements in extension and 90 degrees flexion. Dynamic balancing during the entire range of flexion may be more valuable.

Results: All knees (in vitro and in vivo) initially recorded imbalance in the tibial forces: mean 18N (6–72) in the mediolateral and 26N (13–108) in the anteroposterior direction. After soft-tissue balancing, the mean imbalance reduced by 87%. Even when knees appeared well balanced at zero and 90-degree flexion, there was imbalance [mean 22N (2–34)] at flexion angles between zero and 90 degrees. The 2mm thicker insert increased forces by a mean of 89% (22–180%).

Conclusion: Soft-tissue balance in TKA remains a complex concept. The routine instruments used for soft-tissue balance only detect mediolateral imbalance. Even when accurate static balancing was achieved, dynamic measurements revealed imbalance in mid-flexion. These results explain some of the variability in knee kinematics after TKA and the incidence of mid-flexion instability.

This study measured polyethylene wear and correlated it with design features such as tibiofemoral conformity and contact areas.

Two femoral component designs were tested in a knee wear simulator. The femoral condyles of design A were flat-on-flat in the coronal plane, while those of design B were curved-on-curved. These femoral components were tested with two inserts. Insert PLI had a posterior lip, while insert C had a more curved sagital geometry, to improve stability in the anteroposterior direction. All components were tested for up to five million cycles in bovine serum lubricant. Triaxial forces were monitored to ensure that loading conditions were similar in all combinations tested. Gravimetric wear measurements were made at 500 000 cycle intervals. Contact stresses were measured using pressure sensitive film and dynamic finite element analysis.

Contact stresses were 22% higher for inserts tested with design A compared to design B. Sliding distance, sliding velocity, and patterns of crossing motion were found to be comparable between the two femoral designs. Inserts tested with design A wore significantly more (mean 10.9 mg/million cycles) than design B (mean 5.71 mg/million cycles, p < 0.001). No appreciable differences were found between wear rates of insert PLI and insert C.

Component design can have a significant impact on polyethylene wear rate. Careful control of kinematic and loading conditions allowed for comparison between specific design features. Increase in tibio-femoral contact area led to reduction of contact stresses, which was reflected in the reduced wear rate.

The purpose of this study was to determine if routine x-ray exposure produced any chemical oxidation of Ultra High Molecular Weight Polyethylene (UHMWPE), used for joint arthroplasty.

Three different polyethylene polymers were obtained from Biomet, Depuys and Howmedica. These samples had undergone sterilisation and packaging methods. Rectangular shapes of polymer were cut according to the standards specified by the ASTM (American Society For Testing and Materials). Eight samples of each polymer were obtained and divided randomly in to test and control subgroups. The test samples were exposed to ten x-rays with the standard dose used for the hip joint.

Polyethylene oxidation was measured using Fourier transform infrared spectroscopy. This technique can assess the incorporation of oxygen within the carbonyl region. Radiated and non-irradiated samples were compared in each polymer group.

Oxidation from the Fourier transform infrared spectroscopy was quantified by calculating the area under a signature absorption peak for UHMWPE (methylene band at 1370 cm-1) and an oxidation absorption peak (carbonyl band at 1720 cm-1). The ratio of the area of the oxidation peak to the area of the signature peak yields the carbonyl content, or oxidation, relative to the amount of polyethylene. There was no significant difference in oxidation after exposure to x-rays between test and control UHMWPE samples.

Although numerous studies have looked in to the effects of high dose radiation exposure on polyethylene, effects of routine x-rays have not been studied before. It is common practice to follow-up patients with joint replacements over a long period with xrays at each visit. Present study examined the effects of routine x-rays on oxidation of polyethylene. However there was no detectable oxidation after exposure to x-rays. This study paves way for further research in this direction.

It has been recently suggested that hyponatraemia may be a cause of significant iatrogenic harm in orthopaedic patients. In an attempt to test this theory, this observational study was done to establish the incidence of post-operative hyponatraemia following hip fracture and evaluate its correlation with outcome.

An observational study was carried out on 213 consecutive hip fracture patients. 201 patients completed the requirements of the study (Male-45, Female-156). Mean age was 80 years. Serum sodium concentrations were recorded during the first week of admission. Hyponatraemia defined as significant (Na < 130mmol/L) was identified in 9% at admission and 18% during first week of stay. Incidence of severe hyponatraemia was 3%. There were no acute complications of hyponatraemia in these patients. 78% of hyponatraemia patients had received 5% Dextrose infusion during the postoperative period as their main intravenous fluid. All hyponatraemic patients had their sodium levels restored to normal during their stay.

Long term outcome measures used were mortality, change in residential status, walking ability and use of walking aids at 4 months following fracture. There was 20% mortality at 4 months in the hyponatraemic group and it was 30% in the normal serum sodium group. However this difference was not statistically significant. Hyponatraemia did not significantly influence deterioration in residential status (p< 0. 05), walking independence (p< 0. 05) or increase of walking aids (p< 0. 05).

In hip fracture patients, hyponatraemia whilst common was not associated with a poor outcome and at the same time we did not find any evidence of lapse in the recognition and treatment of hyponatraemia in a general orthopaedic ward. However emphasis should be made to junior medical staff to avoid iatrogenic hyponatraemia by following a proper postoperative fluid regime.