Currently, all details regarding implants are entered into a real time application on the Musgrave Park Hospital site using the Belfast Orthopaedic Information System (BOIS). This is a visual basic client application with data being stored in an SQL server database. This data collection system operates throughout every location within the hospital including the theatre block.

Loss of continuity occurs however when joint replacement takes place in Musgrave Park Hospital and then revision surgery or other procedures are carried out at other locations. The goal therefore of the Northern Ire-land Implant Register is to collect information on all implants performed and their revisions regardless of their location.

The dataset collected is based on the work of the National Joint Replacement Registry. Our system is designed to support and extend that dataset to provide a more comprehensive joint replacement registry database. This means that reports can be provided to individual sites and data entered into the National registry if required at a later stage.

At present every hospital in Northern Ireland is connected to the HPSS network (similar to the HPSSNet in the UK). What has been developed is a web browser based front end, which requires no complex software installation on any client machine. From this web based tool, staff at other locations can access information held at Musgrave Park Hospital, they can select an implant, or record a new implant and then link any revisions or other procedures carried out.

As all of the information is entered directly into the BOIS database, there is no delay in the information being available to all who access the system. This reduces the need for case notes to be transferred to other sites and the need to contact the other site directly regarding the case. The interface also provides a comprehensive reporting capability so that commonly requested standard reports are available for authorized staff to run from their web browser.

We present an overview of how the web interface works in practice and how data is entered into the system.

To maximise the long-term survivorship of any hip prosthesis it is important to recreate joint centre. Normal joint centre is determined by horizontal offset and vertical height of the acetabular and femoral components. In this study joint centre and horizontal offset were analysed in 200 consecutive patients operated on from October 1998 in whom the opposite hip was normal. Joint centre was defined relative to the acetabulum and femur both pre- and post-operatively. On the acetabular side a horizontal line was drawn across the pelvis immediately below each teardrop. A vertical line was drawn at right angles through the middle of each teardrop. Acetabular offset was defined as the horizontal distance from the vertical trans teardrop line to head centre. For femoral offset a screened x-ray was taken to show maximum offset. The anatomical axis was drawn and the offset was defined as the distance from the anatomical axis to head centre.

Our results show on the acetabular side there was an overall tendency to leave the joint centre medial and so decrease acetabular offset. However, we found that 90% of our sockets were placed within 6 mm of normal joint centre. We attribute this accuracy to the principle of visualising the transverse acetabular ligament intra-operatively and using this landmark to control depth of socket insertion. Conversely, on the femoral side there was a slight tendency to increase the offset. Nevertheless, 98% of the custom stems were within 10mm of normal joint centre. When we looked at total horizontal offset i.e. the combination of femoral and acetabular offset we found that joint centre had been restored to within 10mm in 93% of cases.

This study confirms the effectiveness of the custom femoral stem and Duraloc socket in restoring joint centre.

Rapidly progressive cases of primary idiopathic hip osteoarthrosis are well known and recognised. The prevalence reported in the literature varies from 4–18%. Three types have been identified- type 1 (rapid), type 2 (moderate) and type 3 (delayed) depending on the duration of chondrolysis and the subsequent rate of bone loss per year.

We reviewed the charts of all patients deemed to be RPO type 1 who had underwent hip arthroplasty under the care of the senior author (DEB) over a two-year period in an attempt to identify risk factors, which may have contributed to the rapid progression of their disease. All patients were treated using a custom femoral stem and a spiked Duraloc cementless socket following careful preparation of the acetabulum.

We identified 34 patients (40 hips) with type 1 rapidly progressive osteoarthrosis. Over the same time period 991 patients had underwent primary total hip arthroplasty, giving a prevalence of 4%. Of the 34 patients, 29 were female of average age 70.6 years (range, 51–83 years). All of the bilateral cases (6 patients) were female. Body mass index (BMI) for the female group ranged from 20.6 to 41.1Kg/m² (average, 28.2kg/m²) whilst that for the males was on average 25.8Kg/m² (range, 23.4–29.7Kg/m²).

Preoperative erythrocyte sedimentation rate (ESR) was 18mm/hr on average for the female group (range, 2–65mm/hr) and ranged from 3–52mm/hr (average, 20mm/hr) for the male patients. The preoperative Oxford Hip Score averaged 51 points for the female group and 48 points for the male group.

A detailed review of occupational history did not reveal any common occupational hazard. The majority of patients were non-smokers and denied any regular alcohol intake. Twenty-two patients (65%) had a history of hypertension. Twenty-seven patients (79%) had a history of non-steroidal anti-inflammatory use (most common preparation-diclofenac). Twenty-four patients (71%) resided in a rural area.

When compared to a cohort of patients undergoing primary total hip arthroplasty over the same time period, the only statistically significant risk factor identified was female gender.

We conclude, that patients who develop rapidly progressive osteoarthrosis of the hip are difficult to identify due to the absence of specific clinical features. We also outline our experience in the management of these technically challenging cases.

Many factors have been demonstrated to influence the range of knee movement that an individual can achieve.

The purpose of this study was to objectively demonstrate how range of knee movement is affected when the influence of pain is abolished.

Sixty-eight patients with degenerative joint disease presenting for primary total knee arthroplasty were recruited. Using a digital camera, images were taken before and after the induction of anaesthesia with the lower limb in four positions- extension, forced extension, flexion and forced flexion. Camera set up was standard and the range of knee motion was measured from the digital images.

Average arc of motion before anaesthesia was 96° (range, 41°–157°). After induction of anaesthesia, the arc of motion increased to 115° (range, 410–161°). Knee extension improved by an average of 5° (range, 0–15°) and flexion improved by an average of 16° (range, 0–65°).

In conclusion, these results demonstrate that pain has a significant inhibitory effect on the measured range of knee movement before surgical intervention.

Dislocation of the polyethylene-rotating platform is a recognised complication of LCS knee arthroplasty.

We report ten cases of rotating platform dislocation out of 2151 primary total knee arthroplasties (0.5%) performed to date in our unit.

Of the ten cases (3 male: 7 female), six patients had a preoperative valgus deformity, two had a varus deformity and the remaining two patients were in neutral alignment, although the wear was predominantly within the lateral compartment. Two patients also had a previous patellectomy on the side of the platform spinout.

Of the ten cases, six patients were symptomatic as a result of their platform dislocation. The remaining four patients were asymptomatic and mobilising without any difficulty. In these patients, the dislocated platform was diagnosed on x-ray at outpatient review. Time to detection of the platform dislocation ranged from six days to two years.

Three patients required revision of their original insert to a larger, deeper dish insert. Three were managed by open reduction of the original insert. Of the remaining patients, one was managed successfully by closed reduction, one required an arthrodesis and one had the tibial insert cemented to the tibial tray. All patients at latest review have a functional and stable knee joint.

In conclusion, we feel that surgical error was to blame for the majority of our ten cases. Furthermore, we emphasise the importance of producing equal and balanced flexion and extension gaps at the time of knee arthroplasty in order to prevent mobile bearing dislocation. A novel technique for reducing a dislocated rotating platform is also described.

Introduction: Since 1992 over 3000 custom-made cemented titanium femoral components have been implanted during total hip replacement in our centre.

Stems are machined using CAD-CAM. Measurements are made from screened AP and lateral x-rays of known magnification. Normal joint centre is recreated by controlling offset and vertical height of the femoral component.

Method: Joint centre and limb length were analysed radiologically in consecutive 100 patients following total hip replacement for unilateral arthritis. Joint centre was defined relative to the pelvis and femur.

The anatomical axis and offset of the femur were defined using a screened x-ray of known magnification taken to show maximum offset. Femoral centre height was defined relative to the greater trochanter.

Results: In general, acetabular joint centre was placed medial and high, tending to reduce limb length slightly. Conversely, on the femoral side the tendency was to leave the component proud, producing an increase in limb length. Most patients had limb length restored to within 6mm of normal.

This study confirms the effectiveness of the Belfast Custom Stem in restoring joint centre and limb length.

Isolated patello-femoral osteoarthritis has been reported to occur in approximately 5% of patients with gonarthrosis of the knee. We present the results of the surgical management of this disorder in our unit. Thirty-one patients (33 knees) with symptomatic patello-femoral osteoarthritis and minimal tibio-femoral changes underwent LCS total knee replacement without patellar resurfacing.

Average age was 73 years (range, 58–89 years) with a female to male ratio of 5: 1. Average follow-up was 20 months (range, 12–40 months). All except four patients had grade 3 or 4 patello-femoral osteoarthritis according to the classification by Sperner et al.

Preoperatively, all patients had significant knee pain. Sleep disturbance was reported in 21 patients. All but 10 patients required walking aids. Average range of motion was 108° (range, 80°–125°).

At latest review, 21 knees are pain-free, the remaining 12 knees describing only occasional knee pain. Two patients continue to have night pain. Average range of motion was 104° (range, 700 – 135°). Lateral patellar tilt improved in all but five knees by an average of 7° (range, 10–26°). Patellar congruency improved in all but three knees by an average of 18% (range, 3–63%). None of the patients to date have required revision surgery. We suggest that knee arthroplasty without patellar resurfacing is an effective option in older patients with isolated patello-femoral osteoarthritis.

Periprosthetic fractures are a recognised complication of total knee arthroplasty. They may occur intraoperatively or postoperatively and risk factors have been identified which may predispose an individual to such a complication.

We report seven cases of periprosthetic tibial fractures following LCS total knee arthroplasty, a complication only encountered by the senior author following a change in practice from a cemented implant to a cementless one.

In light of this previously unreported complication in our unit, we have attempted to identify common features within this group of patients, that may have contributed to fracture occurrence.

Statistical analysis revealed a highly significant risk of periprosthetic tibial fracture in those patients with a preoperative neutral or valgus knee. Age, gender and diagnosis did not appear to significantly increase the risk of fracture. All patients displayed evidence of reduced bone mineral density in the lumbar spine and femoral neck regions on dual energy x-ray absorptiometry scanning.

We feel that those patients with a preoperative neutral or valgus knee and local evidence of osteopenia represent a high-risk group, in whom particular care in alignment should be taken. In this group it may also be preferable to have the tibial component inserted with cement fixation.