The orthopaedic unit at the Golden Jubilee National Hospital consists of eight consultant orthopaedic surgeons who have a varied practice with regard to navigated TKA with some surgeons using navigation for all cases, some for what are deemed difficult cases and others using it rarely or not at all. One mechanical jig-based system and two different navigation systems are in routine use. The results from the two navigated (nav 1 and nav 2) and non-navigated (non-nav) systems were audited and compared with published studies to determine whether the reported results from randomised controlled trials were reproduced in our routine practice. The primary outcome measure was the mechanical femorotibial (MFT) angle as measured by Hip-Knee-Ankle (HKA) radiographs. This is a standard outcome measure that allowed ready comparison with other studies.

Demographic data and post-operative MFT angles were collected retrospectively for each patient. The HKA digital radiographs (stored on a Picture Archive and Communication system) were taken six to twelve weeks post-operatively. The MFT angle was measured using a standardised protocol, which used the method of Mose to find the centre of the femoral head, the highest point in the femoral notch as the centre of the knee and the middle of the talus for the centre of the ankle. Repeated measurements were taken to identify intra- and inter-observer error.

There were 86 patients in the nav 1 series, 95 in nav 2 and 95 in non-nav. Mean age was nav 1 = 70, nav 2 = 69 and non-nav = 71. Mean BMI was nav 1 = 34, nav 2 = 31.5 and non-nav = 30. Male to female ratio was nav 1 = 51:35, nav 2 = 44:51 and non-nav = 30:65. Intra- and inter- observer comparison showed a maximum difference of 1° for the measurement of MFT angle. For series nav 1 74% of TKAs had a MFT angle in the range ±3°, for series nav 2 this was 85% and for the non-nav series it was 68%.

Much of the literature on RCTs for navigation vs. non navigation outcomes in TKA indicates that over 93 % of patients undergoing navigated TKA have a mechanical axis alignment within the ±3° range, with non-navigated techniques having 73–87% within this range [1,2]. Our audit shows lower percentages for both navigated and non-navigated techniques. Our results are however similar to those obtained by Chauhan et al. [3] with 85% and 66% respectively. The lower numbers of patients falling into the ±3° range may be due to our audit covering a number of surgeons and trainees. The nav 1 series had five consultants and six trainees, nav 2 had two consultants and the non-nav series had four consultant and six trainees. It may also relate to the extent of pre-operative deformities, which were not quantified. In conclusion the high levels of TKA coronal alignment within ±3° seen in many RCTs may not be readily reproducible in a general setting.

Introduction: The knee joint replacement arthroplasty is a very successful procedure. Traditionally we aim to perform the arthroplasty and recreate the patients’ biomechanical axis and correct the coronal plain alignment deformity. Unfortunately till recently there was no fine way of controlling the exact alignment and depending on surgeon to surgeon, a valgus (to anatomical axis) of 3 to 7 degrees is aimed for using mechanical intra or extramedullary jigs. On proper measurements only 70–80% of knees achieve the aimed result at best as can be seen in the literature. With the advent of computer aided navigation we can now achieve the desired alignment in a much higher percentage of patients.

Material: We performed 1000 total knee arthroplasties at our hospital. Out of these 500 were performed using computer navigation and 500 using conventional mechanical jigs. Pre op and post op long leg alignment films were taken using standardised method. The data was collected using oxford scores and from computer navigation machines and plain radiographic analysis. The observers doing the radiographic analysis were blinded as to whether the patient had procedure done by conventional means or by computer navigation. Sub grouping of the deformities was done depending on the amount of deformity.

Results: 500 patients had the operation done by conventional means and the other 500 with computer navigation guidance. Further subgroups were made depending on the amount of pre-existing radiological deformity 0–5, 6–10, 11–15 and more than 15 degrees of varus or valgus deformity. The effect of gender, bmi, surgeon experience, clinical oxford score outcome was also considered. It was clear that the patients who had more severe deformities and valgus deformities had better post operative alignments after the procedure was performed with computer navigation as compared with the conventional means. There was statistically significant difference observed between the subgroups.

Discussion: Orthopaedic surgery has improved with technical advancements over the number of years. With any new procedure it takes a long time to shed the old beliefs and adapt the new concepts. While we have plenty of evidence in literature and from our study that computer navigation can give better desired alignment after total knee arthroplasty especially with more severe deformities, it still needs to be taken up by majority of orthopaedic surgeons. Ours is the first study to demonstrate the difference in the specific subgroups.

Introduction: Impaction allografting is an established method for restoring deficient bone during revision arthroplasty of the hip. Graft augmentation with synthetic materials has been proposed and evaluated experimentally. Our aim was to assess clinically whether migration and wear of implants with a synthetic graft mix would be equivalent to pure allograft.

Materials and Methods: Patient inclusion criteria were: acetabular and or femoral defects from aseptically loosened primary THR undergoing cemented revision with impaction grafting; age 55–80 years; initial diagnosis of osteo arthritis; good health with reasonable daily activity level. Patients were randomized to receive either pure allograft or a 50% mixture with a porous hydroxyapatite material (Apapore60, Apatech, UK). Revision was with the Exeter stem, antibiotic Simplex cement (Stryker Howmedica Ltd), and Ogee cup (Depuy Int. Ltd., Leeds, UK). Tantalum markers were inserted into the pelvis, cup, femur, cement and graft in order to measure migration with radiostereometry (RSA). Patients received a sequence of RSA examinations up to 2 years. A total of 26 patients (18 for the femur) have been analysed.

Results: At 2 years no significant differences were seen in cup wear, or migration of the cup, femoral and pelvic graft markers. Stem migration occurred mainly at the stem cement interface. The rate of distal migration for the femoral head was greater for pure allograft in the first year (p < 0.05), however this rate reduced significantly in year two. Higher medial migration in year one was observed for the proximal medial cement mantle for allograft (p < 0.05).

Conclusions: Improved stability and normal cup wear were observed in a randomized clinical study for a synthetically augmented allograft. This agrees with experimental findings¹. Longer follow up with increased patient numbers is recommended to confirm these findings.

Synthetic graft expanders have recently been developed for use in impaction grafting revision hip arthroplasty, but their true role has yet to be determined.

We performed a series of experiments to investigate the properties of one such porous hydroxyapatite material (IG-Pore, ApaTech Ltd). IG-Pore was mixed with fresh-frozen human allograft chips and impacted into composite femoral models with a similar biomechanical profile to human bone (Sawbones Europe). Exeter hip prostheses (Stryker Howmedica Ltd) were implanted with cement and each model was axially loaded for 18000 cycles at physiological levels using an Instron servohydraulic materials testing machine. Four test groups with 0%, 50%, 70% and 90% IG-Pore were used, and there were eight femora in each group.

Pre- and post-loading radiostereometric analysis was performed to characterise migration of the prosthesis. Total subsidence was measured and was separated into that occurring at the prosthesis-cement and cement-femur interfaces. Cyclical compression and expansion of the graft-containing models was measured using the Instron.

Median values (interquartile range) for total subsidence were 0.43 mm (0.28 to 0.55) for the pure allograft group, 0.31 mm (0.20 to 0.55) for the 50% IG-Pore group, 0.23 mm (0.07 to 0.34) for the 70% allograft group and 0.13 mm (0.06 to 0.18) for the 90% IG-Pore group. These differences were statistically significant (p=0.034, Kruskal-Wallis). Subsidence at the prosthesis-cement interface was also lower for IG-Pore containing models (p=0.019, Kruskal-Wallis), although there was no significant difference at the cement-femur interface. Specimens with a higher proportion of IG-Pore showed smaller cyclical movements on loading (p=0.005, ANOVA).

Higher proportions of IG-Pore do appear to reduce subsidence in a mechanical model of impaction grafting. A randomised clinical trial using RSA to compare a 50% IG-Pore/allograft mix with pure allograft is in progress to investigate the use of this material as a bone graft expander in the clinical setting.

Cement pressurisation is recognised as critical to achieving optimal results in cemented arthroplasty of the hip, but relatively little data exists on the pressures generated by different cement introduction systems. An in vitro experiment was consequently undertaken to measure the mean pressures developed by three such systems: the Howmedica Mark 1 and DePuy Cemvac retrograde cementation systems, and a novel antegrade system consisting of a simple 60ml catheter-tipped syringe and a Miller proximal femoral seal (Zimmer Ltd).

Plastic femoral models (Sawbones Europe) were prepared as for hip arthroplasty, and had a series of three transducers attached to their medial wall. Pressure was recorded continuously during cement introduction and pressurisation, before implanting a hip prosthesis and allowing the cement to cure. The experiment was repeated on ten models for each of the three systems. After cement curing, the femora were split in the coronal plane and examined for air-bubble defects in 7 zones analogous to Gruen’s radiographic zones.

Mean pressure was significantly higher for the syringe system (161.45 ± 28.9 kPa) than the Mark 1 (103.51 ± 22.0 kPa) or Cemvac (92.65 ± 30.7 kPa) systems (p=0.0001, ANOVA). The antegrade syringe system also generated a statistically different distribution of pressure in comparison to the two retrograde systems, with particularly high proximal pressurisation in the former. The median number of zones with defects was 1 (interquartile range 1,2) using the syringe system, 3 (IQR 2,4) with the Mark 1 system, and 3 (IQR1,3) using the Cemvac system. These differences were also statistically significant (p=0.0256, Kruskal-Wallis).

These results have relevance for clinical practice and cement system design, and the various design features of the different systems are discussed.

Cement pressurisation is recognised as critical to achieving optimal results in cemented arthroplasty of the hip, but relatively little data exists on the pressures generated by different cement introduction systems. An in vitro experiment was consequently undertaken to measure the mean pressures developed by three such systems: the Howmedica Mark 1 and DePuy Cemvac retrograde cementation systems, and a novel antegrade system consisting of a simple 60ml catheter-tipped syringe and a Miller proximal femoral seal (Zimmer Ltd).

Plastic femoral models (Sawbones Europe) were prepared as for hip arthroplasty, and had a series of three transducers attached to their medial wall. Pressure was recorded continuously during cement introduction and pressurisation, before implanting a hip prosthesis and allowing the cement to cure. The experiment was repeated on ten models for each of the three systems. After cement curing, the femora were split in the coronal plane and examined for air-bubble defects in 7 zones analogous to Gruen’s radiographic zones.

Mean pressure was significantly higher for the syringe system (161.45 28.9 kPa) than the Mark 1 (103.51 22.0 kPa) or Cemvac (92.65 30.7 kPa) systems (p=0.0001, ANOVA). The antegrade syringe system also generated a statistically different distribution of pressure in comparison to the two retrograde systems, with particularly high proximal pressurisation in the former. The median number of zones with defects was 1 (interquartile range 1,2) using the syringe system, 3 (IQR 2,4) with the Mark 1 system, and 3 (IQR1,3) using the Cemvac system. These differences were also statistically significant (p=0.0256, Kruskal-Wallis).

These results have relevance for clinical practice and cement system design, and the various design features of the different systems are discussed.

Impaction grafting procedures have found a widespread role in revision hip arthroplasty. Synthetic graft expanders have recently been introduced, but the optimal ratio of expander to allograft is unknown.

We performed a series of in vitro experiments to investigate the optimal ratio for one commercially available porous hydroxyapatite material (IG-Pore, ApaT-ech Ltd). IG-Pore was mixed with fresh frozen human allograft chips from osteoarthritic femoral heads and with blood. Graft was impacted into fibre-glass femoral models (Sawbones Europe) with a similar biomechanical profile to human bone, and Exeter hip prostheses (Stryker Howmedica Ltd) were cemented in place. Each model was loaded using an Instron servohydraulic materials testing machine for 18000 cycles. The magnitude and frequency of the loading cycle was based on physiologically measured values. Four test groups with 0%, 50%, 70% and 90% IG-Pore were used, with eight femora in each group.

Tantalum marker beads were attached to the prosthesis, the femoral model and the cement mantle, and radio-stereometric analysis (RSA) was performed pre- and post- loading to determine migration and rotation of the prosthesis in each axis. Pre-loading films were repeated in sixteen cases for precision measurements, and twelve specimens had delayed post-loading films performed to measure any re-expansion of the unloaded graft.

The primary end-point was RSA-measured subsidence of the prosthesis, defined as vertical movement of the tip. Median subsidence was 0.43mm, 0.31mm, 0.24mm and 0.13mm in the 0%, 50%, 70% and 90% IG-Pore groups respectively (P=0.034, Kruskal-Wallis test). The precision, given as the median absolute difference, was 0.0065mm.

All specimens showed a cyclical compression and expansion throughout the loading cycle. Specimens with a higher proportion of IG-Pore tended to be more resistant to this and the mean values for cyclical movement were 1.76 0.27mm, 1.65 0.21mm, 1.57 0.18 mm and 1.45 0.14mm for the 0%, 50%, 70% and 90% IG-Pore groups.

Higher proportions of IG-Pore appear to reduce subsidence in impaction grafting. Other issues such as the handling qualities of the graft and the biological effect of synthetic materials also need to be considered, however. A randomised clinical trial using RSA to evaluate a 50% IG-Pore/allograft mix in comparison to pure allograft is ongoing in our institution, and we hope that this will answer some of these questions definitively.