The iASSIST system is a portable, accelerometer base with electronic navigation used for total knee arthroplasty (TKA) which guides the surgeon to align and validate bone resection during the surgical procedure. The purpose of this study was to compare the radiological outcome between accelerometer base iASSIST system and the conventional system.

Introduction: There is an increased risk of revision for aseptic loosening with a transgluteal approach as described in the Swedish Hip Register. Femoral component malpositioning is itself associated with a poor outcome. A cuff of posteriorly situated glutei during the direct lateral approach may result in levering the proximal stem anteriorly and the tip of the stem posteriorly and does not allow the entry point of the stem to be placed posteriorly at the level of neck resection resulting in possible malpositioning.

The purpose of this study was to determine whether there is a significant difference in femoral component alignment when the posterior and direct lateral approaches are compared.

Materials and methods: Forty patients underwent an direct lateral approach and forty a posterior approach (n = 80). Inclusion criteria included primary hip arthroplasty using a cemented Exeter femoral component. At 6 weeks a standard AP and a modified lateral radiograph were taken. Measurements were taken from digitized radiographs as follows:

1. AP radiograph

Component alignment was defined as A – B and C – D.

Results: A–B was 0.71 for the modified direct lateral approach and 2.56 for the posterior approach. C–D was 1.47 for the direct lateral approach and 1.21 for the posterior approach. This difference was not statistically different using paired t tests as p > 0.05(P=0.69) for lateral views measurements.

Discussion: This study demonstrates that there is no significant difference between direct lateral and posterior approaches as far as femoral component alignment is concerned. The increased revision rate noted by the Swedish Hip Register when a transgluteal approach is likely to be multifactorial, but not likely to be due to femoral component malalignment.

Aim: To test the accuracy of implant positioning in using computer navigation in Resurfacing hip arthroplasty

Materials and methods: Brain Lab was used to register 13 cadavers. The component position was fine tuned to a desirable valgus angle. Wire was passed using navigation. The femoral heads were sectioned after insertion of the prosthesis. The measurements from the screen-shots and the transverse sections were analysed using AutoCad®

Results: The Brain lab Registered the femoral heads to 124.91° ± 14.25° (Range 97° −148° ) CCD. The actual neck shaft angles were 126.11° ± 5.33°. The implants were placed in an angulation’s of 131.46° ± 5.27 ° (Range 116° −137° ) and a version of −0.85° ± 2.1° this gave a valgus of 5.91° ± 13.66°. The position of the wire in the isthmus of the neck was −0.52 mm ± 0.69 mm inferior to the centre and 1.7mm ± 1.9 mm posterior to the centre on the transverse sections (n=6). The components were in 8.69° ± 4.95° (n= 6) valgus to the native neck shaft angle. In only 1 hip the femoral head implanted was of the same size as suggested by navigation, in all the rest of the hips the femoral component was of a larger size. This was because it was felt that implanting a smaller size would cause notching of the superolateral neck.

Conclusion: There is a learning curve involved for registering the femoral heads using computer navigation systems, however the navigation gives the surgeon a distinct advantage of being able to choose the point of entry, implant the prosthesis in as valgus position as possible in relation to the femoral head, translate the implant anteriorly and place the peg in the centre of the femoral neck in both the planes. The computer-aided navigation can optimise the component positioning and thereby provide excellent results.

Aim: To test the accuracy of implant positioning in using computer navigation in Resurfacing hip arthroplasty

Materials and methods: Brain Lab was used to register 13 cadavers. The component position was fine tuned to a desirable valgus angle. Wire was passed using navigation. The femoral heads were sectioned after insertion of the prosthesis. The measurements from the screenshots and the transverse sections were analysed using AutoCad

Results: The Brain lab Registered the femoral heads to 124.91° ± 14.25° (Range 97°–148° ) CCD. The actual neck shaft angles were 126.11° ± 5.33°. The implants were placed in an angulation’s of 131.46° ± 5.27 ° (Range 116° –137° ) and a version of –0.85° ± 2.1° this gave a valgus of 5.91° ± 13.66°. The position of the wire in the isthmus of the neck was –0.52 mm ± 0.69 mm inferior to the centre and 1.7mm ± 1.9 mm posterior to the centre on the transverse sections (n=6). The components were in 8.69° ± 4.95° (n= 6) valgus to the native neck shaft angle. In only 1 hip the femoral head implanted was of the same size as suggested by navigation, in all the rest of the hips the femoral component was of a larger size. This was because it was felt that implanting a smaller size would cause notching of the supero-lateral neck.

Conclusion: There is a learning curve involved for registering the femoral heads using computer navigation systems, however the navigation gives the surgeon a distinct advantage of being able to choose the point of entry, implant the prosthesis in as valgus position as possible in relation to the femoral head, translate the implant anteriorly and place the peg in the centre of the femoral neck in both the planes. The computer-aided navigation can optimise the component positioning and thereby provide excellent results.

Introduction: There is an increased risk of revision for aseptic loosening with a transgluteal approach as described in the Swedish Hip Register. Femoral component malpositioning is itself associated with a poor outcome. A cuff of posteriorly situated glutei during the direct lateral approach may result in levering the proximal stem anteriorly and the tip of the stem posteriorly and does not allow the entry point of the stem to be placed posteriorly at the level of neck resection resulting in possible malpositioning.

The purpose of this study was to determine whether there is a significant difference in femoral component alignment when the posterior and direct lateral approaches are compared.

Materials and methods: Forty patients underwent a direct lateral approach and forty a posterior approach (n = 80). Inclusion criteria included primary hip arthroplasty using a cemented Exeter femoral component. At 6 weeks a standard AP and a modified lateral radiograph were taken. Measurements were taken from digitized radiographs as follows:

AP radiograph

Tip of stem to outer medial cortex.

Component alignment was defined as A – B and C – D.

Results: A–B was 0.71 for the modified direct lateral approach and 2.56 for the posterior approach. C–D was 1.47 for the direct lateral approach and 1.21 for the posterior approach. This difference was not statistically different using paired t tests as p > 0.05(P=0.69) for lateral views measurements.

Discussion: This study demonstrates that there is no significant difference between direct lateral and posterior approaches as far as femoral component alignment is concerned. The increased revision rate noted by the Swedish Hip Register when a transgluteal approach is likely to be multifactorial, but not likely to be due to femoral component malalignment.