The long-term impact of dividing Piriformis when performing a standard posterior approach to the hip has not been assessed. A less invasive approach in which the tendon is preserved has been described (the Piriformis-sparing minimally invasive [PSMI] approach). With advances in MRI technology it is now possible to image structures in close proximity to metal without artifact. The aim of the study was to compare the MRI features (muscle grade and bulk) of the divided and repaired Piriformis tendon group (by the standard posterior approach) with the preserved tendon group (by the PSMI approach). As part of an on-going randomized controlled trial comparing the PSMI approach with the standard posterior approach for total hip replacement, a subgroup of 20 consecutive patients who fulfilled the inclusion criteria were recruited. Patients received preoperative and 3 months and 2 year postoperative MRI scans. Patients and evaluators were blinded to allocation. Outcomes assessed included grade, volume and integrity of Piriformis.Background
Methods
To compare the new technique of computer assisted knee arthroplasty (CAK) against the current gold standard conventional jig based technique (JBK), 75 consecutive patients underwent knee replacement and were randomly allocated to either the CAK or JBK group. The CAK surgery was performed using a freehand technique that avoids violation of the medullary canal. Pre-and post-operative Knee society scores were collected. Post-operative CT scans were performed according to the Perth CT Knee Arthroplasty protocol and pre-and post-operative Maquet views of the limb performed. Intra-operative soft tissue release together with postoperative pain scores and blood loss were also assessed. CT scans performed show a statistically significant improvement in component alignment when using computer assisted surgery for femoral varus/valgus (p=0.032), femoral rotation (p=0.001), tibial varus/ valgus (p=0.047) tibial posterior slope (p=0.0001), tibial rotation (p=0.011) and femoral-tibial mismatch (p=0.037). Standing Maquet limb alignment was also improved (p=0.004) as was blood loss (p=0.0001). CAK surgery took longer, a mean increase of 13 minutes (p=0.0001). This is the first controlled study to assess all seven-alignment characteristics of knee arthroplasty in these two groups of patients. The improvement in alignment resulted in this trial being stopped prematurely as 6 out of 7 of the initial variables had reached significance. It shows a clear improvement in component alignment with computer navigation. The reduction in blood loss in this surgery through not violating the medullary canal will also be beneficial.
The mechanical and anatomical axes are identified, from 3 dimensional landmarks, in both AP and lateral planes. The coronal and sagittal alignment of the pros-theses is then measured against the axes. The rotation of the femoral component is measured relative to the transepicondylar axis. Tibial rotation was measured with reference to the posterior tibial condyles and the tibial tuberosity. Coupled femorotibial rotational alignment was assessed by superimposition of the femoral and tibial axial images. The results of 100 scans show a low inter and intra observer error rate whilst independent assessment shows a mean measurement error of 3mm in a three dimensional plane. The radiation dose is 2.7mSV.
In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source
