Conventional computer navigation systems using bone fixation have been validated in measuring anteroposterior (AP) translation of the tibia. Recent developments in non-invasive skin-mounted systems may allow quantification of AP laxity in the out-patient setting. We tested cadaveric lower limbs (n=12) with a commercial image free navigation system using passive trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° knee flexion and 100N of force applied perpendicular to the tibial tuberosity using a secured dynamometer. Repeatability coefficient was calculated both to reflect precision within each system, and demonstrate agreement between the two systems at each flexion interval. An acceptable repeatability coefficient of ≤3mm was set based on diagnostic criteria for ACL insufficiency when using other mechanical devices to measure AP tibial translation. Precision within the individual invasive and non-invasive systems measuring AP translation of the tibia was acceptable throughout the range of flexion tested (repeatability coefficient ≤1.6 mm). Agreement between the two systems was acceptable when measuring AP laxity between full extension and 40° knee flexion (repeatability coefficient ≤2.1 mm). Beyond 40° of flexion, agreement between the systems was unacceptable (repeatability coefficient >3 mm). These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard invasive system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative follow-up of ACL pathology.
Component malalignment has long been implicated in poor implant survival in Total Knee Arthroplasty (TKA). Malalignment can occur in orientation of bony cuts, and in component cementation/implantation. Several systems exist to aid bony cut alignment (navigation, shape matching), but final implantation technique is common to all TKA. Correction of errors in bony cut alignment at cementation/implantation by surgeons has been described. Changes in alignment at this stage are likely to result in asymmetrical cement penetration, which is implicated in early failure. This study reviewed a consecutive series of 150 primary cemented TKAs using an imageless navigation system (aiming for neutral overall limb alignment). Deviation at implantation was calculated by comparing limb alignment recorded using the trial components with limb alignment recorded with the final implanted components, prior to closure. 136 patients (91%) had a final overall limb alignment within 2° of neutral. Three patients (2%) had a final overall limb alignment greater than 3° from neutral. Deviation occurring at implantation is shown in Figure 1 with deviations distributed around zero (mode 0, median 0.3, range −2 to +4,)
Patients undergoing total knee arthroplasty (TKA) experience significant postoperative pain. This impedes early mobilization and delays hospital discharge. A prospective audit of 1081 patients undergoing primary TKA during 2008 was completed. All patients followed a programme including preoperative patient education, pre-emptive analgesia, spinal/epidural anaesthesia with propofol sedation, intra-articular soft tissue wound infiltration, postoperative high volume ropivacaine boluses with an intra-articular catheter and early mobilization. Primary outcome measure was length of stay. Secondary outcomes were verbal analogue pain scores on movement, time to mobilization, nausea and vomiting scores, urinary catheterization for retention, need for rescue analgesia, range of motion at discharge and six weeks postoperatively. The median day of discharge was postoperative day four. Median pain score on mobilization was three for first postoperative night, day one and two. 35% of patients ambulated on the day of surgery and 95% of patients within 24 hours. 79% patients experienced no nausea or vomiting. Catheterization rate was 6.9%. Rescue analgesia was required in 5% of cases. The median day of discharge was postoperative day four. Median range of motion was 85° on discharge and 93° at six weeks postoperatively. This comprehensive care plan provides satisfactory postoperative analgesia allowing early safe ambulation and discharge.
