Introduction

Computer Assisted Total Knee Arthroplasty (CATKA) has proven benefits of achieving reproducible and accurate component alignment with outcomes comparable to conventional jig based TKR. Optical trackers are required for assessment of alignment and are fixed via bone pins. This technique does present its own unique complications including fracture and infection at the pin- sites. We report our experience of a single surgeon series performing CATKA.

Introduction

Computer assisted total knee replacement (CATKR) has been shown to give reproducible and accurate alignment of the mechanical axis. The benefits of the reproducible technique has been demonstrated in literature but there is little evidence of benefits in training junior surgeons in a clinical setting. We show our experience of CATKR performed by junior staff under supervision by the senior author, looking at component alignment and patient reported outcome measures.

Introduction

Minimally invasive Computer Assisted Total Knee Arthroplasty (MICATKA) has benefits of reduced blood loss, shorter hospital stay, improved post-operative quadriceps function and enhanced post-operative recovery. Our study looked into these factors to compare if there was a significant difference when compared to conventional Computer Assisted Total Knee Arthroplasty (CATKA).

Introduction

Unicondylar knee replacement (UKR) surgery is proven long term results in its benefit in medial compartment OA. However, its results are sensitive to component alignment with poor alignment leading to early failure. The advent of computer navigation has resulted in improved mechanical alignment, but little has been published on the outcomes of navigated UKR surgery. We present the results of 253 consecutive Computer Assisted UKR's performed by a single surgeon.

Introduction

The advent of double bundle ACL (Anterior Cruciate Ligament) reconstruction had been hailed as potentially allowing for more anatomically and physiologically functioning graft, however until recently there had been little evidence of enhanced functional outcomes.

The aim of this study is to explore whether the dimensions of hamstring two strand single bundle grafts, are predictive of the combined four strand single bundle graft that results from combining the single bundle grafts, as well as the impact of double bundle grafts upon the available healing and attachment area within the bony tunnels.

Minimally invasive total knee arthroplasty is growing in popularity. It appears to reduce blood loss, reduce hospital stay, improve post-operative quadriceps function and shorten post-operative recovery. We show our experience of minimally invasive TKA with a computer navigation system.

The first series compared forty MICA TKA and forty conventional computer assisted total knee arthroplasties (CATKA). Component positioning was assessed radiographically with long leg Maquet views. Knee Society Scores (KSS) were recorded pre-operatively and at 6, 12, 18 months. Length of stay and recovery of straight leg raise was also recorded. A second series of fifty MICATKA patients were assessed post-operatively for component alignment using long leg Maquet views. Twenty-two of these patients had assessment of femoral rotation using CT.

In the first series pre-operative KSS showed no significant difference between the two groups. Post-operatively the mean femoral component alignment was 89.7 degrees for MICATKA and 90.2 for CATKA. The mean tibial component alignment was 89.7 degrees for both. KSS at 6, 12, 18 months were statistically better in the MICATKA (p<000.1). Straight leg raise was achieved by day one in 93% of the MICATKA compared to 30% of the CATKA. Length of stay for MICATKA was a mean of 3.25 days with CATKA a mean of 6 days. In the second series the mean femoral component varus/valgus angle was 89.98 degrees, the mean tibial component varus/valgus angle was 89.91 degrees and the mean femoral component rotation was 0.6 degrees of external rotation.

MICATKA is a safe procedure with reproducible results. Alignment is equivalent to CATKA. It gives statistically significant improvement in KSS compared to the open procedure. The length of stay and time to straight leg raise are also reduced. At 2 years follow-up we have seen no revisions and no evidence of loosening radiographically.

Aim: To introduce a new concept of Envelope of Laxity (EoL) in knee arthroplasty surgery for balancing a total knee replacement (TKR).

Methods: Twenty consecutive patients with varus knees undergoing TKR were included in the study. All operations were performed by the senior author using the Stryker Navigation system and the Scorpio cruciate retaining (CR) TKR. After registration with the navigation system initial dynamic varus/valgus curves were recorded from 0–120° flexion to give an EoL of the native knee. Repeated measurements were taken after trial components were initially inserted, then after any soft tissue releases and finally after insertion of actual tibial and femoral components. All measurements were taken with the patellar in situ.

Results: The average deformity in the varus group initially was 6.9° varus at 0°, 8.9° varus at 30°, 6.9° varus at 60° and 5° varus at 90° of knee flexion. Postoperatively values were found to be 0.1°, 0°,0.3°and 0.7°respectively. The initial EoL curves showed a mean increase in laxity of 4° between 30° and 60°compared to 0°–30° and 60°–90° through the range of knee flexion. This was seen less in the outcome curves which tended to show more uniform laxity with only an average of 2° difference throughout flexion.

Conclusions: Traditional balancing devices used in TKR surgery balance knees at 0° and 90°, often with the patellar everted which produces errors. The use of EoL curves allows knees to be balanced throughout the arc of movement from 0–150° with the patellar in situ. This study demonstrates the successful use of the EoL concept and that even when knees are balanced at 0° and 90° they may not be balanced at the mid flexion position where clinical problems often arise. This problem becomes worse with the use of poly radii TKR designs.

Introduction: We investigated the routine use of CT scans in identifying alignment causes for failure as well as in the pre operative planning of the procedure.

Methods: Twenty poorly functioning total knee arthroplasties were analysed using the Perth CT protocol. All patients were awaiting revision total knee arthroplasty and were scanned using a GE multislice CT scanner. The measurements were performed using standard CT software. Knee society scores were obtained pre- and post-operative.

Results: The mean coronal position of the components was 3 degrees of valgus for the femoral component and 2.5 degrees of varus for the tibial component. Fourteen knees had errors of femoral component rotation, which ranged from 1 degree of external rotation to 9 degrees of internal rotation. Nine knees had errors of tibial baseplate rotation with all being internally rotated relative to the PCL/Tibial tuberosity axis from 3 to 12 degrees.

The cumulative error of implantation ranged from 6- 24 degrees in all 7 planes.

Knee society scores improved post-operatively from a mean of 52 pre-operatively to 83 at one year. Compound error also improved to a range of 6 to 10 in all 7 planes.

Conclusions: Revision total knee arthroplasty remains a difficult procedure but is increasing in frequency. The use of a CT protocol allows all coronal, sagittal and rotational errors of a previous implant to be accurately identified prior to surgery. We believe that all knee revision operations should have a CT scan as part of the pre operative planning. Also CT scans may be useful in investigating painful total knee replacements. Total knee replacement failure in some cases maybe explained by a cumulative error in alignment when no other obvious cause is found.

Introduction: Contact stresses, derived from navigation system and conventional TKR alignments, are compared to ideally aligned component stresses.

Methods: This study builds upon the work of previous studies, in which post-operative CT scans from 70 patients were utilized to extract knee component angular alignments from patients undergoing both navigation based and conventional TKR. Knee component (Stryker Orthopaedics Duracon^TM Condylar) FE models were oriented into specific alignment positions. Tibial insert contact stresses were computed under physiologically relevant loads at various flexion angles. FEA was also performed on ideally aligned cases for comparison purposes.

Results: At full extension, the median alignment of conventional TKR induces contact stresses 17.8% above ideal alignment conditions. Navigation based TKR alignment induces stresses 3.5% above ideal alignment conditions. At 45–90° flexion, conventional TKR alignment induces stresses 2.7% above ideal alignment conditions, while comparable navigation based TKR alignment induces stresses that match ideal alignment conditions.

Conclusion: Navigation based TKR procedures improve knee component alignment, which decreases contact stresses in UHMWPE tibial inserts. The result is a reduction in abnormal wear patterns and expected wear rates, with an increase in the structural longevity of knee system components.

Minimally invasive total knee arthroplasty is growing in popularity. It appears to reduce blood loss, reduce hospital stay, improve post-operative quadriceps function and shortens post-operative recovery. We show our experience of minimally invasive TKA with a computer navigation system.

Forty patients who underwent MICATKA were compared with forty patients having conventional CATKA. Component positioning was assessed radiographically with AP long leg standing views. Knee Society Scores, length of stay and recovery of straight leg raise was also recorded pre-operatively and at 6, 12, 18 and 24 months.

Pre-operative Knee Society Scores showed no significant difference between the two groups. Post operatively the mean femoral component alignment was 89.7 degrees for MICATKA and 90.2 for CATKA. The mean tibial component alignment was 89.7 degrees for both. Knees society scores at 6, 12, 18 and 24 months were statistically better in the MICATKA (p< 000.1). However the mean difference in Knee Society Scores had fallen. Straight leg raise was achieved by day one in 93% of the MICATKA compared to only 30% of the CATKA. Length of stay for MICATKA was a mean of 3.25 days with CATKA a mean of 6 days.

MICATKA is a safe procedure with reproducible results. Alignment is equivalent to CATKA. It gives statistically significant improvement in Knee Society Scores compared to the open procedure. The length of stay and time to straight leg raise is also reduced. At a minimum of 2 years follow-up we have seen no revisions and no evidence of radiographic loosening. A randomised multi centre trial is under way and early results are awaited.

The primary objective of navigation systems is to optimise component alignment to improve total knee replacement (TKR) performance. This study utilizes finite element analysis techniques to determine how component alignment affects tibial insert contact stresses. Contact stresses were derived from navigation system and conventional TKR alignments, and were compared to ideally aligned components.

This study builds upon the work of a previous study, in which post-operative CT scans from 70 patients were utilized to extract knee component angular alignments. These patients had been randomised to having either navigation based or conventional TKR.

Knee component finite element models were oriented into specific alignment positions. Tibial insert contact stresses were computed under physiologically relevant loads at various flexion angles. Finite element analysis was also performed on ideally aligned cases for comparison purposes.

At full extension, the median alignment of conventional TKR induces contact stresses 17.8% above ideal alignment conditions. Navigation based TKR alignment induces stresses 3.5% above ideal alignment conditions. At 45–90° flexion, conventional TKR alignment induces stresses 2.7% above ideal alignment conditions, while comparable navigation based TKR alignment induces stresses that match ideal alignment conditions.

Knee component alignment is improved by navigation techniques. This predictive finite element analysis study shows markedly reduced contact stresses for navigation aligned TKR compared to conventional aligned technique. The reduction in tibial insert contact pressures could reduce abnormal polyethylene wear, increasing the structural longevity of knee system components.

Revision total knee replacement is becoming a more common procedure. Landmarks commonly used for alignment are often distorted by the cause of the failure or removing the components themselves. This can make correct alignment and re-creation of joint line height difficult.

We looked at consecutive knee replacements that underwent revision surgery over one year. All cases had revision total knee replacements by the senior author using the Stryker® Navigation System. All cases were assessed radiographically post-operatively with long leg Maquet views. The tibial and femoral component varus/ valgus angles taken from the mechanical axis and the mechanical tibio-femoral angle were measured.

On long leg Maquet views the mean mechanical tibio-femoral angle was 3.25 with a range from 0 to 6, the mean tibial component angle was 90.4 with a range of 89 to 92 and the mean femoral component angle was 90.3 with a range of 89 to 91.

Computer navigation in revision total knee replacement is a safe procedure that gives reproducible results. Postoperative alignment, as measured radiographically, gave good results with tibial and femoral components within 2 degrees to the perpendicular of the mechanical axis. We feel that navigation is helpful in obtaining accurate positioning of components in revision knee surgery.

Revision total knee arthroplasty (TKA) is becoming a more frequent procedure throughout Europe. Painful patello-femoral problems, patellar dislocation, impingement pain as well as aseptic loosening and gross malalignment are among many causes. We investigated the use of CT scans in identifying alignment causes for pain in failed TKA where no other obvious cause is found.

Twenty poorly functioning TKA were analysed using the Perth CT protocol. All patients were awaiting revision TKA and had no obvious evidence of infection or loosening. They were scanned using a GE multislice CT scanner. The measurements were performed using standard CT software. Knee society scores were obtained pre- and post-operatively.

The mean coronal position of the components was three degrees of valgus for the femoral component and 2.5 degrees of varus for the tibial component. Fourteen knees had errors of femoral component rotation, which ranged from one degree of external rotation to nine degrees of internal rotation. The cumulative error of implantation ranged from 6–24 degrees in all planes. Knee society scores improved post-operatively from a mean of 52 pre-operatively to 83 at one year. Compound error also improved to a range of 6 to 10 degrees in all planes.

Revision TKA remains a difficult procedure that is increasing in frequency. The use of a CT protocol allows all coronal, sagital and rotational errors of an implant to be accurately identified prior to surgery. This could be useful in the small groups of patients with painful TKA that have no obvious cause for failure. Total knee replacement failure in these cases maybe explained by a cumulative error in alignment and correction of which may improve their Knee Society Scores.

We believe that a CT scan of a failed TKA is useful as part of the pre operative planning and also in investigating painful TKA where no obvious cause is found.

Introduction: Recently there has been a trend for recommending weight bearing 30û ßexion views as the standard view in place of full extension view for the routine radiography of the Knee. It has been shown that this view can pick up more abnormalities and can show a joint space diminution, which cannot be seen on full extension views. It has not been shown by any study that this is not due to the differential thickness of cartilage in different places on femoral condyle thus implying a natural cause rather than pathological process (abnormal wearing of cartilage) of the observed decrease in joint space. So this prospective randomised double blind study was designed. Methods: 22 patients with arthroscopically proven non osteoarthritic knees were included in the study. Knee radiographs were taken in weight bearing full extension and 30û ßexion PA views. The radiographs were randomised and read by a consultant, registrar & senior house ofþcer. Results: Appropriate statistical tests were applied and results analysed. There was up to 2mm difference in the joint space on the two views. Conclusion: The decrease in the joint space if seen on 30û ßexion views as compared to full extension views may be due to the differential thickness of inherent normal cartilage and so is not always due to a pathological process. Based on this a classiþcation was devised to signify the importance of measured differential thickness in the cartilage of femoral condyle.