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.

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.

The presence of retained metalwork, previou fractures or osteotomies makes TKA surgery challenging. Obstructed intramedually canals can produce difficulty with the use of IM instrumentation whilst the altered alignment can result in problematic soft tissue balancing.

We present a series of 35 patients with deformity who underwent a successful TKA.

Between July 2003 and January 2006 35 patients were operated on between 3 centres. All had extraarticular deformities in either the femur or tibia due to previous fractures or exposure to surgery. All underwent TKA surgery using an image free computer navigation system and extramedullary TKA instrumentation. All patients underwent pre-op and post-operative long eg alignment films.

The pre-operative long eg films showed an alignment of 16 degrees varus to 18 degrees of valgus. Post-operative alignment ranged from 3 degrees varus to 4 degrees valgus. The femoral component position ranged from 88-91 degrees from the mechanical axis whilst the tibial component position ranged from 89-92 degrees from the mechanical axis of the limb.

Total knee arthroplasty in the presence of extraarticular deformity is fraught with problems in regaining limb alignment and soft tissue balancing. This is the largest combined series of patients in which the same navigation system has been used to provide extramedullary alignment and cuts resulting in excellent component positioning and post-operative alignment. We recommend the routine use of computer navigation in these difficult cases.

Introduction: The emergence of Independent Sector Treatment Centres (ISTCs) in the UK for the provision of elective orthopaedic services began in 2002–3. Within our trust the bulk of elective orthopaedic surgery is performed in an ISTC however there is a small but significant cohort of patients who are deemed not suitable for treatment at the ISTC. Patients with a BMI (body mass index) ≥40 or an ASA (American society of anaesthesiologists) grade of 3 or more are automatically rejected. With increasing levels of obesity and an aging population the size of the reject cohort is going to rise. These patients are then returned to the NHS to be placed on a new (complex elective) waiting list for their surgery. The aim of this study was to assess the early outcomes and complications following primary knee arthroplasty on our high risk patients.

Methods: A retrospective review of a consecutive series of 214 primary knee arthroplasties in patients rejected from the ISTC was performed. Data (demographics, ASA grade, BMI, length of stay, complications, range of knee movement and requirement for HDU/ICU) were collected from preoperative assessments, inpatient notes, anaesthetic charts, discharge summaries and follow up clinic letters. All patients were followed up for a minimum of 6 months.

Results: 155 (72%) patients were female. 140 (65%) had ASA of 3 or more. 88 (41%) had a BMI of 40 or more. Median length of stay was 8 days (6 to 11 IQR) and did not vary with increasing BMI but increased to 10 days in the ASA 3 and 12 days in the ASA 4 group. There were a total 90 complications in 71 patients. The most common complications were 22 superficial wound infections (10.3%), 11 Pneumonias (5.1%), and 9 symptomatic DVTs (4.2%). There were 16 severe complications (2 Deep infections, 4 PEs, 2 CVAs, 4 acute renal failures and 4 dislocations) in 15 patients. Patients with a BMI < 40 had a total complication rate of 38% (7.9% severe) compared with 26% (5.7% severe) in BMI ≥40 group. Patients with an ASA < 3 had a complication rate of 31% (4.1% severe) vs. 34% (8.6% severe) in patients with an ASA ≥ 3. HDU/ICU beds were required postoperatively for 20 patients (9 planned and 11 unplanned). At six months 72% achieved a knee range of movement ≥ 0 to 90 degrees. Surgeons who performed high volumes of surgery in this difficult group had lower complications then lower volume surgeons.

Conclusion: This is one of the largest consecutive groups of high risk patients undergoing primary total knee arthroplasty. Our results show that elevated BMI does not appear to adversely affect complication rates in knee arthroplasty in our series although ASA grades of 3 and 4 are associated with increased length of stay and complication rates. It is also clear that small groups of surgeons operating on these difficult patients may reduce complications.

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.

This study was to assess the accuracy of fixed posterior condylar referencing cutting blocks to the accuracy of combined epicondylar/AP axis referencing in femoral component rotation using a computer navigation system.

Seventy-five consecutive patients undergoing TKRs were randomized into two groups. The first received femoral component rotation by a computerized method that combined the epicondylar axis and Whitesides AP axis measurements to determine rotation. The second group had a zero or three-degree posterior referencing external rotation block, depending on which was closest to the epicondylar axis. All patients underwent axial CT scans of the distal femur to determine component rotation around the surgical epicondylar axis.

Femoral component alignment with the combined method as compared to fixed posterior alignment guides is statistically improved (p=0.001). In the posterior referencing group 43% were correctly rotated to the epicondylar axis but another 43% were malrotated by 3 degrees or more. The mean malrotation was 1.72 degrees (range 0–5) In the combined group 82% were correctly rotated and 11% were malrotated by 3 degrees or more. The mean malrotation was 0.51 degrees (range 0–4).

Conclusion: A combined computerized method of using the surgical epicondylar axis and Whitesides AP axis produces superior results when aiming for neutral femoral component rotation. Fixed posterior referencing blocks will produce errors in malrotation in over 50% of cases.

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.

Plain radiographs are a poor indication of the overall coronal, sagittal and axial alignment of a total knee arthroplasty (TKA). We describe a new CT method that allows the mechanical axis in both planes to be defined and seven alignment characteristics to be defined.

A GE Light Speed multislice CT scanner performed a high-speed helical scan from the acetabular roof to the talus in 100 patients following TKA. The knees were scanned in a supine position with the legs in a neutral position. The images were reformatted in coronal, sagittal and axial planes and the mechanical and anatomical axes identified. The femoral component (varus/ valgus, flexion/extension, rotation) as well as the tibial – (varus/valgus, posterior slope and rotation) are measured. Coupled femoro-tibial rotational alignment was assessed by superimposition of the femoral and tibial axial images. The accuracy of this technique has been checked by using a mechanical FARO-arm.

The technique has a low intraobserver error rate of 9% (in each case less than 1 degree) and an accuracy of 3mm in a three-dimensional plane, as determined against an independent FARO arm technique. The CT analysis of 100 patients shows normal tibial baseplate rotation to be 8–12 degrees from the tibial tuberosity.

Conclusion: The CT protocol is the first single radiographic investigation that characterizes all the alignment parameters of a TKA. It sets an excellent standard in planning revision knee surgery and provides a valuable tool in assessing alignment of painful knee replacements as well as in outcome measures of TKA.

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 Revision total knee arthroplasty 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 routine use of CT scans in identifying alignment causes for failure as well as in the pre operative planning of the procedure.

Method 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.

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 base-plate 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.

Discussion 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 in previous implantation 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.

1. The aim of this study was to assess the safety and effectivness of Computer Assisted TKR through minimally invasive incisions.

2. Twenty-two patients underwent MIS CAS TKR surgery over a five-month period, using a Knee Navigation system and Specialist instruments developed for this technique. The length of surgery, time to achieve 90 Flexion, time from end of surgery to first walking, length of stay, blood loss and component alignment were assessed. Complications were also recorded.

The results show the range of surgical time from 100–180 minutes, the time to achieve 90 degrees flexion and SLR from 1–9 hours post surgery. Patients took from 3–12 hours to walk with a frame following surgery and stay as inpatients from 2–5 days. Blood loss ranged from 200–1180 mls. Femoral component varus/valgus ranged from 89–94 degrees, whilst tibial varus/valgus ranged from 87–91 degrees. There were 2 superficial wound infections, which resolved with antibiotics.

3. MIS CAS TKR surgeries can be performed safely and effectively with the aid of computer navigation to produce component alignment comparable to standard open techniques. However it has dramatically improved patient’s recovery after TKR surgery. The effects clearly warrant further investigation in the form of a multi-centre trial.

Aim To compare the new technique of computer assisted knee arthroplasty (CAK) against the current gold standard conventional jig based technique (JBK).

Methods Seventy-Five consecutive patients underwent knee replacement and were randomly allocated to either the CAK or JBK group. Pre and postoperative 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 post operative pain scores and blood loss where also assessed.

Results 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 femoraltibial 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 13minutes(p=0.0001).

Conclusions 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.