Computer-assisted navigation increases precision of component placement in total knee arthroplasty

Mechanical accuracy of navigated minimally invasive total knee arthroplasty (MIS TKA)

This study was designed to provide evidence that computer-navigated minimally invasive total knee arthroplasty (MIS CN-TKA) enables identical mechanical accuracy as conventional computer navigated total knee arthroplasty (CN-TKA) while reducing rehabilitation time and hospital stay of the patients. Two groups of 20 patients requiring total knee arthroplasty due to degenerative or posttraumatic knee osteoarthritis were included. Twenty consecutive patients received conventional CN-TKA and 20 consecutive patients received minimally invasive CN-TKA. Mechanical and rotational alignments were measured preoperatively and 6 months postoperatively on long-standing radiographs, on conventional coronal and sagittal views and on CT-scans of the knee. Length of skin incision, operating time, blood loss, length of hospital stay, postoperative ROM and HSS as well as KSS scores were determined. Postoperative mechanical axis improved significantly in both groups. Coronal and sagittal component positioning were accurate in both groups without significant differences. Rotational alignment showed the desired reproducible values without significant differences between the two groups. The posterior slope of the tibial component was significantly reconstructed to match the preoperative condition in both groups. The coronal alignment of the femoral and tibial components showed accurate reproducible results for implantation of both components in both groups. Length of skin incision was significantly shorter in the MIS CN-TKA. Duration of hospital stay was significantly reduced in the MIS CN-TKA group. Operating time and blood loss were similar in both groups. Postoperative ROM after the first 3 months was significantly higher in MIS CN-TKA, but after 6 months differences were minimal. Clinical outcome scores were identical for both groups 6 months after surgery. The advantages of CN-TKA are well known. Performing computer navigated TKA in combination with a minimally invasive approach in this study lead to a reduction of hospital stay and an initially increased ROM without differences in operating time and blood loss. Computer navigation in TKA preserves accurate coronal, sagittal and rotational components alignment even with a minimally invasive approach.

Analysis of factors affecting operating time, postoperative complications, and length of stay for total knee arthroplasty: nationwide web-based survey

BACKGROUND

This study aimed to clarify the impact of various factors on the operating time, postoperative complications, and length of stay (LOS) after total knee arthroplasty (TKA).

METHODS

We identified 3577 TKAs performed in 345 hospitals in Japan from November 2006 to March 2007. We examined the patient characteristics, surgical procedure details, hospital and surgeon volumes, and outcome variables (operating time, postoperative complications, LOS).

RESULTS

The average operating time was 127 +/- 47 min. The rate of postoperative complications was 9.8%. The average LOS was 35.1 +/- 15.9 days. In multivariate regression analyses, the average operating times were significantly shorter at hospitals with > or = 50 cases per year compared to hospitals with < 10 cases per year and for surgeons with > or =100 total cases compared to surgeons with < 100 total cases. A longer operating time was associated with revision surgery and use of computer navigation. Significant predictors of postoperative complications were age, body mass index, and cerebrovascular disease. Shorter LOS was associated with higher hospital volume and use of a clinical pathway, whereas age, cardiovascular disease, and revision surgery increased the length of stay.

CONCLUSIONS

Postoperative complications following TKA mainly depended on patient-based factors and were not significantly affected by the surgeon's experience.

Navigation-assisted total knee arthroplasty for a knee with malunion of the distal femur

Conventional total knee arthroplasty (TKA) has been developed for several decades. However, very few previous reports describe TKA with less invasive modality for extra-articular angular deformity. Herein, we report a case of navigation-assisted TKA for severe osteoarthritis associated with malunited distal femoral fracture. Fourteen months after navigation TKA surgery, satisfactory alignment, diminished length discrepancy, and improved range of motion were noted. Our report reveals that navigation system without intramedullary reaming is a feasible and less invasive alternative for TKA surgery for complex arthritic knee disorders.

The effect of oxidative aging on the wear performance of highly crosslinked polyethylene knee inserts under conditions of severe malalignment

First-generation crosslinked polyethylene developed for total hip arthroplasty has not gained wide acceptance for knee arthroplasty because of the increased potential for failure under high stresses and the increased risk for oxidative damage caused by free radicals. Sequentially crosslinked polyethylene (SQXL) is a second-generation crosslinked polyethylene that is reported to reduce the level of free radicals and preserve mechanical properties. Three groups of ultrahigh molecular weight polyethylene inserts were wear tested after artificial aging as per ASTM F2003: gamma-irradiated in air (GA-aged), sequentially crosslinked (SQXL-aged), and electron-beam irradiated and remelted (EBeam-aged). Inserts were tested in an AMTI knee wear simulator under malalignment conditions that were two standard deviations from the mean reported for computer-navigated and conventionally aligned techniques. GA-aged inserts delaminated by 500,000 cycles, and were severely damaged after 1 million cycles. None of the highly crosslinked inserts (SQXL-aged or EBeam-aged) delaminated or showed any signs of severe wear. Mean wear rate for GA-aged inserts was 124.6 +/- 49.4 mg/million cycles. Mean wear rates for SQXL-aged and EBeam-aged inserts were significantly lower (1.74 +/- 0.3 and 4.72 +/- 0.7, respectively). These results support the low levels of free radicals and preservation of mechanical properties reported in second-generation crosslinked ultrahigh molecular weight polyethylene.

Does computer navigation in total knee arthroplasty improve patient outcome at midterm follow-up?

Computer navigation assistance in total knee arthroplasty (TKA) results in consistently accurate alignment of prostheses. We aimed to compare the outcome of computer-navigated and conventional TKA and to analyse the radiologically malaligned knees. We analysed 637 primary TKA, carried out by a single surgeon, over five consecutive years and divided them into two cohorts: group 1 = STA (standard instrumentation) and group 2 = CAS (computer-assisted surgery). There was no significant difference between the average Oxford Knee Scores (OKS) of the two groups at any time from one to five years. However, the malaligned TKA at three years had a worse OKS. At medium term there is no difference in clinical outcome measures that can be attributed to the surgeon having used computer-assisted navigation for TKA. But group 1, having a higher proportion of malaligned TKA, might show worsening of OKS at long term.

Radiographic and navigation measurements of TKA limb alignment do not correlate

Precise pre- and postoperative anatomic measurements are necessary to plan, perform, and evaluate total knee arthroplasty (TKA). We evaluated the relationship between radiographic and navigation alignment measurements, identified sources of error in radiographic and navigated alignment assessment, and determined the differences between desired and clinically accepted alignment. Fifty-eight computer-assisted TKAs were performed and limb alignment measurements were recorded both pre- and postoperatively with standard radiographs and with an intraoperative navigation system. Intraoperative navigation produced consistent navigation-generated alignment results that were within 1 degrees of the desired alignment. The difference between preoperative radiographic and navigation measurements varied by as much as 12 degrees and the difference between postoperative radiographic and navigation measurements varied by as much as 8 degrees. This discrepancy depended on the degree of limb deformity. Postoperative radiographic measurements have inherent limitations. Navigation can generate precise, accurate, and reproducible alignment measurements. This technology can function as an effective tool for assessing pre- and postoperative limb alignment and relating intraoperative alignment measurements to clinical and functional outcomes.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Determining femoral component position using CAS and measured resection

To evaluate the ability of computer-assisted surgery (CAS) to accurately size and determine rotational alignment of the femoral component in TKA, the author reviewed femoral component position after 50 consecutive primary TKAs using a femur-first, measured resection workflow. The computer software used allowed femoral rotation to be selected based on epicondylar axis, posterior condylar axis, or anteroposterior axis. The final femoral component size and position was determined by the surgeon to avoid anterior notching, match the posterior-medial condyle resection, and flexed to match the plane of the anterior femoral cortex. Femoral sizing was confirmed intraoperatively with a standard sizing guide. The femoral component was downsized in 52% of patients from the size recommended by the computer software. The posterior condylar axis matched the implanted rotational position of the femoral component to within 1 degrees in 64% of patients in contrast to the epicondylar axis (32%) and anteroposterior axis (26%). CAS provides information to make surgical decisions but does not replace clinical judgment. Landmark referencing may be compromised by limited surgical exposures leading to variation in implant positioning by computer software. A clear understanding of the principles of TKA is critical when using CAS to optimize implant sizing and position.

Computer navigation-assisted versus minimally invasive TKA: benefits and drawbacks

Computer-navigated and minimally invasive TKAs are emerging technologies that have distinct strengths and weaknesses. We compared duration of surgery, length of hospitalization, Knee Society scores, radiographic alignments, and complications in two unselected groups of 81 consecutive knees that underwent TKA using either a minimally invasive approach or computer navigation. The two groups were operated on by two different surgeons over differing timeframes. The mean surgical time was longer in the navigated group by 63 minutes. The Knee Society scores and lengths of hospitalization of the two groups were similar. The postoperative component alignments of the two groups were similar; the mean femoral valgus and tibial varus angles of the navigation group changed from 96 degrees and 88 degrees preoperatively to 95 degrees and 89 degrees postoperatively, respectively, and in the minimally invasive group, the mean femoral valgus angles and tibial varus angles changed from 97 degrees and 88 degrees preoperatively to 95 degrees and 89 degrees postoperatively, respectively. There were 11 major and three minor complications in the navigation group, including one revision, two femoral shaft fractures, four reoperations for knee stiffness, and four instances of bleeding from tracker sites. We believe the higher incidence of complications in addition to the longer operative time in the navigated group may outweigh any potential radiographic benefits.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Computer-assisted and conventional total knee replacement: a comparative, prospective, randomised study with radiological and CT evaluation

After obtaining informed consent, 80 patients were randomised to undergo a navigated or conventional total knee replacement. All received a cemented, unconstrained, cruciate-retaining implant with a rotating platform. Full-length standing and lateral radiographs and CT scans of the hip, knee and ankle joint were carried out five to seven days after operation. No notable differences were found between computer-assisted navigation and conventional implantation techniques as regards the rotational alignment of the femoral or tibial components. Although the deviation from the transepicondylar axis was relatively low, there was a considerable range of deviation for the tibial rotational alignment. There was no statistically significant difference regarding the occurrence pattern of outliers in mechanical malalignment but the number of outliers was reduced in the navigated group.

Minimal invasive and computer assisted total knee replacement compared with the conventional technique: a prospective, randomised trial

Minimal invasive surgery (MIS) in total knee replacement (TKR) has been favoured by several authors and the industry and is asked for by the patients. Computer assisted surgery (CAS) is proposed to support the surgeon in terms of postoperative leg alignment and implant orientation. To prove the hypothesis that MIS in TKR fastens early rehabilitation compared to the standard approach and that CAS-MIS in TKR improves accuracy in implant position compared to the freehand MIS and freehand standard technique, we performed a prospective, randomised short-term trial which was approved by the local ethic committee. In total, 90 patients underwent TKR. The conventional group (n = 30) underwent conventional TKR, the MIS group (n = 30) underwent MIS-TKR without navigation, the CAS-MIS group (n = 30) underwent TKR using navigation and the MIS approach. Groups were comparable regarding patients' specific parameters. The length of incision in extension was significantly lower in the MIS (13.2 cm) and CAS-MIS technique (12.9 cm) compared to the conventional technique (17.3 cm) (P < 0.01). Knee Society and WOMAC Score were similar in all three groups after 1, 6 and 12 weeks, no significant differences were seen between groups at any point of time. Postoperative deviation of the mechanical leg axis was significantly better in the CAS-MIS group compared to the conventional group and the MIS one (P < 0.05). The clinical relevance of our results is that the benefit of the minimal invasive approach in TKR is still not proven and navigation improves postoperative accuracy of leg alignment and component orientation. Our study shows that for the group of patients included there is no statistically significant difference in early rehabilitation between MIS and the conventional approach based on the Knee Society and WOMAC Score. Using the CAS technique restoration of leg axis was more accurate.

Computer assisted versus conventional cemented total knee prostheses alignment accuracy and micromotion of the tibial component

We evaluated the influence of CT-free or CT-based computer assisted orthopaedic surgery (CAOS) on the alignment of total knee prostheses (TK) and micromotion of tibial components. This randomised study compared 19 CT-free, 17 CT-based CAOS TK, and a matched control group of 21 conventionally placed TK. Using Roentgen stereophotogrammetric analysis (RSA) the migration was measured. The alignment and component positions were measured on radiographs. No significant difference in leg and tibial component alignment was present between the three groups. A significant difference was found for micromotion in subsidence, with the conventional group having a mean of 0.16 mm, compared to the CT-free group at 0.01 mm and the CT-based group at −0.05 mm. No clinical significant difference in alignment was found between CAOS and conventionally operated TK. More subsidence of the tibial component was seen in the conventional group compared to both CAOS groups at two year follow-up.

Assessment and validation of CT scanogram to compare per-operative and post-operative mechanical axis after navigated total knee replacement

Our objective was to assess and validate low-dose computed tomography (CT) scanogram as a post-operative imaging modality to measure the mechanical axis after navigated total knee replacement. A prospective study was performed to compare intra-operative and post-operative mechanical axis after navigated total knee replacements. All consecutive patients who underwent navigated total knee replacement between May and December 2006 were included. The intra-operative final axis was recorded, and post-operatively a CT scanogram of lower limbs was performed. The mechanical axis was measured and compared against the intra-operative measurement. There were 15 patients ranging in age from 57 to 80 (average 70) years. The average final intra-operative axis was 0.56 degrees varus (4 degrees varus to 1.5 degrees valgus) and post-operative CT scanogram axis was 0.52 degrees varus (3.1 degrees varus to 1.8 degrees valgus). The average deviation from final axes to CT scanogram axes was 0.12 degrees valgus with a correlation coefficient of 0.9. Our study suggests that CT scanogram is an imaging modality with reasonable accuracy for measuring mechanical axis despite significantly low radiation. It also confirms a high level of correlation between intra-operative and post-operative mechanical axis after navigated total knee replacement.

Current state and future of joint replacements in the hip and knee

Joint replacements of the hip and knee are among the most clinically successful operations. According to figures compiled by the American Academy of Orthopaedic Surgeons, the number of primary total hip replacements performed in the USA was 220,000 in 2003. This was 38% more than in 1996 and this number is expected to rise to 572,000 (plus another 97,000 revisions) by 2030. The number of primary total knee replacements performed in 2003 was approximately 418,000 and is expected to rise exponentially with the increasing numbers of baby boomers and the aging population. Current research focuses not only on extending implant longevity, but also on improving function to meet the increased demands of today's patients, who are likely to be younger and more active than their predecessors two decades ago. Potential advancements in arthroplasty surgery include new, more wear-resistant bearing surfaces, porous metals to enhance osseointegration and replace lost bone stock, a clearer understanding of the biological processes associated with periprosthetic osteolysis, minimally invasive surgery and computer assisted surgery. Long-term studies are needed to establish the efficacy of these new technologies.

Computer assisted orthopedic surgery; its influence on prosthesis size in total knee replacement

Improvement of alignment and position of the components in TKAs using Computer Assisted Orthopaedic Surgery (CAOS) has been described. However, much less is known about the accuracy of CAOS in determining the size of the components. The purpose of this study was to evaluate the size of the femoral and tibial component using the CAOS system from Brainlab. The component sizes were compared to pre-operative templating and post-operative scoring the adequateness of size. Forty TKAs (NexGen) were evaluated: 20 using CAOS and 20 conventional. Statistical analysis of the templated and implanted size indicated a fair agreement for the femur (kappa 0.38) and the tibia (kappa 0.35). In the CAOS group significantly more oversizing occurred for the femoral component (p=0.020). No significant difference was found for the tibial component. We conclude there is a risk of oversizing the femoral component of the NexGen system when using CAOS.

Experience with computer-assisted navigation for total knee arthroplasty in a community setting

This study analyzed the initial experience with computer-assisted navigation for total knee arthroplasty (TKA) in a community hospital. One hundred TKAs performed with a navigation system were compared with 100 performed conventionally. Component alignment results, measured by computed tomography, were grouped as good, fair, poor, or extremely poor, based on deviation from the surgical goal. More navigated knees were classified as good (sagittal, 78%-93%; coronal, 98%; axial, 78%-85%) compared with conventional (sagittal, 47%-64%; coronal, 91%; axial, 89%-90%). Outliers were reduced both in number and severity with navigation. Additional time required to navigate diminished with experience, although improved component alignment was observed from the initial cases. Navigation resulted in improved alignment, with minimal time cost, and is a useful tool for TKA for the community surgeon.

History of computer-assisted orthopedic surgery (CAOS) in sports medicine

Computer-assisted orthopedic surgery and navigation applications have a history rooted in the desire to link imaging technology with real-time anatomic landmarks. Although applications are still evolving in the clinical and research setting, computer-assisted orthopedic surgery has already demonstrated in certain procedures its potential for improving the surgeon's accuracy, reproducibility (once past the learning curve), and in reducing outlier outcomes. It is also being used as an educational tool to assist less experienced surgeons in interpreting measurements and precision placements related to well defined anatomic landmarks. It also can assist experienced surgeons, in real-time, plan their bony cuts, tunnel placement, and with ligament balancing. Presently, the additional time, the expense to acquire the needed software and hardware, and restricted reimbursement have slowed the widespread use of navigation. Its current applications have been primarily in joint replacement surgery, spine surgery, and trauma. It has not been widely used in the clinical setting for sports medicine procedures. Sports medicine applications such as individualizing tunnel placement in ligament surgery, opening wedge osteotomy with and without accompanying ligament reconstruction, and balancing and tensioning of the ligaments during the procedure (allowing real-time corrections if necessary) are currently being evaluated and being used on a limited clinical basis.

Impact of hospital volume on the economic value of computer navigation for total knee replacement

BACKGROUND

An aim of the use of computer navigation is to reduce rates of revisions of total knee replacements by improving the alignment achieved at the surgery. However, the decision to adopt this technology may be difficult for some centers, especially low-volume centers, where the cost of purchasing this equipment may be high. The purpose of this study was to examine the impact of hospital volume on the cost-effectiveness of this new technology in order to determine its feasibility and the level of evidence that should be sought prior to its adoption.

METHODS

A Markov decision model was used to evaluate the impact of hospital volume on the cost-effectiveness of computer-assisted knee arthroplasty in a theoretical cohort of sixty-five-year-old patients with end-stage arthritis of the knee to coincide with the peak incidence of knee arthroplasty in the United States.

RESULTS

Computer-assisted surgery becomes less cost-effective as the annual hospital volume decreases, as the cost of the navigation increases, and as the impact on revision rates decreases. Centers at which 250, 150, and twenty-five computer-navigated total knee arthroplasties are performed per year will require a reduction of the annual revision rate of 2%, 2.5%, and 13%, respectively, per year over a twenty-year period for computer navigation to be cost-effective.

CONCLUSIONS

Computer navigation is less likely to be a cost-effective investment in health-care improvement in centers with a low volume of joint replacements, where its benefit is most likely to be realized. However, it may be a cost-effective technology for centers with a higher volume of joint replacements, where the decrease in the rate of knee revision needed to make the investment cost-effective is modest, if improvements in revision rates with the use of this technology can be realized.

Functional comparison of total knee arthroplasty performed with and without a navigation system

This study was undertaken to compare the clinical and radiological outcomes achieved using total knee arthroplasty (TKA) with and without a navigation system. This study included 43 TKAs performed with a navigation system and 42 TKAs without a navigation system with a minimum two-year follow-up. We compared clinical outcomes including range of motion, Hospital for Special Surgery (HSS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores at the final follow-up. For radiological comparisons, we evaluated radiological alignment on standing radiographs of knees. HSS and WOMAC scores showed significant improvements at final follow-ups in both groups, but showed no significant inter-group differences (p > 0.05). Similarly, no significant differences were observed in range of motion (p = 0.962). TKAs performed with navigation showed significantly better outcomes in terms of mechanical angle and prosthetic alignment outliers than TKAs performed without navigation. However, we could not find any differences in functional outcomes between TKAs performed with or without a navigation system.

Case report : femoral shaft fracture resulting from femoral tracker placement in navigated TKA

Computer-assisted navigation is a surgical tool that may decrease malalignment outliers in TKA. With any new surgical technique, there is the possibility of unexpected complications that raise caution. We report two patients with displaced femoral fractures at optical tracker pin placement sites created for routine performance of navigated TKA. Our experience suggests single bicortical 5-mm pins placed in the femoral shaft have the added risk of creating a stress riser leading to the potential for fracture. Females may have a higher risk for this complication. We believe bicortical pin fixation in the femur or tibia no longer is indicated.

The use of computer-assisted orthopedic surgery for total knee replacement in daily practice: a survey among ESSKA/SGO-SSO members

Computer-assisted orthopedic surgery (CAOS) for total knee arthroplasty is an emerging surgical tool, yet little is known about how it is being used in everyday orthopedic centers. We sought to better understand physicians' current practices and beliefs on this topic through performing a Web-based survey. Between December 2006 and January 2007, a 24-question survey was emailed to 3,330 members of the European Society of Sports Traumatology Knee Surgery and Arthroscopy (ESSKA) and the Swiss Orthopedic Society (SGO-SSO), with 389 (11.7%) agreeing to participate. Of this group, 202 (51.9%) reported that their center was equipped with a navigation system, which was an image-free based system for most (83.2%) and was primarily used for total knee arthroplasty (61.4%). In terms of the proportion of use, 50.5% of respondents used their navigation system in less than 25% of cases, 16.3% in 25-50% of cases, 7.4% in 51-75% of cases, and 25.7% in more than 75% of cases. The potential for improving the alignment of prosthesis was the most strongly cited reason for using a navigation system, while the potential for increasing operation times and the risk of infections were the most strongly cited reasons for not using a navigation system. Approximately half of respondents surveyed believed navigation systems were a real innovation contributing to the improvement of total knee implantation. However, heavy usage of computer-assisted navigation (> or =51% of cases) was observed in only 33.1% of respondents, with only a quarter using it at rates that could be considered frequent (>75% of cases). Forty-eight percent of respondents said they will use a navigation system in more cases and 39.1% that their usage will stay the same. These findings indicate that CAOS is being used only moderately in current practices, though respondents generally had a positive opinion of its potential benefits. Physicians may be awaiting more data before adopting the use of these systems, though survey responses also suggest a projected increase in their use in the coming years.

Evaluation of accuracy of an electromagnetic computer-assisted navigation system in total knee arthroplasty

The objective of this study was to develop a method to assess the accuracy of an electromagnetic technology image-free navigation system for total knee arthroplasty in a leg with normal or abnormal mechanical alignment. An acrylic phantom leg was constructed to simulate tibia and femur deformation. Determination of actual leg alignment was achieved using a digital caliper unit. In the setting of normal alignment, the mean error of the system characterised as the difference between the measured computer navigation and digital caliper angles ranged between 0.8 degrees (frontal plane) and 1.5 degrees (lateral plane). In the setting of abnormal alignment, the mean error ranged between 0.4 degrees (frontal plane) and 1.6 degrees (lateral plane). Deformity had no demonstrable effect on accuracy. The study demonstrates satisfactory in vitro system accuracy in both normal and abnormal leg mechanical alignment settings.

New visualization tools: computer vision and ultrasound for MIS navigation

BACKGROUND

A versatile image acquisition method called echo surgetics has been developed for minimally invasive computer-assisted orthopaedic procedures. The principle of echo surgetics is to use freehand three-dimensional (3D) ultrasound to acquire relevant 3D bone surface and point data transcutaneously, eliminating access problems associated with conventional digitizers. The concept has been implemented in three technologies: Echo Point, Echo Matching and Echo Morphing.

METHODS

Cadaver experiments were carried out to evaluate the accuracy of (a) Echo Point for digitization of the anterior pelvic plane (APP) in total hip arthroplasty, and (b) Echo Morphing for reconstructing the distal femur in minimally invasive knee surgery.

RESULTS AND CONCLUSIONS

Echo Point provided significantly improved results (p < 0.001) over conventional digitization where mean tilt errors exceeded 20 degrees . The Echo Morphing experiments demonstrated that with a reasonable number of points (ca. 1000) and initial attitude (IA) error (ca. 5-10 mm and 5-10 degrees ) we can obtain an average accuracy of approximately 1 mm that is sufficient for most of clinical applications.

Computer navigation did not improve alignment in a lower-volume total knee practice

Postoperative alignment of the implanted prosthesis in computer-navigated TKA has been reported to be superior to that using the conventional technique. There is an assumption that use of computer navigation techniques can make an inexperienced or occasional TKA surgeon perform more like an expert TKA surgeon. To assess improved accuracy in recreation of mechanical alignment in TKA performed using computer navigation, a retrospective review of the experience of one of the authors (WPY) before and after using computer navigation was performed. We reviewed the radiographic results of 104 TKAs (52 computer navigation, 52 conventional technique) and found the accuracy of postoperative radiographic alignment of the implanted prosthesis was not improved by using computer navigation as judged by (1) overall limb alignment (case: varus 1.3 degrees ; control: varus 0.3 degrees ); (2) femoral component alignment (case: 90.3 degrees ; control: 90.3 degrees ); and (3) tibial component alignment (case: 89 degrees ; control: 90 degrees ). Significant factors that affected postoperative overall mechanical alignment in the current navigation series included severity of the preoperative deformity, amount of error in making bone cuts, and experience of the surgeon in using the computer navigation system.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Minimally invasive imageless computer-navigated knee surgery: initial results

The combination of imageless computer-aided surgery (CAS) and minimally invasive surgery (MIS) for total knee arthroplasty (TKA) has not been reported. This study presents the initial 30 procedures in which imageless CAS was combined with MIS for TKA by the senior author. Coronal alignment of femoral and tibial components with respect to the mechanical axis of the lower limb was measured when patients could achieve full extension. Component position was acceptable for all implants. The mean coronal tibial alignment was 90.35 degrees (range, 88 degrees -93 degrees ) and mean coronal femoral alignment 90.10 degrees (range, 88 degrees -93 degrees ) to the mechanical axis. Tourniquet time averaged 90 minutes (range, 60-118 minutes). There was no significant reduction in tourniquet time with increasing familiarity with the technique. Our results demonstrate that CAS combined with MIS for TKA maintains the accuracy of component alignment despite the minimally invasive approach. These initial results demonstrate no significant learning curve associated with the technique.

[Computer-assisted total-knee arthroplasty. Comparison of two successive systems. Learning curve]

PURPOSE OF THE STUDY

The increasing popularity of total-knee arthroplasty has led to many technical improvements both in the field of prosthesis design and implanted material and instrumentation. The recent advent of computer-assisted techniques is the fruit of a search for more precision for the bone cuts and better ligament balance. The purpose of the present study was to demonstrate how easy it is to use navigation systems by examining the difficulties encountered by one operator with navigation experience when the material was changed.

MATERIAL AND METHODS

The first 30 total-knee arthroplasties implanted with a new navigation system were investigated. Elements specifically related to navigation difficulties were studied. The series was composed of 16 women and 14 men, mean age 65.9 years at the time of surgery (range, 43 to 84). Mean BMI was 30.66 (range, 23.05 to 39.54). All patients were reviewed by the operator using a standard X-ray protocol. Mean follow-up was six months. The 30 arthroplasties were consecutive, with no exclusions excepting revision procedures. Primary or post-traumatic degeneration was the main reason for surgery. This series was compared with two prior series of 30 prostheses each, implanted with a different navigation system. The first 30 and last 30 implantations using the previous navigation system were thus compared in terms of operative time and precision (comparison of postoperative alignment and implant position). The study focused on difficulties encountered when using the new system, on intra- and postoperative complications and on assessment of implant position.

RESULTS

All procedures were totally performed with the navigation system, no interruptions. Operative time was lengthened by an average of 18 min (range, 0 to 45 min). There were no complications specifically related to the navigation system. The position of the implants was assessed in the frontal and sagittal plane on the plain X-rays and with a goniometer. Computed tomography was used to assess femoral component rotation. The overall alignment of the lower limb was within the "ideal" range of +/-3 degrees in 97% (average 0.1 degrees varus). The position of the femoral implant and the tibial plate was correct in the frontal and sagittal planes and no internal rotation of the femoral piece was noted on the 27 ct scan studies (mean 1.9 degrees external rotation). Implant accuracy was equivalent to that observed in the series of the last 30 implants using the prior navigation system. The learning curve was shorter.

DISCUSSION

This small series demonstrated the absence of major problems with the new navigation system. The length of the learning curve was acceptable. This study demonstrated that prior experience with navigation is beneficial because the learning curve with the new system was shorter and the accuracy of implantation was equivalent to that achieved with the prior system. Widespread use of computer-assisted surgery should enable continued improvement in ancillary systems in the upcoming years, particularly concerning rotatory position of the femoral implants, which is still a problem. Cost containment will also be a necessary goal.

Improved accuracy of component alignment with the implementation of image-free navigation in total knee arthroplasty

Accuracy of implant positioning and reconstruction of the mechanical leg axis are major requirements for achieving good long-term results in total knee arthroplasty (TKA). The purpose of the present study was to determine whether image-free computer navigation technology has the potential to improve the accuracy of component alignment in TKA cohorts of experienced surgeons immediately and constantly. One hundred patients with primary arthritis of the knee underwent the unilateral total knee arthroplasty. The cohort of 50 TKAs implanted with conventional instrumentation was directly followed by the cohort of the very first 50 computer-assisted TKAs. All surgeries were performed by two senior surgeons. All patients received the Zimmer NexGen total knee prosthesis (Zimmer Inc., Warsaw, IN, USA). There was no variability regarding surgeons or surgical technique, except for the use of the navigation system (StealthStation) Treon plus Medtronic Inc., Minnesota, MI, USA). Accuracy of implant positioning was measured on postoperative long-leg standing radiographs and standard lateral X-rays with regard to the valgus angle and the coronal and sagittal component angles. In addition, preoperative deformities of the mechanical leg axis, tourniquet time, age, and gender were correlated. Statistical analyses were performed using the SPSS 15.0 (SPSS Inc., Chicago, IL, USA) software package. Independent t-tests were used, with significance set at P < 0.05 (two-tailed) to compare differences in mean angular values and frontal mechanical alignment between the two cohorts. To compute the rate of optimally implanted prostheses between the two groups we used the chi(2) test. The average postoperative radiological frontal mechanical alignment was 1.88 degrees of varus (range 6.1 degrees of valgus-10.1 degrees of varus; SD 3.68 degrees ) in the conventional cohort and 0.28 degrees of varus (range 3.7 degrees -6.0 degrees of varus; SD 1.97 degrees ) in the navigated cohort. Including all criteria for optimal implant alignment, 16 cases (32%) in the conventional cohort and 31 cases (62%) in the navigated cohort have been implanted optimally. The average difference in tourniquet time was modest with additional 12.9 min in the navigated cohort compared to the conventional cohort. Our findings suggest that the experienced knee surgeons can improve immediately and constantly the accuracy of component orientation using an image-free computer-assisted navigation system in TKA. The computer-assisted technology has shown to be easy to use, safe, and efficient in routine knee replacement surgery. We believe that navigation is a key technology for various current and future surgical alignment topics and minimal-invasive lower limb surgery.

Computer navigation versus conventional implantation for varus knee total arthroplasty: a case-control study at 5 years follow-up

BACKGROUND

There is no evidence in the current literature of any significant improvement in clinical outcome when comparing computer-assisted total knee arthroplasty (CATKA) with conventional implantation. Analyses of alignment and of component orientation have shown both significant and non-significant differences between the two methods.

OBJECTIVES

We compared computer-assisted and conventional surgery for TKA at 5.4 years follow-up for patients with varus osteoarthritic knees. Our goal was to assess clinical outcome and restoration of normal limb alignment.

MATERIALS AND METHODS

We performed a retrospective case-control study comparing 30 patients who underwent CATKA with 30 subjects who underwent TKA by conventional methods. Patients were matched individually by preoperative clinical conditions and alignment. We analysed intraoperative data (surgical time and intraoperative complications), postoperative complications, lower limb alignment, radiographic complication on X-ray imaging, and clinical outcome through knee and function score and range of motion.

RESULTS AND DISCUSSION

We found no significant clinical difference between the two groups at 5 years post-surgery. However there was a statistically significant improvement in the restoration of the mechanical axis of the lower limb in the coronal plane but not in the sagittal plane. Whether or not this leads to a higher survival rate in the longer term requires further investigation.

Safety and utility of computer-aided shoulder arthroplasty

This study evaluated the safety and utility of a novel, image-free, shoulder navigation system in a cadaver and in an initial cohort of shoulder arthroplasty patients. Shoulder arthroplasty was performed on a cadaver and 27 patients using an image-free navigation system (NaviProtrade mark; Kinamed Navigation Systems LLC, Camarillo, CA). Optical trackers were attached to the proximal humerus and the coracoid process. Prior to and following humeral head resection, the anatomic neck axis (retroversion, inclination) and humeral head diameter were measured with the navigation system. Native glenoid surface orientation was registered, and a navigation tracker was attached to the glenoid reamer. The navigation system recorded change in inclination and version relative to the native glenoid during reaming. The cadaver results demonstrated that the trackers did not impede surgical performance and that system accuracy was 2.6 degrees +/- 2.5 degrees . In the clinical series, the navigation system reported the anatomic humeral neck measurements (retroversion 30.0 degrees +/- 16.0 degrees ; inclination 137.0 degrees +/- 11.7 degrees ), the humeral head diameters (major axis 46.2 mm +/- 4.8 mm; minor axis 43.2 mm +/- 3.8 mm), the humeral neck resection angles (retroversion 29.9 degrees +/- 15.1 degrees and inclination 135.6 degrees +/- 9.1 degrees ), and glenoid reaming orientation relative to the native glenoid (+3.0 degrees +/- 6.3 degrees of version; -6.7 degrees +/- 4.4 degrees of inclination). This initial clinical experience with computer-aided shoulder navigation demonstrates that the procedure is safe and can provide valuable intraoperative measurements. With an anatomic humeral implant system, the navigation system provides real-time feedback on the humeral resection as it relates to anatomic neck geometry. The system also provides real-time angulation of the glenoid reamer relative to preoperative glenoid deformity.

Scientific evidence supporting computer-assisted surgery and minimally invasive surgery for total knee arthroplasty

This review provides an overview of the field of minimally invasive surgery and computer-assisted surgery for total knee arthroplasty. The authors have examined the complete body of literature for scientific evidence supporting the use of these new technologies and how the literature specifically supports commonly asked questions. There is controversy concerning the benefits of minimally invasive surgery and computer-assisted surgery for total knee arthroplasty. However, in most studies the results are similar for minimally invasive surgery compared to standard approaches. Computer-assisted navigation has been found in some studies to improve radiographic alignment of total knee arthroplasty. The authors believe that there is evidence for both technologies to be at least equivalent in terms of results, as well as expectations of increased success with the techniques. Both technologies have led manufacturers to invest more effort into newer prosthetic instrumentations and designs to facilitate these techniques.

Tension controlled ligament balanced total knee arthroplasty: 5-year results of a soft tissue orientated surgical technique

INTRODUCTION

Posterior cruciate ligament (PCL)-retaining prostheses give good outcomes and are commonly used. This retrospective study investigated outcomes from total knee arthroplasty (TKA) using the ligament balancing technique to implant a PCL-retaining knee prosthesis (balanSystrade mark knee system) with either a mobile or a fixed bearing polyethylene inlay.

MATERIALS AND METHODS

A retrospective study was performed on patients treated with TKA at one surgical centre between 1997 and 2001. In this period 182 surgeries were performed. Clinical assessments of the implant used the Knee Society Score (KSS). Subjective assessments used visual analogue scale (VAS) for pain and patient satisfaction. The Western Ontario and McMasters Universities Osteoarthritis Index (WOMAC) was used to assess pain, stiffness and function of the knee. Radiographic analysis was performed to determine frontal and sagittal alignment and loosening.

RESULTS

A total of 109 knee implants in 95 patients (26 men; 69 women) were followed up. Seventy-three cases were not available for follow-up due to bad health or death of the patient; 74% of 109 reviewed implants had fixed bearings and 26% had mobile bearings. The mean age at surgery was 72.9 +/- 7.35 years (range 54.7-92.4). The mean KSS was 160 +/- 28.3 points. The KSS was greater for men and was significantly reduced when another disease was present. The type of bearing, surgical approach, and pre-operative alignment for patients affected by varus or valgus gonarthrosis had no significant impact on KSS and ROM. According to VAS the mean scores for pain and satisfaction were 1.48 (0 = no pain) and 9.2 (10 = very satisfied), respectively. The WOMAC mean scores for pain (87.0), stiffness (82.3) and function (78.6) were high (best outcome score of 100). There were no revisions due to aseptic loosening or wear.

CONCLUSION

Total knee arthroplasty performed with a PCL-retaining prosthesis implanted by using a soft tissue oriented surgical technique is a safe procedure and was associated with good results. So far, there were few complications and no need for revision due to aseptic loosening. In addition, most of the patients reported little pain and were satisfied with the outcome. These good outcomes are comparable with other studies reporting on PCL-retaining prostheses.

Transepicondylar distal femoral pin placement in computer assisted surgical navigation

The use of optical tracking systems in computer assisted surgical navigation requires the rigid fixation of a dynamic reference base to the target bone to be navigated. This report presents the results of a new approach to optical tracker fixation in the distal femur. Four embalmed cadavers were evaluated for pin placement. It was found that placement of pins from medial to lateral parallel to the transepicondylar axis placed the pins well posterior to the center of the intramedullary canal and away from neurovascular structures. Eighty-six consecutive patients underwent total knee arthroplasty using this new technique. All procedures were successful for performing a navigation-assisted total knee replacement. Obesity was not a factor, nor was there any loosening of the pin array during the procedure. There were no wound-healing problems in any patient. At one year follow-up, no patient could identify subjective symptoms related to either the medial epicondylar area or the stab wound portals. No direct neurovascular injuries were noted and no patient developed a fracture of the femur related to the pin sites.

CONCLUSION

A new technique is described that facilitates pin placement for minimally invasive approaches while eliminating complications. Sagittal plane optical array orientation simplifies the surgical technique.

What patient and surgical factors contribute to implant wear and osteolysis in total joint arthroplasty?

Total joint arthroplasty has been a successful operation for decades. Our current patients are younger and more active than those in the past. They place higher demands on themselves and have expectations commensurate with their lifestyles. Time-limited longevity with the large number of anticipated total joint replacement procedures and their potential burden to health care is a growing concern. In the past two decades, implant wear and osteolysis have been identified as major causes for the failure of otherwise well-functioning implants. Osteolysis can be divided into several categories: patient-specific, implant-specific, and the result of surgical factors. Although these categories are interrelated and not mutually exclusive, they enable us to build a framework in which to further advance our understanding of osteolysis and apply this information in a clinically relevant manner.

Computer-assisted total knee arthroplasty versus the conventional technique: how precise is navigation in clinical routine?

Restoration of the mechanical leg axis and component positioning are crucial factors affecting long-term results in total knee arthroplasty (TKA). In a prospective study, 1,000 patients were operated on either using a CT-free navigation system or the conventional jig-based technique. Leg alignment and component orientation were determined on postoperative X-rays. The mechanical leg axis was significantly better in the computer-assisted group (95%, within +/-3 degrees varus/valgus) compared to the conventional group (74%, within +/-3 degrees varus/valgus) (P < 0.001). On average, the operating time was increased by 8 min in the computer-assisted group. No significant differences were seen between senior and younger surgeons regarding postoperative leg alignment and operating time. Computer-assisted TKA leads to a more accurate restoration of leg alignment and component orientation compared to the conventional jig-based technique. Potential benefits in long-term outcome and functional improvement require further investigation.

Interobserver and intra-observer errors in obtaining visually selected anatomical landmarks during registration process in non-image-based navigation-assisted total knee arthroplasty

This study investigated the errors of obtaining visually selected anatomic landmarks for use in the registration process in a passive optical non-image-based computer-assisted total knee arthroplasty system in 5 fresh frozen cadavers. The projected maximum errors in the femoral mechanical axis (due to registration errors of the center of the distal femur) were 0.7 degrees in the coronal and 1.4 degrees in the sagittal plane. The projected maximum errors in the tibial mechanical axis arising from registration errors of the center of the proximal tibia were 1.3 degrees in the coronal and 2 degrees in the sagittal plane. The projected maximum errors in the transepicondylar axis were 9.1 degrees (registration errors of the medial femoral epicondyle) and 7.2 degrees (registration errors of the lateral femoral epicondyle). It should be noted that the results may be partly related to the use of the particular system in this experiment.

Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery

Computer-assisted surgery (CAS) has been advocated as a means to improve limb and prosthesis alignment and assist in ligament balancing in total knee arthroplasty (TKA). Thus, we sought to examine alignment outcomes in CAS vs conventional TKA. A systematic review of literature from 1990 to 2007 was performed. Direct comparison of alignment outcomes was performed using random effects meta-analyses. Twenty-nine studies of CAS vs conventional TKA were identified, and included mechanical axis malalignment of greater than 3 degrees occurred in 9.0% of CAS vs 31.8% of conventional TKA patients. The risk of greater than 3 degrees malalignment was significantly less with CAS than conventional techniques for mechanical axis and frontal plane femoral and tibial component alignment. Tibial and femoral slope both showed statistical significance in favor of CAS at greater than 2 degrees malalignment. Meta-analysis of alignment outcomes for CAS vs conventional TKA indicates significant improvement in component orientation and mechanical axis when CAS is used.

Robotic cadaver testing of a new total ankle prosthesis model (German Ankle System)

BACKGROUND

An investigation was carried out into possible increased forces, torques, and altered motions during load-bearing ankle motion after implantation of two different total ankle prostheses. We hypothesized that the parameters investigated would not differ in relation to the two implants compared.

METHODS

We included two different ankle prostheses (Hintegra, Newdeal, Vienne, France; German Ankle System, R-Innovation, Coburg, Germany). The prostheses were implanted in seven paired cadaver specimens. The specimens were mounted on an industrial robot that enables complex motion under predefined conditions (RX 90, Stäubli, Bayreuth, Germany). The robot detected the load-bearing (30 kg) motion of the 100(th) cycle of the specimens without prostheses as the baseline for the later testing, and mimicked that exact motion during 100 cycles after the prostheses were implanted. The resulting forces, torques, and bone motions were recorded and the differences between the prostheses compared.

RESULTS

The Hintegra and German Ankle System, significantly increased the forces and torques in relation to the specimen without a prosthesis with one exception (one-sample-t-test, each p < or = 0.01; exception, parameter lateral force measured with the German Ankle System, p = 0.34). The force, torque, and motion differences between the specimens before and after implantation of the prostheses were lower with the German Ankle System than with the Hintegra (unpaired t-test, each p < or = 0.05).

CONCLUSIONS

The German Ankle System prosthesis had less of an effect on resulting forces and torques during partial weightbearing passive ankle motion than the Hintegra prosthesis. This might improve function and minimize loosening during the clinical use.

A quantitative method of effective soft tissue management for varus knees in total knee replacement surgery using navigational techniques

Total knee replacement (TKR) has become the standard procedure in management of degenerative joint disease with its success depending mainly on two factors: three-dimensional alignment and soft-tissue balancing. The aim of this work was to develop and validate an algorithm to indicate appropriate medial soft tissue release during TKR for varus knees using initial kinematics quantified via navigation techniques. Kinematic data were collected intra-operatively for 46 patients with primary end-stage osteoarthritis undergoing TKR surgery using a computer-tomography-free navigation system. All patients had preoperative varus knees and medial release was made using the surgeon's experience. Based on these data an algorithm was developed. This algorithm was validated on a further set of 35 patients where it was used to define the medial release based on the kinematic data. The post-operative valgus stress angles for the two groups were compared. These results showed that the algorithm was a suitable tool to indicate the type of medial release required in varus knees based on intra-operatively measured pre-implant valgus stress and extension deficit angles. It reduced the percentage of releases made and the results were more appropriate than the decisions made by an experienced surgeon.

Using navigation intraoperative measurements narrows range of outcomes in TKA

Computer-assisted technology creates a new approach to total knee arthroplasty (TKA). The primary purpose of this technology is to improve component placement and soft tissue balance. We asked whether the use of navigation techniques would lead to a narrow range of implant alignment in both coronal and sagittal planes and throughout the flexion-extension range. Using a prospective consecutive series of 57 navigated TKAs, we assessed intraoperative knee measurements, including alignment, varus-valgus stress angles in extension, and varus-valgus angles from 0 degrees to 90 degrees of flexion comparing postimplant with preimplant. We found fewer outliers with coronal (100% of TKAs within +/-2 degrees) and sagittal (0% of TKAs with fixed flexion greater than 5 degrees) alignment, soft tissue balancing (mean varus and valgus stress angles -3.2 degrees and 2.3 degrees; range, -5 degrees to 5 degrees), and mean femorotibial angle over flexion range 0 degrees (-0.2 degrees; range, -1 degrees to 2 degrees), 30 degrees (-0.2 degrees; range, -5 degrees to 4 degrees), 60 degrees (-0.5 degrees; range, -5 degrees to 7 degrees), and 90 degrees (-0.2 degrees; range, -5 degrees to 10 degrees). This technology allows a narrow range of implant placement and soft tissue management in extension. We anticipate improved ultimate patient outcomes with less tissue disruption.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Comparison of limb and component alignment using computer-assisted navigation versus image intensifier-guided conventional total knee arthroplasty: a prospective, randomized, single-surgeon study of 467 knees

Total knee arthroplasty was performed in 282 knees with image-free navigation (group A) and in 185 with optimized conventional technique (group B). Mean postoperative mechanical axis of the limb was 179.7 degrees in group A and 179.1 degrees in group B (P < .002). There was a higher percentage of knees in group A that had restoration of mechanical axis to +/-1 degrees, +/-2 degrees, and +/-3 degrees of neutral (P < .0001). There were 9.2% outliers (+/-3 degrees) in group A and 21.6% outliers in group B (P < .0001). For knees exceeding 20 degrees varus, there was no significant difference between the mean mechanical axes in the 2 groups. Both components were aligned within 3 degrees of neutral in 90.8% of the knees in group A and 76.2% of the knees in group B (P < .0001).

Coronal plane stability before and after total knee arthroplasty

The success of total knee arthroplasty depends in part on proper soft tissue management to achieve a stable joint. It is unknown to what degree total knee arthroplasty changes joint stability. We used a surgical navigation system to intraoperatively measure joint stability in 24 patients under going primary total knee arthroplasty to address two questions: (1) Is the total arc of varus-valgus motion after total knee arthroplasty different from the arc of varus-valgus motion in an osteoarthritic knee? (2) Does total knee arthroplasty produce equal amounts of varus/valgus motion (ie, is the knee "balanced")? We observed no difference between the total arc of varus-valgus motion before and after total knee arthroplasty; the total amount of motion was unchanged. On average, osteoarthritic knees were "unbalanced" but were "balanced" after prosthesis implantation. We found a negative correlation between the relative amount of varus/valgus motion in extension before and after prosthesis implantation in extension and a positive correlation between how well the knees were balanced after prosthesis implantation in extension and in flexion. Our data suggest immediately after implantation knees retain a greater than normal amount of varus-valgus motion, but this motion is more evenly distributed.

A technical innovation for improving identification of the trackers by the LED cameras in navigation-assisted total knee arthroplasty

OBJECTIVE

To reduce the operating time in computer-assisted navigated total knee replacement (TKR), by improving communication between the infrared camera and the trackers placed on the patient.

MATERIALS AND METHODS

The innovation involves placing a routinely used laser pointer on top of the camera, so that the infrared cameras focus precisely on the trackers located on the knee to be operated on. A prospective randomized study was performed involving 40 patients divided into two groups, A and B. Both groups underwent navigated TKR, but for group B patients a laser pointer was used to improve the targeting capabilities of the cameras.

RESULTS

Without the laser pointer, the camera had to move a mean 9.2 times in order to identify the trackers. With the introduction of the laser pointer, this was reduced to 0.9 times. Accordingly, the additional mean time required without the laser pointer was 11.6 minutes.

CONCLUSION

Time delays are a major problem in computer-assisted surgery, and our technical suggestion can contribute towards reducing the delays associated with this particular application.

Reliability of navigated knee stability examination: a cadaveric evaluation

BACKGROUND

Clinical examination remains empirical and may be confusing in the setting of rotatory knee instabilities. Computerized navigation systems provide the ability to visualize and quantify coupled knee motions during knee stability examination.

HYPOTHESIS

An image-free navigation system can reliably register and collect multiplanar knee kinematics during knee stability examination.

STUDY DESIGN

Controlled laboratory study.

METHODS

Coupled knee motions were determined by a robotic/UFS testing system and by an image-free navigation system in 6 cadaveric knees that were subjected to (1) isolated varus stress and (2) combined varus and external rotation force at 0 degrees, 30 degrees, and 60 degrees. This protocol was performed in intact knees and after complete sectioning of the posterolateral corner (lateral collateral ligament, popliteus tendon, and popliteofibular ligament). The correlation between data from the surgical navigation system and the robotic positional sensor was assessed using the intraclass correlation coefficient. The 3-dimensional motion paths of the intact and sectioned knees were assessed qualitatively using the navigation display system.

RESULTS

Intraclass correlation coefficients between the robotic sensor and the navigation system for varus and external rotation at 0 degrees, 30 degrees, and 60 degrees were all statistically significant at P < .01. The overall intraclass correlation coefficient for all tests was 0.9976 (P < .0001). Real-time visualization of the coupled motions was possible with the navigation system. Post hoc analysis of the knee motion paths during loading distinguished distinct rotatory patterns.

CONCLUSION

Surgical navigation is a precise intraoperative tool to quantify knee stability examination and may help delineate pathologic multiplanar or coupled knee motions, particularly in the setting of complex rotatory instability patterns. Repeatability of load application during clinical stability testing remains problematic.

CLINICAL RELEVANCE

Surgical navigation may refine the diagnostic evaluation of knee instability.

Difference between the epicondylar and cylindrical axis of the knee

Locating the true flexion-extension axis of the knee can play an important role in component placement in a total knee arthroplasty, especially using contemporary computer-assisted surgical navigation. We determined if the commonly used transepicondylar axis is an accurate and reproducible substitute for the flexion-extension axis. Twenty-three fresh-frozen cadaveric distal femurs with intact soft tissue were imaged with computed tomography and reconstructed in three-dimensional virtual space. The transepicondylar axis was compared with a line equidistant from the articular surface of each femoral condyle. Measures were performed by three observers three times for each specimen. Interobserver and intraobserver variations were small, but the differences between axes were approximately 5 degrees. The difference between axes decreased when projected from three-dimensional space to traditional two-dimensional planes (coronal and transverse), explaining why this discrepancy has not been previously documented. The greater difference in three-dimensional space may account for midrange instability reported in total knee arthroplasty. The increased accuracy afforded by computer-assisted surgical navigation in total knee arthroplasty may be lost and increased malposition of components may occur if this discrepancy between reference axes is not appreciated and addressed.

Imageless navigation for TKA increases implantation accuracy

Because we are performing TKAs on heavier, younger patients, greater stress is being put on the implants and is increasing the importance of implantation accuracy. We performed a prospective randomized study to compare the radiographic results and the 3-month clinical outcomes in 100 patients who had TKAs using an imageless navigation system with 100 patients treated using conventional implantation instruments. We measured component alignment by standard radiographs. Clinical outcomes were based on the Insall score, anterior knee pain, feeling of instability, and the step test. The mechanical axis of the limb was within 3 degrees varus/valgus in 92% of the patients who had navigated procedures versus 76% of patients who had conventional surgery. The tibial slope showed a rate of inaccuracy of 3 degrees or less for 98% of the patients in the navigated TKA group versus 80% of the patients in the conventional group. The surgical time was longer for navigated TKA than for the conventional procedure (88 +/- 16 versus 68 +/- 18 minutes, respectively). Clinical outcomes and postoperative blood loss were similar in both groups. The navigation system increased implantation accuracy but did not prevent outliers and did not solve the problems associated with identifying and obtaining accurate component rotation.

Location and number of cortical fixation points and the effect on reference base stability during computer-navigated total knee arthroplasty

This study investigated 2 methods of reference base fixation for computer navigation markers for computer-navigated total knee arthroplasty. Five cadaveric specimens were used to test a 1-pin and 3-pin base system. A navigation system (Stryker Navigation, Kalamazoo, Mich) was used for testing with applied loads and torques to the reference base. Changes in distance from a verification point as well change in alignment were recorded. The change in distance to a reference point as well as the change in alignment data was significantly different at 65 N of applied load with the 3-pin construct being more stable (P = .02). The results suggest that 3-pin fixation in the metaphyseal portion of the distal femur is more stable than a single-pin bicortical construct.