Navigation improves accuracy of rotational alignment in total knee arthroplasty

Influence of the functional status of the anterior cruciate ligament on the posterior medial femoral condyle among varus osteoarthritic knees

Background

Morphologic changes in the posterior medial femoral condyle (PMFC) among varus osteoarthritic knees have not been described in the past. The aims of this study were to compare anterior cruciate ligament (ACL) competent and deficient varus osteoarthritic knees during computer-navigation assisted (CAS) total knee arthroplasty (TKA) in terms of their pre-operative deformity, rotation of the posterior condylar axis (PCA) with respect to Whiteside's axis, and prevalence of PMFC hyperplasia or attrition.

Methods

Data pertaining to pre-operative varus deformity, rotation of the PCA with respect to Whiteside's axis, and presence of PMFC hyperplasia or attrition were analyzed for 250 consecutive patients each, with ACL-competent and deficient knees, who underwent CAS TKA for varus osteoarthritis of the knee.

Results

ACL-deficient knees, compared to ACL-competent knees, were associated with greater pre-operative stressed (9.94° ± 6.14° versus 7.29° ± 4.48°, P < 0.001) and corrected (3.62° ± 4.36° versus 2.41° ± 3.08°, P < 0.001) varus deformities, internal rotation of the PCA with respect to Whiteside's axis (4.06° ± 2.32° versus 3.08° ± 2.03°, P < 0.001), and prevalence of PMFC attrition (8.4 % versus 0 %, P < 0.001) and hyperplasia (27.2 % versus 9.6 %, P < 0.001).

Conclusion

Chronic ACL deficiency in varus osteoarthritic knees may result in progression of the coronal deformity, PMFC attrition, increased internal rotation of the PCA with respect to Whiteside's axis, and eventually PMFC hyperplasia. This needs to be borne in mind during TKA to prevent inadvertent placement of the femoral component in inappropriate rotation.

Dynamic patterns of varus deformity among osteoarthritic knees during computer-navigation assisted total knee arthroplasty and their surgical implications

Aims

The aims of this study were to (a) identify the dynamic patterns of varus deformity among osteoarthritic knees, (b) describe their surgical implications, and (c) compare post-operative lower limb alignment, clinical outcomes and satisfaction among patients with different deformity patterns managed intra-operatively based on deductions drawn from the same.

Methods

Patients with primary osteoarthritis of the knee with an intra-articular varus deformity, undergoing computer-navigation assisted total knee arthroplasty using a sub-vastus approach and the "femur-first" measured resection technique between October 2019 and June 2020 were recruited. Following surgical exposure, the coronal knee deformity was assessed during full extension and 15°, 30°, 45°, 60°, 75°, and 90° of flexion. The levels of bony and/or soft-tissue pathology were identified based on the deformity pattern noted. Mechanical bone resection and indicated soft-tissue releases were performed. Post-operative alignment and outcomes were compared among knees with different deformity patterns.

Results

In all, 127 patients (59.1 % women) with a mean age of 62.4 years were available for follow-up. The mean duration of follow-up was 24.7 months. Five patterns of varus deformity emerged, each indicating different levels of pathology: (i) pattern-1: the deformity increased on flexion, (ii) pattern-2: the deformity decreased on flexion, (iii) pattern-3: the deformity remained constant throughout flexion, (iv) pattern-4: the deformity increased initially, then decreased on flexion, and (v) pattern-5: the deformity decreased initially, then increased on flexion. Individualized soft-tissue release helped restore alignment within 3° of the mechanical axis in all knees. At the two years' follow-up, the clinical outcomes and patient satisfaction were comparable among patients with all deformity patterns.

Conclusions

Knees with primary varus osteoarthritis demonstrate simple dynamic patterns of coronal deformity. An understanding of these patterns permits identification of the levels of pathology and helps in their optimal management, resulting in uniformly satisfactory outcomes.

Component rotational mismatch in the standing position is a potential risk factor for unfavourable functional outcomes after total knee arthroplasty

Purpose

This study assessed rotational mismatch between components after total knee arthroplasty (TKA) in the supine and standing positions and aimed to investigate the effect of rotational mismatch in the standing position on postoperative patient-reported outcome measures (PROMs).

Methods

Seventy-one patients (71 knees) who underwent TKA for medial knee osteoarthritis were used to investigate rotational mismatches between components. Rotational mismatches between components were examined on postoperative standing whole-leg and supine knee radiographs using a three-dimensional-to-two-dimensional model image registration technique, and the angles between the reference axes of the components were measured. Component alignment was evaluated using postoperative computed tomography images, and a questionnaire (2011 version of the Knee Society Score: [KSS 2011]) was mailed to investigate postoperative PROMs.

Results

In the entire cohort, rotational mismatches in the supine and standing positions were similar (p = 0.9315). In 15% of patients, the mismatch was large (>5°) in the supine position but small (<5°) in the standing position (overestimated group). However, in 23% of patients, the mismatch was small (<5°) in the supine position and large (>5°) in the standing position (underestimated group). The underestimated group had severe preoperative varus deformity, resulting in external rotation of both femoral and tibial components. Rotational mismatch in the standing position (p = 0.0032) was a significant risk factor for unfavourable PROMs. Patients with a mismatch in the standing position had significantly lower scores than those without a mismatch (p = 0.0215), exceeding the minimal clinically important difference values.

Conclusions

The underestimated group is clinically important because the surgical procedure and intraoperative assessment of component placement are performed in the supine position. In cases of severe preoperative varus deformity, care should be taken not to place the component in malrotation to avoid rotational mismatch in the standing position.

Level of Evidence

Ⅳ, Case series.

Bridging theory and practice: A comprehensive algorithm for imageless total knee arthroplasty

Total knee arthroplasty (TKA) is a surgical procedure to treat severe knee osteoarthritis. Among several techniques available for performing TKA, imageless TKA is known for achieving precise alignment while minimizing invasiveness. This work proposes a comprehensive algorithm for imageless TKA device to calculate the varus/valgus and flexion/extension angles, as well as resection depths for cutting planes at distal femur and proximal tibia. Moreover, the algorithm calculates the hip-knee-ankle (HKA) and flexion angles of the leg. Initially, the proposed algorithm was validated in a virtual environment using a CT-scanned bone model in Solidworks. Subsequently, for the real-world validation, a SoftBone model was resected with conventional intra and extramedullary rods and cross-checked with the proposed algorithm. For the third validation, another SoftBone model was resected with the proposed algorithm and cuts were measured with a vernier caliper. During this experiment, there was an error of approximately 1 mm for both femoral and tibial resection cases when using an infrared camera with an accuracy of ±0.5 mm. However, this error could be reduced using an infrared camera with higher accuracy.

Computer-assisted revision total knee arthroplasty does not improve postoperative knee prosthesis alignment compared to the conventional technique

Purpose

Computer-assisted surgery (CAS) during primary total knee arthroplasty (TKA) prosthesis alignment. However, literature on its use during revision TKA (rTKA) is scarce. Moreover, the effect of CAS during rTKA on rotational alignment of the prosthesis has not been described yet. The purpose of this study was to assess the effect of CAS during rTKA, focusing on the number of outliers and coronal, sagittal and rotational prosthetic alignment compared to conventional rTKA.

Methods

A prospective cohort study comparing CAS-rTKA with a historical control group (CON-rTKA). The CAS-rTKA group (54 patients/62 knees) underwent rTKA using imageless CAS between 2012 and 2017. The CON-rTKA group (13 patients/23 knees) was operated using the conventional technique between 2002 and 2012. Postoperative alignment was measured using the EOS-2D/3D system (coronal and sagittal planes) and computed tomography scan (rotation).

Results

No significant differences between the CAS-rTKA and CON-rTKA groups were found for coronal and sagittal alignment regarding the mechanical angle of the leg (p = 0.08), mechanical lateral distal femoral angle (p = 0.87), mechanical medial proximal tibial angle (p = 0.40), anatomical proximal posterior tibial angle (p = 0.43) nor femoral (p = 0.80) and tibial rotation (p = 0.15). For the proportions of coronal, sagittal and rotational outliers, no significant differences were found either.

Conclusion

This study showed no evidence that use of CAS during rTKA leads to improved coronal, sagittal or rotational alignment of knee prostheses or a difference of outliers between the groups.

Level of Evidence

Level III, therapeutic.

Restoration of constitutional alignment optimizes outcomes of computer navigated total knee arthroplasty: a prospective randomized controlled trial

PURPOSE

The value of computer navigation in total knee arthroplasty (TKA) for arthritic knees continues to be debated. The purpose of this study was to evaluate the value of navigated TKA associated with updated alignment philosophy.

METHODS

This prospective randomized controlled trial enrolled 38 consecutive patients (76 knees) and were randomly assigned to both groups. The demographic data and perioperative data were recorded. The coronal plane alignment of the knee (CPAK) classification was used to classify knee alignment phenotypes. Radiographic outcomes were measured and subgroup analysis was further performed. Clinical outcomes were evaluated using patient-reported outcome measures (PROMs). Surgery-related complications were recorded.

RESULTS

The distribution of CPAK phenotypes following constitutional aligned TKA was equivalent to the native cohort, whereas the mechanical aligned TKA dramatically altered the phenotype distribution from type I and type II to type V and type IV. Final implant positioning was different between groups, with constitutional aligned TKA having larger cTCA (P = .004), joint line obliquity (P = .006), joint line distance (P = .033) and smaller sFCA (P = .013). Subgroup analysis showed higher actual accuracy of component positioning was achieved in navigated TKA, especially in knees with deformity of > 10° (P < .05). Patients reported higher HSS score at three months postoperatively in constitutional aligned group (P = .002). One patient in navigated group suffered femoral pin site fracture caused by a minor trauma.

CONCLUSION

Computer navigated TKA allows for restoration of constitutional alignment and minimizes soft tissue release, which when compared to mechanical alignment may be associated with superior early outcomes.

Femoral coordinate system based on articular surfaces: Implications for computer-assisted knee arthroplasty

Osteoarthritis knee can be restored by total knee arthroplasty (TKA). Imageless TKA requires several anatomical points to construct a reference coordinate system to measure bone resections and implant placement. Inaccuracies in the definition of the coordinate system lead to malalignment and failure of the implant. While the surgical transepicondylar axis (sTEA) is a reliable anatomical axis to define the lateromedial axis for the femoral coordinate system (FCS), the presence of the collateral ligaments and deterioration of the medial sulcus (MS) make the registration of sTEA a challenging task. In this work, sTEA is assigned using the articular surfaces of the femoral condyles, independent of the lateral epicondyle (LE) and MS. A single 3D arc is marked on each condyle, which is transformed into a 2D arc to get the best-fit curve according to the profile of condyles. The turning point of each best-fit curve, when transformed back to 3D, defines an axis parallel to sTEA. The condyles-based sTEA is measured experimentally on a 3D-printed bone using an Optitrack tracking setup. Using the proposed method, the angle between the aTEA, sTEA, and Whiteside's line was (3.77, 0.55, and 92.72)°, respectively. The proposed method provides the same level of accuracy and improves the anatomical points registration efficiency, as there is no need to register the LE or MS.

Computer-assisted surgery and patient-specific instrumentation improve the accuracy of tibial baseplate rotation in total knee arthroplasty compared to conventional instrumentation: a systematic review and meta-analysis

PURPOSE

To determine whether patient-specific instrumentation (PSI), computer-assisted surgery (CAS) or robot-assisted surgery (RAS) enable more accurate rotational alignment of the tibial baseplate in primary total knee arthroplasty (TKA) compared to conventional instrumentation, in terms of deviation from the planned target and the proportion of outliers from the target zone.

METHODS

The authors independently conducted three structured electronic literature searches using the PubMed, Embase®, and Cochrane Central Register of Controlled Trials databases from 2007 to 2020. Studies were included if they compared rotational alignment of the tibial baseplate during TKA using conventional instrumentation versus PSI, CAS, and/or RAS, and reported deviation from preoperatively planned rotational alignment of the tibial baseplate in terms of absolute angles and/or number of outliers. Methodological quality of eligible studies was assessed by two researchers according to the Downs and Black Quality Checklist for Health Care Intervention Studies.

RESULTS

Fifteen studies, that reported on 2925 knees, were eligible for this systematic review, of which 6 studies used PSI, and 9 used CAS. No studies were found for RAS. Of the studies that reported on angular deviation from preoperatively planned rotational alignment, most found smaller deviations using PSI (0.5° to 1.4°) compared to conventional instrumentation (1.0° to 1.6°). All studies that reported on proportions of outliers from a target zone (± 3°), found lower rates of outliers using PSI (0 to 22%) compared to conventional instrumentation (5 to 96%). Most studies reported smaller angular deviation from preoperatively planned rotational alignment using CAS (0.1° to 6.9°) compared to conventional instrumentation (1.1° to 7.8°). Of the studies that reported on proportions of outliers from a target zone (± 3°), most found fewer outliers using CAS (10 to 61%) compared to conventional instrumentation (17 to 78%).

CONCLUSION

This systematic review and meta-analysis revealed that both CAS and PSI can improve the accuracy of rotational alignment of the tibial baseplate by decreasing angular deviation from the preoperatively planned target and reducing the proportion of outliers from the target zone. The clinical relevance is that PSI and CAS can improve alignment, though the thresholds necessary to grant better outcomes and survival remain unclear.

LEVEL OF EVIDENCE

IV.

Navigated and Robot-Assisted Technology in Total Knee Arthroplasty: Do Outcome Differences Achieve Minimal Clinically Important Difference?

BACKGROUND

In total knee arthroplasty (TKA), computer-assisted navigation (N-TKA) and robotic-assisted methods (RA-TKA) are intended to increase precision of mechanical and component alignment. However, the clinical significance of published patient-reported outcome measure (PROM) differences in comparison to conventional TKA (C-TKA) is unknown.

METHODS

A systematic review was performed to identify all studies reporting perioperative PROMs for either primary N-TKA or RA-TKA with a C-TKA comparison cohort with a minimum 1-year follow-up. Relative improvements in PROMs for the two cohorts were compared to published minimal clinically important difference (MCID) values.

RESULTS

After systematic review, 21 studies (N = 3,214) reporting on N-TKA and eight studies (N = 1,529) reporting on RA-TKA met inclusion criteria. Eighteen of 20 studies (90%) reported improved radiographic outcomes with N-TKA relative to C-TKA; five of five studies reported improved radiographic outcomes with RA-TKA relative to C-TKA. Five of 21 studies (24%) reported statistically significant greater improvements in clinical PROMs for N-TKA relative to C-TKA, whereas only two (10%) achieved clinical significance relative to MCID on a secondary analysis. One of 8 studies (13%) reported statistically significant greater improvements in PROMs for RA-TKA relative to C-TKA, whereas none achieved clinical significance relative to MCID on a secondary analysis. No studies reported a significant difference in revision rates.

CONCLUSION

While most studies comparing RA-TKA and N-TKA with C-TKA demonstrate improved radiographic alignment outcomes, a minority of studies reported PROM differences that achieve clinical significance. Future studies should report data and be interpreted in the context of clinical significance to establish patient and surgeon expectations for emerging technologies.

Imageless Computer Navigation Reduces 5-Year All-Cause Revision Rates After Primary Total Knee Arthroplasty

BACKGROUND

The use of surgical navigation has been shown to reduce revision rates after total knee arthroplasty (TKA) in patients <65 years of age. It is unknown if this benefit extends to older patients. We hypothesized that the use of surgical navigation would reduce rates of all-cause revision in patients of all ages.

METHODS

In this cohort study, we queried the Truven MarketScan all-payer database to identify patients who underwent TKA from 2007 to 2015. Current Procedural Terminology codes were used to create 2 groups based on whether intraoperative navigation was used. Demographics, comorbidities, complications, and revision rates were determined. International Classification of Diseases codes were used to determine reasons for revision.

RESULTS

The conventional TKA cohort included 312,173 patients. The navigation cohort included 20,881 patients. There were not any clinically significant differences in demographics between the cohorts. All-cause revision rates were lower in the navigation cohort at 1 year (0.4% vs 0.5%, P = .04), 2 years (0.7% vs 0.9%, P = .003), and 5 years (0.9% vs 1.3%, P < .001) of follow-up. Revisions for mechanical loosening were more common in the conventional cohort (30.8% vs 21.9%, P = .009). Rates of revision for other causes, including infection, did not differ between groups, with the numbers available.

CONCLUSION

The use of surgical navigation yielded a 30.7% reduction in the all-cause revision rate at 5-year follow-up compared to conventional TKA. This benefit increased as follow-up duration increased. Increased usage of this inexpensive technology, from the current 6.3% in this US cohort, may reduce healthcare costs.

LEVEL OF EVIDENCE

III.

Computer-Navigated versus Conventional Total Knee Arthroplasty: A Meta-Analysis of Functional Outcomes from Level I and II Randomized Controlled Trials

The main purpose of this article is to provide an up-to-date systematic review and meta-analysis comparing functional outcomes of total knee arthroplasty using either computer navigation (NAV-TKA) or conventional methods (CON-TKA) from the latest assemblage of evidence. This study was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Meta-Analysis of Observational Studies in Epidemiology guidelines. All Level I and II randomized controlled trials (RCTs) in PubMed, EMBASE, and Cochrane that compared functional outcomes after NAV- and CON-TKA were included in the review. Selected end points for random effects, pairwise meta-analysis included Knee Society Knee Score (KSKS), KS Function Score (KSFS), KS Total Score (KSTS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and range of motion at three arbitrary follow-up times. A total of 24 prospective RCTs comprising 3,778 knees were included from the initial search. At long-term follow-up (>5 years), NAV-TKA exhibited significantly better raw KSKS (p = 0.001) (low-quality evidence), contrary to CON-TKA, which reflected significantly better raw KSTS (p = 0.004) (high-quality evidence). While change scores (KSKS, WOMAC) from preoperative values favor CON-TKA at short-term (<6 months) and medium-term follow-up (6-60 months), long-term follow-up change scores in KSKS suggest the superiority of NAV-TKA over CON-TKA (p = 0.02) (very low-quality evidence). Overall, sizeable dispersion of nonstatistically significant functional outcomes in the medium term was observed to eventually converge in the long term, with less differences in functional outcome scores between the two treatment methods in short- and long-term follow-up. While raw functional outcome scores reflect no differences between NAV and CON-TKA, long-term follow-up change scores in KSKS suggest superiority of NAV-TKA over its conventional counterpart. Prospective studies with larger power are required to support the pattern of diminishing differences in functional outcome scores from medium- to long-term follow-up between the two modalities.

TKR after posttraumatic and primary knee osteoarthritis: a comparative study

Background

A few literatures reported that the outcomes of total knee replacement (TKR) in posttraumatic osteoarthritis (PTOA) were lower compared to TKR in primary osteoarthritis (primary OA). The study’s purpose was to compare the comorbidity and outcome of TKR among fracture PTOA, ligamentous PTOA, and primary OA. The secondary aim was to identify the effect of postoperatively lower limb mechanical axis on an 8-year survivorship after TKR between PTOA and primary OA.

Methods

Seven hundred sixteen patients with primary OA, 32 patients with PTOA (knee fracture subgroup), and 104 PTOA (knee ligamentous injury subgroup) were recruited. Demography, comorbidities, Charlson Comorbidity Index (CCI), operative parameters, mechanical axis, functional outcome assessed by WOMAC, and complications were compared among the three groups.

Results

PTOA group was significantly younger (p<0.0001) with a higher proportion of men (p=0.001) while the primary OA group had higher comorbidities than the PTOA group, including anticoagulant usage (p=0.0002), ASA class ≥3 (p<0.0001), number of diseases ≥ 4 (p<0.0001), and CCI (p<0.0001). Both the fracture PTOA group (p<0.0001) and ligamentous PTOA group (p = 0.009) had a significantly longer operative time than the primary OA group. The fracture PTOA group had significantly lower pain components and stiffness components than the primary OA group. There was no significant difference in the rate of an aligned group, outlier group, and an 8-year survivorship in both groups.

Conclusion

The outcome following TKR in the fracture PTOA was poorer compared to primary knee OA in the midterm follow-up. However, no difference was detected between the ligamentous PTOA and primary knee OA. The mechanical axis alignment within the neutral axis did not affect the 8-year survivorship after TKR in both groups.

Level of evidence

Level III; retrospective cohort study

Reliability of Imageless Computer-Assisted Navigation for Femoral Rotational Alignment in Total Knee Arthroplasty

Introduction:

The aim of this study was to evaluate the reliability of the femoral component rotation on intra-operative data recorded in a computer-assisted navigation system (CAN-FRA) compared with the post-operative femoral component rotation observed on computed tomography (CT-FRA).

Material and method:

Computer-assisted total knee arthroplasty (TKA) or primary osteoarthritis of the knee was performed in 51 knees in 36 patients with a mean age of 69.51 years. All procedures were performed by a single surgeon using the same implant design. The intraclass correlation coefficient (ICC) was used to compare the intra-operative CAN-FRA with the post-operative CT-FRA. The angle between the anatomical epicondylar axis and the posterior condylar axis of the implant (CT-FRA) was measured at two separate timepoints by three observers who were blinded to the intra-operative CAN-FRA. Internal rotation was defined as rotation in the negative direction, while external rotation was defined as positive.

Results:

The mean intra-operative CAN-FRA was 0.1° ± 2.8° (range -5.0° to 5.5°). The mean post-operative CT-FRA was -1.3° ± 2.1° (range -4.6° to 4.4°). The mean difference between the CAN-FRA and the CT-FRA was -1.3° ± 2.2° (range -7.9° to 2.4°). The respective ICC values for the three observers were 0.92, 0.94, and 0.93, while the respective intra-observer coefficients were 0.91, 0.85, and 0.90. The ICC for the intra-operative CAN-FRA versus the post-operative CT-FRA was 0.71.

Conclusion:

This study shows that using a computer-assisted navigation system in TKA achieves reliable results and helps to achieve optimal positioning of the femoral component and rotation alignment correction.

Comparison of the clinical effects of computer-assisted and traditional techniques in bilateral total knee arthroplasty: A meta-analysis of randomized controlled trials

Background

It is unclear whether there are individual differences in the long-term efficacy of computer-assisted and traditional total knee arthroplasty. The purpose of this study was to perform a meta-analysis comparing the same individuals undergoing computer-assisted and traditional total knee arthroplasty separately to determine whether computer-assisted total knee arthroplasty can provide better lower extremity radiographic results and clinical outcomes.

Methods

We searched literatures to identify relevant randomized controlled trials comparing the effects of computer-assisted and traditional methods in bilateral total knee arthroplasty. After screening, quality evaluation and data extraction according to inclusion and exclusion criteria, the quality and bias risks of the included studies were evaluated. The meta-analysis compared the radiographic results, functional outcomes and complications of the two techniques.

Results

Six clinical controlled trials were included, with total of 1098 patients. The meta-analysis showed that the accuracy in terms of the mechanical axis of the lower extremity, the sagittal alignment of the femoral component and the coronal alignment of the tibial component in computer-assisted total knee arthroplasty was significantly better than those in traditional total knee arthroplasty. There were no differences in the functional results, revision rates or aseptic loosening rates between the two techniques.

Conclusion

After excluding individual differences such as bone development and bone quality, although computer-assisted techniques can better accurately correct the mechanical axis of the lower extremity and the position of prosthesis implantation than traditional techniques, there is no significant difference in the functional results and revision rate of bilateral total knee arthroplasty in the same individual.

Clinical use of computer-assisted orthopedic surgery in horses

OBJECTIVE

To describe clinical applications of computer-assisted orthopedic surgery (CAOS) in horses with a navigation system coupled with a cone beam computed tomography unit.

STUDY DESIGN

Retrospective clinical case series.

ANIMALS

Thirteen adult horses surgically treated with CAOS.

METHODS

Medical records were searched for horses that underwent CAOS between 2016 and 2019. Data retrieved included signalment, diagnosis, lameness grade prior to surgery, surgical technique and complications, anesthesia and surgery time, and information pertaining to the perioperative case management and outcome.

RESULTS

In 10 cases, surgical implants were placed in the proximal phalanx, third metatarsal bone, ulna, or medial femoral condyle. In one case, navigated transarticular drilling was performed to promote ankylosis of the distal tarsal joints. In another case, an articular fragment of the middle phalanx was removed with the help of CAOS guidance. In the final case, a focal osteolytic lesion of the calcaneal tuber was curetted with the aid of CAOS. In seven cases, a purpose-built frame was used for the surgical procedure. All surgeries were performed successfully and according to the preoperative plan.

CONCLUSION

Computer-assisted orthopedic surgery can be an integral part of the clinical case management in equine surgery. To optimize workflow and time-efficiency, the authors recommend designating one team for operative planning and another for the execution of the surgical plan. Specialized equipment, such as the purpose-built frame, will further improve CAOS applications in equine surgery.

CLINICAL SIGNIFICANCE

After they have become familiar with the operational principles, equine surgeons can readily apply CAOS for a broad spectrum of indications.

Influence of a purpose-built frame on the accuracy of computer-assisted orthopedic surgery of equine extremities

OBJECTIVE

To determine the influence of a purpose-built frame on the accuracy of screw placement during computer-assisted orthopedic surgery (CAOS) of the equine extremity.

STUDY DESIGN

Experimental cadaveric study.

SAMPLE POPULATION

Twenty-four paired equine cadaveric limbs obtained from seven horses.

METHODS

Three 4.5-mm cortex screws were inserted in lag technique in three different planes of orientation in the proximal phalanx (P1) by means of CAOS. In the study group (n = 12 limbs), the tracker was anchored on a purpose-built frame designed to stabilize the extremity. In the control group (n = 12 limbs), a conventional tracker array was used that was anchored directly on P1. The stability of both tracker arrays was assessed during the procedure by using fiducial markers. After screw placement, preoperative and postoperative computed tomographic images were assessed to measure surgical accuracy aberrations (SAA) between the planned and achieved screw position. Descriptive statistics and repeated-measures analysis of variance were performed to compare SAA measurements between the study and control group.

RESULTS

Both tracker arrays remained consistently stable in all specimens. Mean overall SAA of screw insertion were lower in the study group (0.7 mm; median, 0.5; range 0-3.4) than in the control group (1.2 mm; median, 0.9; range, 0-4.2 mm).

CONCLUSION

The mean SAA achieved in cortex screw placement using CAOS lies within the range of approximately 1 mm. The use of a purpose-built frame avoided additional drilling of the target bone and improved surgical accuracy compared with the conventional tracker array.

CLINICAL SIGNIFICANCE

The purpose-built frame described in this report can be used to facilitate CAOS in equine orthopedics without compromising surgical accuracy.

Outcomes of Computer-Assisted Surgery Compared with Conventional Instrumentation in 19,221 Total Knee Arthroplasties: Results After a Mean of 4.5 Years of Follow-Up

BACKGROUND

Studies have shown improved alignment in association with the use of computer-assisted surgery (CAS) as compared with conventional instrumentation during total knee arthroplasty (TKA) but have failed to show a consistent clinical benefit. The aim of the present study was to compare the revision rates and functional outcomes following TKA performed with either CAS or conventional instrumentation. Recognizing that selection bias may arise from the preferential use of CAS in difficult or complex cases, the implant survival data and postoperative functional scores were analyzed with reference to whether the surgeon routinely performed TKA with use of CAS or conventional instrumentation.

METHODS

Revision rates and functional data in terms of the Oxford Knee Score (OKS) at 6 months, 5 years, and 10 years were obtained from the New Zealand Joint Registry (NZJR) for 19,221 TKAs performed from 2006 to 2018.These data were analyzed by comparing 2 cohorts of patients: those managed by high-volume surgeons who routinely used CAS ("routine CAS" surgeons) and those managed by high-volume surgeons who routinely used conventional instrumentation ("routine conventional" surgeons). The mean duration of follow-up was 4.5 years (range, 0 to 12 years).

RESULTS

The revision rate per 100 component-years was 0.437 for the "routine CAS" surgeons, compared with 0.440 for the "routine conventional" surgeons (p = 0.724). For patients <65 years of age, the revision rate per 100 component-years was equivalent for the "routine CAS" and "routine conventional" surgeons (0.585 compared with 0.508; p = 0.524). The OKS scores were similar at 6 months (38.88 compared with 38.52; p = 0.172), 5 years (42.26 compared with 41.77; p = 0.206), and 10 years (41.59 compared with 41.74; p = 0.893) when comparing the 2 cohorts. Surgeons who had performed >50 TKAs with use of CAS took 10 minutes longer on average than those who used conventional instrumentation (92 compared with 82 minutes; p = 0.012).

CONCLUSIONS

The present study demonstrated no difference in survivorship or functional outcome scores to support using CAS for TKA. Experienced surgeons using CAS had longer operative durations than comparable surgeons using conventional instrumentation.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Augmented reality-based navigation system applied to tibial bone resection in total knee arthroplasty

Background

This pilot study was performed to examine the accuracy of the AR-KNEE system, an imageless navigation system using augmented reality (AR) technology for total knee arthroplasty. The AR-KNEE system enables the surgeon to view information from the navigation superimposed on the surgical field on a smartphone screen in real time.

Methods

Using the AR-KNEE system, one surgeon resected 10 tibial sawbones with viewing the tibial axis and aiming varus/valgus, posterior slope, internal/external rotation angles, and resection level superimposed on the surgical field. We performed computed tomography of the resected sawbones and measured the varus/valgus, posterior slope, and internal/external rotation angles using a designated computer software. The thickness of the resected bone was measured using digital calipers.

Results

The absolute differences between the values displayed on the smartphone screen and the measurement values for varus/valgus, posterior slope, internal/external rotation angles, and thickness of the resected bone were 0.5° ± 0.2°, 0.8° ± 0.9°, 1.8° ± 1.5°, and 0.6 mm ± 0.7 mm, respectively.

Conclusions

This pilot study using sawbones suggested that the AR-KNEE system may provide reliable accuracy for coronal, sagittal, and rotational alignment in tibial bone resection during total knee arthroplasty.

Technical and surgical causes of outliers after computer navigated total knee arthroplasty

Background

Navigated total knee arthroplasty (TKA) improves implant and limb alignment but outliers continue to exist. This study aimed to determine the technical and surgical causes of outliers.

Methods

This retrospective cohort study included 208 patients who had undergone navigated TKA. Limb and implant alignment indices were measured on post-operative CT scans: mechanical femoro-tibial angle (MFTA); coronal femoral angle (CFA); coronal tibial angle (CTA); sagittal femoral angle (SFA); and sagittal tibial angle (STA). Values outside 0°±3° for MFTA and SFA, 90°±3° for CFA, CTA and STA were considered outliers. Intra-operative navigation data and CT scans were evaluated to categorize the causes of sagittal and coronal plane outliers into hip centre error; ankle centre error; heterogeneous tibial cement mantle; malalignment accepted by surgeon; suboptimal knee balance; and no obvious explanation.

Results

Of the 1040 measurements (five per TKA), the overall incidence of outliers was 10.4% (n = 108). Femoral component outliers (CFA + SFA, n = 51) were all attributable to hip centre error. Tibial component outliers (CTA + STA, n = 43) were attributable to ankle centre error (n = 6), heterogeneous cement mantle (n = 20), malalignment accepted by the surgeon (n = 6) and no obvious cause (n = 11). MFTA outliers were attributable to hip centre error (n = 4) or suboptimal knee balance (n = 10).

Conclusions

Surgeon related errors can be minimized by a meticulous operative technique. These results indicate scope for additional technical improvement, especially in hip centre acquisition, which may further reduce the incidence of outliers.

Investigation of the control of rotational alignment in the tibial component during total knee arthroplasty

BACKGROUND

In this study, rotational errors that occur in relation to the tibial component of total knee arthroplasty (TKA) were investigated intraoperatively using a CT-free navigation system and postoperative CT images to confirm the correctness of the rotation.

METHODS

Forty patients who underwent TKA using the navigation system were examined. These patients were split evenly into two groups, those whose rotational position was confirmed using a mark made manually on the tibia, and those whose rotation was confirmed using the navigation. All patients underwent postoperative CT scanning and were evaluated using the Knee Society Score.

RESULTS

With navigation, a significant difference was found between the rotational positions for which we made a keel hole and those for which the tibial component was inserted unguided. After cementing, the rotational position in the group for which a manual mark was used to confirm the rotation differed significantly from the position for the group for which navigation during cementing was used. Although there were four outliers that had rotational errors over 3° after cementing in the manual mark group, there were no outliers in the navigation group. While there was significant difference in the rotational errors of the tibial component on postoperative CT between two groups, the Knee Society Score did not differ between two groups.

CONCLUSION

The exact rotation of a tibial component cannot be maintained by simply creating a keel hole. The use of a manual mark resulted in rotational errors of the tibial component and the creation of the outliers. Therefore, it is suggested that the use of a navigation system can reduce the occurrence of such errors.

Computer-assisted surgery in total knee replacement: advantages, surgical procedure and review of the literature

Introduction: Total knee replacement (TKR) is one of the most frequent orthopaedic procedures performed every year. At the same time 20% of patients who underwent TKR are not satisfied with the outcome. The reasons are unknown; we think that a mechanical alignment beyond 3° of varus-valgus can represent the most important cause of failure of TKR and consequently patient dissatisfaction. Materials and Methods: Neutral mechanical alignment is the main goal in every TKR: this can be achieved through different tools, such as extramedullary and intramedullary guides, patient-specific instrumentation (PSI) and computer-assisted surgery (CAS). The aim of this review is to compare the different alignment techniques in TKR, to describe CAS procedure and CAS results in recent literature. Results: Regarding the intramedullary guide, there is an increased risk of fatty embolism; there are great limitations on its use, or even impossibility, in cases of bone deformity and sequelae of trauma. Regarding the extramedullary guide, it becomes more difficult to use in cases of great obesity or increased soft-tissue volume around the tibia. PSI for TKR has been introduced to improve alignment, reduce outliers, operation time and the risk of fatty embolism by avoidance of intramedullary canal violation. Recent randomized controlled trials and meta-analysis proved no advantage of PSI in improving mechanical axis and implant survivorship. Discussion: CAS has provided to be a useful tool in assisting the surgeon to achieve more accurate post-operative mechanical axis through precise and reproducible bone cuts and ligament balancing. Two meta-analyses definitively proved that CAS technique improves mechanical axis and implant survivorship and one recent meta-analysis demonstrated that CAS provides better mechanical alignment and higher functional scores at short-term follow-up. (www.actabiomedica.it)

Computer-assisted versus intramedullary and extramedullary alignment system in total knee replacement: Long term follow-up

INTRODUCTION

The aim of this work is to compare in a retrospective study, the radiological results of three series of different total knee replacements performed using Orthopilot computer-based alignment system (Group A, 31 patients), a totally intramedullary alignment system (Group B, 34 patients) and a totally extramedullary alignment system (Group C, 32 patients).

MATERIALS AND METHODS

At a medium follow-up of 15 years, all patients underwent call interview for clinical update. Of the 115 patients initially enrolled in the study, only 97 were available for radiological assessment. Both standing long-leg antero-posterior radiographs and lateral radiographs of the knee had been taken for every patient at 1 year-follow-up and at the last follow-up.

RESULTS

At the last follow-up, the mean hip-knee-ankle angle (HKA) was 179.1° (range: 176°-184°) for group A, 178.6° (range: 173°-186°) for group B and 177.8° (range: 172°-186°) for group C with no statistically significant difference among the 3 groups. The mean frontal femoral component angle (FFC) was 90.5° (range: 87°-94°) for group A, 91.05° (range: 85°-95°) for group B and 91.19° (range: 85°-96°) for group C and there was no statistically significant difference among the three groups. The mean frontal tibial component angle (FTC) was 89.9° (range: 83°-97°) for group A, 90.6° (range: 87°-95°) for group B and 90.8° (range: 86°-95°) for group C and there was no statistically significant difference among the three groups. The mean tibial component inclination in the sagittal plane was 1° (range: 3°-0°) for group A, 3.6° (range: 7°-0°) for group B and 3.1° (range: 6°-0°) for group C.

DISCUSSION AND CONCLUSION

Our results demonstrated statistically significant differences between computer-assisted and extramedullary group, in favour of navigated group in terms of implant position and mechanical alignment. Computer-assisted group showed superior but not statistically significant differences compared to intramedullary alignment system in terms of implant position and mechanical alignment. We advocate the use of computer-assisted system routinely in total knee replacement. As an alternative, we suggest the use of intramedullary system.

Alignment in total knee arthroplasty - A comparison of patient-specific implants with the conventional technique

BACKGROUND

Incorrect positioning and malalignment of total knee arthroplasty (TKA) components can result in implant loosening. Restoration of neutral alignment of the leg is an important factor affecting the long-term results of TKA. The aim of our retrospective study was to compare mechanical axis in patients with conventional and patient-specific TKAs.

METHODS

232 patients who underwent TKA between January 2013 and December 2014 were included to compare postoperative mechanical axis. 125 patients received a patient-specific TKA (iTotal CR®, Conformis) and 107 a conventional TKA (Triathlon®, Stryker). Standardized pre- and postoperative long-leg standing radiographs were retrospectively evaluated to compare the two patient cohorts.

RESULTS

113 (90%) radiographs of patient-specific TKA and 88 (82%) of conventional TKA were available for comparison. The preoperative deviation from neutral limb axis was 9.0° (0.1–27.3°) in the patient-specific TKA cohort and 8.2° (0.2–18.2°) in the conventional TKA group. Postoperatively the patient-specific TKA group showed 3.2° (0.1–8.4°) and the conventional TKA cohort 2.3° (0.1–12.5°) deviation. However, the rate of ± 3° outliers from neutral limb axis was 16% in the patient-specific TKA cohort and 26% in the conventional TKA group.

CONCLUSIONS

Patient-specific TKA demonstrated fewer outliers from neutral leg alignment compared to conventional technique. Potential benefits in the long-term outcome and functional improvement require further investigation.

Current concepts and future perspectives in computer-assisted navigated total knee replacement

BACKGROUND

Total knee replacements (TKR) aim to restore stability of the tibiofemoral and patella-femoral joints and provide relief of pain and improved quality of life for the patient. In recent years, computer-assisted navigation systems have been developed with the aim of reducing human error in joint alignment and improving patient outcomes.

METHODS

We examined the current body of evidence surrounding the use of navigation systems and discussed their current and future role in TKR.

RESULTS

The current body of evidence shows that the use of computer navigation systems for TKR significantly reduces outliers in the mechanical axis and coronal prosthetic position. Also, navigation systems offer an objective assessment of soft tissue balancing that had previously not been available. Although these benefits represent a technical superiority to conventional TKR techniques, there is limited evidence to show long-term clinical benefit with the use of navigation systems, with only a small number of studies showing improvement in outcome scores at short-term follow-up. Because of the increased costs and operative time associated with their use as well as the emergence of more affordable and patient-specific technologies, it is unlikely for navigation systems to become more widely used in the near future.

CONCLUSIONS

Whilst this technology helps surgeons to achieve improved component positioning, it is important to consider the clinical and functional implications, as well as the added costs and potential learning curve associated with adopting new technology.

A new approach for safe planning transfer using semi-automatically adjustable instrument guides

Accurate planning transfer is a prerequisite for successful operative care. For different applications, diverse computer-assisted systems have been developed and clinically evaluated. This paper presents the implementation and evaluation of a new modular concept. The approach is based on passive application specific kinematics that are semi-automatically adjusted using a universal hand-held computer controlled Smart Screw Driver. The system was realized for pedicle screw instrumentation and evaluated according to IEC 60601-1-6 (usability engineering). The accuracies of the drill holes achieved were comparable with robotic approaches, while operation time and radiation were reduced compared with conventional operation techniques. The adjustment procedure has proven high learnability and user satisfaction. The next step will be optimization of the kinematic structure and fixation to the patient in order to increase accuracies of planning transfer as well as evaluation of the overall system by medical staff in preclinical and clinical studies.

Computer-Assisted Total Knee Arthroplasty: Is There a Difference Between Image-Based and Imageless Techniques?

BACKGROUND

Image-based and imageless computer-assisted total knee arthroplasty (CATKA) has become increasingly popular. This study aims to compare outcomes, including perioperative complications and transfusion rate, between CATKA and conventional total knee arthroplasty (TKA), as well as between image-based and imageless CATKA.

METHODS

Using the 9th revision of the International Classification of Diseases codes, we queried the Nationwide Inpatient Sample database from 2005 to 2011 to identify unilateral conventional TKA, image-based, and imageless CATKAs as well as in-hospital complications and transfusion rates.

RESULTS

A total of 787,809 conventional TKAs and 13,246 CATKAs (1055 image-based and 12,191 imageless) were identified. The rate of CATKA increased 23.13% per year from 2005 to 2011. Transfusion rates in conventional TKA and CATKA cases were 11.73% and 8.20% respectively (P < .001) and 6.92% in image-based vs 8.27% in imageless (P = .023). Perioperative complications occurred in 4.50%, 3.47%, and 3.41% of cases after conventional, imageless, and imaged-based CATKAs, respectively. Using multivariate analysis, perioperative complications were significantly higher in conventional TKA compared to CATKA (odds ratio = 1.17, 95% confidence interval 1.03-1.33, P = .01). There was no significant difference between imageless and image-based CATKA (P = .34). Length of hospital stay and hospital charges were not significantly different between groups (P > .05).

CONCLUSION

CATKA has low complication rates and may improve patient outcomes after TKA. CATKA, especially the image-based technique, may reduce in-hospital complications and transfusion without increasing hospital charges and length of hospital stay significantly. Large prospective studies with long follow-up are required to verify potential benefits of CATKA.

What Factors Are Associated With Femoral Component Internal Rotation in TKA Using the Gap Balancing Technique?

BACKGROUND

When using the gap-balancing technique for TKA, excessive medial release and varus proximal tibial resection can be associated with internal rotation of the femoral component. Previous studies have evaluated the causes of femoral component rotational alignment with a separate factor analysis using unadjusted statistical methods, which might result in treatment effects being attributed to confounding variables.

QUESTIONS/PURPOSES

(1) What pre- and intraoperative factors are associated with internal rotation of the femoral component in TKA using the gap balancing technique? (2) To what degree does femoral component rotation as defined by the navigation system differ from rotation as measured by postoperative CT?

METHODS

Three hundred seventy-seven knees that underwent computer-assisted primary TKA attributable to degenerative osteoarthritis with varus or mild valgus alignment in which medial soft tissue release was performed, and those with preoperative radiographs including preoperative CT between October 2007 and June 2014 were included in the study. To achieve a balanced mediolateral gap, the structures released during each medial release step were as follows: Step 1, deep medial collateral ligament (MCL); Step 2, superficial MCL (proximal, above the pes anserine tendon) and semimembranosus tendon; and Step 3, the superficial MCL (distal, below the pes anserine tendon). Knees with internal rotation of the femoral component, which was directed by navigation, to achieve a rectangular mediolateral flexion gap were considered cases, and knees without internally rotated femoral components were considered controls. Univariable analysis of the variables (age, sex, BMI, operated side, preoperative hip-knee-ankle angle, preoperative medial proximal tibial angle, preoperative rotation degree of the clinical transepicondylar axis [TEA] relative to the posterior condylar axis [PCA], coronal angle of resected tibia, resection of the posterior cruciate ligament, type of prosthesis, and extent of medial release) of cases and controls was performed, followed by a multivariable logistic regression analysis on those factors where p equals 0.15 or less. For an evaluation of navigation error, 88 knees that underwent postoperative CT were analyzed. Postoperative CT scans were obtained for patients with unexplained pain or stiffness after the operations. Using the paired t-test and Pearson's correlation analysis, the postoperative TEA-PCA measured with postoperative CT was compared with theoretical TEA-PCA, which was calculated with preoperative TEA-PCA and actual femoral component rotation checked by the navigation system.

RESULTS

After controlling for a relevant confounding variable such as postoperative hip-knee-ankle angle, we found that the extent of medial release (Step 1 as reference; Step 2: odds ratio [OR], 5.7, [95% CI, 2.2-15]; Step 3: OR, 22, [95% CI, 7.8-62], p < 0.001) was the only factor we identified that was associated with internal rotation of the femoral component. With the numbers available, we found no difference between the mean theoretical postoperative TEA-PCA and the postoperative TEA-PCA measured using postoperative CT (4.8° ± 2.7º versus 5.0° ± 2.3º; mean difference, 0.2° ± 1.5º; p = 0.160).

CONCLUSIONS

Extent of medial release was the only factor we identified that was associated with internal rotation of the femoral component in gap-balancing TKA. To avoid internal rotation of the femoral component, we recommend a carefully subdivided medial-releasing technique, especially for the superficial MCL because once the superficial MCL has been completely released it cannot easily be restored.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Lower limb alignment and laxity measures before, during and after total knee arthroplasty: A prospective cohort study

BACKGROUND

This study compared knee alignment and laxity in patients before, during and after total knee arthroplasty, using methodologically similar procedures, with an aim to help inform pre-operative planning.

METHODS

Eighteen male and 13 female patients were recruited, mean age 66years (51-82) and mean body mass index of 33 (23-43). All were assessed pre- and postoperatively using a non-invasive infrared position capture system and all underwent total knee arthroplasty using a navigation system. Knee kinematic data were collected and comparisons made between preoperative clinical and intraoperative measurements for osteoarthritic knees, and between postoperative clinical and intraoperative measurements for prosthetic knees.

FINDINGS

There was no difference in unstressed coronal mechanical femoral-tibial angles for either osteoarthritic or prosthetic knees. However, for sagittal alignment the knees were in greater extension intraoperatively (osteoarthritic 5.2° p<0.001, prosthetic 7.2° p<0.001). For osteoarthritic knees, both varus and valgus stress manoeuvres had greater angular displacements intraoperatively by a mean value of 1.5° for varus (p=0.002) and 1.6° for valgus (p<0.001). For prosthetic knees, only valgus angular displacement was greater intraoperatively (0.9°, p=0.002).

INTERPRETATION

Surgeons performing total knee arthroplasties should be aware of potential differences in alignment and laxity measured under different conditions to facilitate more accurate operative planning and follow-up.

A randomized controlled trial to compare component placement in navigated total knee arthroplasty using original and streamlined registration processes

Background

This randomized controlled trial validated a redesigned version of navigated total knee arthroplasty software with a streamlined registration (Smart) against the previous version (Classic). The objectives were to determine if Smart software had the same accuracy of component positioning and whether registration and operative time were reduced.

Methods

A total of 220 patients were recruited and had a navigated total knee arthroplasty performed. With the exception of the software, all patients had the same perioperative care. At 6-week follow-up with an independent arthroplasty service, all patients had a computerized tomography scan. This was assessed by an independent radiologist to measure the mechanical alignment of the components.

Results

The mean postoperative mechanical femorotibial angles were equivalent between groups (mean difference −0.2°, 95% confidence interval −0.7° to 0.3°, P = .407). Component positions were similar in both groups. Mean registration time was significantly shorter for the Smart group (2 minutes 30 seconds ± 54 seconds) than the Classic group (3 minutes 23 seconds ± 39 seconds), P < .001. The mean operative time was 72 ± 12 minutes in both groups (P = .855). At 6-week follow-up, both groups had similar clinical outcomes with 96.5% of patients being satisfied or very satisfied.

Conclusions

The study verified that a reduced registration time did not alter the accuracy of component placement. However, despite a shorter registration time, the overall surgical time was not reduced.

Averaging rotational landmarks during total knee arthroplasty reduces component malrotation caused by femoral asymmetry

Background

Femoral component malrotation is a common cause of patient dissatisfaction after total knee arthroplasty. The sulcus line (SL) is more accurate than Whiteside’s line as it corrects for variation in the coronal orientation of the groove. The hypothesis is that averaging the SL and posterior condylar axis (PCA) will reduce femoral malrotation.

Methods

The component was inserted at a position between the SL and PCA in 91 patients. An intraoperative photograph was taken showing the landmarks. These were compared to the component position achieved relative to the surgical epicondylar axis (SEA) on a postoperative CT scan. The component position was compared to the position achieved using the individual landmarks.

Results

Relative to the SEA, the final component position was 0.6° (SD 1.4°, range −3.8° to +4.0°), the coronally corrected SL position was −0.7° (SD 2.3°, −5.5° to +4.6°), the PCA position was 0.9° (SD 1.9°, −6.1° to +5.0°). Averaging the landmarks significantly decreased the variance of the component position compared to using the SL and PCA individually. The number of outliers (>3° from SEA) was also significantly less (p < 0.05) for the average position (2/84) when each was compared to the SL (16/84) and PCA (14/84) individually. In 21/84 (25%) of cases, there was more than 4° of divergence between the SL and PCA.

Conclusions

Averaging the SL and the PCA decreases femoral component malrotation. Femora are frequently asymmetrical in the axial plane. Referencing posterior condyles alone to set rotation is likely to cause high rates of patellofemoral malalignment.

Variation in Optimal Sagittal Alignment of the Femoral Component in Total Knee Arthroplasty

Accurate sagittal alignment of the femoral component in total knee arthroplasty is crucial for prosthesis longevity, improved function, and patient satisfaction. However, there is variation in the techniques used to attain optimal sagittal femoral component placement in total knee arthroplasty. Femoral component flexion in imageless navigation is based on the mechanical axis rather than the distal femoral anatomy, and there is significant variability in the anatomy of the distal femur. The purpose of this study was to accurately determine the mean distal femoral flexion angle of a representative population and whether variability of the distal femoral flexion angle correlates with race, femur length, or radius of curvature. The mean degree of distal femoral flexion was determined by assessing distal femoral anatomy on computed tomography scans of paired femurs of 1235 patients without evidence of previous fracture, deformity, or surgical implants. The mean±SD distal femoral flexion angle was 2.90°±1.52°, with 80.2% of knees within 3°±2°. Therefore, placing the component in 3° of flexion from the mechanical axis would attain a satisfactory position in most cases. However, further analysis of the patient data revealed 11.4% of Asians, 7.3% of African Americans, and 8.3% of whites had a distal femoral flexion angle greater than 5°. Additionally, the data revealed a moderately strong negative correlation between the distal femoral flexion and the overall radius of curvature of the femur. This preliminary study highlights the need for improved methods for selecting femoral component position in the sagittal plane when using navigation for total knee arthroplasty. [Orthopedics. 2017; 40(2):102-106.].

Femoral component rotations in different gap tensions in total knee arthroplasty: A prospective randomized controlled trial

BACKGROUND

In total knee arthroplasty (TKA), femoral component rotation is an important factor in the flexion stability and biomechanics of the patellofemoral joint. However, it remains unclear how much tension is appropriate when performing TKA using the gap technique.

METHODS

One hundred fifty TKAs that used the gap technique were randomized into one of the three groups. Gravity group (n=50) included patients who underwent TKA using only the weight of the patient's lower leg. In 20-lbf group (n=50) and 30-lbf group (n=50), a gap-tensioning device was set at 20lbf and 30lbf respectively. The femoral component rotation was measured based on the clinical transepicondylar axis (cTEA) on postoperative CT and any outliers (a femoral component rotation diverging from the cTEA over 3°) were evaluated.

RESULTS

The mean femoral component rotation was -0.82°±2.44° (95% confidence interval [CI], -1.52° to -0.13°) in gravity group, -0.40°±2.22° (95% CI, -1.03° to 0.23°) in 20-lbf group, and 1.37°±2.70° (95% CI, 0.61° to 2.14°) in 30-lbf group. The mean femoral component rotation in 30-lbf group was significantly different from that in gravity group (p<0.001) and 20-lbf group (p<0.001). There were more outliers in 30-lbf group (18% in gravity group, 18% in 20-lbf group, and 36% in 30-lbf group; p=0.043).

CONCLUSIONS

The use of a tensioning device set at 30lbf resulted in an externally rotated femoral component and frequent outliers.

Referencing the sulcus line of the trochlear groove and removing intraoperative parallax errors improve femoral component rotation in total knee arthroplasty

PURPOSE

Firstly, to assess and compare the accuracy and reproducibility of the sulcus line compared to Whiteside's line. Secondly, to assess the accuracy of intraoperative techniques for using the rotational alignment of the trochlear groove to set femoral rotation. Thirdly, to assess the reproducibility of a trochlear alignment guide which removes parallax errors that occur when projecting the sulcus line onto the surface of the femur. Finally, to measure the result of combining the geometrically accurate sulcus line and the posterior condylar axis.

METHODS

Three surgeons measured eight rotational angles on ten cadaveric femora. This included Whiteside's line, the sulcus line and the techniques in which they can be referenced during surgery.

RESULTS

Relative to the anatomical epicondylar axis, the sulcus line (mean -2.8°, SD 2.0°, range -5.4° to 0.8°) had significantly lower variance (F = 5.16, p = 0.036) than Whiteside's line (mean -2.0°, SD 3.7°, range -6.0° to 3.4°). The trochlear alignment guide produced the best results of the intraoperative techniques by maintaining the accuracy of the sulcus line and projecting it onto the distal cut surface of the femur without change in rotational angle.

CONCLUSION

The sulcus line is more accurate and reproducible than Whiteside's line. Removing parallax errors during surgery improves femoral component rotation. The trochlear alignment guide produced accurate results suggesting that it may be beneficial in a clinical setting. Averaging the sulcus line and posterior condylar axis on the cut surface of the femur improved accuracy over the individual landmarks. Femoral component malrotation is a common cause of patient dissatisfaction and revision surgery. By isolating the rotational alignment of the trochlear groove using the sulcus line, and maintaining its accuracy with an intraoperative guide, we can decrease the risk of femoral component malrotation and improve patient outcomes.

Intraoperative Measurements of Joint Line Changes Using Computer Navigation Do Not Correlate With Postoperative Radiographic Measurements in Total Knee Arthroplasty

BACKGROUND

The adverse effects of joint line (JL) changes on kinematics and outcomes of total knee arthroplasty (TKA) have been studied. Some authors have quantified JL changes using intraoperative data from computer navigation, despite no studies validating these measurements to date. We designed a prospective study to determine whether intraoperative measurements of JL changes using computer navigation correlate with measurements obtained on weight-bearing radiographs postoperatively.

METHODS

A total of 195 consecutive patients (195 knees) underwent computer-navigated cruciate-retaining TKA by the senior author. Twenty-four patients had missing radiographic data and were excluded from the study. The final JL change was calculated intraoperatively from the verified bony cuts and planned JL change as determined by the computer. JL position was also measured on preoperative and postoperative radiographs using an anteroposterior method.

RESULTS

One hundred seventy-one knees were evaluated. Using computer-navigated and radiographic measurements, the mean JL change was 1.95 ± 1.5 mm (0-8.0 mm) and 4.05 ± 2.9 mm (0-17.3 mm), respectively. One hundred fourteen (67%) vs 129 (75%) had JL elevation, 44 (26%) vs 30 (18%) had JL depression, and 13 (7%) vs 12 (7%) had no JL change, respectively. Inter-rater and intrarater reliability of radiographic measurements was excellent. We found a poor correlation between computer-navigated and radiographic measurements (r = 0.303).

CONCLUSION

There is a poor correlation between computer-aided and radiographic measurements of JL changes post-TKA. Elevation/depression of the JL needs to be considered in patients who remain symptomatic despite TKA, although the optimal method of assessment remains uncertain.

Do CAS measurements correlate with EOS 3D alignment measurements in primary TKA?

PURPOSE

Objective of this study was to compare intraoperative computer-assisted surgery (CAS) alignment measurements during total knee arthroplasty (TKA) with pre- and postoperative coronal alignment measurements using EOS 3D reconstructions.

METHODS

In a prospective study, 56 TKAs using imageless CAS were performed and coronal alignment measurements were recorded twice: before bone cuts were made and after implantation of the prosthesis. Pre- and postoperative coronal alignment measurements were performed using EOS 3D reconstructions. Thanks to the EOS radiostereography system, measurement errors due to malpositioning and deformity during acquisition are eliminated. CAS measurements were compared with EOS 3D reconstructions. Varus/valgus angle (VV), mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured.

RESULTS

Significantly different VV angles were measured pre- and postoperatively with CAS compared to EOS. For preoperative measurements, mLDFA did not differ significantly, but a significantly larger mMPTA in valgus was measured with CAS.

CONCLUSION

Results of this study indicate that differences in alignment measurements between CAS measurements and pre- and postoperative EOS 3D are due mainly to the difference between weight-bearing and non-weight-bearing position and potential errors in validity and reliability of the CAS system. EOS 3D measurements overestimate VV angle in lower limbs with substantial mechanical axis deviation. For lower limbs with minor mechanical axis deviation as well as for mMPTA measurements, CAS measures more valgus than EOS. Eventually the results of this study are of clinical relevance, since it raises concerns regarding the validity and reliability of CAS systems in TKA.

LEVEL OF EVIDENCE

IIb.

Intraoperative Load-Sensing Variability During Cemented, Posterior-Stabilized Total Knee Arthroplasty

BACKGROUND

Load-sensing technology during total knee arthroplasty (TKA) provides objective measurements of ligamentous balance. The purpose of this study is to assess its intraoperative validity and reliability during TKA.

METHODS

Fifty-four patients underwent TKA using the OrthoSensor VERASENSE tibial insert to assist with ligament balance. The transepicondylar axis (TEA) was used to determine femoral component rotation, and the posterior condylar angle (PCA) was measured. Load measurements were documented at 10°, 45°, and 90° of flexion with the trial (TRIAL) components and with the definitive (FINAL) cemented implants. Adequate balance was defined as a load differential ≤15 pounds between compartments.

RESULTS

Adequate balanced with TRIAL and FINAL implants was observed in 89% TKAs. There was a significant linear correlation of the TRIAL and FINAL loads in the medial compartment throughout range of motion. No correlation between the TRIAL and FINAL loads was identified in the lateral compartment. There was no relationship between an increasing PCA and medial compartment loads at 45° (R² = 0.0006, Y = -0.10X + 7.3 ± 2.3; P = .86) and 90° (R² = 0.004, Y = -0.25X + 6.3 ± 2.1; P = .62) of flexion, suggesting that the compartment loads were not significantly altered with femoral rotation parallel to the TEA. A similar finding was observed in the lateral compartment at all poses.

CONCLUSION

Variability between the TRIAL and FINAL implant measurements was higher in the lateral compartment as compared to the medial compartment. Using the TEA and not the posterior condylar line as a landmark to guide femoral component rotation, the flexion gap is frequently balanced without the need for additional ligament releases.

Computed tomography is not necessary to assess rotation of the femoral component in navigation-assisted total knee replacement

Objective

To demonstrate that postoperative computed tomography (CT) is not needed if navigation is used to determine the rotational position of the femoral component during total knee replacement (TKR).

Methods

Preoperative CT, navigational, and postoperative CT data of 70 TKR procedures were analysed. The correlation between the rotational angulation of the femur measured by CT and that measured by perioperative navigation was examined. The correlation between the femoral component rotation determined by navigation and that determined by CT was also assessed.

Results

The mean femoral rotation determined by navigation was 2.64° ± 4.34°, while that shown by CT was 6.43° ± 1.65°. Postoperative rotation of the femoral component shown by CT was 3.09° ± 2.71°, which was closely correlated with the angle obtained through the intraoperative transepicondylar axis by navigation (Pearson’s R = 0.930).

Conclusions

Navigation can be used to collect the preoperative, intraoperative, and postoperative data and final position of the TKR. The rotation of the femoral component can be determined using navigation without the need for CT.

Clinical outcome is not affected by total knee arthroplasty alignment

PURPOSE

This study aims to analyse the influence on total knee arthroplasty (TKA) clinical outcomes of biomechanical intra-operative computer-assisted surgery-measured parameters, together with radiographic and demographical data.

METHODS

Between 2007 and 2009, 227 computer-assisted surgery (CAS) primary TKAs were performed in 219 consecutive patients. Information about gender, age and body mass index (BMI) was collected for each patient. Before knee replacement, all patients underwent a complete radiographic examination and passive flexion-extension range of motion was recorded. All TKAs were implanted using an image-free knee navigation system. Patients included in the study were evaluated at 3, 6 and 12 months of follow-up and then yearly. At each follow-up, subjects were asked to answer the validated Italian version of the Knee Injury and Osteoarthritis Outcome Score.

RESULTS

One hundred and eighty patients (187 knees) had data available for analysis. Complications were reported in 13 patients (7.0 %). Intra-operative CAS-measured parameters, together with age, BMI, gender, pre- and post-operative radiographic alignment, did not influence TKA clinical results at a mean 2 years of follow-up. On the other hand, higher post-operative flexion arc of movement was suggestive of better clinical outcomes.

CONCLUSION

TKA clinical outcome is influenced by post-operative knee flexion, other than neutral mechanical limb alignment. Therefore, it is recommended to prefer TKA designs that allow high flexion and to encourage early physical rehabilitation.

LEVEL OF EVIDENCE

IV.

Optimal Number of Fixation Pins for Dedicated Mini Jig Cutting Guides During Navigated Total Knee Arthroplasty

PURPOSE

The optimal number of fixation pins for minimally invasive cutting guides in computer-navigated arthroplasty has not been determined. The authors hypothesized that more fixation pins will lead to greater mechanical stability and more accurate resections.

MATERIALS AND METHOD

12 bovine knee joints were divided into three groups with differing numbers of fixation pins. The ASM [Stryker] knee navigation system was utilized to perform resections, and accuracy of alignment and posterior slope was measured. Comparison was performed between the groups to calculate average differences between predicted and actual resection with differing number of pins.

RESULTS

The difference between actual and predicted values showed a trend toward diminishing with a greater number of fixation pins. The mean difference in coronal alignment of predicted versus actual resection was 0.75° for two fixation pins, 0.5° for three pins and 1° for four fixation pins. Similarly, the difference between posterior slope was 2.75°, 2°, and 1°, respectively.

CONCLUSION

This study reveals a trend toward greater accuracy of resections with more fixation pins. Further investigation may be beneficial.

Computer-assisted navigation is beneficial both in primary and revision surgery with modular rotating-hinge knee arthroplasty

PURPOSE

The objective of the present study was to explore the effect of navigation on the reconstruction of the mechanical leg axis, implant positioning and the restoration of the joint line in hinged knee arthroplasty in vivo. We present the first 1- to 3-year clinical and radiological results following computer-navigated implantation of the EnduRo modular rotating-hinge knee arthroplasty system (Aesculap AG, Tuttlingen, Germany) as a primary or revision implant.

METHODS

Thirty-one patients were analysed retrospectively. Indication was revision surgery in 18 patients and complex primary surgery in 13. The clinical and radiological results of 31 patients with a minimum follow-up of 12 months (mean 22.2 ± 6.2 months) were recorded. Age at follow-up was 55.2 ± 9.9 years.

RESULTS

The absolute varus-valgus deviation from the neutral mechanical leg axis was determined at 5.1° ± 5.1° preoperatively and 2.1° ± 1.4° postoperatively. No intraoperative complications or problems with the navigation system were observed. At latest follow-up, no component loosening was detected. Based on the Knee Society Score, a knee score of 64.9 ± 17.7 points and a function score of 67.2 ± 27.3 points were achieved.

CONCLUSIONS

Encouraging short-term clinical and radiological results with the computer-navigated implantation of the modular rotating-hinge EnduRo knee arthroplasty system were found in both primary and revision surgery. The navigation facilitated the reconstruction of the leg axis, implant positioning and the restoration of the joint line.

LEVEL OF EVIDENCE

IV.

The sulcus line of the trochlear groove is more accurate than Whiteside's Line in determining femoral component rotation

PURPOSE

The sulcus line (SL) is a three-dimensional curve produced from multiple points along the trochlear groove. Whiteside's Line, also known as the anteroposterior axis (APA), is derived from single anterior and posterior points. The purposes of the two studies presented in this paper are to (1) assess the results from the clinical use of the SL in a large clinical series, (2) measure the SL and the APA on three-dimensional CT reconstructions, (3) demonstrate the effect of parallax error on the use of the APA and (4) determine the accuracy of an axis derived by combining the SL and the posterior condylar axis (PCA).

METHODS

In the first study, we assessed the SL using a large, single surgeon series of consecutive patients undergoing primary total knee arthroplasties. The post-operative CT scans of patients (n = 200) were examined to determine the final rotational alignment of the femoral component. In the second study, measurements were taken in a series of 3DCT reconstructions of osteoarthritic knees (n = 44).

RESULTS

The mean position of the femoral component in the clinical series was 0.6° externally rotated to the surgical epicondylar axis, with a standard deviation of 2.9° (ranges from -7.2° to 6.7°). On the 3DCT reconstructions, the APA (88.2° ± 4.2°) had significantly higher variance than the SL (90.3° ± 2.7°) (F = 5.82 and p = 0.017). An axis derived by averaging the SL and the PCA+3° produced a significant decrease in both the number of outliers (p = 0.03 vs. PCA and p = 0.007 vs. SL) and the variance (F = 6.15 and p = 0.015 vs. SL). The coronal alignment of the SL varied widely relative to the mechanical axis (0.4° ± 3.8°) and the distal condylar surface (2.6° ± 4.3°).

CONCLUSIONS

The multiple points used to determine the SL confer anatomical and geometrical advantages, and therefore, it should be considered a separate rotational landmark to the APA. These findings may explain the high degree of variability in the measurement of the APA which is documented in the literature. Combining a geometrically correct SL and the PCA is likely to further improve accuracy.

Numerical optimization of alignment reproducibility for customizable surgical guides

PURPOSE

Computer-assisted orthopedic surgery aims at minimizing invasiveness, postoperative pain, and morbidity with computer-assisted preoperative planning and intra-operative guidance techniques, of which camera-based navigation and patient-specific templates (PST) are the most common. PSTs are one-time templates that guide the surgeon initially in cutting slits or drilling holes. This method can be extended to reusable and customizable surgical guides (CSG), which can be adapted to the patients' bone. Determining the right set of CSG input parameters by hand is a challenging task, given the vast amount of input parameter combinations and the complex physical interaction between the PST/CSG and the bone.

METHODS

This paper introduces a novel algorithm to solve the problem of choosing the right set of input parameters. Our approach predicts how well a CSG instance is able to reproduce the planned alignment based on a physical simulation and uses a genetic optimization algorithm to determine optimal configurations. We validate our technique with a prototype of a pin-based CSG and nine rapid prototyped distal femora.

RESULTS

The proposed optimization technique has been compared to manual optimization by experts, as well as participants with domain experience. Using the optimization technique, the alignment errors remained within practical boundaries of 1.2 mm translation and [Formula: see text] rotation error. In all cases, the proposed method outperformed manual optimization.

CONCLUSIONS

Manually optimizing CSG parameters turns out to be a counterintuitive task. Even after training, subjects with and without anatomical background fail in choosing appropriate CSG configurations. Our optimization algorithm ensures that the CSG is configured correctly, and we could demonstrate that the intended alignment of the CSG is accurately reproduced on all tested bone geometries.

Improved femoral component rotation in advanced genu valgum deformity using computer-assisted measured resection total knee arthroplasty

Background

Accurate femoral rotational alignment is of vital importance for successful total knee arthroplasty (TKA). The value of computer-assisted surgery TKA (CAS-TKA) in increasing the accuracy of femoral rotational alignment remains controversial. We hypothesize that outcomes are related to the severity of preoperative varus and valgus deformity and that CAS-TKA may be beneficial under certain circumstances.

Methods

Between January 2007 and December 2013, patients with osteoarthritis and varus angulation in the mechanical axis (MA) ≥ 15° and valgus angulation in the MA ≥ 10° (based on hip-to-ankle standing radiography) who underwent TKA were divided into four groups. CAS-TKA and conventional TKA outcomes were compared in patients who had preoperative advanced genu varum and advanced genu valgum deformities. The accuracy of component alignment and postoperative limb alignment was determined using radiographic parameters and computed tomography (CT).

Results

One hundred and eight patients (144 knees) were included in the analysis. For patients with preoperative advanced genu varum deformity, a significant difference was detected in the sagittal femoral angle (p < 0.001), but no significant improvement of femoral rotational alignment was noted (p = 0.127). In patients with preoperative advanced genu valgum deformity, a significant difference was found in the sagittal femoral angle (p = 0.034). The femoral rotational angle was significantly closer to the proper position in the CAS-TKA group (p < 0.001). When comparing the percentage of knees achieving the proper alignment, there was a decrease in the amount of outlier for the femoral rotational angle for CAS-TKA in advanced genu valgum deformity (p = 0.011).

Conclusions

Our data demonstrate that CAS-TKA is beneficial in obtaining proper femoral rotational alignment in patients with advanced genu valgum deformity (preoperative MA ≥ 10° valgus). In patients with advanced genu varum deformity (preoperative MA ≥ 15° varus), CAS-TKA did not improve the femoral rotational alignment.

Correction of orbital wall fracture close to the optic canal using computer-assisted navigation surgery

BACKGROUND

Repairing orbital wall fractures can result in serious complications, including enophthalmos, diplopia, or even blindness. Especially, surgeons worry about damaging the optic nerve while dissecting the optic canal area. We avoid these complications by using a navigation system that was adapted to stereotactic concept based on three-dimensional imaging of the patient's anatomy. Here, we report 5 cases of orbital wall fracture that were repaired using a navigation system.

METHODS

The Navigation System II (Stryker, Freiburg, Germany) and the iNtellect Cranial Navigation (version 1.1) platform were used for each operation. A computer-assisted navigation surgery was performed according to the following procedures: (1) image set, (2) planning, (3) apparatus setup, (4) registration, and (5) intraoperative navigation. Operations were performed under general anesthesia. Dissection was performed up to the periosteum immediately anterior to the optic canal, near the fracture. Vulnerable surrounding structures were identified with the intraoperative pointer. After navigation, we inserted an implant into the defect, successfully, avoiding damage to the optic canal and optic nerve.

RESULTS

None of the patients had any surgical complications. Postoperative computed tomography scans demonstrated that the fractures were corrected, and continuity was maintained without displacement. The three-dimensional image allowed us to easily visualize intraoperative anatomical structure, allowing us to avoid unnecessary procedures and to correct the orbital wall. The mean volume of fractured orbital cavity was 29.2 cm(3) (range, 28.3-30.4 cm(3)) preoperatively and 27.0 cm(3) (range, 25.9-28.5 cm(3)) postoperatively; thus, the defects were corrected by 2.2 cm(3) (range, 1.3-2.8 cm(3)) on average.

CONCLUSIONS

We used a navigation system to perform accurate and safe surgery in patients with extensive orbital wall fracture, including around the optic canal. By using the functions to visualize the locations indicated by the pointer, we were able to perform successful dissections and implantations in areas adjacent to the optic canal. The good outcomes obtained here provide evidence that surgical correction of the orbital wall using a navigation system is useful in cases of deep, extensive orbital wall fracture.

Subject-specific finite element model with an optical tracking system in total hip replacement surgery

Intra-operative peri-prosthetic femoral fractures are a significant concern in total hip arthroplasty and can occur at any time during surgery, with the highest incidence during implant insertion. This study combines subject-specific finite element analysis modeling with an optical tracking system to characterize the resultant strain in the bone and results of impaction during total hip replacement surgery. The use of ABG II femoral stem (Stryker Orthopaedics, Mahwah, NJ, USA) in the model yielded the following results. Hammer velocity was measured experimentally using a three-dimensional optical tracking system and these data were input into the finite element analysis model so that intra-operative loading scenario could be simulated. A quasi-static explicit simulation and a dynamic loading step using two implant-bone interface friction (0.1 and 0.4 friction coefficients) states were simulated. The maximum swing velocity of a mallet was experimentally measured at 1.5 m/s and occurred just before impaction of the hammer with implant introducer. Two friction states resulted in different results with the lower friction coefficient generating higher strains in the anterior regions of the model and higher displacement of the implant with respect to the femur when compared to the high friction state.

Limited femoral navigation versus conventional intramedullary femoral jig based instrumentation for achieving optimal restoration of mechanical axis post total knee arthroplasty: a prospective comparative study of 200 knees

A prospective comparative study was conducted to compare the mechanical axis post total knee arthroplasty (TKA) between two groups: In the first group of 100 knees (ASM group) Articular Surface Mounted navigation system was used to guide the distal femoral cut. In the second group of 100 knees (JIG group) conventional intramedullary femoral jig was used. The postoperative mechanical axis of the leg was within 3° of neutral alignment in 90% of the TKA in the ASM group (mean 178.12°) as compared to 74% in the JIG group (mean 177.02°). This difference was statistically significant (P<0.05). The data presented show that the use of limited femoral navigation leads to more accurate restoration of mechanical axis alignment when compared to conventional intramedullary femoral jigs.

Short-term outcome after computer-assisted versus conventional total knee arthroplasty: a randomised controlled trial

PURPOSE

To compare the short-term functional outcome after computer-assisted total knee arthroplasty (TKA) versus conventional TKA.

METHODS

23 men and 67 women aged 48 to 80 years were randomised to undergo (1) conventional TKA using an intramedullary guide, (2) conventional TKA using an extramedullary guide, or (3) computer-assisted TKA. Two senior surgeons performed all the TKAs using the same TKA system and the standard anteromedial arthrotomy with eversion of the patella. Patients were assessed by physiotherapists before and 6 months and 2 years after TKA using the Short Form-36 Health Survey, Oxford Knee Score, and Knee Society Score.

RESULTS

Of the 90 patients, 67 and 70 were assessed at 6 months and 2 years after TKA, respectively. No patient developed deep infection or required revision surgery. Functional outcomes of the 3 groups did not differ significantly at the corresponding follow-ups.

CONCLUSION

Significant improvement in the functional outcome was not shown in patients treated with computer-assisted TKA, compared with conventional TKA. Thus, computer-assisted TKA has limited additional short-term benefits. Further studies with longer follow-up are required to examine the benefits of computer-assisted TKA.

Inconsistencies between navigation data and radiographs in total knee arthroplasty are system-dependent and affect coronal alignment

BACKGROUND

Few studies have compared the effect of different computer navigation systems on postoperative alignment in patients who have had total knee arthroplasty (TKA). We examined 2 computed tomography (CT)-free computer navigation systems by comparing the accuracy of intraoperative measurements to postoperative alignment.

METHODS

Patients underwent unilateral TKA performed by a single surgeon using 1 of 2 CT-free navigation systems. We compared final intraoperative tibial and femoral coronal angles and mechanical axis with the same angles measured on standing postoperative radiographs.

RESULTS

Groups of 31 and 50 patients underwent TKA with the 2 systems, respectively. We noted a significant difference in the coronal tibial implant angle (1.29º ± 1.35º) and in the mechanical axis (1.59º ± 2.36º) for one navigation system (both p < 0.001), while only the coronal tibial implant angle showed a significant difference (1.17º ± 1.65º, p < 0.001) for the second system. The number of radiographic outliers also significantly differed. A significantly higher proportion (32%; p < 0.01) of patients in the second cohort exhibited unacceptable malalignment compared with the first cohort (24%).

CONCLUSION

Navigation systems for TKA continue to increase in sophistication and popularity. Owing to the significant difference in the proportion of alignment outliers in the 2 navigation systems tested in this study, orthopedic surgeons should not consider all TKA navigation systems equivalent. Additional investigations are needed to compare the accuracy of a variety of CT-free and CT-based navigation systems and to confirm our finding that accuracy is system-dependent.