Joint line is well restored when navigation surgery is performed for total knee arthroplasty

Can Computer-Assisted Total Knee Arthroplasty Support the Prediction of Postoperative Three-Dimensional Kinematics of the Tibiofemoral and Patellofemoral Joints at the Replaced Knee?

The aim of this study was to analyze the extent to which postoperative patellofemoral joint (PFJ) kinematics assessed at 6-month follow-up after total knee arthroplasty (TKA) mimics the intraoperative kinematics after final component implantation. The study hypothesis, already proved in terms of tibiofemoral joint (TFJ) kinematics, is that the intraoperative assessment of PFJ kinematics after component implantation is also capable of predicting postoperative knee kinematics during activities of daily living. Twenty patients selected for TKA with patellar resurfacing were implanted using surgical navigation, including patellar component positioning via a novel computer-assisted procedure. This allowed for intraoperative TFJ and PFJ kinematic assessment after final component implantation. At 6-month follow-up, all patients were contacted for follow-up control; in addition to clinical examination, this implied postoperative kinematics assessments by three-dimensional video fluoroscopy of the replaced knee during standard activities of daily living. Several traditional PFJ, as well as TFJ, rotations and translations were calculated intra- and postoperatively and then statistically compared. Good postoperative replication of the intraoperative measurements was observed for most of PFJ variables analyzed, as well as those for TFJ. Relevant statistical analysis also supported the significant consistency between the intra- and postoperative measurements. Pertaining to the present findings on a statistical basis, intraoperative measurements performed at both TFJ and PFJ kinematics using a surgical navigation system under passive conditions, are predictive of the overall knee kinematics experienced at postoperative follow-ups by the same replaced knees in typical activities of daily living.

Biomechanical-Based Protocol for in vitro Study of Cartilage Response to Cyclic Loading: A Proof-of-Concept in Knee Osteoarthritis

Osteoarthritis (OA) is an evolving disease and a major cause of pain and impaired mobility. A deeper understanding of cartilage metabolism in response to loading is critical to achieve greater insight into OA mechanisms. While physiological joint loading helps maintain cartilage integrity, reduced or excessive loading have catabolic effects. The main scope of this study is to present an original methodology potentially capable to elucidate the effect of cyclic joint loading on cartilage metabolism, to identify mechanisms involved in preventing or slowing down OA progression, and to provide preliminary data on its application. In the proposed protocol, the combination of biomechanical data and medical imaging are integrated with molecular information about chondrocyte mechanotransduction and tissue homeostasis. The protocol appears to be flexible and suitable to analyze human OA knee cartilage explants, with different degrees of degeneration, undergoing ex vivo realistic cyclic joint loading estimated via gait analysis in patients simulating mild activities of daily living. The modulation of molecules involved in cartilage homeostasis, mechanotransduction, inflammation, pain and wound healing can be analyzed in chondrocytes and culture supernatants. A thorough analysis performed with the proposed methodology, combining in vivo functional biomechanical evaluations with ex vivo molecular assessments is expected to provide new insights on the beneficial effects of physiological loading and contribute to the design and optimization of non-pharmacological treatments limiting OA progression.

Does navigated patellar resurfacing in total knee arthroplasty result in proper bone cut, motion and clinical outcomes?

BACKGROUND

In total knee arthroplasty with patellar resurfacing, patellar bone preparation, component positioning and motion assessments are still not navigated. Only femoral/tibial component positioning is supported by computer-assistance. The aim of this study was to verify, in-vivo, whether knee surgical navigation extended to patellar resurfacing, by original instrumentation and procedures for patellar-based tracking, could achieve accurate patella preparation in terms of original thickness restoration, bone cut orientation, and normal knee motion.

METHODS

An additional navigation system for patellar data acquisition was used together with a standard navigation system for total knee arthroplasty in 20 patients. This supported the surgeon for patellar resurfacing via measurement of removed bone thickness, three-dimensional patellar cut orientations, and patello-femoral motion. Radiological and clinical examinations at 6 and 24-month follow-up were also performed.

FINDINGS

The medio-lateral patellar-bone cut orientation was respectively 0.5° (standard deviation: 3.0°) and 1.4° (1.7°) lateral tilt, as measured via navigation and post-operatively on the Merchant x-ray view. The cranio-caudal orientation was 3.8° (7.2°) of flexion. The thickness variation between patellar pre- and post-implantation was 0.2 (1.3) mm. Immediately after implantation, patello-femoral as well as tibio-femoral kinematics was within the normality. Good radiological and clinical examinations at 6 and 24-month follow-up were also observed.

INTERPRETATION

For the first time, the effect of patellar navigation for its resurfacing was assessed in-vivo during surgery, with very good results for thickness restoration, proper cut orientation, and normal knee motion. These results support the introduction of patella-related navigation-based surgical procedures for computer-assisted total knee arthroplasty.

New comprehensive procedure for custom-made total ankle replacements: Medical imaging, joint modeling, prosthesis design, and 3D printing

Many failures in total joint replacement are associated to prosthesis-to-bone mismatch. With recent additive-manufacturing, that is, 3D-printing, custom-made prosthesis can be created by laser-melting metal powders layer-by-layer. Ankle replacement is particularly suitable for this progress because of the limited number of sizes and the poor bone stock. In this study a novel procedure is presented for subject-specific ankle replacements, including medical-imaging, joint modelling, prosthesis design, and 3D-printing. Three shank-foot specimens were CT-scanned, and corresponding 3D bone models of the tibia, fibula, talus, and calcaneus were obtained. From these models, specimen-specific implant sets were designed according to three different concepts, and 3D-printed from cobalt-chromium-molybdenum powder. Accuracy of the overall procedure was assessed via distance map comparisons between original anatomical and final metal implants. Restoration of natural ankle joint mechanics was check after implantation of each of the three sets. In a special rig, a manually-driven dorsi/plantar-flexion was applied throughout the passive arc. Additionally, at three different joint positions, joint torques were imposed in the frontal and axial anatomical planes. Mean manufacturing errors were found to be smaller than 0.08 mm. Consistent motion patterns were observed over repetitions, with the mean standard deviation smaller than 1.0 degree. In each ankle specimen, mobility, and stability at the replaced joints compared well with the original natural condition. For the first time, custom-made implants for total ankle replacements were designed, manufactured with additive technology and tested. This procedure is a first fundamental step toward the development of completely personalized prostheses. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Raising the Joint Line in TKA is Associated With Mid-flexion Laxity: A Study in Cadaver Knees

BACKGROUND

In a typical osteoarthritic knee with varus deformity, distal femoral resection based off the worn medial femoral condyle may result in an elevated joint line. In a setting of fixed flexion contracture, the surgeon may choose to resect additional distal femur to obtain extension, thus purposefully raising the joint line. However, the biomechanical effect of raising the joint line is not well recognized.

QUESTIONS/PURPOSES

(1) What is the effect of the level of the medial joint line (restored versus raised) on coronal plane stability of a TKA? (2) Does coronal alignment technique (mechanical axis versus kinematic technique) affect coronal plane stability of the knee? (3) Can the effect of medial joint-line elevation on coronal plane laxity be predicted by an analytical model?

METHODS

A TKA prosthesis was implanted in 10 fresh frozen nonarthritic cadaveric knees with restoration of the medial joint line at its original level (TKA0). Coronal plane stability was measured at 0°, 30°, 60°, 90°, and 120° flexion using a navigation system while applying an instrumented 9.8-Nm varus and valgus force moment. The joint line then was raised in two steps by recutting the distal and posterior femur by an extra 2 mm (TKA2) and 4 mm (TKA4), downsizing the femoral component and, respectively, adding a 2- and a 4-mm thicker insert. This was done with meticulous protection of the ligaments to avoid damage. Second, a simplified two-dimensional analytical model of the superficial medial collateral ligament (MCL) length based on a single flexion-extension axis was developed. The effect of raising the joint line on the length of the superficial MCL was simulated.

RESULTS

Despite that at 0° (2.2° ± 1.5° versus 2.3° ± 1.1° versus 2.5° ± 1.1°; p = 0.85) and 90° (7.5° ± 1.9° versus 9.0° ± 3.1° versus 9.0° ± 3.5°; p = 0.66), there was no difference in coronal plane laxity between the TKA0, TKA2, and TKA4 positions, increased laxity at 30° (4.8° ± 1.9° versus 7.9° ± 2.3° versus 10.2° ± 2.0°; p < 0.001) and 60° (5.7° ± 2.7° versus 8.8° ± 2.9° versus 11.3° ± 2.9°; p < 0.001) was observed when the medial joint line was raised 2 and 4 mm. At 30°, this corresponds to an average increase of 64% (3.1°; p < 0.01) in mid-flexion laxity with a 2-mm raised joint line and a 111% (5.4°; p < 0.01) increase with a 4-mm raised joint line compared with the 9-mm baseline resection. No differences in coronal alignment were found between the knees implanted with kinematic alignment versus mechanical alignment at any flexion angle. The analytical model was consistent with the cadaveric findings and showed lengthening of the superficial MCL in mid-flexion.

CONCLUSIONS

Despite a well-balanced knee in full extension and at 90° flexion, increased mid-flexion laxity in the coronal plane was evident in the specimens where the joint line was raised.

CLINICAL RELEVANCE

When recutting the distal and posterior femur and downsizing the femoral component, surgeons should be aware that this action might increase the laxity in mid-flexion, even if the knee is stable at 0° and 90°.

Three-dimensional patellar tendon fibre kinematics in navigated TKA with and without patellar resurfacing

PURPOSE

Physiological elongation and orientation of patellar tendon fibres are among the scopes of total knee arthroplasty, but little is known in the three dimensions. The study aims to assess in vitro these variations at the intact and replaced knee, with and without patellar resurfacing. It was hypothesised that fibre patterns differ before and after prosthesis implantation, and between specific prosthesis designs. It was also expected that patellar resurfacing would affect relevant results.

METHODS

Measurements from 16 intact cadaver knees free from anatomical defects are here reported using a surgical navigation system. Data were collected at the intact joint and after implantation with cruciate-retaining or posterior-stabilised prosthesis designs, with and without patellar resurfacing. Relevant anatomical landmarks and patellar tendon attachments were digitised. Anatomical reference frames in the femur, tibia and patella were defined to measure component implantation parameters. Representative tendon fibres were defined as the straight line segments joining the two extremities. Changes in length and orientation of these fibres were calculated and reported versus flexion at the intact knee and after prosthesis implantation, both with and without patellar resurfacing.

RESULTS

A good intra- and inter-specimen repeatability was found at the intact and replaced knees. In both prosthesis designs, the patterns of fibre lengthening were similar to those in the intact knee, though significant differences were observed before and after patellar resurfacing. Corresponding fibre orientations in the frontal and sagittal planes showed significantly smaller ranges than those in the corresponding intact joints. More natural patterns were observed in the knees implanted with the posterior-stabilised design. Significant correlations were identified between patellar component implantation parameters and both patellar tendon fibre elongation and orientation.

CONCLUSIONS

Differences, however small, in patellar tendon fibre elongation and orientation were observed after total knee arthroplasty. The posterior-stabilised design provided better results, whereas patellar resurfacing affected significantly normal patellar function. In the clinical practice, the present findings can contribute to the understanding of current prosthesis designs and patellar resurfacing, recommending also enhanced care during this surgery.

Importance of joint line preservation in unicompartmental knee arthroplasty: Finite element analysis

Unicompartmental knee arthroplasty (UKA) is an effective surgical technique for pain relief and functional restoration in patients with localized osteoarthritis of the knee joint. However, the role of the joint line in UKA, especially its biomechanical effect, has not been previously investigated. This study numerically evaluates the effects of the joint line on the contact stresses in polyethylene (PE) inserts, articular cartilage, and lateral meniscus using the finite element (FE) analysis. The FE model for joint line was modeled as the orthogonal projection line from the medial tibial plateau to the anatomical axis. The joint line was varied from -6 to +6 mm in 2 mm intervals, and the seven FE models were analyzed and compared under ISO gait loading conditions. The contact stresses in the PE insert, articular cartilage, and lateral meniscus matched those of the reference joint line (0 mm) in the ±2 and ±4 mm joint line cases but significantly differed from the reference in the ±6 mm joint line cases. On the +6 mm joint line, the contact stress was greater on the PE insert than on the articular cartilage, whereas the reverse occurred on the -6 mm joint line. This study confirms the post-operative significance of joint line preservation in UKA implantation surgery. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:347-352, 2017.

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.

Total knee arthroplasty in patients with Ranawat type-II valgus arthritic knee with a marked coronal femoral bowing deformity: comparison between computer-assisted surgery and intra-articular resection

Background

Proper limb and component alignments as well as soft tissue balance are vital for the longevity and optimal long-term outcomes of total knee arthroplasty (TKA). This procedure is technically demanding in patients with Ranawat type-II valgus arthritic knees with marked coronal femoral bowing. Computer-assisted surgery (CAS) and intra-articular bone resection with TKA are the treatments of choice for patients with ipsilateral extra-articular deformity. In theory, both CAS and intra-articular bone resection are beneficial in Ranawat type-II valgus arthritic knees with marked coronal femoral bowing deformity, but the literature on this topic is sparse. We compared the benefits of using these two techniques for TKA under this circumstance.

Methods

Patients who had Ranawat type-II valgus arthritic knees and marked coronal femoral bowing deformity and had undergone TKA at our hospital between 2005 and 2013 were enrolled in this retrospective study. Patients treated with CAS were assigned to the CAS-TKA group; patients treated with intra-articular bone resection were assigned to the Bone-Resect-TKA group. Radiographic parameters and clinical outcomes (International Knee Society (IKS) scores and patellar scores) in both groups were compared.

Results

Forty-seven patients (50 knees) met the inclusion criteria: 22 knees in the CAS-TKA group and 28 knees in the Bone-Resect-TKA group. Lateral retinaculum release was significantly (P = 0.008) higher in the Bone-Resect-TKA group. The joint-line was significantly properly restored in the CAS-TKA group (P = 0.011). The reconstructed mechanical axis was significantly (P = 0.012) closer to normal in the CAS-TKA group than in the Bone-Resect-TKA group. For component alignment, the femoral valgus and femoral flexion angles were significantly better in the CAS-TKA group (P = 0.002 and P = 0.006, respectively), but not the tibial valgus, tibial flexion, or patellar tilting angles. IKS scores and patellar scores were not significantly different between groups at a mean follow-up of 60.2 months.

Conclusions

CAS-TKA was effective for obtaining proper alignment and joint-line restoration in patients with Ranawat type-II valgus arthritic knees and marked coronal femoral bowing deformity, but not for yielding better clinical outcomes. Additional large-scale prospective randomized cohort studies with long-term follow-ups are necessary to make evidence-based recommendations.

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.

Are joint line changes after primary navigated total knee arthroplasty predictable?

BACKGROUND

Navigation systems have been successful in reducing the outlier of leg alignment after total knee arthroplasty (TKA). Less is known about the restoration of the anatomical joint line with computer-assisted knee replacement. The aim of this study was to determine whether joint line changes <3 or ≥3 mm are predictable with several pre- and intraoperative parameters.

METHODS

The study included a total of 180 cases of primary computer-assisted TKA performed using the gap-balancing/tibia-first technique. The final shift of the joint line was calculated using computer verification of proximal tibial and distal femoral cuts. In consideration of the clinical relevance of a 3-mm joint line shift, patients were stratified into two groups: Group I, with joint line change <3 mm, and Group II, with joint line change ≥3 mm. Between groups, variables such as demographics, Kellgren & Lawrence degree of osteoarthritis, preoperative flexion contracture, pre-/intraoperative mechanical leg alignment, flexion/extension gaps, and implant design/sizes were compared statistically.

RESULTS

The absolute joint line shift averaged 1.6 ± 1.3 mm (range 0-6 mm). A joint line shift ≥3 mm was observed in 28 cases (15 %). A statistically significant difference between groups was not identified for any of the parameters. Shift of the joint line did not correlate with the analyzed variables.

CONCLUSIONS

Joint line was adequately restored when computer navigation was carefully applied as a measuring tool for primary TKA. Knee joint deformity, leg alignment, gap balance, and implant type did not aid in predicting the joint line shift.

Computed tomography evaluation in total knee arthroplasty: computer-assisted navigation versus conventional instrumentation in patients with advanced valgus arthritic knees

Arthritic knees with advanced valgus deformity present with soft tissue and osseous anomalies that make total knee arthroplasty (TKA) difficult. We conducted a retrospective chart review of 41 patients (51 knees) to determine whether computer-assisted surgery-TKA (CAS-TKA) is superior to TKA using conventional guiding systems. A significantly higher rate of lateral retinaculum release as well as outlier of sagittal mechanical axes and position of the femoral component (femoral flexion and femoral rotational angle) was recorded in the conventional TKA group versus the CAS-TKA group. Both groups had significant postoperative improvement in clinical performance, but results did not differ significantly between groups. Despite its radiographic benefit, CAS-TKA showed no significant benefit over TKA in short-term clinical functional outcomes when performed by an experienced surgeon.

Comparison of computer-navigated and conventional total knee arthroplasty in patients with Ranawat type-II valgus deformity: medium-term clinical and radiological results

Background

Arthritic knees with Ranawat type-II valgus deformity present with soft tissue contracture and osseous anomalies that make total knee arthroplasty (TKA) difficult. We hypothesized that computer-navigated-TKA (CN-TKA) may be superior to conventional techniques and provide better mid-term radiographic and clinical outcomes in such cases.

Methods

Between January 2002 and January 2009, patients with Ranawat type-II valgus deformity who underwent primary TKA were entered into this retrospective study. Conventional TKA and CN-TKA were compared for the accuracy of component placement, joint line level, and postoperative limb alignment. International Knee Society scores and patellar scores were used for clinical assessment.

Results

A total of 62 patients (70 knees) with a minimum of 5 years of follow-up were studied. Conventional TKA was performed in 36 knees and CN-TKA in 34 knees. A significantly higher rate of lateral retinaculum release was recorded in the conventional TKA group compared to the CN-TKA group. Proper restoration of joint line was achieved using CN-TKA. The range of motion of the knees was similar in both groups preoperative and postoperatively. There were no significant differences in reconstructed mechanical axes, accuracy of component positioning, and difference in perioperative hemoglobin level between the two groups. At a mean follow-up of 6.2 years, both groups had significant postoperative improvements in clinical performance, however the difference did not reach statistical significance between both techniques.

Conclusions

Our findings demonstrate that CN-TKA can properly restored the joint line level for arthritic knees with Ranawat type II valgus deformity. However, no differences in clinical function, limb and component alignment, or survival of the prostheses were noted between the CN-TKA and conventional TKA groups at a mean follow-up of 6.2 years.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-390) contains supplementary material, which is available to authorized users.

Tibio-femoral and patello-femoral joint kinematics during navigated total knee arthroplasty with patellar resurfacing

PURPOSE

In total knee arthroplasty, surgical navigation systems provide tibio-femoral joint (TFJ) tracking for relevant bone preparation, disregarding the patello-femoral joint (PFJ). Therefore, the important intra-operative assessment of the effect of component positioning, including the patella, on the kinematics of these two joints is not available. The objective of this study is to explore in vivo whether accurate tracking of the patella can result in a more physiological TFJ and PFJ kinematics during surgery.

METHODS

Ten patients underwent navigated knee replacement with patellar resurfacing. A secondary system was used to track patellar motion and PFJ kinematics using a special tracker. Patellar resection plane position and orientation were recorded using an instrumented probe. During all surgical steps, PFJ kinematics was measured in addition to TFJ kinematics.

RESULTS

Abnormal PFJ motion patterns were observed pre-operatively at the impaired knee. Patellar resection plane orientation on sagittal and transverse planes of 3.9° ± 9.0° and 0.4° ± 4.1° was found. A good restoration of both TFJ and PFJ kinematics was observed in all replaced knees after resurfacing, in particular the rotations in the three anatomical planes and medio-lateral patellar translation.

CONCLUSIONS

Patella tracking results in nearly physiological TFJ and PFJ kinematics in navigated knee arthroplasty with resurfacing. The intra-operative availability also of PFJ kinematics can support the positioning not only of the patellar component in case of resurfacing, but also of femoral and tibial components.

A method for assessing joint line shift post knee arthroplasty considering the preoperative joint space

BACKGROUND

Accurate comparison of outcomes regarding various surgical options in knee arthroplasty can benefit from an improved method for joint line analysis that takes into account the preoperative joint space.

METHODS

This article describes a new preoperative-based registration method that measures changes in the joint line by overlaying the 3D models of the bones with implants using preoperative CT along with preoperative and postoperative biplanar radiography. The method was tested on six cadaveric specimens for measuring alteration to the medial and lateral joint lines in extension and flexion.

RESULTS

The joint line shift, when measured using the new method, was in the range of -0.2 to 1.3 mm on average (SD=1.3 to 3.8 mm, for medial and lateral, in flexion and extension positions). This was significantly different (p≤0.01) from the results of a previous postoperative-based registration method which did not account for the cartilage thickness in calculating alterations of the joint line (mean=3.9 to 6.8mm, SD=1.2 to 4.3 mm).

CONCLUSION

These results further highlight the importance of considering the preoperative joint space in analyzing the joint line, and demonstrate the utility of the newly introduced method for accurate assessment of changes in the joint line after arthroplasty.

CLINICAL RELEVANCE

The introduced method provides accurate means for investigating joint line alterations in relation to different surgical techniques and the subsequent biomechanical effects after knee arthroplasty.

Three-dimensional implant position and orientation after total knee replacement performed with patient-specific instrumentation systems

Patient-specific instrumentation systems are entering into clinical practice in total knee replacement, but validation tests have yet to determine the accuracy of replicating computer-based plans during surgery. We performed a fluoroscopic analysis to assess the final implant location with respect to the corresponding preoperative plan. Forty-four patients were analyzed after using a patient-specific system based on CT and MRI. Computer aided design implant models and models of the femur and tibia bone portions, as for the preoperative plans, were provided by the manufacturers. Two orthogonal fluoroscopic images of each knee were taken after surgery for pseudo-biplane imaging; 3D component locations with respect to the corresponding bones were estimated by a shape-matching technique. Assuming that the corresponding values at the preoperative plan were equal to zero, discrepancies were taken as an indication of accuracy for the systems. A repeatability test revealed that the technique was reliable within 1 mm and 1°. The maximum discrepancies for all the patients for the femoral component were 5.9 mm in a proximo-distal direction and 4.2° in flexion. Good matching was found between final implantations and preoperative plans with mean discrepancies smaller than 3.1 mm and 1.9°.

Joint line changes after primary total knee arthroplasty: navigated versus non-navigated

PURPOSE

Navigation has been introduced to achieve more accurate positioning of the implants after TKA. The scientific attention was mainly paid on limb alignment rather than restoration of the natural joint line. The aim of our study was to compare the accuracy of the joint line restoration in primary TKA with and without navigation. We hypothesized that joint line reconstruction in navigated TKA is more accurate.

METHODS

A total of 493 primary TKAs operated in a single medical centre were consecutively selected and divided into two groups. 206 cases were performed computer assisted (BrainLab CI-System), whereas 287 knees were implanted conventionally. For both groups, the joint line position of the knee was determined on standardized calibrated standing pre- and postoperative digital radiographs in ap view by a modified method of Kawamura et al. A joint line shift of more than 8 mm was defined as outlier.

RESULTS

In the conventional group, the joint line shift averaged 0.7 mm (±4.4 mm), whereas the findings in the computer-assisted cases were in average 0.6 mm (±4.5 mm). The joint line was located above 8 mm in 6 % of non-navigated versus 6.8 % of navigated primary TKAs. There were no statistically significant differences of joint line shift between the different component types. A statistically significant relation was not found between joint line shift and leg alignment changes.

CONCLUSIONS

Conventional surgical technique allows a precise joint line reconstruction in primary TKA. Navigation did not improve the joint line reconstruction.

LEVEL OF EVIDENCE

Diagnostic study, Level III.

Joint line changes in cruciate-retaining versus posterior-stabilized computer-navigated total knee arthroplasty

INTRODUCTION

This study compared joint line changes and functional outcomes between cruciate-retaining (CR) and posterior-stabilized (PS) computer-navigated total knee arthroplasties (TKAs). With the increased precision offered by computer navigation, we hypothesized that there should be minimal differences in the joint line changes between the groups and thus no significant differences in the clinical outcomes.

MATERIALS AND METHODS

A retrospective study of 195 patients with a minimum of 2-year follow-up following primary surgery was conducted. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups.

RESULTS

CR knees had a significantly lesser mean joint line change of 1.70 mm as compared to 2.34 mm in PS knees (p = .04) but the absolute difference was only 0.64 mm. The PS group had significantly better final range of motion of 122° (±9.9°) as compared to 114° (±15.0°) in the CR group (p < .0001). There were no significant differences in the final outcome scores.

CONCLUSION

Although there is a significant difference statistically in the joint line changes between the groups, this difference is less than 1 mm and probably has no significant clinical impact. This is further affirmed by the fact that there was no significant difference in the clinical outcomes. The increased range seen in PS knees is probably not related to joint line changes.

LEVEL OF EVIDENCE

III.