Influence of intramedullary versus extramedullary alignment guides on final total knee arthroplasty component position: a radiographic analysis

The Alignment of the Tibial Component in Total Knee Arthroplasty: Is a Technology-Assisted System Better Than Conventional Instrumentation?

Background Technologies such as navigation and robotics are aimed at improving tibial alignment in total knee arthroplasties (TKA) and eliminating the errors resulting from the use of manual instrumentation. Methods This prospective study analyzed 130 arthroplasties in order to determine whether navigation can improve the frontal mechanical axis of the tibia and whether the postoperative angulation of this axis differs from the preoperative one. The mean patient age was 71.8 years, and the mean BMI was 31.17. Eighty-six patients were female. The same cemented TKA model and the same imageless navigation system were used in all cases. Results The mean postoperative tibial angle following implantation was 87.65°, without any statistically significant differences with respect to the previous angulation. However, navigation was seen to result in a nearly neutral tibial axis, a larger number of cases (41.5%-60.8% {p = 0.002}) aligned within the safe zone (90° ± 3°), a smaller number of outliers, and a clustering of values around the mean. Conclusions Navigation improves the frontal positioning of the tibial component in total knee arthroplasties but does not offer any advantages as compared with conventional instrumentation.

Tibial Cut Accuracy in Mechanically Aligned Total Knee Arthroplasty Using Extensor Hallucis Longus Tendon to Determine Extramedullary Tibial Guide Position

This study aimed to determine the tibial cut (TC) accuracy using extensor hallucis longus (EHL) tendon as an anatomical landmark to position the total knee arthroplasty (TKA) extramedullary tibial guide (EMTG), and its impact on the TKA mechanical alignment (MA). We retrospectively studied 96 TKA, performed by a single surgeon, using a femoral tailored intramedullary guide technique. Seventeen were prior to the use of the EHL and 79 used the EHL tendon to position the EMTG. We analyzed preoperative and postoperative standing total lower extremity radiographs to determine the tibial component angle (TCA) and the correction in MA, comparing pre-EHL use and post-EHL technique incorporation. Mean TCA was 88.89 degrees and postoperative MA was neutral in 81% of patients. Pre- and postoperative MAs were not correlated. As a conclusion of this study, using the EHL provides a safe and easy way to determine the position of EMTG.

The position of entry point in total knee arthroplasty is associate with femoral bowing both in coronal and sagittal planes

Objective

To investigate the femoral entry point of the intramedullary (IM) guiding rod applied to total knee arthroplasty (TKA) in Chinese subjects and the relationship with femoral bowing in the coronal and sagittal planes through three-dimensional (3D) validation methods.

Methods

Computed tomography (CT) images of 80 femurs in Chinese subjects were imported into Mimics 19.0 to construct 3D models. All operations were conducted by Rhinoceros software 5.0. The position of the IM rod entry point was assessed by calculating the distance between the entry point and the apex of the intercondylar notch (AIN) in the coronal and sagittal planes. The coronal femoral bowing angle (cFBA) and sagittal femoral bowing angle (sFBA) were also measured.

Results

The average optimal entry point was 0.17 mm medial and 12.37 mm anterior to the AIN in males, while it was 0.02 mm lateral and 16.13 mm anterior to the AIN in females. There was a significant difference between males and females in the sagittal plane (t = -6.570, p = 0.000). The mean cFBA was 1.68 ± 2.29°, and the mean sFBA was 12.66 ± 1.98°. The sFBA was strongly correlated with the anterior distance of the proper entry point, and the cFBA was moderately correlated with the lateral distance of the proper entry point.

Conclusions

There was a strong correlation between the position of the entry point and the femoral bowing angle in both the coronal and sagittal planes. Thus, to achieve better alignment, the position of the entry point should be measured individually based on femoral bowing.

Patient satisfaction following total knee arthroplasty using restricted kinematic alignment

AIMS

Alternative alignment concepts, including kinematic and restricted kinematic, have been introduced to help improve clinical outcomes following total knee arthroplasty (TKA). The purpose of this study was to evaluate the clinical results, along with patient satisfaction, following TKA using the concept of restricted kinematic alignment.

METHODS

A total of 121 consecutive TKAs performed between 11 February 2018 to 11 June 2019 with preoperative varus deformity were reviewed at minimum one-year follow-up. Three knees were excluded due to severe preoperative varus deformity greater than 15°, and a further three due to requiring revision surgery, leaving 109 patients and 115 knees to undergo primary TKA using the concept of restricted kinematic alignment with advanced technology. Patients were stratified into three groups based on the preoperative limb varus deformity: Group A with 1° to 5° varus (43 knees); Group B between 6° and 10° varus (56 knees); and Group C with varus greater than 10° (16 knees). This study group was compared with a matched cohort of 115 TKAs and 115 patients using a neutral mechanical alignment target with manual instruments performed from 24 October 2016 to 14 January 2019.

RESULTS

Mean overall patient satisfaction for the entire cohort was 4.7 (SE 0.1) on a 5-point Likert scale, with 93% being either very satisfied or satisfied compared with a Likert of 4.3 and patient satisfaction of 81% in the mechanical alignment group (p < 0.001 and p < 0.006 respectively). At mean follow-up of 17 months (11 to 27), the mean overall Likert, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, Western Ontario and McMaster Universities Osteoarthritis Index, Forgotten Joint Score, and Knee Society Knee and Function Scores were significantly better in the kinematic group than in the neutral mechanical alignment group. The most common complication in both groups was contracture requiring manipulation under anaesthesia, involving seven knees (6.1%) in the kinematic group and nine knees (7.8%) in the mechanical alignment group.

CONCLUSION

With the advent of advanced technology, and the ability to obtain accurate bone cuts, the target limb alignment, and soft-tissue balance within millimetres, using a restricted kinematic alignment concept demonstrated excellent patient satisfaction following primary TKA. Longer-term analysis is required as to the durability of this method. Cite this article: Bone Joint J 2021;103-B(6 Supple A):59-66.

Intra- and inter-observer reliability of implant positioning evaluation on a CT-based three-dimensional postoperative matching system for total knee arthroplasty

Background

The evaluation of postoperative total knee arthroplasty (TKA) alignment mainly relies on measurement data obtained from plain radiographs. The aim of this retrospective observational study was to document the intra- and inter-observer reliability in assessment of TKA component positioning after surgery using a three-dimensional (3D) computed tomography (CT) image matching system.

Methods

Fourteen knees from 14 patients who received primary TKA were included, and images were analyzed by blinded readers not associated with the surgeries. The examiner digitized the reference points according to defined landmarks, and the designated size component was superimposed to the 3D reconstructed CT model for measurement. In addition to the evaluation of implant position against the coronal and sagittal lower limb mechanical axes that were defined based on bony landmarks, implant position against axes connecting implant-based reference points that are easier to indicate was evaluated.

Results

The overall intra- and inter-observer reliabilities determined by the intraclass correlation coefficients (ICC) of the implant alignment measurement for both femoral and tibial components were good (ICC > 0.60), except in the direction of femoral flexion and extension, for both mechanical and implant-based axes. The difference between implant alignment measurements according to the traditional mechanical axis and the implant-based axis ranged between means of 0.08^o and 1.70^o and were statistically significantly different.

Conclusions

The postoperative evaluation of implant position in the coronal and sagittal planes using 3D-CT image matching is reliable and has good reproducibility except for the sagittal alignment assessment of the femoral component. The measured implant position according to the traditional mechanical axis and the implant-based axis were slightly but significantly different.

Extensor hallucis longus tendon is a new distal landmark for coronal tibial component alignment in total knee arthroplasty: A study of magnetic resonance imaging

PURPOSE

In total knee arthroplasty (TKA), various landmarks are generally used to ensure correct osteotomy. In this study, we examined whether the tibialis anterior tendon (TAT) or the extensor hallucis longus tendon (EHLT) could be used as a landmark of the center of the ankle joint in patients with knee osteoarthrosis (OA), using magnetic resonance imaging (MRI).

METHODS

The subjects were 61 patients with OA in 79 knees (males: 8 with 9 knees and females: 53 with 70 knees). With the ankle joint secured in the intermediate position, MRI from the knee joint to the ankle joint was performed in the same foot position. We prepared individual lines connecting the center of the ankle joint with the TAT or EHLT to measure the angle difference (ΔA) from Akagi's line in the knee joint. We analyzed whether the ΔA might be affected by deformity of the knee joint or foot region, and tibial torsion.

RESULTS

At the ankle joint level, the ΔA of EHLT was the smallest, with an average of 1.6 ± 3.4°. The ΔA for the femorotibial angle, hallux valgus angle, and varus-valgus angle showed no correlations with deformity of the knee joint and foot region, or tibial torsion.

CONCLUSIONS

MRI findings showed that EHLT would be useful as a landmark of the ankle joint center in extramedullary tibial osteotomy in TKA for medial knee OA. It was also clarified that the landmark would not be affected by severe deformity of the knee joint, deformity of the foot region, or external torsion of the tibia.

Tibial bowing and tibial component placement in primary total knee arthroplasty in valgus knees: Are we overlooking?

PURPOSE

Tibial bowing in valgus knees with arthritis can lead to component malplacement during total knee arthroplasty (TKA). Incidence of valgus knees with medial tibial bowing, its effect on tibial component placement during primary TKA and methods to improve accuracy of the component placement were studied.

METHODS

Full-length weight-bearing alignment radiograph was taken in 117 patients (149 knees) with valgus deformity undergoing TKA. In these cases, the proximal tibial reference for extramedullary jig placement was planned preoperatively with reference to the tibial spines and classified as four zones.

RESULTS

The mean preoperative hip-knee-ankle (HKA) angle was 192.9° (180.3-234.5°). Bowing >3° was considered significant (p < 0.001) and at this level of bowing, the proximal tibial reference was shifted from centre to medial. Tibial bowing <3° was considered straight and >3° as tibia valga. Tibia was bowed in 70 knees (46.97%). Severity of valgus deformity had strong positive correlation with the tibia valga (p < 0.001). The post-operative medial proximal tibial angle (MPTA) and HKA angle were 91.63° (87.9-95.7°) and 182.6° (178.1-189.7°), respectively. The mean MPTA and post-operative HKA angle in bowed and straight tibiae were 90.35° versus 89.78° (p = 0.547) and 181.5° versus 180.7° (p = 0.5716), respectively, and the difference was not statistically significant.

CONCLUSION

Medial tibial bowing is very common in valgus knees. Tibia valga has a strong positive correlation with the severity of valgus deformity. Accurate tibial component placement can be achieved with a medialized reference point for extramedullary tibial cutting jig in knees with significant tibia valga. The study has been registered in clinical trials registry - India (CTRI/2018/03/012283).

Gender difference in bowing of the sagittal femoral morphology measurement using magnetic resonance imaging

The importance of femoral sagittal bowing on total knee arthroplasty (TKA) has not been actively discussed. Femoral sagittal bowing can lead to cortex damage, fractures, or femoral malalignment. Therefore, the purpose of this study was to evaluate femoral sagittal bowing at different segments of the femur in the Korean population, and to discuss the implications on total knee arthroplasty. Differences in the morphology of femoral sagittal bowing for 978 patients-829 women and 148 men-were evaluated using magnetic resonance imaging. The angle between the femoral mechanical axis and the anterior cortex line was measured for all the patients. In addition, the gender difference in femoral sagittal bowing was investigated. The angle of femoral sagittal bowing with the mechanical axis was 2.8˚ ± 2.2˚. The angles for femoral sagittal bowing were 2.9˚ ± 2.2˚ and 2.3˚ ± 2.6˚ for females and males, respectively. Thus, a gender difference was found in the femoral sagittal bowing (p < 0.05). Excessive sagittal bowing of the femur can affect the final sagittal position of the femoral component, and this has implications for implant design selection. We recommend that surgeons accurately perform pre-operative evaluation of femoral bowing to prevent potential malalignment, rotation, and abnormal stresses between the femur and implant.

Computer-Assisted Technologies in Arthroplasty: Navigating Your Way Today

Computer-assisted technologies that are used in arthroplasty include navigation, image-derived instrumentation (IDI), and robotics. Computer-assisted navigation improves accuracy and allows for real-time assessment of component positioning and soft-tissue tension. It is not clear whether the implementation of these technologies improves the clinical outcome of surgery. High cost and time demands have prevented the global implementation of computer-assisted technologies.

The entry point of intramedullary tibia cutting guide should vary according to the individual tibia morphology in TKA

INTRODUCTION

In total knee arthroplasty (TKA) using the intramedullary tibial cutting guide (IMTCG), the positioning of the IMTCG is important for accurate tibial bone resection. The aim of this study was to evaluate the ideal entry point of IMTCG and affecting radiologic factors.

MATERIALS AND METHODS

From May 2017 to February 2018, 91 consecutive TKAs for osteoarthritis were included. From preoperative full-length radiographs, we measured the medial proximal tibia angle (MPTA), lateral distal tibia angle (LDTA), tibial bowing angle (TBA), medial to lateral width of the tibial plateau, tibial length, and ideal coronal entry point. In preoperative short knee lateral radiographs, we measured the anterior to posterior length of the tibial plateau, tibial posterior slope angle (TPSA), metaphysio-diaphyseal angle (MDA), and ideal sagittal entry point. The ideal coronal and sagittal entry points were defined as the points crossing the tibial plateau and tibial anatomical axis on the coronal and sagittal radiographs, respectively.

RESULTS

The ideal entry point was 51.4 ± 4.3% (SD) from the medial margin and 27.0 ± 5.8% (SD) from the anterior margin of the tibial plateau. However, the range varied from 39.8 to 60.5% on the coronal plane and from 9.6 to 37.7% on the sagittal plane, respectively. As the MPTA (rho = - 0.490) and TBA (rho = - 0.433) were increased, the coronal entry point moved medially. As TPSA (rho = - 0.761) and MDA (rho = - 0.495) were increased, the sagittal entry point moved anteriorly.

CONCLUSIONS

The ideal entry point of IMTCG should vary according to the individual tibial morphology.

Accuracy of tibial positioning in the frontal plane: a prospective study comparing conventional and innovative techniques in total knee arthroplasty

BACKGROUND

Coronal alignment of the tibial component determines functional outcome and survival in total knee arthroplasty (TKA). Innovative techniques for tibial instrumentation have been developed to improve accuracy and reduce the rate of outliers.

METHODS

In a prospective study, 300 patients were allocated to four different groups using a randomization process (two innovative and two conventional) techniques of tibial instrumentation (conventional: extramedullary, intramedullary; innovative: navigation and patient-specific instrumentation (PSI); n = 75 for each group). The aims were to reconstruct the medial proximal tibial angle (MPTA) to 90° and the mechanical tibio-femoral axis (mTFA) to 0°. Both angles were evaluated and compared between all groups three months after the surgery. Patients who presented with a postoperative mTFA > 3° were classified as outliers.

RESULTS

The navigation and intramedullary technique both demonstrated that they were significantly more precise in reconstructing a neutral mTFA and MPTA compared to the other two techniques. The odd's ratio (OR) for producing outliers was highest for the PSI method (PSI OR = 5.5, p < 0.05; extramedullary positioning OR = 3.7, p > 0.05; intramedullary positioning OR = 1.7, p > 0.05; navigation OR = 0.04, p < 0.05). We could only observe significant differences between pre- and postoperative MPTA in the navigation and intramedullary group. The MPTA showed a significant negative correlation with the mTFA in all groups preoperatively and in the extramedullary, intramedullary and PSI postoperatively.

CONCLUSION

The navigation and intramedullary instrumentation provided the precise positioning of the tibial component. Outliers were most common within the PSI and extramedullary technique. Optimal alignment is dependent on the technique of tibial instrumentation and tibial component positioning determines the accuracy in TKA since mTFA correlated with MPTA pre- and postoperatively.

The usefulness of planning using a preoperative lateral leg image to determine accurate posterior tibial slope in total knee arthroplasty

Objective

Sagittal alignment of the tibia following total knee arthroplasty (TKA) can affect various factors, such as durability, range of motion, stability, and even kinematics. The aim of the present study was to investigate whether taking plain preoperative lateral leg X-ray images to plan the posterior tibial slope can give an insert placement with more accurate sagittal alignment.

Methods

A total of 100 patients who underwent total TKA with posterior-stabilized prostheses. were divided into a group of 50 cases in which the posterior tibial slope was determined intra-operatively with only the fibular axis as the landmark, and a group of 50 cases in which determination of the posterior tibial slope was planned preoperatively with reference to preoperative lateral leg images. For the posterior slope, tibial cutting was performed with the posterior slope built into the bone cutting guide of the insert as the target. The angle of the fibular axis and the posterior slope of the tibial insert were measured on the postoperative lateral leg X-ray image, and the difference from the target angle was examined in the two groups.

Results

In the group in which only the fibular axis was used for reference, the mean deviation from the target was 3.96°, while in the group in which planning was carried out preoperatively using lateral leg X-ray images, the mean deviation was 1.59° (P < 0.05).

Conclusion

Drawing up a preoperative plan using lateral leg X-ray images gives a useful landmark at low cost for accurate determination of TKA posterior tibial slope.

Femoral Component Alignment with a New Extramedullary Femoral Cutting Guide Technique

BACKGROUND

Intramedullary (IM) or extramedullary (EM) mechanical guides are used as alignment tools during total knee arthroplasty (TKA) surgery. The EM guide is less invasive; however, the IM mechanical guide is the preferred option since it has shown superior outcomes in several studies. Picture archive and communication system (PACS) images, if available, are extensively used for preoperative planning and intraoperative guidance. This retrospective study compared TKA outcomes using the conventional IM guide and a new EM technique which uses PACS image for preoperative and intraoperative assessment bone resection. To the best of our knowledge, this is the first study with the new EM technique.

MATERIALS AND METHODS

The study was performed on 205 knees (190 patients) for TKA from 2011 to 2013. The perioperative blood loss and the postoperative alignment angles were assessed for both mechanical guides. The angles were measured on the radiographs of the patient. The blood loss was assessed by the blood accumulated in the hemovac drain during the surgery and until 3 days after the surgery.

RESULTS

The new EM guide provided similar postoperative alignment as that obtained with the IM guide.

CONCLUSION

The EM-guided method for femoral bone cutting using PACS films in TKA is as good as the IM method. The additional advantages of less injury to the bone and less fat emboli load to the cardiopulmonary system with the EM method makes it an attractive choice for routine, especially in the elderly and/or simultaneous bilateral, TKA in hospitals without modern computer-assisted navigation systems.

Intramedullary versus extramedullary alignment guides on total knee arthroplasty: a meta-analysis

AIM

A meta-analysis concentrated on the effect of intramedullary and extramedullary systems on total knee arthroplasty.

METHOD

Potential academic articles were identified from Cochrane Library, Medline, PubMed, Embase, ScienceDirect, CNKI, WanFang, VIP and other databases. The STATA version was used to analyze the pooled data.

RESULTS

There are obvious significant differences in drainage volume and transfusion rate. There was no significant difference in lower limb coronal alignment, coronal and sagittal alignment of the femoral component, operation time, postoperative knee score and complications.

CONCLUSION

Our meta-analysis shows that the alignment of the extramedullary distal femur osteotomy is as accurate as intramedullary systems. Furthermore, extramedullary distal femur osteotomy without invading the femoral medullary cavity could reduce postoperative bleeding and the transfusion rate. Furthermore, research is required to test the robustness of our findings when more data is available and by undertaking both Bayesian and frequentist methods. When more data are available, the heterogeneity can be further explored through sensitivity analysis, and the available data can be combined to verify the hypothesis.

Deviation of femoral intramedullary alignment rod influences coronal and sagittal alignment during total knee arthroplasty

BACKGROUND

An intramedullary (IM) rod is used to resect the distal femur vertically to the femoral mechanical axis in the coronal plane in many cases of total knee arthroplasties (TKA). The valgus angle between the mechanical axis and the anatomical axis of the distal femur is estimated preoperatively. It is known the deviation of the IM rod in the femoral canal could influence the femoral component alignment. However, there is no published data regarding how many degrees of deviation to make with the IM rod. The purpose of this study is to measure each deviation of the IM rod using three-dimensional (3D) computer simulations.

METHODS

Preoperative CT scans on 30 knees undergoing TKA were studied. The line connecting central points at 10 and 20 cm proximal from the intercondylar notch was defined as the anatomical axis and the point at which the anatomical axis intersects the surface of the distal femur was considered as the entry point of the IM rod. The medio-lateral (ML) and antero-posterior (AP) deviations between the anatomical axis and the IM rod were measured.

RESULTS

The ML and AP deviations were 0.8 and 1.1° on average. The IM rod was deviated medio-laterally more than 1.0° in three knees (10%).

CONCLUSION

Surgeons should note the ML difference of the resection thickness of the distal femur for coronal alignment. If the ML difference varies greatly from the preoperative planning, they need to adjust at most 1.0° of valgus angle to achieve the appropriate coronal alignment. Level of evidence III, Therapeutic.

Total knee replacement modifies the preoperative tibial torsion angle-similar results between computer-assisted and standard technique

Background

Malpositioning of the components in total knee replacement (TKR) can result in failure or deficient outcomes of the surgical procedure. In the tibial segment, the rotational position of the tray should reproduce the mechanical axis without modifying physiological tibial torsion.

Methods

A randomised, prospective study was made of 74 patients subjected TKR involving the standard technique (38 cases) and navigation surgery (36 cases). A computed tomography study of the knee and ankle was made before the operation and after arthroplasty implantation, in order to identify the position of the prosthetic tibial tray in the transverse axis and the tibial torsion angle.

Results

The rotation of the tibial tray changed from its preoperative to postoperative range, but no significant differences were found between the navigated and the standard groups. The presence of preoperative deformities in the frontal plane did not modify the changes in the rotation of the tibial component. The mean preoperative tibial torsion angle was 17.76º (SD =10.15) of external rotation, with no significant differences in relation to the previous frontal deformity. After TKR, the tibial torsion angle was 15.36º (SD =7.16) (P=0.021). There were no differences in final tibial torsion between the knees operated upon with the standard instruments and those subjected to computer-assisted surgery (CAS; P=0.157).

Conclusions

TKR surgery modifies preoperative tibial torsion. Neither mechanical instrumentation nor navigation surgery precisely reproduces the rotational axis of the leg.

Lateralization of Tibial Plateau Reference Point Improves Accuracy of Tibial Resection in Total Knee Arthroplasty in Patients with Proximal Tibia Vara

Background

The tibial cut referenced to the center of the intercondylar eminence often leads to varus malalignment in the presence of preexisting proximal tibia vara. The purpose of this study was to investigate the effect of lateralization of the lateral tibial plateau reference point (based on the amount of proximal tibia vara) on the postoperative coronal plane alignment.

Methods

In this prospective cohort study, 62 patients (95 knees) with osteoarthritis and proximal tibia vara underwent primary total knee arthroplasty using a lateral tibial plateau reference point for the extramedullary jig. The pre- and postoperative radiographs were obtained for measurement of mechanical axis deviation, degree of tibia vara, proximal lateral reference point of the tibial condyle, and coronal alignment of the femoral and tibial components. The distance between the tibial reference point and the center of the intercondylar eminence was measured intraoperatively.

Results

The mean tibia vara was 7.1° (standard deviation [SD], 2.3°). The mean lateral displacement of the reference point was 7 mm (SD, 2.2 mm). Postoperative tibiofemoral angle was 6° to 10° of valgus in 94% of cases. There was a strong correlation between the magnitude of tibia vara and the amount of lateralization of the tibial reference point (R² = 0.79, p < 0.001).

Conclusions

In total knee arthroplasty patients with proximal tibia vara, reasonable accuracy can be achieved with use of the extramedullary jig for tibial component alignment by lateralizing the proximal tibial reference point.

What is the optimal valgus pre-set for intramedullary femoral alignment rods in total knee arthroplasty?

PURPOSE

In total knee arthroplasty (TKA), intramedullary guides are often used for aligning the distal femoral cutting block. Because of the highly varying angles between the mechanical axis and the anatomical femoral axis (AMA), different valgus pre-sets have been recommended. The present study investigated the optimal valgus pre-set (measuring the AMA in long-leg radiographs or at 5°, 6°, 7° or 8° valgus) to align the cutting block perpendicularly to the mechanical axis.

METHODS

The AMA was preoperatively measured in weight-bearing long-leg radiographs. After alignment of the cutting block by means of an intramedullary rod, deviation of the block from the mechanical femoral axis was measured with a pinless navigation device. The true AMA (tAMA) was calculated by adding the valgus pre-set of the alignment rod to the deviation measured with the navigation device. Mean deviations between the tAMA and (a) the AMA measured by the surgeon, (b) the AMA calculated with the computer software, (c) 5°, (d) 6°, (e) 7° and (f) 8° valgus pre-sets were measured for each patient. The lowest mean differences were determined.

RESULTS

The 40 knees measured showed a mean tAMA of 7.2° valgus (1.7 SD) (range 4°-11.5°). The following mean differences and 95 % limits of agreement were calculated: 2.2 (-1.2, 5.5) to the tAMA for the 5° valgus pre-set, 1.2 (-2.2, 4.5) for 6°, 0.2 (-3.2, 3.5) for 7° and -0.8 (-4.2, 2.5) for 8°. AMA measurements by the surgeon and with the digital medical planning software yielded mean differences of 0.6 (-3.1, 4.3) and 0.4 (-4.1, 4.8), respectively.

CONCLUSION

In the present setting, the best mean distal femoral cutting block alignment perpendicular to the mechanical femoral axis could be achieved with a valgus pre-set of 7° and not by measuring the AMA. Nevertheless, we recommend conducting weight-bearing radiographs of the entire leg prior to TKA for easy detection of any anatomical varieties, old fractures, long stems of total hip arthroplasties or cement. However, surgeons must be aware that exact coronal component alignment can only be achieved by navigational devices.

LEVEL OF EVIDENCE

Diagnostic study, Level II.

Mapping of the anterior tibial profile to identify accurate reference points for sagittal alignment of tibial component in total knee arthroplasty

BACKGROUND

Although standard instrumentation is the procedure most frequently used to implant a Total Knee Arthroplasty (TKA), high rates of malalignment of tibial component are reported using this technique. Anatomical landmarks for sagittal alignment have been little investigated and the best reference axis, which parallels the mechanical axis, is yet to be established.

HYPOTHESIS

Mapping the Anterior Tibial Profile (ATP) may allow the identification of segmental zones of the ATP parallel to the mechanical axis which can be used to align the extramedullary rod.

METHODS

An intramedullary rod was positioned in line with the mechanical axis in 47 dried cadaveric tibiae. The rod was connected to a cutting jig and to an extramedullary rod. Digitalized images of lateral view radiographs were taken and the distance between the ATP and the extramedullary rod was measured at 10-mm intervals and at interpolated distances corresponding to every 2% of the tibial length.

RESULTS

Segmental portions of the ATP exhibit an alignment parallel to the mechanical axis between points located at 58% and 90% and at 62% and 88% of the tibial length. Points placed at 50% of tibial length and 5mm proximal to the ankle joint generate the longer axis parallel to the mechanical axis.

CONCLUSION

The orientation of sagittal tibial cut may be improved by aligning the extramedullary rod parallel to the ATP at definite points. Points placed at 50% of the tibial length and 5mm proximal to the ankle joint may be preferred since they generate the longer axis parallel to the mechanical axis and are more easily identified at surgery.

Extramedullary Tibial Bone Cutting Using Medial Cortical Line in Total Knee Arthroplasty

Purpose

This study aims to identify the effectiveness of the medial cortical line for attaining a more accurate tibial component alignment in proximal tibial resection using an extramedullary alignment rod.

Materials and Methods

The study examined 100 cases of total knee arthroplasty performed from December 2013 to February 2014 in a retrospective manner. On a preoperative anteroposterior (AP) radiograph of the entire tibia, we identified the medial cortical line that runs parallel to the tibial anatomical axis and passes the medial tibial spine, and measured the point where the medial cortical line crosses between the medial malleolus and the lateral malleolus in the ankle joint.

Results

The preoperative AP radiograph of the tibia showed the medial cortical line passing the point 40.4%±0.8% medial to the distance from the medial malleolus to the lateral malleolus including the skin thickness in the ankle joint. When the proximal tibial resection was performed with the extramedullary tibial cutting guide aligned with the medial cortical line, the tibial component angle averaged 0.7°±0.3° varus and the alignment accuracy of the tibial component within 0°±3° varus amounted to 97.0%.

Conclusions

The use of the medial cortical line in proximal tibial resection with an extramedullary tibial cutting guide allowed for relatively accurate alignment of the tibial component.

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.].

Effect of Femoral Resection on Coronal Overall Alignment after Conventional Total Knee Arthroplasty

Background:

A good postoperative alignment in total knee arthroplasty (TKA) is the key to achieving satisfactory results. We assessed the effect of femoral and tibial resection on the overall alignment after conventional TKA.

Methods:

We conducted a retrospective analysis of 212 primary TKAs in 188 patients. Intramedullary (IM)-guided resection was applied on the femoral side while extramedullary (EM)-guided resection was used on the tibial side. Using full-length X-ray, the preoperative femoral valgus angle and lower extremity alignment, as well as 2-week postoperative femoral and tibial prosthetic coronal alignment and overall lower extremity alignment, were measured.

Results:

Postoperatively, good prosthetic alignment was achieved in 191 cases (90.1%) on the tibial side and in 144 cases (67.9%) on the femoral side (χ² = 5.441, P = 0.02). Multiple linear regression analysis was used to assess the effect of different alignment sides on the overall alignment in the coronal plane. Data were divided into five subgroups based on the valgus or varus status of the prostheses. The standardized regression coefficients of the femoral and tibial prosthetic alignment on the overall alignment were 0.666 and 0.414, respectively; in varus on both sides were 0.658 and 0.377, respectively; in valgus, 0.555 and 0.030; femoral side varus and tibial side valgus, 0.702 and 0.211; femoral side valgus and tibial side varus, −0.416 and 0.287. The study showed that the overall low extremity alignment was statistically influenced by the prosthetic alignment, except for the tibial prosthetic alignment when femoral prosthesis was in valgus (P = 0.153).

Conclusions:

In conventional TKA, tibial side EM-guided resection may offer satisfactory postoperative alignment, and femoral resection relying on IM guide may lead to more undesirable results. Postoperative coronal alignment is mainly affected by the femoral resection. Therefore, femoral side operation should receive adequate attention from the surgeons.

Lateralization of Femoral Entry Point to Improve the Coronal Alignment During Total Knee Arthroplasty in Patients With Bowed Femur

BACKGROUND

Intramedullary jigs are most often used for distal femoral bone cuts in total knee arthroplasty (TKA). However, the accuracy of bone cuts in the distal femur may be affected by the presence of diaphyseal deformities of the femur.

METHODS

Sixty-three patients (88 knees) with lateral bowing of the femur underwent primary TKA using a lateralized femoral entry point for intramedullary femoral guide. The following measurements were obtained on the preoperative and postoperative scanograms-mechanical axis deviation, degree of femoral bowing, femoral entry point from the intercondylar sulcus, distance from the center of the knee to the mechanical axis, and coronal alignment of femoral and tibial components.

RESULTS

In 48.8% of cases, the femoral entry point was 3-5 mm lateral to the intercondylar notch, in 44.4% of cases, it was 6-10 mm lateral to the notch, and in 6.8% of cases, it was 10-15 mm lateral to the intercondylar notch. Postoperatively the tibiofemoral angle was 6-10 degrees of valgus in 96% of cases. The postoperative mechanical axis was within 3 mm from the center of the knee in 80 of the 88 knees (90.9%). For every 1° increase in femoral bowing, the entry point was lateralized by an average of 1.04 mm.

CONCLUSION

The location of femoral entry point is important in TKA in patients with coronal plane deformity of the femur. In patients with lateral femoral bowing of 5° or more, a lateralized femoral entry point is useful in allowing straighter passage of long intramedullary femoral rod and this resulted in good mechanical axis alignment and femorotibial component alignment in over 90% of patients in our series.

Appropriate sagittal femoral component alignment cannot be ensured by intramedullary alignment rods

PURPOSE

The intraoperative sagittal cutting block alignment when intramedullary alignment rods are used was investigated. Its absolute orthogonal orientation in relation to the mechanical femoral axis should be analysed. It was hypothesized that (1) alignment rods do not ensure a desired deviation within a range between 0° and 3° flexion as it has been shown to be favourable for clinical and functional outcome. Further, the degree of flexion cannot be (2) foreseen by the surgeon or (3) estimated by clinical or radiological parameters.

METHODS

Forty knees allocated to total knee arthroplasty were included. The distal femoral cutting block was aligned using an intramedullary rod. By means of a navigation device, the sagittal alignment of the cutting block in degrees of flexion was measured.

RESULTS

The mean measured flexion of the cutting block was 4.4° (3.6 SD). Twenty-five per cent (10/40) of the values were within a corridor between 0° and 3° of flexion. The mean difference between expected and measured flexion was -1.5° (-7.6 to 4.7 95 % limits of agreement). The dorsoventral diameter of the distal femur showed a significant influence on measured flexion (R (2) = 0.112, p = 0.035).

CONCLUSION

Intramedullary alignment rods used in the present study do not ensure a distal cutting block alignment between 0° and 3° of flexion in relation to the femoral mechanical axis. The extent of flexion could not be foreseen either by the surgeon. The dorsoventral diameter of the distal femur correlated with measured flexion. However, only limited data is available on influence of femoral component flexion on implant failure or clinical and functional outcome.

LEVEL OF EVIDENCE

Diagnostic study, Level II.

Improving tibial component alignment in total knee arthroplasty

PURPOSE

Tibia torsion may influence the accuracy of extramedullary instrumentations in total knee arthroplasty (TKA). This study assessed whether the effect of tibial torsion may be overcome using a surgical technique in which the extramedullary rod is aligned to reference points at the proximal tibia only.

METHODS

A consecutive series of 94 knees that underwent TKA were analyzed. In the first 47 knees (group 1), a standard procedure for tibial component alignment was performed while in the second group of 47 knees, a modified surgical technique was used including the alignment of the extramedullary rod to the reference points at the proximal tibia only (group 2). Lower limb, femoral, and tibial component alignment were measured on postoperative long-leg radiographs.

RESULTS

Femorotibial mechanical axes angles were similar in the two groups. Femoral component alignment also did not differ between the groups. A neutral alignment of the tibial component was achieved in 17 and 34 % of the knees in group 1 and group 2, respectively (p = 0.04). A malalignment of the tibial component >3° was found in 34 % of knees in group 1 compared with 4 % of those in group 2 (p = 0.0001).

CONCLUSIONS

Coronal alignment of the tibial component may improve by setting the extramedullary rod in line with anatomical references in the proximal tibia only. This technique appears to bypass the influence of tibial torsion on the alignment of the extramedullary guide at the distal tibia. The clinical relevance of the study is that using this technique, the rate of malalignment of the tibial component may be reduced compared to a standard technique in which a fixed reference is used at the ankle joint.

Extramedullary versus intramedullary tibial alignment technique in total knee arthroplasty: A meta-analysis of randomized controlled trials

The aim of this study was to establish whether the use of an extramedullary or intramedullary tibial cutting guide leads to superior mechanical leg axis and implant positioning. A meta-analysis of six randomized controlled trials including 350 knees was performed. For the mechanical axis, frontal tibial component angle and tibial slope, there were no significant differences in the mean values or the number of outliers (±3°) between the extramedullary and intramedullary groups. A reduced tourniquet time was associated with the intramedullary guide. No significant difference in the complication rate was noted between the two groups. Neither extramedullary nor intramedullary tibial alignment was more accurate in facilitating the tibial cut. Use of an intramedullary guide results in a shorter tourniquet time and exhibits a similar complication rate as the extramedullary guide.

Significant Incidence of Extra-Articular Tibia Vara Affects Radiological Outcome of Total Knee Arthroplasty

Purpose

To identify and quantify the presence of extra-articular tibia vara that might influence the mechanical axis alignment after total knee arthroplasty (TKA).

Materials and Methods

A total of 48 TKAs in 30 osteoarthritic Indian patients were prospectively evaluated. The hip-knee-ankle angle (HKA), joint line convergence angle, and varus angulation at the femur and tibia were measured from the preoperative and postoperative standing hip-to-ankle radiographs. Four different methods were used to measure the varus angulation at the tibia: metaphyseo-diaphyseal angle (MDA), the angle between the anatomical axis and mechanical axis of the tibia, the angle between the proximal third and distal third of tibia and the angle between the proximal half and distal half of tibia.

Results

Extra-articular tibia vara quantified using MDA had the most positive correlation with HKA. Receiver operating characteristic plotting showed that MDA of >4° predicts abnormal postoperative HKA. Twenty-eight out of 48 knees had MDA of >4°, and 78.6% of these had postoperative HKA under-correction and 21.4% had less than ideal tibial component position.

Conclusions

A significant inherent extra-articular varus angulation best measured using MDA exists in the proximal tibia in osteoarthritic Indian patients undergoing TKA. MDA of >4° is associated with abnormal postoperative HKA. Computer navigation may be useful for achieving ideal correction in such cases.

Alignment of the tibial component in total knee arthroplasty procedures using an intramedullary or extramedullary guide: double-blind randomized prospective study

Objectives

To evaluate the results obtained through using an intramedullary or extramedullary guide for sectioning the tibia in total knee arthroplasty procedures, with a view to identifying the accuracy of these guides and whether one might be superior to the other.

Methods

This was a randomized double-blind prospective study on 41 total knee arthroplasty procedures performed between August 2011 and March 2012. The angle between the base of the tibial component and the mechanical axis of the tibia was measured during the immediate postoperative period by means of radiography in anteroposterior view on the tibia that encompassed the knee and ankle.

Results

There was no demographic difference between the two groups evaluated. The mean alignment of the tibial component in the patients of group A (intramedullary) was 90.3° (range: 84–97°). In group B (extramedullary), it was 88.5° (range: 83–94°).

Conclusion

In our study, we did not find any difference regarding the precision or accuracy of either of the guides. Some patients present an absolute or relative contraindication against using one or other of the guides. However, for the other cases, neither of the guides was superior to the other one.

Using fibula as a reference can be beneficial for the tibial component alignment after total knee arthroplasty, a retrospective study

PURPOSE

One of the important factors in a successful arthroplasty is component alignment. The primary objective of this study was to determine whether the fibular shaft reference technique is beneficial for the tibial component position on the postoperative plain radiograph after total knee arthroplasty.

METHODS

A total of 42 patients between 2009 and 2011 were analysed retrospectively. The surgeon prepared the tibia using an extramedullary cutting guide and set the posterior tibial slope with respect to the fibular reference rod. In the postoperative radiographic measurements, a true anteroposterior and lateral radiograph of the lower leg covering the whole length of the tibia was used.

RESULTS

Five patients were excluded as they did not meet the inclusion criteria, four patients were excluded due to improper radiographs and the study group was reduced to 33 patients and 35 knees. The mean preoperative tibiofibular angle was 2.1° ± 0.8°. The mean postoperative tibial sagittal angle measurements were 83.3° ± 1.4° (81°-86°). 33 (94 %) Knees gained the desired tibial sagittal angle within the desired alignment (5° ± 3°). The mean postoperative tibial coronal angle was 89.3° ± 1.5°. The tibial component coronal angle of two knees was more than 3 alignment from the neutral mechanical axis.

CONCLUSION

The major clinical relevance of the technique described in the present study is cost-effectiveness, and it does not require any extra time or surgical equipment. This method can be used as an alternative choice for bulky extremities which is a cause of malalignment of the components.

LEVEL OF EVIDENCE

Retrospective case series, Level IV.

Comparison of Postoperative Alignment of Total Knee Replacement Using Computer-Assisted Navigation with Conventional Guiding System in Chinese Population with Significant Coronal Femoral Bowing

Background/Purpose

Coronal femoral bowing is common in Chinese population. This might affect the restoration of mechanical alignment in conventional total knee replacement (TKR). The aim of the study was to compare the postoperative alignment of conventional TKR with computer-assisted navigation TKR (CAN-TKR), to investigate the effect of femoral bowing on postoperative alignment in conventional TKR and to understand the role of CAN-TKR in limbs with significant femoral bowing.

Methods

This is a retrospective study of 331 knees that underwent TKR (either conventional or CAN-TKR) in our centre from January 2010 to June 2012. The incidence of coronal femoral bowing was measured. The postoperative alignments were compared between the two groups.

Results

The incidence of excessive coronal femoral bowing was 41.4%. For patients with or without significant coronal femoral bowing, the CAN-TKR group was significantly better in restoring postoperative mechanical axis and the coronal femoral angle (p < 0.05). Proportions of outliers were also much less in the CAN-TKR group.

Conclusion

CAN-TKR reduces outliers in all patients, and is especially superior in restoring mechanical alignments in patients with significant coronal femoral bowing.

Reliable and reproducible technique to mark center of ankle in total knee arthroplasty

AIM

Bony and soft tissue landmarks have been used in the past to determine the center of the ankle to facilitate the tibial cut using an extramedullary guide in total knee arthroplasty. However literature reports are scanty in regards to the most ideal method available and its reproducibility in marking the center of the ankle intra-operatively.

METHODS

We describe a method of using an electrocardiogram (ECG) lead in determining the center of the ankle, thus facilitating the alignment of the extramedullary guide for the tibia.

RESULTS

Using this technique, in our study the mean lateral tibial component angle was 90.09(84.2°-94.3°). The number of knees in the range of 88°-92.4° were 120 out of 122 knees (98.40%).

CONCLUSION

The described method is reliable and cheap, with reproducibility in determining the tibial cut in total knee arthroplasty.

Effects of tibial torsion on distal alignment of extramedullary instrumentation in total knee arthroplasty

BACKGROUND AND PURPOSE

Whether tibial torsion affects the positioning of extramedullary instrumentation and is a possible factor in malalignment of the tibial component in total knee arthroplasty (TKA) is unknown. We assessed the influence of tibial torsion on distal alignment of extramedullary systems for TKA, using the center of the intermalleolar distance as anatomical reference at the ankle joint.

PATIENTS AND METHODS

We analyzed CT scans of knee and ankle joints of 50 patients with knee osteoarthritis (mean age 73 years, 52 legs). The tibial mechanical axis was identified and translated anteriorly at the level of the medial one-third (proximal AP axis 1), at the medial border of the tibial tuberosity (proximal AP axis 2), and at the level of the talar dome (distal AP axis). The center of the intermalleolar distance and the width of the medial and lateral malleolus were calculated. The proximal AP axes 1 and 2 were translated at the level of the ankle joint and any difference between their alignment and the distal AP axis was calculated as angular and linear values.

RESULTS

The center of the ankle joint was located, on average 2 mm medial to that of the intermalleolar distance. The distal AP axis was externally rotated by 18° and 27° compared to the proximal AP axes 1 and 2, respectively. Overall, the center of the ankle joint was shifted laterally by 9-11 mm with respect to the proximal AP tibial axes.

INTERPRETATION

To avoid a varus tibial cut in TKA, extramedullary alignment systems should be aligned more medially at the ankle joint than previously thought, due to the effect of tibial torsion and-to a lesser extent-to the different malleolar width.

Novel image-matching software for postoperative evaluation after TKA

Although 2-dimensional assessments using postoperative plain radiographs have been used after total knee arthroplasty (TKA) in previous studies, a strong possibility exists that deviation can occur when assessing 3-dimensional (3-D) objects. The purpose of this study was to test the hypothesis that novel 3-D image-matching software could accurately assess the positioning of implants and could be a useful tool in postoperative evaluation after TKA.Total knee arthroplasty was performed in 30 consecutive patients. Intraoperatively, the thickness of each bone cut was measured. Postoperatively, the thickness of each part of the bone cut was measured using Athena Knee (SoftCube Co, Ltd, Osaka, Japan) 3-D image-matching software. The results revealed no significant differences in the medial compartment and significant differences of approximately 1 mm in the lateral compartment. The difference was possibly caused by the remaining cartilage in the lateral compartment. Linear regression analysis revealed a statistically excellent correlation between intra- and postoperative values in all parts of the bone cuts. Although the 3-D image-matching software used in this study was originally developed for preoperative planning in TKA, it is considered accurate enough to assess the positioning of implants with respect to the bone after TKA.

Relative contributions of design, alignment, and loading variability in knee replacement mechanics

Substantial variation in total knee replacement (TKR) outcomes exists within the patient population. Some of this variability is due to differences in the design of the implanted components and variation in surgical alignment, while other variability is due to differences in the applied forces and torques due to anatomic and physiological differences within a patient population. We evaluated the relative contributions of implant design, surgical alignment, and patient-specific loading variability to overall tibiofemoral joint mechanics to provide insight into which measures can be influenced through design and surgical decisions, and which are inherently dependent on variation within the patient population and should be considered in the robustness of the implant design and surgical procedure. Design, surgical, and loading parameters were assessed using probabilistic finite element methods during simulated stance-phase gait and squat activities. Patient-specific loading was found to be the primary contributor to joint loading and kinematics during low flexion, particularly under conditions of high external loads (for instance, the gait cycle with high internal-external torque), while design and surgical factors, particularly femoral posterior radius and posterior slope of the tibial insert became increasingly important in TKR performance in deeper flexion.

Does minimally invasive total knee arthroplasty improve isokinetic torque?

BACKGROUND

Less invasive dissection of the extensor apparatus, one of the aspects of minimally invasive surgical (MIS) TKA, might result in less reduction of postoperative quadriceps strength. However, it is unclear whether MIS is associated with less strength reduction.

QUESTIONS/PURPOSES

We asked whether knee strength (extensor or flexor torque) would be greater in patients having a MIS TKA compared with patients having a standard TKA and whether knee scores, alignment, ROM, tourniquet and operating times, and hospital length of stay were improved.

METHODS

We prospectively recruited 52 patients awaiting MIS or standard TKA, matched for age, weight, height, BMI, sex, and surgically treated side, but not randomized. Isokinetic tests were performed preoperatively and postoperatively to obtain peak values of extensor and flexor torque. Postoperative-to-preoperative ratios and the extensor-flexor torque ratio also were calculated.

RESULTS

Mean baseline extensor torques were 57 Nm and 53 Nm for MIS and standard TKAs, respectively. At 8 weeks postoperatively, absolute values of the mean postoperative knee extensor torque also were similar: 47 and 45 Nm for patients with MIS and standard TKAs, respectively. The postoperative-to-preoperative ratios were 0.8 for extensor and flexor torque in both groups. The extensor-flexor torque ratios were similar between groups.

CONCLUSIONS

Our data suggest a less invasive dissection of the extensor apparatus involved in MIS TKA does not enhance postoperative quadriceps strength.

LEVEL OF EVIDENCE

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

Extramedullary versus intramedullary tibial cutting guides in megaprosthetic total knee replacement

BACKGROUND

In a standard total knee replacement, tibial component alignment is a key factor for the long term success of the surgery. The purpose of this study is to compare the accuracy of extramedullary and intramedullary tibial cutting guides used in indigenous and imported implants respectively, in positioning of the tibial components in megaprosthetic knee replacements.

METHODS

A comparative study of the accuracy of extramedullary and intramedullary tibial cutting guides was carried out in 92 megaprosthetic knee replacements for distal femoral tumors. For the proximal tibia cut for tibial component placement, an extramedullary guide was used in 65 patients and an intramedullary guide was used in 27 patients. Tibial component alignment angles were measured in postoperative X-rays with the help of CAD software.

RESULTS

There was more varus placement in coronal plane with extramedullary cutting guide (-1.18 +/- 2.4 degrees) than the intramedullary guide (-0.34 +/- 2.31 degrees) but this did not reach statistical significance. The goal of 90 +/- 2 degrees alignment of tibial component was achieved in 54% of patients in the extramedullary group versus 67% in the intramedullary group. In terms of sagittal plane alignment, extramedullary guide showed less accurate results (2.09 +/- 2.4 degrees) than intramedullary guide (0.50 +/- 3.80 degrees) for tibial component alignment, though 78% of patients were aligned within the goal of 0-5 degrees of tibial slope angle in extramedullary group versus 63% in intramedullary group. The mean error in the measurements due to rotation of the knee during taking the X-rays was less than 0.1 degrees and distribution of the X-rays with the rotation of knee was similar in both the groups.

CONCLUSIONS

Overall, in megaprosthetic knee replacement intramedullary guides gave more accurate results in sagittal plane and exhibited similar variability as of extramedullary guides in coronal plane.

Cadaveric results of an accelerometer based, extramedullary navigation system for the tibial resection in total knee arthroplasty

INTRODUCTION

In total knee arthroplasty, the accuracy and precision of the tibial resection must be improved. The purpose of this study was to determine the accuracy and time associated with the use of an accelerometer based, extramedullary surgical navigation system for performing the tibial resection.

MATERIALS AND METHODS

Four orthopedic surgeons performed a tibial resection utilizing the KneeAlign™ system, each on five separate, cadaveric tibiae. Each surgeon was assigned a preoperative "target" of varus/valgus alignment and posterior slope prior to each resection. The alignment of each resection was measured using both plain radiographs and computed tomography, along with the time required to use the device.

RESULTS

Regarding coronal alignment, the mean absolute difference between the preoperative "target" and tibial resection alignment was 0.77° ± 0.64° using plain radiograph, and 0.68° ± 0.46° using CT scan measurements. Regarding the posterior slope, the mean absolute difference between the preoperative "target" and the tibial resection was 1.06° ± 0.59° using plain radiograph, and 0.70° ± 0.47° using CT scan measurements. The time to use the KneeAlign™ for the fifth specimen was less than 300 s for all four orthopedic surgeons in this study.

DISCUSSION

This cadaveric study demonstrates that the KneeAlign™ system is able to accurately align the tibial resection in both the coronal and sagittal planes.

Leg alignment and tibial slope after minimal invasive total knee arthroplasty: a prospective, randomized radiological study of intramedullary versus extramedullary tibial instrumentation

The purpose of the study was analysis of leg alignment and tibial slope comparing intramedullary versus extramedullary tibial instrumentation in the Genesis II MIS-TKA (Smith & Nephew, Memphis, USA). A prospective randomized study was performed according to the CONSORT guidelines. All patients (56 patients) for MIS-TKA were included, if the pre-operative standing long leg X-ray demonstrated the tibia eligible for use of both intra- and extramedullary MIS tibial instrumentation. Randomization was performed by envelope selecting intra- or extramedullary tibia MIS instrumentation. All patients were operated by, or under supervision of, one experienced knee surgeon (RJ). Measurements of leg alignment and tibial slope were made on standardized long leg standing X-rays and lateral knee X-rays performed pre-operatively and 4-12 months post-surgery. Leg alignment was defined as being within or outside the range of 3° varus-valgus on the mechanical leg. The tibial slope was compared pre- and post-surgery. In the present study, there was no difference in leg alignment after MIS-TKA comparing intramedullary versus extramedullary tibial instrumentation. Restoration of tibial slope was significantly better with use of the extramedullary tibial instrumentation.

The role of patient, surgical, and implant design variation in total knee replacement performance

Clinical studies demonstrate substantial variation in kinematic and functional performance within the total knee replacement (TKR) patient population. Some of this variation is due to differences in implant design, surgical technique and component alignment, while some is due to subject-specific differences in joint loading and anatomy that are inherently present within the population. Combined finite element and probabilistic methods were employed to assess the relative contributions of implant design, surgical, and subject-specific factors to overall tibiofemoral (TF) and patellofemoral (PF) joint mechanics, including kinematics, contact mechanics, joint loads, and ligament and quadriceps force during simulated squat, stance-phase gait and stepdown activities. The most influential design, surgical and subject-specific factors were femoral condyle sagittal plane radii, tibial insert superior-inferior (joint line) position and coronal plane alignment, and vertical hip load, respectively. Design factors were the primary contributors to condylar contact mechanics and TF anterior-posterior kinematics; TF ligament forces were dependent on surgical factors; and joint loads and quadriceps force were dependent on subject-specific factors. Understanding which design and surgical factors are most influential to TKR mechanics during activities of daily living, and how robust implant designs and surgical techniques must be in order to adequately accommodate subject-specific variation, will aid in directing design and surgical decisions towards optimal TKR mechanics for the population as a whole.

Computed tomographic measurement of gender differences in bowing of the sagittal femoral shaft in persons older than 50 years

Surgeons do not give enough weight to the effects of bowing of the sagittal femoral shaft in total knee arthroplasty (TKA), which can result in damage to the cortex, fractures, or malalignment of the femoral component. To determine gender differences in bowing, we used spiral computed tomography to scan the femurs of 26 men and 47 women older than 50 years who required TKA. Skeletal extraction of the total sagittal femoral shaft from computed tomographic images was done by a matrix laboratory. The extracted curves were evenly divided into 3 sections. Comparison of the curvature on different sections of the same side of the femur showed that the distal third was significantly bowed. In addition, the curvature of the distal third was significantly larger in women than in men. Such morphological characteristics put forward new requirements in how intramedullary guide rods are used in TKA.

Radiographic analysis of a hand-held surgical navigation system for tibial resection in total knee arthroplasty

Tibial intramedullary or extramedullary alignment guides have not been shown to be highly accurate in performing the tibial resection in total knee arthroplasty (TKA). Since May 2010, a total of 42 knees underwent a TKA using a hand-held, accelerometer-based surgical navigation system for performing the tibial resection (KneeAlign; OrthAlign Inc, Aliso Viejo, Calif). Postoperative standing anteroposterior hip-to-ankle and lateral knee-to-ankle radiographs demonstrated that 97.6% of the tibial components were placed within 90° ± 2° to the mechanical axis in the coronal plane, and 96.2% of the components were placed within 3° ± 2° to the mechanical axis in the sagittal plane. The KneeAlign greatly improves the accuracy of tibial component alignment in TKA.

Radiographic results of an accelerometer-based, handheld surgical navigation system for the tibial resection in total knee arthroplasty

In total knee arthroplasty (TKA), intramedullary and extramedullary tibial alignment guides are not proven to be highly accurate in obtaining alignment perpendicular to the mechanical axis in the coronal plane. The objective of this study was to determine the accuracy of an accelerometer-based, handheld surgical navigation system in obtaining a postoperative tibial component alignment within 2° of the intraoperative goal in both the coronal and sagittal planes. A total of 151 TKAs were performed by 2 surgeons using a handheld surgical navigation system to perform the tibial resection. Postoperatively, standing anteroposterior hip-to-ankle radiographs and lateral knee-to-ankle radiographs were performed to determine the varus/valgus alignment and the posterior slope of the tibial components relative to the mechanical axis in both the coronal and sagittal planes. Findings showed that 95.3% of the tibial components were placed within 2° of the intraoperative goal in the coronal plane and 96.1% of the components were placed within 2° of the intraoperative goal in the sagittal plane. Overall, mean postoperative lower-extremity alignment was -0.3°±2.1°, with 97% of patients having an alignment within 3° of a neutral mechanical axis. The handheld surgical navigation system improves the accuracy of the tibial resection and subsequent tibial component alignment in TKA. It is able to combine the accuracy of computer-assisted surgery systems with the ease of use and familiarity of conventional, extramedullary alignment systems, and the ability to adjust both the coronal and sagittal alignments intraoperatively may prove clinically useful in TKA.

Alignment of computer-assisted total knee arthroplasty in patients with altered hip center

This study aimed to determine limb and component alignment after computer-assisted total knee arthroplasty in 30 patients (32 limbs) with an altered hip center due to a prior hip implant or deformed femoral head. There were no outliers greater than ±3° in the postoperative coronal alignment of the limb and the femoral component in relation to the altered hip center. Two limbs (8%) were more than ±3° for coronal alignment of the femoral component in relation to the anatomical hip center and 96% of limbs had less than 2° deviation in relation to the altered hip center. Computer-navigated total knee arthroplasty results in accurate restoration of lower limb and component alignment in patients with prior hip implants or deformed femoral heads where accurate restoration of alignment may be challenging due to altered hip center.

Intramedullary versus extramedullary alignment of the tibial component in the Triathlon knee

Background

Long term survivorship in total knee arthroplasty is significantly dependant on prosthesis alignment. Our aim was determine which alignment guide was more accurate in positioning of the tibial component in total knee arthroplasty. We also aimed to assess whether there was any difference in short term patient outcome.

Method

A comparison of intramedullary versus extramedullary alignment jig was performed. Radiological alignment of tibial components and patient outcomes of 103 Triathlon total knee arthroplasties were analysed.

Results

Use of the intramedullary was found to be significantly more accurate in determining coronal alignment (p = 0.02) while use of the extramedullary jig was found to give more accurate results in sagittal alignment (p = 0.04). There was no significant difference in WOMAC or SF-36 at six months.

Conclusion

Use of an intramedullary jig is preferable for positioning of the tibial component using this knee system.