Tibial component rotation in total knee arthroplasty

Comparison of short-term clinical results between modified kinematically-aligned and guided motion bicruciate stabilized total knee arthroplasty

BACKGROUND

Both kinematically-aligned (KA) total knee arthroplasty (TKA) and bicruciate stabilized (BCS) TKA aim to reproduce the physiological knee kinematics. In this study, we compared the femoro-tibial component rotational mismatch between patients who underwent modified KA-TKA and those who received guided-motion BCS-TKA, and its influence on the clinical outcomes.

METHODS

In this retrospective study, 77 consecutive patients were included and divided into two groups: subjects who underwent modified KA-TKA with Persona (KA Group; n = 42) and those who received BCS-TKA with JOURNEY II (BCS group; n = 35). Range of motion, the 2011 Knee Society Score (KSS), the rotational alignment of the femoral and tibial components, and the correlations between the rotational mismatch and the 2011 KSS subscales were examined.

RESULTS

The postoperative objective knee indicators (P = 0.0157), patient satisfaction (P = 0.0039) and functional activity scores (P = 0.0013) in the KA group were significantly superior to those in the BCS group 1 year postoperatively. There was no significant difference between the two groups observed in the rotational mismatch. In the BCS group, significant negative correlations were identified between the rotational mismatch and objective indicators, patient satisfaction, and functional activity scores but not in the KA group.

CONCLUSIONS

The short-term clinical results following KA-TKA showed superior objective knee indicators, patient satisfaction and functional activity scores. A negative correlation was observed between component rotational mismatch and the 2011 KSS subscales in the BCS group, compared to no relationship found between the two in the KA group. These findings suggested that KA-TKA has a relatively higher tolerance for rotational mismatch than BCS-TKA.

Coronal Knee Alignment and Tibial Rotation in Total Knee Arthroplasty: A Prospective Cohort Study of Patients with End-Stage Osteoarthritis

Several studies have found a relationship between the rotational anatomy of the distal femur and the overall coronal lower limb alignment in knees with osteoarthritis (OA). Less is known about the rotation of the proximal tibia, especially in the context of total knee arthroplasty (TKA), where one of the goals of the surgery is to achieve the appropriate component-to-component rotation. The aim of this study was to investigate the relationship between the coronal alignment of the lower extremity and the relative proximal tibial rotation. A prospective cohort study of patients with an end-stage OA scheduled for TKA was conducted. All patients underwent a computed tomography (CT) scan and a standing X-ray of both lower limbs. A relative femorotibial rotation was measured separately for mechanical and kinematic alignment. A statistically significant correlation was found between the tibial varus and the external tibial rotation (p < 0.001). Out of 14 knees with high tibial varus (>5°), 13 (93%) and 7 (50%) knees had >10° of femorotibial rotation for the mechanical and kinematic alignment landmarks, respectively. In order to keep the component-to-component rotation within the 10° margin, more internal rotation of the tibial component is required in knees with higher tibial varus.

Individualizing a Total Knee Arthroplasty with Three-Dimensional Planning

Total knee arthroplasty (TKA) is evolving from mechanical alignment to more individualized alignment options in an attempt to improve patient satisfaction. Thirteen-year survival of kinematically aligned prostheses has recently been shown to be similar to mechanically aligned TKA, allaying concerns of long-term failure of this newer individualized technique. There is a complex inter-relationship of three-dimensional knee and limb alignment for a TKA. This article will review planning parameters necessary to individualize each knee, along with a discussion of how these parameters are related in three dimensions. Future use of computer software and machine learning has the potential to identify the ideal surgical plan for each patient. In the meantime, the material presented here can assist surgeons as newer individual alignment planning becomes a reality.

Biomechanical comparison of all-polyethylene total knee replacement and its metal-backed equivalent on periprosthetic tibia using the finite element method

BACKGROUND

Total knee arthroplasty (TKA) with all-polyethylene tibial (APT) components has shown comparable survivorship and clinical outcomes to that with metal-backed tibial (MBT). Although MBT is more frequently implanted, APT equivalents are considered a low-cost variant for elderly patients. A biomechanical analysis was assumed to be suitable to compare the response of the periprosthetic tibia after implantation of TKA NexGen APT and MBT equivalent.

METHODS

A standardised load model was used representing the highest load achieved during level walking. The geometry and material models were created using computed tomography data. In the analysis, a material model was created that represents a patient with osteopenia.

RESULTS

The equivalent strain distribution in the models of cancellous bone with an APT component showed values above 1000 με in the area below the medial tibial section, with MBT component were primarily localised in the stem tip area. For APT variants, the microstrain values in more than 80% of the volume were in the range from 300 to 1500 με, MBT only in less than 64% of the volume.

CONCLUSION

The effect of APT implantation on the periprosthetic tibia was shown as equal or even superior to that of MBT despite maximum strain values occurring in different locations. On the basis of the strain distribution, the state of the bone tissue was analysed to determine whether bone tissue remodelling or remodelling would occur. Following clinical validation, outcomes could eventually modify the implant selection criteria and lead to more frequent implantation of APT components.

Reference Axes for Tibial Component Rotation in Total Knee Arthroplasty: Computed Tomography-Based Study of 1,351 Tibiae

BACKGROUND

Many anatomic landmarks have been described for setting tibial component rotation intraoperatively. There is no consensus as to which axis is best for reducing outliers and preventing malrotation.

METHODS

The SOMA (Stryker Orthopaedic Modeling and Analytics) database (Stryker) was used to identify 1,351 computed tomography (CT) scans of the entire tibia. Several reference axes for the tibia (including the Mayo axis, Akagi line, Insall line, anterior condylar axis [ACA], posterior condylar axis [PCA], lateral tibial cortex [LTC], Cobb axis, tibial crest line [TCL], and transmalleolar axis [TMA]) were constructed according to published guidelines. The Berger method served as the reference standard.

RESULTS

The Mayo method (involving a line connecting the medial and middle one-thirds of the tibial tubercle and the geometric center of the tibia) and the Insall line (involving a line connecting the posterior cruciate ligament [PCL] insertion and the intersection of the middle and medial one-thirds of the tibial tubercle) both had low variability relative to the Berger method (7.8° ± 1.0° and 5.1° ± 2.2°, respectively) and a low likelihood of internal rotation errors (0.7% and 1.8%, respectively). No clinically significant gender-based differences were found (<0.7° for all). The same was true for ethnicity, with the exception of consistently greater tibial intorsion in Asian versus Caucasian individuals (mean difference in TCL position, +4.5° intorsion for Asian individuals; p < 0.001).

CONCLUSIONS

This CT-based study of 1,351 tibiae (which we believe to be the largest study of its kind) showed that the Mayo and Insall methods (both of which reference the medial and middle one-thirds of the tibial tubercle) offer an ideal balance of accuracy, low variability, and a reduced likelihood of internal rotation errors. Setting rotation on the basis of distal landmarks (tibial shaft and beyond) may predispose surgeons to substantial malrotation errors, especially given the differences in tibial torsion found between ethnic groups in this study.

LEVEL OF EVIDENCE

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

Biomechanical analysis of all-polyethylene total knee arthroplasty on periprosthetic tibia using the finite element method

BACKGROUND AND OBJECTIVE

Total knee arthroplasty (TKA) with modern all-polyethylene tibial (APT) components has shown high long-term survival rates and comparable results to those with metal-backed tibial components. Nevertheless, APT components are primarily recommended for older and low-demand patients. There are no evidence-based biomechanical guidelines for orthopaedic surgeons to determine the appropriate lower age limit for implantation of APT components. A biomechanical analysis was assumed to be suitable to evaluate the clinical results in patients under 70 years. The scope of this study was to determine biomechanically the appropriate lower age limit for implantation of APT components.

METHODS

To generate data of the highest possible quality, the geometry of the computational models was created based on computed tomography (CT) images of a representative patient. The cortical bone tissue model distinguishes the change in mechanical properties described in three parts from the tibial cut. The cancellous bone material model has a heterogeneous distribution of mechanical properties. The values used to determine the material properties of the tissues were obtained from measurements of a CT dataset comprising 45 patients.

RESULTS

Computational modeling showed that in the majority of the periprosthetic volume, the von Mises strain equivalent ranges from 200 to 2700 με; these strain values induce bone modeling and remodeling. The highest measured deformation value was 2910 με. There was no significant difference in the induced mechanical response between bone models of the 60-year and 70-year age groups, and there was <3% difference from the 65-year age group.

CONCLUSIONS

Considering in silico limitations, we suggest that APT components could be conveniently used on a bone with mechanical properties of the examined age categories. Under defined loading conditions, implantation of TKA with APT components is expected to induce modeling and remodeling of the periprosthetic tibia. Following clinical validation, the results of our study could modify the indication criteria of the procedure, and lead to more frequent implantation of all-polyethylene TKA in younger patients.

Determining the rotational alignment of the tibial component referring to the tibial tubercle during total knee arthroplasty: the tibial tubercle-trochlear groove can be an aid

Background

There is no consensus on anatomic landmarks or reference axes with which to accurately align rotational position of tibial component. Using the tibial tubercle, commonly referring to the Akagi line and the Insall line, for anatomic reference was widely accepted. However, it is unknown about the predictors that may affect the reliability of using the tibial tubercle for aligning tibial component rotation. The aims of our study were (1) to investigate the reproducibility and accuracy of using the tibial tubercle for aligning tibial component rotation and (2) to determine predictors resulting in discrepancies of the tibial component rotation when referring to the tibial tubercle.

Method

A total of 160 patients with osteoarthritis were recruited before total knee arthroplasty. The angle α formed by the tibial anteroposterior (AP) axis and the Akagi line and the angle β formed by the tibial AP axis and the Insall line were measured to quantify the discrepancies of the Akagi line and the Insall line. Independent variables, including the tibial tubercle-to-trochlear groove distance (TT-TG), tibial tubercle to posterior cruciate ligament (TT-PCL), and knee rotation angle (KRA), hip–knee–ankle angle (HKA), medial proximal tibial angle (MPTA), and tibial bowing (TB), were measured. Pearson’s product moment correlation coefficients and multivariable linear regression analysis were calculated to assess relationships between independent variables and the two defined angles.

Results

All defined measurement were available for 140 patients. The Akagi line rotated internally with 1.03° ± 4.25° in regard to the tibial AP axis. The Insall line rotated externally in regard to the tibial AP axis with 7.93° ± 5.36°. Three variables, including TT-TG, TT-PCL, and KRA, tended to be positively correlated with the angle α and the angle β. In terms of a cutoff of TT-TG = 9 mm, 100% cases and 97% cases for using the Akagi line and Insall line, respectively, were located in the defined safe zone (− 5° to 10°).

Conclusion

The tibial tubercle (the Akagi line and Insall line) is found to be a useful and promising anatomic landmark for aligning the tibial component rotation. The TT-TG, with a cutoff value of 9 mm, is helpful to choose the Akagi line or Insall line, alternatively.

Accuracy and Validity of Sharma's Venn Diagram Method for Assessment of Tibial Component Rotation in Total Knee Arthroplasty

BACKGROUND

Malrotation of the tibial component in a total knee replacement leads to anterior knee pain, patella dislocations, extensor mechanism disruptions, knee stiffness and prosthesis loosening. Techniques like free-floating technique, medial 1/3 rd of the tibial tubercle, medial border of the tibial tuberosity, Akagi's line, transcondylar line of tibia, posterior condylar line of tibia, midsulcus of tibial spines, curve on curve technique have been advocated. None of these have been shown to be accurate and reproducible. We developed a novel 'Sharma's Venn Diagram' method to assess the tibial component rotation.

METHODS

Fifty-two consecutive knee replacements were included in a prospective observational study. The average age of the study group was 53.6 years (48-76 years) Thirty-one were females and 3 were males. The patients were followed a minimum of one years (max 2 years, average 1.8 years). 'Sharma's Venn diagram Method (C)' was compared to free-floating method (F) and post-op CT scans using Berger protocol (B).

RESULTS

Tibial rotation calculated using Sharma's Venn diagram method (C) coincided with the final component placement in 50/52 knees. The free floating method (F) coincided with method (C) in 30/52 knees with an average 4.8° external rotation in 5 knees and an average of 5.2° internal rotation in 17 knees. Bland Altman method was used to compare method (C) with Method (F), The difference was statistically significant p < 0.0001.

CONCLUSION

Sharma's Venn diagram method is reliable, accurate and easily reproducible by any surgeon performing tkr and correlates with postoperative 2D CT-based assessment of tibial component rotation.

LEVEL II STUDY

Prospective observational study.

Patellar management during total knee arthroplasty: a review

The optimal management of the patella during total knee arthroplasty (TKA) remains controversial and surgeons tend to approach the patella with one of three general mindsets: always resurface the patella, never resurface the patella, or selectively resurface the patella based on specific patient or patellar criteria.

Studies comparing resurfacing and non-resurfacing of the patella during TKA have reported inconsistent and contradictory findings.

When resurfacing the patella is chosen, there are a number of available patellar component designs, materials, and techniques for cutting and fixation.

When patellar non-resurfacing is chosen, several alternatives are available, including patellar denervation, lateral retinacular release, and patelloplasty. Surgeons may choose to perform any of these alone, or together in some combination.

Prospective randomized studies are needed to better understand which patellar management techniques contribute to superior postoperative outcomes. Until then, this remains a controversial topic, and options for patellar management will need to be weighed on an individual basis per patient.

Cite this article: EFORT Open Rev 2021;6:861-871. DOI: 10.1302/2058-5241.6.200156

A new technique for determining the rotational alignment of the tibial component during total knee arthroplasty

BACKGROUND

We evaluated the effectiveness of our new technique "Range of motion-anatomical (ROM-A) technique" which is the combination of the self-positioning technique "Range of motion (ROM) technique" and the anatomical landmarks technique in determining the tibial component (TC) rotation alignment in total knee arthroplasty (TKA) using a navigation system.

METHODS

This retrospective study included 103 knees who underwent TKA. The ROM-A technique was consisted of two steps. First, the TC was set and marked by the ROM technique in knee extension. Second, the TC was set according to the marking in the knee flexion and the component rotational angle relative to the anatomical tibial anteroposterior (AP) axis was adjusted between 0° and 10° external rotation using the navigation system. The rotational angle of TC relative to the anatomical AP axis was measured using postoperative computed tomography. Moreover, the hypothetical rotational angle of the TC in the ROM technique was calculated only from the intraoperative difference between the two techniques.

RESULTS

The actual rotational angle by the ROM-A technique was externally rotated 3.0°, and the rotational outlier occurred in 3.0%. A significant difference in outlier rate was observed between the two techniques (p = 0.03). The hypothetical rotational angle of TC determined by the ROM technique (the first step only in the ROM-A technique) was externally rotated 4.6° and the TC rotational outlier (difference to AP axis: >10°) occurred in 11.7%.

CONCLUSION

Using the ROM-A technique, the TC was finally fixed in almost all targeted rotational positions, and this technique could reduce the anatomical rotational outlier compared with the ROM technique.

Malrotation of the fixed-bearing posterior stabilized total knee prosthesis causes a postoperative rotational mismatch between the femur and tibia

PURPOSE

This study aimed to identify factors associated with rotational mismatch after total knee arthroplasty (TKA) using fixed-bearing posterior stabilized prosthesis and to evaluate the impact of the rotational mismatch on clinical outcomes.

METHODS

This retrospective cohort study included 159 cases that underwent TKA. Whole-leg computed tomography images were obtained 2 weeks after TKA, with three-dimensional measures of alignment. Rotational alignment of the femoral and tibial components and rotational mismatch between components and between the femur and tibia bones were evaluated. The new Knee Society Score (KSS) was obtained at the final outpatient visit, which was defined as the final follow-up timepoint. Predictive factors were identified for rotational mismatch of the lower extremity and poor new KSS.

RESULTS

The mean follow-up period was 42 ± 16 months. Rotational mismatch ≥ 10° between bones was identified in 56 cases (35%), with a mean mismatch angle of 5.0° ± 9.1° of external rotation of the tibia relative to the femur. Rotational mismatch ≥ 10° between components was identified in three cases (2%; mean 0.3° ± 3.6° of internal tibial rotation). A multivariate regression analysis showed that component malrotation was predictive of post-operative rotational mismatch between bones (p < 0.01) and rotational mismatch ≥ 10° associated with poor new KSS (odds ratio 4.22; p < 0.01).

CONCLUSION

Malrotation of the fixed-bearing posterior stabilized TKA causes a rotational mismatch between the femur and tibia bones. Excessive rotational mismatch between bones greater than 10° is a risk factor for poor postoperative functional outcome. Precise component positioning is essential for improving TKA outcomes.

LEVEL OF EVIDENCE

III.

[Progress in the method of tibial prosthesis rotation alignment in total knee arthroplasty]

OBJECTIVE

To summarize the methods of tibial prosthesis rotation alignment in total knee arthroplasty, and provide reference for clinicians to select and further study the methods of tibial prosthesis rotation alignment.

METHODS

The advantages and disadvantages of various tibial prosthesis rotation alignment methods were analyzed and summarized by referring to the relevant literature at home and abroad in recent years.

RESULTS

There are many methods for tibial prosthesis rotation alignment, including reference to relevant anatomical landmarks, range of motion (ROM) technique, computer-assisted navigation, and personalized osteotomy. The inner one-third of the tibial tuberosity is a more accurate reference anatomical landmark, but the obesity, severe knee deformity and dysplasia have impacts on the precise placement of the tibial prosthesis. ROM technique do not need to refer to the anatomical landmark of the tibia, and aren't affected by landmark variation. It can be used for severe knee valgus deformity and the landmarks that are difficult to identify. However, it may cause internal rotation of tibial prosthesis. Computer- assisted navigation and personalized osteotomy can achieve more accurate alignment in sagittal, coronal, and rotational alignment of femoral prosthesis. However, due to the lack of reliable anatomical landmarkers related to tibia fixation, it is still controversial whether it can help the alignment of tibial prosthesis rotation.

CONCLUSION

The surgeon should master the methods of rotation and alignment of tibial prosthesis, make preoperative plans, select appropriate alignment methods for different patients, and achieve individualization. Meanwhile, several anatomical landmarkers should be referred to properly during the operation, which can be used to detect the correct placement of tibial prosthesis and avoid large rotation error.

A comparative study of weight-bearing and non-weight-bearing 3-dimensional lower extremity alignment in knee osteoarthritis

BACKGROUND

Lower extremity alignment is an important variable with respect to the development and progression of knee osteoarthritis. It is very essential for the preoperative planning of realignment surgeries such as total knee arthroplasty and high tibial osteotomy. Nevertheless, there have been no reports comparing 3D lower extremity alignment between weight-bearing upright and non-weight-bearing horizontal states in osteoarthritic knees in the same subject. Therefore, we determined whether the alignment of the lower extremity in the weight-bearing upright state differed from that in the non-weight-bearing horizontal or supine position in patients with knee osteoarthritis.

METHODS

Adduction-abduction, flexion-extension, and rotational angle of osteoarthritic knees were assessed in weight-bearing upright and non-weight-bearing supine positions. Knee alignment in the supine position was determined from preoperative computed tomography data. In the weight-bearing upright state, alignment was determined using a technique that utilized 2D-3D image-matching with biplanar computed radiography and 3D bone models of the complete lower extremity rebuilt using computed tomography-based information.

RESULTS

We assessed 81 limbs from osteoarthritic knee patients (74 women, 7 men; mean age 75.3 years, range 59-86 years). In the coronal plane, there were varus deformities in both the supine and standing positions, while there was flexion in both the supine upright state and position at the sagittal plane. In the axial plane, the rotation of the tibia to the femur was neutral in the supine position and internal in the upright state.

CONCLUSION

Patient position significantly affects lower extremity alignment in osteoarthritic knees. This study provides important data regarding the preoperative evaluation of realignment surgery in total knee arthroplasty and high tibial osteotomy. We believe that these results are an important contribution to the knowledge regarding knee osteoarthritis.

Methods of intra- and post-operative determination of the position of the tibial component during total knee replacement

AIM OF THE STUDY

To identify the most reliable anatomical landmarks and imaging techniques for assessing the rotation of the tibial component in total knee arthroplasty (TKA).

METHODS

An extensive literature review (from January 2016 to March 2019) was performed. We included studies about primary TKA with details concerning the anatomical landmarks used for implanting the tibial component and also imaging studies assessing tibial component rotation. The final selection comprises only thirty-five articles consistent with the inclusion criteria.

RESULTS

Extra-articular landmarks are not always reliable (even though the tibial tubercle is one of the most popular extra-articular landmarks used to assess the rotation of the tibial component), mainly because they vary and can lead to malrotation of the tibial component. Akagi's line (an intra-articular landmark) is considered to be the most reliable and easy to find during surgery and likewise is not affected by articular deformities. The anterior tibial cortex (intra-articular landmark) also proved to be accurate and reliable with the main advantage being that is palpable after tibial resection. Radiography provides a good and inexpensive option for imaging, but it is insufficient. Magnetic resonance imaging (MRI) is used in some cases but not routinely for assessing TKA components or their orientation. Computed tomography (CT), used together with a well-defined protocol (Berger's method being the preferred choice), remains the "gold standard" for evaluating the rotation of the tibial component after TKA.

CONCLUSION

Currently, the most accurate and reliable anatomical landmarks are represented by Akagi's line and the anterior cortex of the tibia. Post-operatively, through CT and well-established protocols, the rotation of the tibial component can be accurately determined.

A new landmark for measuring tibial component rotation after total knee arthroplasty

BACKGROUND

Existing methods for assessment of total knee arthroplasty (TKA) component rotation on computed tomography (CT) scans are complex, especially in relation to the tibial component. Anecdotal evidence from our practice pointed towards a potential new landmark. The study aims were to check the prevalence of this landmark, define tibial component rotation in relation to it and demonstrate its reliability.

METHODS

Two hundred and eleven CTs undertaken following TKA were reviewed for presence of the landmark. A protocol to measure tibial component rotation in relation to this landmark was developed and the rotation measured using this method and Berger's protocol. Thirty one of the 211 CT scans were measured twice by two observers. Reliability was calculated using the Intraclass Correlation Coefficient (ICC).

RESULTS

The new landmark of a flat area on the lateral cortex of the tibia inferior to the tibial component was identified on all scans. Median tibial component rotation measured using our protocol was 0.0° ± 5.4° and -9.2° ± 5.5° using Berger's protocol. Intra-observer reliability with the new method was excellent (ICCs of 0.899 and 0.871) and inter-observer reliability was good (ICCs of 0.734 and 0.836).

CONCLUSIONS

The new landmark had a very high prevalence and could be used to define tibial component rotation. This measurement of tibial component rotation had acceptable reliability. This landmark has potential for use in the radiological assessment of tibial component rotation following TKA. Further work is required to determine its relationship to anatomical structures and symptoms of tibial component mal-rotation.

The original Akagi line is the most reliable: a systematic review of landmarks for rotational alignment of the tibial component in TKA

PURPOSE

There is no present consensus on the most reliable anatomical landmarks or axes for tibial rotational alignment in total knee arthroplasty (TKA). The goal was therefore to review the literature and compare accuracy and repeatability of different axes for tibial baseplate rotation in TKA.

METHODS

Medline and Embase were searched for articles that reported accuracy in terms of error or discrepancy from the trans-epicondylar axes (TEA), and/or repeatability in terms of intraclass correlation coefficient, of one or more axes used for tibial baseplate rotation in TKA. Twenty-one articles met criteria, and their data were extracted and tabulated.

RESULTS

The selected articles evaluated 15 different axes, 13 for reliability, 12 for repeatability. The lowest errors or discrepancies from the projected TEA were reported for the original 'Akagi line' (posterior cruciate ligament posteriorly to medial border of tibial tuberosity), its variant using the sulcus of the tibial spines as anterior landmark, as well as the anterior tibial border and the curve-on-curve technique. The best inter-observer repeatabilities were reported for 'Akagi line' variants that use the geometric centre of the tibial plateau posteriorly and the medial border of the tibial tuberosity, or the medial sixth of the patellar tendon anteriorly. Considering accuracy and repeatability simultaneously, only two axes were found to satisfy both criteria consistently: the original 'Akagi line' and the anterior tibial border.

CONCLUSIONS

Because of the small number of studies found, the collected evidence remains insufficient to recommend reference axes for intra-operative rotational alignment of the tibial baseplate in TKA. A combination of two or more anatomical landmarks or projected axes could be used to ensure adequate tibial baseplate rotation, while considering individual patient morphology and implant design to optimize knee kinematics and prevent prosthetic overhang.

LEVEL OF EVIDENCE

Level IV, systematic review of level III and IV studies.

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.

A computer-assisted, tibia-first technique for improved femoral component rotation in total knee arthroplasty

Background

The use of navigation for total knee arthroplasty (TKA) improves limb alignment in the coronal and sagittal planes. However, similar improvements in femoral and tibial component rotation have not yet been realized using currently available systems.

Methods

We developed a modified navigated TKA technique in which femoral rotation was set using the resected tibial plane as the reference with the aim of achieving a rectangular flexion gap. Limb alignment was assessed in a cohort of 30 knees using the navigation system. Post-operative limb alignment was measured using long-leg standing radiographs. Computed tomography was used to determine post-operative component orientation.

Results

Sagittal alignment data improved from a mean of 7.8° varus (pre-operative) to 0.0° (post-operative), assessed by intra-operative navigation. Post-operative hip-knee-ankle axis alignment was 0.9° valgus (mean; standard deviation [SD] 1.7°). Mean femoral component rotation was 0.5° internally rotated (SD 2.6°), relative to the surgical transepicondylar axis. Mean tibial component rotation was 0.9° externally rotated (SD 5.5°). No soft tissue releases were performed.

Conclusions

These results confirm that the desired femoral rotation, set using a tibia-first approach with the resected tibial plane as the reference, can be achieved without compromising overall limb alignment. Femoral component rotation was within a narrow range, with a moderate improvement in achieving more consistent tibial component rotation compared with other techniques. This technique may prove to be useful for surgeons wishing to employ a tibia-first philosophy for TKA while maximizing the benefits associated with computer-assisted navigation.

Internal femoral component rotation adversely influences load transfer in total knee arthroplasty: a cadaveric navigated study using the Verasense device

PURPOSE AND HYPOTHESIS

Correct femoral component rotation at knee arthroplasty influences patellar tracking and may determine function at extremes of movement. Additionally, such malrotation may deleteriously influence flexion/extension gap geometry and soft tissue balancing kinematics. Little is known about the effect of subtle rotational change upon load transfer across the tibiofemoral articulation. Our null hypothesis was that femoral component rotation would not influence load across this joint in predictable manner.

METHODS

A cadaveric study was performed to examine load transfer using the orthosensor device, respecting laxity patterns in 6° of motion, to examine load across the medial and lateral compartments across a full arc of motion. Mixed-effect modelling allowed for quantification of the effect upon load with internal and external femoral component rotation in relation to a datum in a modern single-radius cruciate-retaining primary knee design.

RESULTS

No significant change in maximal laxity was found between different femoral rotational states. Internal rotation of the femoral component resulted in significant increase in medial compartment load transfer for knee flexion including and beyond 60°. External rotation of the femoral component within the limits studied did not influence tibiofemoral load transfer.

CONCLUSIONS

Internal rotation of the femoral component will adversely influence medial compartment load transfer and could lead to premature polyethylene wear on the medial side.