Tibial component positioning in total knee arthroplasty: bone coverage and extensor apparatus alignment

Early- to Mid-Term Review of a Prospective, Multi-Center, International, Outcomes Study of an Anatomically Designed Implant with Posterior-Stabilized Bearing in Total Knee Arthroplasty

Background and Objectives: National joint registries report higher total knee arthroplasty (TKA) revision rates in posterior-stabilized (PS) systems compared to non-posterior-stabilized designs. The purpose of this study was to investigate the implant survivorship and clinical outcomes of an anatomic implant with a PS bearing. Materials and Methods: An early- to mid-term follow-up of a prospective, multi-center, non-controlled outcomes study of patients who received primary TKA between November 2014 and June 2017 was performed. A total of 800 cases using PS bearings that were implanted in 664 patients were monitored post-operatively for their implant survivorship and adverse events for up to five years. The Knee Society Knee and Function scores, patient satisfaction, the five-dimensional European Quality of Life questionnaire, and range of motion (ROM) were evaluated pre-operatively and post-operatively at six weeks, six months, one year, two years, three years, and five years. Results: The mean follow-up period was 3.7 ± 1.3 years, and the three-year implant survival rate was 99.3% (95% CI: 98.4%, 99.7%) with five revisions during the five-year follow-up. Patient satisfaction was 96.1% at six weeks and increased to 99.3% at one year. All patient-reported outcome measures significantly (p < 0.0001) increased up to the one-year follow-up and then remained stable up to the five-year follow-up. Conclusions: This study supports the excellent survivorship and patient-reported outcomes of the Persona® Knee system using cemented, fixed bearing, posterior-stabilized components with minimal complications at early- to mid-term follow-up in an international Asian population. Ongoing observations are being performed to investigate the mid- to long-term survivorship and clinical outcomes associated with this knee system.

Undersizing the Tibial Baseplate in Cementless Total Knee Arthroplasty has Only a Small Impact on Bone-Implant Interaction: A Finite Element Biomechanical Study

BACKGROUND

The tibial component in total knee arthroplasty (TKA) is often chosen to maximize coverage of the tibial cut, which can result in excessive internal rotation of the component. Optimal rotational alignment may require a smaller baseplate with suboptimal coverage that could threaten fixation. We asked: "does undersizing the tibial component of a cementless TKA to gain external rotation increase the risk of bone failure?"

METHODS

We developed computational finite element (FE) analysis models from the computed tomography (CT) scans of 12 patients scheduled for primary TKA. The models were implanted with a cementless tibial baseplate that maximized coverage and one or two sizes smaller and externally rotated by 5°. We calculated the risk of bone collapse under loads representative of stair ascent.

RESULTS

Undersizing the implant increased the area at risk of collapse for eight patients. However, the area at risk of collapse for the undersized implant (range, 5.2%-16.4%) was no different (P = .24) to the optimally sized implant (range, 4.5%-17.9%). The bone at risk of collapse was concentrated along the posterior edge of the implant. The area at risk of collapse was not proportional to implant size, and for four subjects undersizing the implant actually decreased the area at risk of collapse.

CONCLUSION

While implants should maximize coverage of the tibial cut and seek support on dense bone, undersizing the tibial component to gain external rotation had minimal impact on the load transfer to the underlying bone. This FE analysis model of a cementless tibial baseplate may require further validation and additional studies to investigate the long-term biomechanical effects of undersizing the tibial baseplate. In conclusion, while surgeons should strive to use the appropriate tibial baseplate for each patient, our model identified only minor biomechanical consequences of undersizing the implant for the immediate postoperative bone-implant interaction and implant subsidence.

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.

Correlation of tibial component size and rotation with outcomes after total knee arthroplasty

INTRODUCTION

Tibial component design and positioning contribute more to patient satisfaction than previously realized. A surgeon needs to decide on the size and rotation, bearing in mind that coverage should be as high as possible, whilst malrotation and overhang should be avoided. No study investigates the impact of each of these components on clinical outcomes in a single cohort.

MATERIALS AND METHODS

This is a retrospective analysis of 1-year postoperative outcomes measured with the Knee Injury and Osteoarthritis Outcome (KOOS) Score, as well as a previously validated rotational CT protocol. Coverage, rotation from Insall's axis, and overhang of an asymmetric tibial baseplate were measured, and positive and negative correlations to clinical outcomes were calculated.

RESULTS

A total of 499 knees were analyzed. Patient average age was 68.4 years. Rotation within 7° internal and 5° external from Insall's axis was a "safe zone". Mean coverage was 76%. A total of 429 knees (94%) had a coverage of at least 70% and 102 knees (22%) greater than 80%. Overhang was detected in 23% of the cohort. Increased coverage was correlated to increased KOOS score and overhang correlated with a decreased KOOS score (p = 0.008).

CONCLUSIONS

This study demonstrates the individual role of three aspects of tibial component implantation properties in postoperative pain and short-term functional outcomes. Upsizing to the point of overhang with rotational tolerance of 7° internal and 3° external to Insall's axis demonstrates best patient reported outcomes. Overhang decreases the clinical outcome by the same margin as loss of 16% of coverage.

Fluoroscopic Intraoperative Images Produce Higher Image Quality and Decrease Total Radiation Exposure Compared to Radiographic X-ray Images in Patients After Primary Total Knee Arthroplasty

BACKGROUND/AIM

Proper radiographic documentation of implant alignment is needed to analyse malrotation and malpositioning. We examined whether intraoperative fluoroscopic images can achieve more accurate image quality than postoperative radiographic X-ray images.

PATIENTS AND METHODS

We prospectively analysed 30 consecutive patients after total knee arthroplasty (TKA). We compared intraoperative fluoroscopic images with postoperative radiographic X-ray images. Radiation exposure was documented.

RESULTS

Fluoroscopic anterior-posterior images could achieve accurate image quality in 77% compared to 60% in radiographic images (p=0.016) and 54% compared to 34% on lateral view, respectively (p=0.008). Very good intra-observer correlation for fluoroscopic images could be achieved for femoral α angle with 0.84. Radiation exposure was 0.087+/-0.128 mGy.

CONCLUSION

We observed significantly better image quality in fluoroscopic images than in radiographic X-ray images. The observed radiation exposure is lower than those expected for radiographic X-ray images. We conclude that fluoroscopic images can produce higher image quality and decreased radiation exposure.

Approximating the maximum tibial coverage in total knee arthroplasty does not necessarily result in implant malrotation

Traditionally, the practice of the tibial component placement in total knee arthroplasty has focused on achieving maximum coverage without malrotation. However, the concept of maximizing coverage has not been well defined or researched and yet biased results are often produced. This study aimed to evaluate the effect of a prioritizing maximum coverage positioning strategy on the rotational alignment by using a strict computer algorithm. Computed tomographic scans of 103 tibial specimens were used to reconstruct three-dimensional tibia models. A virtual surgery was performed to generate the resection plane with a posterior slope of 7° on the proximal tibia. Symmetrical and anatomical tibial components were placed and analyzed with an automated program designed for approximating the maximum coverage based on the coherent point drift algorithm. We found that the average tibial coverage achieved across all specimens and implants was 85.62 ± 3.65%, ranging from 83.64 ± 4.10% to 86.69 ± 3.07%. When placed for maximal tibial coverage, the mean degree of rotation related to the Insall line was − 0.73° ± 4.53° for all subjects, 23% of the tibial components were malrotated. The average percentage position of the baseplate anteroposterior axis over the patellar tendon was 26.95 ± 14.71% from the medial edge. These results suggest that with specific design and proper placement of the component, approximating the maximum tibial coverage in total knee arthroplasty does not necessarily result in implant malrotation. The current tibial baseplates have shown good performance on the coverage when aligned parallel to the Insall line with the anteroposterior axis positioned between the medial 1/3 and medial 1/6 of the patella tendon.

Medial Overhang of the Tibial Component Is Associated With Higher Risk of Inferior Knee Injury and Osteoarthritis Outcome Score Pain After Knee Replacement

BACKGROUND

The aim of this prospective multicenter study is to investigate the association among (1) tibial site-specific overhang of medial, anterior, and lateral overhang in relation to Knee Injury and Osteoarthritis Outcome Score pain 1 year after surgery (1 Y KOOS pain) and (2) the malalignment of TKA components including overall malalignment in relation to 1 Y KOOS pain.

METHODS

From 10 centers, across 4 continents, 323 patients were enrolled from October 2011 to February 2014. Radiographs were analyzed for tibial overhang on medial, anterior, and lateral site and for overall, tibial, femur, and combined malalignment. A 1 Y KOOS pain score <70 represented an unsatisfactory pain level.

RESULTS

A significant association was observed between medial overhang and 1 Y KOOS pain with a cut-off of <70 (P = .04), with an odds ratio of 0.46. No significant associations were observed among the independent variables of lateral and anterior overhang or for overall, tibial, femoral, and combined component malalignment, and the dependent variable of 1 Y KOOS pain <70.

CONCLUSION

This prospective multicenter study showed a significant association between medial overhang of the tibial component and a 1 Y KOOS pain <70. The related odds ratio was 0.46, which demonstrates that medial overhang may lead to a 54% reduced chance for entering an acceptable pain category 1 year after surgery when receiving a TKA.

Posterolateral overhang affects patient quality of life after total knee arthroplasty

PURPOSE

To investigate the appropriate mediolateral placement of symmetrical tibial components and the amount of overhang expected from the posterolateral of tibial components implanted to give ideal coverage and the subsequent incidence of residual knee pain and reduction in functional capacity.

METHOD

A retrospective evaluation was made of 146 consecutive total knee arthroplasties. The posterolateral overhang, rotational alignment and coverage of the tibial component were measured on a post-operative CT scan and the effect of posterolateral overhang on clinical outcomes was analysed 3 years after surgery.

RESULTS

Complaints of local pain in the posterolateral corner were determined in 76 (52.1%) patients. At the Posterolateral corner, overhang was determined in 111 (76%) patients, in the cortical border in 11 (7.6%) patients and underhang in 24 (16.4%) patients. In 71 (48.6%) patients, pain was determined together with oversize and in the evaluation of the overhang of the tibial component in the posterolateral region and the rotation status, there was determined to be overhang in 75 (96.2%) patients where the tibial component was placed in ideal rotation, in 25 (100%) where placement was in external rotation and in 11 (25.6%) where placement was in internal rotation. The mean KSS, KSS-F and WOMAC-P scores were 83.9 ± 6.3, 83.3 ± 7.8 and 4.6 ± 2.9, respectively, in those with posterolateral overhang of the tibial component .The mean KSS, KSS-F and WOMAC-P scores were 86.6 ± 8.4, 89.5 ± 7.8 and 2.8 ± 2.1, respectively, in those with no overhang and the difference was determined to be statistically significant. The amount of overhang was determined as mean 3.6 ± 2.0 mm in those with posterolateral pain and 0.02 ± 3.4 mm in those without pain and the difference was statistically significant.

CONCLUSIONS

This study demonstrated that overhang in the posterolateral region is surprisingly high and negatively affects the clinical results following TKA, thereby presenting a danger to the success of TKA. The risk of posterolateral oversizing can increase with placement of the tibial component in external rotation.

The fibular head projection is of limited use as a radiographic landmark in preoperative planning of total knee arthroplasty

INTRODUCTION

The projection of the fibular head is recommended as a quality indicator of a correct radiographic projection. However, this landmark has yet to be sufficiently validated.

METHODS

The MRIs of 334 knee joints were included. On the MRIs, the distance between the FH and lateral tibial cortical bone was simulated in projections parallel to surgically relevant axes. Then, the Pearson correlation coefficient between the distance of the FH to the lateral tibial cortical bone and the projection plane causing this was determined.

RESULTS

A projection of the knee joint perpendicular to Akagi's line projected the center of the fibular head on average 4.8 ± 2.9 mm laterally of the tibial cortical bone, parallel to the maximum mediolateral axis of the tibia 7.5 ± 3.4 mm, parallel to the posterior condylar axis 5.6 ± 3.6 mm and parallel to the surgical epicondylar axis 6.1 ± 3.5 mm laterally of the tibial cortical bone. An almost linear correlation was seen, with 1.9° tilting of the projection plane per mm change in distance between the fibular head and tibial cortical bone. At the same time, the interindividual scatter was over 60°.

CONCLUSIONS

The rule of thumb for a partial overlap of the fibular head by the tibia in the case of a correct antero-posterior projection plane was also confirmed. However, a considerable interindividual variability of the position of the FH was found, which limits a conclusion regarding the quality of the radiographic projection on the basis of the position of the fibular head.

Influence of mediolateral tibial baseplate position in TKA on knee kinematics and retropatellar pressure

PURPOSE

Anterior knee pain is a major reason for unsatisfied patients after total knee arthroplasty (TKA). Since malposition and increased retropatellar peak pressure are supposed to contribute to pain, we conducted this in vitro study to analyse the influence of mediolateral tibial component position on tibiofemoral and patella kinematics as well as retropatellar pressure.

METHODS

Eight fresh frozen cadaver specimens were tested after a fixed-bearing TKA. To evaluate the influence of mediolateral tibial component position, special inlays with 3 mm of medialization and lateralization were constructed. For the analysis, a weight-bearing knee rig under a loaded squat from 20° to 120° of flexion was used. Tibiofemoral and patella kinematics were measured with an ultrasonic-based three-dimensional motion analysis system. Additionally, retropatellar pressure distribution was registered with a pressure-sensitive film.

RESULTS

Alteration of mediolateral tibial component position by 3 mm did not reveal a significant influence on retropatellar peak pressure (7.5 ± 2.5 vs. 7.2 ± 2.6 MPa). Regarding tibiofemoral kinematics, 3-mm medialization of the tibial baseplate significantly increased lateral femoral rollback and femorotibial external rotation. Medialization of 3 mm also significantly increased the relative medial patella shift and decreased lateral patella tilt.

DISCUSSION

Medialization of the tibial baseplate came along with more lateral rollback and external femorotibial rotation. For the positioning of the tibial baseplate, rotational alignment seems to be more important than mediolateral orientation. Since retropatellar peak pressure remained rather unchanged, the tibial baseplate should be placed by the surgeon looking for a maximal tibial coverage without overhang.

Oversizing the tibial component in TKAs: incidence, consequences and risk factors

PURPOSE

The incidence of anteroposterior overhang of the tibial component after TKA and its effect on clinical outcome were investigated, and the morphometric characteristics of the knees in which tibial baseplates were oversized were identified.

METHOD

One hundred and fourteen consecutive TKAs were retrospectively assessed. The dimensions of the tibia were measured on a pre-operative CT scan and were compared with those of the implanted tibial component. We analysed the effect of anteroposterior and mediolateral size variations on clinical outcomes 1 year after surgery.

RESULTS

An anteroposterior overhang was observed in 87 % of cases on the lateral plateau, in 88 % on the central plateau and in 25 % on the medial tibial plateau. The mean post-pre-operative size differences were 3.2 ± 2.7, 2.8 ± 2.7 and -1.6 ± 2.3 mm, respectively. (Positive value means oversizing). A mediolateral overhang of the tibial component was found in 61 % of the patients. Oversizing was significantly greater and more frequent in females. Patients oversized in the anteroposterior dimension had lower post-operative pain scores. Patients with mediolateral oversizing had decreased flexion 1 year after surgery. Anteroposterior oversizing was observed more frequently in patients with asymmetric tibial plateaus, while mediolateral oversizing was observed more frequently in patients with small tibias.

CONCLUSIONS

This study demonstrates that the incidence of oversized tibial plateau components is surprisingly high and that functional outcomes are lower in the case of mediolateral or anteroposterior oversizing. The risk of oversizing could be predicted as it occurs predominantly in patients with asymmetric proximal tibia and/or small tibia.

LEVEL OF EVIDENCE

IV.

MRI Based Comparison of Tibial Bone Coverage by Five Knee Prosthesis: Anthropometric Study in Indians

This MRI based study evaluates morphological differences of proximal tibia (total cross-sectional area, mediolateral and anteroposterior distance) 8-10 mm distal to the lateral tibial plateau. We evaluated the difference in the coverage of the tibial surface between symmetric and asymmetric tibial trays and difference in coverage between males and females. 150 patients who underwent MRI scans for sports related soft tissue injury without osteoarthritis were studied. The tibial trays of the 5 total knee arthroplasty designs (4 symmetric and 1 asymmetric) were scanned. Mean total tibial coverage of all designs was more than 80%. Asymmetric baseplate had maximum total tibial coverage and maximum rate of optimal fit, with only 2% absolute overhang posterolaterally. Females had better tibial coverage as compared to males.

Anthropometric difference of the knee on MRI according to gender and age groups

The purpose of this study was to analyze the anthropometric data from MRI images that were obtained from the non-arthritic knees in Asian adults, and to identify the existence of morphologic differences between age groups. This cross-sectional study included knee MR images of 535 patients (273 males, 262 females) taken for the evaluation of soft-tissue injuries, excluding cases with cartilage defect and malalignment. The age, gender, height, and BMI were also assessed. The patients were grouped into three different 20-year age groups (20-39, 40-59, and 60-79). The MRI analysis was performed on the anthropometric parameters of distal femur and posterior tibial slope. Age-related differences were found in femoral width, distance from the distal and posterior cartilage surface to the medial/lateral epicondyle, medial posterior condylar offset (PCO), and posterior condylar angle (PCA) (all P < 0.001), but not in lateral PCO, and medial/lateral tibial slopes. In the analysis of covariance analyses, significant interaction between gender and age groups was found in most parameters, but not in PCA, distance from the posterior cartilage surface to the medial epicondyle, or medial tibial slope. We found anthropometric differences among age groups exist in most of distal femoral parameters, but not in posterior tibial slope. The results of this study can be used by manufacturers to modify prostheses to be suitable for the future Asian elderly population.

What is the optimal alignment of the tibial and femoral components in knee arthroplasty?

BACKGROUND

Surgeon-dependent factors such as optimal implant alignment are thought to play a significant role in outcome following primary total knee arthroplasty (TKA). Exact definitions and references for optimal alignment are, however, still being debated. This overview of the literature describes different definitions of component alignment following primary TKA for (1) tibiofemoral alignment in the AP plane, (2) tibial and femoral component placement in the AP plane, (3) tibial and femoral component placement in the sagittal plane, and (4) rotational alignment of tibial and femoral components and their role in outcome and implant survival.

METHODS

We performed a literature search for original and review articles on implant positioning following primary TKA. Definitions for coronal, sagittal, and rotational placement of femoral and tibial components were summarized and the influence of positioning on survival and functional outcome was considered.

RESULTS

Many definitions exist when evaluating placement of femoral and tibial components. Implant alignment plays a role in both survival and functional outcome following primary TKA, as component malalignment can lead to increased failure rates, maltracking, and knee pain.

INTERPRETATION

Based on currently available evidence, surgeons should aim for optimal alignment of tibial and femoral components when performing TKA.

No benefit of patient-specific instrumentation in TKA on functional and gait outcomes: a randomized clinical trial

BACKGROUND

Although some clinical reports suggest patient-specific instrumentation in TKA may improve alignment, reduce surgical time, and lower hospital costs, it is unknown whether it improves pain- and function-related outcomes and gait.

QUESTIONS/PURPOSES

We hypothesized that TKA performed with patient-specific instrumentation would improve patient-reported outcomes measured by validated scoring tools and level gait as ascertained with three-dimensional (3-D) analysis compared with conventional instrumentation 3 months after surgery.

METHODS

We randomized 40 patients into two groups using either patient-specific instrumentation or conventional instrumentation. Patients were evaluated preoperatively and 3 months after surgery. Assessment tools included subjective functional outcome and quality-of-life (QOL) scores using validated questionnaires (New Knee Society Score(©) [KSS], Knee Injury and Osteoarthritis Outcome Score [KOOS], and SF-12). In addition, gait analysis was evaluated with a 3-D system during level walking. The study was powered a priori at 90% to detect a difference in walking speed of 0.1 m/second, which was considered a clinically important difference, and in a post hoc analysis at 80% to detect a difference of 10 points in KSS.

RESULTS

There were improvements from preoperatively to 3 months postoperatively in functional scores, QOL, and knee kinematic and kinetic gait parameters during level walking. However, there was no difference between the patient-specific instrumentation and conventional instrumentation groups in KSS, KOOS, SF-12, or 3-D gait parameters.

CONCLUSIONS

Our observations suggest that patient-specific instrumentation does not confer a substantial advantage in early functional or gait outcomes after TKA. It is possible that differences may emerge, and this study does not allow one to predict any additional variances in the intermediate followup period from 6 months to 1 year postoperatively. However, the goals of the study were to investigate the recovery period as early pain and functional outcomes are becoming increasingly important to patients and surgeons.

LEVEL OF EVIDENCE

Level I, therapeutic study. See the Instructions to Authors for a complete description of levels of evidence.

The influence of tibial morphology on the design of an anatomical tibial baseplate for TKA

BACKGROUND

Finding the right balance between tibial coverage and minimal implant overhang is an important factor in TKA. Another significant cause of failure is component malrotation.

METHODS

An average master shape of the proximal tibia at TKA resection level was calculated using fine slice computed tomographies of 117 cadaveric knees. To find out whether alternate implant contours would be necessary depending on the patient's body size, we established five subgroups to compare. CAD-Analysis was performed to simulate the overhang produced after ±4°/±7°/±10° rotation.

RESULTS

A master shape for the tibial resection cut (with a 5° posterior slope, 7 mm under lateral joint line) could be determined. Neither left vs. right knee joint, nor male vs. female nor the size subdivision appears to alter the calculated master shape significantly. The optimized shape allowing for ±4° of rotational freedom was found to be the best variant.

CONCLUSIONS

Valid methods have been obtained to design a two-dimensional average shape of the tibial plateau. The modifications described in this study might come in useful, when designing future implant designs.

CLINICAL RELEVANCE

An optimized fit at the tibial plateau and lower rates of component malrotation may result in better outcomes after TKA.

Tibial base design and patient morphology affecting tibial coverage and rotational alignment after total knee arthroplasty

PURPOSE

To understand interactions between total knee arthroplasty tibial base design attributes, variations in tibial morphology, and the resulting tibial coverage and rotational alignment.

METHODS

Tibial anthropometric measurements, including aspect ratio (medial-lateral width/anterior-posterior length) and tibial asymmetry, were taken for 14,791 total knee arthroplasty patients and compared with the ability of four different commercial tibial base designs to cover the resected plateau. The anthropometric measurements were also compared with the resulting tibial base rotation, which occurred when rotating the base to maximize coverage.

RESULTS

All four tibial base designs resulted in similar coverage ranging from 80.2 (4.7)% to 83.8 (4.6)%. Mean tibial base rotation when placed to maximize coverage ranged from 3.7 (4.4)° (internal) to 3.8 (4.5)° (external) relative to the medial third of the tibial tubercle. More asymmetric tibiae and tibiae with a lower aspect ratios resulted in increased internal tibial base rotation.

CONCLUSIONS

The four tibial base designs assessed provided similar levels of tibial bone coverage across the patient population, despite different design features. Rotating the tibial base to maximize coverage did not significantly increase the tibial coverage, but induced variability in tibial base alignment. Certain tibial anthropometrics may predispose particular patients to internal tibial base mal-rotation.

Anatomic tibial component design can increase tibial coverage and rotational alignment accuracy: a comparison of six contemporary designs

PURPOSE

The aim of this study was to comprehensively evaluate contemporary tibial component designs against global tibial anatomy. We hypothesized that anatomically designed tibial components offer increased morphological fit to the resected proximal tibia with increased alignment accuracy compared to symmetric and asymmetric designs.

METHODS

Using a multi-ethnic bone dataset, six contemporary tibial component designs were investigated, including anatomic, asymmetric, and symmetric design types. Investigations included (1) measurement of component conformity to the resected tibia using a comprehensive set of size and shape metrics; (2) assessment of component coverage on the resected tibia while ensuring clinically acceptable levels of rotation and overhang; and (3) evaluation of the incidence and severity of component downsizing due to adherence to rotational alignment and overhang requirements, and the associated compromise in tibial coverage. Differences in coverage were statistically compared across designs and ethnicities, as well as between placements with or without enforcement of proper rotational alignment.

RESULTS

Compared to non-anatomic designs investigated, the anatomic design exhibited better conformity to resected tibial morphology in size and shape, higher tibial coverage (92% compared to 85-87%), more cortical support (posteromedial region), lower incidence of downsizing (3% compared to 39-60%), and less compromise of tibial coverage (0.5% compared to 4-6%) when enforcing proper rotational alignment.

CONCLUSIONS

The anatomic design demonstrated meaningful increase in tibial coverage with accurate rotational alignment compared to symmetric and asymmetric designs, suggesting its potential for less intra-operative compromises and improved performance.

LEVEL OF EVIDENCE

III.

Tibial component coverage based on bone mineral density of the cut tibial surface during unicompartmental knee arthroplasty: clinical relevance of the prevention of tibial component subsidence

INTRODUCTION

An optimally implanted tibial component during unicompartmental knee arthroplasty would be flush with all edges of the cut tibial surface. However, this is often not possible, partly because the tibial component may not be an ideal shape or because the ideal component size may not be available. In such situations, surgeons need to decide between component overhang and underhang and as to which sites must be covered and which sites could be undercovered. The objectives of this study were to evaluate the bone mineral density of the cut surface of the proximal tibia around the cortical rim and to compare the bone mineral density according to the inclusion of the cortex and the site-specific matched evaluation.

MATERIALS AND METHODS

One hundred and fifty consecutive patients (100 men and 50 women) were enrolled in this study. A quantitative computed tomography was used to determine the bone density of the cut tibial surface. Medial and lateral compartments were divided into anterior, middle, and posterior regions, and these three regions were further subdivided into two regions according to containment of cortex. The site-specific matched comparison (medial vs. lateral) of bone mineral density was performed.

RESULTS

In medial sides, the mid-region, including the cortex, showed the highest bone mineral density in male and female patients. The posterior region showed the lowest bone mineral density in male patients, and the anterior and posterior regions showed the lowest bone mineral density in female patients. Regions including cortex showed higher bone mineral density than pure cancellous regions in medial sides. In lateral sides, posterior regions including cortex showed highest bone mineral density with statistical significance in both male and female patients. The anterior region showed the lowest bone mineral density in both male and female patients.

CONCLUSION

The mid-region of the medial side and the posterior region of the lateral side are relatively safe without cortical coverage when the component is not flush with all edges of the tibia. Cortical coverage is strongly recommended for the prevention of subsidence of the tibial component in the posterior region of the medial side, and in the anterior region of the lateral side.

Comprehensive assessment of tibial plateau morphology in total knee arthroplasty: Influence of shape and size on anthropometric variability

Better understanding of proximal tibia morphology can lead to improvements in total knee arthroplasty (TKA) through development of tibial tray families that adequately reflect the diversity of global anatomy using an appropriate number of components. We quantified variations in proximal tibial morphology at the TKA level and characterized differences attributable to gender and ethnicity. Virtual TKA was performed on digital models of 347 tibiae, spanning both genders and multiple ethnicities. The geometry of the resection profile was quantified using both a comprehensive set of morphological measurements (reflecting size and shape) and principal component analysis (PCA). The dominant statistical modes of variation were associated primarily with size (plateau dimensions, radii, and area), with lesser contributions associated with asymmetry and aspect ratios. Medial and lateral AP dimensions were strongly correlated with plateau ML width, with minimal differences in correlations due to gender or ethnicity. In conclusion, clinically relevant differences in proximal tibia morphology at the level of TKA resections across genders and multiple ethnicities can be attributed largely to variations in overall proximal tibial size, not gender- or ethnic-specific shape variations.

Rotation in total knee arthroplasty: no difference between patient-specific and conventional instrumentation

PURPOSE

It was our hypothesis that patient-specific instrumentation (PSI) can improve the accuracy of the rotational alignment in TKA based on the concept of the system and on the potential to clearly identify pre-operatively during planning the classical anatomical landmarks that serve as references to set-up the rotation both for the femur and tibia.

MATERIALS AND METHODS

In this prospective comparative randomized study, 40 patients (20 in each group) operated in our institution between September 2012 and January 2013 by the 2 senior authors were included. Randomization of patients into one of the two groups was done by the Hospital Informatics Department with the use of a systematic sampling method. All patients received the same cemented high-flex mobile bearing TKA. In the PSI group, implant position was compared to the planed position using previously validated dedicated software. The position of the implants (frontal and sagittal) was compared in the 2 groups on standard X-rays, and the rotational position was analysed on post-operative CT-scan.

RESULTS

90 % of the patients add <2° or mm of difference between the planned position of the implants and the obtained position, except for the tibial rotation where the variations were much higher. Mean HKA was 179° (171-185) in the PSI group with 4 outliers (2 varus: 171° and 172°:184° and 185°) and 178.3° with 2 outliers (171° and 176°) in the control group. No difference was observed between the two groups concerning the frontal and sagittal position of the implants on the ML and AP X-rays. No significant difference of femoral rotation was observed between the two groups with a mean of 0.4° in the PSI group and 0.2° in the control group (p: n.s). Mean tibial rotation was 8° of internal rotation in the PSI group and 15° of internal rotation in the standard group (p: n.s).

CONCLUSION

Based on our results, we were unable to confirm our hypothesis as PSI cannot improve rotation in TKA. More work needs to be done to more clearly define the place of PSI in TKA, to keep on improving the accuracy of the system and to better define the individual targets in TKA in terms of frontal, sagittal and rotational positioning of the implant for each patient.

LEVEL OF EVIDENCE

Prospective comparative randomized study, Level II.

Can tibial coverage in total knee replacement be reliably evaluated with three-dimensional image-based digital templating?

Objectives

There remains a lack of data on the reliability of methods to estimate tibial coverage achieved during total knee replacement. In order to address this gap, the intra- and interobserver reliability of a three-dimensional (3D) digital templating method was assessed with one symmetric and one asymmetric prosthesis design.

Methods

A total of 120 template procedures were performed according to specific rotational and over-hang criteria by three observers at time zero and again two weeks later. Total and sub-region coverage were calculated and the reliability of the templating and measurement method was evaluated.

Results

Excellent intra- and interobserver reliability was observed for total coverage, when minimal component overhang (intraclass correlation coefficient (ICC) = 0.87) or no component overhang (ICC = 0.92) was permitted, regardless of rotational restrictions.

Conclusions

Measurement of tibial coverage can be reliable using the templating method described even if the rotational axis selected still has a minor influence.

The radiological assessment of total and unicompartmental knee replacements

Radiological assessment of total and unicompartmental knee replacement remains an essential part of routine care and follow-up. Appreciation of the various measurements that can be identified radiologically is important. It is likely that routine plain radiographs will continue to be used, although there has been a trend towards using newer technologies such as CT, especially in a failing knee, where it provides more detailed information, albeit with a higher radiation exposure. The purpose of this paper is to outline the radiological parameters used to evaluate knee replacements, describe how these are measured or classified, and review the current literature to determine their efficacy where possible.

Influence of landmark and surgical variability on virtual assessment of total knee arthroplasty

Given advances in recent years in imaging modalities and computational hardware/software, virtual analyses are increasingly valuable and practical for evaluating total knee arthroplasty (TKA). However, the influence of variabilities at each step in computational analyses on predictions of TKA performance for a population has not yet been thoroughly investigated, nor the relationship between these variabilities and expected variations in surgical practice. Understanding these influences is nevertheless essential for ensuring the clinical relevance of theoretical predictions. Here, a morphological analysis of proximal tibial resections within TKA is proposed and investigated. The goals of this analysis are to quantify the influence of variability in landmark detection on resection parameters and to evaluate this sensitivity relative to expected clinical variability in TKA resections. Results here are directly applicable to population-level computational analyses of morphological and functional TKA performance.

Rotational positioning of the tibial tray in total knee arthroplasty: a CT evaluation

INTRODUCTION

Various surgical techniques have been described to set the rotational alignment of the tibial baseplate during total knee arthroplasty. The self-positioning method ("self-adjustment") aligns the tibial implant according to the rotational alignment of the femoral component which is used as a reference after performing repeated knee flexion/extension cycles. Postoperative computed tomography scanning produces accurate measurements of the tibial baseplate rotational alignment with respect to the femoral component.

HYPOTHESIS

The rotational positioning of the tibial baseplate matches the rotation of the femoral component with parallel alignment to the prosthetic posterior bicondylar axis.

PATIENTS AND METHODS

A 3-month follow-up CT scan was carried out after primary total knee arthroplasty implanted in osteoarthritic patients with a mean 7.8° varus deformity of the knee in 50 cases and a mean 8.7° valgus deformity of the knee in 44 cases. The NexGen LPS Flex (Zimmer) fixed-bearing knee prosthesis was used in all cases. An independant examiner (not part of the operating team) measured different variables: the angle between the anatomic transepicondylar axis and the posterior bicondylar axis of the femoral prosthesis (prosthetic posterior condylar angle), the angle between the posterior bicondylar axis and the posterior marginal axis of the tibial prosthesis, the angle between the posterior marginal axis of the tibial prosthesis and the posterior marginal axis of the tibial bone and finally the angle between the anatomic transepicondylar axis and the posterior marginal axis of the tibial prosthesis.

RESULTS

For the genu varum and genu valgum subgroups, the mean posterior condylar axis of the femoral prosthesis was 3.1° (SD: 1.91; extremes 0° to 17.5°) and 4.7° (SD: 2.7; extremes 0° to 11°) respectively. The tibial baseplate was placed in external rotation with respect to the femoral component: 0.7° (SD : 4.45; extremes -9.5° to 9.8°) and 0.9° (SD: 4.53; extremes -10.8° to 9.5°), but also to the native tibia: 6.1° (SD: 5.85; extremes -4.6° to 22.5°) and 12.5° (SD: 8.6; extremes -10° to 28.9°). The tibial component was placed in internal rotation relative to the anatomic transepicondylar axis: 1.9° (SD : 4.93; extremes -13.6° to 7°) and 3° (SD : 4.38; extremes -16.2° to 4.8°).

DISCUSSION

The tibial component is aligned parallel to the femoral component whatever the initial frontal deformity (P≅0.7). However, a difference was observed between the rotational alignment of the tibial baseplate and the native tibia depending on the initial deformity and could be attributed to the morphological variations of the bony tibial plateau in case of genu valgum.

CONCLUSION

The self-positioning method is a reproducible option when using this type of implant since it allows the tibial component to be positioned parallel to the posterior border of the femur.

The position and orientation of total knee replacement components: a comparison of conventional radiographs, transverse 2D-CT slices and 3D-CT reconstruction

We studied the intra- and interobserver reliability of measurements of the position of the components after total knee replacement (TKR) using a combination of radiographs and axial two-dimensional (2D) and three-dimensional (3D) reconstructed CT images to identify which method is best for this purpose. A total of 30 knees after primary TKR were assessed by two independent observers (an orthopaedic surgeon and a radiologist) using radiographs and CT scans. Plain radiographs were highly reliable at measuring the tibial slope, but showed wide variability for all other measurements; 2D-CT also showed wide variability. 3D-CT was highly reliable, even when measuring rotation of the femoral components, and significantly better than 2D-CT. Interobserver variability in the measurements on radiographs were good (intraclass correlation coefficient (ICC) 0.65 to 0.82), but rotational measurements on 2D-CT were poor (ICC 0.29). On 3D-CT they were near perfect (ICC 0.89 to 0.99), and significantly more reliable than 2D-CT (p < 0.001). 3D-reconstructed images are sufficiently reliable to enable reporting of the position and orientation of the components. Rotational measurements in particular should be performed on 3D-reconstructed CT images. When faced with a poorly functioning TKR with concerns over component positioning, we recommend 3D-CT as the investigation of choice.

Reliability of frames of reference used for tibial component rotation in total knee arthroplasty

This study evaluated seven different frames of reference used for tibial component rotation in total knee arthroplasty (TKA) to determine which ones showed good reliability between bone specimens. An optoelectronic system based around a computer-assisted surgical navigation system was used to measure and locate 34 individual anatomical landmarks on 40 tibias. Each particular frame of reference was reconstructed from a group of data points taken from the surface of each bone. The transverse axis was used as the baseline to which the other axes were compared, and the differences in angular rotation between the other six reference frames and the transverse axis were calculated. There was high variability in the tibial rotational alignment associated with all frames of reference. Of the references widely used in current TKA procedures, the tibial tuberosity axis and the anterior condylar axis had lower standard deviations (6.1° and 7.3°, respectively) than the transmalleolar axis and the posterior condylar axis (9.3° for both). In conclusion, we found high variability in the frames of reference used for tibial rotation alignment. However, the anterior condylar axis and transverse axis may warrant further tests with the use of navigation. Combining different frames of reference such as the tibial tuberosity axis, anterior condylar axis and transverse axis may reduce the range of errors found in all of these measurements.

Is the anterior tibial tuberosity a reliable rotational landmark for the tibial component in total knee arthroplasty?

To analyze the morphology of the tibial plateau, we studied 100 computed tomographic scans of arthritic knees and measured the mediolateral (ML) and anteroposterior (AP) dimensions as well as their aspect ratio using 3 reference axes of rotation: transepicondylar axis (TEA), posterior tibial margin (PTM), and anterior tibial tuberosity (ATT) axis. Relative to the TEA, the PTM was internally rotated by 1.6° ± 5.1°, and the ATT externally rotated by 14.8° ± 7.2°. The AP and ML dimensions and aspect ratio differ significantly when the reference axis was ATT compared with PTM or TEA and variations were greater while using ATT axis. Our data demonstrate (1) that design of the tibial component restricts the choice of rotational alignment and (2) that ATT is not a reliable landmark for rotation of the tibial component.

The mean anatomical shape of the tibial plateau at the knee arthroplasty resection level: an investigation using MRI

Clinical assessments after Total Knee Arthroplasty (TKA) show persisting pain after implantation in over 20% of patients. Impingement of soft tissue around the knee, due to imprecise geometry of the tibial implant, can be one reason for persisting ailment. Two hundred and thirty seven MRI scans were evaluated using an active contour detection algorithm (snake) to obtain a high-resolution mean anatomical shape of the tibial plateau. Differences between female and male, older and younger (<or=40/>40) and left and right averaged shapes were determined. The shapes obtained were asymmetric throughout. Absolute differences between the subgroups fell short of inter-individual variations represented by calculated one-sigma confidence intervals. Our results indicate that a differentiation in TKA tibial plateau design by gender, age, or side is of minor relevance.

Primary stability of tibial components in TKA: in vitro comparison of two cementing techniques

In spite of improvements in cementing technique, migration of tibial component remains a problem in total knee arthroplasty. This study compares the primary stability of tibial components using two different cementing techniques with roentgen stereophotogrammetric analysis (RSA) in vitro. A total of 20 tibia specimens were matched into two groups, 10 specimens per group. Cementing technique was randomized to each group. In the first group only the base and in the second group the base and stem were cemented. The implants and the tibial metaphysis were marked with markers for the RSA analysis. All specimens were tested with an axial load of 2,000 N for 1,000 and 10,000 cycles and RSA analysis was performed. Endpoints for radiosterometric analysis were maximum total point motion, maximum subsidence, lift off, rotation and translation along the x-, y-, and z-axes. After 1,000 and 10,000 cycles, no significant differences could be found, but two tibial components of the surface cementing group showed a migration of more than 2 mm defined as failure compared to six failed tibial components in the full cementing group (P = 0.068). This higher number of failed arthroplasties in the fully cemented prosthesis group demonstrates a disadvantageous load distribution in the tibia apophysis which can cause an early component loosening.

Tibial component overhang following unicompartmental knee replacement--does it matter?

As implants are made in incremental sizes and usually do not fit perfectly, surgeons have to decide if it is preferable to over or undersize the components. This is particularly important for unicompartmental knee replacement (UKR) tibial components, as overhang may cause irritation of soft tissues and pain, whereas underhang may cause loosening. One hundred and sixty Oxford UKRs were categorised according to whether they had minor (<3 mm, 70%) or major (>or=3 mm, 9%) tibial overhang, or tibial underhang (21%). One year post surgery, there was no significant difference in outcome between the groups. Five years after surgery, those with major overhang had significantly worse Oxford Knee Scores (OKS) (p=0.001) and pain scores (p=0.001) than the others. The difference in scores was substantial (OKS=10 points). There was no difference between the 'minor overhang' and the 'underhang' group. We conclude that surgeons must avoid tibial component overhang of 3 mm or more, as this severely compromises the outcome. Although this study showed no difference between minor overhang or underhang, we would advise against significant underhang because of the theoretical risk of component subsidence and loosening.

Lateral versus medial tibial plateau: morphometric analysis and adaptability with current tibial component design

The purpose of this study was to analyze the in vivo dimensions of each tibial plateau for planning of unicompartmental knee arthroplasty (UKA), and to compare the morphometric data to the dimensions of nine current designs of UKA tibial components. Thirty-seven knees (31 females and 6 males) operated on with UKA were studied. All patients were examined postoperatively using computed tomography (CT). There were 18 lateral and 19 medial UKAs. On the CT scan, each operated tibial plateau was measured in the transverse plane at the resection level, just below the full polyethylene tibial component. We measured the length of the anteroposterior (AP) cut as well as the maximal mediolateral dimension of the resected plateau (perpendicular to the AP cut). We compared the measurements with nine current UKA systems: Accuris (Smith and Nephew), Advance (Wright Medical), HLS Uni Evolution (Tornier), Miller-Galante and "ZUK" (Zimmer), Oxford and Oxford alpha (Biomet), Preservation (DePuy) and Unix (Stryker). There was good correlation between patient height and mediolateral dimension (r=0.6), and between patient height and area of total tibial plateau (r=0.7). The anteroposterior dimension was greater for the medial plateau (mean 50.8 mm, SD 3.3) than for the lateral plateau (mean 47.2 mm, SD 3.3). This difference was statistically significant (P=0.0016). Some UKA implants are designed with an asymmetric femoral component, but none have an asymmetric tibial component. The present study suggests, however, that the shape of the medial tibial plateau differs from that of the lateral plateau. This difference can lead to mediolateral overhang for medial UKA, if the surgeon aims for optimal anteroposterior coverage.

The relationship of the medially-offset stem of the tibial component to the medial tibial cortex in total knee replacements in Korean patients

We examined the placement of the stem in relation to the medial tibial cortex when using total knee replacements (TKRs) with medially-offset tibial stems in Korean patients. Measurements were performed on the pre- and post-operative radiographs of 246 osteoarthritic knees replaced between January 2005 and May 2006 using the Genesis II or E-motion TKR with a medially-offset stem. Pre-operatively, we measured the distance between the mechanical axis and that of the tibial shaft and post-operatively, that between the midline of the tibial stem and the axis of the shaft. Knees were identified in which there was radiological contact between the tip of the stem and the medial tibial cortex. The mechanical axis was located medial to the axis of the shaft in 203 knees (82.5%). Post-operatively, the midline of the tibial stem was located medial to the tibial shaft axis in 196 knees (79.7%). In 16 knees (6.5%) there was radiological contact between the tibial stem or cement mantle and the medial tibial cortex. Our study has shown that the medially-offset stem in the tibial component may not be a good option for knees undergoing replacement for advanced osteoarthritis in some Korean patients.

[Diagnosis specific differences in knee joint geometry. A challenge for the correct axial implantation of long stems in total knee arthroplasty]

BACKGROUND

Arthrotic deformities with changes in knee geometry can produce difficulties in implanting long stem knee prosthesis systems using intramedullary alignment. They can result in incorrect lower limb axis and prosthesis positioning. The aim of the presented study was to measure knee geometry in patients with varus and valgus gonarthrosis in order to define diagnosis related differences.

METHODS

A total of 75 patients with indication for total knee arthroplasty were divided in two groups using the weight bearing lower limb axis: patients with varus gonarthrosis (n=43) and with valgus gonarthrosis (n=32). Angles and extensions, important for knee prosthesis implantation, were measured, digitalized and analyzed. The results were investigated for diagnosis specific differences.

RESULTS

After regulation of the measured extension in mean femur/tibia lengths, significant diagnosis specific differences were found: femur condyles were widened towards pathologic weight bearing (P<0.044), and the mechanical tibia axis of the varus gonarthrosis group is transferred to the lateral side (P<0.046) and in projection over the lateral internal cortical substance.

CONCLUSION

The significant differences in deformed arthrotic knees indicate that for an optimal postoperative result the use of standard implants is not always sufficient. Modular knee prosthesis systems can provide adequately for individual demands.

Can normal knee kinematics be restored with unicompartmental knee replacement?

BACKGROUND

Unicompartmental replacement can be an alternative to tibial osteotomy in younger, active patients with unicompartmental knee disease. In unicompartmental replacement, the other compartments and knee ligaments are largely untouched. Therefore, it was hypothesized that the knee kinematics after unicompartmental replacement may also be unchanged. To test this hypothesis, knee kinematics and quadriceps tension were recorded before and after replacement with a unicompartmental design and then with a tricompartmental design.

METHODS

Six human cadaver knees were tested before implantation, after implantation with a bicruciate-retaining unicompartmental knee prosthesis, and after implantation with a posterior cruciate-retaining tricompartmental knee prosthesis. The unicompartmental prosthesis was initially implanted, and it was then revised to a total condylar knee replacement. The knee kinematics were measured with use of an electromagnetic tracking device while the knee was put through dynamic simulated stair-climbing under peak flexion moments of approximately 40 N-m. Quadriceps tension was also measured for all three conditions.

RESULTS

No significant differences in tibial axial rotation were noted between the intact and unicompartmental conditions. However, tricompartmental replacement significantly affected tibial axial rotation (p = 0.001). Femoral rollback was not significantly affected by either unicompartmental or tricompartmental arthroplasty. Quadriceps tension was also similar among all three conditions.

CONCLUSIONS

In this in vitro cadaver study, the tricompartmental replacement significantly changed knee kinematics while the unicompartmental replacement preserved normal knee kinematics.