The influence of tibial slope on maximal flexion after total knee arthroplasty

Addressing sagittal plane imbalance in primary total knee arthroplasty

Aims

Sagittal plane imbalance (SPI), or asymmetry between extension and flexion gaps, is an important issue in total knee arthroplasty (TKA). The purpose of this study was to compare SPI between kinematic alignment (KA), mechanical alignment (MA), and functional alignment (FA) strategies.

Methods

In 137 robotic-assisted TKAs, extension and flexion stressed gap laxities and bone resections were measured. The primary outcome was the proportion and magnitude of medial and lateral SPI (gap differential > 2.0 mm) for KA, MA, and FA. Secondary outcomes were the proportion of knees with severe (> 4.0 mm) SPI, and resection thicknesses for each technique, with KA as reference.

Results

FA showed significantly lower rates of medial and lateral SPI (2.9% and 2.2%) compared to KA (45.3%; p < 0.001, and 25.5%; p < 0.001) and compared to MA (52.6%; p < 0.001 and 29.9%; p < 0.001). There was no difference in medial and lateral SPI between KA and MA (p = 0.228 and p = 0.417, respectively). FA showed significantly lower rates of severe medial and lateral SPI (0 and 0%) compared to KA (8.0%; p < 0.001 and 7.3%; p = 0.001) and compared to MA (10.2%; p < 0.001 and 4.4%; p = 0.013). There was no difference in severe medial and lateral SPI between KA and MA (p = 0.527 and p = 0.307, respectively). MA resulted in thinner resections than KA in medial extension (mean difference (MD) 1.4 mm, SD 1.9; p < 0.001), medial flexion (MD 1.5 mm, SD 1.8; p < 0.001), and lateral extension (MD 1.1 mm, SD 1.9; p < 0.001). FA resulted in thinner resections than KA in medial extension (MD 1.6 mm, SD 1.4; p < 0.001) and lateral extension (MD 2.0 mm, SD 1.6; p < 0.001), but in thicker medial flexion resections (MD 0.8 mm, SD 1.4; p < 0.001).

Conclusion

Mechanical and kinematic alignment (measured resection techniques) result in high rates of SPI. Pre-resection angular and translational adjustments with functional alignment, with typically smaller distal than posterior femoral resection, address this issue.

Posterior tibial slope influences joint mechanics and soft tissue loading after total knee arthroplasty

As a solution to restore knee function and reduce pain, the demand for Total Knee Arthroplasty (TKA) has dramatically increased in recent decades. The high rates of dissatisfaction and revision makes it crucially important to understand the relationships between surgical factors and post-surgery knee performance. Tibial implant alignment in the sagittal plane (i.e., posterior tibia slope, PTS) is thought to play a key role in quadriceps muscle forces and contact conditions of the joint, but the underlying mechanisms and potential consequences are poorly understood. To address this biomechanical challenge, we developed a subject-specific musculoskeletal model based on the bone anatomy and precise implantation data provided within the CAMS-Knee datasets. Using the novel COMAK algorithm that concurrently optimizes joint kinematics, together with contact mechanics, and muscle and ligament forces, enabled highly accurate estimations of the knee joint biomechanics (RMSE <0.16 BW of joint contact force) throughout level walking and squatting. Once confirmed for accuracy, this baseline modelling framework was then used to systematically explore the influence of PTS on knee joint biomechanics. Our results indicate that PTS can greatly influence tibio-femoral translations (mainly in the anterior-posterior direction), while also suggesting an elevated risk of patellar mal-tracking and instability. Importantly, however, an increased PTS was found to reduce the maximum tibio-femoral contact force and improve efficiency of the quadriceps muscles, while also reducing the patellofemoral contact force (by approximately 1.5% for each additional degree of PTS during walking). This study presents valuable findings regarding the impact of PTS variations on the biomechanics of the TKA joint and thereby provides potential guidance for surgically optimizing implant alignment in the sagittal plane, tailored to the implant design and the individual deficits of each patient.

Increase in the Posterior Tibial Slope Provides Better Joint Awareness and Patient Satisfaction in Cruciate-Retaining Total Knee Arthroplasty

The effect of the posterior tibial slope (PTS) in cruciate-retaining total knee arthroplasty (CR-TKA) on clinical outcomes remains unclear. We aimed to investigate (1) the effect of alteration of the PTS on clinical outcomes, including patient satisfaction and joint awareness, and (2) the relationship between the patient-reported outcomes, the PTS, and compartment loading. Based on the alteration of the PTS after CR-TKA, 39 and 16 patients were stratified into increased and decreased PTS groups, respectively. Clinical evaluation was performed by the Knee Society Score (KSS) 2011 and the Forgotten Joint Score-12 (FJS-12). Compartment loading was intraoperatively assessed. KSS 2011 (symptoms, satisfaction, and total score) was significantly higher (p = 0.018, 0.023, and 0.040, respectively), and FJS ("climbing stairs?") was significantly lower (p = 0.025) in the increased PTS group compared with the decreased PTS group. The decrease in both medial and lateral compartment loading of Δ45°, Δ90°, and ΔFull was significantly greater in the increased PTS group than in the decreased PTS group (p< 0.01 for both comparisons). Medial compartment loading of Δ45°, Δ90°, and ΔFull significantly correlated with KSS 2011 for "symptom" (r = - 0.4042, -0.4164, and -0.4010, respectively; p = 0.0267, 0.0246, and 0.0311, respectively). ΔPTS significantly correlated with medial compartment loading differentials of Δ45°, Δ90°, and ΔFull (r = - 0.3288, -0.3792, and -0.4424, respectively; p = 0.0358, 0.01558, and 0.0043, respectively). Patients with increased PTS showed better symptoms and higher patient satisfaction compared with those with decreased PTS following CR-TKA, possibly due to a greater decrease in compartment loading during knee flexion.Level of evidence:level IV, therapeutic case series.

Clinical evaluation of the first semi-active total knee arthroplasty assisting robot made in China: a retrospective propensity score-matched cohort study

OBJECTIVE

The precision of overall alignment and knee morphotype after robot-assisted total knee arthroplasty has been fully confirmed. This study aims to conduct a clinical evaluation of the first China-made semi-active total knee arthroplasty assisting robot.

METHODS

After a 1 : 2 propensity score matching, that is, a matched cohort study, patients were matched to the robot group (52 cases) and the conventional group (104 cases). The robot group received osteotomy according to preoperative planning, while the conventional group adopted preoperative planning based on the full-length radiograph and received conventional osteotomy. Perioperative clinical indicators, such as operation time, tourniquet time, hospitalization days, intraoperative bleeding, and hemoglobin level of the two groups were recorded; radiological indicators of postoperative prosthesis position, including hip-knee-ankle angle, frontal femoral component angle, frontal tibial component angle, lateral femoral component angle, and lateral tibial component angle were also recorded; deviations and outliers of the radiological indicators were calculated.

RESULTS

Compared with the conventional group, the operation time and tourniquet time of the robot group were longer, and the postoperative hemoglobin level decreased less, the differences were statistically significant; the lateral tibial component angle of the conventional group was 80.9°±3.6°, which was smaller than 86.7 °±2.3° of the robot group, the difference was statistically significant ( P <0.001); except for lateral femoral component angle, the absolute deviations of the radiological indicators in the robot group were significantly smaller than that in the conventional group ( P ≤0.001); the outliers of the radiological indicators in the robot group were significantly smaller than that in the conventional group with a statistical difference ( P <0.05).

CONCLUSION

Compared with the conventional group, the operation time of the robot group was relatively longer, but the perioperation blood loss was less. The robot group could better control the posterior inclination of the tibial prosthesis, and the absolute deviations and outliers of the prosthesis position were relatively smaller. There was no difference in short-term clinical score between the two groups.

The effect of posterior tibial slope on anteroposterior stability in posterior cruciate retaining total knee arthroplasty

BACKGROUND

It has been suggested that the posterior tibial slope (PTS) plays an important role in increasing the anteroposterior stability following total knee arthroplasty. Although the relationship between the PTS and the flexion range has been investigated many times, studies on the relationship between PTS and anterior-posterior stability are limited. The primary aim of this study was to investigate the relationship and effects of PTS on anteroposterior stability in posterior cruciate retainer total knee arthroplasty.

METHODS

154 primary TKAs were identified retrospectively to analyze the any association between PTS and anteroposterior laxity following posterior cruciate-retaining total knee arthroplasty in the overall study populations. Anteroposterior displacement was measured at the final follow-up based on the following two procedures: KT-1000 arthrometer and sagittal drawer radiographic images. In addition, the relationship between PTS and functional scores-ROM was examined.

RESULTS

There was no correlation between patients' posterior tibial slope and postoperative VAS (r: -0.060, p:0.544), WOMAC (r:0.037, p:0.709), KSS (r: -0.073, p:0.455). In addition, there was no significant correlation between postoperative knee ROM and postoperative PTS (r:0.159, p:0.106). Moreover, no correlation was found between KT-1000 arthrometer and 20 degrees AP translation with PTS. There was a negative correlation between PTS and 70 degrees AP translation (r: -0.281, p:0.008).

CONCLUSIONS

This study aimed to clarify the association between instability and AP laxity in flexion of implanted knees, and to determine what degree of AP laxity results of instability. A fundamental finding of this study was that; the optimum TS angle to increase anterior-posterior stability after total knee arthroplasty is between ≥ 4 to < 6 degrees, we also proved that there is no relationship between stability and patient satisfaction.

An investigation into whether changes in the posterior tibial slope affect the outcome of cruciate-retaining total knee arthroplasty by affecting tibiofemoral articular contact kinematics

Aims

The outcomes of total knee arthroplasty (TKA) are affected by many factors. This study aims to evaluate whether changes in the posterior tibial slope (PTS) affect patients' outcomes after cruciate-retaining TKA by affecting tibiofemoral articular contact kinematics. It was hypothesized that changes in PTS affect the outcomes of PCR TKA by affecting tibiofemoral articular contact kinematics.

Methods

A total of 60 knees (30 patients) that underwent posterior cruciate-retaining TKA (with the same size prosthesis) for medial osteoarthritis were assessed preoperatively and one year postoperatively. Before and after TKA, changes in the PTS, as seen on lateral radiographs, were noted. The knees were placed in groups according to these PTS changes (preoperative value - postoperative value): group 1 >3° change and group 2 ≤3° change. Knee kinematics were observed under mid-flexion weight-bearing conditions and were compared between the two groups using the two-dimensional/three-dimensional registration technique. Pain was measured using the visual analog scale, and knee function was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Knee Society Score (KSS).

Results

Group 2 experienced paradoxical anterior motion of the medial femoral condyle postoperatively, but group 1 did not. A comparison of the results of the TKA between the two groups showed a significant difference in pain using the visual analog scale, and knee function of the KSS and the WOMAC (P < 0.05). The postoperative results were better in group 1 than in group 2.

Conclusions

These results suggest that achieving a greater change in the PTS improves outcomes in patients undergoing posterior cruciate-retaining TKA because it reduces the paradoxical motion of the medial femoral condyle.

CT-based analysis of posterior tibial slope in a Turkish population sample: A retrospective observational study

Posterior tibial slope (PTS) is important for the success of high tibial osteotomy and unicondylar knee arthroplasty applications, as it provides anterior cruciate ligament function. In the literature, different studies have been carried out with various imaging methods to measure PTS in populations of different ethnic origins. In this study, it was aimed to detect PTS in the medial (MPTS) and lateral (LPTS) tibial condyles with computed tomography in a Turkish population sample and to compare the results between age groups (<65, ≥ 65), genders, sides, and literature data. In our sample, 39 left and 33 right knee images of 37 men and 35 women with a mean age of 52.01 ± 21.27 were evaluated. The tibial proximal anatomical axis was determined by the midpoint method. The MPTS and LPTS was evaluated by two different observers according to this axis. Thereby the global PTS (GPTS) was calculated as an arithmetic mean of MPTS and LPTS values. Measurements were repeated 2 weeks after the first measurement and values were analyzed. A significant difference was found between the mean of MPTS, LPTS, and GPTS in the whole population (P = .002), in men (P = .02) and in women (P = .02). On the other hand, there was no significant difference compared according to age, gender, and side by mean of same parameters. In comparison of the results of our Turkish population sample with other studies in the literature, MPTS and LPTS were similar to Chinese (P = .22, P = .07) and Japanese (P = .96, P = .67) populations, while different to White Asian (P < .001, P < .001) and Korean (P < .001, P < .001) populations. The midpoint method is a safe measurement method in computed tomography-based studies for the evaluation of PTS. Implant designs produces for different populations may not be suitable for the Turkish population. More comprehensive and detailed studies are needed to represent the Turkish population.

The language of knee alignment : updated definitions and considerations for reporting outcomes in total knee arthroplasty

Orthopaedic surgeons are currently faced with an overwhelming number of choices surrounding total knee arthroplasty (TKA), not only with the latest technologies and prostheses, but also fundamental decisions on alignment philosophies. From 'mechanical' to 'adjusted mechanical' to 'restricted kinematic' to 'unrestricted kinematic' - and how constitutional alignment relates to these - there is potential for ambiguity when thinking about and discussing such concepts. This annotation summarizes the various alignment strategies currently employed in TKA. It provides a clear framework and consistent language that will assist surgeons to compare confidently and contrast the concepts, while also discussing the latest opinions about alignment in TKA. Finally, it provides suggestions for applying consistent nomenclature to future research, especially as we explore the implications of 3D alignment patterns on patient outcomes.Cite this article: Bone Joint J 2023;105-B(2):102-108.

Effect of Posterior Tibial Slope Change on Postoperative Range of Motion and Clinical Outcomes after Posterior Cruciate-Substituting Total Knee Arthroplasty

The posterior tibial slope (PTS) is usually adjusted by less than 5 degrees, without considering its individual difference, during posterior cruciate-substituting (PS) total knee arthroplasty (TKA). The effect of these individual changes of PTS would be important because clinical results depending on postoperative PTS were reported conflictingly. We investigated the effect of the change in PTS on the postoperative range of motion (ROM) and clinical scores after PS TKA. We retrospectively reviewed 164 knees from 107 patients who underwent PS TKA with a 2-year follow-up. We analyzed the preoperative and postoperative PTS, ROM, visual analog scale pain scale, Western Ontario and McMaster University Index (WOMAC), Hospital for Special Surgery Knee Score, Knee Society Score, and Forgotten Joint Score (FJS). The association of the absolute change in PTS with ROM and clinical scores was analyzed using correlation analysis and multiple regression analysis. As a result, the mean PTS and mean ROM changed from 9.6 ±  3.4 and 120.1 ±  15.4 degrees preoperatively to 2.0 ±  1.3 and 128.4 ±  9.3 degrees postoperatively, and the mean PTS change was 7.6 ±  3.5 degrees. The PTS change had no statistically significant association with the postoperative ROM and clinical scoring systems, although it did have a weak positive correlation with WOMAC function, No 10 (difficulty in rising from sitting) (correlation coefficient = 0.342, p = 0.041), and moderate positive correlation with the FJS, No. 6 (awareness when climbing stairs) (correlation coefficient = 0.470, p = 0.001). The authors concluded that the amount of change in PTS did not affect the postoperative ROM and clinical scores, although proximal tibial resection with a constant target of PTS resulted in individually different changes in the PTS after PS TKA.

The Relationship Between Posterior Tibial Slope and Knee Range of Movements in Posterior Stabilized Total Knee Replacement: A Navigation-Assisted Analysis of 120 Cases

Background

Posterior tibial slope (PTS) is one of the factors that determine the postoperative range of movement (ROM) in total knee replacement (TKR). While biomechanical factors influencing ROM such as PTS, soft-tissue balancing, and choice of implants are surgeon-dependent, non-biomechanical factors such as physiotherapy and pain are subjective and beyond the surgeon’s control. Using navigation, we avoided these factors and objectively correlated the difference in PTS with ROM.

Methodology

A total of 120 cases of posteriorly stabilized (PS) TKR were included. The X-ray-measured difference in PTS was compared to the corresponding change in the ROM intraoperatively using the TKR navigation system. Based on the change in PTS, the cases were classified into three groups, and the intergroup variability of mean postoperative ROM, mediolateral laxity difference (MLD), and residual flexion (RF) was calculated.

Results

An average MLD of 1.39 mm in extension and 1.79 mm in flexion and an average RF of 3.18 degrees were seen. This uniformity neutralizes the effects of these factors on the ROM. The mean difference in the PTS in the three groups was 4.45, 10.76, and 17.98 degrees, and the mean change in the ROM was 3.07, 1.47, and 2.84 degrees, respectively. There was no statistically significant change in ROM with that of change in PTS.

Conclusions

In our study, it was shown statistically that the coronal and sagittal planes were uniformly balanced using navigation assistance, and the PTS and the postoperative ROM were the only variables. The correlated results showed that a change in the PTS does not affect the postoperative ROM in PS TKR using the implant system used in our study.

Measurement of Tibial Orientation Helps Select the Optimal Insert Thickness to Personalize PCL Tension in a Medial Ball-in-Socket TKA

As the conformity of a medial ball-in-socket total knee arthroplasty (TKA) provides intrinsic anterior-posterior (A-P) stability, surgeons cannot rely on the manual examination of sagittal laxity to identify the optimal insert thickness. Instead, the present study determined whether measuring tibial axial orientation in extension and 90° flexion with an insert goniometer could identify the optimal thickness that, when implanted, provides high postoperative function. In twenty-two patients that underwent unrestricted caliper-verified kinematic alignment (KA) with a PCL retaining implant, two surgeons measured tibial orientation in extension and 90° flexion with 10, 11, 12, and 13 mm thick insert goniometers. Each TKA had one insert thickness that restored either the maximum external tibial orientation in extension, the maximum internal tibial orientation at 90° flexion, or both relative to 1 mm thinner and thicker inserts. In addition, the 6-month median [interquartile range] Forgotten Joint Score of 73 (54–87) and Oxford Knee Score of 42 (38–45) indicated high satisfaction and function. In conclusion, surgeons using a medial ball-in-socket TKA design can measure external tibial orientation in extension and internal tibial orientation at 90° flexion with an insert goniometer. Furthermore, implanting an insert with the thickness that provided the maximum orientation values resulted in high postoperative function, thereby personalizing PCL tension.

Cemented Patellar Implant Malposition: A Non-Issue for the Painful Total Knee Arthroplasty

BACKGROUND

Non-optimal patellofemoral relationships may influence treatment decisions during revision total knee arthroplasty (TKA). We performed this study to determine whether patellar implant malposition or patellar tilt is associated with inferior patient-reported outcome scores or patient satisfaction after primary TKA.

METHODS

We identified 396 TKA patients (439 knees) from an institutional registry who had undergone patellar resurfacing, with preoperative and 6-week postoperative radiographs available, and patient-reported outcome measures (PROMs) completed at least 1 year after surgery (mean 505 days). Preoperative patient demographic characteristics, patient-reported expectations, National Institutes of Health - Patient Reported Outcomes Measurements Instrument Systems global health, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement, and University of California Los Angeles activity scores were compared between 60 TKAs performed with non-optimal patellofemoral relationships (36 patellar implant malposition, 24 patellar tilt) and 379 TKAs performed with optimal patellar implant placement.

RESULTS

There were no differences between the 2 cohorts regarding demographic features, preoperative radiographic disease severity, expectations, and PROMs; or postoperative tibiofemoral component alignment, PROMs, and patient-reported satisfaction (P = .48). Knee Injury and Osteoarthritis Outcome Score for Joint Replacement improved similarly (P = .62) for patients with optimal resurfacing (48.5-77.6 points) and non-optimal resurfacing (47.7-76.6 points). A similar proportion of optimal and suboptimal resurfaced patients reported being satisfied with their TKA (92.7% vs 88.1%, P = .29).

CONCLUSION

Although suboptimal patellofemoral relationships may prompt treatment considerations during revision TKA, the data obtained from this study do not suggest that patellar implant malposition or patellar tilt independently contribute to postoperative pain, functional limitation, or dissatisfaction.

LEVEL OF EVIDENCE

This is a level III, retrospective cohort study.

Tibial sagittal and rotational alignment reduce patellofemoral stresses in posterior stabilized total knee arthroplasty

Patellofemoral joint complications remain an important issue in total knee arthroplasty. We compared the patellofemoral contact status between cruciate-retaining and posterior-stabilized designs with varying degrees of tibial sagittal and rotational alignment using a computer simulation to ensure proper alignments in total knee arthroplasty. Knee kinematics, patellofemoral contact force and quadriceps force were computed using a musculoskeletal modeling program (LifeMOD/KneeSIM 2010; LifeModeler, Inc., San Clemente, California) during a weight-bearing deep knee bend. Two different posterior tibial slope (PTS)s (3° and 7°) and five different tibial tray rotational alignments (neutral, internal 5° and 10°, and external 5° and 10°) were simulated. Patellofemoral contact area and stresses were next computed using finite element analysis. The patellofemoral contact force for the posterior-stabilized design was substantially lower than the cruciate-retaining design after post-cam contact because of increasing femoral roll-back. Neutral rotational alignment of the tibial component resulted in smaller differences in patellofemoral contact stresses between cruciate-retaining and posterior-stabilized designs for PTSs of 3° or 7°. However, the patellar contact stresses in the cruciate-retaining design were greater than those in posterior-stabilized design at 120° of knee flexion with PTS of 3° combined with internal rotation of the tibial component. Our study provides biomechanical evidence implicating lower PTSs combined with internal malrotation of the tibial component and the resultant increase in patellofemoral stresses as a potential source of anterior knee pain in cruciate-retaining design.

Effect of anterior tibial bowing on measurement of posterior tibial slope on conventional X-rays

PURPOSE

The posterior tibial slope (PTS) has different biomechanical effects on the knee. Especially in revision ACL reconstruction, a precise analysis is essential. Therefore, we investigate the influence of the anterior tibial bowing angle on the posterior slope measurement. Our hypothesis of the present study is that the short tibial X-rays underestimate the PTS in cases with increased anterior bowing of the tibia.

METHODS

The PTS was measured on 162 true longitudinal radiographs of the complete tibia (lateral mechanic axis). The average age of the patients was 35.7 years (range 19-59 years) and the most common diagnosis was failed anterior cruciate ligament reconstruction. Using this X-ray, the slope on the short axis and the slope on the entire axis were measured. In addition, the angle of the anterior bowing was determined.

RESULTS

The mean PTS for the lateral mechanic axis of the tibia was 10.6° (± 3.5) in contrast to 11.6° (± 3.5) for the short tibial axis. These two measurements differ significantly. (p  < 0.001). The mean anterior tibial bowing angle on the lateral X-rays of the whole tibia was 2.3° (± 2.0). There is a significant positive, relationship between tibial bowing angle and PTS as referenced by the lateral mechanic axis (Spearman's correlation, r = 0.273 and p < 0.001).

CONCLUSION

With increasing anterior tibial bowing, the posterior tibial slope on the short knee radiograph is underestimated compared to the slope measurement on the lateral mechanic axis.

Measurement of Posterior Tibial Slope in Healthy Indian Population: A CT-Based Study

BACKGROUND

Recreation of near normal posterior tibial slope is required for proper knee biomechanics after unicondylar as well as total knee arthroplasties. It is also required for proper functioning of anterior cruciate ligament after high tibial osteotomies. Researchers have found differences in values of posterior tibial slopes in individuals of different ethnicities. So far there is no study measuring the posterior slopes of medial and lateral tibial plateau separately in knees of healthy Indian population via three dimensional imaging modalities like computed tomography.

AIM

The aim of our study is to find out the slopes of medial and lateral tibial plateau separately through computed tomography (CT) scans.

MATERIALS AND METHODS

CT-based measurements of posterior tibial slopes were done in 62 healthy knees. There were 55 males and 7 females.

RESULTS

Age groups were in the range of 17-45 years. Mean values of Posterior tibial slope of medial and lateral tibial plateau for combined sample were 8.60° ± 3.51° and 7.94° ± 3.91°. Mean values of medial and lateral tibial plateau for males were 8.33° ± 3.51° and 7.71° ± 4.07° respectively; while for females were 10.69° ± 2.86° and 9.77° ± 1.32°, respectively.In our study, there was a large range of slopes, extending from + 0.6° to 15.6° for medial tibial slope, from 0° to 15° for lateral tibial slope.

CONCLUSION

The minimum values of Medial tibial plateau slope are very low as compared to the previous study done in Asian population. Further CT based studies are required to measure values of posterior tibial slope for larger sample from Indian population. The implant design suitable and their implantation guidelines for western population may not be appropriate for Indian population.

Radiographic measurement of the posterior tibial slope in normal Chinese adults: a retrospective cohort study

Background

Measurement of the posterior tibial slope (PTS) angle has important applications in total knee replacement surgery, high tibial osteotomy, and anterior cruciate ligament reconstruction. This study aimed to determine the mean PTS of knee joints in healthy Chinese adults, and provide data to guide knee surgery in China.

Methods

A retrospective analysis of 1257 (n = 1233, 50.4% male) plain X-ray films of participants aged 25–59 years was performed. The picture archiving and communication system was used for PTS measurement. The PTS was defined as the angle between the vertical line of the tangent of the anterior tibial cortex of the proximal tibia, and the tangent line of the tibial cortex. Two imaging physicians conducted the PTS measurements independently, and both the inter- and intraclass correlation coefficients (ICCs) were calculated.

Results

The mean PTS value was 7.68 ± 3.84° (range: 0–21°). The left PTS was significantly smaller in males than in females (7.22 ± 3.89 vs 8.05 ± 3.60; P = 0.005). Additionally, the PTS in participants aged 25–29 years was significantly larger than that in the other age groups (Left side: 8.64 ± 3.73 vs 6.92 ± 3.42, 7.42 ± 3.75, 7.53 ± 3.98; P <  0.001 and Right side: 8.68 ± 3.84 vs 7.48 ± 4.21, 7.13 ± 3.64, 7.66 ± 3.80; P = 0.004). There were no significant differences in PTS between the left and right sides. Two-way analysis of variance suggested that the differences in PTS between age groups were not affected by sex. The interobserver ICC was 0.91 (95% confidence interval [CI]: 0.85–0.94), and the intraobserver ICC was 0.90 (95% CI: 0.82–0.94).

Conclusions

This study demonstrated that there were significant differences in PTS based on sex and age, highlighting the need to provide individualized treatment for knee surgery. It provided valuable information regarding the normal PTS values in Chinese adults and presented regionalised data to guide knee surgery.

Comparison of posterior cruciate retention and substitution in total knee arthroplasty during gait: a systematic review and meta-analysis

Background

To compare the gait patterns between posterior cruciate retention and substitution in total knee arthroplasty (TKA).

Methods

Electronic databases including the PubMed, Embase, CINAHL, Web of Science, and Cochrane databases were searched to identify clinical trials investigating posterior cruciate retention versus substitution in TKA. The outcome measurements were the kinematic gait parameters (flexion at heel strike, maximum flexion during loading response, flexion range during loading, minimal flexion at terminal stance, maximal flexion at the swing, and total flexion during the gait cycle), Knee Society Score (KSS), knee flexion, knee extension, and walking speed. Statistical software Review Manager 5.4 and Stata 14.0 were used for data analysis.

Results

There were finally 9 studies included in this meta-analysis. The results did not reveal differences between posterior cruciate retention (CR) and posterior cruciate substitution (PS) groups in TKA, in terms of kinematic gait parameters, knee extension, walking speed, and KSS. However, the PS group had a significantly larger knee flexion angle than that in the CR group [weighted mean difference = − 3.20, 95% CI − 6.13 to − 0.28, P = 0.03].

Conclusion

Both the posterior cruciate retention and posterior cruciate substitution lead to obvious improvements in patient function and have their advantages in getting a good cup position. The PS design is significantly better on the knee flexion, while there are no statistical differences in kinematic gait parameters and outcome scores between them. This might indicate that surgeons do not necessarily need a PS design to substitute the posterior cruciate ligament during TKA.

High inter- and intraindividual differences in medial and lateral posterior tibial slope are not reproduced accurately by conventional TKA alignment techniques

PURPOSE

The purpose of this study was to describe the medial and lateral posterior tibial slope (MPTS and LPTS) on 3D-CT in a Caucasian population without osteoarthritis. It was hypothesised that standard TKA alignment techniques would not reproduce the anatomy in a high percentage of native knees.

METHODS

CT scans of 301 knees [male:female = 192:109; mean age 30.1 ([Formula: see text] 6.1)] were analysed retrospectively. Tibial slope was measured medially and laterally in relation to the mechanical axis of the tibia. The proportion of MPTS and LPTS was calculated, corresponding to the "standard PTS" of 3°-7°. The proportion of knees accurately reproduced with the recommended PTS of 0°-3° for PS and 5°-7° for CR TKA were evaluated.

RESULTS

Interindividual mean values of MPTS and LPTS did not differ significantly (mean (range); MPTS: 7.2° ( - 1.0°-19.0°) vs. LPTS: 7.2° ( - 2.4°-17.8°), n.s.). The mean absolute intraindividual difference was 2.9° (0.0°-10.8°). In 40.5% the intraindividual difference between MPTS and LPTS was > 3°. When the standard slope of 3°-7° medial and lateral was considered, only 15% of the knees were covered. The tibial cut for a PS TKA or a CR TKA changes the combined PTS (MPTS + LPTS) in 99.3% and 95.3% of cases, respectively.

CONCLUSION

A high interindividual range of MPTS and LPTS as well as considerable intraindividual differences were shown. When implementing the recommended slope values for PS and CR prostheses, changes in native slope must be accepted. Further research is needed to evaluate the impact of altering a patient's native slope on the clinical outcome.

LEVEL OF EVIDENCE

IV.

Tibial baseplate position and posterior cruciate ligament status impact patient-reported outcomes in conforming dual-pivot bearing total knee arthroplasty

Background

In an effort to optimize clinical outcomes and enhance stability, ultracongruent bearings have been increasingly used in primary total knee arthroplasty (TKA). The importance of the posterior cruciate ligament (PCL) and optimal sagittal tibial baseplate position in ultracongruent bearing TKA remains unknown. This study sought to determine whether these modifiable, surgical-technique-dependent variables meaningfully impact patient-reported outcome measures.

Methods

A total of 759 primary TKAs of the same dual-pivot design performed using a consistent surgical technique between January 2016 and April 2019 were retrospectively reviewed. PCL status was recorded, and anteroposterior (AP) tibial baseplate position and posterior tibial slope were measured by two independent blinded raters. Patient-reported outcomes related to pain, function, satisfaction, and activity level were analyzed in relationship to PCL status, posterior tibial slope, and AP tibial baseplate position, in addition to other pertinent covariates.

Results

Median age and body mass index of the cohort were 68.3 years and 33.4 kg/m², respectively, with 73% being female. In multivariate analysis, partial or full release of the PCL was predictive of a knee “always” feeling normal (odds ratio 1.42, P = .041). Furthermore, tibial baseplate position closer to the middle of the tibia was associated with greater improvements in pain with level walking, pain while climbing stairs, and Knee Injury and Osteoarthritis Outcome Score for Joint Replacement total scores (P ≤ .079).

Conclusion

In congruent dual-pivot bearing TKA, partially or fully releasing the PCL and AP tibial baseplate position closer to the middle of the tibia may provide greater improvement in pain and function scores at minimum 1-year follow-up.

The influence of posterior tibial slope on the mid-term clinical effect of medial-pivot knee prosthesis

OBJECTIVE

To evaluate the effect of posterior tibial slope (PTS) on the mid-term clinical outcome following a medial-pivot (MP) prosthesis.

METHOD

Two hundred thirty-three patients from The Affiliated Hospital of Qingdao University, who had undergone a total knee arthroplasty (TKA) with MP prosthesis between January 2015 and December 2015, were retrospectively included in this study. They were divided into 3 groups according to postoperative PTS: A ≤ 5°; B 5-7°; and C ≥ 7°. Multiple assessments were made on the patient postoperatively and recorded in the three groups, the measurements of this study included: the range of motion (ROM), knee scoring system (KSS), Western Ontario and McMaster universities osteoarthritis index (WOMAC), posterior condylar offset (PCO), joint line height, and postoperative complications.

RESULTS

The average post-operative ROM for groups B and C were 108° and 110° respectively; this was significantly higher than that of group A (98°, P < 0.001). The WOMAC scores of patients in group C were significantly lower than those in groups A and B (P < 0.05). However, there were no significant differences in KSS, PCO, and joint line height among the 3 groups (P > 0.05). Only 2 cases of postoperative complications occurred in group C, these were ameliorated after operation.

CONCLUSION

With an increase to PTS, the postoperative ROM can be significantly increased for the patient. However, the knee joint function will not be significantly improved, and the stability of knee joint will not be affected when within the limits of appropriate PTS.

The posterior tibial slope does not influence the flexion angle in posterior-stabilized mobile-bearing total knee arthroplasty

Background

It remains uncertain whether an increase in the tibial slope leads to better flexion in posterior-stabilized (PS) total knee prostheses.

Purpose

To compare the intra-operative flexion angle between standard and an additional 10° posterior slope inserts.

Patients and methods

Between December 2014 and February 2015, 22 patients (25 knees) who underwent PS mobile-bearing primary total knee arthroplasty (TKA) were included. Flexion angles were measured using either standard or specially-made inserts. Differences in flexion angles between the two situations were analyzed to determine the relationship between changes in flexion angle and pre-operative flexion angle or body mass index (BMI), and between intra- and post-operative flexion angle.

Results

The difference between the average flexion angle of standard inserts and specially-made inserts was not statistically significant. Although the correlations between changes in flexion angle due to insert difference and flexion angle, pre-operative flexion angle or BMI were not significant, there was a positive correlation between intra-operative and post-operative flexion at 2 years.

Conclusion

The results showed an additional posterior tibial slope by 10° did not affect the intra-operative flexion angle. Surgeons performing PS mobile-bearing TKA do not need to excessively slope the tibial bone cutting to improve the post-operative flexion angle.

Level of evidence

I, Experimental study.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42836-021-00085-5.

Effects of Posterior Tibial Slope on a Posterior Cruciate Retaining Total Knee Arthroplasty Kinematics and Kinetics

BACKGROUND

It has been hypothesized that increasing posterior tibial slope can influence condylar rollback and play a role in increasing knee flexion. However, the effects of tibial slope on knee kinematics are not well studied. The objective of this study is to assess the effects of tibial slope on femorotibial kinematics and kinetics for a posterior cruciate retaining total knee arthroplasty design.

METHODS

A validated forward solution model of the knee was implemented to predict the femorotibial biomechanics of a posterior cruciate retaining total knee arthroplasty with varied posterior slopes of 0°-8° at 2° intervals. All analyses were conducted on a weight-bearing deep knee bend activity.

RESULTS

Increasing the tibial slope shifted the femoral component posteriorly at full extension but decreased the overall femoral rollback throughout flexion. With no tibial slope, the lateral condyle contacted the polyethylene 6 mm posterior of the midline, but as the slope increased to 8°, the femur shifted an extra 5 mm, to 11 mm posterior of the tibial midline. Similar shifts were observed for the medial condyle, ranging from 7 mm posterior to 13 mm posterior, respectively. Increasing posterior slope decreased the posterior cruciate ligament tension and femorotibial contact force.

CONCLUSION

The results of this study revealed that, although increasing the tibial slope shifted the femur posteriorly at full extension and maximum flexion, it reduced the amount of femoral rollback. Despite the lack of rollback, a more posterior location of condyles suggests lower chances of bearing impingement of the posterior femur and may explain why increasing slope may lead to higher knee flexion.

Machine Learning Algorithms Identify Optimal Sagittal Component Position in Total Knee Arthroplasty

BACKGROUND

Advanced technologies, like robotics, provide enhanced precision for implanting total knee arthroplasty (TKA) components; however, the optimal targets for implant position specifically in the sagittal plane do not exist. This study identified sagittal implant position which may predict improved outcomes using machine learning algorithms.

METHODS

A retrospective review of 1091 consecutive TKAs was performed. All TKAs were posterior cruciate ligament retaining or sacrificing with an anterior-lip (49.4%) or conforming bearing (50.6%) and performed with modern perioperative protocols. Preoperative and postoperative tibial slope and postoperative femoral component flexion were measured with standardized radiographic protocols. Analysis groups were categorized by satisfaction scores and the Knee Society Score question 'does this knee feel normal to you?' Machine learning algorithms were used to identify optimal sagittal alignment zones that predict superior satisfaction and knees "always feeling normal" scores.

RESULTS

Mean age and median body mass index were 66 years and 34 kg/m², respectively, with 67% being female. The machine learning model predicted an increased likelihood of being "satisfied or very satisfied" and a knee "always feeling normal" with a change in tibial slope closer to native (-2 to +2°) and femoral component flexion 0 to +7°. Worse outcomes were predicted with any femoral component extension, femoral component flexion beyond +10°, and adding or removing >5° of native tibial slope.

CONCLUSION

Superior patient-reported outcomes were predicted with approximating native tibial slope and incorporating some femoral component flexion. Deviation from native tibial slope and excessive femoral flexion or any femoral component extension were predictive of worse outcomes.

LEVEL OF EVIDENCE

Therapeutic level III.

Restoring the Patient's Pre-Arthritic Posterior Slope Is the Correct Target for Maximizing Internal Tibial Rotation When Implanting a PCL Retaining TKA with Calipered Kinematic Alignment

INTRODUCTION

The calipered kinematically-aligned (KA) total knee arthroplasty (TKA) strives to restore the patient's individual pre-arthritic (i.e., native) posterior tibial slope when retaining the posterior cruciate ligament (PCL). Deviations from the patient's individual pre-arthritic posterior slope tighten and slacken the PCL in flexion that drives tibial rotation, and such a change might compromise passive internal tibial rotation and coupled patellofemoral kinematics.

METHODS

Twenty-one patients were treated with a calipered KA TKA and a PCL retaining implant with a medial ball-in-socket and a lateral flat articular insert conformity that mimics the native (i.e., healthy) knee. The slope of the tibial resection was set parallel to the medial joint line by adjusting the plane of an angel wing inserted in the tibial guide. Three trial inserts that matched and deviated 2°> and 2°< from the patient's pre-arthritic slope were 3D printed with goniometric markings. The goniometer measured the orientation of the tibia (i.e., trial insert) relative to the femoral component.

RESULTS

There was no difference between the radiographic preoperative and postoperative tibial slope (0.7 ± 3.2°, NS). From extension to 90° flexion, the mean passive internal tibial rotation with the pre-arthritic slope insert of 19° was greater than the 15° for the 2°> slope (p < 0.000), and 15° for the 2°< slope (p < 0.000).

DISCUSSION

When performing a calipered KA TKA with PCL retention, the correct target for setting the tibial component is the patient's individual pre-arthritic slope within a tolerance of ±2°, as this target resulted in a 15-19° range of internal tibial rotation that is comparable to the 15-18° range reported for the native knee from extension to 90° flexion.

Measurement of femoral posterior condylar offset and posterior tibial slope in normal knees based on 3D reconstruction

Background

Femoral posterior condylar offset (PCO) and posterior tibial slope (PTS) are important for postoperative range of motion after total knee arthroplasty (TKA). However, normative data of PCO and PTS and the correlation between them among healthy populations remain to be elucidated. The purpose of this study was to determine PCO and PTS in normal knees, and to identify the correlation between them.

Methods

Eighty healthy volunteers were recruited. CT scans were performed followed by three-dimensional reconstruction. PCO and PTS were measured and analyzed, as well as the correlation between them.

Results

PTS averaged 6.78° and 6.11°, on the medial and lateral side respectively (P = 0.002). Medial PCO was greater than lateral (29.2 vs. 23.8 mm, P <  0.001). Both medial and lateral PCO of male were larger than female. On the contrary, male medial PTS was smaller than female, while there was no significant difference of lateral PTS between genders. There was an inverse correlation between medial PCO and PTS, but not lateral.

Conclusions

Significant differences exhibited between medial and lateral compartments, genders, and among individuals. An inverse correlation exists between PCO and PTS in the medial compartment. These results improve our understanding of the morphology and biomechanics of normal knees, and subsequently for optimising prosthetic design and surgical techniques.

Variations in medial and lateral slope and medial proximal tibial angle

PURPOSE

The primary objective of this study was to quantify the variations of the medial posterior tibial slope (MPTS) and the lateral posterior tibial slope (LPTS), as well as of the medial proximal tibial angle (MPTA), and to determine the fraction of patients for which standard techniques including different alignment techniques would result in alteration of the patient's individual posterior tibial slope (PTS) and MPTA. Furthermore, it was of interest if a positive correlation between PTS and MPTA or between medial and lateral slope exists.

METHODS

A retrospective study was performed on CT-scans of 234 consecutively selected European patients undergoing individual total knee replacement. All measurements were done on three-dimensional CAD models, which were generated on the basis of individual CT-scans, including the hip, knee, and ankle center. Measurements included the medial and lateral PTS and the MPTA. PTS was measured as the angle between the patient's articular surface and a plane perpendicular to the mechanical axis of the tibia in the sagittal plane. MPTA was defined as the angle between the tibial mechanical axis and the proximal articular surface of the tibia in the coronal plane.

RESULTS

Analysis revealed a wide variation of the MPTS, LPTS, and MPTA among the patients. MPTS and LPTS varied significantly both interindividually and intraindividually. The range of PTS was up to 20° for MPTS (from - 4.3° to 16.8°) and for LPTS (from - 2.9 to 17.2°). The mean intraindividual difference between MPTS and LPTS in the same knee was 2.6° (SD 2.0) with a maximum of 9.5°. MPTA ranged from 79.8 to 92.1° with a mean of 86.6° (SD ± 2.4). Statistical analysis revealed a weak positive correlation between MPTA and MPTS.

CONCLUSION

The study demonstrates a huge interindividual variability in PTS and MPTA as well as significant intraindividual differences in MPTS and LPTS. Therefore, the question arises, whether the use of standard techniques, including fixed PTSs and MPTAs, is sufficient to address every single patient's individual anatomy.

LEVEL OF EVIDENCE

III.

A sagittal reference line using the preoperative radiograph in total knee arthroplasty

BACKGROUND

We evaluated the accuracy of a sagittal alignment of tibial component in total knee arthroplasty (TKA) with the sagittal reference line using the preoperative radiograph.

METHODS

We evaluated 151 patients who underwent primary TKA with posterior cruciate substituting type implant. For 75 patients, the sagittal reference line using preoperative radiograph (group A) was used, while for 76 patients the sagittal reference using intraoperative fibular shaft line (group B) was used. The parallel line (line S) to the anatomical axis of the tibia in the lateral plain radiograph was used as the sagittal reference. The distance from line S to proximal tibia cutting area and to skin surface 20 cm distal to the cutting area was measured in preoperative radiographs. Next, the distance to the extramedullary guide rod was applied intraoperatively, reflecting the results. The intraoperative fibular shaft line was determined using the connecting line between the tip of fibular head and the lateral malleolus. The postoperative tibial component slope angle and the difference to the target slope angle were compared.

RESULTS

The difference to the target angle was 1.8 ± 1.3° in group A, whereas the difference was 2.5 ± 1.4° in group B (p = 0.04). The patients with difference within 3° to the target angle were 78.7% in group A and 61.8% in group B (p = 0.024).

CONCLUSION

The sagittal reference line using the preoperative lateral radiograph was helpful as a reference guide for the tibial slope in TKA.

Relationship between the form and function of implant design in total knee replacement

The implant design in total knee replacement affects postoperative functionality greatly, therefore, its optimization is of major concern. However, little is known about how implant design parameters affect active knee kinematics. Comprehensive in silico and in vitro sensitivity analyses were performed, based on one patient-specific, physical knee implant set and corresponding bone and knee implant surface geometry data. The implant surfaces were parametrized and varied systematically, resulting in 85 different knee implant surface models. In addition, four variations of extensor mechanism parameters, being the muscular attachment points defining the Q-Angle, were investigated. The variations were evaluated in a patient-specific multibody simulation model and an experimental testing rig and contributions of different implant designs and extensor mechanism parameters on kinematics were analysed. The results of the in silico and in vitro analyses showed good qualitative agreement. The highest deviations from the implant's reference kinematics were found for parameter variations of the femoral sagittal radii, the lateral trochlear elevation, the tibial sagittal slopes, the mediolateral position of the patellar ridge and the mediolateral position of the tuberositas tibiae. The implant design parameters identified with the highest functional relevance should be focused on in implant design. As the tuberositas tibiae's position constituted a main impact factor, it should also be considered during implant design and preoperative planning. Due to the competing influence of implant design parameters on active kinematics, respective parameters should be designed which are compatible to each other to avoid adverse constraints and associated functional limitations.

Clinical value of CT-based patient-specific 3D preoperative design combined with conventional instruments in primary total knee arthroplasty: a propensity score-matched analysis

Purpose

To evaluate the operation and early clinical effect in primary total knee arthroplasty (TKA) about the novel combination of CT-based patient-specific three-dimensional (3D) preoperative design and conventional osteotomy instruments, compared with the conventional method.

Methods

After a 1:1 propensity score-matching (PSM), patients were matched to the novel technique group and the conventional group, 109 cases in each group. The conventional group adopted a preoperative design based on a full-length radiograph (FLX) and received TKA with conventional osteotomy instruments. The novel technique group used a CT-based patient-specific 3D preoperative design combined with conventional osteotomy instruments; during the surgery, the femoral entry point, femoral valgus osteotomy angle, the fix point of tibial plateau extramedullary guide pin, and the position of tibial extramedullary positioning rod were accurately selected according to the preoperative 3D design to ensure accurate intraoperative implementation. The lower limb alignment, component position, operation time, tourniquet time, hospital stay, blood loss volume, incidence of postoperative complications, visual analog scale (Vas) score, and New Knee Society Score System (NEW-KSS) at 1 day before operation and 1, 6, and 12 months after operation were recorded and compared.

Results

The novel technique group was significantly better than the conventional group in controlling lateral tibial component angle (LTC) (P < 0.001), and the novel technique group had lower percentages of hip-knee-ankle angle (HKA) outliers (P < 0.001) and overcorrection (P = 0.003). The operation time, tourniquet time, and hospital stay of the novel technique group was shorter (P < 0.05). In 1 month after the operation, the novel technique group achieved a significantly better VAS score (P < 0.05), but a similar NEW-KSS score (P > 0.05) when compared with the conventional group. But in 6 and 12 months after surgery, no statistical differences were seen in the above two scores (P > 0.05).

Conclusion

The novel technique of CT-based patient-specific 3D preoperative design combined with conventional instruments can improve the accuracy of osteotomy in primary total knee arthroplasty, with benefits of significantly reducing pain and rapid recovery during the early postoperative period, but having no obvious effect on outcome after a 1-year follow-up.

The use of an asymmetrical tibial tray in TKA optimises tibial rotation when fitted to the posterior tibial plateau border

PURPOSE

The aim of this study was to evaluate the suitability of positioning an asymmetrical tibial tray relative to the posterior tibial edge and to analyse the relationship between the posterior fit and tibial rotation after computer-assisted total knee arthroplasty (TKA). It was hypothesised that an asymmetrical tray would adjust to the posterior border of the tibial plateau with proper tibial rotation.

METHODS

Ninety-three consecutive knees underwent total knee arthroplasty using a Persona fixed-bearing system (63 varus deformities and 30 valgus deformities) and a 3-month follow-up CT scan. An independent examiner measured different variables: the femoral angle between the clinical epicondylar axis and the posterior condylar line of the femoral component, the tibial angle between the posterior borders of the tibial tray and the tibial plateau, and the tibial rotation with respect to the femoral component. These measurements were also compared between varus and valgus subgroups.

RESULTS

For the varus and valgus subgroups, the mean postoperative femoral angle was 2.1º ± 1.2º and 2.5º ± 1.0º, respectively (n.s.). The mean posterior fitting angle of the tibial tray was 0.1º ± 2.4º and 1.4º ± 3.2º for the varus and valgus subgroups, respectively, with a significant difference between groups (p = 0.03). The tibial rotations with respect to the femoral component for the varus and valgus groups were 0.9º ± 3.3º and 2.2º ± 3.1º of external rotation, respectively (n.s.).

CONCLUSIONS

This study demonstrated that fitting an asymmetrical tibial tray to the posterior border of the tibial plateau could optimise tibial rotation. The posterior border was considered to be a reliable and easily identifiable landmark for proper tibial rotation and coverage during a primary TKA.

LEVEL OF EVIDENCE

IV.

Total knee arthroplasty: posterior tibial slope influences the size but not the rotational alignment of the tibial component

PURPOSE

The reasons leading to rotational tibial malalignment in total knee arthroplasties (TKAs) remain unclear. A previous cadaver study has shown an increase in internal rotation of the anatomical tibial axis (ATA) after the tibial cut. This study investigates the influence of tibial slope on the ATA and the size of the resected tibial surface.

METHODS

CT scans of 20 cadaver knees were orientated in a standardized coordinate system and used to determine the position of the centres of rotation of the medial and lateral tibial articular surfaces and, hence, of the ATA, after a virtual resection of 6 mm with 0°, 3.5°, 7° and 10° slope, respectively. Furthermore, at each slope, the radii of the medial and lateral tibial articular surfaces after resection were calculated.

RESULTS

Compared to resection of 6 mm with 0° slope, a slope of 3.5° resulted in a mean external rotation of the ATA of 0.9° (SD, 1.5°; P = 0.025). A slope of 7° resulted in a mean external rotation of the ATA of 1.0° (SD 2.0°; P = 0.030) and a slope of 10° had no influence on the rotation of the ATA. The radii of the medial and lateral articular surfaces of the cut tibiae were larger than those of the uncut tibia (P < 0.001).

CONCLUSION

Differences in the posterior tibial slope should not contribute to a rotational malalignment when using the ATA to align the prosthetic tibial plateau. Although statistically significant, the change in ATA with increasing slope was negligible.

A Validated Forward Solution Dynamics Mathematical Model of the Knee Joint: Can It Be an Effective Alternative for Implant Evaluation?

BACKGROUND

Mathematical modeling is among the most common computational tools for assessing total knee arthroplasty (TKA) mechanics of different implant designs and surgical alignments. The main objective of this study is to describe and validate a forward solution mathematical of the knee joint to investigate the effects of TKA design and surgical conditions on TKA outcomes.

METHODS

A 12-degree of freedom mathematical model of the human knee was developed. This model includes the whole lower extremity of the human body and comprises major muscles and ligaments at the knee joint. The muscle forces are computed using a proportional-integral-derivative controller, and the joint forces are calculated using a contact detection algorithm. The model was validated using telemetric implants and fluoroscopy, and the sensitivity analyses were performed to determine how sensitive the model is to both implant design, which was analyzed by varying medial conformity of the polyethylene, and surgical alignment, which was analyzed by varying the posterior tibial tilt.

RESULTS

The model predicted the tibiofemoral joint forces with an average accuracy of 0.14× body weight (BW), 0.13× BW, and 0.17× BW root-mean-square errors for lateral, medial, and total tibiofemoral contact forces. With fluoroscopy, the kinematics were validated with an average accuracy of 0.44 mm, 0.62 mm, and 0.77 root-mean-square errors for lateral anteroposterior position, medial anteroposterior position, and axial rotation, respectively. Increasing medial conformity resulted in reducing the paradoxical anterior sliding midflexion. Furthermore, increasing posterior tibial slopes shifted the femoral contact point more posterior on the bearing and reduced the tension in the posterior cruciate ligament.

CONCLUSION

A forward solution dynamics model of the knee joint was developed and validated using telemetry devices and fluoroscopy data. The results of this study suggest that a validated mathematical model can be used to predict the effects of component design and surgical conditions on TKA outcomes.

Systematic effects of femoral component rotation and tibial slope on the medial and lateral tibiofemoral flexion gaps in total knee arthroplasty

Purpose

To quantify the effects of the systematic internal and external femoral component rotations and tibial slope on the medial and lateral tibiofemoral gaps in total knee endoprostheses.

Methods

Nineteen knee cadaver specimens with an intact ligament apparatus were fixed in a custom frame, facilitating physiological flexion motion. Virtual total knee arthroplasty (TKA) was performed on three-dimensional models obtained from computed tomography ​scans (0° and 90° flexions) with systematically altered femur rotations and tibial slopes.

Results

Both the femur rotation and the tibial slope influenced the medial and lateral tibiofemoral flexion gaps (p ​< ​0.001), and the effects differed between the medial and lateral sides (p ​< ​0.001). The medial tibiofemoral flexion gap increased by 2.90 ​± ​0.34 ​mm and decreased by 2.66 ​± ​0.26 ​mm for 7° external and internal femur component rotations, respectively (both with p ​< ​0.001). The lateral tibiofemoral flexion gap decreased by 3.11 ​± ​0.31 ​mm and increased by 3.29 ​± ​0.33 ​mm for 7° external and internal femur component rotations, respectively (both with p ​< ​0.001).

Conclusion

For established surgical methods, we recommend a neutral femur rotation for a 0° tibial slope and a 3° external femur rotation for a tibial slope of 9–10°. The translational potential of this research shows that while the rotation of the femoral component in extension has no effect on the gap size, owing to the axis of rotation being perpendicular to the gap, for a 90° flexion, we not only observe differences in the gap size between the medial and lateral ​but also unequal differences on either side depending on the inward or outward rotation. The main reason for this is the position of the axis of rotation, which is not precisely half way between the lateral and medial contact points. The results show that rotation of the femoral component always creates an unbalanced flexion gap.

The translational potential of this article

The article points out the differences in the tibiofemoral gap in total knee endoprostheses due to the systematic internal and external femoral component rotation. While in lower leg extension there are no differences seen, in 90° knee-flexion there are unequal differences within the medial and lateral compartment that show a mathematical relationship towards the femoral compartment rotation which needs to be intraoperatively considered.

Manipulation under anesthesia as a therapy option for postoperative knee stiffness: a retrospective matched-pair analysis

INTRODUCTION

Due to demographic changes, total knee arthroplasty (TKA) is one of the most frequently performed orthopedic surgeries. Therapies for associated postoperative complications, such as postoperative knee stiffness (PKS), are becoming increasingly important. The aim of this retrospective matched-pair analysis was to evaluate mid-term-results following manipulation under anesthesia (MUA).

MATERIALS AND METHODS

Fifty-one patients with PKS were evaluated and 51 matched-pair patients without PKS after primary TKA were chosen for the control group. In addition to the range of motion, the functionality was recorded by Knee Society Score (KSS), Western Ontario and Mc Masters Universities Osteoarthritis Index (WOMAC), and Short-Form-12 Questionnaire (SF-12). Experience of pain was mapped using a 10-point Numeric Rating Scale (NRS), and the analgesic requirement was mapped using the WHO step scheme. A final follow-up examination was conducted approximately three years after TKA. To evaluate potential risk factors for the development of PKS, TKA alignment was measured via postoperative X-ray images.

RESULTS

Improvement of the average knee flexion of 35.7° and total flexion of 107.4° was detected in PKS patients after MUA. The flexion of the control group was 112.4°; no significant between-group difference was present regarding prosthesis type, sex, age and BMI. Regarding KSS, WOMAC, and SF-12, the MUA cohort achieved statistically-relevant lower overall scores than the control group, p = 0.006, p = 0.005, p = 0.001, respectively. Significantly higher experiences of pain and a higher need for analgesics in MUA patients were reported (p = 0.001 and p < 0.001, respectively). Radiological evaluation of the prosthesis alignment did not show any differences between the two groups.

CONCLUSIONS

MUA can improve mobility after PKS, whereby MUA seemed to be a functional therapy option for PKS. Compared to the control group, the MUA group showed lower functional values and an increased experience of pain. A correlation between prosthesis malalignment and MUA could not be detected radiologically. Further studies are necessary to investigate the reasons for PKS.

[Balancing technique using bone cuts]

BACKGROUND

Kinematic alignment means a surgical technique that focuses on intraarticular balance and laxity and takes into consideration the prearthritic state of the knee joint.

AIM

The aim of kinematic alignment is a constitutionally aligned joint space line and balanced tension of the soft tissue covering. By avoiding the proximalization of the joint line and the release of the ligaments, the risk of destabilization of the original physiology of the joint is reduced.

METHODS

After resections and recuts of the distal femur, a natural distal femoral joint line in full extension and the posterior line in 90° should be maintained or restored. Therefore, the flexion-extension axis of the femur, around which the knee joint moves, does not change. The principle of KA unequivocally requires the distal femoral cut to be performed before resection of the posterior femoral condyles.

RESULTS

The result is a natural knee joint alignment that approximately replicates the anatomy of the femoral and tibial axes. Release of the ligaments is rarely required and all necessary adjustments are usually made using bone recuts.

High variability of proximal tibial asymmetry and slope: a CT data analysis of 15,807 osteoarthritic knees before TKA

PURPOSE

As the correct rotational and sagittal alignment of the tibial tray are of key importance for optimal total knee arthroplasty (TKA) function, the objective of this study was to determine these individual variations in the proximal tibial geometry in terms of posterior tibial slope (PTS) and tibial surface asymmetry by analysing a large dataset of computer tomography (CT) information.

METHODS

A retrospective two-part review was performed on 15,807 datasets that were generated during the design phase for a customized TKA implant. First, 15807 CAD (computer-aided-design) models derived from CT data were used to conduct the analysis on the variation of the PTS. Second, the axial cut of each proximal tibia in a consecutively selected subset of 2202 datasets was used to measure the tibial asymmetry.

RESULTS

The majority (65.5%) of tibiae had a posterior slope between 5° and 10°, while 26.5% of knees had a slope > 10°. The asymmetry measured as offset between the lateral and medial posterior boundaries was highly variable, with overall an increasing proportion of patients with high asymmetry with increasing tibial ML width. Only 14% of tibiae exhibited symmetric (< 2 mm offset) lateral and medial plateaus, and 22% had an offset > 5 mm.

CONCLUSION

This study from an extraordinary large data base reveals that tibial posterior slope and asymmetry of the tibial profile vary largely between patients receiving TKA with increasing tibial asymmetry with ML width. CT scans might help to preoperatively better select the best fitting TKA, otherwise surgeons intraoperatively will often have to deal with compromises regarding fitting, sizing and rotational issues.

LEVEL OF EVIDENCE

Retrospective case series, Level IV.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Reproducing the Native Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty: Technique and Clinical Implications

Total knee arthroplasty (TKA) profoundly influences knee biomechanics. Using an arbitrary (often 3° to 5°) posterior tibial slope (PTS) in all cases seldom will restore native slope. This study examined whether the native PTS could be reproduced in cruciate-retaining TKA and how this would influence clinical outcome. Radiographic and clinical outcomes of 215 consecutive TKAs using the PFC sigma cruciate-retaining implant were evaluated. The tibial bone cut was planned to be made parallel to the native anatomical slope in the sagittal plane. The PTS was measured with reference to the proximal tibial medullary canal (PTS-M) and the proximal tibial anterior cortex (PTS-C) on true lateral radiographs using a picture achieving and communication system. Knee range of motion (ROM), Knee Society Score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Short Form Health Survey (SF-12) were evaluated. Mean preoperative PTS-M was 6.9°±3.3°, and mean postoperative PTS-M was 7.0°±2.4°. Mean preoperative PTS-C was 12.2°±4.2°, and mean postoperative PTS-C was 12.6°±3.4°. Preoperative and postoperative PTS were not significantly different for both techniques (P>.05). An arbitrary 3° as an acceptable range for PTS-M was achieved in 144 knees (67%) (group 1), and 71 knees (33%) had a difference of more than 3° (group 2). Group 1 had a significantly larger gain in ROM (P=.04) as well as improved Knee Society, WOMAC, and SF-12 physical scores compared with group 2 (P<.01). The modified surgical technique reproduced the native tibial slope in cruciate-retaining TKA. Reproduction of the native PTS within 3° resulted in better clinical outcomes manifested by gain in ROM and knee functional outcome scores. [Orthopedics. 2020; 43(1):e21-e26.].

The Effect of Posterior Tibial Slope on Joint Gap and Range of Knee Motion in Mobile-Bearing Unicompartmental Knee Arthroplasty

BACKGROUND

It is widely known that the posterior tibial slope (PTS) has an influence on the clinical outcome of arthroplasty. However, the influence of PTS on unicompartmental knee arthroplasty (UKA) is still not fully clear. The objective of this study is to reveal the effect PTS has on knee flexion and extension joint gap and the postoperative range of motion in mobile-bearing UKA. Moreover, we investigated an adequate PTS angle in mobile-bearing UKA.

METHODS

Oxford UKA was performed so that the flexion gap would be equal to the extension gap. Correlation between the gap value difference from 90° to 120° of the knee flexion and the PTS was evaluated. Correlation between postoperative range of motion and the PTS was also evaluated to find whether a small degree of PTS would cause knee flexion restriction.

RESULTS

The PTS had a moderate positive correlation with the flexion gap difference. However, the PTS had no correlation with the knee flexion angle both postoperative and 1 year after surgery.

CONCLUSION

It was suggested that the degree of the PTS should not be so large to avoid joint looseness throughout every knee angle. Increasing the degree of the PTS had the potential to dislocate the bearing. Since a small degree of the PTS does not have an influence on the clinical outcome, surgeons should aim to cut the tibia with a posterior slope of less than 7°.

Preoperative planned distance between the skin surface and the guide rod provides accurate posterior tibial slope in total knee arthroplasty

BACKGROUND

Although sagittal tibial alignment in total knee arthroplasty (TKA) is important, no landmark exists to achieve reproducible slope. It is theoretically demonstrated that the preoperative planned distance between the skin surface and the rod can be a useful guide for the tibial slope in the previous imaging study. We conducted this retrospective study to confirm whether the results of the study are repeatable in an intra-operative situation.

METHODS

Fifty-five consecutive TKAs using the distance from the extramedullary cutting guide rod to the skin surface as a reference guide for the tibial slope were performed and tibial component positioning was compared with 55 knees performed using the accelerometer-based portable navigation. The tibial component alignment was evaluated with a computed tomography (CT)-based three-dimensional (3D) software.

RESULTS

The absolute mean deviation from the targeted slope in the proposed method was significantly smaller than the portable navigation (1.0° and 1.7°, respectively, p = 0.0025). The outlier rate beyond 3° was 0% in the proposed technique (16.4% in the portable navigation, p = 0.0014).

CONCLUSIONS

The preoperative planned distance between the skin surface and the guide rod is a useful technique to provide accurate posterior tibial slope in TKA.

Biomechanical effects of posterior tibial slope on unicompartmental knee arthroplasty using finite element analysis

BACKGROUND

The effects of the posterior slope of the tibial prosthesis on unicompartmental knee arthroplasty have not been fully evaluated and controversies still exist.

OBJECTIVE

This study evaluates the effects of the posterior slope of the tibia on contact stresses in polyethylene inserts and articular cartilage using finite element analysis.

METHODS

We generated a computational model followed by the development of a posterior tibial slope (PTS) from -1° to 15° cases with increments of 2° PTS models. Using a validated finite element (FE) model, we investigated the influence of the changes in PTS on the contact stress in the medial polyethylene insert and lateral cartilage. The FE model's loading condition is level walking, a normal daily activity.

RESULTS

The contact stress increased on the lateral articular cartilage as the PTS increased. The contact stress on the polyethylene insert differed from the contact stress on the lateral articular cartilage, and it generally increased as the PTS decreased. However, in the initial stance phase when an axial force was exerted, it increased as the PTS increased.

CONCLUSIONS

Our results show that an offset of ±2° from the initial anatomical tibial slope does not biomechanically affect the outcome.

Blackburne-Peel ratio predicts patients' outcomes after total knee arthroplasty

PURPOSE

Alterations in patellar height and posterior tibial slope (PTS) are frequently measured radiographic parameters associated with postoperative impairments after total knee arthroplasty (TKA). Few studies correlate the clinical outcome of TKA with the radiological indices. Both the modified Insall-Salvati ratio (mISR) and the Blackburne-Peel ratio (BPR) were hypothesised to correlate with the clinical outcome after TKA.

METHODS

A total of 282 computer navigated primary LCS^®-TKAs, implanted in our institution from 2008 to 2012, were included. Data (ROM, FJS-12, WOMAC, and revision surgery) were collected independently and prospectively. Patellar height (mISR, BPR), joint-line position, and PTS were measured on pre- and postoperative radiographs. Bivariate and multiple regression analyses were performed.

RESULTS

Mean mISR (1.5-1.4) and BPR (0.8-0.6) decreased from preoperatively to 1 year follow-up. Mean joint-line shift in a cranial direction was 2 mm after TKA implantation. Analysis of dichotomous variables (presence of PB and PPB or not) only showed significantly lower flexion in patients with PPB (p < 0.001). However, multiple regression revealed that BPR was a significant positive independent predictor for FJS-12 (p = 0.016) and flexion (p < 0.001) at 1 year follow-up. Postoperative PTS (p < 0.01) and initial patella height (p < 0.001) were both predictive for BPR at follow-up, while the joint-line height was not.

CONCLUSIONS

The BPR is a useful and reliable radiographic parameter to predict patient outcomes 1 year after primary navigated TKA. Lowering the BPR should be avoided, as this may lead to significant restrictions in terms of ROM and PROMs.

LEVEL OF EVIDENCE

Level 3.

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

Objective

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

Methods

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

Results

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

Conclusion

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

Comparison of the biomechanical effect of posterior condylar offset and kinematics between posterior cruciate-retaining and posterior-stabilized total knee arthroplasty

BACKGROUND

The effect of the changes in the femoral posterior condylar offset (PCO) on anterior-posterior (AP) translation and internal-external (IE) rotation in cruciate-retaining (CR) and posterior-stabilized (PS) total knee arthroplasty (TKA) remains unknown. The purpose of this study was to compare the kinematics in CR and PS TKA with respect to the difference in prosthetic design and PCO change through a computational simulation.

METHODS

We developed three-dimensional finite element models with the different PCOs of ±1, ±2 and ±3 mm in the posterior direction using CR and PS TKA. We performed the simulation with different PCOs under a deep knee bend condition and evaluated the kinematics for the AP and IE in CR and PS TKA.

RESULTS

The more tibiofemoral (TF) translation in the posterior direction was found as PCO translated in posterior direction for both CR and PS TKA compared to the neutral position. However, the change of the AP translation with respect to the PCO change in CR TKA was greater than PS TKA. The more TF external rotation was found as PCO translated in the anterior direction for both CR and PS TKA compared to the neutral position. However, unlike the TF translation, the TF rotation was not influenced by the PCO change in both CR and PS TKA.

CONCLUSION

The PCO magnitude was influenced by a postoperative change in the kinematics in CR TKA although a relatively smaller effect was observed in PS TKA. Hence, surgeons should be aware of the PCO change, especially for CR TKA.

Influence of Posterior Tibial Slope on Kinematics After Cruciate-Retaining Total Knee Arthroplasty

BACKGROUND

The purpose of this study was to investigate the influence of posterior tibial slope (PTS) on knee kinematics after cruciate-retaining total knee arthroplasty (CR-TKA). These influences were evaluated using a prosthesis designed with high geometric conformity to the medial articular surface under the weight-bearing condition of deep knee bending.

METHODS

We evaluated 71 knees (52 patients) after CR-TKA using 2- to 3-dimensional registration techniques. All patients were categorized into 2 groups: group A (PTS ≤ 7°) and group B (PTS ≥ 8°). We compared in vivo knee kinematics during deep knee bending under weight-bearing conditions between the 2 groups. The anteroposterior position of the nearest points, flexion angles, and external rotation angles of the femoral components relative to the tibial components were evaluated. Additionally, the knee flexion angles of the femur relative to the tibia obtained from the installation angles of the components were evaluated.

RESULTS

PTS did not affect the external rotation angles and anteroposterior position. The postoperative maximum flexion angle and range of motion between the femur and tibia in group B were significantly greater than those in group A.

CONCLUSION

PTS of 8° or more in CR-TKA using prosthetics designed with high geometric conformity to the medial articular surface did not affect the anteroposterior position and external rotation, but increased the postoperative maximum flexion angle and range of motion.