Femoral flexion position is a highly variable factor in total knee arthroplasty: an analysis of 593 conventionally aligned total knee replacements

Prediction of Postoperative Range of Motion after Mobile-Bearing Medial Unicompartmental Knee Arthroplasty from the Preoperative Range of Motion and Other Preoperative Factors

Postoperative flexion after unicompartmental knee arthroplasty might be predicted from the preoperative range of motion and other preoperative factors, but this has not been sufficiently investigated. Between 2013 and 2017, 198 patients (198 knees) underwent unilateral knee arthroplasty with medial mobile-bearing unicompartmental knee arthroplasty. Range of motion was measured preoperatively and at the time of final follow-up. To investigate the accuracy of the prediction of preoperative to postoperative gain or loss of the flexion angle, we performed receiver operating characteristic analysis. Logistic regression analysis was used to evaluate other predictive factors. Change in flexion angle was significantly strongly and negatively correlated with the preoperative flexion angle (R = - 0.688; 95% confidence interval: -0.755 to -0.607; p < 0.001). Preoperative flexion angle was suggested to be a significant predictor of gain or loss of the flexion angle with the area under the curve of 0.781; the cutoff value calculated using the Youden index was 140 degrees. Logistic regression analysis showed that in addition to the preoperative flexion angle of the operated side, the postoperative flexion range was significantly affected by the patient's height and by the preoperative flexion angle of the contralateral knee. If the preoperative flexion angle in Oxford mobile-bearing medial unicompartmental knee arthroplasty is <140 degrees, the postoperative flexion angle may be improved; if it exceeds 140 degrees, the postoperative flexion angle may worsen. This predictive ability is further improved by consideration of the patient's height and the range of motion on the contralateral side.

[Trends in navigation-handheld systems]

Navigation-assisted surgical procedures in orthopedics and trauma surgery have become increasingly widespread over the last 20 years. In addition to applications in spinal surgery, they are primarily available for knee and hip endoprosthetics. On the one hand, computer-assisted procedures have been increasingly expanded with robotic assistance systems in recent years, and on the other hand, so-called handheld navigation systems have been developed, which enable specialized use directly in the operating field at lower acquisition costs. The aim of this overview is to describe current handheld systems and to present the respective technical principles and the available scientific results. Three handheld systems for TKA use, two for THA use and one system to support pedicle screw placement on the spine are presented.

A Three-dimensional Comparison of Pre- and Post-component Position in a Series of Off-label Robotic-assisted Revision Total Knee Arthroplasties

Background

The application of robotic-assisted arthroplasty in revision knee scenarios continues to evolve. This study compares the pre- and post-revision implant positions in series of revision total knee arthroplasties (TKA) using a robotic arm system.

Methods

Twenty-five consecutive off-label robotic-assisted revision TKA were performed. After virtual revision femoral and tibial components were positioned to achieve "balanced" medial and lateral flexion and extension gaps, the existing primary implants (PI) were removed, and bone cuts were executed with the robotic arm system. Preoperative coronal, sagittal, and axial position of the PI was compared to the final planned positions of the robotic revision implants (RRI) for each subject. A repeated measures ANOVA using the absolute difference in millimeters and degrees between the PI and RRI orientation was completed.

Results

Intra-operatively, the virtual gaps were balanced within the planning software followed by successful execution of the plan. There was a statistically significant difference between posterior condylar offset and tibial component positioning for RRI compared to PI. There was no difference between the distal femoral component values between PI and RRI.

Conclusions

The sagittal alignment of the revision implants, specifically the femoral posterior condylar offset and tibial component slope, are statistically significant considerations for a stable revision TKA with off-label use of a robotic-arm system. Other potential benefits may include appropriate implant sizing which can affect the resultant ligamentous tension important for a functional revision TKA. Future research and software iterations will be needed to determine the overall accuracy and utility of robotic-assisted revision TKA.

Association of sagittal alignment of tibial and femoral components with clinical outcome in total knee arthroplasty: A prospective cohort study

Background

In total knee replacement component alignment is a very crucial parameter to achieve better clinical outcomes. Only a few studies exist in the literature on the association between sagittal alignment of components and clinical outcomes. The study aimed to measure the functional outcome and association between the sagittal alignment of total knee replacement components and their clinical outcome.

Material & methods

Prospectively we collected data of 81 knees (cases) following total knee replacement. The sagittal femoral angle, anterior and posterior tibial slopes were assessed on 2nd postoperative week using a lateral radiograph. Based on these measures 2 groups were made. Group A comprises of the femoral component which was further divided into A1 (41 cases) and A2 (40 cases) based on the component's sagittal femoral angle in flexion or extension.Group B comprises of Tibial component subgrouped based on the degree of Tibal angle as the posterior tibial slope or anterior tibial slopes. The B1 subgroup has posterior tibial slope of more than 5° (23 cases), B2 posterior tibial slope within 5° (53 cases), and B3 anterior tibial slope (5 cases). Preoperative and follow-ups at one month, 6 months, and 3 year; the functional assessment was performed using the American Knee Society score and Oxford knee scores. The duration to raise the leg straight (in days) was also measured.

Results

52 patients (81 total knee replacement cases) with a mean age of 62.88 ± 8.21 were enrolled. Results showed significant improvement in mean American Knee Society score (preoperative 32.91 ± 2.61 to 86.68 ± 2.52 postoperatively at 3 years; P < 0.001) and mean Oxford knee score (preoperative 34.69 ± 1.06 to 19.20 ± 1.91 postoperatively at 3-years; P < 0.001). The correlation of American Knee Society score between the femoral component angle and tibial component angle suggested that the maximum correlation was between Group A2 (Femoral angle = 91 to 95) and Group B2 (Tibal angle = 86 to 90), with p-value <0.0001.

Conclusions

There is a positive association between the proper sagittal alignment of femoral component and tibial component in total knee replacement with clinical outcome. The functional outcome (in terms of mean American Knee Society score) is better when the femoral component is positioned in extension and the posterior tibial slope of less than 5° is achieved.

Preoperative Virtual Total Knee Arthroplasty Surgery Using a Computed Tomography-based 3-dimensional Model With Variation in Reference Points and Target Alignment to Predict Femoral Component Sizing

Background

The purpose of this study was to investigate the size differences of 19 different femoral component placements from the standard position in total knee arthroplasty using 3-dimensional virtual surgery.

Methods

Three-dimensional bone models were reconstructed from the computed tomography data of 101 varus osteoarthritic knees. The distal femoral bone was cut perpendicular to the femoral mechanical axis (MA) in the coronal plane. Twenty different component placements consisting of 5 cutting directions (perpendicular to MA, 3° and 5° extension relative to MA [3°E-MA and 5°E-MA, respectively], and 3° and 5° flexion relative to MA [3°F-MA and 5°F-MA, respectively]) in the sagittal plane, 2 rotational alignments (clinical epicondylar axis [CEA] and surgical epicondylar axis [SEA]), and 2 rotational types of anterior reference guide (central [CR] and medial [MR]) were simulated.

Results

The mean anteroposterior dimension of femur ranged from 54.3 mm (5°F-MA, SEA, CR) to 62.5 mm (5°E-MA, CEA, MR). The largest and smallest differences of anteroposterior dimension from the standard position (3°F-MA, SEA, and CR) were 7.1 ± 1.3 mm (5°E-MA, CEA, and MR) and −1.2 ± 0.2 mm (5°F-MA, SEA, and CR), respectively. Multiple regression analysis revealed that flexion cutting direction, SEA, and CR were associated with smaller component size.

Conclusions

The femoral component size can be affected easily by not only cutting direction but also the reference guide type and the target alignment. Our findings could provide surgeons with clinically useful information to fine-tune for unintended loose or tight joint gaps by adjusting the component size.

[Future implications of navigation in total knee arthroplasty]

BACKGROUND

After more than two decades of experience with computer-assisted knee arthroplasty, extensive experience and study data are available, allowing a profound evaluation. Undoubtedly, computer-assisted knee arthroplasty has been proven to achieve excellent results for implant positioning and long-leg axis reconstruction. Thus, computer-assisted knee arthroplasty represents the current gold standard to avoid unintended malpositioning of total knee components for neutrally aligned implants and individualized implant alignment (kinematic alignment, adjusted mechanical alignment, and others). Previous studies could not show significant differences in functional outcomes and patient satisfaction. However, recent meta-analyses showed relevant advantages of computer-assisted knee arthroplasty. These results could be based on further developments in software-assisted soft tissue balancing and more sensitive evaluation methods of follow-up examinations.

LONG-TERM OUTCOME

Further, international registries show advantages of computer-assisted knee arthroplasty regarding long-term outcomes. In particular, the Australian arthroplasty registry describes a significantly lower revision rate due to aseptic loosening/osteolysis in the computer-assisted knee arthroplasty group, analyzing a period of up to 17 years. These positive effects can already be proven six months following surgery.

FUTURE PROSPECTS

However, despite demonstrated benefits, computer-assisted knee arthroplasty has not yet become established in daily routine, and wide regional variations in its use are observed. Newer developments such as robotic-assisted knee arthroplasty, primarily based on navigation techniques, are currently being heavily promoted. However, this new technology must justify its enormous additional costs and prove its advantages compared to computer-assisted knee arthroplasty. In the backdrop of the development of computer-assisted knee arthroplasty, this might be a difficult task.

The accelerometer-based navigation system demonstrated superior radiological outcomes in restoring mechanical alignment and component sagittal positioning in total knee arthroplasty

Background

This study aimed to determine whether the accelerometer-based navigation (ABN) could improve the accuracy of restoring mechanical axis (MA), component positioning, and clinical outcomes compared to conventional (CON) total knee arthroplasty (TKA).

Methods

A total of 301 consecutive patients (ABN: 27, CON: 274) were included. A 1:4 propensity score matching (PSM) was performed between the two groups according to preoperative demographic and clinical parameters. The postoperative MA, femoral coronal angle (FCA), femoral sagittal angle (FSA), tibial coronal angle (TCA) and tibial sagittal angle (TSA) were compared. Absolute deviations of aforementioned angles were calculated as the absolute value of difference between the exact and ideal value and defined as norms if within 3°, otherwise regarded as outliers. Additional clinical parameters, including the Knee Society knee and function scores (KSKS and KSFS) and range of motion (ROM), were assessed at final follow-up (FU) (mean FU was 21.88 and 21.56 months respectively for ABN and CON group). A secondary subgroup analysis and comparison on clinical outcomes were conducted between norms and outliers in different radiological parameters.

Results

A total of 98 patients/102 knees were analyzed after the PSM (ABN: 21 patients/24 knees, CON: 77 patients/78 knees). In the ABN group, the mean MA, FCA and TSA were significantly improved (p = 0.019, 0.006, < 0.001, respectively). Proportions of TKAs within a ± 3°deviation were significantly improved in all the postoperative radiological variables except for TCA (p = 0.003, 0.021, 0.042, 0.013, respectively for MA, FCA, FSA, and TSA). The absolute deviations of FSA and TSA were also significantly lower in the ABN group (p = 0.020, 0.048, respectively). No significant differences were found in either mean value, absolute deviation or outlier ratio of TCA between two groups. On clinical outcomes, there were no significant differences between two groups, although KSKS, KSFS and ROM (p < 0.01, respectively) dramatically improved compared to baseline. The subgroup analysis also demonstrated no statistical difference on clinical outcomes between the outliers and norms in varied radiological parameters.

Conclusions

The ABN could improve the accuracy and precision of mechanical alignment and component positioning without significant improvement of clinical outcomes. Further high quality studies with long term FU are warranted to comprehensively evaluate the value of the ABN.

Patient-Specific Instrumentation Accuracy Evaluated with 3D Virtual Models

There have been remarkable advances in knee replacement surgery over the last few decades. One of the concerns continues to be the accuracy in achieving the desired alignment. Patient-specific instrumentation (PSI) was developed to increase component placement accuracy, but the available evidence is not conclusive. Our study aimed to determine a PSI system’s three-dimensional accuracy on 3D virtual models obtained by post-operative computed tomography. We compared the angular placement values of 35 total knee arthroplasties (TKAs) operated within a year obtained with the planned ones, and we analyzed the possible relationships between alignment and patient-reported outcomes. The mean (SD) discrepancies measured by two experienced engineers to the planned values observed were 1.64° (1.3°) for the hip–knee–ankle angle, 1.45° (1.06°) for the supplementary angle of the femoral lateral distal angle, 1.44° (0.97°) for the proximal medial tibial angle, 2.28° (1.78°) for tibial slope, 0.64° (1.09°) for femoral sagittal flexion, and 1.42° (1.06°) for femoral rotation. Neither variables related to post-operative alignment nor the proportion of change between pre-and post-operative alignment influenced the patient-reported outcomes. The evaluated PSI system’s three-dimensional alignment analysis showed a statistically significant difference between the angular values planned and those obtained. However, we did not find a relevant effect size, and this slight discrepancy did not impact the clinical outcome.

Optimal Sagittal Insertion Depth and Direction of Femoral Intramedullary Rod in Total Knee Arthroplasty in Chinese Osteoarthritis Patients

Objective

To identify the optimal femoral intramedullary rod insertion depth and direction on the sagittal plane in total knee arthroplasty (TKA) of Chinese osteoarthritis (OA) patients.

Methods

From January to December 2019, CT data were collected for 85 consecutive entire lower extremity Chinese OA patients. A three‐dimensional method was used to simulate intramedullary rod penetration. The intramedullary rods were inserted toward the anterior (TA), center (TC), and posterior (TP) of the femoral canal, respectively. Four penetration depths of 150, 200, 250, and 300 mm from the joint line were set. The intersection angle was measured between the simulated intramedullary rod and the mechanical axis of the femur (FMA) on the sagittal plane.

Results

Our study included 85 Chinese OA patients: 46 women, with a mean age of 65.7 ± 8.4 years (range, 51–85 years) and 39 men, with a mean age of 65.6 ± 8.1 years (range, 46–86 years). The intersection angle between the FMA and the femoral anatomical axis was smaller in men, 2.4° ± 1.6° (range, 0°–4.8°), than in women, 3.5° ± 2.3° (range, 0.7º–8.2°), with a significant statistical difference (P < 0.01). In the comparison of the intersection angle between the simulated intramedullary rod and the FMA, there was no statistical difference between TA200 and TC200 in women (P > 0.05). The proportions were up to 91% and 96% of TA200 at 0°–3° and 0°–5° intervals, respectively, but just 63% and 78% in TC200. In TA150, 76% of intersection angles were greater than 5°. Only approximately 60% in TA250 and TA300 were within the 0°–5° interval and 40% were less than 0°. Only 57% of intersection angles in TC150 were in the 0°–3° interval. TC250, TC300, and TP150 were mostly below 0°. In men, there were statistical differences between all groups. All intersection angles were greater than 5° in TA150. TA200 and TA250 were mostly greater than 5° (87% and 59%, respectively) and 72% of intersection angles were within 0°–5° interval in TA300. TC150 had 92% of intersection angles within the 0°–5° interval but only 62% between the 0° and 3° interval. In the TC200, up to 90% and 97% were within 0°–3° and 0°–5° intervals, respectively. TC300, TP150, and TP200 were mostly below 0°.

Conclusion

We described an innovative method for rapidly, simply, and accurately identifying the sagittal insertion depth and direction of the femoral intramedullary rod in TKA, which can optimize the position of the femoral prosthetic component on the sagittal plane in TKA.