Differences between native and prosthetic knees in terms of cross-sectional morphology of the femoral trochlea: a study based on three-dimensional models and virtual total knee arthroplasty

Differences in Trochlear Morphology of a New Femoral Component Designed for Kinematic Alignment from a Mechanical Alignment Design

Because kinematic alignment (KA) aligns femoral components in greater valgus and with less external rotation than mechanical alignment (MA), the trochlear groove of an MA design used in KA is medialized, which can lead to complications. Hence, a KA design has emerged. In this study, our primary objective was to quantify differences in trochlear morphology between the KA design and the MA design from which the KA design evolved. The KA and MA designs were aligned in KA on ten 3D femur-cartilage models. Dependent variables describing the morphology of the trochlea along the anterior flange, which extends proximal to the native trochlea, and along the arc length of the native trochlea, were determined, as was flange coverage. Along the anterior flange, the KA groove was significantly lateral proximally by 10 mm and was significantly wider proximally by 5 mm compared to the MA design (p < 0.0001). Along the arc length of the native trochlea, the KA groove was significantly lateral to the MA design by 4.3 mm proximally (p ≤ 0.0001) and was significantly wider proximally by 19 mm than the MA design. The KA design reduced lateral under-coverage of the flange from 4 mm to 2 mm (p < 0.0001). The KA design potentially mitigates risk of patellofemoral complications by lateralizing and widening the groove to avoid medializing the patella for wide variations in the lateral distal femoral angle, and by widening the flange laterally to reduce under-coverage. This information enables clinicians to make informed decisions regarding use of the KA design.

Mismatch between trochlear coronal alignment of arthritic knees and currently available prosthesis: a morphological analysis of 4116 knees and 45 implant designs

PURPOSE

In up to a fifth of total knee replacements (TKR), surgeons are not capable of achieving good clinical and functional results. Despite comprehensive diagnostic workup, an underlying cause is not always identified in these patients. The purpose of this study is to compare native and prosthetic trochlear anatomies, to evaluate a potential source of morphologic mismatch and theoretically, of poor clinical outcomes.

METHODS

Native trochlear angles of 4116 knee CTs from 360 Knee Systems database of arthritic pre-operative TKR patients were evaluated. A semi-automated tridimensional analysis was performed to define the native trochlear angle in the coronal plane (NTA) among other 142 parameters. An active search was conducted to identify currently available TKR models; prosthetic trochlear orientation in the coronal plane (PTA) was extracted from the technical data provided by manufacturers.

RESULTS

The mean native trochlear angle (NTA) was 1.6° ± 6.6° (valgus) with a range from - 23.8° (varus) to 30.3°(valgus). A valgus NTA was present in 60.6% of the knees and 39.4% of them had a varus NTA. 89 TKR models were identified; trochlear details were available for 45 of them, of which 93% were designed with a valgus orientation of the prosthetic trochlear angle (PTA) and 6.9% showed a neutral (0°) PTA. Varus alignment of PTA was not present in any system. Angular numeric values for PTA were available for 34 models; these ranged from 0° to 15° of valgus, with a median value of 6.18° (SD ± 2.88°).

CONCLUSION

This study shows a significant mismatch between native and prosthetic trochlear angles. A relevant proportion of the studied knees (41.45%) fall out of the trochlear angle range of currently available implants; representing a potential source for biomechanical imbalance. While further research is warranted to fully understand the clinical implications of the present study, manufacturers may need to take these findings into account for future implant designs.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Wide variation in tibial slopes and trochlear angles in the arthritic knee: a CT evaluation of 4116 pre-operative knees

PURPOSE

As surgeons continue to grapple with persistent issues of patient dissatisfaction post-TKA, the literature has focused on the coronal plane when considering alignment strategies but has largely ignored the sagittal and axial planes. The purpose of this retrospective observational cohort study is to evaluate variability in knee anatomy and alignment beyond the coronal plane and rationalise how this relates to existing arthroplasty alignment philosophies.

METHODS

4116 knee CTs from 360 Knee Systems© database of arthritic pre-operative TKA patients were evaluated. Standardised bony landmarks were used in each CT to determine the hip-knee angle, medial proximal tibial angle, lateral distal femoral angle, medial plateau posterior tibial slope, lateral plateau posterior tibial slope, trochlea angle (TA) to distal femoral angle (TA-DFA) and TA to posterior condylar angle (TA-PCA). Analysis was performed to determine the distributions of each measure across the cohort population.

RESULTS

Both the medial and lateral PTS ranged from 5° anterior to 25° posterior. 22.6% of patients had differential PTS greater than 5°. 14.5% have greater lateral PTS (mean difference to medial PTS of 4.8° ± 5.0°), whilst 31.0% have greater medial PTS (mean difference to lateral PTS of 5.7° ± 3.2°). 14% of TA-DFAs and 5.2% of TA-PCAs vary greater than 10°.

CONCLUSION

This study demonstrates a wide variation in tibial slope, differential slope between the medial and lateral tibial plateau as well as variation in the trochlear geometry. There has been an overemphasis in the literature on coronal alignment, ignoring the considerable variability present in tibial and patellofemoral morphology. Existing arthroplasty techniques are based on assumptions that may not adequately address the anatomy of morphologic outliers and could lead to dissatisfaction.

LEVEL OF EVIDENCE

III-retrospective cohort study.

Intraoperative analysis of patellofemoral joint morphology before and after total knee arthroplasty

Background

Patellofemoral problems after total knee arthroplast (TKA) are frequent and often associated with a change in the geometry of the trochlear groove.

Objective

The present study aimed to analyze the feasibility of intraoperative examination of the patellofemoral joint geometry before and after the implantation of bicondylar total knee replacements without exposing the patient to radiation.

Material and methods

The patellofemoral joint morphology geometries of 33 patients before and after implantation of a bicondylar total knee replacement was intraoperatively analyzed using a digital scanning method. Femoral surface geometries were extracted from intraoperatively recorded tactile scanning data using an in-house algorithm. The geometries were then characterized by sulcus height, medial femoral condyle height and lateral femoral condyle height.

Results

Our preliminary results show that these key geometric parameters are only partially restored after TKA leading to a distinctly different shaped profile of the anterior distal femur. Maximum and minimum mean differences in sulcus height, medial femoral condyle height, and lateral femoral condyle height before and after surgery were 2.00 mm/−3.06 mm, 2.51 mm/−6.25 mm and 2.74 mm/−3.58 mm, respectively.

Conclusion

A new method for intraoperative analysis of the patellofemoral joint morphology before and after TKA without radiation exposure was developed and utilized. Even with the use of modern total knee designs, the patellofemoral articulation is considerably changed postoperatively as quantified by the key parameters of sulcus height, medial femoral condyle height, and lateral femoral condyle height. This may result in altered knee biomechanics and might explain persistent patellofemoral disorders, which are often reported by patients after TKA.

Using Statistical Shape Models to Optimize TKA Implant Design

(1) TKA implants should well fit on each patient’s anatomy. Statistical Shape Models (SSM) statistically represent the anatomy of a given population. The aims of this study were to assess how to generate a valid SSM for implant design and provide guidelines and examples on how to use the SSMs to evaluate the anatomic fit of TKA components. (2) Methods: A Caucasian SSM was built from 120 anatomies (65 female, 55 male) and an Asian SSM was based on 112 patients (75 female, 37 male). These SSMs were used to generate a database of 20 bone models. The AP/ML dimensions of the bone models were compared to those of the input population. Design input parameters, such as the tibial contour, trochlea, and femur curvature were extracted from the SSMs. Femur and patella components were virtually implanted on the bone models. (3) Results: the dimensions of the generated bone models well represented the population. The overhang of the femoral component as well as the coverage and peak restoration of the patella component were visualized. (4) Conclusions: SSMs can be used to efficiently gain input into TKA design and evaluate the implant fit on the studied population.

Three-dimensional morphometric differences of resected distal femurs and proximal tibias in osteoarthritic and normal knees

BACKGROUND

There is a paucity of data concerning the morphological differences of resected distal femurs and proximal tibias in osteoarthritic (OA) and normal knees. The objective of this study was to determine whether morphometric differences in the surfaces of resected distal femurs and proximal tibias exist between OA and normal knees in a Chinese population.

METHODS

Ninety-four OA knees and ninety-five normal knees were evaluated in Chinese individuals. Computed tomography was used to measure the femoral mediolateral (fML), medial anteroposterior (fMAP), lateral anteroposterior (fLAP), medial condylar width (fMCW), lateral condylar width (fLCW), medial posterior condylar curvature radii (fMCR), lateral posterior condyle curvature radii (fLCR), fML/fMAP aspect ratio, tibial mediolateral (tML), middle anteroposterior (tAP), medial anteroposterior (tMAP), and lateral anteroposterior (tLAP) tML/tMAP aspect ratio to determine the morphologic differences between OA and normal knees.

RESULTS

The average fMCW and tMAP dimensions of OA knees were larger than those of normal knees in both male and female (p <0.05). The fMAP/fML aspect ratio and tMAP/tML aspect ratio were also significantly different in both sexs (p <0.05). OA knees have an oval-shaped distal femur with a wider ML length and more spherical-shaped proximal tibiae with relatively narrow ML dimensions.

CONCLUSIONS

The study revealed the morphological differences in fMCW, tMAP, fMAP/fML and tMAP/tML between OA and normal knees in both males and females. These findings may provide guidelines that can be used to design better knee implants that are more size-matched for OA knees.

Modern total knee arthroplasty designs do not reliably replicate anterior femoral morphology

PURPOSE

Biomechanical studies suggest that PF tracking is not reliably restored to physiological values in TKA despite surgical technique optimization. A clinical observation is that current TKA designs may not replicate anterior femoral offset. The aim was to examine the intraoperative resection thicknesses of the anterior femoral condyles during TKA and correlate these findings relative to modern prostheses.

METHODS

This was a retrospective analysis of 199 patients who underwent 233 TKAs using a single implant design with measured anterior femoral condylar resection thicknesses. The aim was to restore posterior condylar offset whilst minimizing overstuffing of the anterior compartment of the knee by choosing the smallest prosthesis to allow for the maximal anterior resection as close to the cortex without inducing notching. Prosthetic measurements from 7 commonly used TKAs were collected by analysis of 3D models of median sized explants.

RESULTS

An average of 7.9 mm (SD 2.5 mm, range 2-16.5 mm) and 11.5 mm (SD 2.5 mm, range 2-21 mm) was resected from the medial and lateral aspects of the anterior femur, respectively. The average anterior flange thickness for the prosthesis data set was 6.6 mm (SD 0.6 mm, range 6.1-7.9 mm) medially and 7.6 mm (SD 0.7 mm, range 6.8-9.0 mm) laterally. Comparison across patients who received the median prosthesis size of 5 (SD 1.3, range 2-8) was inadequately restored by 1.4 mm (p < 0.00001) medially and 3.4 mm (p < 0.00001) laterally.

CONCLUSION

Host anatomy is not routinely restored during TKA. The surgical teaching to aim for an anterior femoral osteotomy close to the anterior cortex will result in understuffing of the PFJ and based on current prosthesis designs, the risk of overstuffing is not as significant as once believed. Future prostheses and surgical techniques should aim to restore not only posterior femoral but also anterior femoral offset.

LEVEL OF EVIDENCE

IV, Case series.

Gender-related morphological differences in sulcus angle and condylar height for the femoral trochlea using magnetic resonance imaging

PURPOSE

This study aimed to elucidate the primary differences in trochlear morphology between men and women utilizing three-dimensional magnetic resonance image reconstruction of the femoral trochlea.

METHODS

Differences in anthropometric femoral trochlea data of 975 patients (825 women, 150 men) were evaluated. The following morphological parameters were measured at three flexion angles (15°, 30°, and 45°) of the femoral trochlea: the sulcus angle, condylar height, and the trochlear groove orientation and mediolateral groove position.

RESULTS

The sulcus angle was significantly greater in women than in men at 15° and 45° flexions (P < 0.05). However, there was no gender difference found in the sulcus angle at 30° flexion. Medial and lateral condylar height values were greater in men than in women for the three flexion angles (P < 0.01). The trochlear groove orientation and mediolateral groove position showed no gender-related differences.

CONCLUSIONS

Magnetic resonance image reconstruction demonstrated that measurement of trochlear morphology varied significantly between men and women. This study provides guidelines for the design of a suitable femoral component for total knee arthroplasty, considering gender-specific differences in the Korean population. Biomechanical guidelines for total knee arthroplasty in Korean individuals can be optimized using our finding, so as the risk of patellar dislocation to be decreased. Surgeons should be aware of gender differences in femoral trochlear to optimize choice of implant.

LEVEL OF EVIDENCE

III.