Relationship between the tibial anteroposterior axis and the surgical epicondylar axis in varus and valgus knees

Setting the Tibial Component Rotation Based on Femoral Landmarks Allows Congruent Knee Kinematics in Robotic-Assisted Medial Unicompartmental Knee Replacement

The accurate positioning of the prosthetic components is essential for achieving successful results in medial unicompartmental knee arthroplasty (mUKA). The tibial component rotation in image-based robotic-assisted UKA is usually based on tibial bony landmarks matched to the pre-operative CT model. The study aimed to evaluate whether setting the tibial rotation on femoral CT-based landmarks allows congruent knee kinematics. We retrospectively analyzed data from 210 consecutive image-based robotic-assisted mUKA cases. In every case, we set the tibia rotation landmark parallel to the posterior condylar axis and centered it on the trochlea groove defined on the preoperative CT scan. The implant positioning was primarily set parallel to this rotation landmark and then adjusted based on tibial sizes avoiding component over- or under-hang. During surgery, we recorded the knee kinematics under valgus stress to reduce the arthritic deformity. A femoral-tibial contact point was recorded over the entire range of motion and displayed as a tracking profile on the tibia implant. The femoro-tibial tracking angle (FTTA) was then calculated based on a tangent line to the femoro-tibial tracking-points and the difference to the femur-based rotation landmark. In 48% of the cases, we could position the tibia component exactly to the femoral rotation landmark, whereas in 52% of cases, minimal adjustments were made to avoid component’s under- or over-hang. The mean tibia component rotation (TRA) with reference to our femur-based landmark was +0.24° (SD ± 2.9°). The femur-based tibia rotation landmark showed a high correspondence to the FTTA with 60% of the cases having less than 1° of deviation. Mean FTTA was +0.7° (SD ± 2.2°). The mean difference between the absolute value of the TRA and the FTTA (|TRA| − |FTTA|) was −0.18° (SD ± 2°). Setting the tibial component rotation based on CT scan femoral landmarks and not on tibial anatomical landmarks is a reliable method to obtain congruent knee kinematics during image-based robotic-assisted medial UKA with less the 2° deviations on average.

Effect of the posterior sagging control device to the posterior tibial translation during posterior-stabilized total knee arthroplasty with modified gap technique

PURPOSE

In modern total knee arthroplasty (TKA), flexion and extension gaps between the femur and tibia are equilibrated before implanting the final components. Uncontrolled intraoperative posterior tibial translation (PTT) could cause an artifactual widening of the flexion gap, which could lead surgeons to alter the femoral component size. We designed an intraoperative posterior sagging control device to prevent intraoperative PTT. In this study, we investigated whether the use of this device could prevent artifactual widening of the flexion gap.

METHODS

Twenty-five patients, 21 women and four men, aged 74.2 years, were enrolled in this prospective study. All patients underwent postero-stabilized TKA using a navigation system. Intraoperative PTT, flexion and extension gaps with or without using the posterior sagging control device were measured with navigation system. These measurements were compared with or without the posterior sagging control device and after the final implantation also.

RESULTS

There were significant differences between the measurements performed with or without the posterior sagging control device when compared to the post-implantation measurements. The use of the device reduced the number of patients with a >3 mm increase in flexion gap from 7 (28%) to 1 (4%).

CONCLUSION

This study suggests that the posterior sagging control device prevents PTT and artificial flexion gap widening. This could prevent an unnecessary increase in component size.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Preoperative tibiofemoral rotational alignment is a risk factor for component rotational mismatch in total knee arthroplasty

BACKGROUND

Rotational mismatch between the femoral and tibial components is reported to be a risk factor for unsuccessful total knee arthroplasty (TKA). However, the rotational mismatch can still occur even when each component is aligned within the desired angle. Therefore, there may be other unknown factors. This study aims to investigate a risk factor for component rotational mismatch in TKA. The authors hypothesized a significant correlation between the rotational mismatch angle and not only the rotational alignments of components, but also the preoperative tibiofemoral rotation angle.

METHOD

This retrospective cohort study included 79 knees who underwent TKA. Computed tomography images were obtained preoperatively and 2 weeks after surgery for the component positional measurement. The postoperative component rotational mismatch angle between the tibial and femoral components and the rotational alignment of each tibial and femoral component to anatomical axes was evaluated. In addition, the preoperative rotational angle between the tibia and femur bones and patients' demographics were also investigated. The correlation between the postoperative component rotational mismatch angle and perioperative variables was analyzed to identify risk factors for component rotational mismatch.

RESULTS

The mean component rotational mismatch angle was 1.8° of internal rotation of the tibial component relative to the femoral component, and the angle ranged from 11.3° of internal rotation to 7.3° of external rotation of the tibial component. Multivariate regression analysis showed that the preoperative rotational alignment between the tibia and femur and the rotational alignment of each component were influential factors in the postoperative component rotational mismatch angle.

CONCLUSION

The preoperative tibiofemoral rotational alignment and the rotational alignment of each tibial and femoral component and are risk factors for the postoperative component rotational mismatch in TKA.

Does component axial rotational alignment affect clinical outcomes in Oxford unicompartmental knee arthroplasty?

BACKGROUND

Limited studies have examined the relationship between axial rotational alignment and functional outcome in mobile-bearing UKA. The aims of this study was to determine the correlation between component axial rotational alignment and functional outcomes, and to recommend a safety range for component rotation for Oxford UKA.

METHODS

A retrospective study of 83 Oxford UKA was performed in 67 patients. Postoperative CT scans and clinical assessments were performed at a mean follow up of 21 months. Functional outcomes were measured by the OKS, modified KSS and KFS scores. A moving threshold analysis was performed to evaluate the relationship between different rotational alignment cut-off values and functional outcome scores.

RESULTS

The mean femoral and tibial components were positioned with a mean of 4.8° and 7.5° external rotation (ER), respectively. Increasing tibial external rotation was negatively correlated with clinical outcome scores while increasing femoral component rotation did not correlate with clinical outcomes. Better functional scores were observed at mean femoral and tibial rotation angles between 2-6° ER (1.2-6.6°) and 1-8° ER (0.5-8.8°), respectively; with the highest OKS, KSS and FKS observed at 3-4° ER for femoral component, and 4-5° ER for tibial component.

CONCLUSION

Femoral component axial rotation between 2°- 6° ER, and tibial component axial rotation between 1° and 8° ER correlated with significantly better functional scores. Surgeons should be especially aware of the relatively high variability in tibial component rotation and its implications of functional outcomes.

Tibiofemoral rotation alignment in the normal knee joints among Chinese adults: a CT analysis

Background

Consensus on tibial rotation in total knee arthroplasty (TKA) remains controversial. The present study aimed to investigate the closest anatomical reference to surgical epicondylar axis (SEA) among 10 tibial markers in Chinese adults.

Methods

This study included examination of 122 normal lower extremities. Briefly, 10 axes were drawn on the axial sections: transverse axis of tibia (TAT), axis of medial edge of patellar tendon (MEPT), axis of medial 1/3 of patellar tendon attachment (M1/3), Akagi line, Insall line, axis of medial border of tibial tubercle (MBTT), and axis of anterior border of the tibia 1–4 (ATC1–4). The mean angles between TAT and SEA and that between other axes and the line perpendicular to SEA were measured. Pairwise differences among the 10 tibial axes were examined by applying one-way analysis of variance (ANOVA) and paired t-test.

Results

In all the knees, the mean angles of M1/3, Akagi line, Insall line, MBTT, ATC1, ATC2, ATC3, and ATC4 axes were compared to the line perpendicular to the projected SEA and found to be 10.2 ± 5.1°, 1.4 ± 5.0°, 11.9 ± 5.4°, 3.6 ± 4.8°, 12.0 ± 6.9°, 7.2 ± 8.6°, 7.1 ± 10.4°, and 6.6 ± 13.5° external rotation, respectively, and the MEPT axis was 1.6 ± 4.5° internal rotation. The mean angle for TAT was 4.1 ± 5.3° external rotation. The M1/3 and Insall line were significantly more externally rotated than Akagi line, MEPT, MBTT, TAT, ATC2, ATC3, and ATC4 axes. No significant differences were noted between the TAT axis and the MBTT axis and among the ATC2, ATC3, and ATC4 axes.

Conclusion

The Akagi line, MBTT, and TAT showed good consistency with SEA in the axial femorotibial alignment with knee in extension. The middle segment of the anterior tibial crest also demonstrated good alignment consistency with SEA for the axial femorotibial alignment. Hence, these markers can be used as reliable references for rotational alignment of the tibial component in TKA.

Rotational alignment errors can occur in unicompartmental knee arthroplasty if anatomical landmarks are misused: A preoperative CT scan analysis

BACKGROUND

Accurate implant positioning, including rotation, is essential for successful unicompartmental knee arthroplasty (UKA). This study defined the rotational error that would result in medial UKA when using the medial edge of the tibial tubercle (TT) rather than the medial tibial spine for determining tibial component rotation, and in lateral UKA when aligning the anterior edge of the sagittal tibial cut with the lateral edge of the patellar tendon.

METHODS

Preoperative computed tomography (CT) scans were reviewed in 88 knees undergoing medial (n = 71) and lateral (n = 17) UKAs. In medial UKA, the angle between a line along the long axis of the medial tibial spine and a line drawn to the medial edge of the TT was measured. In lateral UKA, the angular relationship between the longitudinal axis of the lateral tibial spine and the lateral edge of the patellar tendon was measured.

RESULTS

In medial UKA, an average angular error of 9.6° of external rotation could result if the medial edge of the TT is used to set tibial implant rotation. In lateral UKA, the error of the sagittal tibial cut was an average of 7.1° of excessive external rotation if it is referenced on the lateral edge of the patellar tendon.

CONCLUSIONS

The preoperative CT scan analysis showed that using the medial edge of the TT and lateral edge of the patellar tendon to set tibial implant rotation may result in excessive external rotation in medial and lateral UKAs, which could result in kinematic mismatch, suboptimal contact areas and rotational malalignment.

Compensatory Function of the Subtalar Joint for Lower Extremity Malalignment

It is important to evaluate the subtalar joint and hip-knee-ankle alignment to understand lower extremity alignment. In this review, we focused on the compensatory changes in the subtalar joint alignment for the deformity of the knee and ankle joint, reviewing previous research. The subtalar joint alignment was compensatory valgus in patients with varus knee and ankle deformity, whereas it was uncertain whether the subtalar joint alignment was compensatory varus in patients with valgus knee and ankle deformity. The subtalar joint valgus alignment improved after total knee arthroplasty or high tibial osteotomy for varus knee deformity, even if the deformity was severe. In contrast, whether the subtalar joint alignment changed after the surgery for ankle or valgus knee deformity has not been considered. Further research on the compensatory function of the subtalar joint is needed.

Preoperative tibial mechanical axis orientation and articular surface design influence on the coronal joint line orientation relative to the ground during gait after total knee arthroplasties

PURPOSE

Neutral lower limb alignment does not necessarily produce a horizontal joint line after total knee arthroplasty (TKA). The orientation of the pre- and postoperative tibial mechanical axes (TMAs-G), tibial component, and joint line relative to the ground were evaluated.

METHODS

The study group included 46 knees, 23 posterior-stabilized (PS) and 23 bicruciate-stabilized (BCS) TKAs. Using whole-leg standing radiographs, the static orientation of the pre- and postoperative TMAs-G and the tibial component as well as the postoperative alignment were measured. Applying image-matching techniques, the dynamic coronal orientation of the tibial component and joint line over the stance phase of gait were analysed. The correlation between static and dynamic orientation of the tibial component and differences in the joint line between the PS and BCS TKAs were evaluated.

RESULTS

In standing, the postoperative TMA-G (0.8° ± 2.8°) and tibial component (1.5° ± 2.4°) were laterally tilted with a strong correlation. The preoperative lateral tilt of the TMA-G (7.9° ± 5.1°) was a significant predictor of the postoperative TMA-G. The lateral tilt of the tibial component increased to 5.1° ± 2.4° on dynamic analysis, and was moderately correlated to static orientation. The dynamic orientation of the joint line was smaller for the BCS (1.8° ± 2.4°) compared to the PS (5.5° ± 2.7°) TKA.

CONCLUSION

Even with a mechanically well-aligned TKA, a lateral tilt of the tibial component was identified due to the lateral tilt of the postoperative TMA-G and the stance phase of gait. The BCS can better accommodate the residual lateral tilt of the joint line due to the 3° medial inclination of the joint surfaces of the implant. This study increases the awareness of surgeons regarding the possibility of the coronal joint line orientation to influence preoperative TMA-G and be accommodated by articular surface design, even in mechanically aligned TKA.

LEVEL OF EVIDENCE

IV.

Deviation of femoral intramedullary alignment rod influences coronal and sagittal alignment during total knee arthroplasty

BACKGROUND

An intramedullary (IM) rod is used to resect the distal femur vertically to the femoral mechanical axis in the coronal plane in many cases of total knee arthroplasties (TKA). The valgus angle between the mechanical axis and the anatomical axis of the distal femur is estimated preoperatively. It is known the deviation of the IM rod in the femoral canal could influence the femoral component alignment. However, there is no published data regarding how many degrees of deviation to make with the IM rod. The purpose of this study is to measure each deviation of the IM rod using three-dimensional (3D) computer simulations.

METHODS

Preoperative CT scans on 30 knees undergoing TKA were studied. The line connecting central points at 10 and 20 cm proximal from the intercondylar notch was defined as the anatomical axis and the point at which the anatomical axis intersects the surface of the distal femur was considered as the entry point of the IM rod. The medio-lateral (ML) and antero-posterior (AP) deviations between the anatomical axis and the IM rod were measured.

RESULTS

The ML and AP deviations were 0.8 and 1.1° on average. The IM rod was deviated medio-laterally more than 1.0° in three knees (10%).

CONCLUSION

Surgeons should note the ML difference of the resection thickness of the distal femur for coronal alignment. If the ML difference varies greatly from the preoperative planning, they need to adjust at most 1.0° of valgus angle to achieve the appropriate coronal alignment. Level of evidence III, Therapeutic.

Tibiofemoral rotational alignment affects flexion angles in navigated posterior-stabilized total knee arthroplasty

PURPOSE

To investigate the tibiofemoral rotational profiles during navigated posterior-stabilized (PS) total knee arthroplasty (TKA) and investigate the effect on post-operative maximum flexion angles.

METHODS

Twenty-five subjects, treated with navigated PS TKA, were enrolled, and the effect of posterior cruciate ligament (PCL) resection and component implantation on tibiofemoral rotational kinematics was statistically evaluated. Then, the effect of rotational alignment changes on the post-operative maximum angles was retrospectively examined in 96 subjects using the multiple regression analysis.

RESULTS

Tibial internal rotation was significantly increased in full extension (p < 0.01 and <0.001, respectively) and at 60° and 90° flexion (p < 0.05) after PCL resection, which further increased after implantation, compared with that before resection. The amount of tibial internal rotation from 90° flexion to maximum flexion was significantly decreased after PCL resection and implantation, compared with that before resection (p < 0.05). The internal changes in the rotational alignment were independent factors for the minimal improvement in the post-operative maximum flexion angles (R ² = 0.078, p = 0.0067).

CONCLUSION

PCL resection changed the tibial rotational alignment and decreased the amount of tibial internal rotation. The implantation of PS components further increased the internal rotational alignment and could not compensate for the tibiofemoral rotation. Finally, the internal changes in rotational alignment affected the improvement of the maximum flexion angles, suggesting that rotational alignment is an important factor for improving post-operative maximum flexion angles.

LEVEL OF EVIDENCE

II.

In vivo kinematics of gait in posterior-stabilized and bicruciate-stabilized total knee arthroplasties using image-matching techniques

PURPOSE

This study aimed to evaluate the effects of two types of total knee arthroplasty (TKA) designs: posterior-stabilized (PS) and bicruciate-stabilized (BCS) on in vivo kinematics during gait.

METHODS

Continuous X-ray images of the gait were taken using a flat panel detector for 23 PS and BCS TKAs. We analyzed the tibiofemoral implant flexion angle, anteroposterior (AP) translation, axial rotation, and anterior/posterior cam-post contact using image-matching techniques.

RESULTS

Double knee actions were demonstrated for the PS and BCS design (35 and 61%, respectively, p = 0.08). The tibiofemoral AP positions were significantly more posterior at peak extension (- 1.7 ± 2.2 and 1.0 ± 2.5 mm, respectively, p < 0.01) and anterior at peak flexion (1.3 ± 2.3 and - 0.8 ± 2.8 mm, respectively, p = 0.01) for the PS design than for the BCS design, with a significant difference in AP translation (3.0 ± 3.9 mm anterior and 1.7 ± 2.8 mm posterior, respectively, p < 0.01). Anterior/posterior tibial post contacts were found in 83/4% and 74/30% for the PS and BCS designs, respectively, with a significant difference in posterior contact (p = 0.72/0.04, respectively).

CONCLUSION

The knee flexion pattern, tibiofemoral AP translation, axial rotation, and cam-post contact during gait varied, depending on the type of implant, the PS and BCS designs.

The medial border of the tibial tuberosity as an auxiliary tool for tibial component rotational alignment during total knee arthroplasty (TKA)

PURPOSE

The objective of this study was to quantify the amount of ensuing internal rotation of the tibial component when positioned along the medial border of the tibial tubercle, thus establishing a reproducible intraoperative reference for tibial component rotational alignment during total knee arthroplasty (TKA).

METHODS

The angle formed from the tibial geometric centre to the intersection of both lines from the middle of the tibial tuberosity and its medial border was measured in 50 patients. The geometric centre was determined on an axial CT slice at 10 mm below the lateral tibial plateau and transposed to a slice at the level of the most prominent part of the tibial tuberosity. Similar measurements were taken in 25 patients after TKA, in order to simulate the intraoperative appearance of the tibia after making its proximal resection.

RESULTS

This angle was found to be similar (n.s.) in normal and post-TKA tibiae [median 20.4° (range 15°-24°) vs. 20.7° (range 16°-25°), respectively]. In 89.3 % of the patients, the angle ranged from 17° to 24°. No statistical difference (p n.s.) was found between women and men in both normal [median -20.7° (range 16°-25°) vs. 19.9° (range 15°-24°)] and post-TKA tibiae [median 21.4° (range 19°-24°) vs. 20° (range 16°-25°)].

CONCLUSION

This study found that in 90 % of the patients, the medial border of the tibial tuberosity is internally rotated 17°-24° in relation to the line connecting the middle of the tuberosity to the tibial geometric centre. Since this anatomical landmark may be more easily identifiable intraoperatively than the commonly used "medial 1/3", it can provide a better quantitative reference point and help surgeons achieve a more accurate tibial implant rotational position.

LEVEL OF EVIDENCE

Cohort and case control studies, Level III.

Femoral sizer design can increase anterior notching during total knee arthroplasty

BACKGROUND

The anteroposterior (AP) portions of the distal femur are generally resected externally rotated relative to the posterior condylar line (PCL) in non-navigated/measured-resection total knee arthroplasty (TKA). Some femoral sizing devices allow rotational adjustment before sizing (rotation-modified sizing devices), while others do not (rotation-unmodified sizing devices). When rotation-unmodified sizing devices are used, the stylus attached to the sizing device identifies the proximal/anterior flange cut assuming the femoral component is aligned parallel to the PCL. However, if the AP cutting device is externally rotated then unexpected notching of the anterior cortex can occur.

METHODS

We simulated TKA surgery in 100 Japanese varus osteoarthritic knees using three-dimensional planning software. The femoral component was aligned parallel to the PCL and the AP component position was determined so proximal anterior flange was just touching the anterior cortex. Next, the femoral component was externally rotated parallel to the surgical epicondylar axis (SEA). If the proximal anterior flange penetrated femoral bone, the length and thickness of anterior notching were measured.

RESULTS

The proximal anterior flange rested on the anterior cortex or penetrated the femoral bone in all knees. There was a strong positive correlation between PCA and length of anterior notching. Anterior notching more than 10mm length or one-millimeter thickness occurred in most cases (82.4% and 70.6%, respectively) where the posterior condylar angle (PCA) was more than four degrees.

CONCLUSIONS

Anterior femoral notching is influenced by the design of the femoral sizing guide and subsequent rotation of cutting blocks, especially in knees with a large PCA.

A lateralized anterior flange improves femoral component bone coverage in current total knee prostheses

BACKGROUND

Poor femoral implant fit to resected bone surfaces recently has been the motivation for several new total knee arthroplasty implant designs. Implant overhang risks adverse soft-tissue interaction while uncovered cut bone surfaces (underhang) risks increased postoperative bleeding or development of heterotopic bone.

METHODS

Femoral implant fit was studied systematically, and without the influence of surgical variation, by virtually implanting standard and narrow width femoral components (Bi-Surface 5) using preoperative computed tomography data for 150 varus osteoarthritic knees in Japanese patients. Overhang and underhang rates and bone widths were determined by gender.

RESULTS

Narrow femoral components helped avoid or minimize overhang in most female and some male knees. Although anterior width in the narrow components closely matched female bone width, the femoral component was necessarily displaced laterally to avoid overhang in the anteromedial portion. Consequently, there was significant medial underhang in the distal and posterior zones.

CONCLUSIONS

Ideally, the anterior femoral flange should be shifted 2 to 2.5mm laterally relative to the distal and posterior aspects to provide optimal femoral bone coverage in this prosthesis. The current study also confirmed that this modification can be generalized to the other two currently available "narrow type" prostheses. This geometric modification might allow surgeons to select a femoral component with slightly wider mediolateral dimensions in the distal and posterior aspects to minimize underhang, while eliminating anterior overhang.

LEVEL OF EVIDENCE

III.

Dynamic Three-Dimensional Analysis of Lachman Test for Anterior Cruciate Ligament Insufficiency: Analysis of Anteroposterior Motion of the Medial and Lateral Femoral Epicondyles

PURPOSE

To evaluate dynamic three-dimensional (3D) kinematic properties of the anterior cruciate ligament (ACL)-insufficient knees and healthy contralateral knees in awake patients during the Lachman test using biplane fluoroscopy.

MATERIALS AND METHODS

Ten patients with unilateral ACL-insufficient knees and healthy contralateral knees were enrolled in this study. Each patient underwent the Lachman test three times in the awake state. The knee joint motions were captured using biplane fluoroscopy. After manual registration of 3D surface data from 3D-computed tomography to biplane images, dynamic 3D kinematic data were analyzed.

RESULTS

The average anteroposterior (AP) translation of the medial femoral epicondyle of the ACL-insufficient knees (11.5±4.2 mm) was significantly greater than that of the contralateral knees (7.7±3.5 mm) (p<0.05). However, there was no statistically significant side-to-side difference in the average AP translation of the lateral femoral epicondyle. During the Lachman test, the distal femur was more externally rotated than the proximal tibia, which showed significant difference between both sides.

CONCLUSIONS

During the Lachman test, the medial femoral epicondyle of the ACL-insufficient knee exhibited greater AP motion than that of the contralateral knee, whereas there was no significant side-to-side difference with regard to the AP motion of the lateral femoral epicondyle.

Rotational alignment of tibial components in mobile-bearing TKA: posterior substituted vs. PCL retaining

PURPOSE

The medial border of the tibial tubercle (MBTT) is one of the fixed anatomic landmarks for tibial component setting during total knee arthroplasty (TKA). In mobile-bearing TKA using a tibial cut first technique, the final tibial component rotation can be guided by the position it achieves following several flexion-extension cycles. In this study, tibial component angle (TCA) and tibial rotational angle (TRA) were determined in dependence of retention or resection of the posterior cruciate ligament (PCL).

METHODS

The TCA and TRA were examined in 206 patients who underwent primary TKA (PCL retaining: 104 knees, PCL substituting: 102 knees). The tibial component rotation was intraoperatively setting between the parallel to the axis of the most medial aspect of the tibial tubercle as the anterior anatomic landmark and the center of the tibial component as the posterior landmark at the maximum coverage with the osteotomized tibial plateau with its adjustment after several knee flexion-extension exercises. A postoperative quantitative three-dimensional computed tomography technique was used for measurements by a single observer.

RESULTS

The TCA showed a divergence of 0.21° external to the MBTT in the PCL-retaining design and 1.62° internal divergence in the PCL-substituting design. The TRA showed an internal divergence of 0.88° in the PCL-retaining design and an internal divergence of 2.12° in the PCL-substituting design. There were no significant differences between the two designs.

CONCLUSIONS

The MBTT might be regarded as a reliable landmark for obtaining an acceptable tibial rotational setting in mobile-bearing TKA despite PCL retention.

Effect of rotational alignment on outcome of total knee arthroplasty

BACKGROUND AND PURPOSE

Poor outcomes have been linked to errors in rotational alignment of total knee arthroplasty components. The aims of this study were to determine the correlation between rotational alignment and outcome, to review the success of revision for malrotated total knee arthroplasty, and to determine whether evidence-based guidelines for malrotated total knee arthroplasty can be proposed.

PATIENTS AND METHODS

We conducted a systematic review including all studies reporting on both rotational alignment and functional outcome. Comparable studies were used in a correlation analysis and results of revision were analyzed separately.

RESULTS

846 studies were identified, 25 of which met the inclusion criteria. From this selection, 11 studies could be included in the correlation analysis. A medium positive correlation (ρ = 0.44, 95% CI: 0.27-0.59) and a large positive correlation (ρ = 0.68, 95% CI: 0.64-0.73) were found between external rotation of the tibial component and the femoral component, respectively, and the Knee Society score. Revision for malrotation gave positive results in all 6 studies in this field.

INTERPRETATION

Medium and large positive correlations were found between tibial and femoral component rotational alignment on the one hand and better functional outcome on the other. Revision of malrotated total knee arthroplasty may be successful. However, a clear cutoff point for revision for malrotated total knee arthroplasty components could not be identified.

An Anatomic Study on Whether the Patella is Centered in an Ideal Anteroposterior Radiograph of the Knee

BACKGROUND

Currently, an anteroposterior radiograph of the knee is judged based on a centered position of the patella between the femoral condyles. We are not aware of any anatomic literature supporting this recommendation.

QUESTIONS/PURPOSES

Orthogonal images are required for accurate assessment of knee deformity. Although an image with the patella centered at the distal femur is generally accepted as a true anteroposterior (AP) radiograph of the knee, there is minimal anatomic data to support that this view is orthogonal to a true lateral view of the knee where the condyles are overlapped. We designed an anatomical study to test the relationship between these two radiographic views.

METHODS

We studied 428 well-preserved cadaveric skeletons ranging from 40 to 79 years of age at death. Centering of the patella was calculated based on distal femoral and patellar widths. Multiple regression analysis was then performed to determine the relationship between patellar centering and age, gender, ethnicity, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), femoral anteversion, and contralateral centering.

RESULTS

Average patellar centering was 0.13 ± 0.04, indicating that the average patella was laterally positioned in the distal femur. Only mLDFA and contralateral centering showed statistically significant independent correlations with patellar centering with modest standardized beta coefficients of 0.10 and 0.23, respectively.

CONCLUSIONS

In the average specimen, the patella is laterally deviated by 13% of the condylar width. Clinicians should be aware that a lateral view with the femoral condyles overlapped is not always orthogonal to a patella-centered AP view when planning and implementing deformity correction.

Rotational alignment of the tibial component affects the kinematic rotation of a weight-bearing knee after total knee arthroplasty

PURPOSE

The purpose of this study is to elucidate how the rotational malalignment of prosthesis after total knee arthroplasty affects the rotational kinematics in a weight-bearing condition.

METHODS

In this study of 18 knees replaced with the posterior stabilizing fixed-bearing system, which has a relatively low-restricting design, rotational angles between the femoral and tibial components and between the femur and tibia during stair climbing were evaluated in vivo in three dimensions using radiologically based image-matching techniques. Rotational alignments of the components were assessed by postoperative CT. The correlations between the rotational alignments and the rotational angles during stair climbing were evaluated.

RESULTS

Rotational alignment of the tibial component significantly correlated with rotational angles between the components as well as between bones during stair climbing. Rotational malalignment of the tibial component toward internal rotation caused a rotational mismatch of the tibial component toward internal rotation relative to the femoral component in 0° extension and caused a rotational mismatch of the tibia (bone) toward external rotation relative to the femur (bone). The knee in which the tibial component was placed close to the AP axis of the tibia did not show any rotational mismatch between either components or bones.

CONCLUSIONS

Rotational alignment of the tibial component affects the kinematic rotation of the replaced knee during a weight-bearing condition even though using a low-restricting designed surface, and the AP axis can be a reliable reference in determining rotational alignment for the tibial component.

The surgical epicondylar axis is a consistent reference of the distal femur in the coronal and axial planes

PURPOSE

Various rotational landmarks including the surgical epicondylar axis (SEA) are used for preoperative planning and intra-operative reference of total knee arthroplasty (TKA) in the axial plane. The aim of the study was to elucidate the relationships between the SEA and other femoral anatomical landmarks, including the mechanical axis, distal and posterior knee joints, the trochlear groove, and the anterior femoral condyle, in both the coronal and axial planes.

METHODS

Angular and linear measurements were taken of sixty femora using Orthomap3D, which has a tool to analyse computed tomography image data that makes it possible to measure three-dimensional distances and angles precisely. The inter- and intra-observer reliabilities of these measurements were evaluated. Comparisons were made according to height, weight, body mass index, and gender.

RESULTS

The angle between the mechanical axis and the SEA was 90.2° (95% CI 90.0°-90.4°). There was a significant correlation for each linear measurement between the SEA and the distal/posterior knee joint line and for each linear measurement between the SEA and the anterior medial/lateral femoral condyle. A significant difference was observed between genders in the linear measurements. Significant correlations were found between height and weight and linear parameters.

CONCLUSION

Knowledge of the relationships between the SEA and other femoral anatomical landmarks is useful in preoperative planning, intra-operative landmark, and postoperative assessment of TKA. The SEA is a consistent parameter of femoral alignment in the coronal plane and a stable reference for femoral rotation in the axial plane.

LEVEL OF EVIDENCE

III.