Inter-observer reliability of measurements performed on digital long-leg standing radiographs and assessment of validity compared to 3D CT-scan

Which Knee Phenotypes Exhibit the Strongest Correlation With Cartilage Degeneration?

BACKGROUND

Although articular wear has been thoroughly investigated, the effects of abnormal limb alignment on cartilage degeneration over time remain poorly understood. An exact assessment of the correlation between lower limb alignment abnormalities and MRI-observed articular degradation may be helpful for understanding the progression of osteoarthritis and planning future treatment.

QUESTION/PURPOSE

In patients with moderate to advanced osteoarthritis, (1) is there a correlation between overall alignment of the knee and the location of cartilage degradation over time, as measured by cartilage metrics on MRI? (2) Is there a correlation between tibial alignment and the location of cartilage degradation over time, as measured by cartilage metrics on MRI? (3) Is there a correlation between femoral alignment and the location of cartilage degradation over time, as measured by cartilage metrics on MRI?

METHODS

Between April 2020 and September 2022, we retrospectively evaluated 3106 patients aged 45 to 79 years who were at risk of experiencing knee osteoarthritis. Of those, we considered as potentially eligible 600 symptomatic index knees with radiographic evidence of osteoarthritis-Kellgren-Lawrence Grades 2 or 3-at the baseline visit. Of those, 22% (134 of 600) were excluded because of a lack of proper alignment measurements, leaving 466 knees with measurements of radiologic alignment angles and quantitative MRI cartilage measurements of 16 subregions of the femorotibial compartment at baseline and 12 and 24 months, and 64 knees at the 48-month visit for investigation in the current study. Data regarding cartilage measurements of the patellofemoral compartment were not available for analysis. The knees were categorized into one of the possible 25 different phenotypes of the lower extremity established by previous research, based on the neutral, valgus, or varus distal mechanical angle of the femur and proximal tibial mechanical angle on full-limb radiographs. We applied ANOVA to estimate the effect size of the overall, femoral, and tibial alignments on the location of cartilage degradation over time, as measured by cartilage metrics on MRI.

RESULTS

We found that the overall combinations of a valgus femur with valgus tibia or a valgus femur with varus tibia were associated with the highest loss of cartilage in the internal medial tibial subregion and anterior lateral tibial subregion (η 2 p = 0.39 and 0.17, respectively). For the tibia, we found that the combination of a valgus femur with valgus tibia was associated with an increase in the area of subchondral bone denuded of cartilage in the central lateral tibial subregion (η 2 p = 0.2). For the femur, we found that the combination of a valgus femur with valgus tibia was associated with loss of cartilage thickness in the central weightbearing lateral femorotibial compartment (η 2 p = 0.15).

CONCLUSION

We found that certain alignment patterns are associated with rapid deterioration of cartilage and exposure of subchondral bone, even over short time periods. In particular, the valgus femur with valgus tibia and valgus femur with varus tibia phenotypes deserve special attention, because they exhibited a strong, atypical correlation with the internal medial tibial subregion and anterior lateral tibial subregion, respectively. This is important because valgus and varus malalignment cause isolated lateral and medial compartment disease, respectively. Therefore, these findings suggest that a more individualized approach for limb axis deformities is valuable, and hint at a more meticulous radiologic and clinical investigation, perhaps using different imaging modalities, especially when assessing the exact cartilage state and planning an intervention. Future studies, ideally biomechanical, might help in assessing the long-term effects of the various phenotypes on cartilage degradation and their relevance in reconstructive surgery.

LEVEL OF EVIDENCE

Level II, prognostic study.

Varus placement of the tibial component reduces the potential risk of fracture with adequate bony coverage in the Oxford unicompartmental knee arthroplasty

A short keel-cortex distance (KCD), especially to the posterior cortex, is a potential risk factor for tibial plateau fracture after Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study aimed to evaluate the effect of tibial component alignment in the coronal plane and tibial proximal morphology on the KCD. Included in this study were 51 patients scheduled for primary Oxford medial unicompartmental knee arthroplasty (UKA). The anterior and posterior KCD were preoperatively assessed using 3D simulation software with the component set perpendicular to the tibial mechanical axis (neutral), 3° valgus, 3° varus, and 6° varus, relative to neutral alignment. We evaluated the existence of overhanging medial tibial condyle where the medial eminence line, the line including the medial tibial eminence parallel to the tibial axis, passes outside of the tibial shaft. In all component alignments, patients with a medial overhanging condyle had significantly shorter posterior KCD than those without. In patients with a medial overhanging condyle, the posterior KCD significantly increased when the tibial component was placed in 3° varus (4.6 ± 1.5 mm, P = 0.003 vs neutral, P < 0.001 vs 3° valgus) and 6° varus (5.0 ± 1.4 mm, P < 0.001 vs neutral, P < 0.001 vs 3° valgus) compared with in neutral (3.5 ± 1.9 mm) or 3° valgus (2.8 ± 1.8 mm). In OUKA, varus implantation increased the KCD. This could potentially decrease the risk of fracture, even in knees with the overhanging medial condyle. Conversely, valgus implantation of the tibial component shortened the KCD, and should therefore be avoided.

Distribution of coronal plane alignment of the knee classification does not change as knee osteoarthritis progresses: a longitudinal study from the Toei study

PURPOSE

The purpose of this study was to investigate the coronal plane alignment of the knee (CPAK) phenotypes of individuals with knee osteoarthritis (OA) progression. We hypothesized that distributions of CPAK phenotypes would be similar throughout OA progression, despite arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) changing.

METHODS

A total of 248 patients (79 men and 169 women) participated in the first study in 2012 and the fifth study in 2020. Patients with progression of knee OA for eight years were included. Knee OA progression was defined as advancement from KL grade 0-2 to KL grade 3 or 4. Alignment parameters, including the aHKA, JLO, hip-knee-ankle angle (HKA), lateral distal femur angle (LDFA), medial proximal tibial angle (MPTA), and joint line convergence angle (JLCA), were measured. Changes in distribution of CPAK classifications and alignment parameters were investigated. Alignment parameters were compared using a paired t-test. Statistical significance was defined as p < 0.05.

RESULTS

The study included 48 patients (60 knees). The distributions of all CPAK phenotypes were similar between 2012 and 2020. MPTA (83.7° ± 2.8° vs. 82.3° ± 4.8°, p < 0.01), aHKA (- 3.6° ± 3.8° vs. - 4.9° ± 6.2°, p = 0.01), and JLO (171.1° ± 4.6° vs. 169.5° ± 5.1°, p < 0.01) decreased significantly, and JLCA (1.17° ± 2.2° vs. 3.1° ± 4.7°, p < 0.01) and HKA (4.8° ± 3.9° vs. 8.0° ± 5.4°, p < 0.01) increased significantly. In contrast, LDFA (87.4° ± 3.2° vs. 87.2° ± 3.1°, p = n.s.) did not change significantly.

CONCLUSIONS

The CPAK classification system can predict constitutional alignment, even with knee OA progression, and enables surgeons to perform individualized preoperative alignment planning according to knee phenotypes.

Arithmetic hip knee angle measurement on long leg radiograph versus computed tomography-inter-observer and intra-observer reliability

BACKGROUND

Pre-operative alignment is important for knee procedures including total knee arthroplasty (TKA), especially when considering alternative alignments. The arithmetic Hip Knee Angle (aHKA) is a measure of coronal alignment calculated using the medial proximal tibial (MPTA) and lateral distal femoral angles (LDFA). Traditionally, aHKA is measured on long leg radiographs (LLR). This study assesses the reproducibility of aHKA measurement on LLR and robotic-assisted TKA planning CT.

METHODS

Sixty-eight TKA patients with pre-operative LLR and planning CTs were included. Three observers measured the LDFA, MPTA and aHKA three times on each modality and intra-observer and inter-observer reliability was calculated. Statistical analysis was undertaken with Pearson's r and the Bland-Altman test.

RESULTS

Mean intra-observer coefficient of repeatability (COR) for LLR vs. CT: MPTA 3.50° vs. 1.73°, LDFA 2.93° vs. 2.00° and aHKA 2.88° vs. 2.57° for CT. Inter-observer COR for LLR vs. CT: MPTA 2.74° vs. 1.28°, LDFA 2.31° vs. 1.92°, aHKA 3.56° vs. 2.00°. Mean intra-observer Pearson's r for MPTA was 0.93 for LLR and 0.94 for CT, LDFA 0.90 for LLR and 0.91 for CT and aHKA 0.92 for LLR and 0.94 for CT. Inter-observer Pearson's r for LLR compared to CT: MPTA 0.93 vs. 0.97, LDFA 0.91 vs. 0.90, aHKA 0.91 and 0.95.

CONCLUSION

When compared to LLR, CT measurements of MPTA, LDFA and aHKA are more reproducible and have a good correlation with LLR measurement. CT overcomes difficulties with positioning, rotation, habitus and contractures when assessing coronal plane alignment and may obviate the need for LLRs.

Comparing inter- and intraobserver reliability between two-dimensional and three-dimensional measurements in the tibial component position of unicompartmental knee arthroplasty

In unicompartmental knee arthroplasty (UKA), the tibial component has a small coronal plane width, the tibia and tibial component rotations are mismatched, and the large tibial component posterior tilt may make accurate measurements of component positions difficult in radiography. The study aimed to assess the intra- and interobserver reliabilities of radiographic (2D) and 3D computed tomography (3D-CT) measurements and to determine the minimum detectable change (95% confidence level, MDC95) in the tibial component position measurements in UKA. The study included 23 females and 7 males. Two surgeons measured the tibial component position. Intraclass and interclass correlation coefficients (ICC) were calculated to obtain reliability, and Bland-Altman analysis was performed to assess systematic errors. The MDC95 was calculated according to MDC95 = standard error of measurement × 1.96 × √2. In the 2D and 3D- CT measurements, intraobserver reliability for coronal and sagittal positions of the tibial component were sufficiently reliable, where ICCs were >0.8. In the coronal plane, the ICCs for interobserver reliability were lower in 2D (ICC, 0.5-0.7) than in 3D-CT (ICC > 0.9). Bland-Altman plots showed systematic bias in sagittal alignment in the 2D assessment. In the 3D assessment of intra- and interobserver reliability, the MDC95 of the coronal, sagittal, and axial planes was <2°. In the 2D intra- and interobserver reliability, the MDC95 of the coronal and sagittal planes was >2°. The 2D measurement had a risk of misidentifying the tibial component position in UKA.

Comparison of weight-bearing full-length radiography and three-dimensional computed tomography scan-based models to assess knee joint coronal alignment following total knee arthroplasty

BACKGROUND

The validity of standing long-leg radiography (LLR) - the standard method for evaluating coronal alignment after total knee arthroplasty (TKA) - remains controversial. We evaluated the measurement reliability and validity of LLR following TKA by comparing postoperative radiographs with three-dimensional computed tomography (3DCT) scans of the lower extremities.

METHODS

We retrospectively collected the data of 55 knees from 44 patients who underwent postoperative 3DCT and 5-day and 6-month LLR for coronal alignment evaluation following TKA. The coronal femoral component angle (CFA) and coronal tibial component angle (CTA) were measured using 3DCT and LLR images. Correlations between the hip-knee-ankle angle (HKAA), CFA and CTA were analysed using Pearson's correlation coefficient (PCC); Bland-Altman plots were constructed to assess agreement between 5-day and 6-month radiographic and 3DCT scan measurements.

RESULTS

The mean difference in HKAA between 3DCT, and 5-day and 6-month LLR was 1.3 ± 1° and 1.1 ± 0.7°, respectively. Differences of >1° in HKAA between 3DCT, and 5-day and 6-month LLR were observed in 31 (56.4%) and 28 (50.9%) knees, respectively; differences of >2° in these parameters were observed in 15 (27.3%) and nine (16.4%) knees, respectively. The 3DCT scan and radiograph measurements of HKAA, CFA and CTA were strongly correlated (PCC, 0.81-0.92; P < 0.001). Bland-Altman plot validity was within acceptable limits.

CONCLUSION

LLR shows good reliability and validity for measuring coronal alignment. When comparing 3DCT scans and radiographs, a high number of HKAA values differed by more than 1° and 2°; this indicates that rigorous alignment evaluation requires 3DCT measurements.

Varus placement of the tibial component of Oxford unicompartmental knee arthroplasty decreases the risk of postoperative tibial fracture

AIMS

A fracture of the medial tibial plateau is a serious complication of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). The risk of these fractures is reportedly lower when using components with a longer keel-cortex distance (KCDs). The aim of this study was to examine how slight varus placement of the tibial component might affect the KCDs, and the rate of tibial plateau fracture, in a clinical setting.

METHODS

This retrospective study included 255 patients who underwent 305 OUKAs with cementless tibial components. There were 52 males and 203 females. Their mean age was 73.1 years (47 to 91), and the mean follow-up was 1.9 years (1.0 to 2.0). In 217 knees in 187 patients in the conventional group, tibial cuts were made orthogonally to the tibial axis. The varus group included 88 knees in 68 patients, and tibial cuts were made slightly varus using a new osteotomy guide. Anterior and posterior KCDs and the origins of fracture lines were assessed using 3D CT scans one week postoperatively. The KCDs and rate of fracture were compared between the two groups.

RESULTS

Medial tibial fractures occurred after surgery in 15 patients (15 OUKAs) in the conventional group, but only one patient (one OUKA) had a tibial fracture after surgery in the varus group. This difference was significant (6.9% vs 1.1%; p = 0.029). The mean posterior KCD was significantly shorter in the conventional group (5.0 mm (SD 1.7)) than in the varus group (6.1 mm (SD 2.1); p = 0.002).

CONCLUSION

In OUKA, the distance between the keel and posterior tibial cortex was longer in our patients with slight varus alignment of the tibial component, which seems to decrease the risk of postoperative tibial fracture.Cite this article: Bone Joint J 2022;104-B(10):1118-1125.

Kinematic alignment matches functional alignment for the extension gap: a consecutive analysis of 749 primary varus osteoarthritic knees with stress radiographs

PURPOSE

The alignment goal in total knee arthroplasty (TKA) remains debated. Two major strategies have emerged based on recreating the native knee: kinematic and functional alignment (KA and FA). Recently a new Coronal Plane Alignment of the Knee (CPAK) classification for KA, based on bony landmarks, was described considering joint line obliquity and the arithmetic HipKneeAnkle angle (aHKA). Valgus corrected HKA medial angle (vcHKA) was measured on distractive valgus preoperative radiographs compensating for cartilage wear and ligament balance in varus osteoarthritis. The purpose of this study was to determine if aHKA accounts for differences in medial laxity for the extension gap by comparing vcHKA to aHKA. The hypothesis was that no significant difference would be observed between the two measurements.

METHODS

This is a retrospective analysis of 749 knees in consecutive patients presenting to a single-centre with primary medial osteoarthritis. Patients underwent standardized weight bearing long-leg and valgus stress radiographs. Tibial mechanical angle (TMA), femoral mechanical angle (FMA) and vcHKA were measured using digital software. aHKA and vcHKA were compared to determine differences due to soft tissue balancing.

RESULTS

The mean FMA was 91.3 ± 2.2° (range 82°-97°), the mean TMA was 85.7 ± 2.5° (range 75°-98°), the mean aHKA was 177.0 ± 3.0° (range 164°-185°) and the mean vcHKA was 176.6 ± 3.1° (range 165°-192°). No significant difference was observed between aHKA and vcHKA (p = 0.06). A significant correlation was found between vcHKA and TMA (ρ = 0.3; p < 0.001) and between vcHKA and FMA (ρ = 0.41; p < 0.001).

CONCLUSION

This study showed that vcHKA was similar to aHKA confirming that aHKA accounts for ligamentous medial laxity. Therefore, kinematic alignment based on the CPAK classification matches the pre-arthritic coronal alignment of the knee for the extension gap.

LEVEL OF EVIDENCE

IV.

Mechanical alignment for primary TKA may change both knee phenotype and joint line obliquity without influencing clinical outcomes: a study comparing restored and unrestored joint line obliquity

PURPOSE

In total knee arthroplasty (TKA), knee phenotypes including joint line obliquity are of interest regarding surgical realignment strategies. The hypothesis of this study is that better clinical results, including decreased postoperative knee pain, will be observed for patients with a restored knee phenotype.

METHODS

A retrospective analysis was performed on prospective data, including 1078 primary osteoarthritic knees in 936 patients. The male:female ratio was 780:298, mean age at surgery was 71.3 years ± 8.0. International Knee Society Scores and standardized long-leg radiographs (LLR) were collected preoperatively and at 2 years follow-up after TKA. Patients were categorized using the Coronal Plane Alignment of the Knee (CPAK) classification including the lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) measured on LLR by a single observer, allowing knee phenotypes to be categorized considering the arithmetic hip-knee-ankle (aHKA) angle (MPTA-LDFA) as measure of constitutional alignment, and joint line obliquity (JLO) (MPTA + LDFA). Clinical results were compared between patients with surgically restored preoperative constitutional knee phenotype to patients without restored constitutional knee phenotypes. Descriptive data analysis such as means, standard deviations and ranges were performed. T tests for independent samples were performed to compare group differences. Comparisons of categorical data were performed using the χ² test. Significance was set at p < 0.05.

RESULTS

A third of patients (33.4%) had constitutional knee varus with apex distal JLO. 63.5% of patients had preoperative apex distal JLO. Postoperatively, 57.8% of patients had a neutral HKA (- 2° to 2°) and a neutral JLO (- 3° and 3°), with only 18% of patients with restored constitutional knee phenotype. Of these patients, statistically less postoperative pain was observed in patients where apex distal JLO was restored compared to non-restored apex distal JLO (pain score 46.7 vs. 44.6; p = 0.02) without clinical relevance. Other categories of restored JLO or arithmetic HKA angle were not associated with improved outcomes.

CONCLUSION

This study showed that performing mechanical alignment for primary TKA resulted in most cases in a change of the preoperative knee phenotype. These results emphasize the relevance of considering joint line obliquity to better understand preoperative knee deformity and better restore knee phenotypes with a more personalized realignment strategy to potentially improve TKA postoperative results.

LEVEL OF EVIDENCE

III.

Angular accuracy of plain radiographic measurements in leg alignment: Teleoroentgenogram versus orthoroentgenogram

BACKGROUND

The purpose of the present study was to evaluate the accuracy of the measurements associated with leg alignment on a teleoroentgenogram and an orthoroentgenogram.

METHODS

The models being irradiated were manufactured and represented 10° varus and 15° varus leg alignment, in which the true values of hip-knee-ankle angle (HKAA), mechanical axis (MA) length, and percentage of MA (%MA) were already known. HKAA, MA length, and %MA were measured in various radiographic conditions of the teleoroentgenogram and orthoroentgenogram. Then, the differences between the radiographic measurement values and the corresponding true values were analyzed.

RESULTS

Regarding HKAA, the teleoroentgenogram provided accurate angular measurements with minimal differences between the measurement and true value in both the 10° and 15° varus models, irrespective of the radiographic condition. In the orthoroentgenogram, the modified method measured accurate HKAA; however, the standard method showed significant angular measurement errors with a 0.6° and 1.0° difference from the true value in the 10° and 15° varus models, respectively. This angular measurement error of HKAA in the standard orthoroentgenogram became significantly larger with object-to-image distance. Regarding MA length, the orthoroentgenogram exhibited accurate length measurements. In contrast, the teleoroentgenogram showed a significant length measurement error for the MA length. Regarding %MA, significant differences from the true values of 2.0% and 2.4% were observed in the modified orthoroentgenograms of the 10° and 15° varus models, respectively. The teleoroentgenogram and standard orthoroentgenogram reproduced the accurate measurement value of %MA in the 10° and 15° varus models.

CONCLUSION

A teleoroentgenogram is a reliable modality for accurate angular measurements such as HKAA and %MA. An orthoroentgenogram has the potential to measure both HKAA and length accurately if the radiographic condition was modified; however, measurement error in %MA may occur.

Computed Tomography-Based Patient-Specific Instrumentation Loses Accuracy with Significant Varus Preoperative Misalignment

Patient-specific instrumentation (PSI) has been introduced to simplify and make total knee arthroplasty (TKA) surgery more precise, effective, and efficient. We performed this study to determine whether the postoperative coronal alignment is related to preoperative deformity when computed tomography (CT)-based PSI is used for TKA surgery, and how the PSI approach compares with deformity correction obtained with conventional instrumentation. We analyzed pre- and post-operative full length standing hip-knee-ankle (HKA) X-rays of the lower limb in both groups using a convention > 180 degrees for valgus alignment and < 180 degrees for varus alignment. For the PSI group, the mean (± SD) pre-operative HKA angle was 172.09 degrees varus (± 6.69 degrees) with a maximum varus alignment of 21.5 degrees (HKA 158.5) and a maximum valgus alignment of 14.0 degrees. The mean post-operative HKA was 179.43 degrees varus (± 2.32 degrees) with a maximum varus alignment of seven degrees and a maximum valgus alignment of six degrees. There has been a weak correlation among the values of the pre- and post-operative HKA angle. The adjusted odds ratio (aOR) of postoperative alignment outside the range of 180 ± 3 degrees was significantly higher with a preoperative varus misalignment of 15 degrees or more (aOR: 4.18; 95% confidence interval: 1.35-12.96; p = 0.013). In the control group (conventional instrumentation), this loss of accuracy occurs with preoperative misalignment of 10 degrees. Preoperative misalignment below 15 degrees appears to present minimal influence on postoperative alignment when a CT-based PSI system is used. The CT-based PSI tends to lose accuracy with preoperative varus misalignment over 15 degrees.

Staging Bilateral Total Knee Arthroplasties Reduces Alignment Outliers

BACKGROUND

Patients frequently present with bilateral symptomatic knee osteoarthritis and request simultaneous total knee arthroplasties (TKAs). Technical differences between simultaneous and staged TKAs could affect clinical and radiographic outcomes. We hypothesized that staged TKAs would have fewer mechanical alignment outliers than simultaneous TKAs.

METHODS

We reviewed 87 simultaneous and 72 staged TKAs with at least 2 years of follow-up. Radiographic assessment was done using standing long leg and lateral radiographs of the knee. Coronal and sagittal measurements were performed by 4 blinded observers on 2 separate occasions with an intraobserver agreement of 0.95 and interobserver of 0.92.

RESULTS

The first simultaneous knee had no difference in the probability of establishing the mechanical axis outside 3° of neutral (45%) compared to the first staged knee (54%, P = .337). However, the second simultaneous knee (49%) was more likely to establish the axis outside mechanical neutral compared to the second staged knee (28%; odds ratio 2.54, confidence interval 1.31-4.94, P = .006). There was an increased risk of deep venous thrombosis with staged TKA (odds ratio 2.96, confidence interval 1.28-6.84, P = .011), but other perioperative complication rates were not significantly different. There were no clinically significant differences in range of motion or Knee Society Score.

CONCLUSION

There is a significantly increased risk of establishing the second knee outside mechanical neutral during a simultaneous TKA compared to staged bilateral TKAs, possibly related to a number of surgeon-related and system-related factors. The impact on clinical outcomes and radiographic loosening may become significant in long-term follow-up.

Short distance from the keel to the posterior tibial cortex is associated with fracture after cementless Oxford UKA in Asian patients

PURPOSE

Tibial plateau fractures are serious complications of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study examined where the fracture lines arises and evaluated the keel-cortex distances (KCDs) using three-dimensional computed tomography (3D-CT) and the effects of technical error (assessed by tibial component positions) and proximal tibial morphology on the KCDs.

METHODS

This retrospective study included 217 OUKAs with cementless tibial components. Fifteen patients had tibial fractures after surgery. Anterior and posterior KCDs and fracture line origins were assessed using 3D-CT postoperatively. Proximal tibial morphology was assessed using the medial eminence line (MEL), which runs parallel to the tibial axis and passes through the tip of the medial intercondylar eminence of the tibia on long-leg anteroposterior radiograph. Knees had overhanging medial tibial condyle if the MEL passed medially to the medial tibial cortex. KCDs were compared between patients with/without fractures. Tibial component positions were evaluated, considering effects of tibial morphologies and component positions on fracture prevalence and KCDs.

RESULTS

Fracture lines were found between the keel and posterior cortex in 12/15 patients. Posterior KCDs were significantly shorter in patients with fractures than in patients without (2.7 ± 1.6 mm vs 5.2 ± 1.7 mm, P < 0.001). Patients with medial overhanging condyles were more likely to have fracture (10/51 vs 5/166, P < 0.001) and had significantly shorter posterior KCD than those without (3.6 ± 1.5 mm vs 5.5 ± 1.8 mm, P < 0.001). Patients with tibial component that was set too medial, low, and valgus had higher rates of fracture than those without (7/39 vs 8/178, P = 0.008). Medial (r = 0.30, P < 0.001), low (r = -0.33, P < 0.001), and valgus implantations (r = 0.35, P < 0.001) of tibial components were related to shorter posterior KCDs.

CONCLUSION

Short posterior KCD after OUKA is a risk factor for postoperative tibial fracture. Patients with either malposition of the tibial component (too medial, low, and valgus) and/or a medial overhanging condyle exhibit a shorter distance of posterior KCD and higher rate of fracture.

LEVEL OF EVIDENCE

Level III.

Primary osteoarthritic knees have more varus coronal alignment of the femur compared to young non-arthritic knees in a large cohort study

PURPOSE

Many surgeons are performing total knee arthroplasty (TKA) with an aim to reproducing native anatomical coronal alignment. Yet, it remains unclear if primary osteoarthritic and non-osteoarthritic populations have similar knee coronal alignment. This study aims to describe and compare the distribution of femoral and tibial coronal alignment in a large primary osteoarthritic cohort and a young non-osteoarthritic cohort.

METHODS

This is a retrospective analysis of a monocentric prospectively gathered data, from 1990 to 2019, of 2859 consecutive primary osteoarthritic knees in 2279 patients. Patients underwent standardized long-leg radiographs. Femoral mechanical angle (FMA) and tibial mechanical angle (TMA) were digitally measured using software. Femoral, tibial and knee phenotypes were analyzed, and descriptive data were reported. Data were compared to a young non-osteoarthritic population previously described.

RESULTS

In osteoarthritic knees, the mean FMA was 91° ± 2.9° (range 86°-100°) and the mean TMA was 87° ± 3.1° (range 80°-94°). No significant difference was observed for FMA and TMA between genders. The most common femoral and tibial phenotypes were varus (38.7%) and neutral (37.1%). The most frequent knee phenotype was a varus femoral phenotype with a neutral tibial phenotype (15.5%), which is different to the non-osteoarthritic population.

CONCLUSION

This study showed the wide distribution of knee phenotypes in a large osteoarthritic cohort. There was more varus distribution of the femoral coronal alignment compared to a non-osteoarthritic population, suggesting consideration and potential adaptation of the realignment strategy of the femoral component during TKA.

LEVEL OF EVIDENCE

III.

The contralateral limb is no reliable reference to restore coronal alignment in TKA

PURPOSE

Implementation of morphometric reference data from the contralateral, unaffected lower limb is suggested when reconstructing the coronal plane alignment in TKA. Limited information, however, is available which confirms this left-to-right symmetry in coronal alignment based upon radiographs. The purpose of the study was, therefore, (1) to verify if a left-to-right symmetry is present and (2) to assess whether the contralateral lower limb would be a reliable reference for reconstructing the frontal plane alignment.

METHODS

Full-leg standing radiographs of 250 volunteers (male, 125; female,125) were reviewed for three alignment parameters (Hip-Knee-Ankle angle (HKA), Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA)). Evaluation of assumed left-to-right symmetry was performed according to two coronal alignment classifications (HKA subdivisions (HKA) and limb, femoral and tibial phenotypes (HKA, FMA and TMA)). Inter- and within-subject variability was calculated, along with correlations coefficients (r) and coefficients of determination (r²). Reliability of the contralateral limb as a personalized reference to reconstruct the constitutional alignment was investigated by intervals, expanding by 1° increments (0.5° increment both to varus and valgus) around the right knee alignment parameters. Subsequently, it was verified whether or not the left knee parameters fell within this interval.

RESULTS

Symmetrical distribution in coronal alignment was found in 79% (HKA subdivision) and 59% (limb phenotype) of the cohort. Gender differences were present for the most common symmetric limb phenotypes (VAR_HKA3° (23.2%) in males and NEU_HKA0° (38.4%) in females). Inter-subject variability was more prominent than the within-subject side differences for all parameters. Correlations analyses revealed mostly moderate correlations between the alignment measurements. Coefficients of determination showed overall weak left-to-right relationship, except for a moderate predictability for HKA (r² = 0.538, p < 0.001) and FMA (r² = 0.618, p < 0.001) in females. FMA and TMA marked weak predictive values for contralateral HKA. Only 60% of left knees were referenced within a 3° interval around the right knee.

CONCLUSION

No strict left-to-right symmetry was observed in coronal alignment measurements. There is insufficient left-to-right agreement to consider the concept of the contralateral unaffected limb as an idealized reference for frontal plane alignment reconstruction based upon full-leg standing radiographs.

LEVEL OF EVIDENCE

I.

Radiographic Comparison of the Mechanical Axis Including Calcaneus to the Conventional Mechanical Axis in Medial Unicompartmental Knee Arthroplasty

Since a hindfoot alignment is not included in the conventional mechanical axis (hip-ankle [HA] line), a mechanical axis including the calcaneus (hip-calcaneus [HC] line) has recently attracted attention as an alternative weight-bearing line. However, there are few reports on unicompartmental knee arthroplasty (UKA) regarding the HC line. Therefore, this study aimed to compare postoperative alignments after UKA between the HA line and the HC line. Postoperatively, HC radiographs were taken in 88 consecutive patients who underwent medial UKA. The hip-knee-ankle (HKA) and hip-knee-calcaneus (HKC) angles were compared in the same patient. Regarding tibial inclination, the conventional tibial component-ankle (TCA) angle was compared with reference to the HC line (tibial component-calcaneus [TCC] angle). The mean postoperative HKA and HKC angles were 2.8 ± 2.7 and 2.0 ± 2.5 degree, respectively. The mean postoperative TCA and TCC angles were 87.7 ± 2.1 and 88.5 ± 2.1 degree, respectively. There were significant differences between the two groups in both lower limb alignment and tibial component angle. The present study indicated that the HKC and the TCC angles significantly decreased the varus alignment by approximately 1 degree compared with the HKA and TCA angles. Neutral in the HA line corresponds to valgus in reference to the HC line, which may result in overcorrection. Surgeons should consider evaluating the HC line in place of the HA line, which may affect preoperative planning and postoperative outcome during UKA. This is a Level II, diagnostic study.

CT based PSI blocks for osteotomies around the knee provide accurate results when intraoperative imaging is used

Purpose

Correction osteotomies around the knee are common methods for the treatment of varus or valgus malalignment of the lower extremity. In recent years, patient specific instrumentation (PSI) guides were introduced in order to enhance the accuracy of these procedures. The purpose of this study was to determine the accuracy of CT based PSI guides for correction osteotomies around the knee of low volume osteotomy surgeons and to evaluate if CT based PSI blocks deliver a high degree of accuracy without using intraoperative fluoroscopy.

Methods

Two study arms with CT based PSI cutting blocks for osteotomies around the knee were conducted. Part one: A retrospective analysis of 19 osteotomies was made in order to evaluate the accuracy in the hands of a low volume surgeon on long-leg radiographs. Part two: A cadaveric study with 8 knees was performed for the purpose of analyzing the accuracy without using intraoperative fluoroscopy on pre- and postoperative CT scans. Hip-Knee-Ankle angle (HKA), lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were analyzed. The mean absolute delta (∂) between the planned and postoperative parameters were calculated. The accuracy of both study arms were compared.

Results

Part one: The mean MPTA ∂, LDFA ∂ and HKA ∂ was 0.9°, 1.9° and 1.5°, respectively. Part two: The mean MPTA ∂ and LDFA ∂ was 3.5° and 2.2°, respectively. The mean ∂ of MPTA is significantly different between clinical patients with fluoroscopic control and cadaveric specimens without fluoroscopic control (P < 0.001). All surgeries were performed without complications such as a hinge fracture.

Conclusion

The clinical use of PSI guides for osteotomies around the knee in the hands of low volume surgeons is a safe procedure. The PSI guides deliver a reliable accuracy under fluoroscopic control whereas their non-use of intraoperative fluoroscopy leads to a lack of accuracy. The use of fluoroscopic control during PSI guided correction osteotomies is highly recommended.

Level of evidence

IV – Retrospective and experimental Study

Navigated total knee arthroplasty: Retrospective study of 600 continuous cases

INTRODUCTION

Computer-assisted navigation in total knee arthroplasty (TKA) has existed for more than 20 years, although its use has been marginal. Its benefits are still largely debated, especially its efficacy for achieving the desired postoperative alignment.

HYPOTHESIS

A neutral hip-knee-ankle (HKA) angle (180°±3°) will be achieved in at least 85% of cases and there will be no difference between the different types of navigation systems used.

MATERIAL AND METHODS

In this retrospective, single-center, single-surgeon study, all the TKAs completed between September 2003 and December 2017 were included, giving a total of 753 navigated TKAs: Navitrack group: 196 Natural Knee II implants (Zimmer) with the Navitrack-OS Knee system (Zimmer CAS); Brainlab group: 557 implants (196 Profix, Smith & Nephew and 361 LCS, DePuy) with the Brainlab Vector Vision system. The aim of navigation was independent of the preoperative alignment and was always to achieve a neutral HKA mechanical axis (180°±3°). The primary endpoint was the postoperative HKA angle. This parameter was used to determine whether the navigation objective was achieved, to define how many patients were outliers and to compare navigation systems to each other. The potential influence of sex, body mass index (BMI) and preoperative deformity were secondary aims. Lastly, the final navigation values were compared to radiological data to detect any potential deviations.

RESULTS

We analyzed 600 of the cases, 160 in the Navitrack group and 440 in the Brainlab group (152 Profix and 288 LCS). A neutral HKA angle was found in 91% patients: 93% for the Navitrack group and 90% in the Brainlab group (90.8% Profix and 89.6% LCS). There was no significant difference between groups (p=0.68), nor between subgroups (p=0.85). An elevated BMI negatively influenced the ability to achieve a neutral HKA (p=0.015), regardless of the system used.

CONCLUSION

In our study of 600 TKA cases done with navigation, the postoperative alignment goal (HKA 180°±3°) was achieved in 91% of cases. There was no difference between navigation systems. Patients with a high BMI were more likely to be outliers (p=0.015).

LEVEL OF EVIDENCE

IV.

3D-surface scan based validated new measurement technique of femoral joint line reconstruction in total knee arthroplasty

Purpose

This study aimed to validate a new joint line measurement technique in total knee arthroplasty for separated assessment of the medial and lateral femoral joint line alteration with 3D-surface scan technology. Separate assessment of the medial and lateral joint line alteration may improve TKA alignment assessment regarding to joint line restoration in kinematic alignment and use of robotic-assisted TKA surgery.

Methods

The medial and lateral joint line difference after TKA implantation on an artificial bone model was analyzed and compared with a 3D-scan and full femoral radiographs pre- and postoperatively. Radiographic analysis included the perpendicular distance between the most distal point of the medial and lateral condyle and the reproduced preoperative lateral distal femoral angle (LDFA). For evaluation of validity and reliability, radiographs were captured initially with true anteroposterior view and subsequently with combined flexion and rotation malpositioning. Reliability of the introduced measurement technique in between three observers was tested with intraclass correlation coefficient (ICC).

Results

Radiographic measurement showed a mean difference of 0.9 mm on the medial side and 0.6 mm on the lateral side when compared to the 3D-surface scan measurement. The reliability of measurement accuracy was ≤ 1 mm in x-rays with < 10° flexion error regardless to malrotation in these images. The ICC test showed very good reliability for the medial joint line evaluation and good reliability for lateral joint line evaluation (ICC 0.92, ICC 0.86 respectively).

Conclusion

The new introduced joint line measurement method showed a sufficient reliability, accuracy and precision. It provides separated information about medial and lateral joint line alteration in TKA surgery in absolute values.

Level of evidence

V - Experimental Study

Imageless robotic handpiece-assisted total knee arthroplasty: a learning curve analysis of surgical time and alignment accuracy

INTRODUCTION

Robotic-assisted surgery techniques are increasing in total knee arthroplasty (TKA). One crucial point is the prolonged time of surgery. The primary objective of this study was to determine the learning curve necessary to minimize the time of surgery. The secondary objective was to evaluate the accuracy of the implant alignment when using an imageless robotic system for TKA.

MATERIALS AND METHODS

In a case-control study, the first 70 consecutive robotic-assisted TKA procedures performed by a single senior surgeon were analyzed with regard to surgery time and implant alignment by comparing the intraoperative plan with the postoperative alignment. The evaluation of the learning curve with respect to surgery time was conducted using cumulative summation (CUSUM) analysis. The joint line height was measured with a new technique. Surgery time and joint line reconstruction were compared to 70 consecutive conventional TKA procedures.

RESULTS

The learning curve for robotic TKA was completed after 11 cases. The learning curve did not influence the accuracy of joint line obliquity, joint line height, or limb alignment. The intraoperative plan designed for the robotic system was precisely implemented. The mean skin-to-skin time in the robotic group after the learning curve was completed did not differ from that in the manual group. A significant positive correlation was observed between the preoperative hip-knee-ankle angle and the postoperative distalization of the joint line in the robotic-assisted TKA group.

CONCLUSION

After completing the initial learning curve of 11 cases, the surgery time required to perform imageless robotic handpiece-assisted TKA was similar to that for the conventional technique. However, no learning curve was observed for the implant positioning when using the imageless robotic system. The implementation of the intraoperative plan was accurate up to < 2°. The precision of the system allows the implementation of different joint balancing approaches between valgus and varus morphotypes.

Robotics improves alignment accuracy and reduces early revision rates for UKA in the hands of low-volume UKA surgeons

PURPOSE

It is known that in uni-compartmental knee arthroplasty (UKA) low-volume surgeons have a higher complication and revision rate than high-volume surgeons. Further, robotic-assisted UKA leads to lower early revision rate as well as fewer limb and joint line outliers compared to conventional UKA. The purpose of this study was to retrospectively analyze the outliers' and revision rate of low-volume UKA surgeons with different robotic systems at short-term follow-up.

METHODS

In this case-control study, 103 robotic-assisted UKAs were included. The procedures were performed between 2016 and 2019 from two low-volume UKA surgeons with an imageless (IL) (63 patients) and image-based (IB) (40 patients) robotic system. Alignment outliers, joint line (JL) reconstruction, complication and revision rates of the two different robotic systems were analyzed. The minimum follow-up was two years. Outliers were defined as a postoperative valgus malalignment greater than 182°. The surgery time for all procedures was evaluated.

RESULTS

The overall revision rate was 3.9% (4 of 103). Two occurred in the IB group (5.0%) and two in the IL group (3.2%). No valgus malalignment outliers were observed in both groups. The mean JL was not distalized by more than 2 mm in both groups (IL: 1.3 ± 1.6 mm vs. IB: 1.8 ± 0.9 mm, p value 0.08). The IL procedures had a significant lower mean surgery time (55 ± 13 min vs. 68 ± 14, p value 0.001).

CONCLUSION

Robotic-assisted UKA is a safe procedure in the hand of low-volume UKA surgeons. Robotic-assisted UKA minimizes overcorrection into valgus mal-alignment. Low revision rates are observed at short-term follow-up for robotic-assisted UKA. The choice of the different robotic systems has no impact on the outcome.

Varus deformity in the proximal tibia and immediate postoperative varus alignment result in varus progression in limb alignment in the long term after total knee arthroplasty

PURPOSE

The aim of this study was to examine and evaluate the factors associated with changes in limb alignment 10 years after total knee arthroplasty (TKA). The hypothesis was that bone morphology and immediate postoperative alignment could be correlated with long-term post-operative alignment changes following TKA.

METHODS

This study retrospectively analysed 136 consecutive primary TKA cases for varus deformity, performed from 2006 to 2008, that could be followed for at least 10 years postoperatively. Anteroposterior long-leg weight-bearing radiographs were obtained within 1 month and at least 10 years after surgery. The hip-knee-ankle (HKA) angle immediately after surgery was compared with that 10 years later; factors correlating with the change in HKA angle (δHKA) were evaluated.

RESULTS

The mean HKA angles were significantly different between immediate and long-term postoperative assessments (0.1° ± 1.9° vs. 1.2° ± 2.9°, p < 0.001). Furthermore, a significant difference was observed in the outlier ratio (> 3° deviation from the 0° of HKA angle) (10% vs. 24%, p = 0.002). δHKA strongly correlated with a higher preoperative tibial plateau tip-to-proximal tibial shaft (TPTPS) angle, higher postoperative HKA angle, lateral distal femoral angle, and lower postoperative medial proximal tibial angle.

CONCLUSION

Varus deformity in the proximal part of the tibia, immediate postoperative varus alignment, and varus position of the femoral and tibial components may lead to varus progression in limb alignment in the long term, even 10 years after TKA; the surgeon should, therefore, weigh the risks of leaving a varus alignment during surgery. Moreover, if the preoperative TPTPS angle is high, the alignment may become varus after TKA, even in patients who have acquired neutral alignment.

LEVEL OF EVIDENCE

IV.

Patient-specific high-tibial osteotomy's 'cutting-guides' decrease operating time and the number of fluoroscopic images taken after a Brief Learning Curve

PURPOSE

Patient-specific cutting guides (PSCGs) have been advocated to improve the accuracy of deformity correction in opening-wedge high-tibial osteotomies (HTO). It was hypothesized that PSCGs for HTO would have a short learning curve. Therefore, the goals of this study were to determine the surgeons learning curve for PSCGs used for opening-wedge HTO assessing: the operating time, surgeons comfort levels, number of fluoroscopic images, accuracy of post-operative limb alignment and functional outcomes.

METHODS

This prospective cohort study included 71 consecutive opening-wedge HTO with PSCGs performed by three different surgeons with different experiences. The operating time, the surgeon's anxiety levels evaluated using the Spielberger State-Trait Anxiety Inventory (STAI), the number of fluoroscopic images was systematically and prospectively collected. The accuracy of the postoperative alignment was defined by the difference between the preoperative targeted correction and the final post-operative correction both measured on standardized CT-scans using the same protocol (ΔHKA, ΔMPTA, ΔPPTA). Functional outcomes were evaluated at 1 year using the different sub-scores of the KOOS. Cumulative summation (CUSUM) analyses were used to assess learning curves.

RESULTS

The use of PSCGs in HTO surgery was associated with a learning curve of 10 cases to optimize operative time (mean operative time 26.3 min ± 8.8), 8 cases to lessen surgeon anxiety levels, and 9 cases to decrease the number of fluoroscopic images to an average of 4.3 ± 1.2. Cumulative PSCGs experience did not affect accuracy of post-operative limb alignment with a mean: ΔHKA = 1.0° ± 1.0°, ΔMPTA = 0.5° ± 0.6° and ΔPPTA = 0.4° ± 0.8°. No significant difference was observed between the three surgeons for these three parameters. There was no statistical correlation between the number of procedures performed and the patient's functional outcomes.

CONCLUSION

The use of PSCGs requires a short learning curve to optimize operating time, reduce the use of fluoroscopy and lessen surgeon's anxiety levels. Additionally, this learning phase does not affect the accuracy of the postoperative correction and the functional results at 1 year.

LEVEL OF EVIDENCE

II: prospective observational study.

Comparison of weight-bearing full-length radiographs and computed-tomography-scan-based three-dimensional models in the assessment of knee joint coronal alignment

BACKGROUND

The aim of the study was to determine any discrepancies among preoperative full-leg standing radiographs (LLR) and supine non-weight-bearing computed tomography (CT)-scan-based three-dimensional (3D) models in the assessment of the lower limb alignment prior to total knee arthroplasty (TKA) and answer the question of whether the LLR study can be obviated in preoperative planning when TKA is performed with patient-specific instrumentation (PSI).

METHODS

LLR and CT-scan-based 3D models of 227 knees (183 patients) were measured. LLR data was then compared to 3D alignment data used to design the PSI for TKA surgery.

RESULTS

Alignment on LLR ranged from 153 to 194° versus 161.5 to 190.5° with CT-scan-based 3D models. The mean (standard deviation, SD) difference among techniques was 1.9° (1.15°) with a statistically significant difference (P = 2e-16, namely P < .0001). Supine CT-scan-based 3D models underestimated the deformity in 167 cases (73.6%), exactly matched the value of LLR in 24 cases (10.6%) and overestimated the deformity in 36 cases (15.8%).

CONCLUSION

CT-scan-based models underestimate the degree of deformity at the knee joint. Despite the accurate information provided by the CT-scan and the 3D models (which is the basis for the planning of bone cuts), weight-bearing LLR should not be overlooked in the planning of TKA surgery to assess the extent of the coronal mediolateral instability.

Intra- and interobserver reliability and agreement in three-dimensional computed tomography measurements of component positions after total knee arthroplasty

BACKGROUND

Accurate evaluation of the postoperative position of total knee arthroplasty (TKA) components is crucial in the analysis of the association of alignments with clinical outcomes. The aim of this study was to investigate the reliability of measurements of component positions after TKA using three-dimensional computed tomography (3D-CT) reconstruction.

METHODS

Two independent orthopedic surgeons (an attending surgeon and a fellow) examined 30 knees after primary TKA. The coronal, sagittal, and rotational positions of the femoral and tibial components were measured twice at an interval of six weeks on 3D-CT images reconstructed using ZedKnee software. Mean intra- and interobserver differences of measured angles were calculated, and the intra- and interobserver reliability was determined using intraclass correlation coefficients (ICCs), with agreement assessed by Bland-Altman analysis.

RESULTS

The mean intraobserver difference between alignment measurements for femoral and tibial components was <2° (range 0.23-1.17°) and the mean interobserver difference was <1° (range 0.22-0.97°). The intra- and interobserver ICCs were >0.8 for all component positions. The only systematic bias found in the intra- and interobserver agreements occurred for the sagittal position of the femoral component.

CONCLUSION

Three-dimensional-CT measurements of component positions after TKA showed good intra- and interobserver reliability for the femoral and tibial components in coronal, sagittal and rotational positions. The intra- and interobserver agreements were favorable for all but the sagittal position of the femur. These results suggest that 3D-CT can be used to evaluate the alignment of all TKA components except for the sagittal position of the femur.

A randomized controlled trial of tibial component migration with kinematic alignment using patient-specific instrumentation versus mechanical alignment using computer-assisted surgery in total knee arthroplasty

AIMS

Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement.

PATIENTS AND METHODS

A total of 47 patients due to undergo TKA were randomized to KA+PSI (n = 24) or MA+CAS (n = 23). In the KA+PSI group, there were 16 female and eight male patients with a mean age of 64 years (sd 8). In the MA+CAS group, there were 17 female and six male patients with a mean age of 63 years (sd 7). Surgery was performed using cemented, cruciate-retaining Triathlon total knees with patellar resurfacing, and patients were followed up for two years. The effect of alignment on tibial component migration and inducible displacement was analyzed irrespective of study group.

RESULTS

There was no difference over two years in longitudinal migration of the tibial component between the KA+PSI and MA+CAS groups (reaching median maximum total point motion migration at two years of 0.40 mm for the KA+PSI group and 0.37 mm for the MA+CAS group, p = 0.82; p = 0.68 adjusted for age, sex, and body mass index (BMI) for all follow-ups). Both groups had mean migrations below acceptable thresholds. There was no difference in inducible displacement (p = 0.34) or PROMS (p = 0.61 for the Oxford Knee Score) between groups. There was no correlation between alignment and tibial component migration or alignment and inducible displacement. These findings support non-neutral alignment as a viable option with this component, with no evidence that it compromises fixation.

CONCLUSION

Kinematic alignment using patient-specific instrumentation in TKA was associated with acceptable tibial component migration, indicating stable fixation. These results are supportive of future investigations of kinematic alignment. Cite this article: Bone Joint J 2019;101-B:929-940.

Due to great variability fixed HKS angle for alignment of the distal cut leads to a significant error in coronal TKA orientation

PURPOSE

For coronal alignment in total knee arthroplasty (TKA) most surgeons use the patient's individual hip-knee shaft (HKS) angle (angle between the anatomical axis and the mechanical axis of the femur). The major problem of the sole use of HKS angle is that the individual patient's distal femoral asymmetry is not considered. The purpose of this study was to determine the variability of the HKS angle, the mechanical femoral angle (FMA) and to evaluate whether or not one of the two angles is more important for TKA alignment strategy. It was the hypothesis that HKS and FMA are not directly related to each other and hence HKS should not be considered as guide for coronal alignment.

METHODS

Prospectively collected CT data of 1480 consecutive patients who underwent 3D reconstructed CT scans before TKA was used for this retrospective registry study [882 women and 598 men, mean age ± standard deviation 71 ± 9 years (34-99 years)]. The CT protocol was modified according to the Imperial Knee Protocol, which is a lowdose CT protocol that includes high-resolution 0.75-mm slices of the knee and 3-mm slices of the hip and ankle joints. All measurements were done using Symbios^® 3D knee preoperative planning's software (Symbios, Yverdon les Bains, Switzerland). The HKS, FMA and hip-knee-ankle (HKA) angles were measured. Angles measured were displayed as mean, standard deviation (SD) and range. In addition, the angles were shown as percentages after categorization. The HKS was categorized between 3° and 9° in 1° increments. The FMA was categorized between 83.5° and 98.5° in 3° increments. The HKA was categorized between 12.5° varus 5.5° valgus in 3° increments. Pearson correlations were used to investigate correlation of HKS and FMA (p < 0.05).

RESULTS

The HKS angle was not constant at 7° but averaged 6°, and ranged from 2.5° to 9°. The FMA angle was on average 93° but varied more than 20°, ranging from 75° (varus) to 104° (valgus). The mean HKA ± SD was - 3.4° ± 5.7° (range - 23.0° to 15.0°). The mean HKSSD was 5.6° ± 0.9° (range 2.5°-8.8°). The mean FMASD was 92.6° ± 2.8° (range 75.2°-103.5°). The Pearson correlations of all measured angles are presented in Table 1. HKS significantly correlated negatively with HKA and FMA (p < 0.001). FMA and HKA were strongly correlated with each other (p < 0.0001). Considering the HKS angle as a constant angle can induce a deviation of up to 5° with respect to an orthogonal distal femoral cutting objective. The great variability of the FMA angle implies that the FMA seems more relevant than the HKS angle to define the strategy of realignment of the lower limb. However, then patient specific instrumentation has to be used to precisely transfer the planning to the surgical technique. Having the aim of a more personalized TKA alignment in mind the individual constitutional knee phenotype should be taken into account.

Two-dimensional measurement misidentifies alignment outliers in total knee arthroplasty: a comparison of two- and three-dimensional measurements

PURPOSE

Two-dimensional (2D) and three-dimensional (3D) measurements of prosthetic alignment and "outliers" after total knee arthroplasty (TKA) might not necessarily be comparable. The aim of this study was to compare the use of 2D and 3D measurements in the identification of prosthetic alignment and outliers after TKA.

METHODS

This cross-sectional study included 159 consecutive TKAs. All patients underwent plain radiography, fluoroscopy-guided radiography, and computed tomography after TKA. The same baseline was used for 2D and 3D measurements. The reliability of prosthetic alignment and outlier identification (> 3° from neutral alignment) was compared between the 2D and 3D measurements.

RESULTS

The mean prosthetic alignment and rate of outliers were not significantly different the between 2D and 3D measurements. The inter- and intra-observer reliabilities were higher for the 3D measurements than for the 2D measurements. The agreement between 2D and 3D measurements in outlier identification was poor, except for femoral coronal alignment. Cohen's κ coefficients were 0.19 in femoral sagittal (poor), 0.02 in tibial coronal (poor), and 0.10 in tibial sagittal (poor) on plain radiography. The values were 0.23 in tibial coronal (poor) and 0.002 in tibial sagittal (poor) on fluoroscopy-guided radiography.

CONCLUSIONS

The agreement between 2D and 3D measurements in the identification of outliers was poor, even on fluoroscopy-guided radiography. Since 2D measurements have an inherent risk of misidentifying alignment outliers, this finding is clinically relevant. To properly analyze the correlation between outliers and clinical results, such as longevity, patient satisfaction, and patient-reported outcome, 3D measurements for prosthetic alignment are desirable.

LEVEL OF EVIDENCE

III.

Noninvasive navigated assessment of the lower limb axis prior to knee arthroplasty: a feasibility study

The purpose of the study was to assess accuracy and repeatability of a noninvasive navigated (NIN) measurement of the lower limb axes by comparison with the conventional, invasive navigated (IN) technique. The tested hypothesis was that NIN measure will significantly differ from IN measure when performed on a supine patient under general anesthesia just prior to knee arthroplasty. The accuracy study involved 20 cases. The following measures were performed with both systems: maximal extension angle, coronal mechanical femoro-tibial angle at the previously assessed maximal extension angle, coronal mechanical femoro-tibial angle at 30° of knee flexion. NIN and IN measures were compared with the appropriate statistical tests. The repeatability study involved 14 cases. The same measures were performed with the NIN system twice by two independent observers. The intra- and inter-observer variability was assessed by the calculation of the intra-class correlation coefficient. After correction for the systematic biases, the differences between the two systems were not significant. A good correlation, a good coherence and an excellent agreement between NIN and IN measures of maximal extension angle and coronal femoro-tibial mechanical angle at maximal extension. But measures at 30° of flexion were inconsistent. The NIN system can be considered as an accurate and precise tool for the assessment of the knee extension angle and the coronal deformation at maximal extension prior to knee arthroplasty. But this system is less accurate and less repeatable when measuring coronal femoro-tibial mechanical angle at 30° of flexion and should not be used for this purpose.

Favourable alignment outcomes with MRI-based patient-specific instruments in total knee arthroplasty

PURPOSE

Patient-specific instruments (PSIs) are already in relatively common use, and their post-operative radiographic results are equal to those for total knee arthroplasty (TKA) with conventional instrumentation. PSI use requires a preoperative MRI scan, CT scan, or a combination of MRI and a long-leg standing radiograph. However, there is no consensus as to which of these modalities, MRI or CT, is the preferred imaging modality when performing TKA with PSIs.

METHODS

This systematic literature review and meta-analysis studied the differences in alignment outliers between CT- and MRI-based PSI for TKA. A search of the Cochrane Database of Systematic Reviews, MEDLINE/PubMed and Embase was conducted, without restriction on date of publication. Only level I evidence studies written in English that included TKA with the use of MRI- and CT-based PSI were selected. A meta-analysis was then performed of the rate of outliers in the biomechanical axis and individual femoral and tibial component alignment. Where considerable heterogeneity among studies was present or the data did not provide sufficient information for performing the meta-analysis, a qualitative synthesis was undertaken.

RESULTS

Twelve randomized controlled trials, studying 841 knees, were eligible for data extraction and meta-analysis. MRI-based PSI resulted in a significantly lower proportion of coronal plane outliers with regard to the lateral femoral component (OR 0.52, 95% CI 0.30-0.89, P = 0.02), without significant heterogeneity (n.s.). There were no significant differences regarding the biomechanical axis or frontal femoral and individual tibial component alignment.

CONCLUSION

This systematic review and meta-analysis demonstrate that alignment with MRI-based PSI is at least as good as, if not better than, that with CT-based PSI. To prevent for malalignment, MRI should be the imaging modality of choice when performing TKA surgery with PSI.

LEVEL OF EVIDENCE

I.

Presence of rotational errors in long leg radiographs after total knee arthroplasty and impact on measured lower limb and component alignment

PURPOSE

Rotation of the lower limb in weight bearing long leg radiographs has a great impact on measured component and lower limb alignment parameters. We asked which rotational errors of long leg radiographs are present in a high volume centre and which radiological and clinical consequences arise regarding measured coronal component and lower limb alignment after total knee arthroplasty.

METHODS

In 100 long leg radiographs coronal femoral and tibial component alignment and hip knee ankle angle (HKA) were measured. Present rotational errors in long leg radiographs were determined by fibular overlap and its impact on alignment parameters calculated.

RESULTS

A mean internal rotation of 8.1° (9.3 SD) with a range between 36° of internal and 16° of external rotation was found in long leg radiographs. This resulted in mean differences between measurements before and after rotational correction regarding femoral and tibial component alignment and HKA of 0.6-0.8° (range 3.5° valgus and 1.6° varus error). Clinically, 11 out of 100 patients were wrongly assigned to either mal- or well-alignment (neutral mechanical alignment within ±3° varus or valgus).

CONCLUSION

Surgeons should be aware of potential rotational errors in long leg radiographs after total knee arthroplasty resulting in wrong measurements. In case of rotational errors, radiographs should be repeated or rotational corrections calculated. For study purposes only radiographs after rotational correction should be accepted.

Measurement of lower limb alignment: there are within-person differences between weight-bearing and non-weight-bearing measurement modalities

PURPOSE

Previous studies have compared weight-bearing mechanical leg axis (MLA) measurements to non-weight-bearing measurement modalities. Most of these studies compared mean or median values and did not analyse within-person differences between measurements. This study evaluates the within-person agreement of MLA measurements between weight-bearing full-length radiographs (FLR) and non-weight-bearing measurement modalities (computer-assisted surgery (CAS) navigation or MRI).

MATERIALS AND METHODS

Two independent observers measured the MLA on pre- and postoperative weight-bearing FLR in 168 patients. These measurements were compared to non-weight-bearing measurements obtained by CAS navigation or MRI. Absolute differences in individual subjects were calculated to determine the agreement between measurement modalities. Linear regression was used to evaluate the possibility that other independent variables impact the differences in measurements.

RESULTS

A difference was found in preoperative measurements between FLR and CAS navigation (mean of 2.5° with limit of agreement (1.96 SD) of 6.4°), as well as between FLR and MRI measurements (mean of 2.4° with limit of agreement (1.96 SD) of 6.9°). Postoperatively, the mean difference between MLA measured on FLR compared to CAS navigation was 1.5° (limit of agreement (1.96 SD) of 4.6°). Linear regression analysis showed that weight-bearing MLA measurements vary significantly from non-weight-bearing MLA measurements. Differences were more severe in patients with mediolateral instability (p = 0.010), age (p = 0.049) and ≥3° varus or valgus alignment (p = 0.008).

CONCLUSION

The clinical importance of this study lies in the finding that there are within-person differences between weight-bearing and non-weight-bearing measurement modalities. This has implications for preoperative planning, performing total knee arthroplasty (TKA), and clinical follow-up after TKA surgery using CAS navigation or patient-specific instrumentation.

LEVEL OF EVIDENCE

III.