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

Distribution of coronal plane alignment of the knee classification in Chinese osteoarthritic and healthy population: a retrospective cross-sectional observational study

BACKGROUND

Few studies have reported the coronal constitutional alignment of the lower limbs in mainland China. This study aimed to analyse the distribution of the coronal plane alignment of the knee (CPAK) classification in the osteoarthritic (OA) and healthy Chinese populations.

MATERIALS AND METHODS

The CPAK distributions of 246 patients (477 knees) with OA and 107 healthy individuals (214 knees) were retrospectively examined using long-leg radiographs. Radiological measurements and CPAK classification of different Kellgren-Lawrence grades in patients with unilateral total knee arthroplasty (TKA) were compared. The clinical outcomes of patients with CPAK type I who underwent mechanical alignment or restricted kinematic alignment during TKA were examined.

RESULTS

The most common distributions in the OA and healthy groups were type I and type II, respectively. In patients who underwent unilateral TKA, the most common distribution of knees graded as Kellgren-Lawrence 3-4 was type I. However, the most common distributions of contralateral knees graded as Grade 0-2 were type I and II. For patients with CPAK type I, the mechanical alignment and restricted kinematic alignment groups did not differ significantly concerning postoperative clinical outcomes at 3 months.

CONCLUSION

The most common distributions in Chinese osteoarthritic and healthy populations were types I and II, respectively. In addition, OA progression may lead to changes in the CPAK classification.

Correcting for asymmetry of the proximal tibial epiphysis is warranted to determine postoperative alignment deviations in kinematic alignment from planned alignment of the tibial component on the native tibia

BACKGROUND

In total knee arthroplasty, unrestricted kinematic alignment aims to restore pre-arthritic lower limb alignment and joint lines. Joint line orientations of the contralateral healthy proximal tibia might be used to evaluate accuracy of tibial component alignment post-operatively if asymmetry is minimal. Our objective was to evaluate left-to-right asymmetry of the proximal tibial epiphysis in posterior tibial slope and varus-valgus orientation as related to unrestricted kinematic alignment principles.

METHODS

High resolution CT images (0.5 mm slice thickness) were acquired from bilateral lower limbs of 11 skeletally mature subjects with no skeletal abnormalities. Images were segmented to generate 3D tibia models. Asymmetry was quantified by differences in orientations required to shape-match the proximal epiphysis of the mirror 3D tibia model to the proximal epiphysis of the contralateral 3D tibia model.

FINDINGS

Systematic and random differences (i.e. mean ± standard deviation) in tibial slope and varus-valgus orientation were - 0.8° ± 1.2° and - 0.2° ± 0.8°, respectively. Ninety five percent confidence intervals on the means included 0° indicating that systematic differences were minimal.

INTERPRETATION

Since random differences due to asymmetry are substantial in relation to random surgical deviations from pre-arthritic joint lines previously reported, post-operative computer tomograms of the contralateral healthy tibia should not be used to directly assess accuracy of tibial component alignment on a group level without correcting for differences in tibial slope and varus-valgus orientation due to asymmetry.

Gender-based differences exist in the functional knee phenotypes classification of the osteoarthritic knee

PURPOSE

To identify gender differences in (1) the coronal alignment of functional knee phenotypes and (2) the JLCA (joint line convergence angle) in relation to the phenotype classification.

METHODS

This study is a retrospective data analysis, including 12,099 osteoarthritic knee computed tomography (5025 male, 7074 female) analysed by Medacta software for hip-knee-ankle angle (HKA), femoral mechanical angle (FMA), tibial mechanical angle (TMA) and JLCA. The data were grouped into genders and combined according to the Functional Knee Phenotypes Classification.

RESULTS

Out of 127 phenotypes for males and 131 for females, 17 common phenotypes were reported. The commonest four were similar for both genders with VARHKA177° NEUFMA93° NEUTMA87° (9.8% males, 9.50% females), followed by VARHKA174° NEUFMA93°VARTMA84° (7.1%) and VARHKA174°VARFMA90° NEUTMA87° (7.0%) for males and VARHKA174° NEUFMA93° NEUTMA87° (6.1%), VARHKA174° NEUFMA93°VARTMA84° (5.1%) for females. The commonest FMA and TMA (91.5° to 94.5° and 85.5° to 88.5°, respectively) were the same for both genders, however, the rest of the male population observed greater femoral varus than the female population (p < 0.001). JLCA values ranged from -28.4° to 8.2° in the overall study population. Males and females had a mean JLCA of -2.96° (±2.6° SD) and -2.66° (±2.8°7 SD), respectively, p < 0.001.

CONCLUSIONS

Gender differences exist within the osteoarthritic knee phenotype. The male varus phenotype is influenced by FMA, while TMA values are similar across genders. JLCA variations show similarities to both TMA and FMA, suggesting JLCA is influenced by bone morphology more than by gender. These differences inform surgical decision-making for the personalised approach to the primary TKA.

LEVEL OF EVIDENCE

Level III.

Only 26% of Native Knees Show an Identical Coronal Functional Knee Phenotype in the Contralateral Knee

BACKGROUND

A comprehensive exploration evaluating left-to-right knee symmetry across all anatomical planes utilizing three-dimensional (3D) scans stands absent from the existing body of research. Therefore, the primary objectives of this investigation involved examining potential differences and resemblances in alignment and structure between left and right non-osteoarthritic (native) knees in various planes (coronal, sagittal, and axial) using three-dimensional single-photon emission computed tomography/computed tomography (SPECT/CT) images.

METHODS

A total of 282 native knees from 141 patients were retrospectively gathered from the hospital's records. Patients, aged between 16 and 45, who underwent Tc99m-methyl diphosphonate SPECT/CT scans for both knees, adhering to the Imperial Knee Protocol, were included. A statistical analysis was conducted, including 23 knee morphometric parameters, comparing left and right knees, and classifying them based on functional knee phenotypes across the coronal, sagittal, and axial planes.

RESULTS

Regarding the functional coronal knee phenotype, 26% of patients (n = 37) exhibited identical phenotypes in both knees (p < 0.001). Significant correlated similarities between the left and right knees were observed in the coronal plane (Pearson's r = 0.76, 0.68, 0.76, 0.76, p < 0.001) and in several morphometric measures in the sagittal plane (Pearson's r = 0.92, 0.72, 0.64, p < 0.001). Moderately correlated similarities were noted in the axial plane (Pearson's r = 0.43, 0.44, 0.43, p < 0.001).

CONCLUSIONS

Only 26% of native knees exhibit an identical coronal phenotype in their contralateral knee, whereas 67% have the adjacent coronal phenotype. Strongly correlated resemblances were established across various left and right knee morphometric parameters in the coronal, sagittal, and axial planes. These findings could enhance decisions in procedures like total knee arthroplasties or osteotomies, where alignment is key to outcomes, and reveal a potential for future artificial intelligence-driven models to improve our understanding and improve personalized treatment strategies for knee osteoarthritis.

A Radiographic Analysis of Coronal Morphological Parameters of Lower Limbs in Chinese Non-knee Osteoarthritis Populations

OBJECTIVES

Analyzing the lower limb coronal morphological parameters in populations without knee osteoarthritis (KOA) holds significant value in predicting, diagnosing, and formulating surgical strategies for KOA. This study aimed to comprehensively analyze the variability in these parameters among Chinese non-KOA populations, employing a substantial sample size.

METHODS

A cross-sectional retrospective analysis was performed on the Chinese non-KOA populations (n = 407; 49.9% females). The study employed an in-house developed artificial intelligence software to meticulously assess the coronal morphological parameters of all 814 lower limbs. The parameters evaluated included the hip-knee-ankle angle (HKAA), weight-bearing line ratio (WBLR), joint line convergence angle (JLCA), mechanical lateral-proximal-femoral angle (mLPFA), mechanical lateral-distal-femoral angle (mLDFA), mechanical medial-proximal-tibial angle (mMPTA), and mechanical lateral-distal-tibial angle (mLDTA). Differences in these parameters were compared between left and right limbs, different genders, and different age groups (with 50 years as the cut-off point).

RESULTS

HKAA and JLCA exhibited left-right differences (left vs. right: 178.2° ± 3.0° vs. 178.6° ± 2.9° for HKAA, p = 0.001; and 1.8° ± 1.5° vs. 1.4° ± 1.6° for JLCA, p < 0.001); except for the mLPFA, all other parameters show gender-related differences (male vs. female: 177.9° ± 2.8° vs. 179.0° ± 3.0° for HKAA, p < 0.001; 1.5° ± 1.5° vs. 1.8° ± 1.7° for JLCA, p = 0.003; 87.1° ± 2.1° vs. 88.1° ± 2.1° for mMPTA, p < 0.001; 90.2° ± 4.0° vs. 91.1° ± 3.2° for mLDTA, p < 0.001; 38.7% ± 12.9% vs. 43.6% ± 14.1% for WBLR, p < 0.001; and 87.7° ± 2.3° vs. 87.4° ± 2.7° for mLDTA, p = 0.045); mLPFA increase with age (younger vs. older: 90.1° ± 7.2° vs. 93.4° ± 4.9° for mLPFA, p < 0.001), while no statistical difference exists for other parameters.

CONCLUSIONS

There were differences in lower limb coronal morphological parameters among Chinese non-KOA populations between left and right sides, different genders, and age.

Femoral neck shortening as a sequela of internal fixation for femoral neck fractures and its effect on the coronal alignment of the limb: a pilot study

INTRODUCTION

Femoral neck shortening is a common phenomenon following osteosynthesis for femoral neck fractures, which was shown to have a negative effect on hip function. There is paucity of literature on the effect of shortening on the ipsilateral limb mechanical axis and knee coronal alignment. We hypothesized that postoperative femoral neck shortening can alter the limb's mechanical axis into valgus.

METHODS

Of 583 patients screened, 13 patients with severe neck shortening (< 10 mm) following femoral neck fracture fixation, were found eligible and agreed to participate. A full-length lower limb radiographs were obtained and radiographic parameters (offset, neck-shaft angle, HKA, mLPFA, mDLFA, mMPTFA, MAD, MAD-r) as well as functional scores were obtained.

RESULTS

Statistically significant differences in mechanical axis deviation ratio (MAD-r) were found between the ipsilateral and the contralateral extremities (0.41 ± 0.16 versus 0.55 ± 0.11, p = 0.03). A correlation between femoral neck length differences and MAD was not statistically significant although a tendency towards lateral deviation of the mechanical axis was noted (r = - 0.5, p = 0.077). A negative correlation was found between a greater difference in the femoral neck length and the SF12 score, both in the physical and the mental parts (r = - 0.69, p = 0.008; r = - 0.58, p = 0.035, respectively).

CONCLUSION

We found a more lateralized mechanical axis in limbs that demonstrated post-operative ipsilateral femoral neck severe shortening. These findings may provide a possible explanation and rationale for knee pain and perhaps for the development of knee osteoarthritis as a sequalae of femoral neck shortening. Further investigation and larger cohort, long-term studies are needed to further explore this hypothesis.

Long leg radiographs underestimate the degree of constitutional varus limb alignment and joint line obliquity in comparison with computed tomography: a radiographic study

PURPOSE

The purpose of this study was to understand if differences exist between computed tomography (CT) and long leg radiographs (LLR) when defining coronal plane alignment of the lower limb in total knee arthroplasty (TKA). It aimed to identify any such differences between the two imaging modalities by quantifying constitutional limb alignment (arithmetic hip-knee-ankle angle (aHKA), joint line obliquity (JLO) and Coronal Plane Alignment of the Knee (CPAK) type within the same population.

METHODS

A retrospective radiographic study compared pre-operative LLR and CT measurements in patients undergoing robotic-assisted TKA. The aHKA, JLO and CPAK types were calculated after measuring the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). The primary outcomes were the mean differences in aHKA (MPTA-LDFA), JLO (MPTA + LDFA) and proportions of CPAK types between LLR and CT groups. The secondary outcomes were the differences in CT-derived MPTA values based on four different tibial sagittal landmarks.

RESULTS

After exclusions, 465 imaging sets were analysed in 394 patients. There was a statistically significant mean difference between LLR and CT, respectively, for both MPTA (87.5° vs. 86.2°; p < 0.01) and LDFA (88.7° vs. 87.3°; p < 0.01). There were also statistically significant differences for aHKA (- 0.2° vs. - 1.1°) and JLO (175.1° vs. 173.4°) for LLR and CT, respectively (both p < 0.01). CT increased the proportion of patients with CPAK Type I (constitutional varus aHKA, apex distal JLO) and CPAK Type II (neutral aHKA, apex distal JLO), and decreased numbers of CPAK Types III-VI. There were significant mean differences in the MPTA using varying sagittal landmarks.

CONCLUSION

Alignment determined by LLRs underestimates the magnitude of both constitutional varus alignment and joint line obliquity compared to CT, differences that notably increase the proportions of patients included in CPAK Types I and II. These distinctions are primarily due to underestimation of proximal tibial varus when measured on LLRs compared to CT, which more specifically defines articular weight-bearing points.

LEVEL OF EVIDENCE

III.

The effect of weight-bearing positions on coronal lower limb alignment: A systematic review

BACKGROUND

The coronal alignment of the lower limb is generally accepted as a major determinant of surgical outcome in total knee arthroplasty (TKA). To achieve the ideal post-operative alignment, surgeons need to be aware of the influence that weight-bearing positions have on the final knee alignment. Therefore, this review aims to define the effect of varying weight-bearing positions on the coronal alignment of the lower limb. We hypothesized that a coronal alignment deformity increases with loading.

METHODS

The PubMed, Medline and google scholar databases were searched systematically in June 2022. Only studies which compared coronal alignment with a standardized radiographic protocol in the single leg, double leg and supine positions were included. To obtain pooled estimates of the effect of different weight-bearing positions, random-effect analysis were fitted using SAS.

RESULTS

Compared to the supine position, double leg weight-bearing positions were found to be associated with a more pronounced varus deformity (mean difference in HKA is 1,76° (95% CI 1,32: 2,21), p < 0.0001)). The mean difference in HKA between double leg and single leg weight-bearing conditions was 1.43° (95% CI (-0,042;2,90), p = 0.0528).

CONCLUSION

The overall knee alignment was found to be influenced by the weight-bearing position. An average difference of 1.76° in HKA-angle was found between a double leg-stance and supine position, tending to increased varus in the former weight-bearing position. It is therefore possible that the deformity could increase by 1.76° if knee surgeons only follow a pre-op planning based on double-leg stance full length radiographs.

The pre-diseased coronal alignment can be predicted from conventional radiographs taken of the varus arthritic knee

INTRODUCTION

The concept of restoring the constitutional, pre-diseased alignment has gained lots of interest among knee surgeons. Previous attempts to use the contralateral limb to bridge the gap between the arthritic and the constitutional alignment were unsuccessful. We investigated the usability of a mathematical formula to predict the constitutional (pre-diseased) coronal alignment once arthritis has occurred. It is our hypothesis that by using the KL grade, CPAK classification and four radiographic measurements of the arthritic knee, the pre-diseased coronal alignment could be predicted.

MATERIAL AND METHODS

Hundred arthritic patients with consecutive X-rays were used to determine a mathematical formula. Five alignment parameters were determined on full-length X-rays: HKA angle, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA) and the tibial joint line angle (TJLA). A refinement of the algorithm was implemented based on a reference cohort, consisted of 250 young adults aged between 20 and 27 years. Moreover, all knees were subdivided based on their CPAK-phenotype and the Kellgren-Lawrence scale (KL scale). An independent arthritic cohort of 289 patients scheduled for primary total knee arthroplasty was included to verify the accuracy of the predicted HKAs (HKAPRED).

RESULTS

In CPAK type 1, the HKAPRED was 3.86° varus (STD 1.39) and the HKAYHA was 4.0° varus. In CPAK type 2, the HKAPRED was 1.68° varus (STD 1.95) compared to a HKAYHA of 1.34° (STD 0.81). The average constitutional HKA is not different in both CPAK 1 (p = 0.61) and CPAK 2 (p = 0.25), and the difference in the mean is estimated to be equal to - 0.14 (95CI - 0.68 to 0.40) in CPAK 1 and 0.35 (95CI - 0.06 to 0.75) in CPAK 2.

CONCLUSION

Using the KL grade, CPAK classification and four radiographic measurements of the arthritic knee, the pre-diseased coronal alignment can be predicted in 80% of the varus knees with an accuracy of ≤ 0.5°. The predicted HKA (HKAPRED) can be very useful in the current and future clinical practice.

Correcting for distal femoral asymmetry is necessary to determine postoperative alignment deviations from planned alignment of the femoral component

BACKGROUND

One method for assessing the accuracy of manual, patient-specific, navigational, and robotic-assisted total knee arthroplasty (TKA) instrumentation is to use a post-operative computer tomogram and determine the deviation of the femoral component alignment relative to the planned alignment in the native (i.e. healthy) contralateral distal femoral epiphysis. However, side-to-side asymmetry might introduce errors which inflate alignment deviations. This study quantified asymmetry in the distal femoral epiphysis.

METHODS

High resolution CT images (0.5 mm slice thickness) were acquired from bilateral lower limb specimens of 13 skeletally mature subjects with no skeletal abnormalities. Images were segmented to generate 3D femur models. Asymmetry was quantified by differences in positions and orientations required to shape-match the distal epiphysis of the mirror 3D femur model to the distal epiphysis of the contralateral 3D femur model.

RESULTS

Asymmetry was due to random rather than systematic differences. Random differences (i.e. standard deviations) in proximal-distal (P-D) and anterior-posterior (A-P) positions were 1.1 mm and in varus-valgus (V-V) and internal-external (I-E) orientations were 0.9° and 1.3°, respectively. These represented substantial relative errors of up to 50 % in previously reported overall alignment deviations.

CONCLUSIONS

Although small in an absolute sense, asymmetry of the distal femur epiphysis introduced substantial relative errors when assessing accuracy of femoral component alignment in TKA. When post-operative computer tomograms are used to assess the accuracy of manual, patient specific, navigational, and robotic-assisted TKA instrumentation, the overall deviation should be corrected for asymmetry to better indicate the accuracy of the surgical technique.

Robotic-assisted medial unicompartmental knee arthroplasty restores estimated pre-arthritic coronal limb alignment: A retrospective cohort study

BACKGROUND

Robotic-assisted medial unicompartmental knee arthroplasty (UKA) aims to restore pre-arthritic (constitutional) limb alignment, by re-tensioning of the medial collateral ligament (MCL). This study aimed to determine whether pre-arthritic coronal alignment was restored following robotic-assisted medial UKA in patients with medial compartment osteoarthritis.

METHOD

A retrospective study was undertaken, including 102 patients with a unilateral robotic-assisted medial UKA and a contralateral unaffected knee. Both the validated arithmetic hip-knee-ankle angle (aHKA) and alignment of the contralateral unaffected knee were used to estimate pre-arthritic alignment. The aHKA is a radiographic method to estimate the pre-arthritic mechanical hip-knee-ankle angle (mHKA). To verify restoration of pre-arthritic alignment, postoperative mHKA was compared to the aHKA. Additionally, postoperative mHKA, joint line congruence (JLCA), and knee joint line obliquity (KJLO) angles were compared between the operative and contralateral unaffected knee. Equivalence between postoperative and pre-arthritic alignment was assessed through the two-one-sided t-test (TOST), using equivalence margins of ±2.0°.

RESULTS

Postoperative mHKA was equivalent to the aHKA (mean difference -0.38°, 90% CI -0.69 to -0.07;p < .001), with 93 knees (91%) restored within 3.0° their aHKA. Postoperative mHKA, JLCA and KJLO were equivalent between the operative and contralateral unaffected knees, with mean differences of -0.65°, -0.65°, and -0.40°, respectively; all p < .001.

CONCLUSIONS

Postoperative and pre-arthritic coronal alignment were equivalent following robotic-assisted medial UKA, with 91% of knees restored within 3.0° of their pre-arthritic mechanical axis. These results demonstrate that both mechanical alignment and joint line congruence are restored by MCL re-tensioning in patients undergoing robotic-assisted medial UKA for medial compartment osteoarthritis.

Ethnical Differences in Knee Phenotypes Indicate the Need for a More Individualized Approach in Knee Arthroplasty: A Comparison of 80 Asian Knees with 308 Caucasian Knees

The purpose of this study was to determine the distribution of functional knee phenotypes in a non-osteoarthritic Asian population. The Stryker Orthopaedic Modeling and Analytics (SOMA) database was searched for CT scans of the lower limb meeting the following inclusion criteria: patient age at time of image >18 and <46 years, no signs of fractures and/or previous surgery and/or degenerative changes, Asian ethnicity. A total of 80 CT scans of 40 patients were included (24 males, 16 females). The hip-knee-ankle angle (HKA), femoral mechanical angle (FMA) and tibial mechanical angle (TMA) were measured. Based on these measurements, each limb was phenotyped according to the previously introduced functional knee phenotype concept. All angles and phenotypes of the present study were compared with previously published data of a non-osteoarthritic Caucasian population (308 legs of 160 patients, 102 males, 58 females). Asian knees had a significantly lower TMA (both genders p < 0.001) but a higher FMA (males p < 0.05, females p < 0.001) than Caucasian knees but showed no difference in the HKA. Asian knees differed significantly with regard to femoral and tibial phenotypes (p < 0.01), but not with regard to limb phenotypes. The high variability of all coronal alignment parameters highlights the importance of a detailed analysis prior to TKA. Ethnical differences underline the need for a more individualized approach in TKA.

Osteoarthritic and non-osteoarthritic patients show comparable coronal knee joint line orientations in a cross-sectional study based on 3D reconstructed CT images

PURPOSE

Recently introduced total knee arthroplasty (TKA) alignment strategies aim to restore the pre-arthritic alignment of an individual patient. The native alignment of a patient can only be restored with detailed knowledge about the native and osteoarthritic alignment as well as differences between them. The first aim of this study was to assess the alignment of a large series of osteoarthritic (OA) knees and investigate whether femoral and tibial joint lines vary within patients with the same overall lower limb alignment. The secondary aim was to compare the alignment of OA patients to the previously published data of non-OA patients. This information could be useful for surgeons considering implementing one of the new alignment concepts.

MATERIAL

Coronal alignment parameters of 2692 knee OA patients were measured based on 3D reconstructed CT data using a validated planning software (Knee-PLAN^®, Symbios, Yverdon les Bains, Switzerland). Based on these measurements, patients' coronal alignment was phenotyped according to the functional knee phenotype concept. These phenotypes represent an alignment variation of either the overall alignment, the femoral joint line orientation or the tibial joint line orientation. Each phenotype is defined by a specific mean and covers a range of ± 1.5° from this mean. Mean values and distribution among the phenotypes are presented and compared between two populations (OA patients of this study and non-OA patients of a previously published study) as well as between HKA subgroups (varus, valgus and neutral) using t tests and Chi-square tests (p < 0.05).

RESULTS

Femoral and tibial joint lines varied within patients with the same overall lower limb alignment. A total of 162 functional knee phenotypes were found (119 males, 136 females and 94 mutual phenotypes). Mean values differed between the OA and non-OA population, but differences were small (< 2°) except for the overall alignment (e.g. HKA). The distribution of OA and non-OA patients among the phenotypes differed significantly, especially among the limb phenotypes.

CONCLUSION

Differences between OA and non-OA knees are small regarding coronal femoral and tibial joint line orientation. Femoral and tibial joint line orientation of osteoarthritic patients can, therefore, be used to estimate their native coronal alignment and plan an individualized knee alignment.

LEVEL OF CLINICAL EVIDENCE

III.