Definitions and consequences of current alignment techniques and phenotypes in total knee arthroplasty (TKA) – there is no winner yet

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PurposeOne of the most pertinent questions in total knee arthroplasty (TKA) is: what could be considered normal coronal alignment? This study aims to define normal, neutral, deviant and aberrant coronal alignment using large data from a computed tomography (CT)‐scan database and previously published phenotypes.MethodsCoronal alignment parameters from 11,191 knee osteoarthritis (OA) patients were measured based on three dimensional reconstructed CT data using a validated planning software. Based on these measurements, patients' coronal alignment was phenotyped according to the functional knee phenotype concept. These phenotypes represent an alignment variation of the overall hip knee ankle angle (HKA), femoral mechanical angle (FMA) and tibial mechanical angle (TMA). Each phenotype is defined by a specific mean and covers a range of ±1.5° from this mean. Coronal alignment is classified as normal, neutral, deviant and aberrant based on distribution frequency. Mean values and distribution among the phenotypes are presented and compared between two populations (OA patients in this study and non‐OA patients from a previously published study).ResultsThe arithmetic HKA (aHKA), combined normalised data of FMA and TMA, showed that 36.0% of knees were neutral within ±1 SD from the mean in both angles, 44.3% had either a TMA or a FMA within ±1–2 SD (normally aligned), 15.3% of the patients were deviant within ±2–3 SD and only 4.4% of them had an aberrant alignment (±3–4 SD in 3.4% and >4 SD in 1.0% of the patients respectively). However, combining the normalised data of HKA, FMA and TMA, 15.4% of patients were neutral in all three angles, 39.7% were at least normal, 27.7% had at least one deviant angle and 17.2% had at least one aberrant angle. For HKA, the males exhibited 1° varus and females were neutral. For FMA, the females exhibited 0.7° more valgus in mean than males and grew 1.8° per category (males grew 2.1° per category). For TMA, the males exhibited 1.3° more varus than females and both grew 2.3° and 2.4° (females) per category. Normal coronal alignment was 179.2° ± 2.8–5.6° (males) and 180.5 > ± 2.8–5.6° (females) for HKA, 93.1 > ± 2.1–4.2° (males) and 93.8 > ± 1.8–3.6° (females) for FMA and 86.7 > ± 2.3–4.6° (males) and 88 > ± 2.4–4.8° (females) for TMA. This means HKA 6.4 varus or 4.8° valgus (males) or 5.1° varus to 6.1° valgus was considered normal. For FMA HKA 1.1 varus or 7.3° valgus (males) or 0.2° valgus to 7.4° valgus was considered normal. For TMA HKA 7.9 varus or 1.3° valgus (males) or 6.8° varus to 2.8° valgus was considered normal. Aberrant coronal alignment started from 179.2° ± 8.4° (males) and 180.5 > ± 8.4° (females) for HKA, 93.1 > ± 6.3° (males) 93.8 > ± 5.4° (females) for FMA and 86.7 > ± 6.9° (males) and 88 > ± 7.2° (females) for TMA. This means HKA > 9.2° varus or 7.6° valgus (males) or 7.9° varus to 8.9° valgus was considered aberrant.ConclusionDefinitions of neutrality, normality, deviance as well as aberrance for coronal alignment in TKA were proposed in this study according to their distribution frequencies. This can be seen as an important first step towards a safe transition from the conventional one‐size‐fits‐all to a more personalised coronal alignment target. There should be further definitions combining bony alignment, joint surfaces' morphology, soft tissue laxities and joint kinematics.Level of EvidenceIII.

Section: Discussionmentioning

confidence: 99%

“…This approach is not based on outcome data yet, but it allows for deeper insight into normality values of the patients treated. Combining the previously presented functional phenotype concept with the normalised data presented in this study can be used to identify the safe zones as well as target zones for personalised alignment techniques [13–15, 26–28]. If one considers values within mean ± 2SDs as “normal”, mean ± 3 SDs as “deviant” and larger than this as “aberrant”, then the coronal alignment was neutral in 22.7% cases, 63.3% were within normality, 12.1% were deviant, and only 1.8% were aberrant.…”

Section: Discussionmentioning

confidence: 99%

Definition of normal, neutral, deviant and aberrant coronal knee alignment for total knee arthroplasty

Hirschmann,

Khan,

Sava

et al. 2024

Self Cite

“…To overcome the described limitations of standardised alignment, various patient-specific techniques have been popularised in recent years [10], however, until now it is unclear which workflow will provide superior results [11]. As in MA, individualised alignment workflows can be divided into tibia-first, gap-balanced techniques and into femur-first, measured-resection approaches.…”

Section: Introductionmentioning

confidence: 99%

Tibia‐first, gap‐balanced patient‐specific alignment technique achieves well‐balanced gaps in 90% of cases by rebuilding bony anatomy within boundaries

Strauch,

Kaufmann,

Graichen

2024

PurposePatient‐specific alignment (PSA) technique tries to achieve balanced gaps and simultaneously rebuild the individual bony phenotype. The hypothesis was: PSA technique achieves balanced knees in a high percentage with more anatomical resections than adjusted mechanical alignment (AMA).MethodsThree hundred sixty‐seven patients underwent navigated total knee arthroplasty (TKA) with a tibia‐first gap‐balanced PSA technique. Resection boundaries for medial proximal tibia angle (MPTA) of 86–92°, mechanical lateral distal femoral angle (mLDFA) of 86–92°, and hip‐knee‐ankle angle (HKA) of 175–185° were defined. Preoperative and intraoperative parameters of HKA, MPTA, mLDFA, and gap widths were recorded. Depending on the coronal deformity, the patients were divided into three groups: varus HKA < 178°; straight 178–182° and valgus HKA > 182°. The stability was analysed by assessing the difference between medial and lateral extension and flexion gaps as well as between flexion and extension gaps. All PSA measurements were compared with data from a previously published AMA series.ResultsPSA achieved balanced gaps in extension, flexion and between flexion/extension in over 90% of cases, being similar to AMA. In PSA, MPTA and mLDFA were restored within 1°, except in extreme varus (MPTA difference 2°) and valgus knees (mLDFA difference 3°). This was caused by the defined boundaries of the alignment technique. This individualised reconstruction led to significantly more anatomical resections of all tibia and femur resections.ConclusionA tibia‐first, gap‐balanced PSA technique achieves balanced joints in more than 90% of cases. By maintaining preoperative MPTA and mLDFA to a high extent, far more anatomical resections, compared to AMA were performed. Future studies need to be conducted to investigate whether those promising intraoperative results correlate with postoperative patient outcomes and whether patients outside the 5° corridor have higher failure rates.Level of EvidenceLevel III, retrospective cohort study.

“…Another study showed 43 knee phenotypes [6]. However, differences by degree of knee deformity were small except for HKAA [5] and individual evaluations of knee phenotype were needed [4,6,11]. The present study identified that %MA without valgus stress and MPTA are more important factors for predicting the degree of postoperative coronal alignment correction than mLDFA; % MA without valgus stress is almost the same as aHKA while a small MPTA reflects a small JLO.…”

Section: Discussionmentioning

confidence: 57%

Small medial proximal tibial angle is a radiographic finding strongly associated with less coronal alignment correction under valgus stress in medial knee osteoarthritis

Ichiyanagi,

Kuriyama,

Sakai

et al. 2024

PurposeThe degree to which varus knees can be corrected manually is important when considering total versus unicompartmental knee arthroplasty (UKA). The primary aim was to clarify the relationship between the degree of coronal alignment correction and radiographic parameters involved in UKA prognosis using preoperative full‐length lower extremity valgus stress radiography. The secondary aim was to identify the factors affecting alignment correction.MethodsThis retrospective observational study included 115 knees with medial osteoarthritis that underwent knee osteotomy or arthroplasty. Percent mechanical axis without valgus stress (%MA: neutral, 50%; varus, <50% and valgus, >50%), mechanical lateral distal femoral angle, lateral bowing femoral angle, medial proximal tibial angle (MPTA), joint line convergence angle, medial and lateral joint space width (LJSW) and medial femoral and tibial joint osteophyte size were measured using preoperative full‐length weight‐bearing radiographs. Correlation and multiple linear regression analyses were used to assess associations between parameters and %MA with valgus stress or amount of %MA change (%MA with valgus stress minus %MA without valgus stress).Results%MA with valgus stress was correlated with all radiographic parameters. %MA change was correlated with parameters except for MPTA and LJSW. Multiple regression analyses showed that %MA without valgus stress and MPTA were associated with both %MA with valgus stress and %MA change. When %MA with valgus stress was set at 30%, 40% and 50%, MPTA cutoff values were 81.6°, 83.5° and 84.9°, and cutoffs for %MA without valgus stress were 10.7%, 17.1% and 25.1%, respectively.ConclusionSmall MPTA is strongly associated with less alignment correction under valgus stress in varus knees. The finding is useful in surgical planning, especially to avoid undercorrection with UKA when valgus stress radiographs are unavailable.Level of EvidenceLevel III.