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. 2025 Jul 2;14(13):4684.
doi: 10.3390/jcm14134684.

Changes of Knee Phenotypes Following Osteotomy Around the Knee in Patients with Valgus or Varus Deformities-A Retrospective Cross-Sectional Study

Jennyfer A Mitterer  1   2 , Stephanie Huber  1   3 , Matthias Pallamar  2 , Sebastian Simon  1   3 , Jan Nolte  1 , Catharina Chiari  2 , Jochen G Hofstaetter  1   3
Affiliations

Changes of Knee Phenotypes Following Osteotomy Around the Knee in Patients with Valgus or Varus Deformities-A Retrospective Cross-Sectional Study

Jennyfer A Mitterer et al. J Clin Med. .

Abstract

Background: Osteotomies around the knee aim to correct varus or valgus malalignment and improve biomechanics. However, little is known about their effect on knee phenotypes, as defined by the Coronal-Plane-Alignment-of-the-Knee (CPAK) and Hirschmann's functional classification. This study evaluated pre- and postoperative phenotypes in patients undergoing high-tibial-osteotomy (HTO) or distal-femoral-osteotomy (DFO). Methods: We retrospectively analysed 214 osteotomies around the knee (HTO: 145; DFO: 69) of 188 patients from our institutional registry. Radiographic parameters were measured using a validated artificial intelligence software, with phenotypes classified by CPAK and Hirschmann classification. Preoperative osteotomy planning was compared to postoperative alignment. Regression was used to assess the influence of demographic and radiographic factors. Results: CPAK types changed in 95.3% of cases. Medial opening HTOs most frequently shifted from CPAK type I (73.8%) to VI (42.3%), while medial closing DFOs transitioned from type III (81.5%) to V (24.1%). Concordance between planned and achieved CPAK types was highest for types III, IV, and V. Postoperative angles were generally smaller than planned for joint-line-obliquity (JLO), lateral-distal-femur-angle, and medial-proximal-tibial-angle (p < 0.001). Neutral JLO was restored in only 48.1%. Preoperative phenotypes NEUmLDFA0° (40.1%) and VARmMPTA3° (32.3%) were most common, while postoperative phenotypes included VALmLDFA3° (52.4%) and VALmMPTA3° (37.7%). Age, sex, and BMI significantly influenced alignment outcomes. Conclusions: Postoperative CPAK classifications shifted significantly across all osteotomy types, with minimal retention of preoperative types. Although most procedures achieved correction within the target HKA range, restoration of a neutral JLO was observed in only half of the cases, emphasizing the importance of phenotype-specific planning and highlight potential limitations of CPAK classification.

Keywords: artificial intelligence; coronal plane classification; knee phenotypes; lower limb alignment; osteotomy around the knee.

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Conflict of interest statement

The “Michael Ogon Laboratory for Orthopaedic Research” received a research grant from “Image Biopsy Lab GmbH”. “Image Biopsy Lab GmbH”. The collection, analysis, and interpretation of data, writing of the report, and the decision to submit the paper for publication were performed by the authors and not influenced by Image Biopsy Lab." Other authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Sankey diagram displaying CPAK changes from pre- to post-operative types, grouped by osteotomy types. Numbers are absolute, frequencies in parentheses. (1A) Changes in CPAK types in the medial opening HTO group, (1B) changes in CPAK types in the medial closing HTO group, (2A) changes in CPAK types in the medial closing DFO group, (2B) changes in CPAK types in the lateral closing DFO group. Changes towards other CPAK types (“Different”) and persistence within the same CPAK type (“Same”) are displayed below the Sankey diagram. CPAK: coronal plane alignment of the knee, HTO: high tibial osteotomy, DFO: distal femoral osteotomy.
Figure 2
Figure 2
Example cases of phenotype changes. Mechanical femur axis (proximal orange line), distal femoral joint line (upper yellow line at the knee), proximal tibial joint line (lower yellow line at the knee), mechanical tibia axis (distal orange line), Mikulicz line (turquoise line) corresponding to the mechanical axis of the lower limb, mechanical-axis-deviation (horizontal turquoise line at the knee), femur length (purple line from the top of the femoral head to medial femoral condyle), and tibia length (purple line from medial femoral condyle to ankle). CPAK: coronal plane alignment of the knee, HTO: high tibial osteotomy, DFO: distal femoral osteotomy. HKA: hip-knee-ankle angle, MAD: mechanical axis deviation, mLDFA: mechanical lateral distal femoral angle, mMPTA: mechanical medial proximal tibial angle, JLCA: joint line convergence angle, aHKA: arithmetic HKA, JLO: joint line obliquity. Ia/Ib: Preoperative CPAK I to postoperative CPAK VI (medial opening HTO). Ia—Preoperative: HKA = −10.3°, MAD = 38.0 mm, mLDFA = 88.7°, mMPTA = 79.5°, JLCA = −1.1°, aHKA = −9.2°, JLO = 168.2°; Ib—Postoperative: HKA = 0.6°, MAD = −2.0 mm, mLDFA = 88.4°, mMPTA = 89.7°, JLCA = −1.7°, aHKA = 2.3°, JLO = 177.1°. IIa/IIb: Preoperative CPAK VI to postoperative CPAK II (medial closing HTO). IIa—Preoperative: HKA = 3.5°, MAD = −14.0 mm, mLDFA = 87.6°, mMPTA = 92.2°, JLCA = −1.2°, aHKA = 4.6°, JLO = 179.8°; IIb—Postoperative: HKA = −2.3°, MAD = 9.0 mm, mLDFA = 87.4°, mMPTA = 86.0°, JLCA = −0.8 °, aHKA = −1.4°, JLO = 173.4°. IIIa/IIIb: Preoperative CPAK III to postoperative CPAK V (medial closing DFO). IIIa—Preoperative: HKA = 6.3°, MAD = −23.0 mm, mLDFA = 82.2°, mMPTA = 90.9°, JLCA = −2.5°, aHKA = 8.7°, JLO = 173.1°; IIIb—Postoperative: HKA = −0.1°, MAD = 0.0 mm, mLDFA = 89.0°, mMPTA = 89.8°, JLCA = −0.8°, aHKA = 0.8°, JLO = 178.8°. IVa/IVb: Preoperative CPAK IV to postoperative CPAK III (lateral closing DFO). IVa—Preoperative: HKA = −9.1°, MAD = 36.0 mm, mLDFA = 92.1°, mMPTA = 86.6°, JLCA = −3.6°, aHKA = −5.5°, JLO = 178.7°; IVb—Postoperative: HKA = −0.9°, MAD = 3.0 mm, mLDFA = 84.3°, mMPTA = 86.4°, JLCA = −3.0°, aHKA = 2.1°, JLO = 170.7°.
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