Abstract
PurposeRecently 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.MaterialCoronal 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).ResultsFemoral 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.ConclusionDifferences 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 evidenceIII.
Highlights
Material and methodsCorrect orientation of the prosthetic components in total knee arthroplasty (TKA) is key to achieve satisfying functional outcomes
The number and distribution of limb, tibial and femoral phenotypes are shown in Figs. 2, 3 and 4
There were 45 different knee phenotypes, 39 in the female and 37 in the male population. Of these 45 knee phenotypes, 27 each covered less than 1% of the population
Summary
Material and methodsCorrect orientation of the prosthetic components in total knee arthroplasty (TKA) is key to achieve satisfying functional outcomes. New individual TKA alignment strategies have been proposed, which aim to improve clinical outcomes by restoring the pre-arthritic alignment of the individual patient [1, 11, 12] Clinical results of these concepts are promising, yet there are still unanswered questions [5, 11, 13]. Our knowledge regarding differences between OA and non-OA patients is limited to conventional radiographs or/and studies with small sample sizes The purpose of this investigation was the following: first, to apply the functional knee phenotype system to OA patients and investigate whether femoral and tibial joint lines vary within OA patients with the same overall lower limb alignment. To assess differences between OA and non-OA patients with regard to overall lower limb alignment
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