gms | German Medical Science

Objectives: The varus-valgus alignment of the native knee differs through the range of motion. Therefore, the coronal alignment of the knee is better characterized by coronal kinematic curve rather than a single tibiofemoral mechanical alignment value. While individual passive kinematic curves have been documented with computer navigation systems and reported for osteoarthritic knees undergoing TKAs, the individual curves of non-arthritic knees have not yet been examined. Furthermore, no data regarding anatomical parameters that determine these curves exist. The primary aim of this study was to document and classify individual coronal plane kinematic curve morphology in non-arthritic tibiofemoral joints. The secondary aim was to detect a possible correlation between the curve morphotype and the coronal plane radiographic anatomy of the distal femur and proximal tibia.

Methods: Thirty one knees (23 patients, 8 bilateral) undergoing primary unicompartmental patellofemoral knee arthroplasty for the treatment of isolated patellofemoral arthritis with non-arthritic tibiofemoral joints were included in this study (mean age 58, SD 9 y, body mass 83.4, SD 16.9 Kg, height 1.7, SD 0.1m, BMI 28, SD 4.1). The patellofemoral joint replacement was performed conventionally; a computer navigation system was used during the operation, purely for the purpose of this study. The coronal plane passive kinematic curves of the tibiofemoral joint were documented intraoperatively with the aid of the computer navigation system and categorized into the following morphotypes as defined by Young et al. [1]: straight, drift, inverse drift, C-shaped, inverse C-shaped, S-shaped, inverse S-shaped. Full length weightbearing radiographs were performed as routine preoperatively. The mechanical lateral distal femoral angle (mLDFA) and mechanical proximal tibial angle (MTPA) were calculated and correlated with the kinematic pattern types.

Results and conclusion: Eight knees had straight, eleven drift, four inverse drift, three C-shape and five inverse C-shape curve morphotype. No S-shape or inverse S-shape curves were recorded. The mLDFA was significantly different among the different curve morphotypes (p=0.002). Paired comparison of mLDFA between the different curve morphotypes revealed highly significant differences between various pairs. The MPTA did not differ across the curve morphotypes (p=0.322).

This study documents intraoperative coronal plane passive knee kinematic curves of healthy tibiofemoral joints, captured with a computer navigation system. While straight curves were documented, the majority of the knees did not have straight curves. Five of the coronal plane kinematic curve types defined by Young et al. [1] were identified; the drift type was the most common. The coronal plane joint curve variation was defined by the distal femoral coronal alignment.