Question: Patellofemoral pain or instability (PFI) is often caused by femoral or tibial maltorsion. Despite normal torsion measurements (CT/MRI) in femur/tibia there are symptomatic patients with clinical high external rotation of the tibia (ROM shifted to external rotation). An intraarticular malrotation of the knee may be the cause for chronic patellar maltracking or patellofemoral instability in these situations. The influence of the intraarticular rotation of the knee has not been considered and described in the literature yet. The aim of this study was to detect and quantify a possible intraarticular malrotation of the knee in symptomatic patients.

Material And Methods

100 patients with patellofemoral pain, instability or a suspected malalignment of the lower extremity that had been examined for torsional abnormalities via MRI were included in a retrospective study between 11/2018 and 05/2020. The torsion of the femur and tibia were measured using the method of Strecker and Waidelich. The intraarticular rotation (IAR) of the knee was measured in full extension; therefore the angle between the posterior femur condylar axis (PFCA) and the proximal posterior tibia plateau axis (PTPA) was analyzed.
Supplementary measurements were made using the following levels and values: 1) femur transepicondylar axis (FTEA); 2) the tibial plateau ellipsis axis (TPEA; axis through the center of two ellipses on the medial and lateral tibial plateau below meniscal level) 3) tibial tuberosity trochlea groove distance (TT-TG) and 4) tibial tuberosity posterior cruciate ligament distance (TT-PCL). In Long leg x-rays („knee forward“) measurements of the mechanical Femur-Tibia-Axis (mFTA), mechanical Medial-Proximal-Tibia-Angle (mMPTA) and Joint-Line-Convergence-Angle (JLCA) were performed.

Results

In 200 analyzed legs of 100 patients (mean age 23.5 ±8,6 (10-53)) the intraarticular rotation of the knee was +5,4 ±5,2° (range -7,7 to +16,4°) external rotation (PFCA to PTPA). The mean femoral torsion was -29,5 ±10,7° (-74,9 to -0,8°) internal torsion, mean tibial torsion +36,9 ±8,4° (+9,7 to +62,3°) external torsion. The additional measurement from FTEA to TPEA showed an intrarticular rotation of +4,7 ±5,2° (-8,0 to 16,6°) external rotation. Mean TT-TG was 16.3 ±4,0mm (6,8 bis 30,1mm) and mean TT-PCL 21,6 ±3,4mm (10,6 to 32,6mm). The leg axis analysis showed the following results: mFTA: 0,9 ±3,0° (-7,1 to 11,5°) valgus; mLDFA: 86,2 ±2,1° (80,2 to 91,4°); mMPTA: 87,6 ±2,5° (82,2 to 96,6°); JLCA: 0,5 ±1,3° (-4,6 to 4,3°) medial convergence.

Conclusion

This study group is a population with expected abnormal torsion or intraarticular rotation. Therefore, normal values for rotation of the knee cannot be defined in this study. However, the range of 24.1° of intraarticular knee rotation may have a decisive influence on the rotational alignment of the lower extremity and on the patellofemoral joint causing PFI or maltracking. This has not been described and sufficiently taken into account in the analysis of patellofemoral disorders yet. Additional studies are necessary to define the normal value and range of intraarticular rotation (IAR) in healthy patients.