Patellar malalignment correlates with increased pain and increased synovial stress hormone levels-A cross-sectional study

Abstract

Purpose: Risk factors for the development of pain in the context of knee osteoarthritis (KOA) remain unclear. Radiological findings often do not correlate with clinical findings, so other pathomechanisms in the development and perception of pain must play a role. The purpose of this study is to investigate the correlation of increased sympathetic nervous system (SNS) activity (measured by subjective and objective chronic stress parameters) with KOA severity, patellofemoral malalignment, and pain.

Methods: 47 patients with KOA were assessed. Radiological measurements of tibiofemoral and patellofemoral parameters (Kellgren-Lawrence-score, patellar tilt (PT), Caton-Deschamps-Index and Hepp´s classification) were performed and correlated with knee-specific questionnaires (WOMAC®, KSS©) and chronic stress questionnaires (PSQ-20). Additionally, parameters associated with chronic stress were quantified in synovial fluid and serum samples from patients.

Results: PT correlated significantly with Caton-Deschamps-Index (r = 0.394,p = 0.006) and with medial patellofemoral joint space (r = 0.516,p<0.001). In addition, asymmetric trochlear groove (Hepp's classification > II) was associated with significantly higher PT values (p = 0.014). A negative correlation between PT and KSS©-symptoms subgroup was found (r = -0.340,p = 0.024). Patients with PT<5° had significantly higher scores in the Knee Society Score©-symptoms subgroup (p = 0.038). A positive and significant correlation between synovial aldosterone levels and PT was observed (r = 0.548,p = 0.042).

Conclusion: The results of this study indicate that patellar malalignment might correlate with increased pain. The previous specification of standard PT values must be reconsidered as even low PT values seem to play a role in the occurrence of patellofemoral osteoarthritis symptoms. Lower PT values might lead to aggravated symptoms in patients with KOA due to a narrow medial patellofemoral joint space. In addition, PT might induce the release of synovial stress biomarkers and thus contribute to the progression of KOA.

Fig 1. Radiological parameters determined in this study.

(A) Mechanical femorotibial angle (B) Medial proximal tibial angle (C) Caton-Deschamps-Index (3,52cm/3,26cm) (D) Patellar tilt (E) Medial and lateral joint space width (F) Patellar thickness (G) Sulcus (135°) and facet (139°) angle (H) Patellar displacement.

Fig 2. Hepp’s classification: (Type I) Both condyles are approximately the same height and width and almost equally rounded.

The sulcus lies approximately in the middle of the trochlea. (Type II) The lateral condyle is slightly wider and clearly higher than the medial one. The sulcus depth is shifted somewhat medially. (Type III) Hypoplasia of the medial condyle and hyperplasia of the lateral condyle. The sulcus is flattened and clearly shifted medially. Compared to the lateral condyle, the medial one becomes shorter and flatter. (Type IV) Flattening of both condyles. The lateral condyle is usually slightly longer and higher than the medial one. The sulcus is flat. (Type V) The sulcus is not present. The trochlea is flat and in extreme cases even convex [21].

Fig 3. PT and patellofemoral malalignment parameters.

(A) Scatter diagram of the relationship between PT and CDI. (B) Scatter diagram of the relationship between PT and the medial patellofemoral joint space. (C) Correlation between both Hepp’s Classification system groups (≤ II and > II) and PT. Each black reference point represents an individual patient. Data represent medians with interquartile range.

Fig 4. Correlations of PT and pain.

(A) Scatter diagram of the relationship between PT and KneeSocietyScore©–Symptoms subgroup. (B) Correlation between both groups (PT < 5° and PT ≥ 5°) regarding KneeSocietyScore©—Symptoms subgroup score. Each black reference point represents an individual patient. Data represent medians with interquartile range.

Fig 5. Correlations of PFOA parameters and chronic stress parameters.

(A) Relationship of Kellgren-Lawrence score and PSQ-20 questionnaire results. Patients were divided in 4 groups according to patellofemoral Kellgren-Lawrence score (B) Scatter diagram of the relationship between PT and synovial ALD concentration. Each black reference point represents an individual patient. Data represent medians with interquartile range.