# Knee rotation significantly increases measured tibial tubercle‐trochlear groove distance in female patients with anterior knee pain: Findings after rotational measurement correction

## TL;DR

Knee rotation significantly affects tibial measurements in female patients with knee pain, and correcting for rotation provides more accurate results.

## Contribution

This study demonstrates that correcting for knee rotation significantly improves the accuracy of tibial tubercle-trochlear groove distance measurements in female anterior knee pain patients.

## Key findings

- Knee rotation increases TT-TG distance by ~0.84 mm per degree of rotation.
- Correcting for knee rotation reduces TT-TG distance and improves correlation with tibial-based measurements.
- Rotational correction enhances the relationship between TT-TG and TT-PCL distance and TTL ratio.

## Abstract

To evaluate the influence of knee rotation angle (KRA) on tibial tubercle‐trochlear groove (TT‐TG) distance measured by computed tomography (CT) in female anterior knee pain (AKP) patients. To assess how correcting for knee rotation affects TT‐TG values. To correlate rotational corrected TT‐TG with the tibial tubercle‐posterior cruciate ligament (TT‐PCL) distance and tibial tubercle lateralisation (TTL) ratio.

A retrospective study was performed on 100 consecutive female AKP patients (183 lower limbs) who underwent torsional CT scans. TT‐TG distance was measured and KRA was determined. Rotational‐corrected TT‐TG (RC TT‐TG) values were calculated by neutralising knee rotation. Moreover, TT‐PCL distance and TTL were measured. Two orthopaedic surgeons independently performed all measurements. Spearman correlation and linear regression analyses were used to evaluate the relationship between KRA and TT‐TG changes.

The mean native TT‐TG was 17.22 ± 4.20 mm, mean KRA was 8.81 ± 5.08° and mean corrected TT‐TG was 9.34 ± 4.70 mm. The difference between noncorrected and corrected TT‐TG distance showed a very strong positive correlation with KRA (ρ = 0.934, p < 0.001). Linear regression analysis demonstrated that KRA explained 73.3% of the variability in TT‐TG changes (R² = 0.733), with TT‐TG decreasing by approximately 0.84 mm for each degree of knee rotation. TT‐TG distance showed a moderate positive correlation with TT‐PCL (ρ = 0.515, p < 0.001). In contrast, rotational‐corrected (RC) TT‐TG demonstrated a stronger correlation with TT‐PCL (ρ = 0.644, p < 0.001). The Spearman correlations show a moderate positive association between the normal TT‐TG and TTL (ρ = 0.451, p < 0.001), while the RC TT‐TG exhibits a stronger correlation with TTL (ρ = 0.539, p < 0.001).

Knee rotation is a significant factor affecting TT‐TG measurement. Measuring TT‐TG after correcting knee rotation to neutral provides a more accurate estimation of this measurement. RC TT‐TG correlates more closely with rotation‐independent tibial‐based measurements.

Level IV.

TT‐TG distance increases with knee rotation, while rotational correction reduces it by ~ 0.84 mm per degree, markedly decreasing pathological values.