Exploring Anatomo-Morphometric Characteristics of Infrapatellar, Suprapatellar Fat Pad, and Knee Ligaments in Osteoarthritis Compared to Post-Traumatic Lesions

Abstract

Several studies have investigated cartilage degeneration and inflammatory subchondral bone and synovial membrane changes using magnetic resonance (MR) in osteoarthritis (OA) patients. Conversely, there is a paucity of data exploring the role of knee ligaments, infrapatellar fat pad (IFP), and suprapatellar fat pad (SFP) in knee OA compared to post-traumatic cohorts of patients. Therefore, the aim of this study was to analyze the volumetric and morphometric characteristics of the following joint tissues: IFP (volume, surface, depth, femoral and tibial arch lengths), SFP (volume, surface, oblique, antero−posterior, and cranio−caudal lengths), anterior (ACL) and posterior cruciate ligament (PCL) (volume, surface, and length), and patellar ligament (PL) (volume, surface, arc, depth, and length). Eighty-nine MR images were collected in the following three groups: (a) 32 patients with meniscal tears, (b) 29 patients with ACL rupture (ACLR), and (c) 28 patients affected by end-stage OA. Volume, surface, and length of both ACL and PCL were determined in groups a and c. A statistical decrease of IFP volume, surface, depth, femoral and tibial arch lengths was found in end-stage OA compared to patients with meniscal tear (p = 0.002, p = 0.008, p < 0.0001, p = 0.028 and p < 0.001, respectively) and patients with ACLR (p < 0.0001, p < 0.0001, p = 0.008 and p = 0.011, respectively). An increment of volume and surface SFP was observed in group b compared to both groups a and c, while no differences were found in oblique, antero−posterior, and cranio−caudal lengths of SFP among the groups. No statistical differences were highlighted comparing volume, surface, arc, and length of PL between the groups, while PL depth was observed to be decreased in end-OA patients compared with meniscal tear patients (p = 0.023). No statistical differences were observed comparing ACL and PCL lengths between patients undergoing meniscectomy and TKR. Our study confirms that IFP MR morphometric characteristics are different between controls and OA, supporting an important role of IFP in OA pathology and progression in accordance with previously published studies. In addition, PL depth changes seem to be associated with OA pathology. Multivariate analysis confirmed that OA patients had a smaller IFP compared to patients with meniscal tears, confirming its involvement in OA.

Keywords: anterior cruciate ligament rupture; infrapatellar fat pad; knee; magnetic resonance; meniscal tear; osteoarthritis; patellar ligament; posterior cruciate ligament; segmentation; suprapatellar fat pad.

Figure 1

(a) IFP (green area), SFP (yellow area), PCL (cyan area), ACL (fuchsia area), and PL (violet area) masks on the central sagittal slice and (b) volumes identification on MR of all the tissues analyzed. IFP: infrapatellar fat pad, SFP: suprapatellar fat pad, ACL: anterior cruciate ligament, PCL: posterior cruciate ligament, PL: patellar ligament, MR: magnetic resonance.

Figure 2

(a) Definition of IFP depth, femoral and tibial arch lengths in the central slice. (b) Definition of antero–posterior (A–P), cranio–caudal (C–C), and oblique (OBL) lengths for the SFP in the central slice, with the definition of SFP arch length on the transversal slice. (c) Definition of PCL and (d) ACL lengths on two different sagittal slices. (e) Definition of PL depth and length on the central sagittal slice and (f) PL arch length on the transversal slice. IFP: infrapatellar fat pad, SFP: suprapatellar fat pad, ACL: anterior cruciate ligament, PCL: posterior cruciate ligament, PL: patellar ligament.

Figure 3

IFP morphometric characteristics in patients with meniscal tear, ACLR, and end-stage OA. (a) IFP volume, (b) IFP surface, (c) IFP depth, (d) IFP femoral arch, and (e) IFP tibial arch. Data are expressed as median and interquartile range. IFP: infrapatellar fat pad. ACLR: anterior ligament cruciate rupture.

Figure 4

SFP morphometric characteristics in patients with meniscal tear, ACLR, and end-stage OA. (a) SFP volume, (b) SFP surface, (c) SFP OBL, (d) SFP C–C (e) SFP A–P, and (f) SFP arch. Data are expressed as median (interquartile range). SFP: suprapatellar fat pad. ACLR: anterior ligament cruciate rupture. SFP= suprapatellar fat pad. OBL: oblique length. C–C: cranio–caudal length. A–P: antero–posterior length.

Figure 5

ACL and PCL morphometric characteristics in patients with meniscal tear, ACLR, and end-stage OA. (a) ACL volume, (b) ACL surface, (c) ACL length, (d) PCL volume, (e) PCL surface, and (f) PCL length. Data are expressed as median (interquartile range). ACL: anterior cruciate ligament. PCL: posterior cruciate ligament. ACLR: anterior ligament cruciate rupture.

Figure 6

PL morphometric characteristics in patients with meniscal tear, ACLR, and end-stage OA. (a) PL volume, (b) PL surface, (c) PL length, (d) PL depth, and (e) PL arc. Data are expressed as median (interquartile range). PL: patellar ligament. ACLR: anterior ligament cruciate rupture.

Figure 7

Spearman correlations among the variables. (a) all patients, (b) meniscal tear patients, (c) ACLR patients, and (d) end-stage OA patients. Negative correlations are displayed in red color, while positive correlations are in blue. The color intensity and the size of the circle are proportional to the correlation coefficients. ACLR: anterior ligament cruciate rupture.