The oblique popliteal ligament: an anatomic and MRI investigation.
OBJECTIVE
Despite being the largest ligament on the posterior aspect of the knee, relatively little is known about the normal morphology of the oblique popliteal ligament (OPL). The aim of this study was to investigate the detailed anatomy of the OPL in cadavers and healthy volunteers.


METHODS
The posterior knee was investigated in 25 cadaver lower limbs (mean age 76 ± 9.5 years; 7 men) by dissection, histology, and serial plastination and in 14 healthy individuals (mean age 23 ± 3.2 years; 11 men) using magnetic resonance (MR) imaging. OPL morphology, attachments sites, ligament length and width, relationship to surrounding structures and histological composition were recorded. Intraobserver reliability was assessed using intraclass correlation coefficients.


RESULTS
The OPL is a distinct expansion of the semimembranosus (SM) tendon and sheath, which courses superolaterally to attach to the posterolateral joint capsule or fabella (when present), at the medial margin of the lateral femoral condyle. The ligament blends with the joint capsule medially and laterally, serves as an attachment site for plantaris, and has connections with popliteus. In 70% of dissections, the OPL divided into two bands, separated by small branches of the middle genicular neurovascular bundle that pierced the posterior joint capsule. Differences in mediolateral length were noted between dissection and MR imaging (43.6 ± 6.2 vs. 57.6 ± 4.4 mm; p < 0.001). At its medial and lateral attachments, the OPL was 23.2 ± 6.9 and 17.4 ± 8.7 mm wide (proximodistal), respectively. The OPL was predominantly composed of transverse collagen layers, with little elastin. While visible on axial MR scans, delineation of its most lateral extent was difficult. Repeatability of selected measurements ranged from good to almost perfect.


CONCLUSIONS
The OPL is a distinct ligament with identifiable anatomical limits. Based on its morphological characteristics, it appears more tendinous than ligamentous in nature. A better understanding of the OPL may help define its importance in the assessment and treatment of posterior knee injuries.
Department of Anatomy, University of Otago, PO Box 913, Dunedin, 9054, New Zealand.
Mandy
M
Hedderwick
Department of Anatomy, University of Otago, PO Box 913, Dunedin, 9054, New Zealand.|Paediatrics and Child Health, University of Otago, Wellington, New Zealand.
Mark D
MD
Stringer
Department of Anatomy, University of Otago, PO Box 913, Dunedin, 9054, New Zealand.
Liam
L
McRedmond
Pacific Radiology Group, Dunedin, New Zealand.
Grant R
GR
Meikle
Department of Anatomy, University of Otago, PO Box 913, Dunedin, 9054, New Zealand. stephanie.woodley@otago.ac.nz.
Stephanie J
SJ
Woodley
D000368:Aged; D059925:Anatomic Landmarks; D002102:Cadaver; D004210:Dissection; D064368:Healthy Volunteers; D006652:Histological Techniques; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D008023:Ligaments, Articular / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D015203:Reproducibility of Results; D055815:Young Adult
Dissection; Immunohistochemistry; Knee; MRI; Oblique popliteal ligament; Plastination