Background:Degenerative medial meniscus posterior root tears (MMPRTs) are reportedly
associated with medial compartment osteoarthritis and meniscal extrusion
with a displaced gap from the root insertion. However, degenerative MMPRTs
have not yet been clearly classified according to arthroscopic findings.Purpose:To classify degenerative MMPRTs according to the tear gap and to investigate
how the classification could reflect the joint condition properly.Study Design:Cohort study; Level of evidence, 3.Methods:Patients who underwent arthroscopic surgery, performed by a single
orthopaedic surgeon, for degenerative MMPRTs between August 2006 and
February 2017 were included. MMPRTs were classified according to tear
patterns observed during arthroscopic surgery (type 1, incomplete root tear;
types 2-5, complete root tears), with each type further divided by the size
of the tear gap, defined as the degree of tear displacement from the root
(type 2, no gap or overlapped; type 3, gap of 1-3 mm; type 4, gap of 4-6 mm;
type 5, gap of ≥7 mm). We compared preoperative factors, including the
Kellgren-Lawrence (K-L) grade, absolute extrusion, relative percentage of
extrusion (RPE), tear gap on magnetic resonance imaging (MRI), and
mechanical alignment, as well as intraoperative factors, including chondral
wear at surgery, between each MMPRT type.Results:A total of 116 root tears were categorized according to this classification:
type 1, 16.4% (19 knees); type 2, 9.5% (11 knees); type 3, 40.5% (47 knees);
type 4, 25.0% (29 knees); and type 5, 8.6% (10 knees). Chondral wear of the
medial femoral condyle (MFC) (P = .001), K-L grade
(P = .001), meniscal extrusion (P =
.001), and tear gap on MRI (P = .001) showed a tendency to
increase with a higher tear type. Chondral wear (ρ for MFC = 0.388; ρ for
MTP = 0.311), K-L grade (ρ = 0.390), and meniscal extrusion (ρ for absolute
extrusion = 0.500; ρ for RPE = 0.451) showed a moderate correlation with
tear type, whereas tear gap on MRI (ρ = 0.907) showed a strong correlation
with tear type.Conclusion:Our study introduces a new classification based on the tear gap that can
concisely describe a degenerative MMPRT. The classification system
demonstrated that a higher tear type (increasing displacement of the tear
gap in arthroscopic surgery) is associated with higher meniscal extrusion,
severe chondral wear, and greater severity of arthritis.