n Case Report
Identical Osteochondritis Dissecans Lesions
of the Knee in Sets of Monozygotic Twins
Itai Gans, MD; Eric J. Sarkissian, MD; Struan F.A. Grant, PhD; Theodore J. Ganley, MD
abstract
Full article available online at Healio.com/Orthopedics. Search: 20131120-23
Osteochondritis dissecans (OCD) is a focal, idiopathic alteration of subchondral bone
structure with the risk for secondary damage to adjacent articular cartilage and the
development of premature osteoarthritis. The exact etiology of OCD is unknown, although repetitive microtrauma and vascular insufficiency have been previously described. A genetic predisposition has been suggested, but the existing evidence is
sparse. There are multiple case reports of twins and siblings with OCD and a few
large family series in the literature, promoting the theory that OCD may have a genetic
component to its etiology.
This article describes 2 sets of monozygotic twins presenting concurrently with OCD
of their dominant knees, offering further support for a genetic component to the etiology of OCD. Interestingly, in both sets of twins, 1 was left-handed and 1 was righthanded. Both sets of twins had simultaneous presentations and clinical courses, lending support to a genetic element to OCD. The development of the OCD lesion in the
dominant knee of each patient suggests an environmental influence, perhaps due to
repetitive microtrauma and overuse.
Recently, a genome-wide linkage study identified a prime candidate locus for OCD.
However, despite the suggested association, genetic and developmental factors in the
development of OCD remain relatively unstudied. The authors believe monozygotic
twins provide an excellent clinical opportunity for future examination of the role of
familial inheritance in the etiology of OCD.
The authors are from the Department of Sports Medicine(IG, EJS, TJG) and the Center for Applied
Genomics (SFAG), The Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania.
The authors have no relevant financial relationships to disclose.
Correspondence should be addressed to: Theodore J. Ganley, MD, Department of Sports Medicine,
The Children’s Hospital of Philadelphia, Philadelphia, PA 19104 ([email protected]).
Received: April 29, 2013; Accepted: August 20, 2013; Posted: December 13, 2013.
doi: 10.3928/01477447-20131120-23
DECEMBER 2013 | Volume 36 • Number 12
A
B
Figure: Anteroposterior radiograph (A) and sagittal
magnetic resonance image (B) of the osteochondritis dissecans lesion in case 2, twin A.
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n Case Report
O
steochondritis dissecans (OCD)
is a focal, idiopathic alteration of
subchondral bone structure with
the risk for secondary damage to adjacent
articular cartilage and the development of
premature osteoarthritis. These changes
most commonly occur at the medial femoral condyle and can manifest as early articular cartilage separation, partial detachment
of an articular lesion, and osteochondral
separation with loose bodies.1 The etiology
of OCD remains unclear, and no theory regarding the cause of OCD is universally accepted.2 Repetitive microtrauma, secondary
effects associated with vascular insufficiency, avascular necrosis, inherited factors, and
genetic predisposition have been proposed
as causes of OCD.2 Despite the suggested
association, genetic and developmental factors remain relatively unstudied, and few
cases of monozygotic twins with OCD of
the knee have been reported.3-5
This article describes 2 sets of monozygotic twins, each with 1 left-handed and
1 right-handed sibling, with dominantknee OCD of the weight-bearing surface
of the femoral condyles.
Case Reports
Case 1
Seventeen-year-old monozygotic twin
brothers concurrently presented to the
authors’ clinic for evaluation of chronic
knee pain. Twin A, a right-hand–dominant
football player, reported activity-induced
right knee pain and a positive history of
intermittent mechanical symptoms. Twin
B, a left-hand–dominant lacrosse player,
reported left knee discomfort. Neither
twin described a traumatic event prior to
symptom onset. On physical examination,
both twins had positive lateral joint line
and lateral femoral condyle tenderness
to palpation. Both twins had stable knees
with full range of motion, no knee effusions, and no signs of pathological laxity.
Plain radiographs of the affected knees
raised suspicion for lateral femoral condyle OCD. Magnetic resonance imaging
(MRI) of twin A’s right knee demonstrat-
e1560
ed a large OCD lesion
at the weight-bearing
portion of the lateral
femoral condyle with
underlying subchondral cystic changes
and a partial discoid
lateral meniscus. Twin
B’s MRI revealed the
same findings in the
left knee. Based on the
low likelihood of heal1A
1B
ing with conservative
Figure
1:
Anteroposterior
radiograph
(A)
and
sagittal
magnetic
resomeasures in both cases,
nance image (B) of the osteochondritis dissecans lesion in case 2, twin A.
the surgeon and family
agreed to proceed with
surgery.
Arthroscopy of twin A’s right knee transarticular drilling of the OCD lesion
revealed a discoid lateral meniscus with was performed. At 14-month follow-up,
intrasubstance delamination and tearing knee radiographs revealed no osseous aband a large, friable OCD lesion exceeding normalities, and the patient had resumed
2.5×2.5 cm with fractured cartilage frag- all activities.
ments. Twin A underwent a partial menisTwin B, a right-hand–dominant male
cectomy, loose body removal, and autolo- athlete, presented at age 16 years for evalgous chondrocyte implantation to address uation of chronic activity-induced right
the unsalvageable OCD lesion.
knee pain. Physical examination revealed
Arthroscopic evaluation of twin B’s normal range of motion and no tenderleft knee revealed a large (3×3 cm) but ness or effusion. Knee radiographs and
intact OCD lesion as well as a partial MRI revealed a 2.9×2.9-cm OCD lesion
discoid lateral meniscus. A partial lateral at the lateral aspect of the medial femoral
meniscectomy and drilling of the OCD condyle with subchondral cystic changes
lesion were performed. Both twins pro- and irregular overlying cartilage (Figure
gressed without complication at a mini- 2). Arthroscopic transarticular drilling
mum 6-month follow-up.
and bone grafting of the OCD lesion were
performed. At 6-month follow-up, knee
Case 2
radiographs revealed no osseous abnorTwin A, a 14-year-old, left-hand–domi- malities, and the patient had resumed all
nant, multisport male athlete, presented to activities.
the authors’ clinic for evaluation of chronic left knee pain. Findings on physical Discussion
examination were within normal limits,
Osteochondritis dissecans can be incawith full range of motion, no tenderness pacitating, potentially leading to premaabout the knee, and no effusion. Knee ture arthritis and considerable pain.3 The
radiographs and MRI indicated a stable, exact etiology of OCD is unknown, but
intact OCD lesion at the lateral aspect of theories include repetitive microtrauma,
the medial femoral condyle (Figure 1). vascular insufficiency, avascular necrosis,
A 6-month trial of nonoperative therapy inflammation, and genetic predisposiconsisting of activity modification, brac- tion.2,4
ing, and physical therapy did not improve
Previously, 3 cases of monozygotic
the patient’s symptoms. Arthroscopic twins with OCD lesions of the knee were
ORTHOPEDICS | Healio.com/Orthopedics
n Case Report
asymptomatic
men,
Nielsen8 noted OCD
in 4.1% of those studied. In addition, 14.6%
of the male relatives of affected men
showed unmistakable
radiographic evidence
of OCD, providing
strong evidence for a
genetic component to
2A
2B OCD. Reports of faFigure 2: Anteroposterior radiograph (A) and sagittal magnetic reso- milial OCD have been
nance image (B) of the osteochondritis dissecans lesion in case 2, twin B.
described by many
others.9-11 Lee et al12
reported 10 cases of
reported by Mackie and Wilkins,3 Mei- bilateral femoral head OCD within a
Dan et al,4 and Onoda et al.5 The current 3-generation family, concluding a likely
authors report the development of OCD in genetic influence. In addition, many re2 sets of monozygotic twin brothers with ports on 3- to 5-generation familial cases
near-simultaneous onsets and parallel of OCD exist,13-15 all with a seemingly
clinical courses. One set of monozygotic autosomal-dominant mode of inheritance
twins presented with both OCD of the lat- with fairly high penetrance. Furthermore,
eral femoral condyle and discoid lateral OCD has been reported to have a high asmenisci. An association between discoid sociation with genetic syndromes, includlateral meniscus and OCD of the lateral ing Stickler’s syndrome,16,17 familial short
femoral condyle has previously been stature,14 and endocrine disorders.18
shown.6 Of particular interest, both sets
More recently, genetic linkage assays
of monozygotic twins in the current re- have demonstrated a few polymorphisms
port had 1 left-handed and 1 right-handed associated with the development of OCD.
twin, with the dominant knee affected in Jackson et al19 identified a mutation in
all cases. The simultaneous presentations COL9A2, located in an exon splice site,
and clinical courses suggest a genetic in- which was found to be associated with
fluence to the disease process, whereas the OCD lesions in 2 unrelated families. In
laterality of the OCD lesions locating to 2010, Stattin et al20 conducted a genomethe dominant knee suggests a component wide linkage study and identified aggreof environmental influence, perhaps sec- can (ACAN) as a prime candidate locus
ondary to microtrauma.
for OCD.
In 1977, Petrie7 conducted a study of
The current literature regarding the ge34 patients with OCD to establish the inci- netic nature of OCD is mostly low evidence of OCD in symptomatic first-degree dence and still lacking. Future higherrelatives. Of 86 symptomatic first-degree quality studies must be conducted to derelatives analyzed clinically and radio- termine the extent of a genetic relationgraphically, only 1 had OCD. Petrie7 con- ship in the etiology of OCD. The current
cluded that genetic causation could not be article described 2 sets of monozygotic
established in OCD. However, many cases twins developing OCD lesions of the
of OCD are asymptomatic, and Petrie7 knee. Both sets of twins presented with
only analyzed symptomatic relatives, in- similar complaints and were found to have
troducing the potential of selection bias.
similar OCD lesions on the weight-bearIn a series of 1000 radiographs of ing surface of their dominant knees. The
DECEMBER 2013 | Volume 36 • Number 12
authors believe that monozygotic twins
offer an excellent opportunity to examine
the possibility of a genetic predisposition
for OCD.
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ORTHOPEDICS | Healio.com/Orthopedics