Surgical Technique
for the
CMI
Carpo Metacarpal Implant
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CONTENTS
INTRODUCTION
A.
B.
C.
FEATURES OF CMI
1.
Unipolar prosthesis
2.
Bone saving
3.
Anatomical metacarpal stem
4.
Press-fit implant
5.
Angled and offset head
INDICATIONS
INSTRUMENTATION
p.3-4
p.5
p.6-7
p.8
p.9
p.10
p.11
p.12
SURGICAL TECHNIQUE
A.
C.
D.
E.
F.
G.
SURGICAL APPROACH
METACARPAL PREPARATION
TRAPEZIUM PREPARATION
IMPLANT SELECTION
LIGAMENTOPLASTY
p.13-14
p.15-16
p.17-19
p.20
1.
APL strip dorsalisation
2.
Distal ECRL strip transfer
p.21-22
p.23-24
p.25
WOUND CLOSURE
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INTRODUCTION
The CMI trapezometacarpal resurfacing implant is designed to
restore strength, mobility, and long-term stability to the failed or
deficient trapezometacarpal joint.
Unlike the trapezometacarpal prosthesis, its
unipolar design and straight-forward surgical
procedure allow achievement of a near
anatomical joint function.
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FEATURES
1. Unipolar prosthesis – no trapezium insert
2. Short metacarpal bone resection
3. Press-fit implant
4. Anatomical metacarpal stem
5. Angled and offset head for better stability
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FEATURES
Unipolar prosthesis
No trapezium insert
Metacarpal resurfacing only
Anatomic design
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FEATURES
Bone saving
Minimal resection of M1

3.5 mm resection of the first Metacarpal (from 7 to 10 mm for a
trapezometacarpal prosthesis)

This technique allows other surgical alternatives in case of failure

Preservation of the thumb height
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FEATURES
Bone saving
The trapezium is not resected but milled. The procedure leads to the
local milling of the arthrosic part of the trapezium (only 1-2 mm deep)
Bone saving compared to a trapezometarcarpal
prosthesis
No risk of trapezium fracture or trapezial
component migration.
Preservation of the thumb height
Maximal congruence of trapezometacarpal joint
Optimal partition of load on the trapezium
Flat trapezium milling stay possible
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FEATURES
Anatomical metacarpal stem
The ovoid Pyrocarbon Stem fits well in M1 thanks to its anatomical
design
• The CMI implant is stable. It
does not rotate inside the
diaphysis
•Optimal partition of load
inside M1 diaphysis
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FEATURES
Press-fit stem
The Pyrocarbon stem is impacted into the M1 shaft (press-fit) and does
not require any cement
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FEATURES
Angled and offset head
The CMI Head is angled and offset to respect the metacarpal
anatomy
Maximum congruence between the trapezium and the CMI implant
Prevents M1 subluxation
1 mm
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INDICATIONS
TMC degenerative arthritis
POST OPERATIVE X-RAY
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INSTRUMENTATION
2
1
2
1
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SURGICAL APPROACH
A dorsal or dorso-radial approach is used. The trapezometacarpal joint
is exposed. Care must be taken to avoid the palmar cutaneous
branch of the median nerve and of the extensor pollicis brevis (EPB).
The superficial branches of the median nerve are then gently
dissected and the tendons are retracted to identify the joint line.
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SURGICAL APPROACH
The capsule is incised longitudinally, while preserving as much as
possible of the articular capsule, scraping M1 base with a periosteal
elevator.
Osteophytes should be removed.
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METACARPAL PREPARATION
Insert the M1 cutting guide into the trapezometacarpal joint.
The cutting guide is used to establish a 3.5 mm resection.
M1 should be maintained in compression against the cutting guide.
The cutting guide accepts saw blades with a maximal thickness of 0.5
mm and maximal breadth of 10 mm.
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METACARPAL PREPARATION
Prepare the metacarpal bone shaft by introducing the broaches centred
on the previous resection. A mark on the instrument indicates the dorsal
side and allows correct orientation of the implant. Press fit of final implant
will be ensured using the biggest broach size that fits the bone shaft.
To make the impaction and extraction of the broaches in the bone shaft
easier, use the extractor screwed on the broach handle.
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TRAPEZIUM PREPARATION
The metacarpal trial corresponding to
the broach is introduced, ensuring its
correct position thanks to its dorsal
mark. Locate the contact point of the
trial on the trapezium, thumb in neutral
position.
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TRAPEZIUM PREPARATION
 Remove the trial.
 With a sharp awl, perform a hole located
in the previous targeted area.
 Insert the reamer in the joint space and
place the reamer central pin into the
hole.
 Prepare the implant head socket by
milling the trapezium arthrosed part using
the powered CMC reamer (low speed).
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TRAPEZIUM PREPARATION
A good axial compression will be maintained with the CMC
reamer handle, and also a good compression on the trapezium,
which should be strongly maintained. The joint is irrigated and
cleared of debris.
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IMPLANT SELECTION
Re-insert the trial and check with X-ray, that the trapezium
socket is sufficient to ensure, in conjunction with a
ligamentoplasty, the joint stability.
Control by X-rays
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LIGAMENTOPLASTY part 1 : APL strip dorsalisation
A distal insertion of the Abductor Pollicis Longus (APL) is reinserted
dorsally. The insertion must be advanced distally on the metacarpal
and strongly anchored through the bone on the middle of M1. Do not
tighten to allow definitive implant insertion.
EPL Extensor
Pollicis Longus
Transfered
APL
Radial Bundle
EPB Extensor Pollicis
Brevis
ECRL Strip
Extensor Carpi Radialis Longus
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LIGAMENTOPLASTY part 1 : APL strip dorsalisation
The final implant is then implanted ensuring
its correct orientation thanks to the implant
holder.
Impact the final implant with the plastic
impactor.
Warning
• No other instrument should be used for
impaction to avoid bearing surface
alteration or damage.
• Close the capsule and pull to apply some
tension on the dorsalised APL.
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LIGAMENTOPLASTY part 2 : Distal ECRL strip transfer
Take a strip of the Extensor Carpi Radialis Longus (ECRL), preserving
its distal insertion ; transfer the strip beneath the radial bundle and
the Extensor Pollicis Longus (EPL). Thus this strip comes to double the
capsule over the transfered APL.
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LIGAMENTOPLASTY part 2 : Distal ECRL strip transfer
This ECRL strip is finally inserted with some tension on the radial side of
M1, trying to insert it as palmar as possible in order to favour thumb
pronation.
Transfered APL
EPL Extensor
Pollicis Longus
Transfered
APL
Radial Bundle
ECRL strip
EPB
EPB Extensor Pollicis
Brevis
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ECRL Strip
Extensor Carpi Radialis Longus
24
WOUND CLOSURE
Closure over a suction drain and immobilization in a "resting position“
for 3 to 4 weeks.
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In Australia contact Orthopaedic Solutions at
www.orthopaedicsolutions.com
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