Introduction
The forearm consists of two bones (radius and ulna) and six joints (elbow: radio-capitalar and
ulno-humeral; wrist: radio-carpal and ulno-triquetral; radio-ulnar: proximal and distal). Unlike
the relationshipbetween the tibia and fibula in the lower extremity the radius and ulna move
functionally relative to eachother to produce the movement of supination and pronation.
Relative to the elbow they move together(flexion and extension). Although most wrist motion
and stability comes from the articulation between theradius and the carpus, the ulna provides
support for the ulnar side and prevents excessive ulnar deviationof the hand. The relationship
between the radius and the ulna is therefore one of the most functionalrelationships between
any two bones.
Exostosis formation of either bone can easily interfere in the function of the elbow, wrist or
forearmrotation. Since osteochondromas form from the growth plates they are usually found
at the ends of thebones but migrate towards the shaft of the bone with growth.
Ulnar Osteochondromas: osteochondromas most commonly form from the distal growth
plate. Unlikethose of the radius the ulnar exostoses are typically sessile (no stalk) while those
of the radius are oftenpedunculated (on a stalk). The osteochondromas of the ulna often lead
to delayed growth of the ulnarelative to the radius. The radius gradually gets longer than the
ulna. The slower growing ulna tethers thegrowing radius leading to increased tilt of the radius
towards the ulna with increasing ulnar deviation of thewrist. Over time, the discrepant rate of
growth leads to subluxation and then dislocation of the proximal end of the radius (radial
head) from the elbow (radio-capitellar joint). Dislocation of the radial head fromthe joint
causes the upper end of the radius to deform into valgus Occasionally anosteochondroma can
develop from the ulnar side of the proximal radio-ulnar joint. This can also contribute to
dislocation of the radial head by pushing the radial head laterally. The ulna also tends to
develop a bowing similar to the radius and moves into a windswept appearance. This bowing
eliminates the interosseous space thus limiting forearm rotation.
Radial Osteochondromas: osteochondromas from the radius can be divided into those
that protrude towards the ulna and those that don’t. The latter don’t impede supination-
pronation motion, while the former do. The radius and ulna may develop ‘kissing exostoses’
that meet in the interosseous space.
Distal radius deformity: the distal radius has a normal inclination towards the ulna of 23º. In
MHE theslower growing ulna may tether the distal radius on the ulnar side leading to increased
distal radial tilt. This increased tilt appears as ulnar deviation of the hand. With time the carpus
will subluxe ulnarly and proximally.
Proximal radius deformity: the ulnar tether also exerts a dislocating force on the radio-
capitellar joint. As the radial head subluxes it comes to rest against the lateral condyle of the
humerus. To adapt to this chronic position the radial neck may grow into valgus. With time,
the radial head may completely dislocated and protrude posteriorly.
Length discrepancy: The entire forearm is shorter than the other side. The shortening
is predominantly in the ulna. Some shortening is also present in the radius.
Clinical signs and symptoms: Patients are limited in their forearm rotation range of
motion. The wrist is usually ulnarly deviated. There may be a prominence or bump if the radial
head is subluxed or dislocated. This may be tender to being bumped. Elbow flexion and
extension is usually not affected. A flexion deformity of the elbow may be present.
Treatment considerations
Exostoses that are obviously impeding forearm rotation (e.g. kissing exostoses), are usually
resected. It is important to do this via two separate incisions to avoid a cross union between
the radius and ulna.
Lengthening and deformity correction can be performed as the first stage in the absence of
exostoses that limit motion, or as the second stage if exostoses are resected first.
Lengthening Reconstruction Surgery (LRS):
LRS refers to distraction surgery using external fixation to lengthen and correct deformities of
the forearm. The problem in MHE ranges from simple to complex.
Simple cases: In simple cases, the primary deformity is relative shortening of the ulna. The
radial tilt is minimal and does not need to be addressed. There is no subluxation/dislocation
of the radial head. The problem is therefore just shortening of the ulna. If this is left
untreated the secondary deformities of the radius will develop. The treatment is to perform
an isolated lengthening of the ulna. I prefer to do this with a circular external fixator even
though the lengthening is linear. A circular fixator allows simultaneous fixation of the radius to
the ulna. Without fixation of the radius, lengthening of the ulna will transport the radial head
distally. This occurs because of the tough interosseous membrane between the radius andthe
ulna. The osteotomy of the ulna is usually at its proximal end. This allows correction of any
flexion deformity of the ulna (elbow) and leads to faster healing than if the osteotomy is made
through the mid-diaphyseal (middle) section of the ulna.
Complex cases: In more complex cases the surgical plan includes correction of the distal radial
deformity and or radial head dislocation. A circular external fixator is used. Proximally both
the radius and ulna are fixed. The ulnar osteotomy is made proximally and the radial
osteotomy is made distally. This type of frame simultaneously corrects shortening of the ulna
and tilt of the distal radius. If the radial head is dislocated then the treatment is staged. The
first step is to lengthen the ulna with a pin connecting theradius and ulna distally. This
transports the radius distally and reduces the radial head. If the radial head does not reduce
spontaneously then at a second stage surgery the radio-capitellar joint is opened and the
radial head reduced at surgery and is held with an olive wire. If there is both distal radial tilt
and dislocation of the radial head then the radial head is reduced first and then at a second
stage the wire pulling the radius and ulna distally is removed and the distal radius
osteotomized for deformity correction and lengthening.
With staged surgeries many of the deformities of MHE of the forearm can be corrected.
Combined with removal of the obstructing exostoses improved range of motion of forearm
rotation is obtained.
Does hemiepiphysiodesis stapling have a role in MHE? I have no experience with this in the
upper extremity. Theoretically, it should work for the distal radius. We are considering
correction of the distal radial tilt by stapling in combination with overlengthening of the ulna.
Overlengthening of the ulna can helpdelay recurrence. Overlengthening of up to 2 cm is
practical. Fixation of the hand is not required if thelengthening of the radius is less than 3 cm.
Paley 5 step method for forearm correction
Step 1: Resect osteochondromas
Step 2: Correct ulnar bowing to increase interosseous space
Step 3: Correct distal radial tilt
Step 4: Correct length discrepancy between bones
Step 5: Reduce subluxation radial head
Multiple Exostoses
The Forearm
By Dror Paley M.D., FRCSC
Director of the Paley Advanced Limb Lengthening Institute
at
St. Mary’s Hospital in West Palm Beach, Florida.
Dr. Paley was the founder and director of the Rubin Institute for Advanced
Orthopedics and the co-director of the International Center for Limb
Lengthening until May 2009.
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