Multiple Hereditary Exostoses of the Forearm video presentation 4/8/09
Biology of Limb Length video presentation 4/02/09
Limb Lengthening Methods video presentation 4/2/09
Multiple Osteochondromas
There are a variety of problems related to the exostoses of Hereditary Multiple Osteochondromas. The
majority of these problems relate to bothersome bony protrusions with their affect on surrounding joints,
muscles, tendons, nerves, blood vessels and skin. Osteochondromas can also affect growth plates and
lead to limb deformities and length discrepancies. The focus of this article will be on the limb deformities
and discrepancies secondary to the multiple osteochondromas.
Lower Limb
Osteochondromas are believed to bud off the growth plates. The cartilaginous cap of the
osteochondroma has the same structure as the growth plate. It grows in length and width in
the same fashion as a growth plate leads to growth in length and width of the end of a bone.
For reasons unknown some osteochondromas tether the growth of the growth plate when
they bud off. This can lead to asymmetric growth (less growth on the osteochondroma side
and more growth on the opposite side of the growth plate) and consequently limb deformity.
This tethering effect can also decrease overall limb growth leading to a shorter final limb length
than expected. If the opposite lower limb is not as affected then the result is a lower limb
length discrepancy (LLD). Although both lower limbs often appear to be equally affected by
osteochondromas, LLD is not uncommon indicating that one side is more tethered at the
growth plate than the other.
The tethering effect of the osteochondroma on growth is directly related to the size of the
growth plate it came from. The larger the growth plate the less effect the osteochondroma
has on longitudinal growth because the force of growth in the remaining healthy part of the
growth plate is so great. The smaller the growth plate the greater is the tethering effect since
the percent of the growth plate involved is so great. Good examples of this are the fibula in
the lower limb and the ulna in the upper limb. We shall discuss the ulna separately below. In
the lower leg where there are two adjacent bones (tibia and fibula), an osteochondroma
tethering the growth of one bone and not the other will lead to a deformity since the two
bones are attached together. Therefore if the fibula is growing slower than the tibia the leg
will grow towards the fibula. This leads to a valgus deformity (knock-kneed) of the upper tibia
and a valgus deformity of the ankle (tilted outward). Osteochondromas between the tibia and
fibula can also lead to deformity of the adjacent bone. For example an osteochondroma of the
distal tibia can lead to deformity of the adjacent fibula near the ankle.
Osteochondromas of the distal femur (lower end of femur near the knee), do not typically lead
to any deformity or length discrepancy on their own. They protrude into the surrounding soft
tissues and can lead to symptoms related to soft tissue impingement due to their bulk. On
occasion they do lead to deformity of the knee which is related to the tethering of soft tissues
and not to bony deformity. For example osteochondromas around the knee can lead to
locking and flexion deformity of the knee joint (the knee joint catches in a certain position and
will not straighten out).
Osteochondromas of the upper femur sprout off the femoral neck. Depending on the
direction they come from they lead to different problems. Commonly they lead to asymmetric
growth of the neck of the femur resulting in a valgus femoral neck (more vertical than usual).
This is usually not a problem. Valgus of the neck of the femur is usually symmetric and
therefore does not lead to a leg length discrepancy. When the osteochondroma is too near
the hip joint or if it expands the capsule of the hip joint, this can result in a hip joint
contracture or subluxation. The typical hip joint contracture is fixed flexion deformity of the
hip from an anterior osteochondroma. Patients present walking leaning forward with
hyperlordosis of the spine (sway back) as they try and compensate for the leaning forward
effect of the hip by arching their back. Subluxation of the hip occurs due to the effect of the
osteochondroma pushing the hip out of joint combined with the effect of the valgus of the
femoral neck. The bigger problem with osteochondromas of the femoral head and neck is
limitation of hip motion and femero-acetabular impingment pain anteriorly and/or posteriorly
depending on the location of the exostoses.
Treatment of the Lower Limb Deformities.
Femero-acetabular impingement
The best way to treat this problem is ‘safe’ surgical dislocation of the hip according to the
technique of Ganz from Switzerland. This safeguards the circulation of the femoral head
avoiding avascular necrosis of the femoral head. The osteochondromas can be resected under
direct vision and the femoral head templated with a spherical template to acertain if the
femoral head is spherical. The range of motion of the hip greatly imporves after this surgery.
It can be combined with a varus osteotomy using a blade plate for fixation.
Valgus Knee Deformity (Knock knee deformity)
This deformity is usually in the upper tibia. There is usually a large osteochondroma involving
the upper end of the fibula. The fibular osteochondroma often tethers or envelops the
peroneal nerve. This is a very important nerve that is responsible for controlling the muscles
that pull the foot up and out. Injury to this nerve results in a drop foot (inability to pull the
foot up). Correction of the valgus deformity of the upper tibia requires an osteotomy (bone
cut) of the upper tibia. All osteotomies of the upper tibia to correct valgus stretch the
peroneal nerve even in patients without HME. In patients with HME and a fibular exostosis the
nerve is very tethered and stretched even before surgery. The nerve can actually be inside
the bone if the osteochondroma envelops it. Therefore to correct the deformity safely the
nerve must first be found above the fibula and decompressed around the neck of the fibula.
The osteochondroma of the fibula should be resected. If the upper fibular growth plate is
considered to be damaged beyond recovery then a segment of the fibula should be removed
so that the two ends of the fibula do not join together again to prevent re-tethering of the
tibia. Only after all of this is performed can an osteotomy of the tibia be carried out safely to
correct the valgus deformity. The valgus deformity can either be corrected all at once or
gradually. Correcting it all at once is usually performed by taking out a wedge shaped piece of
bone and then closing the wedge to straighten the tibia. This can be fixed in place with a
metal plate or with an external fixator. Gradual correction is carried out by minimal incision
technique to cut the bone. The correction is achieved by use of an external fixator. This is a
device that fixes to the bone by means of screws or wires that attach to an external bar or
set of rings. Adjustment of the external fixator slowly corrects the deformity. This opens a
wedge instead of closes a wedge of bone. This has the advantage of adding length to the leg
which if the leg is short already is advantageous. This type of external fixator is also used for
limb lengthening. Therefore if there is a LLD the angular correction can be performed
simultaneous with lengthening. Gradual correction is safer than acute (all at once) correction
for correction of the valgus deformity.
Another way to address the valgus knee deformity without addressing limb length discrepancy
is hemi-epiphyseal stapling of the growth plate. This is perhaps the most minor procedure
possible and involves insertion of one or two metal staples on the medial side (inside) of the
growth plate of the upper tibia. The metal staple straddles the growth zone on the medial side
preventing growth of the medial growth plate while permitting growth on the lateral side. This
allows the tibia to slowly autocorrect its alignment. It is a very slow process and may require
several years. Once the tibia is aligned the staple can be removed permitting resumption of
growth from the medial side. There is a small risk of damaging the medial growth plate which
could lead to a varus bowing deformity of the tibia. Stapling can also be used in the distal tibia
to correct the ankle deformity.
Valgus deformity of the ankle
Patients complain of walking on the outer border of the foot. Viewed from behind this posture
of the foot is very apparent. This deformity is often well tolerated. The lower end of the tibia
tilts outwards towards the fibula. The lower end of the fibula is the lateral malleolus. It is
important for stability of the ankle. Since the fibula grows less than the tibia the lateral
malleolus is often underdeveloped leading to lateral shift of the talus (ankle bone). This can
eventually lead to arthritis of the ankle. Lateral tilt of the ankle joint is compensated by the
subtalar joint (joint under the ankle) by inversion of the foot (turning of the foot in). Since
this is a longstanding process the subtalar joint becomes fixed in this position of
compensation for the ankle joint. Therefore if one tries to fix the ankle joint tilt completely the
foot will end up tilted inwards and the patient will be standing on the outer border of the foot.
Therefore one either has to accept the valgus ankle or correct it together with the subtalar
joint fixed deformity. This is best done with a circular external fixator (Ilizarov device). This
correction involves gradual correction of a minimally invasive osteotomy of the lower tibia and
fibula together with distraction (pulling apart) of the subtalar joint contracture.
Flexion deformity of the knee
This deformity is usually related to tethering or locking of the soft tissues around the knee by
distal femoral or proximal tibial osteochondromas. The treatment involves resection of the
offending exostosis and lengthening of the hamstring tendons if needed.
Flexion deformity of the hip/subluxation of the hip/valgus upper femur
This is treated by resecting the offending osteochondroma of the femoral neck. This hip
capsule has to be opened to access these. At the same time to reduce the hip subluxation
(hip coming out of joint) a varus osteotomy of the upper femur should be done (bending the
femur inwards towards the joint). The bone can be fixed either by an internal metal plate or
an external fixator.
Limb Length Discrepancy
Limb length discrepancy under 2cm is usually not noticeable and does not require treatment.
LLD over 2cm is usually noticed by the individual affected leading to self compensation by
walking on the ball of the foot (toe down) or by tilting the pelvis and curving the spine
(scoliosis). Untreated LLD can lead to lower back pain, and long leg arthritis of the hip. These
take many years to develop. Individuals who compensate for LLD by walking on the ball of the
foot often develop a tight Achilles tendon. The easiest way to treat LLD is by using a shoe
lift. I generally prescribe a shoe lift one cm less than the LLD. Shoe lifts of up to 1cm can be
easily accommodated inside a shoe. Greater than 1cm should be added to the outside of the
shoe. Wearing a shoe lift prevents problems of the back, hip and ankle from developing. LLD
can also be equalized surgically. This can be done by either shortening the long leg or
lengthening the short leg. In children shortening the long limb is achieved by surgically closing
the growth plate of the lower femur or the upper tibia prematurely (epiphysiodesis). This is a
small minimally invasive procedure with few complications. The accuracy of this method
depends on the ability of the surgeon to predict the LLD at maturity and the rate of growth of
the long limb. The accuracy of LLD equalization with this method is ± 1cm. After growth of
the skeleton has ceased (skeletal maturity) epiphysiodesis is no longer an option. Shortening
in adults is carried out by removing a segment of the bone and fixing the bone in place with a
metal rod that is inserted into the marrow cavity (locked intramedullary nail). In the femur this
procedure can be done through very small incisions, and shortening up to 5cm (2 inches) can
be safely achieved. In the tibia this procedure requires bigger incisions and has greater risk
and is usually limited to 3cm (1.25 inches).
Lower limb lengthening is the other way to correct LLD and can be carried out in both children
and adults and at almost any age. To lengthen a limb the bone is cut through a very small
incision (1cm) and then the two ends of the bone are pulled apart at a gradual rate of
1mm/day (1/25 inch/day). Since bone is a living substance it grows new bone to repair the
break. By pulling the bone apart at a gradual rate, we prevent the bone ends from joining
together. Instead new bone if formed in the growing gap between the bone ends. Once the
desired lengthening is achieved the bone is held in place until it joins together. The new bone
that was formed in the gap becomes stronger as calcium accumulates in it. Eventually this new
bone achieves the strength of normal bone. There are various devices that are used for limb
lengthening. The majority of these are external fixators. An external fixator is an external
frame or brace that attaches directly to the bone by means of thin (1.8mm- 1/16”) tensioned
wires or thicker (6mm- ¼”) screws (half-pins). The frame of the fixator is either shaped like a
bar (monolateral fixator: e.g Orthofix, EBI, Wagner, monotube) or has rings and arches
(circular fixator: Ilizarov, Taylor Spatial Frame, Sheffield). More recently these systems have
become hybridized and have elements of both monolateral and circular fixators. The circular
fixators can be attached to the bone by means of wires that go from one side of the limb to
the other passing through the skin on one side, then through the bone and then exiting the
skin on the other side. Wires have much smaller diameters than half-pins and achieve their
strength by being tensioned across the ring, like tensioning a guitar string. Half pins are of
much larger diameter and only pass through the skin on one side. They fix to the bone by
means of a screw-like thread. To lengthen the limb the fixator has a screw mechanism which
allows for small adjustments that pull the bone apart. The bone is pulled apart because the
fixator which is attached to the bone above and below the break in the bone, lengthens as the
screw mechanism is turned. The typical lengthening rate is 1/4mm, 4 times a day, for a total
of 1mm/day. There is even a motorized attachment which can be used for lengthening
(Autogenesis). This lengthens at the same rate of 1mm/day divided into hundreds of small
lengthenings. This may reduce the pain of lengthening. It is also more gentle on the soft
tissues (nerves, muscles) that must stretch and grow as the bone is pulled apart.
The most common complication with external fixator lengthening is superficial pin infection.
This minor complication is to be expected. It is also easily treated by taking oral antibiotics at
the first sign of infection (redness, tenderness, and drainage around a pin site). Deeper
infection of the soft tissues and bone is quite rare, but if it occurs usually requires removal
and possible replacement of the problem pin, IV antibiotics and sometimes surgery to debride
(remove dead tissue) the soft tissue and bone. Other complications include tightness of
muscles which can limit the range of motion of the adjacent joints or even pull the adjacent
joints into a fixed position that interferes with function (e.g. equinus contracture of the ankle
(fixed toe down position) is due to tightness of the Achilles tendon that develops during
lengthening). To prevent problems with joints and muscles it is essential to do daily range of
motion and stretching exercises with physical therapy, and to maintain that stretch by using
foot or knee splints. Sometimes it is necessary to either immobilize a joint by extending the
external fixation across the joint to hold the joint in a functionally good position (e.g. foot
fixation at 90° with tibial lengthening to prevent equinus). In some cases it may be necessary
to surgically lengthen some of the tendons or fascia to prevent or treat contractures (e.g.
Achilles tendon lengthening). Bone complications can also occur. These include too rapid or
too slow bone formation. Too rapid formation (premature consolidation) can prevent further
lengthening and requires rebreaking the bone to continue lengthening. To prevent this the
lengthening rate may have to be increased. Poor bone formation can also occur (delayed
consolidation). This requires more time in the external fixator until the bone is fully healed.
Complete or partial failure of bone formation leads to a bone defect and may require a bone
graft to get the bone to heal.
There are two phases to the lengthening process. The first is the distraction phase when the
bone is being pulled apart at one mm per day. The second is the consolidation phase when
the bone is hardening while it is being held in place by the external fixator. The fixator cannot
be removed until the bone is completely healed. If the fixator is removed before that time the
bone will bend, shorten and/or break. The best way to tell if the bone is fully healed is by x-
ray. Even with x-rays it is not uncommon to misjudge the strength of the bone and remove
the fixator prematurely. In many cases we apply a cast for an additional month of protection
to minimize the risk of refracture. It is better to leave the fixator on an extra month than to
take it off a day too early. Patients are often impatient at this stage and push their doctors to
take the frame off. An experienced limb lengthening surgeon turns a deaf ear to these
frustrations and refuses to remove the frame until the x-rays suggest that the bone is strong
enough that it will not break or bend upon removal. Most of the complications of lengthening
occur during the distraction phase or after removal. Few complications other than pin
infection arise during the consolidation phase.
External fixator lengthening has been the standard for the past one hundred years of the
history of limb lengthening. In the past decade internal lengthening devices have emerged.
These permit gradual lengthening by means of a fully implantable telescopic intramedullary rod
(a metal rod that fits inside the marrow cavity of the bone). While there are several of these
devices in use worldwide, there is only one at present FDA approved in the USA. This is called
the Intramedullary Skeletal Kinetic Distractor (ISKD). It is manufactured by Orthofix, Inc. At
present it is on a limited release with only a small number of surgeons trained to use it and of
those only two centers with a large experience with its use (Baltimore and Orlando). This
device can only be used in patients who are skeletally mature and therefore is not applicable in
growing children. It is also limited in its ability to correct deformities. Nevertheless it
eliminates all of the problems related to the pins of the external fixator, especially pin site
infections, scars and pin site pain. It also reduces the muscle tethering from the pins and
makes the physical therapy easier. The ISKD does present some new problems not
experienced with external fixator lengthening. There is less control of the lengthening rate
and rhythm which can lead to contractures, nerve problems and bone healing problems. In
the femur there is a higher rate of premature consolidation while in tibia there is a higher rate
of delayed consolidation. Some patients experience severe pain at the onset of lengthening
and require an epidural for several days until this pain goes away. All in all however we
consider this a major advance. We have performed over 50 such surgeries with good
success. One has been done for MHE.
Deciding between lengthening and shortening is based on a few factors. Shortening is only
applicable for discrepancies less than 5cm. Shortening is a much smaller procedure while
lengthening is a bigger procedure and longer treatment. Lengthening has a higher
complication rate. Shortening cannot correct deformity on the short leg. Lengthening can
simultaneously correct deformity and length discrepancy. Shortening will decrease the
patients height by the amount of shortening (max 5cm : 2 inches). Lengthening does not
decrease height. Therefore in someone with less than 5cm of LLD and no deformity who is
not short or concerned about the height loss, epiphysiodesis or shortening are good
alternatives for equalization or LLD. Most cases do have associated deformities and therefore
our preference is to perform one operation to simultaneously correct the LLD and the
deformity at the same time.
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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Multiple Exostoses of the Forearm
By Dror Paley, M.D.
|
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
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