Forearm Osteotomy for Multiple Hereditary Exostoses

 

 

 

DEFINITION

Multiple hereditary exostoses (MHE), first described by Boyer3 in 1814, is a familial disorder with an autosomal dominant mode of inheritance exhibiting very high penetrance and variable expressivity.12 Also known as multiple osteochondromatosis, multiple osteochondromata, multiple cartilage exostoses, diaphyseal aclasis, or metaphyseal aclasis5, 23

 

 

ANATOMY

 

Knowledge of the normal anatomy and biomechanics of the forearm in the immature individual is instrumental in understanding the pathogenesis of the deformity and ultimately in planning appropriate treatment.

 

During forearm pronation-supination, the relationship between the radius and ulna changes. This rotational movement requires near-anatomic alignment of both as well as integrity of the proximal and distal radioulnar joints and the interosseous membrane. Minimal axial or rotational bone deformity, asymmetric bone shortening, or ligament instability can hinder this function.

 

The ulna acts like a swivel hinge around which the radius rotates. The axis of forearm rotation is oblique.

 

PATHOGENESIS

 

The most common genetic mutations are in the EXT-1 and EXT-2 genes.6

 

 

Approximately 10% of individuals with manifestations of multiple exostoses have no family history of MHE.22 The prevalence of MHE in the general population is estimated to be at least one in 50,000, with a median age of first diagnosis of 2 to 3 years of age (exostoses rarely develop before age 2 years).22 An average of five or six

exostoses, involving both upper and lower extremities, is found at the time of the first consultation.9

 

 

The presence of exostoses is almost always evident by the age of 12 years.

 

Osteochondromas develop at numerous sites in the immature skeleton, they may affect any bone except the skull. They most commonly affect the ends of long bones and flat bones including the scapula and pelvis.

 

Osteochondromas consist of a base or stalk covered by a cartilaginous cap. They arise from the peripheral aspect of the growth plate of bones that undergo endochondral ossification.14

 

They are the product of abnormal proliferation of chondroblasts and subsequent defective remodeling of the metaphysis. This leads to the two main characteristics of this condition: skeletal metaphyseal exostoses and retardation of longitudinal bone growth.

 

They migrate away from the physis with longitudinal growth.14

 

In MHE, the exostoses vary greatly in number, location, size, and configuration. They tend to have a more irregular and bizarre shape than solitary osteochondromas.

 

 

Should always be continuous with the medullary cavity of the bone from which they arise

 

 

Once skeletal maturity is reached, the lesions will become quiescent.22 Lesions that enlarge after skeletal maturity should be investigated to exclude malignant change.

 

NATURAL HISTORY

 

Deformity of the forearm is seen in 30% to 60% of the individuals with MHE.22 The forearm deformities can be progressive and result in a variable amount of weakness, pain,4 functional limitation, and aesthetic deformity.

 

The deformities are almost always accompanied by discrepancy in length between the two bones. Asynchronous longitudinal growth between paired bones leads to a greater risk of anatomic distortion. Most

of the longitudinal growth of the ulna occurs at the distal physis,15 which is also the more commonly affected physis (30% to 85% of the cases).22, 23

 

The affected ulna typically remains relatively shortened and curved, and this often leads to significant bowing of the radius. When the ulna is shorter, the ulnar-sided soft tissue acts as a tether, causing bowing of the radius. In addition, the local presence of the exostosis itself causes radial bowing by disturbing hemiepiphy-

seal growth.15

 

A serious risk associated with MHE is the potential for malignant transformation of an exostosis into chondrosarcoma. This can occur at any age, but it is exceedingly rare during childhood.22

 

Patients affected by MHE have a normal life expectancy unless malignant degeneration and metastasis develop.9 The risk of malignant degeneration in adults with MHE has been reported to range from 0.57% to 5%.12, 22, 31

 

MHE can have a serious influence on the quality of life of affected individuals, affecting sporting participation, occupation, and daily activities.8

HISTORY AND PHYSICAL FINDINGS

 

The diagnosis is rarely difficult as 90% of affected individuals have a positive family history, and therefore initial history taking should focus on the symptoms and functional impairment that exist.

 

 

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FIG 1 • A. Significant ulnar deviation of the wrist, which can also be present in these patients. B,C. The patient has limited pronation and supination. D. Obvious radial head dislocation, reported. E. Patient with severe involvement of the left forearm.

 

 

Physical examination of the upper extremity should assess for location of disease burden and common associated findings.

 

 

It is a common finding that the deformity is quite asymmetric. One forearm may be heavily affected, whereas the other relatively spared.

 

Shortening of the forearm, specifically relative shortening of the ulna, increased radial bow and possible radial head dislocation.

 

A mild flexion deformity of the elbow is often present.

 

At the wrist level, an increased ulnar tilt of the radial epiphysis, ulnar deviation of the hand, and progressive ulnar translocation of the carpus are often present. These deformities can lead to a loss of radial deviation of the hand and loss of pronation-supination of the forearm (FIG 1).

 

The loss of forearm pronation-supination may develop early and become progressively more severe as the child

ages.26 Pronation-supination may be limited due to altered mechanical alignment, osteochondroma blocking motion, or radial head dislocation. The greater the number of osteochondromas and shorter the ulna, the greater the loss of motion.10, 32

 

Radial head dislocation is reported to occur in 22% of the affected forearms.23 It may present as pain, a mass on the lateral side of the elbow, altered carrying angle, decreased elbow range of motion or decreased pronation-supination, or catching.

 

It is possible to have neurologic impingement from either direct compression by an osteochondroma or through deformity including radial head dislocation.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Plain radiographic evaluation is usually sufficient to confirm the diagnosis and to determine the number, location, and morphology of the exostoses (FIG 2).

 

Like solitary osteochondromas, the exostoses may be described as sessile or pedunculated; they nearly always point away from the physis, however in the hand they may not. In MHE, the lesions tend to be larger and have a more bizarre shape (see FIG 2).

 

At least two full views of the forearm (true anteroposterior and lateral containing both the elbow and the wrist) are necessary to properly assess the ulnar variance, the radial articular angle (RAA), the carpal slip, and the

relative radial bow. These radiographic measurements are useful in the surgical planning phase (FIG 3).2

 

 

 

FIG 2 • Radiographs showing large osteochondroma of distal ulna affecting the epiphysis and causing significant tethering of the radius. Characteristically, the distal ulna is narrow with a pointed end.

 

 

P.684

 

 

 

FIG 3 • The RAA and carpal slip (CS). A. The RAA is defined as the angle between a line running along the articular surface of the radius and another line that is perpendicular to a line joining the center of the radial head to the radial border of the distal radial epiphysis (the radial styloid in skeletally mature individuals). The normal range of the angle is 15 to 30 degrees. B. CS is measured by determining the percentage of the lunate that is in contact with the radius. First, a line is drawn from the center of the olecranon through the ulnar border of the

radial epiphysis (the radial articular surface in skeletally mature individuals).1 This line normally bisects the lunate. An abnormal CS is defined as being present when ulnar displacement of the lunate exceeds 50%. (Adapted from Akita S, Mursae T, Yonenobu K, et al. Long-term results of surgery for forearm deformities in patients with multiple cartilaginous exostoses. J Bone Joint Surg Am 2007;89:1993-1999.)

 

 

Alterations of the radial head on radiographs must always be assessed. They range from flattening to subluxation and complete radial head dislocation.

 

Masada et al15 morphologically classified the involvement of the forearm in MHE into three types ( FIG 4). This classification is also used for treatment planning.

 

Computed tomography (CT), magnetic resonance imaging (MRI), and magnetic resonance angiography are performed at times for specific and symptomatic lesions. These can be especially helpful to detail the anatomic

position relative to soft tissue structures or when malignant transformation is suspected.27

 

 

 

FIG 4 • Masada classification of the involvement of the forearm in MHE. (Adapted from Masada K, Tsuyuguchi Y, Kawai H, et al. Operations for forearm deformity caused by multiple osteochondromas. J Bone Joint Surg Br 1989;71:24-29.)

 

 

In older children and teenagers, irregular areas of calcification of the cartilaginous cap may be present. Extensive calcification with changes in the shape, thickness of the cartilaginous cap, or a lesion enlarging more rapidly than the growth of the child should raise suspicion of possible chondrosarcoma transformation.

 

 

DIFFERENTIAL DIAGNOSIS

Langer-Giedion syndrome Madelung deformity Chondrosarcoma

 

 

NONOPERATIVE MANAGEMENT

 

Patients with MHE can often be managed successfully using a conservative approach.

 

 

Exostoses alone can often be surprisingly well tolerated and result in minimal loss of function.26 It has been reported that forearm function in untreated adults with MHE is subjectively greater than the one objectively

measured.17

 

The conspicuous number of lesions and the fact that they are mostly asymptomatic warrant a cautious surgical approach.

 

A dislocated radial head that is not symptomatic should be left alone.

 

Attempts at relocating a dislocated radial head have been unsuccessful.2, 19

 

SURGICAL MANAGEMENT

 

Surgical treatment of forearm deformities in MHE remains controversial. A number of operative techniques have been proposed.5, 10, 15, 20, 24

 

The main surgical indications are to

 

 

Improve forearm function (pronation-supination)2

 

 

Relieve pain from external trauma or irritation of the surrounding soft tissue4 Improve appearance10

 

Exclude malignancy when there is a rapid increase in size of a lesion18

 

When evaluating the surgical indications in an individual patient, it is important to distinguish between the functional deficit and the cosmetic appearance.

 

 

The postoperative appearance of the forearm has been shown to be unrelated to the functional outcome.17

 

Despite many maintaining good function even without treatment,2, 17 a percentage of patients find the

appearance of the shortening, angulation, and deformities unacceptable.17 If surgery is being undertaken for aesthetic rather than functional purposes, the hopes, concerns, and expectations of patient and parents must be thoroughly discussed and accurately outlined.

 

 

A mass or deformation may be removed; however, a scar shall be added.

 

Restoration of range of motion and improvement of radiographic parameters are unpredictable but may occur.2, 11

 

 

Some5, 15, 18 advocate an aggressive approach based on the rationale that forearm deformities may lead to functional impairment especially if radial head dislocation occurs.2, 26

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Surgical treatment employed includes excision of the exostoses and ulnar lengthening and associated radial osteotomy when indicated.

 

 

Radiographic indications cited include relative ulnar shortening (with or without bowing) of more than 1.5 cm, RAA of greater than 30 degrees, carpal slip of more than 60%, and bowing of the radius or the ulna (or

both).5

 

Predication of radial head dislocation has remained one of the most difficult aspects of MHE forearm care.

 

 

The most common association with radial head dislocation is isolated distal ulnar osteochondromas.7

 

However, our approach reflects that the presence of forearm deformities alone is relatively unrelated to functional impairment,2, 17, 26 and therefore we do not recommend surgical correction of the deformities only to prevent a possible, but not predictable, future functional impairment.

 

Symptomatic dislocation of the radial head is an indication for surgical intervention when it interferes with joint motion or causes significant pain.

Procedures

 

Exostosis excision alone is indicated when a lesion becomes symptomatic or when it directly causes limitation of forearm pronation-supination.

 

 

This procedure alone does not necessarily correct the forearm deformity. Excision of a distal ulnar osteochondroma may lead to remodeling of the radius.11

 

Ulnar tether release is indicated when there is significant wrist deformity present secondary to ulnar

shortening.

 

When the distal epiphyseal plate of the ulna has lost its growth potential and resultant significant radial bowing exists, extensive ulnar tether release is our preferred technique to improve wrist position and potentially decrease the risk of radial head subluxation/dislocation. Lengthening may temporarily level the joint; however, the physis will not provide growth and recurrent deformity is common.

 

May be combined with osteochondroma excision or radial osteotomy

 

If the patient has significant growth potential remaining, ulnar tether release alone can lead to radial correction.

 

Ulnar lengthening with or without radial osteotomy remains a common procedure.

 

Acute10, 30 and gradual1, 13, 16, 20, 28 lengthenings have been used.

 

Ulnar lengthening levels the joint and relieves tension on the ulnar-sided soft tissues.

 

Anatomic structure, alignment, and potential for remodeling of the DRUJ needs to be considered prior to lengthening the ulna.

 

Lengthening will not restore growth to the distal ulna, the remaining growth potential and possible recurrence of deformity needs to be considered.

 

There are incumbent risks associated with lengthening procedures. The risks and benefits must be considered. The time to union or consolidation of bone regenerate is commonly 2 to 3 months.

 

Radial osteotomy is performed in the skeletally mature or nearly skeletally mature patient.

 

 

Significant remodeling of the radius is unlikely in the older patient. Radial osteotomy acutely corrects the radial deformity.

 

Combination with osteochondroma excision and ulnar-sided procedures is common.

 

Consider staging procedures if the level of surgery is similar on the radius and ulna to minimize the risk of synostosis or loss of correction.

 

Distal radial hemiepiphysiodesis with stapling has been used in the past.15, 25 It has not gained widespread use.

 

Treatment for symptomatic radial head dislocation is usually limited to salvage procedures.

 

Surgical excision may be performed once the patient is skeletally mature. Excision before this time may lead to instability, growth disturbance, and possible worsening of the wrist or elbow deformity.

 

Formation of a single-bone forearm has been successfully used in the skeletally immature and skeletally mature patient.19, 21, 29

 

In rare instances, exostosis excision with osteotomy or ulnar lengthening may be effective in relocating the radial head.16

 

 

 

TECHNIQUES

• Exostosis Excision and Ulnar Tethering Release

   

  The location of the incision in the distal forearm varies depending on where the osteochondroma is located. Planning of this is important, as the ability to access the distal ulna is imperative whether the osteochondroma is located on the distal ulna or radius.

   

  If the patient has ulnar involvement only, the incision can be placed on the subcutaneous border of the ulna between the flexor carpi ulnaris and the extensor carpi ulnaris (ECU). Care must be taken to identify and preserve the dorsal branch of the ulnar nerve.

   

  If the patient has osteochondroma of both the radius and ulna, the incision has to be modified to allow exposure of both bones as well as the distal ulna.

   

  A tourniquet of appropriate size is used.

   

  Once the initial incision is made, the soft tissues are cleared from around the base, and the osteochondroma is carefully exposed and excised, ensuring that the cartilage cap is not breeched.

   

  If near the physis, resection should proceed from the base nearest the physis and away from it (TECH FIG 1). Care must be taken to preserve satisfactory bony cortex for stability.

   

  Bone wax is applied to the base of the resected osteochondroma to minimize bleeding and potential for bone regrowth.

   

  Next, the distal ulna is exposed and the ulnar tethering force is released.

   

  This is usually done by transecting the distal ulna through the ulna styloid or epiphyseal area, leaving the triangular fibrocartilage complex attached to the distal fragment.

   

  The ECU subsheath needs to be released for a maximal correction.

   

  A radiocarpal wire can be used to maintain radiocarpal alignment in addition to a long-arm cast in the early postoperative period.

   

  P.686

   

   

   

  TECH FIG 1 • A. Exposure of large osteochondroma of the distal ulna. B. Dissection and exposure of the osteochondroma. Significant tethering is present distally. C. After excision of osteochondroma and release of ulnar tethering.

   

• Distal Radial Osteotomy

   

  Radial osteotomy can be performed if the forearm bowing and deformity is severe, especially close to skeletal maturity (TECH FIG 2A).

   

  Preoperative radiographs are used for osteotomy planning. The site and magnitude of correction are determined, aiming for normalization of the RAA.

   

  A volar flexor carpi radialis (FCR) bed approach is made (unless another appropriate approach has been used for osteochondroma excision).

   

  Pronator quadratus is reflected, leaving a small cuff of tissue along the radial border for later repair.

   

  A closing wedge osteotomy is normally selected. A closing wedge osteotomy reduces radial height; however, this is not problematic when ulnar shortening has occurred.

   

   

   

  TECH FIG 2 • A. Prior to distal radial dome osteotomy. B. Early postoperative radiograph. C. Postoperative outcome at skeletal maturity.

   

   

  A dome osteotomy is selected when there is no significant ulnar shortening.

   

  Wire fixation is usually adequate for the osteotomy (either two stout K-wires or multiple smaller caliber wires).

   

  Wires may be preplaced in the radial styloid before completion and displacement of the osteotomy. They are inserted percutaneously into the radial styloid.

   

  Once the osteotomy is displaced, the wires are driven across until they obtain bicortical fixation.

   

   

   

  Adequacy of correction and final alignment is checked using fluoroscopy (TECH FIG 2B,C). Pronator quadratus is repaired using interrupted absorbable sutures.

   

• Radial Head Excision

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An incision is made over the prominent radial head with the forearm in pronation to protect the posterior interosseous nerve.

 

Dissection is then carried down in the interval between the anconeus muscle and ECU.

 

TECH FIG 3 • A. Patient with painful radial head dislocation. B. Exposure of the radial head. Forearm is in a pronated position to protect the posterior interosseous nerve. C. Radial head exposed before excision. D. Excised radial head. Significant degenerative changes are present.

The radial head is then exposed and excised (TECH FIG 3).

Layered closure is then performed and the extremity is immobilized for 2 weeks, followed by institution of range-of-motion exercises.

 

 

 

PEARLS AND PITFALLS
	Surgical ▪ Be aware of the risk of creating a synostosis. Use separate approaches or approach staged procedures if both sides of the distal radius and ulna require surgical treatment.     Excision of ▪ When resecting pedunculated osteochondromas, ensure that the axilla is osteochondromas clear of soft tissue—this is particularly so in the proximal radius as the radial nerve may become entrapped. Cutaneous nerves are also commonly draped over the surface of symptomatic lesions around the wrist. Be aware of the physis when resecting osteochondromas. Minimize any additional trauma.     Ulnar tether ▪ Ensure that the ECU subsheath is completely released for maximal release correction.     Radial osteotomy ▪ Preplaced K-wires need to be almost parallel to the radial cortex to be correctly aligned once the osteotomy is displaced. If using a dome osteotomy for correction of increased radial inclination, orient

 

 

	the concavity of the dome toward the joint to avoid excess translation. Have a low threshold for a limited fasciotomy if a forearm osteotomy has been performed.     Radial head ▪ Distorted anatomy means the radial/posterior interosseous nerve may be in a excision location that you do not expect it to be. Avoid posterior dissection and further disruption of the lateral ulnar collateral ligament (LUCL). Repair the soft tissue envelope to minimize secondary instability.

 

 

 

P.688

 

 

 

FIG 5 • A. Radiograph of a 5-year-old child prior to ulnar tether release with increased radial slope and severely affected distal ulnar physis. B. Seven years after ulnar tether release.

 

POSTOPERATIVE CARE

 

Exercises to maintain the range of motion of the fingers are encouraged immediately after surgery regardless of the technique used.

 

In cases of ulnar tethering release, casting is performed for 4 weeks, followed by range-of-motion exercises and splinting.

 

If an osteotomy was performed, casting is continued until radiographic evidence of healing is seen.

OUTCOMES

Many MHE patients do not need surgery. In patients who require surgery, ulnar tether release, with or

 

without exostoses excision, with or without radial osteotomy, provides reliable results with the few

complications (FIG 5). In selected patients, this can greatly improve function in addition to the improved cosmesis of the extremity.

Ulnar lengthening is reserved for select patients.

For symptomatic radial head dislocations, radial head excision usually leads to a consistent, reproducible result; however, formation of single-bone forearm can certainly be beneficial, especially in the skeletally immature patient.

 

 

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