JBJS | Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Treatment of Hip and Knee Problems in Myelomeningocele*†

The Journal of Bone & Joint Surgery, Volume 80, Issue 7

Instructional Course Lecture | July 01, 1998

Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Treatment of Hip and Knee Problems in Myelomeningocele*†

WALTER B. GREENE, M.D.‡, COLUMBIA, MISSOURI

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An Instructional Course Lecture, American Academy of Orthopaedic Surgeons

The Journal of Bone & Joint Surgery. 1998; 80:1068-82

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Introduction

Introduction | Problems about the Hip | Problems about the Knee | Overview | References

In the 1960s, effective techniques were developed for shunting hydrocephalus and for early closure of neural tube defects. As a result, orthopaedic surgeons were presented with the challenge of managing an emerging population of children who had myelomeningocele. Initially, the musculoskeletal problems in these children were treated with the modalities and expectations that had been learned from the treatment of poliomyelitis. However, it soon became apparent that the management of children who have myelomeningocele was not so simple. Additional factors include a decrease or loss of sensation affecting some or all parts of the lower extremities, associated congenital anomalies of the spine and lower extremities, and muscle imbalance that affects skeletal development over the entire period of growth. Furthermore, some patients who have myelomeningocele have a static encephalopathy that impairs coordination and results in the loss of strength of the lower and upper extremities^29,30,45. Also, progressive neurological deterioration may occur because of tethered cord syndrome or syringomyelia². As a result, the evaluation and treatment of musculoskeletal problems in these patients can be quite difficult.

The purpose of this Instructional Course Lecture is to review the natural history of myelomeningocele as well as the types of deformity that are associated with it, the treatment options that are available, and the expected results of treatment of hip and knee problems related to myelomeningocele. Although other factors must be considered, the neurological level is the key to understanding the hip and knee deformities seen in these patients. Unless otherwise specified, a modification of the classification system described by Asher and Olson³ will be used to define the neurological level (Table I). This classification is based on muscle strength, is simple to use, and, in my experience, has been helpful in predicting gross motor function and potential problems.

Before any decision is made concerning the treatment of hip and knee deformities in myelomeningocele, the physician and the parents must understand the realistic goals with respect to functional walking—that is, walking independently either in the community or about the house²³. Patients who have thoracic myelomeningocele may be able to walk during the first decade of life, but experience has shown that these patients become dependent on a wheelchair as they attain adult body mass^{4,5,14,19,23,37,43}. Even patients who have upper lumbar (first or second lumbar) myelomeningocele seldom retain the capacity for functional walking by the time growth is complete⁵. The prognosis is certainly better for patients who have mid-lumbar (third or fourth lumbar) myelomeningocele or lumbosacral (fifth lumbar or first sacral) myelomeningocele; however, it must be remembered that even these patients may eventually lose the capacity for functional walking because of other factors. Indeed, it previously was thought that all patients who had sacral myelomeningocele were able to walk independently²³. However, in one study of thirty-six such patients who were evaluated as adults, six had become dependent on a wheelchair as a result of neurological deterioration, ulceration of the feet, and other problems⁷.

*Printed with permission of the American Academy of Orthopaedic Surgeons. This article will appear in Instructional Course Lectures, Volume 48, American Academy of Orthopaedic Surgeons, Rosemont, Illinois, March 1999.

†No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

‡Department of Orthopaedic Surgery, M562 Health Science Center, University of Missouri, Columbia, Missouri 65212.

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TABLE I DEFINITION OF NEUROLOGICAL LEVEL*

*Based on the lowest level of antigravity (at least grade-3) strength on the patient's best side.

Level	Function
Thoracic	No grade-3 strength in muscles of lower extremity
L1-L2	Hip flexion or adduction
L3	Knee extension
L4	Knee flexion
L5	Ankle dorsiflexion
Sacral	Ankle plantar flexion

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TABLE I DEFINITION OF NEUROLOGICAL LEVEL*

*Based on the lowest level of antigravity (at least grade-3) strength on the patient's best side.

Level	Function
Thoracic	No grade-3 strength in muscles of lower extremity
L1-L2	Hip flexion or adduction
L3	Knee extension
L4	Knee flexion
L5	Ankle dorsiflexion
Sacral	Ankle plantar flexion

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Figs. 1-A and 1-B: Photographs of a patient who had myelomeningocele at the thoracic level. Fig. 1-A: Measurement of extension of the hip in the neutral plane demonstrates a 60-degree flexion contracture.

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Fig. 1-B If the extremity is positioned in abduction, the flexion contracture will be underestimated.

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Figs. 2-A, 2-B, and 2-C: Anteroposterior radiographs of a boy who had myelomeningocele at the third lumbar level. Fig. 2-A: At one year and six months of age, there is early subluxation of the left hip. Bilateral dysplasia ultimately developed, and the patient had a bilateral staged adductor myotomy, transfer of the iliopsoas, and femoral osteotomy.

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Fig. 2-B At five years of age, there is adequate containment. Note the size of the iliac window necessary for a standard Sharrard transfer.

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Fig. 2-C At sixteen years of age, the containment is satisfactory. The patient was able to walk about the community with use of a knee-ankle-foot orthosis on the left, an ankle-foot orthosis on the right, and forearm crutches.

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Fig. 3 Anteroposterior radiograph of a twenty-three-year-old woman who had myelomeningocele at the fourth lumbar level. She was able to walk about the community with use of forearm crutches and an ankle-foot orthosis on each side. She did not have any operations on the hip.

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Fig. 4 Anteroposterior radiograph of a two-year and six-month-old girl with myelomeningocele at the fourth lumbar level in whom early subluxation of the right hip developed. She was managed with transfer of the external oblique muscle, adductor myotomy, and femoral osteotomy. Blade-plate fixation of the osteotomy site and good suture techniques for the tendon transfer made it possible for the cast to be removed after four weeks of immobilization.

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Figs. 5-A and 5-B: Anteroposterior radiographs of a boy who had myelomeningocele at the mid-lumbar level. Fig. 5-A: Bilateral dislocation of the hip was evident at the age of two months. The patient was managed with iliopsoas recession and adductor myotomy.

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Fig. 5-B At the age of two years and seven months, the hips were located but still dysplastic. Additional procedures will most likely be necessary, but the improvement in the interval definitely made the procedure worthwhile.

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Figs. 6-A, 6-B, and 6-C: A boy who had myelomeningocele at the fourth lumbar level and subluxation of the left hip. Fig. 6-A: Anteroposterior radiograph made at the age of seven years. Two years later, the subluxation had progressed and there was 52 per cent migration.

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Fig. 6-B Anteroposterior radiograph made after Chiari pelvic and proximal femoral osteotomies.

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Fig. 6-C Anteroposterior radiograph made at the age of sixteen years. There was still satisfactory coverage.

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Figs. 7-A, 7-B, and 7-C: A boy who had myelomeningocele at the fourth lumbar level. Fig. 7-A: Photograph showing severe flexion contracture of the knee, which developed at the age of eleven years following a period of inactivity imposed by a burn injury to the lower extremity. The patient was managed with a radical posterior release of the contracture.

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Fig. 7-B Lateral radiographs, made after the first postoperative cast-wedging, demonstrating posterior subluxation of the tibia. A Quengle cast was used to provide anterior translation of the tibia.

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Fig. 7-C Photograph, made at the completion of treatment with the cast, showing full extension of the knee. Fourteen years after the procedure, the patient was still able to walk about the community with use of forearm crutches and a bilateral ankle-foot orthosis.

Problems about the Hip

Introduction | Problems about the Hip | Problems about the Knee | Overview | References

Natural History

The neurological level is a critical factor in determining the type of deformity of the hip. Patients who have thoracic myelomeningocele lack active movement of the lower-extremity muscles. Therefore, the lower extremities tend to lie in abduction, external rotation, and flexion. This posture may facilitate early stabilization of the hip joint, but it also causes the progressive development of a flexion-abduction-external rotation contracture. It is important to note that the severity of the flexion contracture will not be appreciated if the hip is allowed to abduct while the Thomas test is performed (Figs. 1-A and 1-B). Tightness of the iliotibial band also causes external tibial torsion and contributes to a flexion deformity of the knee. In addition, tethered cord syndrome, which is more common in patients who have thoracic myelomeningocele, may cause spasticity of the adductors and subluxation of the hips similar to that observed in patients who have cerebral palsy.

A contracture of the unopposed hip flexors typically develops in patients with upper lumbar myelomeningocele. A mild contracture of the unopposed hip adductors may also occur; however, the restriction of hip abduction is usually mild and is not clinically important.

Patients who have mid-lumbar myelomeningocele typically have normal strength in the hip flexors and adductors but no function of the hip extensors or abductors. Therefore, a flexion contracture of the hip and some limitation of abduction frequently develop in these patients. More importantly, this pattern of muscle imbalance predisposes to progressive subluxation of the hip.

The probability of subluxation or a severe flexion contracture of the hip is low in patients who have lumbosacral myelomeningocele. This is particularly true if the myelomeningocele is at the sacral level, but adequate stability and an adequate range of motion of the hip are usually maintained even in patients with fifth lumbar myelomeningocele who have only grade-2 or 3 strength of the hip abductors and absent or trace strength of the hip extensors. Apparently, this degree of activity of the hip abductors combined with activity of the hamstrings can be an effective counterbalance to hip flexors and adductors of normal strength. These patients should have periodic radiographs during early childhood to monitor the development of the hip joint.

In a multicenter study of 1061 patients who had myelomeningocele, measurement of the flexion contractures of the hip in older children (nine to eleven years old) revealed that the greatest average value was in the patients who had thoracic or upper lumbar myelomeningocele⁸. Dislocation, defined as no area of congruity between the femoral head and the acetabulum, was most commonly observed in the patients who had thoracic myelomeningocele. Dislocation tended to occur by the age of three to four years in the patients who had mid-lumbar myelomeningocele, but those who had thoracic or upper lumbar myelomeningocele continued to have dislocation of the hip even after the age of ten years. By the age of nine to eleven years, there had been no dislocation or operation on the hip in 42 per cent of the patients who had third lumbar myelomeningocele, 67 per cent of the patients who had fourth lumbar myelomeningocele, and 80 per cent of the patients who had fifth lumbar myelomeningocele. A possible criticism of this study is that the authors excluded hips that were subluxated, a factor that is particularly relevant for patients who have mid-lumbar myelomeningocele.

In a review by Fraser et al.²¹, subluxation or dislocation at the age of one year was observed in twenty-five of twenty-nine patients who had third lumbar myelomeningocele and in eight of nineteen who had fourth lumbar myelomeningocele. Of the fifteen hips that were stable at the age of one year, only one subsequently dislocated.

Treatment of Problems in Children Who Have Thoracic or Upper Lumbar Myelomeningocele

Numerous studies have demonstrated that the ability to walk is not affected by dislocation of the hip in patients who have thoracic or upper lumbar myelomeningocele^{4,5,8,14,19,21,24,25,37}. Therefore, reconstructive procedures to correct dysplasia of the hip are rarely indicated for these patients since relocation of the hip does not provide functional gains and may cause complications, such as pathological fracture or the more devastating complication of a stiff hip joint.

Because children who have myelomeningocele at an upper level rarely retain the ability to walk after reaching adulthood, some authors have recommended that these patients use a wheelchair when they are young^10,42. Others have advocated an intensive program of bracing and gait-training during early childhood^12,31. Charney et al.¹² found that, with such therapy, forty-five (52 per cent) of eighty-seven patients who had myelomeningocele at an upper level were able to walk about the community by five years of age. However, deficient balance reactions and weakness of the upper extremities coupled with the extensive bracing that is needed prevent some of these children from achieving a functional walking ability.

The potential benefits of walking by patients with myelomeningocele at an upper level include strengthening of the upper extremities, protection against obesity, better bone density, and prevention of contractures of the lower extremities. However, in my opinion, the most striking and important benefit is the tremendous sense of accomplishment that these children express when they achieve the ability to be upright and to move around a room like other children of their age. This psychological boost has also been noted in other reports on children who have myelomeningocele at an upper level^26,31. Furthermore, in one study, patients with this level of myelomeningocele who were managed with bracing and early walking had fewer fractures and pressure sores and were more independent in transfers, even when they eventually switched to a wheelchair, compared with patients who had always used a wheelchair³¹. However, these children were hospitalized more often, for operative procedures to allow bracing. Obesity, dexterity of the upper extremities, and the ability to perform other activities of daily living did not differ between the two groups.

My approach to the treatment of problems related to the hip in patients who have myelomeningocele begins at birth. At this age, it is not possible to identify which children are candidates for bracing and walking; therefore, all parents are taught a therapy program that targets anticipated problems. For patients who have thoracic and upper lumbar myelomeningocele, the program includes stretching exercises for the iliotibial band, the hip and knee flexors, and the ankle plantar flexors.

Patients with myelomeningocele at an upper level who have good upper-body strength and adequate balance reactions are candidates for bracing and walking. The braces for these patients must extend proximal to the hip, and walking is most easily achieved with a swing-to or swing-through gait. Because of the coordination and upper body strength that are required for such walking, gait-training should be delayed until the child is approximately two years old (range, eighteen to thirty-six months). Between the age of one year and the initiation of gait-training, a standing frame can be helpful. This device positions the child upright and also acts to stretch flexion contractures at the hip and knee. The wooden base of the frame is large enough to prevent falling. Parents are taught how to construct a simple table with a semicircular cutout. When the child is in the standing frame, the table is positioned around the child to allow him or her to play and do other activities in an upright position.

The brace that is initially prescribed for patients who have myelomeningocele at an upper level provides adequate support and has maximum adaptability for growth. A pelvic band is adequate for most patients who have second lumbar myelomeningocele, but patients who have thoracic myelomeningocele need a more extended plastic mold to support the lower part of the trunk. For patients who have lumbar kyphosis, the molded trunk support also minimizes skin ulceration over the spinal gibbus. Drop-lock hinges are used at the hips, but knee joints are not part of the initial orthotic. The incorporation of knee joints into a brace made for a small child markedly restricts how much the brace can be lengthened as the child grows. This brace has few disadvantages because young children can sit comfortably in most chairs without bending the knees. However, before the child goes to school, a brace that does have drop-lock knee hinges is prescribed.

A parapodium is an option for patients who have myelomeningocele at an upper level and are not candidates for independent walking. The swivel-walker type of parapodium, although more expensive, has many advantages²⁸. Its heavy base prevents the child from falling, and the swivel action makes it possible for a child who has deficient balance reactions to propel himself or herself around the house, to a limited degree. The psychological boost and the additional benefits accrued from being in an upright position make the effort worthwhile.

Children with myelomeningocele at an upper level who are candidates for walking and who have flexion contractures of the hip of more than 25 to 30 degrees must be managed operatively in order to achieve optimum bracing and walking ability. The procedure is best done when the child is ready to start gait-training. If the operation is performed at an earlier age, the contractures will recur. Patients who have thoracic myelomeningocele do not have pain postoperatively, and the procedure usually can be done on an outpatient basis.

All components of the hip deformity should be corrected³². A lateral approach, centered over the greater trochanter, provides adequate exposure and minimizes problems with wound-healing and recurrent contracture. The iliotibial band, gluteus medius and minimus, tensor fasciae latae, sartorius, rectus femoris, and iliopsoas tendon are released sequentially. To protect the femoral vessels during exposure of the iliopsoas tendon, the femoral nerve should be identified first as it crosses the pelvic brim and then the femoral nerves and vessels should be retracted medially. With severe contractures, it is also necessary to release the external rotators and the anterolateral aspect of the joint capsule.

The flexion contracture of the hip should be completely corrected by the end of the procedure. Failure to achieve full correction predisposes to early recurrence. Therefore, even when the operation is performed unilaterally, both hips are draped so that the contralateral hip can be fully flexed in order to assess the flexion contracture adequately during the procedure.

The lower extremities are immobilized postoperatively in a bilateral above-the-knee cast with a cross-bar that keeps the hips in 5 to 10 degrees of abduction and 20 to 30 degrees of internal rotation. This type of cast prevents the skin problems that are associated with a spica cast. Immediately after the operation, the child is positioned with the hips in some degree of flexion. As the swelling and pain decrease, the hips are positioned to gain full extension. The child is then kept in either the supine or the prone position with the hips fully extended for at least eighteen hours a day. Short periods of sitting are allowed to facilitate feeding, transportation, and other activities. The cast is worn for four weeks. A longer period of immobilization does not seem to lower the risk of recurrent contracture and increases the risk of pathological fracture. To minimize the risk of recurrent contracture, it is important that bracing begin directly after the cast treatment has been discontinued.

Treatment of Problems in Children Who Have Mid-Lumbar Myelomeningocele

Before these patients are discharged from the newborn nursery, the parents are taught a stretching program that targets the unopposed hip flexors and adductors. Radiographs of the pelvis are made during periodic visits to the clinic. If subluxation occurs, it usually does so before the age of three years.

The role of operative intervention for dysplasia of the hip in children who have myelomeningocele at the mid-lumbar level is controversial. Some authors have noted no association between walking ability and dislocation of the hip, whereas others have reported that dysplasia reduced the walking ability of patients who had mid-lumbar myelomeningocele^{3-5,14,19,20,24,25,43}. Asher and Olson³, in a study that combined detailed analysis and clear separation of the patients who had third lumbar myelomeningocele from those who had fourth lumbar myelomeningocele, demonstrated a significant association between hip deformities and walking ability in both groups. In fact, deformity of the hip was the only variable that was significantly associated (p < 0.05) with walking status in the group that had third lumbar myelomeningocele. Only one of the eight patients who had third lumbar myelomeningocele (average age, sixteen years) and a unilateral or bilateral dislocation of the hip was capable of functional walking compared with five of the twelve patients who had third lumbar myelomeningocele but did not have a dislocation. Although the many variables involved make statistical analysis difficult, it has been my observation that hip dysplasia adversely affects walking ability as patients who have mid-lumbar myelomeningocele reach the second decade of life.

It is also true that the treatment of dysplasia of the hip in patients who have mid-lumbar myelomeningocele is difficult and is not universally successful. The final decision to operate must be tempered by the analysis of other factors, including the strength of the upper extremities, balance reactions, the strength of the quadriceps and medial hamstring muscles, and the severity of the acetabular and proximal femoral malalignment. Furthermore, it is important to do whatever is necessary to stabilize the hips with the first operation. The goal of treatment of hip problems in patients who have myelomeningocele is to minimize the number of operations needed and the period of immobilization in a spica cast¹⁷. Repeated attempts at reconstruction of the hip predisposes to pathological fracture or, even worse, a stiff hip that affects wheelchair activities and accelerates the development of painful arthrosis.

Posterolateral transfer of the iliopsoas, as described by Sharrard³⁹, is meant to correct muscle imbalance and to stabilize or correct dysplasia of the hip in patients who have myelomeningocele. The concept of the Sharrard procedure is to transfer the deforming force of the iliopsoas to a position where it can substitute for the non-functional hip extensors and abductors. The iliopsoas tendon and the iliacus muscle are freed up so that both can be transferred through a drill-hole made in the ilium. This requires the creation of a relatively large window. The iliopsoas tendon is inserted through the drill-hole into the posterior aspect of the greater trochanter, and the origin of the iliacus is sutured to the ilium in a position corresponding to the origin of the gluteus medius.

Initially, the Sharrard procedure was done on virtually all patients with myelomeningocele who had a dysplastic hip³⁹. However, disenchantment was subsequently voiced^{5,11,17,18,41}. The operation was noted to be extensive and to seldom provide active antigravity extension. Furthermore, a high rate of recurrent subluxation was reported in some series^{5,11,17,18,41}. Additional analysis, however, revealed that the latter problem was partly related to the inclusion of patients who had thoracic or upper lumbar myelomeningocele; we now understand that this procedure is inappropriate for these patients.

Posterolateral transfer of the iliopsoas should be limited to a select group of patients. In 1983, Sharrard⁴⁰ recommended that the transfer should be combined with an adductor release, should be done before osseous deformity develops (between one and two years of age), and should be limited to patients who have fourth lumbar myelomeningocele. The third guideline is perhaps too stringent as good results have been observed in patients with third lumbar myelomeningocele who have good (grade-4) strength of the quadriceps muscle^11,25,43.

The study by Stillwell and Menelaus⁴³ provided useful data concerning the effectiveness of the Sharrard procedure. It should be noted that all forty-seven patients in that series had release of the adductors to obtain 60 degrees of abduction. Most of the operations were performed before the patients were three years old. Ten years or more postoperatively, the results were relatively good: thirty-five patients (74 per cent) were capable of functional walking and most of these thirty-five could climb stairs. Functional walking was associated with the neurological level and at least grade-3 strength of the quadriceps. At the time of follow-up, none of the three patients who had second lumbar myelomeningocele, ten of the sixteen patients who had third lumbar myelomeningocele, thirteen of the fifteen patients who had fourth lumbar myelomeningocele, and twelve of the thirteen patients who had fifth lumbar myelomeningocele were capable of functional walking. A flexion contracture of more than 20 degrees was not observed in any patient, and only five of the seventy-nine hips had a contracture of 20 degrees. Before the operation, eight hips were subluxated and twenty-three were dislocated. At the most recent follow-up evaluation, two hips were subluxated and two were dislocated. No patient in that study was excluded from the analysis because of loss of neurological function.

It is now clear that posterolateral transfer of the iliopsoas does not provide active extension or abduction against gravity, and it is doubtful that this out-of-phase transfer provides any noticeable extension or abduction during the gait cycle. A recent study using three-dimensional gait analysis revealed no improvement in abnormal pelvic obliquity in patients with fourth lumbar myelomeningocele who had been managed with iliopsoas transfer¹⁸. In my opinion, the primary benefit of posterolateral transfer of the iliopsoas is that it not only removes a deforming force but also provides an active restraint or tenodesis effect that greatly minimizes the risk of a recurrent flexion contracture of the hip. When there is no flexion contracture, walking mechanics are improved and, more importantly, standing is possible with little or no support. In contrast, patients with mid-lumbar myelomeningocele who have a flexion contracture of more than 20 degrees cannot stand and rest but must expend considerable energy just to stay upright. As a result, walking is difficult. The iliopsoas transfer, combined with an adductor release and osteotomies as needed, can stabilize progressive subluxation of the hip and help to maintain functional walking (Figs. 2-A, 2-B, and 2-C), but whether this approach is optimum for these patients is still debatable.

Transfer of the external oblique muscle has been advocated as an alternative to transfer of the iliopsoas for patients who have myelomeningocele at the mid-lumbar level as well as a dysplastic hip^15,35,44. This procedure does not weaken the iliopsoas. Therefore, the power of the hip flexors and the ability to climb stairs should be maintained. Some authors¹⁶ have stated that transfer of the external oblique muscle improves hip mechanics during mid-stance; however, gait-analysis studies have demonstrated that the transferred external oblique muscle mainly functions during the swing phase of gait¹⁶. Therefore, it is doubtful that this transferred muscle imitates the activity of the hip abductors or extensors during walking.

Phillips and Lindseth³⁵ described the results of transfer of the external oblique muscle in forty-seven patients (eighty-nine hips). With that method, the hip adductors were transferred to the ischium and the tensor fasciae latae were moved to a more lateral position. Although those authors reported functional walking by all patients, the duration of follow-up averaged only 4.5 years and six patients were excluded from the analysis because of loss of neurological function. With the more limited follow-up and the exclusion of certain patients, it is doubtful that the results reported by Phillips and Lindseth are markedly different than those observed after transfer of the iliopsoas.

In a study of thirty-four children (sixty-six hips) with third, fourth, or fifth lumbar myelomeningocele who had a femoral osteotomy combined with transfer of the external oblique and adductor muscles, Tosi et al.⁴⁴ reported the maintenance of stability of thirty-seven (73 per cent) of fifty-one hips in the twenty-six children who remained neurologically stable; however, only eight of fifteen hips in the eight children who had a progressive loss of neurological function remained stable. The poorest results were for the hips that had dislocated previously. Only two of the ten hips in this group had a successful result. The transferred muscle was noted to be weak as no patient demonstrated active abduction even in the supine position. The average duration of follow-up in that study was relatively long (10.9 years), but the wide range of follow-up (0.7 to 20.0 years) limits conclusions concerning functional status as these children reached adult body size. At the most recent evaluation, twenty-one (81 per cent) of the twenty-six children who had not lost neurological function were able to walk about the community.

It is difficult to compare studies of transfer of the iliopsoas with those of transfer of the external oblique muscle. Reports vary with regard to how the neurological level and the results are defined. In addition, the definition of progressive loss of neurological function is imprecise, and not all studies have provided a separate analysis of patients with such loss. Furthermore, it seems that, in the large series, the procedure was done on virtually all patients who had mid-lumbar myelomeningocele^35,43,44. Perhaps this protocol was used because previous authors had suggested that the muscle imbalance in these patients eventually causes dysplasia of the hip and that tendon transfers should be done, if possible, before marked subluxation and osseous changes develop^11,40. However, it is now understood that progressive dysplasia does not develop in all patients who have myelomeningocele at the mid-lumbar level (Fig. 3), and experienced observers, such as Broughton et al.⁸, now recommend a selective approach for operative intervention.

In my opinion, both transfers are major procedures and are indicated only for patients in whom subluxation has developed and who have at least grade-4 strength of the quadriceps. Transfer of the external oblique muscle has the advantage of maintaining the function of the iliopsoas, but the external oblique muscle is relatively small and there is a legitimate concern that patients managed with this procedure are at greater risk for recurrent dysplasia and a recurrent flexion contracture of the hip. Maintaining neutral extension of the hip and the ability to stand without the support of the upper extremities is a long-term benefit of transfer of the iliopsoas; however, moving the entire iliacus muscle to the posterior aspect of the ilium is an extensive dissection. Perhaps the results would be just as good if only the iliopsoas tendon was transferred to the greater trochanter and the iliacus muscle was left in place. Longer follow-up after transfer of the external oblique muscle as well as comparative gait-analysis studies will allow a more definitive statement concerning the best approach.

The Role of Concomitant Procedures

Whether one prefers transfer of the external oblique muscle or the iliopsoas, it is clear that either procedure must be combined with release or transfer of the adductors, to correct adduction contractures and to provide a better biomechanical environment for the transfer. This concept was corroborated by Yngve and Lindseth⁴⁸, who documented better radiographic results when adductor and abductor procedures had been combined.

Transfer of the adductors to the ischium should provide better power of hip extension, but this concept has not been proved. Compared with adductor myotomy, transfer of the hip adductors requires more dissection and, in children who had cerebral palsy, was associated with a pull-out rate of 33 per cent (eleven of thirty-three hips) despite an average duration of immobilization in a cast of 5.7 weeks²⁷. In my opinion, this duration of immobilization is contraindicated for patients who have myelomeningocele.

Muscle transfers for the treatment of dysplasia of the hip associated with myelomeningocele are insufficient to correct severe osseous deformities. Malalignment of the proximal part of the femur or the acetabulum is particularly common after the age of three years, and this problem should be corrected either before or at the same time as the muscle transfers. A femoral varus rotation osteotomy corrects abnormal valgus angulation and anteversion. The type of pelvic osteotomy that best serves these patients is less clear. Acetabular deficiency in patients who have myelomeningocele is often global (anterior and posterior)⁹. For that reason, a Pemberton or modified Dega procedure may be better than other pelvic osteotomies that are commonly used for the management of young children who have congenital dislocation of the hip^33,34.

Patients who have myelomeningocele are at risk for pathological fracture, particularly after immobilization in a spica cast. Therefore, such immobilization should be limited to four weeks, an approach that requires adequate fixation of the sites of both the tendon transfers and the osteotomies (Fig. 4).

Dysplasia of the Hip before the Age of One Year in Children Who Have Mid-Lumbar Myelomeningocele

Subluxation or dislocation of the hip that develops before the age of one year in patients who have mid-lumbar myelomeningocele is difficult to treat. Typically, the problem is noted in the first few months of life. Use of a Pavlik harness or some other brace designed for congenital dysplasia of the hip is seldom successful over the long term for patients who have myelomeningocele. Furthermore, when the hip extensors are non-functional, these braces exacerbate a flexion contracture in a neonate.

Transfer of the iliopsoas or the external oblique muscle has also not been successful in this group of patients. In the study by Stillwell and Menelaus⁴³, five of nine patients who had had an iliopsoas transfer before they were one year old were not walking at the time of the most recent follow-up, at least ten years postoperatively. Tosi et al.⁴⁴ reported redislocation of two of four hips that had had transfer of the external oblique muscle and femoral osteotomy after initial treatment with a Pavlik harness. The reason for the dislocations is unclear, but they may be explained by the timing of the operation in this unique subset of patients. In my experience, when dysplasia develops in the first year of life in patients who have mid-lumbar myelomeningocele, it develops by the age of three or four months. Indeed, many of these patients probably have dislocation of the hip at birth, but the treatment of other medical problems prevents its documentation. If intervention is delayed, the rapid growth during infancy coupled with an underlying muscle imbalance may result in severe dysplasia that cannot be stabilized with soft-tissue procedures.

My method of treatment for this problem is an iliopsoas recession and adductor myotomy⁶. The operation is typically performed between the age of two and four months because, by that time, other medical problems have stabilized. The iliopsoas recession moves the psoas tendon to a position at which it cannot block a concentric reduction or compress the medial femoral circumflex artery. The hips can then be reduced and immobilized in a position of extension, abduction, and internal rotation. This position, although good for the stabilization of congenital dysplasia, was abandoned because of its association with avascular necrosis. However, after an adductor myotomy and iliopsoas recession, the risk of avascular necrosis from positioning the hips in extension is virtually eliminated.

Immobilization after the iliopsoas recession and adductor myotomy can be accomplished effectively with the application of a bilateral above-the-knee cast with cross-bars that keep the hips in abduction and internal rotation. Use of this cast eliminates the serious nursing problem that occurs when small infants who have neurogenic dysfunction of the bowel and bladder are placed in a spica cast. Extension of the hip can be adequately maintained with appropriate positioning. Immobilization typically lasts for two months and is followed by treatment with an abduction splint.

My experience with this method for treating myelomeningocele is limited to three patients, but the dislocation was corrected in all three (Figs. 5-A and 5-B). If dysplasia of the hip recurs, reconstructive procedures can be performed without the surgeon having to contend with the extreme acetabular dysplasia and joint contractures that would have developed without the described treatment.

Dysplasia of the Hip in Older Children Who Have Mid-Lumbar Myelomeningocele

Progressive subluxation of the hip in an adolescent patient presents a dilemma. Muscle imbalance coupled with complicated acetabular dysplasia leads to a substantial rate of recurrent subluxation. There is no set answer for this group of patients. Certainly, the evaluation should include assessment for a possible tethered cord syndrome and consideration of a computed tomography scan with reconstruction to define the extent and location of the acetabular deformity^1,9. Treatment must be individualized, but I have most often performed a Chiari pelvic osteotomy and femoral varus rotation osteotomy in this group of patients (Figs. 6-A, 6-B, and 6-C). I have also recommended observation or no treatment for adolescent patients who have a history of operations, no functional abductor muscles, and a markedly dysplastic acetabulum. In this situation, the chance of success is low and reconstructive operations may cause the hip to become stiff and painful.

Problems about the Knee

Introduction | Problems about the Hip | Problems about the Knee | Overview | References

Operative treatment of the knee is needed considerably less often than operations on the hip and foot in children who have myelomeningocele. However, it has recently become apparent that arthropathy of the knee may develop in relatively young adults who have myelomeningocele. In a study of adult patients who ranged in age from twenty-three to thirty-nine years, Williams et al.⁴⁶ noted severe symptoms related to the knee in 24 per cent (seventeen) of seventy-two patients who functioned as community ambulators²³. Patients with myelomeningocele who have absent or diminished strength of the hip abductors and the ankle plantar flexors walk with an increased valgus-external rotation thrust applied to the knee during mid-stance. These forces are exacerbated when these patients walk without the use of forearm crutches, a situation that is almost universal during the adolescent years. As they reach the second decade of life, these patients should be counseled concerning the abnormal biomechanics and the fact that total joint arthroplasty is not a good option for them as young adults. Most importantly, they need to understand that the use of forearm crutches can decrease the abnormal forces acting to accelerate degenerative arthrosis of the knee joint.

Congenital hyperextension of the knee is occasionally seen in patients who have thoracic myelomeningocele. Patients who have rigid deformities should not be managed with a cast because the risk of skin ulceration or bowing of the tibia is too great. Treatment involves either a V-Y lengthening of the quadriceps tendon, a percutaneous release, or a division of the patellar ligament^13,36,38. The latter is a simple procedure, and it is my preferred method for the treatment of extension deformities of the knee in patients who have thoracic myelomeningocele.

The natural history of flexion contracture of the knee associated with myelomeningocele was described by Wright et al.⁴⁷. Patients who had thoracic myelomeningocele had the most severe deformity; the flexion contracture averaged 30 degrees at maturity. However, the standard deviation was large for all groups except the patients who had sacral myelomeningocele. Therefore, severe deformities are less likely to occur in patients who have lumbar myelomeningocele but they may occur.

Bracing and walking are affected by flexion contractures of more than 20 to 25 degrees. My primary reason for release of a knee flexion contracture associated with myelomeningocele is to improve or allow bracing. Unless there is a tethered cord, the severity of the flexion contracture of the knee is not markedly different when measured with the hip in flexion. This indicates that contraction of the posterior aspect of the knee capsule, as opposed to the hamstrings, is the primary pathological finding. Therefore, a complete release of the capsule is necessary to correct the problem.

My technique for releasing a flexion contracture of the knee is through a single midline posterior incision. Occasionally, two incisions, one posteromedial and one posterolateral, are used in a small child who has a severe contracture. In either case, the incision does not cross the popliteal crease. If the hamstrings have at least grade-3 strength, they are lengthened; however, if these muscles are weak, a tenotomy is done. Because the gastrocnemius is inactive in these patients, the medial and lateral heads are released from the femoral condyle. The posterior aspect of the knee capsule is incised from the posterior margin of the medial collateral ligament to the posterior margin of the lateral collateral ligament. Occasionally, one or both cruciate ligaments must be released.

If full extension is not achieved, wedging of the cast is initiated on the second or third postoperative day. After a radical posterior knee release, no more than two or three wedges are required to obtain full extension. To perform the wedging, the cast is cut almost circumferentially at the level of the adductor tubercle (the instant center of knee motion). To prevent anterior translation and breakage of the cast, an anterior strip (four to five centimeters long) is left intact. The integrity of this tongue of plaster is enhanced by two vertical cuts (six centimeters long) at the medial and lateral margins of the strip. The child is then placed in the prone position with the feet hanging off the table. The knee is extended, and the corrected position is secured by a block of wood inserted on the posterior margin of the cast. The block is made with a lip on either end to prevent dislodgment and skin ulceration. A roll of plaster of Paris secures the block and stabilizes the cast.

Skin ulceration may develop at the heel after postoperative cast-wedging, despite appropriate precautions. This is not surprising because the heels of these patients are insensate. Frequent inspection of the cast identifies the problem before serious complications occur.

When a patient has a severe contracture, cast-wedging may cause posterior subluxation of the tibia (Figs. 7-A, 7-B, and 7-C). Although this problem is uncommon in patients with myelomeningocele who have had a posterior release of the knee capsule, a lateral radiograph should be made to exclude the possibility. If posterior subluxation occurs, alternative treatment, such as the use of a Quengle cast²² with anti-subluxation hinges or two-pin skeletal traction through the distal aspect of the femur and the proximal aspect of the tibia, is necessary to correct the subluxation and obtain full extension.

In my experience, comprehensive posterior release for flexion contracture of the knee has been useful. In a series of thirty-four patients, the average flexion contracture was 38 degrees (range, 20 to 74 degrees) before this procedure and 5 degrees (range, 0 to 25 degrees) at the time of the most recent follow-up. In addition, the level of walking was improved in conjunction with subsequent brace-fitting and gait-training. Extension of the knee is typically maintained over the long term in patients who have mid-lumbar myelomeningocele; however, patients who have thoracic myelomeningocele usually lose most of the correction when they stop walking. Other factors that are associated with a poor result include delayed cast-wedging and tethered cord syndrome.

Extension osteotomy of the distal aspect of the femur is another technique that can be used to treat a flexion deformity of the knee⁴⁹. This procedure, however, has several disadvantages that, for the most part, preclude its use in children who have myelomeningocele. The osteotomy does not correct the primary deformity but rather straightens the knee by creating a second deformity. More importantly, there is rapid recurrence of the deformity when the procedure is performed at a young age, the time when most flexion deformities in patients who have myelomeningocele are treated.

Overview

Introduction | Problems about the Hip | Problems about the Knee | Overview | References

While the treatment of hip and knee deformities associated with myelomeningocele can be quite challenging, progress has been made in our understanding of these problems. A procedure to correct severe contractures of the hip and knee may be indicated for a patient with myelomeningocele at an upper level who is a candidate for bracing and walking; however, the parents must understand that the deformity will recur when walking stops. Procedures to stabilize progressive subluxation of the hip are indicated for patients with a lesion at the mid-lumbar level who have good strength of the quadriceps. The procedure should correct the hip-flexor and adductor imbalance and should also correct severe osseous deformities. At present, it is unclear whether transfer of the iliopsoas or transfer of the external oblique muscle is the better procedure.

References

Introduction | Problems about the Hip | Problems about the Knee | Overview | References

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Broughton, N. S.; Menelaus, M. B.; Cole, W. G.; and Shurtleff, D. B.: The natural history of hip deformity in myelomeningocele. J. Bone and Joint Surg.,75-B(5): 760-763, 1993.75-B(5)760 1993

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Fig. 1-B If the extremity is positioned in abduction, the flexion contracture will be underestimated.

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Fig. 2-B At five years of age, there is adequate containment. Note the size of the iliac window necessary for a standard Sharrard transfer.

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Fig. 6-B Anteroposterior radiograph made after Chiari pelvic and proximal femoral osteotomies.

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Fig. 6-C Anteroposterior radiograph made at the age of sixteen years. There was still satisfactory coverage.

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Fig. 7-B Lateral radiographs, made after the first postoperative cast-wedging, demonstrating posterior subluxation of the tibia. A Quengle cast was used to provide anterior translation of the tibia.

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TABLE I DEFINITION OF NEUROLOGICAL LEVEL*

*Based on the lowest level of antigravity (at least grade-3) strength on the patient's best side.

Level	Function
Thoracic	No grade-3 strength in muscles of lower extremity
L1-L2	Hip flexion or adduction
L3	Knee extension
L4	Knee flexion
L5	Ankle dorsiflexion
Sacral	Ankle plantar flexion

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TABLE I DEFINITION OF NEUROLOGICAL LEVEL*

*Based on the lowest level of antigravity (at least grade-3) strength on the patient's best side.

Level	Function
Thoracic	No grade-3 strength in muscles of lower extremity
L1-L2	Hip flexion or adduction
L3	Knee extension
L4	Knee flexion
L5	Ankle dorsiflexion
Sacral	Ankle plantar flexion