Van Alexzander's

LIMB LENGTH DISCREPANCY

Mark T. Dahl, MD

Pediatric limb length discrepancies (LLDs) clinically manifest in a broad spectrum of congenital, developmental, or post-traumatic conditions. When evaluating a child with limb length discrepancy, the cause and changing magnitude during growth must be considered. Asymmetry in limb lengths is not considered pathologic. Discrepancies of 1 cm to 1.5 cm are common, generally do not cause any symptoms, and may not require treatment.

This article addresses LLD in children from diagnosis through treatment. The purposes of this article are to identify the causes of LLD, describe the clinical examination for detecting LLD, present potential side effects of LLD, provide indications for treatment, and show how treatment methods are selected.

CAUSES OF LIMB LENGTH DISCREPANCY

Although LLD is a common problem worldwide, the exact incidence is not known. Many studies focus on the behavior of limb inequality in specific disorders.(2, 10, 11) A study by Kawamura and colleagues (8) detected LLD in athletes, showing a discrepancy of more than 5 mm in 51 of 141 study participants. Common causes of congenital and acquired LLD for children are listed in Table 1.

 

Clinical Significance of Limb Lengthening

The long-term effects of LLD are poorly documented. Problems associated with LLD include structural scoliosis, lower back pain, degenerative arthrosis of the lumbar and sacroiliac articulations, long leg degenerative hip and patellofemoral arthrosis, equinus contracture of the ankle, foot callosities, cosmetically unappealing shoe lift or prosthesis, cosmetically unappealing gait disturbance, and increased energy consumption during gait.

Compensation and Tolerance

Patients respond differently to LLD; therefore, it is difficult to quantify a magnitude of LLD beyond which a patient is intolerant. Many features may make one patient intolerant of a LLD discrepancy that would not trouble another. Certainly, a 6-foot-tall patient tolerates a 2-cm discrepancy with little or no trouble, whereas a 5-foot-tall patient would be less tolerant of the same discrepancy.

Because of their inherent flexibility, children tolerate discrepancies better than adults. The quick onset of LLD also influences its tolerance. For example, a previously "normal" adult who suddenly has a 5-cm discrepancy caused by an accident does not compensate as well as if the discrepancy had been there since childhood. Patients with additional clinical problems, such as contractures, arthrosis, joint arthroplasty, arthrodesis, axial malalignment, muscle weakness, or spasticity, have limited ability to compensate for a LLD.

EXAMINING FOR LIMB LENGTH DISCREPANCY

Clinical Examination

The initial clinical examination is simple. Examination begins with the patient shoeless and standing with both feet flat on the floor. The patient is viewed from both the front and rear sides. From the rear, relative hip, knee, and foot heights are observed. One-cm blocks are inserted under the shorter limb until the iliac crests are level and the trunk is balanced (Fig. 1). Leveling the pelvis should eliminate scoliosis if it is a result of LLD.

Measuring the Discrepancy 

To determine the true discrepancy, the patient is placed in a supine position and then measured (using a tape measure) from the prominence of the anterior iliac crest to the lower prominence of the medial malleous. The relative knee heights are measured with the hips and knees flexed. Foot heights and lengths are obtained by direct observation.

Neuromuscular, vascular, and joint examination is necessary. Axial malalignment should also be observed for asymmetry. If an LLD is found, observing gait offers insight on the compensatory mechanisms.

Analyzing Gait

Adaptations of walking occur as a means of smoothing gait and minimizing energy expenditure. The patient's gait is evaluated for the compensatory mechanisms (adaptations) of pelvic tilting, long knee flexion, and vaulting on the short side. Another form of compensation, used less frequently, is pelvic internal rotation to lengthen stride. Patients with fixed deformities of the spine, pelvis, hip, knee, or ankle may not be able to use the usual compensation mechanisms. For these patients, walking can be difficult.

Figure 1. Visual examination. A, A child with 3.5 cm of limb shortening. B, The amount of lift needed under the heel to achieve a level pelvis is shown.

Although gait motion analysis is primarily used for evaluating children with cerebral palsy, (6) recent studies indicate gait disturbance in mature patients with mild to moderate LLD (2.5 to 6 cm) without axis deviation (Fig. 2). Analysis of oxygen consumption shows little change in patients with mild LLD; however, easy fatigue is a common complaint of these patients (Mark T. Dahl, MD, and Tom Novacheck, MD, unpublished observation, 1995).

Figure 2. Normal gait involves bending the knee, flexing the hip, lifting the leg, swinging the foot forward, striking the ground, and pushing off. This child with a 7cm limb length discrepancy (LLD) toe-walks on the short side to smooth the gait.

Radiologic Assessment

A history and clinical examination may not always allow for an accurate diagnosis. A screening leg length radiograph, known as a scanogram, aids in making a complete diagnosis (Fig. 3). In growing children, a scanogram should be accompanied by a bone age film of the wrist, used to correlate skeletal maturation with chronologic age. Serial scanograms and bone age films are used by the orthopedic surgeon to predict the maturity of the discrepancy and plan treatment when necessary.

Figure 3. This scanogram shows a 9.1-cm limb length discrepancy with a shorter left side than right side. Without moving the patient, separate exposures of the hips, knees, and ankles were obtained by placing a scale directly on the film. The scanogram should be accompanied by a bone age film in growing children to
correlate skeletal maturation with chronologic age.

TREATMENT

An LLD may be only one factor affecting the child's development. Features including scoliosis, pelvic obliquity, contractures, dysplasias, and angular deformities must be identified. The medical condition of the child becomes critical when factors that influence healing are present (e.g., diabetes mellitus or poor nutrition). Treatment should be determined based on the cause, pattern and prediction of growth, and on symptoms. The comprehensive management of an LLD is also dependent on the experience of the treating surgeon and the family support system surrounding the child.

Many methods of equalization (surgical and nonsurgical) are available for treating LLD (Fig. 4). The treating surgeon should review all possible options to determine the best one for the patient. Collaboration with the patient and family is necessary. The surgeon who treats a patient on the basis of his or her bias may be doing a disservice to the patient.

Figure 4. Recommended treatment for each level (0 to >20 cm) of LLD.

Nonsurgical Treatment

A lift is indicated when the inequality affects the gait pattern, shoe wear, function, or causes pain. A 1-cm lift can fit comfortably inside of the shoe; however, larger inserts can render the foot unstable in the shoe. Lifts placed on the sole of the shoe function well up to approximately 3 cm. Beyond this, the shoe becomes heavy and awkward. Compliance depends on the patient and family. A smaller lift may be cosmetically unacceptable to some patients, whereas a larger lift works well and is accepted when the child is young and understands that the lift is temporary until surgery can be performed.

Determining the size of a lift depends on individual circumstances. In general, half of the existing discrepancy relieves the symptoms. A child with a 3-cm difference and backache may benefit from a 1-cm sole lift and 0.5-cm heal insert. In many cases, completely equalizing the LLD is undesirable (i.e., muscle weakness about the hip, knee, or ankle) and may cause a further compensation to clear the foot while it swings through.

Surgical Shortening

Limb shortening can be accomplished in one of two ways: (1) the physeal growth center can be retarded or arrested prematurely by epiphysiodesis (growth plate arrest), or (2) the long bone can be shortened by resecting a segment of the bone.

Epiphysiodesis

In 1933, Phemister (9) described epiphysiodesis as a technique to equalize discrepancies of 2 cm to 5 cm; however, multiple, large incisions created morbidity for the child. In recent years, percutaneous techniques have replaced Phemister's method, allowing outpatient surgery with minimal morbidity (Fig. 5).(1, 4) The greatest problem with epiphysiodesis is selecting the proper timing of surgery. Epiphysiodesis is most commonly performed 2 to 3 years prior to maturity (girls, age 11 or 12 years; boys, age 12 or 13 years). For best results, patient referral should occur early, by age 7 or 8 years, which allows the orthopedic surgeon to observe and record the pattern of growth and appropriately time the growth plate arrest.

Figure 5. Case example. A, Areas of surgical arrest. B, Eight weeks after epiphysiodesis, early signs of arrested growth are present.

Bone Shortening (Resection)

This technique is reserved for patients who are not candidates for limb lengthening, do not wish to undergo lengthening, or are skeletally too mature for epiphysiodesis. Performing surgery on the "normal" leg is objectionable to some, but in experienced hands poses little risk of injury to the limb.

Experience shows that it is easier and safer to shorten the femur than the tibia.(2) Common techniques of bone resection include open resection in the subtrochanteric region with plate fixation or resection in the shaft with intramedullary rod fixation. Both methods require a secondary, minor procedure to remove the implant (Fig. 6).

Figure 6. Case example. A, A 1 5-year-old female adolescent had a 6.4-cm LLD secondary to congenital hemihypertrophy. A limp and low back pain were present. B, A left femoral shortening procedure was performed. C, An intermedullary rod was removed. D, The symptoms were completely relieved.

Surgical Lengthening

Increasing bone length has been attempted by a variety of methods, including creating arteriovenous shunts, implanting foreign material under the epiphysis, stripping the adjacent periosteum, ganglionectomy, or mechanical distraction. Of these, only mechanical distraction is a practical method of limb lengthening.

Mechanical bone lengthening was first reported by Codivilla (2) in 1905. He performed a transverse osteotomy through which an abrupt intraoperative distraction occurred. The lengthening site was held in place with plaster and a fraction pin. It required prolonged bed rest and was associated with extreme complications. In recent years, technical advances in limb lengthening have focused on the development of external fixators that allow for weight bearing and maintenance of joint function during gradual bone and soft-tissue regeneration. The introduction of each new fixation device has added new principles and operative techniques for treating skeletal deformities (Fig. 7).

Figure 7. Case example. A, An 18-year-old woman had a severe limp, low back pain, and knee pain associated with a 9.1-cm postphyseal trauma LLD. B, The radiograph shows early separation of an osteotomy with a monolateral fixator providing distraction. C, The bone was lengthened 1 mm per day. D, An active ambulating patient heals more quickly than a nonactive patient. E, The end result with limp and back pain alleviated.

In the past 15 years, the primary advancement in limb lengthening has been the method described by Ilizarov, (7) whose biologic principle of distraction osteogenesis has revolutionized limb lengthening. Distraction osteogenesis is based on the body's ability to regenerate bone and soft tissue. Ilizarov's circular external fixation system is complex but provides for multilevel corrections (Fig. 8).

Figure 8. Case example. A, A child with a congenitally short limb was treated using the llizarov apparatus (Smith and Nephew Orthopedics, Memphis, TN) to lengthen the leg and simultaneously correct a second deformity. B, Wearing the fixator during maturation of bone regenerate. C, The result shortly after fixator removal.

Process of Limb Lengthening

Treating LLD often becomes a process that occurs over a prolonged period of time. This process is different from most orthopedic treatment procedures, which are performed in a single operation. A child whose family is not capable of sustained follow-up may be a poor candidate for limb lengthening.

Preoperative Planning. The best method of treatment offers an achievable outcome with the least risk. To achieve this, a preoperative plan is devised and a problem list is made. The list takes into consideration the deformity features (relative risk), underlying condition, treatment goals, the patient's and family's expectations, and the surgeon's experience. Once complete, this list is written on an overlay tracing or computer digitization of the radiograph.

Patient Education. Through patient education, a detailed course of events can be presented that prepares the child and family both physically and emotionally for the prolonged treatment. Strict patient compliance and rapport throughout treatment is vital.

Precise Surgical Technique. The surgical techniques of fixator assembly and application all require instruction and practice. Special seminars to learn these techniques are available; however, a difficult learning curve exists with this treatment and requires commitment on the part of the surgeon.⁵

Complications. Avoiding complications in limb lengthening is a constant challenge. Pin tract infections are the most common problem associated with lengthening and are controlled with local wound care and oral antibiotics. It is uncommon for an experienced surgeon to find it necessary to alter pin sites when infections occur; however, complications of fracture, axis deviation, and soft tissue contractures continue to make limb lengthening a challenging form of treatment for patients and limb length specialists. Complication prevention is achieved by assessing the risk and predicting the complications before they occur.

Postoperative Care. Postoperative care during the gradual correction process requires a coordinated approach between the surgeon and a multidisciplinary team that includes a limb-fixator nurse, physical therapist, and many other members. Weekly clinic visits during lengthening or deformity correction are necessary. Visits occur monthly during the healing phase. Physical therapy and graded return to normal function are continued throughout treatment. The fixators are removed on an outpatient basis.

Daily Activity. A normal lifestyle during treatment is encouraged. The regeneration of new bone relies heavily on blood flow occurring during functional use of the limb. Although treatment time is long, children are able to remain mobile and active, making this treatment very successful (Fig. 9).

Figure 9. Patients undergoing the process of limb lengthening are encouraged to pursue normal activities. A, The boy on the right continued his participation in competitive swimming during a tibial lengthening. B, These 3-year-old children remained very active during treatment. C, Maintaining joint function is essential.

SUMMARY

The surgical management of LLD has gradually evolved from a time when patients were bedridden in traction for prolong periods of time to the point at which much of the treatment time is spent in mobility. Improved surgical techniques, such as percutaneous epiphysiodesis and distraction osteogenesis, have contributed greatly to the success of surgery for LLD. Factors affecting outcome and patient satisfaction must be weighed carefully before selecting treatment for LLD.

References

1. Canale T, Russel T, Holcomb R: Percutaneous epiphysiodesis: Experimental study and preliminary clinical results. J Ped Orthop 6:150-156, 1986

2. Codivilla A: On the means of lengthening in the lower limbs, the muscles and tissues which are shortened through deformity. Am J Orthop Surg 2:353-369, 1905

3. Coleman SS, Scott SM: The present attitude toward the biology and technology of limb lengthening. Clin Orthop 264:76-83, 1991

4. Dahl MT, Kennedy T: Single entry percutaneous epiphysiodesis: Outpatient management of limb length discrepancy. J Pediatr Orthop, submitted

5. Dahl MT, Gulli B, Berg T: Complications of limb lengthening: A learning curve. Clin

Orthop 301:10-18, 1994

6. Gage JR (ed): Gait Analysis in Cerebral Palsy. London, MacKeith, 1991

7. Ilizarov GA: Modern techniques in limb lengthening: Clinical application of the tension-stress effect for limb lengthening. Clin Orthop 250:8-26, 1990

8. Kawamura B, Hosono S, Takahashi T: The principles and technique of limb lengthening. International Orthopaedics (SICOT) 5:69-83, 1981

9. Phemister D: Operative arrestment of longitudinal growth of bones in the treatment of deformities. J Bone Joint Surg Am 15:1-15, 1933

10. Shapiro F: Developmental patterns of lower extremity discrepancies. J Bone Joint Surg Am 64:639-651, 1982

11. Torode IP: The behavior of limb inequality in specific disorders. In Menelaus MB (ed): The Management of Limb Inequality. London, Churchill-Livingstone, 1991, pp 37-8