Chapter 45

Distal Femoral Osteotomy for Crouch Gait

Tom F. Novacheck

DEFINITION

• Crouch gait is defined as walking with excessive knee flexion during stance.

• Crouch is a common walking pattern in neuromuscular conditions, particularly for individuals with cerebral palsy.

• Many potential abnormalities of bone alignment and joint flexibility can accompany or lead to crouch gait.

• Persistent crouch in adolescence frequently results in fixed knee flexion deformity and patella alta.

• Potential contributing factors include hamstring contracture, hip flexion deformity, foot deformity, loss of plantarflex-ion–knee extension couple, excessive femoral anteversion, and external tibial torsion. Weakness and impaired motor control are contributing factors. For some patients, disorders of balance or sensory impairments are major contributors.1

• Fixed knee flexion deformity is oftentimes associated with patella alta. Fixed knee contracture and patella alta are the components of the pathology that are treated with these procedures.

  ANATOMY

• Typical knee extension range is 0 degrees (full knee extension).

• Posterior capsular contracture can result from the imbalance between spastic or contracted hamstrings and knee extensor dysfunction (often associated with patella alta).

• Distal femoral anatomy is normal, although torsional deformity (excessive femoral anteversion) is commonly seen in neuromuscular conditions, especially cerebral palsy.

  PATHOGENESIS

• The pathogenesis of knee flexion deformity and crouch gait in cerebral palsy will be described, as it is the most common condition to be treated with this technique. However, other causes of knee flexion deformity and persistent crouch could be treated similarly.

• Preterm, perinatal, or infantile brain injury leads to static encephalopathy.

• This neurologic disorder causes hypertonia (commonly spasticity), impaired motor control, and weakness.

• Typical muscle growth results from the tension produced by normal bone growth and age-appropriate, typical gross and fine motor activities.

• Musculotendinous growth in children with cerebral palsy is delayed because spastic muscle does not grow normally in response to stretch and delays in attainment of typical functional activities.

• Bone growth and joint development are also adversely affected by a lack of normal functional activities, as well as spasticity and musculotendinous contracture.

  NATURAL HISTORY

• Crouch gait is not uncommon at 5 to 7 years of age. At these ages, the primary causes are spasticity, weakness, and impaired balance mechanisms.

• If crouch persists during later childhood, musculotendinous contractures of the two-joint muscles (psoas, hamstrings, rectus femoris, and gastrocnemius) develop. Persistent alignment in a crouch position leads to excessive elongation of the one-joint muscles (gluteus maximus, quadriceps, and soleus), which are primarily responsible for normal upright posture.1

• The soleus, in particular, is responsible for restraining the forward movement of the tibia over the plantigrade foot (also known as the plantarflexion–knee extension couple).1 As a result, the ground reaction force vector typically falls near the knee joint in midstance, minimizing the demand on the quadriceps to maintain knee extension.

• If weak or elongated, the ankle plantarflexors are no longer able to restrain the forward movement of the tibia over the plantigrade foot (loss of the normal plantarflexion–knee extension couple).

• Further growth leads to loss of knee joint mobility and the development of posterior capsular contracture.

• For some patients in adolescence, pain from stress fractures or from excessive stress in the patellofemoral joint itself can lead to a precipitous worsening of crouch.

• Knee pain, decreased ambulatory function, or the loss of walking ability in adulthood in individuals with cerebral palsy is common.3

  PATIENT HISTORY AND PHYSICAL FINDINGS

• Physical examination methods include the following:

  • Knee range of motion: Loss of extension indicates a posterior capsular contracture; loss of flexion could be due to quadriceps contracture and especially rectus femoris spasticity or contracture if the knee is flexed in the prone position. Normal upright walking requires full knee extension range of motion.

  • The examiner should palpate the inferior pole of the patella and tibial tubercle. This distance is typically equal to patellar length. The patella is pushed medial to lateral to detect patellar instability. Patella alta, which can be a cause of knee pain or can contribute to knee extensor dysfunction, is suspected if:

    • The distance from the inferior pole of the patella to the tibial tubercle exceeds patellar height.

    • The patella is unstable medial to lateral.

    • The patellar tendon (as opposed to the patella) lies in the patellofemoral groove.

    • With the knees in extension, the superior pole of the patella is typically one fingerbreadth proximal to the ad-ductor tubercle.

  • Knee extension lag test: Normal extension lag is 0 degrees. Terminal knee extension strength is required to control knee flexion during loading response.

  • Hamstring contracture: Normal popliteal angle can be as much as 30 degrees during preadolescence. It is commonly

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greater in boys than in girls. For differential diagnosis purposes, it is important to identify all potential contributors to crouch gait.

• If resistance is felt as the popliteal angle is being assessed, hamstring spasticity is identified. If the knee is flexed with the patient prone and the hip extended, spasticity of the rectus femoris is identified.

  • Spasticity is one of the primary causes of the series of events that ultimately leads to crouch. If severe enough, direct spasticity treatment may be necessary.

• A complete examination of the patient should also include evaluation of associated abnormalities to identify all potential contributors to crouch gait, including hip flexion deformity, hamstring contracture, femoral anteversion, tibial torsion, foot deformity or instability, balance disorder, and visual or sensory disturbances.

  IMAGING AND OTHER DIAGNOSTIC STUDIES

• A plain lateral radiograph of the knee in maximum extension should be obtained to assess for fixed knee flexion contracture and patella alta (FIG 1).

• If the knee is held in maximum extension, the femoral–tibial angle on the lateral radiograph represents the degree of true knee flexion deformity.

• The knee is extended maximally with a bolster just below the patella to assess the true degree of patella alta. Patella alta can be documented using the Insall ratio or the Koshino index.2

• Inferior-pole sleeve avulsion injuries of the patella are common in children with spastic cerebral palsy and can be identified on the lateral radiograph. The development of a stress fracture is typically painful and can lead to the rapid progression of crouch over a short period.

• Computerized gait analysis provides much-needed insight to create a problem list to guide treatment decision making by identifying the numerous other contributors to crouch listed above.

  DIFFERENTIAL DIAGNOSIS

• Knee extensor lag with or without patella alta

• Hamstring spasticity or contracture

• Hip flexor spasticity or contracture

• Femoral anteversion

• Tibial torsion (typically external)

   

   

   

  FIG 1 • Lateral radiograph of knee in maximum extension. Patellar position and degree of knee contracture can be assessed from this view.

• Ankle plantarflexor insufficiency

  • Foot deformity

  • Excessive midfoot instability

  • Soleus weakness: primary versus iatrogenic from prior Achilles tendon lengthening

    NONOPERATIVE MANAGEMENT

• Physical therapy (stretching and strengthening) helps minimize the development of musculotendinous contracture secondary to spasticity and weakness.

• Botulinum toxin injections or oral spasmolytic agents can help manage spasticity.

• Functional strengthening of the muscle groups that contribute to crouch (ankle plantarflexors, knee extensors, and hip extensors) can help correct muscle imbalance.

• Nighttime knee extension splinting with knee immobilizers or bivalved casts can help prevent a flexed knee position during the night, thereby minimizing the development of knee capsular contracture.

  SURGICAL MANAGEMENT

  Preoperative Planning

• The lateral radiograph of the knee in maximum extension should be reviewed for the degree of knee contracture, patellar height, presence of a stress fracture at the inferior pole of the patella, and the status of skeletal maturation (see Fig 1).

• Gait analysis data should be reviewed to assess for knee extension lag, degree of crouch, presence of hip flexion contracture, spasticity or contracture of the rectus femoris, and hamstrings length and for the presence of tibial torsion, femoral anteversion, and foot deformity.

• Examination under anesthesia for femoral anteversion and coronal-plane malalignment of the knee should be accomplished before positioning.

• Other deformities can be addressed concurrently under the same anesthetic.

  Positioning

• If severe femoral anteversion is present, a proximal femoral osteotomy may be required in addition to the distal osteotomy, as it is difficult to correct more than 25 to 30 degrees of malrotation distally.

• Tibial torsion and foot deformity should also be addressed first. While these can be done supine, I prefer prone positioning.

   

   

   

   

  FIG 2 • Positioning for distal femoral extension osteotomy. Supine position allows access for both extension osteotomy and patellar advancement. The procedures are performed under tourniquet control. Note the knee contracture and patella alta.

   

  Prone positioning is preferred as it allows accurate examination and correction of rotational profile consistent with the physical examination methods used in the clinic.

  • The extension osteotomy and patellar advancement are performed supine with the leg draped free (FIG 2).

    Approach

    • The extension osteotomy of the distal femur is performed via a lateral distal femoral incision.

    • The patellar advancement is performed through a direct anterior incision centered over the tibial tubercle.

       

       

       

      TECHNIQUES

       

      DISTAL FEMORAL EXTENSION OSTEOTOMY

      • The procedure is performed under tourniquet control.

      • Through the lateral distal femoral incision, the fascia is opened and the vastus lateralis is reflected from its posterior origin and elevated to expose the distal femur sub-periosteally.

      • Circumferential subperiosteal retractors are placed.

      • Typically a 90-degree adolescent AO blade plate is used for fixation. If no varus or valgus deformity correction is required, the guidewire for chisel placement is placed at a 90-degree angle to the femoral shaft on an AP image in the plane of the tibia (as this will reflect final coronal plane alignment) (TECH FIG 1A).

      • The guidewire entry point is through the anterior portion of the lateral femoral epicondyle in line with the femoral shaft to avoid anterior or posterior translation of the distal fragment. It is placed just proximal to the distal femoral physis if the patient is immature and at the physeal scar if growth is complete.

      • Transverse-plane position is in line with the axis from the lateral to the medial femoral condyle.

      • The chisel is inserted exactly parallel and just proximal to the pin, with the angle guide for the AO chisel aligned parallel to the tibia (TECH FIG 1B). The angle between the AO chisel guide and the femoral shaft is equal to the degree of knee contracture and the extension to be obtained.

• Depending on preoperative assessment, a second pin can be placed proximal to the osteotomy site to assist with rotational control. It can be placed at a converging angle in the transverse plane to match the degree of derota-tion desired.

• The distal osteotomy is performed first. The oscillating saw blade is aligned exactly parallel and 10 to 15 mm proximal to the chisel (TECH FIG 1C).

• The second osteotomy is performed perpendicular to the femoral shaft, typically meeting the first osteotomy at the posterior cortex (although with more severe deformities, a cuneiform wedge including several millimeters of posterior cortex may also be removed to avoid neu-rovascular stretch).

• The anterior wedge of bone is removed (TECH FIG 1D).

• Varus–valgus deformities can be corrected by altering the guide pin placement in the coronal plane or bending the implant to match the desired correction.

• The osteotomy is realigned by derotating if necessary and extending the knee.

• The chisel is replaced with the Synthes AO blade plate.

• The femoral shaft is reduced to the plate and held with a Verbrugge clamp (TECH FIG 1E).

• After an initial screw is placed in compression to hold alignment, final coronal plane alignment is assessed. Proper mechanical axis alignment is confirmed if the elec-

   

  A B C D

   

  TECH FIG 1 • Distal femoral extension osteotomy. A. Blade plate is held an-teriorly over the leg to position guidewire 90 degrees to femoral shaft (Carm view orthogonal to tibia, not femur). B. The chisel guide is parallel to the tibia. C. Distal osteotomy is parallel to chisel; proximal osteotomy is perpendicular to shaft. D. Anterior wedge of bone removed. E. Knee in full ex-

  E tension after blade plate is reduced to the femoral shaft.

   

  TECHNIQUES

   

  trocautery cord, aligned directly over the hip and ankle joint centers, also passes directly over the knee joint center.

  • Final coronal plane alignment can be adjusted if necessary by laterally displacing the distal fragment further by impacting the plate more completely or by removing the plate and adjusting its angle accordingly.

• The final screws are placed.

• Any significant posterior bone prominence should be re-sected with the oscillating saw.

• A Hemovac drain can be placed posteriorly.

• The wound is closed in layers.

   

  PATELLAR ADVANCEMENT

  • If the patient is skeletally immature, transposition of a tibial tubercle bone block would cause an anterior growth arrest. Instead, the patellar tendon is advanced without violating its insertion (TECH FIG 2A).

  • A T-shaped periosteal incision is made just distal to the tibial tubercle apophysis.

  • Medial and lateral flaps of periosteum are elevated (TECH FIG 2B).

  • The tendon is separated from the cartilaginous tibial tubercle apophysis using a fresh scalpel, working at the junction of the fibers of the patellar tendon and the cartilage (TECH FIG 2C). It is best to err on the side of leaving a few fibers of tendon on the cartilage than to inadvertently injure the cartilage. Care must be taken to maintain an adequate thickness of tendon (about 2 mm) without defects.

  • The next step is placement of a tension band from the patella to the tibia to protect the repair. A guidewire for the 2.7-mm cannulated AO drill bit is passed percutaneously transversely through the midportion of the patella.

  • The cannulated drill bit is drilled across the patella from lateral to medial. The guidewire is removed, leaving the drill bit in place.

     

• A suture passer is passed retrograde through the drill bit from medial to lateral, and then the drill bit is removed.

• A 2-mm Fibertape suture is passed through the drill hole using the suture passer.

• Using a long right-angle clamp, the ends of the Fibertape suture are passed along the edges of the patellar tendon via a subcutaneous tunnel to the anterior incision.

• Using a similar technique as described for the patella, a transverse drill hole is placed in the tibia and the suture is passed through it (TECH FIG 2D).

• The patella is advanced distally by tensioning the Fibertape until the inferior pole of the patella is at the femoral–tibial joint line, at which point the knot in the Fibertape is tied (TECH FIG 2E).

• Two baseball (Krackow) stitches are placed in the patellar tendon, one medially and one laterally, using 0 Ethibond suture (TECH FIG 2F).

• These sutures are tied deeply under the periosteal flaps.

• The periosteal flaps are then sewn over the patellar tendon (TECH FIG 2G).

• The wound is closed in routine fashion.

   

   

   

   

   

   

   

  A B C

   

   

   

   

   

   

   

   

  D E F

   

   

   

  TECH FIG 2 • Patellar advancement. A. Patellar tendon redundancy after extension osteotomy. B. Periosteal flaps distal to tibial tubercle apophysis.

  C. Patellar tendon after sharply dividing the tendon from the cartilaginous apophysis. D. Fibertape placed transversely across patella (here shown as open procedure, now performed percutaneously as described in the text).

  E. Fibertape tied to hold patella down in final position. F. Medial and lateral Krackow sutures in patellar tendon. G. Tendon advanced under periosteal flaps, flaps repaired over tendon, and Fibertape along medial and lateral edges of

  G tendon.

   

   

   

  TIBIAL TUBERCLE ADVANCEMENT

  • For skeletally mature patients, the patellar tendon and tibial tubercle are exposed.

  • A small tibial tubercle bone block with patellar tendon attached is created with an oscillating saw and completed with an osteotome. The typical size is the width of the patellar tendon, 2 to 2.5 cm in length and 7 to 10 mm thick.

  • The 2-mm Fibertape is placed identical to the previous description.

  • A receptacle site for the tibial tubercle bone block is created at the appropriate level.

  • The distally excised bone block is impacted into the original tibial tubercle site.

     

• The tibial tubercle is inserted into its receptacle site and secured with a single 4.5-mm AO screw, overdrilling the tibial tubercle fragment to compress the bone block and countersinking to avoid screw prominence.

  TECHNIQUES

   

• The typical advancement is 2 to 2.5 cm.

• By keeping the tibial tubercle bone block relatively short in length, a small bridge of intact anterior cortical bone can provide a proximal buttress to resist proximal migration of the tibial tubercle bone block postoperatively.

• The knee should be able to flex 60 degrees at this point without excessive tension or disruption of the repair.

• The wound is closed in routine fashion.

   

  PEARLS AND PITFALLS

  Recurrence of knee flexion deformity ■ If a distal femoral extension osteotomy is performed without patellar advancement, there and persistence of crouch is a high risk of these postoperative problems.

  Patellar advancement in isolation ■ This is effective to treat crouch in the presence of a knee extension lag without knee

  flexion contracture.

  Avoiding sciatic nerve palsy ■ Postoperative immobilization in flexion during the time of acute swelling (first 3 days)

  and resection of the posterior bony prominence on the distal fragment have helped minimize this complication.

  Loss of patellar fixation ■ Supporting patellar advancements with a Fibertape tension band has minimized this

  complication.

  Increased anterior pelvic tilt ■ Detecting and treating hip flexion deformity as well as rectus femoris spasticity and

  contracture (simultaneous rectus femoris transfer) have been helpful, but this finding seems to be common with surgical intervention at this age.

  Genu varum and valgum ■ Distal femoral osteotomy requires meticulous care to ensure optimal postoperative

  alignment in all three planes.

  • Contractures between 10 and 25 degrees are typically appropriate for this compensatory osteotomy of the distal femur.

  • In growing children with relatively small deformities, anterior distal femoral figure 8 plating may be a consideration.

  • The treatment of flexion contractures of 30 degrees or greater introduces significant distal femoral deformity.

  • Modest transverse-plane deformities can easily be corrected but again this requires meticulous attention to detail.

  • Malrotation greater than 30 degrees is difficult to correct with this technique.

  • Preoperative coronal-plane deformities can be corrected, and care must be taken to avoid creation of postoperative varus–valgus deformities.

   

   

  POSTOPERATIVE CARE

  • AP and lateral radiographs are reviewed to confirm proper alignment (FIG 3).

  • The knee is immobilized for 3 days in 20 to 30 degrees of flexion in a Robert Jones dressing to avoid sciatic nerve stretch.

  • Then a knee immobilizer is used for 6 weeks.

  • Use of a continuous passive motion (CPM) machine is begun on the third postoperative day; initially the range is from 0 to 30 degrees, and it is advanced to 90 degrees by 6 weeks postoperatively.

  • After 3 weeks, active range of motion and weight bearing are initiated. Once quadriceps strength and control are sufficient, the knee immobilizer can be discontinued.

    OUTCOMES

    • Knee flexion deformity and patella alta can reliably be corrected.5

    • Preoperative stress fractures and knee pain are improved or resolved in the vast majority of patients.

    • Worsened anterior pelvic tilt is commonly seen and does not seem to be a result of persisting contracture or weakness.

    • Crouch gait is corrected effectively for those who have the combined procedure of extension osteotomy and patellar advancement. Crouch is also effectively treated in the absence of knee contracture with patellar advancement alone, as long as other musculotendinous contractures and bone or joint deformities are concurrently addressed.

       

       

       

       

       

      found to be safe (low rate of persisting anterior knee pain postoperatively) and necessary to treat crouch.

      • The natural history of crouch gait is one of worsening. With these procedures, walking ability is either maintained or improved, as indicated by gait analysis and a functional mobility scale.4

        COMPLICATIONS

      • Sciatic nerve palsy

      • Loss of patellar fixation

      • Recurrence of deformity

      • Wound breakdown or infection

    A B ■ Increased anterior pelvic tilt

     

    FIG 3 • Postoperative radiographs. A. On the AP view, the blade can be seen just proximal to the growth plate and the osteotomy parallel to the blade. B. The lateral view shows the blade insertion anterior in the distal femur to avoid anterior translation of the distal fragment, the posterior bone prominence of the distal fragment (in this case not felt to be large enough to warrant resection), the overcorrected patellar position (distal pole at femoral–tibial joint line), and the drill holes in the patella and proximal tibia for the Fibertape tension band.

     

• Distal femoral extension osteotomy without patellar advancement has a high risk of recurrence of contracture and typically results in only partial improvement in crouch.

• An overcorrection of patellar position compensates for weakness, impaired motor control, and spasticity and has been

REFERENCES

1. Gage JR. Treatment principles for crouch gait. In: Gage JR, ed. The Treatment of Gait Problems in Cerebral Palsy. London: MacKeith Press, 2004:382–397.

2. Koshino T, Sugimoto K. New measurement of patellar height in the knees of children using the epiphyseal line midpoint. J Pediatr Orthop 1989;9:216–218.

3. Murphy KP, Molnar GE, Lankasky K. Medical and functional status of adults with cerebral palsy. Devel Med Child Neurol 1995;37: 1075–1084.

4. Novacheck TF, Stout JL, Tervo R. Reliability and validity of the Gillette Functional Assessment Questionnaire as an outcome measure in children with disabilities. J Pediatr Orthop 2000;20:75–81.

5. Stout JS, Gage JR, Schwartz MH, et al. Distal femoral extension osteotomy and patellar tendon advancement for the treatment of persistent crouch gait: outcome in individuals with cerebral palsy. J Bone Joint Surg Am 2008;90A:2470–2484.