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Simple technique for anterior hemi-epiphysiodesis with cannulated screws does not violate knee cartilage
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Development of a knee flexion deformity is a common problem among pediatric patients with diverse neuromuscular problems. In children with cerebral palsy and other associated disorders, short or tightened hamstrings lead to a flexion deformity of the knee. If not corrected, the deformity can progress to a fixed knee flexion contracture with associated bony changes including patella alta, tibial tubercle elevation, patellar fragmentation and development of ovoid-shaped femoral condyles. Children with a knee flexion contracture subsequently demonstrate several gait abnormalities, including development of crouch gait.
Current treatments for fixed knee flexion deformity are varied, and each treatment has several known complications. Options include posterior capsule release with or without PCL resection, knee extension osteotomy, serial casting and anterior hemi-epiphysiodesis (guided growth). While effective, posterior capsule release with or without PCL resection places several important neurovascular structures at risk and may destabilize the knee.
Knee extension osteotomy, though well-described and effective, involves a significant amount of surgery and a period of non-weight bearing leading to further weakness. Significant shortening, creation of a secondary deformity and, in a growing child, quick remodels are also possible with this procedure. Serial casting also has been attempted, but its efficacy is questionable for large deformities and can result in posterior tibial subluxation.
Anterior screw placement for anterior hemi-epiphysiodesis is shown.
Anterior hemi-epiphysiodesis results in gradual correction of the flexion contracture.
Images: Cobb L
Anterior hemi-epiphysiodesis with plates or staples has also been described. Disadvantages of this technique are hardware irritation, and the need for an open growth plate and the need to violate the knee cartilage with hardware.
We present a simple technique for anterior hemi-epiphysiodesis using cannulated screws. This method does not violate the knee cartilage, is extra-articular and results in less hardware prominence (Figure 1).
Indications for surgery
Indications for this procedure include a clinically significant fixed knee flexion contracture in a child with at least 2 years of growth remaining and absence of hamstring shortening. A clinically significant knee flexion contracture corresponds to a popliteal angle of greater than 20°. In our practice, all patients undergo a preoperative gait analysis to determine the rotation of the pelvis, which can indicate shortened hamstrings that require lengthening at the time of surgery. Contraindications include closed growth plates or prior extension osteotomy with a recurvatum deformity of the femur.
Technique
The patient is placed supine on the operating table and leg is prepped and draped. A tourniquet is not routinely used because expected blood loss is minimal. Hamstrings are lengthened if indicated on gait analysis. If a fixed knee flexion contracture remains after hamstring lengthening, then anterior distal femur hemi-epiphysiodesis is performed. A lateral flouroscopy shot of the knee is then obtained. Lateral views can be obtained by moving the C-arm or, if hip range of motion is adequate, by rotating the hip, though this must produce a true lateral view of the knee.
Using flouroscopic guidance, a non-threaded 0.62-inch K-wire or similar guide pin is inserted percutaneoulsy and drilled in antegrade fashion across only the lateral portion of the anterior physis of the distal femur, taking care to avoid penetration of the distal articular surface. Position of the K-wire is then confirmed on AP and lateral fluoroscopic views.
Care is taken to place the K-wire outside the trochlear groove to avoid screw irritation on the undersurface of the patella. K-wires are measured using a second K-wire to ascertain screw length. The K-wires are then over-drilled using a cannulated drill. The drill is removed and a cannulated fully threaded screw at least 4.5 mm in diameter is inserted over the K-wire.
Screws are inserted subcortically to avoid potential irritation of the patella (Figure 2). The procedure is repeated on the anterior and medial physis. The K-wires are removed and the knee is taken through a full range of motion with fluoroscopy in the AP and lateral positions to evaluate for crepitus and ensure the screws remain subcortical and do not irritate the patella. If there are any concerns, screw position should be changed so it does not interfere with patellar motion.
Postoperative immobilization is determined based on other procedures performed, as no specific immobilization is needed for this procedure. Often the patient has had a concomitant hamstring lengthening, for which we use knee immobilizers or long leg extension casts if there is a residual knee flexion contracture. Postoperative therapy protocols are centered at early ambulation and motion to try to preserve strength.
Radiographs (Figures 3 and 4) are taken at postoperative visits of 6 weeks, 3 months, 6 months and 1 year to assess the effect of the epiphysiodesis. The screws do not need to be removed unless bothersome or there is concern regarding over-correction.
Placement of cannulated screws on AP knee view is shown.
Anterior hemi-epiphysiodesis results are shown on a lateral knee radiograph.
Simple, effective method
Anterior hemi-epiphysiodesis using cannulated screws is a simple and effective method for the treatment of knee flexion deformity in the pediatric population. This operative technique is a minimally invasive way to impart sagittal correction about the knee in children with knee flexion contractures. Unlike non-growth modulation techniques, this procedure does not result in immediate correction and, therefore, is primarily used as a supplement to other techniques, such as therapy, bracing or soft tissue procedures.
Follow-up data will be necessary to determine efficacy and long-term complications.
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- For more Information:
- Leah Cobb MD; and James J. McCarthy, MD, can be reached at Cincinnati Children’s Hospital Medical Center, Department of Orthopaedics — MLC# 2017, 3333 Burnet Ave. ML C2107, Cincinnati OH 45229-3039; Cobb’s email: leah.cobb@cchmc.org; McCarthy’s email: james.mccarthy@cchmc.org.
Disclosures: Cobb and McCarthy report no relevant financial disclosures.