Featured Case: 14-year-old high school athlete with a 3.8cm idiopathic femoral limb length discrepancy

In our Featured Case series, NuVasive® will showcase innovative cases and how our unique technology is integrated to create a cohesive system to address key patient pathologies. Our mission at NuVasive is to change patient lives and we are constantly focused on how to deliver improved patient outcomes, increase OR safety and efficiency, and extend our technology to future applications.

Surgeon: Christopher Iobst, M.D. from Nationwide Children’s Hospital
Limb Lengthening System: Precice Stryde™

Detailed Problem List
• 14-year-old female approaching skeletal maturity
• Idiopathic limb length discrepancy with right femur 3.8cm longer than the left femur
• Symmetric mild bilateral genu valgum (Zone 1)

Brief Clinical History
14-year-old female volleyball player presenting for a scoliosis evaluation after a school screening exam. Patient had no previous history of fracture or infection involving the lower extremities. There was no family history of limb length discrepancy. She was currently not having any significant low back, hip, or knee pain.

Physical Examination
On physical examination, she was found to have a positive Trendelenberg gait. She was able to walk with both feet in a plantigrade position but tended to flex her right knee in stance. She had a normal foot progression angle in both limbs. In an upright standing position, a small curve in the spine was noted. However, the curve disappeared when blocks were placed under the left foot to level the pelvis. Forward flexion of the spine while her left foot was standing on the blocks demonstrated no deformity. In the standing position, observation from the front determined that her
limb alignment appeared symmetric and she did not have any noticeable genu varum or genu valgum deformity. Examination from behind while standing showed asymmetric knee heights with the left knee joint located higher than the right knee joint. Her spine was straight in an upright sitting position. Supine exam revealed a positive Galeazzi test (right knee higher than the left knee). Both knees were stable to ligamentous exam. There were no joint contractures noted in either hip, knee or ankle. In the prone position, she had symmetric internal and external rotation of both hips and a normal thigh foot angle on both sides. She had intact sensation and normal muscle strength in both lower extremities.

Radiographic Analysis
Standing full length bilateral lower extremity radiographs were obtained. A 2.5cm block under the left foot did not fully correct her limb lengths. An additional 1.3cm of discrepancy was present creating a total discrepancy of 3.8cm. Analysis of the individual segments reveals the tibias to be symmetric in length but the right femur is 3.8cm longer than the left femur. The mechanical axis is symmetrically slightly lateral to neutral in both knees (Zone 1) (Fig. 1). The mLDFA measurements show a 4 degree difference between the two sides (Fig. 2).

Treatment Strategy

The decision making process was as follows:

1. Since the patient is essentially skeletally mature, an epiphysiodesis is no longer an option to correct the limb lengths.

2. Shortening of the right femur was discussed as a management option but the family opted for lengthening of the left femur since she was a volleyball player and did not want to sacrifice any height.

3. Since the femur was the primary source of her leg length discrepancy, this was the bone that was chosen for the lengthening.

4. While it was recognized that the left lower extremity has mild distal femoral varus and compensatory proximal tibial valgus, the decision was to minimize the number of surgeries by focusing on just correcting the limb length discrepancy. Based on her skeletal maturity, she was not a candidate for guided growth.

5. Since the distal femoral physis was still open, an antegrade rather than a retrograde femoral nail was chosen.

6. Based on surgeon preference, however, a trochanteric entry antegrade nail was used.

Surgical Planning
1. Since the femur was the segment chosen for lengthening, dedicated AP and Lateral radiographs of the left femur were obtained (Figs. 3a, 3b).

2. On the AP view, the appropriate length of the nail and diameter of the nail were determined (10mm x 335mm). It is recommended to over-ream 2mm to safely insert the nail. Therefore, this extra 2mm needs to be taken into account when determining the nail diameter size.

3. On the lateral view, the proposed diameter of the nail was double checked to make sure it would fit safely in both planes. The apex of the sagittal bow was identified as the proposed osteotomy site. An osteotomy at this level will allow passage of the straight nail into the curved bone.

4. The proposed osteotomy site is confirmed on the AP view. To ensure that at least 5cm of the thick portion of the nail remains in the distal segment throughout lengthening (for maximum stability), the osteotomy should not be within 11.5cm of the distal tip of the nail. (11.5cm = amount of desired lengthening (3.5cm) + 5cm thick portion of nail + 3cm male portion of nail extending out of female portion of nail). To avoid compromising the proximal interlocking screw location, the osteotomy should not be within 6cm of the proximal end of the nail. The area between the proximal and distal
osteotomy limits is the safe osteotomy zone (Fig. 4)

1. The nail length was confirmed by measuring with ruler (Fig. 5).

2. Vent holes were placed at the proposed osteotomy site (Fig. 6).

3. A guide wire was placed percutaneously into medial tip of the greater trochanter.

4. Gradual reaming over a ball tipped guide wire was performed. The reaming allows bone graft to spill out of the vent holes around the osteotomy site. It is recommended to ream 2mm greater than the diameter of the nail to allow minimal force during the nail insertion process.

5. The nail is inserted up to the vent holes and the osteotomy is completed. The nail is then passed into the distal fragment.

6. Proximal and distal locking screws are placed.

7. Nail function is tested in the operating room and 1mm lengthening is performed (Figs. 7a, 7b).

(A) Magnet

(B) Prelengthening lead screw space

(C) Postlengthening lead screw space after 1mm intraoperative lengthening

8. The location of the magnet is marked on the skin with
a skin marker.

Postoperative Course
1. She started gait training in physical therapy on postoperative day 0. She was allowed immediate partial weight bearing (50-75 lbs. of body weight).

2. She had a dynamic knee extension brace made postoperative. This was placed in the operating room and used nightly (10-12 hours a day).

3. She was taught a home program of strengthening and range of motion exercises to keep knee extension full and minimum knee flexion to 75-90 degrees.

4. On postoperative day 7, she started distraction at 0.75mm/day with three separate 0.25mm treatments using the ERC.

5. Weekly follow up appointments to check health of regenerate formation, joint alignment, amount of length gained and hip/knee range of motion until target goal length of 3.8cm was obtained (Figs. 8a, 8b).

6. At end of distraction phase (7 weeks) she maintain 0-130 degree left knee range of motion (Figs. 9a, 9b, 9c).

7. She was advanced to full weight bearing with crutches (80 days postoperatively) (Figs. 10a, 10b).

8. She advanced to full weight bearing without crutches (100 days postoperatively) (Figs. 11a, 11b).

9. She did not require narcotic pain medication during the entire postoperative process.

10. She has returned to all activities without restrictions at five months after surgery (Figs. 12a, 12b, 12c).

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