Femur Lengthening with PRECICE Internal Lengthening Nail

Abstract

This is a case illustrating a 4.5 cm femur lengthening for congenital LLD. The Precice internal lengthening nail was used and the recovery was fast with normal unassisted walking at 4 months.

Brief Clinical History:

The patient is a 25 year old male with congenital LLD of 4.5 cm and without deformity. No previous treatment was rendered. The patient and the family were not interested in limb lengthening using external fixation at earlier points in his life.

Preoperative Problem List

1. Congenital LLD of 4.5 cm
2. Short femur

Treatment Strategy

1. Femur lengthening using an internal lengthening nail
2. Antegrade approach
3. Osteotomy at the apex of the femur anterior bow on the lateral x-ray
4. Iliotibial band  (ITB) tenotomy

Basic Principles

1. Make osteotomy at apex of anterior bow so that a longer straight nail can be inserted.
2. Piriformis or trochanteric entry can be used based on surgeon preference. Patients less than 19 years of age should have trochanteric entry to avoid avascular necrosis.
3. Nail length choice and osteotomy location requires planning: The goal is to have at least 5 cm of thick part of the nail in the distal segment at the end of distraction (for optimal stability), and with distraction, the thick part of the nail is pulled out of the distal segment. In this case a 305 mm nail was used. Subtract 30mm (starting length of the small diameter telescopic part of nail) and 45 mm (lengthening planned) and 50 mm (minimum length of thick part in the distal segment).
   
   In this case, 305-(30+45+50)= 180mm. The osteotomy must be less than 180mm from the proximal end of the bone. In this case, 150 mm was chosen without a problem.
4. Reaming 1.5 to 2 mm over the diameter of the nail should be done. In this case a 10.7 mm nail was used and the bone was reamed to 12.5 mm.
5. Although lengthening should ideally be done along the mechanical axis of the femur, when using an IM nail, lengthening is along the anatomic axis. Theoretically, this could increase valgus alignment. In a normally aligned limb, intramedullary lengthening along the anatomical axis of the femur results in a lateral shift of the mechanical axis by approximately 1 mm for each 1 cm of lengthening. In practical terms, this is not a substantial problem. Compare figures 2A to 5A and you will notice no increase in valgus. During lengthening, mild varus of the bone offsets the medialization of the distal femur.

Technical Pearls:

1. Use rotation markers to prevent rotational deformity. Place rotational pins parallel to each other.
2. Correct preoperative rotational deformity (not present in this case) by placing the rotational pins with the amount of angular deformity to be corrected. Use an intra-operative goniometer. After osteotomy correct the rotation and make the pins parallel.
3. Varus or valgus deformity (not in this case) can be corrected by performing the osteotomy at the apex of deformity, acutely correct deformity and then insert nail.
4. Rotate osteotomy around the IM nail before insertion of locking screws to assure a complete osteotomy.
5. I prefer to insert the distal interlocking screws to prevent malrotation. The leg and rod are rotated to get “perfect circles” needed for freehand distal locking screw insertion. Then the leg is carefully positioned using the rotational pins as guides and the proximal interlocking screws are easily inserted using the jig.

Avoiding and Managing Problems

1. Avoid propagation of the osteotomy to optimize the angular control of the nail. In this case the small proximal medial propagation of the osteotomy led to mild varus.
2. If the canal diameter is greater than the IM nail at the osteotomy site, blocking screws should be inserted to prevent deformity. They work by narrowing the IM canal. Blocking screws are to be inserted in the concavity of the anticipated deformity.
3. Mark the location of the magnet in the nail on the skin. The external magnet controller must be placed directly over the nail magnet to actuate a distraction.
4. Predrill the osteotomy before reaming. This decreases pressure in the IM canal during reaming and protects against fat embolism syndrome.
5. The ITB tenotomy helps prevent knee contracture during distraction.

Cross- References

1. Tibia lengthening with Precice internal lengthening nail
   Limb Lengthening and Reconstruction Surgery Case Atlas; Article ID: 383587; Chapter ID: 228
2. Femoral Lengthening (12 cm) with two Precice nail lengthenings. Management of a broken Precice nail during the first lengthening
   Limb Lengthening and Reconstruction Surgery Case Atlas; Article ID: 383566; Chapter ID: 207
3. Combined deformities of the femur and tibia with 9 cm shortening treated with a retrograde femoral motorized lengthening nail and a tibial plate
   Limb Lengthening and Reconstruction Surgery Case Atlas; Article ID: 383564; Chapter ID: 205

References and Suggested Reading

Burghardt RD1, Paley D, Specht SC, Herzenberg JE: The effect on mechanical axis deviation of femoral lengthening with an intramedullary telescopic nail. J Bone Joint Surg Br. 2012 Sep;94(9):1241-5. doi: 10.1302/0301-620X.94B9.28672

Kirane Y, Fragomen AT, Rozbruch SR: Precision of the Precice Internal Lengthening Nail, Clin Orthop Rel Res. 2014. Epub Digital Object Identifier (DOI) 10.1007/s11999-014-3575-0.

Rozbruch SR, Birch JG, Dahl MT, Herzenberg JE: Motorized Intramedullary Nail for Treatment of Limb Length Discrepancy.  J Am Acad Orthop Surgeons, 2014 July

Authors