Precice Nail
The Precice Intramedullary Limb Lengthening System (Precice Nail) is a revolutionary device in the field of limb lengthening. Previously limb lengthening has been performed using external fixation devices such as the Ilizarov Frame of the LRS rail unilateral external fixator.
The basic principle is to create a fracture in the bone (‘corticotomy’) and wait for new bone (‘callus’) to begin forming. This callus can be stretched very slowly at a rate of about 1mm per day to restore length of a short limb. Once length is regained, the bone will mature, a process that can take several months.
When using an external fixator, this is done by adjustments either of struts in a device such as the Taylor Spatial Frame, or winding out the frame with spanners 4 times a day in the case of the Ilizarov Frame.The Precice ILLRS however has a Neodymium magnet within a titanium nail, connected to a multi-stage gearbox that drives a piston that is in turn connected to cross-locking screws through the bone at each end.
An external remote control (ERC) contains a further pair of Neodymium magnets that rotate, and when applied to the skin over the surface of the nail cause the nail to lengthen gradually.The ERC is applied 3 or 4 times a day for a few minutes, and thus lengthening is achieved without the need for pins and wires through the skin.
Unlike external fixation however, the nail device is not strong enough to support immediate full weight bearing and crutches are needed until bone forms, which may be several months in the case of longer lengthening. The overwhelming majority of these cases are for a leg length discrepancy either due to a growth deformity or post fracture shortening, but at the Royal National Orthopaedic Hospital we have been extending the indications to include the management of combined deformity with shortening, shortening below hip replacement, in the presence of other internal fixation and even in the case of multi planar deformity combined with intra-operative deformity reduction using a Taylor Spatial Frame.
Tibial lengthening
Antegrade femoral lengthening
Retrograde femoral lengthening below previous hip replacement
From a patient's perspective:
Before surgery, a thorough clinical assessment is necessary. The causes of shortening are generally either a problem of growth, or a problem of fracture with bone shortening. Each have their own specific problems.
In cases where growth has not progressed as expected, it may be part of a syndrome and there may be other congenital problems such as ligament abnormalities. Patients often have adapted by (for example) tiptoeing, and may have caused contractures of the ankle due to always being in that position. Back pain is not unusual, but if the leg length inequality has been long-standing the reverse may be true ie correcting it might cause back pains, though these usually resolve with physiotherapy if the spine remains flexible.
In post traumatic cases there is commonly associated soft tissue damage to muscles, skin and ligaments that can cause problems during lengthening, so in either case a thorough clinical assessment is necessary, usually accompanied by a standing whole leg measurement film to assess length and alignment. Occasionally a CT is also needed to assess rotational deformity accurately.
In terms of preparation for surgery attention to adequate nutrition and vitamin D levels is important, but particularly important is doing as much muscle stretching as possible. The surgery causes the bone to lengthen, but in femoral lengthening the quads and hamstrings will get painfully tight, and in tibial lengthening muscle tightness can bring about plantar-flexion contracture of the ankle. In addition, the eccentric placement of the calf muscles to the back and lateral side of the calf cause a deforming force to the bone to bend it unless additional screws are used to prevent this.
Preop stretching of the quads is achieved by knee flexion exercises, but since the rectus femoris component of the quads runs across the front of the hip joint, stretches must be preformed with the hip extended. Hamstring, ITB and adductor stretches are also vital.
Quads stretch
Hamstring stretch
ITB stretch
The surgery is usually a 3 day stay in hospital. For femoral lengthening the options are either to go in at the upper end adjacent to the hip joint(antegrade nailing), or from the lower end through the knee (retrograde nailing). The former route is preferable since retrograde lengthening has to be done through the articular surface lining the knee which might cause problems in later life. In simultaneous deformity correction however, retrograde nailing allows much greater change of alignment by tilting the lower fragment.
Valgus and shortening corrected by retrograde implant insertion.
The surgery is usually a 3 day stay in hospital. For femoral lengthening the options are either to go in at the upper end adjacent to the hip joint(antegrade nailing), or from the lower end through the knee (retrograde nailing). The former route is preferable since retrograde lengthening has to be done through the articular surface lining the knee which might cause problems in later life. In simultaneous deformity correction however, retrograde nailing allows much greater change of alignment by tilting the lower fragment.
The centre of the bone is cored out (reamed) to allow room for the fixation device. In adulthood this bone marrow no longer produces blood forming cells, so this bone is not critical.
The bone is divided by drill holes, then cracking it with a metal osteotome before the rod is reinserted and fixed above and below the osteotomy with screws. The rod is then tested in theatre by 0.5- 1mm of lengthening. Usually the osteotomy process can result in lengthening of 3 or 4 mm so overall about 5mm of length is gained immediately. The wounds are closed with stitches and simple dressings applied.
The rod is not strong enough on its own to allow weight-bearing, so 2 crutches are used. It is important to keep blood flowing in the leg to reduce DVT risk, so the natural pattern of walking with just the weight of the leg on the floor is undertaken ie 'touchdown weightbearing'.
Once the patient is safe and mobile on crutches, notably safe on stairs, transferring in and out of bed, on and off a toilet etc they are allowed home. This is usually 3 days post op. Before discharge however the use of the External Remote Control (ERC) is demonstrated either by the company representative or a specialist nurse. It is applied over a mark on the skin that must be maintained and reapplied as needed with an indelible marker pen.
At about day 6 post op lengthening is commenced at between 0.6 and 1mm per day, divided into 2 or 3 increments. About a week after the start of lengthening an xray should show the opening of the osteotomy gap, and further lengthening continues with the rate adjusted according to the quality of bone formation on xray.
Patients are usually given anticoagulant prophylaxis for 2 weeks post-operatively by self administered low molecular weight heparin injections. If there are higher risks for Deep Vein Thrombosis (DVT) then a longer regime, perhaps using tablets, is recommended.
Once full length is achieved there is a further wait of four to six weeks to allow the formation of calcification within the regenerate callus. Weight-bearing is progressed depending on bone formation.
Physiotherapy throughout is important to prevent muscle shortening and joint contracture, but the majority is advice only. It is vital therefore that the patient themselves do the rigorous stretching program necessary to avoid contracture; if they cannot do this then further lengthening would have to be abandoned.
Finally, once range of movement, muscle strength, spinal flexibility and joint mobility has been regained it is many months or even a year later.
At 12 to 18 months post lengthening a day case operation is needed to remove the implant. This is usually straightforward, but is still sore for a couple of weeks. In the longer term there is no remaining internal metalwork, and the regenerate bone is indistinguishable from normal bone.
