Page 8 - DISCUSSION

The goals of implantable distraction nails are to avoid many of the known complications of external fixators while making the process of lengthening more predictable and better tolerated by the patients. Some of the previously designed lengthening nails were fraught with complications. Rate control was a point of concern particularly for the ISKD, the implant for which the term “runaway nail” was coined (Paley D; Unpublished study). The amount of rotation needed to activate the unidirectional lengthening mechanism fell securely within what can be considered normal physiological movement. Many series report problems with implants that lengthened at a rate higher than was desired, and prevention of rapid distraction was difficult and unpredictable at best.

Simpson et al27 reported that 7 of their 33 (21.2%) ISKD nails were classified as runaway implants. Interestingly, a total of 15/33 (45.4%) of their nails experienced rate control complications, with 7 lengthening too quickly, and another 7 being overly difficult to lengthen. Elsewhere in the literature, we can find reports of ISKD nails that lengthened at rates much >1 mm/d, or were classified as runaway nails ranging from 9% (1/11),32 to 18.9% (7/37)33 to 83.3% (10/12) in the series by Mahboubian and colleagues.30,34 The article by Wang and colleagues reports that 5 of their 16 nails lengthened uncontrollably, forcing them to ask these patients to modify their weight-bearing and activity level from week to week based on the rate of distraction of the nail. If it were distracting too slowly, they would be asked to increase their weight-bearing and to become more active, and vice versa (Wang).27,29,35 At best, this was a very imperfect way of controlling the rate of distraction of the ISKD. There are additional series that further detail runaway nail rates that range from 9%32 to 20%.32,36 The article by the ISKD’s designer37 reviewed his initial series of 20 nails in 18 patients.36 They reported lengthening rates of up to 1.7 mm/d but no mention is made as to how many patients lengthened at such a rapid rate. In an unpublished study by Paley, of 350 ISKD lengthenings, distraction rates of up to 5 mm/d were documented.36

A large majority of patients with runaway nails went on to develop poor regenerate or nonunion at the distraction site. Although the article by Cole and colleagues observed 0 nonunions or patients who required a later bone graft procedure, other articles since document rates of runaway nail patients requiring additional surgery in the form of either bone grafting or exchange nailing that range from 20% (Wang 1/5, 5/7,33 to 6/727) to 86%.29.

Certainly, poor regenerate formation/nonunion is not exclusive to intramedullary nails that fail to maintain safe rate control, but rather, this remains a well-known complication for all limb lengthening procedures.1 Although only 1/5 of the runaway nails in the article by Wang and colleagues required later bone grafting, a total of 6 of their 16 ISKDs (37.5%) required an additional surgery to treat poor regenerate or nonunion.29 Simpson et al27 needed to treat only 6/8 (75%) of his runaway nails with additional surgery, although, a total of 8/33 (24.2%) nails ultimately required this approach. Five of the 7 (71.4%) runaway nails in Kenawey et al’s33 series required bone graft and/or exchange nailing, along with an additional 3 nails that similarly developed deficient bone healing, for a total of 8/37 (21.6%). Singh et al22 reported that 3/24 (12.5%) of their Fitbone nail segments required later bone grafting, and Baumgart et al36 saw that 1/12 (8.3%) Fitbone segments need additional surgery to achieve adequate healing.

The paper by Kenawey et al28 found a significant association between poor regenerate and age of patients >30, total lengthening >4 cm, smoking, and a distraction rate >1.5 mm/d.

One risk that has been reported to be a predisposing factor to poor regenerate is a distraction rate >1.5 mm/d.28 This is entirely avoided with the Precice nail. In comparison with results listed above, only 3 of our 65 implant segments went on to develop poor regenerate of nonunion that necessitated an additional bone grafting surgery. Uncontrolled distraction was not seen in any of our cases.