Bilateral humeral lengthening through unilateral external fixators in rhizomelic achondroplasia - how endangered is the radial nerve?

Objectives In patients with achondroplasia, functional impairments due to rhizomelic upper extremities can be improved through bilateral humeral lengthening. Intramedullary methods are generally preferred, but due to anatomical particularities (open physes, extremely short and narrow bones), internal bone lengthening nails can rarely be implanted. Thus lengthening through unilateral external fixators is still the gold standard in these patients. The occurrence of radial palsy (RP) during treatment is a dreaded complication.

Methods Retrospective analysis of radiographs and clinical data of 29 patients with achondroplasia (14 girls, 15 boys) who received bilateral humeral lengthening, with special focus on incidence and outcome of RP. Distraction started in average 6.7 (6.0-8.0) days after surgery.

Results and Conclusion Of 29 patients, intramedullary lengthening was possible in only one patient (15.3 years). 28 patients received bilateral humeral lengthening through unilateral external fixators (Limb Reconstruction System (LRS), Orthofix, Lewisville, USA). The average age at fixator application was 9.0 (5.1 - 17.1) years. Distraction distance was an average 89.2 (32.0-120.0) mm. RP occurred in 16 of 56 extremities (28.6 %). There were two bilateral RP, and in one patient a RP occurred twice in the same extremity (directly postoperatively and, after full recovery, again during distraction). 13 of 16 RP (81.3 %) occurred within the first four days postoperatively, of which eight (50.0 %) were found right after surgery. Three RP (18.8 %) developed secondary during distraction. To prevent a secondary RP due to pressure caused by hematoma, in 42 of 56 cases (75.0 %) a Redon’s drain was applied at the osteotomy site. In 14 cases (25.0 %) no drain was applied. Eight of the 42 patients with drain (19.0 %) and five of the 14 patients without drain (35.7 %) suffered a RP within the first four days postoperatively (P-value 0.2). In all cases with RP a full sensorimotor recovery (5/5 muscle strength according to MRC) was observed within an average 11.0 (2.0 - 25.0) weeks postoperatively.

In humeral lengthening of patients with achondroplasia through unilateral external fixators, RP is a frequent complication. Most RP are observed right after surgery. As pressure on the radial nerve through a fracture hematoma may be a possible cause for secondary RP, it is recommended to apply a Redon’s drain. Even though in most cases a complete regression is observed, RP hinders the timely start of distraction or may require premature distraction termination, resulting in an overall extended duration of treatment and unplanned revision surgeries. This should be discussed thoroughly with the families in advance.

Abb.1 Humeral lengthening through LRS unilateral external fixator. Initial radiographs, 2 weeks, 3 months and 7 months postoperatively.

Stichwörter Humeral lengthening, achondroplasia, rhizomelia, LRS, unilateral external fixator.

Publication History

Article published online:
15 October 2020