Most forearm deformities in patients with HME are caused by ulna shortening[2, 18, 19]. The distal ulna is affected by exostoses, which lead to dysplasia and shortening. Moreover, it tethers the ulnar side of the distal radius, hinders the growth of the distal radius, increases the RAA and CS, and weakens the support provided by the ulna to the wrist joint. On the other hand, the pressure of the radius increases, and with increasing age, the radius bends gradually, resulting in dislocation of the radial head. Therefore, treatments of forearm deformity caused by HME should primarily involve the early correction of ulnar shortening.
The aim of this study was to present the clinical results of 37 children who underwent surgical ulnar lengthening. In this study, two types of unilateral external fixations were selected: the monorail (Group A) and multi-joint fixators (Group B). Table 2 and Table 3 show that the US, RAA, CS, elbow flexion, forearm pronation, and MEPS values significantly improved in both group A and group B (p < 0.05). Only supination in group B did not significantly change, which might be attributed to the small sample size. The appearance and function of the upper limb significantly improved in the two groups, and the effect of unilateral external fixation on ulnar lengthening was obvious.
Some other methods of ulnar lengthening have been used. Some scholars [2, 25] have used bone grafting and steel plate fixation to treat ulnar shortening by 2 cm or less with satisfactory results. However, due to the bending of the radius and the influence of exostosis, the target length cannot be obtained in a single operation. Another common method is to use the Ilizarov ring[4, 6]. However, the circular external fixator has a complex structure and requires multi-needle and multi-plane fixation, which increases the risk of needle infection and neurovascular injury. In addition, in the process of lengthening, many parts of the Ilizarov ring need to be adjusted, which is not convenient for the parents of the patients. The Ilizarov ring is bulky, which affects daily activities and joint function exercise. In this study, two types of unilateral external fixations were selected. The operation was simple, the devices were light and comfortable to wear, and the potential of lengthening met the clinical needs.
The optimal timing of surgical intervention is controversial. One view [2, 9, 21, 22] is that early surgery can slow or prevent the progression of deformities, especially the dislocation of the radial head, while for patients with dislocation, early surgery often leads to self-reduction. Another view [11, 23, 24] is that surgery should be postponed until the patient is 10 years old or at the age of epiphyseal closure. We believe that the timing of surgery should be determined on the basis of not only age but also the actual condition of the patients. For patients with obvious forearm and wrist deformities, a US value larger than 1.5 cm , radial head dislocation, enlargement of an exostosis, dysfunction, or chronic pain, the operation should be performed early. When the radial head has been dislocated for a long time, the morphology of the humerus and radius joint, annular ligament and other soft tissue structures may change, the failure rate of surgical reduction is high, and the function of the forearm may be poor. As shown in Fig. 3 (A-E), at the age of 3.5 years, a girl had good forearm appearance and function, without dislocation of the radial head. At the age of 6.5 years, the radial head was dislocated, the upper limb force line was obviously skewed, elbow flexion and forearm rotation were limited, and the operation was performed. At the three-year follow-up, the reduction of the radial head was satisfying, and the ulnar shortening deformity was corrected.
For complications, no fractures, neurovascular problems, or recurrences of exostoses were observed in the two groups. Pin site infections (5 cases in total) easily recovered. For radial head dislocation in patients with type IIa and type IIb deformities, no special procedures were performed during the operation, all cases self-reduced during ulna lengthening, and no cases of redislocation were found. This result suggests that it may be best not to treat radial head dislocation. The interosseous membrane can transmit the forces leading to lengthening, and the reduction of the radial head can be reached gradually.
Ulna deviations and poorly regenerated bone formation were more likely to occur in group B than in group A. The occurrence of these complications may be related to the position of the osteotomy and direction of the nail. It has been reported that the diameter of the osteotomy site is negatively related to the time of bone healing. Some scholars have suggested that the osteotomy point should be located at the maximum bending point, and the distance between the osteotomy point and the distal end of the ulna should be larger than 42% of the total length of the ulna. We suggest that the proximal part is selected, avoiding the maximum curvature as much as possible. Four Schanz pins were placed in the same plane in parallel to each other.
A patient with type IIb deformity is shown in Fig. 4 (A-C). The two groups of Schanz pins were located at the maximum bending plane of the ulna arch, and the nails were not positioned in parallel to each other or in the same plane. During the lengthening process, the joint of the external fixator became loose, and the dorsal angle of the ulnar arch gradually increased. Another patient with a type I defromity is shown in Fig. 4 (D-F). Although the Schanz pins avoided the maximum bending plane of the ulna arch, they were positioned in parallel to each other; however, they were not located in the same plane, so the force line was skewed, and the ends of the osteotomy region were separated during the extension process, leading to nonunion. Although the joints of the fixator were pressurized and locked, they were still loose during the extension process. The monorail external fixator should be used to effectively avoid this situation.
Whether exostoses should be removed is still debated. Akita et al. found that exostosis resection can significantly improve the rotational function of the forearm but that it affects the US, RRA and CS values very little. We believe that the resection of exostoses can open the epiphysis of the distal ulna, enable the ulna to obtain a certain growth potential, reduce the effect of local tissue on the radius and correct deformities of the wrist. In this study, 37 patients underwent exostosis resection. The function of the forearm significantly improved.
Our study presents some limitations. This study is a retrospective study, with a small sample size and a short follow-up time. The clinical efficacy and complications remain to be further verified by a long-term prospective randomized controlled study.