A Study of Radial-Head Dislocation in Children with Transverse Partial Hemimelia of the Upper Limb
Leon M. Kruger, M.D. Nicholas R. Breyan, M.D.
This report presents the results of a study involving 15 patients with the terminal transverse upper-extremity deficiency termed partial hemimelia. Accordingly, these children retained proximal segments of both radius and ulna of varying lengths with no other more distal bone present, but with normal bony structures above the elbow ( Fig. 1 ). Each of these patients had a functioning elbow which permitted the use of a below-elbow prosthesis. The standard prosthetic prescription has been a below-elbow plastic-laminate socket with flexible leather elbow hinges, a triceps pad, a friction wrist, and a hook ( Fig. 2 ). In the very young patient, preflexed elbow sockets have been prescribed, and several children have been fitted with Muenster sockets. In no instance has a rigid elbow joint been used.
In the embryo the upper limb appears at one month as a bud on the lateral body wall. This bud grows rapidly, with the distal end flattening to form a platelike structure for the hand which is partially separated from the remaining proximal portion by a constriction. The plate develops ridges that are first separated by grooves and then project freely as the digits. A second constriction representing the elbow divides the proximal cylindrical segment into forearm and arm. At about five weeks, a denser core appears in the center of the limb bud as the forerunner of the bony elements of the limb. About two weeks later this core transforms into cartilage and by eight weeks the first centers of ossification appear. During the time that the core for the skeleton is appearing, the precursors of the muscle masses also appear. Splitting of the premuscle masses into individual masses for the various muscles begins proximally and extends distally. By the end of seven weeks the differentiation of muscles in the hand has occurred.
The exact cause of the deficiency under discussion is not known, although such factors as drugs, irradiation, and vitamin deficiencies have been implicated.
This study was stimulated by an encounter with a 14-year-old girl who, on a routine clinic visit, complained of pain at the elbow. X-rays revealed that the radial head was dislocated. This dislocation caused pressure at the anterior socket brim which in turn increased the pressure of the posterior wall against the olecranon, resulting in a traumatic olecranon bursitis. The prosthesis was discontinued temporarily, and the olecranon bursitis was treated by intrabursal steroid injection with excellent relief. The prosthesis was modified by cutting out a relief for the dislocated head of the radius and the patient has done well since. It seemed reasonable to assume that this condition had occurred in other cases and that a review of patients with terminal transverse hemimelia currently under care was indicated. Nineteen patients were contacted but only 15 responded in time to be included in the study.
In the 15 patients reviewed, 16 extremities were involved. One patient, a male, had bilateral involvement. Eight males and seven females comprised the series. The average age of the patients when first seen was two years and three months-the youngest child being three months of age, and the oldest nine years, five months of age. At the time of fitting the shortest stump was 1 in. and the longest 3 ½ in., with an average of 2.1 in.
All prior x-rays on these patients were reviewed and new films obtained if none had been made within the previous 12 months. Particular attention was now paid to the relationship of the radial head with the capitellum. The results are shown in Table 1 .
Dislocations Usually Asymptomatic
Thirteen of the 16 extremities evaluated were found to have radial-head dislocations at the elbow ( Figs. 3 and 4 ). Of the two patients who were found to be poor wearers, one had a dislocation; the other did not. Neither had symptoms of discomfort. The only patient with pain symptoms was the one who had stimulated the study, as described previously. Ten of the extremities were found to have been dislocated at the time of fitting of the prosthesis. The one patient with bilateral involvement had only the right elbow dislocated. Of the 10 extremities with radial-head dislocation present at the time of fitting of the prosthesis, only one patient had developed pain symptoms some 14 years after fitting. Of the remaining three patients with radial dislocations two were not dislocated at the time of prosthetic fitting and were found to be dislocated only when the children were called in for follow-up x-rays. No films of the third patient were available for evaluation at the time of initial fitting but the child was found to have a dislocation when called in for x-ray.
This study has pointed out the high incidence of dislocation of the radial head in patients with terminal transverse partial hemimelia of the upper limb. Dislocations were found in 13 of 16 extremities evaluated (81 per cent). It was noted also that 77 per cent, or 10 of the 13 radial-head dislocations were present prior to the prescription of the initial prosthesis. It would appear, therefore, that the phenomenon of radial-head dislocation in these children is not a function of the prosthesis, but rather is inherent in the disability itself. One could postulate that radial dislocation in these children is possibly due to an absence or deficiency of the ligamentous structures about the elbow, particularly with reference to the radial head and the most proximal section of the radius. This deficiency would involve the annular ligament and less importantly perhaps the oblique cord which runs from the tubercle of the ulna at the base of coronoid process to the radius, a little below the radial tuberosity. However, the importance of these ligamentous structures in this problem cannot be evaluated without cadaver dissection. The more likely explanation, however, is that these children have short stumps with consequent absence of the pronator teres; and the biceps muscle is therefore acting unopposed and is providing both a supinat-ing and a flexing force, thus causing dislocation of the radial head. That the foregoing explanation is indeed the case becomes apparent when one considers that the radius and ulna are invested in muscle masses which perform in a synergistic fashion and that in these children there is an absence and/or incomplete function of one or more of the components which normally maintains the equilibrium. Thus the remaining components of the system are unopposed and can therefore exert their distorting forces.
In conclusion it is noted that no description of this phenomenon could be found in an extensive review of the pertinent literature for the past 10 years. This lack of information may be related, at least in part, to the fact that apparently dislocation of the radial head is seldom accompanied by pain, either with or without a prosthesis.
Shriners Hospital for Crippled Children Springfield, Massachusetts