Scapular deformity in obstetric brachial plexus palsy and the Hueter-Volkmann law; a retrospective study

Abstract

Background: The Hueter-Volkmann law describes growth principles around joints and joint deformation. It states that decreased stress leads to increased growth and that excessive stress leads to growth retardation. Aim of this study was to test the possible results of this principle by measuring the effect of dorsal humeral head subluxation on scapular growth in children with Obstetrical Brachial Plexus Lesions (OBPL). According to the Hueter-Volkmann law, subluxation should result in decrease of growth of the dorsal length of the scapula (by increased dorsal pressure) and increase of the ventral length (decreased pressure).

Methods: 58 children (mean age 20 months, range 1-88 month) with unilateral OBPL and good quality MRI of both shoulders were included. On MRI, humeral head subluxation, joint deformation, and ventral and dorsal scapular lengths were measured. Data were expressed as a ratio of the normal side.

Results: In affected scapulas both ventral and dorsal side were smaller compared to the normal side. Reduction of growth on the affected side was more marked on the dorsal side than on the ventral side (6.5 mm respectively 4.5 mm, p < 0.001). The balance of growth reduction as expressed by the ratio of ventral and dorsal length was strongly related to subluxation (R(2) = 0.33, p < 0.001) and age (R(2) = 0.19, p < 0.001).

Conclusions: The Hueter-Volkmann law is incompletely active in subluxated shoulders in OBPL. Dorsal subluxation indeed leads to decrease of growth of the dorsal length of the scapula. However, decreased stress did not lead to increased growth of the ventral length of the scapula.

Figure 1

Transversal MRI projection. FISP acquisition MRI in axial plane showing affected and normal contralateral shoulder. In the affected right shoulder there is a convex glenoid form (Birch type 2) and humeral head subluxation. The contralateral left shoulder is normal.

Figure 2

Mid glenoid level. On MRI partitions in axial plane the upper and lower end of the glenoid were defined (broken lines). The level exactly between these ends (solid line) was determined to be the mid glenoid level, at which measurements were done.

Figure 3

Method of measuring scapula lengths. Schematic drawing showing the method of measuring the lengths of ventral (VS) and dorsal(DS) side off the scapula at mid glenoid level.

Figure 4

Method of measuring subluxation. Schematic drawing showing the method of measuring humeral head subluxation. The percentage of the humeral head anterior to the drawn line indicates subluxation.

Figure 5

Subluxation and VS/DS. Relation between joint subluxation and ratio of scapular length on ventral and dorsal aspect (VS/DS) in the affected shoulder. Increasing posterior subluxation (normal value is 50%, with increasing subluxation this percentage decreases) leads to predominant reduction of scapular length on the posterior side, which leads to an increased ratio VS/DS.