Arm rotated medially with supination - the ARMS variant: description of its surgical correction

Abstract

Background: Patients who have suffered obstetric brachial plexus injury (OBPI) have a high incidence of musculoskeletal complications stemming from the initial nerve injury. The presence of muscle imbalances and contractures leads to typical bony changes affecting the shoulder, including the SHEAR (Scapular Hypoplasia, Elevation and Rotation) deformity. The SHEAR deformity commonly occurs in conjunction with Medial Rotation Contracture (MRC) of the arm. OBPI also causes muscle imbalances at the level of the forearm, that lead to a fixed supination deformity (SD) in a small number of patients. Both MRC and SD will cause severe functional limitations without surgical intervention.

Methods: Fourteen OBPI patients were diagnosed with MRC of the shoulder and SD of the forearm along with SHEAR deformity during a 16 month study period, with eight patients available to long-term follow-up (age range 2.2 - 18 years). Surgical correction of the MRC was performed as a triangle tilt or humeral osteotomy depending on the age of the child, after which, the patients were treated with a radial osteotomy to correct the fixed supination deformity. Function was assessed using the modified Mallet scale, examination of apparent supination and appearance of the extremity at rest.

Results: Significant functional improvements were observed in patients with surgical reconstruction. Mallet score increased by an average of 5.2 (p < 0.05). Overall forearm position was not significantly changed from an average of 5 degrees to an average of 34 degrees maximum apparent supination after both shoulder rotation and forearm rotation corrective surgeries.

Conclusion: The simultaneous presence of two opposing deformities in the same limb will visually offset each other at the level of the wrist and hand, giving the false impression of neutral positioning of the limb. In reality, the neutral-appearing position of the hand indicates a fixed supination posture of the forearm in the face of a medial rotation contracture of the shoulder. Both of these deformities require surgical attention, and the presence of concurrent MRC and SD should be monitored for in OBPI patients.

Figure 1

Neutral position in OBPI patients with medial rotation contracture. A. A 9-year-old male patient with MRC showing the typical positioning of the elbow crease (towards the body) and with the dorsum of the hand visible anteriorly. B. An 18-year-old female patient with MRC and SD (ARMS variant) (Patient 5). Elbow crease is positioned as the patient in panel A because of the MRC, but the hand appears to be positioned normally because of the coexisting SD. Elbow and hand positioning are highlighted with red circles in both panels

Figure 2

Apparent supination in OBPI patients with medial rotation contracture. A. A 9-year-old male patient with MRC showing a lack of supination ability of the left arm due to the medial rotation position of the upper arm. B. An 18-year-old female patient with MRC and SD (ARMS variant) showing apparently normal supination of the left arm (Patient 5). Note the position of the left elbow crease as compared with the right side.

Figure 3

Measuring scapular elevation to quantitate the extent of the SHEAR deformity. A 3D-reconstruction of axial bilateral CT images rotated into the anterior view is used to measure scapular elevation. The area of each portion of both scapulas is measured as indicated (areas A-D). The area above the scapula is divided by the total scapular area and corrected for rotational artifacts by subtraction of the unaffected side from the affected side before multiplying by 100 to obtain percent elevation. Shown here is the CT for patient 1 with 37% scapular elevation.

Figure 4

Modified Mallet scale evaluation of function and arm appearance. In addition to assessing the classical shoulder functions of the classical Modified Mallet system, supination and the resting position are evaluated. In the resting position, medial rotation at the shoulder is scored on a scale of 1 to 5. Fixed forearm supination is noted in the resting position as indicated by the drawings labeled 2A (first web space visible) and 4A (palm visible). Lateral rotation position can also be noted in the resting position. A total Mallet score is calculated from the scores for abduction, hand to neck, hand to spine, hand to mouth, and lateral rotation, giving a maximum score of 25. Angles are measured from video stills for abduction, hand to mouth and apparent supination and estimated for lateral rotation.

Figure 5

Arm at resting position. The patient was asked to stand with her arms at resting position. A: Patient 5 prior to any surgery. B: Patient 5 after shoulder correction surgery. C: Patient 5 after forearm osteotomy surgery. Changes in the relative positioning of the volar surface of the forearm to the anterior surface of the arm are visible in the affected left arm.

Figure 6

Hand to nose. The patient was asked to touch her nose with both her hands. A: Patient 5 before any surgery. B: Patient 5 after shoulder correction surgery. C: Patient 5 after forearm osteotomy surgery. Changes in functional position of the left arm and hand are visible.

Figure 7

Supination. The patient was asked to place her arms in front of her with her palms facing the ceiling. A: Patient 5 before any surgery. B: Patient 5 after shoulder correction surgery. C: Patient 5 after forearm osteotomy surgery. Changes in the positioning of the elbow crease and palm are visible in the affected left arm.