Rotation and development of the glenohumeral joint in brachial plexus birth palsy

Abstract

Birth injuries to the brachial plexus occur in 2.2-2.9 livebirths in Sweden. This traction injury to the nerves can cause anything form a transient weakness in the shoulder to a flail limb that does not recuperate on its own. Of those affected 70-80% recover excellent function. The remaining patients most commonly develops an internal rotation contracture in the shoulder joint. The contracture limits the usability of the hand as it becomes more difficult to reach in front of the body and to reach the head, neck, and mouth. Many strategies to handle the contracture and the incongruity of the glenohumeral joint that sometimes coexists. Some of the patients albeit with a good range of motion has difficulty utilizing it because of co-contractions in the muscles used to rotate the shoulder internally and externally. The aims of this thesis are to present evidence-based treatment for rotational problems including glenohumeral joint incongruity, increase the knowledge on the biomechanics in the brachial plexus birth palsy shoulder joint, and to present a method of studying co-contractions about the shoulder in an animal model.

In Paper I 118 patients who had surgery with open subscapularis lengthening and repair a minimum of 7 years (mean 10.4 years) earlier were thoroughly re-examined for range of motion in the shoulder. Functional scores were also recorded. Comparisons were made with the preoperative values. The mean gain in external rotation was 66.5°, the mean loss of internal rotation was 22°, the mean mallet score increased by 3.1 points. The loss of internal rotation turned out to have very small effects on the midline and cross-midline function.

In paper II 61 of the 63 patients with a repositioned shoulder joint from paper I were re-examined using MRI regarding the glenohumeral joint development as measured with the percentage of humeral head in front of the scapular midline (PHHA), glenoid angle and size of the humeral head. All examined patients had a relevant and significant improvement. PHHA increased 27.6% (percentage points), and the glenoid retroversion decreased by 14.8°. at mean 10.2 years follow up. All measurements approached those on the unaffected side at follow up.

Paper III is a biomechanical study into what it is that resists external rotation in the BPBP afflicted shoulder joint as several anatomical structures has been suggested. We recorded the gain in external rotation for each surgical step of our standard operation in 24 consecutive patients and found only small changes in external rotation for most steps. Only when entirety of the subscapularis tenon was divided a substantial gain in external rotation (mean 43°) occurred. We also found that the lengthening of the subscapularis required to achieve a relevant gain in external rotation (mean 12mm) exceeded the mean passive excursion of the subscapularis muscle (mean 3mm).

Paper IV investigates how fluorogold is transported through a neuroma in continuity. By inflicting a crush injury to the superior trunk on one side on 14 juvenile rats. After 4 weeks fluorogold was injected into the infraspinatus and one week after that the spinal cord was harvested and sectioned. We found significantly fewer fluorogold positive cells on the injured side (0.7073) compared to the injured side (1.0663). The fluorogold positive cells on the injured side were dispersed over a larger area indicating some kind of change in direction inside the neuroma. This may be a feasible model to study co-contractions in brachial plexus birth palsy.