Scapulothoracic and glenohumeral contributions to humerothoracic kinematics in single versus double tendon transfers in brachial plexus birth injury patients
Date
2019
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
A brachial plexus birth injury (BPBI) occurs in one to four of every 1000 live births, with about a third experiencing long term sequelae1,2. Typically, patients with residual C5-6 injuries develop several skeletal and functional deficits such as a decreased range of motion, specifically in external rotation and abduction3–8. To improve shoulder function, physicians utilize several procedures including a combination of joint reductions and latissimus dorsi and/or teres major tendon transfers1,3,17–19,9–16. The decision to transfer one versus two tendons is at the surgeon’s discretion, but recently the surgical decision-making has come under scrutiny. Double tendon transfers have demonstrated greater improvement on external rotation Mallet scores, but single tendon transfers are about 50% less likely to lose midline20. Both procedures were shown to have equivalent improvement on Mallet abduction scores20. ☐ There are limitations with the Mallet classification. Specifically, the classification uses an ordinal scale that assesses HT motion and allows for high variability in patient motion within each grade. Consequently, the Mallet classification lacks precision and cannot differentiate GH and scapulothoracic (ST) contribution to HT motion. This study utilized motion capture to analyze the precise ST and GH contributions to joint function in single and double tendon transfer patients. Children with persistent C5-C6 BPBI’s at the time of surgery were recruited at least six months after surgery, allowing for the intended surgical outcomes to take effect. Patients were asked to hold their arm still at several positions including at rest, maximum external rotation, maximum internal rotation, and maximum abduction. ☐ All patients exhibited externally rotated humeral orientations at the GH joint. However, both single and double tendon transfers demonstrated very little GH joint motion from neutral in any position. Instead, tendon transfers appear to re-tension the GH joint into external rotation, but not enough to overcome the ST joint and externally rotate the humerus relative to the patient’s trunk. Our results are contrary to the current literature in several aspects. First, single tendon transfers displayed greater external rotation in all positions compared to double tendon transfers. Second, the double tendon transfer group was able to abduct their arm significantly more than the single tendon transfer group. ☐ Though these results are surprising, they may not be driven by the effect that single or double tendon transfers have on the GH joint. Instead, the results could be impacted by the variation in surgical technique that exists amongst all patients in this study regardless of tendon transfer procedure. All patients’ arms are placed into 90˚ of abduction and externally rotated when the teres major and/or latissimus dorsi tendons are sutured to the humeral head21. However, the exact degree of external rotation is variable from patient to patient and can be affected by the surgical methods of joint reduction during surgery. The results indicate that the inclusion of the teres major locks the GH joint into an externally rotated orientation limiting active rotation. It is unclear if the lack of motion postoperatively is driven by the joint reduction, if the tendon transfer exacerbates the reduced motion, or if there is any active GH joint motion preoperatively at all. ☐ Our conclusion calls into question the recommendation of single tendon transfers when patients demonstrate weak internal rotation. The benefit of separating the latissimus dorsi from the teres major does not appear to produce additional benefit as originally believed. In fact, our findings showed the single tendon transfer externally rotated their arm more than double tendon transfers. Unfortunately, this study was limited to isolated teres major and conjoined latissimus dorsi and teres major tendon transfers. Further research on the differing combinations of joint reductions and tendon transfers would better elucidate the roles both tendons play in augmenting GH and ST joint kinematics.