Jonathan C. Barnwell

Computer Simulation of Nerve Transfer Strategies for Restoring Shoulder Function After Adult C5 and C6 Root Avulsion Injuries

PURPOSE Functional ability after nerve transfer for upper brachial plexus injuries relies on both the function and magnitude of force recovery of targeted muscles. Following nerve transfers targeting either the axillary nerve, suprascapular nerve, or both, it is unclear whether functional ability is restored in the face of limited muscle force recovery. METHODS We used a computer model to simulate flexing the elbow while maintaining a functional shoulder posture for 3 nerve transfer scenarios. We assessed the minimum restored force capacity necessary to perform the task, the associated compensations by neighboring muscles, and the effect of altered muscle coordination on movement effort. RESULTS The minimum force restored by the axillary, suprascapular, and combined nerve transfers that was required for the model to simulate the desired movement was 25%, 40%, and 15% of the unimpaired muscle force capacity, respectively. When the deltoid was paralyzed, the infraspinatus and subscapularis muscles generated higher shoulder abduction moments to compensate for deltoid weakness. For all scenarios, movement effort increased as restored force capacity decreased. CONCLUSIONS Combined axillary and suprascapular nerve transfer required the least restored force capacity to perform the desired elbow flexion task, whereas single suprascapular nerve transfer required the most restored force capacity to perform the same task. Although compensation mechanisms allowed all scenarios to perform the desired movement despite weakened shoulder muscles, compensation increased movement effort. Dynamic simulations allowed independent evaluation of the effect of restored force capacity on functional outcome in a way that is not possible experimentally. CLINICAL RELEVANCE Simultaneous nerve transfer to suprascapular and axillary nerves yields the best simulated biomechanical outcome for lower magnitudes of muscle force recovery in this computer model. Axillary nerve transfer performs nearly as well as the combined transfer, whereas suprascapular nerve transfer is more sensitive to the magnitude of reinnervation and is therefore avoided.

Microcomputed Tomography Characterization of Shoulder Osseous Deformity After Brachial Plexus Birth Palsy: A Rat Model Study

BACKGROUND Shoulder deformities are common secondary sequelae associated with brachial plexus birth palsy. The aim of the present study was to characterize three-dimensional glenohumeral deformity associated with brachial plexus birth palsy with use of microcomputed tomography scanning in a recently developed animal model. METHODS Brachial plexus birth palsy was produced by a right-sided neurotomy of the C5 and C6 nerve roots in seven five-day-old Sprague-Dawley rats. Microcomputed tomography scanning was performed when the rats were four months of age. Glenoid size, version, and inclination; humeral head size; and acromion-glenoid distance were measured. Normal shoulders of age-matched rats (n = 9) served as controls. Statistical analysis was performed with use of the unpaired two-tailed Student t test. RESULTS There were significant increases in glenoid retroversion (-7.6° ± 4.9° compared with 3.6° ± 2.1°; p = 0.038) and glenoid inclination (38.7° ± 7.3° compared with 11.2° ± 1.9°; p = 0.015) in the shoulders with simulated brachial plexus birth palsy in comparison with the normal, control shoulders. The glenohumeral joints were more medialized in the joints with simulated brachial plexus birth palsy as reflected by the acromion-glenoid distance measurement; however, the difference was not significant (3.20 ± 0.51 compared with 2.40 ± 0.18 mm; p = 0.12). Although the mean humeral head height and width measurements, on the average, were smaller in the brachial plexus birth palsy shoulders as compared with the normal, control shoulders, only the measurement of humeral head height was significantly different between the two groups (4.25 ± 2.02 compared with 4.97 ± 0.11 mm [p = 0.008] and 3.56 ± 0.27 compared with 4.19 ± 0.17 mm [p = 0.056], respectively). CONCLUSIONS In this animal model, rats with simulated brachial plexus birth palsy developed gross architectural joint distortion characterized by increased glenoid retroversion and inclination. In addition, humeral heads tended to be smaller four months after simulated brachial plexus birth palsy.

Metaphyseal Ulnar Shortening Osteotomy for the Treatment of Ulnocarpal Abutment Syndrome Using Distal Ulna Hook Plate: Case Series

PURPOSE To determine the efficacy of a transverse ulnar-shortening osteotomy at the metaphysis in combination with osteosynthesis using a low-profile, 2.0-mm, locking compression distal ulna plate for the treatment of ulnocarpal abutment syndrome. METHODS We enrolled into this prospective case series 6 patients with symptomatic ulnocarpal abutment syndrome without distal radioulnar joint ligamentous instability, who had previously failed conservative treatment. We recorded Quick Disability of Arm, Shoulder, and Hand score; wrist range of motion; and visual analog scale score for pain before and after surgery for statistical comparisons. RESULTS All parameters improved after the surgery. The Quick Disabilities of the Arm, Shoulder, and Hand improved from a mean of 65 to 17, and the visual analog score improved from a mean of 7 to 2. No hardware removal was required and no complications were reported. CONCLUSIONS Metaphyseal ulnar-shortening osteotomy provided the functional advantages of a midshaft ulnar-shortening osteotomy with the potential for improved bone healing and the reduced risk for complications. This technique was a useful alternative for treatment of ulnocarpal abutment syndrome, especially in patients with more than 2 mm ulnar positive variance. TYPE OF STUDY/LEVEL OF EVIDENCE Therapeutic IV.

A chronically-denervated versus a freshly-harvested autograft for nerve repair in rats -

Objectives Autologous nerve grafting remains the gold standard for repair of peripheral nerve injuries. Its use, however, is limited by donor nerve availability and donor site morbidity. This is especially problematic after failure of an initial autograft that requires a repeat nerve graft, resulting in a second surgical site with associated morbidity. Based on the molecular differences in nerve degeneration in the proximal and distal segments after transection, we hypothesized that a chronically-denervated proximal stump may be viable for autologous nerve repair. Methods 20 Sprague-Dawley rats underwent right sciatic nerve excision and sural nerve transection. After 8 weeks, nerve repair was performed by harvesting the proximal segment of the sural nerve (n=10) or a fresh sural nerve (n=10) from the contralateral hind limb. Electrophysiological changes were analyzed to compare the fresh and denervated grafts. Results Electrophysiological testing demonstrated higher compound motor action potential in the denervated group compared to the fresh autograft group, however this difference was not statistically significant (p=0.117). Conclusion The proximal segment of a chronically-denervated sural nerve can be as effective as a fresh sural nerve for autologous repair of peripheral nerve injuries in a rodent model.