Kollitz, Kathleen M.

AbstractIntroductionThere is conflicting anatomic and innervation data regarding the rabbit brachial plexus injury model. This study aims to validate a rabbit brachial plexus injury model. We hypothesize the middle trunk (C6, C7) is the primary innervation of the biceps, and when cut and unrepaired, would demonstrate lack of recovery and when repaired would demonstrate evidence of recovery.Materials and MethodsTwenty two male New Zealand white rabbits (3–4 kg) underwent unilateral surgical division of the middle trunk. Five rabbits were randomly assigned to the “no‐repair” group while the remaining 17 rabbits underwent direct coaptation (“repair” group). Rabbits were followed for 12 weeks, with ultrasound measurement of biceps cross‐sectional area performed preoperatively, and at 4, 8, and 12 weeks postoperatively. At a euthanasia procedure, bilateral compound muscle action potential (CMAP) and isometric tetanic force (ITF) were measured. Bilateral biceps muscles were harvested and wet muscle weight was recorded. The operative side was expressed as a percentage of the non‐operated side, and differences between the no repair and repair rabbits were statistically compared.ResultsThe repair group demonstrated significantly higher CMA (23.3 vs. 0%, p < .05), ITF (25.6 vs. 0%, p < .05), and wet muscle weight (65.8 vs. 52.0%, p < .05) as compared to the unrepaired group. At 4 weeks postoperatively, ultrasound‐measured cross‐sectional area of the biceps demonstrated atrophy in both groups. At 12 weeks, the repair group had a significantly larger cross‐sectional area as compared to the no‐repair group (89.1 vs. 59.3%, p < .05).ConclusionsThis injury model demonstrated recovery with repair and lack of function without repair. Longer survival time is recommended for future investigations.

AbstractPurposeAnimal models can be helpful in evaluating new surgical strategies for brachial plexus reconstruction. While several groups have already used the rabbit brachial plexus to model injury, reports conflict in anatomic detail and do not identify a nerve‐muscle pair to measure motor function recovery after reconstruction. The purpose of the current study is to describe the innervations of the biceps and triceps muscles in rabbits, which are both amenable to study in brachial plexus injury models.Materials and MethodsThirteen rabbits weighing 2–2.5 kg were anesthetized. Six rabbits were sacrificed and dissected using loupe and microscope magnification to understand the overall morphology of the brachial plexus. Seven rabbits underwent electrophysiologic investigation. A bipolar nerve stimulator was used to systematically stimulate the roots, trunks and divisions, and nerve branches of the rabbit brachial plexus and compound muscle action potential was used to record muscle response. Nerve length and width measurements were not recorded.ResultsRoots contributing to the brachial plexus were C5, C6, C7, C8, and T1. In contrast to other anatomical studies, T2 did not contribute to the brachial plexus. The triceps was innervated by the radial nerve, which received contributions from C6 (1.6 mA), C7 (1.9 mA), C8, and T1 (12.2 mA).The biceps had dual innervation (proximally and distally). The proximal branch received contributions from C6 (3.5 mA) and C7 (5mA). The distal portion was innervated by a branch from the median nerve, which received innervation from C6, C7, C8, and T1.ConclusionsThe overall structure of rabbit brachial plexus is described and innervation of the biceps and triceps is described in detail. This anatomic investigation will form the basis of a future brachial plexus model of injury and repair.

Background: Outcomes following revision surgery for scaphoid nonunions with osteonecrosis are guarded. We hypothesized that use of free vascularized medial femoral condyle (MFC) bone grafts can lead to healing of the nonunion, increase vascularity of the proximal pole, and restore scaphoid architecture, resulting in acceptable functional outcomes. Methods: We performed a retrospective review of 49 patients who were treated with an MFC bone graft, between May 2005 and September 2016, after prior failure of operative treatment for scaphoid nonunion. The mean time from the injury to the revision surgery with the MFC bone graft was 24 months, and the mean time from the prior, failed surgery was 15 months. Thirty-six of the 49 patients had had a prior bone graft procedure and 6 patients had had 2 previous surgical procedures for the nonunion. The initial internal fixation of the scaphoid fracture was with a scaphoid screw in 43 patients. All patients had documented osteonecrosis of the proximal pole at the time of our surgery. Carpal indices, time to union, pain scores, functional outcomes, and complications were recorded. Results: Forty-one (84%) of the 49 previously operated on scaphoid nonunions healed at a mean of 16 weeks (range, 9 to 31 weeks) after the MFC bone-grafting as confirmed on computed tomography (CT). Radiographs demonstrated significant improvement in carpal alignment following the surgery with the MFC bone graft. Comparison between preoperative and postoperative values showed a trend toward improved grip strength and no important change in total wrist range of motion. Subsequent procedures were performed in 29 patients, 21 of whom had planned Kirschner wire removal. All 24 patients in whom scaphoid union had been achieved and who were available for follow-up were able to work or attend school full-time, and 88% were satisfied or very satisfied with their wrist function. Age, smoking status, body mass index, time to surgery, and preoperative radiographic findings were not found to be significant predictors of failure. Conclusions: MFC grafts increase vascularity and restore scaphoid architecture, promoting union in most patients with the combination of proximal pole osteonecrosis, carpal collapse, and failed prior scaphoid nonunion surgery. Level of Evidence: Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

This study aimed to determine the outcome of free vascularized medial femoral condyle bone grafts in the primary treatment of scaphoid nonunions with scaphoid foreshortening or carpal collapse and intraoperatively documented avascular necrosis. Thirty-two patients (28 male, four female) met the inclusion criteria. Median time from injury to surgery was 70 weeks. Thirty of 32 patients healed at a median of 12 weeks. There was significant improvement from preoperative to postoperative lateral intrascaphoid angle, scapholunate angle, and radiolunate angle. Two scaphoids failed to unite; one patient underwent scaphoidectomy and four-corner fusion 15 months postoperatively after suffering a subsequent injury. Another patient underwent 1,2-intercompartmental supraretinacular artery-based vascularized bone grafting at 4 months postoperatively and then scaphoid excision with four-corner fusion 4 years later. The free vascularized medial femoral condyle bone graft restores scaphoid vascularity and architecture while promoting union in a subset of scaphoid nonunions that has historically been a clinical challenge. Level of evidence: IV