ABSTRACT
Introduction: To evaluate the clinical relevance of the painful anterior apprehension test in shoulder instability. Materials and methods: We performed a retrospective study of 155 patients that underwent arthroscopic anterior Bankart repair between 2014-2016. Exclusion criteria were previous ipsilateral shoulder surgery, bony Bankart lesions, glenohumeral osteoarthritis and concomitant surgery involving rotator cuff tears, biceps tendon pathology and superior labrum from anterior to posterior (SLAP) lesions. The study cohort was divided into three groups: apprehension test with apprehension only, apprehension test with pain only, and apprehension test with both apprehension and pain. Patient demographics, clinical characteristics, radiological imaging, arthroscopy findings and surgical outcomes (Constant, American Shoulder and Elbow Surgeons (ASES), SF-36 scores) were evaluated. Results: A total of 115 (74.2%) had apprehension only, 26 (16.8%) had pain only and 14 (9.0%) had pain and apprehension with the apprehension test. Univariate analysis showed significant differences between the groups in patients with traumatic shoulder dislocation (p=0.028), patients presenting with pain (p=0.014) and patients presenting with recurrent dislocations (p=0.046). Patients with a purely painful apprehension test were more likely to have a traumatic shoulder dislocation, more likely to present only with pain, and less likely to present with recurrent shoulder dislocations. Multivariate analysis showed that none of these factors alone were significant as single predictors for shoulder instability. All three groups were otherwise similar in patient profile, MRI and arthroscopic assessments, and clinical outcomes of surgery. Excellent clinical outcomes were achieved in all groups with no difference in pre-operative and post-operative scores across all groups at all time points. Conclusion: The painful apprehension test may suggest underlying shoulder instability.
ABSTRACT
INTRODUCTION: Medial migration is the paradoxical migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary device, increasingly seen in the management of pertrochanteric hip fractures with the intramedullary nail. We postulate that the peculiar anti-gravity movement of the FNE in the medial migration phenomenon stems from a ratcheting mechanism at the intramedullary nail-FNE interface, which should inadvertently produce unique wear patterns on the FNE that can be seen with high-powered microscopy. By examining the wear patterns on retrieved implants from patients with medial migration, our study aims to draw clinical correlations to the ratcheting mechanism hypothesis. MATERIAL AND METHODS: Four FNEs were retrieved from revision surgeries of four patients with prior intramedullary nail fixation of their pertrochanteric hip fractures complicated by femoral head perforation. The FNEs were divided into two groups based on whether or not there was radiographic evidence of medial migration prior to the revisions. Wear patterns on the FNEs were then assessed using both scanning electron microscopy and light microscopy. RESULTS: Repetitive, linearly-arranged, regularly-spaced, unique transverse scratch marks were found only in the group with medial migration, corresponding to the specific segment of the FNE that passed through the intramedullary component of the PFNA during medial migration. These scratch marks were absent in the group without medial migration. CONCLUSION: Our findings are in support of a ratcheting mechanism behind the medial migration phenomenon with repetitive toggling at the intramedullary nail-FNE interface and progressive propagation of the FNE against gravity.
ABSTRACT
OBJECTIVES: The paradoxical migration of the femoral neck element (FNE) superomedially against gravity, with respect to the intramedullary component of the cephalomedullary device, is a poorly understood phenomenon increasingly seen in the management of pertrochanteric hip fractures with the intramedullary nail. The aim of this study was to investigate the role of bidirectional loading on the medial migration phenomenon, based on unique wear patterns seen on scanning electron microscopy of retrieved implants suggestive of FNE toggling. METHODS: A total of 18 synthetic femurs (Sawbones, Vashon Island, Washington) with comminuted pertrochanteric fractures were divided into three groups (n = 6 per group). Fracture fixation was performed using the Proximal Femoral Nail Antirotation (PFNA) implant (Synthes, Oberdorf, Switzerland; n = 6). Group 1 was subjected to unidirectional compression loading (600 N), with an elastomer (70A durometer) replacing loose fracture fragments to simulate surrounding soft-tissue tensioning. Group 2 was subjected to bidirectional loading (600 N compression loading, 120 N tensile loading), also with the elastomer replacing loose fracture fragments. Group 3 was subjected to bidirectional loading (600 N compression loading, 120 N tensile loading) without the elastomer. All constructs were tested at 2 Hz for 5000 cycles or until cut-out occurred. The medial migration distance (MMD) was recorded at the end of the testing cycles. RESULTS: The MMDs for Groups 1, 2, and 3 were 1.02 mm, 6.27 mm, and 5.44 mm respectively, with reliable reproduction of medial migration seen in all groups. Bidirectional loading groups showed significantly higher MMDs compared with the unidirectional loading group (p < 0.01). CONCLUSION: Our results demonstrate significant contributions of bidirectional cyclic loading to the medial migration phenomenon in cephalomedullary nail fixation of pertrochanteric hip fractures.Cite this article: G. W. Law, Y. R. Wong, A. K-S. Yew, A. C. T. Choh, J. S. B. Koh, T. S. Howe. Medial migration in cephalomedullary nail fixation of pertrochanteric hip fractures: A biomechanical analysis using a novel bidirectional cyclic loading model. Bone Joint Res 2019;8:313-322. DOI: 10.1302/2046-3758.87.BJR-2018-0271.R1.
