1892 - Automatic Extraction of Pelvic Coordinate System and Bony Landmarks from CT Imaging Data for Endoprosthetic Pelvic Reconstruction of Sarcoma Patients

INTRODUCTION: In order to avoid development of hip osteoarthritis, cam-type femoroacetabular impingement (FAI) corrective surgery has become treatment of choice. Surgery involves osteochondroplasty and labral-chondral debridement either through an open surgical dislocation or arthroscopic approaches. The aim of this study was to compare the muscle forces measured in silico during a deep squatting task in patients before surgery and two years following surgery with either of the two approaches. It was hypothesized that there would be no significant differences between approaches.METHODS: Ten male patients were recruited from the senior orthopaedic surgeonu2019s clinical practice that was scheduled to undergo surgery for cam-type FAI. The cam-type FAI was confirmed using computed tomography as patients had either an axial or radial alpha angles larger than 50.5u00b0 or 60u00b0, respectively1. All patients underwent corrective surgery by the same surgeon through either an open surgical dislocation with anterior approach (n=3) or arthroscopic/mini-open approach (n=7). Patients underwent motion analysis about two months prior to surgery and at 2-years post-operatively. The study was approved by the hospital and university research ethics boards and all participants provided informed consent.For the motion analysis, ten infrared cameras and two embedded force platforms were used to record the markers trajectories and the ground reaction forces. Participants were outfitted in 45 retro-reflective markers according with the University of Ottawa Motion Analysis Model marker set2 and performed five trials of a deep squat at a self-selected pace with each foot placed on its own force plate hip-width apart and arms flexed at shoulder height. The data obtained from the motion analysis sessions were inputted into a musculoskeletal simulation software (OpenSim 3.3; SimTK)3 using a generic model. After each participant was scaled, the inverse kinematics and dynamics were performed. The muscle forces were calculated while minimizing the sum of squared muscle activation using the static optimization tool.To compare the differences between the two surgical approaches and between the pre- and post-operative sessions, a mixed linear model (MLM) was performed using SPSS. Surgical approach (hip dislocation vs arthroscopy) and time point (pre-operative vs post-operative) were set as fixed effects, participants were set as random effects in the model, and alpha was set at 0.05 for all tests. Using the MLM, we were able to determine if there was a statistical effect of approach, between pre-operative and post-operative sessions, as well as any interaction between them.RESULTS SECTION: The only muscles which had both a significant surgical approach effect and a significant difference between pre- and post-operative testing were the adductor magnus and sartorius muscles. The arthroscopic group had a 24.7% higher muscle force in adductor magnus whereas the surgical dislocation group had a higher force of 14.1% on the same muscle. Both groups had a reduction in sartorius muscle force, with the arthroscopic group having a 53.3% reduction and the surgical dislocation group having only a 6.7% reduction. Rectus femoris peak muscle force was greater in the open group. No significant differences existed in muscle forces between the two groups for any of the other primary hip flexor or extensor muscles.DISCUSSION: Systematic reviews comparing open, mini-open, and arthroscopic surgical techniques for treating symptomatic FAI are effective in improving pain and function in short-term to midterm studies and are relatively safe procedures4,5. Our study compared muscle forces calculated in silico between participants who underwent FAI corrective surgery with either a hip dislocation or arthroscopic/mini-open procedures. Our findings indicated that no significant differences existed between the two approaches when comparing the primary muscles of the hip joint, i.e. gluteal muscles, hamstrings, etc.The rectus femoris peak muscle force was higher in the open group pre-operatively than in the arthroscopic group. With the limited number of open approach subjects that were in this cohort, it is difficult to determine if the open approach does produce larger peak muscle forces in the rectus femoris. The muscles that did have significant differences had such a small contribution to the total muscle force required to perform the movement that the findings are not clinically meaningful. The major limitation to this study is the small sample size, especially with the hip dislocation approach. Future studies should be designed to specifically address and compare biomechanical outcomes of the different surgeries to determine if significant differences exist between them.SIGNIFICANCE/CLINICAL RELEVANCE: No significant differences in muscle forces existed in patients who underwent FAI surgery with either a hip dislocation or arthroscopic/mini-open approaches.REFERENCES: 1Rakhra et al (2009) Clin. Orthop. Relat. Res. 467, 660-665; 2Mantovani and Lamontagne (2016) J. Biomech. Eng. 139(4); 3Delp et al (2007) IEEE Trans Biomed Eng 54(11), 1940-50; 4Matsuda et al. (2011) Arthroscopy. 27(2), 252-269; 5Botser et al. Arthroscopy. 27(2), 270-278.

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