Conventional pre-operative planning for total hip arthroplasty mostly relies on the patient radiologic anatomy for the positioning and choice of implants. This kind of planning essentially remains a static approach since dynamic aspects such as the joint kinematics are not taken into account. Hence, clinicians are not able to fully consider the evolving behavior of the prosthetic joint that may lead to implant failures. In fact, kinematics plays an important role since some movement may create conflicts within the prosthetic joint and even provoke dislocations. The goal of our study was to assess the relationship between acetabular implant positioning variations and resultant impingements and loss of joint congruence during daily activities. In order to obtain accurate hip joint kinematics for simulation, we performed an in-vivo study using optical motion capture and magnetic resonance imaging (MRI). Motion capture and MRI was carried out on 4 healthy volunteers (mean age, 28 years). Motion from the subjects was acquired during routine (stand-to-sit, lie down) and specific activities (lace the shoes while seated, pick an object on the floor while seated or standing) known to be prone to implant dislocation and impingement. The hip joint kinematics was computed from the recorded markers trajectories using a validated optimized fitting algorithm (accuracy: translational error ≍ 0.5 mm, rotational error < 3°) which accounted for skin motion artifactsand patient-specific anatomical constraints (e.g. bone geometry reconstructed from MRI, hip joint center) (Fig. 1). 3D models of prosthetic hip joints (pelvis, proximal femur, cup, stem, head) were developed based on variations of acetabular cup's inclination (40°, 45°, 60°) and anteversion (0°, 15°, 30°) parameters, resulting in a total of 9 different implant configurations. Femoral anteversion remained fixed and determined as “neutral” with the stem being parallel to the posterior cortex of the femoral neck. Motion capture data of daily tasks were applied to all implant configurations. While visualizing the prosthetic models in motion, a collision detection algorithm was used to locate abnormal contacts between both bony and prosthetic components (Fig. 2). Moreover, femoral head translations (subluxation) were computed to evaluate the joint congruence.Introduction
Methods
Today, there is no clear consensus as to the amplitude of movement of the “normal hip”. Knowing the necessary joint mobility for everyday life is important to understand different pathologies and to better plan their treatments. Moreover, determining the hip range of motion (ROM) is one of the key points of its clinical examination. Unfortunately this process may lack precision because of movement of other joints around the pelvis. Our goal was to perform a preliminary study based on the coupling of MRI and optical motion capture to define precisely the necessary hip joint mobility for everyday tasks and to assess the accuracy of the hip ROM clinical exam. MRI was carried out on 4 healthy volunteers (mean age, 28 years). A morphological analysis was performed to assess any bony abnormalities. Two motion capture sessions were conducted: one aimed at recording routine activities (stand-to-sit, lie down, lace the shoes while seated, pick an object on the floor while seated or standing) known to be painful or prone to implant failures. During the second session, a hip clinical exam was performed successively by 2 orthopedists (2 and 12 years' experience), while the motion of the subjects was simultaneously recorded (Fig.1). These sequences were captured: 1) supine: maximal flexion, maximal IR/ER with hip flexed 90°, maximal abduction; 2) seated: maximal IR/ER with hip and knee flexed 90°. A hand held goniometer was used by clinicians to measure hip angles in those different positions. Hip joint kinematics was computed from the markers trajectories using a validated optimized fitting algorithm which accounted for skin motion artifacts (accuracy: translational error≍0.5 mm, rotational error <3°). The resulting computed motions were applied to patient-specific hip joint 3D models reconstructed from their MRI data (Fig. 2). Hip angles were determined at each point of the motion thanks to two bone coordinate systems (pelvis and femur). The orthopedist's results were compared.Introduction
Methods
In foot and ankle surgery incorrect placement of implants, or inaccuracy in fracture reduction may remain undiscovered with the use of conventional C-arm fluoroscopy. These imperfections are often only recognized on postoperative computer tomography scans. The apparition of three dimensional (3D) mobile Imaging system has allowed to provide an intraoperative control of fracture reduction and implant placement. Three dimensional computer assisted surgery (CAS) has proven to improve accuracy in spine and pelvic surgery. We hypothesized that 3D-based CAS could improve accuracy in foot and ankle surgery. The purpose of our study was to evaluate the feasibility and utility of a multi-dimensional surgical imaging platform with intra-operative three dimensional imaging and/or CAS in a broad array of foot and ankle traumatic and orthopaedic surgery. Cohort study of patients where the 3D mobile imaging system was used for intraoperative 3D imaging or 3D-based CAS in foot and ankle surgery. The imaging system used was the O-arm Surgical Imaging System and the navigation system was the Medtronic's StealthStation. Surgical procedures were performed according to standard protocols. In case of fractures, image acquisition was performed after reduction of the fracture. In cases of 3D-based CAS, image acquisition was performed at the surgical step before implants placement. At the end of the operations, an intraoperative 3D scan was made. We used the O-arm Surgical Imaging system in 11 patients: intraoperative 3D scans were performed in 3 cases of percutaneus fixation of distal tibio-fibular syndesmotic disruptions; in 2 of the cases, revision of reduction and/or implant placement were needed after the intraoperative 3D scan. Three dimensional CAS was used in 10 cases: 2 open reduction and internal fixation (ORIF) of the calcaneum, 1 subtalar fusion, 2 ankle arthrodesis, 1 retrograde drilling of an osteochondral lesion of the talus, 1 Charcot diabetic reconstruction foot and 1 intramedullary screw fixation of a fifth metatarsal fracture. The guidance was used essentially for screw placement, except in the retrograde drilling of an osteochondral lesion where the guidance was used to navigate the drill tool. Intraoperative 3D imaging showed a good accuracy in implant placement with no need to revision of implants. We report a preliminary case series with use of the O-arm Surgical Imaging System in the field of foot and ankle surgery. This system has been used either as intraoperative 3D imaging control or for 3D-based CAS. In our series, the 3D computer assisted navigation has been very useful in the placement of implants and has shown that guidance of implants is feasible in foot and ankle surgery. Intraoperative 3D imaging could confirm the accuracy of the system as no revisions were needed. Using the O-arm as intraoperative 3D imaging was also beneficial because it allowed todemonstrate intraoperative malreduction or malposition of implants (which were repositioned immediately). Intraoperative 3D imaging system showed very promising preliminary results in foot and ankle surgery. There is no doubt that intraoperative use of 3D imaging will become a standard of care. The exact indications need however to be defined with further studies.
