The sacro-iliac joint: A potentially painful enigma. Update on the diagnosis and treatment of pain from micro-trauma.

The sacro-iliac joint (SIJ) located at the transition between the spine and the lower limbs is subjected to major shear forces. Mobility at the SIJ is very limited but increases during pregnancy and the post-partum period. Familiarity with the anatomy and physiology of the SIJ is important. The SIJ is a diarthrodial joint that connects two variably undulating cartilage surfaces, contains synovial fluid, and is enclosed within a capsule strengthened by several ligaments. This lecture does not discuss rheumatic or inflammatory diseases of the SIJ, whose diagnosis relies on imaging studies and blood tests. Instead, it focuses on micro-traumatic lesions. Micro-trauma causes chronic SIJ pain, which must be differentiated from hip pain and spinal pain. The diagnosis rests on specific clinical provocation tests combined with a local injection of anaesthetic. Findings are normal from radiographs and magnetic resonance imaging. Non-operative treatment with exercise therapy and stretching aims primarily to strengthen the latissimus dorsi, gluteus, and hamstring muscles to increase SIJ coaptation. Other physical treatments have not been proven effective. Radiofrequency denervation of the dorsal sensory rami has shown some measure of efficacy, although the effects tend to wane over time. Patients with refractory pain may benefit from minimally invasive SIJ fusion by trans-articular implantation of screws or plugs, which has provided good success rates.

The mechanism in junctional failure of thoraco-lumbar fusions. Part I: Biomechanical analysis of mechanisms responsible of vertebral overstress and description of the cervical inclination angle (CIA).

PURPOSE: The purpose of the study is to describe the biomechanical theory explaining junctional breakdowns in thoraco-lumbar fusions, by taking the example of vertebral compression fractures. Also, a new angle, the cervical inclination angle (CIA), describing the relative position of the head at each vertebral level, is presented. METHODS: For the CIA, the data were collected from 137 asymptomatic subjects of a prospective database, containing clinical and radiologic informations. All the 137 subjects have an Oswestry score less than 15% and a pain score less than 2/10 and were part of a previously published study describing the Odontoïd-hip axis angle (ODHA). For each vertebral level from T1 to T12, the CIA as well as the vertical and horizontal distances was measured in reference to the sella turcica (ST), and a vertical line drawn from the ST. Average values and correlation coefficients were calculated. RESULTS: The CIA is an angle whose average value varies very little between T1 and T5 (74.9°-76.85°), and then increases progressively from T6 to T12. T1-T5 vertebra are always in line within the thoracic spine for each subject and can be considered as a straight T1-T5 segment. In addition, it was found that the vertical inclination of T1-T5 segment is correlated with the C7 slope (R 2 = 0.6383). CONCLUSION: The T1-T5 segment inclination is correlated with the C7 slope, and because the latter defines the cervical curve as previously shown, the T1-T5 segment can be considered as the base from which the cervical spine originates. Its role is, thus, similar to the pelvis and its sacral slope, which is the base from which the lumbar spine originates. The CIA along with the ODHA, which describes the adequacy of the global balance in young and elderly asymptomatic populations, are two important parameters that could help us to better understand junctional breakdowns in thoraco-lumbar fusion surgeries.

The mechanism in junctional failure of thoraco-lumbar fusions. Part II: Analysis of a series of PJK after thoraco-lumbar fusion to determine parameters allowing to predict the risk of junctional breakdown.

PURPOSE: To identify risk factors, in 12 patients with junctional breakdown (JBD) after thoraco-sacral fusions and to test a software locating maximal bending moment on full spine EOS images. METHODS: Twelve patients underwent long fusions for lumbar degenerative pathologies. Preop EOS images were compared to first postop EOS showing JBD. Parameters analyzed were: spinopelvic parameters [pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), sagittal vertical axis (SVA), spinosacral angle (SSA), lordosis, and kyphosis], proximal junctional angle (PJA), odontoid-hip axis angle (ODHA), and CIA. A new software estimated the location of maximum bending moment (M max) before and after JBD. RESULTS: All patients except one had a JBD located between T10 and L1, diagnosed at average follow-up of 18.58 months. JBD was a fracture in six patients, severe adjacent disc degeneration in the remaining. Average PI was 52°. PT increased, SS decreased after JBD versus preop (p > 0.05). Average PJA was 34.5°. Global lordosis (GLL), upper lordosis (ULL), L4-S1 lordosis, and thoracic kyphosis (TK) were increased (p < 0.05). Lower lumbar lordosis (LLL), was not increased postJBD (p = 0.6). SVA, SSA, ODHA, and C7 slope were not modified (p > 0.05). CIA average value decreased by 7.5% after JBD. T1-T5 alignment was correlated to C7 slope before (R 2 = 0.77075) and after JBD (R 2 = 0.85409). ODHA decreased after JBD (p > 0.05). Most JBD occurred at or one level away from preoperative M max location. CONCLUSION: This study confirms the importance of harmonious distribution of lumbar (GLL, ULL, and ILL) and thoracic curves (TK, T1-T5 segment) in thoraco-sacral fusions. All patients showed an exaggerated ULL, resulting in a posterior shift and increased lever arm at the thoraco-lumbar junction, leading to JBD.