Can postoperative Cobb and pelvic obliquity corrections be predicted using supine traction X-rays in non-ambulatory patients with cerebral palsy fused to L5? A case series study.

PURPOSE: This study aimed to determine whether Cobb and pelvic obliquity corrections can be predicted using supine traction radiographs in patients with cerebral palsy (CP) who underwent posterior spinal fusion (PSF) from T2/3 to L5. METHODS: From January 2010 to January 2020, 167 non-ambulatory patients with CP scoliosis underwent PSF using pedicle screws in two quaternary centers with a minimum of 2 years follow-up (FU). Radiological measurements and chart reviews were performed. RESULTS: A total of 106 patients aged 15.6 ± 0.4 years were included. All patients had significant correction of the Cobb angle (MC), pelvic obliquity (PO), thoracic kyphosis (TK), and lumbar lordosis (LL) without loss of correction at the last FU (LFU). Curve flexibility was significantly correlated with Cobb correction (δMC) immediately postoperatively (p < 0.0001, r = 0.8950), followed by the amount of correction in pelvic obliquity under traction (δPOT) (p = 0.0252, r = 0.2174). For correction in PO (δPO), the most significant variable was δPOT (p < 0.0001, r = 0.7553), followed by curve flexibility (p = 0.0059, r = 0.26) and the amount of correction in Cobb under traction (p = 0.0252, r = 0.2174). CONCLUSIONS: Cobb and PO corrections can be predicted using supine traction films for non-ambulatory CP patients treated with PSF from T2/3 to L5. The variables evaluated were interconnected, reinforcing preoperative planning for these patients. Comparative large-scale studies on patient-related clinical outcomes are required to determine whether this predicted correction is associated with improved surgical outcomes and reduced complication rates. LEVEL OF EVIDENCE: IV.

Distal level in scoliosis surgery for non-ambulatory patients with cerebral palsy: is L5 an option? A case series study.

PURPOSE: This study aimed to determine the radiographic outcomes of patients with cerebral palsy (CP) who underwent posterior spinal fusion from T2/3 to L5 at two quaternary hospitals. METHODS: From January 2010 to January 2020, 167 non-ambulatory patients with CP scoliosis underwent posterior spinal fusion using pedicle screws from T2/3 to L5 in both centers, with a minimum of 2 years follow-up (FU). Radiological measurements and chart reviews were performed. RESULTS: A total of 106 patients aged 15.6 ± 0.4 years were included. None of the patients was lost to FU. All patients had significant correction of the Cobb angle (MC) and pelvic obliquity (PO), thoracic kyphosis (TK), and lumbar lordosis (LL), without loss of correction at the last FU (LFU). The mean values for preoperative, immediate postoperative, and LFU were MC 93.4°, 37.5°, and 42.8°; PO 25.8°, 9.9°, and 12.7°; TK 52.2°, 44.3°, and 45°; and LL - 40.9°, - 52.4°, and - 52.9°, respectively. Higher residual PO at LFU was associated with more severe MC and PO baselines, lower implant density, and an apex located at L3. CONCLUSIONS: CP scoliosis and PO can be corrected, and this correction is maintained over time with posterior spinal fusion using pedicle screws, with L5 as the lowest instrumented vertebra. Larger preoperative MC and PO values associated with the apex at L3 appear to be related to residual PO. Comparative large-scale studies of patient-related clinical outcomes are required to determine whether this intervention is associated with improved surgical outcomes and reduced complication rates. LEVEL OF EVIDENCE: IV.

Pin Fracture in Magnetically Controlled Growing Rods: Influence of the Year of Manufacture.

BACKGROUND: Magnetically controlled growing rods (MCGRs) have a known issue with fracture of the internal locking pin resulting in early revisions. The manufacturer reported that rods manufactured before March 26, 2015, had a 5% risk of locking pin fracture. Locking pins made after this date are thicker in diameter and of a tougher alloy; their rate of pin fracture is not known. The aim of this study was to better understand the impact of the design changes on the performance of MCGRs. METHODS: This study involves 46 patients with 76 removed MCGRs. Forty-six rods were manufactured before March 26, 2015, and 30 rods after that date. Clinical and implant data were collected for all MCGRs. Retrieval analysis comprised plain radiographs evaluations, force and elongation testing, and disassembly. RESULTS: The 2 patient groups were statistically comparable. We found that 14 of 27 patients implanted with rods manufactured before March 26, 2015 (group I) had a fracture of their locking pins. Three of the 17 patients with rods manufactured after this date (group II) were also found to have a fractured pin. CONCLUSIONS: Retrieved rods collected at our center and made after March 26, 2015, had far fewer locking pin fractures than those made before this date; this may be due to the change in pin design.

Distal fusion in Duchenne scoliosis: the relevance of preoperative pelvic obliquity. A case series study.

PURPOSE: The aim of this study was to determine clinical and radiographic outcomes for Duchenne Muscular Dystrophy (DMD) patients who underwent posterior spinal fusion from T2/3 to L5 (without pelvic fixation), at this single centre. METHODS: From January 2012 to January 2020, 29 consecutive DMD scoliosis patients underwent posterior spinal fusion using pedicle screws from T2/3 to L5 in a single center with a minimum of 3 years follow-up (FU). Radiologic measurements and chart review were performed. RESULTS: Twenty nine patients aged 14 ± 1.5 years were included. No patient was lost to FU. All patients had significant correction in Cobb angle, pelvic obliquity (PO) and lumbar lordosis (LL), without loss of correction at last FU. The mean values for preoperative, immediate postoperative and last FU were CA 62o, 15o and 17o, PO: 21o, 8o and 9o; and LL 10o, -41o and -41o respectively. Correction in CA was independent of any variable analysed including implant density, rod diameter, traction, or bone density. Regarding PO, it was inversely related to age and independent of all other variables. Factors associated with postoperative complications were age and respiratory function. CONCLUSIONS: It appears from our results that pelvic fixation might not always be required in DMD scoliosis surgery, when using pedicle screws with lowest instrumented vertebra at L5. However, larger preoperative PO values can be related with residual PO. It seems that probably related to the underlying condition, early surgery may decrease incidence of complications. LEVEL OF EVIDENCE: IV.

Rod Fracture in Magnetically Controlled Growing Spine Rods.

BACKGROUND: The mechanisms of fracture in magnetically controlled growing rods (MCGRs) and the risk factors associated with this are poorly understood. This retrospective analysis of explanted MCGRs aimed to add understanding to this subject. METHODS: From our cohort of over 120 retrieved MCGRs, we identified 7 rods that had fractured; all were single-rod constructs, retrieved from 6 patients. These were examined and compared with 15 intact single-rod constructs. Retrieval and fractographic analyses were used to determine the failure mode at the fracture site and the implant's functionality. Cobb angle, degree of rod contouring, and the distance between anchoring points were computed on anteroposterior and lateral radiographs. RESULTS: 5/7 versus 3/15 rods had been inserted after the removal of a previously inserted rod, in the fractured versus control groups. All fractured rods failed due to bending fatigue. Fractured rods had greater rod contouring angles in the frontal plane ( P = 0.0407) and lateral plane ( P = 0.0306), and greater distances between anchoring points in both anteroposterior and lateral planes ( P = 0.0061 and P = 0.0074, respectively). CONCLUSIONS: We found all failed due to a fatigue fracture and were virtually all single rod configurations. Fracture initiation points corresponded with mechanical indentation marks induced by the intraoperative rod contouring tool. Fractured rods had undergone greater rod contouring and had greater distances between anchoring points, suggesting that it is preferable to implant double rod constructs in patients with sufficient spinal maturity to avoid this complication. CLINICAL RELEVANCE: Level III.

Blood titanium levels in patients with large and sliding titanium implants.

BACKGROUND: Titanium, which is known to be a highly biologically inert element, is one of the most commonly used metals in orthopaedic implants. While cobalt and chromium blood metal ion testing is routinely used in the clinical monitoring of patients with metal-on-metal hip implants, much less is known about the levels of titanium in patients with other implant types. The aim of this study was to better understand the normal ranges of blood titanium levels in patients implanted with large and sliding titanium constructs by comparison with reference levels from conventional titanium hips. METHODS: This study examined data collected from 136 patients. Over a period of 24 months, whole blood samples were collected from 41 patients implanted with large titanium implants: long (range 15 to 30 cm) spine rods with a sliding mechanism ("spine rods", n = 18), long bone tumour implants ("tumour implants", n = 13) and 3D-printed customised massive acetabular defect implants ("massive acetabular implants", n = 10). This data was compared with standard, uncemented primary titanium hip implants ("standard hips", 15 cm long) (n = 95). Clinical, imaging and blood titanium levels data were collected for all patients and compared statistically between the different groups. RESULTS: The median (range) of blood titanium levels of the standard hip, spine rods, femoral tumour implants and massive acetabular implants were 1.2 ppb (0.6-4.9), 9.7 ppb (4.0-25.4), 2.6 ppb (0.4-104.4) and 5.7 ppb (1.6-31.5) respectively. Spine rods and massive acetabular implants had significantly greater blood titanium levels compared to the standard hips group (p < 0.001). CONCLUSION: This study showed that titanium orthopaedic implants that are large and/or have a sliding mechanism have higher blood titanium levels compared to well-functioning, conventionally sized titanium hips. Reassuringly, the increased levels did not appear to induce adverse metal reactions. This study provides useful baseline data for future studies aimed at assessing blood titanium levels as a biomarker for implant function.