Preclinical Bench Testing on a Novel Posterior Dynamic Deformity Correction Device for Scoliosis.

STUDY DESIGN: Biomechanical test. OBJECTIVE: To summarize the preclinical tests performed to assess the durability of a novel fusionless dynamic device for the treatment of adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA: The minimal invasive deformity correction (MID-C) system is a distractible posterior dynamic deformity correction device designed to reduce scoliosis for AIS patients, to maintain curve correction, and to preserve spinal motion. To overcome the challenges of wear and fatigue of this procedure, the system has two unique features: polyaxial joints at the rod-screw interface and a ceramic coating of the moving parts. METHODS: Five biomechanical tests were performed: Static compression to failure, fatigue loading per ASTM F 1717 with 5.5-mm screws for 10 million cycles (MC) at 5 Hz, wear assessment, wear test of the polyaxial joint under 100 N load for 10 MC, and wear particle implantation in rabbits. RESULTS: The system failed through buckling of the rod with loads over 3000 N (400% of human body weight). Dynamically, the system maintained 700 N for 10 MC with 5.5 mm screws. The maximum total steady-state wear rate was 0.074 mg/MC (0.03 per polyaxial joint and 0.014 mg/MC for the ratchet mechanism). Histologic evaluation of the particle injection sites indicated no difference in the local tissue response between the control and test articles. At 3 and 6 months postinjection, there were neither adverse local effects nor systemic effects observed. CONCLUSIONS: The unique design features of the MID-C system, based on polyaxial joints and ceramic coating, resulted in favorable static, fatigue, and wear resistance properties. Wear properties were superior to those published for artificial spinal discs. Long-term outcomes from clinical use will be required to correlate these bench tests to the in vivo reality of clinical use. LEVEL OF EVIDENCE: Level V.

Diagnosing spinal osteomyelitis: a comparison of bone and Ga-67 scintigraphy and magnetic resonance imaging.

PURPOSE: The objective of this investigation was to compare the accuracies of bone and Ga-67 scintigraphy and magnetic resonance imaging (MRI) for diagnosing spinal osteomyelitis and to determine the optimal radionuclide approach to this disorder. METHODS: Twenty-two patients, with 24 sites of possible spinal osteomyelitis, who underwent three-phase bone scintigraphy with SPECT, Ga-67 scintigraphy with SPECT, and MRI with and without contrast were included in this retrospective review. Bone scans were interpreted as three-phase studies, delayed planar images alone, delayed planar plus SPECT, and SPECT alone (to identify uptake patterns). Sequential bone/ Ga-67 images were interpreted as planar and as SPECT studies. Planar and SPECT Ga-67 images were also interpreted alone. Precontrast MRI studies were used to identify osteomyelitis, whereas postcontrast images were used to identify soft tissue infection. RESULTS: Eleven sites of spinal osteomyelitis were identified. Tracer uptake in two contiguous vertebrae, as noted on SPECT, was the most accurate bone scan criterion for detecting spinal osteomyelitis (71 %). SPECT bone/Ga-67 was significantly more accurate (92%) than both planar bone/Ga-67 (75%) and bone SPECT (P = 0.15 and P = 0.2, respectively). SPECT Ga-67 was as accurate as SPECT bone/Ga-67 and as sensitive as MRI (91 %); the radionuclide study was slightly but not significantly more specific (92% vs. 77%) than MRI. Of 11 sites of extraosseous infection, 10 were identified on MRI, 9 on SPECT Ga-67, 7 on planar Ga-67, and none on bone scintigraphy. CONCLUSIONS: Spinal osteomyelitis and accompanying soft tissue infection can be diagnosed accurately with a single radionuclide procedure: SPECT Ga-67. This procedure can be used as a reliable alternative when MRI cannot be performed and as an adjunct in patients in whom the diagnosis is uncertain.

Rheumatoid arthritis of the cervical spine.

There is a high incidence of cervical involvement in patients with rheumatoid disease. Early evaluation of the neck, close follow-up with dynamic radiographs of the cervical spine, and careful neurological assessment are important in the care of these patients. Surgical stabilization should be considered early even in the absence of neurological findings when significant instability is noted since outcome is related to preoperative neurological function. The type of fusion performed is determined by a careful assessment of the location of instability, patient factors, and the experience of the surgeon with various techniques. The type of postoperative immobilization should be decided on an individual basis depending on the quality of fixation achieved at surgery. Patients must be observed closely in the postoperative period for development of early complications and followed-up for the appearance of pseudarthrosis or late instabilities.

Retrograde femoral nailing between an ankylosed hip and a stiff knee.

We describe a case of retrograde nailing of a comminuted infraisthmal femur fracture between an ankylosed hip and a stiff knee stemming from heterotopic bone and soft-tissue contracture. A tibial nail directed through the medial femoral condyle was used. At 1 year follow-up the fracture has united anatomically, and the patient has been rehabilitated to his preinjury functional status.