An Anatomic Study Examining Lumbar Pars Interarticularis Distance and Spinal Canal Width in Relation to Lumbar Decompressive Surgery.

BACKGROUND: Lumbar laminectomy is a surgical procedure allowing for decompression of neural structures. A wide laminectomy to adequately decompress neural elements without compromising the structural integrity of the spinal column is ideal. Pars interarticularis fractures with spinal instability after isolated laminectomy from overresection of the posterior elements have been reported. There are limited anatomical studies in the spine literature that measure the pars interarticularis distance (PID) and spinal canal width (SCW) in the lumbar spine. OBJECTIVE: The purpose of this study was to assess the differences in PID and SCW at each level of the lumbar spine and to determine their effects on the extent of laminectomy at each lumbar level. METHODS: We performed an anatomic study measuring PID and SCW in the lumbar spine from 93 skeletally matured osseous specimens. Groups were compared using an independent sample t test, 1-way analysis of variance, and Wilcoxon test, and significance was set at P < 0.05. RESULTS: Our study suggests that the distance between PID and SCW increases from L1 to L5 in African American and Caucasian women and men. However, the respective increase in SCW at each lumbar level is less than the respective increase in PID at the same levels. This trend suggests that there is a wider window available for decompression without compromising spinal stability in the lower lumbar spine compared with the upper lumbar spine. CONCLUSIONS: Our findings suggest that the upper lumbar spine has a narrower window for decompression; therefore, care should be taken to preserve as much of the pars at L1-L3. Understanding the variations in PID and SCW in the lumbar spine will help surgeons perform adequate decompression of a stenotic canal while avoiding postoperative spinal instability. CLINICAL RELEVANCE: Awareness of PID to SCW ratio may help spine surgeons avoid iatrogenic instability, postoperative intractable back pain, spondylolisthesis, or complications involving alterations of the lumbar spine biomechanics.

Complications of a Unilateral Nondisplaced Cervical Facet Fracture in a Patient With Previously Noninstrumented Anterior Cervical Fusion.

Fused motion segments have been documented to alter the biomechanics of the cervical spine and compromise its stability. Current literature describes a growing association between the presence of prior noninstrumented fused cervical segments and the predisposition to acute, traumatic instability at adjacent levels. We present the case of a stable cervical spine fracture pattern in a patient with a history of multilevel noninstrumented anterior cervical spine fusion-initially presenting as a small, nondisplaced unilateral facet fracture that ultimately progressed to overt displacement with kyphosis resulting in acute cervical pain and instability. The patient underwent urgent open reduction and instrumented posterior fixation. We discuss the challenges associated with a timely diagnosis and offer insight into the surgical management of this rare yet potentially catastrophic complication.

Radiation-Induced Necrosis of the Temporal Bone: Diagnosis and Management.

OBJECTIVE: To document our experience with osteoradionecrosis (ORN) of the temporal bone. STUDY DESIGN: Retrospective case review. SETTING: Tertiary care medical center. PATIENTS: Patients who developed exposed necrotic bone of the external auditory canal after radiation therapy to the head and neck. INTERVENTIONS: Temporal bone ORN was managed conservatively in all patients with a combination of systemic antibiotics, antibiotic ear drops, and in-office debridement. Three patients required surgery, two of which were for a cholesteatoma. MAIN OUTCOME MEASURE: The need for surgical intervention in the management of ORN. RESULTS: Twenty-three patients with ORN of the temporal bone comprise the study group. The average age of patients at the time of diagnosis was 58 years (range, 34-75 yr). The parotid gland was the most common primary tumor site (n = 10). The mean lag time from completion of radiotherapy to diagnosis of ORN was 11 years (range, 2-48 yr). The most common presenting symptom was hearing loss (n = 18), followed by tinnitus (n = 13) and otorrhea (n = 13). All 23 patients were managed conservatively with antibiotic therapy and in-office debridement of necrotic bone. None of the patients required temporal bone resection and/or free-flap reconstruction. CONCLUSION: ORN of the temporal bone is a rare adverse event that can occur after radiotherapy for a variety of neoplasms of the head, neck, and central nervous system. Conservative management, which includes directed antibiotic therapy and regular in-office debridement of necrotic bone, can adequately control the disease process and symptomatology, thus avoiding more invasive surgical interventions.

Does the type of tibial component affect mechanical alignment in unicompartmental knee replacement?

PURPOSE: There are a number of factors responsible for the longevity of unicompartmental knee replacements (UKR). These include the magnitude of postoperative alignment and the type of material used. The effect of component design and material on postoperative alignment, however, has not been explored. MATERIALS AND METHODS: We retrospectively reviewed 89 patients who underwent UKR with robotic guidance. Patients were divided into two groups, according to whether they had received an all-polyethylene inlay component (Inlay group) or a metal-backed onlay component (Onlay group). We explored the magnitude of mechanical alignment correction obtained in both groups. RESULTS: Mean postoperative mechanical alignment was significantly closer to neutral in the Onlay group (mean=2.8°; 95% CI=2.4°, 3.2°) compared to the Inlay group (mean=3.9°; 95% CI=3.4°, 4.4°) (R2=0.65; P=0.003), adjusting for gender, BMI, age, side and preoperative mechanical alignment (Fig. 2). Further exploration revealed that the thickness of the tibial polyethyelene insert had a significant effect on postoperative alignment when added to the model (R2=0.68; P=0.01). CONCLUSION: Patients who received a metal-backed Onlay tibial component obtained better postoperative mechanical alignment compared to those who received all-polyethylene Inlay prostheses. The thicker overall construct of Onlay prostheses appears to be an important determinant of postoperative alignment. Considering their higher survivorship rates and improved postoperative mechanical alignment, Onlay prostheses should be the first option when performing medial UKR.

The role of the iliotibial band during the pivot shift test.

PURPOSE: Several studies have suggested that the iliotibial (IT) band plays a role in knee laxity and that it may affect the magnitude of the pivot shift observed. However, the extent of the role played by the IT band, as well as its mechanism of action, is not currently known. This cadaveric study aimed to quantify the effect of the IT band and the hip abduction angle on the magnitude of anterior tibial translation (ATT) during the pivot shift. METHODS: Six fresh-frozen hip-to-toes specimens were used. Serial sectioning of the anterior cruciate ligament (ACL) and the IT band was performed. Lachman and mechanized pivot shift manoeuvres were employed at each stage, and ATT of the lateral and medial compartments was measured using navigation. Three hip abduction angles were tested for each condition: 0°, 15° and 30°. RESULTS: Sequential sectioning of the ACL and the IT band resulted in a significant increase in ATT in both the lateral (Intact = 0 ± 0.5 mm; ACL deficient = 8.1 ± 0.2 mm; ACL + IT deficient = 10.8 ± 0.3 mm) and medial (Intact = 6.7 ± 0.4 mm; ACL deficient = 8.4 ± 0.3 mm; ACL + IT deficient = 9.9 ± 0.3 mm) compartments. No significant increase in ATT was observed after changing the hip abduction angle at each stage. CONCLUSIONS: An increase in the magnitude of the pivot shift and the Lachman was observed as the constraint of the IT band was removed. Additionally, it was shown that the hip abduction angle at which the pivot shift test was performed did not significantly affect the magnitude of ATT in this cadaveric model.

Navigated guide tube for the placement of mini-open pedicle screws using stereotactic 3D navigation without the use of K-wires: technical note.

OBJECT: Three-dimensional spinal navigation increases screw accuracy, but its implementation in clinical practice has been difficult, mainly because of surgeons' concerns about increased operative times, disturbance of workflow, and safety. The authors present a custom-designed navigated guide that addresses some of these concerns by allowing for drilling, tapping, and placing the final screw via a minimally invasive approach without the need for K-wires. In this paper, the authors' goal was to describe the technical aspects of the navigated guide tube as well as pedicle screw accuracy. METHODS: The authors present the technical details of a navigated guide that allows drilling, tapping, and the placement of the final screw without the need for K-wires. The first 10 patients who received minimally invasive mini-open spinal pedicle screws are presented. The case series focuses on the immediate postoperative outcomes, pedicle screw accuracy, and pedicle screw-related complications. An independent board-certified neuroradiologist determined pedicle screw accuracy according to a 4-tiered grading system. RESULTS: The navigated guide allowed successful placement of mini-open pedicle screws as part of posterior fixation from L-1 to S-1 without the use of K-wires. Only 7-mm-diameter screws were placed, and 72% of screws were completely contained within the pedicle. Breaches less than 2 mm were seen in 23% of cases, and these were all lateral except for one screw. Breaches were related to the lateral to medial trajectory chosen to avoid the superior facet joint. There were no complications related to pedicle screw insertion. CONCLUSIONS: A novel customized navigated guide tube is presented that facilitates the workflow and allows accurate placement of mini-open pedicle screws without the need for K-wires.

Pedicle screw navigation: a systematic review and meta-analysis of perforation risk for computer-navigated versus freehand insertion.

OBJECT: In this paper the authors' goal was to compare the accuracy of computer-navigated pedicle screw insertion with nonnavigated techniques in the published literature. METHODS: The authors performed a systematic literature review using the National Center for Biotechnology Information Database (PubMed/MEDLINE) using the Medical Subject Headings (MeSH) terms "Neuronavigation," "Therapy, computer assisted," and "Stereotaxic techniques," and the text word "pedicle." Included in the meta-analysis were randomized control trials or patient cohort series, all of which compared computer-navigated spine surgery (CNSS) and nonassisted pedicle screw insertions. The primary end point was pedicle perforation, while the secondary end points were operative time, blood loss, and complications. RESULTS: Twenty studies were included for analysis; of which there were 18 cohort studies and 2 randomized controlled trials published between 2000 and 2011. Foreign-language papers were translated. The total number of screws included was 8539 (4814 navigated and 3725 nonnavigated). The most common indications for surgery were degenerative disease, spinal deformity, myelopathy, tumor, and trauma. Navigational methods were primarily based on CT imaging. All regions of the spine were represented. The relative risk for pedicle screw perforation was determined to be 0.39 (p < 0.001), favoring navigation. The overall pedicle screw perforation risk for navigation was 6%, while the overall pedicle screw perforation risk was 15% for conventional insertion. No related neurological complications were reported with navigated insertion (4814 screws total); there were 3 neurological complications in the nonnavigated group (3725 screws total). Furthermore, the meta-analysis did not reveal a significant difference in total operative time and estimated blood loss when comparing the 2 modalities. CONCLUSIONS: There is a significantly lower risk of pedicle perforation for navigated screw insertion compared with nonnavigated insertion for all spinal regions.