Causal factors for position-related SSEP changes in spinal surgery.

BACKGROUND CONTEXT: Somatosensory evoked potentials (SSEPs) are effective in detecting upper extremity positional injuries; however, causal factors for which patient population is most at risk are not well established. PURPOSE: To review causal factors for intraoperative SSEP changes due to patient positioning. STUDY DESIGN: A case series with retrospective chart analysis was performed. PATIENT SAMPLE: 398 patient charts and intraoperative neurophysiological monitoring data from patients who underwent thoracolumbar and lumbosacral spine surgery were reviewed in a consecutive sequence from 2012 to 2013. OUTCOME MEASURES: Adverse events (AE) with the upper extremity SSEP recordings were compared to the independent variables, sex, positioning, length of procedure, and body habitus. METHODS: Thoracolumbar and lumbosacral spine surgeries using contemporaneous ulnar and median nerve SSEPs were reviewed. The one-way analysis of variance (ANOVA) test, Chi-square, and independent samples t test were used to determine statistical significance in having an upper extremity SSEP AE to the aforementioned independent variables. RESULTS: The sample consisted of 209 males (52.5 %) and 189 females (47.5 %) (n = 398). AE to the upper extremity SSEP was seen in 44 patients. Sex was found to be statistically significant for isolated ulnar nerve AE (P ≤ 0.001) with males being most at risk (87.5 %). AE for isolated median nerve SSEP was statistically significant for supine and prone positions (P = 0.043). Length of procedure was statically significant for isolated ulnar nerve SSEP AE (P = 0.039). BMI was statistically significant for generalized upper extremity SSEP AE (P = 0.016), as well as isolated ulnar SSEP AE (P = 0.006), isolated median SSEP AE (P ≤ 0.001) and contemporaneous median and ulnar SSEP AE of the same limb (P ≤ 0.001). CONCLUSION: Sex, patient positioning, length of procedure, and BMI are determinants for upper extremity neural compromise during thoracolumbar and lumbosacral spine surgeries.

Motor Evoked Potential Recordings from the Urethral Sphincter Muscles (USMEPs) during Spine Surgeries.

Bowel and bladder function are at risk during tumor resection of the conus, cauda equina, and nerve roots. This study demonstrates the ability to acquire transcranial electrical motor evoked potentials (TCeMEPs) from the urethral sphincter muscles (USMEPs) by utilizing a urethral catheter with an embedded electrode. A retrospective analysis of intraoperative neurophysiological monitoring (IONM) data from nine intradural tumors, four tethered cord releases, and two spinal stenosis procedures was performed (n = 15). The cohort included seven females and eight males (median age: 38.91 years). A catheter with embedded urethral electrodes was used for recording TCeMEPs and spontaneous electromyograph (s-EMG) from the external urethral sphincter (EUS). USMEPs were obtained in 14 patients (93%). The reliability of TCeMEP from the external anal sphincter (EAS) was variable across all patients. In patient 7, the TCeMEP recordings from the urethral sphincter were not present before incision; however, following the resection of the tumor, the USMEP recordings were obtained and remained stable for the remainder of the procedure. Patient 7 had subsequent improvement in bladder function postoperatively. Patient 4 exhibited a 50% increase in the amplitude of the USMEP following tumor resection and exhibited improved bladder function as well postoperatively. In this small series, we were able to acquire consistent and reliable MEPs when recorded from the urethral sphincters. More study is needed to establish a better understanding of the value added by this modality. USMEPs can be attempted in surgeries that put the function of the pelvic floor at risk.

Factors associated with prolonged wound drainage after primary total hip and knee arthroplasty.

BACKGROUND: Prolonged wound drainage following total hip or total knee arthroplasty has been associated with an increased risk of postoperative morbidity. The purpose of this study was to determine the pharmacologic, surgical, and patient-specific factors that are associated with prolonged wound drainage and the relationship of this complication to the length of hospital stay and the rate of wound infections. METHODS: We conducted a retrospective observational study of 1211 primary total hip arthroplasties and 1226 primary total knee arthroplasties. Prospectively collected data included body mass index, intraoperative blood loss, surgical time, type of prophylaxis against deep venous thrombosis, and length of hospital stay. The association of these factors with the duration of postoperative wound drainage was analyzed. An acute infection developed after fifteen primary total hip arthroplasties and ten primary total knee arthroplasties. The patients with an acute postoperative infection were compared with their uninfected counterparts, and an odds ratio was determined to estimate the risk of prolonged wound drainage resulting in a wound infection. RESULTS: Morbid obesity was strongly associated with prolonged wound drainage in the total hip arthroplasty group (p = 0.001) but not in the total knee arthroplasty group (p = 0.590). An increased volume of drain output was an independent risk factor for prolonged wound drainage in both groups. Patients who received low-molecular-weight heparin for prophylaxis against deep venous thrombosis had a longer time until the postoperative wound was dry than did those treated with aspirin and mechanical foot compression or those who received Coumadin (warfarin); this difference was significant on the fifth postoperative day (p = 0.003) but not by the eighth postoperative day. Prolonged wound drainage resulted in a significantly longer hospital stay in both groups (p < 0.001). Each day of prolonged wound drainage increased the risk of wound infection by 42% following a total hip arthroplasty and by 29% following a total knee arthroplasty. CONCLUSIONS: Morbid obesity, the use of low-molecular-weight heparin, and a higher drain output were associated with a prolonged time until the postoperative wound was dry following a primary total hip arthroplasty, whereas a higher drain output was the only risk factor associated with prolonged drainage following a primary total knee arthroplasty. Prolonged drainage was associated with a higher rate of infection following a primary total hip arthroplasty, whereas obesity was the only identified independent risk factor for postoperative infection following a primary total knee arthroplasty.

Contemporaneous Evaluation of Intraoperative Ulnar and Median Nerve Somatosensory Evoked Potentials for Patient Positioning: A Review of Four Cases.

Somatosensory evoked potentials (SSEPs) are a valuable tool for assessing changes in peripheral nerve pathways caused by patient positioning during spinal surgeries. These changes, when left undiagnosed, may lead to postoperative neurological sequelae. Why an upper extremity SSEP attenuates due to positioning is not necessarily clear and can be multifactorial, affecting the peripheral nerves or elements of the brachial plexus. A conduction block can occur at any point along the course of the nerve secondary to entrapment, compression, and ischemia. These mechanisms of injury may be caused by extreme body habitus, the length of the procedure, or the patient's metabolic underpinnings. The goal of neuromonitoring for positional injury is to predict and prevent both peripheral nerve and brachial plexus injuries. Using ulnar and median nerve SSEPs contemporaneously may lead to better identification of compromised structures when an SSEP change to one or both of the nerves occurs. The investigators provide four case reports where intraoperative SSEP assessment of contemporaneous ulnar and median nerves prevented postoperative upper extremity neural deficits.

The effect of end screw orientation on the stability of anterior instrumentation in cyclic lateral bending.

BACKGROUND CONTEXT: Screw pullout at the proximal or distal end of multilevel anterior instrumentation can occur clinically. Previous laboratory studies have shown that angulation of vertebral body screws increases screw pullout strength and stability in toggling. PURPOSE: To determine the effect of end screw angulation on instrumentation construct stability after cyclic, lateral bending. STUDY DESIGN: A biomechanical study in calf spines comparing two anterior spinal instrumentation constructs, one with parallel polyaxial screws and the other with angled polyaxial end screws. METHODS: Sixteen instrumented constructs were made from eight thoracic (T8-T12) and eight lumbar calf spines (L1-L5). Eight (four lumbar specimens and four thoracic specimens) had five bicortical screws inserted mid-body and parallel to the end plates. The other eight specimens had two screws angled toward the superior end plates of the top two vertebrae; the middle vertebra had a mid-body screw parallel to the end plate, and the bottom two vertebrae had screws angled towards their inferior end plates. The constructs were then cycled in lateral bending, and the displacements of the two instrumentations with a 10 N-m bending load were compared. RESULTS: After 10,000 cycles, constructs with parallel end screws exhibited twice the average displacement than those with angled screws: 5.4 mm versus 2.9 mm (p=.031). CONCLUSION: The use of angled screws at the ends of anterior constructs demonstrated increased construct stability after cycling compared with traditional transverse screws. Although angled screw insertion is technically more difficult and is possible only with specific screw designs, its use might increase instrumentation longevity.

Motor evoked potentials for femoral nerve protection in transpsoas lateral access surgery of the spine.

Detecting potential intraoperative injuries to the femoral nerve should be the main goal of neuromonitoring of lateral lumber interbody fusion (LLIF) procedures. We propose a theory and technique to utilize motor evoked potentials (MEPs) to protect the femoral nerve (a peripheral nerve), which is at risk in LLIF procedures. MEPs have been advocated and widely used for monitoring spinal cord function during surgical correction of spinal deformity and surgery of the cervical and thoracic spine, but have had limited acceptance for use in lumbar procedures. This is due to the theoretical possibility that MEP recordings may not be sensitive in detecting an injury to a single nerve root considering there is overlapping muscle innervation of adjacent root levels. However, in LLIF procedures, the surgeon is more likely to encounter lumbar plexus elements than nerve roots. Within the substance of the psoas muscle, the L2, L3, and L4 nerve roots combine in the lumbar plexus to form the trunk of the femoral nerve. At the point where the nerve roots become the trunk of the femoral nerve, there is no longer any alternative overlapping innervation to the quadriceps muscles. Insult to the fully formed femoral nerve, which completely blocks conduction in motor axons, should theoretically abolish all MEP responses to the quadriceps muscles. On multiple occasions over the past year, our neuro-monitoring groups have observed significantly degraded amplitudes of the femoral motor and/or sensory evoked potentials limited to only the surgical side. Most of these degraded response amplitudes rapidly returned to baseline values with a surgical intervention (i.e., prompt removal of surgical retraction).

Periprosthetic femoral fractures above total knee replacements.

Periprosthetic femoral fractures above total knee replacements can be managed by a variety of methods, including casting, open reduction and internal fixation, external fixation, or revision arthroplasty. Because no single method has emerged as the optimal choice for all such fractures, it is important to understand which options are appropriate for each fracture pattern. Early classification systems focused on displacement as a major indication for either surgical or nonsurgical management. However, recent techniques and current implants have made surgical management preferable for most periprosthetic fractures. Classification based on fracture location can help guide such treatment. Generally, intramedullary nails are best for proximal fractures, fixed-angle devices for fractures originating at the component, and revision arthroplasty for very distal fractures or those with implant loosening.

Thermal energy in arthroscopic surgery of the wrist.

Thermal energy in arthroscopic surgery needs further follow-up evaluation to clarify the potential benefits, specifically with respect to thermal shrinkage. Although the initial findings are promising, the long-term results need to be compared with other accepted standards of management. Preliminary findings seem to show that the addition of these surgical instruments and expanding operative techniques have definite roles in arthroscopic wrist surgery, as demonstrated through meticulous synovectomies and precise tissue debridement, along with the possible thermal shrinkage potential.

Instability following total hip arthroplasty.

Dislocation is the second most common complication of total hip arthroplasty. Most dislocations occur early in the postoperative period and are caused by patient factors, surgical factors, or a combination of both. Patient factors that predispose to postoperative dislocation include previous surgery and neurologic impairment. Surgical factors include surgical approach, component orientation, and prosthetic and/or bony impingement. Evaluation of patients undergoing total hip arthroplasty requires a thorough history and physical examination, as well as a detailed radiographic assessment. Closed treatment of instability is successful in two thirds of cases; the remainder require surgical management. Surgical techniques used to treat or minimize risk of further dislocation include revision arthroplasty, trochanteric advancement, use of elevated rim liners, and use of constrained liners.

Saphenous nerve somatosensory evoked potentials: a novel technique to monitor the femoral nerve during transpsoas lumbar lateral interbody fusion.

STUDY DESIGN: A retrospective analysis of a case series was performed. OBJECTIVE: To describe a novel technique to monitor femoral nerve function by analyzing the saphenous nerve somatosensory evoked potential (SSEP) during transpsoas surgical exposures of the lumbar spine. SUMMARY OF BACKGROUND DATA: During transpsoas direct lateral approaches to the lumbar spine, electromyography monitoring is frequently advocated; however, sensory and motor neurological complications are still being reported. Femoral nerve injury remains a feared complication at the L3-L4 and L4-L5 levels. The current neurophysiological monitoring modalities are not specific or sensitive enough to predict these injuries after the retractors are placed. The authors have developed a technique that is hypothesized to reduce femoral nerve injuries caused by retractor compression by adding saphenous nerve SSEPs to their neurophysiological monitoring paradigm. METHODS: Institutional review board approval was granted for this study and the medical records along with the intraoperative monitoring reports from 41 consecutive transpsoas lateral interbody fusion procedures were analyzed. The presence or absence of intraoperative changes to the saphenous nerve SSEP was noted and the postoperative symptoms and physical examination findings were noted. RESULTS: SSEP changes were noted in 5 of the 41 surgical procedures, with 3 of the patients waking up with a femoral nerve deficit. None of the patients with stable SSEP's developed sensory or motor deficits postoperatively. No patient in this series demonstrated intraoperative electromyography changes indicative of an intraoperative nerve injury. CONCLUSION: Saphenous nerve SSEP monitoring may be a beneficial tool to detect femoral nerve injury related to transpsoas direct lateral approaches to the lumbar spine. LEVEL OF EVIDENCE: 4.

A proposed classification of supracondylar femur fractures above total knee arthroplasties.

A new classification system is proposed for supracondylar femur fractures above total knee arthroplasties based on fracture location relative to the femoral component. Radiographs of 28 cases were evaluated and classified according to the proposed system by 12 physicians: 3 trauma specialists, 3 adult reconstruction specialists, 3 musculoskeletal radiologists, and 3 orthopaedic residents. The same 12 physicians reevaluated the same 28 cases 3 months later. The mean reliability coefficient for all observers was 0.74 (substantial agreement). The coefficient for reproducibility after 3 months was 0.85 (almost perfect). The power of the study was 80%. The proposed classification system is easy to use and has good interobserver reliability among orthopaedic residents, orthopaedic attendings--trauma and reconstruction--and radiologists. Intraobserver reliability was also excellent at 3 months.

Use of structural bone graft with cementless acetabular cups in total hip arthroplasty.

We retrospectively studied 15 primary and 13 revision total hip arthroplasties in which structural acetabular bone grafts were used in conjunction with cementless acetabular cups (for 11 type I segmental acetabular defects and 17 type III combined segmental/cavitary acetabular defects). Mean follow-up was 7.7 years in the primary and 6.8 years in the revision group. Radiographic analysis was performed to assess graft incorporation, component migration, bone-implant radiolucencies, and polyethylene wear. Two acetabular components (7.1%) were radiographically loose and demonstrated component migration. One of the two patients with these components also showed evidence of eccentric polyethylene wear. Three patients (10.7%) exhibited eccentric polyethylene wear. All grafts were well-incorporated radiographically without evidence of resorption. Modified Harris hip scores for all patients improved postoperatively.

The effect of an attachable lateral support plate on the stability of intertrochanteric fracture fixation with a sliding hip screw.

BACKGROUND: Use of a sliding hip screw (SHS) alone for some unstable intertrochanteric femur fractures can allow excessive medial shaft displacement during impaction. This study evaluated the effect of an attachable lateral support plate on these fractures after loading. METHODS: Unstable, three-part intertrochanteric fractures were created in 10 matched pairs of embalmed femurs that were instrumented with 135-degree SHSs with or without an attachable lateral support plate. Under physiologic loading, inferior and lateral head displacements and lag screw sliding distances were measured. RESULTS: After 10,000 cycles at 750 N, all measurements for femurs with the lateral support plate were significantly less than for the femurs with the SHS alone: mean lateral difference was 1.7 mm (34%) (p < 0.05), mean inferior difference was 3.0 mm (38%) (p < 0.05), and mean lag screw sliding difference was 4.5 mm (58%) (p < 0.05). CONCLUSION: The addition of an attachable lateral support plate to an SHS significantly decreased displacement of the femoral head after cyclic loading.

Efficacy of abduction bracing in the management of total hip arthroplasty dislocation.

A retrospective review of total hip arthroplasty (THA) dislocations was performed to determine the effectiveness of abduction bracing following closed reduction. Patients were grouped as a first-time dislocation (n = 91) or recurrent dislocation (n = 58) and whether or not they received an abduction brace; re-dislocation defined failure of treatment. The mean follow-up was 4.0 years in the first-time group and 3.7 years in the recurrent group. Among patients treated for first-time dislocations, 61% re-dislocated with a brace and 64% of nonbraced patients re-dislocated. In the recurrent group, 55% re-dislocated with a brace, whereas 56% re-dislocated without a brace. Chi-square analysis revealed that observed differences were not significant. There was no significant difference among groups with regards to age, sex, operative side, or significant surgical parameters. Abduction bracing following closed reduction of THA dislocation is ineffective in preventing re-dislocation.