Larger stem to bone diameter ratio predicts lower cemented endoprosthesis failure

BACKGROUND AND OBJECTIVES

With continued advances in treatment options, patients with endoprosthetic reconstruction are living longer and consequently relying upon their devices for a longer duration. Major causes of endoprosthesis failure include aseptic loosening and mechanical failure. In the setting of tumor resection, loss of bone stock and use of radiation therapy increase the risk for these complications. As such, considerations of remaining native bone and stem length and diameter may be increasingly important. We asked the following questions: (1) What was the overall rate of endoprosthesis failure at a minimum of 5-year follow-up? (2) Does resection length increase implant failure rates? (3) Does implant size and its ratio to cortical width of bone alter implant failure rates?

METHODS

We retrospectively analyzed patient outcomes at a single institution between the years of 1999-2022 who underwent cemented endoprosthetic reconstruction at the hip or knee and identified 150 patients. Of these 150, 55 had a follow-up of greater than 5 years and were used for analysis. Radiographs of these patients at time of surgery were assessed and measured for resection length, bone diameter, stem diameter, and remaining bone length. Resection percentage, and stem to bone diameter ratios were then calculated and their relationship to endoprosthesis failure were analyzed.

RESULTS

Patients in this cohort had a mean age of 55.8, and mean follow-up of 59.96 months. There were 78 distal femoral replacements (52%), 16 proximal femoral replacements (10.7%), and 56 proximal tibial replacements (37.3%). There were five patients who experienced aseptic loosening and six patients who experienced mechanical failure. Patients with implant failure had a smaller mean stem to bone diameter (36% vs. 44%; p = 0.002). A stem to bone diameter of 40% appeared to be a breaking point between success and failure in this series, with 90% of patients with implant failure having a stem: bone ratio less than 40%. Stem to bone ratio less than 40% increased risk for failure versus stems that were at least 40% the diameter of bone (6/19 [31.6%] vs. 0/36 [0%]; odds ratio 0.68; p < 0.001). Resection length did not appear to have an impact on the rates of aseptic loosening and mechanical failure in this series.

CONCLUSIONS

Data from this series suggests a benefit to using stems with a larger diameter when implanting cemented endoprostheses at the hip or knee. Stems which were less than 40% the diameter of bone were substantially more likely to undergo implant failure.

Cemented-augmented fixation of metastatic humeral lesions without segmental bone loss results in reliable outcomes

Background

Treatment of metastatic lesions to the humerus is dependent on patient's pain, lesion size and location, and post-operative functional goals. Surgical options include plate or nail fixation [open reduction internal fixation (ORIF)], or endoprosthetic replacement (EPR), with cement augmentation. The objective of this study was to perform a single institution retrospective analysis of outcomes by method of reconstruction, tumor volume, and pathologic diagnosis.

Methods

The records of 229 consecutive patients treated surgically for appendicular metastatic disease from 2005-2018 at our musculoskeletal oncology center were retrospectively reviewed following institutional review board (IRB) approval. Indications for surgical treatment at the humerus included patients who presented with impending and displaced pathologic fractures.

Results

Sixty patients (34 male, 26 female) with a mean age of 62.9±12.2 were identified who were treated surgically at the proximal (n=21), diaphyseal (n=29), or distal (n=10) humerus. Forty-nine (82%) patients presented with displaced pathologic fractures. The remaining eleven patients had a mean Mirels score of 9.5. There was no difference in overall complication rate between EPR or ORIF [4/36 (11%) versus 2/24 (8%); P=0.725]. Mean Musculoskeletal Tumor Society (MSTS) scores were 83% for both EPR and ORIF, with no differences in subgroup analyses at the proximal, diaphyseal, or distal humerus. Patients with cortical destruction on anterior posterior (AP) and lateral imaging were at increased risk for mechanical failure [2/6 (33%) versus 0/18 (0%), P=0.015].

Conclusions

In conclusion, when pathologic pattern permits, cement-augmented fixation allows for stabilization of pathologic bone, while minimizing risk of soft-tissue detachment, while EPR resulted in similar outcomes in patients with more extensive bone destruction. Increased tumor volume was associated with lower MSTS scores.

Complications following allograft reconstruction for primary bone tumors: Considerations for management

Introduction

The aim of this study was to investigate complication rates and types following allograft reconstruction and discuss unique considerations for management.

Methods

Seventy-four consecutive patients underwent large segment allograft reconstruction following resection of primary musculoskeletal tumors from 1991 to 2016. Mean patient age was 32 ± 20 years (range, 5-71 years). Minimum follow-up was 2 years unless patients were lost to disease prior. Mean follow-up was 105 months.

Results

Thirty-five patients had complications requiring subsequent surgery at a mean of 30 months (range, 1-146 months) post-operatively. Individual complication rates were 29%, 50%, and 42% for Allograft Prosthetic Composite, Intercalary, and Osteoarticular allograft reconstruction, respectively. Risk factors for complication included age less than 30 (OR 4.5; p = 0.002), male gender (OR 2.8; p = 0.031), chemotherapy (OR 4.4; p = 0.003), lower extremity disease (OR 3.4; p = 0.025). In patients with complications, limb-retention rate was 91% and mean MSTS scores were 23.6.

Conclusion

Despite considerable complication rates, management with a systematic approach results in successful outcomes with limb-retention greater than 90% and mean MSTS scores of 79%. In carefully selected patients, allografts provide a reliable method of reconstruction with treatable complications occurring at a mean of 30 months.

Supplemental Bone Grafting in Giant Cell Tumor of the Extremity Reduces Nononcologic Complications

BACKGROUND

Giant cell tumors (GCTs) are treated with resection curettage and adjuvants followed by stabilization. Complications include recurrence, fracture, and joint degeneration. Studies have shown treatment with polymethylmethacrylate (PMMA) may increase the risk of joint degeneration and fracture. Other studies have suggested that subchondral bone grafting may reduce these risks.

QUESTIONS/PURPOSES

Following standard intralesional resection-curettage and adjuvant treatment, is the use of bone graft, with or without supplemental PMMA, (1) associated with fewer nononcologic complications; (2) associated with differences in tumor recurrence between patients treated with versus those treated without bone grafting for GCT; and (3) associated with differences in Musculoskeletal Tumor Society (MSTS) scores?

METHODS

Between 1996 and 2014, 49 patients presented with GCT in the epiphysis of a long bone. Six patients were excluded, four who were lost to followup before 12 months and two because they presented with displaced, comminuted, intraarticular pathologic fractures with a nonreconstructable joint surface. The remaining 43 patients were included in our study at a mean followup of 59 months (range, 12-234 months). After resection-curettage, 21 patients were reconstructed using femoral head allograft with or without PMMA (JB) and 22 patients were reconstructed using PMMA alone (FRP, KSB); each surgeon used the same approach (that is, bone graft or no bone graft) throughout the period of study. The primary study comparison was between patients treated with bone graft (with or without PMMA) and those treated without bone graft.

RESULTS

Nononcologic complications occurred less frequently in patients treated with bone graft than those treated without (10% [two of 21] versus 55% [12 of 22]; odds ratio, 0.088; 95% confidence interval [CI], 0.02-0.47; p = 0.002). Patients with bone graft had increased nononcologic complication-free survival (hazard ratio, 4.59; 95% CI, 1.39-15.12; p = 0.012). With the numbers available, there was no difference in tumor recurrence between patients treated with bone graft versus without (29% [six of 21] versus 32% [seven of 22]; odds ratio, 0.70; 95% CI, 0.1936-2.531; p = 0.586) or in recurrence-free survival among patients with bone graft versus without (hazard ratio, 0.94; 95% CI, 0.30-2.98; p = 0.920). With the numbers available, there was no difference in mean MSTS scores between patients treated with bone graft versus without (92% ± 2% versus 93% ± 1.4%; mean difference 1.0%; 95% CI, -3.9% to 6.0%; p = 0.675).

CONCLUSIONS

Compared with PMMA alone, the use of periarticular bone graft constructs reduces postoperative complications apparently without increasing the likelihood of tumor recurrence.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Customizable orthopaedic oncology implants: one institution's experience with meeting current IRB and FDA requirements

Background

Customizable orthopaedic implants are often needed for patients with primary malignant bone tumors due to unique anatomy or complex mechanical problems. Currently, obtaining customizable orthopaedic implants for orthopaedic oncology patients can be an arduous task involving submitting approval requests to the Institutional Review Board (IRB) and the Food and Drug Administration (FDA). There is great potential for the delay of a patient’s surgery and unnecessary paperwork if the submission pathways are misunderstood or a streamlined protocol is not in place.

Purpose

The objective of this study was to review the existing FDA custom implant approval pathways and to determine whether this process was improved with an institutional protocol.

Methods

An institutional protocol for obtaining IRB and FDA approval for customizable orthopaedic implants was established with the IRB at our institution in 2013. This protocol was approved by the IRB, such that new patients only require submission of a modification to the existing protocol with individualized patient information. During the two-year period of 2013–2014, eight patients were retrospectively identified as having required customizable implants for various orthopaedic oncology surgeries. The dates of request for IRB approval, request for FDA approval, and total time to surgery were recorded, along with the specific pathway utilized for FDA approval.

Results

The average patient age was 12 years old (7–21 years old). The average time to IRB approval of a modification to the pre-approved protocol was 14 days (7–21 days). Average time to FDA approval after submission of the IRB approval to the manufacturer was 12.5 days (7–19 days). FDA approval was obtained for all implants as compassionate use requests in accordance with Section 561 of the Federal Food Drug and Cosmetic Act’s expanded access provisions.

Conclusions

Establishment of an institutional protocol with pre-approval by the IRB can expedite the otherwise time-consuming and complicated process of obtaining customizable orthopaedic implants for orthopaedic oncology patients.

Level of evidence

Retrospective case series, Level IV. See the Guidelines for authors for a complete description of levels of evidence.

Linea Aspera as Rotational Landmark for Tumor Endopostheses: A Computed Tomography Study

This computed tomography study examined the reliability of the linea aspera as a rotational landmark in tumor endoprosthetic replacement by determining its cross-sectional location on the femur.

An innovative approach to concave-convex allograft junctions: a biomechanical study

Allograft bone is often used in oncologic and trauma limb salvage procedures. In this study, we hypothesize that a concave-convex allograft junction with plate fixation would improve multiple aspects of the reconstruction process, allowing for a larger contact surface area between the allograft junction and increased uniformity in pressure distribution at the junction. Thirty large femoral artificial polyresin femurs were randomly separated into 2 groups: allograft junctions fixed with flat locking plates and allograft junctions fixed with prebent locking plates. Each group was then randomly subdivided into 3 sets: concave-convex allograft junctions, matched transverse-cut allograft junction, and non-matched transverse-cut allograft junctions. All but 1 reconstructions of concave-convex allograft junctions, compared with non-matched or matched transverse-cut allograft junctions fixed with flat or pre-bent locking plates showed statistically significantly greater mean contact surface area and greater mean percent contact surface area (P<.05). Concave-convex allograft junctions demonstrated increased mean contact surface area, mean percent contact surface area, and a more uniform pressure distribution. We believe our approach to allograft junctions using concave-convex reamers may improve multiple aspects of the reconstruction process, allowing for increased contact surface area between the allograft junction, increased uniformity in pressure distributions at the allograft junction, and decreased length of time taken for intraoperative preparation.

Comparison of phenol and argon beam coagulation as adjuvant therapies in the treatment of stage 2 and 3 benign-aggressive bone tumors

Argon beam photocoagulation has gained popularity as an adjuvant therapy for the treatment of giant cell tumors of bone and other stage 2 or 3 benign-aggressive bone tumors. Although argon beam photocoagulation has been considered a safe and reasonable adjuvant treatment with acceptable recurrence rates, it has never been directly compared with the commonly described phenol as adjuvant. The purpose of this study was to determine whether argon beam photocoagulation is as effective as phenol in preventing recurrence without affecting functional outcome as an adjuvant to surgical curettage. We retrospectively reviewed 93 consecutive patients with a minimum 10-month follow-up between 1992 and 2007 who were treated with curettage and either phenol or argon beam photocoagulation. Functional outcomes and complications were recorded. Overall, 16 (17.2%) of 93 patients who were initially treated with 1 of the adjuvants had pathologically confirmed recurrences. No additional recurrences were noted after retreatment, leading to an overall recurrence rate of 17.1% with phenol and 14.8% with argon beam photocoagulation (P=.726). While avoiding the toxic effects of phenol, argon beam photocoagulation provides for statistically equivalent recurrence rates, functional outcomes, and complication rates in the treatment of benign-aggressive bone tumors.

Infected total femoral replacements: evaluation of limb loss risk factors

A complication of total femoral replacement (TFR) is periprosthetic infection. Studies have shown that infected endoprostheses have a significant amputation rate, as high as 36.7%. This study examined possible risk factors that may attribute to unsalvageable TFRs following periprosthetic infections, including age, sex, primary vs secondary TFRs, number of irrigation and debridements, recent history of periprosthetic infection, early vs late infection, use of antibiotic cement, and the number of postoperative antibiotics. In a retrospective chart review, 10 patients who had periprosthetic infections of their TFRs were identified from our orthopedic surgical database between 2000 and 2010. Seven of 10 TFRs were unsalvageable due to infection. The 2 greatest risk factors that influenced unsalvageable TFR were age older than 50 years and recipients of secondary TFRs. All 6 patients older than 50 years had unsalvageable TFRs, whereas 1 of 4 patients younger than 50 years had an unsalvageable TFR (P<.05). Similarly, all 6 patients who received secondary TFRs had unsalvageable TFRs, whereas 1 of 4 patients who received a TFR as the primary method of treatment had an unsalvageable TFR (P<.05). No other risk factors showed statistical significance or could be identified as possible risk factors. Surgeons should educate patients who fall into high-risk categories about the benefits of early intervention, such as amputation, that could prevent additional surgeries and decrease the lengths of hospitalizations.

An evaluation of brachytherapy and external beam radiation used with wide-margin surgical resection in the treatment of extra-abdominal desmoid tumors

Surgical resection has had control rates of 53% to 77% in the treatment of extra-abdominal desmoid tumors. Surgical excision combined with external beam radiation therapy (EBRT) has had local control rates of up to 83% in some series. The purpose of this study was to evaluate the effectiveness of resection combined with radiotherapy (brachytherapy, EBRT, or both) in the treatment of extra-abdominal desmoid tumors. We retrospectively reviewed the charts of 24 consecutive patients (27 histologically confirmed extra-abdominal desmoid tumors). Patients were included in the study if they had a lesion that was potentially resectable with a wide margin, allowing for limb salvage, and if they did not have a contraindication to radiotherapy. Limb functioning was assessed with the Musculoskeletal Tumor Society (MSTS) scoring system. Seventeen patients (7 men, 10 women) with 19 tumors met the inclusion criteria. Mean age at diagnosis was 23.4 years. Follow-up (mean, 4.28 years) involved serial clinical examinations and magnetic resonance imaging of tumor sites. After surgery, the tumors were treated with brachytherapy (n = 6), EBRT (n = 10), or both (n = 3). Two of the 17 tumors in patients with negative margins of resection recurred locally (local control rate, 88.2%). Mean MSTS score was 29/30 (96.7%). The role of surgery, radiotherapy, chemotherapy, hormone therapy, and other treatments for extra-abdominal desmoid tumors is not well defined. When wide-margin resection and radiotherapy can be performed with limb preservation surgery, local control and complication rates compare favorably with those of other reported methods of treatment. Given the results and limitations of our study, we cannot make a definitive recommendation as to which modality--brachytherapy or EBRT--should be used in the treatment of extra-abdominal desmoid tumors.

Distal femur defects reconstructed with polymethylmethacrylate and internal fixation devices: a biomechanical study

Benign aggressive distal femur tumors are treated with curettage, adjuvant phenol or argon, and polymethylmethacrylate (PMMA) packing. For large defects, an internal fixation device is added to reduce the fracture risk. The purpose of this study is to compare the strength of locking plates to other fixation devices for stabilization of these defects. Lateral condyle defects in young, fresh frozen femurs were packed with PMMA and augmented by internal fixation. Three groups of 4 matched pairs of femurs were organized for the following comparisons: (1) stacked Steinmann pins vs crossed screws; (2) stacked pins vs locking plates; and (3) crossed screws vs locking plates. Specimens were subjected to axial load-to-failure testing on an MTS machine. There was no difference in load-to-failure strength (P=.177) using Steinmann pins or crossed screws. Locking plate constructs were stronger (P=.028) than Steinmann pin constructs. Locking plate constructs were also stronger (P<.001) than crossed-screw constructs. Steinmann pin constructs failed with severe intra-articular fractures; crossed screw constructs failed with bulging of the defects, articular impaction, and minimal fracture propagation. Locking plate constructs failed with extra-articular spiral shaft fractures.

Case report: elevated serum beta human chorionic gonadotropin in a woman with osteosarcoma

Human chorionic gonadotropin is a glycoprotein hormone normally synthesized by placental syncytiotrophoblast cells. It also is secreted by gestational trophoblastic tumors, gonadal tumors, and even various nongonadal tumors, including bone and soft tissue sarcomas, as a paraneoplastic syndrome. The literature contains one case report of beta human chorionic gonadotropin production from a primary bone sarcoma occurring in a male patient. We report a woman of childbearing age who presented with a distal femur lytic lesion, clinical symptoms suggestive of pregnancy, and elevated serum beta human chorionic gonadotropin. Although the clinical diagnosis of a sarcoma was never in doubt, we present this case to emphasize a need to exclude pregnancy in women of childbearing age to avoid delay in biopsy and subsequent management. Positive immunohistochemical staining of the biopsy specimen established the tumor cells as the source of beta human chorionic gonadotropin.

Granular cell tumor of the extremity: magnetic resonance imaging characteristics with pathologic correlation

OBJECTIVE

The purpose of this study is to delineate the magnetic resonance (MR) appearance of a granular cell tumor (GrCT) of the extremity and to correlate the imaging appearance with the microscopic findings.

DESIGN AND PATIENTS

A retrospective review of five patients with a histopathologic diagnosis of GrCT and pre-operative MR imaging of the neoplasm was done. The images were reviewed by two musculoskeletal radiologists in a consensus fashion. Lesion location, size, shape, margination, and signal intensity characteristics were assessed. MR findings were correlated with histopathological examination.

RESULTS

The benign subtype of GrCT is usually isointense or brighter than muscle on T1-weighted sequences, round or oval in shape, superficial in location, and 4 cm or less in size. On T2-weighted sequences, benign lesions may demonstrate a high peripheral signal, as well as a central signal intensity that is isointense to muscle or suppressed fat. A significant stromal component in the tumor and, hypothetically, a ribbon-like arrangement of tumor cells may influence the signal intensity demonstrated on the T1 and T2-weighted sequences. The malignant subtype may demonstrate signal intensity characteristics and invasion of adjacent structures often seen with other aggressive neoplasms; sizes larger than 4 cm and association with major nerve trunks can be seen.

CONCLUSION

Benign GrCT has imaging characteristics which may distinguish this tumor from other soft tissue neoplasms, as well as the malignant type of this tumor.

Treatment of advanced metastatic lesions of the acetabulum using the saddle prosthesis

Current methods of treating advanced patients with metastatic periacetabular disease are complex and result in high complication rates. The purpose of this study was to show whether the implantation of the saddle prosthesis would serve as an additional tool to help treat metastatic disease in these patients. From 1991 to 2003, 20 patients with advanced metastatic periacetabular lesions (Harrington Class III) were treated using the saddle prosthesis. Goals of surgery were a decrease in pain, functional restoration, and ambulation. The mean age was 61 years. Average length of followup was 20 months. Postoperatively, ambulation was achieved in 16 of 20 patients. There were four postoperative complications (20%) in three patients. Surgical goals were met in 18 of 20 patients. The MSTS-ISOLS emotional score was 2.9 of 5. The average total MSTS-ISOLS score was 16.6 of 30 (55%). Using the Allan scoring system consisting of analgesia, independence and ambulation, and mobility, all scores had significant improvements postoperatively. Careful surgical indications and technique should result in a stable, functional reconstruction allowing patients the ability to ambulate outside the house with a cane. Patients can expect to be emotionally satisfied with the procedure while using nonnarcotic analgesia and can expect an improved quality of life despite bone metastasis.

Biomechanical study of pins in cementing of contained proximal tibia defect

Defects from curettage for giant cell tumors of bone frequently have been reconstructed with bone cement with or without reinforcement pins. The biomechanical basis for the addition of reinforcement pins was examined using a model of a contained defect in the proximal tibia. Fifty-four cadaveric proximal tibia in matched pairs were divided into five test groups: intact tibia, medial metaphyseal contained defect, defect reconstructed with cement alone, defect reconstructed with cement and pins inserted within the medullary canal, and defect reconstructed with cement and pins inserted through the cortex. Specimens were tested to failure during one cycle of compressive loading. Defect specimens were significantly weaker and less stiff than intact specimens, establishing the validity of the model-contained defects. For the reconstructions, there was no statistically significant difference in load to failure, stiffness, energy to failure, or displacement for the polymethylmethacrylate treatment alone when compared with matched specimen receiving polymethylmethacrylate and pins treatment. Similarly, there was no statistical difference in biomechanical properties in comparing matched specimens treated with polymethylmethacrylate alone or polymethylmethacrylate/pins (cortex). For contained defects of the proximal tibia that are typical after curettage for giant cell tumor, there appears to be no biomechanical advantage to use of reinforcement pins in the cement.

Complications after limb salvage surgery

Orthopedic oncology patients gain a chance at an active, disease-free life through the use of limb salvage surgery. This goal is reached with meticulous technique, detailed operative planning, and the use of endoprosthetic replacements and/or bone grafting. This article will address the late complications of limb salvage surgery, including aseptic loosening, prosthetic fracture and dislocation, as well as graft fracture and nonunion.

Operative management of metastases to the pelvis and acetabulum

Bone metastases to the acetabulum and pelvis can be a devastating and debilitating problem. In certain patients, operative reconstruction of the involved hip can lead to maintenance of independence, pain control, and an increase in the overall quality of life for their remaining life span. These procedures are technically challenging and are associated with a higher complication rate than that for patients having surgery for nonneoplastic disease. They are probably best performed by surgeons with specific training and expertise in tumor surgery and acetabular reconstruction. With proper patient selection, appropriate component use, and competent surgical technique, good-to-excellent results can be obtained.

The opto-kinetic cervical reflex during formation flight

BACKGROUND

Weather formation flight is a difficult task prone to episodes of spatial disorientation. Therefore, investigation of sensory reflexes under these conditions is critical. Recent studies have shown that the opto-kinetic cervical reflex (OKCR) occurs during VMC flight conditions and serves to establish the horizon retinal image as a stabilized primary visual-spatial cue. The purpose of this research was to investigate the OKCR and field of view (FOV) during formation flight under VMC and IMC.

HYPOTHESES

During VMC tasks pilots will align their heads with the visible horizon, but not under IMC. As FOV is decreased, there will be a significant reduction in OKCR-induced head movement.

METHODS

There were 2 experiments conducted in which a total of 26 pilots completed simulated flight tasks in a stationary dome. Head tilt was examined as a function of aircraft bank with unrestricted FOV in Experiment I. Experiment II examined head tilt under three FOV conditions (40 degrees , 60 degrees and 100 approximately circular).

RESULTS

During VMC maneuvers pilots exhibited significant OKCR. There were no differences in head tilt between Solo Figure 8 and Formation Figure 8 VMC conditions. Pilots did not tilt their heads under IMC Formation Flight. FOV did not significantly affect the OKCR.

CONCLUSIONS

Pilots exhibit the OKCR during Formation and Solo VMC tasks. However, the OKCR is reduced when compared with low level navigation tasks, indicating a difference in the visual cues between tasks. Pilots do not exhibit OKCR during IMC flight; therefore, the OKCR will have an impact on formation flights in and out of clouds leading to sensory conflicts caused by repeated realignment of visual and vestibular systems.

Comparison of sitting height measurement using three anthropometric measuring techniques

Accurate, reproducible, anthropometric measurements are essential in the aviation community. Three methodologies were evaluated to determine how they compared with respect to variability and accuracy. One of the methods, an anthropometric chair, is currently used to screen naval aviation candidates. Another method, employing anthropometers (calipers), has been widely used for anthropometric surveys. A third method, referred to as the digital anthropometric video imaging device (DAVID), is a computer-based technique that digitizes a video image for the purpose of determining anthropometric measurements. For this comparison study, sitting height was measured by 15 subjects using the 3 cited methods. An evaluation of sitting height was used because of its importance to aviation and because it requires attention to both posture and measurement technique. Statistical analysis showed no statistical difference between the three methodologies.

Effects of FOV and aircraft bank on pilot head movement and reversal errors during simulated flight

BACKGROUND

Recent studies have shown that while flying under visual meteorological conditions (VMC) pilots tilt their head to keep the horizon stabilized on their fovea. This reflex, referred to as Opto-Kinetic Cervical Reflex (OKCR), may improve spatial awareness by establishing the horizon retinal image as a stabilized primary visual-spatial cue. Since the limited field of view (FOV) provided by helmet-mounted displays (HMDs) significantly decreases visual stimuli, the purpose of this research was to determine how reduced FOV affects head movements.

HYPOTHESES

As FOV is decreased, there will be a significant reduction in OKCR-induced head movement. Reduced FOV will also increase control reversal errors.

METHODS

Twelve pilots completed simulated flight tasks in a stationary dome. Head tilt, pitch, and yaw were examined as a function of aircraft bank and FOV (40 degrees, 60 degrees and 100 degrees circular). The number of control reversal errors was analyzed to investigate signs of spatial disorientation.

RESULTS

During VMC manuevers pilots exhibited significant OKCR; however there were no significant differences among the three levels of FOV. FOV significantly affected head pitch movements under both VMC and instrument meteorological conditions (IMC). Pilots yawed their heads in the direction of aircraft bank under VMC. Pilots committed 22 reversal errors out of 72 trials (30.55%). The magnitude of the error was largest for the 40 degrees FOV condition.

CONCLUSIONS

Pilots exhibit the OKCR under all tested levels of FOV and also make head yaw movements in order to keep the way point in sight during banking maneuvers. Pilots demonstrated stick reversal errors when transitioning from following a lead aircraft under both VMC and IMC conditions.

Aviation spatial orientation in relationship to head position and attitude interpretation

BACKGROUND

Conventional wisdom describing aviation spatial awareness assumes that pilots view a moving horizon through the windscreen. This assumption presupposes head alignment with the cockpit "Z" axis during both visual (VMC) and instrument (IMC) maneuvers. Even though this visual paradigm is widely accepted, its accuracy has not been verified. The purpose of this research was to determine if a visually induced neck reflex causes pilots to align their heads toward the horizon, rather than the cockpit vertical axis.

HYPOTHESIS

Based on literature describing reflexive head orientation in terrestrial environments it was hypothesized that during simulated VMC aircraft maneuvers, pilots would align their heads toward the horizon.

METHODS

Some 14 military pilots completed two simulated flights in a stationary dome simulator. The flight profile consisted of five separate tasks, four of which evaluated head tilt during exposure to unique visual conditions and one examined occurrences of disorientation during unusual attitude recovery.

RESULTS

During simulated visual flight maneuvers, pilots tilted their heads toward the horizon (p < 0.0001). Under IMC, pilots maintained head alignment with the vertical axis of the aircraft.

CONCLUSION

During VMC maneuvers pilots reflexively tilt their heads toward the horizon, away from the Gz axis of the cockpit. Presumably, this behavior stabilizes the retinal image of the horizon (1 degree visual-spatial cue), against which peripheral images of the cockpit (2 degrees visual-spatial cue) appear to move. Spatial disorientation, airsickness, and control reversal error may be related to shifts in visual-vestibular sensory alignment during visual transitions between VMC (head tilt) and IMC (Gz head stabilized) conditions.

Advantages of a simple contact switch for human locomotion

A simple, inexpensive foot switch was fabricated to record the duration of surface contact for part or all of the foot during human locomotion. The device incorporated electrically conductive metallic foil in a thin foam insole. Advantages over a more conventional thick-soled sandal were documented for the same subjects by examining kinematic values (read from movie film) and electrical signal data (produced by the switch). A person's characteristic manner of placing and lifting the foot while wearing conventional shoes could in some instances distort readings of stance duration by many tens of msec, but the new switch assembly eliminated ambiguities of measurement and interpretation.