Regina P. Woon

The Results of Metal-On-Metal Hip Resurfacing in Patients Under 30 Years of Age

Degenerative hip conditions most commonly affect older patients. However, many cases occur in younger patients. Total hip arthroplasty is the conventional approach; however, hip resurfacing is a viable option. Fifty-three metal-on-metal resurfacings in 46 patients under age 30 were performed. Patients had a variety of etiologies, and were followed clinically and radiographically with mean follow-up of 98.2 months. Clinical scores and x-rays were compared pre-operatively and post-operatively. The last follow-up SF-12 and UCLA scores significantly improved post-operatively (P<0.0001). Range of motion scores also improved (P<0.001), and the mean Harris Hip Score was 88. There were 6 revisions. The Kaplan-Meier survivorship estimate at 8 years was 95%. Metal-on-metal hip resurfacing appears to be an effective procedure for younger patients. Longer-term data are needed for confirmation.

Results of Conserve Plus® Metal-On-Metal Hip Resurfacing for Post-Traumatic Arthritis and Osteonecrosis:

The safety and efficacy of metal-on-metal surface arthroplasty in post-traumatic arthritis and post-traumatic osteonecrosis (PT OA and PT ON) cases has not previously been thoroughly investigated. This study compared the outcomes of metal-on-metal hip resurfacing (HR) in patients performed for an indication of OA secondary to trauma to compared to PT ON. Metal-on-metal resurfacing arthroplasties were performed on 62 hips, 43 with PT OA and 19 with PT ON with secondary osteoarthritis. There were 51 males and 11 females. All patients were followed up clinically and radiographically with a mean follow-up of 87.2 months. Clinical outcome scores, survivorship, and radiographs were compared between the PT OA and PT ON group. The clinical outcomes for the PT ON and PT OA groups were similar with a survival rate of 95% (95% CI 82.1% to 98.8%) for the PT OA group alone at 8 years and 91% for those with PT OA with ON at 8 years (95% CI 50.8%-98.7%). The Kaplan-Meier survivorship curves for the cohorts of PT OA and PT ON patients were not statistically significantly different (Log rank, p=0.6036). Metal-on-metal hip resurfacing appears to be a safe and effective procedure for the treatment of both post-traumatic osteoarthritis and osteonecrosis.

Is there a relationship between thoracic dimensions and pulmonary function in early-onset scoliosis?

Study Design. Cross-sectional retrospective analysis. Objective. To examine the degree of correlation between thoracic dimension outcome measures and pulmonary function in early-onset scoliosis (EOS). Summary of Background Data. Change in thoracic dimension (TD) measurements and spine length are commonly reported outcome measures after treatment for EOS. Although ultimately improving or maintaining pulmonary function is the goal of EOS treatment strategies, it is unclear whether commonly reported 2-dimensional TD measurements represent good predictors of pulmonary function. Methods. A cross-sectional analysis of patients including all diagnoses obtained from 2 EOS databases containing TD measurements and pulmonary function data was performed. Relationships between individual TD measurements and pulmonary function measurements were assessed using the Pearson correlation analysis. TD measurements (pelvic inlet width, T1–T12 height, T1–S1 height, and coronal chest width) and standard pulmonary function measurements were compared. TD percentiles normalized for pelvic inlet width were also calculated and correlated with pulmonary function measurement percentiles. Univariate and multivariate linear regression analyses determined whether TD measurements could predict pulmonary function. Results. There were 121 patients (65 females, 56 males) in the study. Mean age at evaluation was 9.3 years (range, 2.7–18.1 yr). T1–T12 height, T1–S1 height, maximal chest width, and pelvic inlet width were all significantly correlated with forced air volume expelled in 1 second, total forced air volume, and total lung capacity (correlation coefficients [r] 0.33–0.61; all P < 0.001). T1–T12 predicted percentile (normalized for pelvic width) was significantly correlated with forced air volume expelled in 1 second and total forced air volume predicted percentiles (r = 0.32, P < 0.001 and r = 0.27, P = 0.004, respectively). Regression analysis determined that T1–T12 percentile was a significant predictor of forced air volume expelled in 1 second percentile and total forced air volume percentiles. Regression analysis found no predictive factors of total lung capacity percentile. Conclusion. Traditional 2-dimensional TD measurements (T1–T12 height) used to measure outcomes in EOS can be used as weak predictors of pulmonary function outcome. However, better outcome measures need to be developed, such as 3-dimensional and dynamic measurements. Level of Evidence: 3

Survivorship of Conserve® Plus Monoblock Metal-on-Metal Hip Resurfacing Sockets: Radiographic Midterm Results of 580 Patients

Resurfacing systems use press-fit, monoblock, cobalt chrome alloy acetabular sockets because of the materials ability to withstand stresses while accommodating a large femoral head. Despite the widespread use of these types of sockets for both hip resurfacing and total hip replacement, there is a paucity of literature assessing the outcomes of these cups in particular. The 10 year survivorship of the Conserve® Plus monoblock acetabular component used in this study was 98.3% with small pelvic osteolytic lesions suspected in only 2.3%. This study highlights the excellent radiographic survivorship profile of the Conserve® Plus socket.

High performance of metal-on-metal bearings: a case report.

There has been considerable initial success with the use of total hip and resurfacing metal-metal implants tempered by poor performance of certain bearing designs, specifically small and/or abnormal component orientation. With a growing number of reports relating to adverse local tissue reactions, the need to monitor ion levels is crucial. This report presents a case of an extremely active bilateral metal-metal implant patient who had severe arthritis of the left hip and was originally treated with a cementless metal-on-polyethylene surface replacement. This implant lasted 12~years and after complete wear through of the polyethylene, the prosthesis was converted to metal-on-metal total hip. The patient continued to cycle vigorously and engaged in downhill skiing. Eventually his contralateral hip developed arthritis and he underwent metal-on-metal surface arthroplasty. Since his last surgery 8~years ago, the patient has resumed his activities, cycling an average of 6,400 miles and skiing over 60~days a year. He has been followed clinically and radiographically for 23 years with ion levels measured serially.

Does the Type of Metal Instrumentation Affect the Risk of Surgical Site Infection in Pediatric Scoliosis Surgery

STUDY DESIGN Retrospective cohort study. OBJECTIVES To determine the association of implant metal composition with the risk of surgical site infection (SSI) following pediatric spine surgery. SUMMARY OF BACKGROUND DATA SSI is a well-described complication following pediatric spine surgery. Many risk factors have been identified in the literature, but controversy remains regarding metal composition as a risk factor. METHODS This was a retrospective study of patients who underwent posterior spinal instrumentation procedures between January 1, 2006, and December 31, 2008, at three large childrens hospitals for any etiology of scoliosis and had at least 1 year of postoperative follow-up. Procedures included posterior spinal fusion, growth-friendly instrumentation, and revision of spinal instrumentation. The Centers for Disease Control and Prevention definition of SSI was used. A chi-squared test was performed to determine the relationship between type of metal instrumentation and development of an SSI. RESULTS The study included 874 patients who underwent 1,156 total procedures. Overall, 752 (65%) procedures used stainless steel instrumentation, 238 (21%) procedures used titanium instrumentation, and the remaining 166 (14%) procedures used cobalt chrome and titanium hybrid instrumentation. The overall risk of infection was 6.1% (70/1,156) per procedure, with 5.9% (44/752) for stainless steel, 6.7% (12/238) for titanium, and 6.0% (10/166) for cobalt chrome. The multiple regression analysis found no significant differences in the metal type used between patients with and without infection (p = .886) adjusting for etiology, instrumentation to pelvis, and type of procedures. When stratified based on etiology, the multiple regression analyses also found no significant difference in SSI between two metal type groups. CONCLUSIONS This study found no difference in risk of infection with stainless steel, titanium, or cobalt chrome/titanium instrumentation and is adequately powered to detect a true difference in risk of SSI. LEVEL OF EVIDENCE Level II, prognostic.

Childhood development after maternal metal-on-metal hip resurfacing

Metal-on-metal (MoM) hip resurfacing has been used in many young, active patients, including women of childbearing age. While ion levels have been measured in mothers with MoM hip resurfacing and their babies, little is known about how these ions affect child development. Out of 1300, MoM hip resurfacing surgeries, we had 48 women of childbearing age (defined as 40 years of age or younger at the time of surgery). These women were contacted to see if they had had pregnancies after their surgery, and those who had were sent surveys asking about their pregnancies and the development of their children. Eleven women reported pregnancies, and eight returned the surveys. There were no significant differences between women with pregnancies and those without pregnancies in any demographic or clinical measures. From the eight women who completed surveys, there were seventeen pregnancies resulting in fourteen births. There were complications in three of the births resulting in two premature births, but no children were born with birth defects. Overall, the children appear to be developing normally. Based on this unique data, we do not feel that MoM hip resurfacing is contraindicated for women of childbearing age, but power analyses show that we cannot draw conclusive results from our sample. We recommend that other groups publish their own data to allow us to generate sufficient sample sizes to draw meaningful conclusions.

Surgeon Survey Shows No Adverse Events With MRI in Patients With Magnetically Controlled Growing Rods (MCGRs)

STUDY DESIGN Surgeon survey. OBJECTIVES To determine if magnetic resonance imaging (MRI) following implantation of magnetically controlled growing rods (MCGRs) is associated with any adverse events. SUMMARY OF BACKGROUND DATA Magnetically controlled growing rods have been shown to reduce the need for repeated surgical procedures and improve costs when compared to traditional growing rods, but concerns about MRI compatibility exist. MRIs are often clinically indicated in the EOS population. METHODS Pediatric spine surgeons who are members of the Growing Spine Study Group, Childrens Spine Study Group, and early international users of this technology were surveyed regarding MRI use after performing MCGR surgery. RESULTS A total of 118 surgeons were surveyed. Four surgeons reported that 10 patients had an MRI with an implanted MCGR. Loss of fixation (0%, 0/10), movement of implants (0%, 0/10), unintended lengthening/shortening (0%, 0/10), or noticeable heating of MCGR (0%, 0/10) were not observed. No problems were observed with function of the MCGR following MRI, and a mean of 2.1 mm was obtained at the next lengthening (range, 0.5-3.0 mm). Two patients had brain MRIs, both of which could be interpreted. All cervical spine MRIs could be interpreted without excessive artifact (100%, 7/7). Six patients had MRIs of the thoracic or lumbar spine, but these were considered uninterpretable as a result of artifact from the MCGR device (0%, 0/6). CONCLUSION These are the first reported cases of MRI use in humans with MCGR. There were no adverse events observed. MCGR rods lengthened as expected following MRI. MRIs of the brain and cervical spine were able to be interpreted, but MRIs of the thoracolumbar spine could not be interpreted because of MCGR artifact. MRIs can be safely performed in patients with MCGRs; however, MRIs of thoracic and thoracolumbar spine may be of limited clinical benefit because of artifact. LEVEL OF EVIDENCE Level IV, case series.STUDY DESIGN Surgeon survey. OBJECTIVES To determine if magnetic resonance imaging (MRI) following implantation of magnetically controlled growing rods (MCGRs) is associated with any adverse events. Magnetically controlled growing rods have been shown to reduce the need for repeated surgical procedures and improve costs when compared to traditional growing rods, but concerns about MRI compatibility exist. MRIs are often clinically indicated in the EOS population. METHODS Pediatric spine surgeons who are members of the Growing Spine Study Group, Childrens Spine Study Group, and early international users of this technology were surveyed regarding MRI use after performing MCGR surgery. RESULTS A total of 118 surgeons were surveyed. Four surgeons reported that 10 patients had an MRI with an implanted MCGR. Loss of fixation (0%, 0/10), movement of implants (0%, 0/10), unintended lengthening/shortening (0%, 0/10), or noticeable heating of MCGR (0%, 0/10) were not observed. No problems were observed with function of the MCGR following MRI, and a mean of 2.1 mm was obtained at the next lengthening (range, 0.5-3.0 mm). Two patients had brain MRIs, both of which could be interpreted. All cervical spine MRIs could be interpreted without excessive artifact (100%, 7/7). Six patients had MRIs of the thoracic or lumbar spine, but these were considered uninterpretable as a result of artifact from the MCGR device (0%, 0/6). CONCLUSION These are the first reported cases of MRI use in humans with MCGR. There were no adverse events observed. MCGR rods lengthened as expected following MRI. MRIs of the brain and cervical spine were able to be interpreted, but MRIs of the thoracolumbar spine could not be interpreted because of MCGR artifact. MRIs can be safely performed in patients with MCGRs; however, MRIs of thoracic and thoracolumbar spine may be of limited clinical benefit because of artifact. LEVEL OF EVIDENCE Level IV, case series.

How precise are clinical height measurements in scoliosis patients

Background: The purpose of this study was to determine the accuracy of height measurements in patients with scoliosis at five pediatric institutions and the influence on treatment decisions. Clinical height measurements are used to monitor growth in children and adolescents and may impact treatment recommendations. To our knowledge, measurement variability of patient height in scoliosis clinics has not been evaluated. Methods: At the five participating centers, patient height was measured by clinical staff members using their institution’s standard clinic protocol and then by an attending Scoliosis Research Society member surgeon using one identical protocol among the five centers. To negate the possibility of the Hawthorne Effect, the clinical staff members who completed the initial height measurements were unaware of the subsequent SRS spine surgeon measurements or the protocol used for measurement. Results: The mean height difference in measurement between surgeons and clinical staff for all five centers was 0.7 cm (Center 1: 0.5 cm, Center 2: 0.5 cm, Center 3: 0.9 cm, Center 4: 0.6 cm, Center 5: 1.2 cm). Twenty-three percent (21/92) of patients had measurements that were more than 1 cm different between the clinical staff and surgeon measurement. Conclusions: Our study found a mean 7 mm clinical height measurement variation between surreptitious measurements by SRS surgeons and standard clinical protocol. This variability can lead to inappropriate treatment decisions if growth is used as an indication for brace treatment. With such variability in clinical height measurement, one may want to consider using criteria for bracing independent of height measurement.

The Effect of Arm and Body Position on Respiratory Ventilation in High School Athletes: A Pilot Study

Context: A commonly encountered clinical scenario in athletic training is determining what body position is best for pulmonary recovery after strenuous training. Coaches often advise athletes to put their hands behind their heads following rigorous training, but this practice has no scientific support. Objective: The purpose of this study is to determine how arm and body position affects ventilation in high school athletes. Our hypothesis is that a position in which the athlete is bent forward with the hands on the knees maximizes ventilation. Design: Case series. Methods: Seventeen healthy members of a high school track team, 8 females and 9 males with a mean age of 16.3 years (range: 14.6–18.5 years), performed a maximal voluntary ventilation (MVV) test using a portable spirometer in three different positions: standing with (1) hands behind the head, (2) arms at the sides, and (3) leaning forward with hands resting on the knees. Results: The MVV performed with hands on knees (120.2 ± 5.9 L/min) was sign...