Joshua T. Carothers

Mobile-Bearing Total Knee Arthroplasty

An extensive database search was completed to perform a meta-analysis of outcomes of mobile-bearing total knee arthroplasty. Nineteen manuscripts encompassing 3506 total knee arthroplasty met criteria for analysis (average follow-up, 8.6 years). Data were subdivided based on design type and included rotating platform, meniscal bearing, and anterior-posterior glide-rotation subgroups. Fifteen-year survivorship of rotating platform designs (96.4%) was greater than meniscal bearing implants (86.5%). Mean component loosening (0.33%) and bearing instability (<1%) for all subgroups were uncommon. Implants placed prior to 1995 exhibited higher rates of bearing complications (1.6% vs 0.1%). Excellent results were obtained with mobile-bearing TKA over 2 decades. Loosening and bearing instability were uncommon. Bearing complications lessened after 1995, possibly secondary to improved surgical technique.

Comprehensive morphologic evaluation of the hip in patients with symptomatic labral tear.

A torn acetabular labrum is a well-documented source of hip pain, but the mechanism of injury is debated because the relationship between the bone morphology and labral tears is poorly understood. We compared hips with and without labral abnormalities to determine the relative incidence of morphologic abnormalities. The study group consisted of patients with a labral tear confirmed by arthroscopy or arthrotomy at the time of open débridement or periacetabular osteotomy. We compared the affected hip with the contra-lateral, unaffected hip to ascertain signs of hip dysplasia and impingement. We observed differences in the center edge angle, acetabular depth to width index, acetabular index of elevation, femoral head extrusion, lateral and superior subluxation, Sharps angle, peak to edge distance, and acetabular retroversion. Similar differences occurred in the subgroup analyses. Symptomatic labral tears correlated with abnormal hip morphology as reflected by radiographic measurements of dysplasia and impingement. This relationship occurred in patients with hip dysplasia and patients without obvious femoral head uncovering. Our findings suggest abnormal hip morphology may be a risk factor for labral tears.Level of Evidence: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Single-Leg-Stance (Flamingo) Radiographs to Assess Pelvic Instability: How Much Motion Is Normal?

BACKGROUND Chronic pelvic instability is a relatively uncommon cause of pelvic and low-back pain. Patients present with feelings of instability and mechanical symptoms. Static radiographs are often inadequate to detect abnormal relative motion between the hemipelves consistent with chronic pelvic instability; dynamic views of the pelvis are required. We assessed the amount of physiologic motion present at the pubic symphysis in normal adult men and nulliparous and multiparous women with alternating-single-leg-stance radiographs. METHODS Forty-five asymptomatic adult volunteers (fifteen in each group) were evaluated with a standing anteroposterior pelvic radiograph as well as with anteroposterior pelvic radiographs made with the subjects assuming both right and left single-leg stance. The subjects completed a questionnaire to determine their eligibility for participation in the study, and an examination was performed to exclude certain physical anomalies that might alter the radiographic findings. RESULTS The mean total translation (and standard deviation) at the pubic symphysis, as measured by three blinded observers, was 1.4 +/- 1.0, 1.6 +/- 0.8, and 3.1 +/- 1.5 mm for the men, nulliparous women, and multiparous women, respectively. With the numbers available, we found no significant difference between the translation in the men and that in the nulliparous women (p = 0.63). The multiparous women had significantly more translation than did either the nulliparous women (p = 0.002) or the men (p = 0.0005). There was a significant positive association between the number of pregnancies and the total translation (p < 0.0001). CONCLUSIONS The use of anteroposterior pelvic radiographs made with the subject alternating between right and left single-leg stance demonstrated, with high interobserver reliability, that multiparous women had a significantly different physiologic range of pubic translation as compared with men and nulliparous women. The ranges of physiologic motion at the pubic symphysis measured on the single-leg-stance radiographs in this study can be used to identify pathologic amounts of motion at this site. CLINICAL RELEVANCE This investigation suggests that up to 5 mm of physiologic motion can occur at the pubic symphysis in asymptomatic individuals, as demonstrated by alternating-single-leg-stance radiographs.

Primary Total Knee Arthroplasty in Super-obese Patients: Dramatically Higher Postoperative Complication Rates Even Compared to Revision Surgery

This study utilized a national database to evaluate 90 day postoperative complication rates after total knee arthroplasty (TKA) in super obese (BMI > 50 kg/m(2)) patients (n = 7666) compared to non-obese patients (n = 1,212,793), obese patients (n = 291,914), morbidly obese patients (n = 169,308) and revision TKA patients (n = 28,812). Super obese patients had significantly higher rates of local and systemic complications compared to all other BMI groups as well as those undergoing revision TKA with higher rates of venous thromboembolism (VTE), infection, and medical complications. Super obesity is associated with dramatically increased rates of postoperative complications after TKA compared to non-obese, obese, and morbidly obese patients as well as those undergoing revision TKA.

Total Hip Arthroplasty After Failed Internal Fixation of Proximal Femoral Fractures

Between February 1987 and October 2008, we performed 102 total hip arthroplasties (THAs) after failed internal fixation of a prior hip fracture. There were 39 intertrochanteric fractures and 63 femoral neck fractures. Etiology of failure included 35 cases of osteonecrosis, 32 cases of arthritis, 25 cases of early failure of fixation, and 10 cases of nonunion. There were 12 patients who had early surgical complications related to the procedure (11.8%, 12/102). These included 5 patients who had dislocations (4.9%), 4 periprosthetic fractures (3.9%), 2 hematomas (2.0%), and 1 infection (1%). Of these 102 THAs, 50 were available for at least 2 years of follow-up (mean, 3.2 years). At a minimum 2-year follow-up, THA after failed internal fixation of hip fracture in these patients was clinically successful with an elevated risk of periprosthetic fracture and dislocation.

Common Errors in the Execution of Preoperative Templating for Primary Total Hip Arthroplasty

We reviewed 75 primary total hip arthroplasty preoperative and postoperative radiographs and recorded limb length discrepancy, change in femoral offset, acetabular position, neck cut, and femoral component positioning. Interobturator line, as a technique to measure preoperative limb length discrepancy, had the least amount of variance when compared with interteardrop and intertuberosity lines (Levene test, P = .0527). The most common error in execution of preoperative templating was excessive limb lengthening (mean, 3.52 mm), primarily due to inferior acetabular cup positioning (Pearson correlation coefficient, P = .036). Incomplete medialization of the acetabular component contributed the most to offset discrepancy. The most common errors in the execution of preoperative templating resulted in excessive limb lengthening and increased offset. Identifying these errors can lead to more accurate templating techniques and improved intraoperative execution.

Metal-on-Metal Total Hip Arthroplasty

Although metal-on-metal total hip arthroplasty (MOM THA) has been used for over 3 decades, substantial improvements in manufacturing and design have led to improved durability with modern implants. Reported advantages of the use of MOM THA include very low wear and subsequent osteolysis, increased range of motion to impingement secondary to the availability of larger diameter femoral heads, and the potential to monitor implant performance by serial assessment of metal ion levels. Clinical results of both first-generation and second-generation MOM THA have revealed good survivorship and a low incidence of osteolysis. Although the advantages of low wear and increased range of motion have made MOM THA an attractive bearing surface option, more widespread use of MOM bearing surfaces has been tempered with concern for increased metal ion levels and hypersensitivity reactions.

Inaccuracies in the Use of Magnification Markers in Digital Hip Radiographs

BackgroundWith the ubiquity of digital radiographs, the use of digital templating for arthroplasty has become commonplace. Although improved accuracy with digital radiographs and magnification markers is assumed, it has not been shown.Questions/PurposesWe wanted to (1) evaluate the accuracy of magnification markers in estimating the magnification of the true hip and (2) determine if the use of magnification markers improves on older techniques of assuming a magnification of 20% for all patients.MethodsBetween April 2013 and September 2013 we collected 100 AP pelvis radiographs of patients who had a THA prosthesis in situ and a magnification marker placed per the manufacturer’s instructions. Radiographs seen during our standard radiographic review process, which met our inclusion criteria (AP pelvic view that included a well-positioned and observed magnification marker, and a prior total hip replacement with a known femoral head size), were included in the analysis. We then used OrthoViewTM software program to calculate magnification of the radiograph using the magnification marker (measured magnification) and the femoral head of known size (true magnification).ResultsThe mean true magnification using the femoral head was 21% (SD, 2%). The mean magnification using the marker was 15% (SD, 5%). The 95% CI for the mean difference between the two measurements was 6% to 7% (p < 0.001). The use of a magnification marker to estimate magnification at the level of the hip using standard radiographic techniques was shown in this study to routinely underestimate the magnification of the radiograph using an arthroplasty femoral head of known diameter as the reference. If we assume a magnification of 20%, this more closely approximated the true magnification routinely. With this assumption, we were within 2% magnification in 64 of the 100 hips and off by 4% or more in only four hips. In contrast, using the magnification marker we were within 2% of true magnification in only 20 hips and were off by 4% or more in 59 hips.ConclusionWe found the use of a magnification marker with digital radiographs for preoperative templating to be generally inaccurate, with a mean error of 6% and range from −5% to 15%. Additionally, these data suggest that the use of a magnification marker while taking preoperative radiographs of the hip may be unnecessary, as simply setting the software to assume a 20% magnification actually was more accurate.Level of EvidenceLevel III, diagnostic study.

Primary Total Knee Arthroplasty: The Impact of Technique

• Understand the rationale for mobile-bearing total knee arthroplasty • Understand the management of extra-articular deformities during total knee arthroplasty • Understand the implications of posterior cruciate ligament release and how it affects balancing of the flexion and extension gaps during total knee arthroplasty.

Polyethylene exchange in a second-generation cementless acetabular component.

Some have suggested that isolated polyethylene exchange in a well-fixed Harris-Galante II acetabular component (Zimmer, Warsaw, Ind) necessitates cementing the liner or complete revision because the locking mechanism is suboptimal. We reviewed 29 hip revisions during which the polyethylene was exchanged using the native locking mechanism. Mean follow-up was 5.1 years (2-13 years). Of the 29 patients, one had a disengagement of the revision polyethylene at 2.5 years. At the time of this patients original revision, one of the tines was fractured, but a direct exchange was performed. There were 4 other revisions (one for loosening and 3 for instability). There were no other complications attributable to the direct polyethylene exchange and no further reoperations. This series suggests that polyethylene exchange with the Harris-Galante II prosthesis can be performed safely using the native locking mechanism in the absence of fractured tines.