Functional Anatomy of the Hip Joint.

BACKGROUND: The functional anatomy of the osteoarthritic hip joint in the sagittal plane has not been defined. The purpose of this study was to define the functional anatomy of the hip using clinical and radiographic analyses. METHODS: 320 hips had preoperative standing and sitting lateral spine-pelvis-hip X-rays. Radiographic pelvic measurements were pelvic incidence (PI) and sacral slope (SS), and hip measurements were anteinclination (AI) and pelvic femoral angle (PFA). Pelvic tilt (PT) was calculated as PI-SS. A triangle model was created from the clinical data that illustrates the functional motion of the hip during postural changes from standing to sitting. RESULTS: Pelvic motion was coordinated with hip motion, even with spinopelvic imbalance and stiffness. Pelvic motion (ΔSS) varied for all 5 types of imbalance, but pelvic motion (ΔSS) and acetabular motion (ΔAI) changed with a 1:1 ratio and inversely with femoral motion (ΔPFA) with a 1:1 ratio. The triangle model showed similar results with ΔSS, ΔPT, and ΔAI changing in a 1:1:1 ratio, and femur motion inversely changing with a 1:1 ratio. CONCLUSION: The functional anatomy of the hip joint can be visually illustrated using a triangle model. Pelvic angles SS, PT, and AI change in unison, whereas femoral motion (ΔPFA) changes inversely with pelvic motion (ΔSS) in a 1:1 ratio. This coordinated mobility explains the limitations of the Lewinnek safe zone, which include only the acetabulum.

Is Combined Anteversion Equally Affected by Acetabular Cup and Femoral Stem Anteversion?

BACKGROUND: To create a safe zone, an understanding of the combined femoral and acetabular mating during hip motion is required. We investigated the position of the femoral head inside the acetabular liner during simulated hip motion. We hypothesized that cup and stem anteversions do not equally affect hip motion and combined hip anteversion. METHODS: Hip implant motion was simulated in standing, sitting, sit-to-stand, bending forward, squatting, and pivoting positions using the MATLAB software. A line passing through the center of the stem neck and the center of the prosthetic head exits at the polar axis (PA) of the prosthetic head. When the prosthetic head and liner are parallel, the PA faces the center of the liner (PA position = 0, 0). By simulating hip motion in 1-degree increments, the maximum distance of the PA from the liner center and the direction of its movement were measured (polar coordination system). RESULTS: The effect of modifying cup and stem anteversion on the direction and distance of the PA's change inside the acetabular liner was different. Stem anteversion influenced the PA position inside the liner more than cup anteversion during sitting, sit-to-stand, squatting, and bending forward (P = .0001). This effect was evident even when comparing stems with different neck angles (P = .0001). CONCLUSION: Cup anteversion, stem anteversion, and stem neck-shaft angle affected the PA position inside the liner and combined anteversion in different ways. Thus, focusing on cup orientation alone when assessing hip motion during different daily activities is inadequate.

The Effect of Functional Pelvic Tilt on the Three-Dimensional Acetabular Cup Orientation in Total Hip Arthroplasty Dislocations.

BACKGROUND: Anterior and posterior pelvic tilt appears to play a role in total hip arthroplasty (THA) stability. When changing from the standing to the sitting position, the pelvis typically rotates posteriorly while the hips flex and this affects the femoro-acetabular positions. This case-control study compares changes in 3-D acetabular cup orientation during functional pelvic tilt between posterior THA dislocations vs stable THAs. METHODS: Standing and sitting 3-D cup orientation was compared between fifteen posterior dislocations vs 233 prospectively followed stable THAs. 3-D cup orientation was calculated using previously validated trigonometric algorithms on biplanar radiographs. Those algorithms combine the angles in the three anatomical planes (coronal inclination, transverse version, and sagittal ante-inclination) in the standing position with the change in sagittal pelvic tilt from standing to sitting to calculate the 3-D orientation in the sitting position. RESULTS: The standing cup orientation of the dislocated THAs was only characterized by a lower coronal inclination (P = .039). Compared with the controls, from standing to sitting, they showed less posterior pelvic tilt (P < .001). This led to a significant lower coronal inclination (P < .001) and sagittal ante-inclination (P < .001) in the sitting position but similar transverse version (P = .366). CONCLUSIONS: Comparing posterior THA dislocations to stable THAs, there is a lower increase of all three orientation angles from standing to sitting. This leads to a decreased sitting coronal inclination and sagittal ante-inclination which may lead to an increased risk of impingement ensued by THA instability. By contrast, the transverse version was not significantly different in both positions. This confirms the importance of biplanar data on functional cup orientation. LEVEL OF EVIDENCE: Diagnostic, Level III.

Spinopelvic Motion and Impingement in Total Hip Arthroplasty.

The stability of a total hip arthroplasty relies on proper positioning of the acetabular cup. Recent research has shown that this cup position is more dynamic than previously thought. The 3-dimensional orientation of the acetabular cup changes when the pelvis tilts anteriorly or posteriorly. These changes in pelvic tilt are directly related to the biomechanics of the lumbosacral junction. In normal physiology, the lumbar spine straightens with sitting and becomes more lordotic with standing. This directly translates to posterior or anterior pelvic tilt due to the rigid sacroiliac attachments. During sitting, increased posterior pelvic tilt opens the acetabulum to accommodate flexion and internal rotation of the hip. This helps prevent anterior impingement and posterior hip dislocation. During standing, anterior pelvic tilt increases superior coverage of the acetabulum. This helps prevent posterior impingement and anterior hip dislocations. When lumbosacral motion becomes pathologic, spinopelvic motion changes and acetabular cup orientation is affected. In cases of decreased lumbosacral motion, patients rely on greater hip motion to reach standing or sitting positions. This can cause pathologic impingement. In addition, traditional safe zones for cup position may not apply in the presence of pathologic spinopelvic motion. This article discusses the normal physiology of spinopelvic motion, the patterns of pathologic change, and the clinical implications therein.

Functional Safe Zone Is Superior to the Lewinnek Safe Zone for Total Hip Arthroplasty: Why the Lewinnek Safe Zone Is Not Always Predictive of Stability.

BACKGROUND: The Lewinnek "safe zone" is not always predictive of stability after total hip arthroplasty (THA). Recent studies have focused on functional hip motion as observed on lateral spine-pelvis-hip x-rays. The purpose of this study was to assess the correlation between the Lewinnek safe zone and the functional safe zone based on hip and pelvic motion in the sagittal plane. METHODS: Three hundred twenty hips (291 patients) underwent primary THA using computer navigation. Two hundred ninety-six of these hips (92.5%) were within the Lewinnek safe zone as determined by inclination of 40° ± 10° and anteversion of 15° ± 10°. All patients had preoperative and postoperative standing and sitting lateral spinopelvic x-rays. The combined sagittal index (CSI), a combination of sagittal acetabular and femoral position, was measured for each patient and used to assess the functional safe zone. Data analysis was performed to identify hips in the Lewinnek safe zone inside and outside the sagittal functional safe zone. Predictive factors for hips outside the functional safe zone were identified. RESULTS: Of the 296 hips within the Lewinnek safe zone, 254 (85.8%) were also in the functional safe zone. Forty-two patients were outside the functional safe zone based on CSI; 19 had an increased standing CSI and 23 had a decreased sitting CSI, all were considered at risk for dislocation. Predictive factors for falling outside the functional safe zone were increased femoral mobility (P < .001, r = 0.632), decreased spinopelvic mobility (P < .001, r = 0.455), and pelvic incidence (P < .001, r = 0.400). CONCLUSION: In this study, 14.2% of hips within the Lewinnek safe zone were outside the functional safe zone, identifying a potential reason hips dislocate despite having "normal" cup angles. The best predictor for falling outside the functional safe zone, both preoperatively and postoperatively, was femoral mobility, not the sagittal cup position (ie, cup anteinclination). LEVEL OF EVIDENCE: Level III, retrospective review.

The Opioid Crisis and the Orthopedic Surgeon.

Opioid use and abuse has become a national crisis in the United States. Many opioid abusers become addicted through an initial course of legal, physician-prescribed medications. Consequently, there has been increased pressure on medical care providers to be better stewards of these medications. In orthopedic surgery and total joint arthroplasty, pain control after surgery is critical for restoring mobility and maintaining patient satisfaction in the early postoperative period. Before the opioid misuse epidemic, orthopedic surgeons were frequently influenced to "treat pain with pain medications." Long-acting opioids, such as OxyContin were used commonly. In the past decade, there has been a paradigm shift in favor of multimodal pain control with limited opioid use. This review will discuss 4 major topics. First, we will describe the pressures on orthopedic surgeons to prescribe narcotic pain medications. We will then discuss the major and minor complications and side effects associated with these prescriptions. Second, we will review how these factors motivated the development of alternative pain management strategies and a multimodal approach. Third, we will look at perioperative interventions that can reduce postoperative opioid consumption, including wound injections and peripheral nerve blocks, which have shown superb clinical results. Finally, we will recommend an evidence-based program that avoids parenteral narcotics and facilitates rapid discharge home without readmissions for pain-related complaints.

The Current Knowledge on Spinopelvic Mobility.

Recent studies may suggest that our conventional knowledge of risk factors for dislocation may need rethinking. Previous studies have demonstrated a large majority of total hip arthroplasty instability with acetabular cups implanted in safe zones. Recently discovered spinopelvic motion is a coordinated biomechanical relationship among acetabular anteversion, pelvic tilt, and lumbar lordosis. Classification includes normal, hypermobile, stiff, stuck standing, stuck sitting, and fused. Normal spinopelvic motion from standing to sitting occurs with hip flexion, posterior sacral tilt, and decreased lumbar lordosis to accommodate a flexed femur and prevent impingement and dislocation. Acetabular cup implantation ideally is adapted based on spinopelvic interactions. This may lower the rate of impingement and subsequent dislocation. These new biomechanical interactions may provide a better understanding of the safe zones of anteversion and inclination.

Outpatient Arthroplasty is Here Now.

Substantial advances have been made in arthroplasty to minimize surgical trauma and maximize perioperative pain control, which has enabled patients to regain mobility within hours of surgical intervention and be safely discharged to home the same day. Surgeons should understand the indications and contraindications for the safe performance of outpatient arthroplasty in a hospital and ambulatory surgical center setting as well as know how to optimize, medically manage, prepare, and rehabilitate patients. To undertake outpatient arthroplasty, surgeons must be knowledgeable in multimodal anesthesia techniques, effective venous thromboembolism prophylaxis, blood management, and wound management. In addition, surgeons must learn the subtle nuances of specialized surgical techniques that lend themselves to outpatient arthroplasty, including partial knee, muscle-sparing total hip, less invasive total knee, and total shoulder techniques.

Posterior Mini-Incision With Primary Total Hip Arthroplasty: A Nine to Ten Year Follow Up Study.

The question has been raised as to whether small incision surgery will compromise long term results of total hip arthroplasty. We report nine to ten years' outcome with posterior mini-incision. Radiographs were measured for component position, polyethylene wear, fixation, and osteolysis. Sixty-two of the original 86 patients (76 of 100 hips) were alive and available for study with 17 patients deceased (with known results) and seven (8%) lost to follow-up. The result was rated as excellent in 70 of 75 remaining hips (93%). Eighty-nine of 93 hips (96%) with known results had the original implants. Radiographically, wear was a mean 0.015 ± 0.009 mm/year, and no hip had impending failure. There were four revisions, 2 for dislocation, 1 for fracture, and 1 for loose cup.

Precision of robotic guided instrumentation for acetabular component positioning.

Robotic computerized instrumentation that guides bone preparation and cup implantation in total hip arthroplasty was studied. In 38 patients (43 hips) intraoperative cup inclination and anteversion were validated by postoperative CT scans. Planned inclination was 39.9°±0.8° and with robotic instrumentation was 38. 0°±1.6° with no outliers of 5°; on the postoperative CT scan there were 5 outliers (12%). Planned anteversion was 21.2°±2.4° and intraoperatively was 20.7°±2.4° with no outlier of 5°; on the CT there were 7 outliers (16%). The center of rotation (COR) was superior by a mean 0.9±4.2 mm and medial by 2.7±2.9 mm. This robotic instrumentation achieved precision of inclination in 88%, anteversion in 84% and COR in 81.5%.

Early Postoperative Femur Fracture After Uncemented Collarless Primary Total Hip Arthroplasty: Characterization and Results of Treatment.

Thirty Vancouver type B periprosthetic fractures occurred within 90 days of total hip arthroplasty were identified using two institutional databases. Twenty-eight of these fractures were of a stereotyped fracture pattern consisting of a displaced fracture of the femoral neck including the lesser trochanter and a variable amount of the proximal medial femoral cortex creating a roughly triangular fragment. Time from operation until fracture was 2-88 days (mean 28). Mechanism of injury was fall from standing height in 12, no defined trauma in 11, stumble without fall in 5, and twisting motion in 2. Fracture treatment consisted of femoral revision in 24, fracture fixation in two, and nonoperative in four. Of the 24 treated with revision, 21 had healed fractures and stable revision stems.

Tourniquet use during cementation only during total knee arthroplasty: a randomized trial.

BACKGROUND: Total knee arthroplasty with the use of a tourniquet during the entire operation has not been shown to improve the performance of the operation and may increase the risk of complications. QUESTIONS/PURPOSES: We asked whether the limited use of a tourniquet for cementation only would affect (1) surgical time; (2) postoperative pain and motion of the knee; (3) blood loss; or (4) complications such as risk of nerve injuries, quadriceps dysfunction, and drainage compared with use of a tourniquet throughout the procedure. METHODS: Seventy-one patients (79 knees) were randomized to either use of a tourniquet from the incision through cementation of the implants and deflated for closure (operative tourniquet group) or tourniquet use only during cementation (cementation tourniquet group). The initial study population was a minimum of 30 knees in each group as suggested for randomized studies by American Society for Testing and Materials standards; termination of the study was determined by power analysis performed after 40 knees in each group showed any statistical solution to our questions would require a minimum of 260 more cases. Patients were excluded who were considered in previous randomized studies as high risk for complications, which might be attributed to the tourniquet. RESULTS: There were no differences in terms of surgical time, pain scores, pain medicine requirements, range of motion, hemoglobin change, or total blood loss. One major complication (compartmental syndrome) occurred in a patient with tourniquet inflation until closure. No other complications were attributed to the use of a tourniquet. CONCLUSIONS: With the numbers available, our results suggest that there are no important clinical differences between patients who had a tourniquet inflated throughout the procedure compared with those who had it inflated only during cementation. Tourniquet inflation for cementation only provides the benefit of bloodless bone for fixation and may eliminate the risks associated with prolonged tourniquet use.

Preoperative radiographic findings associated with postoperative spinopelvic risk factors for instability following total hip arthroplasty.

Postoperative spinopelvic changes are associated with increased dislocation risk following total hip arthroplasty (THA). The aim of this study was to identify preoperative patient and radiographic factors associated with high-risk postoperative spinopelvic parameters. A retrospective review of consecutive THA patients who received preoperative and postoperative sitting and standing lateral lumbar spine-hip radiographs with minimum radiographic and clinical follow-up of 10 months was performed. Patient demographics were recorded and preoperative standing and sitting sacral slope (SS), anteinclination, pelvic femoral angle (PFA), and combined sagittal index (CSI) were measured. High-risk patients were defined by decreased spinopelvic motion (∆SS from sitting to standing of >10°), increased hip motion (∆PFA from sitting to standing of >10°), or decreased CSI of >10° at final follow-up compared with preoperative measurements. Univariate and multivariate regression analyses were used to identify preoperative demographic and radiographic factors associated with these high-risk categories. One hundred and fifty-three patients were included with an average age of 62 years, average body mass index of 27.8 kg/m2 , and average follow-up of 16.2 months. At 1-year follow-up, 43 (28.1%) patients demonstrated a decreased ∆SS > 10° and 67 (43.7%) patients demonstrated an increased ∆PFA > 10° compared with preoperative values. Sitting CSI decreased by >10° in 17 (11.1%) patients. Preoperative increased sitting PFA (adjusted odds ratio [aOR] 1.057, p < 0.001) and decreased preoperative hip motion (∆PFA) were associated with decreased sitting CSI of >10° at 10-month follow-up. Increased spinopelvic motion (∆SS) and decreased hip motion (∆PFA) preoperatively are associated with postoperative radiographic changes that be associated with increased dislocation risk.

Increased dislocation rates following total hip arthroplasty in patients with ankylosing spondylitis.

BACKGROUND: Patients with ankylosing spondylitis (AS) experience abnormal spinopelvic motion due to chronic inflammation of the axial skeleton, predisposing them to impingement and dislocation. The purpose of this study was to evaluate total hip arthroplasty (THA) dislocation rates in AS patients and evaluate the effects of age and gender on dislocation risk. METHODS: Patients who underwent primary THA from 2005 to 2014 were identified using the PearlDiver database. AS patients were compared to age- and gender-matched controls without AS. Patients with a history of spine pathology or spine surgery were excluded. Univariate analyses were performed based on age and sex to evaluate dislocation rates at 90 days, 6 months, 1 year, and 5 years postoperatively. RESULTS: A total of 2792 THA patients (59.6% male) with AS were identified and compared to an age- and gender-matched control group of 5582 THA patients (59.5% male) without AS or known spine pathology. At final follow-up, there were 96 dislocations (3.4%) in the AS group and 138 (2.5%) dislocations in the control group (OR 1.40; 95% CI, 1.08-1.83; p = 0.0118). AS patients ⩾70 years old had higher dislocation rates at all time points (OR range, 1.75-2.09; p < 0.05) compared to controls. At 5-year follow-up, dislocation-free survivorship was 95.7% (95% CI, 94.5-96.9%) for AS patients ⩾70 years old compared to 97.3% (95% CI, 96.6-98.0%) for patients ⩾70 years old without AS. CONCLUSIONS: Older AS patients have higher dislocation rates following THA. This effect is likely related to decreased spinopelvic motion in the sagittal plane, predisposing patients to impinge and dislocate.