Capsular ligaments provide a passive stabilizing force to protect the hip against edge loading.

AIMS: In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading. METHODS: Torque-rotation curves were obtained from nine cadaveric hips to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line-of-action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral, and pubofemoral ligaments in all positions. The functioning ligament forces and stiffness were determined at 5 Nm rotational restraint. In each position, the contribution of engaged capsular ligaments to the joint reaction force was used to evaluate the net force vector generated by the capsule. RESULTS: The medial and lateral arms of the iliofemoral ligament generated the highest inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest inbound force in flexion with adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.8° inbound per Nm of internal capsular restraint, preventing edge loading. CONCLUSION: The capsular ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimizing complications related to joint instability. Cite this article: Bone Joint Res 2021;10(9):594-601.

Capsular Ligament Function After Total Hip Arthroplasty.

BACKGROUND: The hip joint capsule passively restrains extreme range of motion, protecting the native hip against impingement, dislocation, and edge-loading. We hypothesized that following total hip arthroplasty (THA), the reduced femoral head size impairs this protective biomechanical function. METHODS: In cadavers, THA was performed through the acetabular medial wall, preserving the entire capsule, and avoiding the targeting of a particular surgical approach. Eight hips were examined. Capsular function was measured by rotating the hip in 5 positions. Three head sizes (28, 32, and 36 mm) with 3 neck lengths (anatomical 0, +5, and +10 mm) were compared. RESULTS: Internal and external rotation range of motion increased following THA, indicating late engagement of the capsule and reduced biomechanical function (p < 0.05). Internal rotation was affected more than external. Increasing neck length reduced this hypermobility, while too much lengthening caused nonphysiological restriction of external rotation. Larger head sizes only slightly reduced hypermobility. CONCLUSIONS: Following THA, the capsular ligaments were unable to wrap around the reduced-diameter femoral head to restrain extreme range of motion. The posterior capsule was the most affected, indicating that native posterior capsule preservation is not advantageous, at least in the short term. Insufficient neck length could cause capsular dysfunction even if native ligament anatomy is preserved, while increased neck length could overtighten the anterior capsule. CLINICAL RELEVANCE: Increased understanding of soft-tissue balancing following THA could help to prevent instability and improve early function. This study illustrates how head size and neck length influence the biomechanical function of the hip capsule in the early postoperative period.

Primary total hip arthroplasty with a tapered Trabecular Metal™ coated femoral component: experience with a minimum 24-month follow-up.

We prospectively reviewed the clinical and radiological outcome of the first 32 patients (32 hips) undergoing primary total hip arthroplasty using a Trabecular Metal™ coated tapered femoral component. Seventeen males and 15 females were included. Average age was 71.6 years (range 61.5-85 years). Mean duration of follow-up was 34 months (range 24-48 months) Average preoperative Oxford, Harris, and WOMAC scores were 34, 51, and 44, respectively. Mean postoperative scores were 18, 82, and 11, respectively (P < 0.001 for all scores). All patients reported relief of preoperative pain. There were no revisions. These results suggest that the Trabecular Metal™ taper femoral component successfully relieves pain and leads to a significant functional improvement in patients with symptomatic hip arthritis in the early postoperative period.

The gait of patients with one resurfacing and one replacement hip: a single blinded controlled study.

PURPOSES: Post arthroplasty gait analysis has up till now been performed on subjects walking slowly on flat ground rather than challenging them at faster speeds or walking uphill. We therefore asked: (1) Is there a measurable difference in the performance of hip resurfacing arthroplasty (HRA) and total hip arthroplasty (THA) limbs at patients' self-determined fastest walking speeds and steepest inclines? and (2) Is there a relationship between the observed differences between the gait of HRA and THA implanted limbs and patient walking speeds and inclines. METHODS: In an ethically approved study we recruited patients with bilateral hip arthroplasties: one HRA and one THA. Nine subjects were assessed using an instrumented treadmill at a range of speeds and inclines by a blinded observer. The ground reaction forces of subjects were recorded and an age, sex and BMI matched control group was used for comparison. RESULTS: Increasing walking speed correlated strongly with between leg differences in weight acceptance (r = 0.9, p = 0.000) and push-off force (r = 0.79, p = 0.002). HRA implanted limbs accepted significantly more weight at top walking speeds (1208 N ± 320 versus 1279 N ± 370, p = 0.026) and pushed off with greater force when walking uphill (818 N ± 163 versus 855 ± 166, p = 0.012). HRA limbs more closely approximated to the gait of the normal control group. CONCLUSIONS: Arthroplasty implants do have an impact on the gait characteristics of patients. Differences in gait are more likely to be evident when assessment is made at fast speeds and walking uphill. This study suggests that HRA may enable a more normal gait.

Primary and revision total hip arthroplasty in osteogenesis imperfecta.

Due to an increasing lifespan, patients with osteogenesis imperfecta have a high incidence of hip osteoarthritis. The presence of recurrent fractures and deformities make primary and particularly revision total hip arthroplasty challenging. We present a series of patients with osteogenesis imperfecta undergoing total hip arthroplasty at a tertiary referral centre with a median follow-up of 7.6 years (4 to 35 years). There were four primary total hip arthroplasties and eight revision total hip arthroplasties performed in four patients. Three femoral components were custom computer assisted design computer assisted manufactured. The survival rate of the primary total hip arthroplasty was 16% and there were ten complications: five intraoperative fractures, one case of septic loosening and four cases of aseptic loosening. Patients with pre-operative acetabular protrusio were significantly more likely to require revision surgery (p = 0.02). At latest follow-up, the median Oxford hip score was 41 (37 to 46). As the largest series of primary and revision total hip arthroplasty performed in patients with osteogenesis imperfecta, we report good medium to long-term outcomes. Preoperative planning and consideration of custom made prostheses have an important role in these complex cases.

Posterior femoral neck impingement secondary to excess acetabular anteversion in hip resurfacing arthroplasty.

Component malposition in resurfacing arthroplasty can cause impingement, reduced range of motion, increased metal wear, and early failure. It is therefore important that any component malposition is recognized early and monitored carefully. We present a case of delayed diagnosis of excess acetabular component anteversion causing posterior femoral neck impingement and pain. We correlate the degree of damage found intraoperatively with the degree of component malposition on the radiographs. This is used as a platform to discuss the optimum positioning of hip resurfacing components and the radiographic methods used to determine component position postoperatively.

The Birmingham mid-head resection arthroplasty--minimum two year clinical and radiological follow-up: an independent single surgeon series.

We report the results of the Birmingham Mid-Head Resection Arthroplasty (BMHR) for patients with poor femoral head bone quality where standard hip resurfacing is contraindicated. This is a clinical and radiological follow-up of the first 35 consecutive procedures (34 patients, 16 male, 18 female) performed by an independent surgeon. The mean follow-up was 2.8 years (2.1 to 4.1) and no patients were lost to follow-up. The mean age at the time of surgery was 50.4 years (23.8 to 69.4). There were no failures. The mean HHS improved from 46.6 (25 to 70) pre-operatively to 96.1 (72 to 100) post-operatively. The mean OHS was 36.4 (19 to 53) pre-operatively and 14.2 (12 to 34) post-operatively. The mean WOMAC score was 45.6 (7 to 92) pre-operatively and 4.3 (0 to 28) post-operatively. The mean UCLA activity score was 4.5 (1 to 9) pre-operatively and 7.6 (5 to 10) post-operatively. Radiographic analysis did not show any adverse features such as stress shielding, loosening or femoral neck narrowing. The BMHR provides an excellent alternative to conventional total hip arthroplasty in patients with poor femoral head bone quality who are not suitable for standard resurfacing.

Radiology of the resurfaced hip.

Hip resurfacing arthroplasty is an increasingly common procedure for osteoarthritis. Conventional radiographs are used routinely for follow-up assessment, however they only provide limited information on the radiological outcome. Various complications have been reported in the scientific literature although not all are fully understood. In an effort to investigate problematic or failing hip resurfacings, various radiological methods have been utilized. These methods can be used to help make a diagnosis and guide management. This paper aims to review and illustrate the radiographic findings in the form of radiography, computerized tomography (CT), magnetic resonance imaging (MRI), and ultrasound of both normal and abnormal findings in hip resurfacing arthroplasty. However, imaging around a metal prosthesis with CT and MRI is particularly challenging and therefore the potential techniques used to overcome this are discussed.

Custom cementless THA in patients with skeletal dysplasia results in lower apparent revision rates than other types of femoral fixation.

BACKGROUND: Patients with skeletal dysplasia are prone to degenerative hip disease thus requiring THA at a younger age than the general population. This is a technically demanding procedure with high complication and revision rates. Achieving good femoral fixation can be challenging because of the abnormal features of the hip. QUESTIONS/PURPOSES: We therefore determined: (1) survivorship, (2) function, (3) radiographic findings, and (4) complications associated with a cementless custom-made femoral component used in THAs for patients with skeletal dysplasia and compared these parameters with those from other types of femoral fixation. PATIENTS AND METHODS: Between 1992 and 2005, 40 THAs were performed in 25 patients with skeletal dysplasia using custom-made cementless femoral components. There were 15 men and 10 women with a mean age of 37.5 years (range, 18-61 years) and a mean height of 145 cm (range, 120-173 cm). Patients were followed clinically and radiographically for a minimum of 4.3 years (mean, 10.1 years; range, 4.3-18.2 years). RESULTS: The survivorship rates for the femoral and acetabular components were 92% and 70%, respectively, at 220 months. Revision arthroplasty was performed in four of 40 hips (10%). In two, the acetabular component was revised for aseptic loosening, one had both components revised for aseptic loosening, and one had an isolated femoral component revision for deep infection. The mean Harris hip score improved from 41 (range, 27-57) preoperatively to 80 (range, 51-94) at final followup. There were two intraoperative proximal femoral fractures and one dislocation. CONCLUSIONS: When compared with studies with equal followup, custom-made cementless components in THAs for patients with skeletal dysplasia apparently had lower revision and complication rates with comparable function and higher midterm survival.

Revision of failed hip resurfacing to total hip arthroplasty rapidly relieves pain and improves function in the early post operative period.

We reviewed the results of 25 consecutive patients who underwent revision of a hip resurfacing prosthesis to a total hip replacement. Revisions were performed for recurrent pain and effusion, infection and proximal femoral fractures. Both components were revised in 20 cases.There were 12 male and 13 female patients with average time to revision of 34.4 and 26.4 months respectively. The mean follow up period was 12.7 months (3 to 31). All patients reported relief of pain and excellent satisfaction scores. Two patients experienced stiffness up to three months post operatively.Pre operative Oxford, Harris and WOMAC hip scores were 39.1, 36.4 and 52.2 respectively. Mean post operative scores at last follow up were 17.4, 89.8 and 6.1 respectively (p < 0.001 for each score). These results show that conversion of hip resurfacing to total hip arthroplasty has high satisfaction rates. These results compare favourably with those for revision total hip arthroplasty.

How many orthopedic surgeons does it take to write a research article? 50 years of authorship proliferation in and internationalization of the orthopedic surgery literature.

Publications are considered to indicate academic achievement and can lead to various rewards, including job opportunities and research funding. Recent years have seen a rising trend in the number of articles published, multiple authorship, and internationalization of the biomedical literature. The goal of this study was to analyze the trends in authorship over the past 50 years to determine whether the orthopedic literature parallels trends seen in other areas of the biomedical literature. We performed an observational study with analysis of the number of authors and geographic origin of articles published in the Journal of Bone and Joint Surgery British Volume (JBJS) and Clinical Orthopaedics and Related Research (CORR). We analyzed 2776 articles (CORR, n=1809; JBJS, n=967) published between 1958 and 2008 at 10-year intervals. There has been a significant increase in the mean number of authors per article from 1.638 to 4.08 (P<.0001) and 1.633 to 4.540 (P<.0001) for CORR and JBJS, respectively between 1958 and 2008. There has been a significant increase in the international contribution to both journals (P<.0001). The number of countries contributing to articles increased from 5 to 39 and from 17 to 33 for CORR and JBJS, respectively. These findings are similar to other areas of the biomedical literature. The reasons for this proliferation are multifactorial, including multicenter trials and inappropriate authorship. Guidelines for authorship and preparation of manuscripts from the International Committee of Medical Journal Editors or from individual journals are widely available, and every effort should be made to adhere to them to prevent inappropriate authorship proliferation in the future.

What is the midterm survivorship and function after hip resurfacing?

BACKGROUND: Hip resurfacing arthroplasty is a common procedure that improves functional scores and has a reported survivorship between 95% and 98% at 5 years. However, most studies are reported from the pioneering rather than independent centers or have relatively small patient numbers or less than five years followup. Various factors have been implicated in early failure. QUESTIONS/PURPOSES: Our purposes were to determine: (1) the midterm survival of the BHR; (2) the function in patients treated with hip resurfacing; and (3) whether age, gender, BMI, or size of components related to failure. METHODS: We reviewed the first 302 patients (329 hips) on whom we performed resurfacing arthroplasty. We assessed the survivorship, change in functional hip scores (HHS, OHS, WOMAC, UCLA), and analyzed potential risk factors (age, gender, BMI, component size) for failure. The mean age at the time of surgery was 56.0 years (range, 28.2-75.5 years). The minimum followup was 5 years (mean, 6.6 years; range, 5-9.2 years). RESULTS: Kaplan-Meier analysis showed survival of 96.5% (95% CI, 94.7-98.4) at 9 years taking revision for any cause as the endpoint. All functional hip scores (HHS, OHS, WOMAC, UCLA) improved. Survivorship was higher in men compared with women. The component sizes and body mass index were smaller in the revised group compared with the nonrevised group. CONCLUSIONS: Medium-term survivorship and functional scores of hip resurfacing are comparable to those from the pioneering center. Hip resurfacing remains a good alternative to THA, particularly in the younger male population with relatively large femoral head sizes.

Custom uncemented revision stems based on a femoral classification.

From the outcome of 175 cases, a group of 4 types of custom-designed HA-coated hip stems, based upon an incremental scale of bone condition, was demonstrated to be sufficient for use with the variety of cavitary defects encountered in revision hip surgery. Harris Hip Score evaluation showed a significant improvement in hip pain and function. Radiographic measurements of axial migration over a 4-year period were less than 2 mm. The migration data were similar across the 4 types of revision stem. A follow-up using DEXA scans showed preservation of bone in all regions up to 4 years, which justifies the design rationale for the close fit of the stems in the proximal region in achieving initial stability and strain transfer.

Metal on metal hip resurfacing versus uncemented custom total hip replacement--early results.

INTRODUCTION: There is no current consensus on the most appropriate prosthesis for treating symptomatic osteoarthritis (OA) of the hip in young, active patients. Modern metal on metal hip resurfacing arthroplasty (HR) has gained popularity as it is theoretically more stable, bone conserving and easier to revise than total hip arthroplasty. Early results of metal on metal resurfacing have been encouraging. We have compared two well matched cohorts of patients with regard to function, pain relief and patient satisfaction. METHODS: This prospective study compares 2 cohorts of young, active patients treated with hip resurfacing (137 patients, 141 hips) and custom uncemented (CADCAM) stems (134 patients, 141 hips). All procedures were performed by a single surgeon. Outcome measures included Oxford, WOMAC and Harris hip scores as well as an activity score. Statistical analysis was performed using the unpaired student's t-test. RESULTS: One hundred and thirty four and 137 patients were included in the hip replacement and resurfacing groups respectively. The mean age of these patients was 54.6 years. The mean duration of follow up for the hip resurfacing group was 19.2 months compared to 13.4 months for the total hip replacement group.Pre operative oxford, Harris and WOMAC scores in the THA group were 41.1, 46.4 and 50.9 respectively while the post operative scores were 14.8, 95.8 and 5.0. In the HR group, pre- operative scores were 37.0, 54.1 and 45.9 respectively compared to 15.0, 96.8 and 6.1 post operatively. The degree of improvement was similar in both groups. CONCLUSION: There was no significant clinical difference between the patients treated with hip resurfacing and total hip arthroplasty in the short term.