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.

Return to sporting activity after Birmingham hip resurfacing arthroplasty: Mid term results

BACKGROUND

Hip resurfacing arthroplasty (HRA) is primarily indicated for young, active patients with disabling coxarthrosis who wish to remain active and return to sports after surgery. Relatively few prospective studies have assessed return to sporting activity and impact of gender and age on this.

MATERIALS AND METHODS

Seventy-nine consecutive patients treated with HRA were included. Patients were reviewed clinically and radiologically. Function was assessed using the modified University of California Los Angeles (UCLA) activity score. The Oxford, Harris and WOMAC hip scores were calculated.

RESULTS

Average age at the time of surgery was 54.9 years (range 34.5-73.6 years). Average preoperative and postoperative UCLA scores were 4 and 7.6 respectively. Patients were involved in 2 (0-4) sporting activities preoperatively and 2 (0-5) postoperatively. Preoperative and postoperative Oxford Hip Scores, Harris Hip Score and WOMAC scores were 40, 46 and 51 and 16, 94 and 3 respectively (P < 0.0001). Patients returned to sports at an average of 3 months postoperatively.

CONCLUSION

Patients were able to return to sports by 3 months and perform the same number of activities at preoperative intensity. Activity levels are maintained up to the medium term with few complications.

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.

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.

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.

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.

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.

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.

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.

A displaced acetabular component causing femoral neck notching following hip resurfacing

We describe the case of a patient who developed a notch on the femoral neck following a hip resurfacing operation as a result of a displaced acetabular component. The acetabular cup displaced in the coronal plane and impinged on the femoral neck leading to a large notch in the inferior femoral neck.

Revision of the Birmingham Hip Resurfacing cup: technical notes and the use of a novel technique to overcome unique problems

The number of hip resurfacing procedures performed in the United Kingdom has doubled in the last four years reflecting its popularity among orthopaedic surgeons. Of the available options the Birmingham Hip Resurfacing (BHR) prosthesis has been the most popular choice in this country. Despite this revision rates have been shown to be higher in the resurfacing group compared to the total hip arthroplasty group particularly in the early postoperative period. Revision of the BHR acetabular component is technically demanding due to several unique design features of this component. We discuss these features and describe a novel reliable and reproducible technique for revision of the BHR cup.

Optimizing for head height, head offset, and canal fit in a set of uncemented stemmed femoral components

When inserting an uncemented hip stem, the objectives are to obtain a close fit of the stem in the canal and anatomic head placement. Our goals were to formulate a set of stems which would satisfy these two objectives, and to test the resulting templates on sequential radiographs of hip replacement patients. Using 98 cases for which a custom primary hip had been designed, thirteen dimensional parameters for a hip stem were defined, most importantly proximal medial width (PMW), proximal lateral width (PLW), head offset (HOF), head height (HHT), mid-stem diameter (BD), and distal diameter (DD). These parameters were analyzed in 155 patients' radiographs, and the resulting data were evaluated to obtain the optimal combinations of parameters. A 14-size stem system was defined and evaluated on the AP radiographs of 103 successive hip replacement patients. For each stem diameter between 11 and 17 mm, two pairs of PMW and PLW values, equivalent to 'varus' and 'valgus' shapes, provided the best fit for the population of radiographs. The template analysis showed that out of 103 cases, 93% of offsets were within 4mm of ideal, while 81% of heights were within 1mm of ideal, and 99% were within 4mm of the ideal. Canal fit was within 1.5mm in the proximal-medial Gruen Zone 7 in 58% of the cases. The dimensional parameters of the 14 size system enabled the close matching of the important dimensional parameters simultaneously. The error that did occur could largely be corrected by modular heads and by minor canal broaching. By providing two stem shape variations for each stem diameter, our system achieved an accurate head center position while simultaneously obtaining a sufficiently close fit in the canal.

Does Chiari osteotomy compromise subsequent total hip arthroplasty?

We compared 28 total hip arthroplasties done in dysplastic hips after previous Chiari osteotomy (group I) with a well-matched control group of 50 primary procedures (group II) done during the same period at an average follow-up of 5 years (range, 25-199 months). Group I required significantly less acetabular augmentation, had significantly shorter operative times, had less intraoperative blood loss, and had fewer complications than group II. There was no significant difference between the 2 groups in terms of clinical or radiographic outcome. Total hip arthroplasty after a successful Chiari osteotomy leads to medium-term results similar to those of other dysplastic hips. In our experience, less bone grafting was required, better coverage of the cup by host-bone was obtained, and the center of motion of the hip was more anatomic. Chiari osteotomy may delay the need for total hip arthroplasty, may facilitate acetabular reconstruction, and does not seem to compromise the medium-term clinical or radiographic outcome.

Two-stage uncemented revision hip arthroplasty for infection

We treated 50 consecutive patients with infected total hip arthroplasties according to a standard protocol. Previous surgery to eradicate the infection had been attempted in 13 patients and discharging sinuses were present in 20. Aspiration arthrography was routinely carried out before our interventions. The first stage was a meticulous removal of all foreign and potentially infected material. Samples were taken for culture and a thorough lavage carried out. Antibiotic-loaded beads were placed in the femoral shaft and an antibiotic-loaded cement ball in the acetabulum. At the second stage an uncemented arthroplasty was introduced. Bone allograft was used in 18 patients. The interval between procedures was usually three weeks, but this was extended if the wound was slow to heal or there was extensive bony destruction. Appropriate antibiotics were given for three months. At a mean follow-up of 5.8 years the rate of reinfection was 8% (4 patients). Two of these patients have had another, successful, two-stage revision. At this medium-term review, a satisfactory clinical and radiological outcome was obtained in all except two patients.

Stability and bone preservation in custom designed revision hip stems

Three types of uncemented femoral stems were designed for patients having revision hip surgery, with the goals of promoting axial stability and preserving proximal bone stock. These stems were made individually using computer design and manufacturing technology. Various design features were examined using nonlinear finite element analysis. All stems had lateral, medial, and anterior flares in the proximal region, proximal hydroxyapatite coating, and a collar. Based on a published classification system, the three designs were found suitable for variously encountered cavitary defects. For cases involving small amounts of bone destruction, a primary type of stem was used. With severe cases, an extended polished stem was used. For the worst cases, an extended stem with longitudinal cutting flutes and complete hydroxyapatite coating was necessary. The axial migration was measured radiographically for a 2-year period. The migration rates were comparable with those seen in cemented primary and in custom primary hydroxyapatite coated stems. Dual energy x-ray absorptiometry data were obtained during a 4-year postoperative period. Average bone density in all regions was maintained within 12% of the immediate postoperative values. It was concluded that the proposed system for treating patients needing revision hip surgery showed desirable properties that were comparable to primary hip replacements.

Design and application of combined hip-knee intramedullary joint replacements

Cases in which there is a total hip arthroplasty and a stemmed total knee arthroplasty in the same femur, with loosening of 1 or both components, with serious endosteal bone loss or even a fracture between the stems present a difficult reconstruction problem. We describe a reconstruction using a combined hip and stemmed knee, designed so that they could be rigidly connected during the surgical procedure. The advantages of this implant design are that the entire femur with its muscle attachments is preserved, and the inherent stability allows for immediate weight bearing. To determine the viability of the connection between the hip and the knee, a stress analysis was carried out using finite element analysis. Guidelines were thus provided for the required metal and cement thicknesses. Three case examples are presented with an average follow-up of 3 years. It was shown that the combined hip-knee implant could provide successful results for these difficult reconstructive problems in appropriately selected cases.

Acetabular reconstruction with morcellized allograft and ring support: a medium-term review

Acetabular bone stock deficiency is commonly encountered in revision hip surgery. A number of techniques are available to address this problem, including the use of particulate allograft with reconstruction rings in an effort to provide a stable construct and replenish bone stock. Our technique and results using such devices in complex acetabular deficiencies are described. In the setting of a large nmedial segmental or cavitary acetabular defect, morcellized bone-graft is used to reconstitute the acetabular floor. This graft is reverse reamed until its depth allows screw fixation of a metallic support ring. The screws also serve to compress the graft. A polyethylene acetabular component is then cemented into the reconstituted acetabulum with full freedom of orientation. A series of 48 patients in whom this technique was employed is presented. These cases have been clinically and radiologically reviewed with a mean follow-up of 64 months (range, 25-102 months). Good bony incorporation with stable acetabular components was seen in all but the two cases in which sepsis predominated.

Uncemented total hip arthroplasty with subtrochanteric derotational osteotomy for severe femoral anteversion

Total hip joint arthroplasty (THA) in the presence of severe femoral anteversion (>50 degrees) is technically demanding. This problem is often encountered in patients with osteoarthritis secondary to hip joint dysplasia or congenital dislocation. We describe a method of THA in which an uncemented femoral prosthesis is used in conjunction with subtrochanteric derotational osteotomy. This technique allows the restoration of the normal proximal femoral anatomy, including the abductor muscle lever arm without resorting to greater trochanteric transfer. Correction of the excessive femoral anteversion avoids the tendency for postoperative anterior instability. The osteotomy site may also serve as the site for femoral shortening or angular correction when required, which preserves the normal femoral flare. The prostheses used were custom CAD/CAM (computer-assisted design/computer-assisted manufacturer) in design and had the following features: a close intramedullary proximal fit, with collar, lateral flare, and hydroxyapatite coating to achieve early proximal fixation, and longitudinally cutting fluted stem to provide immediate rotational stability across the osteotomy site. Although we used CAD/CAM custom prostheses, off-the-shelf uncemented hip prostheses with similar design features have become available. We report on 7 patients who underwent THA using this technique. The average patient age was 49 years (range, 34-61 years) with a mean follow-up period of 31 months (range, 16-60 months). To date, all cases have had a satisfactory outcome with evidence of union at the osteotomy site. Harris hip scores improved from an average of 44 preoperatively to 91 by the end of follow-up period. One case was complicated by delayed union at the osteotomy site, which was successfully corrected with bone grafting and temporary plate stabilization.