The effect of hip resurfacing on oxygen concentration in the femoral head

Mid-term clinical and radiographic outcome of metal-on-metal hip resurfacing through an anterolateral approach

PURPOSE

The aim of this retrospective study was to evaluate the medium-term clinical and radiographic results of current generation metal-on-metal resurfacing prostheses performed through anterolateral approach.

MATERIALS AND METHODS

Fifty-seven hips in 52 patients underwent resurfacing arthroplasty. Two patients died from unrelated causes, leaving 55 hips in 35 males (3 bilateral) and 15 females (2 bilateral), with a mean age at surgery of 56.2 years (range, 27-70 years). Clinical and radiographic assessment was carried out preoperatively and at follow-up in all the survived cases. The cumulative survival rate was determined according to the method of Kaplan-Meier.

RESULTS

At a mean follow-up of 5.2 years (range, 1.8-9.1 years), 2 HRs of the same female patient were revised because of early loosening of the acetabular component. Deep venous thrombosis and transient femoral nerve palsy occurred both in 1 case. No specific complications of HR were observed. Average Harris hip score improved significantly from 59.8 points (range, 30.4-90.6) preoperatively to 93.7 points (range, 53-100) at the latest examination. Neck narrowing showed an average of 3.27%, but it never exceeded 10%. Nonprogressive acetabular radiolucencies and osteolysis were detected both in 2 hips. A high rate of patients (32, 60.4%) developed heterotopic ossifications, although low-grade in most cases (27, 84.4%). The cumulative survival rate at 9.1 years with revision for any reason as the end point was 93.0%.

CONCLUSIONS

The early clinical and radiographic results of modern metal-on-metal hip resurfacing performed through an anterolateral approach are promising, but longer-term follow-up studies are necessary.

Metal-on-Metal Hips: Ten-Year Clinical and Radiographic Outcomes of the ADEPT Metal-on-Metal Hip Resurfacing and Modular Total Hip Arthroplasty

BACKGROUND

The aim of this study is to update the 10-year follow-up survivorship and metal ions levels of a cohort of metal-on-metal (MoM) hip resurfacing (HR) and large-diameter-head (LDH) total hip arthroplasty (THA).

METHODS

The study is a retrospective analysis of prospectively collected data that compared the outcomes of 24 MoM HR (21 patients) and 15 (11 patients) modular LHD MoM THA at >10 years follow-up. Baseline characteristics as well as intraoperative and postoperative information were collected, including complications, revisions, clinical and radiographic outcomes, and serum metal ions level (Cobalt, Chromium). Metal ion levels were compared using a two-tailed unpaired t-test and Wilcoxon signed-rank test (jamovi v2.3.3.0, Sydney, NSW, AU).

RESULTS

No significant differences were detected in gender, BMI, and ASA score between the two groups. Patients in the modular THA group were significantly older (57 years vs. 46 years; p < 0.05). The HR overall survivorship was 91.7% (22 of 24 hips) with survivorship from implant failure and/or aseptic loosening and/or metal debris related 100% of problems. The modular THA overall survivorship was 86.7% (13 of 15 hips) with survivorship from implant aseptic loosening and metal ions complications of 93.4% (14 of 15 hips). No significant difference was noted when comparing clinical outcomes. Metal ions were significantly lower in the HR group (Co 25.8 nmol/L vs. 89 nmol/L; p < 0.001-Cr 33.5 nmol/L vs. 55.2 nmol/L; p = 0.026).

CONCLUSION

Both implants reported excellent and comparable clinical outcomes at >10 years follow-up. The Adept HR reported remarkable survivorship, in line with the registry data, proving once again its reliability in young active males. The modular LDH THA, despite being discontinued, presented higher reliability and a lower failure rate when compared with similar withdrawn MoM implants. Trunnionosis did not appear to be a significant problem in this particular modular design.

Short and mid-term outcomes and functional results in metal-on-metal hip resurfacing arthroplasty at 5 years follow-up: the Spanish experience

Background

Hip resurfacing arthroplasty (HRA) and in particular, Birmingham hip resurfacing (BHR), is commonly employed as an alternative to total hip arthroplasty (THA) in young patients, as it allows for preservation of femoral bone stock and resumption of physical activity. The aim of our study was to investigate 5-year survival and functional outcomes of BHR arthroplasty in young Spanish osteoarthritis (OA) patients.

Methods

This is an observational, prospective, cohort study of patients who underwent BHR between June 2005 and December 2009 at a Spanish public hospital with a minimum follow-up of 5 years. All surgeries were performed by a single surgeon (RLM). Survival was analyzed using the Kaplan-Meier method. Functional outcomes and return to work and physical activities were also assessed.

Results

Five-year survival rate of the prosthesis was 95.74% (95% CI: 95.77–98.07), and estimated 10-year survival was 92.92% (95% CI: 85.07–96.72). Harris hip score significantly increased from 41.13 to 97.63 (p < 0.001) at 5-year follow-up. Average time for returning to work and sporting activities was 3.89 (SD: 2.39) and 3.47 (SD: 1.18) months respectively. Failure occurred in 14 patients, 8 of whom experienced femoral neck fractures.

Conclusions

Our data support the short and mid-term efficacy of BHR arthroplasty in young OA patients, indicating good implant survival, improvement in patients’ functionality and a swift return to work and physical activities after surgery.

Bone penetration of intravenous flucloxacillin and gentamicin as antibiotic prophylaxis during total hip and knee arthroplasty

Aims

To investigate the bone penetration of intravenous antibiotic prophylaxis with flucloxacillin and gentamicin during hip and knee arthroplasty, and their efficacy against Staphylococcus (S.) aureus and S. epidermidis.

Patients and Methods

Bone samples from the femoral head, neck and acetabulum were collected from 18 patients undergoing total hip arthroplasty (THA) and from the femur and tibia in 21 patients during total knee arthroplasty (TKA). The concentration of both antibiotics in the samples was analysed using high performance liquid chromatography. Penetration was expressed as a percentage of venous blood concentration. The efficacy against common infecting organisms was measured against both the minimum inhibitory concentration 50, and the more stringent epidemiological cutoff value for resistance (ECOFF).

Results

The bone penetration of gentamicin was higher than flucloxacillin. Relative to ECOFF, flucloxacillin concentrations were effective against S. aureus and S. epidermidis in all THAs and 20 (95%) TKAs. Gentamicin concentrations were effective against S. epidermidis in all bone samples. Gentamicin was effective against S. aureus in 11 (61.1%) femoral neck samples in THA. Effective concentrations of gentamicin against S. aureus were only achieved in four (19%) femoral and six (29%) tibial samples in TKA.

Conclusion

Flucloxacillin and gentamicin were found to penetrate bone during THA and TKA. Gentamicin was effective against S. epidermidis in both THA and TKA, while levels were subtherapeutic against S. aureus in most TKAs. Bone penetration of both antibiotics was less in TKA than THA, and may relate to the use of a tourniquet. Using this antibiotic combination, effective cover against the two common infective organisms was achieved in all THAs and all but one TKA. Cite this article: Bone Joint J 2017;99-B:358–64.

Hip arthroplasty for treatment of advanced osteonecrosis: comprehensive review of implant options, outcomes and complications

Surgical treatment for late stage (post-collapse) osteonecrosis of the femoral head is controversial. In these situations, the outcome of joint preservation procedures is poor. There are several arthroplasty options for late-stage disease. The clinical outcomes of hemiarthroplasty and hemiresurfacing are unpredictable because of progressive acetabular cartilage degeneration. Total hip resurfacing may be associated with further vascular insult to the femoral head and early failure of the implant. Total hip replacement with metal-on-conventional polyethylene bearing surfaces has been the gold standard, but implant survivorship is limited in young active patients due to wear and osteolysis. Newer alternative bearing surfaces may have improved wear characteristics, but their durability must be confirmed in longer-term studies.

Resurfacing of the humeral head: An analysis of the bone stock and osseous integration under the implant

Cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint restoration with minimal bone loss. Good clinical results have been reported, but due to the radiopaque metal shell no data is available on the structure, osseous integration, and bone stock under the implant. 14 hemi-CSRAs (4 manufacturers) with two geometries (crown [n = 7]/ stem [n = 7] fixation) were retrieved from patients undergoing revision due to glenoidal erosion. Histological sections cutting through the implant centre and bone were analysed. Quantitative histomorphometry evaluated the bone-implant-contact and compared the bone-area to native humeral retrievals (n = 7). The bone-implant-interface was further assessed by scanning-electron-microscopy (SEM) and energy-dispersive-x-ray (EDX). Qualitative histology revealed a reduced and inhomogeneous bone stock. Obvious signs of stress shielding were observed with bone predominantly visible at the stem and implant rim. Quantitative histomorphometry confirmed the significantly reduced bone-area (9.2 ± 3.9% [crown 9.9 ± 4.3%, stem 8.6 ± 3.6%]) compared to native humeri (21.2 ± 9.1%; p < 0.05). Bone-implant-contact was 20.5 ± 5.8% (crown 21.8 ± 6.2%, stem 19.2 ± 5.6%) which was confirmed by SEM and EDX. Altogether, CRSA shows satisfactory bone ingrowth at the interface suggesting sufficient primary stability to allow osseous integration. However, clear signs of stress shielding with an inhomogeneous and reduced bone stock were observed. The impact on the long-term-results is unclear requiring further investigation.

Anatomical considerations in adult femoral neck fractures: how anatomy influences the treatment issues?

Femoral neck fractures in physiologically young adults are relatively uncommon. The reported incidence of avascular necrosis and nonunion rates remain relatively high despite the advancement in understanding and surgical management. Understanding the normal femoral neck anatomy and its relationship to presenting fracture pathology in young adults could help to lessen reported high complication rates to provide better clinical outcomes.

Metal-on-metal hip surface replacement

Metal-on-metal resurfacing of the hip (MoMHR) has enjoyed a resurgence in the last decade, but is now again in question as a routine option for osteoarthritis of the hip. Proponents of hip resurfacing suggest that its survival is superior to that of conventional hip replacement (THR), and that hip resurfacing is less invasive, is easier to revise than THR, and provides superior functional outcomes. Our argument serves to illustrate that none of these proposed advantages have been realised and new and unanticipated serious complications, such as pseudotumors, have been associated with the procedure. As such, we feel that the routine use of MoMHR is not justified.

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):17–21.

Survivorship of standard versus modified posterior surgical approaches in metal-on-metal hip resurfacing

Objectives

Metal-on-metal hip resurfacing (MOMHR) is available as an alternative option for younger, more active patients. There are failure modes that are unique to MOMHR, which include loosening of the femoral head and fractures of the femoral neck. Previous studies have speculated that changes in the vascularity of the femoral head may contribute to these failure modes. This study compares the survivorship between the standard posterior approach (SPA) and modified posterior approach (MPA) in MOMHR.

Methods

A retrospective clinical outcomes study was performed examining 351 hips (279 male, 72 female) replaced with Birmingham Hip Resurfacing (BHR, Smith and Nephew, Memphis, Tennessee) in 313 patients with a pre-operative diagnosis of osteoarthritis. The mean follow-up period for the SPA group was 2.8 years (0.1 to 6.1) and for the MPA, 2.2 years (0.03 to 5.2); this difference in follow-up period was statistically significant (p < 0.01). Survival analysis was completed using the Kaplan–Meier method.

Results

At four years, the Kaplan–Meier survival curve for the SPA was 97.2% and 99.4% for the MPA; this was statistically significant (log-rank; p = 0.036). There were eight failures in the SPA and two in the MPA. There was a 3.5% incidence of femoral head collapse or loosening in the SPA and 0.4% in the MPA, which represented a significant difference (p = 0.041). There was a 1.7% incidence of fractures of the femoral neck in the SPA and none in the MPA (p = 0.108).

Conclusion

This study found a significant difference in survivorship at four years between the SPA and the MPA (p = 0.036). The clinical outcomes of this study suggest that preserving the vascularity of the femoral neck by using the MPA results in fewer vascular-related failures in MOMHRs.

Cite this article: Bone Joint Res 2014;3:150–4

Assessment of femoral head and head-neck junction perfusion following surgical hip dislocation using gadolinium-enhanced magnetic resonance imaging: a cadaveric study

BACKGROUND

The purpose of the present study was to quantify perfusion to the femoral head and head-neck junction using gadolinium-enhanced magnetic resonance imaging following three surgical dislocations of the hip (trochanteric flip osteotomy, standard posterior approach, and modified posterior approach).

METHODS

The medial femoral circumflex artery was cannulated in fifty fresh-frozen cadaveric hips (twenty-five pelvic specimens). One hip on each pelvic specimen was randomly chosen to undergo one of the three surgical dislocations, and the contralateral hip was used as a control. Gadolinium enhancement on the magnetic resonance imaging scan was quantified in both the femoral head and head-neck junction by volumetric analysis using custom magnetic resonance imaging analysis software. A polyurethane compound was then injected, and gross dissection was performed to assess the extraosseous vasculature.

RESULTS

Magnetic resonance imaging quantification revealed that the trochanteric flip osteotomy group maintained almost full perfusion (mean, 96% for the femoral head and 98% for the head-neck junction). The standard posterior approach almost completely compromised perfusion (mean, 4% for the femoral head and 8% for the head-neck junction). Six specimens in the modified posterior approach group demonstrated partial perfusion (mean, 32% in the femoral head and 26% in the head-neck junction). Three specimens in the modified posterior approach group demonstrated almost full perfusion (mean, 96% in the femoral head and 97% in the head-neck junction). Gross dissection revealed that all specimens in the standard posterior approach group and seven of ten in the modified posterior approach group sustained disruption of the ascending branch of the medial femoral circumflex artery. All specimens in the standard posterior approach group demonstrated disruption of the inferior retinacular artery. The inferior retinacular artery remained intact in nine of ten specimens in the modified posterior approach group. One specimen in the modified posterior approach group that had disruption of both the ascending medial femoral circumflex artery and inferior retinacular artery demonstrated a substantial decrease in perfusion (7% in the femoral head and 5% in the head-neck junction).

CONCLUSIONS

The trochanteric flip osteotomy preserves the vascular supply to the femoral head and head-neck junction. The standard posterior approach disrupts the vascular supply and should be completely abandoned for surgical hip dislocation. Despite reduced enhancement, substantial perfusion of the femoral head and head-neck junction was present in the modified posterior approach group, likely because of the preservation of the inferior retinacular artery. The modified posterior approach produced variable results, indicating that improvement to the modified posterior approach is needed.

CLINICAL RELEVANCE

Our study provides previously unreported quantitative magnetic resonance imaging data on the perfusion to the femoral head and head-neck junction during common surgical approaches to the hip.

Early failure of the Durom prosthesis in metal-on-metal hip resurfacing in Chinese patients

Hip resurfacing (HR) is being used increasingly as an alterative to total hip arthroplasty in osteonecrosis (ON) and ankylosing spondylitis (AS) of the hip. We performed 141 consecutive HR arthroplasties in 111 patients comprising 3 etiology groups: ON, AS, and osteoarthritis (OA). After retrospective study of retrieved components, we hypothesized that the main reason for revision was femoral loosening in the ON group (4 of 46 hips; 8.7%) and femoral-neck fracture in the AS group (3 of 58 hips; 5.2%). Necrotic areas were seen on femoral heads retrieved from patients with femoral loosening, whereas femoral heads were fixed tightly to components in patients with femoral-neck fractures. Etiology may be an important risk factor for postoperative complications.

The effect of surgical approach on the histologyof the femoral head following resurfacing of the hip: Analysis of retrieval specimens

OBJECTIVES

We aimed to determine the effect of surgical approach on the histology of the femoral head following resurfacing of the hip.

METHODS

We performed a histological assessment of the bone under the femoral component taken from retrieval specimens of patients having revision surgery following resurfacing of the hip. We compared the number of empty lacunae in specimens from patients who had originally had a posterior surgical approach with the number in patients having alternative surgical approaches.

RESULTS

We found a statistically significant increase in the percentage of empty lacunae in retrieval specimens from patients who had the posterior approach compared with other surgical approaches (p < 0.001).

CONCLUSIONS

This indicates that the vascular compromise that occurs during the posterior surgical approach does have long-term effects on the bone of the femoral head, even if it does not cause overt avascular necrosis. Cite this article: Bone Joint Res 2013;2:200-5.

Patterns of changes in femoral bone mineral density up to five years after hip resurfacing

This is a prospective study of 26 patients (29 hips) on the patterns of change in the Bone Mineral Density (BMD) in various zones of the femoral neck and proximal femur five years after hip resurfacing. We have found that BMD continues to positively change up to five years after hip resurfacing. This was observed primarily in the trochanteric and superior neck regions. In both these regions BMD had decreased by up to 10% at six-weeks and three-months after surgery and then had recovered to preoperative level by one year. A regression analysis to assess the influence of age, gender, BMI, preoperative BMD, component size and orientation revealed that the best predictor of change in BMD at five years in the trochanteric area was acetabular component inclination.

DAP, Macaulay W. Longitudinal evaluation of time related femoral neck narrowing after metal-on-metal hip resurfacing

AIM: To track the short-term neck narrowing changes in Birmingham metal-on-metal hip resurfacing (MOMHR) patients.

METHODS: Since 2001, the Center for Hip and Knee Replacement started a registry to prospectively collect data on hip and knee replacement patients. From June 2006 to October 2008, 139 MOMHR were performed at our center by two participate surgeons using Birmingham MOMHR prosthesis (Smith Nephew, United States). It is standard of care for patients to obtain low, anteriorposterior (LAP) pelvis radiographs immediately after MOMHR procedure and then at 3 mo, 1 year and 2 year follow up office visits. Inclusion criteria for the present study included patients who came back for follow up office visit at above mentioned time points and got LAP radiographs. Exclusion criteria include patients who missed more than two follow up time points and those with poor-quality X-rays. Two orthopaedic residency trained research fellows reviewed the X-rays independently at 4 time points, i.e., immediate after surgery, 3 mo, 1 year and 2 year. Neck-to-prosthesis ratio (NPR) was used as main outcome measure. Twenty cases were used as subjects to identify the reliability between two observers. An intraclass correlation coefficient at 0.8 was considered as satisfied. A paired t-test was used to evaluate the significant difference between different time points with P < 0.05 considered to be statistically significant.

RESULTS: The mean NPRs were 0.852 ± 0.056, 0.839 ± 0.052, 0.835 ± 0.051, 0.83 ± 0.04 immediately, 3 mo, 1 year and 2 years post-operatively respectively. At 3 mo, NPR was significantly different from immediate postoperative X-ray (P < 0.001). There was no difference between 3 mo and 1 year (P = 0.14) and 2 years (P = 0.53). Femoral neck narrowing (FNN) exceeding 10% of the diameter of the neck was observed in only 4 patients (5.6%) at two years follow up. None of these patients developed a femoral neck fracture (FNF).

CONCLUSION: Femoral neck narrowing after MOMHR occurred as early as 3 mo postoperatively, and stabilized thereafter. Excessive FNN was not common in patients within the first two years of surgery and was not correlated with risk of FNF.

The distribution of vascular foramina at the femoral head/neck junction: implications for resurfacing arthroplasty

Reaming for resurfacing arthroplasty may endanger the blood supply at the head-neck junction, possibly predisposing to osteonecrosis and femoral neck fracture. The current study hypothesizes that reaming endangers femoral head vasculature. Vascular foramina were identified on 16 cadaveric femora and registered on computed tomographic models. Virtual reaming was performed after templating of resurfacing components. Almost half (41.8%) of foramina was located in the anterosuperior quadrant. Loss of foramina after reaming averaged 28% (P = .03), with up to 34.6% and 33.1% loss in the anterosuperior and posterosuperior quadrants, respectively. Reaming for resurfacing arthroplasty endangers a substantial number of vascular foramina. Notching or malpositioning of components may worsen injury to the vascular supply and could subsequently increase the risk of implant failure.

Early complications of hip resurfacing

There has been a rapid increase in the number of hip resurfacing procedures for the treatment of symptomatic osteoarthritis over the last decade. We examine our early complications associated with this procedure. Eight hundred forty consecutive hip resurfacing procedures by 1 surgeon using 1 prosthesis were assessed. The complications seen within the first 12-month postoperative period were analyzed. Specific patient selection criteria were used. Complications such as loosening, femoral neck notching, femoral neck fracture, deep vein thrombosis, stress fracture, nerve palsy, and infection were noted. Complications linked with loosening were categorized to either the femoral or acetabular component. A total of 86 early complications were observed in the 840 resurfacings. Twenty-three (2.7%) required operative intervention, and 10 (1.2%) were converted to stemmed hip arthroplasties. Of these 86 complications, the most common complication was deep vein thrombosis, 19 instances (2.26% occurrence in 840), followed by femoral neck fracture, 11 (1.31%); infection, 10 (1.19%); femoral notching, 10 (1.19%); transient nerve palsy, 8 (0.95%); acetabular loosening, 6 (0.71%); hematoma, 5 (0.60%); and stress fracture, 4 (0.48%). The fractures occurred mostly in patients older than 60 years.

Scintigraphic assessment of bone status at one year following hip resurfacing: Comparison of two surgical approaches using SPECT-CT scan

Objectives

To study the vascularity and bone metabolism of the femoral head/neck following hip resurfacing arthroplasty, and to use these results to compare the posterior and the trochanteric-flip approaches.

Methods

In our previous work, we reported changes to intra-operative blood flow during hip resurfacing arthroplasty comparing two surgical approaches. In this study, we report the vascularity and the metabolic bone function in the proximal femur in these same patients at one year after the surgery. Vascularity and bone function was assessed using scintigraphic techniques. Of the 13 patients who agreed to take part, eight had their arthroplasty through a posterior approach and five through a trochanteric-flip approach.

Results

One year after surgery, we found no difference in the vascularity (vascular phase) and metabolic bone function (delayed phase) at the junction of the femoral head/neck between the two groups of patients. Higher radiopharmaceutical uptake was found in the region of the greater trochanter in the trochanteric-flip group, related to the healing osteotomy.

Conclusions

Our findings using scintigraphic techniques suggest that the greater intra-operative reduction in blood flow to the junction of the femoral head/neck, which is seen with the posterior approach compared with trochanteric flip, does not result in any difference in vascularity or metabolic bone function one year after surgery.

Metabolic development of necrotic bone in the femoral head following resurfacing arthroplasty. A clinical [18F]fluoride-PET study in 11 asymptomatic hips

BACKGROUND AND PURPOSE

One concern regarding resurfacing arthroplasty is the viability of the diminished femoral head and the postoperative risk of collapse, or a femoral neck fracture. (18)F-fluoride positron emission tomography (F-PET) enables us to assess bone viability despite there being a covering metal component. By F-PET studies, we recently showed the absence of metabolism in the remaining part of femoral heads, 1-4 years after surgery in 11 of 46 consecutive cases. We now present the further development of bone metabolism in these 11 cases.

PATIENTS AND METHODS

10 patients (11 chips) with previously shown loss of femoral head metabolism were evaluated by radiography and repeated F-PET scans, 3-6.5 years after surgery. The size of the area with low (18)F-fluoride PET uptake in the femoral head was compared to that in earlier PET images.

RESULTS

No patients had any clinical symptoms; nor was any necrotic bone area visible in plain radiographs. On F-PET scans, 2 patients showed a diminished area with low uptake, 4 were unchanged, and 5 had enlarged areas.

INTERPRETATION

Bone metabolism surrounding a volume of bone with no metabolic activity changes dynamically even 5 years after surgery. The presence of bone with minor uptake of F-tracer, indicating low or no bone metabolism, with further progression in 5 of 11 cases leads us to conclude that resurfacing THA should be used restrictively.

Maximum temperatures of 89°C recorded during the mechanical preparation of 35 femoral heads for resurfacing

BACKGROUND AND PURPOSE

We noticed that our instruments were often too hot to touch after preparing the femoral head for resurfacing, and questioned whether the heat generated could exceed temperatures known to cause osteonecrosis.

PATIENTS AND METHODS

Using an infra-red thermal imaging camera, we measured real-time femoral head temperatures during femoral head reaming in 35 patients undergoing resurfacing hip arthroplasty. 7 patients received an ASR, 8 received a Cormet, and 20 received a Birmingham resurfacing arthroplasty.

RESULTS

The maximum temperature recorded was 89°C. The temperature exceeded 47°C in 28 patients and 70°C in 11. The mean duration of most stages of head preparation was less than 1 min. The mean time exceeded 1 min only on peripheral head reaming of the ASR system. At temperatures lower than 47°C, only 2 femoral heads were exposed long enough to cause osteonecrosis. The highest mean maximum temperatures recorded were 54°C when the proximal femoral head was resected with an oscillating saw and 47°C during peripheral reaming with the crown drill. The modified new Birmingham resurfacing proximal femoral head reamer substantially reduced the maximum temperatures generated. Lavage reduced temperatures to a mean of 18°C.

INTERPRETATION

11 patients were subjected to temperatures sufficient to cause osteonecrosis secondary to thermal insult, regardless of the duration of reaming. In 2 cases only, the length of reaming was long enough to induce damage at lower temperatures. Lavage and sharp instruments should reduce the risk of thermal insult during hip resurfacing.

Anatomy of the medial femoral circumflex artery with respect to the vascularity of the femoral head

We performed a series of 16 anatomical dissections on Caucasian cadaver material to determine the surgical anatomy of the medial femoral circumflex artery (MFCA) and its anastomoses. These confirmed that the femoral head receives its blood supply primarily from the MFCA via a group of posterior superior nutrient arteries and the posterior inferior nutrient artery. In terms of anastomoses that may also contribute to the blood supply, the anastomosis with the inferior gluteal artery, via the piriformis branch, is the most important. These dissections provide a base of knowledge for further radiological studies on the vascularity of the normal femoral head and its vascularity after dislocation of the hip.

Effects of cobalt and chromium ions at clinically equivalent concentrations after metal-on-metal hip replacement on human osteoblasts and osteoclasts: implications for skeletal health

Metal-on-metal hip replacement (MOMHR) using large diameter bearings has become a popular alternative to conventional total hip arthroplasty, but is associated with elevated local tissue and circulating levels of chromium (Cr) and cobalt (Co) ions that may affect bone health. We examined the effects of acute and chronic exposure to these metals on human osteoblast and osteoclast formation and function over a clinically relevant concentration range previously reported in serum and within hip synovial fluid in patients after MOMHR. SaOS-2 cells were cultured with Co(2+), Cr(3+) and Cr(6+) for 3 days after which an MTS assay was used to assess cell viability, for 13 days after which alkaline phosphatase and cell viability were assessed and for 21 days after which nodule formation was assessed. Monocytes were isolated from human peripheral blood and settled onto dentine disks then cultured with M-CSF and RANKL plus either Co(2+), Cr(3+) or Cr(6+) ions for 21 days from day 0 or between days 14 and 21. Cells were fixed and stained for TRAP and osteoclast number and amount of resorption per dentine disk determined. Co(2+) and Cr(3+) did not affect osteoblast survival or function over the clinically equivalent concentration range, whilst Cr(6+) reduced osteoblast survival and function at concentrations within the clinically equivalent serum range after MOMHR (IC(50) =2.2 μM). In contrast, osteoclasts were more sensitive to metal ions exposure. At serum levels a mild stimulatory effect on resorption in forming osteoclasts was found for Co(2+) and Cr(3+), whilst at higher serum and synovial equivalent concentrations, and with Cr(6+), a reduction in cell number and resorption was observed. Co(2+) and Cr(6+) within the clinical range reduced cell number and resorption in mature osteoclasts. Our data suggest that metal ions at equivalent concentrations to those found in MOMHR affect bone cell health and may contribute to the observed bone-related complications of these prostheses.

Assessment of femoral neck fracture risk for a novel proximal epiphyseal hip prosthesis

BACKGROUND

This study addresses the risk of femoral neck fracture associated with resurfacing hip prostheses. A novel cemented Proximal Epiphyseal Replacement (PER) featuring a short curved stem was investigated.

METHODS

Seven pairs of femurs were in vitro tested. One femur of each pair was randomly assigned for PER implantation. The contralateral femur was tested intact. All femurs were loaded to failure in a validated, physiological configuration. High-speed videos (10,000-12,000 frames/s) were acquired to identify the location of fracture initiation. For comparison, data were included from Birmingham Hip Resurfacing previously tested in an identical fashion (N=3).

FINDINGS

Relative to the contralateral intact femurs, the failure load of the PER and Birmingham implants was 15.4% higher and 10.0% lower, respectively. In six of the seven PER implants, fracture initiation (neck or inter-trochanteric) was similar to the contralateral intact femurs, suggesting comparable stress distribution. Conversely, fracture initiation in the Birmingham implants occurred at the lateral prosthesis rim, which differed substantially from the intact femurs. No correlation existed between bone quality and strengthening/weakening effect of the PER (failure load of implant as a percentage of intact: R^2=0.067). Conversely, Birmingham implantation weakened the femurs with lower density (R^2=0.92). Therefore, unlike most resurfacing prostheses, the PER seems suitable also for osteoporotic subjects.

INTERPRETATION

This study seems to confirm that resurfacing with a Birmingham Hip tends to reduce the strength of the proximal femur. The opposite seemed to happen with the PER, which slightly reduced the risk of neck fracture, also in low-quality bones.

Femoral head viability following resurfacing arthroplasty. A clinical positron emission tomography study

Hip resurfacing (HR) carries attendant risks of avascular necrosis (AVN) and femoral neck fracture. We used fluoride positron emission tomography (PET) scans to analyze bone metabolism 2-5 years after surgery in 35 cases. Three of the patients had been clinical failures. Using PET scans in the remaining 32 cases, 7 were found to have an area of non-viable bone in the femoral head. This was seen following both posterior and antero lateral approaches. Fluoride PET is a sensitive and useful method for evaluating bone metabolism following HR.

Bone mineral density of the proximal femur after hip resurfacing arthroplasty: 1-year follow-up study

Background

Hip resurfacing arthroplasty (HRA) is considered a bone-preserving procedure and may eliminate proximal femoral stress shielding and osteolysis. However, in addition to implant-related stress-shielding factors, various patient-related factors may also have an effect on bone mineral density (BMD) of the proximal femur in patients with HRA. Thus, we studied the effects of stem-neck angle, demographic variables, and physical functioning on the BMD of the proximal femur in a one-year follow-up.

Methods

Thirty three patients (9 females and 24 males) with a mean (SD) age of 55 (9) years were included in the study. BMD was measured two days and 3, 6, and 12 months postoperatively and 10 regions of interest (ROI) were used. Stem-neck angle was analyzed from anteroposterior radiographs.

Results

Three months postoperatively, BMD decreased in six out of 10 regions of interest (ROI) on the side operated on and in one ROI on the control side (p < 0.05) compared to the second postoperative day. At 12 months, BMD had increased in 7 ROIs on the operated side and one ROI on the control side (all p < 0.001). Correlation was found between the stem-neck angle and BMD in ROIs 2, 3, 7, and 9 (r = 0.36 - 0.61). In multiple regression analysis, stem-neck angle, age, sex, body mass index, and walking distance did not explain the BMD changes.

Conclusions

After an early drop, the BMD of the upper femur was restored and even exceeded the preoperative level at one year follow-up. From a clinical standpoint, the changes in BMD in these HRA patients could not be explained by stem-neck angle or patient related factors.

Narrowing of the femoral neck after resurfacing arthroplasty of the hip: a comparison of cemented and uncemented femoral components

We performed a radiographic review of a consecutive series of 87 resurfacing arthroplasties of the hip, performed between 2004 and 2006. There were 54 cemented femoral components and 33 uncemented femoral components. All of the procedures were performed by the same surgeon using the same approach. There was no difference between the groups with regards to gender, age, pre-operative diagnosis and the average diameter of the components. The primary outcome measured was the neck-prosthesis ratio on standard anterior-posterior pelvis radiographs taken post-operatively and at a minimum follow up of two years. The difference between the immediate post-operative ratio and the most recent radiograph was statistically significant in patients with cemented femoral components (p=0.006), but not in the group with uncemented components (p=0.173). We have demonstrated a difference in narrowing of the femoral neck between cemented and uncemented femoral components in the first two years following surgery.

A modified posterior approach preserves femoral head oxgenation during hip resurfacing

In 11 patients, the oxygenation was measured in the superolateral quadrant of the femoral head during resurfacing with a modified posterior approach, designed to preserve the blood supply, using a gas-sensitive electrode. These were compared with measures from 10 patients in whom the standard posterior approach was used. The modified approach patients maintained a significantly (P < .005) higher amount of relative oxygenation after the approach, 78% (standard deviation [SD], 45%) vs 38% (SD, 26%), and acetabular component implantation, 74% (SD, 56%) vs 20% (SD, 28%). The modified posterior approach, unlike the standard extended approach, does not significantly compromise the blood supply to the head; and we recommend this approach be considered for hip resurfacing.

Femoral-head vascularity after hip surface arthroplasty

BACKGROUND

iatrogenic devascularization of the femoral head is as an area of concern following hip resurfacing arthroplasty, with probable implications on short-term failure and long-term survival of the implant.

MATERIALS AND METHODS

we assessed the vascularity of 25 resurfaced femoral heads in 20 patients by comparison with preoperative and postoperative Tc-99m methylene diphosphonate (MDP) bone scintigraphy images, the postoperative scans being done 9 months after the surgery.

RESULTS

eight out of 25 hips (32%) showed <55% of their preoperative uptake at a mean of 9 months after surgery and were categorized as showing reduced vascularity.

CONCLUSION

our study reveals reduction in vascularity of the femoral-head remnant as a frequent occurrence after hip resurfacing. Our study also highlights the role of bone scintigraphy as tool in assessing the vascularity of resurfaced femoral heads.

Audit-induced change reduces complications of the Ganz trochanteric flip approach

INTRODUCTION

The Ganz trochanteric flip approach aims to avoid the potential risk of avascular necrosis in hip conserving surgery and may reduce the risk of femoral neck fractures, neck thinning and femoral head implant migration in hip resurfacing. Our initial audit revealed the complications of non-union and trochanteric screw irritation to be associated with this approach. We, therefore, modified our selection criteria and re-audited our results.

SUBJECTS AND METHODS

The initial audit (IA) ran between January 2003 and November 2007 after which an age limit of 50 years was recommended. The re-audit (RA) ran between November 2007 and December 2008 where one of the senior authors stopped using the approach in the over 50 year age group whilst the other senior author continued on selected patients over 50 years.

RESULTS

There were 545 hips in the IA and 152 hips in the RA group. The incidence of non-union decreased in the RA after the change of selection criteria (6.2% [IA] vs 1.3% [RA]). In both audit groups, the incidence of non-union increased with age, and in the RA no non-unions were observed under the age of 50 years. The incidence of screw irritation and the necessity for removal remained relatively unchanged (20.7% [IA] vs 28.3% [RA]) with a combined incidence of 22.4%.

CONCLUSIONS

The trochanteric flip approach to the hip can be used safely with an acceptable complication rate in young adult impingement and resurfacing surgery. Caution must, however, be exercised in patients over 50 years of age as they have a higher incidence of trochanteric non-union. In addition, all patients should be consented for the possibility of screw removal as a second procedure.

Avascular necrosis associated with fracture of the femoral neck after hip resurfacing: histological assessment of femoral bone from retrieval specimens

The cause of fracture of the femoral neck after hip resurfacing is poorly understood. In order to evaluate the role of avascular necrosis we compared 19 femoral heads retrieved at revision for fracture of the femoral neck and 13 retrieved for other reasons. We developed a new technique of assessing avascular necrosis in the femoral head by determining the percentage of empty osteocyte lacunae present. Femoral heads retrieved as controls at total hip replacement for osteoarthritis and avascular necrosis had 9% (sd 4; n = 13) and 85% (sd 5; n = 10, p < 0.001) empty lacunae, respectively. In the fracture group the percentage of empty lacunae was 71% (sd 22); in the other group it was 21% (sd 13). The differences between the groups were highly significant (p < 0.001). We conclude that fracture after resurfacing of the hip is associated with a significantly greater percentage of empty osteocyte lacunae within the trabecular bone. This indicates established avascular necrosis and suggests that damage to the blood supply at the time of surgery is a potent risk factor for fracture of the femoral neck after hip resurfacing.

Hip resurfacing through a modified anterolateral approach, as compared with the Ganz trochanteric flip osteotomy: a two year follow-up study

Hip resurfacing arthroplasty has conventionally been undertaken through the posterior approach. There has been evidence in the recently published literature to suggest that the posterior approach may compromise the blood supply to the femoral head, by disruption of the posterolateral hip capsule. Ganz et al have proposed the trochanteric 'flip' osteotomy through a lateral approach, to permit surgical dislocation of the hip without damaging the blood supply. The disadvantages, however, are that early full weight bearing is not permitted and there is an incidence of trochanteric delayed or non-union, which may require further treatment. We describe a technique of hip resurfacing through a modified anterolateral approach preserving the posterolateral capsular blood supply. We describe our experience using this approach, and compare the results with our previously used Ganz trochanteric osteotomy. At a mean follow-up of two years, the outcome scores were not significantly different, and both groups had similar abductor strength. There were two cases of delayed union in the Ganz group, one of which required revision; there were no complications in the modified anterolateral group.

The influence of the size of the component on the outcome of resurfacing arthroplasty of the hip

The survivorship of contemporary resurfacing arthroplasty of the hip using metal-on-metal bearings is better than that of first generation designs, but short-term failures still occur. The most common reasons for failure are fracture of the femoral neck, loosening of the component, osteonecrosis of the femoral head, reaction to metal debris and malpositioning of the component. In 2008 the Australian National Joint Registry reported an inverse relationship between the size of the head component and the risk of revision in resurfacing hip arthroplasty. Hips with a femoral component size of ≤ 44 mm have a fivefold increased risk of revision than those with femoral components of ≥ 55 mm irrespective of gender. We have reviewed the literature to explore this observation and to identify possible reasons including the design of the implant, loading of the femoral neck, the orientation of the component, the production of wear debris and the effects of metal ions, penetration of cement and vascularity of the femoral head. Our conclusion is that although multifactorial, the most important contributors to failure in resurfacing arthroplasty of the hip are likely to be the design and geometry of the component and the orientation of the acetabular component.

Hip resurfacing arthroplasty: a review of the evidence for surgical technique, outcome, and complications

Hip resurfacing arthroplasty has reemerged as a valid reconstruction option for the osteoarthritic hip. Patient selection is critical for excellent surgical outcomes, especially when compared with total hip arthroplasty. However, concerns regarding surgical technique and postsurgical complications persist. The authors review the evidence for surgical technique, outcomes, and complications related to modern metal-on-metal hip resurfacing arthroplasty.

Association of osteonecrosis and failure of hip resurfacing arthroplasty

Osteonecrosis (ON) has been reported in femoral remnants removed after failure of hip resurfacing arthroplasty. Experimental and clinical studies have further described thermal effects of the cementation technique, damage of extraosseous blood vessels, and intraoperative hypoxemia as possible causative factors. We analyzed histologically a series of 123 retrieved specimens with a preoperative diagnosis other than ON to investigate the incidence and extent of advanced ON. ON was found in 88% of cases and associated with 60% (51 of a total of 85) of periprosthetic fractures. The fracture incidence correlated with the extent of ON. Collapse of necrotic tissue in three (2%) cases resulted in disconnection of the bone stock-femoral component. We observed smaller regions of superficial ON in the majority of the remaining femoral remnants with periprosthetic fractures and in hips that failed for reasons other than fracture.

The vascular network in the femoral head and neck after hip resurfacing

The purpose of this study was to determine whether femoral neck fracture after cemented resurfacing hip arthroplasty (RHA) arises from intraosseous vascularity around the femoral head-neck junction. We implanted a replica of the femoral head component into osteoarthritic femoral heads and compared the intraosseous vascularity network between the femoral heads with and without the RHA procedure using microangiography through a retinacular artery with micro-computed tomography. Our results showed no significant difference in the vascularity around the femoral head-neck junction between the groups with and without the RHA procedure. These results suggest that deterioration of the intraosseous vascular network around the head-neck junction after RHA was not severe enough to induce complete avascularity.

Osteonecrosis following resurfacing arthroplasty

BACKGROUND AND PURPOSE

One of the main concerns regarding resurfacing arthroplasty is the viability of the remaining part of the femoral head, and the postoperative risk of a femoral neck fracture or collapse. In contrast to radiographic methods, positron emission tomography using the radiotracer [18F]-fluoride (Fluoride-PET) enables us to visualize the viability of bone in the remaining part of the head, despite the presence of the covering metal component.

PATIENTS AND METHODS

This is preliminary prospective study of 14 patients who underwent an ASR resurfacing arthroplasty. Apart from clinical and radiographic analyses, all patients were analyzed by PET scan 1 week, 4 months, and 1 year after surgery.

RESULTS

1 patient had a minor region of osteonecrosis on PET scan at 1 week and at 4 months. After 1 year, the necrosis had increased to include most of the head. 2 other patients, normal at 4 months, had developed equally large osteonecrosis at 1 year. A fourth patient had a minor osteonecrosis at 1 year. None of the patients had clinical symptoms, and the necrotic areas were not visible on plain radiographs.

CONCLUSIONS

We found Fluoride PET to be a sensitive and useful method for evaluation of bone metabolism at resurfacing arthroplasty. 3 of the 14 patients had developed osteonecrosis, involving most of the head at 1 year. The late onset of the phenomenon does not support the hypothesis of surgically damaged vascularity. The presence of this complication together with the lack of visibility on plain radiographs gives reason for concern.

Bone density of the femoral neck following Birmingham hip resurfacing

BACKGROUND

Resurfacing is a popular alternative to a standard hip replacement in young arthritic patients. Despite bone preservation around the femoral component, there is little information regarding the bone quality.

PATIENTS AND METHODS

32 patients underwent consecutive Birmingham hip resurfacing. The bone density of the femoral neck was measured preoperatively and then at 6 weeks, 3 months, 1 year, and 2 years. The femoral neck was divided into regions of interest. Results were available for 27 hips in 26 patients.

RESULTS

The overall femoral neck bone density showed a trend towards a decrease at 6 weeks and 3 months but returned to the preoperative level at 1 year, and was maintained at 2 years. The combined superior regions of the neck showed a statistically significant decrease in bone density at 6 weeks and 3 months. This returned to preoperative levels at 1 year and was maintained at 2 years.

INTERPRETATION

Bone density appears to decrease at 6 weeks and 3 months, suggesting that care is necessary until bone density begins to recover.

Evaluation of a new fluoroscopy-based navigation system in the placement of the femoral component in hip resurfacing

Prosthesis-specific mechanical alignment instruments for the precise and reproducible positioning of the femoral component constitute one of the major improvements in modern hip resurfacing prostheses. However, mechanical failure of the femoral component is mostly attributable to the surgical technique, and in particular to notching of the femoral neck. In order to evaluate a novel computer-assisted fluoroscopy-based planning and navigation system, six DUROMTM hip resurfacing prostheses were implanted into artificial femurs by means of computer-assisted fluoroscopy-based navigation and prosthesis-specific mechanical alignment instruments. Subsequently, the planning and navigation system was tested within the scope of a cadaver study on three fixed whole-body preparations (six femurs). The average difference between planned and actual angle of the prosthesis was 0±0.7° for fluoroscopy-based navigation versus 6.5±7.8° for the in-vitro use of the prosthesis-specific mechanical alignment instruments, and 1±1.4° for fluoroscopic navigation in the cadaver study. The average discrepancy between planned and actual anterior offset was −1.2±1.2 mm versus 0.8±4 mm, and 0.3±2.2 mm in the cadaver study, and the time required for the total of five planning and navigation steps was 17.2±1.5 min versus 14±0.8 min and 20.2±2.5 min respectively. No notching of the femoral neck occurred under fluoroscopy nor under conventional treatment. During in-vitro studies, use of the computer-assisted fluoroscopy-based planning and navigation system resulted in enhanced accuracy compared with conventional prosthesis-specific mechanical alignment instruments. The system has yielded initial promising results within the scope of the cadaver study.

Clinical experience of Ganz surgical dislocation approach for metal-on-metal hip resurfacing

Although the posterior approach is the most commonly used for hip resurfacing, concerns remain in terms of risk of femoral neck fracture secondary to an osteonecrotic event. The purpose of this study was to look at the short-term results of metal-on-metal hip resurfacing done by the vascular-preserving surgical approach as developed by Ganz in 116 hip resurfacing arthroplasties performed in 106 patients (86 men, 20 women; mean age, 46.5 years; range, 19-62). At a mean follow-up of 38.3 months (range, 12-84), Harris Hip Scores improved significantly from 53.1 to 90.16 (P < .001). There were 10 nonunions (8.7%) and 21 hips (18.3%) requiring screw removal for painful bursitis. Two hips underwent conversion to total hip arthroplasty: one at 18 months for femoral loosening and one at 7 years for acetabular loosening. Although the trochanteric slide approach as developed by Ganz provides excellent exposure to the hip joint and preserves femoral head vascularity, it does carry some inherent morbidity in regard to the greater trochanter.