Abstract
There has been a change in emphasis in the oral questions in the last 2 years to higher-order thinking and judgement. Exam revision should be less book reading and more being practical and adept at managing complex clinical conditions. Examiners would argue if you have been well trained in the basics it isn’t too difficult to apply these basic principles to various clinical situations that you may be tested on in the oral exam. If you haven’t managed periprosthetic joint infection (PJI) then it’s going to be doubly difficult to answer the real-life practical questions that are related to managing a patient with this condition.
We have aimed the candidates’ answers for a 7–8 score, so they are significantly more detailed than what would be required for a bare pass. Aiming for the minimum to pass will generally be unsuccessful and is not recommended.
Introduction
There has been a change in emphasis in the oral questions in the last 2 years to higher-order thinking and judgement. Exam revision should be less book reading and more being practical and adept at managing complex clinical conditions. Examiners would argue if you have been well trained in the basics it isn’t too difficult to apply these basic principles to various clinical situations that you may be tested on in the oral exam. If you haven’t managed periprosthetic joint infection (PJI) then it’s going to be doubly difficult to answer the real-life practical questions that are related to managing a patient with this condition.
We have aimed the candidates’ answers for a 7–8 score, so they are significantly more detailed than what would be required for a bare pass. Aiming for the minimum to pass will generally be unsuccessful and is not recommended.
Structured oral examination question 1
EXAMINER: These are the radiographs of a 65-year-old gentleman who had a primary left THA 14 years ago (Figure 3.1a and b). Over the last 2 weeks, he has had increasing pain in the left hip and he has contacted his GP who has referred him back to you on an urgent basis. Postoperatively, he was progressing well, and he has no history of any trauma. He is now unable to weight bear fully on the left leg and has night pain.
CANDIDATE: This is an AP pelvic radiograph showing a left cemented Exeter THA. I am concerned that there is an area of radiolucency around the tip of the greater trochanter. The acetabular component appears well fixed. My worry here is that this gentleman may have a periprosthetic joint infection. Every painful prosthetic joint is potentially infected.
EXAMINER: So how are you going to proceed with this patient?
CANDIDATE: I would want to take the patient to theatre and perform an aspiration of the hip to rule out infection.
EXAMINER: You are sure? Are you not jumping in a bit fast? Is there anything else you might want to find out beforehand?
CANDIDATE: I would want to take a full history from the patient. A number of patients who develop infection have early wound problems such as prolonged redness, induration, swelling or discharge. There may be a history of repeated courses of antibiotics. The wound may have become frankly infected requiring washout in theatre.
Onset of hip pain following a problem-free interval and an episode of sepsis is suggestive of haematogenous seeding of infective organisms from elsewhere. I would enquire if there was a history of bacteraemia from a UTI, chest infection or dental extraction.
Pain from an infected prosthesis is typically non-mechanical and unrelated to physical activity and not relieved by rest.
I would also like to explore more fully host risk factors for infection such as diabetes, rheumatoid arthritis, depression, obesity, hypothyroidism, immunosuppression (steroids, DMARDs), smoking and poor dentition. Lifestyle factors such as heavy alcohol intake and smoking.
Having taken a full history, I would perform a comprehensive clinical examination, looking at the scar for any evidence of infection such as erythema, warmth, a sinus, etc. What is the hip ROM and is there pain associated with ROM? I would also like to examine the abdomen, knee and lumbar spine to exclude other potential sources of haematogenous infection/cause for the hip pain. I would then request an FBC, CRP and ESR to look for evidence of raised inflammatory markers.
EXAMINER: How helpful are these?
CANDIDATE: They have relatively low sensitivity and low specificity as markers of prosthetic joint infection. Berbari et al. (level 2) published a systematic review in the JBJS American edition in 2010 on the use of inflammatory markers for diagnosis of prosthetic joint infection.1 They concluded that IL-6 is a much more sensitive test for infection. Unfortunately, IL-6 assays are not readily available in most NHS hospitals and certainly not in my trust at present.
CANDIDATE: The association between diabetes and PJI may be mediated by impaired leukocyte function and microvascular complications which may impair wound healing.
In addition, factors associated with diabetes, such as hyperglycaemia, hyperlipidaemia, hypertension and increased oxidative stress, upregulate cellular and inflammatory reactions and play a part in atherothrombosis that may cause impaired wound healing. Hyperglycaemia has also been shown to increase biofilm formation.
EXAMINER: The paper actually reported that IL-6 was more accurate than CRP or ESR rather than sensitive. The wound was oozy postoperatively but settled down. A large part of picking up periprosthetic infection is obtaining a good history and examination along with a high index of clinical suspicion.2
Figure 3.1a and 3.1b Anteroposterior (AP) pelvis and lateral radiographs demonstrating a left Exeter THA.
CANDIDATE: Spangehl et al. (level 1) demonstrated a sensitivity of 0.86, a specificity of 0.94, a positive predictive value of 0.67 and a negative predictive value of 0.98 with initial image-guided aspiration in 180 patients undergoing revision hip arthroplasties.3 They reported that aspiration alone is not sufficient for the diagnosis because of the risk of false positive and false negative results. They suggested that aspiration was not necessary in low-probability cases with a normal ESR and CRP. Aspiration would be indicated if pretest probability for infection was high (acute onset of pain, systemic illness, sinus formation), particularly if the CRP/ESR was normal, or in all cases where the CRP or ESR was high. A normal CRP and ESR does not always exclude a PJI, however.
EXAMINER: How would you perform a hip aspiration?
CANDIDATE: I would perform this in theatre under II control. I would fully prepare and drape the skin. I would incise the skin with a small nick to minimize the risk of skin contamination and also perform two separate aspirations to reduce the risk of false positives. If both are positive with the same organism this would be suggestive of infection.
EXAMINER: What about if one aspirate only is positive?
CANDIDATE: If only one aspirate is positive then it is a tricky situation. It is a soft positive result and I think it would be reasonable to repeat hip aspiration 2 weeks later.
EXAMINER: Joint aspiration did not grow any organisms after 48 h of culture. Is there anything else you may wish to consider in terms of establishing a diagnosis of a periprosthetic joint infection?
CANDIDATE: 48 h for bacterial culture may not be long enough to identify certain bacteria. For example, low-virulence organisms such as Propionibacterium acnes may take up to 2 weeks to culture successfully. I would speak to the microbiology lab and make sure they are performing extended cultures on the material sent.
EXAMINER: Isn’t that normal for most labs to do?
CANDIDATE: My own local hospital policy is to perform extended culture for 5 days on any suspected PJI, but I am not sure if this has been universally agreed on. I would speak to the microbiology lab regardless to make sure I was notified promptly if extended culture grew any organism as this may significantly change my management plans. Synovial fluid culture has a sensitivity of 52% and specificity of 95%. Sensitivity at 52% is poor.
The differential white cell count from synovial fluid analysis is useful in diagnosing a PJI. For hips, a WCC > 4200/μl and/or a granulocyte percentage > 80% has a sensitivity of 85% and a specificity of 90%. I realize there are some difficulties getting the microbiology department to perform regular counts. Pus swabs are not regarded as useful anymore.
The Gram stain itself has a very low sensitivity (< 25%). Use of antibiotics prior to the aspiration of the hip joint can lead to reduced sensitivity of the synovial fluid analysis. Ideally, any antibiotics the patient is still on should be discontinued for up to 2 weeks in order to improve the pick-up rate of any synovial fluid culture.
There are modern biomarkers such as α-defensin (Synovasure, Zimmer Biomet), neutrophil elastase 2 (ELA2), bactericidal/permeability increasing protein, neutrophil gelatinase-associated lipocalin (NGAL) and lactoferrin which have recently shown promise in diagnosing PJI, but there are still no reliable data to prove their sensitivity and specificity to date.4 One potential advantage of such biomarkers is the fact that they are not reliant on the bacteria and, therefore, pre-administered antibiotics should not affect their sensitivity. Synovial tissue biopsy can also be taken which can improve the sensitivity of microbiological culture and samples should also be sent for histology. A minimum of three tissue samples should be taken and ideally more than six samples.
Neutrophil granulocytes are indicators of bacterial infections (in acute infections). Leucocyte esterase has been shown as being as sensitive and specific as Synovasure and much more cost effective.
EXAMINER: Are there any other tests you might want to perform that could diagnose infection before going ahead with surgery?
CANDIDATE: The use of nuclear imaging (technetium-99 triple-phase bone scan, gallium imaging, labelled-leukocyte scans or FDG-PET imaging) for the detection of periprosthetic joint infection is worth considering but controversial. The AAOS clinical practice guidelines summary from 2010 reported a weak recommendation for their use.5,6
COMMENT: It may be enough just to mention the uncertainties with nuclear imaging or you may have to quantify your answer more fully. It is a judgement decision, but don’t persist with your answer if the examiners want to move on. Technetium-99 bone scans are sensitive but not specific. Some investigators have found that a negative scan rules out infection, others report that a scan can occasionally be negative with infection if there is inadequate blood supply to the bone. A technetium-99m bone scan identifies areas of increased bone activity through preferential uptake of the diphosphonate by metabolically active bone. Increased uptake occurs with loosening, infection, heterotopic bone formation, Paget’s disease, stress fractures, modulus mismatch of a large uncemented stem, neoplasm, reflex sympathetic dystrophy and other metabolic conditions. In the uncomplicated THA, uptake around the lesser trochanter and shaft is usually insignificant by 6 months, but in 10% of cases, uptake may persist at the greater trochanter, prosthesis tip and acetabulum for more than 2 years. The pattern of uptake has not been found to consistently reflect the presence or absence of infection. Gallium imaging likewise has a poor sensitivity and accuracy. The use of leukocyte scans is generally preferred, having a higher sensitivity (88–92%) and specificity (73–100%), but their usefulness for the diagnosis of infection continues to be debated. FDG-PET is expensive and limited to a few institutions, and although very sensitive does not allow differentiation between an inflamed aseptically loosened prosthesis and an infected one.
CANDIDATE: Tsukayama et al. proposed a four-stage system consisting of early postoperative, late chronic, and acute hematogenous infections, and positive intraoperative cultures of specimens obtained during revision of a presumed aseptically loose THA.7,8
Early postoperative infection presents less than 1 month after surgery with a febrile patient and a red swollen discharging wound. With late postoperative infection, the patient is well, the wound has healed well, there is a worsening of hip pain and a never pain-free interval. Acute haematogenous infection can occur several years after surgery with a history of bacteraemia (UTI or other source of infection) and severe hip pain in a previously well-functioning hip. Positive intraoperative culture (at least three samples from different locations taken with clean instruments) occurs when a preoperative presumptive diagnosis of aseptic loosening was made.
McPherson et al. have also developed a staging system for periprosthetic hip infections that included three categories: infection type (acute versus chronic), the overall medical and immune health status of the patient, and the local extremity (wound) grade.9
EXAMINER: How do you diagnose PJI?
CANDIDATE: I would use the criteria of the musculoskeletal infection society. PJI can be diagnosed when one out of two major and four out of six minor criteria exist (Table 3.1).
Major criteria are (1) a sinus tract communicating with the prosthesis and (2) two positive periprosthetic cultures with phenotypically identical organisms.
A pathogen is isolated by culture from at least two separate tissue or fluid samples obtained from the affected prosthetic joint.
The six minor criteria are (1) elevated ESR and CRP, (2) elevated synovial leukocyte count, (3) elevated synovial neutrophil percentage (PMN%), (4) presence of purulence in the affected joint, (5) single positive culture, (6) positive histological analysis of periprosthetic tissue.
PJI may be present if fewer than four of these criteria are met.
COMMENT: The MSIS criteria were modified in 2013. Essentially three from five minor criteria (Table 3.1).
EXAMINER: How will you manage this patient assuming that your diagnosis of an acute PJI is now made?
CANDIDATE: As the diagnosis of a PJI has been made within 2 weeks and assuming that there are positive microbiological results with a known organism and sensitivities to antimicrobial therapy, there remains the option of undertaking a DAIR-type procedure. DAIR stands for Debridement, Antibiotics and Implant Retention, in which the prosthesis is retained with exchange of any mobile components such as a liner and head exchange while keeping the acetabular socket and stem in place. A DAIR should only be undertaken if the PJI is acute and ideally within 3 weeks of the PJI starting, although some units such as Oxford will undertake a DAIR at up to 6 weeks or so. The optimum management of a PJI involves a multidisciplinary team approach with MSK radiologists, bone infection microbiologists, histopathologists, plastic surgeons and experienced revision arthroplasty surgeons with a specialist interest in managing PJIs. The success rate of DAIR procedures is around 90–95%.10 The Oxford group have recently published a case control study comparing DAIR versus a two-stage revision and showed a 98% 5-year survivorship rate with DAIR and better outcome with DAIR.11
EXAMINER: This patient had a delay in diagnosing the PJI and was only seen 2 months after the onset of their clinical presentation. How would you manage the patient now?
CANDIDATE: The patient is now outside the window of opportunity to undertake a DAIR. If there was a microbiological result with a known organism and sensitivities, then a single-stage revision could be undertaken, especially if the patient had multiple comorbidities and the surgical stress of having a two-stage procedure might compromise the patient. In this case, it is critical that all cement is removed as well as all the components and a thorough debridement with complete excision of infected soft tissues is undertaken.
EXAMINER: What are the prerequisites for a one-stage procedure?
CANDIDATE: Prerequisites include a known organism sensitive to antibiotics, no pus present, elderly patients or patients with multiple medical problems. It is also indicated in healthy individuals devoid of re-infection risk who have adequate bone and soft tissue for reconstruction and a low-virulence pathogen.
EXAMINER: What are the reported success rates for a single-stage revision?
CANDIDATE: Buchholz et al., who pioneered one-stage revisions at the Endo-Klinic in Hamburg, reported a success rate of 77% in 583 revisions, but only after extensive bone and soft-tissue resection, which compromised long-term function.12 These results were published in 1981 and can be viewed as somewhat historic now. Raut et al. from Wrightington reported a success rate of 86% in 57 cases at average follow-up of 7 years despite many discharging sinuses.13,14 Hanssen and Rand summarized the results of single-stage exchange and found a cumulative success rate of 83% when antibiotic-loaded cement was used, but only 60% when it was not.15 A recent RCT has been started to compare a single- versus two-stage revision.16 In 11 studies with 1225 patients with a hip PJI receiving exclusively one-stage revision, the rate of re-infection at 2 years was 8.6% (95% CI 4.5–13.9). After two-stage revision exclusively in 28 studies with 1188 patients, the rate of re-infection at 2 years was 10.2% (95% CI 7.7–12.9). The authors conclude that on the basis of a systematic review of published data, there is no difference in the re-infection rate between one-stage and two-stage revision THA for PJI.
EXAMINER: What are the advantages to performing a two-stage procedure?
CANDIDATE: It is particularly important to perform a two-stage revision with more severe infections or virulent organisms, as the success rate of a single-stage procedure is much less in these situations.
EXAMINER: That’s not what I asked.
CANDIDATE: It is more versatile for reconstruction allowing the use of either cemented or cementless components and bone allograft in patients with severe bone loss. It allows clinical assessment of the response to antibiotics prior to re-implantation.
EXAMINER: What are the disadvantages of a two-stage procedure?
CANDIDATE: It can be difficult to nurse patients between stages and the second-stage surgery can be difficult due to soft-tissue scarring, limb shortening, disuse atrophy, loss of bone density and distortion of anatomy.
EXAMINER: Have a look at this radiograph below (see Figure 3.1c). What is going on with the right hip?
CANDIDATE: This is a cement spacer in a patient who has had a first-stage revision for infection and an articulating cement spacer such as a PROSTALAC spacer has been used. The potential complications of using such a spacer are that it can dislocate or fracture and it costs more money to perform a two-stage procedure. An alternative would be to use a nail or multiple wires with cement coating around the wires to act as a temporary spacer. There is also the option of loosely cementing a THA in place (using a polished tapered stem and cementing a liner for the socket) ((The “Kiwi” Prostalac)) which has the advantage of allowing the patient to mobilize full weight bearing postoperatively and, if necessary, the THA spacer could be left in more permanently if the patient’s medical condition precludes further surgery or the patient decided against second-stage revision.
EXAMINER: So, you perform the first-stage revision, how long will you keep the patient on antibiotics?
CANDIDATE: The duration of antibiotic treatment and timing between stages remains controversial. Current practice suggests delaying the second stage for at least 6 weeks pending good clinical progress with antibiotics and wound healing. A number of surgeons re-implant at 3 months, treating the patient with 6 weeks antibiotics and then a further 6 weeks without antibiotics, regularly monitoring the CRP/ESR for any signs of elevation and checking clinical progress for any signs of reoccurrence of infection such as sinus discharge or increasing hip pain. Antimicrobial therapy will be guided by the microbiology advice given and this is why the management of PJI is best undertaken as part of an MDT review. In general, however, 2 weeks of targeted intravenous antibiotics followed by a further 4 weeks or so of oral antibiotics is the norm.
CANDIDATE: Stop operating and investigate. I would undertake a root-cause analysis to identify the source or cause of these infections.
EXAMINER: Go on.
CANDIDATE: I would want to know if the same organism had been identified in the five cases, particularly if the organism was Staphylococcus aureus as this may suggest a nasal carrier in theatre. Nasal swab cultures would need to be taken of relevant theatre staff and appropriate treatment started.
We would want to investigate for a breakdown in theatre sterility. I would involve microbiology and investigate the laminar flow system to see if it was correctly working.
There may be issues with the preparation of the instruments set such as packaging integrity and expiry date. A sterilization indicator should be present, and the packaging must be dry.
There may be a breakdown in the precautions that must be taken by the scrub practitioner during the procedure, such as the sterile field not being constantly observed and too much movement around the sterile field, including the opening and closing of doors and a wide space not being observed between scrubbed staff.
Taylor et al. showed that sets opened outside the confines of the laminar hood have significantly higher colony-forming unit (CFU) counts during and after surgery.17 Very few centres follow Sir John Charnley’s technique of opening the instrument sets under the canopy at each stage of the operation.
Madhavan’s paper from Bristol in the Annals of the Royal College of Surgeons England specifically looked at breakdown in theatre discipline during total joint replacement.18 They noted that slackness had crept into the theatre protocol, such as corridor from changing room to theatre and theatre personnel attire.
EXAMINER: Screening has shown that you, the surgeon, were found to be a Staphylococcus aureus nasal carrier. You have been treated with decolonization and are now clear. Would you mention this to your patients when you are listing them for joint arthroplasty?
CANDIDATE: Yes.
EXAMINER: Are you sure?
CANDIDATE: Yes, patients should be informed that I was a nasal carrier at the time of listing for surgery.
EXAMINER: Are you absolutely sure?
CANDIDATE: Yes, patients need to be told to make sure they are happy.
COMMENT: Wrong answer. It is not expected that a surgeon informs patients when he/she is listing them for surgery that they were previous nasal carriers but have been successfully treated and are now clear.
EXAMINER: Do you know any papers that have looked at theatre sterility?
CANDIDATE: The classic paper on theatre sterility was published by Lidwell et al. in 1982.19 This was an MRC randomized study which showed a decrease in infection rates following joint replacements carried out in ultraclean theatres.
The deep infection rate was 3.4% in conventional theatres, 1.7% with ultraclean air and body exhaust and 0.2% when this was combined with prophylactic antibiotics.
EXAMINER: That’s fine. Let’s move on.
Reading list
| Musculoskeletal Infection Society (MSIS) diagnostic criteria | ||
|---|---|---|
| Major criteria | or | Minor criteria |
| A sinus tract communicating with the prosthesis | Elevated ESR and CRP (ESR [30 mm/h; CRP [10 mg/l]) | |
| A pathogen is isolated by culture from two separate tissue or fluid samples obtained from the affected prosthetic joint | Elevated synovial fluid WBC count (3000 cells/l) | |
| Elevated synovial fluid neutrophil percentage (65%) | ||
| Isolation of a microorganism in one periprosthetic tissue or fluid culture | ||
| 5 neutrophils per high-powered field in 5 high-power fields observed from histologic analysis of periprosthetic tissue at ×400 magnification | ||
Figure 3.1c Anteroposterior (AP) radiograph of first-stage PROSTALAC spacer.
Structured oral examination question 2
EXAMINER: This is an AP radiograph of a 52-year-old female who presents to your clinic with non-specific right hip pain. She had a right metal-on-metal hip resurfacing procedure performed 3 years ago (Figure 3.2a).
CANDIDATE: The AP radiograph demonstrates a higher abduction angle (lateral opening) than normal. The current recommendations are for an acetabular abduction angle of 40°. Several studies have demonstrated the importance of optimal cup positioning with regard to wear, metal ion levels and the revision rate. High cup angle has been consistently reported to lead to greater wear and higher serum metal ion levels. The head size appears small; the current recommendations are that unless a minimum 46-mm head size can be used the procedure should not be performed because of the risks of ALVAL and pseudotumours. There is no radiolucency about the metaphyseal stem, no obvious narrowing of the neck and no divot sign.
EXAMINER: What do you mean by a divot sign?20
CANDIDATE: A divot sign is a depression in the neck contour just below the junction with the femoral component often associated with a reactive exostosis. It is believed to be caused by repetitive bone to component abutment due to impingement.
EXAMINER: What is a pseudotumour and what is the difference between ALVAL and pseudotumour?
CANDIDATE: ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion) is a histological diagnosis caused by metal particulate debris. Patients present with localized hip pain and a localized osteolytic reaction. A more severe inflammatory reaction is termed a pseudotumour. This is diagnosed on an MRI scan. The umbrella term ‘adverse reactions to metal debris’ (ARMD) is now preferred to cover a wide spectrum of destructive involvement including metallosis, pseudotumours and ALVAL.
COMMENT: Pseudotumour, aseptic lymphocytic vasculitis-associated lesions (ALVAL) and metallosis are terms often used interchangeably to describe the same process. In June 2008, the NJR first introduced the term ARMD for surgeons to select as an indication for revision surgery, given ARMD is considered the most inclusive term for these abnormal reactions.
CANDIDATE: Several studies have described an association between pseudotumours and increased wear of retrieved components. Influencing factors include implant size and implant design (clearance and cover [arc angle]). In addition, acetabular component positioning and femoral head–neck offset influence the risk of impingement and edge loading usually associated with high wear rates.
Despite this, Campbell et al. reported that in 32 THA revised due to pseudotumour several patients demonstrated minimum wear features, suggesting a hypersensitivity cause.21
Therefore, the origin of pseudotumours is probably multifactorial caused either by excessive wear, metal hypersensitivity, a combination of the two, or an as yet unknown cause. Pseudotumour-like reactions have also been reported in non-metal-on-metal bearings. In these cases, the histological findings showed accumulations of macrophages and giant cells again suggesting an excessive wear origin.
EXAMINER: What are the risk factors for pseudotumours?
CANDIDATE: Significant risk factors for the development of pseudotumour include female sex, age less than 40 years, small component size, hip dysplasia and specific implant designs (ASR).
EXAMINER: How are you going to investigate this patient?
CANDIDATE: A careful history and examination of the patient is required. It is crucial to determine if the pain is arising from intrinsic (indicating hip pathology) or extrinsic sources (referred pain).
Extrinsic sources would include referred pain from the spine or pelvis, peripheral vascular disease, stress fracture, tendinitis or bursitis about the hip.
Intrinsic causes include aseptic loosening, avascular necrosis, infection. (Long pause.)
EXAMINER: What are the latest Medicines and Healthcare Products Regulatory Agency (MHRA) recommendations (2017) (Prompt)? (Table 3.2.)
CANDIDATE: In essence, the latest MHRA guidelines with input from the BHS and BOA risk stratifies patients into high-risk and low-risk groups based on patient factors, device implanted and whether they are symptomatic. Having an ASR hip is automatically high-risk and therefore patients should have annual surveillance together with cobalt and chromium levels, MARS MRI and OHS. On the other hand, a Birmingham hip resurfacing, which is an ODEP 10 A device, in patients who are asymptomatic, should be followed-up in the first year, at 7 years and then every 3 years after that. Stemmed large MoM devices are higher risk than resurfacing hips and therefore the follow-up guidance is different, and these patients require closer review.
EXAMINER: Anything else?
CANDIDATE: I am not sure.
EXAMINER: ALVAL may occur in both asymptomatic and symptomatic patients and early detection should give a better revision outcome if this is necessary. Essentially all MoM/resurfacing hips require some sort of clinical follow-up for life and should not be discharged even if well functioning.
COMMENT: Additional clinic slots are required for follow-up of MoM hip patients and this can be a significant burden on resources. Interferes with new/follow-up ratios.
EXAMINER: This is the MRI scan obtained. What does it show? (Figure 3.2b and 3.2c.)
CANDIDATE: The MRI is a T2-weighted image coronal view, which demonstrates an intra-pelvic mass.
EXAMINER: This was a pseudotumour. In fact, the mass could be felt clinically when examining the abdomen.
What are you going to do?
CANDIDATE: This patient requires urgent revision surgery to the hip.
EXAMINER: She is very scared of surgery and would prefer to avoid it.
CANDIDATE: I would stress the importance of early revision surgery as the longer the MoM resurfacing implant is left in place the more extensive the soft-tissue destruction will likely be.
CANDIDATE: The pseudotumour needs to be managed with aggressive debridement of all involved soft tissue. It is important to do a thorough debridement of the abnormal tissue similar to the treatment of infection. The surgery should be performed by an experienced hip surgeon.
Although she is still relatively young I would use a metal and PE bearing surface. I would want to use first- or second-generation highly cross-linked PE. A ceramic bearing surface has the potential for catastrophic fracture. We are already revising for a rare complication and we don’t want anything to go wrong again. However, I would use an uncemented implant. I would keep the option of using a dual mobility acetabular cup as the soft tissues may be so poorly compromised that the hip is unstable. Another possibility is to use a constrained cup if the hip is unstable with significant abductor muscle destruction, but I would prefer to avoid using this implant if possible as components will loosen early in this situation.
It would be sensible to get a second opinion from an experienced hip surgeon as per British Hip Society guidelines to confirm and support the appropriateness of my management plan. In my region, all revision arthroplasty cases are discussed as part of a revision clinical network involving several hospitals within a geographical region. I would certainly ensure that this case is discussed with other colleagues within the revision network meeting.
CANDIDATE: There was a double-blinded study from New Zealand (level 1 evidence) recently published in the American JBJS edition comparing HXLPE to conventional PE. HXLPE liners had significantly reduced wear present and were associated with a greater implant survival rate at 10 years compared to conventional UHMWPE liners.22
EXAMINER: Why did surgeons bother with MoM hip resurfacing procedures? The old Charnley cemented hip replacement with trochanteric osteotomy worked equally as well with excellent long-term results reported from the surgeons at Wrightington.
CANDIDATE: The perceived advantages of MoM hip resurfacings included better restoration of hip biomechanics, improved proprioceptive feedback, improved wear characteristics with no PE-induced osteolysis, increased levels of postsurgical activity, greater range of movement, reduced risk of dislocation, improved femoral bone stock mass because the neck and most of the head are retained and ease of conversion to a THA if the implant should fail.
EXAMINER: What are the contraindications for resurfacing?
CANDIDATE: These include severe osteoporosis, insufficient bone stock in the femoral head, large cysts at the femoral neck or head, a narrow femoral neck, notching of the femoral neck, extensive ON and severe obesity (BMI > 35 kg/m2).
Other contraindications include a history of chronic renal disease, metal hypersensitivity, those with anatomical abnormalities in the acetabulum or proximal femur and certainly caution in women of childbearing age.
EXAMINER: Is resurfacing contraindicated in women of childbearing age?
CANDIDATE: No, although most surgeons would now avoid a resurfacing procedure in a female regardless of whether they were of childbearing age.
EXAMINER: Is there a role for resurfacing at all?
CANDIDATE: Data from the latest NJR annual report showed that less than 1% of all hip replacements were resurfacings. There may be a role for this implant to be used in young male individuals who are likely to trash their hip.
EXAMINER: What do you mean by trashing your hip?
CANDIDATE: A patient who has to do very heavy manual work as part of his job or who just wants to play football or rugby regardless.
COMMENT: Candidates should mention that:
Nowadays very few resurfacing hips are performed (< 1% NJR data 14th report 2017).
Although they are not contraindicated they would generally only be indicated in a very small, select number of individuals.
Surgery should ideally be performed by a specialized hip resurfacing surgeon.23
Cases should ideally be discussed with hip colleagues and a consensus view reached as to whether to proceed with resurfacing.
Candidates should be able to discuss:
The poorly performing implants (ASR) and subgroups of patients at risk for ARMD (female sex, age < 40 years, small component size, malpositioning of the acetabular component, hip dysplasia, known nickel allergy).
Complications of MoM hips.
A follow-up clinic protocol.
Large MoM jumbo hip replacements are now contraindicated as a primary procedure due to metal wear and corrosion at the trunnion.
EXAMINER: These are her postoperative radiographs (Figure 3.2d). We kept her non-weight bearing for 6 weeks as there was quite an extensive anterior wall defect in the acetabulum, but she has done very well. The hip pain has settled, and the abdominal mass resolved. We were very lucky as the extensive soft-tissue destruction that sometimes can be seen with this condition was absent24.
CANDIDATE: Several recent studies report identical Harris hip scores but a greater percentage of patients with resurfacing involved in high-demand activities. There is a higher revision rate in hip resurfacing compared to conventional THA.25
EXAMINER: What factors are associated with higher revision rates for hip resurfacing procedures?
CANDIDATE: These would include ON (relative contraindication), hip dysplasia (technically difficult, more suitable reconstructive options available), female sex, inflammatory arthritis (relative contraindication), increased age (deteriorating bone quality), a small femoral implant and specific implant designs (ASR).
COMMENT: Causes of revision primary hip resurfacing procedure include fracture (39%), loosening/lysis 29%, infection 9%, ARMD (6%), pain (5%), dislocation (3%), other (8%). Australian Joint Registry 1999–2008.
COMMENT: MoM hips are still a hot topic, but viva themes would be more about how to manage ARMD, when to revise and clinic follow-up protocol. Resurfacing is rarely performed these days (< 1%), so the safest option is not to mention this as a possible arthroplasty option unless specifically brought into the discussion by the examiners.
Figure 3.2a Anteroposterior (AP) radiograph right MoM hip resurfacing implant.
| Device implanted |
|
| ||
| Patient and device group | Symptomatic and asymptomatic | Symptomatic | Asymptomatic | |
| Resurfacing devices with 10 A ODEP rating | |||
| Frequency of follow-up after primary operation date | Annually while the device remains implanted | Annually while the device remains implanted | Annually for the first 5 years, 2-yearly to 10 years and 3-yearly thereafter | First year, once at 7 years and 3-yearly thereafter |
| Questionnaire | Oxford Hip Score assessment | Oxford Hip Score assessment | Oxford Hip Score assessment | Oxford Hip Score assessment |
| Imaging |
|
|
|
|
| Blood metal level test | All patients | All patients | All patients | All patients |
| Consider need for revision | If imaging is abnormal and/or blood metal levels rising, and/or hip-related clinical function/Oxford Hip Score deteriorating | If imaging is abnormal and/or blood metal levels rising, and/or hip-related clinical function/Oxford Hip Score deteriorating | If imaging is abnormal and/or blood metal levels rising, and/or hip-related clinical function/Oxford Hip Score deteriorating | If imaging is abnormal and/or blood metal levels rising, and/or hip-related clinical function/Oxford Hip Score deteriorating |
Whole blood should be used to test for cobalt and chromium metal levels.
Figure 3.2b and c T1 coronal and transverse MRI of right MoM hip resurfacing implant demonstrating ALVAL mass.
Figure 3.2d Anteroposterior (AP) radiograph of revised hip demonstrating uncemented THA with screw fixation acetabulum.
Structured oral examination question 3
EXAMINER: This is an AP radiograph of a 78-year-old man presenting with increasing right hip pain. He had a THA performed 17 years ago (Figure 3.3a).
CANDIDATE: The AP radiograph demonstrates severe osteolysis of both femoral and acetabular components. There are radiolucent lines at the bone cement interface located circumferentially around all three Dee and Charnley zones in the acetabulum. The femoral component has separated from the femoral cement with lucencies in all seven Gruen zones.
I am unfamiliar with the type of implant used for the femur. On the radiograph shown i can not determine if a cement plug has been used or not.
COMMENT: Score 6 candidates should ideally be able to recognize a Charnley and Exeter stem. Score 7 candidates should recognize a Stanmore prosthesis (banana-shaped). Score 8 candidates should be able to weave in somewhere in the discussion that when revising a Stanmore prosthesis, it is particularly important due to its banana shape to clear the shoulder of the prosthesis removing any cement or bone overhanging the proximal aspect of the greater trochanter. Otherwise stem removal will be obstructed and/or difficult or a greater trochanter fracture will occur.
CANDIDATE: First-generation cementing techniques involved hand-mixing of cement and finger packing of bone cement in the doughy phase into an unplugged, unwashed femoral canal. Clinical results with first-generation cementing have been variable and in general have produced some disappointing results due to the inability to produce a consistent cement mantle.
Second-generation technique involved plugging the medullary canal, cleaning the canal with pulsed lavage and inserting cement in a retrograde manner using a cement gun. This reduced the incidence of gross voids and filling defects in the mantle.
EXAMINER: Are you sure pulsed lavage was used?
CANDIDATE: Yes.
COMMENT: Take the hint that your answer may be wrong. Second-generation technique involves essentially using a gun and bone plug (restrictor) and nothing else. The bone is thoroughly cleaned before cement insertion but not pulsed lavage.
EXAMINER: What else?
CANDIDATE: Third-generation techniques involved porosity reduction via vacuum mixing or centrifugation and cement pressurization.
Fourth-generation cementing techniques include stem centralization both proximally and distally to ensure an adequate and symmetrical cement mantle. This is important as uneven and excessively thin cement mantles are associated with early failure and revision.
COMMENT: Distal centralisers are often included as a third generation technique. Some books list only 3 generations of cementing techniques omitting the fourth.
CANDIDATE: The quality of the cement mantle has been described by Harris and Barrack using a scale of A to D.26
Complete filling of the medullary cavity by cement, a so-called ‘white-out’ at the cement–bone interface, is graded ‘A’. Slight radiolucency of the cement–bone interface was defined as ‘B’. Radiolucency involving 50–99% of the cement–bone interface or a defective or incomplete cement mantle was graded ‘C’. Grade ‘C2’ was given to a defect where the tip of the stem abuts the cortex with no intervening cement. Radiolucency at the cement–bone interface of 100% in any projection, or a failure to fill the canal with cement such that the tip of the stem was not covered, was classified ‘D’.
EXAMINER: What are you going to do?
CANDIDATE: I would want to take a full history from the patient. I would enquire about pain.
I would also want to exclude the possibility of infection (septic loosening) and would ask about problems with the hip postoperatively such as wound infection requiring washout or a prolonged course of antibiotics. A history of fever, chills or a sinus tract suggests infection. Night pain, rest pain or constant pain would also suggest infection.
With aseptic loosening typically, the pain is aggravated by weight bearing. Pain is significant with the first few steps of walking (start-up pain) which improves slightly with further walking, only to worsen again with further walking. The pain is always improved with rest and rarely constant.
With aseptic loosening of a THA examination may reveal shortening of the affected limb, an antalgic gait and a Trendelenberg positive test is usually present. Pain at the extremes of movement suggest loosening.
It is important to exclude other causes of local extrinsic hip pain such as trochanteric bursitis, tendinitis or impingement. Extrinsic remote sources of hip pain should also be excluded, particularly the lumbar spine, especially if the pain has neurogenic features such as radiation below the knee, numbness, paraesthesia or dysesthesias. Pulses and skin temperature should be checked to rule out a vascular cause for pain.
EXAMINER: Assume there is no infection in the hip and referred causes of pain have been ruled out. What are you going to do?
CANDIDATE: I would assess the patient. Find out how bad the pain is and whether the hip should be revised or whether symptoms are manageable, and the patient can be reviewed regularly at the orthopaedic follow-up clinic. Based on the current radiographic appearances I would have some concerns with the natural progression of the condition and the possibility of catastrophic periprosthetic fracture occurring.
EXAMINER: The patient can only walk about 200 yards before severe pain.
CANDIDATE: I would offer him revision hip surgery provided comorbidity issues have been optimized and the risks of surgery had been discussed and understood. Both components would need to be revised.
EXAMINER: What are the complications that you would need to mention to the patient when consenting for surgery?
CANDIDATE: I would mention
Infection.
Dislocation. Usually component malpositioning or laxity of soft tissues around the hip.
Fracture/perforation femoral shaft.
Nerve palsy (peroneal, sciatic, femoral) 2–7%.
Vascular injury (femoral, iliac, obturator).
Leg-length discrepancy.
Heterotopic ossification.
Death (cardiac/pulmonary).
DVT/PE.
In addition, the patient has significant bone loss on both the femoral and acetabular side, so I would plan to use donor femoral head allograft to attempt to restore bone stock. An ETO is helpful if there is a large amount of cement to remove distally but will increase operating time and blood loss. An osteotomy site can also go on to either malunion or non-union. I would prefer to avoid its use in this particular case.
I would warn him that he might need a period of partial weight bearing if there were concerns with initial implant stability due to excessive osteolysis and bone loss.
EXAMINER: You mentioned about the bone loss. How do you plan for this?
CANDIDATE: Bone loss can be classified on the femoral side by using either the AAOS (Table 3.3) or the Paprosky classification system (Table 3.4).
The Paprosky classification evaluates the femoral diaphysis for its ability to support an uncemented, fully porous coated prosthesis. It is less detailed than the AAOS classification but is more useful in decision making if an uncemented revision is to be performed.
Figure 3.3a Anteroposterior (AP) radiograph of loose cemented right THA.
I Segmental defect
|
II Cavitary defect
|
| III Combined segmental and cavity defect |
IV Malalignment
|
| V Femoral stenosis |
| VI Femoral discontinuity |
Table 3.4 Paprosky classification system for femoral defects.
| I Minimal metaphyseal cancellous bone loss with normal intact diaphysis |
| Type I defects are seen after removal of uncemented component without biological ingrowth on surface. Usually seen with Austin Moore type prosthesis or resurfacing procedures. The diaphysis and metaphysis are intact and there is partial loss of the calcar and anteroposterior (AP) bone stock |
| II Extensive metaphyseal cancellous bone loss with normal intact diaphysis |
| Often seen after removal of cemented prosthesis. Calcar deficiency and major AP bone loss |
| IIIA Metaphysis severely damaged with > 4 cm diaphyseal bone for distal fixation |
| • Grossly loose femoral component |
| • First-generation cementing techniques |
| IIIB Metaphysis severely damaged with < 4 cm diaphyseal bone for distal fixation |
| Type IIIB defects extend slightly further than Type IIIA; however, reliable fixation can be achieved just past the isthmus of the femur |
| • Cemented with cement restrictor |
| • Uncemented with substantial distal osteolysis |
| IV Extensive metaphyseal and diaphyseal bone loss/isthmus non-supportive |
| Extensive defect with severe metaphyseal and diaphyseal bone loss and a widened canal that cannot provide adequate fixation for a long stem |
Acetabular bone loss
Acetabular defect classification systems are used to predict the extent of intraoperative bone loss and guide reconstructive options.
Several classification systems exist; the three most commonly used are the American Academy of Orthopaedic Surgeons (AAOS) system (Table 3.5), the Gross and associates system (Table 3.6) and the Paprosky classification system (Table 3.7).
| Type I Segmental defects |
| Peripheral – superior/anterior/posterior |
| Central – medial wall absent |
| Type II Cavitary defects |
| Peripheral – superior/anterior/posterior |
| Central – medial wall intact |
| Type III Combined segmental and cavitary bone loss |
| Type IV Pelvic discontinuity |
| Separation of anterior and posterior columns |
| Type V Arthrodesis |
Table 3.6 Gross and associates classification system.
| Type | Description |
|---|---|
| I | No substantial loss of bone stock |
| II | Contained loss of bone stock (columns and/or rim intact) |
| III | Uncontained loss of bone stock (< 50% acetabulum) |
| IV | Uncontained loss of bone stock (> 50% acetabulum) |
| V | Contained loss of bone stock with pelvic discontinuity |
Table 3.7 Paprosky classification of acetabular bone defects.
| Type | Radiographic finding | Intraoperative finding | Trial stability |
|---|---|---|---|
| I Minimum bone loss | No cup migration | Intact rim and no distortion. No major osteolysis. Bone loss minimal | Full |
| No substantial bone loss | Small focal areas contained bone loss | ||
| Columns intact | |||
| II Anterior and posterior columns intact and supportive | |||
| Migration less than 2 cm superomedially or laterally | |||
| Minimal ischial lysis | |||
| Minimal tardrop lysis | |||
| IIA Cavitary defect medial to a thinned superior rim | Superior (or superomedial) migration of < 2 cm Up and in | Superomedial bone loss but intact superior rim (contained cavity) | Full |
| IIB Superior acetabular rim is missing | Superior (or superolateral) migration of < 2 cm Up and out | Uncontained superior rim defect < 1/3 | Full |
| IIC | Straight medial wall defect | Uncontained medial wall defect | Full |
| Cup medial to Kohler line Teardrop may be obliterated Protrusio | Rim intact and rim columns supportive | ||
| III Columns non-supportive | |||
| IIIA | Superolateral cup migration > 3 cm Up and out | Unsupportive dome | Partial |
| Moderate ischial lysis | Columns intact | ||
| Partial teardrop destruction | Host–bone contact of 40–60% | ||
| Kohler line intact | |||
| IIIB | Superomedial migration > 3 cm Up and in | Risk of pelvic discontinuity | None |
| Severe ischial destruction | Bone contact of < 40% | ||
| Teardrop loss | Rim defect of > 50% | ||
| Migration medial to Kohler line |
Gross and associates classification system (Table 3.6)
This classification is based on the nature of the bone graft needed for reconstruction determined on standard preoperative AP and lateral radiographs. A bone defect is considered uncontained if morselized bone graft cannot be used to fill the defect.
Paprosky acetabular bone loss classification
This classification is based on information that can be obtained from AP radiographs. Four radiographic criteria are assessed:
1. Superior migration of the hip centre
Indicates damage to anterior and posterior columns
Supero-medial indicates greater damage to anterior column
Supero-lateral indicates greater damage to posterior column
2. Ischial osteolysis
Bone loss inferior posterior column and posterior column
3. Teardrop osteolysis
Inferior anterior column and medial wall
4. Position of the implant relative to Kohler’s line
Deficiency of anterior column and/or medial wall deficiency
A trial component with full inherent stability does not change position when the surgeon pushes its rim or performs a trial reduction. A trial component with partial inherent stability does not change position with removal of the inserter, but does not withstand the force of pushing on the rim or performance of a trial reduction. A trial component with no inherent stability changes position with the simple act of removing the inserter.
The Paprosky classification (Table 3.7) is often used clinically in preference to the AAOS classification as it not only predicts bone loss encountered intraoperatively, but also assists in determining reconstructive options.
CANDIDATE:
I would counsel the patient regarding the natural history of the condition and recommend revision is undertaken on an urgent basis as the situation is likely to deteriorate and may lead to catastrophic periprostatic fracture.
I would get an anaesthetic review to make sure the patient was fit enough for surgery, the risks acceptable and also so they could order any special tests such as echocardiogram or pulmonary function tests if required.
I would cross-match for 4 units and make sure the cell saver(Figure 3.3b) was available.
EXAMINER: What dose of tranexamic acid?
CANDIDATE: 1 g IV and if needed a further dose of 1 g IV at closure.
I would order one femoral head frozen allograft and have freeze-dried allograft available if required.
I would liaise with my anaesthetic colleagues in case an HDU bed was needed postoperatively.
I would obtain the original operative notes to check what surgical approach was used and which implants were inserted.
I would make sure the company rep is available at the time of surgery.
I would ask the theatre coordinator to make sure there was an appropriate skill mix and experience in theatre on the scrub side to deal with complicated revision hip cases.
I would ideally make sure the case wasn’t performed at the weekend when fewer staff are generally available or last case on a Friday with the possibility of a long theatre overrun.27
I would need to make sure the implant removal kit would include curved and straight osteotomies for the cemented cup and femur, ultrasonic tools, high-speed burrs, rongeurs, cement splitters, reverse hooks, drills and Dall miles cabling system.
I would need a flexible light source for visualizing the medullary canal of the femur.
I would prefer to use uncemented components if possible if previously cement was used for fixation. The femoral bone surface after cement removal is often sclerotic, hard and resistant to cement interdigitation. I would also hesitate to use cement as long-term results in revision cases can be poor.
I would plan to use a long-stem uncemented modular tapered fluted revision femoral implant, aiming for a good scratch fit distally. If this could not be achieved, I would use a long-stem uncemented implant with a distal interlocking screw option.
I would use a multihole TM revision acetabular shell and a metal on polyethylene bearing surface. I would attempt to use at least a 32-mm head but preferably a 36-mm head, as this will significantly reduce the risk of postoperative dislocation.
I would prefer to use a posterior approach, incorporating the old incision into this if possible.
If the risk of dislocation was deemed very high I would consider using an anterolateral approach or more preferably a posterior approach but with the use of a dual-motion acetabular cup.
COMMENT: ‘I would’ is what YOU would do. It is probably the most appropriate turn of phrase to use for the exam.
CANDIDATE: I would clear soft tissue and overhanging cement away from the proximal femur to expose the proximal edge of the bone–cement interface.
Flexible osteotomes and a small burr can then be used to further disrupt the cement/implant interface.
An ETO would simplify implant and cement removal, but as mentioned, in this particular situation I would prefer to avoid it.
I would use cement splitters to remove cement along with ultrasonic tools. Cement is split radially and longitudinally and then removed.
OSCAR (Figure 3.3c) (or a similar ultrasonic cement removal system) is useful for getting through a distal cement plug. A combination of sharp cement splitters, cement osteotomes (straight and curved), a Midas Rex high-speed burr, ultrasonic tools and patience is the key to removing the cement mantle. I would be careful about losing cement down the femoral canal and the use of mastoids down the canal can be helpful. I would avoid levering the cement out as this risks an iatrogenic fracture, especially around the greater trochanteric region.
CANDIDATE: The safest way is to disrupt the PE cup from the cement using curved gouges. This prevents inadvertent damage to the bone of the acetabulum bed. After removal of the cup the cement is removed piecemeal. Sometimes a threaded acetabular extractor can be used, threading into a drilled hole until its metal plate is flush with the rim of the acetabular component. The extractor is then toggled to disrupt the fixation interface and allow removal of the component. High-speed burrs are sometimes needed to debulk cement within acetabular anchoring holes.
EXAMINER: And if the socket is uncemented?
CANDIDATE: The order of removal is component liner removal then screw removal (if there are supplementary screws) and finally metal shell removal. If the liner is polyethylene, then drilling into the centre of the liner followed by inserting a screw into the liner hole will usually lift off the liner.
If the liner is ceramic, then the principle is first to disengage the smooth taper lock by a sharp tap into the liner. This is followed by the use of a suction cup with its attached three scallops that contact the peripheral rim of the metal acetabular to remove the liner. Different implants will have their own extraction devices, so it is critical to know all about the implant one is revising and to ensure that the relevant and appropriate kit is available. That is why it is important to have a good system in place whereby old medical records can be easily retrieved to look over well in advance of surgery.
Removing any supplementary screws can be challenging and I would always have the Timex broken screw set available as well as a burr in case the screw heads are gone. Finally, to remove the metal-backed shell, the essential tool required here is the Explant (Figure 3.3d). This has been revolutionary in making the removal of an uncemented acetabular shell easier.
Figure 3.3b Cell saver.
Structured oral examination question 4
EXAMINER: These are the radiographs of a 78-year-old lady who has been referred to the orthopaedic clinic by her GP because of increasing pain in her right hip. Would you care to comment on the radiographs? (Figure 3.4)
CANDIDATE: This is an AP radiograph, demonstrating lower lumbar vertebrae, both hips and proximal femur. The most obvious features in the right hip are loss of joint space, osteophytes, sclerosis and bone cysts. The radiographic features are highly suggestive of osteoarthritis (OA) of the hip.
EXAMINER: How is osteoarthritis classified?
CANDIDATE: OA is classified into primary OA when an obvious cause can be identified, and secondary OA caused by such conditions as osteonecrosis (ON), DDH, posttraumatic, Paget’s disease, slipped capital femoral epiphysis, protrusio acetabuli, and Perthes disease.
EXAMINER: What are the percentages of each type of OA?
CANDIDATE: Various studies have suggested that almost 90% of cases of OA are secondary.
EXAMINER: How are you going to manage this patient?
CANDIDATE: I would take a full history and examination from the patient. Specifically, I would want to know the location of pain and exclude referred pain from the spine. Hip pain is classically located in the buttock or groin radiating to the knee. Pain radiating below the knee to the foot is strongly suggestive of radicular-type pain from the spine. I would inquire whether the patient had difficulty putting shoes and socks on, tying shoe laces, bending to pick up an object from the floor, getting in and out of a car, [Examiner interrupts]
EXAMINER: The patient struggles to walk a quarter of a mile. She has typical symptoms of advanced OA. What are you going to do?
CANDIDATE: Assuming that all conservative options had been tried and have been unsuccessful I would offer her THA.
EXAMINER: What type of hip arthroplasty would YOU perform?
EXAMINER: Why this particular implant?
CANDIDATE: The Exeter THA has excellent peer-reviewed long-term data. It is an implant that I am very comfortable using, I have been trained to use this implant by my consultants, the instrumentation is straightforward and simple to use, the neck cut is not critical, and the introducer allows for even pressure when inserting the implant.
This hip system provides me with the ability to deal with anatomical variants and to recreate offset and leg length and gives me a choice of bearing surfaces and head sizes.
It allows good initial fixation and excellent long-term survival.
It is an ODEP (Orthopaedic Data Evaluation Panel) 13A* rated stem.
EXAMINER: What do you mean by anatomical variants?
CANDIDATE: The shape of the femur.
EXAMINER: The shape of the femur is a more important consideration when using an uncemented implant and is less applicable for a cemented implant.
CANDIDATE: The Exeter stem has different offset sizes, which improves hip abductor function and stability. In recent years smaller offsets and shorter-length ‘CDH’ stems have been introduced to deal with smaller femoral geometry. In smaller femurs oversizing of a femoral component may result in an incomplete or insufficient cement mantle of less than the recommended 2 mm uniform thickness. This may lead to early failure.
EXAMINER: What is the problem with using smaller stems?
CANDIDATE: I am not sure.
EXAMINER: If you use a smaller stem there are concerns with stem breakage and implant failure.
COMMENT: The viva could have gone on to discuss stem geometry affecting cement stresses (avoidance of sharp edges, broad lateral curve), factors predisposing to stem breakage, bending and torsional rigidity of stems, etc.
CANDIDATE: There are three types of femoral shape based on metaphyseal–diaphyseal anatomy. Dorr type A femurs have wide metaphyses and narrow diaphyses, type B have a smooth metaphyseal–diaphyseal transition and type C do not have much difference in the sizes of these two regions.
EXAMINER: So how does this apply to uncemented implants?
COMMENT: Candidates should try to avoid mentioning any loose terms they don’t fully understand as it can lead on to difficult questions.
EXAMINER: What are the survival figures like for the Exeter implant?
COMMENT: Know some papers to quote for your chosen implant.
CANDIDATE:
1. Lewthwaite et al. CORR 200828
Results of Exeter THA in younger patients < 50 years at 10–17 years FU
Survivorship of the femoral stem from all causes was 99%
No stem was revised for aseptic loosening
2. Petheram et al. Bone Joint J 201629
Results of Exeter THA at 20–25 years.
FU study of 382 cemented Exeter THA (350 patients) at a mean age of 66.3 years (17–94).
With an endpoint of revision for aseptic loosening or lysis, survivorship of the stem at 22.8 years was 99.0%
Figure 3.4 Anteroposterior (AP) radiograph demonstrating severe osteoarthritis left hip.
EXAMINER: What are the design principals of the Exeter Stem?
CANDIDATE: The Exeter implant is a loaded taper model and becomes lodged as a wedge in the cement mantle during axial loading, reducing peak stresses in the proximal and distal cement mantle. The stem is allowed to subside initially until radial compressive forces are created in the adjacent cement and transferred to the bone as hoop stresses.
CANDIDATE: I am happy to use either the Hardinge or posterior approach to the hip.
EXAMINER: Make up your mind. Which one are YOU going to do?
CANDIDATE: For the majority of cases I would prefer to use the posterior approach to the hip. In rare instances, I would use a Hardinge anterolateral approach if the risk of dislocation was considered to be high such as neurological or muscular weakness around the hip (Paget’s/CVA), early dementia or substance abuse.
The posterior approach is considered easier to perform and is generally a quicker procedure, limiting operative complications such as blood loss and anaesthetic issues.
The abductor muscles are not disturbed significantly so there is generally no gait abnormality, but the acetabulum is more difficult to see and can make prosthesis positioning difficult, possibly causing an increased dislocation rate due to component malpositioning. The sciatic nerve is at slightly more risk of being injured as well.
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