Persistent groin pain after seemingly successful total hip replacement (THR) appears to have become more common. Recent studies have indicated a high incidence after metal-on-polyethylene and metal-on-metal conventional THR and it has been documented in up to 18% of patients after metal-on-metal resurfacing. There are many causes, including acetabular loosening, stress fracture, and iliopsoas tendonitis and impingement. The evaluation of this problem requires a careful history and examination, plain radiographs and an algorithmic approach to special diagnostic imaging and tests. Non-operative treatment is not usually successful. Specific operative treatment depending on the cause of the pain usually involves revision of the acetabular component, iliopsoas tenotomy or other procedures, and is usually successful. Here, an appropriate algorithm is described

Aims. Iliopsoas impingement occurs in 4% to 30% of patients after undergoing total hip arthroplasty (THA). Despite a relatively high incidence, there are few attempts at modelling impingement between the iliopsoas and acetabular component, and no attempts at modelling this in a representative cohort of subjects. The purpose of this study was to develop a novel computational model for quantifying the impingement between the iliopsoas and acetabular component and validate its utility in a case-controlled investigation. Methods. This was a retrospective cohort study of patients who underwent THA surgery that included 23 symptomatic patients diagnosed with iliopsoas tendonitis, and 23 patients not diagnosed with iliopsoas tendonitis. All patients received postoperative CT imaging, postoperative standing radiography, and had minimum six months’ follow-up. 3D models of each patient’s prosthetic and bony anatomy were generated, landmarked, and simulated in a novel iliopsoas impingement detection model in supine and standing pelvic positions. Logistic regression models were implemented to determine if the probability of pain could be significantly predicted. Receiver operating characteristic curves were generated to determine the model’s sensitivity, specificity, and area under the curve (AUC). Results. Highly significant differences between the symptomatic and asymptomatic cohorts were observed for iliopsoas impingement. Logistic regression models determined that the impingement values significantly predicted the probability of groin pain. The simulation had a sensitivity of 74%, specificity of 100%, and an AUC of 0.86. Conclusion. We developed a computational model that can quantify iliopsoas impingement and verified its accuracy in a case-controlled investigation. This tool has the potential to be used preoperatively, to guide decisions about optimal cup placement, and postoperatively, to assist in the diagnosis of iliopsoas tendonitis. Cite this article: Bone Jt Open 2023;4(1):3–12

Aims

This study aims to answer the following questions in patients with hip osteoarthritis (OA) who underwent total hip arthroplasty (THA): are patient-reported outcome measures (PROMs) affected by the location of the maximum severity of pain?; are PROMs affected by the presence of non-groin pain?; are PROMs affected by the severity of pain?; and are PROMs affected by the number of pain locations?

Aims. Iliopsoas pathology is a relatively uncommon cause of pain following total hip arthroplasty (THA), typically presenting with symptoms of groin pain on active flexion and/or extension of the hip. A variety of conservative and surgical treatment options have been reported. In this retrospective cohort study, we report the incidence of iliopsoas pathology and treatment outcomes. Methods. A retrospective review of 1,000 patients who underwent THA over a five-year period was conducted, to determine the incidence of patients diagnosed with iliopsoas pathology. Outcome following non-surgical and surgical management was assessed. Results. In all, 24 patients were diagnosed as having developed symptomatic iliopsoas pathology giving an incidence of 2.4%. While the mean age for receiving a THA was 65 years, the mean age for developing iliopsoas pathology was 54 years (28 to 67). Younger patients and those receiving THA for conditions other than primary osteoarthritis were at a higher risk of developing this complication. Ultrasound-guided steroid injection/physiotherapy resulted in complete resolution of symptoms in 61% of cases, partial resolution in 13%, and no benefit in 26%. Eight out of 24 patients (who initially responded to injection) subsequently underwent surgical intervention including tenotomy (n = 7) and revision of the acetabular component (n = 1). Conclusion. This is the largest case series to estimate the incidence of iliopsoas pathology to date. There is a higher incidence of this condition in younger patients, possibly due to the differing surgical indications. Arthoplasty for Perthes' disease or developmental dysplasia of the hip (DDH) often results in leg length and horizontal offset being increased. This, in turn, may increase tension on the iliopsoas tendon, possibly resulting in a higher risk of psoas irritation. Image-guided steroid injection is a low-risk, relatively effective treatment. In refractory cases, tendon release may be considered. Patients should be counselled of the risk of persisting groin pain when undergoing THA. Cite this article: Bone Joint J 2021;103-B(2):305–308

Tenotomy of the iliopsoas tendon has been described as an effective procedure to treat refractive groin pain induced by iliopsoas tendinitis. However, the procedure forces the rectus femoris to act as the primary hip flexor and little is known about the long-term effects of this procedure on the peri-articular muscle envelope (PAME). Studies suggest that iliopsoas tenotomy results in atrophy of the iliopsoas and decreased hip flexion strength with poorer outcomes, increasing the susceptibility for secondary tendinopathy. The aim of this study is to describe changes in the PAME following psoas release. All patients who presented for clinical examination at our hospital between 2016 and 2021 were retrospectively reviewed. Patients who presented after psoas tenotomy with groin pain and who were unable to actively lift the leg against gravity, were included. Pelvic MRI was taken. Qualitative muscle evaluation was done with the Quartile classification system. Quantitative muscle evaluation was done by establishing the cross-sectional area (CSA). Two independent observers evaluated the ipsi- and contralateral PAME twice. The muscles were evaluated on the level: iliacus, psoas, gluteus minimus-medius-maximus, rectus femoris, tensor fasciae lata, piriformis, obturator externus and internus. For the qualitative evaluation, the intra- and inter-observer reliability was calculated by using kappastatistics. A Bland-Altman analysis was used to evaluate the intra- and inter-observer reliability for the quantitative evaluation. The Wilcoxon test was used to evaluate the changes between the ipsi- and contra-lateral side. 17 patients were included in the study. Following psoas tenotomy, CSA reduced in the ipsilateral gluteus maximus, if compared with the contralateral side. Fatty degeneration occurred in the tensor fascia latae. Both CSA reduction and fatty degeneration was seen for psoas, iliacus, gluteus minimus, piriformis, obturator externus and internus. No CSA reduction and fatty degeneration was seen for gluteus medius and rectus femoris. Conclusions/Discussion. Following psoas tenotomy, the PAME of the hip shows atrophy and fatty degeneration. These changes can lead to detrimental functional problems and may be associated with debilitating rectus femoris tendinopathy. In patients with psoas tendinopathy, some caution is advised when considering an iliopsoas tenotomy

Aims. Femoroacetabular impingement (FAI) patients report exacerbation of hip pain in deep flexion. However, the exact impingement location in deep flexion is unknown. The aim was to investigate impingement-free maximal flexion, impingement location, and if cam deformity causes hip impingement in flexion in FAI patients. Methods. A retrospective study involving 24 patients (37 hips) with FAI and femoral retroversion (femoral version (FV) < 5° per Murphy method) was performed. All patients were symptomatic (mean age 28 years (SD 9)) and had anterior hip/groin pain and a positive anterior impingement test. Cam- and pincer-type subgroups were analyzed. Patients were compared to an asymptomatic control group (26 hips). All patients underwent pelvic CT scans to generate personalized CT-based 3D models and validated software for patient-specific impingement simulation (equidistant method). Results. Mean impingement-free flexion of patients with mixed-type FAI (110° (SD 8°)) and patients with pincer-type FAI (112° (SD 8°)) was significantly (p < 0.001) lower compared to the control group (125° (SD 13°)). The frequency of extra-articular subspine impingement was significantly (p < 0.001) increased in patients with pincer-type FAI (57%) compared to cam-type FAI (22%) in 125° flexion. Bony impingement in maximal flexion was located anterior-inferior at femoral four and five o’clock position in patients with cam-type FAI (63% (10 of 16 hips) and 37% (6 of 10 hips)), and did not involve the cam deformity. The cam deformity did not cause impingement in maximal flexion. Conclusion. Femoral impingement in maximal flexion was located anterior-inferior distal to the cam deformity. This differs to previous studies, a finding which could be important for FAI patients in order to avoid exacerbation of hip pain in deep flexion (e.g. during squats) and for hip arthroscopy (hip-preservation surgery) for planning of bone resection. Hip impingement in flexion has implications for daily activities (e.g. putting on shoes), sports, and sex. Cite this article: Bone Joint Res 2023;12(1):22–32

Aims. Whether patient-reported pain differs among surgical approaches in total hip arthroplasty (THA) remains unclear. This study’s purposes were to determine differences in pain based on surgical approach (direct anterior (DA) vs posterolateral (PL)) and PL approach incision length. . Patients and Methods. This was a retrospective investigation from two centres and seven surgeons (three DA, three PL, one both) of primary THAs. PL patients were categorized for incision length (6 cm to 8 cm, 8 cm to 12 cm, 12 cm to 15 cm). All patients had cementless femoral and acetabular fixation, at least one year’s follow-up, and well-fixed components. Patients completed a pain-drawing questionnaire identifying the location and intensity of pain on an anatomical diagram. Power analysis indicated 800 patients in each cohort for adequate power to detect a 4% difference in pain (alpha = 0.05, beta = 0.80). Results. A total of 1848 patients (982 DA, 866 PL) were included. PL patients were younger (59.4 years, . sd. 12.9 vs 62.7 years, . sd. 9.7; p < 0.001) and had shorter follow-up (3.3 years, . sd. 1.3 vs 3.7 years, . sd. 1.3; p < 0.001). DA patients reported decreased moderate to severe trochanteric (14% vs 21%; p < 0.001) and groin pain (19% vs 24%; p = 0.004) than PL patients. There were no differences in anterior, lateral, or posterior thigh, back, or buttock pain between cohorts (p = 0.05 to 0.7). PL approach incision length did not impact the incidence or severity of pain (p = 0.3 to 0.7). Conclusion. A significant proportion of patients perceive persistent pain following THA regardless of approach. DA patients reported less trochanteric and groin pain versus PL patients. PL incision length did not influence the incidence or severity of patient-reported pain. Cite this article: Bone Joint J 2019;101-B(6 Supple B):31–36

Young patients undergoing THA or hip used. HOS and iHOT33 have demonstrated to be useful in hip preservation surgery but never used in THA. The aim of the study was to evaluate long-term clinical outcomes with HOS and iHOT33 in hip arthroscopy and THA. We conducted a retrospective study with prospective data collection of 118 consecutive young patients (<65 y.o.) between 2008 to 2012 who underwent hip arthroscopy or THA. The mean follow-up was 12.05 years. All surgeries were done by the same senior surgeon. PROMs used were iHOT-33 and HOS preoperatively, at one year and 10 years. SPSS Statistics Grad Pack 28.0 software was used for statistical analysis. Arthroscopy Group (57 patients): Mean age 35.36 years. 55.93% were male. iHOT33 mean differential improvement was 24.43 at 1 year, 70,17% exceed MCID and 49,1% SCB. HOS mean differential improvement was 16.26 at one year. 54,38 % patients exceed MCID and 49,36% SCB. At 10 years, iHOT33 mean differential improvement was 14,36 and 12.56 for HOS. Regarding complications, 3 patients underwent THA (5.26%) and 10 (17.54%) continued with groin pain. THA Group (61 patients): Mean age 52,54 years. 55.73% were male. Cementless THA was used in all patients with ceramic on ceramic used in 77%. iHOT33 mean differential improvement was 41,57 at 1 year. 95,08% patients exceed MCID and 85,25% SCB. HOS mean differential improvement was 16.57 points at one year. 85,25% patients exceed MCID and 81,97% SCB. At 10 years, iHOT33 mean differential improvement was 20,15 and 14.12 for HOS. Regarding complications, 1 patient underwent DAIR for infection (1.64%) and 1 dislocation with close reduction (1.64%). iHOT33 or HOS scores should be considered to be used in young active patients after hip preserving surgery or THA, with more predictable results at long-term in THA group

Introduction. Despite well-fixed implants, persistent pain following total hip arthroplasty (THA) remains a concern. Various surgical approaches have been advocated, yet whether patient-reported pain differs amongst techniques has not been investigated. This study's purposes were to determine differences in patient-reported pain based on surgical approach (direct anterior –DA versus posterolateral-PL) or PL approach incision length. Our hypothesis was that no differences in patient-reported pain would be present. Methods. A retrospective, IRB-approved investigation from 2 centers was performed. 7 fellowship trained arthroplasty surgeons (3 DA, 3 PL, 1 both) enrolled patients undergoing primary THA for non-inflammatory arthritis. PL approach patients were categorized based on incision length (6–8cm, 8–12cm, 12–15cm). Exclusion criteria were a prior hip surgery, revision procedure, or limited postoperative mobility. All THAs were performed using a cementless titanium, proximally coated, tapered femoral stem and hemispherical acetabular component. All patients had a minimum of 1-year clinical follow-up with radiographically well-fixed components. A pain-drawing questionnaire was administered in which patients identify the location and intensity of pain on an anatomic diagram. Independent Student's t-tests and Chi-square analyses were performed (p<0.05 = significant). Power analysis indicated 800 patients in each cohort would provide adequate power to detect a 4% difference in patient-reported pain (alpha = 0.05, beta = 0.80). Results. 1848 Patients (982 DA, 866 PL) were included. PL patients were younger (59.4 + 12.9 vs. 62.7 + 9.7; p<0.001) and had shorter follow-up (3.3 + 1.3 vs. 3.7 + 1.3 years; p<0.001) versus DA patients. There was no difference in postoperative UCLA score (6.0 + 1.9 vs. 6.0 + 2.0; p>0.9). PL patients reported increased moderate to severe trochanteric (21% vs. 14%; p<0.001) and groin pain (24% vs. 19%; p=0.004) than DA patients. There were no differences in anterior or lateral thigh, posterior thigh, low back, or buttock pain between the two cohorts (p=0.05–0.7). PL approach incision length did not impact the incidence or severity of patient-reported pain (p=0.3–0.7). Conclusion. When specifically queried, a significant proportion of patients experience persistent pain following THA via either a PL or DA approach. PL patients reported greater trochanteric and groin pain, although PL incision length did not impact the incidence or severity of patient-reported pain. Summary Statement. A significant proportion of patient experience persistent pain following THA, with an increased reporting of trochanteric and groin pain in those receiving a posterolateral versus anterior approach

Aims. The present study investigated the five-year interval changes in pseudotumours and measured serum metal ions at long-term follow-up of a previous report of 28 mm diameter metal-on-metal (MoM) total hip arthroplasty (THA). Patients and Methods. A total of 72 patients (mean age 46.6 years (37 to 55); 43 men, 29 women; 91 hips) who underwent cementless primary MoM THA with a 28 mm modular head were included. The mean follow-up duration was 20.3 years (18 to 24). All patients had CT scans at a mean 15.1 years (13 to 19) after the index operation and subsequent follow-up at a mean of 20.2 years (18 to 24). Pseudotumour volume, type of mass, and new-onset pseudotumours were evaluated using CT scanning. Clinical outcomes were assessed by Harris Hip Score (HHS) and the presence of groin pain. Serum metal ion (cobalt (Co) and chromium (Cr)) levels were measured at the latest follow-up. Results. At final follow-up, pseudotumours were observed in 26/91 hips (28.6%). There was an increase in volume of the pseudotumour in four hips (15.4%), no change in volume in 21 hips (80.8%), and a decrease in volume in one hip (3.8%). There were no new-onset pseudotumours. There was no significant difference in HHS between patients with and without pseudotumours. At final follow-up, mean serum Co ion levels and median Co:Cr ratios were significantly greater in patients with pseudotumours, but the serum Cr ion levels were not significantly different. Conclusion. At a mean 20 years of follow-up, pseudotumours were observed in 26/91 hips (28.6%) with no new-onset pseudotumours during subsequent follow-up. Most pseudotumours in small-head MoM THA were static in volume and asymptomatic with normal serum metal ion levels. Cite this article: Bone Joint J 2019;101-B:317–324

Large femoral heads have been used with increasing frequency over the last decade. The prime reason is likely the effect of large heads on stability. The larger head neck ratio, combined with the increased jump distance of larger heads result in a greater arc of impingement free motion, and greater resistance to dislocation in a provocative position. Multiple studies have demonstrated clear clinical efficacy in diminishing dislocation rates with the use of large femoral heads. With crosslinked polyethylene, wear has been shown to be equivalent between larger and smaller heads. However, the stability advantages of increasing diameter beyond 38 mm have not been clearly demonstrated. More importantly, recent data implicates large heads in the increasing prevalence of groin pain and psoas impingement. There are clear benefits with larger femoral head diameters, but the advantages of diameters beyond 38 mm have not yet been demonstrated clinically

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip replacements (THR). Hence, there is great interest in maximising stability to prevent this complication. Head size has been recognised to have a strong influence on the risk of dislocation post-operatively. As femoral head size increases, stability is augmented, secondary to an increase in impingement-free range of movement. Larger head sizes also greatly increase the ‘jump distance’ required for the head to dislocate in an appropriately positioned cup. Level-one studies support the use of larger diameter heads as they decrease the risk of dislocation following primary and revision THR. Highly cross-linked polyethylene has allowed us to increase femoral head size, without a marked increase in wear. However, the thin polyethylene liners necessary to accommodate larger heads may increase the risk of liner fracture and larger heads have also been implicated in causing soft-tissue impingement resulting in groin pain. Larger diameter heads also impart larger forces on the femoral trunnion, which may contribute to corrosion, metal release, and adverse local tissue reactions. Alternative large bearings including large ceramic heads and dual mobility bearings may mitigate some of these risks, and several of these devices have been used with clinical success. Cite this article: Bone Joint J 2014;96-B(11 Suppl A):23–6

Implantation of a large-diameter femoral head prosthesis with a metal-on-metal bearing surface reduces the risk of dislocation, increases the range of movement, minimises the risk of impingement and, in theory, results in little wear. Between February 2004 and March 2007 we implanted 100 consecutive total hip replacements with a metal-on-metal bearing and a large femoral head into 92 patients. There were 51 men and 41 women with a mean age of 50 years (18 to 70) at the time of surgery. Outcome was assessed using the Western Ontario McMaster University osteoarthritis index and the Harris hip score as well as the Devane activity score. These all improved significantly (p < 0.0001). At the last follow-up there were no cases of dislocation, no impingement, a good range of movement and no osteolysis, but seven revisions, two for infection and five for aseptic loosening. The probability of groin pain increased if the other acetabular component inclination exceeded 50° (p = 0.0007). At 4.8 years of follow-up, the projected survival of the Durom acetabular component, with revision for any reason, was 92.4% (. sd. 2.8) (95% confidence interval 89.6 to 95.2). The design of the component made it difficult both to orientate and seat, which when combined with a poor porous coating, produced unpredictable fixation and a low survival at five years

Background. Elite performance has tremendous physical demands and places elite athletes at an increased risk of sustaining a variety of orthopaedic injuries (1–4). Pain around the hip is common in high-level athletes representing up to 6% of all athletic injuries (5–7). Expedient diagnosis and effective treatment are paramount for their future sporting careers and to prevent subsequent joint degeneration. The purpose of this systematic review was to evaluate the outcome and the rate of return to play (RTP) following hip arthroscopy in elite athletes. Methods. A computer-based systematic search followed the PRISMA Guidelines (8) was performed using the 6 most comprehensive databases (CENTRAL, PUBMED, EMBASE, SCOPUS, EBSCO, Google Scholar and Web of Science) and included all published studies from inception until November 1. st. 2018. Weighted means were calculated for the rate of RTP and duration and for patient reported outcome measures (PROMs). Results. After eligibility screening, 17 articles were included with a total of 736 male and seven female patients, 761 hips and a mean age of 27.9±3.6 years. The mean follow-up period was 35.8±13.4 months and 17.1±12.3% of athletes had undergone bilateral hip arthroscopies. Overall, 93.9% (95% CI: 90.5, 96.6, P < 0.0001) of patients demonstrated return to sport after 6.7±2.5 months post-surgery and all PROMs improved post-operatively. During follow-up, 9.6% (95% CI: 5.2, 15.2, P = 0.025) patients needed further intervention. Conclusion. A high percentage of elite athletes return to the same level of competition after hip arthroscopy, with a low rate of further interventions. Hip arthroscopy appears to be an efficacious treatment for elite athletes suffering for hip and/or groin pain

Purpose. Femoroacetabular impingement syndrome (FAI) is a common cause of hip and groin pain in young adults. Physiotherapy and surgery have both been used to treat FAI syndrome, but there is no robust evidence of comparative effectiveness. UK FASHIoN compared the clinical and cost-effectiveness of arthroscopic hip surgery (HA) versus best conservative care in patients with FAI syndrome. Methods. UK FASHIoN was a pragmatic, multicentre, 2 parallel arm, superiority, randomised controlled trial in patients with FAI syndrome. Eligible patients were over 16 without radiographic signs of osteoarthritis, deemed suitable for arthroscopic FAI surgery. Participants were randomly allocated to HA or Personalised Hip Therapy (PHT - a physiotherapist-led programme comprising 6 to 10 sessions). The primary outcome measure was hip-related quality of life using the patient-reported International Hip Outcome Tool (iHOT-33) at 12 months. Secondary outcomes included EQ5D5L, SF12, adverse events, and cost-effectiveness. Primary analysis compared differences in iHOT-33 scores at 12 months by intention to treat. Results. 348 patients were randomised. Time to surgery was 132 days (SD71) versus 47 days (SD52) to PHT. 92.5% were followed-up at 12 months. Baseline mean iHOT-33 scores were 39.2 (SD21) and 35.6 (SD18) in the surgery and PHT groups, and at 12 months 58.8 (SD27) and 49.7 (SD25) respectively. Mean scores in both groups improved over 12 months, but the mean iHOT-33 score increased more in those allocated to HA than to PHT, with an adjusted mean difference of 6.8 points (95% CI 1.7,12.0 p=0.009). One HA patient developed an infection requiring further surgery. Mean overall costs were £3713 for HA and £1283 for PHT. Conclusions. Hip arthroscopy and best conservative care both led to improved hip-related quality of life in patients with FAI syndrome. At 12-month follow-up, improvement was greater in those allocated to hip arthroscopy

Trunnion corrosion in metal-on-polyethylene THA is poorly understood, with multifactorial etiology, and the patients present with “hip pain”. We analysed the presenting symptoms and signs, intraoperative findings and the early results and complications of operative treatment. One surgeon treated 9 patients (6 male, 3 female), mean age 74 years, with the onset of symptoms at a mean of 7 years (range 3–18) after index surgery. The taper size was 12/14 in seven, 14/16 in one, and 6 degree in one hip. The preoperative mean cobalt level was 7.1 ppb (range, 2.2–12.8) and mean chromium level was 2.2 ppb (range, 0.5–5.2). MARS MRI showed fluid collection and pseudotumor in 5, fluid collection only in two, and synovitis/debris in one hip. In one patient, there was no preoperative MRI. There were a myriad of clinical presentations: thigh rash alone in one; diffuse leg pain and hip rash in one; acute pseudo-sepsis in one; iliopsoas tendinitis and diffuse rash in one; trochanteric bursitis in one; groin pain only in one; thigh-buttock pain in two; and diffuse hip pain and limp in one patient. Intraoperatively, 6 patients had liner and ceramic (or oxidized zirconium) head exchange only. Three patients had concurrent acetabular revision: one for broken locking mechanism; one because liner was unavailable, and one had acetabular loosening. The postoperative metal levels decreased in all patients: mean cobalt 0.5 ppb (range, 0–1.8) and mean chromium 0.9 ppb (range, 0–2.6). Seven patients had good pain relief and no complications. There were two major complications requiring reoperation: acute infection at 6 weeks and patient required 2-stage reimplantation; and second patient had recurrent dislocation and was revised to a dual mobility component. Trunnion corrosion in metal-on-polyethylene THA has several clinical presentations, including local skin rash, iliopsoas tendinitis, and other limb dysfunction. There should be a high index of suspicion and serum cobalt/chromium levels are recommended for diagnosis. The patients should be counseled about possible postoperative complications

Aims

Precise implant positioning, tailored to individual spinopelvic biomechanics and phenotype, is paramount for stability in total hip arthroplasty (THA). Despite a few studies on instability prediction, there is a notable gap in research utilizing artificial intelligence (AI). The objective of our pilot study was to evaluate the feasibility of developing an AI algorithm tailored to individual spinopelvic mechanics and patient phenotype for predicting impingement.

Aims

The Birmingham Hip Resurfacing (BHR) was introduced in 1997 to address the needs of young active patients using a historically proven large-diameter metal-on-metal (MoM) bearing. A single designer surgeon’s consecutive series of 130 patients (144 hips) was previously reported at five and ten years, reporting three and ten failures, respectively. The aim of this study was to extend the follow-up of this original cohort at 25 years.

Aims

Achieving accurate implant positioning and restoring native hip biomechanics are key surgeon-controlled technical objectives in total hip arthroplasty (THA). The primary objective of this study was to compare the reproducibility of the planned preoperative centre of hip rotation (COR) in patients undergoing robotic arm-assisted THA versus conventional THA.

Introduction. A recent paper suggested implanting an uncemented acetabular shell which is 6mm or greater than the native femoral head in total hip arthroplasty (THA) significantly increased the risk of postoperative pain. We retrospectively analyzed 265 Delta ceramic-on-ceramic (DCoC) THA comparing the native femoral head size to the implanted shell and reviewing if the patient suffered with post-operative pain (POP). Methods. 265 consecutive THAs were performed using the Corail and Pinnacle prostheses with DCoC bearing. Native femoral head size was calculated retrospectively on pre-operative radiographs using TraumaCad software. All patients were sent questionnaires requesting information on satisfaction, sounds, postoperative pain and complications. Statistical analysis was then undertaken on the data. Results. Questionnaires were returned by 169 patients (189 hips). 42 patients reported postoperative pain. Patients suffering with pain had an average difference between native head and implanted shell of +6.8mm, compared to those without of +5.4mm. A shell of +6mm larger than the native head was associated with a statistically significant increase in the risk of postoperative pain (P=0.01). Patients with groin pain were more likely to have a smaller native head (46.1 Vs 47.3mm (P=0.046)). Patients with pain were more likely to complain of noisy hips (P=0.001). 70% of patients described being satisfied to the point where they forgot they had a THA. The dislocation rate was 1.1%. Discussion. A +6mm difference between native head and implanted shell was found to be a significant predictor of postoperative pain. We propose that to reduce the risk of postoperative pain, a limit of +4mm should be used. Overall complications were low and patients were very satisfied with their THA