Aims. The localization of necrotic areas has been reported to impact the prognosis and treatment strategy for osteonecrosis of the femoral head (ONFH). Anteroposterior localization of the necrotic area after a femoral neck fracture (FNF) has not been properly investigated. We hypothesize that the change of the weight loading direction on the femoral head due to residual posterior tilt caused by malunited FNF may affect the location of ONFH. We investigate the relationship between the posterior tilt angle (PTA) and anteroposterior localization of osteonecrosis using lateral hip radiographs. Methods. Patients aged younger than 55 years diagnosed with ONFH after FNF were retrospectively reviewed. Overall, 65 hips (38 males and 27 females; mean age 32.6 years (SD 12.2)) met the inclusion criteria. Patients with stage 1 or 4 ONFH, as per the Association Research Circulation Osseous classification, were excluded. The ratios of anterior and posterior viable areas and necrotic areas of the femoral head to the articular surface were calculated by setting the femoral head centre as the reference point. The PTA was measured using Palm’s method. The association between the PTA and viable or necrotic areas of the femoral head was assessed using Spearman’s rank correlation analysis (median PTA 6.0° (interquartile range 3 to 11.5)). Results. We identified a negative correlation between PTA and anterior viable areas (rho −0.477; p = 0.001), and no correlation between PTA and necrotic (rho 0.229; p = 0.067) or posterior viable areas (rho 0.204; p = 0.132). Conclusion. Our results suggest that residual posterior tilt after FNF could affect the anteroposterior localization of necrosis. Cite this article: Bone Jt Open 2024;5(5):394–400

Aims. Hyaline cartilage has a low capacity for regeneration. Untreated osteochondral lesions of the femoral head can lead to progressive and symptomatic osteoarthritis of the hip. The purpose of this study is to analyze the clinical and radiological long-term outcome of patients treated with osteochondral autograft transfer. To our knowledge, this study represents a series of osteochondral autograft transfer of the hip with the longest follow-up. Methods. We retrospectively evaluated 11 hips in 11 patients who underwent osteochondral autograft transfer in our institution between 1996 and 2012. The mean age at the time of surgery was 28.6 years (8 to 45). Outcome measurement included standardized scores and conventional radiographs. Kaplan-Meier survival curve was used to determine the failure of the procedures, with conversion to total hip arthroplasty (THA) defined as the endpoint. Results. The mean follow-up of patients treated with osteochondral autograft transfer was 18.5 years (9.3 to 24.7). Six patients developed osteoarthritis and had a THA at a mean of 10.3 years (1.1 to 17.3). The cumulative survivorship of the native hips was 91% (95% confidence interval (CI) 74 to 100) at five years, 62% (95% CI 33 to 92) at ten years, and 37% (95% CI 6 to 70) at 20 years. Conclusion. This is the first study analyzing the long-term results of osteochondral autograft transfer of the femoral head. Although most patients underwent conversion to THA in the long term, over half of them survived more than ten years. Osteochondral autograft transfer could be a time-saving procedure for young patients with devastating hip conditions who have virtually no other surgical options. A larger series or a similar matched cohort would be necessary to confirm these results which, in view of the heterogeneity of our series, seems difficult to achieve. Cite this article: Bone Jt Open 2023;4(7):523–531

Aims. Surgical treatment of young femoral neck fractures often requires an open approach to achieve an anatomical reduction. The application of a calcar plate has recently been described to aid in femoral neck fracture reduction and to augment fixation. However, application of a plate may potentially compromise the regional vascularity of the femoral head and neck. The purpose of this study was to investigate the effect of calcar femoral neck plating on the vascularity of the femoral head and neck. Methods. A Hueter approach and capsulotomy were performed bilaterally in six cadaveric hips. In the experimental group, a one-third tubular plate was secured to the inferomedial femoral neck at 6:00 on the clockface. The contralateral hip served as a control with surgical approach and capsulotomy without fixation. Pre- and post-contrast MRI was then performed to quantify signal intensity in the femoral head and neck. Qualitative assessment of the terminal arterial branches to the femoral head, specifically the inferior retinacular artery (IRA), was also performed. Results. Quantitative MRI revealed a mean reduction of 1.8% (SD 3.1%) of arterial contribution in the femoral head and a mean reduction of 7.1% (SD 10.6%) in the femoral neck in the plating group compared to non-plated controls. Based on femoral head quadrant analysis, the largest mean decrease in arterial contribution was in the inferomedial quadrant (4.0%, SD 6.6%). No significant differences were found between control and experimental hips for any femoral neck or femoral head regions. The inferior retinaculum of Weitbrecht (containing the IRA) was directly visualized in six of 12 specimens. Qualitative MRI assessment confirmed IRA integrity in all specimens. Conclusion. Calcar femoral neck plating at the 6:00 position on the clockface resulted in minimal decrease in femoral head and neck vascularity, and therefore it may be considered as an adjunct to laterally-based fixation for reduction and fixation of femoral neck fractures, especially in younger patients. Cite this article: Bone Jt Open 2021;2(8):611–617

Aims. Eccentric reductions may become concentric through femoral head ‘docking’ (FHD) following closed reduction (CR) for developmental dysplasia of the hip (DDH). However, changes regarding position and morphology through FHD are not well understood. We aimed to assess these changes using serial MRI. Methods. We reviewed 103 patients with DDH successfully treated by CR and spica casting in a single institution between January 2016 and December 2020. MRI was routinely performed immediately after CR and at the end of each cast. Using MRI, we described the labrum-acetabular cartilage complex (LACC) morphology, and measured the femoral head to triradiate cartilage distance (FTD) on the midcoronal section. A total of 13 hips with initial complete reduction (i.e. FTD < 1 mm) and ten hips with incomplete MRI follow-up were excluded. A total of 86 patients (92 hips) with a FTD > 1 mm were included in the analysis. Results. At the end of the first cast period, 73 hips (79.3%) had a FTD < 1 mm. Multiple regression analysis showed that FTD (p = 0.011) and immobilization duration (p = 0.028) were associated with complete reduction. At the end of the second cast period, all 92 hips achieved complete reduction. The LACC on initial MRI was inverted in 69 hips (75.0%), partly inverted in 16 hips (17.4%), and everted in seven hips (7.6%). The LACC became everted-congruent in 45 hips (48.9%) and 92 hips (100%) at the end of the first and second cast period, respectively. However, a residual inverted labrum was present in 50/85 hips (58.8%) with an initial inverted or partly inverted LACC. Conclusion. An eccentric reduction can become concentric after complete reduction and LACC remodelling following CR for DDH. Varying immobilization durations were required for achieving complete reduction. A residual inverted labrum was present in more than half of all hips after LACC remodelling. Cite this article: Bone Joint J 2023;105-B(2):140–147

Aims. To investigate whether idiopathic osteonecrosis of the femoral head (ONFH) is related to impaired osteoblast activities. Methods. We cultured osteoblasts isolated from trabecular bone explants taken from the femoral head and the intertrochanteric region of patients with idiopathic ONFH, or from the intertrochanteric region of patients with osteoarthritis (OA), and compared their viability, mineralization capacity, and secretion of paracrine factors. Results. Osteoblasts from the intertrochanteric region of patients with ONFH showed lower alkaline phosphatase (ALP) activity and mineralization capacity than osteoblasts from the same skeletal site in age-matched patients with OA, as well as lower messenger RNA (mRNA) levels of genes encoding osteocalcin and bone sialoprotein and higher osteopontin expression. In addition, osteoblasts from patients with ONFH secreted lower osteoprotegerin (OPG) levels than those from patients with OA, resulting in a higher receptor activator of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) ligand (RANKL)-to-OPG ratio. In patients with ONFH, osteoblasts from the femoral head showed reduced viability and mineralized nodule formation compared with osteoblasts from the intertrochanteric region. Notably, the secretion of the pro-resorptive factors interleukin-6 and prostaglandin E. 2. as well as the RANKL-to-OPG ratio were markedly higher in osteoblast cultures from the femoral head than in those from the intertrochanteric region. Conclusion. Idiopathic ONFH is associated with a reduced mineralization capacity of osteoblasts and increased secretion of pro-resorptive factors. Cite this article: Bone Joint Res 2021;10(9):619–628

Aims. Avascular femoral head necrosis in the context of gymnastics is a rare but serious complication, appearing similar to Perthes’ disease but occurring later during adolescence. Based on 3D CT animations, we propose repetitive impact between the main supplying vessels on the posterolateral femoral neck and the posterior acetabular wall in hyperextension and external rotation as a possible cause of direct vascular damage, and subsequent femoral head necrosis in three adolescent female gymnasts we are reporting on. Methods. Outcome of hip-preserving head reduction osteotomy combined with periacetabular osteotomy was good in one and moderate in the other up to three years after surgery; based on the pronounced hip destruction, the third received initially a total hip arthroplasty. Results. The described pathology is quite devastating, and extensive joint preserving surgery (which has been shown successful in Perthes’ cases) was less successful in this patient cohort. Conclusion. Supraselective angiography may be helpful to improve pathomechanical understanding and surgical decision making. Cite this article: Bone Jt Open 2022;3(9):666–673

Aims. Bone marrow-derived mesenchymal stem cells obtained from bone marrow aspirate concentrate (BMAC) with platelet-rich plasma (PRP), has been used as an adjuvant to hip decompression. Early results have shown promise for hip preservation in patients with osteonecrosis (ON) of the femoral head. The purpose of the current study is to examine the mid-term outcome of this treatment in patients with precollapse corticosteroid-induced ON of the femoral head. Methods. In all, 22 patients (35 hips; 11 males and 11 females) with precollapse corticosteroid-induced ON of the femoral head underwent hip decompression combined with BMAC and PRP. Mean age and BMI were 43 years (SD 12) and 31 kg/m² (SD 6), respectively, at the time of surgery. Survivorship free from femoral head collapse and total hip arthroplasty (THA) and risk factors for progression were evaluated at minimum five-years of clinical follow-up with a mean follow-up of seven years (5 to 8). Results. Survivorship free from femoral head collapse and THA for any reason was 84% and 67% at seven years postoperatively, respectively. Risk factors for conversion to THA included a high preoperative modified Kerboul angle (grade 3 or 4) based on preoperative MRI (hazard ratio (HR) 3.96; p = 0.047) and corticosteroid use at the time of decompression (HR 4.15; p = 0.039). The seven-year survivorship for patients with grade 1 or 2 Kerboul angles for conversion to THA for articular collapse, and THA for any reason, were 96% and 72%, respectively, versus THA for articular collapse and THA for any reason in patients with grade 3 or 4 Kerboul angles of 40% (p = 0.003) and 40% (p = 0.032). Conclusion. At seven years, hip decompression augmented with BMAC and PRP provided a 67% survivorship free from THA in patients with corticosteroid-induced ON. Ideal candidates for this procedure are patients with low preoperative Kerboul angles and can stop corticosteroid treatment prior to decompression. Cite this article: Bone Jt Open 2021;2(11):926–931

Aims. Ganz’s studies made it possible to address joint deformities on both the femoral and acetabular side brought about by Perthes’ disease. Femoral head reduction osteotomy (FHRO) was developed to improve joint congruency, along with periacetabular osteotomy (PAO), which may enhance coverage and containment. The purpose of this study is to show the clinical and morphological outcomes of the technique and the use of an implemented planning approach. Methods. From September 2015 to December 2021, 13 FHROs were performed on 11 patients for Perthes’ disease in two centres. Of these, 11 hips had an associated PAO. A specific CT- and MRI-based protocol for virtual simulation of the corrections was developed. Outcomes were assessed with radiological parameters (sphericity index, extrusion index, integrity of the Shenton’s line, lateral centre-edge angle (LCEA), Tönnis angle), and clinical parameters (range of motion, visual analogue scale (VAS) for pain, Merle d'Aubigné-Postel score, modified Harris Hip Score (mHHS), and EuroQol five-dimension five-level health questionnaire (EQ-5D-5L)). Early and late complications were reported. Results. The mean follow-up was 39.7 months (standard deviation (SD) 26.4). The mean age at surgery was 11.4 years (SD 1.6). No major complications were recorded. One patient required a total hip arthroplasty. Mean femoral head sphericity increased from 46.8% (SD 9.34%) to 70.2% (SD 15.44; p < 0.001); mean LCEA from 19.2° (SD 9.03°) to 44° (SD 10.27°; p < 0.001); mean extrusion index from 37.8 (SD 8.70) to 7.5 (SD 9.28; p < 0.001); and mean Tönnis angle from 16.5° (SD 12.35°) to 4.8° (SD 4.05°; p = 0.100). The mean VAS improved from 3.55 (SD 3.05) to 1.22 (1.72; p = 0.06); mean Merle d’Aubigné-Postel score from 14.55 (SD 1.74) to 16 (SD 1.6; p = 0.01); and mean mHHS from 60.6 (SD 18.06) to 81 (SD 6.63; p = 0.021). The EQ-5D-5L also showed significant improvements. Conclusion. FHRO associated with periacetabular procedures is a safe technique that showed improved functional, clinical, and morphological outcomes in Perthes’ disease. The newly introduced simulation and planning algorithm may help to further refine the technique. Cite this article: Bone Joint J 2024;106-B(5 Supple B):40–46

Aims. Hip arthroplasty aims to accurately recreate joint biomechanics. Considerable attention has been paid to vertical and horizontal offset, but femoral head centre in the anteroposterior (AP) plane has received little attention. This study investigates the accuracy of restoration of joint centre of rotation in the AP plane. Methods. Postoperative CT scans of 40 patients who underwent unilateral uncemented total hip arthroplasty were analyzed. Anteroposterior offset (APO) and femoral anteversion were measured on both the operated and non-operated sides. Sagittal tilt of the femoral stem was also measured. APO measured on axial slices was defined as the perpendicular distance between a line drawn from the anterior most point of the proximal femur (anterior reference line) to the centre of the femoral head. The anterior reference line was made parallel to the posterior condylar axis of the knee to correct for rotation. Results. Overall, 26/40 hips had a centre of rotation displaced posteriorly compared to the contralateral hip, increasing to 33/40 once corrected for sagittal tilt, with a mean posterior displacement of 7 mm. Linear regression analysis indicated that stem anteversion needed to be increased by 10.8° to recreate the head centre in the AP plane. Merely matching the native version would result in a 12 mm posterior displacement. Conclusion. This study demonstrates the significant incidence of posterior displacement of the head centre in uncemented hip arthroplasty. Effects of such displacement include a reduction in impingement free range of motion, potential alterations in muscle force vectors and lever arms, and impaired proprioception due to muscle fibre reorientation. Cite this article: Bone Joint Res 2022;11(3):180–188

Aims. The lateral centre-edge angle (LCEA) is a plain radiological measure of superolateral cover of the femoral head. This study aims to establish the correlation between 2D radiological and 3D CT measurements of acetabular morphology, and to describe the relationship between LCEA and femoral head cover (FHC). Methods. This retrospective study included 353 periacetabular osteotomies (PAOs) performed between January 2014 and December 2017. Overall, 97 hips in 75 patients had 3D analysis by Clinical Graphics, giving measurements for LCEA, acetabular index (AI), and FHC. Roentgenographical LCEA, AI, posterior wall index (PWI), and anterior wall index (AWI) were measured from supine AP pelvis radiographs. The correlation between CT and roentgenographical measurements was calculated. Sequential multiple linear regression was performed to determine the relationship between roentgenographical measurements and CT FHC. Results. CT-measured LCEA and AI correlated strongly with roentgenographical LCEA (r = 0.92; p < 0.001) and AI (r = 0.83; p < 0.001). Radiological LCEA correlated very strongly with CT FHC (r = 0.92; p < 0.001). The sum of AWI and PWI also correlated strongly with CTFHC (r = 0.73; p < 0.001). CT measurements of LCEA and AI were 3.4° less and 2.3° greater than radiological LCEA and AI measures. There was a linear relation between radiological LCEA and CT FHC. The linear regression model statistically significantly predicted FHC from LCEA, F(1,96) = 545.1 (p < 0.001), adjusted R. 2. = 85.0%, with the prediction equation: CT FHC(%) = 42.1 + 0.77(XRLCEA). Conclusion. CT and roentgenographical measurement of acetabular parameters are comparable. Currently, a radiological LCEA greater than 25° is considered normal. This study demonstrates that those with hip pain and normal radiological acetabular parameters may still have deficiencies in FHC. More sophisticated imaging techniques such as 3D CT should be considered for those with hip pain to identify deficiencies in FHC. Cite this article: Bone Jt Open 2022;3(1):12–19

Cite this article: Bone Joint Res 2023;12(1):5–8.

Large ceramic femoral heads offer several advantages that are potentially advantageous to patients undergoing both primary and revision total hip replacement. Many high-quality studies have demonstrated the benefit of large femoral heads in reducing post-operative instability. Ceramic femoral heads may also offer an advantage in reducing polyethylene wear that has been reported in vitro and is starting to become clinically apparent in mid-term clinical outcome studies. Additionally, the risk of taper corrosion at a ceramic femoral head–neck junction is clearly lower than when using a metal femoral head. With improvements in the material properties of both modern ceramic femoral heads and polyethylene acetabular liners that have reduced the risk of mechanical complications, large ceramic heads have gained popularity in recent years. Cite this article: Bone Joint J 2013;95-B, Supple A:63–6

This preliminary study evaluates a combination of bone morphogenetic protein (BMP)-7 and non-vascularised autologous fibular grafting (AFG) for the treatment of osteonecrosis of the femoral head. BMP-7/AFG combination was applied in seven pre-collapse femoral heads (five Steinberg stage II, two stage III) in six patients. Pre- and post-operative evaluation included clinical (Harris hip score (HHS), visual analogue scale (VAS) for pain) and radiological assessment (radiographs, quantitative CT) at a mean follow-up of 4 years (2 to 5.5). A marked improvement of function (mean HHS increase of 49.2) and decrease of pain level (mean VAS decrease of 5) as well as retention of the sphericity of the femoral head was noted in five hips at the latest follow-up, while signs of consolidation were apparent from the third post-operative month. One patient (two hips) required bilateral total hip replacement at one year post-operatively. In the series as a whole, quantitative-CT evaluation revealed similar densities between affected and normal bone. Heterotopic ossification was observed in four hips, without compromise of the clinical outcome. In this limited series AFG/BMP-7 combination proved a safe and effective method for the treatment of femoral head osteonecrosis, leading to early consolidation of the AFG and preventing collapse in five of seven hips, while the operative time and post-operative rehabilitation period were much shorter compared with free vascularised fibular grafts. Cite this article: Bone Joint J 2014;96-B:31–5

Free vascularised fibular grafting has been reported to be successful for adult patients with osteonecrosis of the femoral head (ONFH). However, its benefit in teenage patients with post-traumatic ONFH has not been determined. We evaluated the effectiveness of free vascularised fibular grafting in the treatment of this condition in children and adolescents. We retrospectively analysed 28 hips in 28 patients in whom an osteonecrotic femoral head had been treated with free vascularised fibular grafting between 2002 and 2008. Their mean age was 16.3 years (13 to 19). The stage of the disease at time of surgery, and results of treatment including pre- and post-operative Harris hip scores, were studied. We defined clinical failure as conversion to total hip replacement. All patients were followed up for a mean of four years (2 to 7). The mean Harris hip score improved from 60.4 (37 to 84) pre-operatively to 94.2 (87 to 100) at final follow-up. At the latest follow-up we found improved or unchanged radiographs in all four initially stage II hips and in 23 of 24 stage III or IV hips. Only one hip (stage V) deteriorated. No patient underwent total hip replacement. Free vascularised fibular grafting is indicated for the treatment of post-traumatic ONFH in teenage patients

Background. Using one-stage bilateral free vascularized fibular grafting (FVFG) to treat avascular necrosis of the femoral head (ANFH) remains controversy due to potential high-risk and technical complexity. The purpose of the present study was to evaluate the safety and effectiveness of one-stage bilateral FVFG procedure versus unilateral FVFG in the treatment of ANFH. Methods. One-stage bilateral FVFG was performed for 26 patients with bilateral ANFH between March 2001 and September 2006. The clinical and radiographic outcomes, hospital stays, and postoperative complications in this group were compared with those from another 33 patients (40 hips) receiving unilateral FVFG. Results. The two groups had similar hospital stays, clinical outcome, and few complications. In an average follow-up of 36 months, one major and five minor complications were encountered in the onestage bilateral group, and one major and three minor complications in the unilateral group. The mean Harris hip scores increased from 63.8±16.795%CI: 61.266.4 to 84.2±1795% CI: 81.586.9 points in the unilateral group and from 61.7±22.295%CI: 58.664.8 to 82.0±16.6 95%CI:79.784.3 points in the one-stage bilateral group. In radiographic, there was no obvious difference in progression of collapse between the two groups. Conversion to hip arthroplasty was performed in 2 (5%) hips in the unilateral group and none in the one-stage bilateral group, with no statistically significant difference between the two groups. Conclusion. Using one-stage bilateral FVFG to treat ANFH is a safe and effective method with minor postoperative morbidity

Abstract. Objectives. To analyse the costs and benefits of sending femoral head specimens for histopathological analysis and whether our practice had changed since the original study five years ago. Methods. The cohort definition was patients who had both undergone hip hemiarthroplasties (HHAs) and had femoral head specimens sent for histopathological analysis at our tertiary care institution from 2013 to 2016. Retrospective review of clinical and electronic notes was performed on these patients for history of malignancy, histopathological diagnosis of femoral head, indication for histopathological examination and radiological studies. The total number of HHAs performed at the centre and the costs involved in analysing each femoral head specimen were identified. Results. A total of 805 HHAs were performed at the centre. We identified 56 femoral head specimens from 56 patients (6.96%) that were sent for histopathological analysis after HHA. 29 patients (51.79%) had a known history of malignancy. Three femoral head specimens (10.34%) were histologically positive for malignancy. Two patients had hip radiographs demonstrating metastasis to the femoral head. The third patient had a PET-CT scan two weeks prior to fracture that did not show signs of metastatic disease. 27 patients (48.21%) had no history of malignancy. None of their femoral head specimens were found to be histologically positive for malignancy. 10 patients had no appropriate indication for histopathological analysis. The cost savings for 27 patients with no previous history of malignancy ranged from €2,295 to €9,504. The cost savings for 10 patients with no appropriate indication ranged from €850 to €3,520. Conclusions. Histopathological analysis of femoral head specimens after HHA has little benefit for patients without a history of malignancy. The practice at our institution had not changed significantly in the past five years. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Aims. The aims of this study were to review the surgical technique for a combined femoral head reduction osteotomy (FHRO) and periacetabular osteotomy (PAO), and to report the short-term clinical and radiological results of a combined FHRO/PAO for the treatment of selected severe femoral head deformities. Patients and Methods. Between 2011 and 2016, six female patients were treated with a combined FHRO and PAO. The mean patient age was 13.6 years (12.6 to 15.7). Clinical data, including patient demographics and patient-reported outcome scores, were collected prospectively. Radiologicalally, hip morphology was assessed evaluating the Tönnis angle, the lateral centre to edge angle, the medial offset distance, the extrusion index, and the alpha angle. Results. The mean follow-up was 3.3 years (2 to 4.6). The modified Harris Hip Score improved by 33.0 points from 53.5 preoperatively to 83.4 postoperatively (p = 0.03). The Western Ontario McMasters University Osteoarthritic Index score improved by 30 points from 62 preoperatively to 90 postoperatively (p = 0.029). All radiological parameters showed significant improvement. There were no long-term disabilities and none of the hips required early conversion to total hip arthroplasty. Conclusion. FHRO combined with a PAO resulted in clinical and radiological improvement at short-term follow-up, suggesting it may serve as an appropriate salvage treatment option for selected young patients with severe symptomatic hip deformities

Aims. In this study, we aimed to visualize the spatial distribution characteristics of femoral head necrosis using a novel measurement method. Methods. We retrospectively collected CT imaging data of 108 hips with non-traumatic osteonecrosis of the femoral head from 76 consecutive patients (mean age 34.3 years (SD 8.1), 56.58% male (n = 43)) in two clinical centres. The femoral head was divided into 288 standard units (based on the orientation of units within the femoral head, designated as N[Superior], S[Inferior], E[Anterior], and W[Posterior]) using a new measurement system called the longitude and latitude division system (LLDS). A computer-aided design (CAD) measurement tool was also developed to visualize the measurement of the spatial location of necrotic lesions in CT images. Two orthopaedic surgeons independently performed measurements, and the results were used to draw 2D and 3D heat maps of spatial distribution of necrotic lesions in the femoral head, and for statistical analysis. Results. The results showed that the LLDS has high inter-rater reliability. As illustrated by the heat map, the distribution of Japanese Investigation Committee (JIC) classification type C necrotic lesions exhibited clustering characteristics, with the lesions being concentrated in the northern and eastern regions, forming a hot zone (90% probability) centred on the N4-N6E2, N3-N6E units of outer ring blocks. Statistical results showed that the distribution difference between type C2 and type C1 was most significant in the E1 and E2 units and, combined with the heat map, indicated that the spatial distribution differences at N3-N6E1 and N1-N3E2 units are crucial in understanding type C1 and C2 necrotic lesions. Conclusion. The LLDS can be used to accurately measure the spatial location of necrotic lesions and display their distribution characteristics. Cite this article: Bone Joint Res 2024;13(6):294–305

Aims. In metal-on-polyethylene (MoP) total hip arthroplasty (THA), large metal femoral heads have been used to increase stability and reduce the risk of dislocation. The increased size of the femoral head can, however, lead to increased taper corrosion, with the release of metal ions and adverse reactions. The aim of this study was to investigate the relationship between the size of the femoral head and the levels of metal ions in the blood in these patients. Methods. A total of 96 patients were enrolled at two centres and randomized to undergo MoP THA using either a 32 mm metal head or a femoral head of between 36 mm and 44 mm in size, being the largest possible to fit the thinnest available polyethylene insert. The levels of metal ions and patient-reported outcome measures (Oxford Hip Score, University of California, Los Angeles Activity Scale) were recorded at two and five years postoperatively. Results. At five years, the median levels of chromium, cobalt, and titanium were 0.5 μg/l (interquartile range (IQR) 0.50 to 0.62), 0.24 μg/l (IQR 0.18 to 0.30), and 1.16 μg/l (IQR 1.0 to 1.68) for the 32 mm group, and 0.5 μg/l (IQR 0.5 to 0.54), 0.23 μg/l (IQR 0.17 to 0.39), and 1.30 μg/l (IQR 1 to 2.05) for the 36 mm to 44 mm group, with no significant difference between the groups (p = 0.825, p = 1.000, p = 0.558). There were increased levels of metal ions at two years postoperatively in seven patients in the 32 mm group, compared with four in the 36 mm to 44 mm group, and at five years postoperatively in six patients in the 32 mm group, compared with seven in the 36 mm to 44 mm group. There was no significant difference in either the OHS (p = 0.665) or UCLA (p = 0.831) scores between patients with or without an increased level of metal ions. Conclusion. In patients who underwent MoP THA, we found no differences in the levels of metal ions five years postoperatively between those with a femoral head of 32 mm and those with a femoral head of between 36 mm and 44 mm, and no corrosion-related revisions. As taper corrosion can start after five years, there remains a need for longer-term studies investigating the relationship between the size of the femoral head size and corrosion in patients undergoing MoP THA. Cite this article: Bone Joint J 2024;106-B(3 Supple A):31–37