Financial analysis of revision hip surgery at a tertiary referral centre as classified using the British Hip Society Revision Hip Complexity Classification.

Aims: The burden of revision total hip arthroplasty (rTHA) continues to grow. The surgery is complex and associated with significant costs. Regional rTHA networks have been proposed to improve outcomes and to reduce re-revisions, and therefore costs. The aim of this study was to accurately quantify the cost and reimbursement for a rTHA service, and to assess the financial impact of case complexity at a tertiary referral centre within the NHS. Methods: A retrospective analysis of all revision hip procedures was performed at this centre over two consecutive financial years (2018 to 2020). Cases were classified according to the Revision Hip Complexity Classification (RHCC) and whether they were infected or non-infected. Patients with an American Society of Anesthesiologists (ASA) grade ≥ III or BMI ≥ 40 kg/m2 are considered "high risk" by the RHCC. Costs were calculated using the Patient Level Information and Costing System (PLICS), and remuneration based on Healthcare Resource Groups (HRG) data. The primary outcome was the financial difference between tariff and cost per patient episode. Results: In all, 199 revision episodes were identified in 168 patients: 25 (13%) least complex revisions (H1); 110 (55%) complex revisions (H2); and 64 (32%) most complex revisions (H3). Of the 199, 76 cases (38%) were due to infection, and 78 patients (39%) were "high risk". Median length of stay increased significantly with case complexity from four days to six to eight days (p = 0.006) and for revisions performed for infection (9 days vs 5 days; p < 0.001). Cost per episode increased significantly between complexity groups (p < 0.001) and for infected revisions (p < 0.001). All groups demonstrated a mean deficit but this significantly increased with revision complexity (£97, £1,050, and £2,887 per case; p = 0.006) and for infected failure (£2,629 vs £635; p = 0.032). The total deficit to the NHS Trust over two years was £512,202. Conclusion: Current NHS reimbursement for rTHA is inadequate and should be more closely aligned to complexity. An increase in the most complex rTHAs at major revision centres will likely place a greater financial burden on these units.

Is medical dissolution treatment for uric acid stones more cost-effective than surgical treatment? A novel, solo practice, retrospective cost-analysis of medical vs. surgical therapy.

INTRODUCTION: Effective medical dissolution therapy (MDT) for uric acid stones is more cost-effective than surgical treatment; however, treatment failure may be associated with increased cost. We aimed to study the cost-effectiveness of MDT for uric acid stones vs. surgical management. METHODS: We performed a retrospective study within our institution of all patients receiving MDT for uric acid stones from 2008-2019. All patients had a known history of uric acid stones, urine pH ≤5.5, and <500 Hounsfield units on preoperative computed tomography (CT). The cost of treatment in the dissolution group was compared to the cost of primary surgical treatment in a theoretical matched cohort. Cost was estimated using local Medicare reimbursement scales. Statistical analysis was performed with SPSS Statistics. RESULTS: A total of 28 patients were identified, of which 18 were included in the study. Complete and partial dissolution occurred in six (33%) and four (22%) patients, respectively. Five (28%) patients developed symptoms and underwent ureteral stent placement. Ureteroscopy and percutaneous nephrolithotomy (PCNL) were each performed in three (17%) patients in whom dissolution treatment was not effective on followup CT. Following dissolution trial, six (33%) patients had residual stone burden requiring surgical intervention. The average cost of treatment, including surgeries, was $14 604 in the dissolution group vs. $17 680 in the surgical cohort. The average cost to achieve stone-free status in patients with complete, partial, or no response to dissolution were $1675, $10 124, and $21 584, respectively, while primary surgical treatment for the same patients would cost $15 037, $10 901, and $20 511, respectively. CONCLUSIONS: Successful MDT is highly cost-effective. Incomplete response to dissolution can stem from several reasons and contributes to higher costs and likely decreased quality of life.

Comparison of Acetabular Measurements Between 2 Validated Software Programs Used in Hip Preservation Surgery.

BACKGROUND: Validated software tools (Clinical Graphics [CG] and Hip2Norm) permit measurement of the percentage of femoral head coverage (%FHC), which aids in morphological classification and prediction of outcome after hip preservation surgery. PURPOSE: (1) To assess whether acetabular parameter measurements determined from 2 commonly used software systems are comparable. (2) To determine which parameters influence the correlation or differences between software outputs and measurements. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: The study included 69 patients (90 hips) who underwent periacetabular osteotomy and had comprehensive preoperative imaging available. Lateral center-edge angle (LCEA), acetabular index (AI), and %FHC were determined using 3-dimensional computed tomography (CT) measurements by CG and Hip2Norm software. Images of 18 pelvises were segmented to determine spinopelvic parameters and subtended acetabular angles. Between-group measurements were compared using correlation coefficients and Bland-Altman analyses. The difference in the outputs of the 2 programs was defined as delta (Δ). Radiographic parameters were tested to assess whether they were responsible for differences in %FHC between software programs. RESULTS: Strong correlations between LCEA (ρ = 0.862) and AI (ρ = 0.825) measurements were seen between the Hip2Norm and CG programs. However, weak correlation was seen in the estimate of %FHC (ρ = 0.358), with the presence of a systematic error. Hip2Norm consistently produced lower anterior, posterior, and total %FHC values than CG. The %FHC determined by CG, but not Hip2Norm, correlated with acetabular subtended angles (P < .05). Pelvic tilt measured on CT did not correlate with pelvic tilt estimated by Hip2Norm (P = .56), and ΔPelvicTilt strongly correlated with the difference in %FHC by the 2 software programs (ρ = 0.63; P = .005), pelvic incidence (ρ = 0.73; P < .001), and pelvic tilt (ρ = -0.91; P < .001) as per CT. CONCLUSION: The correlation of %FHC between Hip2Norm and CG was weak (ρ = 0.358). The difference in measurements of %FHC correlated with ΔPelvicTilt. The %FHC determined by CG strongly correlated with the segmented acetabular subtended angles and thus more likely reflected true values. Hip preservation surgeons should be aware of these measurement differences because %FHC is important in the diagnosis and prognosis of acetabular dysplasia.

Do acetabular parameters measured on 2D imaging correlate with CT, and can lateral centre-edge angle predict femoral head coverage?

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 R2 = 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.

Outcomes and rates of dissolution therapy for uric acid stones.

INTRODUCTION: To describe the outcomes and quantify the rate of uric acid stone medical dissolution therapy using automated, software-generated stone volume measurements. METHODS: A sample of patients treated with oral dissolution therapy was reviewed from a single institution between 2008 and 2019. Baseline patient demographics, metabolic urine testing and stone characteristics were collected. Computed tomography (CT) scan images were evaluated using the quantitative Stone Analysis Software (qSAS) to obtain total stone volume (TSV), maximum diameter (MD) and stone number. Rate of dissolution using total stone volume was calculated over the treatment period. RESULTS: Twenty-seven patients were started on oral dissolution therapy, corrected for renal function. After mean duration of 180 days (range 41-531), 16 patients failed treatment resulting in surgical therapy. Twenty stones in 11 patients showed complete or partial dissolution. Compared to those who failed treatment, patients with complete or partial dissolution had lower 24 h urinary uric acid and higher treatment urine pH. Thirteen (65%) stones showed complete dissolution after a mean 167.6 days. Rate of change for responders was 4.73 mm3 or 0.6% of total stone volume per day. Time to dissolution of one half of stone volume based on total stone volume was 86 days (12.30 weeks). DISCUSSION/CONCLUSIONS: Software-calculated total stone volume may be an effective method of measuring uric acid stone response to oral alkalization therapy. Stone volume decreased by 50% after 12.3 weeks of treatment and could be an important benchmark for oral dissolution therapyoral dissolution therapy. Further studies with a larger sample and validation of the software are needed to confirm if this can be used to guide surveillance schedules for dissolution therapy.

Acetabular Morphology and Spinopelvic Characteristics: What Predominantly Determines Functional Acetabular Version?

BACKGROUND: In addition to the relative size of the acetabular rim and how the pelvis is positioned in space, the plane in which the acetabular version is calculated also affects its measurement. PURPOSE: To determine the relative contribution of pelvic and acetabular characteristics on morphological version (measured relative to the anterior pelvic plane angle [APPA]) and functional version (measured relative to the horizontal table). STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Included were 50 acetabular dysplasia patients and 109 asymptomatic controls. Using image analysis software, morphological parameters of the pelvis and acetabulum were determined from 2-dimensional computed topography: pelvic incidence, pelvic tilt angle, sacral slope, APPA, morphological and functional acetabular versions, and subtended angles (measure of acetabular rim prominence relative to the femoral head center) around the acetabular clockface in 30° increments. Correlation and multivariable regression analyses were performed with morphological and functional version as dependent variables and spinopelvic and acetabular parameters as independent variables. RESULTS: Morphological version was moderately associated with differences between anterior and posterior subtended angles (R = 0.68 [P < .001] and R = 0.57 [P < .001] for differences at 165° and 15° and 135° and 45°, respectively). Functional version was moderately associated with pelvic tilt angle (R = 0.56; P <.001) and the difference in subtended angles between anterior and posterior rims (R = 0.61 [P < .001] and R = 0.50 [P < .001] for differences at 165° and 15° and 135° and 45°, respectively). Multivariate analysis revealed a good model for predicting morphological version (R 2 = 0.44; P < .01) and functional version (R 2 = 0.58; P < .01). Subtended angle difference between 165° and 15° (B = 0.36 [95% CI, 0.24-0.49]; P < .001) was most strongly related to morphological version, and pelvic tilt angle (B = 0.57 [95% CI, 0.46-0.68]; P < .001) was most strongly related to functional version. CONCLUSION: Functional acetabular version was influenced most strongly by pelvic tilt angle rather than the relative prominence of the acetabular rims. Before determining surgical management for version abnormalities, it would be prudent to assess pelvic mobility and characteristics in different functional positions. In patients with minimal pelvic tilt change dynamically, corrective osteotomy would be the treatment of choice to improve functional version.

Is a periacetabular osteotomy as efficacious in retroversion as it is in dysplasia? : The role of femoral anteversion on outcome.

AIMS: Periacetabular osteotomy (PAO) is an established treatment for acetabular dysplasia. It has also been proposed as a treatment for patients with acetabular retroversion. By reviewing a large cohort, we aimed to test whether outcome is equivalent for both types of morphology and identify factors that influenced outcome. METHODS: A single-centre, retrospective cohort study was performed on patients with acetabular retroversion treated with PAO (n = 62 hips). Acetabular retroversion was diagnosed clinically and radiologically (presence of a crossover sign, posterior wall sign, lateral centre-edge angle (LCEA) between 20° and 35°). Outcomes were compared with a control group of patients undergoing PAO for dysplasia (LCEA < 20°; n = 86 hips). Femoral version was recorded. Patient-reported outcome measures (PROMs), complications, and reoperation rates were measured. RESULTS: The mean Non-Arthritic Hip Score (NAHS) preoperatively was 58.6 (SD 16.1) for the dysplastic hips and 52.5 (SD 12.7) for the retroverted hips (p = 0.145). Postoperatively, mean NAHS was 83.0 (SD 16.9) and 76.7 (SD 17.9) for dysplastic and retroverted hips respectively (p = 0.041). Difference between pre- and postoperative NAHS was slightly lower in the retroverted hips (18.3 (SD 22.1)) compared to the dysplastic hips (25.2 (SD 15.2); p = 0.230). At mean 3.5 years' follow-up (SD 1.9), one hip needed a revision PAO and no hips were converted to total hip arthroplasty (THA) in the retroversion group. In the control group, six hips (7.0%) were revised to THA. No differences in complications (p = 0.106) or in reoperation rate (p = 0.087) were seen. Negative predictors of outcome for patients undergoing surgery for retroversion were female sex, obesity, hypermobility, and severely decreased femoral anteversion. CONCLUSION: A PAO is an effective surgical intervention for acetabular retroversion and produces similar improvements when used to treat dysplasia. Femoral version should be routinely assessed in these patients and when extremely low (< 0°), as an additional procedure to address this abnormality may be necessary. Females with signs of hypermobility should also be consulted of the likely guarded improvement. Cite this article: Bone Jt Open 2021;2(9):757-764.

Does bladder stone composition predict kidney stone composition?

INTRODUCTION Bladder stones have historically been associated with urinary stasis secondary to bladder outlet obstruction (BOO). Recent studies indicate that the role of BOO in bladder stone formation is minor. We evaluate the role of urinary lithogenic factors in bladder stone formation by comparing the compositions of bladder stones and kidney stones in patients with multi-site urinary calculi. MATERIALS AND METHODS: We identified patients who were treated for concomitant bladder stones and kidney stones between 2008-2019, and had both stone compositions available. Patients with bladder stone size < 10 mm, urinary foreign bodies, encrusted stents or tumors were excluded. Data regarding urinary symptoms, residual volumes, stone composition and 24-hours urine data were collected. RESULTS: We identified 40 males with a median age of 72 years (IQR 6-14), median residual volume of 76 mL (IQR 41-200), and a median prostate volume of 52 mL (IQR 32-102). Bladder outlet procedures were performed concomitantly with cystolitholapaxy in 21 (53%) patients. The most common bladder stone and kidney stone compositions were CaOx (47.5% and 65%), uric acid (32.5% and 22.5%), calcium phosphate (15% and 10%), and struvite (5% and 2.5%), respectively. Bladder stone and kidney stone compositions were identical in 70% of patients. Bladder stone composition was predictive of kidney stone composition, regardless of the PVR, bladder stone size, or whether an outlet procedure was performed. CONCLUSION: We found a high concordance between bladder stone and kidney stone composition, suggesting that metabolic abnormalities have a significant role in bladder stone formation. Bladder stone composition can be used to guide surgical and medical treatment for kidney stones in metabolically active stone patients.

Hypermobility, age 40 years or older and BMI >30 kg m-2 increase the risk of complications following peri-acetabular osteotomy.

The peri-acetabular osteotomy (PAO) is a powerful surgical procedure for correcting symptomatic acetabular dysplasia, but it carries the potential for significant surgical complications. This study aims to determine the complication profile of PAO in a series performed by an experienced single surgeon. This was as retrospective review of 223 hips in 200 patients (23 bilateral, 22 males and 201 females). Complication data were collected from notes and radiographic review and graded according to a modified Dindo-Clavien classification. Each hip could be recorded as having more than one complication. Mean age at surgery was 28.8 years (range 13-48), mean weight was 70.9 kg (range 45-115 kg). Diagnosis was dysplasia in 185 hips, retroversion in 25 and a combination in 13. Mean follow-up was 26 months. In all, 61.4% of hips (137) had no complications; 74.0% had no complications or a Grade I complication (one that did not change management); 52 hips (23%) required pharmaceutical interventions (Grade II complications). Six hips (2.7%) suffered a major complication (Grade III or IV) as a direct consequence of the PAO. There were no Grade V complications (death). Hypermobility (Beighton's score of ≥6, Odds ratio (OR) 2.525 P = 0.041), age 40 years or older (OR 3.126 P = 0.012) and BMI >30 (OR 2.506 P = 0.031), but not Tonnis grade (P = 0.193) increased the risk of more severe complications following a PAO. This single surgeon series from a high volume centre demonstrates that age 40 years or older and BMI >30 kg m-2 and hypermobility increase the risk of more severe of complications.

What is the pelvic tilt in acetabular dysplasia and does it change following peri-acetabular osteotomy?

To quantify the pelvic tilt (PT) in patients with symptomatic acetabular dysplasia and determine if it represents a compensatory mechanism to improve femoral head coverage, we studied a cohort of 16 patients undergoing 32 bilateral staged PAOs for acetabular dysplasia and compared this to a matched cohort of 32 patients undergoing PAO for unilateral acetabular dysplasia all with >1 year follow-up. The change in PT was determined with two validated methods, namely, the sacro-femoral-pubic (SFP) angle and the pubic symphysis to sacroiliac index (PS-SI). Despite an improvement in the lateral centre-edge and Tönnis angles to within normal limits following PAO, patients with unilateral and bilateral acetabular dysplasia have similar PT pre-operatively (8° ± 5°) and post-operatively (9° ± 5°). A change of >5° was observed in only six patients (13%) using the SFP angle, and five patients (10%) using the PS-SI, all increased (posterior rotation of the pelvis). No patients were observed to have a change in PT >10°. The observed PT in our study group is equivalent to that found in the normal population and in patient with symptomatic acetabular retroversion. These findings all suggest that PT is morphological rather than a result of a compensatory mechanism, and even if it was compensatory, it does not appear to reverse significantly following PAO. The target for acetabular reorientation, therefore, remains constant.

Spinopelvic Characteristics in Acetabular Retroversion: Does Pelvic Tilt Change After Periacetabular Osteotomy?

BACKGROUND: Acetabular retroversion may lead to impingement and pain, which can be treated with an anteverting periacetabular osteotomy (aPAO). Pelvic tilt influences acetabular orientation; as pelvic tilt angle reduces, acetabular version reduces. Thus, acetabular retroversion may be a deformity secondary to abnormal pelvic tilt (functional retroversion) or an anatomic deformity of the acetabulum and the innominate bone (pelvic ring). PURPOSE: To (1) measure the spinopelvic morphology in patients with acetabular retroversion and (2) assess whether pelvic tilt changes after successful anteverting PAO (aPAO), thus testing whether preoperative pelvic tilt was compensatory. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A consecutive cohort of 48 hips (42 patients; 30 ± 7 years [mean ± SD]) with acetabular retroversion that underwent successful aPAO was studied. Spinopelvic morphology (pelvic tilt, pelvic incidence, anterior pelvic plane, and sacral slope) was measured from computed tomography scans including the sacral end plate in 21 patients, with adequate images. In addition, the change in pelvic tilt with aPAO was measured via the sacrofemoral-pubic angle with supine pelvic radiographs at an interval of 2.5 ± 2 years. RESULTS: The spinopelvic characteristics included a pelvic tilt of 4° ± 4°, a sacral slope of 39° ± 9°, an anterior pelvic plane angle of 11° ± 5°, and a pelvic incidence of 42° ± 10°. Preoperative pelvic tilt was 4° ± 4° and did not change postoperatively (4° ± 4°) (P = .676). CONCLUSION: Pelvic tilt in acetabular retroversion was within normal parameters, illustrating "normal" sagittal pelvic balance and values similar to those reported in the literature in healthy subjects. In addition, it did not change after aPAO. Thus, acetabular retroversion was not secondary to a maladaptive pelvic tilt (functional retroversion). Further work is required to assess whether retroversion is a reflection of a pelvic morphological abnormality rather than an isolated acetabular abnormality. Treatment of acetabular retroversion should focus on correcting the deformity rather than attempting to change the functional pelvic position.

Transverse debridement and acute shortening followed by distraction histogenesis in the treatment of open tibial fractures with bone and soft tissue loss.

This retrospective case series evaluates the technique of transverse debridement, acute shortening and subsequent distraction histogenesis in the management of open tibial fractures with bone and soft tissue loss, thereby avoiding the need for a soft tissue flap to cover the wound. Thirty-one patients with Gustilo grade III open tibial fractures between 2001 and 2011 were initially managed with transverse wound extensions, debridement and shortening to provide bony apposition and allowing primary wound closure without tension, or coverage with mobilization of soft tissue and split skin graft. Temporary monolateral external fixation was used to allow soft tissues resuscitation, followed by Ilizarov frame for definitive fracture stabilization. Leg length discrepancy was corrected by corticotomy and distraction histogenesis. Union was evaluated radiologically and clinically. Patients' mean age was 37.3 years (18.3-59.3). Mean bone defect was 3.2 cm (1-8 cm). Mean time to union was 40.1 weeks (12.6-80.7 weeks), and median frame index was 75 days/cm. Median lengthening index (time in frame after corticotomy for lengthening) was 63 days/cm. Mean clinic follow-up was 79 weeks (23-174). Six patients had a total of seven complications. Four patients re-fractured after frame removal, one of whom required a second frame. Two patients required a second frame for correction of residual deformity, and one patient developed a stiff non-union which united following a second frame. There were no cases of deep infection. Acute shortening followed by distraction histogenesis is a safe method for the acute treatment of open tibial fractures with bone and soft tissue loss. This method also avoids the cost, logistical issues and morbidity associated with the use of local or free-tissue transfer flaps and has a low rate of serious complications despite the injury severity.

The oblique plane deformity in slipped capital femoral epiphysis.

BACKGROUND: Slipped capital femoral epiphysis (SCFE) is commonly treated with in situ pinning. However, a severe slip may not be suitable for in situ pinning because the required screw trajectory is such that it risks perforating the posterior cortex and damaging the remaining blood supply to the capital epiphysis. In such cases, an anteriorly placed screw may also cause impingement. It is also possible to underestimate the severity of the slip using conventional radiographs. The aim of this study was to describe and evaluate a novel method for calculating the true deformity in SCFE and to assess the interobserver and intraobserver reliability of this technique. METHODS: We selected 20 patients with varying severity of SCFE who presented to our institution. Cross-sectional imaging [either axial computed tomography (CT) scans or magnetic resonance imaging (MRI) scans] and anteroposterior (AP) pelvis radiographs were assessed by four reviewers with varying levels of experience on two occasions. The degree of slip on the axial image and on the AP pelvis radiographs were measured and, from this, the oblique plane deformity was calculated using the method as popularised by Paley. The intraclass correlation coefficient (ICC) was calculated to determine the interobserver and intraobserver reliabilities between and amongst the raters. RESULTS: The interobserver reliability for the calculated oblique plane deformity in SCFE ICC was 0.947 [95 % confidence interval (CI) 0.90-0.98] and the intraobserver reliability for the calculated oblique plane deformity of individual raters ranged from 0.81 to 0.94. The deformity in the oblique plane was always greater than the deformity measured in the axial or the coronal plane alone. CONCLUSION: This method for calculating the true deformity in SCFE has excellent interobserver and intraobserver reliability and can be used to guide treatment options. This technique is a reliable and reproducible method for assessing the degree of deformity in SCFE. It may help orthopaedic surgeons with varying degrees of experience to identify which hips are suitable for in situ pinning and those which require surgical dislocation and anatomical reduction, given that plain radiographs in a single plane will underestimate the true deformity in the oblique plane. LEVEL OF EVIDENCE: Level II diagnostic study.

Obesity, knee osteoarthritis and knee arthroplasty: a review.

The incidence of obesity is rising worldwide. Obesity is a risk factor for developing osteoarthritis in the knee. Obesity and knee osteoarthritis are independently disabling conditions and in combination pose difficult therapeutic challenges. This review will discuss obesity, osteoarthritis, and the problems associated with knee osteoarthritis in an obese population. Treatment options including surgery and its success will be discussed.

Basic science considerations in primary total hip replacement arthroplasty.

Total Hip Replacement is one of the most common operations performed in the developed world today. An increasingly ageing population means that the numbers of people undergoing this operation is set to rise. There are a numerous number of prosthesis on the market and it is often difficult to choose between them. It is therefore necessary to have a good understanding of the basic scientific principles in Total Hip Replacement and the evidence base underpinning them. This paper reviews the relevant anatomical and biomechanical principles in THA. It goes on to elaborate on the structural properties of materials used in modern implants and looks at the evidence base for different types of fixation including cemented and uncemented components. Modern bearing surfaces are discussed in addition to the scientific basis of various surface engineering modifications in THA prostheses. The basic science considerations in component alignment and abductor tension are also discussed. A brief discussion on modular and custom designs of THR is also included. This article reviews basic science concepts and the rationale underpinning the use of the femoral and acetabular component in total hip replacement.

Endocytosis-dependent desensitization and protein synthesis-dependent resensitization in retinal growth cone adaptation.

It has been proposed that growth cones navigating through gradients adapt to baseline concentrations of guidance cues. This adaptation process is poorly understood. Using the collapse assay, we show that adaptation in Xenopus laevis retinal growth cones to the guidance cues Sema3A or netrin-1 involves two processes: a fast, ligand-specific desensitization that occurs within 2 min of exposure and is dependent on endocytosis, and a slower, ligand-specific resensitization, which occurs within 5 min and is dependent upon protein synthesis. These two phases of adaptation allow retinal axons to adjust their range of sensitivity to specific guidance cues.