William L Walter

• MBBS, PhD
• Professor at Royal North Shore Hospital; The University of Sydney

Alumina ceramic-on-ceramic bearings perform exceptionally well under standard hip simulator conditions, but in vivo some retrieved bearings have shown an unusual stripe pattern of wear. We studied 16 bearings retrieved from a series of 1,588 cementless hip arthroplasties with third generation alumina ceramic-on-ceramic bearings to characterize the...

The aim of this study was to evaluate the outcome of joint arthroplasty in obese and non-obese patients. We reviewed 2,026 consecutive primary total hip and 535 primary total knee arthroplasties performed for osteoarthritis. Patients were separated into two groups according to their body mass index (BMI): non-obese (BMI < 30) and obese (BMI ≥ 30)....

Alumina ceramic-on-ceramic bearings perform exceptionally well under standard hip simulator conditions, but in vivo some retrieved bearings have shown an unusual stripe pattern of wear. We studied 16 bearings retrieved from a series of 1,588 cementless hip arthroplasties with third generation alumina ceramic-on-ceramic bearings to characterize the...

(1) Background: Imageless computer navigation systems have the potential to improve the accuracy of acetabular cup position in total hip arthroplasty (THA). Popular imageless navigation methods include locating the patient in a three-dimensional space (registration method) while using a baseline to angle the acetabular cup (reference plane). This s...

Radiographic landmark annotation determines patients’ anatomical parameters and influences diagnoses. However, challenges arise from ambiguous region-based definitions, human error, and image quality variations, potentially compromising patient care. Additionally, AI landmark localization often presents its predictions in a probability-based heatma...

Introduction Pelvic incidence - lumbar lordosis (PI-LL) mismatch is often considered when assessing spinopelvic alignment in the sagittal plane. The mismatch is conventionally obtained by measuring 2 separate angles on lateral spinopelvic radiographs. This study describes a simplified approach for assessing spinopelvic mobility and measuring the PI...

Hip resurfacing arthroplasty (HRA) is a bone conserving alternative to total hip arthroplasty. We present the early 2-year clinical and radiographic follow-up of a novel ceramic-on-ceramic (CoC) HRA in an international multi-centric cohort. Patients undergoing HRA between September 2018 and January 2021 were prospectively included. Patient-reported...

Pelvic tilt (PT) is an important parameter for orthopedic surgeries involving hip and spine, typically determined from sagittal pelvic radiographs. However, various challenges can compromise the feasibility of measurement from sagittal imaging, including obscured landmarks, anatomical variations, hardware interference, and limited medical resources...

This study aims to identify preoperative risk factors for iliopsoas tendonitis after total hip arthroplasty, a complication typically attributed to acetabular cup position and orientation, using a validated iliopsoas impingement detection simulation. Analyzing CT scans and X‐rays of 448 patients using a validated preoperative planning protocol, pat...

Background: Accurate pre-surgical templating of the pelvic tilt (PT) angle is essential for hip and spine surgeries, yet the reliability of PT annotations is often compromised by human error, inherent subjectivity, and variations in radiographic quality. This study aims to identify challenges leading to inadequate annotations at a landmark dimensi...

Iliopsoas tendonitis, typically caused by impingement with the acetabular cup, occurs in up to 18% of patients after total hip arthroplasty (THA) and up to 30% of patients after hip resurfacing arthroplasty (HRA). We have developed a simulation for detecting iliopsoas impingement and validated it in a previous study of THA patients. However, due to...

Purpose Accurate pre-surgical templating of the pelvic tilt (PT) angle is pivotal for hip and spine surgeries. Yet, the reliability of these annotations is often questioned due to human errors, inherent subjectivity, and variations in radiographic quality. This research delves into the precision of PT annotations, identifies challenges leading to s...

The purposes of this study are to, firstly, develop techniques to accurately identify extensor mechanism malalignment by measuring the alignment of the quadriceps tendon (QTA) with computerized tomography (CT) scans. Secondly, to investigate correlations between QTA and lower limb bony anatomical variations within a representative normal population...

Importance: Ischemic heart disease remains the leading cause of mortality following hip and knee arthroplasty. Due to its antiplatelet and cardioprotective properties, aspirin has been proposed as an agent that could reduce mortality when used as venous thromboembolism (VTE) prophylaxis following these procedures. Objective: To compare aspirin w...

Background: Navigation in total hip arthroplasty has been shown to improve acetabular positioning and can decrease the incidence of mal-positioned acetabular components. This study aimed to assess two surgical guidance systems by comparing intra-operative measurements of acetabular component inclination and anteversion with a post-operative CT sca...

Background: The accurate measurement of pelvic tilt is critical in hip and spine surgery. A sagittal pelvic radiograph is most often used to measure pelvic tilt, but this radiograph is not always routinely obtained and does not always allow the measurement of pelvic tilt because of problems with image quality or patient characteristics (such as hi...

Hip resurfacing arthroplasty (HRA) is a bone conserving alternative to total hip arthroplasty. We present the early 1 and 2-year clinical and radiographical follow-up of a novel ceramic-on-ceramic (CoC) HRA in a multi-centric Australian cohort. Patient undergoing HRA between September 2018 and April 2021 were prospectively included. Patient-reporte...

Navigation in total hip arthroplasty has been shown to improve acetabular positioning and can decrease the incidence of mal-positioned acetabular components. The aim of this study was to assess two surgical guidance systems by comparing intra-operative measurements of acetabular component inclination and anteversion with a post-operative CT scan. W...

Imageless computer navigation systems have the potential to improve acetabular cup position in total hip arthroplasty (THA), thereby reducing the risk of revision surgery. This study aimed to evaluate the accuracy of three alternate registration planes in the supine surgical position generated using imageless navigation for patients undergoing THA...

Accurate measurement of pelvic tilt (PT) is critical in diagnosing hip and spine pathologies. Yet a sagittal pelvic radiograph with good quality is not always available. Studies explored the correlation between PT and sacro-femoral-pubic (SFP) angle from anteroposterior (AP) radiographs yet demonstrated conflicting conclusions about its feasibiliti...

The spinopelvic alignment is often assessed via the Pelvic Incidence-Lumbar Lordosis (PI-LL) mismatch. Here we describe and validate a simplified method to evaluating the spinopelvic alignment through the L1-Pelvis angle (L1P). This method is set to reduce the operator error and make the on-film measurement more practicable. 126 standing lateral ra...

Pelvic tilt (PT) is always described as the pelvic orientation along the transverse axis, yet four PT definitions were established based on different radiographic landmarks: anterior pelvic plane (PT a ), the centres of femoral heads and sacral plate (PT m ), pelvic outlet (PT h ), and sacral slope (SS). These landmarks quantify a similar concept,...

Dislocation is one of the most common complications in total hip arthroplasty (THA) and is primarily driven by bony or prosthetic impingement. The aim of this study was two-fold. First, to develop a simulation that incorporates the functional position of the femur and pelvis and instantaneously determines range of motion (ROM) limits. Second, to as...

Iliopsoas impingement occurs in between 5-30% of patients after hip arthroplasty and has been thought to only be caused by an oversized cup, cup malpositioning, or the depth of the psoas valley. However, no study has associated the relationship between preoperative measurements with the risk of impingement. This study sought to assess impingement b...

In 2021, Vigdorchik et al. published a large multicentre study validating their simple Hip-Spine Classification for determining patient-specific acetabular component positioning in total hip arthroplasty (THA). The purpose of our study was to apply this Hip-Spine Classification to a sample of Australian patients undergoing THA surgery to determine...

Iliopsoas tendonitis occurs in up to 30% of patients after hip resurfacing arthroplasty (HRA) and is a common reason for revision. The primary purpose of this study was to validate our novel computational model for quantifying iliopsoas impingement in HRA patients using a case-controlled investigation. Secondary purpose was to compare these results...

Human error is usually evaluated using statistical descriptions during radiographic annotation. The technological advances popularized the “non-human” landmarking techniques, such as deep learning, in which the error is presented in a confidence format that is not comparable to that of the human method. The region-based landmark definition makes an...

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 de...

Background: Pelvic tilt (PT) is described as the pelvic orientation along the transverse axis, yet 4 PT definitions were established based on radiographic landmarks: anterior pelvic plane (PT a ), the center of femoral heads to sacral plate (PT m ), pelvic outlet (PT h ), and sacral slope (SS). These landmarks quantify a similar concept, yet unders...

Objective: There is no information about surfing after hip resurfacing arthroplasty (HRA). We did a retrospective study aiming to evaluate the safety and feasibility to resume surfing-an extreme sport with high-impact physical activity-after HRA. Design: Retrospective case series. Setting: Specialist Orthopaedic Group, Mater Hospital Sydney, N...

Purpose The purposes of the present research were to assess the accuracy and usability of the inertial navigation system (INS). Materials and Methods The accuracy of the device navigation subsystem was assessed using benchtop testing. The usability was assessed through simulated use with surgeons. These results were compared to recent cadaveric re...

Background: Incorrect acetabular component positioning in total hip arthroplasty (THA) has been associated with poor outcomes. Computer-assisted hip arthroplasty increases accuracy and consistency of cup positioning compared to conventional methods. Traditional navigation units have been associated with problems such as bulkiness of equipment and r...

Background Alumina ceramic-on-ceramic (CoC) bearings are used in total hip arthroplasty (THA) due to their wear-resistant and inert properties. In this study, we assessed the clinical and radiographic outcomes of patients undergoing primary cementless CoC THA at a minimum follow-up of 20 years. Methods A series of 301 consecutive primary THAs in 2...

Despite growing evidence supporting the evaluation, classification, and treatment of acetabular bone loss in revision hip replacement, advancements have not been systematically incorporated into a single document, and therefore, a comprehensive review of the treatment of severe acetabular bone loss is needed. The Stavros Niarchos Foundation Complex...

Background: The use of computer navigation has been shown to produce more accurate cup positioning when compared with non-navigated total hip arthroplasty (THA), but so far there is only limited evidence to show its effect on clinical outcomes. The present study analyzed data from the Australian Orthopaedic Association National Joint Replacement R...

Purpose The minimal important change (minimal amount of change vs. baseline that a patient recognizes as a clinical change) and minimum clinically important difference (smallest difference between two measurements that are deemed important by patients) are important values to evaluate the clinical relevance of changes over time and differences betw...

Background: Patient reported outcome measurements (PROMs) that exhibit a substantial ceiling effect show clustering of participant’s scores towards the upper limit of a scale and consequently have low discriminatory power among high end scores. This study aimed to compare ceiling effects at 1 and 2 years postoperatively across commonly used patient...

Update This article was updated on September 4, 2020, because of a previous error. On page 1211, in the author affiliation section, “W.L. Walter, MBBS, PhD ³ ” now reads “W.L. Walter, MBBS, PhD 3,4 ,” the affiliation for Dr. Van Onsem that had read “ ³ Specialist Orthopedic Group, The Mater Clinic, North Sydney, New South Wales, Australia” now read...

PurposeTo investigate the validity, responsiveness and ceiling effect of the recently introduced KOOS-12 and compare its performance to the KOOS, OKS, WOMAC and UCLA activity scales.Methods Patients from an independent multicentre study examining a medially stabilized knee system prospectively completed the KOOS, OKS, WOMAC and UCLA preoperatively...

The COVID-19 pandemic has caused us all to stop our normal activities and consider how we can safely return to caring for our patients. There are many common practices (such as an increased use of personal protective equipment) which we are all familiar with that can be easily incorporated into our daily routines. Other actions, such as cleaning mo...

Background: Joint stability is one of the goals of any joint replacement. The contribution of prosthesis design to sagittal stability in total knee arthroplasty (TKA) has emerged as an area of interest. The purpose of this study was to evaluate the sagittal stability of four prosthesis types and determine the effect on patient reported outcome mea...

Background Femoral rotational asymmetry (FRA) is the difference in rotational alignment between the trochlear groove and posterior condyles. We hypothesize that FRA increases as the tibial plateau becomes more varus due to internal rotation of the posterior condyles and external rotation of the trochlear groove to ensure a vertical trochlear groove...

Aims We describe a surgical technique of limited femorotomy for removing proximally coated cementless femoral stems utilizing a limited femoral osteotomy and report patient outcome data. Methods Patients who had undergone revision hip surgery utilizing this technique were identified from the prospectively maintained database. We reviewed clinical...

Aims Between 15% and 20% of patients remain dissatisfied following total knee arthroplasty (TKA). The SAIPH knee system (MatOrtho, Surrey, United Kingdom) is a medial ball and socket TKA that has been designed to replicate native knee kinematics in order to maximize the range of movement, stability, and function. This system is being progressively...

Ceramic on ceramic bearings are used in around a fifth of all total hip arthoplasties carried out in Australia. The Australian Orthopaedic Assocation National Joint Replacement Registry data from 2016 shows that ceramic has better fifteen year survivorship than any other bearing surface, even in patients under the age 55 years. Wear rates can be me...

Total Hip Resurfacing is a good alternative to conventional total hip arthroplasty. According to the 2016 Australian Joint Registry report, only 0.8% of all total hip arthroplasties were resurfacings. It is mostly done on patients under the age of 65years but recently there has been an increase in the >65 year group. According to the registry, resu...

Introduction The sulcus line (SL) is a three-dimensional landmark that corrects for individual variation in the coronal alignment of the trochlear groove in contrast to the traditional Whiteside's line (WL). Femoral rotational asymmetry (FRA) is an anatomical variation in which the posterior condyles and trochlear groove are not perpendicular to ea...

Background: Squeaking is an on-going complication with a variable incidence of 0.5%-20.7%. The mechanism of squeaking has not been understood completely and is most likely multifactorial in nature. Previously, we have reported on a squeaking rate of 7.3% at 2 years. Our current results show a substantial increase in the squeaking incidence from 7....

Objective: To evaluate spinopelvic changes after hip arthroplasty in standing and ready-to-rise positions. Methods: We compared pelvic tilt, sacral slope, cobb's angle, and hip flexion on pre and postoperative spinopelvic radiographs. Results: Standing: All postoperative indices were similar to preoperative ones except sacral slope (mean diffe...

The accuracy of cup position in total hip arthroplasty is essential for a satisfactory result as malpositioning increases the risk of complications including dislocation, high wear rate, loosening, squeaking, edge loading, impingement and ultimately failure. We studied 166 patients in a single-surgeon-series of matched cohorts of patients who under...

Ceramic-on-ceramic (CoC) articulations were developed as an alternative bearing to conventional metal-on-polyethylene (MoP) bearings in order to decrease bearing surface wear and hopefully increase implant longevity. Overall, CoC bearings have the lowest rate of wear among all bearing [1] surfaces and are not associated with complications such as o...

Intra-operative changes in pelvic position during total hip arthroplasty (THA) can affect acetabular orientation. We evaluated these changes during supine THA using a proprietary mobile application called PelvicTracker. Twenty-two patients undergoing THA using direct anterior approach were included in the study. In the sagittal plane, the pelvis wa...

Background: Dislocation is a leading cause of revision after primary total hip arthroplasty (THA). Although more common in the first few years after the procedure, dislocation can occur at any time. This study investigated the difference in late dislocation in ceramic-on-ceramic (CoC) bearings compared with metal-on-polyethylene and ceramic-on-pol...

Zirconia in Zirconia toughened alumina ceramic hip replacements exists in an unstable state and can transform in response to stress giving the material improved fracture toughness. Phase transformation also occurs under hydrothermal conditions such as exist in vivo. To predict the hydrothermal aging that will occur in vivo accelerated aging procedu...

Objectives: This study aimed to characterise and qualitatively grade the severity of the corrosion particles released into the hip joint following taper corrosion. Methods: The 26 cases examined were CoC/ABG Modular (n = 13) and ASR/SROM (n = 13). Blood serum metal ion levels were collected before and after revision surgery. The haematoxylin and...

Squeaking is a well-recognized complication for hard-on-hard bearings. The nature of squeaking is not yet completely understood however it is considered a multifactorial phenomenon. Patient, implant, and surgical factors play a role in squeaking. It is believed that mechanisms damaging the fluid film lubrication in which these bearings function opt...

Long-term clinical studies report excellent survival rates using third generation ceramic bearings. Wear rates in hips revised for non-bearing causes are reported at 0.6mm³/year for heads and 0.5mm³/year for liners. This study aims to analyse high volumetric wear and late onset fracture cases as a possible failure mechanism from a material perspect...

Kinematics of a medial ball and socket and a single radius cruciate retaining total knee arthroplasty designs were compared using KneeKG in this study.

Osteloysis following metal-on-UHMW polyethylene Total Hip Arthroplasty (THA) is well reported, as is lack of osteolysis following Ceramic-on-Ceramic (CoC)THA. Early ceramic failures did report some osteolysis, but in flawed implants. As 3rd and now 4th generation ceramic THAs come into mid- and long-term use, the orthopaedic community has begun to...

BACKGROUND: The design of femoral component used in total hip arthroplasty is known to influence the incidence of periprosthetic femoral fractures (PFFs) in cementless hip arthroplasty. OBJECTIVE: This study was undertaken to determine if 2 potential changes to an existing ABG II-standard cementless implant - addition of a roughened titanium plasma...

In this booklet you will find recommendations for the clinical assessment of the noisy THR, from diagnostics to therapy and adequate management, as well as monitoring, possible prevention, and patient information. A clinical algorithm in the form of a flowchart and two clinical cases as an example are also included.

Subject-specific finite element (FE) modeling methodology could predict peri-prosthetic femoral fracture (PFF) for cementless hip arthoplasty in the early postoperative period. This study develops methodology for subject-specific finite element modeling by using the element deactivation technique to simulate bone failure and validate with experimen...

Intra-operative peri-prosthetic femoral fractures are a significant concern in total hip arthroplasty and can occur at any time during surgery, with the highest incidence during implant insertion. This study combines subject-specific finite element analysis modeling with an optical tracking system to characterize the resultant strain in the bone an...

Modular hip implants allows for the adjustment of leg length, offset, and the ability to remove the head for acetabular exposure during primary and revision surgery. The design of the Morse taper facilitates the intimate contact of the conical trunnion of the femoral stem (male component), with the conical bore of the femoral head (female component...

Background Metal-on-metal (MoM) hip resurfacings have been associated with the potential development of metallic debris and its associated pathology. Serum cobalt and chromium levels are a reliable surrogate marker of wear rates in MoM bearings. The aim of the study was to examine the trend in serum metal ion levels in the initial 2-year post-opera...

We describe the clinical and radiological results of cementless primary total hip replacement (THR) in 25 patients (18 women and seven men; 30 THRs) with severe developmental dysplasia of the hip (DDH). Their mean age at surgery was 47 years (23 to 89). In all, 21 hips had Crowe type III dysplasia and nine had Crowe type IV. Cementless acetabular c...

We analysed the results of 206 consecutive total hip replacements performed using large diameter ceramic-on-ceramic bearings. At an average follow up of 28 months, the mean Harris Hip Score improved from 54 to 92. 15 (7.3%) hips were noted to squeak. There was no significant difference between silent and squeaking hips with regards to age, weight,...

1420 primary cementless THRs with a minimum follow-up of 10-years were stratified according to BMI: non-obese (BMI < 30 kg/m2) and obese (BMI ≥ 30 kg/m2). Median age at surgery was younger in obese patients (p < 0.001). We case-matched 82 THRs in obese patients with 162 THRs in non-obese patients. No difference between groups was found in improveme...

Purpose: The aim of this study is to describe the influence of sitting and standing posture on sagittal pelvic inclination in total hip replacement patients to assist with correct acetabular component positioning. Methods: Lateral radiographs of the pelvis and lumbar spine in sitting and standing positions were extracted. Pelvic tilt was measure...

An orthopaedic device for generating one or more strain signals representative of the strain in a bone in response to a force applied to the bone. The device includes an encircling member (11) for encircling the bone of a subject and a sensor member (13) connected thereto, the sensor member including a strain sensor (14). In a preferred embodiment...

During revision of a conventional polyethylene joint replacement, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the polyethylene granuloma tissues. We developed a human/rat xenograft model to investigate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and peripros...

We report on 397 consecutive revision total hip replacements in 371 patients with a mean clinical and radiological follow-up of 12.9 years (10 to 17.7). The mean age at surgery was 69 years (37 to 93). A total of 28 patients (8%) underwent further revision, including 16 (4%) femoral components. In all 223 patients (56%, 233 hips) died without furth...

We present two cases of spontaneous fractures of the S-ROM femoral stem prosthesis implanted by different surgeons within 5 years of implantation. Both the stems fractured in the mid-distal stem at the junction of the main body and the slotted portion. Both fractures affected the posterior tine only. Our aim in publication is to ensure that this is...

We reviewed 380 hip resurfacings cases between December 1999 and Dec 2012. 11 cases (2.89%) squeaked postoperatively. Mean follow-up was 88.6 months (19-130 months). Mean time to squeak was 11.3 months (3-22 months). Ten (91%) cases were male and nine (81%) cases had a Birmingham hip resurfacing. Cases were matched for age, gender, BMI and implant...

We present a long-term follow-up report of 33 cementless total hip arthroplasties in 27 patients who have an established diagnosis of Paget’s disease. The medium term results of this series were reported in 2007 (Lusty et al. Journal of Arthroplasty. 2007;22:692). Fourteen cases were available for follow-up at an average of 12.3 years (range 10–17)...

During total hip arthroplasty, use of a modular femoral neck on a stemmed implant allows optimization of neck anteversion, length, and offset, resulting in more accurate balance. We performed a retrospective analysis of a consecutive cohort of patients who had undergone total hip arthroplasty with a modular-neck hip system with ceramic-on-ceramic b...

Squeaking arising from a ceramic-on-ceramic (CoC) total hip replacement (THR) may cause patient concern and in some cases causes patients to seek revision surgery. We performed a meta-analysis to determine the incidence of squeaking and the incidence of revision surgery for squeaking. A total of 43 studies including 16 828 CoC THR that reported squ...

In this retrieval study, modular junctions of retrieved S-ROM® implants were examined to determine the extent of corrosion at the head-neck and stem-sleeve junctions. Corrosion severity was graded in relation to the bearing surface material over time. It was found that the corrosion at the head-neck taper is greater for cobalt-chrome femoral heads...

We report the clinical and radiological outcomes of a series of contemporary cementless ceramic-on-ceramic total hip replacements (THRs) at ten years in patients aged ≤ 55 years of age. Pre- and post-operative activity levels are described. A total of 120 consecutive ceramic cementless THRs were performed at a single centre in 110 patients from 199...

In Australia, one quarter of our population is obese, and over half is overweight, with the upward trend predicted to continue to increase for the next 20 years or so. This summary paper looks at the influence of obesity on the outcome of total joint arthroplasty, including our own experience in particular with 535 consecutive primary cementless to...