Introduction: In total hip arthroplasty (THA) an optimal fit and fill of the stem is essential for stable fixation. Thus femur morphology must be studied during pre-op planning (implant choice, sizing, positioning) or when a new stem is to be designed. Using plain AP x-ray analysis and the definition of a simple two-level parameter (canal flare index, CFI), Noble et al. identified an age related transition of the endosteal canal in AP view from a ‘champagne flute’ to a ‘stove pipe’. This reference data is 2D only, limited to the endosteal geometry and the elderly age range was defined as 60–90yrs so that the number of octogenerians > 80yrs was too low to analyze morphological features of this rapidly growing and critical THA patient population.

In this study the endosteal and periosteal femur morphology of subjects > 80yrs was studied using 3D CT analysis. It was the goal to

describe age related changes of the femur morphology in 3D,

Methods: High-resolution CT-scans (slice thickness 1mm) were made of 170 consenting volunteers (m/ f=101/69). The old group consisted of 119 subjects ≥80yrs (m/f=65/54, mean age: 84.1yrs [80–105]) and the young group of 51 subjects < 80yrs (m/f=36/15, mean age 67.8yrs [39–79]). After thresholding the bone boundaries in Mimics V12 (Materialise, B), the endos-teal and periosteal coordinates were analyzed for width, wall thickness, surface areas and various CFI’s relating dimensions at 20mm above LT and at a distal level (e.g. 60mm below LT, isthmus): Surface CFI (3D-CFI), frontal and lateral CFI based on the AP and ML projections (2D-CFI) and flaring in each of the four directions (1DCFI).

Results: The surface CFI was sign. lower in subjects ≥80yrs (5.08 ±1.23) than in subjects < 80yrs (6.61 ±1.72, p< 0.0001). This difference was sign. larger in females than in males (−32% vs. −17%), an observation valid with reference to any distal level. Equivalent age differences were found in both the frontal and lateral 2D-CFI as well as the medial, lateral and anterior 1D-CFI with changes in the anterior direction (−26.3%) being most dominant. In addition wall thickness was sign. reduced in the very elderly. E.g. at 20mm above LT, the medial wall measured 10.40mm at < 80yrs and 7.61 at ≥80yrs, a reduction of −27% (p< 0.001). In females (−35%) this difference was sign. larger (males: −23%, p< 0.001) even when corrected for height.

Discussion: The age driven transition of proximal femur morphology continues in the octogenarian population. This transition is not limited to two discrete levels in the AP plane as previously reported but it is a continuous 3D phenomenon with high directional asymmetry. In addition, this transition also affects the wall thickness and the periosteal shape. Furthermore a strong gender effect was identified with aging females showing increasingly and asymmetrically less flaring and thinner walls. An age and gender specific THA stem design seems necessary to fit the morphed femur. The asymmetric transition prohibits the effective use of current implant systems with proportionally scaled dimensions but favors a matrix sizing scheme with frontal and lateral dimensions changing independently.

Due to demographic changes patients > 80yrs (octogenarians) are a rapidly growing group in total hip arthroplasty (THA). Stem design, choice, sizing and surgical insertion are more important in these patients as complications such as fractures are critical. Age and gender driven differences regarding canal shape (flare index, CFI), cortical wall thickness (WT) and bone mineral density (BMD) have been studied before only in isolation. Using CT, this study aims to investigate these parameters in combination and in 3D with a focus on the very elderly, identifying the regions critical for THA.

High-resolution CT-scans (1mm slices) of 168 femora (M/F=100/68) were analyzed in 3D (Mimics V12). Flaring indices were based on the dimensions measured 20mm proximal to the lesser trochanter (LT) and 60mm distal to LT: intramedullary surface area (3D-CFI), frontal/lateral planes (2D-CFI) and flaring of the 4 sides medial (med), lateral (lat), anterior (ant), posterior (post) (1D-CFI). WT was calculated subtracting periosteal and endosteal dimensions and BMD was measured in Hounsfield Units (HU). An octogenarian group (80+: n=117, mean age 84yrs [80–105]) was compared to a typical THA age group (80−: n=51, mean age 68yrs [39–79]).

Age and gender had significant effects on several parameters but at different levels, e.g. 2D frontal CFI was more influenced by the small age difference (80+ vs 80−=12%, p< 0.01) than gender (F vs M=2%). However, regarding lateral canal width, gender (F vs M=7%, p< 0.01), was more influential than age (80+ vs 80−=3%). The age-related changes on the shape occurred in 3D (3D-CFI 80+ vs 80−=23%, p< 0.01), but were asymmetrical between the 4 sides (e.g. 1D-CFI 80+ vs 80−: med=11%, p< 0.01) vs ant=27%, p< 0.01). Age and gender did not only effect shape, but also cortical WT, e.g. proximally octogenarian females had 35% less WT than the typical THA age group while males only had 14% lower WT (p< 0.01). Age, gender and shape asymmetry was also reflected in BMD distribution. on the medial side, the BMD gender difference in the octogenarians was small (=1%, p=0.61) but high on the anterior side (12%, p< 0.01). The most critical configurations for the octogenarians were found proximally on the posterior side with the lowest WT, lowest BMD and largest gender difference.

The complex transition of the proximal femur affects shape, WT and BMD, continues in the very elderly and differs between genders. It produces femoral canals and bone stock different from the typical THA patient group. Conventional stems may not fit properly. Surgical implant choice, sizing and templating should consider this asymmetric age plus gender effect on shape, WT and BMD to avoid complications such as periprosthetic fracture, excessive migration or luxation in this vulnerable age group. A major risk zone is the posterior wall where age transition and gender differences are high and WT and BMD low.

Introduction: While conventional acetate x-rays came at a fixed size and magnification, digital x-rays are freely scalable on the screen and thus must be individually calibrated for surgical measurements (templating). The standard technique is calibration by a reference object (ruler, ball, coin) to be placed into the x-ray. In clinical practice, x-rays are often taken without a calibration object, the object may be malpositioned or the bucky system’s objectfilm distance is unknown to scale with a fixed magnification. Thus calibration based on an anatomic dimension would be a useful alternative in clinical practice.

In this study x-ray calibration using the femoral head diameter as derived by an anatomic formula is compared to the standard technique of using a calibration ball and acetate type fixed magnification.

Methods: In a prospective study three calibration Methods: were applied to post-op AP digital x-rays of 42 patients (m/f=12/30, height: 151–185cm) following primary total hip arthroplasty (ABG-II, 28mm heads) using a common templating software (Endomap): M1) 30mm metal ball lateral to the affected side at the height of the trochanter, M2) a fixed magnification of 121% (average of bucky system as derived from a pilot study) and M3) anatomic calibration by assigning to the natural femoral head of the contralateral side its diameter derived by an anatomic formula. The gender specific linear relationship between height (h [cm]) and the bony femoral head diameter (d [mm]) was obtained from a CT study (n=120): Males: d=0.156h+23.941, Females: d=0.154h+20.040). For each method applied by two independent observers, the implant’s metal head was measured and the relative error [%] calculated.

Results: The standard technique, calibration by a reference object produced a relative error (mean +/−SD) of 2.01+/−1.82% (max=7.9%). Fixed magnification had sign. less error at 1.41+/−1.3% (max=6.5%, p< 0.05). Anatomic calibration produced sign. higher errors at 2.77+/−1.96% (max=8.4%, p< 0.05). Inter-rater reliability was highest for the fixed magnification (r=0.93) and less for ball calibration (r=0.67) and anatomic calibration (r=0.52).

Discussion: It was shown once more that in THR fixed magnification of digital x-rays is on average more accurate and reliable than using a calibration object such as a ball. The theoretical benefit of individual calibration is lost by the variability in landmark palpation, object placement and patient movement though last can be limited by taping the object (e.g. coin) to the skin. Anatomic calibration based on the current formula cannot replace the use of calibration objects. However its error is within clinically tolerable ranges and it can be used when no calibration object is available or the system’s magnification is unknown. The error may be reduced by more accurate height measurements.

Introduction: Issues regarding total joint replacement (TJR) are perceived differently between patients and doctors and this may lead to patients being unsatisfied about their consultation or even their procedure as questions were not satisfactorily answered. However, even in a research setting, the real patient concerns are difficult to capture as questionnaires bias the answers to the expectations of the researchers and free interviews require too large numbers for monitoring purposes.

Internet keyword search is an indicator of true patient interest as searches are entered in privacy. It is now technologically possible to monitor search term frequency over time, per region and identify the most frequent related searches.

It is the aim of this study to identify the most popular and fastest rising search terms regarding TJR in Europe by studying internet search history.

Methods: Keywords regarding TJR were analysed in Google Insight, a new application which allows the history of search term frequency (relative popularity to a maximum of 100) to be tracked for any time period since 2004. The 10 most frequently searched related terms are evaluated as well as the fastest growing searches regarding the subject in comparison to the previous year. Keywords analysed were: hip replacement and knee replacement (in UK and USA) and their language equivalents in German, French, Spanish, Dutch and Polish to compare national differences.

Results: In the non-English speaking countries, the top 10 search terms are mostly variants of the original keyword (e.g. total hip surgery instead of replacement). The most popular non-synonymous terms relate to the post-op care such as recovery, rehabilitation or physiotherapy. Their prevalence is higher with knee than hip replacement. No top or fastest growing search term referred to pain, complications or longevity. Only rarely implant type related searches are popular in non-English speaking countries (Spain: hip resurfacing, NL: hemi-knee). Also in the UK and USA searches regarding aftercare are most popular but TJR pain is on the rise, especially with knees. In the UK rising search interests includes NHS issues and two product names (Oxford knee, Birmingham hip). In the USA, search focus is even more specific including most major company names plus cost issues.

Discussion: Internet keyword search history seems a promising tool to monitor and analyse public interest in issues of health care provision across nations. In the context of TJR, a dominant and rising interest was found in recovery issues. It appears beneficial to increase the availability and quality of such information (e.g. instructional videos of rehab exercises). Trends towards patient marketing and cost are still weak in Europe. Professional societies or health care providers may try to steer such interest towards objective information sources.

Introduction: Clinical outcome scores such as the DASH shoulder score suffer from subjectivity, a ceiling effect and pain dominance masking functional changes which shall be assessable to address rising patient demands and improve the clinical validation of modern therapeutic improvements. Lab based motion analysis may provide such data but it is too costly, time consuming and complex for routine clinical follow-up. Inertia sensor based motion analysis (IMA) can produce objective movement parameters while being fast, cheap and easy to operate.

In this study, a simple and clinical feasible inertia sensor based motion analysis (IMA) shoulder test is defined and tested for its

reliability,

Methods: An inertia sensor (41x63x24mm, 39g) comprising 3D accelerometers (±5g) and 3D gyroscopes (±300°/sec) was taped onto the humerus in a standardised position. Healthy subjects (n=100, 40.6 ±15.7yrs) and 50 patients (55.6 ±12.7yrs, m/f 17/33) with confirmed unilateral shoulder pathology (39 subacromial impingement, 11 other) were measured. Two motion tasks (hand-behind-head, hand-to-back) were performed on both shoulders. Using automated algorithms, a simple motion parameter was calculated by adding the peak-to-peak angular rates per axis. The relative asymmetry between both shoulder sides was scored (healthy control within subject). Patients were also assessed using the DASH score and the Simple Shoulder Test (SST).

Results: The test produced high intra- (r2=0.90) and inter-observer reliability (r2=0.83). Asymmetry was > 3 times higher in patients (36.3%) than healthy controls (9.6%, p< 0.001). Using a threshold (> 16% asymmetry) healthy and pathological subjects could be distinguished with high diagnostic sensitivity (98.0%) and specificity (81.0%). The non-affected shoulders of the patient group did not differ from the shoulder of the healthy group (p=0.18). Sub-group analysis comparing the 30 best performing healthy to the 10 highest asymmetry pathological shoulders also revealed sign. lower range of motion, shorter motion path and longer cycle times (p< 0.01). Visual signal analysis exposed specific motion patterns (e.g. healthy: overshooting at point of task achievement, pathological: drift or tremble at rest position). IMA asymmetry was only weakly correlated with DASH or SST (r2< 0.25).

Discussion: The IMA shoulder test and asymmetry score showed high reliability and diagnostic power meeting or exceeding common clinical scores. The fast assessment (t< 60s) of a simple motion tasks makes it suitable for routine clinical follow-up to supplement classic scores. Weak correlations with DASH and SST show that the test adds an objective functional dimension to outcome assessment.

Introduction: Increasing numbers and incidence rates of noisy (squeaking, scratching, clicking) ceramic-on-ceramic (CoC) total hip arthroplasties (THA) are being reported. The etiology seems to always involve stripe wear producing a stick-slip effect in the bearing which excites vibrations. As stripe wear is also found in silent CoC bearings, a theory has been developed that the vibrations become audible only via amplification through the vibrating stem (bell-clapper theory). This was supported by showing that the excitation frequency and the resonance frequency of the plain stem are similar. However, stem resonance in-vivo would be influenced by the periprosthetic bone damping and transmitting stem vibrations. Thus, if the bell-clapper theory were true, noisy CoC hips should show periprosthetic bone different to silent hips.

This study compares stem fit& fill and periprosthetic bone between noisy and silent CoC hips.

Methods: In a consecutive series of 186 primary CoC hips with identical stems, cups (Stryker ABG-II) and femoral heads (Alumina V40, 28mm) a survey identified 38 noisy hips (incidence rate: 20.4%, squeakers: n=23). Stem fit& fill and cortical wall thickness (CWT, medial and lateral) were measured on post-op AP x-rays according to the method of Kim & Kim. Measurements were repeated by a single blinded observer in a control group of silent hips matched for gender, age, stem size and follow-up time (4.6yrs). Fit& fill and CWT were compared between the noisy and silent group at proximal, mid-stem and distal level and on the medial and lateral side.

Results: The endosteal canal width was equal in noisy (N) and silent hips (S) at all levels (e.g. proximal: N=39.7+/−5.5mm, S=41.3+/−5.7mm). On the lateral side also cortical wall thickness (CWT) was the same at all levels (e.g. proximal: N=2.0+/−0.8mm, S=1.9+/−0.9mm). However, on the medial side, noisy hips had higher CWT at proximal (N=4.9+/−2.8mm, S=3.0+/−2.1mm, p< 0.01) and mid-stem level (N=6.2+/−2.1mm, N=4.6+/−1.7mm, p< 0.001). Also Fit& fill was slightly higher (proximal: N=66%, S=62%; mid-stem: N=63%, S=59%, p< 0.05). Differences and significance levels increased when only squeakers were considered.

Discussion: Despite equal endosteal canal widths and lateral cortical wall thickness for noisy and silent hips, noisy hips had sign. thicker medial walls at proximal (+63%) and mid-stem level (+35%) where also fit& fill was higher. This gives evidence that periprosthetic bone (PPB) may play a role in the development of audible noise in CoC hips by providing particular conditions of support, damping and transmission for an oscillating stem which influences noise frequency and intensity. Comparing PPB at different time points indicated that the differences are less due to post-op remodeling but more to pre-op conditions, surgical canal preparation and possibly stem design. The findings shall be verified by a DEXA study.

Early prediction of outcome following hip fracture surgery would save valuable time towards arranging post-op rehabilitation benefiting the patient and health economics. The study aim was to develop a prognostic scoring system for elderly hip fracture patients, which on admission is able to predict rehabilitation needs at discharge based on pre-injury factors.

A simple and fast prognostic scoring system was developed based on age, pre-injury level of “independence in activities of daily living” (Katz), medical co-morbidities, cognitive functioning (MMSE) and presence of a caregiver, to predict rehabilitation needs at discharge (0–8 points). Rehabilitation options were direct return to pre-injury living situation (group 1), transfer to an orthopaedic rehabilitation unit for a period shorter than 3 months (group 2), or transfer to a psychogeriatric or orthopaedic rehabilitation unit for a period longer than 3 months (group 3). Rehabilitation needs as predicted and the clinical decision by independent, blinded observers were compared. The score was validated in a prospective study on a consecutive cohort of 77 hip fractured patients.

Overall positive predictive value (PPV) of the prognostic score was 0.87 (CI 0.77–0.93), a marked improvement compared to previously published scoring systems with a PPV of 0.68 (CI 0.55–0.79). PPV per group (0.80, 0.92, 0.87) was highest for the most critical groups 2 and 3. In-hospital mortality was 1.3 percent. The average length of hospital stay (LOS) was 11.4 days.

Using the score fast and reliable prediction of rehabilitation needs could be made already on admission gaining maximum time for the preparation of adequate discharge destinations improving care and reducing costly LOS.

Polyethylene (PE) wear particle induced osteolysis remains a major cause of failure in total hip arthroplasty (THA), so that routine clinical measurement of wear stays important. Crosslinked PE promises very low wear rates so that measurement accuracy becomes increasingly important to distinguish alternative materials. The rising use of large femoral heads causes lower linear head penetration also requiring improved accuracy. Digital x-rays and wear measurement software have become standard, but during archiving and exchange of x-rays, image format, resolution or compression are often changed without knowing the effects on wear measurement. This study investigates the effect of digital x-ray resolution and compression on the accuracy of two software programs to measure wear.

The 8-year post-op digital x-rays of 24 THA patients (Stryker ABG-II, 28mm metal femoral head against Duration or conventional PE) were taken from the hospital PACS (Philips Diagnost H, AGFA ADC Solo, Siemens Medview) as DICOM at 5.1 MPix resolution. Images were converted to compression-free TIFF format using Irfanview V4.1. Wear (linear head penetration) was measured using Roman V1.7 and Martell Hip Analysis Suite 7.14. The x-rays were smoothened (Irfanview V4.1, Median Filter: 3) as recommended in literature for compatibility with Martell’s edge detection algorithm. Wear was measured twice by two independent observers at original format and resolution and then once by a single observer at three subsequently halved resolutions (2.6, 1.3, 0.65MPix) and three jpeg compressions (90%, 50%, 20%). Intra- and inter-observer reliability (R) was compared to the reliability of measuring manipulated images (Pearson’s r). The mean absolute wear differences (AD) were calculated versus the original x-ray.

The mean total wear was 0.98+/−0.59mm (0.3–2.4mm) equaling an annual of wear rate of 0.11mm/yr. Using Roman, Intra-R (0.97) and Inter-R (0.96) were high and AD low (0.10 and 0.20mm). Reduced image resolution caused the R to drop only slightly to 0.95 (2.6MPix), 0.92 (1.3MPix) and 0.94 (0.65MPix) while AD remained low (< 0.20mm). Also compression hardly affected R (90%:0.96, 50%: 0.94, 20%:0.93) nor AD (< 0.20mm). Using Martell Intra-R (0.99) and Inter-R (0.87) were also high but dropped with reducing resolution (0.82, 0.72, 0.34, AD: 0.4–1.1mm) but hardly with increased compression (0.95, 0.92, 0.94, AD< 0.20mm).

Low resolution and high compression do not have to be critical for wear measurement accuracy and reliability when edge detection is performed by a trained human eye. This way interpolating the ball and cup perimeters and locating their centers can be performed at accuracy below pixel size (ca. 0.40mm at 0.65MPix). Automatic edge detection is less robust to reducing resolution but performs at high compression. If image size needs to be reduced compression is preferable to reducing resolution.

In orthopaedics new objective functional outcome tools are required to validate the benefits of new surgical techniques or implants for which classic scores such as the KSS, HHS or Womac have been shown not to be discriminative enough. Inertia based motion analysis (IMA) is a cheap, fast and simple technique which requires no gait lab or specialist personnel and thus is suitable for routine clinical outcome assessment. IMA on gait has been validated for total knee replacement (TKR) but normal gait was considered not demanding enough for certain orthopaedic differences. Sit-stand-Sit is a more demanding task of daily activity which can be assessed quickly during consultation. This study investigates whether an IMA assessed sit-stand-sit test can differentiate healthy subjects from pre-op TKR patients.

Rising (sit-to-stand) from a chair and sitting down (stand-to-sit) at comfortable, self-selected speed was measured three time using a triaxial accelerometer (range: +/−2g, f=100Hz, 64×62×13mm, m=54g) taped to the sacrum. The chair (no armrests) was height adjustable (legs at 90deg flexion) to level the effort for different body heights.

70 healthy volunteers (f/m=48/22, age range: 17–81yrs) were compared to a pathological group of 20 patients with knee osteoarthritis indicated for unilateral TKR (Biomet Vanguard) measured at 1–10 days pre-op (f/m=11/9; mean age: 65.6yrs, range: 45–79; KSS: 43.5, range: 5–65). The healthy group was split into two subgroups, an age-matched “Old” group (> 50yrs: n1=28, mean age: 65.2yrs) and a “Young” group (< 50yrs: n2=32, mean age: 28.0yrs).

Motion parameters derived were the time to stand up (Tup), time to sit down (Tdwn), the time difference between rising and sitting down (Tu−d) and the combined time of rising and sitting down (tu+d) as mean values and per individual repetition.

All motion parameters were sign. slower with higher variance for the pre-TKR versus the healthy subjects, even when compared to the age-matched subgroup (except Tu−d). Threshold values could be defined to delineate healthy from pathological performance, e.g. Tup> 220ms (6/70=9% vs 17/20=85%, p< 0.01) or Tdwn> 240ms (4/70=6% vs 18/20=90%, p< 0.01) producing high test sensitivity (90%, C.I. 72–98) and specificity (94%, C.I. 89–97). In some false positives (3/6) originally unknown orthopaedic problems were identified in retrospect.

The simple IMA assessed sit-stand-sit test produced motion parameters comparable to values reported for smaller subject groups using methods unsuitable for routine clinical application (e.g. electrogoniometry). Healthy and pathological motion could be distinguished with high sensitivity and specificity even versus age matched controls supporting the validity to use the IMA assessed sit-stand-sit test to complement classic outcome scores with an objective functional component.

Modern orthopaedics increasingly demands objective functional outcome assessment beyond classic scores and tests suffering from subjectivity, pain dominance and ceiling effects. Inertia based motion analysis (IMA) is a simple method and validated for gait in knee arthroplasty patients. This study investigates whether IMA assessed stair climbing can distinguish between healthy and pathological subjects and is able to diagnose a meniscal tear (MT).

Following standard physical examination (McMurray, rotation pain), 37 patients (18–72yrs) received arthroscopy suspecting a meniscal tear resulting from trauma, degeneration or both. Arthroscopy identified the presence or absence of MT and the osteoarthritis level (Outerbridge).

Prior to arthroscopy, the ascending and descending five stairs twice at preferred speed and without the use of handrails was measured using a triaxial accelerometer (62×41×18mm; m=53g; f=100Hz) taped to the sacrum. Based on peak detection algorithms, temporal motion parameters were derived such as step time up and down (Tup, Tdown), the difference between step time up and down (Tup-down), step irregularity (step time difference of subsequent steps) and step asymmetry (step time difference between affected and non-affected leg).

Patients were compared to a control group of 100 healthy subjects (17–81yrs) without any known orthopaedic pathology. Using the results of arthroscopy, test sensitivity and specificity for differentiating healthy and pathologic subjects and for diagnosing MT were calculated based on threshold values.

Sensitivity and specificity for detecting pathological motion was 0.68 (CI 0.50–0.81) and 0.92 for the most sensitive parameter (Tdown). Sensitivity and specificity to detect MT was 0.74 and 0.25 percent overall compared to 0.53 and 0.50 for the McMurray. Sensitivity increased to 1.00 when MT was combined with a chondropathy scale III or IV (McMurray 0.33).

IMA assessed stair climbing can distinguish healthy and pathological subjects and detect the presence of MT with better sensitivity than classic scores especially when combined with severe chondropathy. IMA is a simple and fast clinical outcome measure suitable for routine follow-up and may support the diagnosis of meniscal tears prior to arthroscopy.

While squeaking ceramic bearings in total hip arthroplasty are increasingly reported in the literature, the etiology remains unclear. Cup inclination and anteversion have been correlated with the phenomenon but even amongst well positioned cups bearing noise is observed. Most studies do not distinguish between different types of noise or incidence rate and do only investigate actively complaining patients. This study analysed the incidence of ceramic bearing noise in a single type of hip implant and investigates correlations with patient, implant and surgery parameters.

In a consecutive series of 145 ceramic-on-ceramic primary hips (Stryker ABG-II, 28mm head) in 132 patients (m/f=72/60, avg. age=54yrs) and an average follow-up of 3.0 (1–7) years, noisy bearings were identified by a patient questionnaires stating the type of noise (squeaking, clicking, scratching, combinations), time of initial incidence, incidence rate (permanent, often, sometimes, rare) and type of movement. Patient demographics (age, gender, height, weight, BMI, side of surgery, leg length difference), implant parameters (cup and stem size, neck length) and surgery parameters (cup and stem position, leg length correction) were recorded and compared between the noisy and silent groups (t-test, Fisher Exact test).

Twenty-eight noisy hips (19.3%) were identified with 14 patients reporting squeaking, 16 clicking and 5 scratching including 7 with a combination of noises. Quasi permanent noises were reported for 7 hips (2 often) but in 17 cases the noise appeared only sometimes (2 rare). The average time of first incidence was 1.74 years port-op with 7 hips reporting noise directly after operation and 15 after 2 years or more. Silent and noisy hips were statistically not different regarding age, gender, follow-up time, side of operation, height, weight, BMI, cup and stem size, leg length difference or stem position. Significant differences were identified with the noise group having a steeper cup inclination (49.9° vs 46.9°, p< 0.05) and less frequent shorter (−2.7mm) necks (0 vs 22%, p< 0.01) but more frequent longer (+4mm) necks (50% vs 37%, p< 0.05). Leg length correction was performed less frequent (31 vs 55%, p< 0.01). In the noise group 5 (17%) and in the silent group only 1 (0.9%) cup revisions was performed (p< 0.01).

The incidence of noisy ceramic bearings was higher than usually reported (< 5%) as not only actively complaining subjects but all patients were interviewed. Cup position was confirmed to be a contributing factor but patient weight, height or BMI did not play a role. However, the use of long necks, the absence of short necks and less frequently performed leg length corrections significantly contributed to producing bearing noise. Biomechanical restoration, preoperative planning and soft tissue tension seem to be important factors in bearing noise etiology.

In joint arthroplasty and in knee replacement in particular, the currently used patient assessment scores like KSS, are characterized by subjective ceiling effects. To monitor patients accurately in time, objective function assessment is required which is impossible with the classic scores. A single time point comparison study showed that an acceleration based gait test is reliable to analyze gait and to distinguish between knee pathologies. How-ever the use of an accelerometer to monitor functional changes over time is never reported before and will be investigated in this study. A representative group of 29 TKP patients (11 men, mean age 72yrs, weight 85kg, height 1.68m) operated for osteoarthritis receiving unilateral TKP (Stryker Scorpio) were monitored for 3 months. Classic scores (ROM, KSS, WOMAC, VAS, PDI) and the gait test was performed pre, 2 and 6 weeks and 3 months postoperative. Gait was analyzed using a triaxial accelerometer fixed to the sacrum while walking 6 times 20meters at preferred speed. Movement parameters like step frequency, step time, step length, speed and up/down displacement were calculated based on a peak detection algorithm. The gait test was compared with the classic scores using Pearson correlation. The paired t-test was used to investigate the changes after surgery (p< 0.05). Significant correlations were shown between all classic scores and all movement parameters (except up/down displacement and step length). The function KSS and PDI showed significant correlations with most gait parameters, while all Womac scores did not. Two weeks after surgery, the classic scores reached the preoperative scores. For instance function KSS was 57.21 preoperative and reached a score of 59.75 at 2 weeks postoperative. No significant changes were shown between preoperative and 2 weeks postoperative for the VAS, KSS and PDI. In contrast all gait parameters were significantly impaired at 2 weeks postoperative (step time of 0.63s) compared to preoperative (step time of 0.72s) and reached the preoperative functional abilities only at 6 week follow up or still later (step time of 0.64s). Between the 2nd and 6th week postoperative, significant changes were shown in all classic scores, ROM and in speed, up/down displacement. After 6 weeks postoperative KSS, PDI, ROM and the frequency improved significantly. The correlations between all movement parameters and function KSS and PDI indicates that these scores are more function based due to inclusion of objective function measures like ROM, while the Womac contains only questions about ADLs. According to the classic scales, patients show at 2 weeks similar skills as preoperative, while the gait test shows that patients are performing less at 2 weeks and reach the pre operative ability at 6 weeks. This suggest that the addition of the gait test give more information about the functional changes a patient experiences after surgery.

We have investigated the accuracy of the templating of digital radiographs in planning total hip replacement using two common object-based calibration methods with the ball placed laterally (method 1) or medially (method 2) and compared them with two non-object-based methods. The latter comprised the application of a fixed magnification of 121% (method 3) and calculation of magnification based on the object-film-distance (method 4). We studied the post-operative radiographs of 57 patients (19 men, 38 women, mean age 73 years (53 to 89)) using the measured diameter of the prosthetic femoral head and comparing it with the true value.

Both object-based methods (1 and 2) produced large errors (mean/maximum: 2.55%/17.4% and 2.04%/6.46%, respectively). Method 3 applying a fixed magnification and method 4 (object-film-distance) produced smaller errors (mean/maximum 1.42%/5.22% and 1.57%/4.24%, respectively; p < 0.01). The latter results were clinically relevant and acceptable when planning was allowed to within one implant size. Object-based calibration (methods 1 and 2) has fundamental problems with the correct placement of the calibration ball. The accuracy of the fixed magnification (method 3) matched that of object-film-distance (method 4) and was the most reliable and efficient calibration method in digital templating.

Femoral neck fracture is a serious complication in hip resurfacing arthroplasty and reducing its risk is a major challenge. From a biomechanical point of view changing the geometrical characteristics in surgery could affect the stresses in the femoral neck. We analysed standing AP X-rays of 85 randomly selected patients having pain in the pelvic region in order to gain better understanding of the geometrical influences. Patients were selected on age, weight, pelvis visibility and no deformations of the proximal femur. A variety of geometrical characteristics has been measured and analysed using the two-sided t-test.

A significant difference was found between men and women, which was compared to previous publications in order to verify the measurement method. Statistical indication could not be found for leg-dominancy influencing geometrical dimensions. This is not mentioned in literature, but it is mentioned that the BMC and BMD differs between the legs. Several linear relations have been found between geometrical characteristics and demographics. The average head-neck ratio for both left and right was about 1.4 and the ratio of the abductor moment arm and body moment arm was about 2.1. The linear relation between femoral head diameter and femoral neck diameter indicates that the femoral component should be chosen according to the natural head diameter. The ratio between the abductor arm and body arm in combination with the bodyweight determines the static stresses in the femoral neck and can be changed in surgery by altering the hip axis length and neck shaft angle.

Conclusion: The geometrical characteristics can be changed in surgery and can reduce the stresses in the neck, but in hip resurfacing these changes are relatively small. The question is how much can the geometry be changed and could these changes lead to complications.

In joint arthroplasty the currently used patient assessment scores suffer from subjectivity, a low ceiling effect and pain dominance. These effects mask functional differences which are important for today’s demanding patients. Functional assessment tools are needed which can objectively monitor patient outcome. This study investigates whether an acceleration based gait test is able to assess TKR patients.

A cohort of 24 patients (11m, 13f) operated for osteoarthritis receiving unilateral TKR (Stryker Scorpio) were monitored for 3 months post-operative. Classic scores including subscores (KSS, Womac, VAS, PDI) and a gait test were measured pre-operative, at 2 weeks, 6 weeks and 3 months post-operative. Gait was analyzed using a triaxial accelerometer fixed to the sacrum while walking 6 times a 20m distance at preferred speed. Movement parameters like step frequency, step time, step number, vertical displacement, asymmetry and irregularity were calculated based on a peak detection algorithm.

All classic scores were significantly intercorrelated (e.g. KSS and Womac, R=−0.73) indicating a degree of redundancy. Significant correlations were shown between several gait parameters and the KSS, PDI and VAS. Most correlations between gait parameters and a classical score were found for the KSS function subscore indicating it as the most objective functional assessement amongst the classic scores. In contrast Womac did not correlate with any gait parameter. This lack WOMAC capturing objective function was reported before using functional tests.

The classic scales and the gait test cover different dimensions of surgical outcome supporting their combined use to follow up patients The accelerometer based gait test is clinically valid for the follow-up of TKR patients.

To clinically diagnose and postoperatively monitor the younger or more demanding orthopaedic patients it becomes increasingly important to measure function beyond the capacity of classic scores suffering from subjectivity, pain dominance and ceiling effects. This study investigates whether a stair climbing test with accelerometer derived motion parameters in a group of healthy subjects is clinically feasible and valid to distinguish between demographic differences.

The ascending and descending of stairs (preferred speed, no handrails) was measured in 46 healthy subjects (19m/27f, no orthopaedic pathology) using a triaxial accelerometer attached with a belt to the sacrum. The study group was divided in two age groups: young group (15m/16f; age: 25 [21–38]) and old group (4m/11f; age: 67 [54–74]). Motion parameters were derived by acceleration peak detection algorithms based on step times: tup, tdown, tup-tdown,, step irregularity: irrup, irrdown and asymmetry: asymup, asymdown.

Step times were slightly higher ascending (tup=606ms) than descending (tdown=575ms, p< 0.05). The step time difference between ascending and descending (tup-tdown=31ms) showed a significant difference between the young (47ms) and elderly (−7ms). All subjects with descending times ≥20ms slower than ascending (6/46) were elderly. Irregularity and asymmetry were similar between stepping direction and age groups. Asymmetry identified the dominant leg with equal or faster steps than the non-dominant leg in 43/46 cases. Motion parameters were not correlated to gender, height or BMI.

Slower step times down than up seem a promising parameter to detect general or bilateral orthopaedic pathologies. Asymmetry identifying the dominant leg shall detect unilateral pathologies. The accelerometer assessed stair test seems suitable for routine clinical follow-up complementing classic scores.

Introduction: Simulator wear studies of crosslinked polyethylene (PE) show promising results but long-term clinical investigations addressing concerns about in-vivo aging, PE deterioration, late wear and osteolysis are scarce. This study reports the longest published follow-up comparing conventional to crosslinked PE.

Methods: Crosslinked PE (Stryker Duration: 3MRad gamma irradiation in N2, post-irradiation annealed) was compared to conventional PE (3MRad gamma irradiation in air) in a MTS hip simulator and a prospective randomized clinical study involving 48 THA patients (Stryker ABG-II stem and cup, 28mm ball diameter) with a mean follow-up of 8 (7–9) years. Patients were followed-up annually using the HHS, radiographs and wear measurements applying a digital Livermore method.

Results: Forty patients (23 conventional, 17 Duration) were left for analysis (five premature deaths, 3 loss to follow-up). Both groups were statistically non-different (p> 0.1) regarding age (63.9 years), gender, BMI, stem size, cup size, cup inclination and liner thickness leaving the insert material as the only variable. Pre-op HHS (39.7) and post-op HHS (93.7) were also not different.

At 8-years the wear rate was significantly (p< 0.01) lower for Duration [0.088 ± 0.03 mm/yr (0.02–0.14)] than conventional PE [0.142 ± 0.07 mm/yr (0.05–0.31)]. This reduction (−38%) compared well to the simulator (−45%) and did not change over time (−33% at 5-years). Radiolucencies and signs of osteolysis were also less in the Duration group (n.s.).

Discussion: In-vivo wear reduction by crosslinked PE is similar as predicted by the simulator and does not seem to deteriorate over time. Concerns over higher levels of residual free radicals after annealing instead of remelting do not seem justified. The lower wear correlated with reduced radiographic signs of osteolysis which may result in superior survival at longer follow-up.

Introduction: Wear of the polyethylene (PE) acetabular component is widely regarded as the primary factor limiting the longevity of total hip arthroplasties (THA). To compare wear patterns of different polyethylene inserts computer assisted measurement techniques for in vivo polyethylene wear were developed. This study was performed to investigate which software out of four programs is most precise and easy to use in daily clinical practice.

Materials and Methods: 24 anteroposterior digital radiographs of patients with a THA (Stryker ABG-II with N2Vac and Duration PE inserts in metal backed cups) with an average of 8.0 years follow-up were measured twice by a blinded single observer for linear wear (head penetration) in a single image analysis. Four computer assisted wear measurement methods were compared, the commercially available Martell Hip Analysis suite 7.14 and Rogan Hyperview, a not yet available Rogan beta-version called View Pro-X and Roman v1.70, freely available software to download from the internet. While both Rogan software can read the DICOM format from the hospital image server, images had to be converted for Martell (greyscale TIFF only) and Roman (any format).

The annual wear rates were compared and intra-observer variability was calculated as the difference between both measurements (precision). The average time it takes to measure one image (without format conversions) was documented and practicality of daily clinical use was evaluated.

Results: The annual wear rates measured were (mean +/− SD): Martell=0.09+/−0.21,, Hyperview=0.14 +/−0.10, Pro-X=0.12+/−0.07 Roman=0.12 +/−0.06. Martell was the only method measured negative wear (7/24 cases).

The precision was (mean +/− SD): Martell = 1.74+/−1.53, Hyperview = 0.36 +/−0.92, Pro-X = 0.10+/−0.11 Roman = 0.08 +/−0.08.

The average measuring time per image was: Martell = 94s, Hyperview = 94s, Pro-X = 92s Roman = 158s.

Discussion: The Roman method is the most precise and easiest to use in daily practice, but takes the longest time to measure. The Rogan View Pro-X software is nearly as precise and easy to use but not on the market yet. It is an improvement over the Hyperview which looses precision by using a elliptical interpolation necessary for non-metal backed cups instead of circular interpolation which is more precise for metal backed cups. The Mar-tell method produced the intolerable low precision and in some cases “negative wear”. Only on large patient groups it may produce realistic average wear rates. We found out that the Martell edge detection method, originally developed for scanned analogue x-rays, functions inferiorly with digital images, the coming hospital standard. Image processing (smoothening) of the digital x-rays did increase accuracy and precision. We recommend the Roman software, a digital version of the Livermore method, for precision, ease of use and cost.

Introduction: In uncemented total hip arthroplasty (THA) stem sizing and stem insertion affect the fit and fill of the prosthesis in the medullary canal. This study investigates how tightness of the stem fit influences bone remodelling and if there is a correlation between radiological and clinical Results: Methods: In a retrospective study a consecutive series of 64 patients following uncemented THA with a proximally coated anatomic stem (ABG-II, Stryker) was followed-up for 5 years using the Merle d’Aubigne (MdA) clinical score. Radiographic analysis of bone remodelling features per Gruen zone (R1 to R7) was performed on AP and lateral x-rays at 5 years. Femoral fit was measured at three levels (proximal, mid-stem, distal) on the direct postop x-ray using the femoral fit ratio (f) of Kim and Kim (tight femoral fit: f≥0.8, non-tight: f< 0.8). The medullary canals were categorised according to Noble (normal, stove pipe, champagne flute). Bone remodelling was compared to literature values of the ABG-I stem and correlated to clinical findings.

Results: The MdA improved from 9.6 pre-op to 17.1 at 5 years with no difference between tight and non-tight implants. Lateral thigh pain (LTP) occurred in 10/64 cases (3 requiring medication). Patients with LTP had significantly lower proximal (0.75 vs 0.80) and distal fit & fill (0.72 vs 0.79. LTP was equally frequent with a normal or varus position.

Proximal bone resorption occurred in 27% (R1) or 34% (R7) which is lower than the values reported for the ABG-I stem (R1: 48%, R7: 45%). Bone resorption was significantly higher with tight than non-tight mid-stem fit (69% vs 27%, p=0.04). The same trend was true for tight distal fit (56% vs 37%).

Cancellous densifications were frequent at mid-stem level (R2: 83%, R6:88%) but much less distally (R3: 44%, R5:25%). No influence of fit & fill was measured.

Cortical densifications were noted in 16% (ABG-I 15%) overall with a higher proportion measured for tight distal fit (25%) than loose distal fit (6%, p=0.07). A similar observation was made for cortical thickening (11% overall, tight:non-tight=16%:6%). Pedestal formation (17% overall) was more likely with a non-tight proximal fit (23% vs 12%) and mid-stem fit (20% vs 8%)

A proximal tight fit was achieved more frequently with normal (55%) and stovepipe femora (50%) than champagne flute femora which had the highest proportion of tight distal fit (85%).

Discussion: At 5 years femoral implant fit influenced bone remodelling reactions which are in agreement with the design philosophy of proximally press-fitting anatomic stems. However, implant fit could not be correlated to clinical outcome yet. This may require a longer follow-up.

As LTP occurred with non-tight fit it seems that elastic mismatch is not the main cause.

Less proximal bone resorption and less distal densifications confirm the design changes from ABG-I to ABG-II.

INTRODUCTION: In total knee arthroplasty (TKA) it still remains undecided whether the patella should be resurfaced or not. This study used two accelerometer based motion analysis systems to study if functional tests are able to detect a difference in patients with or without a resurfaced patella.

METHOD: Retrospective study of a cohort of 53 unilateral TKA patients (Stryker Scorpio). With one surgeon always resurfacing and the other one routinely retaining the patella, patients were divided into a resurfaced group (RS, n=31) and a non-resurfaced group (NR, n=22).

Patients were clinically assessed for 2 years using the Knee Society Score (KSS). At final follow-up patients were assessed once using two accelerometer based motion tests (Dynaport Knee Test and Minimod Gait Test; McRoberts, Netherlands). The knee score is composed of four sub scores (Locomotion, Rise & Descend, Transfers, Lift & Move). The gait test records walking parameters such as step frequency, length and speed plus various parameters of step asymmetry, irregularity and efficiency. Statistical analysis was performed using the van Elteren’s test (KSS data) and a stratified regression analysis (Dynaport and Minimod data)

RESULTS: The mean pre-op KSS was not different between the groups (RS=42.7+/−16.5, NS=50.5+/−13.8, p=0.08). Differences remained non-significant post-op at three months (RS=42.7+/−16.5, NS=50.5+/−13.8, p=0.08), at final follow-up (RS=42.7+/−16.5, NS=50.5+/−13.8, p=0.08) and regarding total improvement (RS=8.7, NS=5.1, p=0.29).

The Dynaport knee test showed a significant functional advantage for patella resurfacing (RS=44.1+/−12.1, NR=39.7+/−19.2, p=0.04). The sub score Rise & Descend showed the largest advantage for patella resurfacing (RS=44.7, NR=39.7, p=0.04). The other sub scores also favored resurfacing but were not significant. The Minimod Gait test favoured RS in most parameters but at non-significant levels.

DISCUSSION: Using the KSS it was not possible to identify resurfacing or retaining the patella as the superior choice in TKA. However, using performance based tests it was possible to measure significant differences in favour of patella resurfacing but only when the motion tasks were most demanding and depending on patella-femoral function such as during Rise & Descend (stair climbing, slope walking, stepping onto blocks). This indicates a relevant functional benefit of patella resurfacing for the patient. Functional parameters derived from less demanding tasks such as normal gait (Mini-mod) could not verify this benefit.

The advantage of patella resurfacing may be less due to pain relief but due to a functional benefit during demanding motion tasks for which standard clinical scores and low demanding tests do not account for sufficiently and objectively enough. We recommend complementing the classic evaluation tools with demanding functional tests.