Objective

This study compared the primary stability of two commercially available acetabular components from the same manufacturer, which differ only in geometry; a hemispherical and a peripherally enhanced design (peripheral self-locking (PSL)). The objective was to determine whether altered geometry resulted in better primary stability.

Patient reported outcome measures (PROMs) are important for assessing the results of lower limb arthroplasty. Unrealistic or uneducated expectations may have a significant negative impact on PROMs even when surgery is technically successful. This study's aim was to quantify pre-operative expectations of Scottish patients undergoing total hip and knee replacement (THR/TKR).

100 THR and 100 TKR patients completed validated questionnaires (from the Hospital for Special Surgery) prior to their operation after receiving standard pre-operative information (booklet, DVD, consultations). Each patient rated expectations from very important to not having the expectation. A total score was calculated using a numerical scale for the grading of each expectation. Univariate regression analysis was used to investigate the relationship between demographics and expectation score.

The THR cohort had mean age 66.2 (SD 10.5), 53% female, mean BMI 29.0 (SD 5.1) and mean Oxford score 44 (SD 7). The TKR cohort had mean age 67.6 (SD 8.5), 59% female, mean BMI 32.8 (SD 5.8) and mean Oxford score 44 (SD 8). 100% THR and 96% TKR patients had 10 or more expectations of their operation. All expected pain relief. Other improvements expected were: walking for 100% THA and 99% TKA patients; daily activities for 100% THAs and 96% TKAs; recreational activities for 96% THAs and 93% TKAs; sexual activity for 66% THAs and 59% TKAs; psychological well-being for 98% THAs and 91% TKAs. Regression analysis showed increasing age lowered expectations in both THR (p=0.025) and TKR (p=0.031) patients but that gender, BMI and Oxford score were not significantly related to expectations.

This study highlights that patients expect far more than pain relief and improved post-operative mobility from their operation. It is important to discuss and manage these expectations with patients prior to surgery. By doing so, patient satisfaction and PROMs should further improve.

Recent debate about changing population demographics and growing demands of younger patients has suggested a future explosion in the requirements for primary and revision lower limb arthroplasty (TKA/THA). This could represent a significant challenge for healthcare providers. This study aimed to predict the demands for lower limb arthroplasty in Scotland from 2010–2035.

Population figures (2004–2010) and projected population data (five year increments) were obtained from the National Records of Scotland. The numbers of arthroplasties from 2004–2010 were provided by the Scottish Arthroplasty Project. Data were divided into three age groups (40–69, 60–79, 80+). The first model used mean incidence for each age group from 2006–2010 applied to the projected population figures. The second used linear regression to give predicted incidences 2015–2035 which were then applied to the projected population. The third-for revisions – used incidence per number of primary arthroplasties.

For primary TKA model 1, comparing to 2010, showed demand increasing by 10% in 2020 and by 31% (to 8,650 procedures) in 2035. Model 2 gave increases of 60% and 161% respectively. An increase was found across all age groups with 60–79 more than doubling and 80+ increasing fourfold by 2035 (model 2). The revision TKA models predicted between 670 and 2,000 procedures by 2035. For primary THA models 1 and 2 showed demand increasing by 40% in 2020 and then by 60% and 110% (11,000 and 14,500 procedures) in 2035 respectively. All age groups had increasing demand with 60–79 doubling and 80+ tripling by 2035 (model 2). The revision THA models predicted between 1,300 and 2,100 procedures by 2035.

These projections show large increases in the numbers of both primaries and revisions over the next two decades. They highlight that current resources may be insufficient or the selection criteria for surgery may need to be revisited.

The routine use of a fixed distal femoral resection angle in total knee arthroplasty (TKA) assumes little or no variation in the angle between the anatomical and mechanical femoral axes (FMA angle) in different patients. The aims of this study were threefold, firstly to investigate the distribution of FMA angle in TKA patients, secondly to identify any correlation between the FMA angle and the pre-operative coronal mechanical femoro-tibial (MFT) angle and in addition to assess post-operative MFT angle with fixed or variable distal femoral resection angles.

277 primary TKAs were performed using either fixed or variable distal femoral resection angles (174 and 103 TKAs respectively), with intramedullary femoral and extramedullary tibial jigs. The variable distal femoral resection angles were equal to the FMA angle measured on pre-operative Hip-Knee-Ankle (HKA) digital radiographs for each patient. Outcomes were assessed by measuring the FMA angle and the pre- and post-operative MFT angles on HKA radiographs.

The FMA angle ranged from 2° to 9° (mean 5.9°). Both cohorts showed a correlation between FMA and pre-operative MFT angles (fixed: r = -0.499, variable: r = -0.346) with valgus knees having lower FMA angles. Post-operative coronal alignment within ±5° increased from 86% in the fixed angle group to 96% when using a variable angle, p = 0.025. For post-operative limb alignment within ±3°, accuracy improved from 67% (fixed) to 85% (variable), p = 0.002.

These results show that the use of a fixed distal femoral resection angle is a source of error regarding post-operative coronal limb malalignment. The correlation between the FMA angle and pre-operative varus-valgus alignment supports the rational of recommending the adjustment of the resection angle according to the pre-operative deformity (3°-5° for valgus, 6°-8° for varus) in cases where HKA radiographs are not available for pre-operative planning.

Arthritic knees, for the purpose of surgical correction during arthroplasty, are generally thought to be either varus knees or valgus knees and soft tissue releases are done in accordance with the same concept. This view is dependent on the clinical deformity in extended knee and the plain AP radiograph of the extended knee. This concept is now challenged by the observations from our study of the arthritic knee kinematics using computer aided navigation when performing total knee replacement arthroplasty. We performed 283 total knee replacements with computer aided navigation. Imageless navigation was used with Stryker and Orthopilot systems. Bone trackers were fixed to the bones and through real time infrared communication the data was collected. The knee kinematics were recorded before and at the end of surgery. This included measurement of biomechanical axis with the knee extended and then gradually flexed. The effect of flexion on the coronal alignment was recorded real time on the computer. The results were then analysed and compared with plain radiographic deformity on long leg films.

Majority of the knees did not behave in a true varus or valgus fashion. We classified the deformity into different groups depending on the behavior of the knee in coronal plane as it moves from extension to flexion. 2 degree was taken as minimum deviation to signify change, as the knee bends from full extension to flexion. The classification system is as follows

Neutral

Deformity - Varus/Valgus to start with in extension

Gp1

Deformity remains the same as the knee flexes

Gp2

Decreasing deformity but does not reach neutral in flexion

Gp3

Decreasing deformity and crosses to opposite (Varus to valgus or valgus to varus) deformity in flexion

Gp4

Deformity first increases and then decreases but does not reach neutral

Traditional releases of medial or lateral structures without realising the true picture of what happens when the knee is flexed, may not be correct. From our study it is clear that not all arthritic varus or valgus knees behave in the same way. Some of the releases we perform conventionally may not be required or need to be modified depending on the knee kinematics.

In Total Knee Arthroplasty (TKA) restoring the mechanical alignment of the knee joint is essential. This can be improved by considering the individual variability in the angle between the mechanical and anatomical axes of the femur (FMA angle). However with the traditional instrumentation and the use of the most common fixed distal femoral resection angle of 6° we assume little or no variation in the FMA angles in different patients. In a previous study we showed that the FMA angle had a wide distribution and that there was a good correlation between the FMA angle and the pre-operative lower limb alignment in the coronal plane. Our hypothesis was that improved post operative limb alignment would be achieved with traditional instrumentation by individual measurement of the FMA angles pre-operatively and adjusting the distal femoral resections accordingly. In the study we compared the post-operative coronal limb alignment for a cohort of patients with a variable distal femoral resection angle to the previous cohort of fixed distal femoral resection angle.

The study consisted of 103 patients undergoing 103 consecutive primary TKAs between October 2008 and March 2009. All patients had pre- and post-operative Hip-Knee-Ankle digital radiographs and had TKAs performed using a variable distal femoral cut angle. The FMA angle and the mechanical femoro-tibial (MFT) angles were measured in all cases. Inter-observer variation was measured by second observer readings. We compared our results with the group of 158 consecutive patients undergoing 174 primary TKAs operated between January and October 2007 using fixed distal femoral resection angle.

Patient demographics of the two cohorts (age, gender, BMI) were similar.

The pre-operative coronal deformity for the variable cohort was less than the fixed, mean 3.7° varus (SD 5.8°) compared to 4.7° varus (SD 7.9°). The FMA angles for the variable cohort ranged from 4° to 8°, (the fixed cohort from 2° to 9°). The variable valgus resection angles cohort showed a correlation between FMA and pre-operative MFT angles as had previously been shown in the fixed cohort (r = −0.499 and r = −0.346 respectively). Post op alignment showed that accuracy within ±5° increased from 86% (fixed resection angle group) to 96% (variable resection group). When using the more commonly quoted accuracy of within ±3°, this changed from 67% (fixed resection angle group) to 85% (variable resection group). These improvements were statistically significant (chi-squared 0.025 and 0.002, respectively). To further evaluate the effect of using variable angles we analysed the improvement of each of the different groups of deformity identified in the previous study (> 8° varus, 8° varus to 1° valgus, > 2° valgus). The range was reduced in both the extreme varus and valgus groups with the variable angles. The most significant improvement was found in the valgus group with the median reducing from 3° to 2° and range from 14° to 8°.

It seems logical to use a variable distal femoral resection angle based on the patient’s individual anatomy. By doing so, our results show significant improvement of postoperative limb alignment compared to traditional method of using fixed distal femoral resection angle. In units where preoperative long leg film radiographs are available, measuring the FMA angle and setting the distal femoral resection angle guide accordingly improves the postoperative limb alignment. However, where long leg radiographs are not available, changing the distal femoral resection angle according to the pre-operative varus-valgus deformity is likely to improve the post operative limb alignment. (e.g. 4°–5° distal femoral resection angle for preoperative valgus, 6° for preoperative mild/moderate varus, and 7°–8° for preoperative severe varus).Computer navigation, however, enables us not only to use customised distal femoral cut for each patients, but it also provides many other useful information such as dynamical limb alignment through motion, component rotation, soft tissue balancing.

Many studies have already been published to prove the improved accuracy in achieving the ideal post-operative long leg alignment when using computer navigation in total knee arthroplasty (TKA). Surgeons who use traditional instrumentation with a fixed distal femoral resection angle (most commonly 6°) assume little or no variation in the angle between the anatomical and mechanical axis of the femur (FMA angle) in different patients.

The aims of this study were to investigate the distribution of the FMA angle in pathological knees of patients about to undergo TKA and to analyse if there was any correlation between the FMA angle and the pre-operative lower limb alignment in the coronal plane (varus or valgus).

The study consisted of 158 consecutive patients undergoing 174 primary TKA between January and October 2007. All patients had pre-operative digital Hip-Knee-Ankle radiographs. The FMA angle and the mechanical femorotibial angle (MFT angle) were measured in all cases. Intra- and inter-observer variation was measured by second observer readings and repeated measurements.

The mean age of the study cohort was 69.9 years (SD 8.7 years). There were 75 male and 99 female knees. The repeatability for measurement of the FMA angle was good (intra-observer Intra Correlation Coefficient (ICC) = 0.91, inter-observer ICC = 0.85) and for the measurement of MFT angle was very good (intra-observer ICC = 0.99, inter-observer ICC = 0.99). There were 135 knees with a varus or neutral alignment and 39 knees with valgus alignment. The median alignment was 6.5° varus ranging from 23° varus to 16° valgus. The FMA angle was between 2° and 9°, with a median of 6°. The FMA angle was 6° in 35.4% of cases, 5° in 22.9% and 7° in 18.3%. There was a statistical significant correlation between the FMA angle and the pre-operative lower limb alignment (Pearson correlation coefficient = −0.5, p < 0.001), with valgus knees having on average a lower FMA angle. The group of females and males had statistically different FMA angles (Mann-Whitney, p < 0.001) with females having on average a lower FMA angle. Cluster analysis based on the original clinical definitions of severe varus, varus and valgus gave three groups of FMA angle for MFT angle < 8° varus, MFT angle of 8° varus to 1° valgus and MFT angle > 1° valgus. There was a statistically significant difference in median FMA angle between these three groups (Kruskal-Wallis, p < 0.001).

This study indicates that one of the main reasons why optimal post-operative coronal alignment cannot be achieved with a fixed distal femoral resection angle is the fact that the FMA angle has a wide, natural distribution. It is possible that better results may be achieved with traditional instrumentation by individual measurement of FMA angle for each patient pre-operatively and adjusting the distal femoral resection to account for this. However, with computer navigation the distal femoral cut is adjusted for each patient.

Introduction: The knee joint replacement arthroplasty is a very successful procedure. Traditionally we aim to perform the arthroplasty and recreate the patients’ biomechanical axis and correct the coronal plain alignment deformity. Unfortunately till recently there was no fine way of controlling the exact alignment and depending on surgeon to surgeon, a valgus (to anatomical axis) of 3 to 7 degrees is aimed for using mechanical intra or extramedullary jigs. On proper measurements only 70–80% of knees achieve the aimed result at best as can be seen in the literature. With the advent of computer aided navigation we can now achieve the desired alignment in a much higher percentage of patients.

Material: We performed 1000 total knee arthroplasties at our hospital. Out of these 500 were performed using computer navigation and 500 using conventional mechanical jigs. Pre op and post op long leg alignment films were taken using standardised method. The data was collected using oxford scores and from computer navigation machines and plain radiographic analysis. The observers doing the radiographic analysis were blinded as to whether the patient had procedure done by conventional means or by computer navigation. Sub grouping of the deformities was done depending on the amount of deformity.

Results: 500 patients had the operation done by conventional means and the other 500 with computer navigation guidance. Further subgroups were made depending on the amount of pre-existing radiological deformity 0–5, 6–10, 11–15 and more than 15 degrees of varus or valgus deformity. The effect of gender, bmi, surgeon experience, clinical oxford score outcome was also considered. It was clear that the patients who had more severe deformities and valgus deformities had better post operative alignments after the procedure was performed with computer navigation as compared with the conventional means. There was statistically significant difference observed between the subgroups.

Discussion: Orthopaedic surgery has improved with technical advancements over the number of years. With any new procedure it takes a long time to shed the old beliefs and adapt the new concepts. While we have plenty of evidence in literature and from our study that computer navigation can give better desired alignment after total knee arthroplasty especially with more severe deformities, it still needs to be taken up by majority of orthopaedic surgeons. Ours is the first study to demonstrate the difference in the specific subgroups.

Introduction: The geometry of uncemented press-fit ace-tabular cups is important in achieving primary stability to ensure bony ingrowth. This study compares the in vitro primary stability of two widely used designs.

Methods: The primary stability of two uncemented ace-tabular cup designs (true hemispheric and peripherally enhanced) with the same 52mm diameter and produced by the same manufacturer, was tested in vitro. Polyethylene blocks of low and high density -representing softer and harder bone- were reamed using the manufacturers’ reamers. The cups were seated using an Instron 5800R machine. Peak failure loads and moments during uniaxial pull-out and tangential lever-out tests were used as measures of primary stability. Eighty tests were performed.

Results: Low density substrate: no difference between the two designs for seating force or stability, with the substrate under-reamed by 2mm.

High density substrate: the cups could not be adequately seated with a 2mm under-ream. Seating was achieved with 1mm under-ream for the hemispheric and 1mm over-ream for the peripherally enhanced design. There was a statistically significant difference in seating forces, with the hemispheric cup requiring less force (6264±1535N vs 7858±2383N, p< 0.05). There was a statistically significant difference in the stability ratio of pull-out force to seating force, favouring the hemispheric cup.

Discussion: No difference was seen in the low density substrate between the 2 cups.

In the high density, the hemispheric design had better characteristics (lower seating force and higher pull-out force to seating force ratio) than the peripherally enhanced design, which are more favourable in clinical settings.

Short leg radiographs remain the standard radiographs available in many UK hospitals. The aim of this study was to see if these radiographs are reliable when assessing the post-operative alignment of total knee arthroplasty in comparison to a Hip-Knee-Ankle (long leg) radiograph.

Twenty consecutive 6 week post-operative long leg radiographs, taken with a standardised protocol, and a short leg radiograph derived from the same digital image were each examined on two separate occasions by two observers. On the long leg radiograph the anatomical and mechanical axis were calculated and on the short leg radiograph the anatomical and surrogate mechanical axis were calculated. These data were used to investigate intra- and inter-observer error. A single observer also collected the same measurements on an additional 30 radiographs (total of 50) to further investigate any patterns of error.

On long leg radiographs, intra-observer agreement was good for both anatomical and mechanical axis for both observers (Intraclass Correlation Coefficients [ICC] of 0.95 to 0.98). The anatomical axis on short leg radiographs was also good (ICC = 0.92 and 0.76). Intra-observer agreement for the short leg radiograph derived mechanical axis was not as consistent (ICC = 0.73 and 0.56). Inter-observer variability was good for long leg radiographs for both anatomical (ICC = 0.89) and mechanical (ICC = 0.95) axis. On short leg radiographs, however, agreement was not as good, in particular for the mechanical axis (ICC = 0.51), but also the anatomical (ICC = 0.73). Taking the long leg radiograph values as the “gold standard” there was a difference in the magnitude of errors seen on short leg radiographs dependant on the knee alignment. Varus aligned knees (n=24) had an average error of 1.2° (0° to 3°) for the anatomical axis and 1.6° (0° to 4°) for the mechanical axis. Perfectly aligned knees (n=8) had an average error of 3.0° (1° to 6°) for the anatomical axis and 2.9° (1° to 5°) for the mechanical axis. Valgus aligned knees (n=18) had an average error of 3.4° (0° to 8°) for the anatomical axis and 5.8° (2° to11°) for the mechanical axis. Using a Mann-Whitney test the magnitude of error was greater for valgus knees for both anatomical (p< 0.0001) and mechanical (p< 0.00001) axes when compare to varus knees. Interestingly all except one knee measured on the long leg radiograph as valgus aligned appeared to be in varus on the short leg radiograph.

In conclusion, short leg radiographs are inadequate to make any comment on leg alignment in total knee arthroplasty. This is most pronounced in a valgus aligned knee.

Introduction: Computer navigated total knee replacement does not require the use of intramedullary alignment rods, and is thus less invasive than traditional methods.

One previous study has suggested that the computer-assisted technique may reduce blood loss in comparison to traditional methods. This study (Kalairajah et al, 2005) used blood volume loss from drainage bottles as a primary outcome measure (n=60). Hidden (internal) blood losses were not accounted for.

Our study uses a more accurate method of assessing blood loss, and the sample size is larger (n=136; 68 standard TKR versus 68 computer assisted TKR).

Methods: 136 TKR patients were included, of which 68 had standard TKR and 68 computer assisted. Patients were matched such that in each group half had BMI in the range 20–30, and half had BMI between 30–40. Patients were also matched for gender. All patients had Tranexamic acid at the start of the procedure.

Total body blood volume was calculated using the formula of Nadler, Hidalgo & Bloch (1962). This was then used, together with haematocrit and volume re-infused or transfused, to calculate true blood loss, as described by Sehat, Evans, and Newman (2004). This method is considered to be more reliable than measuring drain output, as it takes account of “hidden” losses. The navigated and non-navigated groups were compared using Student’s t-test.

Results: The average blood loss was 583ml in the standard TKR group, and 442ml in the computer assisted TKR group. This difference was statistically significant (p=0.003).

Conclusions: A previous study found reduced blood loss when performing total knee replacement using computer navigation, compared with traditional methods. Our study confirmed this finding, using a larger sample size, and a more reliable method of assessing blood loss.

Our study found that overall blood loss was less for both groups, when compared to the findings of Kalairajah Y et al. We suspect that this difference was due to our departmental policy that all patients receive tranexamic acid at the start of joint replacement procedure.

Computer navigated total knee replacement is less invasive than traditional methods, as it avoids the use of intramedullary alignment rods. A previous study (Kalairajah et al, 2005) has shown that computer-assisted techniques may reduce blood loss in comparison to traditional methods. Our study uses a more accurate method of assessing blood loss, and the sample size is larger.

136 TKR patients were selected from a prospectively collected database of all those undergoing arthroplasty at our institution; 68 had standard TKR and 68 had a computer assisted TKR. In each group, half had BMI in the range 20–30, and half had BMI between 30–40. There were an equal number of males and females in each group. All patients received a standardised anaesthetic, and had tranexamic acid at the start of the procedure.

Total body blood volume was calculated from patient height, weight and sex, using the model described by Nadler, Hidalgo & Bloch (1962). This was then used, together with pre- and post-op haematocrit and volume re-infused or transfused, to calculate true blood loss, as described by Sehat, Evans, and Newman (2004). This method is considered to be more reliable than measuring drain output, as it takes account of “hidden” (internal) losses.

The average blood loss was 603ml in the standard TKR group, and 448ml in the computer assisted TKR group. Student’s t-test showed that this difference was statistically significant (p = 0.007). Regression analysis showed no significant difference between obese and non-obese patients, nor a difference between sexes. Blood loss in both groups was lower than in a previous study, which we attribute to our department’s routine use of tranexamic acid.

We conclude that computer-assisted total knee replacement leads to significant reduction in blood loss when compared with traditional techniques. This confirms previous reports.