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.
Background: Selective ultrasound screening of neonatal hips with risk factors has been undertaken in Lanarkshire from 2001. Referral reasons included family history, breech, clicky hip and instability. Patients are examined by an orthopaedic surgeon with a special interest and scanned by static Graf technique. Our experience with selective screening and its effect on late DDH is presented. Methods: All ultrasound screening data was collected prospectively and entered into a database. Late presenters were identified at the tertiary centre by case note and X ray review. Population data was obtained from the Scottish registry. Results: Between 2001–2005, there were 30,824 live-births. 405 babies (910 hips) were identified as being at risk. 5(1.2%) were identified as Graf III/IV. Three responded to splinting, 1 required closed reduction and 1 open reduction. 11 who had initially normal scans were noted to have abnormal acetabular index (>30) at 6 months. 2 required open reduction, 1 closed reduction and the rest eventually normalised with follow up. True late presentation was identified (> 3 months) in 11 children. Mean age at diagnosis was 14.7m (4–29 mts). 7(64%) did not have any identifiable risk factors. 4 had risk factors, but had escaped screening. 8 underwent open and 3 closed reduction. 7 derotation osteotomies and 1 pelvic osteotomy were additionally performed. Discussion: The identifiable incidence of DDH in Lanarkshire is 0.87/1000. The incidence of true late presenting DDH in the same population was 0.35/1000. If all hips with risk factors had been successfully screened it would reduce to 0.22/1000. Selective screenings can minimise the incidence of late presenting DDH if rigorously implemented. Majority of late presenters do not have risk factors and are likely to escape detection with a selective screening programme. This suggests a different natural history in late presenting cases.
Aim: To assess the efficacy of selective ultrasound screening for DDH, with and without an orthopaedic examination. Method: From 2002 our secondary DDH screening program was changed. Newborns with risk factors were referred directly for hip ultrasound. The orthopaedic surgeon was not involved if ultrasound was normal. An audit for 1997–2001 found an average annual incidence of 0.57(29 cases). The audit was extended to 2005 by identifying late DDH cases presenting from 2002 onwards, using the same criteria. Results: Ninety-six cases were identified. After excluding children born outside Glasgow 36 cases were left for audit. The yearly incidence per 1000 live-births is shown below. The average incidence for 2002–2005 was 0.95. No significant difference between the two periods was found (p= 0.3). Average age at diagnosis was 14.9 months. Two had risk factors but had not been screened. Thirty-one hips were dislocated, two were subluxed and one had borderline dysplasia that resolved. Twenty needed open reduction. Sixteen of 22 patients over 1 year at treatment required open reduction compared to 5 of 13 treated age 1 year or less (p = 0.046). Ten had femoral osteotomy, five a pelvic osteotomy, and five both femoral and pelvic osteotomy. There was one postoperative infection. Conclusion: Direct ultrasound screening of infants with risk factors without concomitant assessment by an orthopaedic surgeon has not significantly altered the incidence of late DDH.
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 1° valgus. There was a statistically significant difference in median FMA angle between these three groups (Kruskal-Wallis, p 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.
We performed a radiologic assessment of the Trident Peripheral Self-Locking cup 2 years after implantation to assess early migration behaviour and to establish if incomplete postoperative seating correlated with early instability. A retrospective analysis of 30 cases was performed using EBRA. No cups had acetabular screws. Average total migration was 1.5 mm (range 0.1 to 5.9 mm). Seventeen showed total migration >1 mm and 7 of these showed further migration >2 mm (range 2.3 to 5.9 mm). Twenty cups demonstrated incomplete seating on initial post-operative radiographs (mean 1.4 mm, range 0.3 to 3.0). No relationship between incomplete seating and migration was identified (p = 0.86). The majority of gaps consolidated at differing times within the 2 year period. Oxford Hip scores showed significant improvement after surgery (p = 0.001) and this was independent of migration (p = 0.76). At 5 years there were no revisions for aseptic loosening.The majority of the cups demonstrated early radiographic instability, and this was not related to incomplete seating. Five year functional outcome appears good and independent of migration and initial seating.
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