Background and purposeTotal hip arthroplasty (THA) patients have reduced muscle strength after rehabilitation. In a previous efficacy trial, 4 weeks’ early supervised maximal strength training (MST) increased muscle strength in unilateral THA patients <65 years. We have now evaluated muscle strength in an MST and in a conventional physiotherapy (CP) group after rehabilitation in regular clinical practice.Patients and methods60 primary THA patients were randomized to MST or CP between August 2015 and February 2016. The MST group trained at 85–90% of their maximal capacity in leg press and abduction of the operated leg (4 × 5 repetitions), 3 times a week at a municipal physiotherapy institute up to 3 months postoperatively. The CP group followed a training program designed by their respective physiotherapist, mainly exercises performed with low or no external loads. Patients were tested pre- 3, 6, and 12 months postoperatively. Primary outcomes were abduction and leg press strength at 3 months. Other parameters evaluated were pain, 6-min walk test, Harris Hip Score (HHS) and Hip disability and Osteoarthritis Outcome Score (HOOS) Physical Function Short-form score.Results27 patients in each group completed the intervention. MST patients were substantially stronger in leg press and abduction than CP patients 3 (43 kg and 3 kg respectively) and 6 months (30 kg and 3 kg respectively) postoperatively (p ≤ 0.002). 1 year postoperatively, no intergroup differences were found. No other statistically significant intergroup differences were found.InterpretationMST increases muscle strength more than CP in THA patients up to 6 months postoperatively, after 3 months’ rehabilitation in clinical practice. It was well tolerated by the THA patients and seems feasible to conduct within regular clinical practice.

Hydroxyapatite-coated standard anatomical and customised femoral stems are designed to transmit load to the metaphyseal part of the proximal femur in order to avoid stress shielding and to reduce resorption of bone. In a randomised in vitro study, we compared the changes in the pattern of cortical strain after the insertion of hydroxyapatite-coated standard anatomical and customised stems in 12 pairs of human cadaver femora. A hip simulator reproduced the physiological loads on the proximal femur in single-leg stance and stair-climbing. The cortical strains were measured before and after the insertion of the stems. Significantly higher strain shielding was seen in Gruen zones 7, 6, 5, 3 and 2 after the insertion of the anatomical stem compared with the customised stem. For the anatomical stem, the hoop strains on the femur also indicated that the load was transferred to the cortical bone at the lower metaphyseal or upper diaphyseal part of the proximal femur. The customised stem induced a strain pattern more similar to that of the intact femur than the standard, anatomical stem.

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Background and purposeCustomized femoral stems are designed to have a perfect fit and fill in the femur in order to achieve physiological load transfer and minimize stress shielding. Dual-energy X-ray absorptiometry (DXA) is regarded as an accurate method for detection of small alterations in bone mineral density (BMD) around hip prostheses. We present medium-term DXA results from a randomized study comparing a customized and an anatomical femoral stem.Methods100 hips were randomized to receive either the anatomical ABG-I stem or the Unique customized femoral stem, both uncemented. DXA measurements were conducted postoperatively and after 3, 6, 12, 24, 36, and 60 months, and BMD was computed for each of the 7 Gruen zones in the proximal femur.ResultsResults from 87 patients were available for analysis. 78 completed the 5-year follow-up: 35 patients in the ABG group and 43 patients in the Unique group. In both groups, we found the greatest degree of bone loss in the proximal Gruen zones. In zone 1, there was 15% reduction in BMD in the ABG-I group and 14% reduction in the Unique group. In zone 7, the reduction was 28% in the ABG-I group and 27% in the Unique group. The only statistically significant difference between the groups was found in Gruen zone 4, which is distal to the tip of the stem, with 1.6% reduction in BMD in the ABG-I group and 9.7% reduction in the Unique group (p = 0.003).Interpretation5-year DXA results showed that because of stress-shielding, proximal bone loss could not be avoided—either for the anatomical ABG-I stem or for the customized Unique stem.

The aim of the study was to investigate the effect of maximal strength training on postural sway after total hip arthroplasty, performed before and after a battery of physical performance tests that resemble daily living activities. Design: This study is an exploratory study based on data from a 3-mo randomized controlled trial involving 54 total hip arthroplasty patients performing maximal strength training or conventional rehabilitation. At 3, 6, and 12 mos postoperatively, postural sway was evaluated in two gait tests; ie, one test before and one test after conducting a battery of physical performance tests. Results: At 3 mos postoperatively, postural sway in the test after was significantly higher for the conventional rehabilitation group than the maximal strength training group (P = 0.045); however, there was no between-group difference at the test before (P = 0.670). Postural sway was also significantly higher in the test after compared with the test before in the conventional rehabilitation group (P < 0.001). No difference was found between the test before and test after in the maximal strength training group (P = 0.713). At 6 and 12 mos postoperatively, there were no statistically significant within-or between-group differences in postural sway. Conclusions: Increased muscular strength limits postural sway 3 mos postoperatively in total hip arthroplasty patients after a demanding battery of physical performance tests simulating daily living activities.

Background: Surgical approach influences short-term muscular strength, and leg-strength asymmetry has been demonstrated after total hip arthroplasty (THA). We evaluated muscular strength, physical function and patient-reported outcome measures (PROMs) up to 12 months postoperatively, in patients operated on using 3 different surgical approaches. Methods: 60 patients scheduled for primary THA were allocated to the direct lateral (DLA), posterior (PA) or anterior (AA) approach. The following parameters were evaluated: leg press and abduction strength, pain, 6-minute walking test, Harris Hip Score and Hip disability and Osteoarthritis Outcome Score-Physical Function Shortform (HOOS-PS). Results: Abduction strength in the DLA group was significantly more reduced than the PA and AA groups 12 months postoperatively (p < 0.001). A significant interleg difference in abduction (p < 0.01) and leg press (p < 0.03) persisted in all groups up to 6 months, and up to 12 months in the DLA (p < 0.05). In the AA group, interleg difference in leg press was present up to 12 months (p = 0.01). Pain scores were higher in the DLA than the AA group at 6 months (p = 0.01). Patients in the PA group had better HOOS-PS score than those in the DLA group 3 months postoperatively (p = 0.02). No intergroup differences in pain or PROMs were found 12 months postoperatively. Conclusion: Patients operated via the DLA had reduced muscular strength, HOOS-PS scores and higher pain scores than those who underwent PA and AA type surgery. The non-operated leg was significantly stronger than the operated leg in all groups 6 months postoperatively and this persisted up to 12 months postoperatively for the DLA and AA groups. Clinical Trial Protocol number: ClinicalTrials.gov (NCT01506024).

The ability to vary femoral offset and neck angles in total hip arthroplasty increases the amount of flexibility in the mechanical reconstruction of the hip joint. The present study investigates the changes in strain pattern and bone-implant micromotion caused by increased femoral offset in combination with retroversion or reduced neck-shaft angle, made possible by a large experimental femoral head. A cementless femoral stem was inserted in 10 human cadaver femurs. Three femoral head configurations were tested: the standard situation, an increased offset combined with retroversion, and increased offset combined with reduced neck-shaft angle. The femurs were loaded in a hip simulator that was able to reproduce the conditions that correspond to one-legged stance and stair climbing. There was a statistically significant increase in strain for the experimental head at several strain gauge rosettes compared to the standard head. The largest significant increase in strain was 14.2 per cent on the anterior side of the femur. The largest mean total point motion was 44 microm in the distal coating area for the configuration with increased femoral offset and retroverted neck axis. The clinical relevance of the changes in strain distribution is uncertain. The femoral stem showed excellent initial stability for all test situations.

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