Purpose: The purpose was to investigate the relationship between distal radius fracture malunion and arm-related disability.

Methods: This prospective population-based cohort study included 143 patients above 18 years with acute distal radius fracture treated at one emergency hospital with either closed reduction and cast (55 patients) or with closed reduction and external and/or percutaneous pin fixation (88 patients). The patients were evaluated with the disabilities of the arm, shoulder and hand (DASH) questionnaire at baseline (inquiring about disabilities before fracture) and at 6, 12 and 24 months after the fracture. The 12-month follow-up also included the SF-12 health status questionnaire as well as clinical and radiographic examination. The patients were classified according to the degree of malunion (defined as dorsal tilt > 10 degrees or ulnar variance > 0 mm) into three groups; no malunion, malunion involving either dorsal tilt or ulnar variance, and malunion involving both dorsal tilt and ulnar variance. A Cox regression analysis was performed to determine the relationship between the 1-year DASH score (≥ 15 or < 15) and malunion adjusting for age, sex, fracture AO type, and treatment method and the relative risk (RR) of obtaining the higher DASH score was calculated. The number needed to harm (NNH) associated with malunion was calculated.

Results: The mean DASH score at 1 year after fracture was about 10 points worse with each degree of increased malunion. The degree of malunion also correlated with SF-12 score, grip strength and supination. The regression analysis showed significantly higher disability with each degree of malunion compared to no malunion; for malunion involving either dorsal tilt or ulnar variance the RR was 2.4 (95% CI 1.0–5.7; p=0.038), and for malunion involving both dorsal tilt and ulnar variance the RR was 3.2 (95% CI 1.4–7.5; p=0.007). The NNH was 2.5 (95% CI 1.8–5.4).

Conclusion: Malunion after distal radius fracture was associated with higher arm-related disability.

Background: RSA cannot discern whether a single prosthesis is fixed or migrating below the detection level. Samples of patients usually show migration values that appear to be continuously distributed. Is there a dichotomy between stable and migrating prostheses?

Methods: We analysed the migration of 147 cemented acetabular cups of 7 different designs, by use of a new set of algoritms for frequency distribution analysis called Rmix. The migration vector lengths were assumed to be a compound of log-normal distributions. The algoritm then calculated if the observed frequency distribution is best explained by one or more log-normal distributions.

Results: After 2 years there was a significant dichotomy (p=0.006) between 2 lognormal subgroups within the sample. Neither cup design, sex or operating department could explain the dichotomy into two groups, which appears to reflect the existence of two different types of behaviour. The migration along the 3 axes in space, showed a similar dichotomy. During the second year, around 80 % of the patients belonged to a distinct, normally distributed subgroup with a mean not different from 0 mm and a small variation, corresponding to the measuring error. The remainder differed significantly from this subgroup and showed migration.

Interpretation: The majority of the cups belonged to a subpopulation that appeared completely stableduring the second year. For a single type of prosthesis, the relative size of the stable subgroup might be a good index of the expected performance.

Background: In a previous randomized studiy using Röntgen Stereometric Analysis (RSA), we showed that oral bisphosphonates reduce the mean migration distance during the first 6 months. In a similar randomized study, bisphosphonates applied locally at the operation had a similar effect. These studies showed a 0.1 mm difference in mean value between groups. Does such a small difference matter? We addressed this question by use of frequency analysis.

Methods: The 2 previous studies were combined for analysis, and designated as bisphosphonate (n=44) or control treated (n=49). We analysed the migration vector (for the center of the rigid body) by use of a set of algoritms for frequency distribution analysis called Rmix. The migration vector lengths were assumed to be a compound of log-normal distributions. The frequency analysis determined if the observed frequency distributions were best described as a single, or a sum of 2 or more lognormally distributed subgroups.

Results: After 6 months, the control patients had formed 2 subgroups, one comprising 85% of the patients. The dichotomy was significant (p=0.016).

After 2 years, the dichotomy persisted (p=0.027). In the bisphosphonate-treated patients, no dichotomies could be found. The distribution of the migration vector length appeared similar to the larger and less migrating subgroup among the controls.

Discussion: The risk of aseptic loosening for cemented knees is extremely small. However, the migrating subgroup among our control patients may be at risk of loosening, and would have run a high risk if they were young and active. This subgroup did not appear with bisphosphonate treatment

Summary: In previous comparisons we found a slight decrease in mean value with bisphosphonates. The present analysis shows that this reflects the disappearance of a small subgroup with large migration.