It is generally appreciated that the internal structure and external shape of living bone adapt to mechanical stimuli according to Wolff’s law. However, the precise details of bone adaptation to external forces are not fully understood and there has been no previous investigation of the association between specific loading conditions and the skeletal architecture of a particular anatomical area using case-specific observations in a group of individuals. The aim of the present study was to investigate a previously unreported correlation between the maximum wrist joint reaction force and the volar tilt angle of the distal radius using parameters radiographically obtained parameters from normal wrist joints.

Using free body analysis of the forces acting on the distal radius for the loading condition that corresponds to the lift of a weight using the supinated hand, the wrist joint reaction force F and the angle formed between the vector of F and the long axis of the radius have been expressed as a function of the lifted weight, the lever-arm of the wrist flexor tendons and that of the lifted weight. Measurements of the volar tilt angle of distal radius and the lever-arms of the flexor tendons and the lifted weight were performed from lateral wrist radiographs of 30 normal wrists. Subsequently, using the equations obtained from free body analysis, the maximum wrist joint reaction force F and the angle that the latter forms with the long axis of the radius were calculated for each the cases. Statistical analysis compared the angle of the maximum wrist force and the volar tilt of the distal radius (two-tailed paired t-test) and correlated (a) the angle of the maximum wrist force and the volar tilt angle and (b) the maximum joint reaction force and the volar tilt angle.

Results showed no significant difference (p=0.33, 95% confidence interval −0.64° to 0.22°) but a statistically significant correlation (R² = 0.74, r = 0.86, p < 0.001) between the angle of the maximum wrist force and the volar tilt angle of the distal radius. Additionally, an inverse relationship between the volar tilt angle and the magnitude of the maximum wrist force (R² = 0.71, r =−0.84, p< 0.001) was found.

These observations may explain the mechanism of the phylogenetical development of the volar tilt angle and support the ‘minimum effective strain’ theory of adaptive bone remodeling1. The importance of accurate restoration of the volar tilt during treatment of distal radius fractures, especially in wrists that are normally characterised by a low volar tilt angle, is also emphasized by the results of the present study.

Patient disability and handicap following wrist injuries have been the focus of recent research interest¹. However, the relative importance of each of the commonly-reported and easily-measured clinical outcome parameters such as the range of wrist movement and the grip strength on the level of actual wrist disability following distal radial fractures has not been investigated previously. The present study investigates the correlation between measurements of specific clinical parameters and the patient-rated wrist joint function following wrist fractures.

A prospective assessment of unstable (AO types 23-A2, -A3, -C1 and -C2) fractures of the distal radius treated by closed reduction and percutaneous K-wire fixation followed by cast immobilisation was undertaken. One hundred consecutive observations were made during various follow-up time periods up to one year in a group of twenty-five patients (fifteen female and ten male patients, mean age 43 years – range 18 to 67 years). The clinical parameters tested were the range of wrist dorsiflexion, palmarflexion, pronation and supination (measured using a goniometer) and the mass grip strength (Jamar grip dynamometer) following removal of the plaster cast, expressed as percentage of the affected side relative to the opposite normal side. Additionally, each patient completed the Patient-Rated Wrist Evaluation (PRWE) Score¹. A stepwise multiple regression multivariate model was employed to statistically analyse the relative effect (expressed as the regression coefficient, b) of each clinical parameter on the ‘Function Score’ part of the PRWE Score. Furthermore, the association between each clinical parameter and the Function Score part of the PRWE Score was also investigated using single-patient observations by calculating the correlation coefficient (r).

The results of the statistical analysis (Minitab 12.1) gave the following regression (b) and correlation (r) coefficient values: grip strength (b=0.77, r=0.80), dorsiflexion (b=0.58,r=0.78),pronation (b=0.39,r=0.70),supination (b=0.38, r=0.63), palmarflexion (b=0.32, r=0.62).

The present study shows that grip strength (expressed as percentage that of the unaffected side) is the most reliable index of wrist disability and the most sensitive indicator of return of wrist function, followed by the range of wrist dorsiflexion and pronation. Wrist supination and palmarflexion are the clinical outcome variables showing the weakest correlation with the wrist function as rated by the patients. These observations may facilitate correct interpretation and comparisons of the results of clinical studies on various methods of treatment of wrist trauma.