Distal radius fractures are among the most common osteoporotic fractures
 and account for an estimated 17% of fractures treated in US emergency departments
 with a female–male ratio of about 3:1
. Corresponding to the demographic development, osteoporotic fractures of the wrist, humerus spine or hip can be expected to increase further in the coming years and with it the burden on healthcare resources
[4, 5]. Regardless of the fact whether these fractures are treated surgically or by casting, patients are at least immobilized for two to six weeks or more. Physical and occupational therapy as a key element in rehabilitation starts after the removal of the fixation device. However, during the period of fixation, patients often keep their injured hand in rigid postures, in which the volar plates and adjacent ligaments of the digital joints are shortened
. Different methods of treatment, but especially the long immobilization periods lead to overall complication rates ranging from 6 to 80% and have been associated with poor functional outcomes
. These complications not only include complex and regional pain syndrome, stiffness, nerve injury, tendon and ligament injuries, but a massive reduction in range of motion (ROM), muscular atrophy, and loss of movement representation
. As a result, the final hand function is often suboptimal
. Previous studies have indicated that 20% of patients with distal radius fracture had persistent symptoms, and 10% continued to have functional impairments after the typical recovery period
. In a study by consortium partners we demonstrated that the risk of losing independence after a wrist fracture is almost as high as after a hip fracture
. This partly relates to upper extremity dysfunction with activities of daily living such as eating, getting dressed and washed.
The goal for rehabilitation after wrist fractures is to achieve complete and rapid recovery of ROM, strength, and function of the wrist and hand. Improvement of the functional outcome after wrist fracture can probably not only be found in changing the operative technique
. Hence, for improvement of functional outcome, one has to focus on the postoperative rehabilitation period
[13, 14]. A patient would need a treatment procedure that is more active without actually stressing the bone and that may prevent from the negative side effects as well as from the central reorganization that takes place as a result of immobilization. This leads to a temporary forgetting of the function of the affected limb
, and results in the inefficiency of the central control of movements. Immobilization has shown to result rather rapidly in changes of motor and sensory representations in the brain of peripheral organs such as finger, arm, or leg
[16, 17]. For example, Langer et al.
 showed a decrease in cortical thickness in the left primary motor and somatosensory area as well as a decrease in the grey matter in the left corticospinal tract after at least 14 days of limb immobilization.
Several studies have shown that sensory input does not exclusively result from actually performed movements. Imagined movements without actually moving the limbs (explicit motor imagery) as well as observational learning (mirror therapy) also generate sensory input
[18–21]. Mirror therapy (MT), in which a mirror is placed in the patient's midsagittal plane, so that he/she can see his/her unaffected arm/hand as if it was the affected one, has mainly been studied for two different purposes: pain relief
, and motor recovery post-stroke
[23–25]. Furthermore, MT has been shown to increase ipsilateral primary motor excitability in healthy controls
, which may account for the improvement in motor function. Mental practice (MP) represents a class of training or therapy regimes in which an internal representation of a movement is repeatedly simulated in mind from a first-person perspective, without actual physical movement, and is effective in motor recovery in neurological and orthopedic rehabilitation
[27–29]. Proposed mechanisms for improved motor recovery with MT and MP include reconciliation of motor output and sensory feedback MT,
 and graded activation of cortical motor networks MP,
. According to Jeannerod
[32, 33] MP and the preparation of movements share common mechanisms and are functionally equivalent
. Furthermore, the activation of pre-motor “mirror neurons”, which have intimate connections with visual processing areas, is thought to prime the primary motor cortex and to be important in imitating motor action
In orthopedic rehabilitation MP as well as MT has only received minor attention as a promising psychological complement to conventional physical therapy approaches. Three studies have examined the effects of MT in patients after hand surgery other than amputation
[18, 38, 39]. While Rosén and Lundborg
 reported three different cases (e.g. tendon repair) when MT was applied in combination with traditional hand training (no further details regarding the number of training sessions or duration were given), Altschuler and Hu
 as well as Rostami et al.
 examined hand function with different orthopedic conditions in one (insufficient information on intervention), respectively 12 patients (15 sessions à 30 minutes). Both studies conducted MT in combination with physical therapy. All three studies reported improvements in objective as well as subjective measures of hand function. None of these studies had the goal to overcome the effects of immobilization. There are mixed results on the effects of MP during disuse or immobilization
[40–45]. Some researchers have found support for mental imagery to maintain muscle strength and flexibility
[42, 44] Schott & Limberger: Effects of mental practice on gait after total hip endoprosthesis, in prep], while others have not
[40, 41, 43, 45]. Methodological inconsistencies could account for many of the contradictory findings within the literature. Studies vary in the participants’ age and health status, the type of imagery, the content of imagery, as well as intervention length. Explicit imagery has been shown to create the greatest physiological benefits but only few studies specifically elaborate on their imagery script. Protocols for imagery intervention also varied among researchers from as little as 10 days to 7 weeks in duration with varying numbers of sessions per day. To our knowledge, only two studies examined the efficacy of explicit motor imagery and MT so far
[42, 46]. Ietswaart and colleagues
 found no enhanced improvement as a result of MP with motor imagery in upper hand function of stroke patients. Frenkel
 examined the efficacy of a MP combined with MT after knee endoprothesis surgery, but only found significant results for the criterion flexion. No other studies exist with regard to patients with orthopedic injuries, comparing the efficacy of MT or MP.
The purpose of this randomized study is to determine whether explicit motor imagery or MT during the immobilization period after distal radius fracture results in a greater recovery of central aspects of hand function. The objective of this study is to establish the effectiveness of daily training of movement imagery with the affected arm (MP) or the healthy arm (MT). It will also be examined whether enhanced functional recovery of the hand due to MP or MT is also associated with increases in the amount of activities of daily living. It will be investigated whether the benefit of motor-cognitive approaches for distal radius fracture patients is related to their individual differences in motor imagery ability.