Primary stiff shoulder or “frozen shoulder” has been classically regarded as a self-limiting entity that should be managed conservatively. Considering the theoretical benign prognosis of this condition, there is still controversy on several characteristics of the disease that once identified, could help to recommend additional therapies in a selected subgroup of patients in order to reduce the impact of the disease on the patient. For instance, the presence of certain factors, like the duration of the symptoms, could be useful to establish a prognosis and, thus, select an individualized specific treatment option. Traditionally, Reeves [8] described three clinical phases in the evolution of idiopathic frozen shoulder. The first one, the “freezing” phase, develops within the first 3–9 months and presents with diffuse pain and progressive stiffness. The patient may attribute the symptoms to a trivial injury. Pain usually precedes the restriction in motion, but not necessarily. The second one, the “frozen” phase, is characterized by diminished pain and an established stiffness. It typically lasts for 4–12 months. The last phase is called the resolution or “thawing” phase. Pain and stiffness start to gradually improve along a period of time that can last from 12 to 24 months. Although new classifications have been proposed, all of them stress the fact that the process is continuous and that the three phases are highly variable and may overlap. The duration of the condition is from 1 to 3.5 years with a mean of 30 months. It is not unusual that the opposite shoulder is affected subsequently between 6 months and 7 years after initial onset of symptoms of the first shoulder [8].

The degree of recovery is variable and depends on the cause of the frozen shoulder as well as other factors that remain controversial [10]. Studies regarding the natural course of frozen shoulder are very scant. Russell et al. [9] have pointed out that including a “nontreatment” group in a comparative study could incur in conflict with ethical restrictions. This is one of the reasons why it is difficult to assess what the evolution without any kind of treatment would be. The other important difficulty is the delay in recognition and diagnosis in the early phases. It has been published that the mean duration of shoulder pain prior to the initial evaluation is approximately 9 months [6]. Moreover, most of the studies regarding the natural history of frozen shoulder do not specify if any kind of physical therapy, oral treatment, or injections were performed during the follow-up.

Codman [2] originally described a self-limited course of frozen shoulder with a treatment that consisted of supervised neglect with analgesia, physical therapy, or steroid injection. Other studies have confirmed this self-limiting course and have reported rates of recovery in more than 90 % of patients [3, 5, 10]. However, residual pain and restriction in motion are not uncommon. Binder et al. [1] reported a series of 40 patients prospectively followed for a mean of 44 months. Although 18 patients (45 %) had residual symptoms in terms of pain at final follow-up, only one was severe. However, 16 patients (40 %) had not reached a complete range of motion when compared to the age- and gender-matched control group. Five patients presented with severe restriction in range of motion and four had developed the same symptoms in the uninvolved shoulder. They found three prognostic factors of worse outcome: dominant arm involvement, manual labor, and mobilization therapy. Men showed more restriction than women at final follow-up, but this difference was not statistically significant. Traumatic onset and duration of symptoms at presentation were not factors related to outcome. Reeves [8] published a long-term follow-up study with similar results. At 5–10-years follow-up, 3 of 49 patients presented with severe disability and 22 with mild disability. Some other authors, on the other hand, have obtained better results, as Grey et al. [4], in which series 24 of 25 patients with untreated frozen shoulder achieved complete recovery.