John Mennell introduced the theory of joint play as a therapeutic manual medicine technique through his book Joint Pain: Diagnosis and Treatment Using Manipulative Techniques in 1964. Since its introduction, this valuable and time-tested principle has not been further expanded on, nor has it received any research in today’s age of evidence-based medicine. Nevertheless, joint play is readily used and essential to the pain-free function of synovial joints, both in principle and as a technique of manual medicine.

Joint play is defined by Mennell as small movements within a synovial joint that are independent of voluntary muscle contraction (1). These movements measure not more than 1/8 inch in any plane and follow the contour of the opposing joint surfaces. By nature, joint play is an involuntary movement that is inherent to the musculoskeletal system and cannot be introduced by voluntary muscles. It provides roll, glide, distraction, and spin combinations for joint motion and occurs in the shape of the joint surfaces (3). Capsular laxity allows for this motion, which is essential for the proper functioning of normal, painless active and passive range of movements (1,2,3). All movements of living anatomy are based on the summation of the movements of joint play and the movements of voluntary muscles. Although small, these precise involuntary movements are important, as their integrity greatly affects the performance of the gross voluntary movements of synovial joints.

To better understand the concept of joint play, joint dysfunction needs to be defined. According to Mennell, joint dysfunction is the loss of joint play movement that cannot be recovered by the action of voluntary muscles (1). This pathologic condition is readily reversible in its early stages and is common in life but cannot be demonstrated after death, which presents a difficulty in researching this concept. Yet, if joint dysfunction is left uncorrected, restricted voluntary movement and joint pain develop. Therefore, recognizing joint dysfunction as a pain-producing pathologic condition makes the restoration of normal joint play by manipulation a logical and reasonable treatment.

Joint dysfunction is further defined by Mennell as more than a diagnosis; it is also an invaluable sign of some serious pathologic process or joint disease (1). The distinction between these two entities, the clinical diagnosis and the physical examination sign, can be made only by careful evaluation including history, clinical examination, radiographic study, and often laboratory investigation.

In the traditional teaching of musculoskeletal medicine, emphasis is usually placed on the deficiencies of the muscles in the evaluation of functional loss, thereby focusing rehabilitation on muscular retraining and development. Joint disease, however, is often the cause of secondary muscle changes, particularly atrophy and spasm.
Even in light of this knowledge, treatment is often aimed at the joint only when gross clinical and/or radiographic changes are demonstrated, which then often neglects the muscles. Neither approach is complete. With this in mind, Mennell reminds clinicians of four basic truisms in practice (1):

Mennell states there is a vicious circle of effects that develops in any musculoskeletal problem, but the prime fault usually lies in the synovial joint (1). Mennell derived the manual medicine principle and technique of joint play from his work in determining that the prime fault of joint dysfunction is in the synovial joints. If the prime fault can be corrected, the secondary abnormalities are usually corrected also.

Diagnosis of joint dysfunction is best achieved by clinical means. Static radiographs do not demonstrate such subtle pathology, and although stress radiographs may be used to demonstrate the end range of joint play movement, the cost of films, repeated exposure, and time to complete the detailed examination for such small movements make this an unreasonable option. Because joint dysfunction does not cause any known biochemical alterations, laboratory methods are of no assistance. Although this sounds contrary to previous statements regarding the distinction between joint dysfunction as diagnosis or sign, the important difference is that laboratory and radiographic evaluations rule out underlying joint pathology when joint dysfunction is a clinical sign rather than the diagnosis. As is true for other techniques, the prerequisite for successful treatment is accurate diagnosis.

A much more readily available means of diagnosing joint dysfunction is a careful physical examination. There may be individual variations in the degree of joint play at any specific synovial joint, but there is no variation of technique in eliciting each movement at each joint. In the examination of a joint, Mennell clearly defines ten general rules that must be followed when using this manipulative technique (1):