Range of motion required for Auslan: a biomechanical analysis

Auslan is used by the Australian deaf community and relies heavily on hand, wrist, and elbow movement. Upper limb injury or dysfunction may require surgical intervention to alleviate pain and provide a stable skeleton for function, leading to partial or complete reduction in motion. The aim of this study was to assess the wrist, forearm, and elbow motion required to communicate via Auslan, to tailor optimal interventions in this population.


Introduction
Effective communication facilitates the passage of information from one individual to another, allowing interpersonal relationships to blossom, trust to be built and new opportunities to be created. 1 Information can be exchanged via various modalities, including speaking, writing, or the use of gestures. 2 Sign language (SL) is a visual form of communication that utilizes hand, arm and body movements to convey meaning to others. 2 Auslan (Australian SL) was developed in the early 1980s to convey the nuances and complexities found in the spoken language, and is used by the Australian deaf community. 3 Like all variants of SL, Auslan relies heavily on hand gestures, as well as wrist and elbow movement, and the presence of upper limb (UL) dysfunction can significantly impair a deaf individual's ability to communicate. 2 UL dysfunction can result from trauma, tumour, infection or degeneration, and may be addressed by a variety of surgical and non-surgical modalities. However, intervention in the deaf must take into account the specific requirements of this cohort, as surgical modalities that aim to alleviate pain and provide a stable skeleton for function may result in either partial or complete reduction in range of motion (ROM), potentially impairing the patient's ability to communicate.
Little information in present in the literature regarding the ROM required in the UL to effectively communicate via SL. Thus, the aim of this study was to assess the ROM required at the wrist, forearm and elbow to communicate via Auslan, providing guidance in tailoring optimal interventions in the deaf population.

Methods
Ethics approval was granted by the relevant institutional Human Research Ethics Committee. Two native Auslan communicators were recruited for the biomechanical analysis, with informed written consent obtained prior to commencement. Each participant was fitted with 26 reflective markers applied to predetermined locations on the thorax and upper limbs according to the Vicon Upper Limb Model. Ten 16-megapixel Vicon Vantage cameras (Vicon Motion Systems, Los Angeles, CA, USA) recorded marker trajectories at 100 Hz.
Each volunteer was requested to sign 28 pre-selected Auslan words and phrases, including a brief introduction about themselves (Table 1). Data was collected for both upper limbs simultaneously and participants repeated each word or phrase five times. Data was processed using a modified Vicon Upper Limb Bodybuilder model to output the coronal, sagittal and axial plane motion at the joints in question. Outliers were removed and a minimum of three repetitions of each sign were analysed. Descriptive statistics were utilized to present the required range for each anatomical segment. A negative value for range of motion at the elbow represents a flexed posture relative to full extension, and not hyperextension.

Results
The participants were both right-handed males, and aged 32 and 62 years respectively. Both participants did not have any prior upper limb pathology and demonstrated a full and pain-free range of motion prior to commencement of the study. Table 2 demonstrates the required range of motion in detail, including total joint range, interquartile range, mode and median values. The total range of wrist coronal plane motion required was 56 on the right side, and 41 on the left, with similar interquartile ranges bilaterally ( Table 2). Maximum wrist sagittal plane motion (flexion and extension) utilized was also similar bilaterally, at 122 and 114 , although the interquartile range did differ. 25 of axial plane motion was required in the right arm for effective communication, compared to 14 in the left UL. Although similar ranges of motion were required bilaterally when assessing elbow flexion and extension, the actual arcs differed, with 111 noted on the right UL (165 flexion to À54 extension) and 123 on the left (143 flexion to À20 extension).

Discussion
This study assesses the ROM needed in the wrist, forearm and elbow to communicate using Auslan, and finds that sagittal plane elbow and wrist motion, as well as coronal plane wrist variation, is of greater importance than axial plane rotation across the forearm. Many of the chosen words and phrases were conveyed using relative elbow flexion and generous wrist motion, with the forearm held in a neutral position. End-range elbow extension was not recorded in any word or phrase, lending to the prioritization of elbow flexion over extension when considering intervention in those communicating via Auslan.
Elbow ROM required for communication via Auslan varied between left and right arms, but was greater than 100 on both. Morrey, Askew 4 established a required range of motion of 100 (30 -130 of flexion, as well as 50 supination and 50 pronation)  for adult functional and positional tasks, using a tri-axial goniometer. More recent studies using three-dimensional optical tracking and motion analysis (similar to that used in the current study) described a greater required arc for contemporary tasks, from 23 to 149 of flexion. 5 The sagittal plane elbow motion required for communication via Auslan is therefore greater than that necessitated by daily activities, and any pathology restricting this arc may impair the deaf individual's ability to interact. Welsink, Lambers 6 performed a systematic review of outcomes following total elbow arthroplasty, noting a mean ROM of 30 to 129 of flexion from 9379 joints-patients must be carefully counselled on likely limitations prior to undergoing this, or any other, elbow operation. Normal sagittal plane motion in the wrist has been reported as between 75-85 of flexion and 70-75 of extension, whilst functional range has been nominated as an arc between 5 of flexion and 30 of extension. [7][8][9] The current study found that although overall required range of sagittal plane wrist motion in the studied Auslan speakers was similar bilaterally, the left wrist functioned most commonly in a position of extension, whilst the right cycled between flexion and extension. Approximately 80% of normal sagittal range was utilized to complete the prescribed words and phrases. This requirement is an important consideration when managing end-stage wrist arthritis, and was noted by Sivakumar, Piercey 10 in their report of wrist arthroplasty performed for recalcitrant inflammatory wrist arthropathy. In this setting, a detailed understanding of the outcomes of particular prostheses is key-in their systematic review, Yeoh and Tourret 11 noted that while utilization of the Motec system (Swemac, Linkoeping, Sweden) with its unique ball-and-socket design achieved an sagittal plane arc of 122 , other prostheses yielded far less. Thus, adequate patient selection, preoperative counselling and prosthesis choice is necessary when dealing with end-stage wrist pathology in the deaf community.  Forearm axial plane motion was found to be least important when communicating via Auslan. Approximately 10% of the reported normal range of 70 of pronation and 85 of supination was required, with the Auslan interpreters needing a 25 arc on the right and 14 arc on the left to sign the prescribed phrases. 5,9 It must be recognized, however, that individual sign dialects have differing demands, with Shealy, Feuerstein 12 previously reporting that end range pronation was a frequently observed position in an assessment of American Sign Language (although this was based on video analysis of interpreters at work, as opposed to laboratory analysis). Further, each individual may communicate in different styles within the same dialect. The studied Auslan speakers demonstrated inter-participant variance, particularly in sagittal plane elbow motion, where a 19 difference was noted for the right arm, and 45 for the left. Lesser variability was seen in other planes of motion. Thus, individual and regional variations and demands must be considered when considering therapeutic modalities.
The strengths and limitations of this study are as follows. The motion analysis utilized afforded a high degree of accuracy (to the single degree) compared to prior studies, where goniometers or measurements via frame by frame observations of footage were used. 12 However, the inclusion of only two volunteers limits generalizability. Whilst it is noted that those who communicate via Auslan may vary their movements to tailor their desired message, factors such as inter-speaker 'accents', the recipient audience, and the level of enthusiasm appropriate to the conversation were not assessed. Further, range of motion in the hand and shoulder, as well as other metrics such as speed and fluidity of movement, were not considered in the analysis, and would be potential targets for future research.

Conclusion
Maintenance of upper limb motion is key for communication using sign language. This study investigates the required ROM at the elbow, forearm and wrist to effectively interact via Auslan, finding that effective communication requires greater motion than what has been previously described for function. It provides a basis for future research, as well as a resource to consult when counselling deaf patients for operative intervention of upper limb pathology. Future research in the ROM required in the hand and shoulder, as well as required speed and fluidity of movement, would be useful.