As mentioned on the home page, for this project we are tasked with creating design requirements, specifications, and justifications to be able to create a prototype within the Design Control framework. This is to ensure the device meets user needs and intended uses. Listed below are our current design requirements, specifications, and justifications.
| Requirement | Specification | Justifications |
|---|---|---|
| 1. The device must incorporate structures that replicate the upper extremity. | 1.1 The device must include muscle structures for biceps brachii, triceps brachii, common extensor group, and common flexor group 1.2 The device must include ligament structures for anterior band of the MCL and the LCL complex 1.3 The device must include bone structures for humerus, ulna, and radius 1.4 The device must include tendon structures for each included muscle that connect the muscle to bone 1.5 The device must include skin and filler material. | Stability of the elbow comes from primary and secondary static constraints. Primary constraints include the ulnohumeral articulation, anterior band of the MCL, and the LCL. Secondary constraints are the radiohumeral articulation, common extensor group, and common flexor group.1,2 The biceps brachii and triceps brachii are also main stabilizers of the elbow.1 |
| 2. The device’s structures that replicate muscle must have similar material properties to human muscles. | 2.1 Materials for muscles must have an ultimate tensile strength of 3.6 ± 1.7 MPa3,4 2.2 Stiffness of material used for muscles must be 0.210 ± 0.021 N/mm 5 | In order to maintain accuracy to human tissue, the device must have materials for muscles that react the same way to tensile loading as an actual human arm would react. As such, tensile strength and stiffness is an acceptable property to replicate how muscles would react to the same load. |
| 3. The device’s structures that replicate tendons must have similar material properties to human tendons. | 3.1 Tensile strength of material used for tendons must be 17.5 ± 6.3 MPa6,7 3.2 Stiffness of material used for tendons must be 104 ± 52 N/mm6,7 | Components that have similar material properties to human tissue will replicate the sensation of manipulating a human arm. Tensile strength and stiffness are acceptable properties to use for replicating how tendons behave when subjected to tension. Values determined from tensile tests of the long head biceps tendon and triceps tendon.1,2 Tendons are assumed to be homogeneous throughout their entire length with respect to material properties.1,2 |
| 4. The device’s structures that replicate ligaments must have similar material properties to human ligaments. | 4.1 Ultimate tensile strength of the ligaments must be 20.67 ± 6.2 MPa.9 4.2 Stiffness of material used for the ligaments must be 30.36 ± 23.15 N/mm.8 | Components that have similar material properties to human tissue will replicate the sensation of manipulating a human arm. Having similar stiffness and ultimate tensile strength of the ligaments will allow users to obtain the most realistic feel. This will also allow users to feel the difference between the healthy ligaments and the torn ligaments when these parameters are altered. |
| 5. The device must be able to simulate different pathologies. | 5.1 The device must simulate a complete tear of MCL and LCL 5.2 The device must simulate simple, posterior elbow dislocation | Simulating a tear of the elbow MCL and LCL will allow users of the device to practice varus-valgus stress tests to assess ligament integrity and learn how to diagnose an injury to these ligaments. Simulating a simple posterior elbow dislocation with no additional bone fractures or soft tissue injury will allow users of the device to practice elbow joint reduction.10 |
| 6. The device must measure force in the tricep, bicep, MCL, and LCL. | 6.1 The device must measure tensile force from 0-360N with an accuracy of 90%. | Having a readout for force will be crucial in determining whether or not the user performing the ligament integrity tests or joint dislocations performed them correctly and in a way that would not further injure the patient. |
| 7. The device must incorporate external feedback. | 7.1 The device must alert user when ligaments are under load approaching their tensile strength of 14.4 MPa, muscles are approaching their tensile strength of 1.9 MPa, and tendons are approaching their tensile strength of 11.2 MPa. 7.2 The device must alert the user if the elbow joint angle exceeds 105 degrees in flexion or 40 degrees in extension when simulating injuries.11 7.3 The device will provide alerts using visual and audio cues | Alerting the user when their exerted force is approaching the ligament material’s ultimate tensile strength serves to notify the user when a ligament is about to tear and further injure patient. Alerting the user when the range of motion of an injured elbow joint is exceeded simulates when a real patient would experience pain. The use of universally recognized color cues indicates to the user how to adjust treatment before harming the patient. |
| 8. The device must replicate the size of average adult human arm. | 8.1 Device length from the glenohumeral axis to tip of middle finger must be between 27.5 and 29.5 inches.13,14 8.2 Circumference of forearm must be between 9.3 and 11.7 inches.16,17,18 8.3 Circumference of mid-upper arm must be between 12.5 and 14 inches.13 | It is important that users of this device practice on a model that is of similar size to a human arm 8.1 Values determined using average male and female height data from the CDC and anthropometric segment length as a function of body height. These values were consistent with average arm length found in literature.13,14,15 8.2 Values determined using average male and female forearm circumference from literature.16,17,18 Measurement of circumference is at largest part of the forearm. 8.3 Values determined using CDC data for mid-upper arm circumference. Measurement of circumference is at the midpoint of the upper arm. |
| 9. The device must replicate range of motion of average human elbow. | 9.1 Elbow flexion must be between 142 and 154 degrees.19,20 9.2 Elbow extension must be between -10 and 4.7 degrees.19,20 | It is important that users of this device practice on a model that has the same range of motion as a human arm. Values determined using average human elbow flexion and extension angles for both males and females. |