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Electrogoniometer (Jackson Group, Second Generation)

Health Sciences · Robert W. Jackson Arthroscopy

2021.JAC.45.1 – An articulated instrument consisting primarily of a jointed aluminum and stainless steel framework housing six servos, one linear and five rotary. The rotary servos are black in colour and have wires soldered to three tabs along their sides. Several wires have become detached from the tabs. The wires joining the servos are gathered using black electrical tape.

Bar-like elements protrude from either end of the instrument. One such element is adjustable in length using a knurled screw. These are used to attach the instrument to contact pads of rigid plastic that are strapped to the subject’s leg.

The central portion of the instrument consists of two piston-like elements comprising the linear servo and its housing. A 9-pin serial port is located at the centre of one side of this assembly.
This instrument includes to contact pads:  

2021.JAC.45.2 – Is a curved pad of rigid plastic lined on one side with a textured material. Attached with rivets are two loops for securing elasticized velcro straps. The ends of two straps are riveted along the opposite edge, though have been severed. Velcro pads are affixed vertically along the center of one side of the convex side of the pads. This pad is slightly larger than 2021.JAC.45.3

2021.JAC.45.3 – Is very similar to 2021.JAC.42, though slightly smaller.

Accession Number: 2021.JAC.45.1-3

Alternative Name:

Instrumented Spatial Linkage Device (ISLD); Spatial Goniometer

Primary Materials: Stainless Steel, Aluminum


Dimensions (cm): Height = 6.5, Width =12.5, Length= 50


The Instrumented Spatial Linkage Device (ISLD) is a form of spatial goniometer designed to measure the complex motion of the knee. It uses six servos (five rotary and one linear) to capture the knee’s six degrees of freedom. Its main purpose is to diagnose injuries to the Anterior Cruciate Ligament (ACL ) in a non-invasive manner by identifying the extended “gliding” femoral-tibial motion of pathogenic knees.

The device is attached at two points above and below the knee. When the instrumented subject walks, the motion of the knee is captured through the movement of the servos. These analog electrical signals produced by the servos are converted to digital signals and fed into a computer. A heel-strike foot switch is used to mark the beginning of a step.

The ISLD, developed by Jackson, his students, and associated researchers and technicians, went through at least three major versions between from late 1970s to the late 1990s. This example is likely the instrument referred to as the “the 1990 device” in later texts (see Dill 1998, 36).


This instrument appears to be in good cosmetic condition. There are light scratches and abrasions across its aluminum surfaces. Some steel components, such as the two pistons of the linear servo, are lightly oxidized. Several solder joints between the rotary servos and the connecting wires have failed and the wires are disconnected. The Velcro straps of the two rigid pads (2021.JAC.45.2 and 3) have been cut.
This instrument represents only the central portion of a larger apparatus. For instance, a heel-strike mechanism, an analog-to-digital converter, and a computer system was necessary to record data from this instrument.

Associated Instruments:


University of Toronto Faculty of Engineering

Date of Manufacture: c. 1990


The Robert W. Jackson Arthroscopy Collection was acquired by the University of Toronto from Dr. Jackson’s family on November 12th, 2020.

Additional Information and References:

Howard J. Marans (1985) Computerized Knee Electrogoniometry- A Three-Dimensional Motion Analysis of Normal and Anterior Cruciate Ligament Deficient Subjects. Unpublished M.S. Thesis, Institute of Medical Science, University of Toronto.

John G. Cinats (1989) The Calibration of an Instrumented Spatial Linkage Electrogoniometer. Unpublished M.S. Thesis, Institute of Medical Science, University of Toronto.

Shannon Dill (1998) Six Degree of Freedom Dynamic Knee Laxity Measurement Device. Unpublished M.S. Thesis. The University Of Texas At Arlington.

Historical Notes:

A very common injury, often sports related, involves damage to the knee’s Anterior Cruciate Ligament (ACL). Medical researchers have explored a very long list of non-invasive methods for diagnosing ACL injuries by measuring the motion of the knee. This is a challenging task because the knee joint’s movement is a complex combination of several rotations and translations. 

One analytical method, called “computerized knee electrogoniometry, uses an “instrumented spatial linkage device” (ISLD), a form of spatial goniometer. This ISLD consists of a flexible arrangement of servos applied to the knee joint. Actuated by the knee, the instrument produces electrical signals analogous to the knees motion. These are converted to digital information that is subsequently analyzed by computer. This method of fully capturing the translations of the knee was an improvement on earlier models that simplified the movement into basic rotations. 

The ISLD approach presents engineering challenges beyond the complexity of the electrical system itself. For instance, the instrument must be sufficiently stiff and secure to capture the motion of the knee movement of the instrument against the skin extraneous motion (“soft tissue error”). It must be fixed securely in place without interfering with the subject’s natural gait. It also poses data processing challenges: The instrument captures superpositions of several motions. Individual translations and rotations must afterwards be derived algorithmically from the processed data. [Maranz 2005, 6]

Work on this instrumentation and its underlying mathematics was initiated in the early 1970s by Kinzel et al. Robert W. Jackson began working on ISLDs in 1974 while at the Orthopaedic and Arthritic Hospital (now called the Holland Orthopaedic & Arthritic Centre). An instrument was developed with the University of Toronto Faculty of Engineering. It went through at least three major iterations over several decades, two of which are represented in this collection. This was further developed through efforts of Bartel et al of the Faculty of Engineering Design at the University of Waterloo. This group constructed an artificial calibration knee to quantify the reproducibility of the instrument’s data. Based on their findings, several improvements were made to the design. [Cinats, 1989, 20]

An early example (2021.JAC.44 in this collection) is described in Marans 1985. This is characterized as “a modified version of the one developed by Izak in 1974”. Collaborators included Carles Mizzi, a staff member at the Biomedical Engineering Department of Toronto Western Hospital, who served as engineering technician. This version used software written in Fortran by Neil Glossop, an aerospace engineer. Marans determined that ACL deficient knees showed a significant increase in anterior-posterior translation relative to control subjects.

A second version, referred to in later sources as “the 1990 device” (20201.JAC.45 in this collection), is discussed by John Cinats in 1990. Cinats’ work focused on developing improved calibration techniques. This redesign introduced a much-improved attachment system among numerous other changes.

A third redesigned version is described by Shannon Dill 1998 at the Tom Landry Sports Medicine & Research Center in Dallas Texas. This was meant to reduce soft tissue error through a lower mass device as well as through improving the accuracy of the potentiometers. This collection does not have an example of this version.

  • Donated to UTSIC