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Electrogoniometer (Jackson Group, Early)

Health Sciences · Robert W. Jackson Arthroscopy

An articulated instrument consisting primarily of a jointed aluminum and stainless steel framework housing six servos, one linear and five rotary. The five rotary servos each have blue cylindrical caps with wiring soldered to tabs near the centre of the top surface. A bundle of multi-coloured wires, emerging from one end of the instrument, is gathered using two clear zip ties.

A linear servo, consisting of two piston-like elements, is located near the centre of the instrument. Rectangular black stickers with rounded edges have been placed along each side of the linear servo, four on one side, three on the other.

Accession Number: 2021.JAC.44

Alternative Name:

Instrumented Spatial Linkage Device (ISLD); Spatial Goniometer

Primary Materials: Stainless Steel, Aluminum


Each servo was numbered with a small white label. Labels 2 and 4 are missing.

Dimensions (cm): Height = 5, Width =6.5, Length= 27


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 an early version in use before the 1990s. Several improvements were made to the design from the 1970s to the mid-80s, though it is currently unclear whether this involved multiple instruments or modifications to a single instrument.


This instrument appears to be in good cosmetic condition. There are small areas of oxidation, for instance on several socket cap screws. The power and data cables have been cut. This instrument represents only of the central portion of a larger apparatus. For instance, the arrangement for securing the device to the limb, consisting of padded rubber straps and two padded plates are not present. The power and data cables are not included, nor is instrumentation such as the heel-strike mechanism, the analog-to-digital converter, a magnetic tape-based data recorder, a two-channel oscilloscope for monitoring the data, or the associated PDP 11/34 computer system.

Associated Instruments:


University of Toronto Faculty of Engineering

Date of Manufacture: c. 1974 – 1984


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